秦岭造山带与渭河地堑地电结构研究

Electrical structure study on the Qinling orogenic belt and Weihe graben

秦岭造山带作为典型的陆内复合造山带，发生过强烈的构造变形，与北部的渭河地堑形成独具特色的盆山构造体系，目前其深部结构状态与盆山耦合响应缺乏深层动力学过程的理解，为此以跨越秦岭造山带、渭河地堑布设一条170km的大地电磁测深剖面，通过宽频带和长周期大地电磁观测，构建秦岭造山带和渭河地堑深部地电结构，研究结果表明：1）秦岭造山带存在多重叠置的巨厚岩石圈，南秦岭与北秦岭地壳尺度存在明显的结构化差异；2）扬子地块向北楔入到南秦岭岩石圈地幔中，南、北秦岭之间在上地幔存在低阻条带痕迹表明了楔入作用的前缘位置；3）渭河地堑存在巨厚的沉积盖层，厚度由南向北逐渐减薄，由南侧的7～8km减到北侧的3—4km。渭河地堑下地壳至上地幔区域分布的两个低阻块体表明其岩石圈存在明显的电性差异，这种差异性的存在表征了华北地块南向挤压作用背景下软流圈上涌的贡献。

The Qinling orogenic beh is a typical intracontinental orogenic belt which has experienced strong deformation. The Qinling orogenic belt and the Weihe graben located in the north formed the unique basin-mountain system. However, the deep structure and the mechanism of basin- mountain system coupling is not clear for lacking of the comprehension of deep dynamics. A 170 km magnetotelluric profile across the Qinling orogenic belt and the Weihe graben was conducted. We finally constructed a deep electrical structure model of Qinling orogenic belt and Weihe graben through broadband and long-period magnetotelluric observation. The research reveals： 1）The multiple superimposed thick lithosphere exists in the Qinling orogenic belt and there is an obvious architecture difference between the South Qinling and the North Qinling; 2） The Yangtze block wedged into the mantle of South Qinling and the wedge front is characteristic by the low-resistivity layer between the South and North Qinling orogenic belt; 3）The thick sedimentary cover layer pinches gradually from south to north, from 7 - 8 km north to 3-4 km south. The existence of two low-resisitivity block located in the lower crust and upper mantle indicates the lithospheric electrical structure difference, which manifests the asthenosphere upwelling under the background of the North China block.