JUNGGAR, TURFAN AND ALAKOL BASINS AS LATE PERMIAN TO EARLY TRIASSIC EXTENSIONAL STRUCTURES IN A SINISTRAL SHEAR ZONE IN THE ALTAID OROGENIC COLLAGE, CENTRAL-ASIA

The Junggar, Turfan and Alakol basins in northwestern China and Kazakhstan formed as Late Permian to ?Early Triassic extensional structures in a broad sinistral shear zone between large strike-slip faults that separate two main domains of the Altaid orogenic collage. This extension was in response to an inferred large (>1000 km) sinistral motion of the East European craton with respect to the Angaran craton during this time. Deformation associated with the formation of the basins was taken up in part by counter-clockwise rotations of crustal blocks with respect to the Altaid orogenic collage and to the Angaran craton. This event is the only important phase of extension in a region otherwise dominated by compressional tectonics throughout the Phanerozoic. The basement rocks of these basins formed by Altaid subduction-accretion through the latter half of the Palaeozoic and the region was subsequently thrown into compression again during the Mesozoic Cimmeride and Cenozoic Alpide evolution.