LATE PALEOZOIC CRUSTAL BLOCK ROTATIONS WITHIN THE GONDWANA SECTOR OF PANGEA

From the Late Carboniferous to the onset of the Triassic, Gondwana was transected by several major shear systems the location of which was c ontrolled by weak zones joining the ancient cratons. These shear syste ms subdivided Gondwana into mega-blocks each of which experienced rota tional motions at different angular speeds. Collisions between Gondwan a and Laurussia in the north and between Gondwana and the palaeo-Pacif ic Plate in the west resulted in a counterclockwise rotation for the G ondwana mega-blocks during the latest Carboniferous and Early Permian. These rotational motions led to the opening of fault-controlled basin s along shear zones in the interior of Gondwana and a 10,000 km long t ranstensional basin system partly inboard of the convergent margin of the supercontinent. Southward propagation of the collision zone betwee n Gondwana and the palaeo-Pacific Plate during the Late Permian and Ea rly Triassic caused the mega-blocks within Gondwana to rotate clockwis e. Except for the Tethys Sea margin of Gondwana, these motions increas ed the compressional stresses within the interior of the supercontinen t resulting in crustal uplift and the formation of the Gondwanan and N ew England fold belts. The primary driving mechanism of the rotational plate motions was collisional tectonics during periods of plate-bound ary reorganisation. Temporal changes in the motions of the mega-blocks are believed to be linked to the greater relevance of the mantle conv ection system during the Mesozoic and which culminated in the breakup of the supercontinent. (C) 1998 Elsevier Science B.V. All rights reser ved.