华南岩石圈三维结构

3D Lithospheric structure of South China

从穿过华南陆块的6条P波地震层析剖面出发,综合引用海量出版物中部分成果,对华南岩石圈三维结构作了初步探讨。以川湘黔裂陷槽和钦杭断裂为界,可以将华南岩石圈分成三大部分。在钦杭断裂东南为华夏岩石圈。它是东南亚西太平洋低速带的一部分,它与东南亚西太平洋低速带的其他地区的共同特点是它们的岩石圈地幔都受到软流圈物质上升而被改造。部分地区幔源物质侵入地壳,形成丰富的矿藏。川湘黔裂陷槽以西的地区为上扬子岩石圈。它在地表是一个热块体,但在深部有延伸超过200 km的高速基底。上扬子岩石圈受到其西攀西地幔柱的改造,在壳幔过渡带产生峨眉山岩浆房,在古生代末曾引发玄武岩的大面积喷发,至今仍在滇西留有岩浆房,并产生丰富的热泉。在川湘黔裂陷槽与钦杭断裂之间的是中扬子岩石圈。中扬子在地表是一个冷块体,在湘中实测热流值低到小于20 mW m-2,根据热流值计算得到的岩石圈厚度达到300 km。具有低速、低电阻率特征。根据大地电磁测深得到的结果也与地热流计算得到的相似。

Starting with 6 P wave tomography profiles across the South China block,the authors approached 3D structure of the South China lithosphere.The South China block can be divided into three parts bounded by Qin-Hang fault zone and Chuan-Xiang-Gui rift.To the southeast of Qin-Hang fault zone there is Cathaysia lithosphere which is a part of the SE Asia-West Pacific low velocity lithosphere,formed by intrusive uplifting of ashenospheric materials.To the west of Chuan-Xiang-Gui rift is the Upper Yangtze lithosphere,which is hot near the surface but has a high velocity root at depth.On the west part of upper Yangtze block,Paleozoic mantle plume in the Panxi area formed a magma chamber at the crust-mantle transformed zone,resulting in basalt eruption in vast areas.Between the Chuan-Xiang-Gui rift and the Qin-Hang fault zone is mid-Yangtze lithosphere,which is cold and whose resistivity is low.The thickness calculated by heat flow and magnetotelluric sounding reached 300 km.