Éditeur(s) : HAL CCSD Elsevier
Résumé : In this paper, we present optically and infrared stimulated luminescence (OSL and IRSL) ages for four samples from alluvial fan surfaces in the Astaneh Valley. This valley is located in the north-east part of the Alborz range in Iran. Our morphologic interpretations recognize at least three generations of fans in the study area, all of which have been displaced along the left-lateral strike-slip Astaneh fault. Because of the dry, loose, and sometimes complex juxtaposition of the target sediments, we collected the samples in total darkness beneath dark plastic layers placed atop the pit openings. Luminescence ages of the fans are similar to 55 ka, similar to 32 ka and similar to 16 ka. These ages are concurrent with periods of loess deposition and wet climatic conditions previously recorded in the Arabia-Iranian region. They allow estimation of a horizontal slip rate of similar to 2 mm/yr along the Astaneh fault, which is consistent with additional slip rates determined for the Holocene period along faults further west of the Astaneh fault.
ISSN: 1871-1014

hal-00617777
https://hal.archives-ouvertes.fr/hal-00617777
DOI : 10.1016/j.quageo.2011.03.001

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In the Gulf of Cadiz key segment of the Africa-Iberia plate boundary (North-East Atlantic ocean), three main different modes of tectonic interference between a recently identified wrench system (SWIM) and the Gulf of Cadiz Accretionary Wedge (GCAW) were tested through analog sand-box modeling: a) An active accretionary wedge on top of a pre-existent inactive basement fault; b) An active strike-slip fault cutting a previously formed, inactive, accretionary wedge; and c) Simultaneous activity of both the accretionary wedge and the strike-slip fault. The results we obtained and the comparison with the natural deformation pattern favor a tectonic evolution comprising two main steps: i) the formation of the Gulf of Cadiz Accretionary Wedge on top of inactive, Tethyan-related, basement faults (Middle Miocene to ~ 1.8 Ma); ii) subsequent reactivation of these basement faults with dextral strike-slip motion (~ 1.8 Ma to present) simultaneously with continued tectonic accretion in the GCAW. These results exclude the possibility of ongoing active SWIM wrench system cross-cutting an inactive GCAW structure. Our results also support a new interpretation of the SWIM wrench system as fundamentally resulting from strike-slip reactivation of an old (Tethyan-related) plate boundary.
ISSN: 0025-3227

insu-00643630
https://hal-insu.archives-ouvertes.fr/insu-00643630
https://hal-insu.archives-ouvertes.fr/insu-00643630/document
https://hal-insu.archives-ouvertes.fr/insu-00643630/file/Duarte_etal_2011_MS-1.pdf
DOI : 10.1016/j.margeo.2011.09.014

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Northwest Iran is characterized by a high level of historical and instrumental seismicity related to the ongoing convergence between the Arabian and Eurasian plates. In this region, the main right-lateral strike-slip fault known as the North Tabriz fault (NTF) forms the central portion of a large crustal fault system called the Tabriz fault system (TFS). The NTF is a major seismic source along which at least three strong and destructive earthquakes have occurred since 858 AD. The two most recent destructive seismic events occurred in 1721 AD and 1780 AD, rupturing the SE and NW fault segments, respectively. This paper reports paleoseismological and quantitative geomorphologic investigations on the SE segment of the NTF, between the cities of Bostanabad and Tabriz. These observations help to improve our understanding of the seismic hazard for Tabriz city and its surrounding areas. Our field investigations revealed evidence of successive faulting events since the Late Quaternary. Paleoseismic investigations indicate that since 33.5 kyr, the SE segment of the NTF has experienced at least three major (M>7.5) seismic events, including the 1721 AD earthquake (M=7.6–7.7). Along the NW segment of the fault, however, our results suggest that the amount of strong (M~7.5) seismic events during the same period is significantly greater than along the SE segment. One possible explanation of such a difference in seismic activity is that the Late Quaternary-Holocene coseismic slip rate is decreasing along the NTF from the northwest to the southeast. This explanation contradicts the former hypothesis of a constant slip rate along the whole length of the NTF. In addition, more distributed deformation along several parallel fault branches, in a wider fault zone of the SE segment of the NTF may be considered as additional evidence for the estimation of lower rate of deformation along the fault segment. Such a slip distribution pattern can explain the existence of smaller (~300 m) Pliocene-Quaternary cumulative dextral offsets along the SE fault segment than the measured cumulative offsets along the NW segment (~800 m) of the NTF.
ISSN: 0040-1951

hal-01089420
http://hal.upmc.fr/hal-01089420
http://hal.upmc.fr/hal-01089420/document
http://hal.upmc.fr/hal-01089420/file/Solaymani%20Azad%20et%20al.%2C%202014%20%28accepted%29.pdf
DOI : 10.1016/j.tecto.2014.11.010

Éditeur(s) : HAL CCSD Oxford University Press (OUP): Policy P - Oxford Open Option A Oxford University Press (OUP)
Résumé : International audience
While the kinematics of Anatolia plate and the North Anatolian Fault System (NAFS) has been studied extensively, the slip rate and locking depth along the NAFS are usually assumed constant in the analyses due to the lack of sufficient data. This is also partly due to the reasonably good fit of Euler small circle and partly due to the lack of spatial resolution of observations to determine slip rates independently from locking depths. On the other hand, recent geodetic studies show a contrast for locking depth between Marmara and other parts of the NAFS, implying a non-uniform locking depth across the NAFS. In this study, we analyse new GPS data and homogenously combine available data sets covering the eastern part of the NAFS to form the most complete data set. In particular, we incorporate the first results of Turkish Real-Time Kinematic GPS Network (CORS-TR) into our data set. A detailed analysis of three profiles within the NAFS reveals an increase of locking depth in the middle profile to 19.1 ± 3.4 km from 11.9 ± 3.5 km in the easternmost profile while the slip rate is nearly constant (20–22 mm yr−1), which implies a variation of strain rate of ∼100 nanostrain yr−1. Assuming a constant locking depth throughout whole NAFS gives an average locking depth of 14.3 ± 1.7 km. Our best estimates of slip rates in block modelling which takes the variation of locking depths into account are in the range between 22.5 and 22.8 mm yr−1 over eastern part of the NAFS.
ISSN: 0956-540X

hal-01218392
https://hal.archives-ouvertes.fr/hal-01218392
DOI : 10.1093/gji/ggv274

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 Oxford University Press (OUP)
Résumé : Geophysical Journal International, v. 173, n. 2, p. 473-482, 2008. http://dx.doi.org/10.1111/j.1365-246X.2008.03718.x
International audience
The western Provence in southern France is an intraplate low deforming region, cut by large sinistral strike-slip faults as the Nîmes Fault. The deformation rate of this fault was estimated at 0.1 mm yr−1 from geological and morphological observations. Nevertheless, some large earthquakes occurred in this area in historical times inducing well-documented partial destructions on the roman monument 'Pont-du-Gard'. In order to investigate if this area is seismically active, we installed a temporary seismological network of 14 stations between the cities of Nîmes and Avignon for a 1-yr period (2002 July–2003 June). We recorded and located a total amount of 80 earthquakes of magnitude Ml smaller than 2.8, and of 153 quarry blasts. The seismic event locations are interpreted in terms of regional tectonics as well as of geometry at depth of the Nîmes Fault and of possible seismic activity of the Roquemaure Fault. At the beginning of 2002 September, a catastrophic storm occurred in the same area with cumulated precipitations at 600 mm in 28 hr, causing casualties and major inundations and damages. We identified a clear and sudden increase of the seismic activity as an immediate consequence of this exceptional meteorological phenomenon. We interpret this rainfall triggering of earthquakes as the response of the crust to an abrupt vertical loading. The geological context of this zone is characterized by the presence of sedimentary basins and of an important karstic network in a calcareous environment allowing the retention of a third of the total rainwater volume during few weeks after the catastrophic storm. Month by month inversion of the seismic wave velocities for only the first 1-km thick layer of the crust allows investigating the influence of the stored water. A clear decrease of both P- and S-velocities, and an increase of the Vp/Vs ratio are evidenced. The variations obtained are at 2, 6 and 4.5 per cent for P-, S-velocities and Vp/Vs ratio, respectively. These variations are discussed in confront of previous studies and can be directly related to the known water volume.
ISSN: 0956-540X

hal-00407884
https://hal.archives-ouvertes.fr/hal-00407884
https://hal.archives-ouvertes.fr/hal-00407884v2/document
https://hal.archives-ouvertes.fr/hal-00407884/file/rigoGJI2008.pdf
DOI : 10.1111/j.1365-246X.2008.03718.x

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : We use InSAR to measure deformation and kinematics of the Mw = 4.9 Borujerd (2005/05/03) and Mw = 6.1 Chalan-Chulan (2006/03/31) earthquakes that occurred in the Zagros fold-and-thrust belt. The focal mechanism of the 2006 event is consistent with right lateral strike-slip motion and the event ruptured the Dorud-Borujerd segment of the Main Recent Fault. An Envisat interferogram spanning the 2006 event shows peak ground deformation of 9 cm in the satellite line-of-sight along a 10 km long fault portion. The interferogram spanning the 2005 earthquake is rather related to atmospheric artefact than to ground deformation. Dislocation models of the 2006 Chalan-Chulan event indicate dextral slip amounting to a maximum of 90 cm at a depth of 4 km. The predicted vertical displacements are in good agreement with differential levelling data. The 2006 event filled only a small part of the seismic gap located between large M = 7 events that occurred in 1909 and 1957.
ISSN: 0954-4879

hal-00411313
https://hal.archives-ouvertes.fr/hal-00411313
DOI : 10.1111/j.1365-3121.2008.00797.x

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 American Geophysical Union
Résumé : International audience
The Yakutat-St. Elias collision in SE Alaska and adjacent Canada represents a prime example of present-day tectonics associated with an indentor corner. Its eastern syntaxis is marked by high exhumation, a sharp structural bend, and strain concentration at the transition from shortening to oblique transpression. Here we present GPS velocity and strain rate fields that cover the syntaxis, including 11 new stations in the core of the St. Elias Mountains. These data are corrected for transient deformation (glacial isostatic adjustment and postseismic and interseismic loading) to produce residual velocities and strain rates representative of long-term tectonics. The main features of these velocity and strain rate fields are a peak in strain rates (strain knot) in the syntaxis at the junction between the main fault systems and a rapid rotation from convergence-parallel to convergence-normal orientations of the velocities and shortening axes around the syntaxis, leading to shortening across the southern Denali Fault. These features are consistent with the strain and tectonic patterns expected near an indentor corner at the transition from shortening to transpression, with a combination of diffuse and localized deformation. The GPS velocities and strain rates show diffuse deformation around the syntaxis, from pure convergence-parallel shortening in the orogenic wedge to oblique extension that accommodates the strain rotation at the front of the syntaxis. This indentor-corner model also results in a near-zero strike-slip rate on the southern Denali Fault and shows no clear evidence for a throughgoing fault hypothesized to link the Fairweather and Totschunda Faults.
ISSN: 0148-0227

hal-01243510
https://hal.archives-ouvertes.fr/hal-01243510
DOI : 10.1002/2014JB011842

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

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Baikal Rift System in southern Siberia is one of the main intracontinental extensional features on Earth. The rift system represents the northwestern boundary of the Amuria plate and in that respect can be considered as an evolving plate boundary. The Baikal Rift System has been widely studied both in terms of geology and geophysics and many models have been proposed for its formation and evolution. However, the age of the initiation of deformation and the mechanism driving this deformation are still largely debated. While major extension has occurred since the Late Miocene-Pliocene, the onset of extension seems older than the India-Asia collision, implying that several driving mechanisms may have acted together or in relay through time. In this work, we review the available data and models for deformation in an area encompassing the Baikal Rift System, the Sayan ranges to the west and the Transbaikal to the east. Using a synthesis of this data and our own field and mapping observations, we show that the Baikal Rift System, along with transpressional deformation in the Sayan ranges and transtension in the Transbaikal area, can be explained through major left-lateral strike-slip systems. The deformation is strongly controlled by inherited crustal and lithospheric structures, and is distributed over a wide area within the western Amuria plate that consequently cannot be considered as a rigid block. Such distributed deformation is likely to have a strong effect on the structure of the future continental margin if extension evolves towards the formation of oceanic crust.
ISSN: 1342-937X

hal-00903612
https://hal.archives-ouvertes.fr/hal-00903612
DOI : 10.1016/j.gr.2012.07.017

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 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 American Geophysical Union
Résumé : International audience
We investigate upper mantle anisotropy beneath the Pyrenean range along three N-S profiles across the mountain belt. The results of a first profile that operated in 1993 in the central part of the belt have been presented elsewhere. We present the results of two other profiles that ran in 1995-1996 and 1996-1997 in the eastern and western part of the belt, respectively and propose an interpretation of the whole results. Teleseismic shear waves (SKS, SKKS, and PKS) are used to determine splitting parameters: the fast polarization direction φ and the delay time δt. Teleseismic shear wave splitting in the eastern Pyrenees displays homogeneous φ values trending N100°E and δt values in the range 1.1 to 1.5 s. A station located in the southern Massif Central, 100 km north of the range, is characterized by different splitting parameters (φ = N70°E, δt = 0.7 s). In the western part of the belt, anisotropy parameters are similar across the whole belt (φ = N110°E and δt = 1.3 to 1.5 s). Most of the measured delay times, including those obtained in the central part of the range, are above the global average of the SKS splitting (around 1 s). At the belt scale, φ is generally poorly correlated with recent estimations of the absolute plate motion, which predicts a fast direction ranging between N50°E and N80°E. Instead, the orientation of φ (N100°E) is parallel to the trend of the Pyrenean belt but also to Hercynian preexisting structures. This parallelism supports an anisotropy primarily related to frozen or active lithospheric structures. We show that a signature related to the Pyrenean orogeny is likely for the stations located in the internal domains of the belt. By contrast, the anisotropy measured at the stations located on the external parts of the belt could reflect a pre-Pyrenean (Hercynian) deformation. We suggest that a late Hercynian strike-slip deformation is responsible for this frozen upper mantle anisotropy and that the Pyrenean tectonic fabric developped parallel to this preexisting fabric. Finally, no particularly strong splitting is related to the North Pyrenean Fault, commonly believed to represent the plate boundary between Iberia and Eurasia.
ISSN: 2169-9313

hal-01388841
http://hal.univ-reunion.fr/hal-01388841
http://hal.univ-reunion.fr/hal-01388841/document
http://hal.univ-reunion.fr/hal-01388841/file/Barruol_Aniso_Pyr_JGR1998.pdf
DOI : 10.1029/98JB02790

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
Physical modeling of oblique subduction is performed to study the mechanism of strain partitioning. The model is two-layer and includes the elasto-plastic lithosphere (the overriding and subducting plates) and the low-viscosity liquid asthenosphere. The subduction is driven by a push force from a piston and a pull force when the density contrast Ap between the subducting plate and the asthenosphere is positive. We vary both Ap and the interplate friction (frictional stresses). Slip partitioning is obtained only in the models with high interplate friction and only when the overriding plate contains a weak zone. This zone in the models corresponds either to locally thinned litho-sphere or to cut (fault). The horizontal, trench-normal component of the interplate friction force [Ffh[ can be comparable with the absolute value of the horizontal component of the nonhydrostatic interplate pressure force [Fph [ in the subduction zone. Ffh is always negative (compression), while Fph can be either negative (compressional subduction regime) or positive (extensional regime). High friction, which promotes partitioning, can completely cancel the extensional (suction) force Fph. Back arc tension and strike-slip faulting appear thus as conflicting processes, although they can coexist in the same subduction zone, depending on the relative values of relevant forces. It appears that high friction can exist only in compressional subduction zones where partitioning should develop more easily. This conclusion is supported by the comparison of two oblique subduction zones, having similar geometry: the compressional southern Kurile zone (strong partitioning) and extensional southern Ryukyu zone (no lithospheric-scale partitioning). Other factors controlling the strain partitioning are the length of the oblique subductlon zone, the boundary conditions at the transverse limits of the forearc sliver, and of course, the obliquity of subduction.
ISSN: 2169-9275

hal-01261396
https://hal.archives-ouvertes.fr/hal-01261396
https://hal.archives-ouvertes.fr/hal-01261396/document
https://hal.archives-ouvertes.fr/hal-01261396/file/chemendaJGR2000.pdf
DOI : 10.1029/1999JB900332

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 Elsevier Masson
Résumé : International audience
The seismological study of recent seismic crises near Oleron Island confirms the coexistence of an extensional deformation and a transtensive regime in the Atlantic margin of France, which is different from the general western European stress field corresponding to a strike-slip regime. We argue that the switch of the principal stress axes σ1/σ2 in a NW-SE vertical plane is linked with the existence of crustal heterogeneities. Events of magnitude larger than 5 sometimes occur along the Atlantic margin of France, such as the 7 September 1972 (ML = 5.2) earthquake near Oleron island and the 30 September 2002 (ML = 5.7) Hennebont event in Brittany. To test the mechanism of local strain localization, we model the deformation of the hypocentral area of the Hennebont earthquake using a 3D thermo-mechanical finite element code. We conclude that the occurrence of moderate earthquakes located in limited parts of the Hercynian shear zones (as the often reactivated swarms near Oleron) could be due to local reactivation of pre-existing faults. These sporadic seismic ruptures are favoured by stress concentration due to rheological heterogeneities.
ISSN: 1631-0713

hal-00936220
https://hal.archives-ouvertes.fr/hal-00936220
DOI : 10.1016/j.crte.2013.07.004

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We investigated the structure of the upper mantle beneath southeastern Brazil using teleseismic shear wave splitting measurements. Measurements were performed on seismic data recorded in the Ribeira and Brasilia Neoproterozoic belts, which wrap around the southern termination of the São Francisco craton and disappear westward under the Paraná basin. In the northern Ribeira belt, dominated by thrust tectonics, the fast shear wave polarization planes trend on average N080°E, whereas in the central domain, dominated by strike-slip tectonics, fast shear waves are polarized parallel to the structural trend (N065°E). Stations located above the main transcurrent fault display large delay times (> 2.5 s). Such values, among the largest in the world, require either an unusually large intrinsic anisotropy frozen within the lithosphere, or a contribution from both the lithospheric and asthenospheric mantle. Within the southern Brasilia belt, fast split shear waves are polarized parallel to the structural trend of the belt, at a high angle from the APM. Although part of our data set strongly favors an origin of anisotropy related to a fabric frozen in the lithospheric mantle since the Neoproterozoic, a contribution of the asthenospheric flow related to the present day plate motion is also required to explain the observed splitting parameters.
ISSN: 0012-821X

hal-01389116
http://hal.univ-reunion.fr/hal-01389116
http://hal.univ-reunion.fr/hal-01389116/document
http://hal.univ-reunion.fr/hal-01389116/file/Heintz_SKS_Brazil_EPSL2003_hal.pdf
DOI : 10.1016/S0012-821X(03)00163-8

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
We use digital elevation models and satellite imagery data completed with field observations to develop an integrated morphotectonic analysis of the anomalous topography of the Central Cordillera of Patagonia between 46 degrees S and 48 degrees S, in a region overlying subducted segments of the Chile Spreading Ridge. This region shows a number of peculiar features, not expected in a normal subduction-related belt located away from a buried spreading center. First, it is characterized by overall short-wavelength topography and highly contrasted reliefs, typical of deeply incised young mountain belts, but surprisingly, also by an average very low elevation of similar to 900 m. Second, the Cordillera lacks central high reliefs; instead, there is a central, depressed domain with average low slope gradients including the deepest point of the study area (300 m below sea level in the bottom of Lake General Carrera/Buenos Aires). This depressed area is flanked by western and eastern regions of higher elevation having opposite general slope dips. To the east, the central Patagonian Cordillera is now separated from the flat plains of the Pampean domain (representing its former piedmont) and several elevated basaltic plateaus (mesetas) by 160 degrees N-180 degrees N trending morphotectonic corridors and the western border scarps of the mesetas. These scarps correspond to neotectonic features controlled by recent vertical faults, mostly active after 3 Ma. Remnants of a former peneplain, the Avellanos surface, are widespread within the entire Cordilleran region. From geological evidence, this peneplain formed between 15 and 4 Ma and was connected originally with the mesetas domain and now is dissected by these corridors. It is shown that a negative inversion related to extensional and strike-slip faulting occurred in the frontal region of the Cordillera at 3 Ma synchronously with the emplacement of magmatic products. Timing of the extensional deformation in central Patagonia is concomitant with the migration at depth of different segments of the South Chile Ridge, which entered the trench at 6 and 3 Ma, respectively, and the consequent opening of a slab window allows asthenospheric hot mantle to reach lithospheric regions. Finally, migration of segments of the Chile Spreading Ridge since 6 Ma triggered regional uplift of the Cordillera followed by limited extension in relation with increased thermal weakening of the crust.
ISSN: 0278-7407

hal-00486334
https://hal.archives-ouvertes.fr/hal-00486334
DOI : 10.1029/2009TC002453