Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : International audience
We provide new constraints on the modes of mantle exhumation and denudation in the pre-orogenic Pyrenees by investigating the poorly known peridotites located east of the Lherz body, in eastern Ariè ge (Vicdessos, Urs, Bestiac, Caussou and Prades main peridotitic bodies). We show that: (1) numerous peridotite bodies, not described so far, are constituted by decametric to sub-metric outcrops scattered between and around the main outcrops identified by Monchoux (1970); (2) most of the peridotites form blocks and lenses of various sizes, from millimetric monocrystalline grains to hectometric olistoliths, embedded in debris flows involving mainly Mesozoic metasediments; these peridotites can therefore be linked to the S-type peridotites of Lagabrielle et al. (2010), and share similarities with the peridotites of Lherz region (Clerc et al., 2012). All originated from tectono-sedimentary processes associated with mantle exhumation in relation with extreme thinning and breakoff of the continental basement; (3) the various petrographic characters of these peridotites and their heterogeneity in serpentinisation degree imply a peculiar mode of exhumation, which merges mantle fragments inherited from different structural levels; (4) the lack of tectonic structures such as faults and shear planes associated with the ultramafic-rich breccia formation and the presence of neoformation of metamorphic minerals within the matrix preclude their origin as cataclasites related to the Latest Cretaceous and Tertiary Pyrenean contractional deformation. The peridotites of eastern Ariè ge are indisputable witnesses of the presence of an inverted hyper-extended Cretaceous passive margin forming the current North Pyrenean zone. The geometry of the extensional system was complex and probably associated with strike-slip faults and transcurrent motion. ß 2016 The Authors. Published by Elsevier Masson SAS on behalf of Acadé mie des sciences. This is an open access article under the CC BY-NC-ND license (http://creativecommons. org/licenses/by-nc-nd/4.0/).
ISSN: 1631-0713

Droits : http://creativecommons.org/licenses/by-nc-nd/
insu-01280502
https://hal-insu.archives-ouvertes.fr/insu-01280502
https://hal-insu.archives-ouvertes.fr/insu-01280502/document
https://hal-insu.archives-ouvertes.fr/insu-01280502/file/1-s2.0-S1631071316000043-main.pdf
DOI : 10.1016/j.crte.2015.12.003

Éditeur(s) : HAL CCSD
Résumé : International audience
Aegean extension is a process driven by slab rollback that, since 45 Ma, shows a twostage evolution. From Middle Eocene to Middle Miocene it is accommodated by localized deformation leading to i) the exhumation of high-pressure metamorphic rocks from mantle to crustal depths, ii) the exhumation of high-temperature rocks in core complexes and iii) the deposition of Paleogene sedimentary basins. Since Middle Miocene, extension is distributed over the whole Aegean domain giving a widespread development of onshore and offshore Neogene sedimentary basins. We reconstructed this two-stage evolution in 3D at Aegean scale by using available ages of metamorphic and sedimentary processes, geometry and kinematics of ductile deformation, paleomagnetic data and available tomographic models. The restorationmodel shows that the rate of trench retreat was around 0.6 cm/y during the first 30 My and then accelerated up to 3.2 cm/y during the last 15 My. The sharp transition observed in the mode of extension, localized versus distributed, which occurred in Middle Miocene correlates with the acceleration of trench retreat and is more likely a consequence of the Hellenic slab tearing documented by mantle tomography. The development of large dextral NE-SW strike-slip faults during the second stage of Aegean extension, since Middle Miocene, is illustrated by the 450 Km-long fault, recently put in evidence, offshore from Myrthes to Ikaria and onshore from Izmir to Balikeshir, in western Anatolia. Therefore, the interaction between the Hellenic trench retreat and the westward displacement of Anatolia started in Middle Miocene,almost 10 Ma before the propagation of the North Anatolian Fault in the North Aegean. This raises a fundamental issue concerning the dynamic relationship between slab tearing and Anatolia displacement
ISSN: 0438-9557

insu-01574659
https://hal-insu.archives-ouvertes.fr/insu-01574659
https://hal-insu.archives-ouvertes.fr/insu-01574659/document
https://hal-insu.archives-ouvertes.fr/insu-01574659/file/EFFECTS_OF_SLAB_ROLLBACK_ACCELERATION_ON_AEGEAN_EX.pdf
DOI : 10.12681/bgsg.11697

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Field study, thermochronology and geochemistry of the east Lungmu Co (LMC) range highlight some of the geological events that shaped western Tibet. The LMC fault zone has long been interpreted as the boundary between the Tianshuihai terrane of Laurasian affinity and the Qiangtang block of Gondwanian affinity. In the LMC range, the Paleozoic series is intruded by the Mangtsa leucogranite whose zircon have a U/Pb age of 116.9 ± 1 Ma and by mafic rocks with U/Pb zircon ages ranging from 116.9 ± 1 to 95.1 ± 1.7 Ma. Geochemistry of the mafic rocks indicates that they have been emplaced in a supra-subduction zone setting, probably the north dipping Nujiang suture zone. 40Ar/39Ar micas ages of the granite indicate that cooling below ~ 350 °C occurred between 105 and 85 Ma. 40Ar/39Ar K-feldspar data suggest a fast cooling event at 60-55 Ma, which we relate to the reactivation of the LMC suture zone as a thrust at the onset of the India-Eurasia collision. The last, and still active, deformation event corresponds to left-lateral strike-slip faulting along the ENE-WSW LMC fault.
ISSN: 1342-937X

hal-00660491
https://hal.archives-ouvertes.fr/hal-00660491
DOI : 10.1016/j.gr.2011.07.026

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : This study describes normal fault zones formed in foreland arkosic turbidites (the Grès d'Annot Formation, SW French Alps) under deep diagenesis conditions (~200 °C) and highlights the occurrence of two markedly different fault-rock types: (1) the foliated fault rocks of the Moutière-Restefond area; and (2) the dilatant fault rocks of the Estrop area. The deformation of (1) is dominated by intra- and transgranular fracturing, pressure solution of quartz and feldspar grains and syn-kinematic phyllosilicate precipitation resulting from feldspar alteration. The combination of these mechanisms results in a strongly anisotropic strain with intense shortening normal to the foliation (pressure solution) and extension parallel to the foliation (quartz- and calcite-sealed extension veins). This deformation implies local mass transfer that may be achieved without (or with limited) volume change. The deformation of (2) is expressed as dilatant quartz-sealed veins and breccia textures in which the main mechanisms are transgranular fracturing and quartz precipitation. Type (2) implies fault volume increase, isotropy of deformation and mass transfer at distances larger than in type (1). This study discusses the origins of (1) and (2) and shows that the permeability of (1) is anisotropic, with higher values than the host rocks parallel to the Y main deformation axis (i.e. perpendicular to the slip vector), whereas the permeability of (2) is isotropic and equivalent to that of the host rocks.
ISSN: 0954-4879

hal-01115177
https://hal.archives-ouvertes.fr/hal-01115177
DOI : 10.1111/ter.12100

Éditeur(s) : HAL CCSD Geological Society of America
Résumé : International audience
Fluid-rock interactions can control earthquake nucleation and the evolution of earthquake sequences. Experimental studies of fault frictional properties in the presence of fluid can provide unique insights into these interactions. We report the first results from experiments performed on cohesive silicate-bearing rocks (microgabbro) in the presence of pressurized pore fluids (H2O, drained conditions) at realistic seismic deformation conditions. The experimental data are compared with those recently obtained from carbonate-bearing rocks (Carrara marble). Contrary to theoretical arguments, and consistent with the interpretation of some field observations, we show that frictional melting of a microgabbro develops in the presence of water. In microgabbro, the initial weakening mechanism (flash melting of the asperities) is delayed in the presence of water; conversely, in calcite marble the weakening mechanism (brittle failure of the asperities) is favored. This opposite behavior highlights the importance of host-rock composition in controlling dynamic (frictional) weakening in the presence of water: cohesive carbonate-bearing rocks are more prone to slip in the presence of water, whereas the presence of water might delay or inhibit the rupture nucleation and propagation in cohesive silicate-bearing rocks.
ISSN: 0091-7613

hal-01054327
https://hal.archives-ouvertes.fr/hal-01054327
DOI : 10.1130/G34916.1

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Borborema Province of northeastern Brazil is divided into three main domains: northern, central, and southern. Several U-Pb zircon ages of plutons and orthogneisses became available in the recent years in the central and northern domains, but similar results are scarce in the southern domain. This study reports U-Pb dates for single zircon grains from one orthogneiss (Jupi orthogneiss) and two plutons (Cachoeirinha syenitic pluton and Cabanas granite) south of the East Pernambuco shear zone system (EPSZ). The results provide geochronological constraints on the timing of deformation and magmatism in this part of the southern domain and allow correlations with the central domain. The Jupi orthogneiss was emplaced and deformed during development of the regional flat-lying foliation. A Pb-206/U-238 weighted apparent mean age of 606 +/- 8 Ma is interpreted as the crystallization age of the protolith of the orthogneiss and consequently the age of high-grade Brasiliano metamorphism. The NNE-trending Cachoeirinha pluton is only locally affected by strike-slip deformation, whereas the ENE-trending Cabanas granite is intensely affected by deformation related to the EPSZ. The 587 8 Ma and 573 4 Ma ages of the Cachoeirinha pluton and Cabanas granite, respectively, bracket the main period of activity of the EPSZ. Tectonomagmatic activity in the study area is similar to the age of Brasiliano events in the central domain, north of the EPSZ. In addition, xenocrystic zircons in the Jupi orthogneiss and Cabanas granite are interpreted as inherited from Paleoproterozoic source rocks, suggesting the presence of widespread reworked old crust in the southern domain, similar to the central domain. These results support the idea that the central and southern domains belonged to the same crustal block before the onset of the Brasiliano orogeny.
ISSN: 0895-9811

hal-00411394
https://hal.archives-ouvertes.fr/hal-00411394
DOI : 10.1016/j.jsames.2007.06.003

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
Located east of Guadeloupe, the island of La Désirade exhibits the oldest rocks of the Lesser Antilles arc and the eastern Caribbean plate. An old magmatic basement is composed of (1) late Jurassic ophiolitic complex with meta-basaltic pillow lavas and interbedded radiolarites, (2) acid igneous complex comprising meta-quartz-diorite and meta-rhyolitic lavas flows, and (3) meta-diabasic/microdioritic dyke swarm complex. We present and discuss the discovery of synmetamorphic thrust tectonics in this island. Based on detailed structural analysis we evidenced two main compressive events. The first event (D1) is characterized by pervasive folding associated with thrust development. In the northeastern part of the island, a major thrust fault, the Grand Abaque Thrust, has been discovered which displaces for several kilometers the acid igneous complex onto the ophiolitic unit. The second deformation event (D2) is featured by a main pervasive cleavage S2 observed at the regional scale associated with upright folding (F2) and by the development of two sets of conjugated steeply dipping strike-slip shear zones, dextral 130°N and sinistral 20°N striking, respectively. Microstructural observations indicate that Greenschist facies metamorphism is clearly contemporaneous with the development of D1 and D2 superimposed tectonic structures. Ar/Ar geochronology was performed on two bulk of adularia minerals sampled in the northeast volcanic complex within a deformed zone related to a D2 event. These analyses yield well-defined and concordant plateau ages at 106.2 ± 1.7 Ma and 107.2 ± 1.8 Ma. Thus, shortening and thickening tectonics occurred during Lower Cretaceous (Albian). In the available framework of Caribbean geodynamics, the synmetamorphic thrust tectonics we discovered in the French Lesser Antilles is related to the collision between an Aptian-Albian oceanic plateau and the Andean-Cordilleran east-dipping subduction zone. Our results support subduction polarity reversal during Lower Cretaceous.
ISSN: 0278-7407

hal-00620555
https://hal.archives-ouvertes.fr/hal-00620555
DOI : 10.1029/2011TC002875

Éditeur(s) : HAL CCSD
Résumé : This work provides new constraints on the development and on the distribution of the deformation in the upper mantle and particularly beneath transform plate boundaries. USArray experiment and the remarkable increase of the dataset in California for the past ten years allowed us to scrutinize the lateral variations of the anisotropy in the vicinity of the San Andreas Fault zone. We have confirmed and increased the detection of two layers of anisotropy beneath this plate boundary. The first layer, located in the lithosphere, is related to the deformation induced at the fault, and the other one, located in the asthenosphere, is coherent with the anisotropy observed far from it, its origin is however less clear. We show that the deformation zone associated both to the San Andreas, Calaveras and Hayward Faults, is likely 40 km wide at 70 km depth. We then performed numerical thermomechanical modeling (ADELI) of the displacement of a transform plate boundary associated with the computation of the development of crystallographic fabrics using a viscoplastic selfconsistent approach (VPSC). We analyzed the distribution of the deformation in the model ant looked after the possible interactions at depth between deformation caused at surface by the strike-slip dynamic of the fault and the shearing at the base of the lithosphere caused by the horizontal displacement of the plates. Elastic properties derived from the crystallographic fabrics modeled, show that such interactions exist and induce, beneath the fault zone, a progressive rotation of the crystallographic fabrics with depth. Seismological signature of these smooth rotations is however not relevant with the presence of two anisotropic layers as proposed beneath California. We thus consider that a decoupling zone exists between the lithosphere and the asthenosphere beneath the California to account for the sharp separation between a lithospheric and an asthenospheric deformation. We furthermore estimate that anisotropy observed far form the San Andreas Fault in California cannot be explained only by the drag of the asthenosphere by the North America lithosphere as proposed in our article. Indeed, we can only expect few tenths of second of splitting delay from the anisotropic properties derived from the numerical modeling of a plate moving in the same direction and in the same velocity than the North American lithosphere only for 10 Ma of displacement. As delays observed in California rather reach 1.5 s, anisotropy in this region thus requires the existence of an active asthenospheric flow to be explained.
Le travail réalisé pendant cette thèse a permis d'apporter de nouvelles contraintes sur le développement et la distribution de la déformation dans le manteau supérieur et plus particulièrement au niveau des grandes limites de plaques décrochantes. Grâce à l'apport de l'expérience USArray et d'une dizaine d'années d'enregistrements sismologiques supplémentaires, nous avons pu étudier, de manière précise, les variations d'anisotropie dans le voisinage de la Faille de San Andreas. Nous avons confirmé et étendu l'observation de deux couches anisotropes sous cette limite de plaque. On y observe une première couche localisée dans la lithosphère marquant la déformation induite à la limite de plaque, et une autre, asthénosphérique, cohérente avec l'anisotropie observée loin de la faille et d'origine plus discutée. Nous avons montré que la zone de déformation associée aux failles de San Andreas, Calaveras et d'Hayward a, vraisemblablement, une largeur d'au moins 40 kilomètres en base de lithosphère, sous chacune de ces failles. Nous avons ensuite procédé à la modélisation thermomécanique (ADELI) de la migration d'une limite de plaques décrochante couplée à une modélisation du développement de fabriques cristallographiques par une approche viscoplastique auto-cohérente (VPSC). Ceci nous a permis d'y observer le développement de la déformation et les conséquences des possibles interactions entre la déformation décrochante en surface et le cisaillement en base de lithosphère dû au déplacement horizontal des plaques. Les propriétés élastiques déduites des fabriques cristallographiques modélisées montrent que de telles interactions existent et provoquent, sous la limite de plaques, une rotation des orientations cristallographiques avec la profondeur. Le signal associé à ces rotations progressives n'est toutefois pas cohérent avec la présence de deux couches d'anisotropie comme proposée sous la faille de San Andreas. Nous pensons par conséquent qu'il existe, sous la Californie, une zone de découplage entre la lithosphère et l'asthénosphère, permettant d'individualiser une déformation lithosphérique d'une déformation asthénosphérique. Nous estimons, en outre, que l'anisotropie observée dans l'asthénosphère sous la Californie ne peut être expliquée seulement par le cisaillement induit par le déplacement de la lithosphère Nord Amérique. En effet, les propriétés anisotropes obtenues par modélisation à partir d'une plaque se déplaçant dans une direction et une vitesse proche de celle de la plaque Amérique du Nord montrent qu'on ne peut espérer guère plus que quelques dixièmes de seconde de délai au bout de 10 Ma de déplacement. Les déphasages mesurés en Californie étant de l'ordre de 1,5 s, il est donc nécessaire d'invoquer la présence d'écoulements mantelliques actifs sous cette région.
https://tel.archives-ouvertes.fr/tel-00767124

tel-00767124
https://tel.archives-ouvertes.fr/tel-00767124
https://tel.archives-ouvertes.fr/tel-00767124/document
https://tel.archives-ouvertes.fr/tel-00767124/file/theseBonnin.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In northeastern Vietnam, the major tectonic episode responsible for nappes emplacement is Triassic. These allochtonous structures are intruded by granitic melts. Two post-tectonic massifs showing no sign of deformation have been dated by the LA-ICPMS zircon U-Pb techniques. Dating reveals a multiphase history with zircon cores showing evidence of Proterozoic magmatism. The emplacement of the Phia Bioc granite intrusive in allochtonous units is 248-245 Ma, an age which assesses a younger limit for the major nappes tectonic. This tectonic could be synchronous of the tectonometamorphic strike-slip faulting events (250-245 Ma) defined in the Truong Son Belt as the Indosinian orogen. The Phia Bioc intrusion is probably linked with the intra-plate magmatism of the Emeishan Large Igneous Province or with magma- tism associated with the Paleotethys closure. The age of the Phia Oac granite intrusion in displaced units is much younger, at 87.3 ± 1.2 Ma. This granite is probably linked to the magmatic activity produced dur- ing the Paleo-Pacific plate subduction under the SE Asia continental plate during the Mesozoic. Although the Cenozoic Red River fault system is close to these two plutons, this last thermotectonic episode has not been strong enough to disturb the U/Pb system. Zircons rims do not show any Tertiary magmatic or meta- morphic overprint.
ISSN: 0743-9547

hal-00681725
https://hal.archives-ouvertes.fr/hal-00681725
DOI : 10.1016/j.jseaes.2011.12.012

Éditeur(s) : HAL CCSD National Research Council Canada
Résumé : International audience
Back-arc extension in the Aegean, which was driven by slab rollback since 45 Ma, is described here for the first time in two stages. From Middle Eocene to Middle Miocene, deformation was localized leading to i) the exhumation of high-pressure metamorphic rocks to crustal depths, ii) the exhumation of high-temperature metamorphic rocks in core complexes and iii) the deposition of sedimentary basins. Since Middle Miocene, extension distributed over the whole Aegean domain controlled the deposition of onshore and offshore Neogene sedimentary basins. We reconstructed this two-stage evolution in 3D and four steps at Aegean scale by using available ages of metamorphic and sedimentary processes, geometry and kinematics of ductile deformation, paleomagnetic data and available tomographic models. The restoration model shows that the rate of trench retreat was around 0.6 cm/y during the first 30 My and then accelerated up to 3.2 cm/y during the last 15 My. The sharp transition observed in the mode of extension, localized versus distributed, in Middle Miocene correlates with the acceleration of trench retreat and is likely a consequence of the Hellenic slab tearing documented by mantle tomography. The development of large dextral NE-SW strike-slip faults, since Middle Miocene, is illustrated by the 450 Km-long fault zone, offshore from Myrthes to Ikaria and onshore from Izmir to Balikeshir, in western Anatolia. Therefore, the interaction between the Hellenic trench retreat and the westward displacement of Anatolia started in Middle Miocene, almost 10 Ma before the propagation of the North Anatolian Fault in the North Aegean.
ISSN: 0008-4077

insu-01271296
https://hal-insu.archives-ouvertes.fr/insu-01271296
https://hal-insu.archives-ouvertes.fr/insu-01271296/document
https://hal-insu.archives-ouvertes.fr/insu-01271296/file/Brun%20etal%20CJES%202016.pdf
DOI : 10.1139/cjes-2015-0203

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In this contribution we present a reconstruction of the overall lithotectonic architecture, from inner zones to external ones, of the Paleoproterozoic Trans North China Orogen, within the North China Craton. Moreover, forward thermobarometrical modeling on a kyanite-bearing gneiss yields a reliable prograde P-T-t-D path. In addition, 40Ar/39Ar dating on rocks from distinct litho-tectonic units helps us to distinguish several tectono-metamorphic events during the orogenic development. Considering these results, we propose a geodynamic model involving three cratonic blocks, namely the Western, Fuping and Eastern Blocks, separated by two oceans, the Lüliang and Taihang Oceans. The opening of oceanic basins occurred around 2.2-2.3 Ga. After the westward subductions of oceanic lithosphere, the Trans-North-China Orogen was built up through a polyphase tectonic evolution within the period 1900-1800 Ma. The first event (D1) corresponded to the emplacement of lower and upper nappes herein called the Orthogneiss-and-Volcanites Unit (OVU) and the Low-Grade-and-Mafic Unit (LGMU), respectively. The syn-metamorphic D1 deformation (1880 ± 10 Ma) is characterized by a NW-SE stretching and mineral lineation with a top-to-the SE sense of shear. During ongoing compression of the thickening orogenic crust, a second deformation event D2 (1850 ± 10 Ma) was responsible for (1) syn-anatectic lateral flow and exhumation of the orogenic root and (2) folding of the middle and upper parts of the orogenic wedge that consequently acquired a fan-type geometry. The late D3 (1830 ± 10 Ma) and D4 (1810 ± 10 Ma) events are related to late-orogenic normal and strike-slip shearing, respectively. In our present state of knowledge, the Paleoproterozoic Trans-North China Orogen might be regarded as the assemblage of two continent-continent collisional belts, both of which are characterized by nappe stacking accommodated by top-to-the E/SE ductile shearing. Continental subduction, crustal thickening, partial melting of overthickened crust, exhumation of HP rocks and deposition of syn-orogenic detrital basins are typical features of modern collisional-type orogens.
ISSN: 0301-9268

Droits : info:eu-repo/semantics/OpenAccess
insu-00628119
https://hal-insu.archives-ouvertes.fr/insu-00628119
https://hal-insu.archives-ouvertes.fr/insu-00628119/document
https://hal-insu.archives-ouvertes.fr/insu-00628119/file/Trap-PrecambrianResearch-2011.pdf
DOI : 10.1016/j.precamres.2011.09.008

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Peridotite xenoliths with a broad range of textures provides evidence for consistent microstructural evolution in a vertical transect of the shallow lithospheric mantle (35?55 km depth) beneath the Persani Mountains, SE Carpathians, Romania, due to ongoing plate convergence in the Carpathian Arc nearby. The recrystallized grain size, crystal preferred orientations strength, and resulting seismic anisotropy vary continuously and display a strong correlation to equilibrium temperatures, suggesting a continuous change in deformation conditions with depth. The shallowmost xenoliths have microstructures typical of high stress deformation, marked by strong recrystallization to fine grain sizes, which results in weak crystal preferred orientations and anisotropy. The deepest xenoliths have coarse-grained porphyroclastic microstructures and strong crystal preferred orientations. Replacive orthopyroxene structures, consuming olivine, and high H2O concentrations in the pyroxenes are observed in some xenoliths indicating limited percolation of fluids or volatile-rich melts. Despite the high stress deformation and high H2O contents in some of the studied xenoliths, analysis of olivine crystallographic orientations indicates that [100] slip systems, rather than ?wet? [001] accommodate most of the deformation in all samples. Seismic anisotropy estimated from the measured olivine and pyroxene crystal preferred orientations suggests that the strike-parallel fast SKS polarization directions and ~ 1 s delay times measured in the SE Carpathians are likely the consequence of convergence-driven belt-parallel flow in the lithospheric mantle.
ISSN: 0012-821X

hal-00317303
https://hal.archives-ouvertes.fr/hal-00317303
DOI : 10.1016/J.EPSL.2008.04.035

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
Sandbox experiments, using a two-dimensional and a three-dimensional approach, are used to study the deformation of margins in response to seamount subduction. Successive mechanisms of deformation are activated during the subduction of conical seamounts. First, reactivation of the frontal thrusts and compaction of the accretionary wedge is observed. Then, back thrusting and, conjugate strike-slip faulting develops above the leading slope of the subducted seamount. The basal d6collement is deflected upward in the wake of the subducting high, and a large shadow zone develops behind the seamount trailing slope. Consequently, frontal accretion is inhibited and part of the frontal margin is dragged into the subduction zone. When the main d6collement returns to its basal level in the wake of the seamount, the margin records a rapid subsidence and a new accretionary wedge develops, closing the margin reentrant. The sediments underthrusted in the wake of the seamount into the shadow zone, are underplated beneath the rear part of the accretionary wedge. Substantial shortening and thickening of the deformable seaward termination of the upper plate basement, associated with basal erosion is observed. Seamount subduction induces significant material transfer within the accretionary wedge, favors large tectonic erosion of the frontal margin and thickening of the rear part of the margin. The subduction and underplating of relatively undeformed, water-ladden sediments, associated with fluid expulsion along the fractures affecting the margin could modify the fluid pressure along the basal ddcollement. Consequently, significant variations of the effective basal friction and local mechanical coupling between the two plates could be expected around the subducting seamount.
ISSN: 0278-7407

hal-01261523
https://hal.archives-ouvertes.fr/hal-01261523
https://hal.archives-ouvertes.fr/hal-01261523/document
https://hal.archives-ouvertes.fr/hal-01261523/file/Dominguez2000-Tectonics.pdf
DOI : 10.1029/1999TC900055

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Parentis and Arzacq-Mauleon basins located in front of the V-shaped oceanic propagator in the Bay of Biscay present evidence for extreme crustal thinning. In this paper we investigate the 3D structure of these rift basins, based on field observations and the interpretation of seismic data. We compare these results with those obtained from two different and independent inversion methods: first a 3D gravity inversion and second the standard Euler deconvolution.;For the Mauleon Basin our results show that the positive gravimetric anomaly identified above its southern margin is the consequence of two shallower high density bodies that are separated by the Pamplona fault and a deeper high density body. The high density bodies can be explained by the presence of mid-crustal and mantle rocks that were exhumed or uplifted at shallower depth during Early Cretaceous rifting before they were reworked and integrated to the Pyrenean chain during compression phase. Also, during this reactivation phase, some slices of the exhumed mid-crustal and mantle rocks were sheared off and were integrated in the present-day thrust belt in the Mauleon basin. For the Parentis Basin we can demonstrate, based on seismic data and gravimetric inversion methods, a decrease in extension from west to east, which is compatible with the V-shape geometry of the overall basin. Along strike, a change in the fault geometry from downward concave top-basement detachment faults to upward concave high-angle faults can be observed eastwards, i.e. towards the termination of the basin. A key structure, controlling the evolution of the Parentis Basin, is the east-west trending Ibis fault. We interpret this fault to have initially formed as a strike slip fault before it was reactivated during later crustal thinning. At present, it forms the limit between an upper plate sag basin to the north and a lower plate sag basin, floored at least locally by a top-basement detachment faults to the south. The strong asymmetry of the basin is supported by the shape of the basin and the results of standard Euler deconvolution.
ISSN: 0040-1951

hal-00523444
https://hal.archives-ouvertes.fr/hal-00523444
DOI : 10.1016/j.tecto.2010.04.023

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Properly assessing the extent and magnitude of fault ruptures associated with large earthquakes is critical for understanding fault behavior and associated hazard. Submarine faults can trigger tsunamis, whose characteristics are defined by the geometry of seafloor displacement, studied primarily through indirect observations (e.g., seismic event parameters, seismic profiles, shipboard bathymetry, coring) rather than direct ones. Using deep-sea vehicles, we identify for the first time a marker of coseismic slip on a submarine fault plane along the Roseau Fault (Lesser Antilles), and measure its vertical displacement of ∼0.9 m in situ. We also map recent fissuring and faulting of sediments on the hangingwall, along ∼3 km of rupture in close proximity to the fault's base, and document the reactivation of erosion and sedimentation within and downslope of the scarp. These deformation structures were caused by the 2004 M w 6.3 Les Saintes earthquake, which triggered a subsequent tsunami. Their characterization informs estimates of earthquake recurrence on this fault and provides new constraints on the geometry of fault rupture, which is both shorter and displays locally larger coseismic displacements than available model predictions that lack field constraints. This methodology of detailed field observations coupled with near-bottom geophysical surveying can be readily applied to numerous submarine fault systems, and should prove useful in evaluating seismic and tsunamigenic hazard in all geodynamic contexts.
ISSN: 0012-821X

insu-01557932
https://hal-insu.archives-ouvertes.fr/insu-01557932
https://hal-insu.archives-ouvertes.fr/insu-01557932/document
https://hal-insu.archives-ouvertes.fr/insu-01557932/file/EPSL-2006-escartin.pdf
DOI : 10.1016/j.epsl.2016.06.024

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The South East Sayan area,Wof the Lake Baikal is subjected to a very complex tectonic setting where the extensional stress field of the Baikal Rift System meets the compressional stress field generated by the India­Asia collision further south. Using satellite images, aerial photographs, SRTM DEM, field mapping of geomorphological structures, and published neotectonics and geological data we show that most of the relief in the SE Sayan initiated during Late Pliocene­Pleistocene through compressive reactivation of inherited structures. By Late Quaternary, clockwise rotation of the compressive field generated strike­slip faulting and local, secondary extension still within a general compressional stress field. We demonstrate that the formation of the small-scale extensional basins within the East Sayan range is not linked to general the extension in the Baikal Rift System nor to a possible asthenospheric plume acting at the base of the crust but rather to the rotation of small rigid tectonic blocks driven by the compression.
ISSN: 0743-9547

insu-00605062
https://hal-insu.archives-ouvertes.fr/insu-00605062
DOI : 10.1016/j.jseaes.2010.10.011

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Dahomey belt in Togo and Benin is an important segment of the larger West Gondwana Orogen. Here, we review the geodynamic evolution of the Dahomey belt and discuss new U–Pb and Lu–Hf zircon data in light of similar data previously acquired on the geologically related Northern Borborema Province, in NE Brazil. Eighteen samples from different tectonic settings and regions within the belt were collected for zircon isotopic investigation. Passive margin deposits of the Atacora Structural Unit and lower units of the Volta Basin have detrital zircon signatures compatible with the flanking West Africa Craton. The arc-related magmatism resulted from the east-dipping subduction of the Goiás-Pharusian oceanic lithosphere and is represented by a variety of granitoids emplaced in the Benino-Nigerian Shield between 670 and 610 Ma. These granitoids were mainly sourced from crustal reservoirs with subordinate juvenile input. Detrital zircon ages from syn-orogenic deposits in Benino-Nigerian Shield suggest that arc development could have started as early as 780 Ma. The main period of melting in the internal part of the belt, the Benino-Nigerian Shield, is related to crustal thickening and occurs only ca. 30 m.y. after initiation of the continental collision, marked by the ca. 610 Ma ultra-high pressure (UHP) metamorphism recorded at Lato Hills. Foreland development represented by the upper units of the Volta basin developed soon after continental collision and persisted with the development of the west-verging thrust front synchronously with the main period of crustal melting due to collision at ca. 580 Ma. The subvertical Transbrasiliano Lineament in South America, that corresponds to the Kandi Lineament in Africa, provides a present-day fit between NW Africa and NE Brazil. Restoration of the movement of the Transbrasiliano-Kandi Lineament (strike-slip plate boundary) places the Dahomey belt and Borborema Province (NE Brazil) along the same section of the West Gondwana Orogen. This configuration would explain some of the misfits previously discussed in the literature and aligns the UHP eclogites in Togo and NE Brazil.
ISSN: 0301-9268

hal-01358584
https://hal.archives-ouvertes.fr/hal-01358584
DOI : 10.1016/j.precamres.2016.01.032

Éditeur(s) : Gauthier-villars
Résumé : The area located west of the Fiji Islands was previously interpreted as a strike-slip deformation zone. Based on comparison with the Galapagos propagating rift in the East Pacific the area is reinterpreted in terms of a propagating accretion zone.
Le domaine de morphologie particulière situé à l'ouest des îles Fidji a été interprété comme une zone de déformation décrochante. Il est, par comparaison avec la zone de propagation des Galapagos sur la dorsale Est Pacifique réinterprété comme une zone d'accrétion en propagation
Comptes Rendus de l'Academie des Sciences Serie II (1251-8069) (Gauthier-villars), 1993-09 , Vol. 317 , N. 5 , P. 671-678

Droits : Académie des Sciences
http://archimer.ifremer.fr/doc/00183/29473/27836.pdf
http://archimer.ifremer.fr/doc/00183/29473/

Éditeur(s) : HAL CCSD
Résumé : International audience
Hundreds of Paleoproterozoic gold occurrences are known in the Tapajós Gold Province, northern Brazil. However, few deposits have been analysed in detail to understand the genesis of these systems. In this study, we present data concerning the largest deposit presently known in this Province, the Tocantinzinho deposit. A strike-slip fault system controls the emplacement of the mineralized rocks and the development of the brittle fracturing that host the main gold mineralization. Hydrothermal activity played an important role in the mineralization processes.
Mineral Resources in a Sustainable World
Nancy, France

hal-01356009
https://hal.archives-ouvertes.fr/hal-01356009

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Paleostress orientations were calculated from fault populations at 24 sites along the SW-NE segment and five sites along the E-W. Yasin segment of the Karakoram-Kohistan Suture Zone in NW Pakistan They demonstrate the importance of combined thrusting and strike-slip faulting. However, several paleostress tensor directions are distinguished, a dominant NW-SE compression and a minor E-W compression are compatible with the recent evolution of this part of the Hindu Kush. From the lack of both systematic overprinting-relationships and spatial trend (the two tensors were obtained at different locations) we conclude that in each location any of these two shortening directions can dominate Heterogeneously distributed extension is found in some places and is likely due to local conditions These paleostress tensors substantiate a transpressional regime due to far-field Himalayan compression and document the long-term background of the seismogenic deformation in this region.
ISSN: 0743-9547

hal-00496459
https://hal.archives-ouvertes.fr/hal-00496459
DOI : 10.1016/j.jseaes.2010.01.004