Structural styles and chronological evidences from Dulong-Song Chay tectonic dome: Earlier spreading of south china sea basin due to late mesozoic to early cenozoic extension of south china block

Abstract

The South China Sea basin expanded firstly from Late Mesozoic to Early Cenozoic, and then at 32-17 Ma. The second stage of extension formed immediately after the first stage, and both extensions are consistent with the forming mechanism. New structural analysis and geochronological data are both inconsistent with the current models of backarc extension and extension by strike-slip fault. New data of structural styles and geochronometry in the Dulong-Song Chay metamorphic dome indicate at least two epoches of major extensional tectonics: the D 2 deformation of the rising and exhumation of the dome occurred at 237-228 Ma; and the D 2 deformation overprinted and re-deformed on the dome at 86-78 Ma. Of them, the D 2 deformation shows a consistent forming time, extensional direction and tectonic regime amongst the Dulong-Song Chay dome, South China block and the north margin of the South China Sea basin. Regional geology shows that the north margin of the South China Sea basin belongs to the South China block. Therefore, we interpret that the Late Mesozoic to Early Cenozoic extensional tectonics occurred in the north margin of the South China Sea basin as a result of the interplate deformation of the South China block The Ailaoshan-Red River sinistral slip strengthened the Cenozoic extension in the South China Sea.