Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This paper provides a synthesis of current data and interpretations on the crustal structure of the Pyrenean-Cantabrian orogenic belt, and presents new tectonic models for representative transects. The Pyrenean orogeny lasted from Santonian (~84 Ma) to early Miocene times (~20 Ma), and consisted of a spatial and temporal succession of oceanic crust/exhumed mantle subduction, rift inversion and continental collision processes at the Iberia-Eurasia plate boundary. A good coverage by active-source (vertical-incidence and wide-angle reflection) and passive-source (receiver functions) seismic studies, coupled with surface data have led to a reasonable knowledge of the present-day crustal architecture of the Pyrenean-Cantabrian belt, although questions remain. Seismic imaging reveals a persistent structure, from the central Pyrenees to the central Cantabrian Mountains, consisting of a wedge of Eurasian lithosphere indented into the thicker Iberian plate, whose lower crust is detached and plunges northwards into the mantle. For the Pyrenees, a new scheme of relationships between the southern upper crustal thrust sheets and the Axial Zone is here proposed. For the Cantabrian belt, the depth reached by the N-dipping Iberian crust and the structure of the margin are also revised.The common occurrence of lherzolite bodies in the northern Pyrenees and the seismic velocity and potential field record of the Bay of Biscay indicate that the precursor of the Pyrenees was a hyperextended and strongly segmented rift system, where narrow domains of exhumed mantle separated the thinned Iberian and Eurasian continental margins since the Albian-Cenomanian. The exhumed mantle in the Pyrenean rift was largely covered by a Mesozoic sedimentary lid that had locally glided along detachments in Triassic evaporites. Continental margin collision in the Pyrenees was preceded by subduction of the exhumed mantle, accompanied by the pop-up thrust expulsion of the off-scraped sedimentary lid above. To the west, oceanic subduction of the Bay of Biscay under the North Iberian margin is supported by an upper plate thrust wedge, gravity and magnetic anomalies, and 3D inclined sub-crustal reflections. However, discrepancies remain for the location of continent-ocean transitions in the Bay of Biscay and for the extent of oceanic subduction. The plate-kinematic evolution during the Mesozoic, which involves issues as the timing and total amount of opening, as well as the role of strike-slip drift, is also under debate, discrepancies arising from first-order interpretations of the adjacent oceanic magnetic anomaly record.
ISSN: 0040-1951

insu-01683989
https://hal-insu.archives-ouvertes.fr/insu-01683989
https://hal-insu.archives-ouvertes.fr/insu-01683989/document
https://hal-insu.archives-ouvertes.fr/insu-01683989/file/teixell-tectono-2018.pdf
DOI : 10.1016/j.tecto.2018.01.009

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 Société géologique de France
Résumé : The Maguelone shore extends along the northern coast of the Gulf of Lions margin, West of the Rhone delta and East of some high gradient coastal streams that have been providing most of the elastic sediments to the Gulf of Lions margin since the early Miocene. This 10 km wide area comprises an onshore small coastal watershed (15 km long) in low-lying carbonate hills, kilometer wide marshes, sandy beach and shoreface featuring local low sedimentation. Deposit architecture in such a coastal zone records dynamics of incised valley fill under the influence of rivers and wave/current hydrodynamics in a microtidal environment during an eustatic cycle.;A detailed analysis of about 250 km of very high resolution seismic profiles, tens of cores and outcrops data revealed the evolution of the Maguelone coastal system from Late-Quaternary to present-day. It highlighted also dominant denudation processes in the upstream catchments associated to the formation of incised valley seaward during Quaternary. Combination of this inherited morphology together with hydrodynamics controlled the lagoonal environment evolution since the last transgression. In particular, the Maguelone shore is characterized by the formation of built-over-rias lagoonal systems and records an evolution from partially protected lagoon to isolated lagoon environment. These two stages of lagoon evolution correspond to distinct deposit environments. Correlation of fauna contents with deposit geometry improves lagoonal environment models.
EISSN: 1777-5817

hal-00486370
https://hal.archives-ouvertes.fr/hal-00486370
DOI : 10.2113/gssgfbull.181.2.211

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Hengshan–Wutaishan area forms part of the Trans-North-China Belt developed in response to the final amalgamation of the North China Craton. The Hengshan–Wutaishan domain and the adjacent Fuping massif constitute the largest and the most representative rock exposure of the belt. A structural study allows us to redefine the lithological and tectonic units that compose the architecture of the Hengshan–Wutaishan domain and to propose that the Trans-North-China Belt was built up through a polyphase tectonic evolution within the period 1900–1800 Ma. The first event (D1) corresponds to the emplacement of lower and upper nappes herein called the Orthogneiss and Volcanites Unit (OVU) and the Low Grade Mafic Unit (LGMU), respectively. The OVU mainly consists of rocks formed in an arc system and metamorphosed under amphibolite facies conditions whereas the LGMU represents oceanic crust rocks with an arc component that underwent greenschist facies metamorphism. The syn-metamorphic D1 deformation is characterized by a NW–SE stretching and mineral lineation with a top-to-the SE sense of shear that corresponds to the sense of nappe motion. U–Th–Pb EPM chemical dating on monazite from three metapelites of the OVU gives isochron ages of 1884 ± 11 Ma, 1886 ± 5 Ma and 1887 ± 4 Ma interpreted as the age of the prograde amphibolite facies metamorphism coeval with nappe stacking during the D1 event. The D2 event corresponds to a widespread crustal melting of the OVU and underlying basement rocks in Hengshan related to the exhumation of deep structures about 20–30 Ma after nappe emplacement. The migmatite contains blocks of retrograded eclogite or HP-granulitic restites, and is characterized by the development of a pervasive foliation and lineation. A late D2 event represents the folding stage of the migmatitic foliation during the completion of a dome. The Orthogneiss and Volcanics Unit and the Low Grade Mafic Unit are unconformably covered by weakly metamorphosed to unmetamorphosed sediments belonging to the Hutuo Supergroup. These rocks were deformed by a ductile D3 event, characterized by a NW–SE trending stretching lineation, south verging folds associated with an axial planar slaty cleavage and an E–W crenulation lineation. Lastly, a left-lateral wrenching along the Zhujiafang Shear Zone separates the northern and southern parts of Hengshan. Our structural study shows that there is no significant difference between the southern part of Hengshan and the lower part of Wutaishan, both areas belong to OVU and show a structural continuity. We suggest that this polyphase deformation developed in response to a north-westward subduction of an old ocean, named the Lüliang Ocean, beneath the Western Block, followed by collision with a micro-continent named the Fuping Block at not, vert, similar1890–1880 Ma.
ISSN: 0301-9268

insu-00151594
https://hal-insu.archives-ouvertes.fr/insu-00151594
https://hal-insu.archives-ouvertes.fr/insu-00151594/document
https://hal-insu.archives-ouvertes.fr/insu-00151594/file/Trap-PrecambrainResearch-2007.pdf
DOI : 10.1016/j.precamres.2007.03.001

Éditeur(s) : HAL CCSD Elsevier
Résumé : Detailed sedimentological investigations on numerous outcrops and drill-core sections in the 2.1-Ga-old Franceville basin, Gabon, provide evidence for a large-scale injectite network. The injectites were formed by the injection of sands through a thickness of about 150 m of the FB1 Member, and now cover a minimum area of 70 km2 corresponding to the Bangombé plateau, but are also recognized close to Franceville 35 km farther south-east. The injectite lithology corresponds to a mud- or carbonate-supported sandstone characterized by a loose and uncompacted fabric contrasting with the host-rock. Because the injectites are often parallel to subparallel to the stratification, they were misinterpreted as depositional beds by previous authors. At outcrop, the injectite bodies exhibit sill, dyke, wing and protrusive geometries emplaced during early burial within poorly compacted material, with partial wall erosion and dissociation. The source of the sand material is attributed to a channel-levee turbidite depositional system located in the lower part of the FB1 Member. These deposits were buried by a thick biochemical muddy cap deposited during a starvation phase, which increased the seal capacity of the system. This type of architecture has a high potential to develop compaction disequilibrium during burial. Moreover, in the case of the Francevillian injectites, the abundance of microbial organic matter favoured early methane degassing and lateral charging of the sand reservoir. The overpressure in the channels was periodically released during early burial, through the effect of rapid sedimentary and tectonic loading, and possible seismic activity. The fluidized sand was injected according to a symmetrical wing pattern. Thus, the injected masses caused a local decrease in the grade of the lateritic manganese ore deposit of the Bangombé plateau.
ISSN: 0301-9268

hal-01667217
https://hal.archives-ouvertes.fr/hal-01667217
DOI : 10.1016/j.precamres.2017.09.022