Ocean—Continent Transition Process Reveled by Worldwide Comparison of Crust and Upper Mantle Structures
Name
Institution
State Key Lab of Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy
of Geological Sciences, Beijing, 100037
Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029
Abstract:Based on geophysical investigations of worldwide crust and upper mantle, this paper analyzes ocean—continent transition process and lithospheric thickening process. The ocean—continent transition process contains five stages: ① crustal thickening during co expansion of an ocean, ② trench formation of and early subduction, ③ mature subduction and formation of trench—arc—basin belts, ④ convergence and migration of subduction zones, and ⑤ island—continent collision and connection to a continent. Geophysical profiles show that the crustal thickening during co expansion occurs in passive continental margins, sedimentation, magma underplating and ultra pressure hydraulic fracturing resulting in formation of trenches. After formation of trenches the passive continental margins become active, tectonic mechanics tends to subduction. In the mature subduction stage the expansion of ocean basins keeps compensation with the crustal shortening of the subduction, while opening of back arc basins or marginal seas indicates the mature subduction stage. During the post mature subduction stage, marginal sea micro plates are narrowing and subduction zones are convergence and migrating. Crowded and short subduction zones with different subduction directions can cause local extension basins, they all mix together. As crustal thickening and gravity equilibrium go on, the arc belts would uplift and finally connecting to a continent via island—continent collision, becoming a special unit of continental lithosphere, i.e. the phanerozoic eon ocean—continent zone.