New insigths into the West Siberian Basin from the satellite mission GRACE
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The West Siberian Basin covers an area of ~3.2 x10(6) sq.km and is among the most extended basins in the world. Recent investigations have revealed that the basin contrains and extensive layer of flood basalts of late Permian-Triassic age, which have been set into relation to the basalts of the Siverian traps. In the northern part of the basin, the basalts overly older sediments that reach locally over 15 km in thickness. Our work aims at reducing the observed gravity field to the basement level, estimating the contribution of the sediments and of the basalt layer to the gravity field. Published seismic sections with well-calibration are used for constraining the sediment isopachs and for estimating the density-depth functions. We also make use of published models on crustal thickness and besement depth and the gravity field derived from the integration of the satellite mission GRACE with terrestrial gravity measurements. The resulting 3D-density model is used for inferring density anomalies in the lower crust and upper mantle and allows calculating the total load acting on the crust and estimating the isostatic state of the region. A key question related to the formation of the basin is, whether a high density anomaly in the crust or upper mantle has contributed to the large scale subsidence of the basin, as has been postulated for other large scale basins. The lower crust shows considerable density variations, that allow making a segmentation of the basin into four blocks, the southern, mid, northern and north-western segments. We identify several rift structures and estimate the amount of basalt-filling. The eatern part of the basin towards the Siberian Platform shows an evident arch-shaped density increase in the lower crust, which is coincident with a rift extending for more than 1500 km length and bending into the Yenisey-Khatanga trough.