Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Mosha and North Tehran faults correspond to the nearest seismic sources for the northern part of the Tehran megacity. The present-day structural relationships and the kinematics of these two faults, especially at their junction in Lavasanat region, is still a matter of debate. In this paper, we present the results of a morphotectonic analysis (aerial photos and field investigations) within the central part of the Mosha and eastern part of the North Tehran faults between the Mosha valley and Tehran City. Our investigations show that, generally, the traces of activity do not follow the older traces corresponding to previous long-term dip-slip thrusting movements. The recent faulting mainly occurs on new traces trending E-W to ENE-WSW affecting Quaternary features (streams, ridges, risers, and young glacial markers) and cutting straight through the topography. Often defining en-echelon patterns (right- and left-stepping), these new traces correspond to steep faults with either north- or south-dipping directions, along which clear evidences for left-lateral strike-slip motion are found. At their junction zone, the two sinistral faults display a left-stepping en-echelon pattern defining a positive flower structure system clearly visible near Ira village. Further west, the left-lateral strike-slip motion is transferred along the ENE-WSW trending Niavaran fault and other faults. The cumulative offsets associated with this left-lateral deformation is small compared with the topography associated with the previous Late Tertiary thrusting motion, showing that it corresponds to a recent change of kinematics.
ISSN: 0040-1951

hal-00617778
https://hal.archives-ouvertes.fr/hal-00617778
DOI : 10.1016/j.tecto.2010.09.013

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
The Ama Drime range located at the transition between the high Himalayan range and south Tibet is a N-S active horst that offsets the South Tibetan Detachment System (STDS). Within the horst, a paragneissic unit, possibly attributed to the upper Himalayan crystalline series, overly the lower Himalayan crystalline series Ama Drime orthogneissic unit containing large metabasite layers and pods that have experienced pressure >= 1.4 GPa. Combining structural analysis with new and published pressure-temperature (P-T) estimates as well as U-Th/Pb, Ar-39/Ar-40 and (U-Th)/He ages, the P-T-deformation-time (P-T-D-t) paths of the main units within and on both sides of the horst are reconstructed. They imply that N-S normal faults initiated prior to 11 Ma and have accounted for a total exhumation <= 0.6 GPa (22 km) that probably occurred in two phases: the first one until similar to 9 Ma and the second one since 6 to 4 Ma at a rate of similar to 1 mm/yr. In the Ama Drime unit, 1 to 1.3 GPa (37 to 48 km) of exhumation occurred after partial melting since similar to 30 Ma until similar to 13 Ma, above the Main Central Trust (MCT) and below the STDS when these two fault systems were active together. The switch from E-W (STDS) to N-S (Ama Drime horst) normal faulting between 13 and 12 Ma occurs at the time of propagation of thrusting from the MCT to the Main Boundary Thrust. These data are in favor of a wedge extrusion or thrust system rather than a crustal flow model for the building of the Himalaya. We propose that the kinematics of south Tibet Cenozoic extension phases is fundamentally driven by the direction and rate of India underthrusting.
ISSN: 0278-7407

hal-00486405
https://hal.archives-ouvertes.fr/hal-00486405
DOI : 10.1029/2009TC002551

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In the framework of the Africa-Europe convergence, the Mediterranean system presents a complex interaction between subduction rollback and upper-plate deformation during the Tertiary. The western end of the system shows a narrow arcuate geometry across the Gibraltar arc, the Betic-Rif belt, in which the relationship between slab dynamics and surface tectonics is not well understood. The present study focuses on the Western Betics, which is characterized by two major thrusts: 1/ the Internal/External Zone Boundary limits the metamorphic domain (Alboran Domain) from the fold-and-thrust belts in the External Zone; 2/ the Ronda Peridotites Thrust allows the juxtaposition of a strongly attenuated lithosphere section with large bodies of sub-continental mantle rocks on top of upper crustal rocks. New structural data show that two major E-W strike-slip corridors played a major role in the deformation pattern of the Alboran Domain, in which E-W dextral strike-slip faults, N60 thrusts and N140 normal faults developed simultaneously during dextral strike-slip simple shear. Olistostromic sediments of Lower Miocene age were deposited and deformed in this tectonic context and hence provide an age estimate for the inferred continuous westward translation of the Alboran Domain that is accommodated by an E-W lateral (strike-slip) ramp and a N60 frontal thrust. The crustal emplacement of large bodies of sub-continental mantle may occur at the onset of this westward thrusting in the Western Alboran domain. At lithosphere-scale, we interpret the observed deformation pattern as the subduction upper-plate expression of a lateral slab tear and its westward propagation since Lower Miocene.
ISSN: 0040-1951

insu-01163695
https://hal-insu.archives-ouvertes.fr/insu-01163695
https://hal-insu.archives-ouvertes.fr/insu-01163695/document
https://hal-insu.archives-ouvertes.fr/insu-01163695/file/Frasca-2015.pdf
DOI : 10.1016/j.tecto.2015.05.017

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Lithospheric-scale faults related to oblique subduction are responsible for some of the most hazardous earthquakes reported worldwide. The mega-thrust in the Sunda sector of the Sumatran oblique subduction has been intensively studied, especially after the infamous 2004 Mw 9.1 earthquake, but its onshore kinematic complement within the Sumatran subduction, the transform Sumatran Fault System, has received considerably less attention. In this paper, we apply a combination of analysis of Digital Elevation Models (ASTER GDEM) and field evidence to resolve the kinematics of the leading edge of deformation of the northern sector of the Sumatran Fault System. To this end, we mapped the northernmost tip of Sumatra, including the islands to the northwest, between 4.5°N and 6°N. Here, major topographic highs are related to different faults. Using field evidence and our GDEM structural mapping, we can show that in the area where the fault bifurcates into two fault strands, two independent kinematic regimes evolve, both consistent with the large-scale framework of the Sumatran Fault System. Whereas the eastern branch is a classic Riedel system, the western branch features a fold-and-thrust belt. The latter contractional feature accommodated significant amounts (c. 20%) of shortening of the system in the study area. Our field observations of the tip of the NSFS match a strain pattern with a western contractional domain (Pulau Weh thrust splay) and an eastern extensional domain (Pulau Aceh Riedel system), which are together characteristic of the tip of a propagating strike-slip fault, from a mechanical viewpoint. For the first time, we describe the strain partitioning resulting from the propagation of the NSFS in Sumatra mainland. Our study helps understanding complex kinematics of an evolving strike-slip system, and stresses the importance of field studies in addition to remote sensing and geophysical studies.
ISSN: 0040-1951

hal-01467196
https://hal.archives-ouvertes.fr/hal-01467196
DOI : 10.1016/j.tecto.2016.04.050

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Longmen Shan (Sichuan, China) is characterised by an unusual morphology which results from a Triassic prism tectonics and a more recent Neogene thick-skin thrusting. Among its specific features is the high elevation of the internal zones in continuity with the Songpan Garze fold-and-thrust belt (SG), which is associated with an abrupt 20 km Moho offset between the Sichuan Basin and the Tibetan plateau as revealed by the analysis of teleseismic data acquired by a dense seismic network. The jump in crustal thickness is located at the apex of the Wenchuan shear zone (WSZ) and marks the western boundary of the metamorphosed units of SG characterized by temperatures varying from 590 degrees C down to 300 degrees C as commonly observed in mature accretionary wedges. Both the structural style marked by intense shortening in tight kink folds and geophysical data suggest the presence of an horizontal discontinuity at similar to 15 km depth over a thick crust (similar to 63 km).;The Longmen Shan east of the WSZ is characterized by thick-skin detachment which thrusts the internal sedimentary units and the Proterozoic basement over the series of the Sichuan Basin deposited on a thinner crust of similar to 44 km thick. The major front is the Beichuan Fault Zone (BFZ) which brought the internal zones onto Triassic and Jurassic series with lower temperatures (less than 400 degrees C). Locally, temperatures of similar to 425 degrees C are found just below the klippes.;These results are in agreement with an original contact of the SG zone represented by an accretionary wedge of sediments thrusted over the margin of the continental crust of the Yangtze craton in the early stage (Indosinian) of the evolution. The present-day slow E-W component of the convergence, added to the difference in crustal thickness caused the Yangtze crust to indent the Songpan Tibetan crust which was softened by a high thermal regime. As a response the edge of the Tibet crust was inflated to the bottom (up to 70 km), whereas to the top, the crystalline massif were exhumed and pushed the deformation eastward as emerging and blind thrusts. This configuration reflects a moderate shortening of the crust which behaves as a soft thick material abutting the resistant and cold Yangtze crust.
ISSN: 0040-1951

hal-00534849
https://hal.archives-ouvertes.fr/hal-00534849
DOI : 10.1016/j.tecto.2010.03.018

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : Structural, metamorphic, and geochronologic work shows that the Ampelos/Dilek nappe of the Cycladic blueschist unit in the eastern Aegean constitutes a wedge of high-pressure rocks extruded during early stages of orogeny. The extrusion wedge formed during the incipient collision of the Anatolian microcontinent with Eurasia when subduction and deep underthrusting ceased and the Ampelos/Dilek nappe was thrust southward over the greenschist-facies Menderes nappes along its lower tectonic contact, the Cycladic-Menderes thrust, effectively cutting out a ∼30- to 40-km-thick section of crust. The upper contact of the Ampelos/Dilek extrusion wedge is the top-to-the-NE Selçuk normal shear zone, along which the Ampelos/Dilek nappe was exhumed by ∼30–40 km. Detailed Rb-Sr and 40Ar/39Ar dating of mylonites demonstrates that both shear zones operated between 42 and 32 Ma. There is no evidence for episodic motion during the ∼10 Myr life span of the shear zones, suggesting that both shear zones operated in a steady, nonepisodic fashion. Our data provide supporting evidence that simultaneous thrust-type and normal sense shearing can accomplish the early exhumation of deep-seated rocks
ISSN: 0278-7407

hal-00405013
https://hal.archives-ouvertes.fr/hal-00405013
DOI : 10.1029/2005TC001872

Éditeur(s) : HAL CCSD
Résumé : National audience
Crustal-scale models for the Pyrenees based on ECORS reflection profileshave around 20 years now. In recent years, new understandingswere gained on the reconstruction to the preorogenic times, namelya scenario of extreme crustal attenuation and mantle exhumation ; inturn, this has implications on the interpretation of the present-day structure,as new models for the chain must consider feedbacks between themid-Cretaceous hyperextension and the Pyrenean inversion. On the WcentralPyrenean traverse, the southern part comprises 3 S-vergent basementthrust units, the Lakora, Gavarnie and Guarga units, flanked by thedetached cover of the Jaca piggyback basin and the Ebro basin, wherethe Mesozoic is thin and Late Cretaceous-Tertiary synorogenic carbonateand detrital sequences record a southward depocenter migration.To the N, the Chaînons Béarnais belt (CB) is a system of Jurassic to LowerCretaceous carbonate anticline ridges separated by synclines withthick Albian-Cenomanian flysch, covered to the north by Upper Cretaceousflysch sequences. The CB is thrust southwards together with theLakora thrust unit and northwards onto the Aquitaine basin. CB foldinglargely results from the rising and squeezing of diapirs initiated duringthe Jurassic-Early Cretaceous extension. Pieces of crust and mantle liftedin the diapirs attest that the CB derive from a Cretaceous domainof hyperextended continental crust and exhumed mantle. Moho reflectionsin the ECORS-Arzaq profile constrain the present deep structure.Restoration leads to a Mesozoic cover detachment over the N-Iberianand S-European margins. Inversion began by subduction of the exhumedmantle and folding and pop-up thrusting of the CB cover onto themargins. From the mid-late Eocene onwards, continental collision wasaccommodated by wedging and thrust stacking in the Iberian crust, involvingthe piggyback formation of S-vergent basement thrusts in theupper crust, and the northward subduction of the lower crust.
24 ème Réunion des sciences de la Terre 2014
Pau, France

insu-01080831
https://hal-insu.archives-ouvertes.fr/insu-01080831

Éditeur(s) : Amer Geophysical Union
Résumé : After the January 12, 2010, Haiti earthquake, we deployed a mainly offshore temporary network of seismologic stations around the damaged area. The distribution of the recorded aftershocks, together with morphotectonic observations and mainshock analysis, allow us to constrain a complex fault pattern in the area. Almost all of the aftershocks have a N-S compressive mechanism, and not the expected left-lateral strike-slip mechanism. A first-order slip model of the mainshock shows a N264 degrees E north-dipping plane, with a major left-lateral component and a strong reverse component. As the aftershock distribution is sub-parallel and close to the Enriquillo fault, we assume that although the cause of the catastrophe was not a rupture along the Enriquillo fault, this fault had an important role as a mechanical boundary. The azimuth of the focal planes of the aftershocks are parallel to the north-dipping faults of the Transhaitian Belt, which suggests a triggering of failure on these discontinuities. In the western part, the aftershock distribution reflects the triggering of slip on similar faults, and/or, alternatively, of the south-dipping faults, such the Trois-Baies submarine fault. These observations are in agreement with a model of an oblique collision of an indenter of the oceanic crust of the Southern Peninsula and the sedimentary wedge of the Transhaitian Belt: the rupture occurred on a wrench fault at the rheologic boundary on top of the under-thrusting rigid oceanic block, whereas the aftershocks were the result of the relaxation on the hanging wall along pre-existing discontinuities in the frontal part of the Transhaitian Belt. Citation: Mercier de Lepinay, B., et al. (2011), The 2010 Haiti earthquake: A complex fault pattern constrained by seismologic and tectonic observations, Geophys. Res. Lett., 38, L22305, doi:10.1029/2011GL049799.
Geophysical Research Letters (0094-8276) (Amer Geophysical Union), 2011-11 , Vol. 38 , N. L22305 , P. 7 p.

Droits : 2011 by the American Geophysical Union
http://archimer.ifremer.fr/doc/00054/16557/14071.pdf
DOI:10.1029/2011GL049799
http://archimer.ifremer.fr/doc/00054/16557/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In the Chalkidiki Peninsula of northern Greece a thrust complex made of a basement (Vertiskos Unit), a cover (Circum–Rhodope belt) and arc/back-arc units (Chortiatis Magmatic Suite and eastern Vardar Ophiolites) is exposed in the Chalkidiki Peninsula of northern Greece. The complex forms the western part of the Rhodope Metamorphic Province and lies on the hanging-wall of the Kerdylion Detachment, the structure responsible for the exhumation of the Southern Rhodope Core Complex and the most prominent and visible ductile structure related to the Tertiary Aegean extension. The Chalkidiki thrust complex arguably preserves a complete record of Cretaceous deformation and related fabrics. In this contribution we describe the geometry of foliation, stretching lineation and shear sense(s) on a regional scale. The regional foliation strikes NW–SE and displays different patterns in the three studied units: (i) dominantly dipping at low angle in the Vertiskos Unit, (ii) affected by upright folding in the Circum–Rhodope belt and (iii) systematically steeply dipping to the NE in the Chortiatis Magmatic Suite. Stretching lineation trend dominantly SW–NE in the three mentioned units. On the basis of new mapping, neglecting local perturbations and deformation related to Tertiary extension, we infer the regional kinematics of Cretaceous syn-metamorphic thrusting and subsequent exhumation of the metamorphic units. Thrusting took place toward the SW (in present-day coordination) and the related fabrics are recorded throughout the metamorphic pile. On the contrary, exhumation-related fabrics are related to shear toward the NE and are preferentially recorded in the uppermost part of the metamorphic pile suggesting that extension was more localised and of less finite intensity compared to thrusting.
ISSN: 0040-1951

insu-01231485
https://hal-insu.archives-ouvertes.fr/insu-01231485
DOI : 10.1016/j.tecto.2015.09.034

Éditeur(s) : HAL CCSD MAIK Nauka/Interperiodica
Résumé : Interaction between surface processes and deep tectonic processes plays a key role in the structural evolution, kinematics and exhumation of rocks in orogenic wedges. The deformation patterns observed in analogue models applied to natural cases of present active or ancient mountain belts reflect several first order processes that result of these interactions. Internal strain partitioning due to mechanical behaviour of a thrust wedge has a strong impact on the vertical component of displacement of tectonic units that in return favour erosion in domains of important uplift. Such strain partitioning is first controlled by tectonic processes, but surface processes exert a strong feed back on wedge dynamics. Indeed, material transfer in thrust wedges not only depends on its internal dynamics, it is also influenced by climate controlled surface processes involving erosion and sedimentation. Effects of erosion are multiple: they allow long term localization of deformed domains, they favour important exhumation above areas of deep underplating and combined with sedimentation in the foreland they contribute to maintain the wedge in a critical state for long time periods. The simple models illustrate well how mountain belts structure, kinematics of tectonic units and exhumation are determined by these complex interactions.
ISSN: 0016-8521

hal-00561361
https://hal.archives-ouvertes.fr/hal-00561361
DOI : 10.1134/S0016852110060075

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) : HAL CCSD Springer Verlag
Résumé : International audience
We show here that the Amalaoulaou complex, in the Pan-African belt of West Africa (Gourma, Mali), corresponds to the lower and middle sections of a Neoproterozoic intra-oceanic arc. This complex records a 90-130-Ma-long evolution of magmatic inputs and differentiation above a subducting oceanic slab. Early c. 793 Ma-old metagabbros crystallised at lower crustal or uppermost mantle depths (25-30 km) and have geochemical characteristic of high-alumina basalts extracted from a depleted mantle source slightly enriched by slab-derived sedimentary components ((La/Sm)(N) < 1; epsilon(Nd): +5.4-6.2; Sr-87/Sr-86: 0.7027-0.7029). In response to crustal thickening, these mafic rocks were recrystallised into garnet-granulites (850-1,000A degrees C; 10-12 kbar) and subject to local dehydration-melting reactions, forming trondhjemititic leucosomes with garnet-clinopyroxene-rutile residues. Slightly after the granulitic event, the arc root was subject to strong HT shearing during partial exhumation (detachment faults/rifting or thrusting), coeval with the emplacement of spinel- and garnet-pyroxenite dykes crystallised from a high-Mg andesitic parental magma. Quartz and hornblende-gabbros (700-660 Ma) with composition typical of hydrous volcanic rocks from mature arcs ((La/Sm)(N): 0.9-1.8; epsilon(Nd): +4.6 to +5.2; Sr-87/Sr-86: 0.7028-0.7031) were subsequently emplaced at mid-arc crust levels (similar to 15 km). Trace element and isotopic data indicate that magmas tapped a depleted mantle source significantly more enriched in oceanic sedimentary components (0.2%). Exhumation occurred either in two stages (700-660 and 623 Ma) or in one stage (623 Ma) with a final exhumation of the arc root along cold P-T path (550A degrees C, 6-9 kbar; epidote-amphibolite and greenschist facies conditions) during the main Pan-African collision event (620-580 Ma). The composition of magmas forming the Cryogenian Amalaoulaou arc and the processes leading to intra-arc differentiation are strikingly comparable to those observed in the deep section of exposed Mezosoic oceanic arcs, namely the Kohistan and Talkeetna complex. This evolution of the Amalaoulaou oceanic arc and its accretion towards the West African craton belong to the life and closure of the Pharusian Ocean that eventually led to the formation of the Greater Gondwana supercontinent, a similar story having occurred on the other side of the Sahara with the Mozambique Ocean.
ISSN: 0010-7999

hal-00639447
https://hal.archives-ouvertes.fr/hal-00639447
DOI : 10.1007/s00410-011-0624-5

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
We studied the patterns, rates and evolution of fluvial terraces and fault system during the building process of an intracontinental transpressional mountain in the Gobi-Altay (Mongolia). By analyzing incisions and offsets of fluvial terraces and alluvial fans, we show that the massif has grown by outward migration of thrust faults through time. On the northern flank, the present bounding thrust fault began its activity ~600 ka ago, while a more internal sub-parallel fault was still active until ~200-100 ka. Vertical offset of an alluvial fan abandoned ~100 ka ago allows an estimate of 0.1 mm/yr Upper Pleistocene - Holocene uplift rate. The morphology of the catchment-piedmont system strongly suggests a periodical formation of the alluvial surfaces, controlled by the climatic pulses, at the beginning of the wet interglacial periods. The abandonment of the alluvial terraces lags by several thousand years the abandonment of the alluvial fans, showing a diachronous incision propagating upstream. The incision rate deduced from the different elevations of straths exceeds of one order of magnitude the rock uplift rate. This excess is mostly due to ongoing drainage network growth at the core of the massif, and incision due to alluvial apron entrenchment near the outlet. This implies that fluvial response is mainly controlled by drainage growth, interaction with piedmont and cyclic climatic variations, rather than by rock uplift.
ISSN: 0278-7407

hal-00323558
https://hal.archives-ouvertes.fr/hal-00323558
https://hal.archives-ouvertes.fr/hal-00323558v2/document
https://hal.archives-ouvertes.fr/hal-00323558/file/Vassallo2007.pdf
DOI : 10.1029/2006TC002081

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 Oxford University Press (OUP)
Résumé : International audience
We carried out morphotectonic studies along the left-lateral strike-slip Bogd Fault, the principal structure involved in the Gobi-Altay earthquake of 1957 December 4 (published magnitudes range from 7.8 to 8.3). The Bogd Fault is 260 km long and can be subdivided into five main geometric segments, based on variation in strike direction. West to East these segments are, respectively: the West Ih Bogd (WIB), The North Ih Bogd (NIB), the West Ih Bogd (WIB), the West Baga Bogd (WBB) and the East Baga Bogd (EBB) segments. Morphological analysis of offset streams, ridges and alluvial fans-particularly well preserved in the arid environment of the Gobi region-allows evaluation of late Quaternary slip rates along the different faults segments. In this paper, we measure slip rates over the past 200 ka at four sites distributed across the three western segments of the Bogd Fault. Our results show that the left-lateral slip rate is similar to 1 mm yr(-1) along the WIB and EIB segments and similar to 0.5 mm yr(-1) along the NIB segment. These variations are consistent with the restraining bend geometry of the Bogd Fault.;Our study also provides additional estimates of the horizontal offset associated with the 1957 earthquake along the western part of the Bogd rupture, complementing previously published studies. We show that the mean horizontal offset associated with the 1957 earthquake decreases progressively from 5.2 m in the west to 2.0 m in the east, reflecting the progressive change of kinematic style from pure left-lateral strike-slip faulting to left-lateral-reverse faulting. Along the three western segments, we measure cumulative displacements that are multiples of the 1957 coseismic offset, which may be consistent with a characteristic slip. Moreover, using these data, we re-estimate the moment magnitude of the Gobi-Altay earthquake at M-w 7.78-7.95.;Combining our slip rate estimates and the slip distribution per event we also determined a mean recurrence interval of similar to 2500-5200 yr for past earthquakes along the different segments of the western Bogd Fault. This suggests that the three western segments of the Bogd Fault and the Gurvan Bulag thrust fault (a reverse fault bounding the southern side of the Ih Bogd range that ruptured during the 1957 earthquake) have similar average recurrence times, and therefore may have ruptured together in previous earthquakes as they did in 1957. These results suggest that the western part of the Bogd Fault system, including the Gurvan Bulag thrust fault, usually behaves in a 'characteristic earthquake' mode.
ISSN: 0956-540X

hal-00639467
https://hal.archives-ouvertes.fr/hal-00639467
https://hal.archives-ouvertes.fr/hal-00639467v2/document
https://hal.archives-ouvertes.fr/hal-00639467/file/rizzaGJI2011.pdf
DOI : 10.1111/j.1365-246X.2011.05075.x

Éditeur(s) : Université Nice Sophia Antipolis
Résumé : The Lesser Antilles is a case study of a very slow subduction (~2 cm/yr) of an old oceanic lithosphere (~84-100 Ma). The region presents a relatively low seismic activity, especially along the interplate contact, and the seismic hazard associated with a possible mega-thrust earthquake is still poorly known. This PhD thesis is a first step toward assessing the ability of the Lesser Antilles subduction zone to produce such a large subduction event. To do so, it aims at constraining the downdip width of the interplate's seismogenic zone. The lack of coverage of permanent seismological stations is a major limitation in the exploration of the Lesser Antilles subduction zone. It is due to the presence of only small aligned islands at far distances from the potentially seismogenic interplate area. Several oceanographic cruises were therefore planned that notably allowed the repeated deployment of ocean bottom seismometers; some of them being left for a few months of background seismicity recording. This thesis specifically focuses on two sets of wide-angle seismic data acquired offshore the Dominica and Martinique islands. From their analysis 3D and 2D tomographic models were produced respectively over the forearc region and across the whole subduction complex. These models constrain the plates' seismic structure as well as their geometry. They allow the discussion of how the imaged structures affect the subduction processes and give a first estimation of the downdip width of the seimogenic zone, defined as the segment of the interplate between the backstop and the upper plate's Moho. The joint interpretation of seismic models and earthquake localizations then refine this first assessment. Epicenter distribution from height months of seismic recording shows indeed that seismicity concentrates within the inner forearc region. The strong velocity gradient that characterize its basement suggests it is denser and more rigid than the more deformable outer forearc basement. The updip limit of the seismogenic zone could then lie arcward of the backstop at the contact of the interplate and the seaward end of the inner forearc crust. At depth, interplate earthquake mechanisms are observed between 35 and 45 km depth and interpreted to have occurred at the downdip limit of the seismogenic zone. The latter could reach a depth over 10,km deeper than the contact of the upper plate's Moho with the interplate, and therefore lie within the mantle wedge. All together, these results imply a large downdip width of the seismogenic zone (~70 km) offshore the Dominica and Martinique islands. Further work is, however, needed in order to fully comprehend the ability of the Lesser Antilles subduction zone to produce a possible mega-thrust earthquake. This would necessitate the evaluation of seismic coupling at the interplate contact and the possible segmentation of the seismogenic zone, for instance, due to the subduction of oceanic ridges.
Les Petites Antilles présentent un contexte géodynamique caractérisé par la subduction à très faible vitesse (~2 cm/an) d'une lithosphère océanique âgée (~84-100 Ma). L'activité sismique y est relativement faible, notamment à l'interplaque, où l'aléa sismique lié à un éventuel séisme de méga-chevauchement reste encore mal contraint. Cette thèse se veut être une première étape dans l'évaluation de la capacité de la zone de subduction des Petites Antilles à générer un tel évènement. Dans ce but, ces travaux tentent d'appréhender l'extension en profondeur du domaine sismogène de l'interplaque. Le manque de couverture des stations sismologiques permanentes est un inconvénient majeur dans l'exploration des Petites Antilles. Il s'explique en raison du peu de terres émergées et de leur éloignement de la zone potentiellement sismogène de l’interplaque. La région a donc fait l'objet de plusieurs campagnes océanographiques qui ont permis, notamment, le déploiement de sismomètres fond de mer (OBS); certains instruments étant restés immergés plusieurs mois afin de procéder à une écoute de la sismicité. Les travaux réalisés au cours de cette thèse se sont focalisés sur deux jeux de données de sismique grand-angle acquis au large des îles de la Dominique et de la Martinique. Leur analyse a permis la construction de modèles tomographiques 3D et 2D respectivement à l'échelle de l'avant-arc et de l'ensemble de la subduction. Ces modèles renseignent sur la structure sismique des plaques en convergence ainsi que sur leur géométrie. Ils permettent de discuter le rôle de la structure dans le fonctionnement de la subduction et d’obtenir une première estimation de l'extension en profondeur de la zone sismogène en considérant la portion de l'interplaque comprise entre le butoir et le Moho de la plaque supérieure. Dans un second temps, l'interprétation conjointe des modèles tomographiques et des localisations des séismes locaux a permis d'affiner cette estimation. Huit mois d'enregistrement de la sismicité montrent en effet une concentration des épicentres dans la région interne de l’avant-arc. Celle-ci présente un socle épais, à fort gradient de vitesse interprété comme plus dense et rigide que le socle de la région externe de l'avant-arc, plus déformable. La limite amont de la zone sismogène pourrait donc se situer en retrait de la position du butoir au contact de l'interplaque et de la limite entre ces deux zones de l'avant-arc. En profondeur, des mécanismes interplaques sont observés entre 35 et 45 km et interprétés comme des marqueurs de la limite aval de la zone sismogène. Cette dernière pourrait donc atteindre une profondeur jusqu'à 10 km supérieure à la limite précédemment évoquée et se trouver, par conséquent, au contact du manteau lithosphérique. L'ensemble de ces résultats suggèrent une extension en profondeur de la zone sismogène (i.e une largeur) de près de 70 km face aux îles de la Dominique et de la Martinique. Ces travaux doivent cependant être poursuivis afin d’évaluer pleinement la capacité de la zone de subduction des Petites Antilles à générer un éventuel séisme de méga-chevauchement. Le taux de couplage à l'interplaque doit être précisé ainsi que sa possible segmentation en lien, par exemple, avec à l'entrée en subduction des rides océaniques.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00172/28335/26628.pdf
http://archimer.ifremer.fr/doc/00172/28335/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Contractional deformation of highly porous sandstones is poorly explored, as compared to extensional deformation of such sedimentary rocks. In this work we explore the highly porous Aztec Sandstone in the footwall to the Muddy Mountain thrust in SE Nevada, which contains several types of deformation bands in the Buffington tectonic window: 1) Distributed centimeter-thick shear-enhanced compaction bands (SECBs) and 2) rare pure compaction bands (PCBs) in the most porous parts of the sandstone, cut by 3) thin cataclastic shear-dominated bands (CSBs) with local slip surfaces. Geometric and kinematic analysis of the SECBs, the PCBs and most of the CSBs shows that they formed during ∼E–W (∼100) shortening, consistent with thrusting related to the Cretaceous to early Paleogene Sevier orogeny of the North American Cordilleran thrust system. Based on stress path modeling, we suggest that the compactional bands (PCBs and SECBs) formed during contraction at relatively shallow burial depths, before or at early stages of emplacement of the Muddy Mountains thrust sheet. The younger cataclastic shear bands (CSBs, category 3), also related to E–W Sevier thrusting, are thinner and show larger shear offsets and thus more intense cataclasis, consistent with the initiation of cataclastic shear bands in somewhat less porous materials. Observations made in this work support earlier suggestions that contraction lead to more distributed band populations than what is commonly found in the extensional regime, and that shear-enhanced compaction bands are widespread only where porosity (and permeability) is high.
ISSN: 0191-8141

hal-01171854
https://hal.archives-ouvertes.fr/hal-01171854
DOI : 10.1016/j.jsg.2015.02.014

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
Résumé : In this work on a complete transect of the west‐central Pyrenees, we combine low temperature thermochronology (apatite fission tracks, AFT) with a detailed structural analysis to describe vertical movements related to the thrusting system evolution, and to determine the influence of the latter on the sedimentation/burial/exhumation cycle of thesynorogenic deposits of the southern foreland basin (Jaca and Ainsa basins). AFT analysis from a transect of the south‐Pyrenean basin show the southward decrease of the fission track reset level from the southern edge of the Axial Zone to the South‐Pyreneanfrontal thrust, implying the southwards decrease of the burial amount from more than 5kmin the north to less than 3km in the south assuming an average geothermal gradient of 25°C.km‐1. The structural setting of the Jaca basin attests that the burial of the synorogenicsediments was mainly due to the sedimentary accumulation. AFT data from the northernpart of the basin display a late Oligocene‐early (middle) Miocene cooling event. Newinterpretation of industrial seismic reflection profiles across the Jaca basin suggests that the Oturia thrust is rooted in the Bielsa basement thrust, responsible for the early (‐middle) Miocene out‐of‐sequence tectonic reactivation of the southern flank of the Axial Zone (Jolivet et al., 2007). These results reveal a lower Miocene (Burdigalian ‐?Langhian) out‐of sequence episode of tectonic activity of the interior of the south‐Pyrenean foreland basin. AFT data from the Axial Zone and the North‐Pyrenean Zone confirm the general southwardmigration of the thrusting system, and also bring evidence of the late Oligocene‐lowe rMiocene out‐of‐sequence tectonic reactivation of the northern flank of the Axial Zone. All these results attest of a late Oligocene‐lower Miocene (Burdigalian‐?Langhian) "pop‐up" reactivation of the inner part of the west‐central Pyrenees, younger than the sealing of thesouth‐Pyrenean front (Aquitanian‐?Burdigalian) which is classically considered to mark the end of the Pyrenean compression. These results lead us to propose a new crustal scale evolution model of the west‐central Pyrenees in 3 stages: (i) From the Late Cretaceous to themiddle Eocene, the orogenic prism is characterised by the absence of relief, related to theinversion of Cretaceous extensional structures leading to the accretion of thin crustal units; (ii) The late Eocene‐Oligocene stage corresponds to the continental collision, marked by the creation of important relief associated with the accretion of thick crustal units; (iii) During the early Miocene, the inner part of the Pyrenean wedge is tectonically reactivated.
Ce travail de thèse concerne une transversale complète des Pyrénées centro-occidentales, où on a combiné la thermochronologie basse température (traces de fission sur apatites, TFA) avec une analyse structurale détaillée pour décrire les mouvements verticaux associés à l'évolution du système chevauchant, et pour déterminer l'influence de ce dernier sur le cycle sédimentation/enfouissement/exhumation des dépôts synorogéniques du bassin d'avant‐chaine sud (bassins de Jaca et Ainsa). L'analyse TFA complète les données déjà publiées dans la Zone Axiale et la Zone Nord‐Pyrénéenne, e tconstitue la première étude de ce genre dans un bassin d'avant‐chaîne pyrénéen. Les données TFA sur la transversale du bassin sud‐pyrénéen montrent une diminution vers le sud du degré d'effacement des traces de fission, traduisant la diminution vers le sud de la quantité d'enfouissement, supérieure à 5 km au nord et inférieure à 3 km au sud dans l'hypothèse un géotherme de 25°.km‐1. Le contexte géologique montre que l'enfouissement est principalement lié à l'accumulation des dépôts synorogéniques. Les données TFA de lapartie nord du bassin montrent un refroidissement d'âge Oligocène supérieur‐Miocèneinferieur (moyen). Par ailleurs, une nouvelle interprétation de profils de sismiques réflexiondans le bassin de Jaca montre que le chevauchement d'Oturia s'enracine dans lechevauchement de socle de Bielsa, responsable de l'exhumation tectonique hors‐séquencedu bord sud de la Zone Axiale au Miocène inférieur (‐moyen) (Jolivet et al., 2007). Cesrésultats attestent donc de l'exhumation tectonique hors‐séquence au Miocène inférieur (Burdigalien‐ ?Langhien) de la partie nord du bassin d'avant‐chaine sud‐pyrénéen. Des données TFA obtenues dans la Zone Axiale et la Zone Nord‐Pyrénéenne confirment lamigration générale vers le sud du système chevauchant, et mettent également en évidencela réactivation tectonique hors‐séquence du bord nord de la Zone Axiale à l'Oligocèneterminal‐Miocène inférieur. L'ensemble de ces résultats atteste donc de la réactivation en " pop‐up " de la parties interne des Pyrénées centre‐ouest à l'Oligocène supérieur‐Miocèneinférieur (Burdigalien‐ ?Langhien), postérieurement au scellement du front sud‐pyrénéen (Aquitanien‐ ?Burdigalien) classiquement considéré comme marquant la fin de lacompression pyrénéenne. Ces données nous ont permis de proposer un nouveau modèle d'évolution crustale des Pyrénées centro‐occidentales en 3 grandes étapes : (i) du Crétacé supérieur à l'Eocène moyen, le prisme est caractérisé par une absence de relief, en lien avec l'inversion de structures extensives crétacées conduisant à l'accrétion de petites écailles crustales ; (ii) la période Eocène supérieur‐Oligocène correspond à la collision continentale proprement dite, et est marquée par la création d'importants reliefs associés à l'accrétion d'épaisses unités crustales ; (iii) au Miocène inférieur, la partie interne du prisme pyrénéen est réactivée.
https://tel.archives-ouvertes.fr/tel-00772154

Droits : info:eu-repo/semantics/OpenAccess
tel-00772154
https://tel.archives-ouvertes.fr/tel-00772154
https://tel.archives-ouvertes.fr/tel-00772154/document
https://tel.archives-ouvertes.fr/tel-00772154/file/thesemeresse.pdf

Éditeur(s) : HAL CCSD
Résumé : Several major earthquakes have struck the 2500 km long Himalayan range during the past century. However, both the maximum size of such earthquakes and the probability of occurrence of a magnitude 9 megaquake are still a mater of debate. In this framework it is of key importance to investigate the lateral segmentation of the Himalayan arc in order to deepen our understanding of the mechanisms that control such events as well as their extents. Besides the remarkably uniform tectonic set-up and the fact that most studies on the Himalayas have focused on Central Nepal, several indications of along strike changes can be gathered.This thesis brings new constraints on lateral variations of crustal structure and of deformation between western Nepal (~80°E) and eastern Bhutan (~92°E).The first part of this thesis focuses on the lateral variations of crustal structure. In the past three years we have carried out four land gravity campaigns. We have established 366 new gravity measurement points to fill the data gaps in central and western Nepal as well as in Bhutan. This new dataset, together with available seismological data, is used to constrain thermo-mechanical models of the bending of the India plate underneath the Himalayas. While the inferred crustal geometry does not exhibit major along-strike variations over central and eastern Nepal, the shorter wavelength flexure of the lithosphere in Bhutan is associated with a weaker upper mantle rheology.The second part focuses on the lateral variations of recent deformation in the Himalayas. Fifteen years of paleoseismological investigations have extended the catalogue of major Himalayan events over the last millennium. Combining these information with secular loading, we assess the spatial and temporal stress changes on the Main Himalayan Thrust along the orogen over the last nine centuries. Our calculations indicate that inter-seismic loading has now nearly overcome the Coulomb stress decrease caused by the great ~1100 medieval earthquake. Our results also point out that the 1897 Shillong plateau earthquake does not have a major influence on the stress accumulated on the Main Himalayan Thrust since then. In order to better characterize active tectonics in the Bhutan Himalayas where no studies were done so far, we carried out a morphotectonic analysis in the south-central part of the kingdom. We show that the same amount of Holocene deformation is accommodated on the frontal thrust in Bhutan as on the neighbouring portions of the Himalayan arc. We also find evidences for two major (M>8) earthquakes on this thrust in the Bhutan Himalayas during the last millennium. Our results therefore show that Bhutan cannot be considered as a seismic gap. They also challenge the interpretation of one single ~1100 medieval mega-event that would have ruptured the Main Frontal Thrust from central Nepal to eastern Bhutan.
Au cours du dernier siècle, plusieurs séismes majeurs ont affecté l'Himalaya. Cependant, la taille maximale de ces événements et la probabilité d'occurrence de méga-séismes avec des magnitudes proches de 9 sont toujours matière à débat. L'étude de la segmentation de l'arc Himalayen est donc primordiale afin de comprendre les mécanismes qui contrôlent ces séismes ainsi que leur extension spatiale. La compréhension du cycle sismique en Himalaya est aujourd'hui essentiellement basée sur des études menées au Népal central, ce qui limite notre connaissance de son fonctionnement tri-dimensionnel. Ce travail de thèse permet d'apporter de nouvelles contraintes sur les variations latérales de la déformation crustale dans la zone comprise entre l'ouest Népal (~80°E) et l'est Bhoutan (~92°E). La première partie de cette thèse est consacrée à l'étude des variations latérales de la structure lithosphérique. Quatre campagnes gravimétriques ont été réalisées entre 2010 et 2012. Elles ont permis d'étendre le réseau gravimétrique Népalais jusqu'à l'ouest Népal et d'établir le premier réseau gravimétrique Bhoutanais. Ce nouveau jeu de données, combiné avec les données sismologiques disponibles, permet de contraindre des modèles thermo-mécaniques de la flexure de la plaque Indienne sous l'Himalaya. Les résultats suggèrent qu'il n'existe pas de variations latérales majeures du comportement mécanique de la lithosphère Indienne entre le centre et l'est Népal contrairement au Bhoutan où une rigidité flexurale plus faible est nécessaire pour expliquer les données.La deuxième partie de cette thèse est consacrée à l'étude des variations latérales des déformations récentes dans le prisme Himalayen. Les études paléosismologiques menées depuis 15 ans en Himalaya ont permis d'étendre le catalogue des événements majeurs sur le dernier millénaire. En intégrant à la fois les contraintes disponibles sur ces séismes majeurs et le chargement séculaire, nous étudions les variations spatiales et temporelles de l'état de contrainte du chevauchemlent Himalayen principal le long de l'arc. Nos calculs montrent que même dans la cas où un méga-séisme se serait produit en ~1100 en Himalaya, le chargement séculaire a quasiment compensé la chute de contrainte associée. Les modèles montrent aussi que le séisme du Shillong ne joue pas un rôle majeur sur les contraintes accumulées sur le chevauchement Himalayen depuis 1897 au niveau du Bhoutan. Enfin, nous présentons les premières contraintes sur la tectonique active au Bhoutan. L'étude morphotectonique réalisée au centre du Sud-Bhoutan a permis de montrer que la majeure partie de la déformation Holocène est accommodée au niveau du front Himalayen, comme au Népal. Nous montrons aussi des évidences de ruptures de surface avec des décalages verticaux de plusieurs mètres associés à deux séismes majeurs sur le dernier millénaire. Ces évidences remettent en cause l'interprétation d'un méga-séisme en ~1100.
https://tel.archives-ouvertes.fr/tel-01002381

NNT : 2013MON20074
tel-01002381
https://tel.archives-ouvertes.fr/tel-01002381
https://tel.archives-ouvertes.fr/tel-01002381/document
https://tel.archives-ouvertes.fr/tel-01002381/file/35970_BERTHET_2013_archivage_cor.pdf