Tectonic controls on initial continental rifting and the evolution of young ocean basins—a planetary perspective

Abstract

A review and comparison of planetary tectonic literature and terrestrial interpretations of both oceanic and continental tectonics suggests that the Earth, in common with other terrestrial planets, may have developed a global tectonic grid very early in its history. This grid, still preserved in ancient continental crustal fragments, is maintained by both vertical and lateral fracture propagation. It influences both the direction of initial continental rifting and the location and orientation of sea-floor fracture zones in a developing young ocean basin. Sea-floor spreading directions must continue to be controlled by the direction of easiest slip along major intercontinental wrench faults; the Atlantic Ocean appears to be still in this stage. Development of subduction zones around the margin of an ocean basin permits greater freedom in spreading direction. At this stage, as represented by the Pacific Ocean, ridge jumps and changes in spreading direction may occur as the spreading geometry readjusts to more closely reflect stresses associated with underlying convection cells. At subduction zones, rejuvenation tectonics still operate; thick, cold oceanic crust may impose its tectonic grain on the relatively thin, over-riding edge of the continental plate; but young, thin, and hot oceanic crust is forced to conform to the tectonic grain of thick, cold continental crust. Examples of both effects can be seen along the eastern margin of the Pacific. It is concluded that the structure and evolution of young ocean basins is strongly influenced by ancient fracture patterns in the adjacent continental blocks. Although greater freedom for readjustment develops as an ocean basin matures, the continued need to move, or interact with, major blocks of continental lithosphere continues to impose severe limitations on directions and rates of spreading until subduction zones decouple oceanic and continental lithosphere. Both oceanic and continental tectonics can best be understood in terms of mutual interactions between plate tectonics, rejuvenation tectonics, and continental remnants of an original ancient global-scale tectonic grid.