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
Résumé : Sand intrusions (or injectites) are most often the product of post-depositional remobilization of sand leading to its injection into the surrounding rocks. While injectites were recognized for the first time nearly 200 years ago, their emplacement process has been studied for a couple of decades only, since the concepts of deep sea depositional environments have allowed us to better understand their emplacement processes. However, these processes are still relatively poorly understood. Our approach is based on the study of injectites in the Lower Congo Basin from seismic and well data, which we compare to a fossil system in the SE France basin. We have shown that: (1) In buried turbidite channel systems draping deposits on the channel flanks and terraces of channels have the same geophysical signature as 'wing-like' injectites. Finally, the only criterion for identifying seismic injectites is the presence of bedding-discordant seismic reflections, and in the best case the associated uplift of the overlying seismic reflectors. (2) Seismic-scale conical and saucer-shaped sand injectites have been identified in the Lower Congo Basin. The remobilization is likely due to overpressuring induced by the buoyancy effect of hydrocarbons trapped in the margins of a lobe buried underneath 160 m of sediment, followed by the sudden injection of fluidized sand associated with fault reactivation of faults (with a possible role of nearby salt diapirs). (3) A network of injectites (dykes, sills/wings and laccoliths) was formed in the Vocontian basin during the late Albian and/or early Cenomanian, from a lower-middle Albian turbidite channel. The emplacement is probably due to the early compartmentalization of the channel during its burial and the increase of the sedimentation rate generating overpressure; and the subsequent large influx of deep fluids triggering injection. The injection of sand was polyphased: a first episode formed the sills and another emplaced the dykes. Sills/wings and dykes propagated about 2 km laterally away from the parent sand body and about 200 m up to the surface, revealing a much more extended lateral than vertical reach, contrary to the classically accepted idea from the interpretation of seismic data. (4) The emplacement of this large network of injectites was governed by hydrofracturing. Therefore, its morphology is dependent on the host rock heterogeneity (isotropy, fractures), the paleo-stress orientation (ó3 = NW-SE) and the burial depth of the source (300-600 m) at the time of injection. The study of this fossil network allows us to define the relationship between morphology of the injected network and stress state at the time of injection. This relationship can be extrapolated to constrain the morphology of subsurface networks beyond seismicvisibility. (5) Sands injected into low permeability lithologies bear evidence to a major event of fluid escape in the studied basin, but also channeled fluids long after their formation. In this way, injectites both attest to specific episodes of fluid migration in sedimentary basins and contribute to long-lived re-routing of migrating fluids once emplaced. The injection of sand is associated with the sudden escape of fluids, probably resulting from a significant tectonic and/or sedimentary event; in addition, the architecture of injectite networks is governed by the local paleo-stress and heterogeneity in the host rock. Consequently, characterizing injectite networks is an important step in understanding the plumbing systems of continental margins, i.e. the post-depositional evolution of sedimentary basins.
Les intrusions sableuses (ou injectites) sont le plus souvent le produit de la remobilisation post-dépositionnelle des sédiments et de l'injection du sable dans les roches environnantes. Bien que reconnues pour la première fois il y a près de 200 ans, elles ne sont réellement étudiées que depuis quelques dizaines d'années, depuis que les concepts sur les environnements de dépôt dans les domaines marins profonds nous permettent de mieux comprendre les processus de mise en place. Cependant, ces processus restent encore aujourd'hui relativement mal compris. Notre approche repose sur l'étude d'injectites dans le bassin du Bas-Congo a partir de données de sismique et de puits que nous comparerons a un système fossile dans le bassin du SE de la France. Nous avons montre que : (1) Dans des systèmes de chenaux turbiditiques enfouis, les dépôts de drapage sur les marges et terrasses de chenaux présentent la même signature géophysique que les injectites de type "wing". Finalement, le seul critère sismique d'identification des injectites est la présence de réflexions sismiques sécantes vis-a-vis de la stratigraphie associée dans le meilleur des cas au soulèvement des réflecteurs sismiques sus-jacents. (2) Des injectites d'échelle sismique en forme de cône et d'assiette ont été identifiées dans le bassin du Bas-Congo. La remobilisation résulte probablement des pressions anormales induites par l'effet de flottabilité des hydrocarbures piégés dans les marges d'un lobe enfoui sous 160 m de sédiment, puis de l'injection soudaine du sable fluidise associée a la réactivation de failles (possible rôle des diapirs de sel a proximité). (3) Un réseau d'injectites (dykes, sills/wings et laccolites) s'est formé dans le bassin Vocontien entre la fin de l'Albien supérieur et/ou le début du Cénomanien, depuis un chenal turbiditique de l'Albien inférieur-moyen. La mise en place résulte probablement de la compartimentalisation précoce du chenal au cours de son enfouissement et de l'augmentation du taux de sédimentation générant la surpression et de l'apport ulterieur d'importante quantité de fluides profonds déclenchant l'injection. L'injection du sable a été polyphasée : une première injection a formé des sills et une suivante des dykes. Les sills/wings et les dykes se sont propagés latéralement au chenal source sur environ 2 km et vers la surface sur environ 200 m, mettant en évidence une forte remobilisation latérale plutôt que verticale, contrairement a l'idée classiquement admise a partir de l'interprétation des données sismiques. (4) La formation de ce large réseau d'injectites a été gouvernée par des mécanismes d'hydrofracturation. Par conséquent, sa morphologie a été dépendante des hétérogenéités de la roche hôte (milieu isotrope, fracture), des directions de paléo-contraintes (ƒÐ3 = NWSE) et de la profondeur d'enfouissement de la source (300-600 m) au moment de l'injection. L'étude de ce réseau fossile permet de définir les relations entre morphologie du réseau injecté et état de contraintes au moment de l'injection. Cette relation peut être extrapolée de façon à contraindre la morphologie des réseaux de subsurface au-delà de la visibilité sismique. (5) Les sables injectés dans des lithologies de faible perméabilité témoignent d'un épisode d'échappement de fluide important dans les bassins étudiés mais ont aussi guide les fluides longtemps après leur formation. Les injectites contribuent ainsi a l'initiation épisodique et la pérennisation de migrations de fluides dans les bassins sedimentaires. Le processus d'injection est associé a l'échappement brutal de fluides, résultant vraisemblablement d'un évènement tectonique et/ou sédimentaire important, et l'architecture des réseaux d'injectites est gouverné par les paléo-contraintes locales et les hétérogénéités de la roche hôte. Par conséquent, la caractérisation des réseaux d'injectites est une étape importante dans la compréhension de la plomberie des marges, c'est-a-dire l'évolution post-dépôt des bassins sédimentaires.
https://tel.archives-ouvertes.fr/tel-01011486

tel-01011486
https://tel.archives-ouvertes.fr/tel-01011486
https://tel.archives-ouvertes.fr/tel-01011486/document
https://tel.archives-ouvertes.fr/tel-01011486/file/These_Monnier_2013_banalisee.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : A synthesis of backscatter imagery coupled with a large 3D seismic dataset in the Lower Congo Basin (LCB) reveals a patchy distribution of features interpreted to be associated with fluid seepage from 300 m to 2500 m water depth. With the exception of one region of anomalous backscatter positive-relief mounds, all inferred seep sites occur in negative-relief pockmarks. The extensive 3D seismic dataset in the LCB offers a unique opportunity to study the plumbing system that is feeding surface cold seep systems, and in general, to reconstruct the relationship between tectonics and fluid flow in continental margins. The fluid seeps in the LCB are associated with morphologically, stratigraphically or tectonically controlled focused fluid flow. The integration of the geophysical datasets, backscatter imagery coupled to 3D seismic, clearly indicates that fluid seeps are not randomly distributed, but their seabed organization reflects 1) the location of the underlying structure (reservoir or trap) where the fluids are coming from, 2) the geometry and morphology of the reservoir/trap, and 3) the discontinuities in the sedimentary column along which fluids have migrated. In the LCB seafloor pockmarks are always associated with underlying tectonic structures (fault zones, salt diapirs, polygonal faults) or buried sedimentary bodies (turbiditic channels, erosional surfaces), whereas they never occur above sub-horizontal parallel-stratified fine-grained sediments. Even if triggering processes can not be clearly defined here, we propose a model of seafloor fluid seep organization, which represents a new tool for identifying the geometry of flow pathways and the underlying buried bodies where the fluids are originating from. This qualitative 3D model provides insight into the geohydrologic processes of continental margins.
ISSN: 0025-3227

hal-00406640
https://hal.archives-ouvertes.fr/hal-00406640
DOI : 10.1016/j.margeo.2007.06.003

Éditeur(s) : HAL CCSD
Résumé : This thesis aims to analyze the active tectonics and the seismic hazard for three main cities of NW Iran (Tehran, Tabriz and Zandjan) using morphotectonics and paleoseismology. Within the Tehran capital, we focused our analysis on the Mosha-North Tehran (M-NT) active fault system. Our investigations show that this fault system is mainly dominated by left-lateral faulting. Along the eastern part of the M-NT fault system, we found evidences of at least seven strong (M>7) paleoearthquakes during the past 10 ka (recurrence interval : 1100-1400 yrs). Our study along the central portion of the fault system (in Abali region) suggests that it corresponds probably to the source of the 1830 AD historical earthquake (M=7.1, Io= IX). Within Tabriz region, we studied the SE segment of the North Tabriz fault. We found evidences of at least three strong events, which occurred during the past 33.5 ka. The North Tabriz dextral fault corresponds to the central portion of a fault system (TFS), and contains two fault segments (NW and SE). Our paleoseismological analysis shows a variation of the slip rate, which decreases from NW to SE along the strike-slip fault. The western (Mishu) and eastern (Bozghush) terminations of the fault system correspond to oblique-compression zones. TFS belongs to the eastern portion of a regional fault system (GSKT), linking the active extension within the central part of the collision and the active compression to the East. Finally, we focus on the Zandjan area, where no important historical seismicitiy is recorded. There, based on morphotectonics analysis we discovered a large active fault network, whose southeastern part affects the Zandjan city. To conclude this work, we replace our observations within the general geodynamic framework of the Arabia- Eurasia collision. One of the striking pictures is the occurrence of opposite kinematics along the M-NT (and other range parallel faults within the south Central Alborz) and the North Tabriz fault systems that have the same trend. This shows the rapid variation of the regional stress field in the Northern Iran.
L'objectif de ce mémoire de thèse est l'étude de la tectonique récente et l'évaluation de l'aléa sismique pour trois villes importante, Téhéran, Tabriz et Zandjan, situées dans le nord-ouest de l'Iran. Dans la capitale de l'Iran, Téhéran, nous nous sommes concentrés sur le système de faille active de Mosha-Nord Téhéran. Nos travaux démontrent que ce système est essentiellement décrochant sénestre. Nos analyses paléosismologiques sur la portion est de ce système (dans la vallée de Tar) montrent au minimum les évidences de sept grands événements sismiques (M>7) pendant les derniers 10000 ans (l'intervalle de récurrence est de 1100 à 1400 ans). Les études que nous avons mené dans la partie centrale de ce système (région d'Abali) révèlent qu'il pourrait être la source du dernier événement sismique ayant affecté la ville de Téhéran en 1830 AD. Dans la région de Tabriz, nous nous sommes intéressés au segment SE de la faille décrochante dextre de Nord Tabriz où nous avons trouvé les évidences de trois grands séismes pendant les derniers 33500 ans. Nos études montrent que la faille Nord Tabriz qui est la portion centrale d'un système de faille (TFS) est constituée par deux segments NW et SE dextres. Notre étude paléosismologique suggère une variation de la vitesse qui diminue du NW vers SE le long de ces segments. Les extrémités ouest (Mishu) et est (Bozghush) de ce système correspondent à des zones compressives qui absorbent les déplacements horizontaux sur les segments NW et SE. D'un point de vue général la TFS est une partie d'un système de failles régionales (GSKT) qui relie une zone d'extension active dans la partie centrale de la collision Arabie-Eurasie et une zone de compression active à l'Est. Enfin, à Zandjan qui est une ville située dans une région de lacune sismique, nous avons découvert un important réseau de failles actives. Le tracé sud-est de ce réseau de failles passe par la ville de Zandjan. En conclusion, les localisations et les cinématiques des systèmes de faille étudiés sont discutées dans le cadre géodynamique général de la collision Arabie-Eurasie. On remarquera que la faille majeure de Nord Tabriz qui correspond essentiellement à un décrochement dextre a la même direction NW-SE que les décrochements sénestres présents dans la chaîne de l'Alborz (les failles de : Mosha, Talaghan et Manjil). Cette observation nécessite une variation de la direction de compression entre ces deux régions.
https://tel.archives-ouvertes.fr/tel-00539739

tel-00539739
https://tel.archives-ouvertes.fr/tel-00539739
https://tel.archives-ouvertes.fr/tel-00539739/document
https://tel.archives-ouvertes.fr/tel-00539739/file/thesesoleymani.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Upon subduction, the oceanic crust transforms to blueschists and eclogites, with seismic properties that gradually become similar to those of the surrounding mantle. In order to evaluate the anisotropy of blueschists and glaucophane-bearing eclogites, the elastic constants of glaucophane single-crystal plates from the Sesia-Lanzo Zone (Aosta Valley, Western Alps) were measured using Brillouin spectroscopy at ambient conditions. The mean P- and S-wave velocities are 7.8 and 4.6 km s−1 respectively, and the anisotropy is high (38.1% (AVP) and 27.3% (AVS)). Glaucophane develops strong LPO, characterized by the [001]-axes concentrated sub-parallel to the lineation, and the {110} poles concentrated sub-perpendicular to the foliation in both blueschist and eclogite rocks. The measured LPO is in good agreement with viscoplastic selfconsistent numerical models. Seismic properties of glaucophane-bearing blueschist and eclogite are calculated by combining measured LPO and the single-crystal elastic moduli of glaucophane with the other main mineral constituents of the rock: mostly epidote for blueschist, and omphacite and garnet for eclogite. Blueschists present stronger anisotropies (AVP=16.1% and AVS=10.3%) than eclogites (AVP=2.9% and AVS=1.7%). The shear-wave splitting and resulting delay times for a 7-km thick layer of eclogite or blueschist are low for the eclogite (b0.03 s), but signi!cant for blueschist (0.16 s). Application to the subducted oceanic crust yields a decrease of velocity contrast with the surrounding mantle and of anisotropy at depth depending on the temperature of the slab. The details of the velocity variations in subducted oceanic crust are dif!cult to reconcile with the blueschist-eclogite transition as probed by exhumed metamorphic rocks and may require additional phases such as lawsonite or chemical variations such as oxidation state.
ISSN: 0040-1951

hal-00564518
https://hal.archives-ouvertes.fr/hal-00564518
DOI : 10.1016/j.tecto.2010.09.011

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
No major earthquake occurred in North Chile since the 1877 Mw 8.6 subduction earthquake that produced a huge tsunami. However, geodetic measurements conducted over the last decade in this area show that the upper plate is actually deforming, which reveals some degree of locking on the subduction interface. This accumulation of elastic deformation is likely to be released in a future earthquake. Because of the long elapsed time since 1877 and the rapid accumulation of deformation (thought to be 6-7 cm yr−1), many consider this area is a mature seismic gap where a major earthquake is due and seismic hazard is high. We present a new Global Positioning System (GPS) velocity field, acquired between 2008 and 2012, that describes in some detail the interseismic deformation between 18°S and 24°S. We invert for coupling distribution on the Nazca-South America subduction interface using elastic modelling. Our measurements require that, at these latitudes, 10 to 12 mm yr−1 (i.e. 15 per cent of the whole convergence rate) are accommodated by the clockwise rotation of an Andean block bounded to the East by the subandean fold-and-thrust belt. This reduces the accumulation rate on the subduction interface to 56 mm yr−1 in this area. Coupling variations on the subduction interface both along-strike and along-dip are described. We find that the North Chile seismic gap is segmented in at least two highly locked segments bounded by narrow areas of weak coupling. This coupling segmentation is consistent with our knowledge of the historical ruptures and of the instrumental seismicity of the region. Intersegment zones (Iquique, Mejillones) correlate with high background seismic rate and local tectonic complexities on the upper or downgoing plates. The rupture of either the Paranal or the Loa segment alone could easily produce a Mw 8.0-8.3 rupture, and we propose that the Loa segment (from 22.5°S to 20.8°S) may be the one that ruptured in 1877.
ISSN: 0956-540X

hal-00941279
https://hal.archives-ouvertes.fr/hal-00941279
DOI : 10.1093/gji/ggt183

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Iran is an active continental domain accommodating the convergence between the Arabia and Eurasia plates. In northwestern Iran, deformation between the Central Iranian block and the Caucasus domain is mainly accommodated by right lateral strike-slip on the Tabriz fault. Cities and villages, including the city of Tabriz, have been destroyed by several strong historical earthquakes (M similar to 7). In this study, we compare the slip-rates estimated from geodetic measurements (radar interferometry and UPS) with those determined by dating a geomorphological offset of an alluvial fan along the Tabriz fault. The GPS measurements along two profiles normal to the Tabriz fault suggest a slip-rate of 7.3 +/- 1.3 mm yr(-1). The persistent scatterer radar interferometry analysis of Envisat satellite archives from 2003 to 2010 shows a velocity gradient (6 +/- 3 mm yr(-1)) across the Tabriz fault in agreement with GPS results. Moreover, it reveals that most of the area located south of the Tabriz fault is affected by subsidence, and that some sections of the fault probably act as barriers to fluid migration which may have an impact on its mechanical behaviour. West of Tabriz morphotectonic investigations on an alluvial fan surface show a right-lateral cumulative offset of 320 +/- 40 m Luminescence analyses of the coarse matrix alluvial fan deposits provide an age of 46 +/- 3 ka. This yields a slip-rate comprised between 6.5 and 7.3 mm yr(-1) along this segment. These results suggest that the Late Quaternary slip-rate is in agreement with the present-day slip-rate estimated by geodetic measurements, showing no slip-rate changes during the past 45 000 yr. Short-term variations within the 45 000 yr related to temporal earthquake clustering over few seismic cycles cannot be ruled out, but if they exist, they do not affect the geodetic and the geomorphological estimates. This study is in agreement with previous ones suggesting that long-term slip-rates (i.e. averaged over several tens of seismic cycles) are consistent with geodetic estimated slip-rates (i.e. extrapolated from few years of interseismic observations), and suggests that perturbations of fault slip-rates are related to variations over few seismic cycles.
ISSN: 0956-540X

hal-00844695
https://hal.archives-ouvertes.fr/hal-00844695
https://hal.archives-ouvertes.fr/hal-00844695v2/document
https://hal.archives-ouvertes.fr/hal-00844695/file/rizza2013.pdf
DOI : 10.1093/gji/ggt041

Éditeur(s) : HAL CCSD Société géologique de France
Résumé : International audience
The Messinian salinity crisis (MSC) is characterized by gigantic erosion that remodels the margins while a thick, essentially evaporitic and detrital, sedimentary sequence forms in the deep basins. Based on recent (MAURESC, 2003) and earlier (MESEA 1, 1990; MAGIRAA, 1996; GEOBREST, 2002) seismic reflection data, this work brings to light the record of the MSC on the Provençal margin, which has until now been rarely explored from this perspective. Beyond its strictly regional interest, this study fits into a larger synthesis of MSC seismic markers in the Mediterranean and Black Sea marine domain [Lofi et al., 2011] and employs the new nomenclature established on this occasion. The results obtained reveal a Messinian detrital body (CU unit) of 625 metres maximum thickness at the foot of the margin, accumulating at the mouths of the principal canyons. Its form, facies and extension assimilate it to clastic fans, fed by subaerial erosion linked to the MSC. The relative geometry of CU and the Messinian units MU and UU deposited in the deep basin give indications to their chronostratigraphic relations. The deposition of the CU unit is posterior to the basal part of the mobile unit consisting of halite (MU), but contemporary to its top. These results agree with the recent scenarii, which propose that the precipitation of MU in the basin began early, during the lowering of the sea level, and ended at a low level during the MSC [Blanc, 2000; Martin et al., 2001; Sage et al., 2005; Ryan, 2009]. The UU unit surmounts MU and is subdivided into two sub-units with perceptibly different seismic facies : UU1 at the base and UU2 at the summit. UU1 could correspond to a unit containing more halite and/or more clastic material than UU2. The UU1 sub-unit could be partially contemporary to the CU unit. Concerning salt tectonics and its markers, three structural provinces have been evidenced in the sector of study, respectively : an upslope domain in extension (normal faults), an intermediary domain in translation (tabular MU) and a downslope domain in contraction (salt diapirs). These domains are directly linked to the gravity spreading and/or gliding of the brittle sedimentary cover formed by the CU, UU and Plio-Quatenary units and of the mobile level, MU. In the study area, a close relation between the distribution and thickness of CU and salt tectonics has additionally been evidenced at the mouths of the large Messinian canyons, being best expressed where CU is thick.
EISSN: 1777-5817

hal-00622998
https://hal-brgm.archives-ouvertes.fr/hal-00622998
DOI : 10.2113/gssgfbull.182.2.181

Éditeur(s) : HAL CCSD European Geosciences Union
Résumé : International audience
Earth deformation is a multi-scale process ranging from seconds (seismic deformation) to millions of years (tectonic deformation). Bridging short- and long-term deformation and developing seismotectonic models has been a challenge in experimental tectonics for more than a century. Since the formulation of Reid's elastic rebound theory 100 years ago, laboratory mechanical models combining frictional and elastic elements have been used to study the dynamics of earthquakes. In the last decade, with the advent of high-resolution monitoring techniques and new rock analogue materials, laboratory earthquake experiments have evolved from simple spring-slider models to scaled analogue models. This evolution was accomplished by advances in seismology and geodesy along with relatively frequent occurrences of large earthquakes in the past decade. This coincidence has significantly increased the quality and quantity of relevant observations in nature and triggered a new understanding of earthquake dynamics. We review here the developments in analogue earthquake modelling with a focus on those seismotectonic scale models that are directly comparable to observational data on short to long timescales. We lay out the basics of analogue modelling, namely scaling, materials and monitoring, as applied in seismotectonic modelling. An overview of applications highlights the contributions of analogue earthquake models in bridging timescales of observations including earthquake statistics, rupture dynamics, ground motion, and seismic-cycle deformation up to seismotectonic evolution.
ISSN: 1869-9510

hal-01553120
https://hal.archives-ouvertes.fr/hal-01553120
https://hal.archives-ouvertes.fr/hal-01553120/document
https://hal.archives-ouvertes.fr/hal-01553120/file/rosenau2017.pdf
DOI : 10.5194/se-8-597-2017

Éditeur(s) : HAL CCSD
Résumé : International audience
The « METYSS » cruise was carried out in June 2009 onboard the R/V « Téthys II » along the eastern Sardinian and south-eastern Corsican margins, western Tyrrhenian Sea, in order to better constrain the potential links between deformation related to either crustal tectonics or salt tectonics and sediment accumulation, especially during the Messinian and Plio-Quaternary times. We acquired 15 high-resolution seismic reflection profiles (about 1200 km in cumulative length) along the south-eastern Corsican margin, immediately north of the Bonifacio Strait and along the upper and middle parts of the eastern Sardinian margin, from the continental slope to the Cornaglia Terrace. The Tyrrhenian Sea is considered as a Neogene back-arc basin that opened during continental rifting and oceanic spreading related to the eastward migration of the Apennine subduction system from Tortonian to Pliocene times (Jolivet et al., 2006). Rifting of the Tyrrhenian Sea started first along the Eastern Sardinian margin during the Tortonian-Messinian times and therefore the series of that age should be considered as syn-rift sediments (Sartori et al., 2004). The « METYSS » seismic profiles clearly illustrate that this part of the Tyrrhenian was highly segmented during the rifting stage by N-S trending normal faults delineating ridges (e.g., Baronie Ridge) and basins (e.g., Sardinian Basin and Cornaglia Terrace), as previously described for example by Thommeret (1999) and Sartori et al. (2004). The Messinian sedimentary units and especially the « Upper Unit » (UU, Lofi et al., this congress, corresponding to the « Upper Evaporites » in the previous literature) are, without any doubt, of syn-rift age, as they display a fan-shaped stratal geometry. The Mobile Unit (MU, Lofi et al., this congress), i.e. the Messinian halite, is clearly imaged in the study area and its spatial repartition can be outlined. The highly-variable thickness of the confined salt basins could be due to the initial basin geometry (i.e. before the Messinian salinity Crisis) or to the syn-rift character of the deposition. Southeastward of the study area, in the vicinity of the Cornaglia Seamount, salt tectonics appears surprisingly vigorous. More surprisingly, several normal faults seem to have remained active in recent times, if not even at present time. Fault slip has been recorded by bathymetric scarps and associated footwall debris flows interfingered within the Plio-Quaternary sequence, even though the eastern Sardinian margin is usually considered to be passive now. Moreover, some amount of tectonic inversion is visible on some normal faults that show contractional or transpressional components of late slip. In addition, this “post-rift” deformation can be illustrated within the Plio-Quaternary sequence by a regional unconformity. Consequently, numerous mass-transport deposits and channel-levees systems observed in the Plio-Quaternary cover could be partly controlled by tectonic activity. These very preliminary results require further investigations in order to better decipher the role of crustal tectonics and salt tectonics, salt-related structures being very efficient markers to discriminate between the respective contribution of gravity-driven, salt tectonics and deep-seated, crustal tectonics (Gaullier et al., 2010). Finally, we aim to precisely determine the relative vertical movements (tilting, subsidence, magmatism. . . ) and geodynamical history of the different segments of the area since 6 Ma.
Geophysical Research Abstracts
Vienne, Austria

hal-00537828
https://hal-brgm.archives-ouvertes.fr/hal-00537828
https://hal-brgm.archives-ouvertes.fr/hal-00537828/document
https://hal-brgm.archives-ouvertes.fr/hal-00537828/file/EGU2010-15469_ref6821.pdf

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : Mantle xenoliths in Pliocene alkali basalts of the eastern Betics (SE Iberia, Spain) are spinel ± plagioclase lherzolite, with minor harzburgite and wehrlite, displaying porphyroclastic or equigranular textures. Equigranular peridotites have olivine crystal preferred orientation (CPO) patterns similar to those of porphyroclastic xenoliths but slightly more dispersed. Olivine CPO shows [100]-fiber patterns characterized by strong alignment of [100]-axes subparallel to the stretching lineation and a girdle distribution of [010]-axes normal to it. This pattern is consistent with simple shear or transtensional deformation accommodated by dislocation creep. One xenolith provides evidence for synkinematic reactive percolation of subduction-related Si-rich melts/fluids that resulted in oriented crystallization of orthopyroxene. Despite a seemingly undeformed microstructure, the CPO in orthopyroxenite veins in composite xenoliths is identical to those of pyroxenes in the host peridotite, suggesting late-kinematic crystallization. Based on these observations, we propose that the annealing producing the equigranular microstructures was triggered by melt percolation in the shallow subcontinental lithospheric mantle coeval to the late Neogene formation of veins in composite xenoliths. Calculated seismic properties are characterized by fast propagation of P waves and polarization of fast S waves parallel to olivine [100]-axis (stretching lineation). These data are compatible with present-day seismic anisotropy observations in SE Iberia if the foliations in the lithospheric mantle are steeply dipping and lineations are subhorizontal with ENE strike, implying dominantly horizontal mantle flow in the ENE-WSW direction within vertical planes, that is, subparallel to the paleo-Iberian margin. The measured anisotropy could thus reflect a lithospheric fabric due to strike-slip deformation in the late Miocene in the context of WSW tearing of the subducted south Iberian margin lithosphere.
ISSN: 0278-7407

Droits : info:eu-repo/semantics/OpenAccess
hal-01685809
https://hal.archives-ouvertes.fr/hal-01685809
https://hal.archives-ouvertes.fr/hal-01685809/document
https://hal.archives-ouvertes.fr/hal-01685809/file/Hidas_et_al-2016-Tectonics.pdf
DOI : 10.1002/2016TC004165

Éditeur(s) : HAL CCSD
Résumé : The territory of Armenia was located in the collision zone between Arabia and Eurasia, and is the seat of active intercontinental deformations, which was attested by the many historical earthquakes that have occurred in this region. All these destructive earthquakes show a strong regional seismic activity, and therefore it is important to evaluate the seismic hazard associated with active structures that generates this seismicity.This study presents the results of the analysis of the active tectonics within the northwestern and southeastern extensions of the Pambak-Sevan-Syunik fault (PSSF), a major right-lateral strike-slip fault cutting through Armenia (NW - SE). Quantifying the deformations in terms of geometry, kinematics, slip rates and earthquake activity, using cosmogenic 3He, OSL/IRSL and radiocarbon dating techniques, reveal different behaviors between the two regions.Within the northwestern extension, in the region of Amassia, the PSSF bends to the west and splits into two main WNW-ESE trending reverse faults defining a compressional pop-up structure. We estimate an uplift rate and a shortening rate of 0.5 ± 0.1 mm/y and 1.4 ± 0.6 mm/y, respectively. This suggests that most of the ~2 mm/y right lateral movement of the PSSF seems to be absorbed within the Amasia pop-structure.Within the southeastern extension, in the region of Tsghuk volcano, the PSSF shows signs of dying out at the southernmost tip of the Syunik graben. A very slow NS trending normal faulting associated with a slight right-lateral movement characterizes the tectonic activity in the region of Tsghuk volcano. We estimate vertical slip rates, EW stretching rate, and right-lateral slip rate of ~0.2 mm/y, ~0.1 mm/y and ~0.05 mm/y, respectively. These results lead to the conclusion that the right lateral movement observed further north along the PSSF is mainly transferred within other active faults further west within the Karabagh (Hagari fault or other structures further northwestwards).
L’Arménie se situe dans la zone de collision entre Arabie et Eurasie et est le siège d’une déformation intracontinental active comme l’atteste les nombreux tremblements de terre historiques qui s’y sont produits. Tous ces séismes, destructeurs, attestent d’une forte activité sismique régionale, et il est par conséquent important d'évaluer l’aléa sismique associé aux structures actives qui génère cette sismicité.Le travail présenté ici, expose les résultats de l’analyse de la tectonique active au niveau des terminaisons nord-ouest et sud-est de la faille de Pambak-Sevan-Syunik (PSSF), une des failles décrochant majeure qui traverse l'Arménie du NW au SE. La quantification des déformations en termes de géométrie, cinématique, vitesse de glissement et paléosismicité, en utilisant les méthodes de datation 3He cosmogénique, OSL/IRSL et radiocarbone, révèlent des comportements différents entre les deux régions.Au niveau de la terminaison nord-ouest, dans la région d’Amassia, la faille PSSF s’incurve vers l'ouest et se subdivise en deux branches de direction WNW-ESE, et de cinématique inverse, définissant une structure en pop-up. Nous estimons une vitesse de soulèvement de 0.5 ± 0.1 mm/an et une vitesse de raccourcissement NNE-SSW de 1.4 ± 0.6 mm/an. Ces résultats suggère que l’essentiel des ~2 mm/an de mouvement dextre estimés le long de la faille de PSSF sont absorbés au niveau du pop-up d’Amassia.Au niveau de la terminaison sud-est, dans la région du volcan Tsghuk, la faille PSSF semble disparaitre. Le peu d’activité tectonique est caractérisée par des failles normales sub-méridiennes associées à une légère composante décrochant dextre. Nous déterminons une vitesse de glissement vertical de ~0,2 mm/an, une vitesse d’extension ~EW de ~0,1 mm/an associée à une composante dextre de ~0,05 mm/an. Ces résultats suggèrent que le mouvement dextre observé le long de la faille de PSSF plus au nord, a été transféré sur d'autres failles plus à l'ouest dans le Karabakh (faille Hagari ou autres structures situés encore plus au NW).
https://tel.archives-ouvertes.fr/tel-01621440

NNT : 2016MONTT152
tel-01621440
https://tel.archives-ouvertes.fr/tel-01621440
https://tel.archives-ouvertes.fr/tel-01621440v2/document
https://tel.archives-ouvertes.fr/tel-01621440/file/2016_MKRTCHYAN_archivage.pdf

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
Nowadays, technological advances in satellite imagery measurements as well as the development of dense geodetic and seismologic networks allow for a detailed analysis of surface deformation associated with active fault seismic cycle. However, the study of earthquake dynamics faces several limiting factors related to the difficulty to access the deep source of earthquake and to integrate the characteristic time scales of deformation processes that extend from seconds to thousands of years. To overcome part of these limitations and better constrain the role and couplings between kinematic and mechanical parameters, we have developed a new experimental approach allowing for the simulation of strike-slip fault earthquakes and analyze in detail hundreds of successive seismic cycle. Model rheology is made of multilayered visco-elasto-plastic analog materials to account for the mechanical behavior of the upper and lower crust and to allow simulating brittle/ductile coupling, postseismic deformation phase and far-field stress transfers. The kinematic evolution of the model surface is monitored using an optical system, based on subpixel spectral correlation of high-resolution digital images. First, results show that the model succeed in reproducing the deformation mechanisms and surface kinematics associated to the main phases of the seismic cycle indicating that model scaling is satisfactory. These results are comforted by using numerical algorithms to study the strain and stress distribution at the surface and at depth, along the fault plane. Our analog modeling approach appears, then, as an efficient complementary approach to investigate earthquake dynamics.
ISSN: 0278-7407

hal-01174176
https://hal.archives-ouvertes.fr/hal-01174176
DOI : 10.1002/2014TC003701

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
We surveyed the junction between the central and southern Philippine Trench and the Sangihe Trench near 6øN using swath bathymetry, gravity, and magnetics. These data, along with seismicity, allow us to discuss the genetic relations between these trenches and the forces acting on converging plates. Our final model favors the northern extension of the Halmahera Arc up to 8øN, with three segments offset left-laterally along NW-SE transform faults. Accretion of the northern segment to Mindanao Island 4 to 5 m.y. ago resulted in the failure within the Philippine Sea Plate east of the arc. Initiation of the Philippine Trench between 7øN and 10øN agrees with the maximum recorded depth of the Philippine Trench floor (10,000 m below sea-level) and Philippine Sea slab (200 km). South of 6øN (trench junction), another segment of the arc is being subducted beneath the Sangihe margin, while south of 3øN, the southern segment of the Halmahera Arc is still active. The rapid southward shallowing of the trench floor along the southern Philippine Trench, the type of faulting affecting both sides of the trench, the lack of significant interplate seismicity, and the concentration of the seismicity beneath the Miangas-Talaud Ridge are interpreted as a slowing down of the subduction along this branch of the Philippine Trench compared with the rest of the subduction zone. The Sangihe deformation front has been recognized up to 7øN but seems active only south of 6øN.
ISSN: 2169-9275

hal-01261614
https://hal.archives-ouvertes.fr/hal-01261614
https://hal.archives-ouvertes.fr/hal-01261614/document
https://hal.archives-ouvertes.fr/hal-01261614/file/lallemandJGR1998.pdf

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
The reactivation of faults with near-optimal orientations is commonly considered to control the state of stress in the crust. Near the surface, where a principal stress direction is vertical, the attitude of such faults is explained by Anderson's theory. This raises the questions of how prevalent this type of faulting actually is in current seismicity, down to what depth it frequently occurs, and what range of friction angles explains it best. The Global Centroid Moment Tensor catalog is analyzed to address these questions. Dip-slip and strike-slip mechanisms are dominant, and oblique slips are relatively rare for well-constrained events with depths shallower than 30 km. Preferred Andersonian faulting is the simplest, but not the unique, explanation for this dominance. Isolating reverse, strike- slip, and normal events reveals an asymmetry in the distribution of nodal plane dips and plunges of the P, B, and T axes between reverse and normal faulting. Assuming that the most frequent events correspond to reactivation near optimal orientations yields 40-60 degrees and 0-20 degrees friction angles for reverse and normal faults, respectively. This indicates that reverse and normal faulting mechanics are not symmetrical with respect to stress configuration as predicted by Anderson's theory.
ISSN: 8755-1209

hal-00412159
https://hal.archives-ouvertes.fr/hal-00412159
DOI : 10.1029/2007RG000240

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The volume comprises some of the contributions presented during the 10th edition of the Alpine Meeting "CorseAlp 2011". It has been held in Saint Florent (Corsica) between 10th and 16th of April 2011 under the auspices of Societé Geologique de France, Società Geologica Italiana and the INGV (Istituto Nazionale di Geofisica e Vulcanologia) and with the collaboration of colleagues of Université de Corse (M.-M. Spella, M. and J. Ferrandini and L. Ciancaleoni) and the support of the city council of S. Florent. The meeting was framed in the series of "Alpine Workshops" e.g., Siegesmund et al. (2008), Handy and Rosenberg (2011), which are held every two years to develop interdisciplinary research on Alpine-type orogens. It hosted a variety of topical sessions from regional geology to process-oriented field and laboratory studies and gave the opportunity to collect multidisciplinary and multiscale approaches to geodynamic studies including continental rifting and ocean opening, oceanic and continental subduction, late- to post orogenic extension, exhumation of deep seated rocks, back-arc opening and microcontinent rotation, interfering orogenic-scale tectonics and surface processes, tectonics and seismic hazard within the Alpine chain and Mediterranean realms.
ISSN: 0040-1951

hal-00795580
https://hal.archives-ouvertes.fr/hal-00795580

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
Subduction of a narrow slab of oceanic lithosphere beneath a tightly curved orogenic arc requires the presence of at least one lithospheric scale tear fault. While the Calabrian subduction beneath southern Italy is considered to be the type example of this geodynamic setting, the geometry, kinematics and surface expression of the associated lateral, slab tear fault offshore eastern Sicily remain controversial. Results from a new marine geophysical survey conducted in the Ionian Sea, using high-resolution bathymetry and seismic profiling reveal active faulting at the seafloor within a 140 km long, two-branched fault system near Alfeo Seamount. The previously unidentified 60 km long NW trending North Alfeo Fault system shows primarily strike-slip kinematics as indicated by the morphology and steep-dipping transpressional and transtensional faults. Available earthquake focal mechanisms indicate dextral strike-slip motion along this fault segment. The 80 km long SSE trending South Alfeo fault system is expressed by one or two steeply dipping normal faults, bounding the western side of a 500+ m thick, 5 km wide, elongate, syntectonic Plio-Quaternary sedimentary basin. Both branches of the fault system are mechanically capable of generating magnitude 6–7 earthquakes like those that struck eastern Sicily in 1169, 1542, and 1693.
ISSN: 0278-7407

insu-01256887
https://hal-insu.archives-ouvertes.fr/insu-01256887
https://hal-insu.archives-ouvertes.fr/insu-01256887/document
https://hal-insu.archives-ouvertes.fr/insu-01256887/file/GutscherEtal_2015_Tectonics.pdf
DOI : 10.1002/2015TC003898

Éditeur(s) : HAL CCSD
Résumé : The Deep Basin of the Gulf of Mexico (DBGM) extends over eastern Mexico, the southeastern part of the United States, west of the Atlantic Ocean. This study, based on the interpretation and integration of seismic profiles, exploration wells and outcrop studies, focus on the deep part of the Gulf of Mexico, where bathymetry varies from 200 to 3750 m, thus comprising both the continental slope and the abyssal plain. The first part of this thesis focus on the description of the sedimentary infill of the western part of the Gulf of Mexico, in the Veracruz State, and to its geodynamic controls. The geodynamic evolution of the Deep Basin of the Gulf of Mexico (DBGM) begins during the Triassic-Jurassic with the break-up and the opening of a continental rift, in the southern part of the North American lithospheric plate. This opening induced a relative movement of the Yucatan Block towards the southeast. This intra-continental rifting episode was followed by a stage of post-rift thermal subsidence in the basins of the continental margin in the west, coeval with oceanic accretion in the DBGM. The thermal subsidence of the margin was subsequently modified by the Laramian orogeny, which impacted strongly the overall architecture of the margin as well as its litho-stratigraphic evolution, inducing the deposition of siliciclastic deposits in various morphotectonic provinces: i.e., near the tectonic front of the Sierra Madre Oriental (SMO), within the adjacent Chicontepec foreland basin, over the Tuxpan Platform (Golden Lane), across the continental slope and up to the deep abyssal plain, these two last morphotectonic provinces belonging to the DBGM. During the Early Paleogene, the effects of the thermal subsidence of the passive margin were stressed by the tectonic load of the Laramian orogen (i.e., the Sierra Madre Oriental, SMO), thus allowing the development of a foreland basin flexural. In this geodynamic framework, the main sedimentary transfers developed from the tectonic front "SMO" in the west, towards the DBGM in the east, the main source for clastic sediments being linked to the erosion of the "SMO" mountains. During the Paleocene and the Early Eocene, the architecture of the silici-clastic syn-tectonic sediments deposited in submarine fans was characterized by sliding, turbidites with A and B Bouma facies, as well as levees and channels. After the stop of the flexural subsidence, the thermal subsidence of the passive margin resumed during the Late Eocene, the Oligocene and the Neogene, allowing the development of a new sedimentary prism, prograding eastwards toward the DBGM. This sedimentary infill was again made up of levees-channels, sand bars and delta systems. During the Neogene, an extensional system with listric faults and roll-over features developed across the slope of the DBGM, due to an active detachment developing within overpressured Eocene-Oligocene clays. This gravitational gliding of Neogene series accounted also for the development of compressional features at the toe of the slope. Approximately 60% of the Miocene siliciclastic sediments have been trapped in growth strata and slope basins associated with this complex gravitational system, ranging from river-delta features towards gravity slides associated with slump facies. The second part of this thesis aims at a quantification of these various processes, including the construction of balanced cross sections, forward Thrustpack kinematic modelling coupling the development of a basal detachment, lithospheric flexure, erosion and sedimentation, as well as subsequent stratigraphic modelling with the Dionisos software, the later aiming at predicting the sand versus clay ratios in Neogene siliciclastic deposits of the DBGM and its surroundings.
Le bassin profond du Golfe du Mexique (BPMG) est localisé à l'est du Mexique, au sud-est des États-Unis et à l'ouest de l'Océan Atlantique. Cette étude de la partie profonde du Golfe du Mexique est basée sur l'intégration de données de sismique, de forages pétroliers et d'études de terrain; elle comprend toute la pente continentale et la plaine abyssale, avec une bathymétrie qui varie de 200 à 3750 m. La première partie de cette thèse est consacrée à la description du remplissage sédimentaire de la bordure occidentale du Golfe du Mexique, dans le secteur de Veracruz, en liaison avec son évolution géodynamique. L'évolution géodynamique du BPMG commence au Trias-Jurassique avec la rupture et la propagation d'un rift continental, dans le secteur sud de la plaque nord américaine. Cette ouverture et le déplacement relatif vers le sud-est du bloc crustal du Yucatan sont à l'origine du BPGM. Cette géodynamique de rift continental est suivie d'une étape post-rift accompagnée de l'océanisation du bassin. Les bassins de la marge passive ont poursuivi leur évolution sous l'effet de la subsidence thermique à l'ouest du Golfe du Mexique, tandis que de la croûte océanique se formait dans le BPGM. Cette subsidence thermique de la marge a ensuite été perturbée par l'orogénèse Laramienne, qui a remodelé l'architecture stratigraphique silico-clastique des dépôts du Tertiaire entre les éléments morphotectoniques suivants: lefront tectonique de la Sierra Madre Orientale (SMO), le bassin d'avant-pays Chicontepec, la Plateforme de Tuxpan-Faja de Oro, la pente continentale et la plaine abyssale, ces deux dernières provinces morphotectoniques appartenant au BPGM. Pendant le Paléogèneinférieur, les effets de la subsidence thermique de la marge passive ont été accentués par la charge tectonique de l'orogénèse laramienne (SMO), permettant ainsi le développement d'un bassin flexural d'avant-pays. Au cours de cette étape, les principaux transferts sédimentaires se sont effectués du front tectonique "SMO" vers le BPGM. La source principale de sédiments clastiques est liée à l'érosion de la chaîne de montagnes "SMO". Pendant le Paléocène et l'Éocène inférieur, l'architecture des premiers sédiments silico-clastiques syn-tectoniques déposés dans des éventails sous-marins sont caractérisés par des figures de glissement, des faciès turbiditiques A et B de Bouma, des chenaux-levées. Après l'arrêt de la subsidence flexurale, la subsidence thermique de la marge passive s'est poursuivie pendant l'Éocène supérieur, l'Oligocène et le Néogène, permettant le développement d'un nouveau prisme sédimentaire progradant. Les remplissages sédimentaires sont encore constitués de chenaux et de levées, avec des barres de sable associées à des systèmes deltaïques sur la plateforme. Pendant le Néogène, un système de failles listriques s'est développé sur la pente du BPGM, au-dessus d'une surface de décollement située, dans la région d'étude, dans les argiles de l'Éocène-Oligocène. Ce système de failles de croissance a piégé plus de 60% des sédiments silico-clastiques du Miocène. Ce remplissage sédimentaire évolue latéralement de faciès fluviaux deltaïques vers des faciès de pente affectés de glissements gravitaires et associés à des turbidites. La deuxième partie de cette thèse est consacrée à une approche quantitative basée sur des modélisations structurales (coupes équilibrées et modélisations cinématiques directes avec Thrustpack, couplant décollement gravitaire, flexure lithosphérique, érosion et sédimentation), puis sédimentaires (prise en compte des transferts de matériel clastique depuis la partie émergée de la chaîne jusqu'au bassin profond, à l'aide du logiciel Dionisos, afin de mieux comprendre les processus de piégeage des sédiments grossiers dans les structures de croissance et les bassins perchés de la marge.
https://tel.archives-ouvertes.fr/tel-00435120

tel-00435120
https://tel.archives-ouvertes.fr/tel-00435120
https://tel.archives-ouvertes.fr/tel-00435120/document
https://tel.archives-ouvertes.fr/tel-00435120/file/thesealzaga.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Reef positions record the interaction between eustasy and tectonics, and have been used worldwide to characterize vertical deformations of upper-plates at different time-scales and constrain the seismic behavior of megathrusts. Along the Lesser Antilles volcanic arc, high-resolution marine geophysical data were collected on the 2–20 km wide eastern Martinique reef platform to reconstruct its stratigraphic and morphologic history, and understand the influence of local normal faulting, volcanism and plate-scale subduction processes on Holocene and Late Pleistocene reef development. The subsiding Martinique platform's stratigraphy is composed of multiple superimposed sea-level highstand deposits separated by subaerial exposure surfaces of sea-level low stands. The carbonate platform consists of two laterally-extensive carbonate units (unit U2 overlying unit U3) that extend to the platform edge to a depth of − 95 m MSL (mean sea level), and form two morphologic terraces, M2 and M3 respectively. The landward portion of unit U2 is partially overlain between 0 and − 60 m MSL by the living reef tract U1. The current reef is composed of a landward fringing reef, a lagoon and a seaward barrier reef, the latter forming a double-bank barrier around the Caravelle Peninsula. In near-shore multi-channel seismic profiles, a distinct reflector at ~− 35 m MSL, probably a subaerial exposure surface E1, separates the reef sequence formed during the last transgression from a Pleistocene fossil reef tract forming unit U2. Offshore of Mount Pelée volcano (Late Pleistocene), the Holocene reef did not develop above unit U2, whose upper surface is incised by channels and apparent sinkholes. During the Holocene transgression, the possibility of excessive turbidity due to volcanic activity may have inhibited reef development in this area. The un-dated unit U2 probably developed 120–130 ka ago during the last interglacial (MIS 5.5) + 6 m MSL highstand as thick, extensive reefs deposited all along the Lesser Antilles arc. Due to subsidence, MIS 5.5 reefs are not represented by onshore facies, except along the southern Sainte Anne Peninsula where normal faulting and uplift balances island-scale subsidence. Based on unit U2's present elevation and assuming an MIS 5.5 age and + 6 m MSL sea level, Martinique has subsided at maximum 0.3 m/ky, likely due to subduction processes that question the coupling state of the megathrust.
ISSN: 0025-3227

hal-01307036
https://hal.archives-ouvertes.fr/hal-01307036
DOI : 10.1016/j.margeo.2015.08.001

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