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The India–Asia collision zone is the archetype to calibrate geological responses to continent–continent collision, but hosts a paradox: there is no orogen-wide geological record of oceanic subduction after initial collision around 60–55 Ma, yet thousands of kilometers of post-collisional subduction occurred before the arrival of unsubductable continental lithosphere that currently horizontally underlies Tibet. Kinematically restoring incipient horizontal underthrusting accurately predicts geologically estimated diachronous slab break-off, unlocking the Miocene of Himalaya–Tibet as a natural laboratory for unsubductable lithosphere convergence. Additionally, three endmember paleogeographic scenarios exist with different predictions for the nature of post-collisional subducted lithosphere but each is defended and challenged based on similar data types. This paper attempts at breaking through this impasse by identifying how the three paleogeographic scenarios each challenge paradigms in geodynamics, orogenesis, magmatism or paleogeographic reconstruction and identify opportunities for methodological advances in paleomagnetism, sediment provenance analysis, and seismology to conclusively constrain Greater Indian paleogeography.

The India-Asia collision zone is the archetype to calibrate geological responses to continent-continent collision, but hosts a paradox: There is no orogen-wide geological record of oceanic subduction after initial collision around 60-55 Ma, yet thousands of kilometers of post-collisional subduction occurred before the arrival of unsubductable continental lithosphere that currently horizontally underlies Tibet. Kinematically restoring incipient horizontal underthrusting accurately predicts geologically estimated diachronous slab break-off, unlocking the Miocene of Himalaya-Tibet as a natural laboratory for unsubductable lithosphere convergence. Additionally, three endmember paleogeographic scenarios exist with different predictions for the nature of post-collisional subducted lithosphere but each is defended and challenged based on similar data types. This paper attempts at breaking through this impasse by identifying how the three paleogeographic scenarios each challenge paradigms in geodynamics, orogenesis, magmatism or paleogeographic reconstruction and identify opportunities for methodological advances in paleomagnetism, sediment provenance analysis, and seismology to conclusively constrain Greater Indian paleogeography.

The pressure-temperature-time (P-T-t) evolution of metamorphic rocks is directly related to geodynamics as different tectonic settings vary in their thermal architecture. The shapes of P-T paths and thermobaric ratios (T/P) of metamorphic rocks have been extensively used to distinguish different tectonic domains. However, the role of metamorphic timescales in constraining tectonic settings remains underutilized. This is because of the poorly understood relationship between them, and the difficulty in accurately constraining the onset and end of a particular metamorphic event. Here, we show why and how the intrinsic relationship between thermal regime, rheology and rate of motion controlled by the heat, mass and momentum conservation laws translate to differences in heating, cooling, burial, exhumation rates of metamorphic rocks and thereby, to the duration of metamorphism. We compare the P-T-t paths of the orogenic metamorphic rocks of different ages and in particular, analyse their retrograde cooling rates and durations. The results show that cooling rates of the metamorphic rocks are variable but are dominantly 100 °C/Ma) during the late Neoproterozoic to Phanerozoic. To seek what controlled this secular change in metamorphic cooling rates, we use thermomechanical modelling to calculate the P-T-t paths of crustal rocks in different types of continental orogenic settings and compare them with the rock record. The modelled P-T-t paths show that lithospheric peel-back driven orogenic settings, which are postulated as an orogenic mode operating under the hotter mantle conditions of late Archean to early Proterozoic, are characterised by longer durations of metamorphism and slower cooling rates (a few 10s of °C/Ma) as compared to the modern orogenic settings (a few 100s of °C/Ma) operating under relatively colder mantle conditions. This is because peel-back orogens feature: (1) hot lithospheres with very high crustal geotherms being sustained by high mantle heat-flow and profuse magmatism, and (2) distributed deformation patterns that limit vertical extrusion (exhumation) of the metamorphic rocks along localized deformation zones and instead, trap them in the orogenic core for a long time. In contrast, modern orogens mostly involve colder lithospheres and allow rapid exhumation through localized deformation, which facilitates faster cooling of hot, exhumed metamorphic rocks in a colder ambience. Thus, we propose that the secular change in metamorphic cooling rates indicates a changing regime of orogenesis and thereby, of plate tectonics through time. Predominance of the slower metamorphic cooling rates before the Neoproterozoic indicate the occurrences of peel-back orogenesis and truncated hot (collisional) orogenesis during that time, while the appearance of faster cooling rates since the late Neoproterozoic indicates the transition to modern style of orogenesis. A transition between these orogenic styles also accounts for the prolonged longevity (>100 million years) of many Precambrian orogenic belts as compared to the Phanerozoic ones. This study underscores the strength of timescales in combination with P-T paths to distinguish tectonic settings of different styles and ages. ISSN:1342-937X ISSN:1878-0571

International audience; Although the Helvetic nappes of the Western Alps have been widely studied, their style, amount, and timing of deformation during the Alpine orogeny remain a subject of controversy. The discussion partly arises from various interpretations of the external crystalline massifs geometry and of the cover/basement relationships. Here, we apply structural analysis based on new field data, microtectonics, and 3D geological modeling on the Aiguilles Rouges and Mont-Blanc massifs, to better quantify their tectonic evolution and their relationship with the nappe stacking. Our results show large thrusting of the Helvetic Mesozoic sedimentary cover above the Aiguilles Rouges basement towards the WNW. The basal contact of the Helvetic nappes, which we call the Helvetic Basal thrust (HBT), often corresponds to a décollement level localized above the Triassic unconformity, but that locally also affects the basement. We suggest that most of the subalpine ranges are klippes above the HBT, and estimate the shortening of the thrust from previously published cross-sections to be between 13 and 32 km. According to published ages, we argue that the HBT was active in the Oligo-Miocene, between ∼30 and ∼14 Ma. After ∼14 Ma and until ~6 Ma, the HBT is offset by late steep out-of-sequence faults, including back-thrusts and the Mont-Blanc shear zone that was previously a ramp of the HBT. The transition of the major thrust system from the HBT rooting above (east) of the Mont-Blanc to the Alpine sole thrust rooting below (west) of the Aiguilles Rouges occurred between 18 and 14 Ma.

Key in understanding the geodynamics governing subduction and orogeny is reconstructing the paleogeography of ‘Greater India’, the Indian plate lithosphere that subducted since Tethyan Himalayan continental collision with Asia. Here, we discuss this reconstruction from paleogeographic, kinematic, and geodynamic perspectives and isolate the evolution scenario that is consistent with all three. We follow recent constraints advocating a ~58 Ma initial collision and update a previous kinematic restoration of intra-Asian shortening with a recently proposed model that reconciles long-debated large and small estimates of Indochina extrusion. Our new reconstruction is tested against paleomagnetic data, and against seismic tomographic constraints on paleo-subduction zone locations. The resulting restoration shows ~1000–1200 km of post-collisional intra-Asian shortening, leaving a 2600–3400 km wide Greater India. From a paleogeographic, sediment provenance perspective, Eocene sediments in the Lesser Himalaya and on undeformed India may be derived from Tibet, suggesting that all Greater Indian lithosphere was continental, but may alternatively be sourced from the contemporaneous western Indian orogen unrelated to India-Asia collision. A quantitative kinematic, paleomagnetic perspective prefers major Cretaceous extension and a ‘Greater India Basin’ opening within Greater India, but data uncertainty may speculatively allow for minimal extension. Finally, from a geodynamic perspective, assuming a fully continental Greater India would require that subduction rates close to 20 cm/yr was driven by a down-going lithosphere-crust assemblage more buoyant than the mantle, which seems physically improbable. We conclude that the Greater India Basin scenario is the only sustainable one from all three perspectives. We infer that old pre-collisional lithosphere rapidly entered the lower mantle sustaining high subduction rates, whilst post-collisional continental and young Greater India basin lithosphere did not, inciting the rapid India-Asia convergence deceleration ~8 Myr after collision. Subsequent absolute northward slab migration and overturning caused flat slab subduction, Tibetan shortening, arc migration and arc volume decrease.

In many mountain belts, deformation concentrates along mechanically weak fault zones inherited from earlier tectonic events. This work investigates the effects of two modes of structural weakening on the orientation of rifting and later tectonic inversion with respect to the imposed divergence/convergence direction in a high-resolution 3D finite difference model with a viscous-frictional rheology. In the first set of experiments, weakening consists in a decrease in frictional strength with increasing shear strain. The generated normal faults strike orthogonal to the imposed divergence direction. These faults are reactivated during tectonic inversion and absorb 50 to 70 percent of accumulated strain. In the second set of experiments, frictional strength is a decreasing function of shear strain rate. The generated faults are oblique to the divergence direction, implying oblique fault slip. Fault reactivation depends on the obliquity of the inverted rift to convergence direction, where larger obliquity leads to more intense fault reactivation. These new numerical results are compared to previous analogue and numerical models on the one hand, and natural examples of intracontinental mountain ranges due to tectonic inversion on the other hand. These comparisons demonstrate that both modes of frictional weakening should be taken into account when seeking to understand large-scale rifting and inversion tectonics., Financial support was provided by the Swiss National Science Foundation (grant 2-77297-15).

El distrito Casposo se ubica en el borde oriental de la Cordillera Frontal, departamento de Calingasta, en el oeste de la provincia de San Juan, Argentina. El mismo se conforma de un extenso sistema de vetas epitermales de baja sulfuración, dentro del cual se desarrolla una mina en explotación (actualmente inactiva). Desde el inicio de sus actividades en el año 2011 y hasta el 2015, esta mina produjo un total de 283.200 oz de Au y 9,5 Moz de Ag. La geología del yacimiento está caracterizada por afloramientos de una secuencia marina (Formación La Puerta), depositada entre el Carbonífero y el Pérmico temprano, que fue intensamente deformado durante la fase orogénica San Rafael (Pérmico inferior). Sobre esta secuencia, y mediante una importante discordancia angular (Superficie San Rafael), tuvo lugar un importante magmatismo representado por el Grupo Choiyoi, de naturaleza subalcalina que evolucionó desde términos calcoalcalinos hacia composiciones shoshoníticas. Entre los 269,7 Ma y los 256,7 Ma (Pérmico medio a superior) este magmatismo presentó su mayor intensidad y volumen, resultando en una potente secuencia piroclástica con presencia de discordancias intraformacionales (Sección inferior y superior), que es intruída por cuerpos subvolcánicos (denominados Dacita Casposo y Andesita Cerro Pelado). Este vulcanismo evolucionó de manera sincrónica a la intrusión de importantes cuerpos plutónicos de grandes dimensiones como la Granodiorita Casposo, que potencialmente podrían representar las partes más profundas del mismo sistema magmático, aunque una importante falla N-S separa ambos ambientes. Durante las etapas terminales de este periodo, entre los 263,6 Ma y los 256,7 Ma, se habría instalado el sistema hidrotermal responsable de la formación del yacimiento, en cercana asociación con un conjunto de cuerpos subvolcánicos denominados Dique Félsico e Intrusivo Félsico. Luego del emplazamiento de la mineralización, y mediante un período de actividad magmática nula de ~ 12 Ma, ocurrió una reactivación del magmatismo a partir de los 249,7±2 Ma (Triásico Medio) que resultó en la intrusión de una sucesión de familias de diques de composiciones intermedias a ácidas (denominados Diques Básicos, Diques Riolíticos Porfíricos y Diques de Aplitas). El yacimiento abarca un área de aproximadamente 100 km2 formado por vetas que exhiben una marcada zonación composicional: las puramente silíceas concentradas en la zona de operaciones de mina (Mercado, Aztec, B Vein, Inca), vetas cuarzo-carbonáticos (Cerro Norte, Lucía), y las puramente carbonáticas con pulsos silíceos (Oveja Negra, Aurora, Casposo Norte, Leñador y Julieta). Las texturas predominantes son las de relleno de espacios abiertos, como los bandeados coloformes con desarrollo de ginguros, crustiformes, cocardas, masivas y brechas con cemento de sulfuros. Del detallado análisis estructural realizado sobre las secciones transversales y plantas de la zona de mina, se determinó un vector de máxima apertura NE-SO actuando en simultáneo a la formación de la mineralización (control sin-mineral), que luego habría sido afectada por al menos dos eventos posteriores de fallamiento (control post-mineral). A partir del análisis de detallado de la mineralogía y textura de la veta Inca, se discriminaron 9 pulsos que fueron agrupados en 6 episodios principales, siendo 5 de ellos de naturaleza hidrotermal y 1 de del tipo tectónico-hidrotermal. Los pulsos P1 y P2 son estériles. En el pulso P3 precipitan cuarzo-calcedonia con textura bandeada coloforme, y adularia subrómbica a pseudoacicular, con minerales de mena alojadas en bandas oscuras tipo ginguro. La mena se compone de electrum (10% Au – 90% Ag) y plata nativa, sulfosales como tetraedrita (rica en Ag), pirargirita y polibasita, teluros y seleniuros (naumanita y hessita) y sulfuros de metales base (esfalerita, galena y calcopirita). En el P4 precipitan sulfuros finos a gruesos junto a un cuarzo macizo, los minerales de mena se corresponden con sulfosales como la tetraedrita, y sulfuros de metales base. La evolución de los pulsos continúa hacia una composición donde predominan las arcillas verdes y las texturas brechosas en el P5. Continuo, aparece otro pulso silíceo y estéril (P6), con grandes cristales de adularia subrómbica. La secuencia sigue con un cuarzo microcristalino negro, masivo, de grano fino que posee la particularidad de exhibir molibdenita mostrando una extraña textura dendrítica (P7). En el pulso P8 actúan en simultáneo una componente hidráulica y otra tectónica, que generaron una brecha de matriz negra donde el cemento es masivo y posee anomalías de Mo; en ocasiones presenta pátinas azuladas que tiñen los clastos de los pulsos previos. Por último, se reconoce un evento menor que forma finas vetillas de carbonatos (P9). La mineralización se habría originado a partir del ascenso de soluciones cloruradas reducidas, con pH neutro a levemente alcalino, con salinidades del 7% NaCl eq. y con evidencias de ebullición; en tanto que los datos de isótopos estables establecen un origen producto de mezcla entre aguas meteóricas y magmáticas. La presencia de calcita de hábito hojoso, texturas de reemplazo de cuarzo y adularia pseudoacicular, bandeados coloformes y brechas, sumado a la coexistencia entre inclusiones fluidas ricas en fase vapor y líquido, evidencian a la ebullición como el factor responsable para la depositación metalífera. Por último, por las características observadas se puede clasificar ala Veta Inca como un sistema epitermal clásico de baja sulfuración, aunque ciertos atributos como las salinidades moderadas, la elevada relación Ag/Au, la presencia de sulfosales como tetraedrita, pirargirita y polibasita, y la presencia de esfalerita pobre en Fe, evidencian un estado de sulfuración intermedia., The Casposo district is located on the eastern edge of the Cordillera Frontal, Calingasta department, in the west of the San Juan province, Argentina. It consists of a larguest system of low sulfidation epithermal veins, within which there is an operating mine (currently inactive). Since the beginning of its activities in the year 2011 and until 2015, this mine produced a total of 283.200 oz of Au and 9,5 Moz of Ag. The geology of the deposit is characterized by outcrops of a marine sequence (La Puerta Formation), deposited between the Carboniferous and Early Permian, which was intensely deformed during the San Rafael orogenic phase (Lower Permian). Over this sequence, and through an important angular unconformity (San Rafael Surface), an important magmatism took place, represented by the Choiyoi Group, of subalkaline nature that evolved from calcalkaline to shoshonitic compositions. Between 269,7 Ma and 256,7 Ma (middle to upper Permian) this magmatism reached its highest intensity and volume, resulting in a thick pyroclastic sequence with the presence of intraformational unconformities (lower and upper section), which is intruded by subvolcanic bodies (Dacite Casposo and Andesita Cerro Pelado). This volcanism evolved synchronously with the intrusion of important large plutonic bodies such as the Casposo Granodiorite, which could potentially represent the deepest parts of the same magmatic system, although a major N-S fault separates both environments. During the terminal stages of this period, between 263,6 Ma and 256,7 Ma, the hydrothermal system responsible for the formation of the deposit would have been installed, in close association with a set of subvolcanic bodies called Felsic Dike and Felsic Intrusive. After the emplacement of the mineralization, and through a period of null magmatic activity of ~ 12 Ma, a reactivation of magmatism occurred from 249,7±2 Ma (Middle Triassic) that resulted in the intrusion of a succession of families of dykes of intermediate to acid compositions (Basic Dykes, Porphyritic Rhyolitic Dykes and Aplite Dykes). The deposit covers an area of approximately 100 km2 formed by veins that shows a marked compositional zoning: purely siliceous veins concentrated in the area of mine operations (Mercado, Aztec, B Vein, Inca), quartz-carbonate veins (Cerro Norte, Lucía), and purely carbonate veins with siliceous pulses (Oveja Negra, Aurora, Casposo Norte, Leñador and Julieta). The predominant textures are those of open space filling, such as colloform banding with the development of ginguros, crustiforms, cocards, massive and breccias with sulfide cement. From the detailed structural analysis carried out on the cross-sections and plans of the mine area, a vector of maximum NE-SW opening was determined, acting simultaneously with the formation of mineralization (syn-mineral control), which would have been affected by at least two subsequent faulting events (post-mineral control). From the detailed analysis of the mineralogy and texture of the Inca vein, 9 pulses were discriminated and grouped into 6 main episodes, being 5 of them of hydrothermal nature and 1 of tectonic-hydrothermal type. Pulses P1 and P2 are barren. Pulse P3 precipitates quartz-chalcedony with colloform banded texture, and subrhombic to pseudo-acicular adularia, with ore minerals hosted in dark gingurobands. The ore consists of electrum (10% Au - 90% Ag) and native silver, sulfosalts such as tetrahedrite (Ag-rich), pyrargyrite and polybasite, tellurides and selenides (naumanite and hessite) and base metal sulfides (sphalerite, galena and chalcopyrite). In P4, fine to coarse sulfides precipitate along with massive quartz, the ore minerals correspond to sulfosalts such as tetrahedrite, and base metal sulfides. The evolution of the pulses continues towards a composition dominated by green clays and brecciated textures in P5. Continuously, another siliceous and barren pulse appears (P6), with large crystals of subrhombic adularia. The sequence continues with a black, massive, fine-grained microcrystalline quartz that has the particularity of exhibiting molybdenite showing a strange dendritic texture (P7). In the P8 pulse, a hydraulic and a tectonic component act simultaneously, generating a black matrix breccia where the cement is massive and has Mo anomalies; sometimes it shows bluish patinas that stain the clasts of the previous pulses. Finally, a minor event that forms fine carbonate veins (P9) is recognized. The mineralization would have originated from the ascent of reduced chloride solutions, with neutral to slightly alkaline pH, with salinities of 7% NaCl eq. and with evidence of boiling, while the stable isotope data establish an origin product of mixing between meteoric and magmatic waters. The presence of platycalcite, quartz replacement textures and pseudoacicular adularia, colloform banding and breccias, along with the coexistence between vapor and liquid phase rich fluid inclusions, evidence boiling as the responsible factor for the ore deposition. Finally, due to the characteristics observed, the Inca Vein can be classified as a classic low sulfidation epithermal system, although certain attributes such as moderate salinities, high Ag/Au ratio, the presence of sulfosalts such as tetrahedrite, pyrargyrite and polybasite, and the presence of Fe-poor sphalerite, evidence an intermediate sulfidation state., Facultad de Ciencias Naturales y Museo

Терско-Каспийский прогиб – крупная структурно-тектоническая единица, расположенная на стыке двух разновозрастных и различных по составу элементов земной коры, которые из-за общей геодинами-ческой обстановки приобрели статус единого мегапрогиба с характерными литолого-стратиграфическими, термобарическими, геохимическими и нефтегенерационными характеристиками, что подтверждается гео-лого-геофизическими исследованиями и промышленными скоплениями в пределах пространства изуче-ния., The Terek-Caspian trough is a large structural-tectonic unit located at the junction of two elements of the Earth's crust of different ages and different composition, which, due to the general geodynamic condition, acquired the status of a united mega-trough with characteristic lithological and stratigraphic, thermo-baric, geochemical and oil-generating characteristics, which is confirmed by geological and geophysical studies and industrial accumula-tions within the study area.

International audience; Resolving the timing of initiation and propagation of continental accretion associated with increasing topography and exhumation is a genuinely challenging task using low-temperature thermochronology. We present an integrated thermo-mechanical and low-temperature thermochronology modelling study of tectonically-inverted hyperextended rift systems. Model low-temperature thermochronology data sets for apatite (U-Th)/He, apatite fission-track, zircon (U-Th)/He and zircon fission-track systems, which are four widely used thermochronometric systems in orogenic settings, are generated from fourteen locations across a model collisional, doubly-vergent orogen. Our approach allows prediction of specific, distinct low-temperature thermochronology signatures for each domain (proximal, necking, hyperextended, exhumed mantle) of the two rifted margins that, in turn, enable deciphering which parts of the margins are involved in orogenic wedge development. Our results show that a combination of zircon (U-Th)/He and apatite fission-track data allows diagnostic investigation of model orogen tectonics and offers the most valuable source of thermochronological information for the reconstruction of the crustal architecture of the model inverted rifted margins. The two thermochronometric systems have actually very close and wide closure windows, allowing to study orogenic processes over a larger temperature range, and therefore over a longer period of time. Comparison of model data for inverted rifted margins with model data for non-inverted, purely thermally-relaxed rifted margins enables assessing the actual contribution of tectonic inversion with respect to thermal relaxation. We apply this approach to one of the best-documented natural examples of inverted rift systems, the Pyrenees. Similarities between our thermochronometric modelling results and published low-temperature thermochronology data from the Pyrenees provide new insights into the evolution of the range from rifting to collision. In particular, they suggest that the core of the Pyrenean orogen, the Axial Zone, consists of the inverted lower plate necking and hyperextended domains while the Pyrenean retrowedge fold-and-thrust belt, the North Pyrenean Zone, represents the inverted upper plate distal rifted margin (exhumed mantle, hyperextended and necking domains). This is in good agreement with previous, independent reconstructions from literature, showing the power that our integrated study offers in identifying processes involved in orogenesis, especially early inversion, as well as in predicting which domains of rifted margins are accreted during mountain building.; Identifier au moyen de la thermochronologie basse température le moment à partir duquel l’accrétion continentale s’amorce et se propage est une tâche difficile. Dans cette étude, nous couplons modélisation thermomécanique de systèmes hyper-amincis inversés et thermochronologie basse température pour prédire la signature thermochronologique de quatre systèmes basse température communément utilisés en domaine orogénique ((U-Th)/He sur apatite, traces de fission sur apatite, (U-Th)/He sur zircon et traces de fission sur zircon). Notre approche de modélisation permet de prédire les signatures thermochronologiques basse température propres à chaque domaine de marge du système extensif (domaine proximal, zone de neck, domaine hyper-aminci et domaine de manteau exhumé). Ces signatures permettent en retour d’identifier les domaines de marge impliqués dans l’accrétion continentale qui suit l’extension. Nos résultats montrent que la combinaison des signatures thermochronologiques des systèmes (U-Th)/He sur zircon et traces de fission sur apatite renseigne sur les processus mis en jeu lors de la formation d’un orogène collisionnel à double vergence, ainsi que sur l’architecture des marges inversées durant l’orogénèse. Les deux systèmes thermochronométriques possèdent en effet des gammes de température de fermeture voisines et relativement larges, permettant d’étudier les processus orogéniques sur un intervalle de températures plus grand, et donc sur une période de temps plus longue. La comparaison des signatures thermochronologiques prédites dans un modèle thermomécanique d’inversion avec celles prédites dans un modèle de relaxation thermique, sans convergence postérieure à l’extension, permet d’apprécier la nécessaire contribution des processus tectoniques d’inversion par rapport au processus de relaxation thermique postrift. Nous appliquons notre approche à l’un des exemples naturels les mieux documentés de systèmes de rift inversé, les Pyrénées. Les similitudes qui existent entre nos prédictions thermochronométriques et les données de thermochronologie basse température publiées pour les Pyrénées fournissent de nouvelles informations sur la formation et l’évolution de l’orogène pyrénéen. En particulier, ces similitudes suggèrent que la zone interne de déformation pyrénéenne, la Zone Axial, est constituée des domaines de neck et hyper-aminci de la plaque inférieure, inversés durant l’accrétion, tandis que le prisme orogénique qui se développe sur la plaque européenne, la Zone Nord-pyrénéenne, représente la marge distale inversée de la plaque supérieure. Ce résultat est en accord avec les précédentes reconstructions publiées de la dynamique pyrénéenne, démontrant ainsi le potentiel de notre approche dans l’identification des processus impliqués dans l’orogenèse, notamment l’inversion précoce, ainsi que dans la prédiction du type de domaine de marge accrété lors de la formation des chaînes de montagnes.

Mountain height at convergent plate margins is limited by the megathrust shear force, but it remains unclear how this constraint affects the topographic evolution and mountain building at the transition from subduction to collision. Generally, mountain height increases during the subduction-collision transition in response to crustal thickening or processes like mantle delamination and slab breakoff, but the main parameters controlling how much mountain height increases remain poorly understood. Here we show, based on analytical and finite-element force-balance models, that the increase in mountain height depends on the magnitude of the megathrust shear force and the reduction of submarine margin relief. During the subduction stage, the shear force is balanced by the gravitational effect of the margin relief and the deviatoric stresses in the upper plate are low. When the submarine margin relief is reduced during the closure of the ocean basin, the effect of the gravitational force decreases and the upper plate experiences enhanced deviatoric compression, which allows the mountain height to increase until a near-neutral stress state beneath the high mountains is restored. If the increase in mountain height cannot keep pace with the submarine relief reduction, the compression of the upper plate increases by a few tens of MPa, which promotes tectonic shortening and mountain building. Our analysis implies that mountain height can increase by hundreds of meters to a few kilometers during collision, depending primarily on the trench depth during the subduction stage and possible syncollisional changes of the megathrust shear force.

The Himalaya are among the youngest and highest mountains in the world, but the exact timing of their uplift and origins of their biodiversity are still in debate. The Himalayan region is a relatively small area but with exceptional diversity and endemism. One common hypothesis to explain the rich montane diversity is uplift-driven diversification—that orogeny creates conditions favoring rapid in situ speciation of resident lineages. We test this hypothesis in the Himalayan region using amphibians and reptiles, two environmentally sensitive vertebrate groups. In addition, analysis of diversification of the herpetofauna provides an independent source of information to test competing geological hypotheses of Himalayan orogenesis. We conclude that the origins of the Himalayan herpetofauna date to the early Paleocene, but that diversification of most groups was concentrated in the Miocene. There was an increase in both rates and modes of diversification during the early to middle Miocene, together with regional interchange (dispersal) between the Himalaya and adjacent regions. Our analyses support a recently proposed stepwise geological model of Himalayan uplift beginning in the Paleocene, with a subsequent rapid increase of uplifting during the Miocene, finally giving rise to the intensification of the modern South Asian Monsoon.

Cretaceous porphyry copper deposits of northern Chile (28º-29º30’ S) are genetically related with dacitic to dioritic porphyries and they represent a still poorly-explored target for Cu resources. The porphyries correspond to stocks distributed into two separated discontinuous NS trending belts of different age. The location of these porphyries is generally adjacent to orogen-parallel major fault systems that extend along the studied segment and also have a marked temporal relationship with deformation events registered along these structures. A first episode of Cu-bearing porphyry emplacement took place between 116 and 104 Ma (Mina Unión or Frontera, Cachiyuyo, Punta Colorada, Dos Amigos, Tricolor porphyries). These Early Cretaceous dacite to diorite porphyries are spatially associated with the eastern segments of the Atacama Fault System, which records sinistral transpression that started at 121 Ma producing ground uplift, consequent denudation and exhumation of the Early Cretaceous magmatic arc. This resulted in a change from marine to continental deposition with an angular unconformity in the site of the back-arc basin after of eastward migration of the deformation around 112-110 Ma. At the scale of the continental margin, this deformation is correlated with early stage of the Mochica Orogenic event described in Perú. A second episode of Cu-bearing porphyry emplacement occurred between 92 and 87 Ma (Elisa, Johana, Las Campanas and La Verde deposits), which are spatially and temporally associated with the regional-scale Las Cañas-El Torito reverse fault, active between 89 and 84 Ma, during the Peruvian Orogenic Phase. This fault up thrust to the west part of the Chañarcillo Group rocks (Lower Cretaceous) over the younger upper levels of the Cerrillos Formation (Upper Cretaceous). The integrated geological mapping and geochemical data of the Early to Late Cretaceous volcanic rocks indicates that both Early Cretaceous sinistral transpression and Late Cretaceous east-west compression were not significant in promote changes in magma genesis, except for slight changes in trace element ratios (increase in Th/Ta, Nb/Ta and La/Yb) suggesting that the Late Cretaceous deformation event produced only slightly increase in crustal thickness (>40 km), but far from being comparable to major Cenozoic orogenic phases, at least along the magmatic arc to back-arc domains in the study area. Finally, our study give insights about regional geological parameters that can be used as a first order guide for exploration of Cu resources along Cretaceous magmatic belts of northern Chile, where both Early and Late Cretaceous Cu-bearing porphyry intrusions are restricted to a large structural block bounded to the west and east by Cretaceous fault systems.

Central Anatolia (Turkey) is a small and nascent example of a high orogenic plateau, providing a natural laboratory to study processes driving plateau rise. The 1-km-high plateau interior uplifted since c. 8–5 Ma, with a further phase of kilometre-scale uplift affecting the southern plateau margin since 0.45 Ma. Several causes of plateau rise have been proposed: peeling or dripping delamination of the lithospheric mantle; asthenospheric upwelling through slab gaps created by slab fragmentation or break-off, and; continental underthrusting and crustal shortening below the southern plateau margin. The Neogene history of the plateau has not been diagnostic of the causes of plateau rise. We thus evaluate proposed uplift causes in the context of the Anatolian orogenesis, which formed the plateau lithosphere during subduction since the Cretaceous. We combine this analysis with available constraints on uplift, and geophysical data that illuminate the modern mantle (and crustal) structure. Our analysis suggests that lithospheric dripping, which followed arc magmatism and shortening in the Kirsehir Block (eastern Central Anatolia), is the most likely cause of plateau interior uplift. Lithospheric dripping is, however, an unlikely sole driver of multi-phase uplift along the southern plateau margin. There, underthrusting of the African continental margin, recorded by c. 11–7 Ma thrusting on Cyprus, is a viable cause of uplift since 0.45 Ma, but cannot account for earlier uplift since c. 8–5 Ma. Instead, slab break-off below the southern plateau margin is likely in light of geophysical data. On the SW plateau margin, small-scale peeling delamination of the Central Taurides by the Antalya slab since early Miocene times accounts for >150 km slab retreat with no corresponding upper-plate deformation. A southwest-travelling wave of subsidence and uplift signalled this retreat and may have contributed to coeval oroclinal bending of the western Central Taurides and southeastward thrusting of the Lycian Nappes.

In this paper we present a series of thermo-mechanical experiments on continent-continent collision zones to investigate the role of lateral strength contrasts in terms of collision dynamics and orogen geometries. Our results show that differences in crustal rheology, may lead to a variety of different patterns of deformation and crustal geometries. Upper plate indentation forms a sequence of foreland propagating thrust units made of brittle upper crust on the lower plate. The strong deformation of the lower plate stands in stark contrast to the undeformed upper plate. In contrast, subduction of strong lithosphere beneath a weak upper plate forms a complex pattern of deformation. Deformation initiates on the lower plate and forms an antiformal stack made of brittle upper crust, before it indents the upper plate. Hence, deformation is present on both, the lower and upper plate, despite differences in initial strength. The outcome of this study has direct implications to natural collision zones, where differences in strength between the upper and lower plate exist. For example, along strike variability of upper vs. lower plate shortening in the Alps are likely to be controlled by contrasts in crustal strength. Furthermore, we suggest that the antiformal stack in the axial zone of the Pyrenees might indicate a strong lower plate at the onset of collision. Our results may therefore provide important constraints for the rheological state of continents during collision.

International audience; New fieldwork and tectonic analysis has been carried out along the Andean morphotectonic frontline between 46°30’ and 47°30′S. The right lateral transtensional Marques–Zeballos Pass fault system (MZPRS) controlled the 800–1200 m uplift of the Andes at 16.1–18.1 Ma. Our data and analysis indicate that there was no lower Miocene contractile event along the Andean morphotectonic frontline. The Main Andean Thrust (MAT), which is deeply rooted in the upper crust is a retroarc thrust dipping 10–15° westward, and provides evidence for major crustal shortening at ~120 Ma. At that time the arc volcanic strata of the Ibañez Fm (148–178 Ma) was transported eastward above the rift volcanic Quemado Fm (144179 Ma), which lies unconformably on the Deseado basement massif.The geologic records from the fieldwork together with the available data allow us to identify the processes controlling the dynamic evolution of the two main topographic features of the studied Andean segment. (1) Upward convection originating from the subducted South Chile Ridge −1 segment (SCR −1) is dynamically sustaining the high topography of the North Patagonian Icefield (4070 m at the Mt. San Valentin, ~2 km higher than the Southern South Volcanic Zone). This, together with the locus of maximum moisture being at 47°S during glacial events has resulted in producing the two largest glacial lobes of Patagonia. (2) The 180 km long, E–W trending antiformal arch structure of the Mt. Zeballos Ridge (MZR, a hinge zone trending N–S along the MZPRS) straddling the Andes and the Foreland is proposed to be the morphological “twin” of the South American Plate Moho Plateau (SAM MOHO P). The SAM MOHO P controls the location of both the MZPRS and the MZR boundaries location through time. The Patagonia Slab Window and SAM asthenospheric dynamics (upward and corner flows, respectively) and their in–depth interaction appear to control the morphotectonic evolution of the whole studied segment through a powerful feedback loop between tectonics, morphology, and climate, at least for the past 3–4 Myr.

En la actualidad existe un gran interés en utilizar materiales de construcción que puedan ofrecer grandes ventajas cuando estos son adicionados al concreto, sobre todo cuando se tiene una alta contaminación ambiental y se quiere mitigar, generando concretos sostenibles. Con la presente investigación se buscó evaluar si las dunitas pueden ser incluidas en los concretos como agregados verdes con el fin de que estas ayuden en la absorción de CO2 y se puedan mitigar las emisiones de gases efecto invernadero a la atmosfera. Las dunitas se definen como rocas de origen magmático, es una roca intrusiva con gran contenido de olivino, hace parte del grupo de las peridotitas y no presenta contenido de cuarzo en su mineralogía. At present there is a great interest in using construction materials that can offer great advantages when they are added to concrete, especially when there is high environmental pollution and you want to mitigate, generating sustainable concrete. With this research, we sought to assess whether dunites can be included in concrete as green aggregates in order to help them absorb CO2 and mitigate greenhouse gas emissions to the atmosphere. Dunitas are defined as rocks of magmatic origin, it is an intrusive rock with a high olivine content, it is part of the peridotite group and does not have quartz content in its mineralogy. Ingeniero Civil http://unidadinvestigacion.usta.edu.co Pregrado

Many orogens on the planet result from plate convergence involving subduction of a continental margin. The lithosphere is strongly deformed during mountain building involving subduction of a plate composed generally of accreted continental margin units and some fragments of downgoing oceanic crust and mantle. A complex deformation involving strong partitioning of deformation modes and kinematics produces crustal shortening, accompanied by crustal thickening. Partitioning depends on three main factors: (1) rheologic layering of the lithosphere; (2) interaction between tectonics and surface processes; (3) subduction kinematics and 3D geometry of continental margins (oblique convergence, shape of indenters). Here we present an original view and discussion on the impact of deformation partitioning on the structure and evolution of orogens by examining the Taiwan mountain belt as a case study. Major unsolved questions are addressed through geological observations from the Taiwan orogen and insights from analogue models integrating surface processes. Some of these questions include: What is the role played by décollements or weak zones in crustal deformation and what is the impact of structural heterogeneities inherited from the early extensional history of a rifted passive continental margin? What is the relationship between deep underplating, induced uplift and flow of crustal material during erosion (finite strain evolution during wedge growth)? Are syn-convergent normal faults an effect of deformation partitioning and erosion? What is the role of strain partitioning on the location of major seismogenic faults in active mountain belts? What can be learned about the long-term and the present-day evolution of Taiwan?

Key in understanding the geodynamics governing subduction and orogeny is reconstructing the paleogeography of ‘Greater India’ the Indian plate lithosphere that subducted since Tethyan Himalayan continental collision with Asia. Here, we discuss this reconstruction from paleogeographic, kinematic, and geodynamic perspectives and isolate the evolution scenario that is consistent with all three. We follow recent constraints advocating a ~58 Ma initial collision and update a previous kinematic restoration of intra-Asian shortening with a recently proposed model that reconciles long-debated large and small estimates of Indochina extrusion. Our new reconstruction is tested against paleomagnetic data, and against seismic tomographic constraints on paleo-subduction zone locations. The resulting restoration shows ~1000–1200 km of post-collisional intra-Asian shortening, leaving a 2600–3400 km wide Greater India. From a paleogeographic, sediment provenance perspective, Eocene sediments in the Lesser Himalaya and on undeformed India may be derived from Tibet, suggesting that all Greater Indian lithosphere was continental, but may alternatively be sourced from the contemporaneous western Indian orogen unrelated to India-Asia collision. A quantitative kinematic, paleomagnetic perspective prefers major Cretaceous extension and a ‘Greater India Basin’ opening within Greater India, but data uncertainty may speculatively allow for minimal extension. Finally, from a geodynamic perspective, assuming a fully continental Greater India would require that subduction rates close to 20 cm/yr was driven by a down-going lithosphere-crust assemblage more buoyant than the mantle, which seems physically improbable. We conclude that the Greater India Basin scenario is the only sustainable one from all three perspectives. We infer that old pre-collisional lithosphere rapidly entered the lower mantle sustaining high subduction rates, whilst post-collisional continental and young Greater India basin lithosphere did not, inciting the rapid India-Asia convergence deceleration ~8 Myr after collision. Subsequent absolute northward slab migration and overturning caused flat slab subduction, Tibetan shortening, arc migration and arc volume decrease.

In this paper we present a series of thermo-mechanical experiments on continent-continent collision zones to investigate the role of lateral strength contrasts in terms of collision dynamics and orogen geometries. Our results show that differences in crustal rheology, may lead to a variety of different patterns of deformation and crustal geometries. Upper plate indentation forms a sequence of foreland propagating thrust units made of brittle upper crust on the lower plate. The strong deformation of the lower plate stands in stark contrast to the undeformed upper plate. In contrast, subduction of strong lithosphere beneath a weak upper plate forms a complex pattern of deformation. Deformation initiates on the lower plate and forms an antiformal stack made of brittle upper crust, before it indents the upper plate. Hence, deformation is present on both, the lower and upper plate, despite differences in initial strength. The outcome of this study has direct implications to natural collision zones, where differences in strength between the upper and lower plate exist. For example, along strike variability of upper vs. lower plate shortening in the Alps are likely to be controlled by contrasts in crustal strength. Furthermore, we suggest that the antiformal stack in the axial zone of the Pyrenees might indicate a strong lower plate at the onset of collision. Our results may therefore provide important constraints for the rheological state of continents during collision.

The most important Cenozoic marine transgression in Patagonia occurred during the late Oligocene–early Miocene when marine waters of Pacific and Atlantic origin flooded most of southern South America including the present Patagonian Andes between ~41° and 47° S. The age, correlation, and tectonic setting of the different marine formations deposited during this period are debated. However, recent studies based principally on U–Pb geochronology and Sr isotope stratigraphy, indicate that all of these units had accumulated during the late Oligocene–early Miocene. The marine transgression flooded a vast part of southern South America and, according to paleontological data, probably allowed for the first time in the history of this area a transient connection between the Pacific and Atlantic oceans. Marine deposition started in the late Oligocene–earliest Miocene (~26–23 Ma) and was probably caused by a regional event of extension related to major plate reorganization in the Southeast Pacific. Progressive extension and crustal thinning allowed a generalized marine flooding of Patagonia that reached its maximum extension at ~20 Ma. It was followed by a phase of compressive tectonics that started around 19–16 Ma and led to the growth of the Patagonian Andes. The youngest (~19–15 Ma) marine deposits that accumulated in the eastern Andean Cordillera and the extra-Andean regions are coeval with fluvial synorogenic deposits and probably had accumulated under a compressive regime. Fil: Encinas, Alfonso. Universidad de Concepción; Chile Fil: Folguera Telichevsky, Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina Fil: Bechis, Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Diversidad Cultural y Procesos de Cambio. Universidad Nacional de Río Negro. Instituto de Investigaciones en Diversidad Cultural y Procesos de Cambio; Argentina Fil: Finger, Kennet. University of California; Estados Unidos Fil: Zambrano, Patricio. Universidad Andrés Bello; Chile Fil: Pérez, Andrés Felipe. Universidad de Concepción; Chile Fil: Bernabé, Pablo. Universidad de Concepción; Chile Fil: Tapia, Francisca. Universidad de Concepción; Chile Fil: Riffo, Ricardo. Universidad de Concepción; Chile Fil: Buatois, Luis Alberto. University of Saskatchewan; Canadá Fil: Orts, Darío Leandro. Universidad Nacional de Río Negro. Sede Alto Valle. Instituto de Investigaciones en Paleobiología y Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Nielsen, Sven Nikolaus. Universidad Austral de Chile. Instituto de Ciencias de la Tierra; Chile Fil: Valencia, Víctor V.. Washington State University; Estados Unidos Fil: Cuitiño, José Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico de Geología y Paleontología; Argentina Fil: Oliveros, Verónica. Universidad de Concepción; Chile Fil: De Girolamo Del Mauro, Lizet. Universidad de Concepción; Chile Fil: Ramos, Victor Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina

Questions on formation of modern geomorphological structure and flora of Mountain Dagestan are considered.

Across the world we observe spectacular mountain belts that formed as a result of two colliding plates. Frequently this process is disturbed by the influence of neighbouring geological processes, such as the formation of adjacent mountain belts, adding significant kinematic and geometric complexities to the collisional systems. To understand the relative contributions of the processes involved it is essential to identify the individual interfering processes and to quantify their influence on the evolution of the mountain system. The Eastern Alps (Europe) is such a complex mountain belt and is the prime target of this research with particular interest in the transitions to the neighbouring Dinaric mountain belt and the Pannonian Basin. These transitions provide a unique opportunity to unravel the effects of interfering tectonic processes based on field studies, low temperature geochronology and physical analogue modelling. The geological evolution of the Eastern Alps and Dinarides is largely related to the motion of the African continental plate towards the European plate, with the microcontinent Adria located in between the two. The plate motion of the latter plays a key role in driving the deformation of the Eastern Alps as well as the Dinaric mountain chain. With respect to the Eastern Alps the Adriatic plate is traditionally viewed as a bulldozer that deforms, uplifts and laterally displaces the Eastern Alps. However, we show that these geological processes are also compatible with a tectonic scenario in which the Adriatic plate subducts below the Alps. The subduction also provides a crucial mechanism to create the formation of the Southern Alps, which affects at the same time the geological evolution of the northern Dinarides. The experimental results also strongly suggest that the geological evolution of the Eastern Alps during the last 30 Ma is best explained by phases of oblique and subsequent orthogonal Alps-Adria convergence. This has led to the characteristic deformation patterns of the Eastern Alps: significant crustal thickening in the west and dominant lateral displacements of crustal units in the east. These differences in deformation style are confirmed by our new field observations and low temperature age data which also emphasize a tectonic link to the contemporaneous opening of the Pannonian Basin and associated extension. The data thereby disclose that the coeval collision and extension is critical for the rapid exhumation of metamorphosed rocks around 17 Ma at the transition from the Alps to the Dinarides. At the same time, a recorded phase of accelerated uplift during the last 10 Ma is rather related to the absence of extension in combination with ongoing Alps-Adria collision and deep seated processes. The integrated results of this thesis demonstrate that subduction/collision processes related to Alps-Adria convergence are strongly influenced by neighbouring and far-fielded processes, which has significant implications for the structural and topographic evolution of the studied region.

Across the world we observe spectacular mountain belts that formed as a result of two colliding plates. Frequently this process is disturbed by the influence of neighbouring geological processes, such as the formation of adjacent mountain belts, adding significant kinematic and geometric complexities to the collisional systems. To understand the relative contributions of the processes involved it is essential to identify the individual interfering processes and to quantify their influence on the evolution of the mountain system. The Eastern Alps (Europe) is such a complex mountain belt and is the prime target of this research with particular interest in the transitions to the neighbouring Dinaric mountain belt and the Pannonian Basin. These transitions provide a unique opportunity to unravel the effects of interfering tectonic processes based on field studies, low temperature geochronology and physical analogue modelling. The geological evolution of the Eastern Alps and Dinarides is largely related to the motion of the African continental plate towards the European plate, with the microcontinent Adria located in between the two. The plate motion of the latter plays a key role in driving the deformation of the Eastern Alps as well as the Dinaric mountain chain. With respect to the Eastern Alps the Adriatic plate is traditionally viewed as a bulldozer that deforms, uplifts and laterally displaces the Eastern Alps. However, we show that these geological processes are also compatible with a tectonic scenario in which the Adriatic plate subducts below the Alps. The subduction also provides a crucial mechanism to create the formation of the Southern Alps, which affects at the same time the geological evolution of the northern Dinarides. The experimental results also strongly suggest that the geological evolution of the Eastern Alps during the last 30 Ma is best explained by phases of oblique and subsequent orthogonal Alps-Adria convergence. This has led to the characteristic deformation patterns of the Eastern Alps: significant crustal thickening in the west and dominant lateral displacements of crustal units in the east. These differences in deformation style are confirmed by our new field observations and low temperature age data which also emphasize a tectonic link to the contemporaneous opening of the Pannonian Basin and associated extension. The data thereby disclose that the coeval collision and extension is critical for the rapid exhumation of metamorphosed rocks around 17 Ma at the transition from the Alps to the Dinarides. At the same time, a recorded phase of accelerated uplift during the last 10 Ma is rather related to the absence of extension in combination with ongoing Alps-Adria collision and deep seated processes. The integrated results of this thesis demonstrate that subduction/collision processes related to Alps-Adria convergence are strongly influenced by neighbouring and far-fielded processes, which has significant implications for the structural and topographic evolution of the studied region.

Across the world we observe spectacular mountain belts that formed as a result of two colliding plates. Frequently this process is disturbed by the influence of neighbouring geological processes, such as the formation of adjacent mountain belts, adding significant kinematic and geometric complexities to the collisional systems. To understand the relative contributions of the processes involved it is essential to identify the individual interfering processes and to quantify their influence on the evolution of the mountain system. The Eastern Alps (Europe) is such a complex mountain belt and is the prime target of this research with particular interest in the transitions to the neighbouring Dinaric mountain belt and the Pannonian Basin. These transitions provide a unique opportunity to unravel the effects of interfering tectonic processes based on field studies, low temperature geochronology and physical analogue modelling. The geological evolution of the Eastern Alps and Dinarides is largely related to the motion of the African continental plate towards the European plate, with the microcontinent Adria located in between the two. The plate motion of the latter plays a key role in driving the deformation of the Eastern Alps as well as the Dinaric mountain chain. With respect to the Eastern Alps the Adriatic plate is traditionally viewed as a bulldozer that deforms, uplifts and laterally displaces the Eastern Alps. However, we show that these geological processes are also compatible with a tectonic scenario in which the Adriatic plate subducts below the Alps. The subduction also provides a crucial mechanism to create the formation of the Southern Alps, which affects at the same time the geological evolution of the northern Dinarides. The experimental results also strongly suggest that the geological evolution of the Eastern Alps during the last 30 Ma is best explained by phases of oblique and subsequent orthogonal Alps-Adria convergence. This has led to the characteristic deformation patterns of the Eastern Alps: significant crustal thickening in the west and dominant lateral displacements of crustal units in the east. These differences in deformation style are confirmed by our new field observations and low temperature age data which also emphasize a tectonic link to the contemporaneous opening of the Pannonian Basin and associated extension. The data thereby disclose that the coeval collision and extension is critical for the rapid exhumation of metamorphosed rocks around 17 Ma at the transition from the Alps to the Dinarides. At the same time, a recorded phase of accelerated uplift during the last 10 Ma is rather related to the absence of extension in combination with ongoing Alps-Adria collision and deep seated processes. The integrated results of this thesis demonstrate that subduction/collision processes related to Alps-Adria convergence are strongly influenced by neighbouring and far-fielded processes, which has significant implications for the structural and topographic evolution of the studied region.

Swiss Journal of Geosciences, 106 (1), ISSN:1661-8734, ISSN:1661-8726

Se presentan en esta tesis los resultados del estudio del sector andino de los Andes Patagónicos Septentrionales ubicados entre los 41º30´ y los 42º30´S, en las provincias de Río Negro y Chubut. La región estudiada no contaba, hasta el momento, con levantamientos geológicosdetallados debido a la dificultad de acceso que presenta este sector de los Andes. El análisisestratigráfico y morfoestructural del área constituyen los ejes principales del trabajo deinvestigación realizado. Las imágenes satelitales disponibles, así como los datos gravimétricos yrelevamientos magnéticos con los que se pudo contar, complementan la información disponibley contribuyen a dar solidez a las interpretaciones realizadas. Además, se llevaron a cabo análisispetrográficos, geoquímicos y radimétricos. El análisis estratigráfico ha permitido realizar una caracterización de las unidades volcánicas yplutónicas jurásico-cretácicas que resulta considerablemente más precisa que las descripcionespreexistentes. En particular, se ha reconocido además la existencia de una unidad volcánicamiocena, previamente desconocida, que aflora en el sector interno de los Andes entre los 41º 30´ y los 41º 50´S. El análisis morfoestructural revela, a escala local, el carácter sinextensionalde estas rocas y, a escala regional, la existencia de un importante evento de extensión. Lasprecisas dataciones radimétricas (U-Pb LAICPMS en circones) que se presentan en esta tesispermiten asignar este evento al Mioceno Medio a Superior. El análisis morfoestructural realizado permite postular que la faja plegada y corrida desarrolladaa estas latitudes estuvo sometida a condiciones de evolución singulares que no han sidoreconocidas en otros segmentos andinos. A la etapa compresiva que se inició durante el Mioceno Inferior a Medio, y continuó desarrollándose al menos hasta el Mioceno Superior en lazona de antepaís, se sobreimpusieron fenómenos extensionales en el sector occidental interno,de modo que ambos fenómenos podrían incluso haber coexistido durante una parte del procesode estructuración de los Andes. El análisis morfoestructural aporta, por lo tanto, datos valiososque permiten evaluar, en un sentido más amplio, el desarrollo de la deformación en el tiempo yel espacio. Adicionalmente, se discuten una serie de indicios que podrían indicar la existencia deuno o más eventos de deformación desarrollados durante el Jurásico-Cretácico, que deberán serinvestigados a futuro. This thesis is focused on the study of the Andean sector of the North Patagonian Andeslocated between 41º30´ and 42º30´S, in Río Negro and Chubut provinces. This area ischaracterized by a difficult access, reason by which no previous detailed geological surveyswere done. A stratigraphical and morphostructural analysis of the study area was done on thebasis of field mapping and interpretation of satellite images. The interpretations presented inthis thesis were also complemented with gravity and magnetic data, and also withpetrographical, geochemical and geochronological analysis. The stratigraphical analysis allowed a precise characterization of the Jurassic-Cretaceous to Cenozoic volcanic and plutonic units. Additionally, a previously unknown, Miocene volcanicunit outcropping at the inner sector of the Andes, between 41º30´ and 41º50´S, was recognized. A morphostructural analysis reveals, at a local scale, the synextensional character of these rocks. The new radiometric ages presented in this work constrain this event to the middle to late Miocene. The morphostructural analysis allows us to postulate that the fold and thrust belt wassubjected to unique conditions during its evolution, which are not recognized through otherneighbor Andean segments. After the beginning of the compression in the late Miocene, andduring its progression to the foreland zone, middle to late Miocene extensional phenomenaoccurred in the inner Andean sector. Additionally, morphostructural analysis provides valuableinformation in order to evaluate spatial and temporal development of the deformation. Finally,the existence of one or more deformational events acting in Jurassic-Cretaceous times isdiscussed. Fil: Tobal, Jonathan Elías. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

The Australian continent records c. 1860-1800 Ma orogenesis associated with rapid accretion of several ribbon micro-continents along the southern and eastern margins of the proto-North Australian Craton during Nuna assembly. The boundaries of these accreted micro-continents are imaged in crustal-scale seismic reflection data, and regional gravity and aeromagnetic datasets. Continental growth (c. 1860-1850 Ma) along the southern margin of the proto-North Australian Craton is recorded by the accretion of a micro-continent that included the Aileron Terrane (northern Arunta Inlier) and the Gawler Craton. Eastward growth of the North Australian Craton occurred during the accretion of the Numil Terrane and the Abingdon Seismic Province, which forms part of a broader zone of collision between the northwestern margins of Laurentia and the proto-North Australian Craton. The Tickalara Arc initially accreted with the Kimberley Craton at c. 1850 Ma and together these collided with the proto-North Australian Craton at c. 1820 Ma. Collision between the West Australian Craton and the proto-North Australian Craton at c. 1790-1760 Ma terminated the rapid growth of the Australian continent.

Convergent plate margins occur when two adjoining tectonic plates come together to form either a subduction zone, where at least one of the converging plates is oceanic and plunges beneath the other into the mantle, or a collision zone, where two continents or a continent and a magmatic arc collide. Convergent plate margins are arguably the most complicated and dynamic plate boundaries on Earth and have been the subject of many investigations and discussions since the advent of plate tectonic theory. This paper provides a historical background and a review of the development of geological and geodynamic theories on convergent plate margins. Furthermore, it discusses some of the recent advances that have been made in the fields of structural geology, geophysics and geodynamics, which are fundamental to our understanding of this phenomenon. These include: (1) the finding that plates and plate boundaries move at comparable velocities across the globe; (2) the emerging consensus that subducted slabs are between two to three orders of magnitude stronger than the ambient upper mantle; (3) the importance of lateral slab edges, slab tearing and toroidal mantle flow patterns for the evolution of subduction zones; and (4) clear evidence from mantle tomography that slabs can penetrate into the lower mantle. Still, many first-order problems regarding the geodynamic processes that operate at convergent margins remain to be solved. These include subduction zone initiation and the time of inception of plate tectonics, and with it convergent plate margins, on Earth. Fundamental problems in orogenesis include the mechanism that initiated Andean mountain building at the South American subduction zone, the potential episodicity of mountain building with multiple cycles of shortening and extension, and the principal driving force behind the construction of massive mountain belts such as the Himalayas–Tibet and the Andes. Fundamental questions in subduction dynamics regard the partitioning of subduction into a trench and plate component, and the distribution of energy dissipation in the system. In seismic imaging, challenges include improving resolution at mid to lower mantle depth in order to properly understand the fate of slabs, and better constraining the 3-D flow-related anisotropic structure in the surrounding mantle. Future insights into such fundamental problems and into the regional and global dynamics of convergent plate margins will likely be obtained from integrating spatio-temporal data, structural geological data, geophysical data and plate kinematic data into plate tectonic reconstructions and three-dimensional geodynamic models of progressive deformation.

Evidence of two burial–exhumation cycles that took place during a single orogeny has been found in rocks belonging to the Piemonte unit of the Western Alps. An early high pressure event, which resulted from tectonic burial down to pressures of 1.5 GPa, was followed by exhumation to ca. 0.20–0.35 GPa as a result of extensional deformation. Renewed shortening culminated in a second burial episode down to pressures of 0.65–0.80 GPa, before the final exhumation took place. Existing geochronological data allow only ca. 13–19 Ma for the completion of both burial–exhumation cycles. Therefore, we suggest that the evolution of orogens is characterized by multiple short-lived burial–exhumation cycles related to orogen-scale alternance between shortening and extensional deformation.

6 p., mapa col., [EN]This paper discusses the issue of the origin and maintenance of biodiversity on tropical mountains, with emphasis on the Neotropics, and concludes that present-day biodiversity patterns of highland biotas cannot be understood without the combined action of Neogene tectonics and Pleistocene climatic changes., [ES]En este artículo se discute el origen y mantenimiento de la biodiversidad en las montañas tropicales, con énfasis en el Neotrópico, y se concluye que los patrones de biodiversidad de las biotas de gran altura no pueden ser explicados sin la acción combinada de la tectónica neógena y los cambios climáticos del Pleistoceno., Funding was provided by the BBVA Foundation (projects BIOCON 2004-90 and BIOCON 2008-031) and the Higher Council for Scientific Research (CSIC, project 201430E007).

[cat] Aquesta tesi doctoral descriu la cinemàtica dels Pirineus Basco-Cantàbrics, més concretament de la Plataforma Burgalesa, mitjançant la integració de i) geologia de superfície; ii) interpretació de línies sísmiques i pous; i iii) estudis paleomagnètics de rotacions d'eix vertical. La integració d'aquest conjunt de dades permet comprendre la relació entre la Plataforma Burgalesa i les conques d'avantpaís de l'Ebre i del Duero durant la orogènia Pirenaica. Les principals contribucions de la tesi són: i) Presentar un model estructural, el qual honora tots les restriccions imposades per l'estratigrafia, la preconfiguració de l'àrea prèvia a la deformació contractiva i les dades tant superficials com profundes. Aquest model permet comprendre com és la transició entre la deformació pel·licular present a l'est de la zona d'estudi i la deformació no pel·licular present a l'oest. ii) Reinterpretació de l'estructura de Zamanzas localitzada al nord de la Plataforma Burgalesa mitjançant el treball combinat entre geologia de superfície i les dades aportades per els pous d'exploració. iii) Aportar noves dades de vint-i-sis estacions de paleomagnetisme repartides per a la zona d'estudi i que permeten caracteritzar el patró de rotacions d'eix vertical. El resultat final és el de proposar un nou model per a l'evolució de la Plataforma Burgalesa que honra les restriccions imposades tant per la geologia de superfície com les dades d'exploració profunda disponibles fins a la data. Aquest model està caracteritzat per presentar deformació no pel·licular al sector oest mentre que quan el nivell de desenganxament augmenta de potència els encavalcaments es desenganxen i deformen la cobertora presentant un estil estructural pel·licular. Aquesta tesi ha demostrat que la pre-configuració tant de la conca extensiva pròpiament dita com la del seu voltant, tenen una forta implicació en el desenvolupament i estructuració de la Plataforma Burgalesa durant la Orogènia Pirenaica. És durant aquesta etapa en la qual es produeixen rotacions tant horàries com antihoràries en els diferents sectors mostrejats., [eng] This PhD Thesis describes the kinematics of the Burgalesa Platform in the Basque-Cantabrian Pyrenees by the integration of i) surface geology; ii) seismic and well data; and iii) vertical axis rotation paleomagnetic studies. The integration of all the data allow to understand the relationship between the Burgalesa Platform and the Ebro and Duero foreland basins during the Pyrenean Orogeny. The principal contribution of the Thesis is to present a new structural model, that fits all the constraints imposed by the stratigraphy, the pre-configuration of the area prior to the contractive deformation and both the deep and the surface data. This model allows to understand the transition between thin-skinned and the thick-skinned tectonics. The combined work between surface geology and well data has allowed to reinterpret the Zamanzas structure located at the northern boundary of the Burgalesa Platform. Previously, this structure had been interpreted as a set of extensional faults. This Thesis pointed out the mismatches and reinterpret the Zamanzas structure as a popup generated during the Pyrenean Orogeny. The combined interpretation of wells and seismic sections allow to partially comprehend the structure of the area during the extensional event as well as the result of the Pyrenean Orogeny occurred later. This study allowed to determine the distribution of the Lower Cretaceous depocenters during the North Atlantic and the Bay of Biscay opening. Moreover, during this stage salt mobilisation triggered by extension generated areas where the Triassic salt layer was thickened as demonstrated by the well data and the outcropping diapirs. This process accentuated the development of the depocenters. The extensional event also generated the onlap sedimentary geometries in the syn-rift sediments. The extensional model proposed is a combined model with the development of cover forced folding with salt migration at the southern boundary. The Triassic salt decoupled the extension between the basement and the cover and contractional structures were developed such as the back-thrust in the Huidobro area that produced the duplication of the Mesozoic. The early stages of the Pyrenean Orogeny resulted in the development of the San Pedro Structure, with north-directed and basement-involved thrusts, later fossilised by the Duero foreland sediments. To the north, the Burgalesa Platform, characterised by south-directed thrusts rooted into the Triassic salts, was southwards displaced until the San Pedro act as a backstop forcing the Burgalesa Platform to extrude laterally towards the southeast overriding the Ebro Foreland Basin. The paleomagnetic study focussed on determine the possible vertical axis rotations along the Pyrenees, denotes that the amount of sites that some areas have is not present in the Burgalesa Platform and vicinities that lack of sites. For that reason, another objective of this Thesis is to provide new paleomagnetic sites for the study area. The study carried out is made up of twenty-six new sites widely distributed and that allow to characterise the vertical axis rotation pattern. The results obtained reveals that i) the magnetisation of the Cenozoic sediments is prior to deformation and that ii) clockwise and counter clockwise rotation occurred in the Burgalesa Platform and adjacent areas. The evolution models previously proposed for the Burgalesa Platform were based either from surface geology of from geophysical data thus fitting some of the constraints. Because any model integrated all the observations and available data, a new model explaining the Burgalesa Platform evolution has been proposed. This model is characterised by presenting thick-skinned deformation at the western sector whereas, thin-skinned at the eastern one when the Triassic salt layer thickens point in which the thrusts are detach the cover from the basement. The results of this Thesis demonstrate that the pre-configuration of the extensional basin and its vicinities have a strong implication in the development and evolution of the Burgalesa Platform during the Pyrenean Orogeny. Finally, during this evolution, clockwise and counter clockwise rotations occurred in the different sectors as shown by the paleomagnetic studies carried out during this Thesis.

[spa] Los experimentos de multi-sísmicas realizados en el marco de la iniciativa del proyecto ALCUDIA incluyen una incidencia normal y sísmica gran angular de los conjuntos de datos de reflexión sísmica. Estos limitan las estructuras internas, la estructura detallada de la corteza y litosfera y, proporcionan el conocimiento necesario de las propiedades físicas a lo largo de la Zona Central Ibérica. Las imágenes sísmicas de incidencia normal se presentan de Sur a Norte: las estructuras de la Zona Ossa-Morena (Unidad Central), el ondulante domino Ibérico Central, los cuerpos intrusivos graníticos (Granitos de Mora, complejo Anatético de Toledo, etc.) hasta la falla de Toledo, justo al Sur de la cuenca del Tajo. La zona de estudio está caracterizada por una topografía ondulada debido a una serie de sinclinales y anticlinales. La imagen muestra una corteza inferior débilmente reflectante, ~13-18 km de espesor. La topografía sinodal refleja los pliegues, los sistemas de cabalgamientos imbricados, y fallas extensionales lístricas observados por los datos de sísmica de incidencia normal. A niveles más profundos las imágenes revelan estructuras arqueadas y laminares que sugieren estructuras como boundinage. Estas características son interrumpidas hacia el Sur, muy probablemente debido a la existencia de la zona de sutura. La expresión más profunda del afloramiento de la zona de sutura, está ligeramente desplazada hacia el Norte con respecto a su localización en superficie y, esta es vista como un cabalgamiento profundo de una fina capa de corteza inferior. Hacia el límite norte del perfil, debajo la falla de Toledo, una banda de reflectividad buzando hacia norte sugiere un adelgazamiento de la corteza inferior hacia el Norte. La discontinuidad de Mohorovicic se delimita como una fuerte disminución de la reflectividad a la base de la corteza inferior, localizada a unos ~31-33 km de profundidad (10.5 s tempo doble). Los datos de gran ángulo de sísmica de reflexión adquiridos a principios de mayo de 2012, tenían como objetivo proporcionar las distribuciones de las propiedades físicas (velocidades P y S, densidades, y el coeficiente de Poisson) de la corteza bajo la zona de estudio. Este perfil fue diseñado para ser casi coincidente con el perfil de incidencia normal. Los modelos de velocidad de P y S obtenidos revelan importantes variaciones laterales de velocidad en la corteza superior, que son coherentes con la observación de los afloramientos en superficie. La corteza inferior se identifica por un fuerte aumento de la velocidad a ~13 km y ~20 km de profundidad en Zona Central Ibérica y en la Cuenca del Tajo, respectivamente. La base de la corteza está fuertemente limitada por grandes amplitud de las llegadas de PmP y SmS y se encuentra a ~31 km en el extremo sur y a ~35,5 km por debajo del extremo norte del perfil de sísmica de gran ángulo. La sísmica de gran ángulo también se utilizó para producir low-fold stacks para las ondas P y las S. Esto se hizo para tomar una mirada más cercana a la discontinuidad de Moho, y para ser capaces de estimar la estructura interna y generar sismogramas sintéticos donde las fases PmP y SmS serían cualitativamente comparables a las fases observadas en los registros sísmicos. Esto dio lugar restricciones clave en la estructura de la discontinuidad de Moho bajo la Zona Central Ibérica y la Cuenca del Tajo en el orógeno Varisco del Macizo Central Ibérico. Las imágenes revelan una profundización gradual de ~31 km (10,2 s) en la Zona Central Ibérica a ~35,5 km (11,8 s) debajo de la cuenca del Tajo para la discontinuidad de Moho. Los datos sísmicos de gran ángulo y los resultados derivados de ellos son compatibles con las imágenes de incidencia normal., [eng] The multi-seismic experiments carried out under the ALCUDIA research initiative include a normal incidence and a wide-angle seismic reflection datasets. These constrain the internal architecture, the detailed crustal and lithospheric structure and, provide the necessary knowledge on physical properties across the Central Iberia Zone. The normal incidence seismic images from south to north: the suture zone of Ossa-Morena Zone (the Central Unit), the undulating Central Iberian domain, the intruded granitic bodies (the Mora Granite, the Toledo Anatectic complex, etc) up to the Toledo Fault, just south of the Tajo Basin. The study area is characterized by undulating topography characterized by a series of synclines and anticlines. The image shows a weakly reflective upper crust, ~13-18 km thick. The sinusoidal topography reflects the folding, the imbricate thrust systems, and listric extensional faults imaged by the normal incidence data. At deeper levels the image reveals arcuate and laminated events suggesting boudinage like structures. These features are disrupted in the south most probably due to the existence of the suture zone. The deep expression of the outcropping suture zone, is slightly displaced to the north with respect to its surface position and, it is imaged as an under-thrusting of a thin slice of lower crust. Towards the northern end of the transect, beneath the Toledo fault, a north dipping band of reflectivity suggest a significant thinning of the lower crust to the north. The Mohorovicic discontinuity is delineated as a sharp decrease in reflectivity at the base of the lower crust, located at ~31-33 km depth (10.5 s two-way travel-time). The wide-angle seismic reflection data acquired in early May 2012, was aimed to provide the distributions of the physical properties (P- and and S-wave velocities, densities, and Poisson’s ratio) of the crust beneath the study area. It was designed to be nearly coincident with the normal incidence profile. The obtained P- and S- wave velocity models reveal significant lateral velocity variations in the upper crust, which are consistent with the observation from the surface outcrops. The lower crust is identified by a sharp increase in velocity at ~13 km and ~20 km beneath the Central Iberian Zone and the Tajo Basin, respectively. The base of the crust is strongly constrained by the high amplitude PmP and SmS arrivals and it is located at ~31 km in the southern end and at ~35.5 km below the northern end of the wide-angle transect. The wide-angle was also used to produce low-fold P- and S-wave wide-angle stacks. This was done to take a closer look to the Moho discontinuity, and to be able to estimate the internal structure and generate synthetic seismograms in which the PmP and SmS would be qualitatively comparable to the phases observed in the shot records. This place key constraints on the structure of the Moho discontinuity beneath the Central Iberian Zone and the Tajo Basin in the Variscan orogen of the central Iberian Massif. The images reveal gradual deepening from ~31 km (10.2 s) in the Central Iberian Zone to ~35.5 km (11.8 s) beneath the Tajo Basin for the Moho discontinuity. The wide-angle seismic data and the results derived from it are compatible with the normal incidence images.

The surface expression of a lateral polarity change of continental mantle lithosphere subduction has been studied by using lithosphere-scale physical models. Key parameters investigated were: the degree of lateral coupling between adjacent domains of opposing subduction polarity, the width of the zone separating the domains, and the lithosphere geometry and rheology. The model results illustrate an asymmetric lithospheric structure induced by deformation of the downgoing plates, which have been separated by a narrow transition zone. A wide and symmetric orogenic wedge overlying a region of thickened mantle lithosphere and hampered subduction characterizes this transition zone. In addition, interaction between the neighboring subduction domains caused downbending of the upper plates and resulted in the lateral termination of crustal structures and lowering of surface topography. The lateral extent of interaction between the domains strongly depends on the degree of coupling between the domains, the rheology of the mantle lithosphere and the amount of bulk shortening. The modelling results have major implications on the interpretation of seismic and tomographic data from the European Alps in terms of the crust and lithosphere geometries. It appears that an observed lateral change of subduction polarity at mantle depth can explain the variations of wedge build-up between the Western/Central and Eastern Alps.

This thesis investigates the tectonic histories of igneous and metamorphic rocks exposed in the Mérida Andes, Venezuela, and Santander Massif, Colombia from the Late Cambrian to the present day. Zircon U-Pb ages from 52 igneous and metamorphic rocks constrain the main periods of arc magmatism on the north-western corner of Gondwana from ~500 to ~413 Ma and from ~294 Ma to ~196 Ma. Peak Barrovian metamorphic conditions are recorded by anatexis at ~477 Ma and the intrusion of synkinematic granitoids until ~472 Ma. Back-arc extension is recorded at ~453 Ma. High exhumation rates constrained by 40Ar/39Ar and apatite U-Pb data suggest a second orogenic phase at ~250 Ma. Combined isotopic data show that the basement rocks of the studied regions are autochthonous to north-western Gondwana, and that arc magmatism sampled more juvenile sources during extension than during orogenesis. Low temperature thermochronology suggests that the Santander Massif started exhuming at ~40 Ma.

Составлен профиль МСЗ в Осетинском секторе Большого Кавказа. Получена информация о глубинном строении складчатого сооружения. По результатам геолого-геофизического изучения сделаны за- ключения о глубинном строении Большого Кавказа, The MSZ profile of the ossetic sector of the large Caucasus is composed. Information about the deep structure of plicated construction is obtained. The conclusions about the deep structure of the large Caucasus are made according to the results of geological-geophysical study, Геология и геофизика Юга России, Выпуск 4 2013

International audience; The geometric and kinematic evolution of the Andes provides insight onto the nature of the force balance beneath the South American plate. While the Andean load is opposed on its western edge by the force induced by subduction of the Nazca plate, its more elusive eastern counterpart, which we explore herein, requires some contribution from the mantle beneath the South Atlantic. Using a mantle flow model, we show that the Andes owe their existence to basal drag beneath South America caused by a cylindrical convection cell under the South Atlantic. We find that the observed Andean uplift requires both westward push fromactive upwelling beneath Africa andwestward drag toward the downgoing Nazca slab. These mutually-reinforcing downwellings and upwellings amount to 38% and 23% of the total driving force, respectively. Further decomposition reveals that the South Atlantic cell is most vigorous near its center, rendering the net drag force higher where the Andes also reach their highest elevation. Kinematic reconstructions suggest that the South Atlantic cell could have grown owing to the migration of the Nazca slab until ~50 Ma. We propose that from 50 Ma onwards, the cell may have ceased growing westward because (i) it had reached an optimal aspect ratio and (ii) the Nazca slab became anchored into the lower mantle. Continued westward motion of the plates, however, moved the surface expressions of spreading and convergence away from the upwelling and downwelling arms of this cell. Evidence for this scenario comes from the coeval tectonic, morphologic, and magmatic events in Africa and South America during the Tertiary.

International audience; Trench motion and upper plate deformation ultimately respond to mantle flow. Herein I build upon the mantle flow model results of Conrad and Behn (2010) and compute the drag forces underneath all plates, and show that they control the dynamics of plates and plate boundaries. The small misfit angle between between the traction azimuths of mantle traction and absolute plate motion corroborates the idea that convective mantle drag is a prominent driver of plate tectonics. Less intuitive is the fact that the interplay between the drag forces from the upper and lower plates, that amounts to 5 to 8.5 1012Nm 1 (per unit trench length), dictates both trench migration rates and upper plate deformation. At odds with the classic view that assigns the prime role to the idiosyncrasies of subduction zones (slab age, interplate friction, water content etc), I find that the intrinsic properties of subduction zones in fact only modulate this behavior. More specifically, the mean value of the integrated trenchward mantle drag force from the lower and upper plates (from 2 to 6.5 1012Nm 1) controls upper plate deformation. Conversely, it is the difference between the lower and upper plates mantle drag forces (from 3 to 10 1012Nm 1) that controls trench migration rates. In addition, I find that a minimum trenchward force of 2.5 1012Nm 1 must be supplied by mantle drag before trenches can actually advance, and before upper plates undergo compression. This force results from the default tendency of slabs to rollback when solely excited by their own buoyancy, and is thus the effective tensional force that slab pull exerts on the plate interface.

Analysis of 146 new apatite (U-Th)/He ages, six new apatite fission-track ages, and 165 previously published apatite fission-track (AFT) ages from the northern Apennine extending convergent orogen reveals a significant along-strike change in post-late Miocene wedge kinematics and exhumation history. East of ∼11°30′E, age patterns and age-elevation relationships are diagnostic of ongoing frontal accretion and slab retreat consistent with a northeastward-migrating "orogenic wave." Enhanced erosion rates of ∼1 mm/yr over a period of ∼3-5 Ma are recorded on the contractional pro-side of the orogen and ∼0.3 mm/yr on the extending retro-side. West of ∼11°30′E, ongoing exhumation has been restricted to the range core since at least ca. 8 Ma at rates of ∼0.4 mm/yr increasing to ∼1 mm/yr in the Pliocene (ca. 3 Ma) accompanied by post-Pliocene tilting and associated faulting. This pattern can be attributed to either continued convergence (but a switch in the transfer of material into the wedge to a regime dominated by underplating or out-of-sequence shortening), or a slowdown or cessation of frontal accretion and slab retreat with enhanced Pliocene uplift and erosion triggered by a deeper seated process such as lithospheric delamination, complete slab detachment, or slab tear. These findings emphasize that no single model of wedge kinematics is likely appropriate to explain long-term northern Apennine orogenesis and synconvergent extension, but rather that different lithospheric geodynamic processes have acted at different times in different lateral segments of the orogen.

The kinematics and architecture of orogenic systems may be heavily influenced by climate, but little research has focused on the long-term effects of glacial erosion on orogenesis. Low-temperature thermochronometry and subsidiary structural, earthquake relocation, and offshore seismic reflection data from the St. Elias orogen are the basis for a new architectural model and demonstrate an association between glacial denudation and orogenic evolution. These data show that exhumation and deformation within the St. Elias orogen are focused across a thin-skinned fold and thrust belt on the windward flank, whereas the leeward flank functions as a deformational backstop. A previously unrecognized structure beneath the Bagley ice field separates these domains with south-side-up motion. This structure is interpreted to be a backthrust, making the orogen doubly-vergent. Suggestive of accelerated fault motion in response to climate change, bedrock cooling rates within the hanging wall of the backthrust and across the entire subaerial wedge accelerated ~ten-fold coeval with the onset of intense glacial conditions. Within the orogenic wedge, the zone of highest Quaternary exhumation (5 km/myr (±25%)) is focused around a narrow zone where the glacial equilibrium line altitude (ELA) intersects mean topography. This zone of rapid exhumation, not present prior to the onset of intense glacial conditions, cuts across the structural trend of the orogen and is more narrowly focused than the zone of orographic precipitation. Augmented glacial erosion around glacial ELA also coincided with a regional shift in deformation away from prominent forethrusts including the North American-Yakutat terrane suture (Chugach St. Elias fault) and the seaward deformation front (Pamplona zone). Accelerated denudation across the subaerial wedge thus appears to have forced the redistribution of strain along the backthrust and a series of forethrusts that lie beneath the zone of highest glacial flux, which in turn are systematically truncated by the backthrust. In a cause and effect response, the expansion of glaciers therefore appears to have resulted in an orogen scale structural reorganization and a narrowing of the orogenic wedge to preserve topographic slope. The focusing of long-term erosion around glacial ELA and the structural response of the orogenic wedge to Cenozoic climate change have not previously been observed in a real-world orogenic system and imply a high degree of coupling between climate and tectonics in this glacially-dominated orogen. Ph. D.

The origin of high temperatures during regional low-pressure granulite facies metamorphism within the Proterozoic Broken Hill Block, Australia, has been reinterpreted to be the result of burial of anomalously hot rock packages for which the lithospheric geothermal gradient was initially elevated during early rifting ca. 1.71-1.67 Ga, and then maintained during a ca. 1.62 Ga short-lived mid-crustal extensional event. Mid-crustal extension at ca. 1.62 Ga was associated with amphibolite facies metamorphism and elevated lithospheric geothermal gradients, and occurred prior to activity along D2 high-temperature shear zones, peak low-pressure granulite facies metamorphism (ca. 1.60 Ga) and crustal shortening during the Olarian Orogeny (ca. 1.60-1.59 Ga). This reinterpretation places the Broken Hill Block within an environment in which multiple episodes of transient extension (ca. 1.71-1.62 Ga) were followed by a switch to shortening at ca. 1.60 Ga. The interpreted tectonic environment is a continental back-arc setting located in the over-riding plate of a subduction zone along the southern margin of Palaeoproterozoic Australia. Refereed/Peer-reviewed

[1] We develop a two-dimensional discrete element model to investigate the evolution of doubly vergent orogenic and accretionary wedges. This generates the localization of deformation across persistent structures as emergent phenomena unlike many continuum models that require predefined weaknesses to localize strain. The model is used to study how deformation processes evolve for two different boundary conditions, drawing strong comparisons with previous sandbox analogues and computational approaches. The deformational history of the modeled wedges is characterized by three stages defined by an evolution in the mechanisms available to accommodate shortening. The first stage develops a strong retrovergent thrust that initiates at the subduction point; the second stage shows a change in vergence of deformation as thin-skinned thrusting propagates into material carried on the subducting plate thus evolving a folded and thrusted prowedge; finally, a second shallower retrowedge develops in the overriding plate through accretion. This final stage is not present in all sand analogue modeling approaches, and defines a difference in the deformation style. Thresholds in geometry and size regulate the localization and style of deformation and hence the progression through the three stages. The wedges produced show periodicity in the modes of accretion to maintain a geometric form, with deformation localizing across structures that are internally reactivated. Thus prowedges and retrowedges are seen to oscillate about constant taper angles.

The Beyşehir-Hoyran-Hadim Nappes crop out over 700km, from east to west in the Pisidian and Central Taurus Mountains of southern Turkey. During this study, field obsevations of lithological, structural and sedimentological features are combined with igneous geochemical data derived from samples collected to help redefine a series of tectono-stratigraphic units and also determine the origin of the Beyşehir-Hoyran-Hadim Nappes. Above a regionally autochthonous Tauride carbonate platform, the Beyşehir-Hoyran Nappes begin with Ophiolitic Melange, consisting of blocks of neritic and pelagic limestone, basalt, serpentinite, radiolarian chert and, in places, amphibolite-grade metamorphic sole-type rocks, together set in a highly sheared siltstone and mudstone matrix. Locally, large slices of serpentinized harzburgite are incorporated in the melange. The peridotite sheets include lenses of chromitite and dunite and are cut by a series of dolerite dykes. The higher thrust sheets in the Hadim area begin with the Korualan Unit; a thrust sheet (ca. 400m thick) of mainly redeposited carbonates, quartzose sandstones and mudstones of Mid-Late Triassic age, interpreted as a proximal slope/base-of-slope succession. Regionally above is the Huğlu-type Unit; a thrust sheet (ca. 1 km thick) of Mid-Late Triassic intermediate-acidic extrusives, volcaniclastics and minor pelagic carbonates, interpreted as a continental rift. Post-rift subsidence in this thrust sheet is recorded by thin (

42 páginas Las placas litosféricas se mueven una contra otra, conociendo tres tipos de límites de placas que permiten este movimiento: divergentes, convergentes y de transformación. En limites divergentes las placas se separan mientras que en limites convergentes una placa desciende por debajo de la otra y en límites de transformación una placa se desplaza horizontalmente con respecto a la otra. Los limites divergentes se encuentran en los dorsales oceánicos, donde se forma una nueva corteza oceánica por la ascensión y el enfriamiento de magmas basálticos. Los limites convergentes son las márgenes continentales, donde una placa oceánica desciende por debajo de una placa continental Este mecanismo se llama subducción. El mismo destruye la corteza oceánica y crea nuevos magmas que dan lugar a rocas magmáticas de determinadas composiciones químicas. La ascensión y el enfriamiento del magma forman arcos magmáticos encima de la placa continental activa o delante de ella. En el primer caso se trata de márgenes continentales activas, en el segundo de arcos insulares. Las márgenes continentales, donde la corteza continental y oceánica están unidas, se denominan márgenes continentales pasivas. Los dorsales oceánicos y las márgenes continentales activas, siendo límites de placas divergentes y convergentes, respectivamente, constituyen zonas geotectónicas donde se forma la mayor cantidad de rocas magmáticas. Sin embargo, existen otras zonas geotectónicas dentro de las placas, donde se observa actividad magmática. Así tenemos las estructuras de graben, que son zonas de extensión intracontinental limitadas por fallas regionales profundas. Estas fallas Regan hasta el manto superior y ofrecen conductos para la ascensión de magmas. En el caso de una extensión continua, de los graben pueden desarrollarse nuevos océanos. También tenemos los focos calientes, que constituyen zonas donde ascienden magmas del manto y provocan una actividad magmática en la superficie. Focos calientes pueden ubicarse tanto en continentes como en océanos. Eventualmente, los focos calientes intracontientales pueden llegar a una zona de extensión intracontinental. El movimiento de las placas litosféricas está controlado por la formación de una nueva corteza oceánica en los dorsales oceánicos y la subducción y destrucción de la corteza oceánica en las márgenes continentales activas o arcos insulares. Mientras que la cuenca oceánica no está limitada por zonas de subducción, la cuenca oceánica está ensanchándose. Este ensanchamiento continúa hasta en las márgenes continentales pasivas, donde la litosfera está madura enfriada y específicamente pesada, comienza la subducción. A continuación, se describen las diferentes zonas geotectónicas con relevancia para la tectónica de placas La descripción se basa mayormente en Frisch & Loeschke (1986).

Artículo sobre el emplazamiento fallero en la zona de peridotitas de la Hispaniola (República Dominicana), estudiando si es la expresión orogénica de la polaridad reversa en la zona del Caribe en el cretácico medio. New structural data from central Hispaniola suggest that a mid-Cretaceous orogenicevent resulted in the obduction of peridotites onto the early Antillean arc. The MaimoŽn belt,which structurally underlies the peridotites, contains a shear zone composed of myloniticand phyllonitic schists formed by northward thrust emplacement of the peridotites. Penetrativedeformation decreases progressively to the northeast and is observed in the Neocomiansedimentary and volcanic rocks of the Los Ranchos Formation. The unconformablyoverlying, upper Albian Cenomanian limestones are not penetratively deformed, thusbracketing the obduction to Aptian-Albian time. This event is synchronous with chemicalchanges of the arc magmas in Hispaniola, Puerto Rico, and central Cuba. Thus, they mayboth be related to the postulated Greater Antillean polarity reversal.

SUMMARY Whereas the present-day true polar wander and the secular non-tidal acceleration of the Earth have usually been attributed to postglacial rebound, it has recently been suggested that non-glacially induced vertical tectonic movements taking place under non-isostatic conditions can also be effective in changing the Earth's rotation. We present a case study in which we analyse the effects of some simple uplift histories of the Himalayas and the Tibetan Plateau on the rotational axis and on the second-degree zonal harmonic of the geoid, for time-scales of up to a few million years. We first assume a permanent amount of overcompensation, which is consistent with observed geoid anomalies over the Himalayas, and then we model by means of the normal-mode techniques, the viscous relaxation in the mantle, with the elastic lithosphere supporting elastically 2 per cent of isostatic disequilibrium. In our normal-mode analysis, the Earth is divided into five layers: an effectively elastic lithosphere, a viscoelastic shallow upper mantle, transition zone and lower mantle characterized by the Maxwell rheology and an inviscid core. The readjustment of the equatorial bulge due to viscous flow in the mantle is taken into account in our studies by solving the linearized Liouville equations for the conservation of angular momentum, via the Love numbers formalism. Polar wander is sensitive to the rate of relaxation of the modes M1 and M2 due to the discontinuities between the three mantle layers, positioned at 420 and 670 kilometres depth. The rate of readjustment is sensitive to the viscosity of the transition zone whenever the lower mantle/shallow upper mantle viscosity ratio is small. The highest present-day velocity of polar wander due to Himalayan and Tibetan Plateau uplift is estimated to be 1° Myr−1 for an isoviscous mantle that has the same magnitude of the observed value, reduced to 0.1° Myr−1 for a factor 50 viscosity increase in the lower mantle. These numbers are about the same as those found from postglacial rebound that occurs on the short time-scale of a thousand years instead of the million years of our analysis, but represent upper bounds for mountain building, obtained only in the case in which a permanent deviation from isostasy of at least 2 per cent is assumed. In general, the proposed mechanism is less efficient in driving long-term rotation instabilities than deep-seated processes characterized by the same time-scale of a million years such as subduction; polar-wander velocity is extremely sensitive to the depth of the uncompensated anomalous root of the topography for the models in which full mantle relaxation is allowed.

157 p. Se presenta el estudio exploratorio de la edad mínima y la tectonización del Macizo de Abancay, aquí denominado Deflexión de Abancay, en la que la Cordillera de los Andes peruanos presenta una orientación Este-Oeste a lo largo de más de 200 km. Se puede reconocer la superposición de los ciclos orogénicos hercínicos y andinos. La llamada Deflexión de Abancay revela un cambio en la dirección orográfica y estructural. Se hace hincapié en que dicha orientación es muy diferente de la dirección general NO-SE de la zona de la cadena de Los Andes localizada entre el Codo de Santa Cruz en Bolivia y la Deflexión de Huancabamba, El estudio tiene tres partes. En la primera parte se analiza el substrato pre-andino, con el análisis de Edades y la evaluación de la tectónica. La mayor parte de las rocas metamórficas de la Cordillera de Vilcabamba provienen de la tectogénesis herciniana. El extremo Oeste de la Cordillera de Vilcabamba no ha sido explorado (se ha tenido inaccesibilidad a muchas zonas). La segunda parte expone la evolución Andina, en la cual se describe el conjunto de acontecimientos ocurridos entre el inicio del mesozoico y la época actual, la que permite la edificación de la Cordillera. Allí se conjuga que, tras un largo intervalo de sedimentación marina y continental, ocurre un período de plutonismo, volcanismo y sedimentación continental, alternado por fases tectónicas. La tercera parte trata sobre el magmatismo herciniano y andino, anotándose que el magmatismo andino tiene un volumen igual o ligeramente superior al del magmatismo herciniano. Hay nítida zonación de rocas plutónicas y se describen los tipos petrográficos. Finalmente se plantean dos hipótesis. La primera indica que los terrenos metamórficos son mesozoicos, tratándose en ese caso de una intrusión anterior al Malm. La segunda plantea que los terrenos metamórficos son pre-mesozoicos, ante lo cual se estaría en presencia de un complejo herciniano, tardiherciniano o pre-cambriano. Incluye bibliografía.

313 p. Se presenta el estudio de la cadena de los Andes Peruanos, el cual muestra un modelo de evolución global de la Cordillera de los Andes desde la óptica de la tectónica de placas. Este Sistema montañoso es el resultado de la superposición de las orogenias herciniana y andina, que el estudio analiza en las tres principales partes del mismo. Se presenta una introducción que describe sumariamente, a nivel del Perú, las principales características de los dominios, el Oceánico (Placa de Nazca) y el Continental (Placa Sudamericana), así como el límite constituido por la Fosa Perú-.Chile y la zona de subducción. La primera parte trata acerca de las características del substrato siálico de terrenos precámbricos metamorfizados en el curso del ciclo orogénico del precámbrico terminal y su influencia en la evolución andina. En la segunda parte estudia la Cadena Hercínica en el Perú, tratando de mostrar la evolución sedimentaria, tectónica y magmática del Herciniano en el Perú, luego de ubicarlo en el contexto general de la evolución de América del Sur durante el Paleozoico. La tercera parte analiza la Cadena Andina del Perú, que propone una nueva síntesis sobre los Andes Centrales del Perú (Perú - Bolivia), en base a los trabajos de Audebaud y Megard. Denominan Ciclo Andino a la serie de eventos que en los Andes de inicia en del Triásico al Santoniano, y que se caracteriza por sedimentación marina, continental o vulcano-sedimentaria, como primer periodo, y del Cretáceo Superior a la época actual, el segundo periodo. La cuarta parte presenta las reflexiones sobre la evolución de la Cadena de los Andes dentro del cuadro de la tectónica de placas, teniendo como punto central cuándo y cómo se produce la subducción de la placa oceánica pacífica bajo la placa continental sudamericana. Para ello se ha tenido que considerar la organización de las cadenas pre-Mesozoicas por acercamiento al Pacífico. Incluye bibliografía.