Marie-Francoise Brunet1, A. V. Ershov2, Yu. A. Volozh3, M. V. Korotaev2, M. P. Antipov3, J. P. Cadet1
(1) ESA 7072 "Tectonique" CNRS, Paris cedex 05, France
(2) Moscow State University, Moscow, Russia
(3) Russian Academy of Sciences, Moscow, Russia
ABSTRACT: Subsidence Evolution of Two Superdeep Basins: Precaspian and South Caspian Basins
The Precaspian (PCB) and South Caspian (SCB) basins are two superdeep basins containing 20 kilometers of sediments. Their modeling has been undertaken in the frame of the international Peri-Tethys Program. PCB has been trapped at the border of the East-European Platform with the closure of the pre-Urals and Urals oceans. Sediments are perhaps as old as the Riphean. The basement is characterized by a thin crust, where low velocity layer is absent. Its origin is still controversial; either thinned continental or oceanic crust. At the base of the crust, a 8-10 km layer of velocity 8-8.1 km/s is recognized by seismic and gravity observations, this layer may be interpreted as eclogite. SCB is surrounded by compression structures: Caucasus, Kopet Dag and Alborz belts. It is much more recent as the oldest sediments seem to be Jurassic; Plio-Quaternary section reaches 10 km. The crust in the central part is thin with high velocities.
The geodynamics of these two thick basins are compared by the mean of subsidence analysis, characterizing different extensional and compressive phases, alternating with periods of thermal relaxation. Models of crustal thinning and oceanic crust emplacement allow to explain the amount of subsidence during the rifting and thermal post-rift phases. Then models of elastic bending due to compression, combining gravity data and rheological assumptions, allow to fit the increase of subsidence observed during the compression phases. Gravity models permit also to check the presence of a thin high velocity crust below these two basins.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado