赣南燕山早期双峰式火山-侵入杂岩的Rb-Sr同位素定年及意义

Rb-Sr ISOTOPIC DATING AND SIGNIFICANCE OF EARLY YANSHANIAN BIMODAL VOLCANIC-INTRUSIVE COMPLEX FROM SOUTH JIANGXI PROVINCE

通常认为中国东南大陆中生代时地壳裂解作用发生在燕山晚期。对赣南地区广泛分布的双峰式火山岩和A型花岗岩进行了Rb -Sr同位素定年研究 ,确定基性端元玄武岩的Rb -Sr等时线年龄为 170～ 180Ma ,酸性端员流纹岩和A型花岗岩的Rb -Sr等时线年龄为 160～ 180Ma ,表明它们形成于中侏罗世早期。由此提出东南大陆中生代时最早的裂解作用应该始于燕山早期。

There are many granite bodies and bimodal volcanic sedimentary basins near the Pacific coast in Zhejiang and Fujian Provinces. The Rb-Sr isochron ages of the A type granites and bimodal volcanic rocks range from 90 to 110 Ma. Therefore, it is commonly thought that the Southeast China Continent broke up during late Yanshanian period (Cretaceous). However, there also widely exist bimodal volcanic sedimentary basins and A type granite bodies in south Jiangxi Province. These bimodal rocks are regionally similar to those observed in northeast Guangdong and southwest Fujian Provinces. They generally form an EW trending bimodal volcanic rock belt, extending for more than 200 km. The Rb-Sr isotopic dating on the bimodal volcanic rocks and A type granites show that the Rb-Sr isochron ages of basalts range from 173Ma to 179Ma, rhyolites and A type granites are 165Ma and 176Ma respectively. It is suggested that the rifting took place twice during the Mesozoic era in Southeast China Continent and the earliest rifting occurred in the early Yanshanian period (Jurassic).