Search

This paper reports the data on the structure of the northwestern boundary of the Middle Amur sedimentary basin which were obtained after resumption of audiomagnetotelluric soundings. The geoelectric sections for two profiles across the basin strike are constructed, the sedimentary cover and basement structures are studied, and their electrical properties are determined. The compared data of the earlier and present studies show low-resistivity zones of 50-150 Ohm m beneath high-resistivity rocks of 500-1000 Ohm m in the northwestern part of the Ul’dura-Churki uplift at a 2-4 km depth, which are absent in the southwestern part of the uplift. This fact is related to strike-slip-overthrust processes due to graben formation in the area of junction with the Jiamusi-Bureya Massif in the Kur fault zone (YYilan-Yitong branch of the Tan-Lu fault zone) and also to global left-lateral strike-slip displacements and volcanic activity. [ABSTRACT FROM AUTHOR]

The structure and evolution of the passive continental margins of the Arctic Ocean are considered on the example of the South Kara Basin. Its development is associated with the evolution of the West Siberian Plate and the formation of the Arctic Ocean. Until the Late Cretaceous, the South Kara Basin was the north margin of the West Siberian Plate, whose formation is related to the Permian-Triassic processes of riftogenesis accompanied by the eruptions of traps. In the Mesozoic, due to the opening of the Arctic Ocean, the South Kara basin became a part of the continental margin, where the accumulation of marine sandy-clayey rocks continued. [ABSTRACT FROM AUTHOR]

Abstract: The article summarizes results of tectonophysical and geoelectric studies of rift basins in the Baikal region. Their sedimentary cover is intersected by faults, which induce shallow soft deformations in Late Cenozoic sediments. The faults observed in the internal part of the basins correlate with zones of contrast change in the deep structures of the crystalline basement and sedimentary layers. They offset the top of the basement and bottom of the sedimentary layers, and constitute zones of lower resistivity values. Significant variations of electrical parameters can be due to redistribution of conducting fluids in a geological massif, which allows discriminating water-bearing faults from water-free ones. Taken as a whole, the tectonic structure of the basins is best defined by the presence of shallow deformation zones, an asymmetrical morphology and fault-block pattern of both the sedimentary infill and basement of the basins. [Copyright &y& Elsevier]

The article presents a study that explores the geochronologic and structural data from the terranes of the South Anyui suture (SAS) zone in Russia. It indicates that the island arc complexes of the Yarakvaam terrane on the northern margin of the North Asian craton record Early Carboniferous to Neocomian ages in ophiolite, sedimentary, and volcanic rock. It notes that the postcollisional orogenic stage is characterized by sinistral strike slip faults and an extensional environment.

Continental rift zones are long, narrow tectonic depressions in the Earth’s surface where the entire lithosphere has been modified in extension. Rifting can eventually lead to rupture of the continental lithosphere and creation of new oceanic lithosphere or, alternatively, lead to formation of wide sedimentary basins around failed rift zones. Conventional models of rift zones include three characteristic features: surface manifestation as an elongated topographic trough, Moho shallowing due to crustal thinning, and reduced seismic velocity in the uppermost mantle due to decompression melting or heating from the Earth’s interior. Here we demonstrate that only the surface manifestation is observed at the Baikal rift zone, whereas the crustal and mantle characteristics can be ruled out by a new seismic profile across southern Lake Baikal in Siberia. Instead we observe a localized zone in the lower crust which has exceptionally high seismic velocity and is highly reflective. We suggest that the expected Moho uplift was compensated by magmatic intrusion into the lower crust, producing the observed high-velocity zone. This finding demonstrates a previously unknown role for magmatism in rifting processes with significant implications for estimation of stretching factors and modelling of sedimentary basins around failed rift structures. [ABSTRACT FROM AUTHOR]