南海北缘琼东南盆地热结构与莫霍面温度

相对于大陆地区,洋壳或海陆过渡区目前较缺乏岩石圈热结构方面的研究.本文依据琼东南盆地现有热流数据和相关岩石热物性参数,沿分布于盆地内不同位置的4条地震测线计算了不同圈层的热流分配关系(即热结构)及莫霍面温度.计算时根据最新的P-波速度变化分析将该区地壳分为四层,分别为沉积盖层、上地壳、下地壳及下地壳高速层.结果表明:琼东南盆地地幔热流由浅水区向深水区逐渐增加,是控制盆地现今海底热流分布的主要因素;其占海底热流平均比例为76.3±7.0%,具有典型的"冷壳热幔"的岩石圈热结构特征;莫霍面温度范围500~700℃,存在一个低温区和两个高温区,其整体分布与盆地基底以下地壳伸展减薄及断裂发育有关.

Thermal structure and Moho temperature of Qiongdongnan Basin,Northern Margin of the South China Sea

There have been a number of studies on lithospheric thermal structure in continent, but few in oceanic or continent-ocean transition zones. Based on submarine heat flow data and related petrological thermal properties available in Qiongdongnan Basin, we calculate the constitution of heat flow and deep temperature of different layers along four distinct seismic profiles. The crustal structure in this area is divided into four layers based on latest analysis of P-wave velocity variation, that is sediments.upper crust,normal lower crust and anomalous lower crust with high velocity, respectively.The results demonstrate that mantle heat flow increases from shallow water to deep water, which is the predominant factor in the current distribution of submarine heat flow in Qiongdongnan Basin. Besides, its contribution to submarine heat flow is 76.3±7.0% on average, suggesting a typical feature of "Cold Crust and Hot mantle" lithospheric thermal structure. In addition, Moho temperature beneath the Qiongdongnan Basin is mostly in the 500~700℃ range with a lower temperature region and two higher temperature regions, which is primarily ascribed to the extent of the lithospheric thinning of the northern margin and well-developed faults of the South China Sea.