青藏高原电性结构及其对岩石圈研究的意义

Electrical conductivity structure of the Qinghai-Tibet Plateau and its significance for the study of the lithosphere

在西藏近南北向布设了横跨青藏高原的3条大地电磁测深剖面(亚东-雪古拉、达孜-巴木错、那曲-格尔木),采用超宽频带大地电磁测深方法进行了地壳、上地幔电性结构探测研究,发现该剖面具有的主要电性结构特征为:①那曲以南地段,电性层比较薄,低阻体多呈串珠状断续分布,产状明显北倾,倾角为20°～30°。②那曲—雁石坪地段,电性层厚度有所增加,低阻体或高阻体呈近于水平薄板状分布。③雁石坪以北地段,电性层厚度较大,低阻体呈大透镜体状较连续地向南倾,倾角40°左右。④3个地段的电性层差异明显,与构造背景和岩浆活动性关系密切。以上电性特征为研究印度板块和欧亚大陆碰撞机制提供了地球物理依据。

Three nearly N-S-trending magnetotelluric （MT） sounding profiles （Yadong-Xuegula, Dagze-Bam Co, Nagqu-Golmud） were deployed across the Qinghai-Tibet Plateau to detect and study the electrical conductivity structure of the crust and upper mantle using the superwide band MT method. The main characters of the electrical conductivity structure along the three profiles are as follows： （1） in the segment south of Nagqu, the electrical layer is thin, and the low-resistivity bodies are mostly distributed discontinuously in the form of a string of beads and apparently dip north at 20°- 30°; （2） in the segment between Nagqu and Yanshiping, the thickness of the electrical layer is increased, and the low- or high-resistivity bodies occur as subhorizontal thin sheets; （3） in the segment north of Yanshiping, the electrical layer is thicker, and the low-resistivity bodies occur as big lenses dipping south relatively continuously at -40°; and （4） the features of the electrical layers in the three segments are markedly different and closely related to the regional tectonic setting and magmatic activity. These important electrical characters provide important geophysical evidence for studying the mechanism of India-Eurasia collision.