南海热流特征及其构造意义

根据南海 592个热流数据 ,为克服热流站位分布不均及局部异常热流的影响 ,结合各单元的地质史及其地壳厚度等资料对研究区热流特征进行了详细分析。结果表明 ,具拉张背景的区域如北部陆缘、湄公盆地以及北巴拉望盆地具有中等偏高热流 ;海沟区热流相对较低 ,东部海沟区除台西南盆地外均为低热流区 ,而南部边缘东段古海沟区处于热恢复中 ;南部边缘西区因边界断裂的扭张及深部热源的异常补给而具高热流 ;属于剪切断裂带的西部陆缘也具高热流特征 ;中沙—西沙地区热流中等偏高 ,并由NW往SE方向增加 ,而南沙地区热流较低 ,约为 60mW·m- 2 ;海盆的热流基本满足随洋壳年龄增加而降低的规律 ,东部次海盆实测热流与理论预测基本一致 ,而西南次海盆实测热流普遍低于预测值 ;在南海北部下陆坡区识别出一条高热流带 ,该带与前人给出的海盆北缘断裂带位置基本一致。研究区不同区域地热特征直接或间接地受控于其所处的构造环境。据此 ,给出了研究区的热流趋势图。

HEAT FLOW CHARACTERISTICS AND ITS TECTONIC SIGNIFICANCE OF SOUTH CHINA SEA

Up to 592 of heat flow data were collected in the South China Sea (SCS). To overcome the influences of uneven distribution of heat flow stations and local abnormalities of heat flows, the tectonic evolution histories of different areas and their crustal thicknesses are combined in analyzing their geothermal characters. The results show that, the stretched areas such as the northern margin, the Mekong Basin and the north Palawan Basin, have mid--high heat flows; heat flows in the trench areas are lower and are very low in the eastern margin except the SW Taiwan Basin, while heat flows in the eastern part of the southern margin, which is a paleo-trench, are now recovering; heat flows are very high in the western part of the southern margin because of the striking and stretching of the border faults and abnormal heat supplied from the depth; heat flows in the western margin are also very high due to the activities of the strike faults; heat flows in the Zhongsha-Xisha block increase from NW to SE, while heat flows in the Nansha block are lower, about 60 mW m 2; heat flows in sea basins decrease with the increase of crustal age, and unlike those in the east subbasin, heat flows in the SW subbasin are generally lower than the predicted; Especially, one high heat flow zone trending in E-W is firstly recognized in the lower slope area in the northern margin, which coincides nearly with the northern marginal fault zone of the SCS. These analyses show that the geothermal characters of different regions are controlled directly or indirectly by their own tectonic backgrounds, based on which a heat flow trending map is given.