Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Mass balances are often used to calculate sediment fluxes in foreland basins and denudation rates in adjacent mountain ranges on intermediate to long timescales (from a few tens of thousand to a million years). Here, we study the simple Quaternary catchment-alluvial fan system of the Kuitun River, in northern Tian Shan, to discuss some ideas about sediment storage, release, and bypass in relatively short (100 km long) sediment routing systems. This study shows that the Kuitun catchment and piedmont areas clearly present evidence of a significant and temporary storage of sediments during the Pleistocene. These sediments were then excavated and delivered farther into the foreland basin during the Holocene. The difference between the volumes of materials released from the catchment and piedmont areas (5.5 ± 1.7 km3) and the volume stored in a contemporaneous fan downstream (2.6 ± 0.6 km3) indicates that the latter did not trap the whole sediment load transported by the river. The alluvial fan was bypassed by 27 to 78% of this load toward its distal alluvial plain. If this value is well estimated, it implies a major volumetric partitioning of the deposits between the fan and the alluvial plain, with a very high sedimentation rate in the fan (1.97 ± 0.52 mm*y− 1) and a much lower one downstream (0.11 ± 0.11 mm*y− 1). However, this volumetric partitioning might only occur during periods with a very specific hydrological regime such as the Holocene deglaciation. Eventually, the peculiar sediment storage and release pattern within the Kuitun catchment and piedmont areas during the Pleistocene and Holocene complicates the calculation of mean paleodenudation rates using either sediment budgets or in situ produced cosmogenic nuclides.
ISSN: 0169-555X

insu-00985283
https://hal-insu.archives-ouvertes.fr/insu-00985283
https://hal-insu.archives-ouvertes.fr/insu-00985283/document
https://hal-insu.archives-ouvertes.fr/insu-00985283/file/jolivet-et_al-2014_HAL.pdf
DOI : 10.1016/j.geomorph.2014.01.024

Éditeur(s) : HAL CCSD Bureau de recherches géologiques et minières
Résumé : National audience
Les tremblements de Terre sont sans doute l’un des phénomènes les plus catastrophiques associés à la dynamique de notre planète. Leur occurrence peut être associée d’une part au chargement lent et progressif des failles dû au mouvement des plaques tectoniques, mais également à la proximité d’autres séismes qui peuvent localement provoquer une déstabilisation du milieu. Les séismes sont classiquement interprétés dans le cadre de la théorie du cycle sismique (Fig. 1). La période asismique, correspondant au chargement séculaire des contraintes sur le plan des failles, est appelée période inter-sismique. Sa durée, entre 50 et 1000 ans, dépend du contexte géodynamique et notamment de la vitesse de chargement. La phase co-sismique correspond au séisme, i.e. à la phase de nucléation et de propagation de la rupture sismique. La période de temps associée est extrêmement courte et varie suivant les séismes entre quelques secondes à plusieurs minutes pour les méga-tremblements de terre comme celui de Sumatra en 2004 ou plus récemment celui du Japon en 2011. Enfin, suite à la rupture sismique, on considère une phase post-sismique qui correspond à un réajustement mécanique rapide du milieu qui peut s’effectuer sur plusieurs semaines, mois ou même années. La courte échelle de temps des observations sismologiques ou géodésiques (<100 ans) par rapport à la durée d’un cycle sismique (plusieurs centaines d’années) est un facteur limitant. Ainsi, aucun cycle sismique complet n’a pour l’instant pu être documenté.
ISSN: 0292-8477

insu-00913121
https://hal-insu.archives-ouvertes.fr/insu-00913121
https://hal-insu.archives-ouvertes.fr/insu-00913121/document
https://hal-insu.archives-ouvertes.fr/insu-00913121/file/geochronique_cattinetal.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
To test the impact of fluid flow on the reactivity of porous (ultra-)mafic rocks, reactive percolation experiments were realized during which CO2-enriched water was injected at two different injection rates (Q = 0.1 and 1 mL h−1) through sintered analogues of olivine-accumulation zones in basaltic flows at temperature and fluid composition conditions (T = 180 °C; NaHCO3 buffered solution) favorable for CO2-mineralization (carbonation).All experiments resulted in silicate dissolution, carbonate precipitation upstream and (proto-)serpentine formation downstream indicating a decrease in the fluid reactivity along flow paths. The measured bulk carbonation rates ranged from 4 to 7 × 10−8 s−1; these values were significantly lower than previously published values of olivine carbonation rate obtained on powders in closed batch and flow-through reactors. Our study show complex couplings, at pore scale, between fluid flow, localization of reaction zones, and chemical reaction kinetics which in turn control hydrodynamic properties, carbonation rate and efficiency and fluid reactivity. This results in carbonation rates being higher when injection rates are high and permeability ultimately controlling carbonation reactions by limiting fluid input. During experiments, notable changes in permeability occurred for only minor changes in porosity indicating a control by the geometry of the porous network: heterogeneities in the distribution of flow paths favored the localization of precipitated minerals which in turn resulted in the closure of flow paths. This mechanism was particularly efficient at low injection rates. These results imply that controlling the injection rate could allow enhancing/limiting the efficiency of in situ carbonation.
ISSN: 0883-2927

hal-01115284
https://hal.archives-ouvertes.fr/hal-01115284
DOI : 10.1016/j.apgeochem.2014.11.024

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
A network of 26 GPS sites was implemented in Iran and Northern Oman to measure displacements in this part of the Arabia–Eurasia collision zone. We present the GPS velocity field obtained from three surveys performed in 1999 September, 2001 October and 2005 September and the deduced strain tensor. This study refines previous studies inferred from only the two first surveys. Improvements are significant in NE Iran. The present-day shortening rate across the mountain belts of NE Iran is estimated to 5 ± 1 mm yr−1 at about N11°, 2 ± 1 mm yr−1 of NS shortening across the eastern Kopet Dag and 3 ± 1 mm yr−1 of NS shortening across Binalud and Kuh-e-Sorkh. Our GPS measurements emphasize the varying character of the Kopet Dag deformation between its southeastern part with prevailing thrusting at low rates and its northwestern part with dominant strike-slip activity at increasing rates. The principal axes of the horizontal strain tensor appears very homogeneous from the Zagros to the Alborz and the Kopet-Dag (N20°) and in eastern Iran (Makran and Lut block: N30°). Only NW Iran suffers a variable strain pattern which seems to wrap the Caspian basin. The strain tensor map underlines the existence of large homogeneous tectonic provinces in terms of style and amplitude of the deformation.
ISSN: 0956-540X

insu-00346744
https://hal-insu.archives-ouvertes.fr/insu-00346744
DOI : 10.1111/j.1365-246X.2007.03477.x

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
[1] Large changes in magnetic mineral concentration dependent parameters by more than 1 order of magnitude occur over 50–150 cm intervals in two marine sediment cores from the oxygen minimum zone in the Gulf of Aden. High-resolution sedimentological and chemical analyses indicate that these intervals are not associated with turbiditic events or sediment reworking, they do not result from changes in carbonate dilution or differences in sediment properties, and they do not correspond to volcanic layers. Magnetic mineralogical analyses reveal a change in magnetic mineral concentration from a magnetite-goethite assemblage to pure magnetite within the peak. The peaks almost disappear when the abundance of magnetic minerals is calculated after correcting for the magnetic moments of each magnetic mineral. Therefore, under the assumption that the variability of the magnetic parameters results from postdepositional mineralogical transformations, a relatively constant amount of magnetite was present at the surface of the sediment. Changes in redox conditions and nonsteady state diagenesis transformations have effectively been observed along both cores. Large values of total organic carbon coincide with poor preservation of biogenic and detrital magnetite, which reflects reductive dissolution of the finer magnetite grains. At the same levels, Fe 2þ release from reductively dissolved magnetite favored precipitation of goethite. The susceptibility peaks coincide with episodes of magnetite preservation caused by reduced surface
ISSN: 1525-2027

insu-01311064
https://hal-insu.archives-ouvertes.fr/insu-01311064
https://hal-insu.archives-ouvertes.fr/insu-01311064/document
https://hal-insu.archives-ouvertes.fr/insu-01311064/file/ggge2013-14-3779-bouilloux.pdf
DOI : 10.1002/ggge.20234

Éditeur(s) : HAL CCSD
Résumé : The evolution of mountain belt piedmont is controlled by interactions between tectonics, erosion and sedimentation. To study coupling between these processes, we analyze morphometric data collected in the eastern Tian Shan piedmont (NW China) and develop a new analogue modelling technique. The modeling approach uses an experimental set-up and analog material specifically designed to study simultaneously tectonic structures (faults, folds), detailed morphology (drainage basins, channels, alluvial fans, etc.) and stratified sedimentation. Measurement techniques based on laser interferometry and image correlation are also developed to quantify the topographic and kinematic evolution of models.
Our experiments allow a new approach for the study of piedmont morphotectonic evolution. Our results indicate that tectonics mainly controls this evolution. The propagation of deformation and the formation of relief both significantly influence the development of drainage networks, the evolution of drainage basins and the formation of morphotectonic markers. Particularly, a study of alluvial fans and watershed metrics suggests that there is a dynamical equilibrium between uplift, erosion and morphology. In addition, our results show that terrace nucleation is controlled by thrust activity and hydrography adjustments. Folding of terraces responds to a homothetic deformation pattern.
This new methodology brings promising perspectives in the fields of geomorphology, seismotectonics and sedimentology.
L'évolution d'un piémont de chaîne de montagnes est contrôlée par les interactions entre la tectonique, l'érosion et la sédimentation. Pour étudier ces processus, nous avons analysé des données morphométriques issues des piémonts orientaux du Tian Shan (NW Chine) et développé un nouveau type de modélisation analogique. Cette approche utilise un dispositif et un matériau expérimental spécialement conçus pour modéliser simultanément des structures tectoniques (failles, plis), une morphologie détaillée (bassins versants, rivières, cônes alluviaux, etc.) et une sédimentation stratifiée. Des techniques de mesure optique ont été également mises en oeuvre afin de quantifier l'évolution topographique et cinématique des modèles.
Les expériences réalisées offrent une opportunité inédite d'étudier l'évolution morphotectonique d'un piémont. Nos résultats montrent que la tectonique exerce un contrôle de premier ordre sur cette évolution. La propagation de la déformation et la formation des reliefs influencent en effet significativement le développement du réseau de drainage, l'évolution des bassins versants et la formation des marqueurs morphotectoniques. En particulier, l'analyse de la morphométrie des cônes alluviaux et de leurs bassins versants suggère qu'un équilibre dynamique s'installe entre la surrection, l'érosion et la morphologie. Nos résultats montrent également que l'apparition des terrasses est guidée par l'activité des chevauchements et les adaptations de l'hydrographie. Leur modèle de plissement répond à une déformation homothétique.
Cette nouvelle approche ouvre des perspectives d'étude prometteuses en géomorphologie, sismotectonique et stratigraphie.
https://tel.archives-ouvertes.fr/tel-00339145

tel-00339145
https://tel.archives-ouvertes.fr/tel-00339145
https://tel.archives-ouvertes.fr/tel-00339145v2/document
https://tel.archives-ouvertes.fr/tel-00339145/file/These_Graveleau08.pdf

Éditeur(s) : HAL CCSD Himalayan Association Advance Science
Résumé : The Himalayas and the Tibetan Plateau are considered as the classical case of continental collision.
ISSN: 1727-5210

hal-00854401
https://hal.archives-ouvertes.fr/hal-00854401
DOI : 10.3126/hjs.v5i7.1267

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Our knowledge and understanding of the 3-D lithospheric structure of the Himalayas and the Tibetan Plateau is still challenging although numerous geophysical studies have been performed in the region. The GOCE satellite mission has the ambitious goal of mapping Earth's gravity field with unprecedented precision (i.e. an accuracy of 1-2 mGal for a spatial resolution of 100 km) to observe the lithosphere and upper-mantle structure. Consequently, it gives new insights in the lithospheric structure beneath the Himalayas and the Tibetan Plateau. Indeed, the GOCE gravity data now allow us to develop a new strategy for joint gravimetry-seismology inversion. Combined with teleseismic data over a large region in a joint inversion scheme, they will lead to lithospheric velocity-density models constrained in two complementary ways. We apply this joint inversion scheme to the Hi-CLIMB (Himalayan-Tibetan Continental Lithosphere during Mountain Building) seismological network which was deployed in South Tibet and the Himalayas for a 3-yr period. The large size of the network, the high quality of the seismological data and the new GOCE gravity data set allow us to image the entire lithosphere of this active area in an innovative way. We image 3-D low velocity and density structures in the middle crust that fit the location of discontinuous low S-velocity zones revealed by receiver functions in previous geophysical studies. In the deeper parts of our velocity model we image a positive anomaly interpreted to be the heterogenous Indian lithosphere vertically descending beneath the centre of the Tibetan Plateau.
ISSN: 0956-540X

hal-00858024
https://hal.archives-ouvertes.fr/hal-00858024
DOI : 10.1093/gji/ggs110

Éditeur(s) : HAL CCSD American Institute of Physics
Résumé : International audience
In order to be able to provide valuable data in multiparameter measurement field operations, tiltmeters need to have a noise level better or equal than 10-9 rad for a period range from a few minutes to a few years and a long term stability ranging from 10-7 to 10-8 rad/yr. Tiltmeter measurements should also be as much as possible insensitive to thermal disturbances, by taking great care of the horizontality of the base line tube first. Secondly, thermal responses have been assessed. We also took great care of the coupling of our tiltmeters with the bedrock. We've designed a long base tiltmeter with sensors in silica which has a low dilatation coefficient. The linear variable displacement transducer is based on coil coupling (powered by an alternative voltage). Finally we show the results of two 100 m silica water tube tiltmeters which were installed in a mine in the French Vosges massif in the framework of a hydrology research project. These instruments show a remarkably good stability (6.5×10-9 rad/month) and a low noise level (of the order of 10-11 rad). Toroidal and spheroidal free modes of the Earth were observed after the two last major earthquakes on Sumatra.
ISSN: 0034-6748

hal-00708013
https://hal.archives-ouvertes.fr/hal-00708013
https://hal.archives-ouvertes.fr/hal-00708013/document
https://hal.archives-ouvertes.fr/hal-00708013/file/2008_RSI.pdf
BIBCODE : 2008RScI...79c4502B

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Field evidence for syn-deformation migmatization and crystallization along the Karakorum fault contradicts the study of Wang et al. (2012). The ages of such magmatic rocks provide minimum ages for the onset of deformation at similar to 23 Ma in North Ayilari and similar to 19 Ma in Tangtse. The onset of deformation at 12 Ma in the Ayilari range inferred by Wang et al. (2012) from a muscovite Ar/Ar age is a cooling age, thus only a minimum age. The similar to 60 Ma granodiorite bodies, the ophiolitic rocks and the south Kailash thrust that are correlated across the fault to provide a 52 +/- 2 km finite offset do not define reliable piercing points. Such observations as well as our previous work concur to show that the Karakorum fault initiated in the Oligo-Miocene, and has a long-term dextral slip-rate between 7.5 and 13 mm/yr, approximately twice that proposed by Wang et al. (2012).
ISSN: 0012-821X

hal-00829469
https://hal.archives-ouvertes.fr/hal-00829469
DOI : 10.1016/j.epsl.2012.12.012

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The N-S oriented Raghane shear zone (8 degrees 30') delineates the western boundary of the Saharan metacraton and is, with the 4 degrees 50' shear zone, the most important shear zone in the Tuareg shield. It can be followed on 1000 km in the basement from southern Air, Niger to NE Hoggar, Algeria. Large subhorizontal movements have occurred during the Pan-African orogeny and several groups of granitoids intruded during the Neoproterozoic. We report U-Pb zircon datings (laser ICP-MS) showing that three magmatic suites of granitoids emplaced close to the Raghane shear zone at c. 790 Ma, c. 590 and c. 550 Ma. A comprehensive and detailed (158 sites, more than 1000 cores) magnetic fabric study was performed on 8 plutons belonging to the three magmatic suites and distributed on 200 km along the Raghane shear zone. The main minerals in all the target plutons do not show visible preferential magmatic orientation except in narrow shear zones. The AMS study shows that all plutons have a magnetic lineation and foliation compatible with the deformed zones that are zones deformed lately in post-solidus conditions. These structures are related to the nearby mega-shear zones, the Raghane shear zone for most of them. The old c. 793 Ma Touffok granite preserved locally its original structures. The magnetic structures of the c. 593 Ma Ohergehem pluton, intruded in the Aouzegueur terrane, are related to thrust structures generated by the Raghane shear zone while it is not the case of the contemporaneous plutons in the Assode-Issalane terrane whose structures are only related to the subvertical shear zones. Finally, the c. 550 Ma granite group has magnetic structure related to the N-S oriented Raghane shear zone and its associated NNE-SSW structures when close to them, but NW-SE oriented when further. These NW-SE oriented structures appear to be characteristic of the late Neoproterozoic evolution of the Saharan metacraton and are in relation to the convergence with the Murzuq craton. This evolution reflects the rheological contrast existing along the Raghane shear zone marking the western boundary of the Saharan metacraton.
ISSN: 0040-1951

hal-00429354
https://hal.archives-ouvertes.fr/hal-00429354
DOI : 10.1016/j.tecto.2009.04.022

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We use 36Cl surface exposure dating to determine the slip release pattern over the last ~ 15 kyr for the Velino-Magnola fault, a major active normal fault in Central Italy. We sampled the fault at five well-separated sites along its length, and modeled the 36Cl concentrations measured in the 376 samples. We find that the fault broke in at least 9 large earthquakes that occurred in two 5-6 ka-long supercycles. Each cycle included a 4-5 ka-long phase of relative quiescence, followed by a cluster of at least 3 large earthquakes or earthquake sequences that released most of the accumulated strain in ~ 1 ka. All 9 identified events broke the entire fault and produced maximum surface slips of 2-3 m. Though the Velino-Magnola fault seems presently in a stage of relative quiescence, it may re-enter a phase of paroxysmal seismic activity in a few hundred of years
ISSN: 0012-821X

hal-00667280
https://hal.archives-ouvertes.fr/hal-00667280
DOI : 10.1016/j.epsl.2011.05.022

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Sensitive instruments like strainmeters and tiltmeters are necessary for measuring slowly varying low amplitude Earth deformations. Nonetheless, laser and fibre interferometers are particularly suitable for interrogating such instruments due to their extreme precision and accuracy. In this paper, a practical design of a simple pendulum borehole tiltmeter based on laser fibre interferometric displacement sensors is presented. A prototype instrument has been constructed using welded borosilicate with a pendulum length of 0.85 m resulting in a main resonance frequency of 0.6 Hz. By implementing three coplanar extrinsic fibre Fabry-Perot in-terferometric probes and appropriate signal filtering, our instrument provides tilt measurements that are insensitive to parasitic deformations caused by temperature and pressure variations. This prototype has been installed in an underground facility (Rustrel, France) where results show accurate measurements of Earth strains derived from Earth and ocean tides, local hydro-logic effects, as well as local and remote earthquakes. The large dynamic range and the high sensitivity of this tiltmeter render it an invaluable tool for numerous geophysical applications such as transient fault motion, volcanic strain and reservoir monitoring.
ISSN: 0956-540X

hal-01265967
https://hal.archives-ouvertes.fr/hal-01265967
https://hal.archives-ouvertes.fr/hal-01265967/document
https://hal.archives-ouvertes.fr/hal-01265967/file/HCS1.pdf
DOI : 10.1093/gji/ggv358

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
The strike-slip faults of north Tibet accommodate part of the Cenozoic convergence between India and Asia. Along the Karakax valley south of Yecheng and near the Xidatan trough south of Golmud, the active traces of the Altyn-Tagh and Kunlun faults follow narrow belts of metamorphic rocks. The deformation recorded in those mylonites is sinistral strike-slip. Rb/Sr and 40Ar/39Ar ages of deformation from syntectonic fabrics formed at 350–400°C 120 Ma. Argon loss suggests that deformation was associated to a 250–300°C thermal pulse that lasted 5–20 Ma after the onset of movement. Unroofing occurred much later, around 25 Ma when sudden cooling suggests a component of thrusting or more likely normal faulting. The Cretaceous shear may be related to collision between the Qiantang and the Lhasa blocks. The Karakax and Xidatan shear zones may have formed a unique, continuous boundary in the Cretaceous, which was later reused by the Tertiary strike-slip faults, leading to potentially calculable offsets along the Altyn-Tagh fault.
ISSN: 2169-9313

hal-00197562
https://hal.archives-ouvertes.fr/hal-00197562
https://hal.archives-ouvertes.fr/hal-00197562/document
https://hal.archives-ouvertes.fr/hal-00197562/file/Arnaud_JGR000904_def.pdf
DOI : 10.1029/2001JB000904

Éditeur(s) : HAL CCSD
Résumé : International audience
A fiber interferometer interfaced to 3 geo-mechanical elements is presented for applications in geophysics. The fiber sensor is based on an extrinsic fiber Fabry-Perot interferometer (EFFPI) which incorporates a modulation scheme to lock the interferometer at quadrature and to enable displacement measurements below a quarter of the interrogating wavelength. It operates over a relatively large frequency dynamic of ~500000 with a precision better than 2 nm. The fiber interferometer is next interfaced to a differential hydrostatic long baseline inclinometer, a 3-axis borehole tiltmeter and a single-axis seismometer, respectively. Results obtained demonstrate that the fiber interferometrically-interrogated instruments exhibit performances equivalent to or even surpassing those of the reference instruments employed for comparison during their deployment to an underground test site since March 2012. Keywords—modulation-based extrinsic fiber Fabry-Perot interferometer; fiber optique hydrostatic inclinometer; fiber optique borehole tiltmeter; fiber optique seismometer
IEEE SENSORS 2015
Busan, South Korea

hal-01265963
https://hal.archives-ouvertes.fr/hal-01265963
https://hal.archives-ouvertes.fr/hal-01265963/document
https://hal.archives-ouvertes.fr/hal-01265963/file/HCS3.pdf
DOI : 10.1109/ICSENS.2015.7370316

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The timing of E–W extension of the Tibetan plateau provides a test of mechanical models of the geodynamic evolution of the India–Asia convergence zone. In this work we focus on the Kung Co half graben (Southern Tibet, China), bounded by an active N–S normal fault with a minimum vertical offset of 1600 m. To estimate the onset of normal faulting we combined high and medium temperature (U–Pb, Ar/Ar) and low temperature ((U–Th)/He) thermochronometry of the Kung Co pluton, a two-mica granite of the northern Himalayan granitic belt that outcrop in the footwall of the fault. Biotite and muscovite Ar/Ar ages , are close from each other [not, vert, similar 16 Ma ± 0.2 (Ms) and not, vert, similar 15 ± 0.4 Ma (Bt)], which is typical of fast cooling. The zircon and apatite (U–Th)/He ages range from 11.3 to 9.6 Ma and 9.9 to 3.7 Ma respectively. These He ages are indicative of (1) fast initial cooling, from 11.3 to not, vert, similar 9 Ma, gradually decreasing with time and (2) a high geothermal gradient (not, vert, similar 400 °C/km), close to the surface at not, vert, similar 10 Ma. The Kung Co pluton was emplaced at about 22 Ma (U–Pb on zircon) at less than 10 km depth and 520–545 °C. Subsequent to its shallow emplacement, the pluton underwent fast thermal re-equilibration ending around 7.5 Ma, followed by a period of slow cooling caused either by the end of the thermal re-equilibration or by very slow exhumation (0.02–0.03 mm/yr) from not, vert, similar 7.5 Ma to at least 4 Ma. In either case the data suggest that the exhumation rate increased after 4 Ma. We infer this increase to be related to the initiation of the Kung Co normal fault. A critical examination of previously published data show that most not, vert, similar N–S Tibetan normal faults may have formed less than 5 Ma ago rather than in the Miocene as assumed by several authors. Such a young age implies that E–W extension is not related to the Neogene South Tibetan magmatism (25 to 8 Ma). Consequently, models relating E–W extension to magmatism, such as convective removal of the lower lithosphere, may be inappropriate. We rather think that this extension is related with local accommodation of boundary forces and displacements.
ISSN: 0012-821X

hal-00311791
https://hal.archives-ouvertes.fr/hal-00311791
DOI : 10.1016/j.epsl.2007.01.029

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Cold seeps, located on sea floors and frequently fueled with methane, have been much studied for the formation of carbonate nodules, crusts or masses resulting from the activity og communities of anaerobic bacteria. In this paper, we examine the impact of cold seepage on their caging sediments, as far as their geochemical composition and microfaunal content are concerned. To this end, two fossil cold seeps of the Jurassic Beauvoisin site (Vocontian Trough, SE-France) are studied, focusing on the redox-sensitive and/or sulfide-forming trace metals. We observe that: 1) the carbonate edifices of the cold seeps are enriched in specific elements, namely, Sr, Mo As and Sb, compared to their caging marlstones, and 2) the benthic foraminifer populations were present close to the edifices. The Sr enrichment is ascribed to a contamination of the seeping fluids at the contact with underlying evaporites; the Mo-As-Sb enrichment may have several, non-exclusive, origins. We retain two scenarios; in the first one, the enrichment is due to the ascending fluids that could collect these elements when passing through thick shaly formations; in the second scenario, Mo, As and Sb were supplied to the sites of carbonate precipitation together with Fe- and Mn-oxy-hydroxides (the so-called particulate shuttle process). We favor the second scenario (possibly coupled to the first one) because the rather uncommon Mo-As-Sb association is also observed for reducing sediments deposited under the influence of Fe-Mn-shuttling.
ISSN: 0009-2541

hal-00806655
https://hal.archives-ouvertes.fr/hal-00806655
DOI : 10.1016/j.chemgeo.2012.12.012

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Field study, thermochronology and geochemistry of the east Lungmu Co (LMC) range highlight some of the geological events that shaped western Tibet. The LMC fault zone has long been interpreted as the boundary between the Tianshuihai terrane of Laurasian affinity and the Qiangtang block of Gondwanian affinity. In the LMC range, the Paleozoic series is intruded by the Mangtsa leucogranite whose zircon have a U/Pb age of 116.9 ± 1 Ma and by mafic rocks with U/Pb zircon ages ranging from 116.9 ± 1 to 95.1 ± 1.7 Ma. Geochemistry of the mafic rocks indicates that they have been emplaced in a supra-subduction zone setting, probably the north dipping Nujiang suture zone. 40Ar/39Ar micas ages of the granite indicate that cooling below ~ 350 °C occurred between 105 and 85 Ma. 40Ar/39Ar K-feldspar data suggest a fast cooling event at 60-55 Ma, which we relate to the reactivation of the LMC suture zone as a thrust at the onset of the India-Eurasia collision. The last, and still active, deformation event corresponds to left-lateral strike-slip faulting along the ENE-WSW LMC fault.
ISSN: 1342-937X

hal-00660491
https://hal.archives-ouvertes.fr/hal-00660491
DOI : 10.1016/j.gr.2011.07.026

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
Expeditions 304 and 305 of the Integrated Ocean Drilling Program cored and logged a 1.4 km section of the domal core of Atlantis Massif. Postdrilling research results summarized here constrain the structure and lithology of the Central Dome of this oceanic core complex. The dominantly gabbroic sequence recovered contrasts with predrilling predictions; application of the ground truth in subsequent geophysical processing has produced self-consistent models for the Central Dome. The presence of many thin interfingered petrologic units indicates that the intrusions forming the domal core were emplaced over a minimum of 100-220 kyr, and not as a single magma pulse. Isotopic and mineralogical alteration is intense in the upper 100 m but decreases in intensity with depth. Below 800 m, alteration is restricted to narrow zones surrounding faults, veins, igneous contacts, and to an interval of locally intense serpentinization in olivine-rich troctolite. Hydration of the lithosphere occurred over the complete range of temperature conditions from granulite to zeolite facies, but was predominantly in the amphibolite and greenschist range. Deformation of the sequence was remarkably localized, despite paleomagnetic indications that the dome has undergone at least 45 degrees rotation, presumably during unroofing via detachment faulting. Both the deformation pattern and the lithology contrast with what is known from seafloor studies on the adjacent Southern Ridge of the massif. There, the detachment capping the domal core deformed a 100 m thick zone and serpentinized peridotite comprises similar to 70% of recovered samples. We develop a working model of the evolution of Atlantis Massif over the past 2 Myr, outlining several stages that could explain the observed similarities and differences between the Central Dome and the Southern Ridge.
ISSN: 0148-0227

hal-00617528
https://hal.archives-ouvertes.fr/hal-00617528
https://hal.archives-ouvertes.fr/hal-00617528/document
https://hal.archives-ouvertes.fr/hal-00617528/file/2010JB007931.pdf
DOI : 10.1029/2010JB007931

Éditeur(s) : HAL CCSD Oxford University Press (OUP): Policy B - Oxford Open Option A Oxford University Press (OUP)
Résumé : International audience
Peridotites exhumed in the footwall of axial detachment faults at slow-spreading ridges are highly serpentinized. Most mid-ocean ridge detachment settings are magmatically active and hydrous fluid circulation in and near the fault has been shown to be influenced by the presence of melt or magmatic lithologies. Our working area along the Southwest Indian Ridge (62–65°E) is nearly amagmatic and represents an end-member to study the hydrous alteration of exhumed peridotites without these magmatic influences. We use an integrated petrological approach combining microstructural, mineralogical and chemical observations to unravel the sequence of serpentinization in 272 dredged samples of variably serpentinized peridotites and to document the circulation of serpentinizing fluids in and near the exhumation faults. We find that serpentine recrystallization and veins overprint the initial serpentinite mesh texture in ∼25% of the samples. Oxygen isotope data suggest that this sequence developed at relatively high temperatures (271–336°C) and under increasing fluid–rock ratios, from near stoichiometry for mesh texture formation to >10 during recrystallization. Increasing fluid supersaturation relative to serpentine favors the replacement of mesh texture lizardite by chrysotile and polygonal or polyhedral serpentine. We attribute local recrystallization into antigorite to moderate Si-metasomatism, possibly following pyroxene serpentinization. We do not observe the more pronounced Si-metasomatism leading to talc replacing serpentine that is reported for the more magmatically active Mid-Atlantic Ridge detachment settings and is attributed to prior leaching of magmatic rocks. Scales of preferential fluid pathways in our samples evolved from pervasive and close-spaced (<500 µm) microfractures during the formation of the initial serpentine mesh texture, to centimeter-thick planar domains of enhanced fluid flux, spaced at ∼10 cm intervals and probably grouped in corridors that may be up to ∼100 m across. Serpentine minerals are enriched in some fluid-mobile elements (Cl, B, U) relative to the peridotite protolith, and several elements (Al, Fe, Si, Cu, As, Sb, REE) are redistributed at the millimeter to decimeter scale. Serpentinizing fluids were seawater-derived, probably mildly alkaline (small to no europium anomalies), reducing and H2-enriched (formation of magnetite). These fluids may have been similar to, though warmer than, those venting at the ultramafic-hosted Lost City hydrothermal fluid (30°N, Mid-Atlantic Ridge).
ISSN: 0022-3530

hal-01174047
https://hal.archives-ouvertes.fr/hal-01174047
DOI : 10.1093/petrology/egv014