Geosciences Montpellier

Murviel-lès-Montpellier, France

Geosciences Montpellier

Murviel-lès-Montpellier, France
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Doucet L.S.,Jean Monnet University | Doucet L.S.,TIME Higher School | Doucet L.S.,CNRS Magmas and Volcanoes Laboratory | Ionov D.A.,Geosciences Montpellier | And 2 more authors.
Chemical Geology | Year: 2015

The formation age of the Siberian cratonic mantle is not well established as yet. Re-Os data on various mantle-derived materials have shown that it contains Archaean components, but the reported Re-depletion ages show a broad variation range (3.4 to 1Ga) and are commonly ≤2Ga for peridotite xenoliths. We report Hf and Nd isotope data for cpx and garnet separated from nine refractory spinel and garnet peridotite xenoliths from the Udachnaya kimberlite. The cpx from low-opx spinel harzburgites show extremely high εHf values, from +607 to +2084, which testify to long-term evolution of these rocks with high Lu/Hf ratios, consistent with their residual origin and near absence of post-melting enrichments in the Lu-Hf system. Such high εHf values are unusual for cpx from other cratonic peridotites and are higher than those reported for depleted cpx in off-cratonic peridotites. The clinopyroxenes from low-opx spinel harzburgites yield Hf model ages from 1.9 to 1.7Ga while the cpx from high-opx spinel harzburgites yield Hf model ages from 3.0 to 1.9Ga. When plotted together, they define a Lu/Hf isochron with an age of 1.80Ga, which we consider as a robust estimate of the formation age (melt extraction event) because it is obtained on residual rocks that show no evidence for HREE and Hf enrichments and because the model ages for three out of four individual samples are similar to each other. The cpx have high εNd of +94 to +123, which are inconsistent with their low Sm/NdPM of <1 and yield no meaningful age estimates. The consistently high, positive εNd in these cpxs can be interpreted in terms of long-term evolution of refractory peridotites with high Sm/Nd, followed by relatively recent LREE enrichments.We infer that a significant part of the lithospheric mantle in the central Siberian craton may have been formed during a major event (or a series of events) at around 1.8. Ga. Older ages reported for the central Siberian craton may refer to less common materials from cratonic or other domains formed in the Archaean that were later incorporated into the cratonic roots. The transition from the "Archaean" to "modern" tectonic regimes in Siberia and possibly elsewhere may have taken place at 1.8-1.9. Ga rather than at ~. 2.5. Ga, i.e. in the second half of the Paleoproterozoic rather than at the Archaean-Proterozoic boundary, at which time the asthenospheric mantle became generally too cold to experience high-degree melting on a large scale. The ~. 1.8. Ga formation age of the Siberian cratonic mantle is coeval with that for a major part of the ancient continental crust in the central Siberian craton. The temporal crust-mantle links may be explained either by the generation of the initial source materials for continental crust in the same melting event that formed the residual peridotites or, alternatively, by subduction and melting of pre-existing proto-lithosphere destabilized by a major mantle upwelling that formed the residual mantle. © 2014 Elsevier B.V.

Viegas L.G.F.,University of Sao Paulo | Archanjo C.J.,University of Sao Paulo | Vauchez A.,Geosciences Montpellier
Journal of Structural Geology | Year: 2013

The Espinho Branco anatexite, located within a transcurrent, high-temperature shear zone in NE Brazil, was the subject of a comprehensive petrostructural study (Anisotropy of Magnetic Susceptibility - AMS, Anisotropy of Anhysteretic Remanence - AAR, Electron Backscatter Diffraction - EBSD) to evaluate the compatibility of different fabrics with the kinematics of melt deformation. Magnetite dominates susceptibilities larger than 1 mSI and biotite displays [001] lattice directions consistent with AMS k3 axes. In contrast, migmatites with a susceptibility lower than 0.5 mSI and no visible mesoscopic foliation provide crystallographic fabrics distinct from AMS and AAR. However, AAR remains consistent with the regional strain field. These results suggest that the correlation of field, AMS and crystallographic fabrics is not always straightforward despite the relatively simple organisation of the magnetic fabric in the anatexite. We conclude that AMS recorded the final stages of the strain field in the migmatite irrespective of its complex mesoscale structures and contrasting crystallographic fabrics. © 2012 Elsevier Ltd.

Francois T.,CNRS Paris Institute of Earth Sciences | Agard P.,CNRS Paris Institute of Earth Sciences | Agard P.,Institut Universitaire de France | Bernet M.,CNRS Institute of Earth Sciences | And 5 more authors.
Lithos | Year: 2014

The Iranian plateau is a flat ~. 1.5-2. km high plateau thought to result from the collision between the Arabian and Eurasian plates since ~. 30 ± 5. Ma, and may represent a young analogue to the so far better studied Tibetan plateau. In order to constrain the exhumation history of the internal Zagros and of the Iranian plateau, we herein present apatite (U-Th)/He (AHe) and apatite (AFT) and zircon fission-track (ZFT) data on plutonic rocks from the Sanandaj-Sirjan Zone (SSZ), Urumieh-Dokhtar magmatic arc (UDMA), Central Iran and Kopet Dagh. Thermochronologic data show that the SSZ was exhumed early in the collision process (essentially before 25-20. Ma), with a likely acceleration of cooling during the late Eocene, from 0.04 to 0.3. mm/year. Results suggest that cooling of the internal Zagros migrated from the SSZ to the UDMA during a more mature stage of the continental collision, after ~. 17. Ma (i.e., coeval with the outward propagation of deformation and topography fronts in the external Zagros). Constant exhumation rates in the UDMA (~. 0.3. mm/year) suggest that no significant variation of erosion rates occurred since the onset of continental collision. In Central Iran, the overlap of ZFT, AFT and AHe ages from g. neissic samples points to rapid cooling during the late Eocene (~. 42. °C/Myr), which is consistent with previous reports on the formation of Eocene metamorphic core-complexes. © 2014 Elsevier B.V.

Viegas L.G.F.,University of Sao Paulo | Archanjo C.J.,University of Sao Paulo | Hollanda M.H.B.M.,University of Sao Paulo | Vauchez A.,Geosciences Montpellier
Precambrian Research | Year: 2014

Microstructures, U-Pb SHRIMP zircon ages and temperature estimates were used to constrain the fabric evolution and timing of mylonitisation in the Patos shear zone (NE Brazil). Melt-bearing HT-mylonitic orthogneiss displays solid-state fabrics with coarse quartz ribbons and sutured grain boundaries. K-feldspar is often fractured and shows peripheral myrmekite. The textures typically become magmatic at the contacts with the Espinho Branco anatexite. Zircon crystals from two samples of the leucosome show Paleoproterozoic (ca. 2.2. Ga) inherited cores that are enveloped by recrystallised Neoproterozoic rims. These zircon grains define a discordia with lower intercept ages of 558 and 562. Ma but with large analytical errors. A leucogranite with transitional contacts with host diatexites provides a well-constrained zircon mean age of 566. ±. 6. Ma (n=15, 95% conf.), which is considered the best estimate for the peak metamorphic conditions. The transition from HT-mylonites to fine-grained mylonites and ultramylonites is marked by a progressive grain size reduction assisted by recrystallisation. Quartz crystallographic fabrics display [0. 0. 0. 1] concentrations between Z and Y. K-feldspar and plagioclase fabrics record the activity of the (0. 1. 0)[0. 0. 1] and (0. 1. 0)[1. 0. 0] slip systems and, in the lower-temperature tectonites, the (1. 0. 0)[0. 1. 0] slip system. These results suggest a diachronic evolution in which an initial HT northern domain was deformed by intracrystalline slip and melt-assisted granular flow, followed by medium- to low-temperature solid-state creep in the southern shear zone domain. The mylonites therefore record the rheological heterogeneities responsible for the formation of a late continental shear zone that nucleated under partially molten conditions and was later reactivated through melt-absent strain localization following exhumation. © 2014 Elsevier B.V.

Jolivet L.,CNRS Earth Sciences Institute of Orléans | Faccenna C.,Third University of Rome | Huet B.,University of Vienna | Labrousse L.,CNRS Paris Institute of Earth Sciences | And 19 more authors.
Tectonophysics | Year: 2013

We review the geodynamic evolution of the Aegean-Anatolia region and discuss strain localisation there over geological times. From Late Eocene to Present, crustal deformation in the Aegean backarc has localised progressively during slab retreat. Extension started with the formation of the Rhodope Metamorphic Core Complex (Eocene) and migrated to the Cyclades and the northern Menderes Massif (Oligocene and Miocene), accommodated by crustal-scale detachments and a first series of core complexes (MCCs). Extension then localised in Western Turkey, the Corinth Rift and the external Hellenic arc after Messinian times, while the North Anatolian Fault penetrated the Aegean Sea. Through time the direction and style of extension have not changed significantly except in terms of localisation. The contributions of progressive slab retreat and tearing, basal drag, extrusion tectonics and tectonic inheritance are discussed and we favour a model (1) where slab retreat is the main driving engine, (2) successive slab tearing episodes are the main causes of this stepwise strain localisation and (3) the inherited heterogeneity of the crust is a major factor for localising detachments. The continental crust has an inherited strong heterogeneity and crustal-scale contacts such as major thrust planes act as weak zones or as zones of contrast of resistance and viscosity that can localise later deformation. The dynamics of slabs at depth and the asthenospheric flow due to slab retreat also have influence strain localisation in the upper plate. Successive slab ruptures from the Middle Miocene to the Late Miocene have isolated a narrow strip of lithosphere, still attached to the African lithosphere below Crete. The formation of the North Anatolian Fault is partly a consequence of this evolution. The extrusion of Anatolia and the Aegean extension are partly driven from below (asthenospheric flow) and from above (extrusion of a lid of rigid crust). © 2012 Elsevier B.V.

Chawah P.,ESEO | Sourice A.,ESEO | Plantier G.,ESEO | Chery J.,Geosciences Montpellier
Proceedings of IEEE Sensors | Year: 2011

This paper deals with the optimization of an Extrinsic Fiber Fabry-Pérot Interferometer used for very long term (more than one year) and high precision displacement measurements by a real time and adaptive estimation procedure based on a Kalman filter. By performing a sinusoidal laser diode current modulation, a wavelength modulation is created. The Kalman filter takes into account not only the correction of the measurement drift caused by the resultant Optical Power Modulation, but also the correction of the measurement noise and temperature fluctuations. The tracking algorithm is presented, the complete system has been set up, the Kalman filter and the demodulation are programmed on an FPGA board. Experimental results give an estimation error of about 2nm for a 7000nm displacement. © 2011 IEEE.

Leroy S.,University Paris 06 Case 129 | Leroy S.,CNRS Paris Institute of Earth Sciences | d'Acremont E.,University Paris 06 Case 129 | d'Acremont E.,CNRS Paris Institute of Earth Sciences | And 7 more authors.
Earth and Planetary Science Letters | Year: 2010

Evidence of anomalous volcanism is readily observed in the Gulf of Aden, although, much of this oceanic basin remains as yet unmapped. In this paper, we investigate the possible connection of the Afar hotspot with a major off-axis volcanic structure and its interpretation as a consequence of a the anomalous presence of melt by integrating several data sets, both published and unpublished, from the Encens-Sheba cruise, the Aden New Century (ANC) cruise and several other onshore and marine surveys. These include bathymetric, gravity, magnetic, magneto-telluric data, and rock samples. Based upon these observations, interpretations were made of seafloor morphology, gravity and magnetic models, seafloor age, geochemical analyses and tectonic setting. We discuss the possible existence of a regional melting anomaly in the Gulf of Aden area and of the probability of its connection to the Afar plume. Several models that might explain the anomalous volcanism are taken into account, such as a local melting anomaly unrelated to the Afar plume, an anomalously large volume of melt associated with seafloor spreading, and interaction of the ridge with the Afar plume. A local melting anomaly and atypical seafloor spreading prove inconsistent with our observations. Two previously proposed models of plume-ridge interactions are examined: the diffuse plume dispersion called pancaked flow and channelized along-axis flow. We conclude that the configuration and structure of this young ocean basin may have the effect of channeling material away from the Afar plume along the Aden and Sheba Ridges to produce the off-axis volcanism observed on the ridge flanks. This interpretation implies that the influence of the Afar hotspot may extend much farther eastwards into the Gulf of Aden than previously believed. The segmentation of the Gulf of Aden and the configuration of the Aden-Sheba system may provide a potential opportunity to study channeled flow of solid plume mantle from the plume along a segmented ridge and nearby continental margins. © 2010 Elsevier B.V.

Philit S.,Geosciences Montpellier | Soliva R.,Geosciences Montpellier | Labaume P.,Geosciences Montpellier | Gout C.,Total EP
4th International Conference on Fault and Top Seals 2015: Art or Science? | Year: 2015

The understanding of the interplay between fault zone cataclasis and cementation is important since both processes can reduce the permeability of faults in porous sandstones significantly. The case of fault cementation in high-porosity sandstone reservoirs at shallow depth (<2 km; T° <80° C) has almost never been investigated. The macro- And microscopic analysis of a fault zone in the porous Cenomanian quartz arenite sands of Provence (France) shows that silica diagenesis occurs in the most intensely deformed cataclastic parts of the fault zone. This fault zone contains clusters of shear bands and 19 to 48% of its thickness is occupied by low-porosity silicified cataclastic structures. The analysis of the alteration profile around the fault zone reveals the presence of groundwater silcretes in the form of tabular, tightly silicified sandstone bodies. Cold-cathodoluminescence microscopy analyses of the silica cements (of the fault and the silcrete) tend to confirm the groundwater origin of the silica cements from diagenetic processes. This study therefore shows that silica cementation can occur in a fault zone in a shallow context of groundwater silcrete. Consequently, its sealing capacity could be acquired potentially early in the burial history of a sandstone reservoir.

Perroud H.,Geosciences Montpellier | Jaafar O.,Geosciences Montpellier | Pezard P.,Geosciences Montpellier | Lofi J.,Geosciences Montpellier
Near Surface Geoscience 2014 - 20th European Meeting of Environmental and Engineering Geophysics | Year: 2014

The Maguelone experimental site has been the subject of surface and downhole geophysical monitoring of gas injection experiments in a shallow subsurface reservoir. In particular, vertical seismic profiles (VSP) were conducted in two holes located within meters of the gas injection hole, before, during and after a series of injections. The times of first-arrival were obtained by picking and interpreted in terms of seismic velocity models. Before injection, the lateral variability of seismic velocities at the site is underlined. The comparison of seismic velocities between experiments for a single hole brings out the impact of gas injection on the elastic properties of the porous clastic sediments at the injection site.

Taillefer A.,Geosciences Montpellier | Martin G.,Geosciences Montpellier | Soliva R.,Geosciences Montpellier
4th International Conference on Fault and Top Seals 2015: Art or Science? | Year: 2015

Hot springs in continental systems often localize near major faults. Faults may act as drains or barrier for hydrothermal circulation, depending on their core zone constitution and permeability, and the fracture density, opening, and connectivity in their damage zone. The interplay between these processes is still unknown and remains to be studied. The French eastern Pyrénées hot springs are an ideal case to understand how faults controls hydrothermal circulations and hot springs distributions. They align with the brittle normal Têt fault. The basement rocks affected are composed of highly fractured, foliated, gneisses, granites, and metasediments. Photo-interpretation and field work reveal that hot springs discharge in the footwall, along a ductile fault (CMNC), or at the Têt fault linkages with subsidiary brittle faults. Because of the topographic gradient induced by the fault offset, fractures and foliation drive meteoric water toward the deep reservoir where it acquires temperature. Hot waters then use damage zone fracture to rise up, restricted in the footwall because of the presence of main drains in the damage zone and poorly permeable fault rocks in the core zone. Well oriented in-situ stress or seismic activity, could help to maintain the fractures opening, which are generally cemented by zeolites.

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