华南地区樟树—宁德大地电磁测深剖面深部电性结构及热特征

华南地区武夷隆起带及东南沿海陆缘带具备中高温地热的储藏条件, 而深部热源及热通道对于揭示中高温地热的形成机制至关重要.本文对江西樟树—福建宁德包含37个宽频测点的一条410 km长大地电磁测深剖面, 采用非线性共轭梯度二维及三维反演, 获得了岩石圈电性结构模型.研究发现, 扬子地块东缘、武夷隆起带以及东南沿海陆缘带的电性结构存在明显的横向差异性; 武夷隆起带广泛存在地壳尺度的高导体, 东南沿海陆缘带存在壳幔尺度的高导体.结合地表大地热流及华南地区构造演化特征, 本文认为武夷隆起带和东南沿海陆缘带具有不同的热源机制, 即武夷隆起带的热源主要分布在Moho以上, 而东南沿海陆缘带热源来自岩石圈地幔, 二者的热通道具有统一的形式, 均受控于华南地区北东向深大断裂带.基于热源与热通道分析, 本文认为华南地区高温地热的深层动力学机制与古太平洋板块西向俯冲的挤压环境及后撤作用下的伸展环境有关.

The deep electrical structure and thermal characteristics of the Zhangshu-Ningde magnetotelluric profile in South China

The Wuyi uplift belt in South China and the coastal continental margin zone of southeast China possess the storage conditions for medium and high temperature geothermal heat, and the deep heat source and heat channel are essential to reveal the formation mechanism of medium and high temperature geothermal heat. In this study, a lithospheric electrical structure model is obtained by using two-dimensional (2D) and three-dimensional (3D) inversion (nonlinear conjugate gradient) on a 410 km magnetotelluric profile containing 37 sites from Zhangshu, Jiangxi province to Ningde, Fujian province. It is found that significant horizontal differentiation exists in the electrical structure of the eastern margin of the Yangzi block, the Wuyi uplift zone, and the coastal continental margin of southeast China. There are a large number of high conductors in the crust of the Wuyi uplift belt and in the crust-mantle of the southeast coastal continental margin zone. Combined with the surface heat flow and the characteristics of tectonic evolution in South China, we proposed that the Wuyi uplift belt and the southeast coastal continental margin zone have different mechanism of heat source. The heat source of the Wuyi uplift belt is mainly distributed in the crust, while the southeast coastal continental margin zone's heat source is derived from the lithospheric mantle. Their heat channels are unified and both are controlled by the northeast trending fault zone in South China. Based on the analysis of heat source and heat channel, it is concluded that the deep dynamic mechanism of high-temperature geothermal in South China is related to the extruding and extensional environment of the westward subduction and roll back of the Paleo-Pacific plate.