Éditeur(s) : HAL CCSD Geological Society
Résumé : International audience
Deformation mechanisms, long-term kinematics and evolution of fold and thrust belts subjected to erosion are studied through 2D analogue experiments involving large convergence. First-order parameters tested include (1) décollements and/or plastic layers interbedded at different locations within analogue materials and (2) synconvergence surface erosion. Weak layers, depending on their location in the model, favour deformation partitioning characterized by the simultaneous development of underplating domains in the inner part of the wedge (basal accretion) and frontal accretion where the wedge grows forward. Interaction between tectonics and surface processes influences this behaviour. Development of antiformal thrust stacks controlled by underplating shows small- and large-scale cyclicity. Thin plastic layers induce folding processes, which are studied at wedge scale. Recumbent and overturned folds, with large inverted limbs, develop in a shear-induced asymmetric deformation regime via progressive unrolling of synclinal hinges. Surface erosion and underplating at depth induce further rotation (passive tilting) and horizontalization of fold limbs. Model results give insights to discuss the mechanisms responsible for the large-scale structures (i.e. antiformal nappe stacks, klippen and kilometre-scale recumbent fold-nappes) encountered in several mountain belts such as the Montagne Noire (French Massif Central), the Galicia Variscan belt (Spain) and the northern Apennines (Italy).
ISSN: 0016-7649

hal-00937644
https://hal.archives-ouvertes.fr/hal-00937644
DOI : 10.1144/jgs2013-012

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) : HAL CCSD Elsevier
Résumé : International audience
In fold and thrust belts drainage organization and patterns of sedimentation depend conceptually on the ability or not for preexisting reaches to incise uplifting thrust sheets. In this study we investigate experimentally the dynamics of drainage network in a wedge submitted to shortening and erosion. It allows us to reproduce and to monitor the interactions between tectonics, erosion and sedimentation during the development of up to five successive thrust sheets. In the experiments channels adjust to uplift rate by both increasing their slope and narrowing their channels as it is observed in nature. The series of experiments shows that the proportion of persistent preexisting transverse channels increases with the ratio of rainfall over shortening rates. The experiments confirm the view that the competition between discharge and tectonic uplift controls along-strike variations in sediment flux in sedimentary basins by controlling the drainage organization. If the transverse channels draining a wedge are not diverted, a line-source dispersal system develops in front of the active structure. If channels are diverted in the backlimb of the frontal structure it results in point-sourced depositional systems separated by areas fed only by small channels developing in the front of the wedge. Fans accumulated in front of the active structures reveal two stages of sedimentation, one of progradation, while the frontal structure is active and a second one of valley backfilling and thrust sealing during internal deformation of the wedge. The experiments also suggest that spatial variations in rock uplift rate along a thrust front may be evidenced by minimum-discharge variations of persistent transverse channels.
ISSN: 0040-1951

insu-01252482
https://hal-insu.archives-ouvertes.fr/insu-01252482
DOI : 10.1016/j.tecto.2015.09.007

Éditeur(s) : Oxford Univ Press
Résumé : This study presents the results of a deep seismic survey across the north Algerian margin, based on the combination of 2-D multichannel and wide-angle seismic data simultaneously recorded by 41 ocean bottom seismometers deployed along a north-south line extending 180 km off Jijel into the Algerian offshore basin, and 25 land stations deployed along a 100-km-long line, cutting through the Lesser Kabylia and the Tellian thrust-belt. The final model obtained using forward modelling of the wide-angle data and pre-stack depth migration of the seismic reflection data provides an unprecedented view of the sedimentary and crustal structure of the margin. The sedimentary layers in the Algerian basin are 3.75 km thick to the north and up to 4.5-5 km thick at the foot of the margin. They are characterized by seismic velocities from 1.9 to 3.8 km s(-1). Messinian salt formations are about 1 km thick in the study area, and are modelled and imaged using a velocity between 3.7 and 3.8 km s(-1). The crust in the deep sea basin is about 4.5 km thick and of oceanic origin, presenting two distinct layers with a high gradient upper crust (4.7-6.1 km s(-1)) and a low gradient lower crust (6.2-7.1 km s(-1)). The upper-mantle velocity is constrained to 7.9 km s(-1). The ocean-continent transition zone is very narrow between 15 and 20 km wide. The continental crust reaches 25 km thickness as imaged from the most landward station and thins to 5 km over a less than 70 km distance. The continental crust presents steep and asymmetric upper- and lower-crustal geometry, possibly due to either asymmetric rifting of the margin, an underplated body, or flow of lower crustal material towards the ocean basin. Present-time deformation, as imaged from three additional seismic profiles, is characterized by an interplay of gravity-driven mobile-salt creep and active thrusting at the foot of the tectonically inverted Algerian margin.
Geophysical Journal International (0956-540X) (Oxford Univ Press), 2014-09 , Vol. 198 , N. 3 , P. 1486-1503

Droits : 2014 The Royal Astronomical Society
http://archimer.ifremer.fr/doc/00217/32836/32150.pdf
DOI:10.1093/gji/ggu179
http://archimer.ifremer.fr/doc/00217/32836/

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
U-Pb zircon and Ar-Ar amphibole and biotite ages from rocks of the West Congo Belt of Angola indicate that this area underwent two main deformation events of amphibolite facies grade at c. 540 and 490 Ma, which were followed by tectonically assisted exhumation during eastward thrusting of the hinterland domain onto the foreland domain. High-grade conditions in the West Congo Belt are 20-40 Ma younger than in the Ribeira-Araçuai Belt of Brazil, its South American counterpart, or than in the westernmost Kaoko Belt of Namibia, its African correlative. In the present state of knowledge, a more appropriate counterpart to the southern part of the West Congo Belt may be restricted to the Cabo Frio Terrane in the eastern Ribeira Belt, which yields a broadly similar evolution.
ISSN: 0954-4879

hal-00716463
https://hal.archives-ouvertes.fr/hal-00716463
DOI : 10.1111/j.1365-3121.2012.01060.x

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Gibraltar arc, spans a complex portion of the Africa-Eurasia plate boundary marked by slow oblique convergence and intermediate and deep focus seismicity. The seemingly contradictory observations of a young extensional marine basin surrounded by an arcuate fold-and-thrust belt, have led to competing geodynamic models (delamination and subduction). Geophysical data acquired in the past decade provide a test for these models and support a narrow east-dipping, subduction zone. Seismic refraction studies indicate oceanic crust below the western Gulf of Cadiz. Tomography of the upper mantle reveals a steep, east-dipping high P-wave velocity body, beneath Gibraltar. The anisotropic mantle fabric from SKS splitting shows arc-parallel "fast directions", consistent with toroidal flow around a narrow, westward retreating subducting slab. The accompanying WSW advance of the Rif-Betic mountain belt has constructed a thick pile of deformed sediments, an accretionary wedge, characterized by west-vergent thrust anticlines. Bathymetric swath‐mapping images an asymmetric embayment at the deformation front where a 2 km high basement ridge has collided. Subduction has slowed significantly since 5 Ma, but deformation of recent sediments and abundant mud volcanoes suggest ongoing activity in the accretionary wedge. Three possible origins for this deformation are discussed; gravitational spreading, overall NW-SE convergence between Africa and Iberia and finally a WSW tectonic push from slow, but ongoing roll-back subduction. In the absence of arc volcanism and shallow dipping thrust type earthquakes, evidence in favor of present-day subduction can only be indirect and remains the object of debate. Continued activity of the subduction offers a possible explanation for great (M > 8.5) earthquakes known to affect the area, like the famous 1755 Great Lisbon earthquake. Recent GPS studies show SW motion of stations in N Morocco at velocities of 3-6 mm/yr indicating the presence of an independent block, a "Rif-Betic-Alboran" microplate, situated between Iberia and Africa.
ISSN: 0040-1951

insu-00769762
https://hal-insu.archives-ouvertes.fr/insu-00769762
DOI : 10.1016/j.tecto.2012.08.038

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Dien Bien Phu (DBP) Fault strikes nearly perpendicular to the general tectonic framework, separating northwest Vietnam into two compartments. The DBP and Muong Lay granites are exposed respectively east and west of the fault. The U/Pb age of 277 ± 2 Ma obtained for the Muong Lay granite is similar to the age of the Chieng Khuong complex exposed within the Song Ma structure east of the DBP Fault. These two magmatic intrusions are considered as belonging to a same tectonic structure related to the subduction of the Song Ma Ocean under the Indochina Block during the Indosinian orogeny. The DBP Fault with a total post Permian dextral offset of 30-40 km shifts the Song Ma Suture. It could then be connected to the Ailao Shan-Shuanggou suture to the north. The undeformed DBP granite gave a U/Pb age of 230 ± 1 Ma sealing the Indosinian deformation on the fault. The Ladinian-Carnian activity of the fault is confirmed by the 40Ar/39Ar (biotite) age of 228 ± 4 Ma obtained from the paragneiss forming the fault zone. A geodynamic model is proposed to describe the various tectonic phases recorded by on the DBP Fault. It associates field data, stratigraphic observations, and geochronology analyses (U/Pb, Ar/Ar, fission tracks). Following the Late Triassic exhumation of the granite and the end of the Indosinian orogeny marked by the Norian unconformity, the granite was buried under Jurassic and Lower Cretaceous sediments. A strong cooling event during the early Late Cretaceous (100 Ma) is associated with the reactivation of the DBP Fault and the accommodation of a southward thrusting of the Song Da terrane onto the Truong Son Belt. This newly recognised tectonic phase could be associated to the subduction of the Paleo-Pacific plate under the Indochina Block. No data are available yet to constrain the Tertiary evolution of the DBP system. However, the Tertiary deformation is likely similar to the Cretaceous one.
ISSN: 1342-937X

insu-01015379
https://hal-insu.archives-ouvertes.fr/insu-01015379
DOI : 10.1016/j.gr.2013.07.018

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : TECTO LITHO
On the basis of a section across the northwestern Alpine wedge and foreland basin, analogue modeling is used to investigate the impact of surface processes on the orogenic evolution. The basis model takes into account both structural and lithological heritages of the wedge. During shortening, erosion and sedimentation are performed to maintain a critical wedge. Frontal accretion leads to the development of a foreland thrust belt; underplating leads to the formation of an antiformal nappe stack in the internal zones. Important volumes of analogue materials are eroded out of the geological record, which in the case of the Alps suggests that the original lengths and volumes may be underestimated. The foreland basin evolves differently depending on the amounts of erosion/sedimentation. Its evolution and internal structuring is governed by the wedge mechanics, thought to be the main controlling mechanism in the development of the Molasse basin in a feedback interaction with surface processes.
ISSN: 0278-7407

hal-00404424
https://hal.archives-ouvertes.fr/hal-00404424
DOI : 10.1029/2006TC002048

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The deep structure and deformation mechanisms of the Longmen Shan thrust belt (Sichuan, China), at the eastern border of the Tibetan plateau, were largely debated after the devastating Mw 7.9 Wenchuan earthquake (2008). Recent geophysical studies and field investigations have been focused on the active motion of the major Beichuan fault, which ruptured during the earthquake. However, the total exhumation across the fault still remains unclear. In the hanging wall of the Beichuan fault, the South China block is exhumed in the Pengguan massif. Close to the Beichuan fault, the rocks of the Pengguan massif underwent greenschist facies metamorphism associated with brittle-ductile deformation. No metamorphism is observed in the footwall of the fault. In this study, we characterize and date the metamorphic history recorded in the hanging wall of the Beichuan fault in order to constrain the depth and timing of exhumation of the rocks of the Pengguan massif along the fault. A high-resolution petrological approach involving chemical analyses and X-ray maps was used to analyze the micrometric metamorphic minerals. The P-T conditions of the greenschist facies metamorphic event were estimated by an inverse multi-equilibrium thermodynamic approach. The results, 280 ± 30 °C and 7 ± 1 kbar, suggest that the rocks of the Pengguan massif were exhumed from ca. 20 km depth. Our results underline the importance of the thrusting component in the long-term behavior of the Beichuan fault and provide a minimal depth at which the fault is rooted. In situ laser ablation 40Ar/39Ar dating of metamorphic white mica revealed that the greenschist overprint occurred at 135–140 Ma.The Pengguan massif was therefore partially thrusted along the Beichuan fault during the Lower Cretaceous, long before the Eocene-Miocene exhumation phase which is well-constrained by low-temperature thermochronology. Our results provide the first independent depth information for the exhumation history of the Pengguan massif and reveal a previously undocumented Lower Cretaceous tectonic event that marks the onset of the thick-skinned deformation in the external domain of the Longmen Shan (East of the Wenchuan Fault).
ISSN: 0743-9547

hal-01685556
https://hal.archives-ouvertes.fr/hal-01685556
DOI : 10.1016/j.jseaes.2017.04.003

Éditeur(s) : HAL CCSD
Résumé : 1 p.
International audience
The 12th May 2008 Wenchuan earthquake in the Longmen Shan occurred on a large thrust fault largely inherited from an Indosinian structure itself probably controlled by an older structural heritage of the South China block continental margin. Within the whole northeast Tibet region, such a structural inheritance has had a major impact on the Tertiary deformation. It appears of primary importance to assess the pre-Tertiary tectonic evolution of the main blocks involved to understand the actual deformation in the eastern edge of Tibet. Over the past decades, the Proterozoic to Cenozoic tectonic, metamorphic and geochronologic history of the Longmen Shan and Songpan Garzê area have been largely studied. We present a synthesis of the tectonic evolution of the Songpan Garzê fold and thrust belt from Triassic to present. The Songpan-Garzê belt was formed during closure of a wide oceanic basin ?lled with a thick (5 to 15 km) sequence of Triassic ?yschoid sediments. Closure of the basin due to Triassic subduction involved strong shortening, intense folding and faulting of the Triassic series. A large-scale décollement, that presently outcrops along the eastern boundary of the belt (Danba area), allowed the growth of a wide and thick accretionary wedge. It develops in the Paleozoic and Triassic series and separates the accretionary prism from an autochthonous crystalline basement which shares many similarities with the basement of the Yangtze Craton (0.7-0.9 Ga). To the north and northwest, below the thickened Triassic series of the belt, the composition (oceanic or continental) of the basement remains unknown. During the Indosinian orogeny the emplacement of orogenic granites (220 - 150 Ma) was associated to crustal thickening. The isotopic composition of granitoids shows that their magma source were predominantly derived from melting of the proterozoic basement with varying degrees of sedimentary material and negligible mantle source contribution. In the Danba area, the décollement outcrops in a large tertiary antiform with a NNW-SSE axis. It has been exhumed too in the hanging wall of the NE-SW faults of the Tertiary Longmen-Shan belt that marks the present day transition from the Tibetan plateau to the Sichuan basin. These faults have episodically absorbed signi?cant shortening since the Late Triassic. The amount and precise timing of post-triassic deformation are dif?cult to constrain especially because of the dif?culty to isolate the tertiary thermochronological signal from the protracted late Triassic - Cretaceous thermal history. Nonetheless it is generally accepted that Jurassic - Cretaceous tectonism did not modi?ed the general Triassic architecture of eastern Tibet contrarily to the Tertiary deformation. The long-term cooling histories obtained on Mesozoic granites and on the metamorphic series of the Danba dome are very similar showing a very slow and regular cooling during Jurassic andCretaceous, con?rming the absence of major tectonic event between c.a. 150 and 30 Ma. Low temperature thermochronology data indicate that ?nal exhumation and cooling occurred in theTertiary with an acceleration between 10 and 5 Ma along the major tectonic structures. Within the Longmen Shan range, a total denudation of 7 to 10 km is estimated for the late Cenozoic period. Similar amounts of late Tertiary denudation have been estimated along an east-west section across the Xianshuihe fault
Asian climate and tectonics seminar
Utrecht, Netherlands

insu-00610298
https://hal-insu.archives-ouvertes.fr/insu-00610298
DOI : 10.1016/j.jseaes.2010.03.008

Éditeur(s) : HAL CCSD Geological Society of London
Résumé : The Zagros Simply Folded Belt (ZSFB) is an active fold-and-thrust belt resulting from the still continuing continental collision between the Arabian plate and the Iranian plate, which probably started in the Oligocene. The present-day shortening (N25°) is well documented by focal mechanisms of earthquakes and global positioning system (GPS) surveys. We propose in this study a comparison of published palaeostress markers, including magnetic fabric, brittle deformation and calcite twinning data. In addition, we describe the magnetic fabric from Palaeocene carbonates (10 sites) and Mio-Pliocene clastic deposits (15 sites). The magnetic fabrics are intermediate, with magnetic foliation parallel to the bedding, and a magnetic lineation mostly at right angles to the shortening direction. This suggests that the magnetic fabric retains the record of an early layer-parallel shortening (LPS) that occurred prior to folding. The record of LPS allows the identification of originally oblique folds such as the Mand Fold, which have developed in front of the Kazerun Fault. The shape parameter of the magnetic fabric indicates a weak strain compatible with the development of detachment folds in the ZSFB. The palaeostress datasets, covering the Palaeocene to Pleistocene time interval, support several folding episodes accompanied by a counter-clockwise rotation of the stress field direction. The Palaeocene carbonates in the ZSFB record a N47 LPS during early to middle Miocene detachment folding in the High Zagros Belt (HZB). The Mio-Pliocene clastic deposits recorded a N38 LPS prior to and during detachment folding within the ZSFB at the end of the Miocene-Pliocene. Similarly, fault slip and calcite twin data from the ZSFB also support a counter-clockwise rotation from NE to N20 between the pre-folding stage and the late rejuvenation of folds. This counter-clockwise trend of palaeostress data agrees with fault slip data from the HZB. During the late stage of folding in the ZSFB, the Plio-Quaternary palaeostress trends are consistently parallel to the present-day shortening direction.
Tectonic and stratigraphic evolution of Zagros and Makran during the Mesozoic-Cenozoic

hal-00545036
https://hal.archives-ouvertes.fr/hal-00545036
DOI : 10.1144/SP330.6

Éditeur(s) : HAL CCSD
Résumé : International audience
High Pressure - Low Temperature (HP-LT) rocks testify for burying and exhumation of crustal material in subduction zones. The question of their exhumation is nevertheless still unclear. The Aegean domain offers several HP-LT belts. Especially, the Attic-Cycladic Blueschist unit (ACBU) is an example of a HP-LT unit exhumed in a convergent and then in a divergent context. It actually appears in metamorphic core complexes (MCCs) formed in the back-arc of the subduction. The syn-convergence "message" is however difficult to read because of the post-convergence structural and thermal overprint that accompanied the formation of the MCCs. Particularly, the geometry, the timing and the amount of the syn-orogenic exhumation remain unclear. We investigate theses questions with metamorphic petrology (Andros and Ios islands) and phengite population, single grain and in situ 40Ar-39Ar geochronology (Andros, Tinos, Syros and Ios islands). Based on these new constraints and a synthesis of published data, we are able to refine the geometry, the timing and the modes of the exhumation of the ACBU. Data from the whole Cyclades exhibit little differences in the age and P-T conditions at the successive stages of syn-orogenic exhumation. The peak of pressure (500±50 °C-18±1 kbar) has been reached at 50-55 Ma. The onset of the exhumation occurred at 40-45 Ma in blueschist facies conditions, between a basal thrust and a summital detachment. The following decompression was accompanied by cooling until 30-35 Ma (400±50 °C-8±1 kbar). At that time, the boundary conditions switched to extension. The change in boundary conditions is recorded by slowing of the exhumation and isobare heating. The conditions of post-orogenic exhumation differ from an island to another. The onset of post-orogenic exhumation is dated around 30 Ma in the northern Cyclades and 25 Ma in the southern Cyclades. It is related to top-to-the-North deformation in all the studied domain. The end of ductile deformation below the detachments is also diachronous (21 Ma in the North and 18 Ma in the South). Finally, we propose a model for the final steps of the exhumation related to the intrusion of granitic bodies around 14 Ma.
American Geophysical Union, Fall Meeting
San Francisco, United States

insu-00860510
https://hal-insu.archives-ouvertes.fr/insu-00860510
BIBCODE : 2010AGUFM.T23C2301L

Éditeur(s) : HAL CCSD
Résumé : International audience
In the frame of the Africa-Europe convergence, the Mediterranean tectonic system presents a complex interaction between subduction rollback and upper-plate deformation during the Tertiary. The western Mediterranean is characterized by the exhumation of the largest subcontinental mantle massif worldwide (the Ronda Peridotite) and a narrow arcuate geometryacross the Gibraltar arc within the Betic-Rif belt (the internal part being called the Alboran domain), where the relationship between slab dynamics and surface tectonics is not well understood. New structural and geochronological data are used to argue for 1/ hyperstrechting of the continental lithosphere allowing extensional mantle exhumation to shallow depths, followed by 2/ lower miocene thrusting. Two Lower Miocene E-W-trending strike-slip corridors played a major role in the deformation pattern of the Alboran Domain, in which E-W dextral strike-slip faults, N60°-trending thrusts and N140°-trending normal faults developed simultaneously during dextral strike-slip simple shear. The inferred continuous westward translation of the Alboran Domain is accommodated by a major E-W-trending lateral ramp (strike-slip) and a N60°-trending frontal thrust. At lithosphere-scale, we interpret the observed deformation pattern as the upper-plate expression of a lateral slab tear and of its westward propagation since Lower Miocene. The crustal emplacement of the Ronda Peridotites occurred at the onset of this westward motion.The Miocene tectonics of the western Alboran is therefore marked by the inversion of a continental rift, triggered by shortening of the upper continental plate and accommodated by E-W dextral strike-slip corridors. During thrusting and westward displacement of the Alboran domain with respect to Iberia, the hot upper plate, which involved the previously exhumed sub-continental mantle, underwent fast cooling.
AGU Fall Meeting 2015
San Francisco, United States

insu-01242043
https://hal-insu.archives-ouvertes.fr/insu-01242043

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
After Jurassic rifting, numerous carbonate platforms (i.e., the Orizaba, Cordoba and Golden Lane-Tuxpan platforms) developed during the Lower and Middle Cretaceous episode of thermal subsidence along the western passive margin of the Gulf of Mexico, with intervening basinal domains (i.e., the Tampico-Misantla, Zongolica, Veracruz and Deep Gulf of Mexico - DGM - basins).;During the Late Cretaceous-Paleocene, the east-verging Sierra Madre Oriental thrust belt developed, resulting in tectonic uplift and unroofing of the allochthonous units (i.e. tectonic units made up of former Orizaba and Cordoba platforms and Zongolica Basin series). This new topography provided also an important source of clastics to feed the adjacent foredeep, where coeval tectonic loading accounted for the bending of the foreland lithosphere. However, shallow water facies or even emersion persisted until the Eocene in the forebulge area (at the present location of the Golden Lane), preventing locally the clastics to reach the DGM. This topographic barrier was ultimately bypassed by the clastics only during the Oligocene and Neogene, once (1) the prograding clastic wedge had exceeded accommodation, and (2) the long lasting thermal subsidence of the passive margin could overpass the effect of the bending and force the former bulge to sink.;Numerous paleo-thermo-meters (Tmax, Ro), paleo-thermo-barometers (fluid inclusions), PVT and coupled forward kinematic and thermal modeling have been used to calibrate and date the progressive unroofing of the thrust belt. Coupled tectonic and sedimentologic modeling was applied in the foreland to predict the distribution of sand versus shale ratios in the Oligocene to Plio-Quaternary clastic sedimentary wedge of the passive margin, where gravitational gliding of post-Eocene series occurred during the Neogene along major listric faults.;Mantle dynamics are advocated as the main process accounting for post-orogenic uplift and regional tilting of the basement, which initiated a massive transfer of sediments from the Cordillera towards the Gulf of Mexico, from Oligocene onward, resulting in a destabilization and gravitational collapse of the western slope of the Gulf of Mexico in Neogene times.
ISSN: 0040-1951

hal-00445248
https://hal.archives-ouvertes.fr/hal-00445248
DOI : 10.1016/j.tecto.2009.04.012

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
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 Elsevier
Résumé : International audience
In fold-and-thrust belts, shortening is mainly accommodated by thrust faults which are preferential zones for recrystallisation and mass transfer. This study focuses on a detachment fault related to the emplacement of the Monte Perdido thrust unit in the southern Pyrenees. The studied fault zone consists of a 10 m thick intensively foliated phyllonite developed within the Millaris marls, of Eocene age. The lithological homogeneity of the hanging wall and footwall allows us to compare the Millaris marls outside the fault zone with the highly deformed marls located in the fault zone and to quantify the chemical, mineralogical and volumetric changes related to deformation processes along the fault. The Millaris marls are composed of detrital quartz, illite, chlorite, minor albite and pyrite, in a micritic calcite matrix. In the fault zone, the cleavage planes are marked by clay minerals and calcite ± chlorite veins attest to fluid-mineral interactions during deformation. The mineral proportions in all samples from both the fault zone and Millaris marls have been quantified by two methods: (1) X-ray diffraction and Rietveld refinement, and (2) bulk chemical analyses as well as microprobe analyses to calculate modal composition. The excellent agreement between the results of these two methods allows us to estimate mineralogical variations using a modification of the Gresens' equation. During fault activation, up to 45 wt% of calcite was lost while the amounts of quartz and chlorite remained unchanged. Illite content remained constant to slightly enriched. The mineralogical variations were coupled with a significant volume loss (up to 45%) mostly due to the dissolution of micritic calcite grains. Deformation was accompanied by pressure solution and phyllosilicates recrystallisation. These processes accommodated slip along the fault. They required fluids as catalyst, but they did not necessitate major chemical transfers.
ISSN: 0264-8172

hal-00976361
https://hal.archives-ouvertes.fr/hal-00976361
DOI : 10.1016/j.marpetgeo.2013.12.016

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Gulf of Cadiz lies astride the complex plate boundary between Africa and Eurasia west of the Betic-Rif mountain belt. We report on the results of recent bathymetric swathmapping and multi-channel seismic surveys carried out here. The seafloor is marked by contrasting morphological provinces, spanning the SW Iberian and NW Moroccan continental margins, abyssal plains and an elongate, arcuate, accretionary wedge. A wide variety of tectonic and gravitational processes appear to have shaped these structures. Active compressional deformation of the wedge is suggested by folding and thrusting of the frontal sedimentary layers as well as basal duplexing in deeper internal units. There is evidence for simultaneous gravitational spreading occurring upslope. The very shallow mean surface and basal slopes of the accretionary wedge (1° each) indicate a very weak decollement layer, geometrically similar to the Mediterranean Ridge accretionary complex. Locally steep slopes (up to 10°) indicate strongly focused, active deformation and potential gravitational instabilities. The unusual surface morphology of the upper accretionary wedge includes “raft-tectonics” type fissures and abundant sub-circular depressions. Dissolution and/or diapiric processes are proposed to be involved in the formation of these depressions.
ISSN: 0264-8172

insu-00401683
https://hal-insu.archives-ouvertes.fr/insu-00401683
DOI : 10.1016/j.marpetgeo.2007.11.008

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This paper provides a synthesis of current data and interpretations on the crustal structure of the Pyrenean-Cantabrian orogenic belt, and presents new tectonic models for representative transects. The Pyrenean orogeny lasted from Santonian (~84 Ma) to early Miocene times (~20 Ma), and consisted of a spatial and temporal succession of oceanic crust/exhumed mantle subduction, rift inversion and continental collision processes at the Iberia-Eurasia plate boundary. A good coverage by active-source (vertical-incidence and wide-angle reflection) and passive-source (receiver functions) seismic studies, coupled with surface data have led to a reasonable knowledge of the present-day crustal architecture of the Pyrenean-Cantabrian belt, although questions remain. Seismic imaging reveals a persistent structure, from the central Pyrenees to the central Cantabrian Mountains, consisting of a wedge of Eurasian lithosphere indented into the thicker Iberian plate, whose lower crust is detached and plunges northwards into the mantle. For the Pyrenees, a new scheme of relationships between the southern upper crustal thrust sheets and the Axial Zone is here proposed. For the Cantabrian belt, the depth reached by the N-dipping Iberian crust and the structure of the margin are also revised.The common occurrence of lherzolite bodies in the northern Pyrenees and the seismic velocity and potential field record of the Bay of Biscay indicate that the precursor of the Pyrenees was a hyperextended and strongly segmented rift system, where narrow domains of exhumed mantle separated the thinned Iberian and Eurasian continental margins since the Albian-Cenomanian. The exhumed mantle in the Pyrenean rift was largely covered by a Mesozoic sedimentary lid that had locally glided along detachments in Triassic evaporites. Continental margin collision in the Pyrenees was preceded by subduction of the exhumed mantle, accompanied by the pop-up thrust expulsion of the off-scraped sedimentary lid above. To the west, oceanic subduction of the Bay of Biscay under the North Iberian margin is supported by an upper plate thrust wedge, gravity and magnetic anomalies, and 3D inclined sub-crustal reflections. However, discrepancies remain for the location of continent-ocean transitions in the Bay of Biscay and for the extent of oceanic subduction. The plate-kinematic evolution during the Mesozoic, which involves issues as the timing and total amount of opening, as well as the role of strike-slip drift, is also under debate, discrepancies arising from first-order interpretations of the adjacent oceanic magnetic anomaly record.
ISSN: 0040-1951

insu-01683989
https://hal-insu.archives-ouvertes.fr/insu-01683989
https://hal-insu.archives-ouvertes.fr/insu-01683989/document
https://hal-insu.archives-ouvertes.fr/insu-01683989/file/teixell-tectono-2018.pdf
DOI : 10.1016/j.tecto.2018.01.009

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
[1] This article presents (U-Th)/He thermochronological data from the Longmen Shan belt, eastern Tibet. Located between the Songpan-Garze terrane and the Yangtze craton, this mountain range is one of the steepest margins of the Tibetan Plateau and an important area for the comprehension of the mechanisms that control the dynamics of such plateau borders in terms of spatial distribution of deformation or timing of topographic building. We describe several age-elevation transects and perform forward modeling of our data to derive quantitative information on the exhumation of the range. A major phase of exhumation started at 8–11 Ma, with an average rate of $0.65 mm a À1. Comparison of zircon and apatite ages indicates that the eastern part of the range may have experienced a significant decrease in exhumation since 2–3 Ma. We use the distribution of finite exhumation across the major faults of the area to quantify their dip-slip throw rate over the last 10 Ma. The Beichuan Fault, which was activated during the 2008 Sichuan earthquake, is the major active structure of the Longmen Shan since the late Miocene, with an average thrusting slip rate between 0.4 and 1 mm a À1. Conversely, over the same time period, only minor dip-slip activity occurred on the Wenchuan Fault Zone. This distribution in space and time of exhumation and deformation is discussed and compared to the different proposed models for the geodynamical evolution of the eastern Tibetan margin. It also provides an important long-term perspective to put in context the destructive 2008 Sichuan earthquake that struck the central Longmen Shan.
ISSN: 0278-7407

hal-01577059
https://hal-amu.archives-ouvertes.fr/hal-01577059
https://hal-amu.archives-ouvertes.fr/hal-01577059/document
https://hal-amu.archives-ouvertes.fr/hal-01577059/file/godard2009late.pdf
DOI : 10.1029/2008TC002407