Paleocene–early Eocene post-subduction magmatism in Sikhote-Alin (Far East Russia): New constraints for the tectonic history of the Izanagi-Pacific ridge and the East Asian continental margin

摘要

New isotopic, geochemical and geochronological data justify the widespread occurrence of middle Paleocene to early Eocene (60–53?Ma) post-subduction felsic magmatism across the entire Sikhote-Alin territory (southeastern Russia), conform with previous observations in Northeast China, the southern Korean Peninsula, and the Inner Zone of Japan. This igneous activity in East Asia coincided with the reactivation (after tectonic quiescence between ~93–60?Ma) of left-lateral strike-slip displacements along the Tan-Lu and Central Sikhote-Alin faults and with the post-60?Ma cessation of subduction/accretion recorded in the Shimanto belt of SW Japan. The Sikhote-Alin post-subduction igneous A-type rocks present diverse mineralogical and geochemical features that suggest interactions of the subducting plate with anhydrous mantle upwelling through slab tears in the continental margin. The middle Paleocene–early Eocene magmatism is not related to subduction but is synchronous with strike-slip tectonics and the termination of accretionary prism development, suggesting a shift in tectonic regime from oceanic plate subduction at a convergent margin to parallel sliding and initiation of a transform continental margin. These new observations are inconsistent with the current tectonic model of 60–50?Ma Izanagi-Pacific ridge subduction beneath East Asian continental margin.