Aspects of the tectonics of the Greater Caucasus and Western South Caspian Basin

Abstract

The main objectives of this project are to (a) understand the relationship between climate, topography and the tectonics in the Greater Caucasus belt, (b) construct regional geological cross-sections showing major stratigraphic sequences and structures along the belt using the focal mechanisms of the earthquakes events, (c) evaluate the evolution and development of a single fold structure (Yasamal anticline) and (d) investigate strain accommodation mechanisms using 3D Move to unfold the Yasamal structure.

Topographic variations were investigated to understand the interplay between topography, climate and the tectonics of the Greater Caucasus range and compare the findings with other active and inactive belts (Pyrenees, Northern Tibetan Plateau and Himalayas). There is a correlation between elevation changes and climate along the Greater Caucasus belt, where the gradual reduction of the mean altitude, has a close relationship with a wetter climate, and the sharper altitude decrease with a drier climate. And the elevation changes are strongly correlated with the Moho depths underneath the region. The relief along the belt is extremely high, with a strong correlation between the high relief and the large thrusts in the region. And the relief of the eastern part is slightly low compared with the western part of the belt, even though the eastern part is more active than the western part.

The structural study undertaken at regional scale for the Caucasus belt and the western side of the South Caspian Basin gave insights on the style of deformation in the basin and the evolution of the Greater Caucasus belt and the preferred distribution, geometry and formation mechanism of the structural elements. The regional cross-sections along the Greater Caucasus were constructed and constrained by using focal mechanisms show that the belt is deformed by active thrust faults that dip inwards from the margins of the range where the northern thrusts are dipping south, and the southern thrusts are dipping to the north, these results have contrary to some previous models that emphasise only south-directed thrusting.

The spatial arrangement, geometry and temporal evolution of spectacular kilometre-amplitude fold structures actively forming in Cenozoic sediments on the uplifted western margin of the South Caspian Basin are described and strain accommodation mechanisms established using 3D Move to unfold the Yasamal structure enabled a reconstruction of pre-folding templates and predictively model the fold-related deformation at small-scale. The 3D model of the Yasamal anticline shows that the anticline hinge has about 30° south-directed plunging. The area was characterized by a low rate of sedimentation and high rate of uplift in the Upper Pliocene. The minor structures (accommodating the overall strain in the anticline) are developed throughout the entire anticline. Compressional strain is present at the anticline hinge line, and the extensional strain dominates the anticline limbs. Suggesting potential extensional structures development in the anticline flanks, which correspond with the field observations in the Yasamal valley confirming that; the small normal faults are concentrated within the anticline flanks, and the contractional deformation bands along the hinge area of the anticline.