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Murviel-lès-Montpellier, France

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. Source


Ducassou E.,French National Center for Scientific Research | Fournier L.,French National Center for Scientific Research | Sierro F.J.,University of Salamanca | Alvarez Zarikian C.A.,Texas A&M University | And 3 more authors.
Marine Geology | Year: 2015

The base of the Faro contouritic drift (IODP Site U1386) on the northern margin of the Gulf of Cádiz (Algarve margin) is characterized by two sequences of frequent gravity deposits with different ages and compositions. Among these gravity deposits, several relatively thick debrites (up to 12. m) have been observed and studied in detail.Sedimentological analyses have been performed and because of non-turbulent behavior of debris flows, detailed micropaleontological studies could be realized. Planktonic foraminifera thus allowed establishing a detailed biostratigraphy of these deposits. Benthic foraminifer and ostracod assemblages were used to evaluate the origin of the sediment composing these debris flows and estimate their run-out distance.These debrites are dated from Early Pliocene and early Pleistocene, and were deposited in a mesobathyal environment. They comprise silty mud clasts and matrixes with sand content up to 34%. The Early Pliocene debrites are bioclast-rich whereas the Early Pleistocene debrite is enriched in terrigenous particles. The data indicates that these debrites were triggered on the continental shelf and traveled less than 100. km, eroding the seafloor all along their path for the Early Pliocene debrites and only the first part of their path for the early Pleistocene debrite. Matrixes originate from failure areas whereas eroded sediments along the flow pathway are incorporated into the flow as clasts.High abundance of shelf fauna during the Early Pliocene and great supply of terrigenous particles from rivers during the early Pleistocene in the south-western Iberian margin have favored gravity flows from the continental shelf to the slope. The contouritic paleo-moat of the Faro drift has been a determining channeling feature for gravity flows along the Algarve margin during the early Pleistocene, testifying of the strong interaction between MOW circulation and down-slope processes. Tectonic and diapiric activities were significant during Early Pliocene and early Pleistocene on the Algarve margin and could have been triggering parameters of failures related to these debris flows. © 2015 Elsevier B.V. Source


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. Source


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. Source


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. Source

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