Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
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 1 Ga) and are commonly ≤ 2 Ga 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 1.7 Ga while the cpx from high-opx spinel harzburgites yield Hf model ages from 3.0 to 1.9 Ga. When plotted together, they define a Lu/Hf isochron with an age of 1.80 Ga, 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.
ISSN: 0009-2541

hal-01115519
https://hal.archives-ouvertes.fr/hal-01115519
DOI : 10.1016/j.chemgeo.2014.10.018

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 Elsevier
Résumé : International audience
In pre-drift reconstructions, the central and southern parts of the Borborema Province, northeastern Brazil, belong to a large Brasiliano-Pan-African orogenic realm situated to the north of the São Francisco-Congo Craton. In order to better understand the timing and geodynamic setting under which this orogenic system developed, a structural, geochemical and geochronological study was conducted across the east Pernambuco shear zone (EPSZ) system, which separates the Pernambuco-Alagoas Domain (PEAL) from the Central Domain. A sample of the Pinhões orthogneiss (GE-1), in the Central Domain, one sample of a syenitic orthogneiss (CA-34) wrapped by the EPSZ, and one sample of orthogneiss named Altinho (CA-40), in the northern portion of the PEAL, were dated by LA-ICP-MS. The Pinhões orthogneiss yielded an age of 869 ± 9 Ma, interpreted as the emplacement age of the protolith during a late Tonian magmatic episode. Samples CA-40 and CA-34 yielded 206Pb/238U weighted mean ages of 652 ± 6 Ma and 636 ± 3 Ma, respectively, which are interpreted as dating emplacement and crystallization of the magmatic protoliths. However, it is also possible that these rocks were formed during the same magmatic event in view of the identical ages of 646 ± 13 Ma and 646 ± 11 Ma, respectively, given by the less precise upper intercept of the discordia lines. The metaluminous and magnesian nature of the Altinho orthogneiss is akin to the calc-alkalic suite. However, some samples plot in the intraplate field in tectonic discrimination diagrams and the Nd TDM model age of 1.36 Ga is unlike that of juvenile magmas in convergent settings. The Altinho orthogneiss is quite similar in terms of trace elements geochemistry to the syenitic orthogneiss, which has a clearer intraplate affinity, and the dated samples have identical initial Sr isotope ratios (0.7047). Therefore, emplacement in an extensional setting is preferred over a convergent one. Two samples of paragneisses (SB-1 and BB-9) from the PEAL were also dated. The ages of the youngest zircon grains in sample BB-9 (655–642 Ma) overlap the crystallization age of the Altinho orthogneiss, implying that sedimentation is younger than or, at best, synchronous with magmatism. The age of low Th/U grains in samples CA-34 (615 ± 8 Ma) and SB-1 (587 ± 12 Ma) are related to a subsequent metamorphic overprint, which is loosely constrained between 580 and 620 Ma. These observations, combined with evidence provided by previous studies, suggest that the change from an extensional to a contracional setting occurred at ca. 640–630 Ma. In contrast with most collisional orogens, where a long period of oceanic subduction precedes collision, the inferred tectonic evolution suggests that the Brasiliano Orogeny resulted from inversion of continental and/or proto oceanic rifts.
ISSN: 0895-9811

hal-01174177
https://hal.archives-ouvertes.fr/hal-01174177
DOI : 10.1016/j.jsames.2014.09.007

Éditeur(s) : HAL CCSD Springer Verlag (Germany) Springer Verlag
Résumé : International audience
Arenal volcano is nearly unique among arc volcanoes with its 42 year long (1968–2010) continuous, small-scale activity erupting compositionally monotonous basaltic andesites that also dominate the entire, ~7000 year long, eruptive history. Only mineral zoning records reveal that basaltic andesites are the result of complex, open-system processes deriving minerals from a variety of crystallization environments and including the episodic injections of basalt. The condition of the mafic input as well as the generation of crystal-rich basaltic andesites of the recent, 1968–2010, and earlier eruptions were addressed by an experimental study at 200 MPa, 900–1,050 °C, oxidizing and fluid-saturated conditions with various fluid compositions [H2O/(H2O + CO2) = 0.3–1]. Phase equilibria were determined using a phenocryst-poor (~3 vol%) Arenal-like basalt (50.5−wt% SiO2) from a nearby scoria cone containing olivine (Fo92), plagioclase (An86), clinopyroxene (Mg# = 82) and magnetite (Xulvö = 0.13). Experimental melts generally reproduce observed compositional trends among Arenal samples. Small differences between experimental melts and natural rocks can be explained by open-system processes. At low pressure (200 MPa), the mineral assemblage as well as the mineral compositions of the natural basalt were reproduced at 1,000 °C and high water activity. The residual melt at these conditions is basaltic andesitic (55 wt% SiO2) with 5 wt% H2O. The evolution to more evolved magmas observed at Arenal occurred under fluid-saturated conditions but variable fluid compositions. At 1,000 °C and 200 MPa, a decrease of water content by approximately 1 wt% induces significant changes of the mineral assemblage from olivine + clinopyroxene + plagioclase (5 wt% H2O in the melt) to clinopyroxene + plagioclase + orthopyroxene (4 wt% H2O in the melt). Both assemblages are observed in crystal-rich basalt (15 vol%) and basaltic andesites. Experimental data indicate that the lack of orthopyroxene and the presence of amphibole, also observed in basaltic andesitic tephra units, is due to crystallization at nearly water-saturated conditions and temperatures lower than 950 °C. The enigmatic two compositional groups previously known as low- and high-Al2O3 samples at Arenal volcano may be explained by low- and high-pressure crystallization, respectively. Using high-Al as signal of deeper crystallization, first magmas of the 1968–2010 eruption evolved deep in the crust and ascent was relatively fast leaving little time for significant compositional overprint by shallower level crystallization.
ISSN: 0010-7999

hal-01115717
https://hal.archives-ouvertes.fr/hal-01115717
DOI : 10.1007/s00410-014-1040-4

Résumé : L’arc des Petites Antilles résulte de la lente subduction vers l'Ouest des plaques Nord et Sud-Américaines sous la plaque Caraïbes (2cm/an). A la latitude de l’archipel guadeloupéen et à ~150 km à l’Ouest du front de déformation, le bassin d'avant-arc de Marie-Galante forme un bassin perché, incliné vers la fosse et limité vers l’Est par un haut-fond, l’Eperon Karukéra. À cette latitude, le bassin de Marie-Galante domine le prisme d’accrétion de la Barbade et fait face à la ride de Tiburon qui balaye la zone du Nord au Sud depuis la fin du Miocène supérieur. Le remplissage sédimentaire du Bassin de Marie-Galante montre des déformations actives au moins depuis ~30 millions d’années. L’objectif du travail est de reconstituer l’évolution tectono-sédimentaire de ce bassin pour apporter de nouvelles contraintes sur la compréhension globale de la zone de subduction frontale des Petites Antilles. Ce travail s'appuie sur les données de bathymétrie multifaisceaux et de sismique réflexion multi-traces haute résolution acquises lors des campagnes du programme KaShallow. Cette base de données, complétée de profils sismiques plus basse résolution de campagnes antérieures, permet d’avoir une couverture pseudo 3D et à quatre échelles de résolution de l'ensemble du bassin. Un échantillonnage par ROV et carottage ciblé a fourni 40 prélèvements dans les principales unités sismiques. Les analyses pétrologiques et les datations biostratigraphiques autorisent des reconstitutions paléo-environnementales depuis le Paléogène supérieur jusqu’à Actuel. L’interprétation sismique multi-échelle montre un bassin sédimentaire atteignant ~4,5s temps double (~4500 à 5625 m) sur un substratum magmatique pré-structuré. Ce bassin est composé de 5 grands ensembles sédimentaires (E-1, E1, E2, E3 et E4) subdivisés en 13 unités limitées par 14 surfaces de discontinuités. L’organisation séquentielle des unités sismiques permet de mettre en évidence 10 séquences de dépôts de troisièmes ordres (S-1 à S9). Le calage biostratigraphique de l’ensemble des séquences permet de proposer une évolution tectono-sédimentaire du bassin de l’Éocène à l’Actuel. Ainsi, nous distinguons quatre systèmes de failles normales associées à trois phases d’extensions qui contrôlent l’évolution architecturale et sédimentaire du bassin. 1/ Un système N050±10°E hérité, actif dès le Paléogène supérieur, qui contrôle le basculement général du bassin vers le SSE. Il est responsable de la formation de l'escarpement de Désirade d’environ 4500 m de dénivelé. Cette première extension est interprétée comme résultant de la fragmentation de l'avant-arc en réponse à l'augmentation du rayon de courbure de la zone de subduction. 2/ Un système N130°-N150°E, structurant à l’échelle de l’Éperon Karukéra, qui contrôle la sédimentation dès le Miocène inférieur et marque une première phase d'extension transverse à l’arc. 3/ Un système N160°-N180°E qui segmente le Bassin de Marie-Galante en un sous-bassin à l'Ouest et l'Éperon Karukéra à l'Est. Cette seconde extension, globalement perpendiculaire à la marge, s'accompagne d’une subsidence et d'une inversion de la polarité du bassin en réponse à son basculement vers la fosse qui débute au cours du Miocène moyen et se poursuit actuellement à l'Est du bassin. Cette évolution à long terme de l'avant-arc, concomitante avec le recul de l'arc volcanique vers l’Ouest, est considérée comme résultant d’une érosion basale de la plaque supérieure. 4/ Un système N090±10°E plus tardif est localisé au centre du bassin et qui contrôle le développement de plates-formes carbonatées néritiques sur certaines têtes de blocs, comme par exemple à Marie-Galante. Cette dernière extension, parallèle à l’arc, se manifeste dans le bassin à partir du Pliocène inférieur. Elle se superpose au régime d'extension perpendiculaire à l'avant-arc et est interprétée comme l'accommodation du partitionnement de la déformation en réponse à l’obliquité croissante du front subduction vers le Nord.
The Lesser Antilles result of the slow westward subduction of the North and South American plate under the Caribbean plate (2 cm / year). At the latitude of the Guadeloupe archipelago and ~ 150 km to the west of the deformation front, the fore-arc basin of Marie-Galante forms a perched basin tilted to the pit and limited to the East by a shoal, the Spur Karukéra. At this latitude, Marie-Galante basin dominates the accretionary prism of Barbados and faces wrinkle Tiburon sweeping the area from North to South from the late Miocene. The sedimentary fill Basin Marie-Galante shows active deformation since at least ~ 30 million years. The aim of the work is to reconstruct the tectono-sedimentary evolution of the basin to provide new constraints on the overall understanding of the frontal subduction zone Lesser Antilles. This work relies on multibeam bathymetry data and high-resolution seismic reflection multi-traces acquired during campaigns KaShallow program. This database, supplemented by lower resolution of previous campaigns seismic profiles, provides a pseudo-3D coverage and four scales of resolution of the entire basin. ROV sampling and targeted core provided 40 samples in the main seismic units. Petrological analysis and biostratigraphic dating allow paleoenvironmental reconstructions from the upper Paleogene up Actuel. Seismic interpretation multiscale shows a sedimentary basin reaching ~ 4,5s double (~ 4500-5625 m) on a substrate pre-structured magma. This basin consists of 5 main sedimentary units (E-1, E1, E2, E3 and E4) divided into 13 units bounded by discontinuities 14 surfaces. The sequential organization of seismic units allows to highlight sequences 10 deposits of third order (S-1 to S9). The biostratigraphic calibration of all sequences able to offer a tectono-sedimentary evolution of the Eocene basin to Present. Thus, we distinguish four normal fault systems associated with three phases of extensions that control the architectural and sedimentary evolution of the basin. 1 / A system N050 ± 10 ° E inherited assets from the upper Paleogene, which controls the overall pelvic tilt towards the SSE. He is responsible for the formation of the escarpment Désirade about 4500 m elevation. The first extension is interpreted as resulting from the fragmentation of the fore-arc in response to the increase in the radius of curvature of subduction. 2 / A system N130 ° -N150 ° E, structuring across the Spur Karukéra, which controls sediment from the Miocene and marks the first phase of transverse extension arc. 3 / A system N160 ° E ° -N180 which segments Basin Marie-Galante in a sub-basin to the west and the Spur Karukéra in the East. This second extension, generally perpendicular to the margin, is accompanied by subsidence and reversing the polarity of the basin in response to his switch to the pit, beginning during the Middle Miocene and is ongoing in the East the basin. This long-term evolution of the forearc, concurrent with the decline in volcanic arc to the west, is considered as resulting from a basal erosion of the top plate. 4 / A system N090 ± 10 ° later E is located in the center of the basin and controlling the development of neritic carbonate platforms on certain blocks heads, such as Marie-Galante. This latest extension, parallel to the arc occurs in the basin from the lower Pliocene. It is superimposed on the expansion plan perpendicular to the fore-arc and is interpreted as the accommodation of the partitioning of deformation in response to the increasing obliquity front subduction north.

http://www.theses.fr/2014AGUY0799/document

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Paleozoic-early Mesozoic geology of Tibet was controlled by the rift-drift, seafloor spreading and subduction zone tectonics of a Paleo-Tethyan realm, which evolved between the West Cathaysides (WC) and the East Cimmerides (EC). Different suture zones with ophiolites and ophiolitic mélanges, high-pressure metamorphic belts, magmatic arcs and accretionary prism complexes separating different terranes mark multiple subduction-accretion systems within this Paleo-Tethyan domain, reminiscent of the modern Western Pacific Ocean. Discrete basins separated by different continental blocks and magmatic arcs constituted a complex paleogeography of Paleo-Tethys, and these oceanic strands were closed as a result of subduction with different polarities during the late Paleozoic-Triassic. The Longmu Tso Shuanghu-Changning Menglian Suture zone (LS-CMS) in Tibet represents the main tectonic boundary between the WC and EC that developed in the Devonian. The East Kunlun-A’nyemaqen oceanic slab was subducted northward beneath the East Kunlun terrane in northern Tibet, whereas the Sumdo oceanic slab was subducted northward beneath the South Qiangtang-North Lhasa terrane in southern Tibet. The Longmu Tso Shuanghu-Changning Menglian and Jinshajiang-Ailaoshan-Song Ma ophiolites were developed and emplaced in subduction-accretion systems with opposite polarities (westward and eastward) beneath the North Qiangtang-Qamdo-Simao-Indochina terrane in central Tibet. The Jinshajiang-Ailaoshan-Song Ma oceanic slab was subducted westward beneath the North Qiangtang-Simao-Indochina terrane along the Jinshajiang and Ailaoshan-Song Ma trenches in a trench-ridge-trench triple junction plate configuration. The Emeishan mantle plume produced a large Permian basaltic terrane, developed on the western passive margin of the South China block. The final closure of the Paleo-Tethyan oceanic branches resulted in continental collisions and development of a vast Indosinian orogenic collage in the latest Triassic-Jurassic.
ISSN: 0743-9547

insu-01119604
https://hal-insu.archives-ouvertes.fr/insu-01119604
https://hal-insu.archives-ouvertes.fr/insu-01119604/document
https://hal-insu.archives-ouvertes.fr/insu-01119604/file/Xu-JAES-2015.pdf
DOI : 10.1016/j.jseaes.2015.01.021

Éditeur(s) : HAL CCSD Elsevier
Résumé : Hot collisional orogens are characterized by abundant syn-kinematic granitic magmatism that profoundly affects their tectono-thermal evolutions. Voluminous granitic magmas, emplaced between 360 and 270 Ma, played a visibly important role in the evolution of the Variscan Orogen. In the Limousin region (western Massif Central, France), syntectonic granite plutons are spatially associated with major strike-slip shear zones that merge to the northwest with the South Armorican Shear Zone. This region allowed us to assess the role of magmatism in a hot transpressional orogen. Microstructural data and U/Pb zircon and monazite ages from a mylonitic leucogranite indicate synkinematic emplacement in a dextral transpressional shear zone at 313 +/- 4 Ma. Leucogranites are coeval with cordierite-bearing migmatitic gneisses and vertical lenses of leucosome in strike-slip shear zones. We interpret U/Pb monazite ages of 315 +/- 4 Ma for the gneisses and 316 +/- 2 Ma for the leucosomes as the minimum age of high-grade metamorphism and migmatization respectively. These data suggest a spatial and temporal relationship between transpression, crustal melting, rapid exhumation and magma ascent, and cooling of high-grade metamorphic rocks.;Some granites emplaced in the strike-slip shear zone are bounded at their roof by low dip normal faults that strike N-S, perpendicular to the E-W trend of the belt. The abundant crustal magmatism provided a low-viscosity zone that enhanced Variscan orogenic collapse during continued transpression, inducing the development of normal faults in the transpression zone and thrust faults at the front of the collapsed orogen.
ISSN: 0040-1951

hal-00445260
https://hal.archives-ouvertes.fr/hal-00445260
DOI : 10.1016/j.tecto.2009.03.022

Éditeur(s) : HAL CCSD Cambridge University Press (CUP)
Résumé : International audience
This paper presents a synthetic view of the geodynamic evolution of the Zagros orogen within the frame of the Arabia-Eurasia collision. The Zagros orogen and the Iranian plateau preserve a record of the long-standing convergence history between Eurasia and Arabia across the Neo-Tethys, from subduction/obduction processes to present-day collision (from ~ 150 to 0 Ma). We herein combine the results obtained on several geodynamic issues, namely the location of the oceanic suture zone, the age of oceanic closure and collision, the magmatic and geochemical evolution of the Eurasian upper plate during convergence (as testified by the successive Sanandaj-Sirjan, Kermanshah and Urumieh-Dokhtar magmatic arcs), the P-T-t history of the few Zagros blueschists, the convergence characteristics across the Neo-Tethys (kinematic velocities, tomographic constraints, subduction zones and obduction processes), together with a survey of recent results gathered by others. We provide lithospheric-scale reconstructions of the Zagros orogen from ~ 150 to 0 Ma across two SW-NE transects. The evolution of the Zagros orogen is also compared to those of the nearby Turkish and Himalayan orogens. In our geotectonic scenario for the Zagros convergence, we outline three main periods/regimes: (1) the Mid to Late Cretaceous (115-85 Ma) corresponds to a distinctive period of perturbation of subduction processes and interplate mechanical coupling marked by blueschist exhumation and upper-plate fragmentation, (2) the Paleocene-Eocene (60-40 Ma) witnesses slab break-off, major shifts in arc magmatism and distributed extension within the upper plate, and (3) from the Oligocene onwards (~ 30-0 Ma), collision develops with a progressive SW migration of deformation and topographic build-up (Sanandaj-Sirjan Zone: 20-15 Ma, High Zagros: ~12-8 Ma; Simply Folded Belt: 5-0 Ma) and with partial slab tear at depths (~10 Ma to present). Our reconstructions underline the key role played by subduction throughout the whole convergence history. We finally stress that such a long-lasting subduction system with changing boundary conditions also makes the Zagros orogen an ideal natural laboratory for subduction processes.
ISSN: 0016-7568

insu-00616582
https://hal-insu.archives-ouvertes.fr/insu-00616582
https://hal-insu.archives-ouvertes.fr/insu-00616582/document
https://hal-insu.archives-ouvertes.fr/insu-00616582/file/692.full.pdf
DOI : 10.1017/S001675681100046X

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 Dien Bien Phu (DBP) Fault strikes nearly perpendicular to the general tectonic framework, separating northwest Vietnam into two compartments. The DBP and Muong Lay granites are exposed respectively east and west of the fault. The U/Pb age of 277 ± 2 Ma obtained for the Muong Lay granite is similar to the age of the Chieng Khuong complex exposed within the Song Ma structure east of the DBP Fault. These two magmatic intrusions are considered as belonging to a same tectonic structure related to the subduction of the Song Ma Ocean under the Indochina Block during the Indosinian orogeny. The DBP Fault with a total post Permian dextral offset of 30-40 km shifts the Song Ma Suture. It could then be connected to the Ailao Shan-Shuanggou suture to the north. The undeformed DBP granite gave a U/Pb age of 230 ± 1 Ma sealing the Indosinian deformation on the fault. The Ladinian-Carnian activity of the fault is confirmed by the 40Ar/39Ar (biotite) age of 228 ± 4 Ma obtained from the paragneiss forming the fault zone. A geodynamic model is proposed to describe the various tectonic phases recorded by on the DBP Fault. It associates field data, stratigraphic observations, and geochronology analyses (U/Pb, Ar/Ar, fission tracks). Following the Late Triassic exhumation of the granite and the end of the Indosinian orogeny marked by the Norian unconformity, the granite was buried under Jurassic and Lower Cretaceous sediments. A strong cooling event during the early Late Cretaceous (100 Ma) is associated with the reactivation of the DBP Fault and the accommodation of a southward thrusting of the Song Da terrane onto the Truong Son Belt. This newly recognised tectonic phase could be associated to the subduction of the Paleo-Pacific plate under the Indochina Block. No data are available yet to constrain the Tertiary evolution of the DBP system. However, the Tertiary deformation is likely similar to the Cretaceous one.
ISSN: 1342-937X

insu-01015379
https://hal-insu.archives-ouvertes.fr/insu-01015379
DOI : 10.1016/j.gr.2013.07.018

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Massif du Sud is a large ophiolitic complex that crops out in the southern region of New Caledonia (SW Pacific). It is dominated by harzburgite tectonite that locally shows a transitional gradation to massive dunite up section. Clinopyroxene, orthopyroxene and plagioclase progressively appear in dunite up to the transition to layered wehrlite and orthopyroxene-gabbro. The dunite-wehrlite and wehrlite-gabbro contacts are parallel and the latter defines the paleo-Moho.;Highly depleted modal, mineral and bulk rock compositions indicate that harzburgites are residues after high degrees (20-30%) of partial melting mainly in the spinet-stability field. Their relative enrichment in HFSE, LREE and MREE is due to re-equilibration of melting residues with percolating melts. Dunite formed in the Moho transition zone by reaction between residual mantle harzburgite and olivine-saturated melts that led to pyroxene dissolution and olivine precipitation. Rare clinopyroxene and plagioclase crystallized in interstitial melt pores of dunite from primitive, low-TiO2, ultra-depleted liquids with a geochemical signature transitional between those of island arc tholeiites and boninites.;Ascending batches of relatively high-SiO2, ultra-depleted melts migrated through the Moho transition zone and generated wehrlite by olivine dissolution and crystallization of clinopyroxene, orthopyroxene and plagioclase in variable amounts. These liquids were more evolved and were produced by higher degrees of melting or from a more depleted source compared with melts that locally crystallized clinopyroxene in dunite. Ultra-depleted magmas, non-cogenetic with those that formed the Moho transition zone, ascended to the lower crust and generated gabbroic cumulates with subduction-related affinity. Thus, the ultramafic and mafic rocks in the Moho transition zone and lower crust of the Massif du Sud ophiolite are not products of fractional crystallization from a single magma-type but are the result of migration and accumulation of different melts in a multi-stage evolution. The record of high partial melting in the mantle section, and migration and accumulation of ultra-depleted subduction-related melts in the Moho transition zone and lower crust support that the Massif du Sud ophiolite is a portion of forearc lithosphere generated in an extensional regime during the early phases of the subduction zone evolution. Our results show the existence of different types of ultra-depleted melt compositions arriving at the Moho transition zone and lower crust of an infant intraoceanic paleo-arc. Ultra-depleted melts may thus be a significant component of the melt budget generated in oceanic spreading forearcs prior to aggregation and mixing of a large range of melt compositions in the crust.
ISSN: 0009-2541

hal-00429333
https://hal.archives-ouvertes.fr/hal-00429333
DOI : 10.1016/j.chemgeo.2009.06.004

Éditeur(s) : HAL CCSD IODP
Résumé : The Superfast Spreading Crust campaign, echoing long-standing ocean lithosphere community endeavors, was designed to help us understand the formation, architecture, and evolution of ocean crust formed at fast spreading rates. Integrated Ocean Drilling Program (IODP) Expedition 335, "Superfast Spreading Rate Crust 4" (13 April-3 June 2011), was the fourth scientific drilling cruise of the Superfast Spreading Crust campaign to Ocean Drilling Program (ODP) Hole 1256D. The expedition aimed to deepen this basement reference site several hundred meters into the gabbroic rocks of intact lower oceanic crust to address the following fundamental scientific questions: Does the lower crust form by subsidence of a crystal mush from a high-level magma chamber (gabbro glacier), by intrusion of sills throughout the lower crust, or by some other mechanism? How does melt percolate through the lower crust, and what are the reactions and chemical evolution of magmas during migration? Is the plutonic crust cooled by conduction or hydrothermal circulation? What are the role and extent of deeply penetrating seawater-derived hydrothermal fluids in cooling the lower crust and the chemical exchanges between the ocean crust and the oceans? What are the relationships among the geological, geochemical, and geophysical structure of the crust and, in particular, the nature of the seismic Layer 2-3 transition? What is the magnetic contribution of the lower crust to marine magnetic anomalies?
https://hal.archives-ouvertes.fr/hal-00688990

hal-00688990
https://hal.archives-ouvertes.fr/hal-00688990
DOI : 10.2204/iodp.pr.335.2011

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The present study is based on a set of lavas and crosscutting dikes collected by dives along detailed vertical transects on the northern flank of the western part of the Blanco Transform Fault, Northeast Pacific. The studied area consists of a small basin, the Western Blanco Depression (WBD), extending from the southern end of the Juan de Fuca ridge to a pseudofault trace 60 km eastward. The Northern Scarp of the WBD comprises a volcanic unit overlying a sheeted-dike complex. Major and trace element data, coupled with Sr–Nd isotope ratios, reveal a two-component mantle source, composed by an isotopically depleted matrix variably veined by more enriched material. One chemical group (NS2), indistinguishable from the other Northern Scarp samples on the basis of trace element data, has an unusually depleted isotopic composition typical of a nearly pure mantle end-member. Some cogenetic samples of the Northern Scarp have been used to constrain the differentiation modalities. Anorthite and MgO content profiles in plagioclase xenocrysts and phenocrysts reveal (i) the existence of H2O-bearing evolved melts in the mushy zones and (ii) the occurrence of mixing process between these melts and anhydrous mafic liquids. The hydration is supported by other petrographic features such as high magmatic fO2 values, calculated from Fe–Ti oxide pairs, and the presence of pyroxene inclusions in plagioclase phenocrysts. Mixing, consistent with the existence of Ni-rich ferrobasalts, is interpreted to be the consequence of the reservoir refilling by mafic liquids (Mg# = 70). These petrological and geochemical evidences are combined with the evolution of Mg# with depth to suggest a periodic open-system magma chamber evolution beneath the southern end of the Juan de Fuca ridge.
ISSN: 0024-4937

insu-00213426
https://hal-insu.archives-ouvertes.fr/insu-00213426
DOI : 10.1016/j.lithos.2007.06.009

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Over the last decades, numerous studies have emphasized the role of serpentinites in the subduction zone geodynamics. Their presence and role in subduction environments are recognized through geophysical, geochemical and field observations of modern and ancient subduction zones and large amounts of geochemical database of serpentinites have been created. Here, we present a review of the geochemistry of serpentinites, based on the compilation of ~ 900 geochemical data of abyssal, mantle wedge and exhumed serpentinites after subduction. The aim was to better understand the geochemical evolution of these rocks during their subduction as well as their impact in the global geochemical cycle. When studying serpentinites, it is essential to determine their protoliths and their geological history before serpentinization. The geochemical data of serpentinites shows little mobility of compatible and rare earth elements (REE) at the scale of hand-specimen during their serpentinization. Thus, REE abundance can be used to identify the protolith for serpentinites, as well as magmatic processes such as melt/rock interactions before serpentinization. In the case of subducted serpentinites, the interpretation of trace element data is difficult due to the enrichments of light REE, independent of the nature of the protolith. We propose that enrichments are probably not related to serpentinization itself, but mostly due to (sedimentary-derived) fluid/rock interactions within the subduction channel after the serpentinization. It is also possible that the enrichment reflects the geochemical signature of the mantle protolith itself which could derive from the less refractory continental lithosphere exhumed at the ocean-continent transition. Additionally, during the last ten years, numerous analyses have been carried out, notably using in situ approaches, to better constrain the behavior of fluid-mobile elements (FME; e.g. B, Li, Cl, As, Sb, U, Th, Sr) incorporated in serpentine phases. The abundance of these elements provides information related to the fluid/rock interactions during serpentinization and the behavior of FME, from their incorporation to their gradual release during subduction. Serpentinites are considered as a reservoir of the FME in subduction zones and their role, notably on arc magma composition, is underestimated presently in the global geochemical cycle.
ISSN: 0024-4937

hal-00903601
https://hal.archives-ouvertes.fr/hal-00903601
DOI : 10.1016/j.lithos.2013.05.019

Éditeur(s) : HAL CCSD
Résumé : International audience
The core of South East Asia is composed of a mosaic of continental blocks, among which the Indochina and theSouth China blocks (present day northern Vietnam), amalgamated during the Permian and/or the Triassic. LatePermian to Late Triassic geodynamic evolution of these two blocks remains controversial. The main discussionpoints concern the existence and the closure of an oceanic domain separating the Indochina and the South Chinablocks during this period. Especially, the polarity and the timing of the subduction zone that led to the collisionbetween the blocks as well as the present location of the suture delimiting them are a matter of debate. Despite thevaluable information they can provide, the sedimentary basins from northern Vietnam have been neglected in theprevious studies dealing with the geodynamic evolution of South East Asia.To determine the geodynamic evolution of the area, the basins of Sam Nua and Song Da, presently locatedin North Vietnam, have been investigated using a combined approach involving sedimentology, geochronology(U-Pb/zircon) and geochemistry (whole-rock major and trace elements composition of both volcanic and volcaniclasticrocks). The palaeoenvironment evolution, the main unconformities, their age and the tectonic affinitiesof the interbedded volcanic and volcaniclastics series have been characterized for these two basins. Our resultsdemonstrate (i) that the Song Da Basin exhibits a palaeogeographic affinity with the South China block, (ii) theoccurrence of extensive calk-alkaline volcanism and associated volcaniclastic deposits in the Sam Nua Basin,related to the existence of an active magmatic arc during the Early and the lower Middle Triassic, (iii) a Southdipping (present day coordinate) oceanic lithosphere beneath the Indochina block, deduced from the location ofthe magmatic arc south of the potential suture zones, (iv) that an angular unconformity postdates the lower MiddleTriassic volcaniclastic deposits in the Sam Nua basin. This unconformity, crosscutting the subduction relateddeposits, is interpreted as the result of the collision between the Indochina and the South China blocks.
European Geoscience Union General Assembly 2015
Vienne, Austria

insu-01137675
https://hal-insu.archives-ouvertes.fr/insu-01137675

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Spinel (± plagioclase) peridotite xenoliths from the Tallante and Los Perez volcanic centres in the eastern Betics (SE Spain) range from depleted (clinopyroxene-poor) harzburgites to fertile (clinopyroxene-rich) lherzolites and orthopyroxene-free wehrlites. Significantly, only one harzburgite, which is depleted in heavy rare earth elements (HREE), retains the imprint of ca. 20% ancient melting of an original garnet lherzolite source. In contrast, REE abundances of other harzburgites and lherzolites from the eastern Betics have been increased by melt-rock reaction. The whole-rock and mineral compositions of these mantle rocks are largely controlled by three types of modal metasomatism: 1) common clinopyroxene-orthopyroxene addition and olivine consumption which increased FeOt, SiO2 and Al2O3, and decreased MgO compared to the refractory melting products; 2) subordinate orthopyroxene dissolution and precipitation of clinopyroxene and olivine, which led to higher FeOt and MgO and lower SiO2 than in common (orthopyroxene-rich) lherzolites; and 3) rare orthopyroxene consumption and olivine addition that caused higher FeOt and lower SiO2 compared to the original melting residues. These mineral modal and major element variations have been produced mostly by interactions with relatively FeOt-rich/SiO2-poor melts, likely derived from a peridotite-pyroxenite lithospheric mantle with a highly heterogeneous isotopic composition. Melting of the lithospheric mantle in the western Mediterranean was triggered by upwelling of the asthenosphere induced by back-arc extension in the Late Oligocene-Early Miocene. Trapping of small fractions of exotic melts in whole-rocks — likely the parental magmas of Miocene back-arc dykes that intruded the Betic crust — caused local disequilibrium between the trace element signatures and Pb isotopic compositions of clinopyroxene and whole-rock. Subsequent interaction with SiO2-undersaturated magmas, similar to the parental melts of the Pliocene alkali basalts that host the xenoliths, promoted orthopyroxene consumption and clinopyroxene-olivine enrichment at locations close to magma conduits, and finally generated orthopyroxene-free wehrlites. This event constitutes the last episode of the Cenozoic magmatic evolution of the westernmost Mediterranean which is recorded in the mantle xenoliths from the eastern Betics.
ISSN: 0024-4937

hal-01553092
https://hal.archives-ouvertes.fr/hal-01553092
DOI : 10.1016/j.lithos.2016.12.011

Éditeur(s) : HAL CCSD Geological Society of London
Résumé : International audience
The sediments of the Mauges Unit located in the internal zone provide an opportunity of studying the evolution of relief during Palaeozoic time. U-Pb dating on zircon and 39Ar/40Ar on white mica are used to constrain the age and nature of the sources. The first relief identified is marked by an Early Devonian unconformity interpreted as the opening of a northern back-arc basin. Detrital minerals are first reworked from underlying layers indicating a local supply. Magmatic zircons at c. 400 Ma then record the emergence of a magmatic arc. During the Middle Devonian, the gap in the sedimentary record is attributed to an emersion followed by the disappearance of the relief during the Late Devonian. At the Devonian-Carboniferous boundary, the main collision is followed by the onset of a relief. The continental sedimentation in the Ancenis Basin (late Tournaisian-Viséan) is a coarsening-upwards megasequence indicating an increasing and/or approaching relief. The detrital minerals record the progressive exhumation of Variscan metamorphic (mica at c. 350 Ma) and magmatic rocks (zircons at c. 390-340 Ma). The Serpukhovian-Bashkirian sedimentation records the erosion of a proximal metamorphic source (Champtoceaux with micas at c. 350-340 Ma) showing a much shorter drainage system
The Variscan Orogeny: Extent, Timescale and the Formation of the European Crust

ISBN : 978-1-86239-658-6
insu-01016985
https://hal-insu.archives-ouvertes.fr/insu-01016985
DOI : 10.1144/SP405.6

Éditeur(s) : HAL CCSD
Résumé : aucun
Ce travail de thèse s'intéresse à l'événement transamazonien en Guyane Française. Le Transamazonien constitue l'événement géodynamique majeur structurant le bouclier des Guyanes entre 2.2 et 2.0 Ga. L'évolution de l'orogenèse transamazonienne est décrite en termes de croissance crustale, prenant en compte des processus de recyclage archéen ainsi que des processus d'accrétion juvénile et de réactivation thermotectonique au Paléoprotérozoïque. Notre travail axé sur une étude géochronologique (U-Pb et Ar/Ar) et une étude géochimique (éléments majeurs et éléments en trace) a permis de proposer un modèle d'évolution en quatre étapes : une première étape avec la formation d'une croûte océanique juvénile à 2.2 Ga, une seconde étape de croissance crustale, avec la formation de série TTG entre 2.18 et 2.1Ga. Cette seconde étape présente une évolution du contexte de subduction générant les TTG, le résultat est la formation de magmas type «sanukitoïdes». La troisième étape présente la formation de magmas calco-alcalins (2.1 à 2.08 Ga) résultant du «refroidissement» du contexte de subduction déjà initié lors de la seconde étape. Le stade final est caractérisé par la formation de granites d'anatexie crustale (2.1 à 2.06 Ga). Plus globalement, notre étude sur le Transamazonien s'intéresse à la question clé des domaines paléoprotérozoïques, qui est de définir quels types de processus étaient actifs à cette période ? Le Paléoprotérozoïque se situe à la transition entre la période archéenne dominée par des processus de croissance crustale dits «archaïques» et une période récente caractérisée par des processus de croissance crustale dits «modernes».
https://tel.archives-ouvertes.fr/tel-00441743

tel-00441743
https://tel.archives-ouvertes.fr/tel-00441743
https://tel.archives-ouvertes.fr/tel-00441743/document
https://tel.archives-ouvertes.fr/tel-00441743/file/thesenjolvy.pdf

Éditeur(s) : HAL CCSD IODP
Résumé : Integrated Ocean Drilling Program (IODP) Expedition 335 (14 April–4 June 2011) will be the fourth ocean cruise of the "Superfast" campaign to drill a deep hole into intact oceanic basement and will return to Ocean Drilling Program (ODP) Hole 1256D to deepen this scientific reference penetration a significant distance into cumulate gabbros. Cores and data recovered during the Superfast 4 expedition will provide hitherto unavailable observations that will test models of the accretion and evolution of the oceanic crust. Site 1256 was specifically located on oceanic crust that formed at a superfast spreading rate (>200 mm/y) to exploit the observed relationship between spreading rate and depth to axial low velocity zones, thought to be magma chambers, seismically imaged at active mid-ocean ridges. This was a deliberate strategy to reduce the drilling distance to gabbroic rocks because thick sequences of lavas and dikes have proved difficult to penetrate in past. ODP Leg 206 (2002) initiated operations at Site 1256, including the installation in Hole 1256D of a reentry cone with 16 inch casing inserted through the 250 m thick sedimentary cover and cemented into basement to facilitate deep drilling. The hole was then cored ~500 m into basement. IODP Expeditions 309 and 312 (2005) successfully completed the first sampling of an intact section of upper oceanic crust from lavas, through the sheeted dikes, and into the upper gabbros. Hole 1256D now penetrates >1500 meters below seafloor (mbsf) and >1250 m subbasement and currently resides in the dike–gabbro transition zone. The first gabbroic rocks were encountered at 1407 mbsf. Below this lies a ~100 m complex zone of fractionated gabbros intruded into contact metamorphosed dikes. Although previous cruises achieved the benchmark objective of reaching gabbro in intact ocean crust, critical scientific questions remain. These include the following: 1. Does the lower crust form by the recrystallization and subsidence of a high-level magma chamber (gabbro glacier), crustal accretion by intrusion of sills throughout the lower crust, or some other mechanism? 2. Is the plutonic crust cooled by conduction or hydrothermal circulation? 3. What is the geological nature of Layer 3 and the Layer 2/3 boundary at Site 1256? 4. What is the magnetic contribution of the lower crust to marine magnetic anomalies? Hole 1256D is poised at a depth where samples that should conclusively address these questions can be obtained, possibly with only a few hundred meters of drilling. Importantly, as of the end of Expedition 312, the hole was clear of debris and open to its full depth. Increased rates of penetration (1.2 m/h) and enhanced core recovery (>35%) in the gabbros indicate that this return to Hole 1256D could deepen the hole >300 m into plutonic rocks, past the transition from dikes to gabbro, and into a region of solely cumulate gabbroic rocks.
https://hal.archives-ouvertes.fr/hal-00564953

hal-00564953
https://hal.archives-ouvertes.fr/hal-00564953
DOI : 10.2204/iodp.sp.335.2010

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
During the development of the Variscan orogeny, large amounts of granitic melt were produced, giving rise to the intrusion of granitoids at different structural levels. Despite numerous studies, ages available from previous work on the Cevennes granites remain largely imprecise. In order to better constrain the age and emplacement mode of these granites, we have combined U-Pb dating on monazites and zircons and Ar-40/Ar-39 dating on biotites with petrological observations, major element chemical analysis and SEM zircon imaging on five samples from the Aigoual-St Guiral-Liron and Mont Lozere granitic massifs. The results revealed that granitic intrusions and cooling in Southern Cevennes occurred in a short time span at similar to 306 Ma after the main episode of regional metamorphism. Petrological and chemical data suggest that they result from a mixing between mantle-derived basic magmas (lamprophyres) and lower crust acid magmas. At a regional scale the production of these melts occurred at the end of crustal thickening induced by nappe stacking, at the same time as the late anatectic events recorded further north in the Velay dome and the granulite facies metamorphism recorded in metasedimentary granulite enclaves brought up by Tertiary volcanoes of the Velay area (Bournac).
ISSN: 1437-3254

hal-00412183
https://hal.archives-ouvertes.fr/hal-00412183
DOI : 10.1007/s00531-007-0187-x