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EIL-10 Large-scale seismic transects: Images of the Earth?s crust and mantle
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Geological interpretation of the Siberian platform deep structure from transects Batolit and Altai-Severnaya Zemlya
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A.S. Yefimov, Siberian Research Institute of Geology, Geophysics and Mineral Resources (Russian Federation)
A.V. Migursky, Siberian Research Institute of Geology, Geophysics and Mineral Resources (Russian Federation)
D.I. Rudnitskaya, Siberian Research Institute of Geology, Geophysics and Mineral Resources (Russian Federation)
V.S. Staroseltsev, Siberian Research Institute of Geology, Geophysics and Mineral Resources (Russian Federation)
V.I. Valchak, Yeniseigeofizika OJSC (Russian Federation)
N.A. Goryunov, Yeniseigeofizika OJSC (Russian Federation)
A.A. Yevgrafov, Yeniseigeofizika OJSC (Russian Federation)
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Early from DSS and modeling of potential geophysical fields the average Earth's crust thickness in the southern Siberian Platform was 40-45 km. Minimum depths (39 km and less) to the Moho discontinuity ("M") agreed closely with contours of the Irkineeva-Chadobets aulaco-gen. It was logical as the crust is usually thinner in the contrast depression than at its slopes.
Seismic lines of the deep CDPM show that the crust thickness outside the Irkineeva-Chadobets aulacogen are close to the previous estimates. But in the aulacogen itself the M dis-continuity reaches 60 km.
Undoubtedly the aulacogen experienced the Earth's crust thickening stage revealed in strongly faulted, often thrusted, Riphean. Thrusts within the aulacogen are also fixed over the Moho discontinuity. In the "Altai-Severnaya Zemlya" line and cleaving-line lateral to it near the Khorkichskaya area, the Kamov block is thrusted over aulacogen formations. The displace-ment amplitude over the Moho discontinuity exceeds 10 km. One more deep thrust is marked on the "Altai-Severnaya Zemlya" line just south of the Madashenskaya area. Its occurrence and displacement amplitude are close to those of the Khorkich deep thrust. Both ruptures are associ-ated with majors wells in the upper Jurassic. A zone, where Boguchany Manzy block is oppo-sitely thrusted onto Irkineeva-Chadobets aulacogen, is marked in the same line south of the An-gara R.
Deep CDP profiling also shows that sedimentary basins in the territory considered are much more apparent than it has been suggested before. Along the "Batolit" line the Kuyumbin-skaya-Yuzhno-Chunskaya areas reaches 9 km, and the Riphean thickness exceeds 3-5 km over the basement surface. More significant depths (∼15 km) of the Riphean bottom compared with the previous structures are established in the Irkineeva-Chadobets aulacogen at its intersection with the "Altai - Severnaya Zemlya" line.
The interpreted CDP sections allow improving more exactly the Siberian platform base-ment block contours. So, from the analyzed Earth's crust seismic image the boundary between the Magan and Tunguska megablocks is 100-200 km further west of the Taimyr-Baikal master fracture along which it has been drawn before. This boundary coincides with the Irkineeva-Chadobets aulacogen eastern border. Thus, deep CDP studies give a complete pattern of the Earth's crust structure. They are enable to revise and define the Siberian Platform structure and evolution and contributed to its minerageny. Hence, the discovery of large Riphean basins in the western Siberian Platform sub-stantially modifies our conception of hydrocarbon ontogeny, holds more promise for new dis-coveries.
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