Éditeur(s) : HAL CCSD
Résumé : Thrusting fault zone in foreland basins are characterized by highly foliated zones generally enriched in phyllosilicates which can play a major role on the mechanical behaviour of the fault. In this context, investigations of synkinematic clay minerals permit to determine the origin of the fluid from which they precipitated as well as the mechanisms of deformation. Our study is focused on clay mineral assemblages (illite and chlorite) in a major thrust fault located in the Monte Perdido massif (southern Pyrenees), a shallow thrust that affects upper cretaceous-paleocene platform carbonates and lower Eocene marls and turbidites. It implied 3 km of displacement of the Monte Perdido thrust unit with respect to the underlying Gavarnie unit. In this area the cleavage development by pressure-solution is linked to the Monte Perdido and Gavarnie thrust activity. The core zone of the fault, about 6 m thick, consists of an interval of intensely deformed clay-bearing rocks bounded by major shear surfaces. The deformed sediment is markedly darker than the protolith. Calcite-quartz shear veins along the shear planes are abundant. Detailed SEM and TEM observations of highly deformed fault zone samples indicate that clay mineral enrichment in the core zone of the fault is not only related to passive increase by pressure-solution mechanism but that dissolution-recrystallization of phyllosilicates occurs during deformation. A mineral segregation is observed in the highly deformed zone. Newly formed 2M 1 muscovite is present along the cleavage whereas IIb chlorite crystals fill SV2 shear veins suggesting syntectonic growth of phyllosilicates in the presence of fluids in low-grade metamorphic conditions. These mineralogical reactions act as weakening processes and would favour Monte Perdido fault creeping.
Swiss Journal of Geosciences

hal-00795553
https://hal.archives-ouvertes.fr/hal-00795553
DOI : 10.1007/s00015-012-0098-0

Éditeur(s) : Gauthier-Villars
Résumé : The paper summarizes the biostratigraphic results of eighteen dives of the French submersible Cyana at the Mazagan Escarpment (CYAMAZ cruise), based on calcareous nannoplankton and foraminifera. This paper is restricted to the study of the Early Cretaceous to Quaternary post-platform series. Most of the stratigraphical data are based on the determination of calcareous nannofossils (P. Cepek) which, however, are mostly poorly preserved and of rare occurrence. From the 170 studied subsamples 49 are barren of calcareous samples are listed according to the species epithets, separated for the Cretaceous and Tertiary. The biostratigraphy based on foraminifera and the microfacies was studied in thin-section (H. hagn). Foraminiferal microfaunas of Late Cretaceous, Paleocene, Eocene-Oligocene and Quaternary age are described and shown in Plates.
Oceanologica Acta, Special issue (0399-1784) (Gauthier-Villars), 1985

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00247/35827/34337.pdf
http://archimer.ifremer.fr/doc/00247/35827/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This paper focuses on the analyses of the clastic sedimentary infill of the Coastal Plain of Eastern Mexico, which initiated synchronously with the Laramide orogeny in the vicinity of the Golden Lane. Results of these analyses are used as boundary conditions for calibrating/interpreting seismic profiles across more distal depocenters in the offshore of the Gulf of Mexico, from the sea shore and continental slope in the west to the abyssal plain in the east. The objective of the study is to better predict the reservoir distribution in the Deep offshore Basin of the Gulf of Mexico (DBGM), in order to explore for petroleum. The Coastal Plain is underlain by three morpho-tectonic domains: the tectonic front of the Sierra Madre Orientale (SMO), the Chicontepec deep water flexural basin, and the Tuxpan Platform (also known as the Golden Lane). Each domain is characterized by a distinct, dominantly siliciclastic Cenozoic lithostratigraphy. After a Jurassic rifting episode, followed by thermal subsidence, the oceanic basin and its western passive margin were deformed during the Upper Cretaceous and Paleogene, by far field stresses associated with the Cordilleran-Laramide Orogeny. Starting in the Late Cretaceous-Early Paleogene and during the Early Eocene, the tectonic load associated with the Laramide Orogen (Sierra Madre Oriental, SMO) caused flexural subsidence of the foreland located under the Coastal Plain. During this period, a massive transfer of siliciclastic sediments occurred from the Laramide foothills into the adjacent foreland. Sediments were eroded of the Sierra Madre tectonic wedge. Loading by these sediments pushed source units associated with the former passive margin down ward. The first syn-tectonic sediments of the Laramide orogeny were turbiditic silt layers in submarine fans which record also numerous collapse episodes and gravity slides. During the Late Eocene and Oligocene, the flexural subsidence stopped in the hinterland, whereas the subsidence of the passive margin resumed. This resulted in a change in the overall sedimentary architecture of the basin. Paleo-highs and reefs facies of the Golden Lane were flooded. Clastics by-passed the reefs and progradational clastic stratification formed as sediment moved towards the DBGM in the east. The final depositional environment of the continental platform/Coastal Plain became deltaic, marked by a succession of sand bars, levees and channels systems. From Miocene times onward, a system of gravitational listric faults developed near the platform to slope transition, resulting in a coeval compressional system at the transition between the slope and the abyssal plain. This system is driven by sediments charge. Because the sedimentation rate is larger than the subsidence, a large amount of clastics and slumped sediments are deposited in hangingwall basins.
ISSN: 0264-8172

hal-00424586
https://hal.archives-ouvertes.fr/hal-00424586
DOI : 10.1016/j.marpetgeo.2008.03.009

Éditeur(s) : HAL CCSD Société géologique de France
Résumé : International audience
– The 300 km long allochthonous sheet of oceanic mantle forming the New Caledonia ophiolite displays three specific characters: 1) the ophiolite pile lacks concordant sheeted dykes and pillow basalt layers; 2) the ophiolite, refered to as the Peridotite nappe, is thrusted over the basaltic formations of the Poya terrane which are classicaly thought to originate from a different oceanic environment; 3) The basal contact of the ultramafic sheet is remarkably flat all along New-Caledonia and the Peridotite nappe has not been thickened during obduction, rather it experienced significant extension. This suggests that the peridotites have not been emplaced by a tectonic force applied to the rear. New petrological and geochemical results obtained from mantle rocks finally show that the Poya terrane may originate from the same oceanic basin as the peridotites. In this article, we consider such possible cogenetic links and we propose a simple model for the obduction of the New Caledonia ophiolite in which the Poya basalts represent the original cover of the Peridotite nappe. We infer that continuous uplift of the subducted units buried beneath the oceanic lithosphere in the northern part of New Caledonia drove passive uplift of the ophiolite and led to erosion and to initiation of sliding of the basaltic layer. During the Priabonian (latest Eocene), products of the erosion of the basaltic layer were deposited together with sediments derived from the Norfolk passive oceanic margin. These sediments are involved as tectonic slices into an accretionary wedge formed in response to plate convergence. The volcaniclastic sedimentation ends up with the emplacement of large slided blocks of basalts and rafted mafic units that progressively filled up the basin. Obduction process ended with the gravity sliding of the oceanic mantle sheet, previously scalped from its mafic cover. This process is contemporaneous with the exhumation of the HP-LT units of Pouebo and Diahot. Gravity sliding was facilitated by the occurrence of a continuous serpentine sole resulting from metasomatic hydratation of mantle rocks, which developed during the uplift of the Norfolk basement and overlying Diahot and Pouébo units. Progressive emersion of the obducted lithosphere allowed subsequent weathering under subaerial, tropical conditions. Obduction passive et mise en place gravitaire des grandes nappes ophiolitiques : les ophiolites de Nouvelle-Calédonie (SW Pacifique) sont-elles un cas d'école ? Résumé. – La nappe de manteau de Nouvelle-Calédonie, s'étendant sur 300 km de long montre trois caractéristiques im-portantes: 1) La succession ophiolitique ne contient ni dykes, ni basaltes en coussin, 2) l'ophiolite est charriée sur des formations basaltiques (nappe de Poya) que l'on considère classiquement comme originaires d'un bassin océanique dif-férent de celui d'où est issu le manteau, et 3) le contact basal de la nappe ultrabasique est remarquablement plat tout le long de l'île et celle-ci n'a pas été épaissie durant l'obduction. Cela suggère que les péridotites n'ont pas été mises en place en réponse à une poussée tectonique arrière. De nouveaux résultats pétrologiques et géochimiques obtenus sur l'ophiolite montrent en réalité que les basaltes de Poya peuvent être extraits de la fusion du manteau de l'ophiolite. Nous proposons donc un nouveau modèle pour l'obduction, dans lequel les basaltes de Poya forment la couver-ture initiale primitive du manteau de la nappe des péridotites. La surrection progressive des unités profondes enfouies lors de la subduction de la lithosphère du bassin sud-Loyauté à l'Eocène, a permis le soulèvement passif de l'ophiolite et l'érosion puis le glissement des unités basaltiques. Durant le Priabonien, l'accumulation des produits de l'érosion de la couche des basaltes et de la marge passive de Norfolk ont formé les séquences de flysch comprenant localement des débris basaltiques grossiers. Ces sédiments font partie d'un prisme d'accrétion tectonique construit en réponse à la convergence au front de la subduction. La sédimentation détritique se termine par la mise en place de grandes unités ba-saltiques glissées qui comblent le bassin. Le processus de l'obduction se termine par le glissement gravitaire de l'écaille de manteau océanique sur les basaltes. Cet événement est contemporain de l'exhumation des unités HP-BT de Pouébo et du Diahot. Le glissement gravitaire a été facilité par la présence sous l'ophiolite, d'une semelle continue de serpentines résultant de l'interaction du manteau avec des fluides métasomatiques remontant durant l'exhumation des unités en-fouies pendant la subduction continentale. L'émersion progressive de la lithosphère obduite a placé le manteau dans des conditions d'altération supergène tropicale.
EISSN: 1777-5817

hal-01257702
https://hal.archives-ouvertes.fr/hal-01257702
https://hal.archives-ouvertes.fr/hal-01257702/document
https://hal.archives-ouvertes.fr/hal-01257702/file/Lagabrielleetal-BSGF-2012-revised-light.pdf
DOI : 10.2113/gssgfbull.184.6.545

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : International audience
We present new apatite (U–Th)/He (AHe), apatite fission track (AFT) and zircon (U–Th)/He (ZHe) data to unravel the timing of exhumation and thrusting in the western Axial Zone of the Pyrenees and the adjacent North Pyrenean Zone (Chaînons Béarnais). In the north, ZHe data yield cooling signals between 26 and 50 Ma in the Chaînons Béarnais, which are consistent with the onset of thrust-related cooling in the neighboring Mauléon Basin modeled by previous authors. Non-reset Triassic ages are found in the footwall of the North Pyrenean Frontal thrust (Aquitaine Basin). To the south, similar ZHe ages in both the hanging wall and footwall of the Lakora thrust record Late Eocene to Oligocene cooling that we attribute to the activity of the Gavarnie thrust. Thermal modeling of samples from the Lakora thrust hanging wall indicates cooling from Early Eocene times, recording activity of the Lakora thrust. Paleozoic detrital samples from the westernmost Axial Zone and from the Eaux-Chaudes and Balaitous–Panticosa granitic plutons yield AFT signals between 20 and 30 Ma and ZHe between 20 and 25 Ma. Modelling indicates fast cooling during this time, which we attribute to the motion of the Guarga thrust. AHe data from these Axial Zone plutons, combined with modelling, show a post-tectonic signal (8–9 Ma), which indicates renewed erosion after a period without major cooling and exhumation between 20 to 10 Ma.
ISSN: 1631-0713

insu-01301995
https://hal-insu.archives-ouvertes.fr/insu-01301995
DOI : 10.1016/j.crte.2016.01.001

Éditeur(s) : HAL CCSD
Résumé : International audience
At the time of the collision with India (55Ma), the southern margin of Asia was a composite continental domainresulting from an already long history of successive accretions of different terranes having different rheologies.Knowledge about the structure, composition and thermal state of the Tibetan lithosphere through time is thusfundamental to understand the respective contributions of pre-Cenozoïc and Cenozoïc tectonics in the building ofthe Plateau to its present-day elevations.We focused on the boundary between the Qiangtang terrane to the south, and the Songpan-Ganze terrane to thenorth.We jointly studied deep crustal xenoliths and associated (ultra-)potassic magmatism from the Eocene basinsof Nangqian and Xialaxiu (Qinghai Province, China), north of the Qiangtang terrane. The aims were to retrievethe composition and the thermal state of the lower crust during Eocene times, to study the behavior of the lowercrust and lithospheric mantle of the Eastern Qiangtang terrane and the adjacent Songpan-Ganze terrane at the timeof the collision, and the link with the magmatic activity.Crustal xenoliths are of two types: biotite-rich, amphibole bearing metasediments; and garnet-bearing quartzofeldspathicgneisses. Such assemblages are typical of very high-grade amphibolite and granulite faciesmetamorphism; further study should allow us to quantify the pressures and temperatures those rocks experienceduntil the time they were sampled by their host lavas.Major element geochemistry places the c.a. 51-49 Ma (Spurlin et al., 2005) Xialaxiu volcanic field in a fairlydifferentiated (SiO265-70 wt%) high-K field of the calc-alcaline series. Trace element analysis suggests a strongcrustal contamination of the primary mantellic melts. C.a. 38-37 Ma (Spurlin et al., 2005) Nangqian magmaticbodies span across the alkaline series, with high to extreme (K2O6wt%) values. Complex major and traceelement patterns, coupled with high-resolution microprobe data on pyroxene xenocrysts, suggest that enrichmentoccurred at the source by metasomatism of the lithospheric mantle.Further work will precise which mechanisms could have accounted for such a metasomatism of the mantle beneaththe Northern Qiangtang terrane during Eocene, and whether the lower crust had an autochtonous or allochtonousnature.
Geophysical Research Abstracts
Vienne, Austria

insu-01308919
https://hal-insu.archives-ouvertes.fr/insu-01308919

Éditeur(s) : AGU
Résumé : New, high-quality multichannel seismic reflection data from the western New Caledonia offshore domain allow for the first time the direct, continuous connection of seismic reflectors between the Deep Sea Drilling Project 208 drill hole on the Lord Howe Rise and the New Caledonia Basin. A novel seismic interpretation is hence proposed for the northern New Caledonia Basin stratigraphy, which places the Eocene/Oligocene unconformity deeper than previously thought and revisits the actual thickness of the pre-Oligocene sequences. A causal link is proposed between the obduction of the South Loyalty Basin over New Caledonia (NC) and the tectonic history of the northern New Caledonia Basin. Here it is suggested that as the South Loyalty Basin was being obducted during early Oligocene times, the NC Basin subsided under the effect of the overloading and underthrusted to accommodate the compressional deformation, which resulted in (1) the uplift of the northern Fairway Ridge and (2) the sinking of the western flank of New Caledonia. This event also had repercussions farther west with the incipient subsidence of the Lord Howe Rise.
Tectonics (0278-7407) (AGU), 2008-12 , Vol. 27 , N. TC6006 , P. 1-20

Droits : 2008 American Geophysical Union
http://archimer.ifremer.fr/doc/2008/publication-4782.pdf
DOI:10.1029/2008TC002263
http://archimer.ifremer.fr/doc/00000/4782/

Éditeur(s) : Elsevier
Résumé : High-resolution reflection and refraction seismic data were collected in 2004 to investigate, in further detail than allowed by pre-existing low resolution seismic data, the nature of a Bottom Simulating Reflector (BSR) that extends over a broad area of the Fairway Basin, a rifted, continental structure located on the eastern flank of the Lord Howe Rise, to the southwest of New Caledonia. Two main reflectors are documented: the shallower (RN) mimics the seafloor and has a negative polarity while the deeper (RP) does not always mimic the seafloor and has a positive polarity. Using the existing regional seismic lines, we can show that reflector RN can be continuously followed up to DSDP 208 drill hole site. Reflector RP is discontinuous and cannot be traced to DSDP 208. Based on DSDP 208 stratigraphic data, Reflector RN is assigned to the Eocene/Oligocene regional unconformity; reflector RP is interpreted in terms of a diagenetic BSR, likely related to an Opal-A/Opal-CT transition front. Heat flow data collected in 2006 suggest that reflector RP lies too deep to be related to methane hydrates, strengthening our interpretation that RP is of diagenetic origin.
Marine Geology (0025-3227) (Elsevier), 2009-10 , Vol. 266 , N. 1-4 , P. 80-90

Droits : 2009 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/2009/publication-7321.pdf
DOI:10.1016/j.margeo.2009.07.014
http://archimer.ifremer.fr/doc/00000/7321/

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : International audience
New evolutionary models for the Pyrenean orogeny must consider feedbacks between the Mid-Cretaceous hyperextension postulated recently and the Pyrenean inversion. We present a new crustal section of the Pyrenees through the Jaca Basin, the western Axial Zone and the Chaînons Béarnais, which allows identifying the ancient continental margins of the Iberian and European plates and a suture. A sequential restoration allows a reassessment of the style of convergence through time. Restoration leads to a progressively thinned crust in narrow continental margins separated by a domain of exhumed mantle peridotite and overlain by a detached sedimentary lid. Early convergence during the Late Cretaceous and the Earliest Paleogene was accommodated by subduction of the peridotite domain. This was followed in the Eocene by initial collision involving overriding of the Iberian margin onto the European margin along the deep ramp of the North-Pyrenean Frontal thrust, which defines the suture. Subsequent full collision and strong relief generation from the late-Mid or Late Eocene to the Early Miocene were associated with thrust accretion of the Iberian plate, underlain by wedging and northward subduction of the decoupled Iberian lower crust.
ISSN: 1631-0713

insu-01291223
https://hal-insu.archives-ouvertes.fr/insu-01291223
https://hal-insu.archives-ouvertes.fr/insu-01291223/document
https://hal-insu.archives-ouvertes.fr/insu-01291223/file/The%20crustal%20evolution%20of%20the%20west-central%20Pyrenees%20-%20postprint.pdf
DOI : 10.1016/j.crte.2015.10.010

Éditeur(s) : HAL CCSD
Résumé : International audience
Two opposing visions of the Aegean backarc tectonics implicitly contain contrasting images of the rheological behaviour of the lihosphere, supported by different sets of observations. The propagation of the NAF and extension in the Corinth Rift suggest a strongly localising rheology whereas the formation of MCC in the Cyclades and the Rhodope suggests instead a more viscous behaviour. This paradox was the seminal question addressed by the ANR-EGEO programme (2007-2010) that leads to the following conclusions: (1) The exhumation of the Cycladic MCC's is accommodated by the N-dipping North Cycladic Detachment System (NCDS) that partly reworks the Vardar suture and at the base by a series of thrusts, including the basal contact of the Cycladic Blueschists (CBS) over the Cycladic Basement (CB). The activity of LANF is due to the reactivation of pre-existing discontinuities such as thrusts or earlier detachments and much less to the interaction with granitic plutons. (2) Exhumation in the Cyclades has proceeded in two stages: (a) Eocene syn-orogenic exhumation within the subduction lower/upperplate interface while the post-orogenic Rhodope MCC formed further north, (b) Oligo-Miocene post-orogenic extension in an MCC mode coeval with syn-orogenic exhumation in Crete and the Peloponnese. (3) Both stages were associated with slab retreat, as early as the Eocene with an acceleration at 30-35 Ma. (4) The localisation of the presently active steeply-dipping normal faults on the southern margin of the Corinth Rift may have been preceded by a partial reworking of thrusts and syn-orogenic detachments by shallow-dipping decollements. (5) The localisation of the NAF in the Marmara Sea region and the Northern Aegean Sea is now accurately dated between 5.3 and 5 Ma Ma using the erosion and deposition surfaces that mark the Messinian salinity Crisis and nannofossils ages. (6) The formation of MCCs in the Cyclades resulted in the draining of the low viscosity lower crust from the northern Aegean Sea and led to an easier coupling between upper mantle and upper crust, easing the localisation and propagation of the NAF. (7) A comparison between crustal and mantle finite strain suggests that mantle flow due to slab retreat controls the stretching of the crust. Our model involves progressive slab retreat and mantle flow below the overriding plate inducing the observed succession of tectonic episodes with a progressive localisation of extension due to several slab tearing events. There is no paradox in the tectonic history and rheological behaviour of the Aegean lithosphere but an evolution of the kinematic boundary conditions due to slab deformation at depth.
American Geophysical Union
San Francisco, United States

insu-00860518
https://hal-insu.archives-ouvertes.fr/insu-00860518
BIBCODE : 2010AGUFM.T13G..04J

Éditeur(s) : Institut Francais du Pétrole
Résumé : The study of the rock and sediment dredgings carried out on the Armorican margin between 47 and 48° latitude North enables us to precise this latter's paleogeographical and tectonic evolution and to integrate it to the Bay of Biscay's. The microfacies analysis of the rock samples dating back from the Upper Jurassic to the Neogene era demonstrates: - on the one hand, the belonging of the northern edge of the Armorican margin to the Mesogean domain, at least up to the Mid-Cretaceous period; - on the other hand, the persistence of a carbonated platform regime which seems to operate from the Tithonian to the lower Tertiary phase, and on which reef could grow, especially in the Mid-Cretaceous period. Over the whole period, sedimentation compensated for subsidence; - lastly, the increase of subsidence from the Eocene period (accompanied with a decrease in the calcium production?) which is most probably related to the major tectonic phenomena that affected the southern edge of the European plate at that time.
L'étude des dragages de roches et de sédiments effectués sur la marge armoricaine entre 47 et 48° de latitude Nord permet d'en préciser l'évolution paléogéographique et tectonique et de l'intégrer à celle du golfe de Gascogne. L'andyse de microfaciès des échantillons rocheux dont l'âge varie du Jurassique supérieur au Néogène met en évidence : - d'une part, l'appartenance de la bordure nord de la marge armoricaine au domaine mésogéen au moins jusqu'au Crétacé moyen ; - d'autre part, la permanence d'un régime de plate-forme carbonatée qui paraît fonctionner du Tithonique au Tertiaire inférieur, sur laquelle ont pu s'installer des édifices récifaux notamment au Crétacé moyen. Pendant toute cette période la sédimentation a compensé la subsidence ; - enfin, l'accentuation de la subsidence à partir de l'Éocène (accompagnée d'une diminution de la production de calcium ?) qui est vraisemblablement en relation avec les phénomènes tectoniques majeurs qui ont affecté à ce moment la bordure sud de la plaque européenne. [OCR NON CONTRÔLE]
Revue de l'Institut Francais du Pétrole (Institut Francais du Pétrole), 1976-06 , Vol. 31 , N. 3 , P. 401-425

Droits : Institut Francais du Pétrole
http://archimer.ifremer.fr/doc/1976/publication-5100.pdf
http://archimer.ifremer.fr/doc/00000/5100/

Éditeur(s) : HAL CCSD
Résumé : The Restefond fault, located in the Late Eocene-Early Oligocene Alpine foreland basin, affects the well lithified and low porosity Grès d'Annot. The fault core zone is characterized by the occurrence of highly deformed sandstone lenses. Deformation inside the lenses corresponds to mm to sub-mm-spaced cleavage planes rich in phyllosilicates and up to cm-thick and dm-long quartz-calcite pure extensional veins. The cleavages are mostly composed of newly-formed synkinematic white mica and chlorite. By using thermodynamic thermometers based on the chemical composition of chlorite, a temperature of 200 ± 20 °C of fault activity was computed. This temperature shows that the Restefond fault was active at burial conditions comprised between 6.5 and 8 km, assuming a mean geothermal gradient between 25 and 30 °Ckm−1. The petrophysic properties of sandstones from the core zone and in the hanging and foot wall of the fault were determined on drilled plugs following three spacial directions. The permeability of the highly deformed sandstone from the core zone is about one order of magnitude higher than in the host rock. This increase in permeability occurs in the direction parallel to the S-C structures and is explained by the occurrence of well-connected micropores localized between platy phyllosilicates. This study shows that the fault petrophysic properties are mostly controlled by the precipitation of synkinematic phyllosilicates under deep burial conditions.
Swiss Journal of Geosciences

hal-00795551
https://hal.archives-ouvertes.fr/hal-00795551
DOI : 10.1007/s00015-012-0099-z

Éditeur(s) : Gauthier-Villars
Résumé : The littoral area of Benin is a lagoonal-estuarial, indeed even deltaic, environment. Poor in species, the mangrove of Benin belongs to the tropical Atlantic type tending to be humid, considering the "drought belt" which affects this region. It undergoes profound hydrological changes in the course of the different seasons in relation to the Mono and Couffo Rivers. The granulometric analysis and the study of the facies makes clear a lenticular-type sedimentation in relation to numerous and rapid hydrodynamic variations. The clayish quartzose sediment also contains a chemical phase (pyrite is transformed through oxidation into jarosite, gypsum and halite in relation to the micromilieux of evaporation) and an important organic phase - with a pH level ranging from 5 to 6. Kaolinite, from the nearby "Continental terminal", is deposited during calm periods. The smectites seem linked to high energy, sandier deposits and their origin should probably be sought in a far away back country (Eocene, basement).
Oceanologica Acta, Special issue (0399-1784) (Gauthier-Villars), 1982

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00246/35730/34238.pdf
http://archimer.ifremer.fr/doc/00246/35730/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Since Deccan Traps extrusion ~ 65 Ma ago, thick weathering mantles have developed over Peninsular India on both the western coastal lowland and adjacent plateau separated by the Western Ghats Escarpment. Manganiferous lateritic profiles formed by supergene weathering of Late Archean manganiferous protores are exposed on paleolandsurface remnants on both sides of the escarpment. Petrological and geochemical characterizations of samples from those Mn lateritic profiles allowed identifying cryptomelane (K-Mn oxide) dated by 40Ar/39Ar geochronology. The ages obtained document major weathering periods, ca. 53-50 Ma, and ca. 37-23 Ma in the highland, and ca. 47-45 Ma, ca. 24-19 Ma and discrete weathering pulses at ~ 9 Ma and ~ 2.5 Ma in the lowland. Old ages of the highland (53-50 Ma) and the lowland (47-45 Ma) indicate synchronous lateritic weathering across the escarpment at a time the peninsula started to drift across the equatorial belt. Intense weathering periods at ca. 53-45 and ca. 37-23 Ma are interpreted to reflect the Early Eocene climatic optimum and the onset of Asian monsoon regimes, respectively. The ages further indicate that most of the dissection of the highland must have taken place after ~ 23 Ma, whereas the lowland was weakly incised essentially after ~ 19 Ma. Our results also document divergent erosion and weathering histories of the lowland and the highland after the Eocene, suggesting installation of a dual climatic regime across the Western Ghats escarpment.
ISSN: 0009-2541

ird-01419899
http://hal.ird.fr/ird-01419899
http://hal.ird.fr/ird-01419899/document
http://hal.ird.fr/ird-01419899/file/CHEMGE9048R2.va.pdf
DOI : 10.1016/j.chemgeo.2016.04.018

Éditeur(s) : Springer
Résumé : Large benthic foraminifers are considered to be good indicators of shallow marine carbonate environments in fossil series. Over the last 50 years, the palaeoenvironment of Tertiary Nummulites accumulations has been a matter of debate, particularly because of difficulties in interpreting these deposits, and in this way, the absence of analogues in present-day seas does not help. The aim of this paper is to insight the different ways Nummulites tests and clasts may accumulate according to their hydrodynamic behaviour. Based on experimental measurements and on SEM observations, it appears that the high primary skeletal porosity of Nummulites made them easily transportable. The calculated threshold shear velocities confirm that large-sized Nummulites can be moved by weak wave-driven currents. This peculiar hydrodynamic behaviour of Nummulites could explain the diversity of depositional models. Depending on local hydrodynamic conditions, autochthonous Nummulites deposits can be preserved as in situ winnowed bioaccumulations or be accumulated offshore, onshore or alongshore, away from the original biotope.
Facies (0172-9179) (Springer), 2006-05 , Vol. 52 , N. 2 , P. 221-235

Droits : Springer-Verlag 2005
http://archimer.ifremer.fr/doc/00085/19597/17234.pdf
DOI:10.1007/s10347-005-0035-z
http://archimer.ifremer.fr/doc/00085/19597/

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 American Geophysical Union
Résumé : International audience
[1] Based on geological and geophysical data collected from the West Philippine Basin and its boundaries, we propose a comprehensive Cenozoic history of the basin. Our model shows that it is a back arc basin that developed between two opposed subduction zones. Rifting started around 55 Ma and spreading ended at 33/30 Ma. The initial spreading axis was parallel to the paleo-Philippine Arc but became inactive when a new spreading ridge propagated from the eastern part of the basin, reaching the former one at an R-R-R triple junction. Spreading occurred mainly from this second axis, with a quasi-continuous counterclockwise rotation of the spreading direction. The Gagua and Palau-Kyushu ridges acted as transform margins accommodating the opening. Arc volcanism occurred along the Palau-Kyushu Ridge (eastern margin) during the whole opening of the basin, whereas the paleo-Philippine Arc decreased its activity between 43 and 36 Ma. The western margin underwent a compressive event in late Eocene-early Oligocene time, leading to the rising of the Gagua Ridge and to a short subduction episode along Eastern Luzon. In the western part of the basin, the spreading system was highly disorganized due to the presence of a mantle plume. Overlapping spreading centers and ridge jumps occurred toward the hot region and a microplate developed. Shortly after the end of the spreading, a late stage of amagmatic extension occurred between 30 and 26 Ma in the central part of the basin, being responsible for the deep rift valley that cut across the older spreading fabric. Citation: Deschamps, A., and S. Lallemand, The West Philippine Basin: An Eocene to early Oligocene back arc basin opened between two opposed subduction zones,
ISSN: 2169-9313

hal-01261388
https://hal.archives-ouvertes.fr/hal-01261388
https://hal.archives-ouvertes.fr/hal-01261388/document
https://hal.archives-ouvertes.fr/hal-01261388/file/DeschampsJGR2002.pdf
DOI : 10.1029/2001JB001706

Éditeur(s) : HAL CCSD
Résumé : National audience
Crustal-scale models for the Pyrenees based on ECORS reflection profileshave around 20 years now. In recent years, new understandingswere gained on the reconstruction to the preorogenic times, namelya scenario of extreme crustal attenuation and mantle exhumation ; inturn, this has implications on the interpretation of the present-day structure,as new models for the chain must consider feedbacks between themid-Cretaceous hyperextension and the Pyrenean inversion. On the WcentralPyrenean traverse, the southern part comprises 3 S-vergent basementthrust units, the Lakora, Gavarnie and Guarga units, flanked by thedetached cover of the Jaca piggyback basin and the Ebro basin, wherethe Mesozoic is thin and Late Cretaceous-Tertiary synorogenic carbonateand detrital sequences record a southward depocenter migration.To the N, the Chaînons Béarnais belt (CB) is a system of Jurassic to LowerCretaceous carbonate anticline ridges separated by synclines withthick Albian-Cenomanian flysch, covered to the north by Upper Cretaceousflysch sequences. The CB is thrust southwards together with theLakora thrust unit and northwards onto the Aquitaine basin. CB foldinglargely results from the rising and squeezing of diapirs initiated duringthe Jurassic-Early Cretaceous extension. Pieces of crust and mantle liftedin the diapirs attest that the CB derive from a Cretaceous domainof hyperextended continental crust and exhumed mantle. Moho reflectionsin the ECORS-Arzaq profile constrain the present deep structure.Restoration leads to a Mesozoic cover detachment over the N-Iberianand S-European margins. Inversion began by subduction of the exhumedmantle and folding and pop-up thrusting of the CB cover onto themargins. From the mid-late Eocene onwards, continental collision wasaccommodated by wedging and thrust stacking in the Iberian crust, involvingthe piggyback formation of S-vergent basement thrusts in theupper crust, and the northward subduction of the lower crust.
24 ème Réunion des sciences de la Terre 2014
Pau, France

insu-01080831
https://hal-insu.archives-ouvertes.fr/insu-01080831

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
The New Jersey continental shelf extends 150 km off the shoreline. During IODP Expedition 313, siliciclastic deposits of late Eocene to late Pleistocene age were drilled down to 631, 669 and 755 m below seafloor at sites 27A, 28A and 29A respectively in very shallow waters (33.5 to 36 m depth). Pore water salinities display multilayered brackish-salty-brine units 10 to 170 m thick, where low-salinity water is preferentially stored in fine-grained sediments. The sharp boundaries of these buried aquifers are often marked by cemented layers a few centimetres thick. The mineralogy and scanning electron microscope observations of these layers show two phases of cementation by authigenic minerals: (1) the early carbonate cement is frequently associated with pyrite, and (2) the late silicate cement infills the residual porosity. The isotopic compositions of the carbonate cements vary widely: −2.4 < δ¹⁸O ‰ VPDB < +2.8; −15.1 < δ¹³C ‰ VPDB < +15.6. The δ¹⁸O values indicate that the carbonate cements precipitated with pore waters comprising variable mixtures of seawater and ¹⁸O-depleted fresh water originating from submarine groundwater discharge. The δ¹³C values of the carbonate cements are related to organic matter diagenesis, providing ¹³C-depleted dissolved inorganic carbon during bacterial sulphate reduction and anaerobic oxidation of methane, and ¹³C-rich dissolved inorganic carbon during methanogenesis. The diagenetic cementation processes included chemical weathering of reactive silicate minerals by the CO²-rich pore waters issued from organic matter diagenesis that released bicarbonate, cations and dissolved silica, which were further precipitated as carbonate and silicate cements. The estimated range of temperature (18±4 °C) during carbonate precipitation is consistent with carbonate cementation at moderate burial depths; however, silicate cementation occurred later during diagenesis at deeper burial depths.
ISSN: 0276-0460

hal-01559985
https://hal.archives-ouvertes.fr/hal-01559985
DOI : 10.1007/s00367-017-0506-6

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