Impact origin of large intracratonic basins, the stationary Proterozoic crust, and the transition to modern plate tectonics

Abstract

Impacts of large meteorites or comets into Proterozoic continental crust may have opened basins as much as hundreds of kilometers in diameter. We suggest that basalt magma generated through pressure-relief, partial melting flooded the craters to form lava lakes, which evolved into lopoliths capped with flood-basalt flows.

Thermal-contraction subsidence of these heavy igneous rocks created basins that continued to subside under sedimentary loading. Meanwhile, continued partial melting in the upper mantle generated more basalt magma that entered the basin fill as either flows or diabase sills. Continuing igneous activity within the basin, instead of along a hotspot track, implies that the Proterozoic lithosphere was stationary. Sharply limited rifting associated with large Proterozoic basins similarly suggests a nearly stationary crust. Perhaps very large areas of relatively thin continental crust blocked sweeping plate movement.

Thrusting associated with subduction within extremely large impact basins of generally oceanic character may have thickened the Proterozoic crust while diminishing its area. Relatively straight and long mobile belts appeared near the end of Proterozoic time, apparently marking the time when ocean basins became large enough to permit the transition to modern plate tectonic settings.