南海南沙海槽深部热状态及其构造意义

南沙海槽是古南海俯冲消亡、南沙地块与婆罗洲碰撞的关键区域, 其构造演化史记录了南海前世今生的重要信息。为深入认识对其构造变形有重要影响的南沙海槽深部热状态, 本文首先利用热传输方程分析了滑坡体快速堆积的热披覆效应对海槽底部深水区海底观测热流的影响, 然后利用磁异常的频谱分析技术获取南沙海槽及其邻区的居里面深度。结果表明, 受沉积物快速堆积的影响, 南沙海槽底部深水区文莱滑坡范围内现今海底热流测量值仅为深部背景热流的60%~77%, 推测该区深部背景热流约为77~98mW·m^-2; 南沙海槽内居里面深度一般小于16km, 比位于其北侧的南沙岛礁区居里面深度(18~24km)小。现今南沙海槽区深部具有较高的背景热流, 该区较高的热状态与其地壳强烈减薄特征对应, 是华南陆缘裂陷和南海形成演化的结果。

Deep thermal state in the Nansha Trough of South China Sea and its tectonic implications

The Nansha Trough is a key region where the Proto-South China Sea subducted southward below the Borneo, and the Nansha Block collided with Borneo. Its tectonic evolution contains important evolutional information of previous and present South China Sea region. To further understand the deep thermal state in the Nansha Trough, which has a great effect on its tectonic deformation, with a numerical model of the thermal diffusion equation, we first analyzed the thermal blanketing effect of rapid accumulation of sediment on observed heat flow in the deep-water region of the Nansha Trough, and then calculated the Curie depths in the study area with a magnetic spectrum analysis technique. The results show that due to the thermal blanketing of rapid accumulation of the Brunei Landslide, the observed seafloor heat flow is just 60%~77% of the deep background heat flow in the deep-water region, which is about 77~98 mW·m^-2. The Curie depth in the trough region is generally less than 16 km, which is smaller than the Curie depth (18~24 km) in the Nansha Islands and Reefs. Further analyses show that the trough region is of high background heat flow, and the high thermal state in the study area is in accord with its greatly thinned crustal thickness, which is the result of continental rifting of the southern margin of South China, and the evolution of the South China Sea.