川西高温水热活动区深部热结构的地球物理分析

The deep geothermal structure of high-temperature hydrothermal activity region in western Sichuan Plateau:ageophysical study

川西高温水热活动区是地热学研究的典型地区之一,该区温泉、热泉点分布广泛,这些温泉大多沿北西—南东向的金沙江断裂、德格—乡城断裂、甘孜—理塘断裂、鲜水河三条主断裂呈条带状分布.对此高温水热活动区开展地热学分析,是研究青藏高原"东构造结"深部地球动力学过程、开发利用川西高原地热资源的重要基础,具有重要的科学研究意义和实际应用价值.本文针对实测氦同位素所发现的壳幔热结构比,依据重力、航空磁法、地震资料,采用反演莫霍面、居里面深度等方法,对川西高温水热活动区的深部热结构进行了分析.同时对中高温热泉密集出露的巴塘、理塘以及康定水热活动区的典型壳幔热流构与深部背景场进行了对比研究.结果表明,地表氦同位素热流估算的深部热流结构与地球物理异常结果保持较好的对应关系.川西地区热流结构中地壳、地幔的热贡献比较接近:巴塘地区平均Q_c/Q=51.38%、理塘地区平均Q_c/Q=54.39%、康定地区平均Q_c/Q=42.42%.川西地区表现出了"温壳温幔"型的深部热结构,但温地壳背景下形成较高地表热流的原因有待进一步研究.

The high-temperature hydrothermal activity region in the Western Sichuan Plateau is located in the northeast margin of the eastern syntaxis of the Tibetan Plateau.This area is the easternmost part of the Mediterranean-Himalayan geothermal belt,and also a notable region of geothermal research.The hot springs in this region are distributed extensively along the Jinshajiang fault,Dege-Xiangcheng fault,Garzê-Litang fault and Xianshuihe fault,forming the NW-SE strip-like high-temperature hydrothermal activity area.The geothermal analysis of this high temperature hydrothermal activity area is an important foundation for studying the deep geodynamics process of the eastern syntaxis of the Tibetan Plateau,which also contributes toexploiting and utilizing the geothermal resources in the western Sichuan Plateau.In this paper,we compare the crust-mantle thermal structure acquired from the helium isotopes measurement with geophysical results of the aeromagnetic,gravity data and shear wave data.The Moho and Curie point depth is obtained by inversion.Besides,the deep geothermal structure and geophysical background are discussed in the typical anomaly area of Batang,Litang and Kangding.The result shows that the helium isotope heat flux of the surface is in accord with the geophysical anomalies.The thermal contribution of crust and mantle in the Western Sichuan Plateau is relatively close：the average Qc/Q is 51.38% in Batang,54.39% in the Litang area,and 42.42% in the Kangding area.The thermal structure pattern in this region tends to be a＂warm crust-warm mantle＂mode.The formation of high surface heat flux in the warm crust background need to be further studied.