CRUSTAL CONTROL ON THE TEREK-CASPIAN TROUGH EVOLUTION - CONSTRAINTS BASED ON A NEW PALEOTECTONIC ANALYSIS METHOD

The evolution of the Terek-Caspian trough is investigated using a nume rical paleotectonic analysis method based on expanding the tectonic ve locity into a series of functions that depend on spatial coordinates a nd time. The method relies on the same kind of data as backstripping a nalysis, including the thicknesses of the sedimentary strata, their fo rmation periods and facies composition (depth of deposition). It allow s investigating the rate of motion in greater detail than conventional methods, and under certain conditions may be used to estimate the rat e of movements not only for periods of sedimentation, but for periods of erosion as well, and also to determine the position of deep-seated faults, their periods of activity and amount of slip. The analysis has shown that, for the Terek-Caspian trough, it is possible to represent the rate of motion as a sum of two components: the overall motion of the entire profile proportional to the square root of time, and the lo cal component as a function of time and distance along the profile. Wi th regard to the local component, the profile subdivides into two part s, northern and southern, which have tended to be involved in vertical motion of the respectively opposite senses. These parts are separated by a deep-seated fault. This fault has controlled the trough evolutio n for at least 180 Myr. The antiphase movement of its sides may be exp lained by assuming that the fault plane is inclined: a regional compre ssion would then drive one side up and the other down. As the compress ion is removed or changed over by an extension, the sense of movement will be the opposite. Under the assumption that the fault plane plunge s beneath the Caucasus, the phases of compression appear to have occur red 120-140 Myr and 50-75 Myr ago.