Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Madeira Sn-Nb-Ta deposit corresponds to the albite-enriched facies of Madeira granite (Madeira Suite) that is part of a NE-SW alignment of three granitic bodies. Structural analyses suggest that the albite-enriched granite emplacement and development of related structures occurred in a different tectonic setting than earlier facies of the granitic bodies in the NE-SW alignment and that the structure was dominated by a N-NE-trending shortening related to a left-lateral motion along a NE-SW corridor within a Riedel shear. Three types of structures (flat-lying, near vertical fractures, and geodes/miaroles) concentrated the last magmatic-related fluid in the albite-enriched granite. U-Pb in situ zircon dating of the albite-enriched granite yielded an age of 1,822 ± 22 Ma. The other granitic plutons of the Madeira Suite, Água Boa granite (topaz-granite facies), and Europa per-alkaline granite formed at 1,825 ± 14 Ma, 1,831± 11 Ma, and 1,839 ± 10 Ma, respectively. The granite bodies of the Madeira Suite occur in an area occupied by a cauldron complex composed of volcanic sequences (Iricoumé Group) and associated A-type granites (Mapuera Suite), and their formation was controlled by the reactivation of the cauldron structures and the pre-existing structures. The gap between the cauldron complex and the Madeira Suite is no greater than 35 Ma. The geological evolution was reanalyzed from the perspective of an entire extensional environment where three successive episodes of A-type magmatism and basin formation (Urupi Formation) occurred. The data and interpretations of this work imply crucial constraints on the petrologic models proposed for the albite-enriched granite and, consequently, on the genesis of the Madeira deposit
ISSN: 0301-9268

insu-00939888
https://hal-insu.archives-ouvertes.fr/insu-00939888
https://hal-insu.archives-ouvertes.fr/insu-00939888/document
https://hal-insu.archives-ouvertes.fr/insu-00939888/file/BastosNeto-PrecambrianResearch-2014.pdf
DOI : 10.1016/j.precamres.2013.12.021

Éditeur(s) : HAL CCSD
Résumé : This work provides new constraints on the interactions between deformation and percolation of melt or fluids, as well as on the implications of these processes for the seismic properties of the mantle wedge. It is based on the analysis of spinel peridotites from the massif of Ronda (Spain) and two xenolith suites from active subduction zones (Kamchatka, Papua New Guinea). A coupled structural, petrological and geochemical study of these samples shows that they underwent a reactive percolation of melts or Si-rich fluids, which was synchronous to a deformation event occurring under high temperature and low stress conditions, consistent with the PT conditions at the base of the lithosphere or in the asthenosphere. This reactive percolation is responsible for enrichment in pyroxenes, mainly orthopyroxene, which is often localized in bands parallel to the high-temperature foliation. This enrichment is associated with grain size reduction and dispersion of the crystallographic orientation of olivine. The dominant slip system in olivine is {0kl}[100], which results in fast S-wave polarization parallel to the flow direction in the mantle. The decrease in the intensity of the olivine crystal preferred orientations associated with the enrichment in pyroxene results in significant decrease of the anisotropy that may induce an underestimation of the thickness of the anisotropic layer by up to 33%. The observed orthopyroxene enrichment also lowers the Vp/Vs ratio, but cannot explain Vp/Vs < 1.7 mapped locally in the fore-arc mantle in Japan and the Andes. Such low Vp/Vs ratios may however be explained by considering the intrinsic anisotropy of the peridotites, which is generally ignored in large-scale Vp/Vs ratio mapping of the mantle wedge. Infrared analyses show that olivine from the both xenolith collections contains less water than the theoretical saturation calculated for their estimated equilibrium temperature in the spinel stability field. These low water content are similar to those observed in spinel peridotites from other subduction zones and probably record both the low solubility of water in olivine at relatively low pressure and dehydration during exhumation of the xenoliths. These measured water contents as well as theoretical saturation estimations are not sufficient to change the dominant slip direction of in olivine from [100] to [001].
Ce travail apporte de nouvelles contraintes sur les interactions entre déformation et processus d'hydratation et de percolation de magma ou de fluides dans le manteau à l'aplomb d'une zone de subduction et leurs implications sur les propriétés sismiques dans le coin mantellique. Il se base sur l'analyse de péridotites à spinelle provenant du massif de Ronda (Espagne) et deux séries de xénolites issues de zones de subduction actives (Kamchatka, Papouasie-Nouvelle-Guinée). L'étude structurale, pétrologique et géochimique de ces échantillons montrent qu'ils ont subit une percolation réactive de magma ou de fluide synchrone d'une déformation de haute température basse contrainte cohérente avec les condition PT de la base de la lithosphère ou de l'asthénosphère. Cette percolation réactive est responsable d'un enrichissement en pyroxènes, qui est souvent localisé dans des bandes parallèles à la foliation. Cet enrichissement est associé à une dispersion de l'orientation cristallographique de l'olivine. Les systèmes de glissement dominant dans l'olivine sont dans tous les cas {0kl}[100], ce qui implique que la direction de polarisation rapide des ondes S dans la partie supérieure du coin mantellique est parallèle à la direction d'écoulement dans le manteau. La décroissance de l'intensité des OPR de l'olivine associée à l'enrichissement en pyroxènes a pour conséquence une réduction non négligeable de l'anisotropie sismique qui peut induire jusqu'à 33% d'erreur sur l'interprétation de l'épaisseur de la couche anisotrope. Un enrichissement en orthopyroxène peut aussi entraîner une baisse du rapport Vp/Vs, mais ne peut expliquer les rapports Vp/Vs <1,7 cartés dans certains avant-arcs. Cependant de telles valeurs peuvent être expliquées si l'anisotropie des péridotites du coin mantellique est prise en compte. Les analyses par spectroscopie infra-rouge montrent que les olivines des deux séries de xénolites étudiées contiennent moins d'eau que la saturation théorique calculée pour leurs températures d'équilibre dans le domaine du spinelle. Ces faibles concentrations en eau sont similaires à celles observées dans les olivines des péridotites à spinelle des autres zones de subduction. Elles enregistrent probablement la faible solubilité de l'eau dans l'olivine à des pressions relativement basses et la déshydratation au cours de l'exhumation des xénolites. Ces teneurs en eau mesurées ainsi que les estimations de la saturation théorique ne sont pas suffisantes pour changer la direction de glissement dominante dans l'olivine de [100] à [001].
https://tel.archives-ouvertes.fr/tel-00689832

tel-00689832
https://tel.archives-ouvertes.fr/tel-00689832
https://tel.archives-ouvertes.fr/tel-00689832/document
https://tel.archives-ouvertes.fr/tel-00689832/file/These-Soustelle2010.pdf

Éditeur(s) : HAL CCSD
Résumé : High Pressure - Low Temperature (HP-LT) rocks testify for burying and exhumation of crustal material in subduction zones. Their complete exhumation is the result of processes acting during (syn-orogenic) and after (post-orogenic) subduction is active, the latter partly obliterating the first. In the Aegean domain, the Attic-Cycladic Blueschist unit (ACBU) is a HP-LT unit exhumed in metamorphic core complexes (MCCs) in the back-arc domain of the Hellenic subduction zone. This study is an attempt to distinguish features related to syn-orogenic exhumation processes responsible for the first stages of exhumation This syn-orogenic "message" has to be read through the post-convergence structural and thermal overprint that accompanied the formation of the MCCs. Particularly, the geometry, the timing and the amount of the syn-orogenic exhumation has to be determined. We investigate these features with coupled field, metamorphic petrology and radiochronology studies First, based on observations on Ios (southern Cyclades), it has recently been proposed that syn-orogenic exhumation of the ACBU was accommodated by a basal thrust over the Cycladic Basement (CB) [Huet, et al., 2009]. The peak conditions, deduced from pseudosections calculation for the Ios main lithologies, are 500 °C-19 kbar for the ACBU and 550 °C-16 kbar for the CB. Exhumation until 400 °C-8 kbar is considered as syn-orogenic. Second, phengites populations, single grains and in situ 40Ar-39Ar geochronology has been carried out on samples from Tinos and Andros (northern Cyclades), Syros (central Cyclades) and Ios. The results gather in several clusters: 50-55 Ma, 40-45 Ma, 30-35 Ma, and 22-26 Ma. Based on these new P-T-t data and a synthesis of published data, we are able to refine the geometry and the timing of the exhumation of the ACBU. Data from the whole Cyclades exhibit little differences in ages and P-T conditions for the successive stages of exhumation. The peak of pressure (500±50 °C-18±1 kbar) has been reached at 50-55 Ma from Tinos to Ios. The onset of the exhumation occurred at 40-45 Ma in blueschist facies conditions, between a thrust at their bottom and a detachment at their top. The following decompression was accompanied by cooling until 30-35 Ma (400±50 °C-8±1 kbar). At that time, the boundary conditions switched to extension. Finally, we propose a model for the exhumation of HP-LT units accounting for these data. We also consider the rheological implications of the syn-orogenic structuration of the Aegean wedge on the post-orogenic evolution. B. Huet, L. Labrousse, and L. Jolivet [2009] Thrust or detachment? Exhumation processes in the Aegean: Insight from a field study on Ios (Cyclades, Greece), Tectonics, 28, 3, doi:10.1029/2008TC002397.
EGU General Assembly
Vienne, Austria

insu-00839054
https://hal-insu.archives-ouvertes.fr/insu-00839054
BIBCODE : 2010EGUGA..1214098H

Éditeur(s) : HAL CCSD European Geosciences Union
Résumé : We designed a thermo-mechanical numerical model for fast-spreading mid-ocean ridge with variable viscosity, hydrothermal cooling, latent heat release, sheeted dyke layer, and variable melt intrusion possibilities. The model allows for modulating several accretion possibilities such as the "gabbro glacier" (G), the "sheeted sills" (S) or the "mixed shallow and MTZ lenses" (M). These three crustal accretion modes have been explored assuming viscosity contrasts of 2 to 3 orders of magnitude between strong and weak phases and various hydrothermal cooling conditions depending on the cracking temperatures value. Mass conservation (stream-function), momentum (vorticity) and temperature equations are solved in 2-D cartesian geometry using 2-D, alternate direction, implicit and semi-implicit finite-difference scheme. In a first step, an Eulerian approach is used solving iteratively the motion and temperature equations until reaching steady states. With this procedure, the temperature patterns and motions that are obtained for the various crustal intrusion modes and hydrothermal cooling hypotheses display significant differences near the mid-ocean ridge axis. In a second step, a Lagrangian approach is used, recording the thermal histories and cooling rates of tracers travelling from the ridge axis to their final emplacements in the crust far from the mid-ocean ridge axis. The results show that the tracer's thermal histories are depending on the temperature patterns and the crustal accretion modes near the mid-ocean ridge axis. The instantaneous cooling rates obtained from these thermal histories betray these discrepancies and might therefore be used to characterize the crustal accretion mode at the ridge axis. These deciphering effects are even more pronounced if we consider the average cooling rates occurring over a prescribed temperature range. Two situations were tested at 1275-1125 °C and 1050-850 °C. The first temperature range covers mainly the crystallization range that is characteristic of the high temperature areas in the model (i.e. the near-mid-oceanic-ridge axis). The second temperature range corresponds to areas in the model where the motion is mainly laminar and the vertical temperature profiles are closer to conductive. Thus, this situation results in less discriminating efficiency among the crustal accretion modes since the thermal and dynamic properties that are described are common to all the crustal accretion modes far from the ridge axis. The results show that numerical modeling of thermo-mechanical properties of the lower crusts may bring useful information to characterize the ridge accretion structure, hydrothermal cooling and thermal state at the fast-spreading ridges and may open discussions with petrological cooling rate results.
ISSN: 1991-959X

hal-00907012
https://hal.archives-ouvertes.fr/hal-00907012
DOI : 10.5194/gmd-6-1659-2013

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
The ODP/IODP multileg campaign at ODP Site 1256 (Cocos plate, eastern equatorial Pacific) provides the first continuous in situ sampling of fast spreading ocean crust from the extrusive lavas, through the sheeted dikes and down into the uppermost gabbros. This paper focuses on a detailed petrographic and microanalytical investigation of the gabbro section drilled during IODP Expedition 312. The marked patchy and spotty features that can be observed in many Hole 1256D gabbros is mostly due to a close association of two different lithological domains in variable amounts: (1) subophitic domains and (2) a granular matrix. Major and trace element mineral compositions, geothermometry, and petrological modeling suggest that subophitic and granular domains follow one single magma evolution trend formed by in situ fractionation. The subophitic domains correspond to the relative primitive, high-temperature end-member, compositionally similar to the basalts and dikes from the extrusive unit upsection, while the granular domains fit with a magma evolution by crystal fractionation to lower temperatures, up to a degree of crystallization of similar to 80%. Our results support the following scenario for the fossilization of the axial melt lens at ODP Site 1256: relatively primitive MORB melts under near-liquidus conditions fill the melt lens and feed the upper, extrusive crust. Near the melt lens-sheeted dike boundary at lower temperatures, crystallization starts with first plagioclase before clinopyroxene in a mushy zone forming the subophitic domains. At decreasing temperatures, the subophitic domains continue to crystallize, finally forming a well-connected framework. Evolved, residual melt is finally trapped within the subophitic network, crystallizing at near-solidus conditions to the granular matrix. Another important textural feature in Hole 1256D gabbros is the presence of microgranular domains which are interpreted as relics of stoped/assimilated sheeted dikes (transformed to "granoblastic dikes" by contact metamorphism). All these different domains can be observed in close association, often at the thin section scale, demonstrating the extremely complex petrological record of combined crystallization/assimilation processes ongoing in the axial melt lens. Very similar gabbros with a marked spotty/patchy appearance, and bearing the same close association of lithological domains as observed at Site 1256, are known in the so-called "varitextured gabbro" unit from the Oman Ophiolite located at the same structural level, between cumulate gabbros and granoblastic dikes. The close petrological similarity of the gabbro/dike transition between both IODP Hole 1256D and the Oman ophiolite suggests that in situ fractionation and dike assimilation/contamination are major magmatic processes controlling the dynamics and fossilization of the axial melt lens at fast spreading oceanic ridges.
ISSN: 1525-2027

hal-00644798
https://hal.archives-ouvertes.fr/hal-00644798
DOI : 10.1029/2011GC003655

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Subduction processes play a major role in plate tectonics and the subsequent geological evolution of Earth. This special issue focuses on ongoing research in subduction dynamics to a large extent (oceanic subduction, continental subduction, obduction…) for both past and active subduction zones and into mountain building processes and the early evolution of orogens. It puts together various approaches combining geophysics (imaging of subduction zones), petrology/geochemistry (metamorphic analysis of HP-UHP rocks, fluid geochemistry and magmatic signal, geochronology), seismology and geodesy (present-day evolution of subduction zones, active tectonics), structural geology (structure and evolution of mountain belts), and numerical modelling to provide a full spectrum of tools that can be used to constrain the nature and evolution of subduction processes and orogeny. Studies presented in this special issue range from the long-term (orogenic cycle) to short-term (seismic cycle).
ISSN: 0264-3707

insu-01287985
https://hal-insu.archives-ouvertes.fr/insu-01287985
https://hal-insu.archives-ouvertes.fr/insu-01287985/document
https://hal-insu.archives-ouvertes.fr/insu-01287985/file/rolland-2016.pdf
DOI : 10.1016/j.jog.2016.03.006

Éditeur(s) : HAL CCSD
Résumé : International audience
Mylonite-bearing crustal shear zones are exhumed extensions at depth of (potentially seismogenic) brittle faultsat shallow structural level. By concentrating deformation, shear zones play a major role in the rheology and mechanicalbehavior of the continental crust. Analysis of shear zone geometry and microstructures is a useful toolto decipher deformation kinematics, though finite strain estimation is still relatively qualitative. Timing of thedeformation has also been the focus of numerous studies using the complete spectrum of geochronometers. However,only rare examples provide geochronological data that can be unambiguously linked with deformation. Thus,time-scales over which major mylonite zones develop and remain active under ductile conditions as well as theirstrain rates often remain poorly documented. Several sections across the South Armorican Shear Zone (SASZ),a crustal-scale, several km-thick dextral shear zone were investigated by structural, petrological and Ar/Ar radiochronologicalmethods. Finite strain profiles on these sections showed a strong deformation partitioning towardsthe ultramylonite core of the SASZ, with a decrease, of both the C’/S mean angle (from ca. 45 to less than5) and the Quartz grain-size (from ca. 150 to 5 m). In parallel, conventional and in-situ Ar/Ar datings on thefabric-forming white micas were performed on compositionally complex white-micas. Inherited magmatic muscovitescarried by the foliation and newly-formed, syn-tectonic substituted phengites located along the shear bandsyielded 2 age groups for the less deformed samples. Along the shear zone cross-section, the difference betweenthese two ages evolves from 10-15 Ma in weakly deformed domains to zero toward the SASZ core. In addition, thevery fine-grained syn-tectonic phengites yielded the same ca. 300-298 Ma age irrespectively of their distance to thecore of the shear zone, even in slightly deformed rocks distant by several km. These results support a new modelof crustal-scale shear zone activity, where the whole body of the shear zone is active throughout its history, i.e.the actively deforming zone does not get progressively narrower. The strain distribution nevertheless evolves withtime, with an increasingly larger fraction partitioned in the ultramylonitic core. Besides, combination of the finitestrain estimations and the Ar/Ar ages enables us to assess the range of strain rates associated with mylonitization.
EGU General Assembly 2014
Vienne, Austria

insu-01565057
https://hal-insu.archives-ouvertes.fr/insu-01565057

Éditeur(s) : HAL CCSD
Résumé : A section of ancient fast-spreading ocean crust was sampled at Wadi Gideah, located in the Wadi Tayin Massif of the Oman ophiolite. This sample suite was used for generating a coherent data set combining various petro-geochemical and structural investigations, with the aim of building a reference section for advancing our understanding of crustal accretion processes at fast-spreading mid-ocean ridges. Additionally, this study focuses on one outcrop that represents part of the fossil axial melt lens (AML).Major and trace element analyses reveal a trend of chemical evolution up section in the lower crust, with a marked difference between the layered gabbros and the foliated gabbros above. Petrological modeling shows that the chemical evolution up section can be produced by hydrous fractionation crystallization, with melt H2O contents of ~0.8 wt% and 0.8 to 1.2 wt% for the lower and upper crust, respectively. Together with the observed very steep bulk Zr/Hf vs. Zr gradient, high F and Cl content of magmatic amphibole, general Nb-Ta depletion of melts compared with NMORB, and high Sr87/Sr86 ratio compared with modern fast-spread crust, this suggests that Wadi Gideah layered gabbros were accreted by crystallization of ascending melts in sills, in a context of subduction initiation. The distinct changes in chemical trends and average grain size at the layered to foliated gabbro transition are tentatively explained by enhanced hydrothermal cooling deeper than the AML. The gabbro/dike transition displays complex structural and lithological relationships that, together with fractional crystallization modeling, point to episodic vertical movements of the AML. Plagioclase crystallographic preferred orientations (CPO) measured over the whole gabbro section are always consistent with magmatic flow. The CPO strength generally increases downward, with more scattering in the layered gabbro section. From the top to the bottom of the layered gabbros, CPO become progressively more prolate, possibly reflecting increasing shear induced by active mantle flow underneath.Wadi Gideah lower crust recorded a formation history consistent with a hybrid accretion model, combing several processes such as downward magmatic flow and/or upward melt migration in the upper foliated gabbros, sill intrusions in the layered gabbros, and deep hydrothermal circulation. The latter was presumably focused in channels, preserved today as several, up to 100 m wide zones of extensively altered former layered gabbro, cross-cutting the magmatic layering. These metagabbros display significantly higher Sr87/Sr86 ratio, late stage magmatic phases, and evidence for high temperature partial melting.
Une coupe d'ancienne croute océanique rapide a été échantillonnée dans le Wadi Gideah, situé dans le Massif de Wadi Tayin de l'Ophiolite d'Oman. Cette série d'échantillons a permis de générer un jeu de données cohérent, combinant des études pétro-géochimiques et structurales, dans le but de construire une coupe de référence pour mieux contraindre notre compréhension des processus d'accrétion crustale aux dorsales océaniques rapides. Ce travail intègre aussi l'étude détaillée d'un affleurement représentant en partie la lentille magmatique axiale (LMA) fossile.Les analyses d'éléments majeurs et traces révèlent une évolution chimique dans la croûte inférieure, avec une nette différence entre les gabbros lités et les gabbros foliés sus-jacents. La modélisation pétrologique montre que l'évolution chimique vers le haut peut être produite par cristallisation fractionnée hydratée, avec des teneurs en H2O des magmas de ~0.8 wt% dans la croute inférieure et 0.8 to 1.2 wt% dans la croute supérieure. Combiné aux forts gradients de Zr/Hf vs. Zr, aux teneurs élevées de F et Cl dans les amphiboles magmatiques, à l'appauvrissement général en Nb-Ta des magmas comparé aux NMORB, et aux rapports Sr87/Sr86 élevés comparés à la croûte rapide moderne, ceci suggère que les gabbros lités du Wadi Gideah ont été formés par la cristallisation des magmas ascendants dans des sills, dans un contexte d'initiation de subduction. Les changements de signature géochimique et de taille de grain à la transition entre gabbros lités et gabbros foliés témoignent possiblement d'un fort refroidissement hydrothermal plus profond que la LMA. La transition complexe filonien/gabbro montre des relations structurale et lithologiques complexes, qui, combinées o la modélisation de la cristallisation fractionnée, traduisent les mouvements verticaux épisodiques de la LMA. Les orientations préférentielles cristallographiques (OPC) des plagioclases mesurées sur l'ensemble de la coupe dans les gabbros témoignent toujours d'une déformation magmatique. L'intensité des OPC a tendance à augmenter vers le bas, avec une plus forte variabilité dans les gabbros lités. Dans les gabbros lités, les OPC sont de plus en plus linéaires vers le bas, résultant possiblement d'un cisaillement plus fort induit par l'écoulement actif du manteau sous-jacent.La croûte inférieure dans le Wadi Gideah a enregistré une histoire compatible avec un modèle d'accrétion hydride, combinant plusieurs processus tels que l'écoulement magmatique vers le bas et/ou la migration de liquides magmatiques vers le haut dans les gabbros foliés supérieurs, l'intrusion de sills dans les gabbros lités, et une circulation hydrothermale profonde. Cette dernière était probablement concentrée dans des chenaux, préservés aujourd'hui sous la forme de plusieurs zones, dont l'épaisseur atteint 100 m, de gabbros lités fortement altérés, recoupant le litage magmatique. Ces métagabbros ont des rapports Sr87/Sr86 élevés, comportent des phases magmatiques tardives et montrent des évidences de fusion partielle.
https://hal.archives-ouvertes.fr/tel-01302675

tel-01302675
https://hal.archives-ouvertes.fr/tel-01302675
https://hal.archives-ouvertes.fr/tel-01302675/document
https://hal.archives-ouvertes.fr/tel-01302675/file/Th%C3%A8se_Tim-Mueller_2015.pdf

Éditeur(s) : HAL CCSD Seoul National University
Résumé : http://www.episodes.org/backissues/302/abstract2.htm
International audience
The Trans-North China Belt (TNCB) is a Paleoproterozoic collisional orogen (ca. 1.9-1.8 Ga) responsible for the amalgamation of the North China Craton. Detail field works in Lüliangshan, Hengshan, Wutaishan and Fuping massifs where the belt is well exposed, allow us to draw new tectonic map and crustal-scale cross sections. The available petrologic, radiometric, geochronologic data are integrated in a geodynamic evolution scheme for this orogen. The Low Grade Mafic Unit (LGMU) is interpreted as an ophiolitic nappe rooted in a suture zone located in the western part of the Lüliangshan. This ophiolitic nappe overthrusts to the SE upon the Orthogneiss-Volcanites Unit (OVU) that consists of a bimodal volcanicsedimentary series metamorphosed under amphibolite facies conditions intruded by calcalkaline orthogneiss. The OVU is a composite Neoarchean-Paleoproterozoic magmatic arc developed during two stages (ca. 2500 and 2100 Ma) upon a continental basement corresponding to the western extension of the Neoarchean Fuping massif. The OVU overthrusts to the SE the Fuping massif along the Longquanguan shear zone. This stack of nappe, coeval with an amphibolite facies metamorphism, is dated at ca 1880 Ma. Subsequently, the metamorphic series experienced a widespread migmatization at 1850 Ma and was intruded by post-orogenic plutons dated at 1800 Ma. The weakly to unmetamorphosed Hutuo Supergroup unconformably overlies the metamorphosed and ductilely deformed units (OVU and LGMU), but it is also involved in a second tectonic phase developed in subsurface conditions. These structural features lead us to question the ca 2090 Ma age attributed to the Hutuo supergroup. Moreover, in the Fuping massif, several structural and magmatic lines of evidence argue for an earlier orogenic event at ca 2100 Ma that we relate to an older west-directed subduction below the Fuping Block. The Taihangshan Fault might be the location of a possible suture zone between the Fuping Block and an eastern one. A geodynamic model, at variance with previous ones, is proposed to account for the formation of the TNCB. In this scheme, three Archean continents, namely from West to East, the Ordos, Fuping and Eastern Blocks are separated by the Lüliang and Taihang Oceans. The closure of the Taihang Ocean at ca 2100 Ma by westward subduction below the Fuping Block accounts for the arc magmatism and the 2100 Ma orogeny. The second collision at 1900-1880 Ma between the Fuping and Ordos blocks is responsible for the main structural, metamorphic and magmatic features of the Trans-North China Belt.
ISSN: 0705-3797

insu-00152972
https://hal-insu.archives-ouvertes.fr/insu-00152972
https://hal-insu.archives-ouvertes.fr/insu-00152972/document
https://hal-insu.archives-ouvertes.fr/insu-00152972/file/Episodes_TNCB_Faure_et_al.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The late Carboniferous accretionary system of the South Tianshan orogen (North-Western China) underwent complex structural and polymetamorphic evolution. Combined petrological, geochronological and microstructural analysis of (ultra)high-pressure (UHP) metabasites (eclogites and blueschists) enclosed in metapelites show a relict coarse-grained eclogitic fabric S2 surrounded by a dominant fine-grained eclogite and blueschist facies retrograde fabric S2. The S2 fabric is reworked by upright folds F3 that are responsible for a major shortening of the whole accretionary system. For both the eclogite and blueschist, peak and retrograde P–T conditions have been thermodynamically constrained at 25–26 kbar and 425–500 °C and 10–13 kbar and 500−550 °C respectively, suggesting a shared exhumation history. The garnet-whole rock-amphibole isochron in the blueschist yielded Lu–Hf and Sm–Nd ages of 326.0 ± 2.9 Ma and 318.4 ± 3.9 Ma respectively, interpreted to date the prograde to peak metamorphic assemblage. The retrograde path of the eclogite is characterized by heterogeneous omphacite recrystallization into a mylonitic fine-grained matrix and crystallization of blue amphibole. Microstructures in both pristine porphyroclastic and recrystallized fine-grained domains in the eclogite indicate a gradual evolution from constriction-dominated (L>S-type) to flattening-dominated (S>L-type) type of deformation, increase of fabric intensity reflected by gradually growing M-indexes and the development of lattice preferred orientation (LPO) typical for dislocation creep under slightly hydrated conditions. Recrystallization of the matrix in the blueschist is homogeneous, which indicates a matrix dominated channel flow during exhumation. These LPOs evolutions suggest a significant mechanical coupling with the upper plate concomitant with oroclinal bending of the Kazakh orocline. Lock up of Kazakh orocline is responsible for further stress increase resulting in horizontal shortening of South Tianshan accretionary wedge and development of D3 upright folding and steepening of the whole sequence.
ISSN: 1342-937X

hal-01481263
https://hal.archives-ouvertes.fr/hal-01481263
DOI : 10.1016/j.gr.2016.07.007

Éditeur(s) : HAL CCSD Elsevier
Résumé : Different types of fractures and fault rocks occur within the major normal fault zones bordering the NW of the Neogene Penedes basin (NE Spain). In the southwest part of the basin, the main fault is the Baix Penedes fault that places the Upper Jurassic-Lower Cretaceous dolomicrites of the footwall in contact with the Miocene siliciclastic sediments of the hangingwall. Within the footwall damage zone, different fracture systems and their respective associated breccias and cements have been recognized. Using a combination of structural, petrologic and geochemical analyses, we show that these fracture systems evolved from mainly tectonic to mainly karstic features during the progressive development and upward propagation of the fault. The earlier fractures and associated breccias represent the initial stages of the fault propagation, when the process zone formed around the fault tip was dominated by dilatant fracturing (fractures 1 and dilatant breccias B1). The fluid involved in this early deformation precipitated the dolomite cement Cl, in equilibrium with the host-rock in a closed hydrogeological system. Localization of frictional processes generated cataclasites and ultracataclasites along distinct second-order faults (fractures 2). In these fractures, the dolomite cement C2 precipitated in relation to the incipient opening of the hydrological system to percolating meteoric waters. The later fractures and associated breccias represent the late stages of the fault propagation. These structures (fractures 3, fractures 4 and the dilatant breccias B2) were formed when the extensional deformation reached the surface, resulting in an increasingly open hydrogeological system. At these stages, deposition of the dolomitic sediment DS and precipitation of the calcite cements C3, C4 and C5 show the circulation of freshwaters in a vadose meteoric environment, i.e. in karstic conditions.
ISSN: 0375-6742

hal-00512690
https://hal.archives-ouvertes.fr/hal-00512690
DOI : 10.1016/j.gexplo.2009.11.010

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The deep structure and deformation mechanisms of the Longmen Shan thrust belt (Sichuan, China), at the eastern border of the Tibetan plateau, were largely debated after the devastating Mw 7.9 Wenchuan earthquake (2008). Recent geophysical studies and field investigations have been focused on the active motion of the major Beichuan fault, which ruptured during the earthquake. However, the total exhumation across the fault still remains unclear. In the hanging wall of the Beichuan fault, the South China block is exhumed in the Pengguan massif. Close to the Beichuan fault, the rocks of the Pengguan massif underwent greenschist facies metamorphism associated with brittle-ductile deformation. No metamorphism is observed in the footwall of the fault. In this study, we characterize and date the metamorphic history recorded in the hanging wall of the Beichuan fault in order to constrain the depth and timing of exhumation of the rocks of the Pengguan massif along the fault. A high-resolution petrological approach involving chemical analyses and X-ray maps was used to analyze the micrometric metamorphic minerals. The P-T conditions of the greenschist facies metamorphic event were estimated by an inverse multi-equilibrium thermodynamic approach. The results, 280 ± 30 °C and 7 ± 1 kbar, suggest that the rocks of the Pengguan massif were exhumed from ca. 20 km depth. Our results underline the importance of the thrusting component in the long-term behavior of the Beichuan fault and provide a minimal depth at which the fault is rooted. In situ laser ablation 40Ar/39Ar dating of metamorphic white mica revealed that the greenschist overprint occurred at 135–140 Ma.The Pengguan massif was therefore partially thrusted along the Beichuan fault during the Lower Cretaceous, long before the Eocene-Miocene exhumation phase which is well-constrained by low-temperature thermochronology. Our results provide the first independent depth information for the exhumation history of the Pengguan massif and reveal a previously undocumented Lower Cretaceous tectonic event that marks the onset of the thick-skinned deformation in the external domain of the Longmen Shan (East of the Wenchuan Fault).
ISSN: 0743-9547

hal-01685556
https://hal.archives-ouvertes.fr/hal-01685556
DOI : 10.1016/j.jseaes.2017.04.003

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The geologic evolution of the South Armenian Block (SAB) in the Mesozoic is reconstructed from a structural, metamorphic, and geochronologic study including U–Pb and 40Ar/39Ar dating. The South Armenian Block Crystalline Basement (SABCB) outcrops solely in a narrow tectonic window, NW of Yerevan. The study of this zone provides key and unprecedented information concerning closing of the Northern Neotethys oceanic domain north of the Taurides-Anatolides platform from the Middle Jurassic to the Early Cretaceous. The basement comprises of presumed Proterozoic orthogneiss overlain by metamorphosed pelites as well as intrusions of granodiorite and leucogranite during the Late Jurassic and Early Cretaceous. Structural, geochronological and petrological observations show a multiphased evolution of the northern margin of the SAB during the Late Jurassic and Early Cretaceous. A south-dipping subduction under the East Anatolian Platform-South Armenian Block (EAP-SAB) is proposed in order to suit recent findings pertaining emplacement of relatively hot subduction related granodiorite as well as the metamorphic evolution of the crystalline basement in the Lesser Caucasus area. The metamorphism is interpreted as evidencing: (1) M1 Barrovian MP–MT conditions (staurolite–kyanite) at c. 157–160 Ma and intrusion of dioritic magmas at c. 150–156 Ma, (2) near-adiabatic decompression is featured by partial melting and production of leucogranites at c. 153 Ma, followed by M2 HT–LP conditions (andalusite–K-feldspar). A phase of shearing and recrystallization is ascribed to doming at c. 130–150 Ma and cooling at 400 °C by c. 123 Ma (M3). Structural observations show (1) top to the north shearing during M1 and (2) radial extension during M2. The extensional event ends by emplacement of a thick detrital series along radial S, E and W-dipping normal faults. Further, the crystalline basement is unconformably covered by Upper Cretaceous-Paleocene series dated by nannofossils, evolving from Maastrichtian marly sandstones to Paleocene limestones.
ISSN: 0743-9547

hal-01174077
https://hal.archives-ouvertes.fr/hal-01174077
DOI : 10.1016/j.jseaes.2014.07.018

Éditeur(s) : HAL CCSD Taylor & Francis
Résumé : International audience
The Jurassic Mirdita ophiolite crops out in the western branch of the Hellenide-Dinaride ophiolite belt in the Balkan Peninsula; it represents a remnant of the Tethyan oceanic lithosphere developed between the Apulian and Pelagonian microcontinents. Emplaced during the Cretaceous on the western margin of Pelagonia, the Mirdita ophiolite was involved in southwestward thrusting of the Hellenide-Dinaride tectonic units during the Eocene alpine tectonics. It was little affected, however, by these alpine events as marked by nearly horizontal Cretaceous limestone deposits overlying the ophiolite. A continuous section of Middle Jurassic oceanic crust, including thin gabbros, a N-S-trending sheeted dike complex, and extrusive rocks, is exposed in the central part of the ophiolite and thickens eastward within a regional, N-S-trending synform. Peridotite massifs exposed along the western and eastern edges of this synform show major structural and petrological differences. The eastern ultramafic domain has a harzburgitic mantle exhibiting a high-temperature asthenospheric foliation dipping steeply to moderately to the west. Major chromite deposits are restricted to these eastern ultramafic massifs. The western ultramafic domain has a zoned mantle, with asthenospheric harzburgite exposed at its western margin, progressively replaced eastward by plagioclase-peridotites that were highly strained at low temperatures, and that are bounded by amphibole-peridotites along with crustal rocks. The occurrence of plagioclase is ascribed to melt impregnation processes that occurred immediately before or during intense lithospheric deformation. The gabbros in the eastern massifs are thicker (1-2 km and layered, whereas they are highly thin and discontinuous in the western massifs. Mantle peridotites of the western massifs locally are in direct contact with the overlying diabase and volcanic rocks along ductile shear zones. Development of epidote-amphibolite facies metamorphism in upper-crustal rocks was produced by hydrothermal alteration in the oceanic realm, and was intense and widespread in the western domain. The Mirdita ophiolite likely originated in a short-lived, narrow ocean basin, which was closed during the Middle Jurassic by eastward overthrusting of the western domain, and westward subduction of the eastern domain. This constrictional phase was followed by dextral oblique convergence between the Pelagonian and Apulian microcontinents. This model implies a parautochtonous origin of the Mirdita ophiolite between these two microcontinents.
ISSN: 0020-6814

hal-00456063
https://hal.archives-ouvertes.fr/hal-00456063
DOI : 10.1080/00206810902823982

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Slices of polycyclic metasediments (marbles and meta-cherts) are tectonically amalgamated with the polydeformed basement of the Dent Blanche tectonic system along a major Alpine shear zone in the Western Alps (Becca di Salé area, Valtournenche Valley). A combination of techniques (structural analysis at various scales, metamorphic petrology, geochronology and trace element geochemistry) was applied to determine the age and composition of accessory phases (titanite, allanite and zircon) and their relation to major minerals. The results are used to reconstruct the polyphase structural and metamorphic histories, comprising both pre-Alpine and Alpine cycles. The pre-Alpine evolution is associated with low-pressure high-temperature metamorphism related to Permo-Triassic lithospheric thinning. In meta-cherts, microtextural relations indicate coeval growth of allanite and garnet during this stage, at ~ 300 Ma. Textures of zircon also indicate crystallisation at HT conditions; ages scatter from 263 to 294 Ma, with a major cluster of data at ~ 276 Ma. In impure marble, U-Pb analyses of titanite domains (with variable Al and F contents) yield apparent 206Pb/238U dates range from Permian to Jurassic. Chemical and isotopic data suggest that titanite formed at Permian times and was then affected by (extension-related?) fluid circulation during the Triassic and Jurassic, which redistributed major elements (Al and F) and partially opened the U-Pb system. The Alpine cycle lead to early blueschist facies assemblages, which were partly overprinted under greenschist facies conditions. The strong Alpine compressional overprint disrupted the pre-Alpine structural imprint and/or reactivated earlier structures. The pre-Alpine metamorphic record, preserved in these slices of metasediments, reflects the onset of the Permo-Triassic lithospheric extension to Jurassic rifting.
ISSN: 0024-4937

hal-00758123
https://hal.archives-ouvertes.fr/hal-00758123
DOI : 10.1016/j.lithos.2012.05.007

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 Elsevier
Résumé : International audience
Alpine Corsica consists of a stack of variably metamorphosed units of continental and Tethys-derived rocks. It represents an excellent example of high-pressure (HP) orogenic belt, such as the Western Alps, exposed over a small and accessible area. Compared to the Western Alps, the geology of Alpine Corsica is poorly unraveled. During the 1970s-80s, based on either lithostratigraphic or metamorphic field observations, various classifications of the belt have been proposed, but these classifications have been rarely matched together. Furthermore, through time, the internal complexity of large domains has been progressively left aside in the frame of large-scale geodynamic reconstructions. As a consequence, major open questions on the internal structure of the belt have remained unsolved. Apart from a few local studies, Alpine Corsica has not benefited of modern developments in petrology and basin research. This feature results in several uncertainties when combining lithostratigraphic and metamorphic patterns and, consequently, in the definition of an exhaustive architecture of the belt. In this paper we provide a review on the geology of Alpine Corsica, paying particular attention to the available lithostratigraphic and metamorphic classifications of the metamorphic terranes. These data are completed by a new and exhaustive metamorphic dataset obtained by means of thermometry based on Raman Spectroscopy of Carbonaceous Material (RSCM). This technique provides reliable insights on the peak temperature of the metamorphic history for CM-bearing metasediments. A detailed metamorphic characterization of metasediments, which have been previously largely ignored due to retrogression or to the lack of diagnostic mineralogy, is thus obtained and fruitfully coupled with the available lithostratigraphic data. Nine main tectono-metamorphic units are defined, from subgreenschist (ca. 280-300 °C) to the lawsonite-eclogite-facies (ca. 500-550 °C) condition. These units are homogeneous in metamorphism, laterally continuous and have characteristic lithostratigraphic features. This study also suggests a direct link between the pre-orogenic extensional setting and the present-day compressional structure of Alpine Corsica, indicating that large sections of subducted lithosphere were subducted and exhumed as coherent domains. These features provide important insight on the mechanism of stacking and exhumation of HP rocks, and make Alpine Corsica a unique reference for mountain-building processes in Tethyan-type orogens.
ISSN: 0012-8252

hal-00814433
https://hal.archives-ouvertes.fr/hal-00814433
DOI : 10.1016/j.earscirev.2012.10.003

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
The diffusion of titanium along with Ni, Co and Mn in pure synthetic forsterite has been studied as a function of temperature, oxygen fugacity, crystallographic orientation and chemical potentials in the four-component system MgO–SiO2–TiO2–TiO1·5. In over 100 different experimental conditions, no Ti diffusion profiles with the classical shape of the error function were observed. Instead, the profiles vary between ‘stepped’ at high fO2 (probably owing to diffusion on octahedral sites and trapping in tetrahedral sites), to hockey-stick shapes at low fO2 owing to concentration-dependent diffusion. The profile shapes vary systematically between these end-members according to oxygen fugacity. These profile shapes are also reproduced in experiments using natural San Carlos olivine. The change in profile shape is interpreted to be a function of valence-state change from Ti4+ to Ti3+, shown by a sigmoidal log fO2–diffusivity relationship. To distinguish between Ti4+ and Ti3+ in forsterite, a diffusion profile was also investigated using ‘hydroxylation spectroscopy’ whereby a crystal from a diffusion experiment was hydroxylated by annealing in an H2O-rich fluid at moderate pressure and temperature. The point defects associated with the added structural OH were then determined by infrared spectroscopy, providing evidence for the presence of Ti4+ and Ti3+ at intermediate oxygen fugacity. The transition from Ti4+ to Ti3+ occurs at considerably higher fO2 in these diffusion experiments than in equilibrium experiments in similar systems. Titanium diffusion, qualified using a mobility parameter (M), is fastest along the c-axis, at high activity of silica, low oxygen fugacity and high temperature. The rate of Ti diffusion is broadly similar to those of Mn, Ni and Co, and closer to published rates of Mg self-diffusion in olivine than Si self-diffusion. The observed Ti3+ and Ti4+ diffusion occurs on the M-sites. From statistical examination of the large Mn, Ni and Co diffusivity dataset, we determine that there is a 102/3 dependence of diffusion on aSiO2; the cations diffuse more rapidly at high aSiO2. In addition, diffusivity has a 10–1/8 dependence on fO2, suggested to be the result of increased concentration of loosely bound Ti3+–vacancy pairs, which enhance the mobility of other cations. This behaviour is likely to be present in natural systems where trivalent (e.g. Fe3+, Al3+, Cr3+) and divalent cations diffuse together. Consideration should be given to diffusive interference by highly charged, fast-moving cations when extracting time scales from frozen diffusion profiles.
ISSN: 0022-3530

hal-01531344
https://hal.archives-ouvertes.fr/hal-01531344
DOI : 10.1093/petrology/egw067

Éditeur(s) : HAL CCSD
Résumé : This thesis is devoted to the study of the geodynamic evolution of the panafrican belt in NW Angola, lying on the western margin of the Congo craton. This orogenic belt, resulting from the late neoproterozoic - early paleozoic convergence of the São Francisco and Congo cratons, can be subdivided into two main domains: 1) an eastern foreland made of folded neoproterozoic sediments and 2) a western hinterland made of magmatic and metamorphic rocks. Our structural, petrological, geochemical and geochronological studies lead to the recognition of two main units within this hinterland : 1) an upper eastern unit made of gneiss and micaschists (PTmax : 8-12 kbar, 650-680°C) that preserves D1 deformation structures related to the ENE transport of nappes and 2) a western lower unit made of gneiss and migmatites (P-Tmax : 7-9 kbar, 700-750°C) that were affected by a polyphased deformation. Our geochronological study shows that this belt contains ~2Ga old granites that were involved in a polyphased panafrican evolution between 540 Ma for syn-D1 peak metamorphic conditions and 480 Ma for the last stages of recrystallization and exhumation of high grade rocks. The synthesis of all data leads to a precise reconstruction of P-T-D-t paths in both tectonometamorphic units and to comparison of this panafrican belt with similar belts distributed on both sides of the Atlantic ocean. This work attests of the complexity of the geodynamic processes resulting in the Gondwana assembly and implying both large cratonic landmasses and intercalated microplates.
Cette thèse est consacrée à l'étude de l'évolution géodynamique de la chaîne panafricaine au NW de l'Angola, sur la marge occidentale du craton du Congo. Ce segment orogénique, conséquence de la convergence des cratons du São Francisco et du Congo à la fin du Néoprotérozoïque et début du Paléozoïque, peut être subdivisé en un domaine externe plissé et peu métamorphique et un domaine interne formé de roches magmatiques et métamorphiques. Les études structurales, pétrologiques, géochimiques et géochronologiques conduisent à distinguer deux unités principales dans le domaine interne : - l'unité supérieure de gneiss et micaschistes (P-Tmax : 8-12 kbar, 650-680°C) dont la déformation D1 est synchrone de la mise en place des nappes vers l'ENE; - l'unité inférieure dans la partie occidentale constituée de gneiss et migmatites (P-Tmax : 7-9 kbar, 700-750°C) affectés par une déformation polyphasée. L'étude géochronologique démontre l'existence de protolithes granitiques datés à ~2 Ga impliqués dans l'orogénèse pan africaine caractérisée par une histoire polyphasée entre 540 Ma pour le pic du métamorphisme syn-D1 et 480 Ma pour les dernières phases de recristallisation et d'exhumation des roches métamorphiques de haut grade. La synthèse des données permet ainsi de reconstruire précisément les deux chemins P-T-D-t de ces deux unités tectono-métamorphiques et de comparer ce segment panafricain à ceux présents de part et d'autre de l'Atlantique Sud. Ce travail témoigne de la complexité des processus géodynamiques de convergence amenant à l'assemblage du Gondwana impliquant à la fois de larges masses cratoniques et des microplaques intercalées entre ces masses.
https://tel.archives-ouvertes.fr/tel-00770757

Droits : info:eu-repo/semantics/OpenAccess
tel-00770757
https://tel.archives-ouvertes.fr/tel-00770757
https://tel.archives-ouvertes.fr/tel-00770757/document
https://tel.archives-ouvertes.fr/tel-00770757/file/these2012-Nsungani.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The minerals constituting the Earth's upper mantle are nominally anhydrous silicates (NAMs). However they do contain hydrogen as a trace element, decorating point defects in their crystalline structure. Experimental petrology and mineralogy have quantified the maximum concentration under several compositional and thermodynamic conditions, but systematic studies on the hydrogen concentration in minerals from mantle-derived rocks have only recently been carried out. Here, we have compiled the distribution of hydrogen in upper mantle peridotite xenoliths, from which several conclusions can be drawn. NAMs from peridotite xenoliths contain a few ppm wt. H2O in their structure. From the current database, the hydrogen concentrations in olivine regularly increase with increasing depth. The amount of hydrogen in NAMs from peridotite xenoliths from subduction contexts is not higher than in other geological context for similar temperature and pressure conditions. The highest hydrogen concentrations is found in peridotitic olivines from cratonic mantle, and are likely due to the depth of origin. The increasing hydrogen concentration in olivine with increasing depth is likely controlled by the increase of H partitioning into olivine at the expense of orthopyroxene as imposed by a decrease in Al content in opx with depth. However, the sparse data could also indicate that the bulk hydrogen concentration slightly increases with depth > 150 km. In this case, it would suggest, locally (Udachnaya for example), a possible increase in water fugacity due to fluid saturation. Even if the most abundant mineral in mantle rocks is olivine, the bulk hydrogen concentration in peridotites is controlled by the amount of hydrogen stored in pyroxenes. However, hydrogen concentration in olivine remains crucial for consequences on physical properties such as rheology and electrical conductivity. Kinetics of hydrogen transport is reviewed and hydrous melt/fluid percolation appears necessary to homogenize the hydrogen distribution at km-scale. Sampling of natural rock specimens is currently biased (e.g., in favor of optically attractive samples) and needs improvement, which will be achieved by increasing sample diversity (all type of grain sizes, lithologies, geological settings) and size of rock samples, as well as advances in analytical techniques. Acquisition of high quality data will be achieved by studying the co-existing minerals in mantle specimens, exploring each sample by linear and mapping measurements, and using appropriate FTIR calibrations for polarized and unpolarized radiation.
ISSN: 0024-4937

hal-01306676
https://hal.archives-ouvertes.fr/hal-01306676
DOI : 10.1016/j.lithos.2015.11.012