Geochronological and geochemical constraint on the Cenozoic extension of Cathaysian lithosphere and tectonic evolution of the border sea basins in East Asia

摘要

Geochronological and geochemical evidence indicates that continuous volcanism occurred from 92-38 Ma in Maoming and Sanshui basins in Guangdong. However, the source regions changed sharply from the lower crust to the upper mantle at 56 ± 2 Ma. That change might have been related to the time when India began to collide with Tibet (at ca. 55 Ma). The first stage of opening of border sea basins to East Asia also occurred ca. 56 Ma. A set of pull-apart basins in the Cathaysian block as well as the proto-South China Sea, Celebes Sea and West Philippine Sea were formed during Eocene (53-34 Ma). Indochina was extruded through left-lateral slip along the Red River fault between 35-17 Ma, which interrupted the NE directed shear extension in East Asia. No basaltic magmatism related to extension erupted during this interval. Significant extension of the lithosphere occurred along a NE strike in the Cathaysian block, East Sea and Japan Sea since 17 Ma, which also changed the movement direction of the Indochina block from left-lateral to right-lateral slip. The South China Sea possibly opened again during this stage. Isotopic geochemical features of the mantle beneath the border seas are distinct from those of the Pacific Plate and resemble those of the Indian Ocean domain.