中国东南地区岩石圈热结构特征及其构造意义

Thermal Structure of the Continental Lithospheric in Southeast China and Its Tectonic Implications

中国东南地区地质演化复杂,中—新生代构造变形强烈,岩石圈深部热力学状态及其对构造活动的影响有待深入。文章结合最新的大地热流数据与地壳结构Crust 1.0模型,利用稳态热传导方程,以岩石捕虏体温压数据和地震学观测为约束,构建了华南地区扬子克拉通、华夏地块以及南海北缘等不同单元的岩石圈热结构。结果表明该区岩石圈热结构存在强烈的不均一性:除了上扬子地区(四川盆地)为“温壳温幔”的热结构,华南其他大部分地区都表现为“热壳热幔”的特征;同一深度下,华夏地块与南海北缘的深部温度显著高于扬子克拉通;热岩石圈厚度从克拉通内部向沿海地区(NWSE)逐渐降低,也即由四川盆地的~200 km减少到华夏地块的~110 km,再到南海的~70 km。此外,我们还发现陆内地震的分布与岩石圈温度密切相关,地震活动集中分布于600℃等温线以内。总体而言,扬子克拉通中西部岩石圈热结构具有冷而厚的特征,而华夏地块和南海北缘受古太平洋平板俯冲和新生代大陆边缘构造—岩浆作用的改造,表现为热且薄的特征,岩石圈的热弱化进而加速了华南大陆边缘的裂解及随后的南海扩张过程。

Southeast China is tectonically characterized by complex geological evolution and intensive Mesozoic-Cenozoic intracontinental deformation.The thermal structure of the continental lithosphere in SE China and its influence on tectonics still remain open.Here we combine the latest heat flow data with the Crust 1.0 model to construct the lithospheric thermal structure for the Yangtze Craton,Cathaysia Block and South China Sea,using the steady-state heat conduction equation,and constrained by independent xenolith and seismological observations.The results show that the thermal structure is of strong heterogeneity in SE China.Most regions are indicative of a‘hot crust and hot mantle’thermal structure,except for the Upper Yangtze Region(e.g.Sichuan Basin),where the type of‘warm crust and warm mantle’exists.The deep temperatures in the Cathaysia Block and South China Sea are significantly higher than those of the Yangtze Craton at the same depth.The thermal lithosphere thins gradually southeastward from~200 km in the craton interior to~110 km in the Cathaysia Block and then to~70 km in the South China Sea.In addition,the distribution of intracontinental earthquakes is found to be closely related to temperature,i.e.seismicity mainly occurs within the 600℃isotherm.In general,the central-western Yangtze Craton is of cold and thick lithosphere,while the Cathaysia Block and the northern South China Sea is of hot and thin lithosphere,as the results of the Paleo-Pacific plate flat subduction and Cenozoic magmatism in the continental margin.The inherited thermal weakening facilitated the rifting of the SE China continent margin and the subsequent opening of the South China Sea.