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Post-Telbessian Strike-Slip-Related Compressional and Extensional Structures in Central Kazakhstan
Tevelev, Al. V., Tevelev, Arc. V., Zavrazhnov V.N.
(Geological Faculty, Moscow State University, Russia)
Examined area comprises the heterogeneous tectonically Central Kazakhstan region from the Sarysu-Teniz Uplift to the Tokrau Deep. Post-telbessian (after Middle Devonian) history of this region seems to be relatively uniform: all or almost all distinctive structural elements here accommodate Early Carboniferous basins, Late Paleozoic volcanic deeps, granitoid intrusions, etc. Local post-telbessian structures are similar in many aspects: (1) telbessian unconformity are overall very clear, and areas of Low Carboniferous sediments coincide with regions of Upper Paleozoic volcanic rocks; 2) all structures are confining with diagonal (NE and NW) fault net; (3) intrusions located in limits of these structures are of polyhedral shape; (4) sedimentary basins, polyhedral volcanotectonic depressions, feeder zones, intrusive massifs, dykes and their swarms possess regular and similar structural patterns.
Faults controlled post-telbessian structuring are of Late Devonian - Early Permian age; they are usually deep-seated. There is consisting rather strong correlation between fault orientation and its kinematics (or between orientation of structural elements and dynamic conditions of their formation): NW fractures are dextral strike-slip faults, whilst NE trending faults are sinistral ones; zones of intensive deformations formed under compressional conditions are latitude, but extensional dyke swarms and paleovolcanos chains are easy longitude. These dynamic settings maintained for a long time and it is evidenced by repeated using of the same extension zones with magmatic bodies of different age.
Thus, post-telbessian structure of Central Kazakhstan has developed under condition of relatively monotonous stress field with sub-longitudal orientation of main compression and latitudal orientation of main extension. Primarily brittle deformation of upper crust in this region has accompanied by formation of two wrench systems (which are NW system of dextral strike-slip faults and NE system of sinistral strike-slip faults) with complementary set of local compressional and extensional structures; the latter can be described as strike-slip-related in spite of that driven mechanisms of post-telbessian deformation are poorly known. Diversity of relationships between magmatic and non-magmatic members taken part in building of examined structures is caused by thermal history of corresponding regions and are not connected with magnitude of strike-slip opening. Within study area, the dextral and sinistral domains are distinguishing clearly; each of them chiefly contains strike-slip faults of one only orientation and sense of displacement. Local compressional and extensional structures of different generations can interfere in very different manner; however, the regional ratio of amount of compressional and extensional structures is changing during the time reflecting likely the quantitative variations of regional stresses.
The work is supported by RFFI, grants 96-05-65519, 96-05-65521.