Magnetotelluric images of deep crustal structure of the Rehai geothermal field near Tengchong, southern China
Magnetotelluric images of deep crustal structure of the Rehai geothermal field near Tengchong, southern China
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DOI：
10.1046/j.0956-540x.2001.01568.x
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发表时间：
2001-12
影响因子：
2.8
通讯作者：
Denghai Bai;M. Meju;Z. Liao
中科院分区：
文献类型：
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作者：
Denghai Bai;M. Meju;Z. Liao
利用宽频带（0.004-4096 s）大地电磁测深（MT）资料，对印度-欧亚碰撞边缘第四纪火山岩区热海地热田的深部结构进行了研究。张量分析的数据显示弱到强的3-D效果的证据，但近似的2-D成像，我们获得了双模式MT响应的假设的走向与区域规模的故障的趋势一致，并在长时间的主阻抗方位角。随后使用不同的方法对数据进行了反演。快速弛豫反演模型是可比的深度转换不变的阻抗相位数据构造的部分。采用不同初始模型的全域二维共轭梯度反演结果是一致的，并显示出一个由导电帽（50-1000 Ωm）组成的圆顶状结构，该帽在已知地热田的中心部分约5-6 km厚，向外增厚约15-20 km。该异常结构位于电阻率为20-30 Ωm的中地壳带上，向下延伸至约25 km深度，此处似乎存在中等电阻率（> 30 Ωm）的下层。MT图像显示，在雅阁出版的地质，同位素和地球化学的结果，建议存在的岩浆体下的研究领域。
Broadband (0.004–4096 s) magnetotelluric (MT) soundings have been applied to the determination of the deep structure across the Rehai geothermal field in a Quaternary volcanic area near the Indo-Eurasian collisional margin. Tensorial analysis of the data show evidence of weak to strong 3-D effects but for approximate 2-D imaging, we obtained dual-mode MT responses for an assumed strike direction coincident with the trend of the regional-scale faults and with the principal impedance azimuth at long periods. The data were subsequently inverted using different approaches. The rapid relaxation inversion models are comparable to the sections constructed from depth-converted invariant impedance phase data. The results from full-domain 2-D conjugate-gradient inversion with different initial models are concordant and evoke a picture of a dome-like structure consisting of a conductive ( 50–1000 Ωm) cap which is about 5–6 km thick in the central part of the known geothermal field and thickens outwards to about 15–20 km. The anomalous structure rests on a mid-crustal zone of 20–30 Ωm resistivity extending down to about 25 km depth where there appears to be a moderately resistive (> 30 Ωm) substratum. The MT images are shown to be in accord with published geological, isotopic and geochemical results that suggested the presence of a magma body underneath the area of study.