498 results on '"Anisotropy of magnetic susceptibility"'
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452. Rock magnetic evidence of inflation of a flood basalt lava flow
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Cañón-Tapia, Edgardo and Coe, Robert
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- 2002
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453. On the reliability of the AMS ellipsoid by statistical methods
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Guerrero Suárez, Sara, Martín Hernández, Fátima, Guerrero Suárez, Sara, and Martín Hernández, Fátima
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Weak magnetic materials whose susceptibility values are close to the instrument's accuracy show very large errors in the direct evaluation of their ellipsoid parameters. This may lead to misinterpretation of the magnetic fabric, which is often used as a geological indicator. In order to estimate the measurement uncertainties, several statistical methods have been proposed. Within the available statistical methods, the Linear Perturbation Analysis (Hext, 1963) and the non-parametric bootstrap (Constable and Tauxe, 1990) technique have been widely used. In this paper, we make a complete study about these methods to estimate their limitations when applied to n measurements of a single sample. We will analyze which method is better in terms of uncertainties, we will determine when the methods do not provide reliable results and we will establish a measuring protocol. For that, we run simulations for the Linear Perturbation Analysis and the non-parametric bootstrap varying i) the number of measurements, ii) the instrumental error and iii) the shape parameter and the anisotropy degree of the AMS ellipsoid. The results show that both methods are not reliable when the difference between eigenvalues is too close in relation to the instrumental error, but increasing the number of measurements can improve the results.
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- 2014
454. Characteristics of the late Mesozoic tectonic evolution of the South China block and geodynamic implications : Multi-approach study on the Qingyang-Jiuhua, Hengshan and Fujian coastal granitic massifs
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Wei, Wei, Institut des Sciences de la Terre d'Orléans - UMR7327 (ISTO), Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Bureau de Recherches Géologiques et Minières (BRGM) (BRGM), Université d'Orléans, University of Chinese academy of sciences, Yan Chen, Quanlin Hou, and STAR, ABES
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Paleomagnetism ,Amphibole AlTotal geobarometry ,Crétacé Mésozoïque supérieur ,Anisotropie de la susceptibilité magnétique (AMS) ,Extension d’arrière-arc ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,Etude pluridisciplinaire ,Structural observation ,Massif de Qingyang-Jiuhua ,Bloc de Chine du Sud ,Modélisation gravimétrique ,Magma emplacement mechanism ,Gravity modeling ,Mise en place passive de magma granitique ,Late Mesozoic ,Extension lithosphérique ,South China Block lithospheric tectonic evolution ,Analyse multiéchelle ,Magmatisme insulaire-arc ,Paléomagnétisme ,Anisotropy of magnetic susceptibility ,[SDU.STU] Sciences of the Universe [physics]/Earth Sciences ,Micro-continent Ouest Philippines ,zone tectonique de Changle-Nan’ao ,Massif de Hengshan ,Barométrie d’Al-total dans l’amphibole - Abstract
The vast distribution and long duration of the Late Mesozoic magmatism in the eastern part of South China presents a unique case in the world. This offers a natural laboratory to study the process of magma genesis, the magma emplacement mode, the relationship between magmatism and tectonics, the geodynamic role on the magma emplacement and lithospheric evolution. Since 50’s, particularly 90’s of the last century, geoscientists have made important efforts in geological cartography and carried out numerous studies with remarkable scientific achievements, building a solid background to understand the tectonic evolution of the South China Block (SCB). However, certain fundamental questions mentioned above remain unsolved and/or are in hot debate. In order to make progress in these scientific issues, we have carried out in a multi-disciplinary study in the Late Mesozoic Qingyang-Jiuhua massif, Hengshan massif and Fujian coastal zone according to their distance with respect to the paleo subduction zone of the Paleo-Pacific plate, the ages of granitic massifs and related tectonics, including field observation on the structure geology, micro-observation on thin section, U-Pb dating on monazite, AMS, paleomagnetism, gravity modeling and P condition concern the granite emplacement. In the view of deformation in these granitic massifs and their country rocks, mode and influence of regional tectonics on the emplacement, though each studied zone reveals its distinguished characteristics, they show some intrinsic and common relationships between them. With our new results and integrating previous data, in this thesis, we discuss the tectonic context of emplacement of these Late Mesozoic magmatic massifs and the geodynamic evolution of the SCB., We propose a 3-step geodynamic model: (1) during 145-130 Ma period, the Paleo-Pacific plate subducted northwestwardly, the West Philippines micro-continent, approaching to SCB, important subduction-related arc volcanism was produced in the coastal areas of Southeast China coast (Zhejiang-Fujian-Guangdong), forming a back-arc extension tectonic system in SCB; (2) during 130-110 Ma period, due to the collision between the West Philippines microcontinent and SCB, the compressional tectonic structures were developed in the Changle-Na’ao coastal zone, producing ductile deformation zones. However, the inland of the eastern part of SCB was under a NW-SE extensional tectonic regime; (3) during 105-90 Ma period, a new subduction zone was developed in the SE flank of the West Philippines micro-continent, the subducting slab reached the Changle-Nan’ao tectonic belt, with the possible break-off of slab, the asthenospheric ascent was responsible for the important emplacement of plutonic massifs and dykes. The tectonics of the eastern part of SCB was characterized by a general extensional system in this period. This tectonic pattern has been significantly disturbed by the Oligocene-Eocene opening of the South China sea,and the Miocene shortening of the SCB margin in Taiwan. Of course, this model should be improved by more geological, geophysical and geochemical investigations., La vaste distribution géographique et la longue durée du magmatisme au Mésozoïque supérieur (Jurassique et Crétacé) en Chine du Sud présente le cas unique dans le monde. Ceci présente un laboratoire naturel très favorable a l’étude des processus de magmatogénèse, et des modes de mise place des plutons granitiques. Il permet également d’aborder l’analyse des relations magmatisme-tectonique et les contextes géodynamiques de la mise en place de magma dans leur cadre lithosphérique. Depuis les années 50, et surtout les années 90, des scientifiques ont mis un effort important sur la cartographie géologique, mené des études pétrologiques et géochronologiques et ainsi obtenu une base solide pour la compréhension de l’évolution tectonique du Bloc de Chine du Sud (SCB). Cependant, des questions fondamentales restent encore sans réponses ou vivement débattues. Dans le but de progresser sur ces sujets fondamentaux, nous avons mené des études pluridisciplinaires sur les massifs d’âge Mésozoïque supérieur de Qingyang-Jiuhua (Province d’Anhui), Hengshan (Province de Hunan) et certains plutons affleurant dans la zone côtière du Fujian. Le choix des massifs est fonde sur leur distance variable par rapport à la paléozone de subduction, les âges comparables de ces massifs et les déformations associées. Les méthodes d’étude comprennent l’observation de terrain, l’analyse microscopique de lames minces, la datation par U-Pb de monazite, l’ASM, le paléomagnétisme, la modélisation gravimétrique et la barométrie à partir de Al-total dans l’amphibole magmatique. Bien que chaque massif présente des caractéristiques distinctes, ils partagent des points communs du point de vue de leur orientation préférentielle, de la déformation de leurs encaissants et de l’influence de la tectonique régionale sur leur mise en place, D’après nos nouveaux résultats et en intégrant les données précédentes, nous discutons dans cette thèse les contextes tectoniques de mise en place de ces massifs granitiques et l’évolution géodynamique de SCB, et proposons un scénario géodynamique en 3 étapes. (1) Pendant la période 145-130 Ma, la subduction vers le NW de la plaque Paléo-Pacifique sous le continent asiatique fait rapprocher le micro-continent de l’Ouest-Philippines avec le continent de Chine du Sud, produisant l’important magmatisme d’arc et formant un régime tectonique en extension en SCB ? Dans l’arrière-arc; (2) Pendant la période 130-110 Ma, dûe à la collision entre le micro-continent de l’Ouest Philippines et SCB, une structure compressive vers le NW a été développée dans la zone de Changle Nan’ao, produisant des déformations ductiles. Cependant, l’intérieur de la partie orientale du SCB était encore en régime tectonique extensif de direction NW-SE; (3) Pendant la période 105-90Ma, une nouvelle zone de subduction a été développée au SE du micro-continent de l’Ouest Philippines, le panneau subductant atteint la zone de Changle-Nan’ao, avec probablement des morceaux de panneau cassé, provocant l’ascension de l’asthénosphère, responsable de la mise en place d’importants massifs granitiques et de filons. La tectonique de SCB pendant cette période est caractérisée par un système tectonique d’extension générale. Ce dispositif a été significativement perturbe par l’ouverture oligo-miocène de la mer de Chine du Sud et par la compression miocène de la marge à Taiwan. Ce modèle géodynamique reste à être amélioré par de futures investigations géologiques, géophysiques et géochimiques.
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- 2013
455. Strain distribution across a partially molten middle crust: Insights from the AMS mapping of the Carlos Chagas Anatexite, Araçuaí belt (East Brazil)
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Marcos Egydio-Silva, Eurídice Oliveira, Alain Vauchez, Geane Carolina G. Cavalcante, Pierre Camps, Instituto de Geociências [São Paulo], Universidade de São Paulo (USP), Manteau et Interfaces, Géosciences Montpellier, and Université des Antilles et de la Guyane (UAG)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université des Antilles et de la Guyane (UAG)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)
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010504 meteorology & atmospheric sciences ,[SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph] ,[SDE.MCG]Environmental Sciences/Global Changes ,Anatexites ,[PHYS.PHYS.PHYS-GEO-PH]Physics [physics]/Physics [physics]/Geophysics [physics.geo-ph] ,engineering.material ,010502 geochemistry & geophysics ,Feldspar ,01 natural sciences ,Lineation ,Magmatic flow ,Petrology ,0105 earth and related environmental sciences ,Crystallographic preferred orientation ,Geology ,Crust ,Geophysics ,Granulite ,Tectonics ,Magnetic mineralogy ,visual_art ,Araçuaí belt ,Anisotropy of magnetic susceptibility ,CRISTALOGRAFIA ,visual_art.visual_art_medium ,engineering ,Biotite ,Electron backscatter diffraction - Abstract
International audience; The easternmost part of the Neoproterozoic Araçuaí belt comprises an anatectic domain that involves anatexites (the Carlos Chagas unit), leucogranites and migmatitic granulites that display a well-developed fabric. Microstructural observations support that the deformation occurred in the magmatic to submagmatic state. Structural mapping integrating field and anisotropy of magnetic susceptibility (AMS) revealed a complex, 3D structure. The northern domain displays gently dipping foliations bearing a NW-trending lineation, southward, the lineation trend progressively rotates to EW then SW and the foliation is gently folded. The eastern domain displays E-W and NE-SW trending foliations with moderate to steeply dips bearing a dominantly NS trending lineation. Magnetic mineralogy investigation suggests biotite as the main carrier of the magnetic susceptibility in the anatexites and ferromagnetic minerals in the granulites. Crystallographic preferred orientation (CPO) measurements using the electron backscatter diffraction (EBSD) technique suggest that the magnetic fabric comes from the crystalline anisotropy of biotite and feldspar grains, especially. The delineation of several structural domains with contrasted flow fabric suggests a 3D flow field involving westward thrusting orthogonal to the belt, northwestward orogen-oblique escape tectonics and NS orogen-parallel flow. This complex deformation pattern may be due to interplay of collision-driven and gravity-driven deformations.
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- 2013
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456. Magma emplacement into the Lemptégy scoria cone (Chaîne Des Puys, France) explored with structural, anisotropy of magnetic susceptibility, and Paleomagnetic data
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Audray Delcamp, B. van Wyk de Vries, Michael S. Petronis, Physical Geography, and Geography
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Cinder cone ,geography ,Dike ,geography.geographical_feature_category ,monogenetic volcano ,rock magnetism ,paleomagnetism ,Pyroclastic rock ,anisotropy of magnetic susceptibility ,scoria cone construction ,Lemptégy volcano ,Rock magnetism ,Volcanic rock ,Igneous rock ,Geochemistry and Petrology ,microstructures ,Scoria ,Petrology ,Seismology ,Geology ,Trachybasalt - Abstract
The Lemptegy volcano is a small monogenetic scoria cone located in the Chaine des Puys, Auvergne, France, which erupted about 32,000 years ago. A first edifice (Lemptegy 1) formed during a trachybasalt eruption as a group of satellite vents of the Puy de Gouttes scoria cone. A second trachyandesitic edifice (Lemptegy 2) formed soon after and completely covered Lemptegy 1 with an 80-m-high breached cone. Since 1946, the Lemptegy volcano has been quarried for scoria and today offers unprecedented three-dimensional exposure of the subvolcanic plumbing system. To map the internal flow architecture of the plumbing system and to study the subvolcanic deformation of Lemptegy 2, structural mapping, petrographic observations, anisotropy of magnetic susceptibility (AMS), rock magnetic, and paleomagnetic data were collected. Field structural mapping and thin section study of tension gashes, Riedel shears, striations as well as ductile shear zones and bubbles allow the direction and sense of the magma flow to be determined. Twenty AMS sites were established in ten dikes (one to four sites in each dike) with 504 specimens analyzed and 479 specimens used to infer magma flow patterns. Structural data, the maximum susceptibility axis (K 1), and the imbrication of the magnetic foliation (K 1–K 2) planes indicate both upward and downward sense of flow, as well as flow toward and away from the central vent. Rock magnetic experiments reveal that a cubic Fe–Ti oxide phase, likely low-Ti titanomagnetite, is the principal magnetic phase carrying both the remanence and anisotropy. Paleomagnetic data from some sites yield statistically distinct, at the 95 % confidence level, remanence directions while at other sites the data are indistinguishable at the 95 % confidence level. The paleomagnetic results, observed steeply tilted scoria layers, internal unconformities, and faults show that as each dike was emplaced, it displaced earlier dikes evidencing subvolcanic deformation. The Lemptegy 2 volcano shares similarities in terms of inferred eruption style and structures with other scoria cones, such as Cerro Negro (Nicaragua), and thus provides an excellent field laboratory to investigate active scoria cones world-wide.
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- 2013
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457. Late Quaternary paleoseismic sedimentary archive from deep central Gulf of Corinth: time distribution of inferred earthquake-induced layers
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Corina Campos, Eduardo Carrillo, Aurelien van Welden, Efthymios Tripsanas, Christian Beck, Christian Crouzet, Institut des Sciences de la Terre (ISTerre), Centre National de la Recherche Scientifique (CNRS)-PRES Université de Grenoble-Université Joseph Fourier - Grenoble 1 (UJF)-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement [IRD] : UR219-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry]), Instituto de Ciencias de la Tierra, Universidad Central de Venezuela (UCV), Fugro SA Survey, FUGRO, Institut of Oceanography, Hellenic Centre for Marine Research (HCMR), Université de Savoie AAP-2012-16 AGRASM CNRS-INSU CNRS-INSU ARTEMIS, Universidad Simon Bolivar (USB), Universidad Central de Venezuela, Instituto de Ciencias de la Tierra, Caracas, Fugro Survey AS, Skøyen, Oslo, Norway, Fugro Survey SA, The here-presented investigations were funded through different grants and facilities: i) University of Savoie’s AAP-2012-16 AGRASM Grant, dedicated to ASM sedimentological application, ii) CNRS-INSU funding through ISTerre Laboratory. iii) CNRS-INSU ARTEMIS national radiocarbon AMS measurement program.FUNDAYACUCHO Grant N°20093262, ANR-10-BLAN-0619,SISCOR,Aléas, dynamique SISmogène, et couplages sismiques/asismiques d'un systeme de faille actives dans la région ouest du Rift de CORinthe, Grèce(2010), and Université Joseph Fourier - Grenoble 1 (UJF)-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement [IRD] : UR219-PRES Université de Grenoble-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)
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010504 meteorology & atmospheric sciences ,Corinth ,lcsh:QC801-809 ,Time distribution ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,lcsh:QC851-999 ,010502 geochemistry & geophysics ,01 natural sciences ,Lower half ,Turbidite ,On board ,lcsh:Geophysics. Cosmic physics ,Paleontology ,Geophysics ,Paleoseismicity ,Homogeneous ,Homogenite ,Anisotropy of magnetic susceptibility ,lcsh:Meteorology. Climatology ,Siliciclastic ,Sedimentary rock ,Quaternary ,Seismology ,Geology ,0105 earth and related environmental sciences - Abstract
A sedimentary archive corresponding to the last 17 cal kyr BP has been studied by means of a giant piston core retrieved on board R/V MARION-DUFRESNE in the North Central Gulf of Corinth. Based on previous methodological improvements, grain-size distribution and Magnetic Susceptibility Anisotropy (MSA) have been analysed in order to detect earthquake-induced deposits. We indentified 36 specific layers -Homogenites+Turbidites (HmTu) - intercalated within continuous hemipelagictype sediments (biogenic or bio-induced fraction and fine-grained siliciclastic fraction). The whole succession is divided into a non-marine lower half and a marine upper half. The “events” are distributed through the entire core and they are composed of two terms: a coarse-grained lower term and an upper homogeneous fine-grained term, sharply separated. Their average time recurrence interval could be estimated for the entire MD01-2477 core. The non-marine and the marine sections yielded close estimated values for event recurrence times of around 400 yrs to 500 yrs.
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- 2013
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458. ANISOTROPÍA DE SUSCEPTIBILIDAD MAGNÉTICA (ASM) DEL MIEMBRO SUPERIOR DE LA FORMACIÓN AMAGÁ, SECCIÓN QUEBRADA SABALETICAS, SW ANTIOQUEÑO Y SU RELACION CON LOS MOVIMIENTOS DEL SISTEMA DE FALLAS ROMERAL EN EL CENOZOICO TARDIO
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RAMÍREZ L., JACKELINE, SIERRA, GLORIA M., and MARÍN C., MARÍA I.
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fábrica magnética ,Anisotropy of magnetic susceptibility ,Formación Amagá ,Amagá Formation ,anisotropic parameters ,parámetros anisotrópicos ,magnetic fabric ,Anisotropía de susceptibilidad magnética - Abstract
La anisotropía de susceptibilidad magnética (ASM) es una herramienta útil para el análisis de la fábrica magnética de las rocas y de las deformaciones a que han sido sometidas. Estas fábricas anisotrópicas se expresan matemáticamente como un tensor de segundo orden y geométricamente mediante un elipsoide, cuyos ejes K1, K2, K3 representan respectivamente el eje máximo, intermedio y mínimo, y las relaciones entre ellos determinan los parámetros anisotrópicos que establecen las características del elipsoide. Los resultados obtenidos de ASM en la sección quebrada Sabaleticas en el SW antioqueño indican la existencia de al menos dos eventos deformacionales en el Miembro Superior de la Formación Amagá. Estas deformaciones se pueden correlacionar con las descritas por otros autores en zonas a lo largo del sistema Cauca-Romeral. El análisis global de los resultados, se asocian con depositación, enterramiento y levantamiento de los sedimentos de la cuenca Amagá y la superposición de eventos compresionales. The anisotropy of magnetic susceptibility (AMS) is an usefull tool to determine the magnetic fabric and their deformation in sedimentary rocks. The AMS can be expressed mathematically as second order tensors and geometrically as ellipsoids with K1, K2, K3 axes, which represent the maximun, medium and minimun axes respectively. The relationships between the axes determine the ASM parameters which in turn indicate the elipsoid shapes. The ASM results obteined in the Sabaleticas stream section in the SW of Antioquia, may indicate at least two deformational events in the Upper member of the Amagá Formation. These deformations are in coherent with those reported by other authors along the Cauca-Romeral fault system. In a global point of view, the ASM results are related with the activity of Romeral system along the Piedecuesta fault, during the late Cenozoic.
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- 2012
459. Les fluctuations du champ magnétique terrestre : des variations séculaires récentes aux renversements
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FANJAT, Gregory, Géosciences Montpellier, Université des Antilles et de la Guyane (UAG)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Université Montpellier 2, and Pierre Camps
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archeomagnetism ,[SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph] ,[SDE.MCG]Environmental Sciences/Global Changes ,rock magnetism ,[PHYS.PHYS.PHYS-GEO-PH]Physics [physics]/Physics [physics]/Geophysics [physics.geo-ph] ,Secular variations ,anisotropy of magnetic susceptibility ,paleointensity ,anisotropie de susceptibilité magnétique ,paléointensité ,reversal ,Variation séculaire ,archéomagnétisme ,magnétisme des roches ,renversement - Abstract
The Earth's magnetic field shows a large range of temporal variations from the year to several million years. I studied during my PhD thesis several aspects of these fluctuations, from recent secular variations to reversals. The first part of my manuscript deals with archeomagnetism, a discipline that allows to track the temporal variations of the Earth's magnetic field through millennia, mainly from archeological materials. I studied two sets of samples , one from Greece (Neolithic period 6800-3200 B.C.) and the other from Mexico (Palenque, Maya Classic period 320-840 A.D.), to acquire new archeointensity data in order to better constrain the secular variation of the geomagnetic field. By comparing my data with those available in the literature and with the various global and regional models, I showed that the secular variations during the Neolithic in Greece and during the first millennium in Central America are poorly defined. My data suggest that local components, not described by global models, may exist in these regions. They reinforce the importance of developing specific regional models. As a consequence, the acquisition of new high quality data is of main importance. The second part presents the description of a geomagnetic field reversal. This work was based on two points : first by studying transitional directions to provide new constraints on the possible preferred longitudinal paths of virtual geomagnetic poles (VGPs) and second by checking transitional paleointensities obtained on a volcanic sequence in Akaroa volcano (New Zealand). Indeed the transitional field intensity is significantly higher than the field intensity before and after the reversal. We re-sampled this sequence, and the directional results show a complex sequence of N-T-R-T-N-T-R polarity. The transitional VGPs obtained are clustered in two longitudinal bands through Australia and America. This observation seems to reinforce the assumption of a core-mantle interaction over several million years. Following a rock magnetic study, I selected samples that could provide a value for the Thellier and multispecimen paleointensity methods. The obtained paleointensity are relatively low (about 20 μT) during the polarity change and strong at the end of the sequence. Based both on the field strength values and on the radiochronological ages, showing that the sequence was erupted in a very short time, I suggest that only the C4AR.1n-C4Ar.1r reversal was recorded in this sequence. In this assumption, the reversal shows a complex path comparable to other reversals recorded in the northern hemisphere (for example the Steens Mountain ), including a rebound before stabilizing. Finally the last part is devoted to the development of a new methodology and a new apparatus to determine absolute paleointensity. Following the low success rate of paleointensity experiments from the previous study, I decided to test the multispecimen protocol, which can be applied to samples yielding a predominant multidomaine behavior. The main technical drawback of this method lies in the application of the laboratory field along the natural remanent magnetization, a difficult task to perform accurately in standard paleointensity ovens. Thus, we decided to adapt sample holders from our standard oven in order to allow the sample orientation in space and to develop an ultra-fast heating oven prototype particularly well-suited for this method, allowing to apply the laboratory field in the 3 dimensions. I checked the different multispecimen protocols on historical lavas from Reunion and Etna volcano, yielding very different magnetic mineralogies. For all flows, I obtained paleointensities very close from the expected values, regardless from the magnetic mineralogy, revealing the feasibility of our apparatus and the promising interest of the method. The application of various corrections on the statistical estimation of the intensity value or on the cooling rate had no significant impact on my results.; La première partie de ma thèse porte sur l'archéomagnétisme, discipline qui permet de retracer l'évolution temporelle du champ magnétique terrestre au travers des derniers millénaires, principalement à partir des matériaux archéologiques. J'ai étudié deux jeux d'échantillons provenant pour l'un de la Grèce (période néolithique, 6800-3200 avant J.C.) et pour l'autre du Mexique (Palenque, période Maya Classique 320-840 après J.C.), dans le but d'acquérir de nouvelles données d'archéointensité et de mieux contraindre la variation séculaire du champ magnétique terrestre. La comparaison de mes données avec celles disponibles dans la bibliographie et avec les différents modèles globaux et régionaux a mis en évidence que les variations séculaires au Néolithique en Grèce et au cours du premier millénaire en Amérique Centrale sont très mal définies. Mes données suggèrent que des composantes locales, non prisent en compte dans les modèles globaux peuvent exister au niveau de ces régions. Elles renforcent l'intérêt de développer des modèles régionaux précis. Pour ce faire, l'acquisition de nouvelles données de haute qualitéest un élément majeur. La deuxième partie traite de la description d'un renversement du champ magnétique terrestre. Cette étude a été basée sur deux points précis : étudier les directions transitionnelles afin d'apporter de nouvelles contraintes sur le possible confinement longitudinal des pôles géomagnétiques virtuels (PGV) d'une part, et d'autre part vérifier des paléointensités transitionnelles obtenues sur la séquence volcanique d'Akaroa (Nouvelle Zélande), dont l'intensité est significativement supérieure à celles des intensités avant et après le renversement. Nous avons ré-échantillonné cette séquence, et l'évolution directionnelle obtenue pour ce renversement est une succession complexe de polarités N-T-R-T-N-T-R. Les PGV obtenus semblent se regrouper sous deux bandes longitudinales sous l'Australie et l'Amérique, ce qui renforce l'hypothèse d'une interaction entre le manteau et le noyau sur plusieurs millions d'années. Suite à une étude de minéralogie magnétique, j'ai sélectionné les échantillons susceptibles de fournir une valeur de paléointensité par les méthodes de Thellier et du multispecimen. Les paléointensités obtenues sont relativement faibles (environ 20 μT) au cours du changement de polarité et forte à la fin de la séquence. Mon interprétation, basée à la fois sur les valeurs de l'intensité du champ et sur les données radiochronologiques montrant que la séquence s'est mise en place très rapidement, est de considérer que seul le renversement C4Ar.1n-C4Ar.1r a été enregistré dans cette séquence. Dans cette hypothèse, le renversement montre un cheminement complexe comparable à d'autres renversements enregistrés dans l'hémisphère nord (comme celui de la Steens Mountain par exemple), incluant un phénomène de rebond avant de se stabiliser. La troisième partie de ma thèse est consacrée au développement d'une nouvelle méthodologie et d'un nouvel appareillage pour déterminer des paléointensités. Le faible taux de réussite des expériences de paléointensité de l'étude précédente m'a poussé à m'intéresser au protocole multispecimen, qui peut s'appliquer aux échantillons possédant un comportement polydomaine. L'inconvénient technique majeur de cette méthode réside dans l'application du champ le long de l'aimantation naturelle, difficile à réaliser avec précision dans les fours standards. Pour ce faire, nous avons décidé de développer des porte-échantillons permettant d'orienter les échantillons dans l'espace pour le four standard et un prototype de four à chauffage ultra-rapide particulièrement bien adapté avec la possibilité d'orienter le champ appliqué dans les 3 dimensions. J'ai testé les différents protocoles de la méthode sur des laves historiques de la Réunion et de l'Etna, possédant des minéralogies très différentes. Pour l'ensemble des coulées étudiées, j'ai obtenu des paléointensités très proches des valeurs attendues, et ce indépendamment de la minéralogie, révélant ainsi le faisabilité de notre appareillage et le côté prometteur de la méthode. L'application de diverses corrections sur la statistique d'estimation de la valeur de l'intensité ou sur le taux de refroidissement n'ont eu aucun impact notable sur mes résultats.
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- 2012
460. Assessment of petrophysical surface data of the Harşit granitoid in Trabzon, in northeastern Turkey
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Ali Aydin and Sener Ceryan
- Subjects
emplacement ,Turkey ,Pluton ,Granite ,Geochemistry ,Magnetic fabrics ,Fault (geology) ,Deep sea ,Cretaceous ,granitoid ,Harşit granitoid ,zonation ,Geochemistry and Petrology ,Granitic magmas ,Geomorphology ,pluton ,Structural data ,geography ,magnetic anisotropy ,geography.geographical_feature_category ,Late cretaceous ,Tectonic deformations ,Petrophysics ,Tectonics ,Tectonic control ,Surface data ,magnetic fabric ,Geophysics ,assessment method ,Volcano ,Petrofabrics ,Magma ,Anisotropy of magnetic susceptibility ,Eurasia ,Paleocene ,Anisotropy of magnetic susceptibility (AMS) ,Trabzon ,Micro-structural ,Geology ,Petrophysical ,Fault system ,Study areas ,magnetic susceptibility - Abstract
The Harşit granitoid in northeastern Turkey, comprises four separate granite units that are apparently unfoliated. The Harşit granitoid was investigated here by using microstructural, petrofabric and anisotropy of magnetic susceptibility (AMS) data. The structural data of the granitoid were found to be highly compatible with the zonation recognized from AMS measurements. The orientation of magnetic fabrics within the granite units indicates that tectonic deformation might have occurred coevally with the magmatic emplacement of the intrusion. When we evaluated the manners on the scale of the pluton that the disruption took place in the form of uplifting, probably related to a rapid migration of the volcanic front and the documented change from deep sea sedimentation predominant until late Cretaceous to shallower environments during the Paleocene. The possible tectonic control of fault systems on the ascent and emplacement of the granitic magma in the study area, however, cannot be completely ruled out because the Harşit granitoid is situated at or very near the NAF systems in northern Anatolia. In any case, the intrusion is clearly discordant to the regional deformational features formed during the collisional events between the Eurasia and Anatolia plates in northern Turkey. © 2011 Springer Basel AG.
- Published
- 2012
461. Anisotropy of magnetic susceptibility and identification of tilted sediment cores from the Bohai Sea
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Hao, Chen, Wei-min, Sun, and Hong-cai, Zhang
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- 1996
- Full Text
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462. Significance of magnetic and petrofabric in Karoo-feeder dykes, northern Lebombo
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Michael K. Watkeys, Charles Aubourg, Warwick W. Hastie, School of Geological and Computer sciences, University of Natal, Laboratoire des Fluides Complexes et leurs Réservoirs (LFCR), and Centre National de la Recherche Scientifique (CNRS)-Université de Pau et des Pays de l'Adour (UPPA)-TOTAL FINA ELF
- Subjects
010504 meteorology & atmospheric sciences ,[SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph] ,Large igneous province ,[SDE.MCG]Environmental Sciences/Global Changes ,[PHYS.PHYS.PHYS-GEO-PH]Physics [physics]/Physics [physics]/Geophysics [physics.geo-ph] ,engineering.material ,010502 geochemistry & geophysics ,01 natural sciences ,Mantle plume ,Plagioclase ,Petrology ,Geomorphology ,0105 earth and related environmental sciences ,Earth-Surface Processes ,Rift ,Triple junction ,Magma flow ,Northern Lebombo dyke swarm ,Imbrication ,Geophysics ,Monocline ,Magma ,Anisotropy of magnetic susceptibility ,engineering ,Karoo feeder dykes ,Geology - Abstract
International audience; The orientation of magnetic and petrofabric in 14 mafic dykes of the Northern Lebombo dyke swarm (NLDS) has been determined using the anisotropy of magnetic susceptibility (AMS) and mineral shape preferred orientation (SPO) in order to constrain the magma flow direction during dyke emplacement. The N-S striking NLDS intruded the N-S trending; 700. km long Lebombo faulted monocline between 182 and 178. Ma. The Lebombo faulted monocline, which forms the eastern-most sub-province of the Karoo large igneous province (LIP), is essentially a volcanic rifted margin with a protracted magmatic and tectonic history related to the break-up of southern Gondwana. It also forms the southern limb of the Karoo triple-rift system which has been hypothesised to have formed by a mantle plume centred on the triple junction locus. The other two arms of the rift which converge on the triple junction are the WNW trending Okavango dyke swarm (ODS) and NE trending Save-Limpopo dyke swarm (SLDS). In the NLDS it is found that the magnetic fabric, which is of magmatic origin in ~. 50% of the samples, is carried predominantly by stoichiometric magnetite. There is remarkable agreement between the orientations of the AMS and SPO fabrics and at least two dykes show coaxial AMS and mineral SPO fabric consistent with lateral magma flow from the north. This direction is supported by the imbrication of the foliations of the well-defined bulk AMS and plagioclase SPO fabric when viewed in a dyke co-ordinate system. Although steeply plunging maximum axes occur in the SPO fabric, their possible use as magma flow vectors is questioned because they do not necessarily mimic the elongation of plagioclase grains visible in orientated thin sections. The magnetic and petrofabric of the NLDS is interpreted to have developed during lateral magma flow from the locus of the Karoo triple junction.
- Published
- 2011
- Full Text
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463. Magnetic characterisation of folded aeolian sandstones: Interpretation of magnetic fabrics in diamagnetic rocks
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Martin Guiton, Julien Schmitz, Jean-Paul Callot, J. L. Faure, Jean-Marc Daniel, Jean-Marie Mengus, William Sassi, Philippe Robion, IFP Energies nouvelles (IFPEN), Laboratoire Géosciences et Environnement Cergy (GEC), Fédération INSTITUT DES MATÉRIAUX DE CERGY-PONTOISE (I-MAT), Université de Cergy Pontoise (UCP), Université Paris-Seine-Université Paris-Seine-Université de Cergy Pontoise (UCP), and Université Paris-Seine-Université Paris-Seine
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emplacement ,folding ,Diagenetics ,010504 meteorology & atmospheric sciences ,Sedimentary magnetic fabric ,Split Mountain ,Horizontal stress ,010502 geochemistry & geophysics ,01 natural sciences ,sandstone ,Fold ,Anisotropy ,Petrology ,Diamagnetic matrix ,Magnetic domains ,magnetic anisotropy ,Characterisation ,Split ,Structural geology ,Fold (geology) ,Sedimentology ,Magnetic anisotropy ,Geophysics ,eolian deposit ,Anisotropy of magnetic susceptibility ,Diamagnetism ,Susceptibility anisotropy ,Fracture network ,diagenesis ,Geology ,magnetic susceptibility ,fault ,Magnetic domain ,Sand dunes ,Magnetic characterization ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,Magnetic fabrics ,Local deviation ,Tectonic fabrics Engineering controlled terms: Fracture ,Lineation ,Sub-groups ,Structural domains ,strain ,Strain Anisotropy of magnetic susceptibility ,lineation ,0105 earth and related environmental sciences ,Earth-Surface Processes ,Landforms ,paleostress ,Anticline ,Tectonics Engineering main heading: Magnetic anisotropy GEOBASE Subject Index: anticline ,Magnetic susceptibility ,magnetic fabric ,Layer parallel shortenings ,Degree of anisotropy ,Laramide ,tectonic setting Regional Index: Croatia ,fracture ,Existing structure ,Paleostresses ,Bounding faults - Abstract
International audience; This study provides an original example of exploitation of Anisotropy of Magnetic Susceptibility (AMS) for rocks with weak magnetic susceptibility. Within the upper Weber Sandstone at Split Mountain, Utah, 430 cores from 31 sites were collected for magnetic characterization. The magnetic susceptibility ranges from -10 to 10μSI, indicating a mostly diamagnetic matrix, with degree of anisotropy up to 1.6. Specific treatment of magnetic susceptibility allows using diamagnetic data. The fabrics are fairly clustered and triaxial. Sedimentary magnetic fabrics show a foliation plane parallel to the lamina of the sand dunes, without defined lineation. Apart from sedimentary fabrics (70%). Magnetic fabric patterns averaged for sites distributed on the anticline are well defined in sub-groups related to the major structural domains of the anticline. The fracture network at Split Mountain is composed of a dominant N120 set and a secondary N035 set. A scenario of strain record is proposed based on the correlation of (1) fracture sets orientation, (2) diagenetic cementation, (3) paleostresses and (4) distribution of magnetic susceptibility anisotropy. Following the Sevier orogeny and N120 fracture set emplacement, the N035 fracture network and AMS signal were recorded during the Laramide Layer Parallel Shortening phase, with local deviation along pre-existing structures, and recorded a partitioning of the strain during early folding, with a maximum horizontal stress axis perpendicular to the fold bounding faults within the fold.
- Published
- 2010
- Full Text
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464. Structure and Accretion at Mid-Ocean Ridges With High Magma Supply: Perspectives From Seafloor Escarpments and Iceland
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Horst, Andrew Jay and Horst, Andrew Jay
- Abstract
Despite vast amounts of data about the ocean floor, very little is known about processes operating at mid-ocean ridge spreading centers and the generation of oceanic lithosphere that covers approximately 2/3 of Earth's surface. In particular, geologist are uncertain about specific details of magmatic and tectonic processes beneath these divergent plate boundaries and how these processes may vary along the spreading axis. Investigations that combine geologic relationships and magnetic properties continue to yield fundamental tools for understanding and constraining seafloor spreading processes. This thesis contains a collection of studies designed to characterize structural geology and magnetic properties of oceanic crust formed in regions with high magma supply. A brief overview is provided in an introduction to three separate chapters that are considered individual contributions. Chapter one presents paleomagnetic and structural data from sheeted dikes that are used in combination with regional geologic relationships to constrain the deformation and tectonic history of oceanic crust exposed at the tip of a propagating rift on the East Pacific Rise. Chapter two describes the magnetic fabrics of sheeted dikes from seafloor exposures that provide evidence for a wide range of magma flow directions beneath fast-spreading ridges with high and relatively continuous magma supply. Chapter three provides paleomagnetic evidence to support structural observations for significant rotations of crustal blocks within a migrating transform fault zone in North Iceland that may exhibit similar kinematics to other oceanic transforms.
- Published
- 2013
465. Magnetic fabrics and emplacement of the Eisgarn granitoids (Moldanubian Plutonic Complex)
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Paclíková, Jana, Verner, Kryštof, and Buriánek, David
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Mrákotínský a Klenovský pluton ,Moldanubian Plutonic Complex ,anisotropy of magnetic susceptibility ,dvojslídný granit ,Mrákotín and Klenov pluton ,Moldanubický plutonický komplex ,two-mica granite ,anizotropie magnetické susceptibility - Abstract
English abstract We consider our preliminary results of structural and AMS analyses of granitoids of the Mrákotín and Klenov Plutons located in the northeastern part of the Moldanubian Plutonic Complex. Both plutons have a peraluminous, high-K character formed by partial melting of a crustal metasedimentary (metapelite) source at relatively lower temperatures. The Mrákotín pluton (eastern part of the plutonic complex) was emplaced posttectonically at around 327 Ma and records a crucial role of magmatic stoping during magma ascent and emplacement. In contrast, the Klenov pluton (western part of the plutonic complex) was emplaced syntectonically with regional HT-LP tectonometamorphic event (formation of gently to moderately NNE dipping metamorphic schistosity).
- Published
- 2010
466. Reconstruction of the Kozákov lava flow based on magnetic- and mineral-fabric study
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Černá, Aneta, Rapprich, Vladislav, and Hradecký, Petr
- Subjects
minerální stavba ,vulkanologie ,Prackov volcano ,anisotropy of magnetic susceptibility ,kozákovská láva ,prackovský vulkán ,volcanology ,anizotropie magnetické susceptibility ,Kozákov lava ,EBSD ,mineral fabric - Abstract
Combined anisotropy of magnetic susceptibility (AMS) and crystallographic studies were applied on a neogenne lava flow, for which we know the supposed flow path. Samples were studied under microscope, the minerals were analysed on microprobe, the orientation of olivine crystals was determined via EBSD and magnetic properties were studied. AMS data acquired from samples collected from representative outcrops of lava flow show weak preferred orientation of magnetite-ulvöspinel. EBSD analysis suggests only slight orientation of plagioclase in one sample. Analysed composition of olivine corresponds with mathematical model for eruption temperature and crystallization succession. Rootless cone (disorderly breccia cone) in lava body was found and desribed in the abandoned Machův lom quarry.
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- 2010
467. Neotectonics of the northwestern edge of the barreal- Las Peñas belt, precordillera Sur
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Terrizzano, Carla Marina, Cortés, José María, and Rapalini, Augusto E.
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DEFORMACION CUATERNARIA ,TOMOGRAFIA ELECTRICA RESISTIVA ,NEOTECTONICS ,GEOMORFOLOGIA TECTONICA ,TECTONIC GEOMORPHOLOGY ,ANISOTROPIA DE SUSCEPTIBILIDAD MAGNETICA ,NEOTECTONICA ,QUATERNARY DEFORMATION ,ANISOTROPY OF MAGNETIC SUSCEPTIBILITY ,PRECORDILLERA SUR ,TOMOGRAPHY OF ELECTRICAL RESISTIVITY - Abstract
En este trabajo se presenta un estudio neotectónico del extremo noroccidental del cinturón Barreal – Las Peñas, Precordillera Sur, provincias de San Juan y Mendoza. La estratigrafía está caracterizada por un sustrato paleozoico, sucesiones permotriásicas, cuerpos intrusivos neógenos y una cobertura sedimentaria cenozoica. Se ha puesto especial énfasis en la estratigrafía cenozoica, especialmente cuaternaria, habiéndose reconocido cuatro niveles de agradación que fueron asignados al Pleistoceno medio-inferior, al Pleistoceno medio, al Pleistoceno superior y al Holoceno. A partir del análisis estratigráfico, estructural y de la geomorfología tectónica del área y sobre la base de tomografías eléctricas resistivas y datos de anisotropía de susceptibilidad magnética (AMS), se ha caracterizado la deformación neógena y cuaternaria de la región. Las principales unidades morfotectónicas que integran el área de estudio corresponden a los bloques Barreal y Ansilta. Entre ambos se extiende un amplio sector pedemontano que integra parte de la depresión de Barreal - Uspallata. La estructura neógena y cuaternaria del conjunto de esos bloques montañosos está definida por corrimientos de vergencias opuestas, hacia el oeste en el bloque Barreal y hacia el este en el bloque Ansilta. Asimismo, se ha definido un cinturón de deformación cuaternario de ligazón débil a lo largo del valle de Barreal - Uspallata, el cinturón Yalguaraz. El mismo, de dirección NNO y carácter transpresivo sinestral, conecta mecánicamente el sector precordillerano correspondiente al cinturón Barreal – Las Peñas con la región central de la Precordillera Sur y la Cordillera Frontal. En tiempos cuaternarios, el cinturón Yalguaraz muestra tres etapas de deformación. El estilo tectónico es el producto de la interferencia de elementos estructurales en distintas direcciones como consecuencia de la reactivación de estructuras previas, de edad paleozoica y triásica, oblicuas y transversales al orógeno andino. This work presents a neotectonic study of the northwestern edge of the Barreal – Las Peñas belt, Precordillera Sur, San Juan and Mendoza provinces. At the study area, the stratigraphy is characterized by a Paleozoic basement, Permian-Triassic sequences, Neogene intrusive bodies and a Cenozoic sedimentary cover. It was placed a special emphasis on the Cenozoic stratigraphy, especially on the Quaternary one. Four Quaternary aggradation levels were recognized. They were assigned to the Middle to Lower Pleistocene, Middle Pleistocene, Late Pleistocene and Holocene. The Neogene and the Quaternary deformation were characterized by means of stratigraphical and structural analyses, studies of tectonic geomorphology and geophysical methods, such as tomographies of electrical resistivity and anisotropy of magnetic susceptibility (AMS). The Barreal and the Ansilta blocks, and a wide piedmont area between them (Barreal – Uspallata depression), represent the main morphotectonic units of the study area. The Neogene and Quaternary structure of these blocks is defined by oppositevergence thrusts, to the west in the Barreal block and to the east in the Ansilta block. Along the Barreal – Uspallata depression, a Quaternary soft-linked deformation belt, the Yalguaraz belt, was defined. It corresponds to a NNW-trending sinistral transpressive zone which links the Barreal – Las Peñas belt with the central region of the Precordillera Sur and the Cordillera Frontal. During the Quaternary, this belt shows three different deformation stages. The tectonic style of the area is the consequence of the Andean reactivation and interference of transverse and oblique older structures, Paleozoic and Triassic in age. Fil: Terrizzano, Carla Marina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
- Published
- 2010
468. Anisotropy of magnetic susceptibility study of kaolinite matrix subjected to biaxial tests
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Aniruddiia Sengupta
- Subjects
Magnetism ,Biaxial Test ,Soil Science ,Mineralogy ,Strain Localization ,Anisotropy of Magnetic Susceptibility ,Magnetic susceptibility ,Magnetic anisotropy ,Magnetization ,Shear (geology) ,Geochemistry and Petrology ,Kaolinite ,Earth and Planetary Sciences (miscellaneous) ,Composite material ,Anisotropy ,Geology ,Water Science and Technology ,Principal axis theorem - Abstract
The potential for structural failure of consolidated clay materials, which is of great importance in many applications, typically are assessed by measuring the localized strain bands that develop under anisotropic load stress. Most methods are precluded from providing a full understanding of the strain anisotropy because they only give two-dimensional information about the stressed clay blocks. The purpose of the present study was to investigate three-dimensional strain localization in a kaolinite matrix, caused by strain anisotropy due to a biaxial plane-strain test, using a relatively new method known as Anisotropy of Magnetic Susceptibility (AMS). This method involves induction of magnetism in an oriented sample in different directions and measurement of the induced magnetization in each direction. The AMS analyses were performed on core samples from different parts of the deformed kaolinite matrix. The degree of magnetic anisotropy (P′), which is a measure of the intensity of magnetic fabric and a gauge of strain intensity, was shown to be greater in cores containing shear bands than in those containing none. A threshold value for P′ for the deformed kaolinite matrix was identified, above which shear bands may develop. The comparison of the shape parameter (T), obtained from undeformed and deformed samples, illustrated a superimposition of prolate strain over the original oblate fabric of the kaolinite matrix. The orientation of the principal strain axis revealed that reorientation or rotation of the principal axis occurred along the shear bands.
- Published
- 2009
469. Anisotropía de susceptibilidad magnética (ASM) del miembro superior de la formación Amagá, sección quebrada sabaléticas, SW antioqueño y su relación con los movimientos del sistema de fallas Romeral en el Cenozoico tardio
- Author
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Ramírez Londoño, Jackeline, Sierra Lopera, Gloria María, Marín Cerón, María Isabel, Ramírez Londoño, Jackeline, Sierra Lopera, Gloria María, and Marín Cerón, María Isabel
- Abstract
The Anisotropy of Magnetic Susceptibility (AMS) is an usefull tool to determine the magnetic fabric and their deformation in sedimentary rocks. The AMS can be expressed mathematically as second order tensors and geometrically as ellipsoids with K1, K2, K3 axes, which represent the maximun, medium and minimun axes respectively. The relationships between the axes determine the ASM parameters which in turn indicate the elipsoid shapes. The ASM results obteined in the Sabaleticas stream section in the SW of Antioquia, may indicate at least two deformational events in the Upper member of the Amagá Formation. These deformations are in coherent with those reported by other authors along the Cauca-Romeral fault system. In a global point of view, the ASM results are related with the activity of Romeral system along the Piedecuesta fault, during the late Cenozoic., La Anisotropía de Susceptibilidad Magnética (ASM) es una herramienta útil para el análisis de la fábrica magnética de las rocas y de las deformaciones a que han sido sometidas. Estas fábricas anisotrópicas se expresan matemáticamente como un tensor de segundo orden y geométricamente mediante un elipsoide, cuyos ejes K1 , K2, K3 representan respectivamente el eje máximo, intermedio y mínimo, y las relaciones entre ellos determinan los parámetros anisotrópicos que establecen las características del elipsoide. Los resultados obtenidos de ASM en la sección quebrada Sabaleticas en el SW antioqueño indican la existencia de al menos dos eventos deformacionales en el Miembro Superior de la Formación Amagá. Estas deformaciones se pueden correlacionar con las descritas por otros autores en zonas a lo largo del sistema Cauca-Romeral. El análisis global de los resultados, se asocian con depositación, enterramiento y levantamiento de los sedimentos de la cuenca Amagá y la superposición de eventos compresionales.
- Published
- 2012
470. Paleomagnetic and AMS results from Oligocene ash-flow tuffs of the eastern San Juan Mountains : implications for the evolution of the western margin of the San Luis Basin, northern Rio Grande Rift
- Author
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Geissman, John, Roy, Mousumi, Sussman, Aviva, Wawrzyniec, Tim, Mason, Stephanie N., Geissman, John, Roy, Mousumi, Sussman, Aviva, Wawrzyniec, Tim, and Mason, Stephanie N.
- Subjects
- Paleomagnetism
- Abstract
The San Luis Basin (SLB) of the northern Rio Grande rift (RGR) is a spectacular intermontane basin in south-central Colorado. The SLB is an east-dipping, half graben basin that formed in response to extension beginning ca. 26 Ma in the Cordillera. Oligocene ash-flow tuffs exposed in the eastern San Juan Mountains and along the western margin of the SLB provide an excellent opportunity to study the kinematic history of the northern Rio Grande rift using paleomagnetism. Outflow deposits of ash-flow tuffs are generally excellent recorders of the geomagnetic field and can be used to study the vertical-axis rotation component of extension related to the opening of the SLB. Four ash-flow tuffs (Carpenter Ridge, Fish Canyon, Chiquito Peak and Saguache Creek Tuffs) that were erupted between ca. 32 and 27 Ma were sampled at a total of 84 sites for paleomagnetic, rock magnetic, and magnetic fabric data. Paleomagnetic data indicate some complexities with using large-volume, regionally extensive outflow deposits of ash-flow tuffs, specifically that relatively thick outflow deposits (with thicknesses exceeding 100 m) may record paleosecular variation of the geomagnetic field. Even with these complications, the four targeted San Juan ash-flow tuffs may still be evaluated for regional domains of potential vertical-axis rotation. Overall, we observe a lack of vertical-axis rotation along the western margin of the SLB. Shear and fault linkage in the hanging wall of the major normal fault of the SLB does not appear to play a role in the evolution of slightly extended terranes. Distal outflow deposits of ash-flow tuffs may also be difficult, if not impossible, to tell apart and paleomagnetism is used to distinguish two units that have, until presently, been grouped together as the Chiquito Peak Tuff. The magnetic fabric of these Oligocene ash-flow tuffs was also measured and analyzed for complexities due to paleotopography and single-domain magnetic carriers. Preliminary results from
- Published
- 2011
471. Kinematic approach by means of AMS study in the Boltaña anticline (southern Pyrenees
- Author
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Ministerio de Educación y Cultura (España), Ministerio de Ciencia e Innovación (España), Pueyo Morer, Emilio Luis [0000-0001-8480-381X], Barnolas Cortina, Antonio [0000-0002-4124-3426], Mochales López, Tania, Pueyo Morer, Emilio Luis, Casas-Sainz, Antonio M., Barnolas Cortina, Antonio, Ministerio de Educación y Cultura (España), Ministerio de Ciencia e Innovación (España), Pueyo Morer, Emilio Luis [0000-0001-8480-381X], Barnolas Cortina, Antonio [0000-0002-4124-3426], Mochales López, Tania, Pueyo Morer, Emilio Luis, Casas-Sainz, Antonio M., and Barnolas Cortina, Antonio
- Abstract
[EN] In this work we present AMS results obtained from several profiles in the Lutetian, carbon-ate-slope sequence located in the eastern limb of the Boltaña anticline. The AMS analyses allow us todefine the deformational events related to the formation of the Boltaña anticline and its progressiverotation during Eocene (Late Lutetian) times, acting as a passive marker of the deformation, after a veryearly record of LPS during diagenesis.
- Published
- 2010
472. Crystallographic–magnetic correlations in single-crystal haemo-ilmenite: New evidence for lamellar magnetism
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Peter Robinson, Laurie L. Brown, Suzanne A. McEnroe, Florian Heidelbach, and Ann M. Hirt
- Subjects
Haemo-ilmenite ,Magnetic moment ,Natural remanent magnetization ,Magnetism ,Anisotropy of magnetic susceptibility ,Electron backscatter diffraction ,Haematite ,Lamellar magnetism ,Magnetic susceptibility ,Crystallography ,Magnetization ,Geophysics ,Geochemistry and Petrology ,Remanence ,Single crystal ,Geology - Abstract
Geophysical Journal International, 165 (1), ISSN:0956-540X, ISSN:1365-246X
- Published
- 2006
473. Correlations of Neogene ignimbrites in southern Peru – Contribution of physical and magnetic properties to the understanding of emplacement and welding processes
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Paquereau-Lebti, Perrine, Paquereau-Lebti, Perrine, Laboratoire Magmas et Volcans (LMV), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Université Blaise Pascal - Clermont-Ferrand II, Jean-Claude Thouret(J.C.Thouret@opgc.univ-bpclermont.fr), Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), and Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS)
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welding ,stratigraphie ,stratigraphy ,paleomagnetism ,anisotropy of magnetic susceptibility ,physical properties ,anisotropie de susceptibilité magnétique ,ignimbrite ,[SDU.STU.AG] Sciences of the Universe [physics]/Earth Sciences/Applied geology ,géochimie ,Peru ,transport ,Pérou ,propriétés physiques ,soudure ,[SDU.STU.AG]Sciences of the Universe [physics]/Earth Sciences/Applied geology ,paléomagnétisme ,geochemistry - Abstract
Correlations indicate that four ignimbrites were emplaced between middle Miocene and early Pleistocene in the Arequipa area: the Rio Chili Ignimbrite, RCI, 13.35 Ma old; the La Joya Ignimbrite, LJI, 4.83 Ma old; the Arequipa Airport Ignimbrite, AAI, 1.77 Ma old; and the Yura Tuff, YT (1.03-1.84 Ma). Geochemical and isotopic compositions displayed by the ignimbrites, can be explained by increasing magma differentiation and contamination, in two different "crustal domains". The LJI, whose Te ranged from 650 to 680°C, displays the highest welding degree as show by physical properties. The AAI high induration is the consequence of cementation by secondary vapor phase crystallisation. The low degree of anisotropy and large dispersion of AMS directions in the LJI, may reflect turbulent transport of low concentration granular flows. In contrast, the AAI records a well-defined and oriented magnetic fabric, which can be the consequence of dense pyroclastic flows. Flow directions and isopleths map, of the AAI, point to a source now buried under the Chachani volcanic complex., Nos corrélations permettent d'identifier quatre ignimbrites dans la région d'Arequipa, L'Ignimbrite du Rio Chili (IRC: 13.35 Ma), l'Ignimbrite de La Joya (ILJ: 4.83 Ma), l'Ignimbrite de l'Aéroport d'Arequipa (IAA: 1.77 Ma), et les Tufs de Yura (TY: 1.03-1.84 Ma). Les différentes compositions géochimiques et isotopiques sont expliquées par la différenciation des magmas dans deux "domaines crustaux", et par un taux de contamination crustale croissant entre le Pliocène et le Pléistocène. L'étude des variations des propriétés physiques, met en évidence une évolution et un degré de soudure variables selon les ignimbrites. La faible définition de l'orientation de l'ASM dans l'ILJ, pourrait refléter un transport sous la forme d'un écoulement turbulent, d'une coulée de cendres et ponces diluée. La bonne définition de l'orientation de l'ASM dans l'IAA, serait la conséquence d'un transport de coulées granulaires denses. Les directions d'écoulement, et la variation latérale de la taille des fragments lithiques de l'IAA, indiquent une source enterrée sous le complexe volcanique du Chachani.
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- 2006
474. Injection mechanism of clay-rich sediments into dikes during earthquakes
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Lévi, Tsafir, Weinberger, Ram, Aifa, Tahar, Eyal, Yehuda, Marco, Schmuel, Department of Geological and Environmental Science, Ben-Gurion University of the Negev, Ben-Gurion University of the Negev (BGU), Geological Survey of Israel (GSI), Geological Survey of Israel, Géosciences Rennes (GR), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre Armoricain de Recherches en Environnement-Centre National de la Recherche Scientifique (CNRS), Tel Aviv University [Tel Aviv], Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre Armoricain de Recherches en Environnement-Centre National de la Recherche Scientifique (CNRS), and Tel Aviv University (TAU)
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fluid flow ,Dead Sea Transform ,[SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph] ,clastic dikes ,anisotropy of magnetic susceptibility - Abstract
International audience; Clastic dikes may form by simultaneous fracture propagation in rocks and injection of clastic material into the fractures resulting from strong seismic shaking. We studied the mechanisms of clastic-dike formation within the seismically active Dead Sea basin, where hundreds of clastic dikes cross-cut the soft rock of the late Pleistocene lacustrine Lisan Formation. We analyzed the anisotropy of magnetic susceptibility (AMS) of dikes with known formation mechanisms and defined the characteristic AMS signatures, mainly of dikes developed by injection process. Most of the dikes were emplaced due to fluidization of clay-rich sediment and are characterized by triaxial AMS ellipsoids. The dominant triaxial AMS ellipsoids along the dike widths suggest that the fluidization mechanism of clay-rich sediment is different from the known liquefaction process of sand. The AMS analysis supported by field evidence indicates that the injection of clay-rich sediment is characterized by two main regimes: (1) Vertical flow characterized by subvertical V2 axes and subhorizontal V1 and V3 axes. The V2 axes may indicate the flow directions during fast flow. (2) Horizontal slow flow characterized by subvertical V3 axes and subhorizontal V1 and V2 axes. A streaked AMS pattern mainly composed of V2 and V3 axes represents a turbulent flow that generated local eddies simultaneously with the clastic transport. The AMS parameters along the dikes and possible grain imbrications along dike walls support organization of grains under high strain rates. This application of the AMS method provides a petrofabric tool for identifying seismites and inferring their flow kinematics in complex geologic areas.
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- 2006
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475. Magma flow and thermal contraction fabric in tabular intrusions inferred from AMS analysis. A case study in a late-Variscan folded sill of the Albarracin Massif (southeastern Iberian Chain, Spain)
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Carlos Galé, C. Rillo, Enrique Arranz, A. Gil-Imaz, Andrés Pocoví, Marceliano Lago, and E. Guerrero
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geography ,Thermal contraction ,geography.geographical_feature_category ,Lava ,Geology ,Magma flow ,Massif ,Anisotropy of Magnetic Susceptibility ,Late-Variscaan sill ,Magnetic susceptibility ,chemistry.chemical_compound ,chemistry ,Sill ,Iberian Chains ,Magnetic mineralogy ,Magma ,Petrology ,Anisotropy ,Geomorphology ,Magnetite - Abstract
13 pages, 8 figures, 2 tables.-- et al., The effects of different petrological processes on the rock fabric of a folded sill from the Albarracin Massif (southeastern Iberian Chain, Spain) were studied by means of the anisotropy of magnetic susceptibility (AMS) technique. The most outstanding feature of the sill at outcrop-scale is a network of joints linked to thermal contraction, which define polygonal columns. The analysis of the magnetic fabric, taking the orientation of sill walls and column axes as a reference and using the ‘restored’ directional data corresponding to the whole of K3 susceptibility axes, has revealed magnetic fabrics related to two processes: (a) magma flow with a SW-trending flow vector characterized by a curved geometry of the magma foliations and (b) thermal contraction coeval to lava cooling. Early magnetite crystals, grown in a relatively high viscosity calc-alkaline magma, are the main carriers involved in the AMS fabric. Passive rotation of the early magnetic mineralogy within a medium-viscosity magma explains the magnetic fabric linked to both magma flow and near-solidus thermal contraction of the magma. Late-Variscan folding of the sill produced the rigid-body reorientation of the magnetic fabric., Measurements of AMS and IRM data were carried out at the Institute of Earth Sciences ‘Jaume Almera’, C.S.I.C. (Barcelona, Spain), using a susceptibility bridge Kappabridge KLY-2.02 and a Pulse magnetizer. Hysteresis measurements were carried out at the Institute of Materials Science of Aragon (ICMA), CSIC-University of Zaragoza, Spain. We gratefully acknowledge the suggestions and constructive criticism of Prof. L. Geoffroy and those of the anonymous reviewer, which helped to improve the manuscript. This work is included in the objectives, and supported by the research project BTE2002-04168-C03-01 (DGES, Spanish Ministry of Education). Financial support from the University of Zaragoza and from CSIC (PAI2003) is acknowledged.
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- 2006
476. Earthquake-induced clastic dikes detected by anisotropy of magnetic susceptibility
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Ram Weinberger, Tahar Aïfa, Yehuda Eyal, Shmuel Marco, T. Levi, Géosciences Rennes (GR), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre Armoricain de Recherches en Environnement-Centre National de la Recherche Scientifique (CNRS), Dubigeon, Isabelle, and Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre Armoricain de Recherches en Environnement-Centre National de la Recherche Scientifique (CNRS)
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Dike ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,seismites ,[SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph] ,Sediment ,Geology ,Silt ,Structural basin ,clastic dikes ,010502 geochemistry & geophysics ,anisotropy of magnetic susceptibility ,01 natural sciences ,Overpressure ,Sedimentary depositional environment ,Dead Sea transform ,Clastic rock ,Clastic dike ,[SDU.STU.GP] Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph] ,Petrology ,Geomorphology ,0105 earth and related environmental sciences - Abstract
International audience; Clastic dikes form either by passive deposition of clastic material into preexisting fissures or by fracturing and injection of clastic material during seismic shaking or passive overpressure. Because of their similar final geometry, the origin of clastic dikes is commonly ambiguous. We studied the mechanisms of clastic dike formation within the seismically active Dead Sea basin, where hundreds of clastic dikes crosscut soft rock of the late Pleistocene lacustrine Lisan Formation. We analyzed the anisotropy of magnetic susceptibility (AMS) of clastic dikes of known origin and defined characteristic AMS signatures of depositional or injection filling. We discovered that passively filled dikes, which contain brownish silt resembling local surface sediments, are characterized by an oblate AMS ellipsoid and vertical minimum susceptibility axis V3. Dikes that contain green clayey sediment connected to a mineralogically identical detrital layer of the Lisan Formation are characterized by a triaxial AMS ellipsoid, well grouped subhorizontal and parallel to the dike walls' maximum susceptibility axis V1, and subvertical intermediate susceptibility axis V2. Field evidence and AMS analysis indicate that most of these dikes were emplaced by injection inferred to be due to seismically triggered fluidization. This novel application of the AMS provides a petrofabric tool for distinguishing passively filled dikes from injection dikes and, where appropriate, for identifying the latter as seismites.
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- 2006
477. The south-western side of the Calabrian Arc (Peloritani Mountains): geological, structural and AMS evidence for passive clockwise rotations
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Roberta Somma
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Peloritani Thrust Front ,Tyrrhenian back-arc Basin–Calabrian Arc–accretionary wedge system ,Calabrian Arc ,Structural analysis ,Anisotropy of magnetic susceptibility ,Passive rotations ,Subduction ,Vertical axis ,Fold (geology) ,Transpression ,Lineation ,Geophysics ,Sinistral and dextral ,Clockwise ,Geology ,Seismology ,Earth-Surface Processes - Abstract
Geological and structural investigations have been integrated with the results of a study of anisotropy of magnetic susceptibility (AMS) carried out along the south-western side of the Calabrian Arc (NE Sicily; Lat.: 37°50′–38°00′N; Long. 14°57′–15°19′E). The results of this research suggest the occurrence of middle–upper Miocene passive clockwise rotations about a vertical axis. These rotations, superposed on pre-existing (Aquitanian) thrust and fold structures of the Calabrian Arc, have been identified by mapping of rotated (in plan view) regional traces of thrusts, beds, stretching lineations, fold axes and magnetic lineations evidenced by the AMS technique. The driving mechanism responsible for the origin of the recorded rotations could be sought in the geodynamic processes associated with WNW-dipping subduction and development of the Tyrrhenian Basin–Calabrian Arc–Apennines back-arc Basin–accretionary wedge system. According to previous models provided for this area, the southern margin of the mentioned arc-shaped system would be affected by clockwise rotations and by dextral transpression. Our results are consistent with the latter models, suggesting that middle–upper Miocene kilometre-scale clockwise rotations and folding occurred in northern Sicily as a result of dextral transpression along an E–W trend south of parallel 38°N.
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- 2006
478. Heterogeneous internal fabric of the Mount Barcroft pluton, White Mountains, of eastern California: an anisotropy of magnetic susceptibility study
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Michlesen, Karen Joyce, Geological Sciences, Law, Richard D., Morgan, Sven, Spotila, James A., and Glazner, Allen
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White Mountains ,heterogeneous magnetic fabrics ,Mount Barcroft pluton ,AMS ,anisotropy of magnetic susceptibility ,California - Abstract
Anisotropy of magnetic susceptibility (AMS) have been used with great success for determining the internal structure and fabrics of Jurassic and Cretaceous plutons of felsic-intermediate compositions in the White-Inyo Range of eastern California. However, application of the AMS techniques to the Mount Barcroft pluton, located in the northern White Mountains, has yielded anomalous scalar and directional AMS data indicative of unprecedented heterogeneity on the meter-kilometer scale. The 165 Ma Mount Barcroft pluton is primarily of granodiorite composition and was intruded into the Barcroft Structural Break, a northeast striking, steeply dipping structure that juxtaposes Mesozoic metavolcanic rocks to the north against Proterozoic-Paleozoic metasedimentary rocks to the south. Two oriented hand samples (A and B) were collected at each of 78 sites distributed on a 1 kilometer grid pattern across the 5 by 15 kilometer Mount Barcroft pluton and oriented cores were prepared from these hand samples for AMS analysis. Microstructure identification of single thin sections prepared for each sample site yielded primarily magmatic with minor solid-state structures. A highly heterogeneous distribution of scalar parameters (Km, P%, F%, L%, T) was documented both between sample sites and between the A and B cores at individual sites. The heterogeneity may be the result of complex mineral assemblages and the interaction between different magnetic mineral species ranging from single domain to pseudo-single domain to multidomain magnetite. More problematic are the directional parameters between A and B cores in orientation and fabric type (e.g. prolate and oblate susceptibility ellipsoids) occur which cannot be readily explained by a complex mineral assemblage. Different fabric types in A and B cores at individual sample sites could be the result of discrete, temporally unrelated, magma pulses of variable composition and viscosity. Heterogeneity of scalar and directional AMS parameters in the Mount Barcroft pluton, and its contrast with the homogeneous AMS signatures within similar age plutons to the south, may provide evidence for a previously unrecognized magma source beneath the northern White Mountains. Master of Science
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- 2004
479. Tectonic implications of ca. 1.45 Ga granitoid magmatism at the southwestern margin of the East European Craton
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Cecys, Audrius
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southern Sweden ,fysisk geografi ,Mesoproterozoic ,physical geography ,Geology ,Geologi ,Danopolonian orogeny ,structural geology ,anisotropy of magnetic susceptibility ,petrology ,syntectonic ,geochemistry ,granite - Abstract
Between ca 1.53 and 1.40 Ga, the southwestern margin of the East European Craton was subjected to extensive magmatism and deformation. While various suites of anorthositic, mangeritic and charnockitic-granitic rocks were emplaced between ca. 1.53 and 1.50 Ga, a major event of A-type granitic magmatism took place around 1.45 Ga. During that event, numerous voluminous plutons were intruded in a wide region around the southern Baltic Sea (“the SBS region”). Petrologically, the various SBS granitoids are rather similar to each other. Like many A-type granites worldwide, they are enriched in silica, high field strength elements (HFSE) and rare earth elements (REE), and have high Fe/Mg and K/Na ratios. The most common ferromagnesian silicate minerals are biotite and amphibole, clinopyroxene occurring occasionally. Another feature characteristic of the SBS plutons is their formation by the emplacement of multiple pulses of melt. Such pulses were occasionally responsible for separate suites of rocks and appear to have originated from slightly different sources. In general, however, the melt sources of the SBS granitoids were relatively juvenile and rich in aluminum and potassium as well as in HFSE:s and REE:s. The isotopic characteristics of the rocks may also suggest some interaction between crustal and mantle materials. During the ca.1.45-Ga event, the Blekinge-Bornholm region experienced notable regional compression and ENE-WSW shortening. That compression caused syn- and post-magmatic deformation of the involved granitoids as well as deformation and metamorphism of the host rocks. Due to its activity, also EW-striking shear zones were either developed or reactivated and apparently controlled the emplacement of the SBS granitoids. As different from the traditional concept of a liaison between A-type granitic magmatism and anorogenic extension of the crust, the present study thus strongly evidences that the SBS granitoids were intruded during compressional tectonic processes. Causally, they are interpreted to have been related to the Mesoproterozoic Danopolonian orogeny which may have led to the collision of the East European Craton with another proto-continent, possibly Proto-Amazonia (Bogdanova, 2001). Planeten Jordens yttersta lager består av fast berg och kallas jordskorpan. Det finns två olika typer.av jordskorpa. Den ena är ocean, den andra kontinental. Den oceana jordskorpan är relativt tunn och uppbyggs av tunga, basaltiska bergarter. Den nybildas ständigt vid de s.k. mittoceana ryggarna ur smältor som där uppstiger ur Jordens mantel. Efter detta förstörs den dock åter i s.k. subduktionszoner där den dras ned i manteln. Den oceana jordskorpan blir därför aldrig särskilt gammal. Den kontinentala jordskorpan däremot består i huvudsak av tämligen lätta granitiska bergarter. Den kan bli blir bortåt 80 km tjock. Till skillnad från den oceana jordskorpan, dras den lätta kontinentala jordskorpa endast med svårighet ned i jordmanteln inom subduktionszonerna. Den kvarligger därför gärna vid jordytan och kan nå åldrar av flera miljarder år. När jordskorpan rör sig från de mittoceana ryggarna ut mot subduktionszonerna är den uppdelad i fasta s.k. plattor . Därav benämningen plattektonik. Plattorn består oftast av ocean såväl som kontinental jordskorpa. Under sina rörelser kan plattorna rotera, skava mot varandra, brytas sönder eller tryckas ihop. Själva subduktionen i subduktionszonerna är en process där den ena plattan dyker ned under den andra. Antalet plattor har varierat under tidernas lopp, men oftast verkar det ha funnits bortåt tio större plattor och dessutom ett antal småplattor och plattskärvor. Till skillnad från den oceana jordskorpan, nybildas den kontinentala inte vid mittoceana ryggar. Nytillskott uppkommer däremot i subduktionszoner där en del av berggrunden i den nedåtgående plattan ger upphov till smältor (”magmor”) som stiger uppåt mot jordytan. På så sätt bildas vulkaniska öbågar och andra bälten av magmatiska bergarter. Med tiden sammanfogas dessa till större kontinentala landmassor och t.o.m bergskedjor. Sådana processer kallas ”orogena”. En annan typ av orogenes uppkommer när två block av kontinental jordskorpa ”krockar” med varandra efter det att all mellan dem befintlig ocean jordskorpa dragits ned i en subduktionszon. Orogenes av denna typ kallas kollisionsorogenes. Granitiska smältor kan dock även bildas utan samband med orogena processer, dvs på ett ”anorogent” sätt. Dels kan jordskorpan smälta när den utsätts för tension, förtunning samt åtföljande trycksänkning och dels kan ur jordmanteln uppträngande magmor smälta den omgivande berggrunden. Föreliggande avhandling rör granitiska bergarter, dvs. de bergarter som uppbygger det mesta av den kontinentala jordskorpan. Graniter kan bildas antingen genom kompessionalla, vanligen orogena, eller tensionella, i huvudsak anorogena processer. De har mycket att berätta såväl om jordskorpans utveckling som om dess beskaffenhet och sammansättning på djupet. Två grupper av problem behandlades under arbetets gång. Den ena problemgruppen rörde geokemiska, den andra strukturella och tektoniska spörsmål. Dessutom utreddes frågan om den i området kring södra Östersjön vida utbredda gruppen av ca. 1,45 miljarder år gamla graniter av så kallad A-typ har ett orogent eller anorogent ursprung. Denna fråga står i samband med den mer generella frågan om A-gruppens betydelse som indikator av granitsmältornas tektoniska bildningsmiljöer. Konkret omfattade arbetet tektoniska och geokemiska detaljundersökningar av de ungefär 1450 miljoner år gamla A-typs graniterna i Karlshamns- och Stenshuvudsplutonerna i Sverige och dessutom en kemisk-petrologisk undersökning av ett större granitmassiv av samma ålder och karaktär under det fanerozoiska sedimenttäcket i Litauen. Flera tiotal bergartsprov analyserades med avseende på sina kemiska och isotopgeokemiska egenskaper. För Karlshamnmassivets del möjliggjordes därmed en bestämning av hela denna intrusions kemiska uppbyggnad. Liknande information kunde tas fram även för de övriga granitmassiven. Resultaten visar att samtliga dessa granitkroppar har en flerfasig bildningshistoria med en föjld av smärre, delvis kemiskt olika delintrusioner. De tidigare beräknade intrusionsåldrarna kunde preciseras. De strukturella undersökningarna, däribland en detaljerad utredning av den magnetiska susceptibilitetens anisotropi, resulterade i en tektonisk helhetsbild som beskriver Karlshamnmassivets och dess sidobergs utveckling från magmatiska flyt- til först duktila och därefter spröda deformationsstrukturer. Dessa gör det även klart att Karlshamnsplutonen och de andra undersökta A-graniterna måste ha bildats under en tidsperiod som kännetecknades av närmast öst-västlig kompression och förkortning av jordskorpan. Denna tektoniska process kan knappast ha varit annat än orogen. Den hörde sannolikt samman med den danopoloniska kollisionsorogenesen (Bogdanova 2001). Av dessa resultat kan man dra den allmänna slutsatsen att graniter av kemisk A-typ inte nödvändigtvis behöver vara anorogena.
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- 2004
480. Correlating magnetic fabrics with finite strain: comparing results from mudrocks in the Variscan and Appalachian Orogens
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Parés, Josep María, Van der Pluijm, B.A., Parés, Josep María, and Van der Pluijm, B.A.
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New magnetic anisotropy data from Variscan mudstones collected in the Cantabrian Arc, N Spain constrain the corresponding strain (shortening). The results are based on our previous study of mudrocks from the Valley and Ridge Province (Appalachians) where independent strain quantification of pencil structures permitted a correlation between magnetic fabric and tectonic strain. An exponential relationship between the AMS shape parameter T and tectonic shortening was found for the interval of 10-25% shortening: shortening (%)=17*exp(T), relationship that appears to be supported by tectonic strains up to 40%. The T parameter describes the shape of the magnetic susceptibility ellipsoid, which in pelitic rocks appears more sensitive to strain than the degree of anisotropy parameter P (or P¿). In mudrocks from the Cantabrian Arc a positive correlation between T parameter and deformation intensity, reflected by cleavage domains spacing, is observed. Using the above relationship, we estimate the range of tectonic shortening for the Cantabrian mudstones. The correlation between strain and AMS offers a robust estimate of strain magnitude of 10-40% in weakly to moderately deformed clay-rich rocks, where other strain indicators are often lacking or are poorly preserved.
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- 2004
481. An Investigation of AMS in Oman Ophiolite Gabbros
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Trutner, Sarah D.
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- Geology, anisotropy of magnetic susceptibility, magnetic fabric, Oman ophiolite, gabbros
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Crustal accretion processes at mid-ocean ridges are still poorly understood, and several competing models exist that try to explain exactly how magma from the mantle is incorporated into oceanic crust at a crustal spreading center. Ophiolites, or fragments of oceanic crust exposed on land, are useful sites at which to conduct rock fabric studies to understand oceanic crust formation processes. This study focuses on samples of upper foliated gabbros taken from the Oman ophiolite in order to characterize their fabric orientations and contribute to a better model of crustal formation. Much of the focus of this study is on using and interpreting anisotropy of magnetic susceptibility (AMS) as a method for measuring rock fabric directions. From our study site near the Maqsad diapir on the Sumail Massif, we found a magnetic foliation oriented NW-SE, subparallel to the nearest inferred spreading ridge and dipping steeply to the SW. The magnetic lineation from most of our samples was plunging moderately to the NW, towards the diapir. Comparison with shape-preferred orientation (SPO) measurements and other magnetic experiments indicate that our AMS fabrics match well with crystal fabrics, at least in foliation direction, and the magnetic susceptibility of our samples is largely due to secondary magnetite in serpentinized olivine.
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- 2016
482. STRUCTURE DU BATHOLITE DE FERKESSEDOUGOU (SECTEUR DE ZUENOULA, CÔTE D'IVOIRE) : IMPLICATIONS SUR L'INTERPRETATION DE LA GEODYNAMIQUE DU PALEOPROTEROZOÏQUE D'AFRIQUE DE L'OUEST A 2.1 Ga
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Gbele, Ouattara, Ecole doctorale 'Energétique-Matériaux-Ressources Naturelles-Environnement, Université d'Orléans (UO), Université d'Orléans, and Max Vidal(max.vidal@univ-orleans.fr)
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Birimian ,Periplutonic deformation ,Collision ,Magmatic foliation ,[SDE.MCG]Environmental Sciences/Global Changes ,Leucogranite ,West African Craton ,Two-micas granite ,Strike-slip ,Laccolithic form ,Domaine Sasca ,Granite à deux micas ,Craton Ouest Africain ,Foliation magmatique ,Paléoprotérozoïque ,Birimien ,Pull-apart ,Eburnéen ,[SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics ,Eburnean ,Téléanalyse satellitale ,Décrochement ,Multi-cauldron-subsidences ,Déformation périplutonique ,Batholite de Ferkessédougou ,Remote sensing ,Paleoproterozoic ,Anisotropy of magnetic susceptibility ,Ferkessédougou Batholith ,Anisotropie de susceptibilité magnétique ,Imataca ,Forme laccolithique ,Sasca domain - Abstract
In the West African Craton, the 2.1 Ga period is a major stage of leucogranite production. Because of its localization, its extension as much as its history in the geological literature, the batholith of Ferkessédougou (Côte d'Ivoire) is a main element for the interpretation of the Paleoproterozoic geodynamics. Interpreted as a typical granite of eugeosynclinal then as typical of collision of the modern type, it is in any case a NNE-SSW oriented significan crustal accident of Paleoproterozoic : the GFB (Greenville-Ferkessédougou-Bobodioulasso) lineament. Its study and its interpretation fall under the debate of the validity of plate tectonics at this period. As a matter of fact, by remote sensing, we show that this 400 km lenght batholith on about fifty broad consist in an important quantity of adjacent plutons which are petrographically relatively close. The general context of slightly deformed and epizonal metavolcanic and/or metasedimentary birimian age (2.2 Ga to 2.1 Ga) host rocks, as well as the absence of additional tangential deformations express the weakness of the crustal thickening synchronous of its genesis. Its fabric, determined by traditional structural analysis ans AMS (Anisotropy of Magnetic Susceptibility), is double. The first foliation (magmatic) is generally coaxial with varied orientation and dips. This foliation draws curved trajectories and expresses the intrusion of plutons. It is the equivalent of what was brought back to the D1 deformation around older granites. The second foliation (from magmatic to post-solidus), which is much better well-ordered and often constrictive or none coaxial, is the result of a regional strain transcurrent field which refers to the D2 deformation. This latter is well-known in the chrology of the birimian craton. The plutons of the granitic batholith of Ferké are syntectonic of the birimian main shortening (2.1 to 2.07 Ga). From the review of the various models of plutons emplacement, the analysis of the SW sector of Côte d'Ivoire showing two-micas granite dykes and metamorphic facies of higher range, a review of the Imata formations in Surinam, as well as the assessment of structural analysis, we propose a 3D model for the batholith of Ferké. This latter may correspond to a set of small plutons of laccolithic form intruded into the superficial crust between birimian epizonal metasediments known as "metasediments of basin" and gneiss and micaschists of age probably ranging between 2.2 and 2.1 Ga. The plutons may rise from dykes resulting of fracturing by pull-apart opening of the SASCA-Bandaman-Bobodioulasso sedimentary basin. The melting of the old greenstone-belts/TTG type crust (absence of traces of Archean basement), which occurs vertically compared to the subsident basin, will have incorporated material of sedimentary basin. The necessary contribution of heat for the compensation of the weakness of thickening would have been provided by the strike-slip faults of pull-aparts. The volume required for the emplacement of plutons needs a rise of these latters at the end of the extensive period thanks to many cauldron-subsidences. The conditions and modes of the two principal deformations imply a short time between the stabilization of the opening of the basins and thei closing. In addition, the variation of the structural level from North-East towards South-West, particulary towards the probable zone of the equivalent-root in Venezuela-Surinam, shows a deepening and the bringing together of an archean crust towards the SW whereas it was recognized only towards the West up to now (Guinea, Dorsale of Man) or was only suspected towards the East of Ghana.; La période à 2.1 Ga du Craton d'Afrique de l'Ouest est une période de production massive de leucogranites. Le batholite de Ferkessédougou (Côte d'Ivoire) est, tant du point de vue de sa localisation, de son extension, que de son histoire dans la littérature géologique, un élément majeur de l'interprétation de la géodynamique du Paléoprotérozoïque. Tour à tour considéré comme un granite de ride augéosynclinale puis un granite typique de collision de type moderne, il n'en demeure pas moins le jalon d'un accident crustal NNE-SSW important du Paléoprotérozoïque : le linéament GFB (Greenville-Ferkessédougou-Bobodioulasso). Son étude et son interprétation s'inscrivent dans le débat sur la validité de la tectonique des plaques à cette période. Par analyse satellitale, nous montrons que ce batholite de 400 km de long sur une cinquantaine de large est en fait constitué d'une grande quantité de plutons adjacents relativement proches pétrographiquement. Le contexte général de son encaissant métavolcanique et/ou métasédimentaire birimien (2.2 Ga à 2.1 Ga) faiblement déformé et épizonal ainsi que l'absence de déformations tangentielles additionnelles traduisent la faiblesse de l'épaississement crustal synchrone de sa genèse. Sa fabrique déterminée par analyse structurale classique et par analyse de susceptibilité magnétique est double. La première "magmatique" est le plus souvent coaxiale, d'orientation et de pendages variables. Elle dessine des trajectoires courbes et traduit la mise en place des plutons. Elle est l'équivalent de ce qui a été rapporté à la déformation D1 autour de granites anciens. La seconde, magmatique à post-solidus, beaucoup mieux réglée, souvent constrictive ou non-coaxiale, est l'image d'un champ de contrainte régional transcurrent qui se rapporte à la déformation D2 classique dans la chronologie du craton birimien. Les plutons du batholite granitique de Ferké sont syntectoniques de cette grande phase de raccourcissement (2.1 Ga à 2.07 Ga) du birimien. Le passage en revue des différents modèles de plutons, l'analyse du secteur SW de la Côte d'Ivoire présentant des dykes granites à deux micas et des faciès métamorphiques de plus haut grade, un survol des formations de l'Imataca au Surinam, ainsi que le bilan de l'analyse structurale, nous amènent à proposer un modèle 3D pour le batholite de Ferké. Il correspondrait à un ensemble de petits plutons de forme laccolithique engagés dans la croûte superficielle entre les métasédiments épizonaux birimiens dits "de bassin", des gneiss et micaschistes probablement d'âge compris entre 2.2 et 2.1 Ga. Ces plutons seraient alimentés par un faisceau de dykes issus de la fracturation par ouverture en pull-apart du bassin sédimentaire SASCA-Bandama-Bobodioulasso. La fusion de la croûte essentiellement de type ceinture verte/TTG (absence de traces de matériel archéen), à la verticale du bassin subsident, aura incorporé du matériel sédimentaire de bassin. L'apport de chaleur nécessaire à la compensation de la faiblesse de l'épaississement aurait été fourni par le jeu décrochant des fractures majeures des pull-aparts. La place nécessaire à la mise en place des plutons exige une montée de ces derniers à la fin de la période extensive à la faveur de multiples cauldron-subsidences. Les conditions et régimes des deux déformations principales impliquent un lapse de temps très court entre la stabilisation de l'ouverture des bassins et leur fermeture. Par ailleurs, la variation du niveau structural du Nord-Est vers le Sud-Ouest, en particulier vers la zone probable de l'équivalent-racine au Vénézuéla-Surinam, montre un approfondissement et le rapprochement d'une croûte archéenne vers le SW alors qu'elle n'était jusqu'à présent reconnue que vers l'Ouest (Guinée, Dorsale de Man) ou soupçonnée vers l'Est au Ghana.
- Published
- 1998
483. STRUCTURE OF THE FERKESSEDOUGOU BATHOLITH (SECTOR OF ZUENOULA, CÔTE D'IVOIRE) : IMPLICATIONS ON THE INTERPRETATION OF THE GEODYNAMIC OF WEST AFRICAN PALEOPROTEROZOIC AT 2.1 Ga
- Author
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Gbele, Ouattara and Gbele, Ouattara
- Subjects
Birimian ,Periplutonic deformation ,Collision ,Magmatic foliation ,[SDU.STU.TE] Sciences of the Universe [physics]/Earth Sciences/Tectonics ,Leucogranite ,West African Craton ,Two-micas granite ,Strike-slip ,Laccolithic form ,Domaine Sasca ,Granite à deux micas ,Craton Ouest Africain ,Foliation magmatique ,Paléoprotérozoïque ,Birimien ,Pull-apart ,Eburnéen ,Eburnean ,Téléanalyse satellitale ,Décrochement ,Multi-cauldron-subsidences ,Déformation périplutonique ,Batholite de Ferkessédougou ,Remote sensing ,Paleoproterozoic ,[SDE.MCG] Environmental Sciences/Global Changes ,Anisotropy of magnetic susceptibility ,Ferkessédougou Batholith ,Anisotropie de susceptibilité magnétique ,Imataca ,Forme laccolithique ,Sasca domain - Abstract
In the West African Craton, the 2.1 Ga period is a major stage of leucogranite production. Because of its localization, its extension as much as its history in the geological literature, the batholith of Ferkessédougou (Côte d'Ivoire) is a main element for the interpretation of the Paleoproterozoic geodynamics. Interpreted as a typical granite of eugeosynclinal then as typical of collision of the modern type, it is in any case a NNE-SSW oriented significan crustal accident of Paleoproterozoic : the GFB (Greenville-Ferkessédougou-Bobodioulasso) lineament. Its study and its interpretation fall under the debate of the validity of plate tectonics at this period. As a matter of fact, by remote sensing, we show that this 400 km lenght batholith on about fifty broad consist in an important quantity of adjacent plutons which are petrographically relatively close. The general context of slightly deformed and epizonal metavolcanic and/or metasedimentary birimian age (2.2 Ga to 2.1 Ga) host rocks, as well as the absence of additional tangential deformations express the weakness of the crustal thickening synchronous of its genesis. Its fabric, determined by traditional structural analysis ans AMS (Anisotropy of Magnetic Susceptibility), is double. The first foliation (magmatic) is generally coaxial with varied orientation and dips. This foliation draws curved trajectories and expresses the intrusion of plutons. It is the equivalent of what was brought back to the D1 deformation around older granites. The second foliation (from magmatic to post-solidus), which is much better well-ordered and often constrictive or none coaxial, is the result of a regional strain transcurrent field which refers to the D2 deformation. This latter is well-known in the chrology of the birimian craton. The plutons of the granitic batholith of Ferké are syntectonic of the birimian main shortening (2.1 to 2.07 Ga). From the review of the various models of plutons emplacement, the analysis of the SW sector of Côte d'Ivoire showing two-micas granite dykes and metamorphic facies of higher range, a review of the Imata formations in Surinam, as well as the assessment of structural analysis, we propose a 3D model for the batholith of Ferké. This latter may correspond to a set of small plutons of laccolithic form intruded into the superficial crust between birimian epizonal metasediments known as "metasediments of basin" and gneiss and micaschists of age probably ranging between 2.2 and 2.1 Ga. The plutons may rise from dykes resulting of fracturing by pull-apart opening of the SASCA-Bandaman-Bobodioulasso sedimentary basin. The melting of the old greenstone-belts/TTG type crust (absence of traces of Archean basement), which occurs vertically compared to the subsident basin, will have incorporated material of sedimentary basin. The necessary contribution of heat for the compensation of the weakness of thickening would have been provided by the strike-slip faults of pull-aparts. The volume required for the emplacement of plutons needs a rise of these latters at the end of the extensive period thanks to many cauldron-subsidences. The conditions and modes of the two principal deformations imply a short time between the stabilization of the opening of the basins and thei closing. In addition, the variation of the structural level from North-East towards South-West, particulary towards the probable zone of the equivalent-root in Venezuela-Surinam, shows a deepening and the bringing together of an archean crust towards the SW whereas it was recognized only towards the West up to now (Guinea, Dorsale of Man) or was only suspected towards the East of Ghana., La période à 2.1 Ga du Craton d'Afrique de l'Ouest est une période de production massive de leucogranites. Le batholite de Ferkessédougou (Côte d'Ivoire) est, tant du point de vue de sa localisation, de son extension, que de son histoire dans la littérature géologique, un élément majeur de l'interprétation de la géodynamique du Paléoprotérozoïque. Tour à tour considéré comme un granite de ride augéosynclinale puis un granite typique de collision de type moderne, il n'en demeure pas moins le jalon d'un accident crustal NNE-SSW important du Paléoprotérozoïque : le linéament GFB (Greenville-Ferkessédougou-Bobodioulasso). Son étude et son interprétation s'inscrivent dans le débat sur la validité de la tectonique des plaques à cette période. Par analyse satellitale, nous montrons que ce batholite de 400 km de long sur une cinquantaine de large est en fait constitué d'une grande quantité de plutons adjacents relativement proches pétrographiquement. Le contexte général de son encaissant métavolcanique et/ou métasédimentaire birimien (2.2 Ga à 2.1 Ga) faiblement déformé et épizonal ainsi que l'absence de déformations tangentielles additionnelles traduisent la faiblesse de l'épaississement crustal synchrone de sa genèse. Sa fabrique déterminée par analyse structurale classique et par analyse de susceptibilité magnétique est double. La première "magmatique" est le plus souvent coaxiale, d'orientation et de pendages variables. Elle dessine des trajectoires courbes et traduit la mise en place des plutons. Elle est l'équivalent de ce qui a été rapporté à la déformation D1 autour de granites anciens. La seconde, magmatique à post-solidus, beaucoup mieux réglée, souvent constrictive ou non-coaxiale, est l'image d'un champ de contrainte régional transcurrent qui se rapporte à la déformation D2 classique dans la chronologie du craton birimien. Les plutons du batholite granitique de Ferké sont syntectoniques de cette grande phase de raccourcissement (2.1 Ga à 2.07 Ga) du birimien. Le passage en revue des différents modèles de plutons, l'analyse du secteur SW de la Côte d'Ivoire présentant des dykes granites à deux micas et des faciès métamorphiques de plus haut grade, un survol des formations de l'Imataca au Surinam, ainsi que le bilan de l'analyse structurale, nous amènent à proposer un modèle 3D pour le batholite de Ferké. Il correspondrait à un ensemble de petits plutons de forme laccolithique engagés dans la croûte superficielle entre les métasédiments épizonaux birimiens dits "de bassin", des gneiss et micaschistes probablement d'âge compris entre 2.2 et 2.1 Ga. Ces plutons seraient alimentés par un faisceau de dykes issus de la fracturation par ouverture en pull-apart du bassin sédimentaire SASCA-Bandama-Bobodioulasso. La fusion de la croûte essentiellement de type ceinture verte/TTG (absence de traces de matériel archéen), à la verticale du bassin subsident, aura incorporé du matériel sédimentaire de bassin. L'apport de chaleur nécessaire à la compensation de la faiblesse de l'épaississement aurait été fourni par le jeu décrochant des fractures majeures des pull-aparts. La place nécessaire à la mise en place des plutons exige une montée de ces derniers à la fin de la période extensive à la faveur de multiples cauldron-subsidences. Les conditions et régimes des deux déformations principales impliquent un lapse de temps très court entre la stabilisation de l'ouverture des bassins et leur fermeture. Par ailleurs, la variation du niveau structural du Nord-Est vers le Sud-Ouest, en particulier vers la zone probable de l'équivalent-racine au Vénézuéla-Surinam, montre un approfondissement et le rapprochement d'une croûte archéenne vers le SW alors qu'elle n'était jusqu'à présent reconnue que vers l'Ouest (Guinée, Dorsale de Man) ou soupçonnée vers l'Est au Ghana.
- Published
- 1998
484. Magnetic fabrics and microstructures of Paleoproterozoic intrusive bodies of Piedra Alta Terrane, Río de la Plata Craton, Uruguay: a reconnaissance study
- Author
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Pablo Reinaldo Franceschinis, Augusto Ernesto Rapalini, Leda Sánchez Bettucci, Carmen Martínez Dopico, and Florencia Nidia Milanese
- Subjects
piedra alta terrane ,río de la plata craton ,anisotropy of magnetic susceptibility ,Geology ,QE1-996.5 - Abstract
Abstract Small to medium-sized intrusive bodies with ages between 2.1 and 2.0 Ga characterize Piedra Alta terrane and represent the final stabilization of Río de la Plata Craton. A reconnaissance study of petro- and magnetic fabrics based on microscopic observations, anisotropy of magnetic susceptibility and anhysteretic remanent magnetization, was carried out on 41 sites from 14 intrusive bodies, in order to obtain preliminary information on kinematics of their emplacement, degree of deformation, and regional stress regime during this magmatic event. The magnetic fabrics coupled with the microstructural analysis are interpreted as generally reflecting magma kinematics near solidus temperature, although few cases of tectonically modified fabrics at local levels have been interpreted. Field evidence and magnetic fabrics in most plutons show subvertical to high angle E-W to NE-SW trending foliations and subvertical lineations. These data suggest that plutons were probably intruded under a regional extensional to transtensional regime, which controlled the magma ascent and distribution of the intrusions. Lack of metamorphism and low to null deformation shown by the study plutons suggest a late-orogenic character for this magmatism, which has been associated with crustal stabilization after accretionary processes that led to the formation of Río de la Plata Craton in the Orosirian.
- Full Text
- View/download PDF
485. Variaciones de la anisotropia de la susceptibilidad magnética en turbiditas albienses de la Cuenca Vasco-Cantábrica
- Author
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Badillo, J. M., Aranguren, A., Cuevas, Julia, and Tubía, José María
- Subjects
Anisotropy of magnetic susceptibility ,Basque-Cantabrian Basin ,Turbidites - Abstract
The first results extracted from the study of the Anisotropy of magnetic susceptibility (ASM) from 33 turbidites allocated in Basque-Cantabrian basin show the validity of the ASM as a rock fabric analysis tool to determine deposit mechanism and paleocurrents in turbidites
- Published
- 1997
486. Anisotropy of magnetic susceptibility variations in albian turbidiles from the Basque-Cantabrian basin
- Author
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Badillo, J. M., Aranguren, A., Cuevas, Julia, and Tubía, José María
- Subjects
Anisotropy of magnetic susceptibility ,Basque-Cantabrian Basin ,Turbidites - Abstract
The first results extracted from the study of the Anisotropy of magnetic susceptibility (ASM) from 33 turbidites allocated in Basque-Cantabrian basin show the validity of the ASM as a rock fabric analysis tool to determine deposit mechanism and paleocurrents in turbidites
- Published
- 1997
487. Anisotropic magnetic susceptibility in the continental lower crust and its implications for the shape of magnetic anomalies
- Author
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FEDI, MAURIZIO, Rapolla A., Fedi, Maurizio, and Rapolla, A.
- Subjects
magnetic anomaly ,crust (lower) ,anisotropy of magnetic susceptibility - Abstract
Magnetic anisotropy measurements on samples from the lower continental crust were made to test the hypothesis that anisotropy may cause deflection of the peak-to-trough axes of magnetic anomalies caused by mid- to lower crustal sources. Average anisotropy (P′) for these samples is 1.5 but can be as high as 3.4. Magnetic sources with P′ equal to the maximum determined in this study can cause azimuthal rotations of magnetic anomalies by up to about 25°, but P′ lower than or equal to 1.5 causes no significant rotation. Comparison of the model results to the abnormal shape of some magnetic anomalies in southern Italy indicate that these anomalies cannot be related easily to a strong and coherent AMS of the source rocks. The most probable explanation of such shapes is the existence of a strong remanent magnetization in subsequently rotated source bodies. -from Authors
- Published
- 1993
488. Magnetic zoning and the magnetic susceptibility ellipsoïd in the Posets pluton (Central Pyrenees)
- Author
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García Maiztegi, C., Aranguren, A., and Tubía, José María
- Subjects
Posets tonalite ,Anisotropy of magnetic susceptibility ,Magnetic susceptibility zoning ,Central Pyrenees ,Physics::Geophysics - Abstract
This work deals with the magnetic susceptibility and anisotropy of the Variscan Posets pluton in the Central Pyrenees. Magnetic susceptibility values provide a concentric zoning. The measurements of the magnetic anisotropy show the existence ofa N110º E trending band which can be interpreted as a magmatic fault, Este trabajo trata sobre la susceptibilidad magnética y la anisotropía del plutón de Posets varisco en el Pirineo central. Los valores de susceptibilidad magnética aportan una zonación concéntrica. La medición de la anisotropía magnética muestra la existencia de una banda de tendencia N110º E que se puede interpretar como una falla magmática.
- Published
- 1991
489. Zonación magnética y caracterización del elipsoide de la susceptibilidad magnética en el plutón de Posets (Pirineos centrales)
- Author
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García Maiztegi, C., Aranguren, A., and Tubía, José María
- Subjects
Posets tonalite ,Anisotropy of magnetic susceptibility ,Magnetic susceptibility zoning ,Central Pyrenees ,Physics::Geophysics - Abstract
This work deals with the magnetic susceptibility and anisotropy of the Variscan Posets pluton in the Central Pyrenees. Magnetic susceptibility values provide a concentric zoning. The measurements of the magnetic anisotropy show the existence ofa N110º E trending band which can be interpreted as a magmatic fault Este trabajo trata sobre la susceptibilidad magnética y la anisotropía del plutón de Posets varisco en el Pirineo central. Los valores de susceptibilidad magnética aportan una zonación concéntrica. La medición de la anisotropía magnética muestra la existencia de una banda de tendencia N110º E que se puede interpretar como una falla magmática.
- Published
- 1991
490. Fabric analysis in rocks of the Gadag region (southern India) - Implications for time relationship between regional deformation and gold mineralization.
- Author
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Mondal, Tridib Kumar and Mamtani, Manish A.
- Subjects
- *
DEFORMATIONS (Mechanics) , *GOLD mining , *ARCHAEAN , *BASALT , *MAGNETIC susceptibility , *MAGNETIC anisotropy - Abstract
In this paper, the fabric in Archaean age massive metabasalts and granite from the Gadag region (Western Dharwar Craton, southern India) are identified using the anisotropy of magnetic susceptibility (AMS). The magnetic foliation in the rocks is dominantly NW-SE striking. This is inferred to have developed during regional D1/D2 deformation known to have affected the region, which was on account of NE-SW shortening. The plunge of the magnetic lineation varies from NW to SE. This doubly plunging orientation is inferred to be a consequence of superimposition of NW-SE shortening (D3 deformation) over the earlier structure that is known to have resulted in dome-basin geometry in the surrounding metapelitic rocks of the region. Thus it is concluded that the massive rocks preserve evidence of superposed deformation that affected the region, which can be deciphered from the orientation of magnetic fabric data. The Gadag region comprises lode gold deposit (~ 2500 Ma in age), and field investigations show that the quartz veins are dilational with dominantly NW-SE (strike) orientation. The veins are inferred to have formed by dilation under NW-SE shortening during D3. It is envisaged that the NW-SE oriented fabric that formed in the metabasalt during D1/D2, channelized fluid flow, thus leading to vein emplacement during D3. It is concluded that gold deposition in the veins took place during D3, which is related to the final stages of cratonization of the Dharwar craton at ~ 2500 Ma. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
491. Paelomagnetic and petromagnetic studies of Chinese Cenozoic sediments: Paleoclimatic, tectonic, and evolutionary implications
- Author
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Zhang, Rui
- Subjects
- Cenozoic, Paleomonsoon, Magnetostratigraphy, Tectonics, Paleomagnetism, Paleoclimate, Petromagnetism, Anisotropy of magnetic susceptibility, Chinese Loess Plateau
- Abstract
Abstract: The anisotropy of magnetic susceptibility (AMS) was investigated in three Chinese Loess Plateau sedimentary sections along a W–E transect. Previously published models assumed that winter monsoons were responsible for the magnetic fabric formation of loess sequences. In our new interpretation, the stronger summer monsoons from the southeast played the major role in magnetic fabric orientation in the studied west and central parts of the Chinese Loess Plateau. The AMS was generated during the rainy summer monsoon when the sedimentary particles including magnetite were rearranged, settled, and fixed. We reconstruct the summer paleomonsoon routes for the last 130 kyr. These winds prevail from SE to NW but appear to be affected by regional topographic factors. Evidence in the world’s ocean current system indicates an abrupt cooling from 34.1 to 33.6 Ma across the Eocene-Oligocene boundary (EOB) at 33.9 Ma. I describe and date with magnetostratigraphy a section from the north Junggar Basin (Burqin section). Three fossil assemblages revealed through the EOB (34.8, 33.7, and 30.4 Ma) demonstrate that perissodactyl faunas were abruptly replaced by rodent/lagomorph-dominant faunas during climate cooling, and the changes in mammalian communities were accelerated by aridification in central Asia. Paleomagnetic studies of two sections of the northern Junggar Basin, China, are presented from Burqin and Tieersihabahe. Our paleomagnetic results demonstrate counterclockwise tectonic rotations in Burqin and Tieersihabahe (–17.2 ± 9.6° and –11.8 ± 6.1°, respectively) as well as considerable northward latitudinal displacement (12.2 ± 6.5° and 9.7 ± 4.1°, respectively) with respect to Europe. These results are consistent with the motions of contiguous blocks in the same geological time intervals (India, north and south China, Tarim, Amuria, and Kazakhstan). No significant intracontinental shortening or vertical-axis rotation is observed for the Junggar block from 40 Ma to 20 Ma. Our results reveal that the major compression and rotation between Junggar and northern Europe occurred after 20 Ma due to continuous penetration of India into Asia. We interpret the uplift of the Altay Mountains and the formation of the Lake Baikal rift system to be due to such intracontinental compression and relative rotations.
- Published
- 2012
492. Paleomagnetic and AMS results from Oligocene ash-flow tuffs of the eastern San Juan Mountains : implications for the evolution of the western margin of the San Luis Basin, northern Rio Grande Rift
- Author
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Mason, Stephanie N.
- Subjects
- Paleomagnetism, Rio Grande rift, Southern Rocky Mountain Volcanic Field, San Luis Basin, Anisotropy of Magnetic Susceptibility, Ash-flow tuff
- Abstract
The San Luis Basin (SLB) of the northern Rio Grande rift (RGR) is a spectacular intermontane basin in south-central Colorado. The SLB is an east-dipping, half graben basin that formed in response to extension beginning ca. 26 Ma in the Cordillera. Oligocene ash-flow tuffs exposed in the eastern San Juan Mountains and along the western margin of the SLB provide an excellent opportunity to study the kinematic history of the northern Rio Grande rift using paleomagnetism. Outflow deposits of ash-flow tuffs are generally excellent recorders of the geomagnetic field and can be used to study the vertical-axis rotation component of extension related to the opening of the SLB. Four ash-flow tuffs (Carpenter Ridge, Fish Canyon, Chiquito Peak and Saguache Creek Tuffs) that were erupted between ca. 32 and 27 Ma were sampled at a total of 84 sites for paleomagnetic, rock magnetic, and magnetic fabric data. Paleomagnetic data indicate some complexities with using large-volume, regionally extensive outflow deposits of ash-flow tuffs, specifically that relatively thick outflow deposits (with thicknesses exceeding 100 m) may record paleosecular variation of the geomagnetic field. Even with these complications, the four targeted San Juan ash-flow tuffs may still be evaluated for regional domains of potential vertical-axis rotation. Overall, we observe a lack of vertical-axis rotation along the western margin of the SLB. Shear and fault linkage in the hanging wall of the major normal fault of the SLB does not appear to play a role in the evolution of slightly extended terranes. Distal outflow deposits of ash-flow tuffs may also be difficult, if not impossible, to tell apart and paleomagnetism is used to distinguish two units that have, until presently, been grouped together as the Chiquito Peak Tuff. The magnetic fabric of these Oligocene ash-flow tuffs was also measured and analyzed for complexities due to paleotopography and single-domain magnetic carriers. Preliminary results from a comparison between two magnetic fabric techniques are also presented and analyzed. Magnetic fabrics measured for all tuffs in the northeastern San Juan Mountains confirm that their flow was channelized through an Oligocene paleovalley that existed west of Saguache.
- Published
- 2011
493. The dynamics of migmatite domes in extending orogens.
- Author
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Kruckenberg, Seth Caley
- Subjects
- Anisotropy of Magnetic Susceptibility, Metamorphic Core Complex, Migmatite Dome, Naxos Dome, Okanogan Dome, Partial Melting, Geology
- Abstract
Two migmatite domes, the Okanogan dome (Washington state) and the Naxos dome (Cyclades, Greece) record the dynamics of migmatite dome formation in extending orogens. Both domes are exposed in cordilleran-style metamorphic core complexes that developed during extension of previously thickened crust and contain a core of anatectic migmatite mantled by metasedimentary rocks and exposed below crustal detachments. Structural observations in both domes indicate that deformation in dome migmatites took place in the presence of melt and flow within the dome migmatites was coeval with detachment faulting, upper crustal extension, and migmatite dome formation. In the Okanogan dome, the timing of partial melting is constrained by U-Pb sensitive high-resolution ion microprobe (SHRIMP) dating of zircon, monazite, and titanite. Results of the U-Pb analysis document Paleocene-Eocene ages of partial melting and migmatite crystallization in the Okanogan dome based on a range of 206Pb/238U ages from ca. 61-49 Ma for zircon and monazite in migmatite leucosomes of various structural settings, interpreted as the timing of migmatite crystallization. Similar ages of migmatite crystallization are reported in other domes of the northern Cordillera, suggesting that partial melting was widespread in this region during Paleocene to Eocene time. The conditions of metamorphism in the Okanogan dome associated with migmatization are constrained by mineral assemblages and reaction textures preserved in sapphirine- and corundum-bearing orthoamphibole-cordierite gneiss layers that structurally overlie the Okanogan migmatite domain. Petrologic and pseudosection analyses of these Mg-Al-rich layers suggest conditions of metamorphism reached ~ 720-750 ºC at moderate pressure (ca. 4 kbar). An earlier, high-pressure metamorphic history is recorded by relict kyanite pseudomorphed by symplectite and coronal reaction textures. A minimum of 4 kbar of decompression is suggested by the calculated conditions of metamorphism at relatively shallow crustal levels (~13 km) calculated conditions of metamorphism at relatively shallow crustal levels (~13 km) simpler pattern of deformation developed during viscous flow. At the scale of the Naxos dome, lineations obtained by AMS are highly variable in plunge with steeply plunging lineations commonly associated with the cores of subdomes or adjacent synforms and more shallowly plunging lineations elsewhere. The combination of structural and magnetic observations in the Naxos dome suggest that the combined effects of upwelling of low-viscosity migmatites under dominantly NNE-SSW extension, E-W compression, and top-to-the-north shearing likely contributed to the structural pattern recorded in the Naxos dome migmatites. The presence of subdomes within the migmatitic core of the Naxos dome, and discordant structural relationships between the migmatitic foliation and that in the mantling units at some localities in the dome, suggest that the internal dynamics of the migmatites (i.e., buoyancy, convection) were likely significant in the formation of the Naxos dome and subdomes. Multidisciplinary study of the Okanogan and Naxos domes emphasize the role of partial melting and flow of migmatites in the formation of domes developed during extension of previously thickened crust. Observations in both domes suggest that partial melting and flow within the migmatites was kinematically consistent with regional patterns of extension reflecting a component of lateral flow during their formation. The results of metamorphic petrology in the Okanogan dome, and the combined structural and magnetic analysis of the Naxos dome, further suggest that vertical flow of partially molten crust is also an important process in the formation of migmatite domes (and associated subdomes) in extending orogens.
- Published
- 2009
494. An alternative emplacement model for the classic Ardnamurchan cone sheet swarm, NW Scotland, involving lateral magma supply via regional dykes
- Author
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Carl Stevenson, Ken McDermott, Craig Magee, Nick Schofield, and Brian O'Driscoll
- Subjects
geography ,geography.geographical_feature_category ,Swarm behaviour ,Geology ,Magma chamber ,Cone (formal languages) ,Ardnamurchan ,Stress field ,Regional dykes ,Volcano ,Inclined sheets ,Magma ,Anisotropy of magnetic susceptibility ,Cone sheet ,Petrology ,Paleogene ,Cone sheets ,Seismology - Abstract
Sub-volcanic intrusive networks, of which cone sheets are recognised as a major constituent, partially control volcano growth and eruption style. The accepted cone sheet model is that these confocally dipping intrusions originate from an unexposed central magma chamber through dip-parallel magma flow. However, the emplacement mechanism of cone sheets remains poorly understood. The ∼58 Ma cone sheet swarm of Ardnamurchan, NW Scotland, offers an excellent opportunity to further resolve the emplacement dynamics of cone sheets, through studying magma flow, and their importance in volcanic edifice construction. Structural measurements and anisotropy of magnetic susceptibility (AMS) analyses have constrained a lateral magma flow pattern, consistently oriented NW–SE, in the majority of the Ardnamurchan cone sheets. Field observations also highlight the importance of host rock structure and interference between competing local and regional stress fields in controlling intrusion geometry. Our observations suggest cone sheet formation may be linked to laterally propagating NW–SE trending regional dykes, sourced from laterally adjacent magmatic systems (likely the Palaeogene Mull Central Complex), which are deflected around the central complex by stress field interference. Implicitly, edifice construction and potential eruption precursors observed at a volcano may instigate, or result from, magmatic activity in laterally adjacent volcanic systems.
- Full Text
- View/download PDF
495. Magma transport in sheet intrusions
- Author
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Andersson, Magnus and Andersson, Magnus
496. Palaeoenvironmental implications from Lower Volga loess - joint magnetic fabric and multi-proxy analyses
- Author
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Költringer, Chiara, Bradák, Balázs, Stevens, Thomas, Almqvist, Bjarne, Banak, Adriano, Lindner, Martin, Kurbanov, Redzhep, Költringer, Chiara, Bradák, Balázs, Stevens, Thomas, Almqvist, Bjarne, Banak, Adriano, Lindner, Martin, and Kurbanov, Redzhep
497. La utilización de la anisotropía de la susceptibilidad magnética (ASM) en el estudio de la deformación finita: ejemplo en la zona milonítica de Cap de Creus (Catalunya)
- Author
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Parés, J. M.
- Subjects
Shear zone ,Anisotropy of magnetic susceptibility ,Roses Granodiorite - Abstract
The magnetic susceptibility anisotropy (MSA) of the Roses Granodiorite has been studied The magnetic fabric is due to the shear zones that affect these rocks. In this sense, the kmin axes of the MSA are paralel to the foliation poles and the kmax axes are parallel to the direction of the mineral elongation measured in the field The Flinn-type diagram to study the ellipsoid shape indicates oblateness of the MSA ellipsoid, Se ha estudiado la anisotropía de susceptibilidad magnética (ASM) de las Rosas de Granodiorita. El tejido magnético se debe a la zona de cizalla que afecta a estas rocas. En este sentido, los ejes de kmin de la ASM son paralelos a los polos de foliación, y los ejes kmax están paralelos a la dirección del alargamiento del mineral calculado en el campo. El diagrama de Flynn que se usa para estudiar la forma elipsoide indica achatamiento en el elipsoide ASM.
- Published
- 1988
498. Mise en place des granitoïdes hercyniens de la Meseta marocaine, Étude structurale des massifs de Sebt de Brikine (Rehamna), de Zaër et d'Oulmès (Massif Central) et d'Aouli-Boumia (Haute Moulouya). Implications géodynamiques
- Author
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Diot, Hervé and Chopin, Francis
- Subjects
Moroccan Meseta ,Anisotropie de la Susceptibilité Magnétique ,[SDE.MCG] Environmental Sciences/Global Changes ,Meseta marocaine ,cinématique de la croûte ,Anisotropy of magnetic susceptibility ,Granite ,[SDU.STU.TE] Sciences of the Universe [physics]/Earth Sciences/Tectonics ,Structure ,Hercynian orogen ,Crustal kinematic ,Orogène hercynien - Abstract
No abstract available in english, La Meseta marocaine constitue sur la continent africain la continuité de la chaîne hercynienne d'Europe moyenne. La cinématique de mise en place des granitoïdes associés à cet orogène constitue un élément déterminant permettant de retracer l'évolution géodynamique de ce segment hercynien. Les structures de déformation à l'état magmatique caractéristiques de la montée du magma dans la croûte, et les structures de déformation à l'état solide qui concernent à la fois ces plutons et leur encaissant, sont l'empreinte de cette mise en place. Les structures magmatiques (plans et des lignes d'écoulement du magma) sont étudiées, par l'analyse de l'orientation des marqueurs que constituent les premiers cristaux formés dans le magma, et/ou avec la technique de l'anisotropie de la susceptibilité magnétique (ASM). Les granites étudiés se répartissent en deux groupes: 1- ceux dont la mise en place est précoce dans l'orogène et situés en Meseta orientale; ces massifs, d'Aouli et de Bou-Mia, forment un unique corps magmatique situé dans la boutonnière de Midelt; 2- des granites plus tardifs, plus petits et bien circonscrits sont localisés en marge orientale du Bloc côtier de la Meseta occidentale; on les trouve aussi bien au Nord (Zaër et Oulmès dans le Massif Central), qu'au Sud (Tichka, dans le Haut-Atlas). Parmi ces granites de la Meseta occidentale, ceux de Zaër, d'Oulmès et de Sebt de Brilkiine dans le massif de Rehamna, ont fait l'objet d'une cartographie structurale. Les granites de la Meseta orientale (Haute-Moulouya) montrent une homogénéité de faciès et aussi des structures primaires comparables confirmant l'unité magmatique entre les deux corps d'Aouli et de Bou-Mia. Les structures magmatiques et l'analyse de la déformation dans l'encaissant métamorphique ont conduit à envisager une mise en place syn- à tardi-tectonique dans un cisaillement crustal vers l'Ouest, faiblement penté. Les granites de la Meseta occidentale ont été interprétés comme liés à des décrochements crustaux: 1- senestres subméridiens à NNE-SSW pour la granodiorite de Zaër et le granite d'Oulmès sur des accidents ductiles du socle profond; 2- dextre subméridien, pour le granite de Sebt, dont la mise en place est associée à une déformation fragile en "pull-apart". Dans le cas du Zaër, où deux faciès principaux constituent le Batholite, l'analyse structurale et ASM a nettement mis en évidence une mise en place en deux temps, puisqu'un épisode fragile serait responsable de l'injection d'un monzogranite, dans la granodiorite préalablement indurée La compatibilité dans un même système de contrainte, des accidents responsables de ces décrochements crustaux de la Meseta occidentale, a conduit à envisager un modèle géodynamique de la Meseta, en marge sud de l'orogène hercynien. Dans ce schéma, les structures du Maroc hercynien ont été comparées avec celles de son plus proche voisin, la Meseta ibérique. La poursuite des structures compressives vers le SSW, depuis la zone sud-portugaise jusqu'à la zone du Sehoul (au Nord du domaine mésétien marocain) permet d'envisager que ce domaine, situé au Nord de la Meseta, se comporte comme un poinçon dirigé vers le Sud. Cette tectonique, au Sud de la virgation ibéro-armoricaine, est à l'origine d'un décrochement dextre majeur en marge orientale du bloc côtier mésétien. Le décrochement se poursuit depuis la Meseta espagnole jusqu'au domaine atlasique, et est responsable, dans le massif des Rehamna, d'un décro-chevauchement du domaine des bassins carbonifères sur le Bloc côtier.
- Published
- 1989
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