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In order to understand further the emplacement (i.e., volcanic growth) of 22 Icelandite and 3 Rhyodacite cooling units in one of the long volcanic sequences known as Mauna Kuwale of the Wai’anae volcano (ca. 3.3 Ma), Oahu Hawaii we have conducted appropriate rock magnetic experiments described below as well as anisotropy of magnetic susceptibility (AMS) studies of such 25 units. We have undertaken rock magnetic investigations such as continuous and partial thermo-magnetic cycles of low field magnetic susceptibility versus temperature dependence, (k-T) curves experiments. We classified the k-T heating-cooling dependence of susceptibility in three groups A, B and C. Type A: yielded two components of titano-magnetite with a predominat Ti rich phase and occasionally a relevant magnetite component phase. Type B: samples are characterized by Ti poor magnetites. Magnetite dominates as the main magnetic carrier. Type C: k-T curves show one single phase of titanomagnetite, and Ti poor magnetite. The coercivity or remanence, determined by back field magnetization is always

Актуальность работы. Постоянно устанавливаемые признаки пластического течения в ультрамафитах предопределили подход к их изучению, как к метаморфическим породам, с применением нетрадиционного метода петроструктурного анализа. Использование этого метода позволяет реконструировать хронологическую последовательность процессов формирования и пластического деформирования ультрамафитов на уровнях верхняя мантия - земная кора, выявить общую направленность структурно-вещественной эволюции и решить ряд актуальных проблем их минерагении. Цель работы: по результатам выявленной микроструктурной неоднородности дунитов и гарцбургитов, типизации их микроструктур, оценки температур оливин-хромшпинелиевых равновесий и петроструктурного анализа оливина предложить сценарий структурной эволюции ультрамафитов Парамского и Шаманского массива Байкало-Муйского офиолитового пояса на уровнях верхняя мантия - земная кора. Методы исследования. Детальное петрографическое изучение ультрамафитов проводилось на поляризационном микроскопе AxioScope-40 фирмы Carl Zeiss, что позволило провести микроструктурную типизацию дунитов и гарцбургитов. Их типизация основана на морфологических особенностях оливина и была разработана многими исследователями. Количественная оценка деформационных микроструктур оливина в изученных ультрамафитах проводилась с использованием метода стереометрической металлографии. Микроструктурный анализ оливина является неотъемлемой частью петроструктурного изучения ультрамафитов. Он позволяет установить предпочтительные ориентировки минералов по внутреннему строению, которые, в свою очередь, являются отражением термодинамических условий их пластических деформаций. Вещественный состав оливинов и хромшпинелидов установлен на основании микрорентгеноспектральных определений, выполненных в Институте нефтегазовой геологии и геофизики Сибирского отделения Российской академии наук (г. Новосибирск) на микроанализаторе «Camebax». Расчет температурных равновесий проводился с использованием оливин-хромшпинелиевого геотермометра Фабри по вещественному составу сосуществующих оливина и хромшпинелида. Результаты. Для дунитов и гарцбургитов Парамского и Шаманского массивов Байкало-Муйского офиолитового пояса на оригинальном материале проведена идентификация деформационных микроструктур оливина. Они объединены в шесть типов: протогранулярный, мезогранулярный, порфирокластовый, порфиролейстовый, мозаичный (мозаично-лейстовый) и мозаично-паркетовидный. Пространственное распределение выделенных микроструктур в изученных массивах от центра к периферии характеризуется тенденцией уменьшения размера зерен в породах, показывает возрастание степени их пластического деформирования и отражает динамометаморфическую зональность. Петроструктурный анализ оливина в выделенных микроструктурных типах позволил установить термодинамические условия их реализации. Они фиксируют регрессивную направленность метаморфических преобразований ультрамафитов высокотемпературными пластическими деформациями, синтектонической рекристаллизацией и вторичной рекристаллизацией отжига в процессе формирования, перемещения и консолидации ультрамафитов в верхней мантии и земной коре. Установленная эволюция микроструктур оливина отражает рубежи многократно наложенных пластических деформаций, которые при благоприятных условиях могут быть определяющими в локализации хромита, хризотил-асбеста, нефрита, жадеита среди ультрамафитов из офиолитовых комплексов. Relevance of the research. Permanently identified signs of plastic flow in ultramafic rocks predetermined an approach to their study as metamorphic rocks. This approach uses non-traditional method of the petrofabric analysis. This method allows reconstructing the chronological sequence of formation and plastic deformation of ultramafic rocks in the upper mantle-crust, revealing the general trend of structural and matter evolution, and solving a number of urgent problems of the ultramafic mineral genesis. The aim of the study is to develop a scenario of the structural evolution of the Paramsky and Shamansky ultramafic massifs of Baikal-Muya ophiolite belt at the upper mantle-crust levels through the dunite and harzburgite microstructural heterogeneity, typing their microstructures, calculating olivine-chromospinelide thermal equilibrium, and olivine petrofabric analysis. Methods. The detailed petrographic characteristics of ultramafic rocks were performed by the polarizing microscope AxioScope-40 (Carl Zeiss). This study allowed carrying out microstructural typification of dunites and harzburgites. It was based on the morphological features of olivine and it was developed by many researchers. Quantification of deformation microstructures in olivine of ultramafic rocks was studied using the stereometric metallography. Microstructural analysis of olivine is an integral part of the petrofabric study of the ultramafic rocks. It allows determining the preferred orientation of minerals in the internal structure, which in their turn is a reflection of the thermodynamic conditions of their plastic deformation. The olivine and chromospinelide matter composition was determined using micro X-ray spectrum, obtained by microanalyser «Camebax» in the Institute of Petroleum Geology and Geophysics of Siberian Branch of Russian Academy of Sciences (Novosibirsk). The thermal equilibrium was calculated using olivine-chromospinelide Fabry geothermometer on the matter composition of coexisting olivine and chromospinelide. Results. The research provided the identification of the deformation microstructures of olivine for dunites and harzburgites of the Paramsky and Shamansky ultramafic massifs of the Baikal-Muya ophiolite belt. They are grouped into six types: protogranular, mesogranular porphyroclastic, porphyrolath, mosaic (mosaic-lath), mosaic-parquet-like. The spatial distribution of the allocated microstruct ures in the studied massifs from the сenter to the periphery is characterized by reducing the grain size in the rocks. This feature shows the increase in their plastic deformation degree and reflects the dynamometamorphiс zoning. The petrofabric analysis of the olivine in the identified microstructural types allowed determining thermodynamic conditions of their realization. These microstructures reflect a regressive trend of metamorphic transformations of the ultramafic rocks by high-temperature plastic deformations, syntectonic recrystallization, an d secondary annealing recrystallization in formation, transformation and consolidation in the upper mantle - earthґs crust. The identified evolution of the olivine microstructures reflects the limits of repeatedly overlaid plastic deformations, which can be decisive in l ocalization of chromite, chrysotile asbestos, jade, and jadeite within ultramafic rocks of ophiolite complexes under favorable conditions.

Στην παρούσα Μεταπτυχιακή Διατριβή αναλύονται τα παραμορφωτικά και συστασιακά (πετρογραφικά - ορυκτοχημικά) χαρακτηριστικά μυλωνιτιωμένων λιθολογιών από την πλαστική ζώνη διάτμησης του Φελλού (Βορειοδυτική Άνδρος). Η ζώνη διάτμησης του Φελλού είναι μια μεσοσκοπικής κλίμακας δομή, ΒΒΑ διεύθυνσης, με δομικό πάχος της τάξεως των 200 μέτρων. Το κεντρικό τμήμα της ζώνης διάτμησης φιλοξενείται σε μετα-πηλιτικές λιθολογίες και οριοθετείται από έντονα παραμορφωμένα μετα-υπερβασικά και μετα-βασικά λιθολογικά σώματα. Οι μυλωνιτιωμένες λιθολογίες της ζώνης διάτμησης χαρακτηρίζονται σαν S έως S – L τεκτονίτες. Η τεκτονική χαρτογράφηση στην περιοχή μελέτης αποκάλυψε ότι η μυλωνιτική ζώνη αναπτύχθηκε υπο-παράλληλα με το αξονικό επίπεδο ενός ήπια κεκλιμένου συγκλινοειδούς το οποίο έχει υποστεί καθολικό μετασχηματισμό. Οι ρεολογικές αντιθέσεις μεταξύ του πυρήνα της ζώνης διάτμησης και των περιθωρίων της σε συνδυασμό το τεκτονικό περιβάλλον ενός μετασχηματισμένου συγκλινοειδούς έχουν συμβάλλει στον εντοπισμό της παραμόρφωσης στην θέση ανάπτυξης της ζώνης διάτμησης. Σε χαρτογραφική κλίμακα ο προσανατολισμός των γραμμώσεων έκτασης μεταβάλλεται από ΝΝΔ , παράλληλα στη διεύθυνση της ζώνης διάτμησης, σε ΔΒΔ διεύθυνση βύθισης. Η μεταβολή στον προσανατολισμό των γραμμώσεων έκτασης δείχνει ότι η διεύθυνση κίνησης εντός της ζώνης διάτμησης διαμερίζεται χωρικά σε συνιστώσες κίνησης παράλληλα και κάθετα στην παράταξη της μυλωνιτικής φολίωσης. Ο κινηματικός διαμερισμός στην πλαστική ζώνη διάτμησης του Φελλού είναι χαρακτηριστικό γνώρισμα ζωνών διάτμησης πλάγιας συστολής. Ο κινηματικός διαμερισμός που αναγνωρίστηκε, ερευνήθηκε περαιτέρω με την εξέταση της χωρικής κατανομής των κρυσταλλογραφικών αξόνων [c] του χαλαζία, από δείγματα χαλαζιακών φλεβών και χαλαζιακών μυλωνιτών, προσανατολισμένα παράλληλα στη μυλωνιτική φολίωση και κάθετα στη γράμμωση έκτασης (ΧΖ επίπεδο ελλειψοειδούς παραμόρφωσης). Τα ιστολογικά διαγράμματα [c] αξόνων χαλαζία παρουσιάζουν μεταβολές στην τοπολογία τους σε διαφορετικά δομικά επίπεδα της ζώνης διάτμησης και διακριτές διαφορές με τα πρότυπα κρυσταλλογραφικά διαγράμματα [c] αξόνων μονοκλινικής συμμετρίας. Διακριτό χαρακτηριστικό , ειδικά για τα ανώτερα δομικά επίπεδα της ζώνης διάτμησης, είναι η εστίαση των [c] αξόνων σε σημειακά μέγιστα που προβάλλονται σε περιφερειακές θέσεις των κρυσταλλογραφικών διαγραμμάτων. Η βάση , δομικά, της ζώνης διάτμησης βρίσκεται στην ρεολογική διεπιφάνεια μετα-πηλιτών – μετα-βασιτών. Στην επαφή αυτή, ιστολογικά διαγράμματα από γειτονικά δείγματα χαλαζιακών φλεβών παρουσιάζουν συστηματικά διαγράμματα τύπου μικρών κύκλων. Η συστηματικότητα αυτή υποδηλώνει εντοπισμό της γεωμετρίας της παραμόρφωσης στην λιθολογική επαφή των μετα-πηλιτών - μετα-βασίτων. Η ποσοτική ανάλυση της παραμόρφωσης έδειξε ότι η παράμετρος Rxz μεταβάλλεται από 2.1 έως 6.45 ενώ η παράμετρος Flinn κυμαίνεται από 0.01 έως 0.93, υποστηρίζοντας και ποσοτικά ότι η γεωμετρία της παραμόρφωσης ανήκει στο πεδίο της πλάτυνσης. Η γεωμετρία της παραμόρφωσης στο πεδίο της πλάτυνσης είναι ένα επιπλέον διαγνωστικό χαρακτηριστικό των ζωνών διάτμησης πλάγιας συστολής. Η πετρογραφικη εξέταση μυλωνιτιωμένων λιθολογιών εστίασε στην αναγνώριση ζωνωμένων ορυκτών φάσεων με σκοπό την στοιχειοθέτηση των ορυκτοχημικών χαρακτηριστικών τους. Η πετρογραφική εξέταση δειγμάτων από μια επιφανειακή εμφάνιση μεταβασιτών από την βάση της μυλωνιτικής ζώνης συνέβαλλε στην αναγνώριση, σε κλίμακα λεπτής τομής, δύο λιθολογικών τύπων οι οποίοι είναι (α) Γρανατούχος – γλαυκοφανιτικός σχιστόλιθος και (β) Επιδοτιτικός - γλαυκοφανιτικός σχιστόλιθος. Η ορυκτοχημεία ζωνωμένων γρανατών και αμφιβόλων από τους δύο λιθολογικούς τύπους εξετάστηκε μέσω SEM/EDS.Η ορυκτοχημική ανάλυση οδήγησε στην αναγνώριση τριών τύπων ζώνωσης στις αμφιβόλους με τα εξής χαρακτηριστικά (α) Σκούροι πράσινοι πυρήνες σιδηρο-Κεροστίλβης με κροσσιτικά περιθώρια (β) Παλίνδρομη ζώνωση μεταξύ μπλε (σιδηρο-Γλαυκοφανής) και πράσινων αμφιβόλων (σιδηρο-Βαρροϊσίτης) και (γ) Απομονωμένοι κρύσταλλοι με κροσσιτικούς πυρήνες και ριβεκιτικά περιθώρια. Τα περιθώρια των ζωνωμένων γρανατών που εξετάστηκαν βρίσκονται σε ιστολογική ισορροπία με μπλέ αμφιβόλους, το γεγονός αυτό σε συνδυασμό με τα ορυκτοχημικά πειστήρια της κλασμάτωσης του μαγγανιου στους πυρήνες αποδεικνύει ότι η βλάστηση των γρανατών συνέβη σε αυξανόμενες συνθήκες πίεσης και θερμοκρασίας κατά την διάρκεια του υψηλής πίεσης μεταμορφικού γεγονότος. The subject of the present contribution is the analysis of deformation in the Fellos ductile shear zone, which crops out in the island of Andros. Fellos shear zone (FSZ) is an outcrop scale NNE –striking structure with a total structural thickness of, approximately, 200 m. The central main domain of the shear zone is defined by mylonitized metapelitic rocks, bounded by strongly deformed meta-basic and meta–ultrabasic rocks both on top and bottom. Mylonitic rocks in the shear zone can be classified as S to S – L tectonites. Structural mapping revealed that the Fellos shear zone resulted from the complete transposition of a gently inclined synform the axial plane of which is orientated sub – parallel to the mylonitic foliation. The rheological contrasts between the core of the shear zone and its margins in conjunction with the structural framework of a transposed synform are first order influences to the localization of deformation. The map scale pattern of the stretching lineations in the shear zone shows that the lineation swings from a NNE orientation, trending parallel to the strike of the shear zone, to an ESE orientation. This variation shows that transport orientation in the shear zone is spatially partitioned into strike parallel and strike normal movements. This kinematic partitioning in the Fellos shear zone is a characteristic feature of transpressional high strain shear zones. The recognized partitioning was further investigated by examining the pattern of quartz [c]-axes fabrics in quartz veins oriented parallel to the mylonitic foliation as well as in quartz –rich mylonites. Quartz [c] axes fabric diagrams shows variations in their topology at different structural levels of the shear zone and distinct differences with the [c] axes patterns of monoclinic strain symmetry. Distinct feature, especially at the uppermost structural levels of the shear zone, is the point maxima clustering of the [c] axes in peripheral position of the crystallographic diagrams. At the base of the shear zone, in the rheological interface of metapelites with metabasites, the fabric diagrams from neighboring quartz vein specimens shows consistently small circle girdle pattern. This observation denotes localization in the geometry of deformation (flattening) at this lithological contact. Finite strain analysis shows that Rxz varies from 2.1 to 6.45, while the Flinn parameter range between 0.01 and 0.93, supporting quantitatively the flattening geometry of strain. Flattening strain is another diagnostic criterion of transpressional shear zones. The means to constrain the compositional features of the mylonitic rocks was mineral chemistry and petrologic analysis. Petrographic examination, specifically, of a metabasite outcrop from the base of the shear zone revealed, in thin section scale, two lithologic types : (a) Garnet blueschist and (b) Epidote blueschist. The mineral chemistry of zoned garnets and amphiboles from these petrographic types has been examined using SEM/EDS. The microchemical analysis revealed three different zoning patterns in the amphiboles which are characterized by (a) dark green Ferro – hornblende cores with crossite rims (b) Amphiboles with compositional zoning and alternations of blue (Ferro – glaucophane) and green amphiboles (Ferro – barroisite) and (c) Isolated grains with crossite cores and riebeckite rims. Compositional mapping of zoned garnets witnessed fractionation of manganese to the cores, which is the Prima facie evidence of growth zoning. In addition, the almandine rims of the zoned garnets are in textural equilibrium with blue amphiboles, observation which implies that these garnets nucleated during the HP event.

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.

[ES] En el Macizo de Herbeira, situado en el Complejo varisco de Cabo Ortegal (NO del Macizo Ibérico), forma parte de una lámina de cabalgamiento constituida por rocas ultramáficas que han sufrido una compleja historia de deformación. La falla de Trans Herbeira (FTH), divide el macizo en dos sectores diferentes. El sector oriental está formado mayoritariamente por harzburgitas ricas en anfíbol, mientras que el sector occidental es litológicamente más variado, con una sucesión de harzburgita basal, dunita inferior, piroxenita media y dunita superior. Se han observado mediante microscopio óptico y SEM, microfábricas equigranulares y porfiroclásticas que evidencian la sucesión de diferentes fases de deformación. Con el análisis de la orientación cristalográfica preferente (OCP) del olivino mediante técnicas de difracción de electrones retrodispersados (EBSD), se han observado sistemas de deslizamiento (010)[100] y {0kl}[100], los cuales se activan en condiciones de altas temperaturas (>1000 ºC), por lo que estas fábricas se desarrollaron durante una fase de deformación de alta temperatura DA. La activación de sistemas de deslizamiento en la dirección cristalográfica [001], así como la observación patrones axiales (010), indican un descenso de la temperatura durante la deformación, por lo que estos patrones han sido atribuidos a una fase de deformación posterior D1. Las temperaturas y las tasas de deformación, de las diferentes fases de deformación observadas, se han estimado mediante paleopiezometría del olivino. Durante la deformación DA las temperaturas alcanzaron más de 1.000ºC, el esfuerzo diferencial fue muy bajo (3-6 MPa) y las tasas de deformación oscilaron entre 10-9 y 10-15 s-1, condiciones que son propias del manto astenosférico. Las deformaciones posteriores (D1 y D2) corresponden a fases de deformación litosféricas, con esfuerzos diferenciales moderadamente altos (8-35 MPa) y tasas de deformación más lentas, como es característico de las deformaciones no localizadas en estado sólido en la corteza inferior y el manto litosférico (10-12 -10-19 s-1)., [EN] The Herbeira ultramafic massif is located in the structural upper portions of the Cabo Ortegal Variscan Complex, NW Galicia, which form part of a thrust sheet that shows a complex deformational evolution. An important strike-slip fault, the Trans Herbeira Fault, divides the massif into two different zones. The eastern one is composed of amphibole bearing harzburgites, whilst the western one has a more complete lithological succession: basal harzburgite, lower dunite, medium pyroxenite and upper dunite. Equigranular and porphyroclastic microfabrics are observed in these rocks under optical microscope and SEM, providing evidence of a succession of several tectonic stages. The analysis of olivine CPO was carried out through electron backscattering diffraction techniques (EBSD).As a result the operating slip systems may be inferred. During de high temperature deformation stage DA the active slip systems were (010)[100] and {0kl}[100]. The activation of [001] axis along the slip direction occurred at lower temperatures (D1 tectonic stage). The estimation of tectonic stress and strain rate was performed by palaeopiezometry of olivine. During DA deformation the temperature reached more than 1000ºC, the tectonic stress level was very low (3-6 MPa) and the strain rate oscillated between 10-9 s-1 and 10-15 s-1, in accordance to the expected values at the mantle. Finally, the D1 deformation was developed at lower temperature (less than 1000ºC), moderately high tectonic stress level (8-35 MPa), and low strain rates (10-12 s-1 to 10-19 s-1), more coherent with the lower crust or uppermost mantle.

Quartz c-axis fabrics, vorticity of flow and deformation temperatures were analyzed in samples collected in the central sector of the Variscan inner zone in Sardinia (Italy). In order to constrain the kinematics of exhumation of medium- and high-grade metamorphic rocks during D2 post-collisional deformation, we investigated two shear belts with opposing shear senses. These shear belts are developed parallel to the trend of the inner zone which marks the boundary between two metamorphic complexes. Our data suggest that the sinistral shear belt initiated during the early stage of D2 deformation in a simple-shear-dominated regime, whereas the dextral shear belt initiated later in a pure-shear-dominated regime. We document a general non-coaxial flow regime with contemporaneous pure and simple shear components. Geometrical relationships reveal the operation of oblique extrusion during a compressive regime where the coaxial component acted sub-horizontal and orthogonal to the trend of the axial zone. Changes in the kinematics, vorticity of flow and strain geometry that occurred during D2 deformation may be related to post-collisional orogen-parallel displacement caught up in the Variscan orogeny.

High-pressure granulitic tectonites from shear zones at the contacts between the Bacariza Formation and its bounding units developed after eo-Hercynian subduction, during the initial exhumation of the Cabo Ortegal complex. Structural, petrographic, and crystallographic analysis of these tectonites with the EBSD technique enables us to unravel different, syn-metamorphic, deformation mechanisms in the minerals of the high-pressure granulitic assemblage. Dislocation creep and recovery were the main deformation mechanisms in garnet during peak metamorphism, followed by porphyroclast rigid rotation. The matrix minerals accommodated subsequent ductile deformation, still under high-pressure. Mass transfer, anisotropic growth and dislocation creep dominated deformation of augite. Subgrain rotation-recrystallisation by climbaccommodated dislocation creep operated in plagioclase and dislocation creep by prism-slip in quartz. Subsequent, static amphibolite-facies retrogradation was followed by decompression-related microfracturing during exhumation through medium- to upper crustal realms. Ductile rock deformation was non-coaxial and accommodated a top-to-the-NE displacement of hangingwall blocks

High-pressure granulitic tectonites from shear zones at the contacts between the Bacariza Formation and its bounding units developed after eo-Hercynian subduction, during the initial exhumation of the Cabo Ortegal complex. Structural, petrographic, and crystallographic analysis of these tectonites with the EBSD technique enables us to unravel different, syn-metamorphic, deformation mechanisms in the minerals of the high-pressure granulitic assemblage. Dislocation creep and recovery were the main deformation mechanisms in garnet during peak metamorphism, followed by porphyroclast rigid rotation. The matrix minerals accommodated subsequent ductile deformation, still under high-pressure. Mass transfer, anisotropic growth and dislocation creep dominated deformation of augite. Subgrain rotation-recrystallisation by climbaccommodated dislocation creep operated in plagioclase and dislocation creep by prism-slip in quartz. Subsequent, static amphibolite-facies retrogradation was followed by decompression-related microfracturing during exhumation through medium- to upper crustal realms. Ductile rock deformation was non-coaxial and accommodated a top-to-the-NE displacement of hangingwall blocks

Eclogites from the Eastern Belt of the Seve Nappes, Jämtland, Central Scandinavian Caledonides, have an LS fabric in which the foliation S and lineation L are both defined by the shape preferred orientation of omphacite. The orientation distribution diagram of omphacite reveals a crystallographic fabric defined by [001] parallel to L and [010] in a great circle distribution perpendicular to S and L. Optical and electron microscopy studies indicate that the eclogites have been deformed primarily by dislocation creep mechanisms operating in omphacite i.e. whilst garnets contain very low densities of dislocations and can be treated effectively as rigid bodies, omphacites contain defect structures consisting of well-ordered dislocation boundaries which delineate subgrains. The majority of dislocations in omphacite have Burgers vectors 1/2 and [001]. In the absence of extensive recrystallization, the omphacite deformation fabric is explained by multiple crystallographic slip along {110} [001], (100) [001] and {110} assisted by dislocation climb., Les éclogites de la ceinture orientale des nappes de Seve, Jämtland, Calédonides scandinaves centrales, possèdent une fabrique LS pour laquelle la foliation S et la linéation L sont toutes deux définies par une orientation préférentielle de forme de l 'omphacite. Le diagramme de la distribution de l'orientation des omphacites montre une fabrique cristallographique définie par [001] parallèle à L et [010] distribué sur un grand cercle perpendiculaire à S et L. Des études optiques et au microscope électronique indiquent que les éclogites ont été déformées principalement par un mécanisme de fluage par dislocations agissant dans l'omphacite c'est-à-dire que les grenats contiennent une très faible densité de dislocations et peuvent être considérés comme des corps rigides, tandis que les omphacites contiennent des défauts formés par des parois de dislocations bien ordonnées délimitant des sous-grains. La majorité des dislocations dans l'omphacite ont des vecteurs de Burgers 1/2 et [001], En l'absence de recristallisation poussée, la fabrique de déformation de l'omphacite s'explique par de multiples glissements cristallographiques {110} [001], (100) [001] et {110} ., Van Roermund Herman L.M. Petrofabrics and microstructures of omphacites in a high temperature eclogite from the Swedish Caledonides. In: Bulletin de Minéralogie, volume 106, 6, 1983. Eclogites et ultrabasites à grenat - First International Eclogite Conference.

Siliciclastic rocks of the Ruyang Group, southern Shanxi, and the broadly equivalent Gaoshanhe Group, Shaanxi, contain exceptionally well-preserved, large (empty set approximate to 150 mu m) acanthomorphic acritarchs recently interpreted as late Neoproterozoic (Sinian, c. 800-544 Ma) in age. This biostratigraphic interpretation is based on the presence of large acanthomorphs in Sinian successions of South China and elsewhere and the perceived absence of comparable forms in older rocks; it casts doubt on the long-accepted interpretation of Ruyang and correlative rocks as Mesoproterozoic in age (1600-1000 Ma). In contrast, thick marine dolomites in overlying units contain abundant radial fibrous fabrics and a narrow range of delta(13)C values (c. 0+/-1 parts per thousand vs. PDB), features which characterize unambiguously Mesoproterozoic carbonates elsewhere on the North China Platform and on other continents. Age estimates based on petrofabrics and chemostratigraphy are corroborated by a U-Pb zircon age of 999 Ma (no recorded error) for granites which intrude overlying carbonates. Thus, in combination, the available data constrain the Ruyang siliciclastics and overlying carbonates to be older than about one billion years, making Shuiyousphaeridium Yan and other large process-bearing acritarchs from these units among the oldest known distinctly ornamented eukaryotic microfossils., Organismic and Evolutionary Biology