Electrical Property of Deep Structure in Songpan-Aba District
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摘要: 针对青藏高原东部特殊的“三角形”区域——松潘-阿坝地区, 通过两条测线的MT资料分析和反演, 对其深部电性特征进行了揭示, 发现松潘-阿坝区中深层构造较为稳定, 层状特点明显, 地下电性横向变化小, 具有稳定地块的特点.这里存在壳内低阻层, 厚度近10~20km; 深部(岩石圈地幔内部) 的电性结构也有两种类型: 高阻异常区和具有幔内低阻层的次高阻异常区, 全区岩石圈厚度在120km左右, 其四周由深断裂与邻区接触.该区深部电性特征不同于龙门山隆起的电性结构, 也不同于西秦岭构造带, 后者具有高阻基底, 岩石圈厚度或更薄或加厚.Abstract: The magnetotelluric sounding (MT) surveying was recently conducted in the Songpan-Aba district in the northwest of Sichuan, a "delta" specific to the eastern part of the Tibetan plateau. The analysis of the two crossed MT inversion sections reveals a relatively stable block in the middle and deep structures of the Songpan-Aba district with conspicuous layers and few changes in electrical property. A low-resistivity layer about 10-20 km deep was found inside the crust. The electrical property of the deep layer (inside the mantle of the lithosphere) is classified as two types: the high-resistivity anomaly zone and the sub-high-resistivity anomaly zone with the low-resistivity layer inside the mantle. The corresponding lithosphere is about 120 km, so that the deep faults of the district contact their adjacent zones in all directions. The value of resistivity below the crust and upper mantle of the lithosphere is lower than that in its adjacent zones. The electrical property of the deep layer in this district is different from that in the uplifted Longmen Mountain, and also from that in the West Qinling structural zone characterized by both the high-resistivity basement and the thicker or thinner lithosphere.
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图 3 西秦岭南部隆起与松潘-阿坝区交接处MT曲线特征
Fig. 3. MT curves in the adjacent area of south uplift area of West Qinling and Songpan-Aba area
图 4 A线(a) 和B线(b) 视电阻率断面图
Fig. 4. Cross-sections of apparent resistivity of survey profiles A and B
图 5 A线MT资料反演结果断面图
上部实线为莫霍面, 下部实线为岩石层底界面, 两条虚线之间为低阻层
Fig. 5. MT inversion result of profile A
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