Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In the Schistes Lustres of Alpine Corsica (France) serpentinized mantle rocks are associated with continental basement and meta-volcanic/-seclimentary cover rocks. The relationships among these different lithologies are especially well exposed in the Monte San Petrone unit, where Alpine metamorphism reached lawsonite-eclogite conditions. The contact between serpentinites and slivers of continental basement, relatively flat-lying over several kilometers, is characterized by evidence of cataclastic deformation pre-dating Alpine High-Pressure ductile fabrics. The serpentinite/continental basement pair is stratigraphically overlain by metasediments with a typical Jurassic-Cretaceous supra-ophiolitic lithostratigraphy, with metaradiolarites passing upward to marbles and cal cschists. Noticeably, no evidence of cataclastic deformation is found in metasediments. These observations indicate that the lithostratigraphy of the Monte San Petrone unit was established during a pre-Alpine polyphase evolution, which culminated in extensive brittle deformation along a flat-lying detachment fault prior to the deposition of Jurassic sediments. We suggest that the inferred Mesozoic extensional tectonics were related to the opening of the Westem Tethys. The Mesozoic architecture of the Monte San Petrone area, which is typical of an Ocean-Continent Transition (OCT) zone, was preserved despite Alpine deformation and metamorphism, when the different lithologies (i.e. meta-ophiolites, continent-derived rocks and metasediments) underwent a common metamorphic evolution, culminating at T=490-550 degrees C and P= 2.2-2.6 GPa. Similar tectonostratigraphic associations are observed in other high-pressure terranes of Alpine Corsica, suggesting that inherited OCT-type domains may be common in Alpine-type orogens.
ISSN: 0024-4937

hal-00617744
https://hal.archives-ouvertes.fr/hal-00617744
DOI : 10.1016/j.lithos.2011.02.013

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
New outcrops in the Sinis peninsula (Sardinia, Italy) allow a detailed description of the Messinian erosion surface. The correlation between outcrops, industrial seismic data and data collected offshore Oristano from a recent cruise permits reconstruction of the geometry of this surface from presently emerged interfluves to the deep canyons offshore, with: - onshore: an eroded karstic plateau presently cropping out over a 20 km × 5 km area. Well-preserved karst structures occur locally and can form several metres high reliefs. The southernmost edge of the plateau is limited by a cliff. The karstic plateau and the cliff are sealed by transgressive deposits of Pliocene age; - offshore, an interfluve zone with a mostly flat and low-angle dipping plateau, westward dissected by paleovalleys which were identified down to a depth of 2000 m. In the Oristano Gulf, Messinian paleovalleys were also identified. The Capo San Marco paleocliff was probably located on the edge of a canyon. Onshore, only one major erosion surface was identified, located at the top the Messinian sequence. Offshore, this surface extends down to the abyssal plain. The surface was emplaced above deposits related to the Terminal Carbonate Complex. This indicates that the marginal evaporites are older than the major drawdown of the Mediterranean sea-level. The major drawdown is related to the deposition of the deep evaporites.
ISSN: 0037-0738

hal-00407864
https://hal.archives-ouvertes.fr/hal-00407864
DOI : 10.1016/j.sedgeo.2008.06.005

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The analysis of field relationships between allochthonous crystalline slivers, ultramafic units and associated sedimentary cover in the high-pressure Schistes Lustrés units of northern Corsica allows reconstruction of the pre-orogenic architecture of a fossil Mesozoic Ocean-Continent Transition (OCT) of the Tethys basin. The studied area, encompassing the Serra di Pigno and Col de Téghime areas (Cap Corse) is composed of an assemblage of prealpine basement sheets made up of serpentinized mantle rocks, Permian gabbros and gneisses, locally associated with Paleozoic metabasites and micaschists. The sedimentary cover includes numerous intervals of calc-schists, marbles, quartzites, micaschists and dolomitic metabreccias yielding a great variety of lithostratigraphical successions. The metasedimentary sequences do not show affinities with the typical cover series of the Prépiémontais margin domains. This implies an origin from a more internal domain (oceanward) for the studied units. In addition, the sedimentary cover of the ultramafic basement units do not display the characters of the classical Alpine ophiolites but bear lithological features showing affinities with both continental and oceanic environments. We assume that the high variability of the sedimentary successions as well as the presence of a basement composed of continental and upper-mantle rocks is consistent with an origin at an OCT. The acidic basement slivers are regarded as former extensional allochthons of continental crust abandoned during breakup on a newly exhumed seafloor of peridotite composition. Such extensional allochthons, will then logically constitute the most internal continental slices buried at great depth during Alpine subduction. This work shows that a lot has to be expected from a revision of the Schistes Lustrés lithostratigraphy in the light of the new concepts of the evolution of the OCT domains.
ISSN: 0040-1951

hal-00795578
https://hal.archives-ouvertes.fr/hal-00795578
DOI : 10.1016/j.tecto.2012.06.013

Éditeur(s) : HAL CCSD
Résumé : The Neogene geodynamics evolution of the south-Alboran realm in western Mediterranean has been clarified, based on sedimentological and chronostratigraphical studies. This work focuses on three main themes of research, the first is to establish the moments for the opening and closing of the North Rifian Corridor by studying two Neogene basins of the southern edge of the Alboran sea. The second, aims to understand the behavior of these two basins face a major event in the history of the Mediterranean: The Messinian Salinity Crisis. Finally, the third theme aims to understand the modalities Post-MSC reflooding in the southern part of the Alboran realm.The late Miocene evolution of the North Rifian Corridor is clarified on the basis of chronostratigraphic studies of the Neogene Boudinar and Arbaa Taourirt basins (northeastern Morocco). The marine sediments deposited in the Boudinar basin between the early Tortonian and the late early Messinian (10 Ma to 6.1 Ma) and in the late Tortonian-earliest Messinian interval in the Arbaa Taourirt basin. Palaeoenvironmental data record a major drowning in association with extensive tectonics in the Boudinar basin during the early Messinian at ~7.2 Ma. At the same time, prograding conglomerates and sandstones developed over the late Tortonian marls in the Arbaa Taourirt basin. During the late-early Messinian, a shallowing trend occurred in the Boudinar basin. Thus, the North Rifian Corridor opened at ~7.2 Ma ensuring Atlantic-Mediterranean connections, then was progressively restricted during the late-early Messinian and totally closed at ~6.1 Ma. New sedimentological and paleontological studies of the late Messinian-early Pliocene deposits in the Boudinar basin provide new information on the Messinian Salinity Crisis (« MSC ») and the Zanclean reflooding in the Alboran sea. The Messinian erosional surface « MES » is of late Messinian age and was emplaced in subaerial settings. It is polygenic, its original geometry is locally preserved and was re-shaped by the Pliocene transgressive surface. Above the « MES », the Boudinar basin infill is characterized by a wide variety of facies from continental settings to lower offshore conditions. Two major sets are recognized: a latest Messinian-Zanclean set that constitutes a transgressive-regressive megasequence interrupted at the top by a tectonic unconformity, and an Plio-Quaternary regressive set. During the late Messinian Zanclean interval, four successive depositional models were documented. They record major changes in palaeoflow and paleogeography related to base-level fluctuations. No Gilbert-type delta has ben identified at Boudinar. the beginning of base-level rise is marked by normal regressions and by the formation of several lacs and fan-delta complexes on the margins of the basin in the late Messinian and befor the marine reefloding in the early Zanclean. The marine reflooding of the basin appears later, with a transgressive surface of ravinment and a thick package of transgressive deposits. These transgressive deposits onlap over all previous deposits. The major part of the basin infill did not issue from an inner landward position (south of the basin) but from the northwestern side of the basin, i.e. near the Mediterranean. Sediments were subsequently reworked by storms and transported by longshore-drift towards the south. a maximum flooding surface is found several tens of metres above the « MES ». This fiding is consistent with a progressive and not a catastrophic early Zanclean flooding of the westernMediterranean after the Mediterranean base-level fall.
Sur la base d’études sédimentologiques et chronostratigraphiques dans les bassins de Boudinar et d’Arbaa Taourirt (Rif oriental, Maroc), l’évolution géodynamique néogène du domaine sud-Alboran en Méditerranée occidentale a été clarifiée. Ce travail est axé sur trois grandes thématiques de recherche. La première vise à l’établissement d’un cadre chronostratigraphique pour l’ouverture et la fermeture du Couloir Nord Rifain, par l’étude de deux bassins nèogènes de la bordure sud de la mer d’Alboran. La deuxième, vise à comprendre le comportement de ces deux bassins face à un événement majeur de l’histoire de la Mediterranée : la Crise de salinité messinienne. Finalement, la troisième vise à comprendre les modalités de remise en eau de la Méditerranée après la Crise : le reenoiement pliocène. L'évolution du Couloir Nord Rifain au Miocène supérieur est clarifiée sur la base des études chronostratigraphiques des bassins néogènes de Boudinar et d'Arbaa Taourirt (Maroc Nord oriental). Les sédiments marins miocènes se sont déposés entre le Tortonien inférieur et le Messinien inférieur (10 à 6.1 Ma) dans le bassin de Boudinar et entre le Tortonien supérieur et le Messinien inférieur dans le bassin d'Arbaa Taourirt. Les données paléoenvironnementales enregistrent un ennoyage important du bassin de Boudinar en relation avec une tectonique extensive pendant le Messinien inférieur (~7.2 Ma). En même temps, des conglomérats et de grès progradants se sont développés au-dessus des marnes tortoniennes dans le bassin d’Arbaa Taourirt. Le bassin de Boudinar a subi un désapprofondissement au Messinien inférieur. Ces résultats indiquent que le Couloir Nord Rifain s’est ouvert à ~7.2 Ma assurant les communications entre l’Atlantique et la Méditerranée, puis a subi une restriction progressive pendant le Messinien inférieur avant d’être totalement fermé à ~6.1 Ma.De nouvelles études sédimentologiques et paléontologiques des dépôts Messinien supérieur-Pliocène inférieur dans le bassin de Boudinar fournissent des informations sur la Crise de salinité messinienne (« MSC ») et le réennoiement zancléen dans la Mer d'Alboran. L’un des marqueurs majeurs de la Crise est identifié : la surface d’érosion messinienne « MES ». Elle est d'âge Messinien supérieur et a été mise en place dans des conditions subaériennes. Sa géométrie originale n’est préservée que localement et a été remodelée par la surface transgressive du Pliocène inférieur. Au dessus de la « MES » le remplissage sédimentaire du bassin de Boudinar est caractérisé par une grande variété de faciès allant des conditions de dépôts continentales jusqu’à des conditions d’offshore inférieur. Deux ensembles majeurs sont reconnus : un ensemble messinien terminal-zancléen qui constitue une mégaséquence transgressive-regressive, interrompue au sommet par une discordance tectonique, et un ensemble plio-quaternaire regressif. Durant l’intervalle Messinien terminal-Zancléen, quatre modèles de dépôts successifs ont été documentés enregistrant des changements majeurs de paléocourants et de paléogéographies, liés aux fluctuations de niveau de base. Nous n’avons pas identifié de Gilbert delta à Boudinar. La remontée du niveau de base est marquée par une régression normale et par le développement des lacs et de complexes de fan-deltas sur les marges du bassin pendant le Messinien supérieur, avant l’inondation marine au Zancléen basal. Le réennoiement marin du bassin apparait plus tard avec une surface de transgression ravinante et par d’épais dépôts transgressifs, en onlap sur tous les dépôts précédents. La majeure partie du remplissage sédimentaire du bassin n’est pas reçue des reliefs de la bordure sud du bassin, mais du côté Nord-Ouset au bord de la Méditerranée. Les sédiments sont alors remaniés par les tempêtes et transportés vers le sud par la dérive littorale. Une surface d’inondation maximale a été identifiée à plusieurs dizaines de mètres au-dessus de la « MES ». Ceci suggère un ennoiement progressif et non catastrophique, après la chute du niveau de base méditerranéen.
https://tel.archives-ouvertes.fr/tel-01473572

Droits : http://hal.archives-ouvertes.fr/licences/copyright/
tel-01473572
https://tel.archives-ouvertes.fr/tel-01473572
https://tel.archives-ouvertes.fr/tel-01473572/document
https://tel.archives-ouvertes.fr/tel-01473572/file/Th%C3%A8se-achalhi.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Cycladic Blueschist Unit (CBU) represents the northern passive margin of the Adria continental block and ophiolites that are the remnants of the Pindos Ocean, which were affected by high pressure-low temperature metamorphism in the blueschist and eclogite facies during the Eocene. Prior to the Lutetian, the ophiolitic and margin units were thrust towards the SW inside a NE-dipping subduction zone. Two subsequent exhumation stages are characterized by top-to-the-NE senses of shear: i) from mantle depths to lower crustal levels, before 37 Ma, which was accommodated by an extensional inversion of the Vardar suture zone, and ii) from deep crustal levels to the near-surface, between 30 and 20 Ma, which was accommodated by the North Cycladic Detachment. It is during this late stage of ductile exhumation that the central Cyclades Core Complex was exhumed. Segmentation of the CBU by normal faults started at 12 Ma, as recorded by the low temperature thermochronometers, and was coeval with block rotation and folding with NS-trending axes, which were predominantly controlled by the Myrthes-Ikaria strike-slip fault in the centre of the Cyclades. A map restoration of the CBU geometry, prior to segmentation, has been carried out using available structural and paleomagnetic data. The restoration shows that, following the CBU exhumation from mantle depths to crustal levels, a single core complex was exhumed along a single NE dipping detachment.
ISSN: 0040-1951

insu-00672320
https://hal-insu.archives-ouvertes.fr/insu-00672320
DOI : 10.1016/j.tecto.2011.12.025

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : In Vietnam, the Triassic Indosinian collision affected coevally the Truong Son belt and the Kontum Massif,which were not independent tectonic units, but parts of the same Gondwana-derived Indochina continental block. This thermotectonic event took place synchronously throughout Vietnam, during the Lower Triassic 250-240-Ma time interval, as demonstrated by numerous geochronological data, combining Ar-Ar and U-Pb dating methods. Structural and kinematic investigations, in the Indosinian metamorphic rocks, reveal that the collisional process resulted from a consistent northwest-striking convergence of Indochina with respect to the adjacent blocks. It is suggested that this motion was taken up by a pair of opposite subduction zones: to the north, beneath South China, and to the west, beneath western Indochina, along the Song Ma and Po Ko sutures, respectively. Tectonic markers, calc-alkaline subduction-related volcanism and granitic intrusions and the generation of high-pressure rocks that have been recently discovered support this geodynamic setting, at least along Po Ko. Along the northwest-trending Song Ma zone, the obliquity of the convergence during subduction and subsequent collision resulted in the development, within the Truong Son Belt, of a set of subparallel dextral mylonitic shear zones, under amphibolite-facies metamorphism. The intermediate segments remained weakly metamorphic or even almost devoid of metamorphism. Along Po Ko, the convergence was near-orthogonal, with a left-lateral strike-slip component; the ongoing continental subduction resulted in the reworking of the Kontum granulitic basement and the development of Indosinian HP granulitic conditions; the subsequent extension-related exhumation operated approximately in the same northwestwards direction. This Indosinian evolution, applied on a continental crust that had been probably affected, as in South China, by a Caledonian-related event, as judged by the general unconformity of the Lower Devonian sediments, the widespread occurrence of magmatic crystallisation ages of ca 450 Ma (Ordovician-Silurian), and by the approximately similar age of the primary granulitic episode in the Kontum Massif. The similarities of the Devonian facies over central, northern Vietnam and South China imply a land connection, possibly as a consequence of a Caledonian collision along Song Ma, but this does not preclude a further oceanic opening and a closure during the Indosinian.
ISSN: 1631-0713

hal-00411591
https://hal.archives-ouvertes.fr/hal-00411591
DOI : 10.1016/j.crte.2007.10.005

Éditeur(s) : The American Association of Petroleum Geologlists
Résumé : The west African continental margin between Abidjan (Ivory Coast) and Walvis Boy (Southwcst Africa) was surveyed in 1971 by the R/V Jean Charcot. Fiftyeight seismic-reflection (flexotir source), bathymetric (3.5 and 12 kc), gravimetric, and magnetic profiles were obtained. The seaward limit of an evaporitic zone outlined during the survey is at the boundary between continental slope and continental rise. Variation of depth of this limit as a function of latitude shows the presence of a large offset at 11°S which seems to be related to an east-east-southeast line of magnetic seamounts cutting into the continental slope. The Annobon-Cameroun volcanic axis separates the salt zones of the Nigerian basin and Congo-Angola basin. The northern limit of Salt deposition in the Congo-Angola basin is marked near 1°N by a strong southwest-northeast magnetic trend. On the south it extends to necr 14°s. The Walvis Ridge, located farther south, does not seem to have an effect on evaporite deposition. [NOT CONTROLLED OCR]
The American Association of Petroleum Geologlists Bulletin (The American Association of Petroleum Geologlists), 1973 , Vol. 57 , N. 9 , P. 1658-1671

Droits : The American Association of Petroleum Geologlists
http://archimer.ifremer.fr/doc/1973/publication-5123.pdf
http://archimer.ifremer.fr/doc/00000/5123/

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) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
Continental rifts and passive continental margins show fundamental along-axis segmentation patterns that have been attributed to one or a number of different processes: extensional fault geometry, variable stretching along strike, preexisting lithospheric compositional and structural heterogeneities, oblique rifting, and the presence or absence of eruptive volcanic centers. The length and width scales of the rift stage fault-bounded basin systems change during the late evolution of the new plate boundary, and the role of magmatism may increase as rifting progresses to continental rupture. Along obliquely spreading ridges, first-order mid-ocean ridge geometries originate during the synrift stage, indicating an intimate relationship between magma production and transform fault spacing and location. The Gulf of Aden rift is a young ocean basin in which the earliest synrift to breakup structures are well exposed onshore and covered by thin sediment layers offshore. This obliquely spreading rift is considered magma-poor and has several large-offset transforms that originated during late stage rifting and control the first-order axial segmentation of the spreading ridge. Widely spaced geophysical transects of passive margins that produce only isolated 2-D images of crust and uppermost mantle structure are inadequate for evaluation of competing rift evolution models. Using closely spaced new geophysical and geological observations from the Gulf of Aden we show that rift sectors between transforms have a large internal variability over short distances (∼10 km): the ocean-continent transition (OCT) evolves from a narrow magmatic transition to wider zones where continental mantle is probably exhumed. We suggest that this small-scale variability may be explained (1) by the distribution of volcanism and (2) by the along-strike differences in time-averaged extension rate of the oblique rift system. The volcanism may be associated with (1) the long-offset Alula-Fartak Fracture Zone, which may enhance magma production on its younger side, or (2) channeled flow from the Afar plume material along the newly formed OCT and the spreading ridge. Oblique extension and/or hot spot interactions may thereby have a significant control on the styles of rifting and continental breakup and on the evolution of many magma-poor margins.
ISSN: 1525-2027

hal-00504866
https://hal.archives-ouvertes.fr/hal-00504866
https://hal.archives-ouvertes.fr/hal-00504866/document
https://hal.archives-ouvertes.fr/hal-00504866/file/G3-Leroy_al-2010.pdf
DOI : 10.1029/2009GC002963

Éditeur(s) : Public Library Science
Résumé : Like hydrothermal vents along oceanic ridges, cold seeps are patchy and isolated ecosystems along continental margins, extending from bathyal to abyssal depths. The Atlantic Equatorial Belt (AEB), from the Gulf of Mexico to the Gulf of Guinea, was one focus of the Census of Marine Life ChEss (Chemosynthetic Ecosystems) program to study biogeography of seep and vent fauna. We present a review and analysis of collections from five seep regions along the AEB: the Gulf of Mexico where extensive faunal sampling has been conducted from 400 to 3300m, the Barbados accretionary prism, the Blake ridge diapir, and in the Eastern Atlantic from the Congo and Gabon margins and the recently explored Nigeria margin. Of the 72 taxa identified at the species level, a total of 9 species or species complexes are identified as amphi-Atlantic. Similarity analyses based on both Bray Curtis and Hellinger distances among 9 faunal collections, and principal component analysis based on presence/absence of megafauna species at these sites, suggest that within the AEB seep megafauna community structure is influenced primarily by depth rather than by geographic distance. Depth segregation is observed between 1000 and 2000m, with the middle slope sites either grouped with those deeper than 2000m or with the shallower sites. The highest level of community similarity was found between the seeps of the Florida escarpment and Congo margin. In the western Atlantic, the highest degree of similarity is observed between the shallowest sites of the Barbados prism and of the Louisiana slope. The high number of amphi-atlantic cold-seep species that do not cluster according to biogeographic regions, and the importance of depth in structuring AEB cold-seep communities are the major conclusions of this study. The hydrothermal vent sites along the Mid Atlantic Ridge (MAR) did not appear as "stepping stones" for dispersal of the AEB seep fauna, however, the south MAR and off axis regions should be further explored to more fully test this hypothesis.
Plos One (1932-6203) (Public Library Science), 2010-08 , Vol. 5 , N. 8 , P. 1-11

Droits : © 2010 Olu et al.
http://archimer.ifremer.fr/doc/00011/12207/8975.pdf
DOI:10.1371/journal.pone.0011967
http://archimer.ifremer.fr/doc/00011/12207/

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
The El Oro metamorphic province of SW Ecuador is a composite massif made of juxtaposed terranes of both continental and oceanic affinity that has been located in a fore-arc position since Late Paleozoic times. Various geochemical, geochronological, and metamorphic studies have been undertaken on the El Oro metamorphic province, providing an understanding of the origin and age of the distinct units. However, the internal structures and geodynamic evolution of this area remain poorly understood. Our structural analysis and thermal modeling in the El Oro metamorphic province show that this fore-arc zone underwent four main geological events. (1) During Triassic times (230–225 Ma), the emplacement of the Piedras gabbroic unit at crustal-root level (~9 kbar) triggered partial melting of the metasedimentary sequence under an E-W extensional regime at pressure-temperature conditions ranging from 4.5 to 8.5 kbar and from 650 to 900°C for the migmatitic unit. (2) At 226 Ma, the tectonic underplating of the Arenillas-Panupalí oceanic unit (9 kbar and 300°C) thermally sealed the fore-arc region. (3) Around the Jurassic-Cretaceous boundary, the shift from trench-normal to trench-parallel subduction triggered the exhumation and underplating of the high-pressure, oceanic Raspas Ophiolitic Complex (18 kbar and 600°C) beneath the El Oro Group (130–120 Ma). This was followed by the opening of a NE-SW pull-apart basin, which tilted the massif along an E-W subhorizontal axis (110 Ma). (4) In Late Cretaceous times, an N-S compressional event generated heterogeneous deformation due to the presence of the Cretaceous Celica volcanic arc, which acted as a buttress and predominantly affected the central and eastern part of the massif.
ISSN: 0278-7407

hal-01115714
https://hal.archives-ouvertes.fr/hal-01115714
DOI : 10.1002/2014TC003618

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Mechanism and kinematics of the Late Mesozoic continental extension event of eastern Asia are still debated. In order to better constrain its evolution, two granodioritic plutons of the Jiaodong Peninsula have been chosen as targets for a time-constrained palaeomagnetic study. Indeed, plutons are devoid of visible deformation, did not experience rotation along horizontal axis and are precisely dated by U/Pb and 40Ar/39Ar methods. Multidomain (MD) magnetite has been identified as the principal magnetic remanent carrier. The interpolation of existing and new U/Pb and 40Ar/39Ar ages revealed that characteristic remanent magnetisation was acquired in a narrow range of 116 ± 2 Ma. Twenty out of 27 sites present stable magnetic directions calculated from high-temperature or high-coercive components. The observations of the solo normal magnetic polarity for this palaeomagnetic collection and of the magnetic remanent age consistent with the Cretaceous Normal Superchron (CNS) argue that the characteristic magnetic remanence may be considered as primary. Detailed field observations of the intrusive relationship between the plutons and country rocks and Anisotropy of Magnetic Susceptibility (AMS) study reveal the absence of the subsequent deformation of plutons, or rigid rotation of plutons along a horizontal axis. Two palaeomagnetic poles have been therefore calculated from these plutons. Among 12 out 15 Cretaceous palaeomagnetic poles, including the two new poles provided by this study, from the Jiaodong Peninsula and on both sides of Tan-Lu and Muping-Jimo faults are statistically consistent. As a result, the Jiaodong Peninsula behaved as a rigid block as internal deformation appears negligible. The remaining three derived poles are probably due to the secular variation or/and the vicinity of fault zones near of the palaeomagnetic sampling site. Thus, they can not be applied to the peninsula-scaled tectonics. Comparison of these time52 constrained Cretaceous palaeomagnetic results of the Jiaodong Peninsula with those of North China Block (NCB) indicate that the Jiaodong Peninsula was rigidly attached to NCB since, 3 at least, the Cretaceous as residual difference is clearly insignificant with respect to the error brackets. These new palaeomagnetic results confirm that the relative clockwise (CW) rotation of Eastern Liaoning-Korea Block (ELKB) with respect to NCB does not affect the Jiaodong Peninsula as a rigid block, nevertheless, some tectonic structures have been reactivated since Cenozoic and local rotations could be produced. This palaeomagnetic study reveals that the Late Mesozoic extension in Eastern Asia is heterogeneously expressed in time and space. The complete understanding of the mechanism(s) of this extensional event needs further multidisciplinary investigations.
ISSN: 0031-9201

insu-00599546
https://hal-insu.archives-ouvertes.fr/insu-00599546
https://hal-insu.archives-ouvertes.fr/insu-00599546/document
https://hal-insu.archives-ouvertes.fr/insu-00599546/file/Charles_et_al_PEPI2011.pdf
DOI : 10.1016/j.pepi.2011.05.006

Éditeur(s) : HAL CCSD
Résumé : International audience
The Transbaikal region extends over several hundreds of kilometres east of the Baikal Rift System. It is characterized by a number of sub-parallel Mesozoic grabens or half grabens generally filled with late Jurassic to Early Cretaceous clastic sediments interbedded with coal layers (1). Similar basins occur on an even larger area spanning from the Transbaikal region down to Korea implying a large-scale extensional process affecting most of the Amuria plate during the Mesozoic. In the Transbaikal region, the normal faults controlling the edges of the Mesozoic basins are generally superimposed to Palaeozoic ductile shear zones implying a strong localisation of the extensional deformation on inherited structures. Recent studies, associated to our own fieldwork demonstrated that some of the faults were again activated (2), still as extensional faults, during the Tertiary or Quaternary, and that some of them are presently active. The closure of the Mongol-Okhotsk ocean separating the Siberian plate from the Amurian block during the Mesozoic corresponds to a major event in the growth process of the East Asian continent. The oceanic suture zone is situated on the southern edge of the Transbaikal region and its roughly SW-NE direction is parallel to the basins (3). The timing of the closure of the Mongol-Okhotsk ocean is still highly debated: while sedimentological and tectonic data suggest that the oceanic closure and the following collision occurred in early Middle Jurassic (4), paleomagnetic studies advocate for a Early Cretaceous collision (5). Furthermore, several other questions remain on the localization, the size and the fate of the relief that most probably formed during the collision between the Amuria block and the Siberian craton. In order to answer those questions we used low temperature thermochronology data associated to tectonic, sedimentology and palinology to investigate the evolution of the Transbaikal grabens from Mesozoic to Present. Tectonic and thermochronology data provide evidences of exhumation and erosion along the eastern edge of the Siberian craton during the Middle Jurassic as well as a potential continuum of deformation between the Mesozoic extension and the initiation of the Baikal Rift System (6). Sedimentology and palinology reveals that the sediments deposited in the Transbaikal basin did not registered large-scale compressive deformation during or after their Late Jurassic - Early Cretaceous deposition and that they do not correspond to the dismantling of a strong compressive relief.
Geophysical Research Abstracts
Vienne, Austria

insu-00810487
https://hal-insu.archives-ouvertes.fr/insu-00810487

Éditeur(s) : HAL CCSD Elsevier
Résumé : Primary arc melts may form through fluxed or adiabatic decompression melting in the mantle wedge, or via a combination of both processes. Major limitations to our understanding of the formation of primary arc melts stem from the fact that most arc lavas are aggregated blends of individual magma batches, further modified by differentiation processes in the sub-arc mantle lithosphere and overlying crust. Primary melt generation is thus masked by these types of second-stage processes. Magma-hosted peridotites sampled as xenoliths in subduction zone magmas are possible remnants of sub-arc mantle and magma generation processes, but are rarely sampled in active arcs. Published studies have emphasised the predominantly harzburgitic lithologies with particularly high modal orthopyroxene in these xenoliths; the former characteristic reflects the refractory nature of these materials consequent to extensive melt depletion of a lherzolitic protolith whereas the latter feature requires additional explanation.Here we present major and minor element data for pristine, mantle-derived, lava-hosted spinel-bearing harzburgite and dunite xenoliths and associated primitive melts from the active Kamchatka and Bismarck arcs. We show that these peridotite suites, and other mantle xenoliths sampled in circum-Pacific arcs, are a distinctive peridotite type not found in other tectonic settings, and are melting residues from hydrous melting of silica-enriched mantle sources. We explore the ability of experimental studies allied with mantle melting parameterisations (pMELTS, Petrolog3) to reproduce the compositions of these arc peridotites, and present a protolith (‘hybrid mantle wedge’) composition that satisfies the available constraints. The composition of peridotite xenoliths recovered from erupted arc magmas plausibly requires their formation initially via interaction of slab-derived components with refractory mantle prior to or during the formation of primary arc melts. The liquid compositions extracted from these hybrid sources are higher in normative quartz and hypersthene (i.e., they have a more silica-saturated character) in comparison with basalts derived from prior melt-depleted asthenospheric mantle beneath ridges. These primary arc melts range from silica-rich picrite to boninite and high-Mg basaltic andesite along a residual spinel harzburgite cotectic. Silica enrichment in the mantle sources of arc-related, subalkaline picrite-boninite-andesite suites coupled with the amount of water and depth of melting, are important for the formation of medium-Fe (‘calc-alkaline’) andesite-dacite-rhyolite suites, key lithologies forming the continental crust.
ISSN: 0016-7037

hal-01553520
https://hal.archives-ouvertes.fr/hal-01553520
DOI : 10.1016/j.gca.2016.09.030

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Deep crustal and mantle rocks are exhumed in core complex mode of extension in three types of structures: metamorphic core complexes, oceanic core complexes and magma poor passive margins. Using available analogue and numerical models and their comparison with natural examples, the present paper reviews the mechanical processes involved in these different types of extensional setting. Three main aspects are considered: i) the primary role of lithosphere rheology, ii) the lithosphere-scale patterns of progressive deformation that lead to the exhumation of deep metamorphic or mantle rocks and iii) the initiation and development of detachment zones. Crustal core complexes develop in continental lithospheres whose Moho temperature is higher than 750 °C with “upper crust-dominated” strength profiles. Contrary to what is commonly believed, it is argued from analogue and numerical models that detachments that accommodate exhumation of core complexes do not initiate at the onset of extension but in the course of progressive extension when the exhuming ductile crust reaches the surface. In models, convex upward detachments result from a rolling hinge process. Mantle core complexes develop in either the oceanic lithosphere, at slow and ultra-slow spreading ridges, or in continental lithospheres, whose initial Moho temperature is lower than 750 °C, with “sub-Moho mantle-dominated” strength profiles. It is argued that the mechanism of mantle exhumation at passive margins is a nearly symmetrical necking process at lithosphere scale without major and permanent detachment, except if strong strain localization could occur in the lithosphere mantle. Distributed crustal extension, by upper crust faulting above a décollement along the ductile crust increases toward the rift axis up to crustal breakup. Mantle rocks exhume in the zone of crustal breakup accommodated by conjugate mantle shear zones that migrate with the rift axis, during increasing extension.
ISSN: 0040-1951

insu-01610186
https://hal-insu.archives-ouvertes.fr/insu-01610186
https://hal-insu.archives-ouvertes.fr/insu-01610186/document
https://hal-insu.archives-ouvertes.fr/insu-01610186/file/brun-tect-2017.pdf
DOI : 10.1016/j.tecto.2017.09.017

Éditeur(s) : Gauthier-Villars
Résumé : Moored current measurements carried out from 31 March 1990 to 15 September 1991 in two stages at a point (near 6 degrees N) located over the mid-continental slope off French Guiana are presented. Six current meters were positioned between 200 and 2700 m depth. Upper level mean current data showed a northwestward flowing North Brazil Current (NBC) with mean velocity values decreasing from 10 cm/s in the range 200-250 m to almost zero at 800 m depth, the level of the Antarctic Intermediate Waters. In the range 500-800 m, the current reversed in spring in the presence of the southeastward Western Boundary Under Current (WBUC); the mean velocity from February to June 1991 is around 2 cm/s. Deep currents over the continental rise show a strong southeastward Deep Western Boundary Current extending from around 1000 m depth to the bottom (3000 m depth in this case) with mean core speeds of 20 cm/s at 2000-2070 m depth. Transport estimates based on these data and a few Pegasus sections for the mean vertical and lateral extensions of the DWBC yield a value of 21 x 10(6) m(3)/s at that location. Low-frequency current fluctuations were dominated by a well-defined 50- to 70-day period oscillation with peak-to-peak northwestward velocity amplitude of around 90 cm/s at the upper level. The mean vertical eddy kinetic energy distribution showed an abrupt decrease of the energy down to 800 m depth and a slight decrease below and down to the bottom.
Oceanologica Acta (0399-1784) (Gauthier-Villars), 1994 , Vol. 17 , N. 4 , P. 345-354

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00098/20897/18510.pdf
http://archimer.ifremer.fr/doc/00098/20897/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The marine Messinian deposits of Tunisia cover a narrow littoral strip some 300 km long between the northern Bizerte and Cap Bon areas and the central-eastern Sahel region. Litho- and biofacies analysis of six stratigraphic sections reveals the distinctive features of these deposits.;The lower Messinian deposits are characterized by ubiquitous siliciclastics and abundant oolitic/bioclastic limestones organized in an eastward facing ramp. Westward (landward), this ramp changes into coastal lagoons, sometimes containing evaporites. Eastward, the ramp passes to the reefal Pelagian Platform extending as far as Lampedusa.;Two main sedimentary cycles are distinguished: 1) an early Messinian siliciclastic retrogradational then oolitic/bioclastic progradational cycle (Beni Khiar Formation and lower Oued bel Khedim Formation): 2) a late Messinian brackish to continental cycle that probably accumulated in rapidly subsiding lagoons (Cued el Bir Formation and upper Oued bel Khedim Formation). The Tunisian early Messinian cycle is partly eustatically controlled, but the late Messinian cycle cannot be confidently correlated to other well-known Messinian series because of tectonic movements.;The lower Messinian deposits of Tunisia are also characterized by abundant suspension-feeding organisms (molluscs and bryozoans) and rare corals, calcareous algae, echinoids, and larger benthic foraminifers. The proposed palaeoenvironmental model shows that the lower Messinian ramp of Tunisia was located on a current-protected margin and subjected to continent-derived sediment and nutrient supply. Eastward, nutrient influx diminished and a shallow-water isolated carbonate platform with coralgal facies developed between the western and the eastern Mediterranean basins. The main hydrological connection between these two basins occurred through a narrow seaway situated to the northeast of the Pelagian Platform, south of Sicily and Malta.
ISSN: 0031-0182

hal-00475583
https://hal.archives-ouvertes.fr/hal-00475583
DOI : 10.1016/j.palaeo.2009.10.028

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : International audience
We provide new constraints on the modes of mantle exhumation and denudation in the pre-orogenic Pyrenees by investigating the poorly known peridotites located east of the Lherz body, in eastern Ariè ge (Vicdessos, Urs, Bestiac, Caussou and Prades main peridotitic bodies). We show that: (1) numerous peridotite bodies, not described so far, are constituted by decametric to sub-metric outcrops scattered between and around the main outcrops identified by Monchoux (1970); (2) most of the peridotites form blocks and lenses of various sizes, from millimetric monocrystalline grains to hectometric olistoliths, embedded in debris flows involving mainly Mesozoic metasediments; these peridotites can therefore be linked to the S-type peridotites of Lagabrielle et al. (2010), and share similarities with the peridotites of Lherz region (Clerc et al., 2012). All originated from tectono-sedimentary processes associated with mantle exhumation in relation with extreme thinning and breakoff of the continental basement; (3) the various petrographic characters of these peridotites and their heterogeneity in serpentinisation degree imply a peculiar mode of exhumation, which merges mantle fragments inherited from different structural levels; (4) the lack of tectonic structures such as faults and shear planes associated with the ultramafic-rich breccia formation and the presence of neoformation of metamorphic minerals within the matrix preclude their origin as cataclasites related to the Latest Cretaceous and Tertiary Pyrenean contractional deformation. The peridotites of eastern Ariè ge are indisputable witnesses of the presence of an inverted hyper-extended Cretaceous passive margin forming the current North Pyrenean zone. The geometry of the extensional system was complex and probably associated with strike-slip faults and transcurrent motion. ß 2016 The Authors. Published by Elsevier Masson SAS on behalf of Acadé mie des sciences. This is an open access article under the CC BY-NC-ND license (http://creativecommons. org/licenses/by-nc-nd/4.0/).
ISSN: 1631-0713

Droits : http://creativecommons.org/licenses/by-nc-nd/
insu-01280502
https://hal-insu.archives-ouvertes.fr/insu-01280502
https://hal-insu.archives-ouvertes.fr/insu-01280502/document
https://hal-insu.archives-ouvertes.fr/insu-01280502/file/1-s2.0-S1631071316000043-main.pdf
DOI : 10.1016/j.crte.2015.12.003

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The volume comprises some of the contributions presented during the 10th edition of the Alpine Meeting "CorseAlp 2011". It has been held in Saint Florent (Corsica) between 10th and 16th of April 2011 under the auspices of Societé Geologique de France, Società Geologica Italiana and the INGV (Istituto Nazionale di Geofisica e Vulcanologia) and with the collaboration of colleagues of Université de Corse (M.-M. Spella, M. and J. Ferrandini and L. Ciancaleoni) and the support of the city council of S. Florent. The meeting was framed in the series of "Alpine Workshops" e.g., Siegesmund et al. (2008), Handy and Rosenberg (2011), which are held every two years to develop interdisciplinary research on Alpine-type orogens. It hosted a variety of topical sessions from regional geology to process-oriented field and laboratory studies and gave the opportunity to collect multidisciplinary and multiscale approaches to geodynamic studies including continental rifting and ocean opening, oceanic and continental subduction, late- to post orogenic extension, exhumation of deep seated rocks, back-arc opening and microcontinent rotation, interfering orogenic-scale tectonics and surface processes, tectonics and seismic hazard within the Alpine chain and Mediterranean realms.
ISSN: 0040-1951

hal-00795580
https://hal.archives-ouvertes.fr/hal-00795580

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The chronostratigraphy of the lower Miocene deposits of northwestern Sardinia is refined in the Castelsardo Basin. The combination of new 40Ar/39Ar isotopic datings, 19 micropalaeontological datings (calcareous nannofossils, planktonic and large benthic foraminifers) and 16 palaeomagnetic polarity measurements led to a new chronostratigraphic framework. The continental deposits of the first megasequence (Valledoria and Casteldoria members) are possibly Aquitanian. The overlying marine sediments are early Burdigalian (Vaginella depressa Molasse). The marine transgression can be dated to around 19.7 Ma. Marine conditions ceased 18.83 ± 0.13 Ma, the age of the index aerial τ2 ignimbrite. The continental part of the second megasequence (“Lacustre” unit) is early–middle Burdigalian, between 18.8 and 18 Ma. The overlying marine part (Campulandu and Sedini members) is middle–late Burdigalian. The second marine transgression began in the earliest–late Burdigalian, during the Chron C5Dr reversal, at the time of the eustatic Bur 4 event. The Castelsardo basin went through two main extensional tectonic episodes. The first one occurred as the Valledoria Member was deposited and possibly dates back to the Aquitanian. The second one occurred as the uppermost part of the Vaginella depressa Molasse was deposited during the early Burdigalian. The second extensional episode is related to a rapid rotation of Sardinia. Palaeomagnetic results confirm that Corsica and Sardinia acted as a single block which suffered a 28 ± 17° ccw rotation after 19.2 Ma. The Castelsardo basin is held to be an Aquitanian–early Burdigalian intra-arc rift basin that later evolved in a thermally controlled subsident margin of the Ligurian-Provençal Basin during the middle–late Burdigalian.
ISSN: 0031-0182

hal-00498288
https://hal.archives-ouvertes.fr/hal-00498288
DOI : 10.1016/j.palaeo.2010.06.007