Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : The role of the Karakorum fault zone (KFZ) is debated. South of 33°N, ongoing dextral-oblique slip along the SW edge of the Gar basin exhumes metamorphic and magmatic rocks of the Ayilari range. Minerals have recorded a continuum of deformation from temperatures >600–400°C down to <250_C. The 40Ar/39Ar ages, the oldest being 21.2 ± 1.0 Ma, yield minimum estimates for the initiation of the KFZ. These are in agreement with the U-Th/Pb ages constraining the onset of deformation at ca 25–22 Ma. Thermochronologic results show slow cooling for the period ca 21– 14 Ma, followed by rapid cooling between 14 and 4 Ma. These data demonstrate that right-lateral motion was in progress in the early Miocene and that shear continued at least until 4 Ma, pointing to >20 Ma of deformation along the fault. Greenschist facies deformation superimposed upon the medium- to high-grade deformation marks a kinematic change from pure dextral to dextral-normal motion associated with the onset of rapid cooling. At the regional scale, the coexistence of transtension in the Gar basin with transpression documented along the Pangong range farther north suggests another example of the ‘‘zipper tectonics'' model developed along the Red River fault. The kinematic shift induced the rise of the Ayilari range starting at 16–12 Ma and the incision of major river courses. The Indus River might have become captive of the relief at this time. The river's 120 km of apparent offset implies dextral motion at a long-term rate of ca 8.5 ± 1.5 mm/yr.
ISSN: 0278-7407

hal-00197561
https://hal.archives-ouvertes.fr/hal-00197561
https://hal.archives-ouvertes.fr/hal-00197561/document
https://hal.archives-ouvertes.fr/hal-00197561/file/Valli_Karakorum_thermochron_Tectonics_07_pre_print.pdf
DOI : 10.1029/2005TC001913

Éditeur(s) : HAL CCSD Elsevier
Résumé : Hot collisional orogens are characterized by abundant syn-kinematic granitic magmatism that profoundly affects their tectono-thermal evolutions. Voluminous granitic magmas, emplaced between 360 and 270 Ma, played a visibly important role in the evolution of the Variscan Orogen. In the Limousin region (western Massif Central, France), syntectonic granite plutons are spatially associated with major strike-slip shear zones that merge to the northwest with the South Armorican Shear Zone. This region allowed us to assess the role of magmatism in a hot transpressional orogen. Microstructural data and U/Pb zircon and monazite ages from a mylonitic leucogranite indicate synkinematic emplacement in a dextral transpressional shear zone at 313 +/- 4 Ma. Leucogranites are coeval with cordierite-bearing migmatitic gneisses and vertical lenses of leucosome in strike-slip shear zones. We interpret U/Pb monazite ages of 315 +/- 4 Ma for the gneisses and 316 +/- 2 Ma for the leucosomes as the minimum age of high-grade metamorphism and migmatization respectively. These data suggest a spatial and temporal relationship between transpression, crustal melting, rapid exhumation and magma ascent, and cooling of high-grade metamorphic rocks.;Some granites emplaced in the strike-slip shear zone are bounded at their roof by low dip normal faults that strike N-S, perpendicular to the E-W trend of the belt. The abundant crustal magmatism provided a low-viscosity zone that enhanced Variscan orogenic collapse during continued transpression, inducing the development of normal faults in the transpression zone and thrust faults at the front of the collapsed orogen.
ISSN: 0040-1951

hal-00445260
https://hal.archives-ouvertes.fr/hal-00445260
DOI : 10.1016/j.tecto.2009.03.022

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Absolute earthquake hypocenter locations have been determined in the area offshore eastern Taiwan, at the Southernmost Ryukyu subduction zone. Location process is run within a 3D velocity model by combining the Taiwanese and neighboring Japanese networks and using the 3D MAXI technique. The study focuses on the most active seismic cluster in the Taiwan region that occurs in the forearc domain offshore eastern Taiwan. Earthquakes distribute mainly along 2 active planes. The first one aligns along the subduction interface and the second one, shallower affects the overriding margin. Focal mechanisms within the shallow group indicate that nodal planes are either compatible with high-angle back-thrusts or low-angle thrusts. The active seismic deformation exclusively indicates reverse faulting revealing that the forearc basement undergoes trench-perpendicular strong compression. By integrating the seismological image into the regional context, we favor the hypothesis in which the dense seismicity occurring offshore marks the activity of en-échelon high-angle reverse faults accommodating the uplift of a broken piece of Ryukyu Arc basement, called Hoping Basement Rise. The uplift is inferred to be caused by the subduction of an oceanic relief, either exotic block, seamount or oceanic crust sliver. Our favored solution satisfies the narrowness of epicenter's cluster along the Hoping Canyon, and the observation of high-angle active faults on seismic lines crossing the area. Furthermore, this solution is compatible with the active uplift of the Hoping Rise demonstrated from morphological and sedimentological data. We do not exclude the branching of the high-angle reverse faults system onto a splay fault connected with the subduction interface but further investigations are needed to map precisely the 3D distribution of active faults that break the margin.
ISSN: 0040-1951

hal-00407726
https://hal.archives-ouvertes.fr/hal-00407726
DOI : 10.1016/j.tecto.2007.11.018

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Geodetic data support a short-term continental deformation localized in faults bounding lithospheric blocks. Whether major "faults" observed at the surface affect the lithospheric mantle and, if so, how strain is distributed are major issues for understanding the mechanical behavior of lithospheric plates. A variety of evidence, from direct observations of deformed peridotites in orogenic massifs, ophiolites, and mantle xenoliths to seismic reflectors and seismic anisotropy beneath major fault zones, consistently supports prolongation of major faults into the lithospheric mantle. This review highlights that many aspects of the lithospheric mantle deformation remain however poorly understood. Coupling between deformation in frictional faults in the uppermost crust and localized shearing in the ductile crust and mantle is required to explain the post-seismic deformation, but mantle viscosities deduced from geodetic data and extrapolated from laboratory experiments are only reconciled if temperatures in the shallow lithospheric mantle are high (> 800 °C at the Moho). Seismic anisotropy, especially shear wave splitting, provides strong evidence for coherent deformation over domains several tens of km wide in the lithospheric mantle beneath major transcurrent faults. Yet it cannot detect narrow strain localization zones or shallowly dipping faults. Seismic profiling images shallow-dipping seismic reflectors in the lithospheric mantle interpreted as the continuation of normal or, less frequently, inverse faults in the mantle. However the nature of these reflectors is poorly understood. There is a large discrepancy between the scale at which deformation processes are studied (a few kilometers, at most, due to the limited size of continuous mantle exposures at the Earth's surface) and the scale inferred for strain localization in the mantle from geophysical observations (tens of kilometers). Combining data on deformation microstructures and crystal preferred orientations in naturally deformed peridotites and seismologic observations allows nevertheless discussing strain localization processes that may play a role on the development of mantle shear zones.
ISSN: 0040-1951

hal-00750314
https://hal.archives-ouvertes.fr/hal-00750314
DOI : 10.1016/j.tecto.2012.06.006

Éditeur(s) : HAL CCSD
Résumé : International audience
The way faults control upward fluid flow in extensive hydrothermal systems without an abnormal heat source such as volcanic or plutonic activity is still unclear. In the Eastern Pyrénées, an alignment of 29 hot springs (from 29 • C to 73 • C) along the Têt normal Fault offers the opportunity to study this process. Using an integrated multi-scale geological approach including mapping, remote sensing, macro and microscopic analyses of fault zones, we show that hot springs locate close to high topographic reliefs related to fault throw and segmentation. Emergences are always in crystalline rocks at gneiss-metasediments contacts, mostly in the Têt Fault footwall. In more details, they localize either (1) in brittle fault damage zones at the intersection between the Têt Fault and subsidiary faults, and (2) into hercynian ductile faults where dissolution cavities run along shear zones. Using these observations and 2D preliminary numerical simulations, we propose a hydrogeological model of upward hydrothermal flow. Meteoric fluids infiltrate at high altitude in the fault footwall relief where they acquire temperature because of the geothermal gradient. Hydraulic gradient and buoyancy forces allow them to upflow along fault-related permeability anisotropies. The identification and prioritization of the features controlling this kind of system have important implications for geothermal exploration and for the understanding of fluid-flow into the brittle Earth's crust in general.
EGU 2017
Vienne, Austria

hal-01491096
https://hal-brgm.archives-ouvertes.fr/hal-01491096
https://hal-brgm.archives-ouvertes.fr/hal-01491096/document
https://hal-brgm.archives-ouvertes.fr/hal-01491096/file/EGU2017-Taillefer-etal_4996.pdf

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
P>The Strait of Hormuz area is a transition zone between the continental collision of the Zagros (west) and the subduction of an oceanic part of the Arabian Plate beneath the Makran wedge (east). Geology and recent GPS measurements indicate that about 15 mm yr-1 of relative motion in N10 degrees E direction is accommodated by two major fault systems: (1) the NNW-trending Minab-Zendan-Palami (MZP) fault system that connects the Main Zagros Thrust (MZT) to the inner Makran thrust system and the Frontal subduction thrust and (2) the N-trending Sabzevaran-Kahnuj-Jiroft (SKJ) fault system that bounds the Jazmurian depression to the west. We use dense GPS measurements along four transects across these fault systems in order to determine the strains spatial distribution. The northern GPS transect confirms the total fault slip rates for both fault systems estimated by the tectonic analyses (about 10 and 7.3 mm yr-1 in N10 degrees direction across the MZP and SKJ fault systems, respectively). For both fault systems, the elastic deformation spreads over shear zones that are several tens of kilometres wide. However, transects located close to latitude 27 degrees N reveal a much narrower shear zone (similar to 10 km) for the MZP fault system. Moreover, we confirm that most of the present-day strain is transferred towards the frontal subduction thrust rather than towards the inner Makran thrusts. In order to complement this new GPS velocity field with spatially dense measurements, we processed a set of ERS radar images by the radar interferometry (InSAR) technique. We used both a 'stacking' and a 'persistant-scatterers' approach to differentiate the ground deformation signal which spatial gradient is expected to be very low, from the atmospheric signal. Results from these interferograms appear to be relatively in agreement with the GPS-determined strain distribution. Nevertheless, they confirm the absence of any superficial creep behaviour since no sharp discontinuity on interferometric phase can be noted on any interferogram. Finally, we use a purely kinematic 'block model' inversion process to calculate slip rates and locking depths for each fault system from our GPS measurements. These models suggest that the relative quiescence over the last 200 yr has certainly produced a slip deficit as high as 2 m. So, we may wonder if the MZP fault system is not late in the interseismic phase of its earthquake cycle.
ISSN: 0956-540X

hal-00429386
https://hal.archives-ouvertes.fr/hal-00429386
DOI : 10.1111/j.1365-246X.2009.04321.x

Éditeur(s) : Elsevier
Résumé : We describe for the first time a set of large active thrusts and folds near the foot of the easternmost Algerian margin, Western Mediterranean, from swath bathymetry and high-resolution seismic data acquired in 2005 during the Maradja2/Samra cruise. This active system resumes a previous passive margin and creates growth strata deposition on the limbs of large folds, resulting in the development of perched basins at the foot of the margin since less than similar to 1 Ma. They form a set of overlapping fault segments verging toward the Algerian basin, in a way similar to what has been observed off eastern Algiers on the rupture zone of the 2003 Mw 6.8 Boumerdes earthquake. The horizontal shortening rate across large folds is estimated to be of the order of 1 mm/yr. Although no historical earthquakes are reported here, these fault segments could have been responsible for large (M similar to 7.5) events in the past. This young tectonic system further supports the hypothesis of subduction inception of the Neogene oceanic lithosphere in the context of the Africa-Eurasia convergence.
Marine Geology (0025-3227) (Elsevier), 2009-06 , Vol. 261 , N. 1-4 , P. 17-32

Droits : 2009 Published by Elsevier Inc.
http://archimer.ifremer.fr/doc/2009/publication-6850.pdf
DOI:10.1016/j.margeo.2008.05.016
http://archimer.ifremer.fr/doc/00000/6850/

Éditeur(s) : HAL CCSD
Résumé : In order to identify and quantify the Rif (Morocco) present-day deformation, especially those related to active faults (location, geometry, kinematic), we perform a morphotectonic study. The studied area and faults are located in the Northern part (conjugate faults of Al-Hoceima Bay: Trougout, Boujibar and Rouadi), the Eastern part (Nekor fault) and the Southern part of the chain (Rif frontal thrust between Fes and Meknes cities).Morphotectonic tools (DEMs at different scales, satellite and aerial pictures), field studies and Quaternary dating methods (U/Th, OSL, 14C and in-situ cosmogenic isotopes 10Be, 3He, 36Cl) allow us to characterize transtensional deformation in the Northern Rif. Horizontal and vertical slip rates along the N-S-oriented Trougout major fault are ~1.6 mm/yr and ~2 mm/yr respectively. In the Southern part, the Rif frontal thrust shows a shortening rate of ~1.8 mm/yr into Fes and Meknes area. In the Eastern part, the deformation is focused on the Nekor left-lateral strike-slip major fault with ~1.5 mm/yr. Incision features and raised marine terraces involve an uplift of the chain about ~0.2 mm/yr. The overall deformation in the Rif seems to be continuous since the Messinian-Pliocene time.These new morphotectonic constraints are consistent with the GPS measurements showing southwestward overall motion of most of the Rif belt with respect to stable Africa, associated to clockwise rotation. Finally, we propose a geodynamic model in which the Rif, the Alboran sea and the Betics belong to a single microplate bounded by the strike-slip faults of the Betics on the North, the Rif frontal thrust on the South, the Nekor and TASZ (Trans Alboran Shear Zone) strike-slip faults on the East and North-East, and the western Rif folded structures on the West.
L'objectif de cette étude est d'identifier et de quantifier les déformations actuelles dans la chaine du Rif (Maroc), notamment celles associées aux failles actives (localisation, géométrie, cinématique). Pour ce faire, nous mettons en œuvre pour la première fois dans cette région, une approche morphotectonique. Les sites et failles sélectionnés et étudiés se situent dans la partie Nord (les failles conjuguées de la baie d'Al-Hoceima: Trougout, Boujibar et Rouadi), l'Est (la faille de Nékor) et le Sud (front chevauchant sud rifain entre Fes et Meknes).A partir des outils de la morphotectonique (MNTs à différentes résolutions, images satellitaires, photographies aériennes), d'analyses de terrain et grâce aux méthodes de datation du Quaternaire (U/Th, OSL, 14C et isotopes cosmogéniques produits in-situ 10Be, 3He, 36Cl), cette étude met en évidence et quantifie une déformation transtensive dans la partie Nord de la chaine. Les vitesses de glissement horizontales et verticales le long de la faille principale d'orientation méridienne de Trougout sont de ~1.6 mm/an et ~2 mm/an, respectivement. Dans la partie Sud, nous montrons que le front rifain entre Fez et Meknes est actif avec une vitesse de raccourcissement de ~1.8 mm/an. La déformation dans la région Est se localise principalement sur la faille du Nékor avec une vitesse décrochante senestre de ~1.5 mm/an. Par ailleurs, la présence de nombreuses figures d'incision et de surfaces marines soulevées au niveau du littoral Nord témoignent d'une surrection généralisée de la chaine de l'ordre de ~0.2 mm/an. L'ensemble de cette déformation semble être constante depuis la période du Messino-Pliocène. Ces résultats sont cohérents avec les données GPS qui montrent un déplacement de ~5mm/an vers le SW de l'ensemble du Rif associé à un mouvement rotatif horaire, dans le référentiel Afrique stable. D'un point de vue géodynamique, nous proposons que le Rif, la mer d'Alboran et les Bétiques appartiennent à une même microplaque limitée au Nord par les failles décrochantes des Bétiques, au Sud par le chevauchement rifain, à l'Est et au Nord-Est par les failles décrochantes de Nékor et de la TASZ (Trans Alboran Shear Zone) et à l'Ouest par les structures plissées bordières du Rif.
https://tel.archives-ouvertes.fr/tel-01170466

NNT : 2014MON20105
tel-01170466
https://tel.archives-ouvertes.fr/tel-01170466
https://tel.archives-ouvertes.fr/tel-01170466v2/document
https://tel.archives-ouvertes.fr/tel-01170466/file/41875_POUJOL_2014_archivage_cor.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In Western Mediterranean, the Rif belt in Morocco is part of the Gibraltar Arc built during the Tertiary in the framework of Eurasia-Africa convergence. The structural and metamorphic evolution of the internal units of this belt as well as their timing, crucial to constrain the geodynamic evolution of the Alboran Sea, is still largely debated.Our study on the Ceuta Peninsula (Northern Rif) provides new structural, petrological and geochronological data (U-Th-Pb, Ar-Ar), which allow to precise the tectono-metamorphic evolution of the Lower Sebtides metamorphic units with:(1) a syn-metamorphic thrusting event developed under granulite facies conditions (7–10 kbar and 780–820 °C). A major thrust zone, the Ceuta Shear Zone, drove the emplacement of metapelites and peridotitic lenses from the Ceuta Upper Unit over the orthogneisses of the Monte Hacho Lower Unit. This compressional event ended during the Upper Oligocene.(2) an extensional event developed at the boundary between amphibolite and greenschist facies conditions (400–550 °C and 1–3 kbar). During this event, the Ceuta Shear Zone has been reactivated as a normal fault. Normal ductile shear zones contributed to the final exhumation of the metamorphic units during the Early Miocene.We propose that the compressional event is related to the formation of an orogenic wedge located in the upper plate, in a backward position, of the subduction zone driving the geodynamic evolution of the Alboran domain. In this context, the episode of lithospheric thinning could be related to the opening of the Alboran basin in a back-arc position.Furthermore, unlike the previous models proposed for the Rif belt, the tectonic coupling between mantle peridotites and crustal metamorphic rocks occurred in Ceuta Peninsula at a depth of 20–30 km under high temperature conditions, before the extensional event, and thus cannot be related to the back-arc extension.
ISSN: 0040-1951

insu-01682810
https://hal-insu.archives-ouvertes.fr/insu-01682810
DOI : 10.1016/j.tecto.2017.11.028

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
We analyse P-wave receiver functions across the western Gulf of Aden and southern Red Sea continental margins in Western Yemen to constrain crustal thickness, internal crustal structure and the bulk seismic velocity characteristics in order to address the role of magmatism, faulting and mechanical crustal thinning during continental breakup. We analyse teleseismic data from 21 stations forming the temporary Young Conjugate Margins Laboratory (YOCMAL) network together with GFZ and Yemeni permanent stations. Analysis of computed receiver functions shows that (1) the thickness of unextended crust on the Yemen plateau is ∼35km; (2) this thins to ∼22km in coastal areas and reaches less than 14km on the Red Sea coast, where presence of a high-velocity lower crust is evident. The average Vp/Vs ratio for the western Yemen Plateau is 1.79, increasing to ∼1.92 near the Red Sea coast and decreasing to 1.68 for those stations located on or near the granitic rocks. Thinning of the crust, and by inference extension, occurs over a ∼130-km-wide transition zone from the Red Sea and Gulf of Aden coasts to the edges of the Yemen plateau. Thinning of continental crust is particularly localized in a <30-km-wide zone near the coastline, spatially co-incident with addition of magmatic underplate to the lower crust, above which on the surface we observe the presence of seaward dipping reflectors (SDRs) and thickened Oligo-Miocene syn-rift basaltic flows. Our results strongly suggest the presence of high-velocity mafic intrusions in the lower crust, which are likely either synrift magmatic intrusion into continental lower crust or alternatively depleted upper mantle underplated to the base of the crust during the eruption of the SDRs. Our results also point towards a regional breakup history in which the onset of rifting was synchronous along the western Gulf of Aden and southern Red Sea volcanic margins followed by a second phase of extension along the Red Sea margin.
ISSN: 0956-540X

hal-00825194
https://hal.archives-ouvertes.fr/hal-00825194
https://hal.archives-ouvertes.fr/hal-00825194/document
https://hal.archives-ouvertes.fr/hal-00825194/file/RF_Hakim2012_GJI.pdf
DOI : 10.1093/gji/ggt072

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In the Tahalgha district (southwestern Hoggar, Algeria), the Cenozoic volcanism has sampled subcontinental mantle beneath two crustal terranes that collided during the Pan-African orogeny: the “Polycyclic Central Hoggar” to the east and the “Western Hoggar” to the west. Two major lithospheric shear zones separate these terranes: the “4°35” and the “4°50” faults. Mantle xenoliths were collected between the two faults and across the 4°35 fault. In addition to a range in equilibrium temperatures and chemical compositions reported elsewhere, the samples show variations in their microstructures and crystallographic preferred orientations. Equilibrium temperatures and geochemical characteristics allow dividing them into low — (LT; 700–900 °C), intermediate — (IT; 900–1000 °C), and high-temperature (HT; 1000–1100 °C) xenoliths. The LT and IT peridotites occur on both sides of the 4°35 fault; they are usually coarse-grained. HT xenoliths are present only east of the 4°35 fault, in the narrow domain stuck between the two faults; they are fine-grained and extensively affected by annealing and melt–rock reactions. Microstructures and crystallographic textures indicate that deformation in the LT- and IT-xenoliths occurred through dislocation creep under relatively high-temperature, low-pressure conditions, followed by post-kinematic cooling. The fine-grained HT-xenoliths were deformed under relatively high-stress conditions before being annealed.Combining microstructural and CPO data with petrological and geochemical informations suggests that: (1) the LT xenoliths are remnants of the Neoproterozoic lithospheric mantle that preserved microstructural and chemical characteristics inherited from the Pan-African orogeny, and (2) the HT xenoliths record localized Cenozoic deformation associated with melt channeling through feed-back processes that culminated in the formation of high-permeability porous-flow conduits. Limited grain-growth in HT xenoliths suggests that advective heating of melt conduits was transient and rapidly followed by thermal relaxation due to conductive heat loss into wall-rock peridotites represented by the IT xenoliths, then by exhumation due to volcanic activity.
ISSN: 0040-1951

hal-01171761
https://hal.archives-ouvertes.fr/hal-01171761
DOI : 10.1016/j.tecto.2014.11.012

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) : Wiley / Blackwell
Résumé : P>New seismic reflection data from the Grand Banks of Newfoundland and the Newfoundland Basin add to the growing knowledge of the composition, structure and history of this non-volcanic margin. Geophysical imaging is now approaching the extent of that done previously on the conjugate margin along Iberia, providing a valuable database for the development of rifting models. Two parallel profiles over the shelf platform image deep crustal fabric representing Precambrian or possibly Appalachian deformation as well as Mesozoic extension. Progressively more intense extension of continental crust is imaged oceanwards without the highly reflective detachments frequently seen on profiles off Galicia. A landward-dipping event 'L' is imaged sporadically and appears to be analogous to a similar event on the Iberian IAM9 profile. The transition zone is probably exposed serpentinized mantle as interpreted off the Iberian margin although there appears to be a difference in the character of ridge development and reflectivity. The distinctive 'U' reflection identified previously at the base of the Newfoundland Basin deep water sedimentary section and recently identified as one or more thin basalt sills is imaged on newly presented profiles that connect previously published profiles SCR3 and SCR2 showing that 'U' is highly regular and continuous except where interrupted by basement highs. 'U' is also seen to have a major impact on the ability to image underlying basement. A full transect beginning over completely unextended continental crust through to oceanic crust has provided a data set from which estimates of extension and the pre-rifting location of the present continental edge can be made. Two estimates were obtained; 85 km based on faulting and 120 km based on crustal thickness.
Geophysical Journal International (0956-540X) (Wiley / Blackwell), 2009-08 , Vol. 178 , N. 2 , P. 1004-1020

Droits : 2009 Wiley / Blackwell
http://archimer.ifremer.fr/doc/2009/publication-6919.pdf
DOI:10.1111/j.1365-246X.2009.04162.x
http://archimer.ifremer.fr/doc/00000/6919/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
From outcrops located in Provence (South-East France), we describe the distribution, the microstructures, and the petrophysical properties of deformation band networks related to both contractional and extensional tectonic events. In contraction, pervasively distributed networks of reverse-sense compactional shear bands are observed in all folded sand units of the foreland, whereas localized networks of clustered reverse-sense shear bands are only observed close to a large-scale thrust. In extensional setting, networks of clustered normal-sense shear bands are generally observed adjacent to map-scale faults (100 m–10 km scale), although some randomly distributed bands are also observed between these faults. Normal-sense cataclastic faults, i.e. zone of deformation bands containing a localized slip-surface, are also observed to be restricted to sand units, suggesting that faults initiated in the sands during extension, but not during contraction. Shear bands and faults show cataclastic microstructures with high-permeability reduction whereas compactional shear bands show crush microbreccia or protocataclastic microstructures with moderate permeability reduction. This basin-scale analysis underlines the major role of tectonic settings (thrust-fault versus normal-fault andersonian-stress regime) and the influence of inherited large-scale faults on the formation/localization of low-permeability shear bands. We also provide a geometrical analysis of the band network properties (spacing, thickness, shear/compaction ratio, degree of cataclasis, petrophysical properties) with respect to the median grain size, porosity and grain sorting of host sand. This analysis suggests that grain size, although less important than stress-state conditions and the presence of large-scale faults, has a non-negligible effect on band network geometry. No correlations are observed between the grain sorting, porosity and band network geometry.
ISSN: 0264-8172

hal-01116421
https://hal.archives-ouvertes.fr/hal-01116421
DOI : 10.1016/j.marpetgeo.2013.12.020

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We investigate the timing of end of motion along the South Tibet Detachment System (STDS), a major normal fault system that runs parallel to the Himalayan range for more than 1500 km. Near Dinggye (similar to 28 degrees 10'N, 87 degrees 40'E), the STD dips similar to 10 +/- 5 degrees to the North and separates Paleozoic Tethyan series from Upper Himalayan Crystalline Series (UHCS). Immediately below the STD, the UHCS is highly deformed in the STD shear zone, lineations trend NNE and the shear senses are top to the NE. In micaschist, the P-T path constrained by pseudosection and garnet chemistry, shows successive metamorphic conditions of similar to 0.6 GPa and similar to 550 degrees C and 0.5 GPa and 625 degrees C. U/Pb dating of monazites and zircons in deformed and undeformed leucogranites suggests that ductile deformation lasted until at least similar to 16 Ma but ended prior to similar to 15 Ma in the STD shear zone similar to 100 m below the detachment. Ar/Ar micas ages in the footwall span between similar to 14.6 and 13.6 Ma, indicating rapid cooling down to similar to 320 degrees C, and suggesting persistence of normal faulting, at that time. The STDS is cut and offset by the N-S trending Dinggye active normal fault which initiated prior to 11 Ma thus providing a minimum bound for the end of STDS motion. These data are interpreted as reflecting 0.3 GPa (11 km) to 0.6 GPa (22 km) of exhumation along the STDS starting prior to similar to 16 Ma, ending between 13.6 and 11 Ma. The 1000 km long stretch of the STDS east of the Gurla Mandata probably stopped almost synchronously between 13 and 11 Ma ago, coevally with a sudden switch from NNE-SSW to E-W extension at the top of the accretionary prism, with a jump of the major thrust from the lower Main Central Thrust (MCTI) to the Main Boundary Thrust (MBT), and with a change in the India and Asia convergence direction. This synchronism is probably better explained in the frame of a thrust wedge or thrust system model than a lower channel flow model. West of the Gurla Mandata the STDS appears to stop 5 to 3 Ma earlier, possibly related to local interactions with the Karakorum fault in a way that needs to be understood.
ISSN: 0012-821X

hal-00475652
https://hal.archives-ouvertes.fr/hal-00475652
DOI : 10.1016/j.epsl.2009.12.035

Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : International audience
Temperature and fluid pressure conditions control rock deformation and mineralization on geological faults, and hence the distribution of earthquakes1. Typical intraplate continental crust has hydrostatic fluid pressure and a near-surface thermal gradient of 31 ± 15 degrees Celsius per kilometre2, 3. At temperatures above 300–450 degrees Celsius, usually found at depths greater than 10–15 kilometres, the intra-crystalline plasticity of quartz and feldspar relieves stress by aseismic creep and earthquakes are infrequent. Hydrothermal conditions control the stability of mineral phases and hence frictional–mechanical processes associated with earthquake rupture cycles, but there are few temperature and fluid pressure data from active plate-bounding faults. Here we report results from a borehole drilled into the upper part of the Alpine Fault, which is late in its cycle of stress accumulation and expected to rupture in a magnitude 8 earthquake in the coming decades4, 5. The borehole (depth 893 metres) revealed a pore fluid pressure gradient exceeding 9 ± 1 per cent above hydrostatic levels and an average geothermal gradient of 125 ± 55 degrees Celsius per kilometre within the hanging wall of the fault. These extreme hydrothermal conditions result from rapid fault movement, which transports rock and heat from depth, and topographically driven fluid movement that concentrates heat into valleys. Shear heating may occur within the fault but is not required to explain our observations. Our data and models show that highly anomalous fluid pressure and temperature gradients in the upper part of the seismogenic zone can be created by positive feedbacks between processes of fault slip, rock fracturing and alteration, and landscape development at plate-bounding faults.
ISSN: 0028-0836

hal-01685757
https://hal.archives-ouvertes.fr/hal-01685757
DOI : 10.1038/nature22355

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Cycladic Blueschist Unit (CBU) represents the northern passive margin of the Adria continental block and ophiolites that are the remnants of the Pindos Ocean, which were affected by high pressure-low temperature metamorphism in the blueschist and eclogite facies during the Eocene. Prior to the Lutetian, the ophiolitic and margin units were thrust towards the SW inside a NE-dipping subduction zone. Two subsequent exhumation stages are characterized by top-to-the-NE senses of shear: i) from mantle depths to lower crustal levels, before 37 Ma, which was accommodated by an extensional inversion of the Vardar suture zone, and ii) from deep crustal levels to the near-surface, between 30 and 20 Ma, which was accommodated by the North Cycladic Detachment. It is during this late stage of ductile exhumation that the central Cyclades Core Complex was exhumed. Segmentation of the CBU by normal faults started at 12 Ma, as recorded by the low temperature thermochronometers, and was coeval with block rotation and folding with NS-trending axes, which were predominantly controlled by the Myrthes-Ikaria strike-slip fault in the centre of the Cyclades. A map restoration of the CBU geometry, prior to segmentation, has been carried out using available structural and paleomagnetic data. The restoration shows that, following the CBU exhumation from mantle depths to crustal levels, a single core complex was exhumed along a single NE dipping detachment.
ISSN: 0040-1951

insu-00672320
https://hal-insu.archives-ouvertes.fr/insu-00672320
DOI : 10.1016/j.tecto.2011.12.025

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
New magnetotelluric and receiver transfer function studies provide insights from the upper to the lower crust of the eastern Betic Cordillera, which is deformed by large folds, normal faults, and a major transcurrent left-lateral fault, the Carboneras Fault Zone (CFZ). Receiver function analysis determines a NNW dipping Moho reaching 20 degrees that increases in depth, from 20 km south of the CFZ up to 34 km in the Sierra de Los Filabres. In addition, seismic discontinuities determined in the upper crust are interpreted as major contacts between metamorphic complexes that are detached and folded. The MT inversion model reveals a conductive zone, also representing a crustal seismic discontinuity, associated with the Alpujarride/Nevado-Filabride contact and fitting the N vergent geometry of the Sierra Alhamilla antiform. A small flexure at Moho coincides with the CFZ, as revealed by the Bouguer anomaly trend, in agreement with the receiver function results. Moreover, the Bahr strike and tipper angle at the stations placed closest to the CFZ clearly reveal the continuity of the CFZ at least down to approximately 15 km in depth, crossing all the detected crustal discontinuities up to the Moho. The lack of a clear Moho offset associated with the Carboneras Fault supports the idea that some large strike-slip faults tend to accommodate the deformation by a broadening fault zone at lower crustal levels. Its nucleation could occur at the base of a thin crust, where melting processes critically reduced the lithospheric strength during the late Miocene, to then propagate upward, reaching the topographic surface. Northward, the lithosphere comprised moderately larger strength, and the crustal discontinuities favored the development of larger folds with kilometric amplitude instead of strike-slip faults since the late Miocene.
ISSN: 1525-2027

hal-00671024
https://hal.archives-ouvertes.fr/hal-00671024
DOI : 10.1029/2010GC003274

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Fault friction is a parameter that is difficult to assess along fault zones since its determination depends on the knowledge of any factor controlling the state of stress around faults. In brittle homogeneous rocks, a limited number of these factors, such as the shape of the fault surface, the vicinity of fault tips or the remote stress ratio, are crucial to constrain for this determination. In this paper, we propose to analyse a field example in which all these properties are met and where the nature of the slipped structure suggest differences in static friction. We compare the orientations of branching fractures at strike-slip relay zones between en echelon stylolites and en echelon joints both reactivated in shear. The field data are compared with both photoelastic and 3-D numerical models that consider the remote stress conditions and the role of the geometry of the strike-slip segments. Based on field observations, these analyses quantitatively demonstrate the significant role of fault friction on the local stress field orientation and subsequent fracture formation. This work points out that estimations of fault friction based on analyses of fracture patterns or in situ stresses must be accompanied with a thorough investigation of the 3-D fault shape, its segmentation and the remote stress state.
ISSN: 0191-8141

hal-00560999
https://hal.archives-ouvertes.fr/hal-00560999
DOI : 10.1016/j.jsg.2010.01.008

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We review the geodynamic evolution of the Aegea-Anatolia region and discuss strain localisation there over geological times. From Late Eocene to Present, crustal deformation in the Aegean backarc has localised progressively during slab retreat. Extension started with the formation of the Rhodope Metamorphic Core Complex (Eocene) and migrated to the Cyclades and the northern Menderes massif (Oligocene and Miocene), accommodated by crustal-scale detachments and a first series of core complexes (MCCs). Extension then localised in Western Turkey, the Corinth Rift and the external Hellenic arc after Messinian times, while the North Anatolian Fault penetrated the Aegean Sea. Through time the direction and style of extension have not changed significantly except in terms of localisation. The contributions of progressive slab retreat and tearing, basal drag, extrusion tectonics and tectonic inheritance are discussed and we favour a model (1) where slab retreat is the main driving engine, (2) successive slab tearing episodes are the main causes of this stepwise strain localisation and (3) the inherited heterogeneity of the crust is a major factor for localising detachments. The continental crust has an inherited strong heterogeneity and crustal-scale contacts such as major thrust planes act as weak zones or as zones of contrast of resistance and viscosity that can localise later deformation. The dynamics of slabs at depth and the asthenospheric flow due to slab retreat also have influence strain localisation in the upper plate. Successive slab ruptures from the Middle Miocene to the Late Miocene have isolated a narrow stripe of lithosphere, still attached to the African lithosphere below Crete. The formation of the North Anatolian Fault is partly a consequence of this evolution. The extrusion of Anatolia and the Aegean extension are partly driven from below (asthenospheric flow) and from above (extrusion of a lid of rigid crust).
ISSN: 0040-1951

insu-00715950
https://hal-insu.archives-ouvertes.fr/insu-00715950
https://hal-insu.archives-ouvertes.fr/insu-00715950/document
https://hal-insu.archives-ouvertes.fr/insu-00715950/file/Jolivet-Aegean_Tectonophysics-2012.pdf
DOI : 10.1016/j.tecto.2012.06.011