THE ASSEMBLY OF GONDWANALAND

Gondwanaland was assembled in the Neoproterozoic Pan African-Brasilian o orogeny following breakup of the preceding Rodinia supercontinent. T he latter created and set in motion a new system of lithospheric plate s that resulted in the formation of Neoproterozoic mobile belts suturi ng old cratons in Gondwanaland. East Gondwanaland was a fragment of Ro dinia that survived the breakup and, during the Neoproterozoic, was af fected only by intracontinental deformation. In West Gondwanaland, the opening of three oceans, from which Pan African-Brasiliano orogens we re born, is traced to a period of crustal extension, rifting, transpre ssion, magmatic are activity and a few documented terrane collisions ( 1000-720 Ma), bracketed by Rodinia assembly and breakup. All craton co llisions involving closure of oceans (640-590 Mn), postdate the Rodini a breakup. The Pan African-Brasiliano orogeny (720-550 Ma) is redefine d to include only the collision-related deformation, shearing and tect onic escape, and synorogenic magmatism postdating the Rodinia breakup. Two models have been proposed for postorogenic magmatism and uplift, widespread in Gondwanaland: lithospheric mantle delamination caused by continental collision in West Gondwanaland and underplating of basalt ic magma in East Gondwanaland. Isotopic studies suggest large-scale ad dition of supergene water to hot crust in these post orogenic events. The assembly of Gondwanaland proceeded by docking of individual craton s and there is no evidence of one collision between West and East Gond wanaland. After the assembly of Gondwanaland, tectonic and magmatic ac tivity shifted to the accretionary pacific margin, and at the same tim e rifting and calving of terranes accelerated at the opposite margin o f the supercontinent.