THE TIMAN-PECHORA BASIN (NORTHEASTERN EUROPEAN RUSSIA) - TECTONIC SUBSIDENCE ANALYSIS AND A MODEL OF FORMATION MECHANISM

We study the tectonic subsidence of the Timan-Pechora Basin by using a number of exploration wells and lithologic-stratigraphic sections alo ng deep seismic sounding profiles. The tectonic analysis reveals a rap id phase of subsidence in the Late Devonian followed by a slower one. We suggest a two-phase model of persistent subsidence in the basin: (1 ) in the Ordovician (505-438 Ma B.P.), and (2) in the Silurian (438-40 8 Ma B.P.). The thinning of the lithosphere beneath the basin due to t hese rift phases led to the uplift of the asthenosphere and to partial melting. We explain the vertical motions of the crust by a magmatism- eclogitization model. The formation mechanism includes accumulation of magmatic melt below the lithosphere/asthenosphere boundary in the Ear ly-Middle Devonian, a phase transformation of magmatic material to ecl ogites during the cooling, and a flow in the uppermost mantle induced by the evolved heavy bodies since the Late Devonian. We construct a tw o-dimensional numerical model of the flow in the asthenosphere, comput e this flow and describe the resulting changes in surface topography. The model is in keeping with observed gravity, seismic, and subsidence data. Using the results of tectonic subsidence analysis and the model , we interpret the geodynamic evolution of the Timan-Pechora Basin and discuss the effect of eclogitization in the uppermost mantle on the b asin development.