Search results for "TECTONICS"

A tectonic inversion by steps during the Cenozoic : the Dover Strait

2004

Abstract The Boulonnais is a dome incised by a former marine gulf inset into a zone of tectonic inversion from the Middle Eocene, which was already partly excavated at least at the Upper Eocene. New sedimentological and paleopedological data obtained within the Boulonnais, completed with old seismic profiles, allow a better understanding of the inversion process which developed step by step. The initial breaching probably took place in the late Eocene. The Dover Strait was probably opened during the Lutetian, a part of the Oligocene and the late Neogene. Oligocene and Pliocene faunal assemblages are identical on both sides of the Strait. It was closed again for tectonic and eustatic reasons…

A genetic link between synsedimentary tectonics-expelled fluids, microbial sulfate reduction and cone-in-cone structures

2018

14 pages; International audience; The late Jurassic (Tithonian) marlstones of the Boulonnais area (English Channel, France) contains diagenetic carbonate beds and nodules. Some nodules exhibit cone-in-cone structures on their lower face. We studied such nodules using various techniques of imaging and chemical (major and trace-elements) and isotopic analyses (Ccarb, Corg, O and S stable isotopes). We interpret the cone-in-cone to be the end product of carbonate-nodule formation during early diagenesis. The diagenetic carbonate precipitation was induced by microbial activity (bacteria and(?) archeae) fueled by upward-migrating fluids. Fluid expulsion was itself triggered by synsedimentary fau…

Short-term occupations at high elevation during the Middle Paleolithic at Kalavan 2 (Republic of Armenia).

2021

The Armenian highlands encompasses rugged and environmentally diverse landscapes and is characterized by a mosaic of distinct ecological niches and large temperature gradients. Strong seasonal fluctuations in resource availability along topographic gradients likely prompted Pleistocene hominin groups to adapt by adjusting their mobility strategies. However, the role that elevated landscapes played in hunter-gatherer settlement systems during the Late Pleistocene (Middle Palaeolithic [MP]) remains poorly understood. At 1640 m above sea level, the MP site of Kalavan 2 (Armenia) is ideally positioned for testing hypotheses involving elevation-dependent seasonal mobility and subsistence strateg…

Modelo de cabalgamiento profundo para el Alto Atlas (Marruecos). Implicaciones sísmicas en la zona de colisión entre Eurasia y Africa

2007

Previous crustal models of the High Atlas suppose the existence of a mid-crustal detachment where all the surface thrusts merged and below which the lower crust was continuous. However, both seismic refraction data and gravity modeling detected a jump in crustal thickness between the High Atlas and the northern plains. Here we show that this rapid and vertical jump in the depth of Moho discontinuity suggests that a thrust fault may penetrate the lower crust and offset the Moho (deep-rooted “thick skinned” model). The distribution of Neogene and Quaternary volcanisms along and at the northern part of the High Atlas lineament can be related to the beginning of a partial continental subduction…

Geochemical characteristics of Cretaceous carbonatites from Angola

1999

Abstract The Early Cretaceous (138–130 Ma) carbonatites and associated alkaline rocks of Angola belong to the Parana-Angola-Etendeka Province and occur as ring complexes and other central-type intrusions along northeast trending tectonic lineaments, parallel to the trend of coeval Namibian alkaline complexes. Most of the Angolan carbonatite-alkaline bodies are located along the apical part of the Mocamedes Arch, a structure representing the African counterpart of the Ponta Grossa Arch in southern Brazil, where several alkaline-carbonatite complexes were also emplaced in the Early Cretaceous. Geochemical and isotopic (C, 0, Sr and Nd) characteristics determined for five carbonatitic occurren…

The Mulgandinnah Shear Zone; an Archean crustal scale strike-slip zone, eastern Pilbara, Western Australia

1998

Abstract A large part of the deformation in the Archean Pilbara granitoid-greenstone terrain is localized in relatively narrow shear zones. The Mulgandinnah shear zone (MSZ) is a major one of these, with a width up to 8 km, that can be followed for over 70 km along strike in the Shaw Batholith in the eastern Pilbara. It forms part of the Mulgandinnah Lineament, that can be traced to the Lalla Rookh Basin and the Carlindi Batholith in the north, giving it a total length of over 150 km. The MSZ contains both mylonites and ultramylonites, both of which have foliations that are subvertical to steeply dipping, with the ultramylonitic foliation overprinting the mylonitic foliation to form more lo…

Trench-parallel spreading ridge subduction and its consequences for the geological evolution of the overriding plate: Insights from analogue models a…

2018

A series of 3-D asthenospheric-scale analogue models have been conducted in the laboratory in order to simulate the arrival of a spreading ridge at the trench and understand its effect on plate kinematics, slab geometry, and on the deformation of the overriding plate. These models are made of a two-layered linearly viscous system simulating the lithosphere and asthenosphere. We reproduce the progressive decrease in thickness of the oceanic lithosphere at the trench. We measure plate kinematics, slab geometry and upper plate deformation. Our experiments reveal that the subduction of a thinning plate beneath a freely moving overriding continent favors a decrease of the subduction velocity and…

Polyphased mesozoic rifting from the Atlas to the north-west Africa paleomargin

2021

24 pages; International audience; Based on the interpretation of geological maps, seismic reflection and well data complemented with a bibliographic compilation and field work in the Rif, we investigate the factors that control the rift initiation, its development and the formation of oceanic crust in NW Africa. From SE to NW, we examine the Western Sahara Atlas, the Tendrara, the Guercif, and the Rif basins, to establish their geodynamic evolution in relation with the Mesozoic formation of the Central Atlantic and Maghrebian Tethys oceans, respectively. The Triassic extension was diffuse and developed over Lower Carboniferous horst-and-graben structures formed in the NW passive margin of G…

STOP 7: Madona-Trepe ice-marginal ridge at Smeceres sils, East-Latvian Lowland

2014

Fragmentation dynamics within shear bands--a model for aging tectonic faults?

2001

A numerical model for packing of fragmenting blocks in a shear band is introduced, and its dynamics is compared with that of a tectonic fault. The shear band undergoes a slow aging process in which the blocks are being grinded by the shear motion and the compression. The dynamics of the model have the same statistical characteristics as the seismic activity in faults. The characteristic magnitude distribution of earthquakes appears to result from frictional slips at small and medium magnitudes, and from fragmentation of blocks at the largest magnitudes. Aftershocks to large-magnitude earthquakes are local recombinations of the fragments before they reach a new quasi-static equilibrium. The …