摘要
岩石圈-软流圈界面(The Lithosphere-Asthenosphere Boundary,LAB)是地球内部主要界面之一.大地电磁测深(Magnetotelluric,MT)是研究地球壳幔电性结构最有效的方法,利用长周期大地电磁测深数据可以较好地探测LAB.在SinoProbe-01-03课题的资助下,首次获得了华南地区4°×4°网度的高质量大地电磁测深数据.利用一维奥卡姆(Occam)算法反演了MT阻抗的反对角线元素所计算出的平均视电阻率.根据一维地电结构可以将华南地区岩石圈划分为五种类型:以湖南邵阳和贵州施秉为代表的克拉通型,以四川达州和彭州及湖北荆门为代表的构造边界型,以浙江湖州和广东云浮为代表的岩石圈中等改造型,以江西赣州、广东揭阳及福建霞浦为代表的岩石圈强烈改造型,以湖北英山为代表的造山带型.除湖南邵阳、贵州施秉及广东揭阳外,华南地区岩石圈厚度为60~145km.本文研究表明华南地区岩石圈显示出南北两侧上抬、中部下凹、东部受不均匀改造的趋势,这一结果与之前发表的文献所揭示的华南地区岩石圈东薄西厚的典型特征是不同的.研究结果反映华南地区岩石圈稳定性较好,晚中生代以来的构造伸展作用对岩石圈的改造程度有限,可能主要以不同形式的软流圈底辟为主.
The lithosphere-asthenosphere boundary(LAB)is one of the main boundary of the earth′s interior.Magnetotelluric(MT)sounding is the most effective method for investigation of the electrical structure of the crust and upper mantle of the earth.LAB is feasibly detectable by using long-period MT data.The high-quality MT data had been acquired on grid of 4°×4°in South China under SinoProbe-01-03 project. We inverted the average apparent resistivity calculated from the off-diagonal elements by using one-dimension Occam's method.We interpret the recovered 1Dgeoelectric structure by classifying the lithosphere of the South China as five different types:(1)the craton type,the representive data are from Shaoyang(Hunan Province) and Shibing(Guizhou Province)sites;(2)the tectonic boundary type,the representive data are from Dazhou and Pengzhou(Sichuan Province)as well as Jingmen(Hubei Province)sites;(3) the moderate reformed lithosphere type,the representive data are from Huzhou(Zhejiang Province)and Yunfu(Guangdong Province)sites;(4)the strong reformed lithosphere type,the representive data are from Ganzhou(Jiangxi Province)and Jieyang(Guangdong Province)as well as Xiapu(Fujian Province)sites;(5)the orogenic belt type,the representive data is from Yingshan(Hubei Province)site.The lithospheric thicknesses of the South China vary from 60km to 145 km except Shaoyang,Shibing and Jieyang sites.Our results show that the lithosphere of the South China is thinner in the south and north regions,and thicker in the middle region;while the lithosphere of the South China is unevenly reformed in the east region.The results in present study are different from that of the previously published literatures,in most of which indicated that the significant characteristic of the lithospheric thickness of the South China is thinning from west to east.Our results support that the lithosphere of the South China is mechanically strong and hence stable.The tectonic extension occurred since the Late Mesozoic may limitedly reform the lithosphere of the South China,and the most possible reforming mechanism is by hot asthenospheric materials diapiring and underplating.