56Ma:华南岩石圈伸展和南海张开的重要转折时间

56 Ma:An Important Transition Age for Extension of the Cathayisan Lithosphere and Open of the South China Sea

广东四会 吴川断裂带茂名、三水、河源、连平 南雄等盆地火山岩的年代学、岩石学和钕同位素资料表明 ,在 92～ 38Ma存在连续的火山作用 ,并在始新世早期 (约 5 6Ma)火山作用源区从下地壳突然转向上地幔 ,标志着华南岩石圈在这一时间出现大规模伸展减薄。这一重大转折事件与菲律宾海、南海等东亚边缘海盆的最早张开密切相关。

Geochronological and geochemical evidence indicate that there occurred continuous volcanism during 92-38 Ma in the Maoming and Sanshui basins in Guangdong. However, their source regions sharply changed from the lower crust to the upper mantle in the Early Eocene(56±2*!Ma). The first stage open of the border sea basins in East Asia also occurred since 56 Ma. Thus, there were tight relationships between extension of the Cathayian lithosphere and spreading of the border sea basins. A series of pull-apart basins in Cathaysian Block along shear fault of NE striking as well as Proto-South China Sea, Celebes Sea and West Philippine Sea with spreading ridge of NE direction were formed during Eocene.