青藏高原岩石圈三维电性结构

本文报道通过综合大地电磁调查数据研究青藏高原岩石圈三维电阻率模型的初步成果.大地电磁法调查区域已经覆盖了高原大部分面积,为全区三维电阻率成像研究打下了可靠的基础.对多个测区大地电磁数据进行精细的同化处理和反演成像,取得了青藏高原可靠的岩石圈三维电阻率结构图像.成像的区域为28°N—35°N,80°E—104°E.三维反演计算时采用的网格尺寸为20km×20km,垂直方向不等间距剖分为26层.结果表明,青藏高原现今岩石圈电阻率扰动主要反映印度克拉通对亚欧大陆板块俯冲引起的热流体运动和大陆碰撞和拆离产生的构造.在岩石圈地幔,察隅地块、喜马拉雅地块和拉萨地块东部联成统一的高电阻率地块,它们反映了向北东俯冲的印度克拉通.雅鲁藏布江、班公—怒江和金沙江缝合带都有明显的低电阻率异常,表明岩石圈深处有热流体活动.雅鲁藏布江、班公—怒江和金沙江缝合带都有明显的低电阻率异常,也表明它们的岩石圈还有流体活动.青藏高原东部的低阻区沿100°E向地幔下方扩大,反映了金沙江断裂带有切穿岩石圈的趋势.地幔电阻率平面扰动的模式显示,青藏高原东西部的地体碰撞拼合形式和方向是不同的.在青藏高原西部,羌塘、拉萨和喜马拉雅等地体从北到南碰撞拼合.在青藏高原东部,羌塘—拉萨、察隅、印支、雅安和扬子等地体多方向拆离拼合,在地壳造成不正交的拆离带和压扭构造系.从高阻-低阻区的分布看,东部的地体拼合有地幔的根源,今后还会进一步发展.察隅地块岩石圈对青藏高原东部的楔入,使其北部和东部地块的岩石圈发生拆离撕裂,也造成热流体上涌的低电阻率异常.

The three-dimensional resistivity structures of the lithosphere beneath the Qinghai-Tibet Plateau

After multi-team researches in relays, our magnetotelluric investigations have covered most of area of Qinghai-Tibet Plateau, providing a reliable foundation for the study of three-dimensional lithosphere resistivity imaging. A reliable three-dimensional resistivity image set of the Qinghai-Tibet Plateau is obtained by fine assimilation, fusion, processing and inversion of the magnetotelluric data. The imaging area is 28°N-35°N and 80°E-104°E. The mesh size used in the three-dimensional inversion is 20 km by 20 km, the vertical direction is divided into 26 layers with the unequal spacing down to 200 km. The results show that the current lithospheric resistivity anomalies in the Qinghai-Tibet Plateau mainly reflects the thermal fluid movement caused by the subduction of the Indian craton to the Eurasian Plate. In the lithosphere mantle, the Zayu block, the Himalaya block and the eastern part of the Lhasa block are linked to a unified high resistivity anomaly, which reflects the Indian craton subduction to the northeast. The low resistance zone in the eastern Qinghai-Tibet Plateau expands downwards along the 100°E, reflecting the trend of the Jinsha River fault zone cutting through the lithosphere. The disturbance patterns of mantle resistivity clearly show that the splicing format of terranes in the east and west parts of the Qinghai-Tibet Plateau is different. In the western part of the Qinghai-Tibet Plateau, the terranes of Qiangtang, Lhasa and Himalaya are combined along direction from north to south. In the eastern part of the Qinghai-Tibet Plateau, Qiangtang-Lhasa, Zayu, Indochina, Yaan and Yangtze terranes are combined along direction from west to east. The combination of the west terranes has occurred first, and a wide range of deformation structures have been formed in the crust, including orthogonal detachment bands and rift systems. In the east part, the terranes have been combining afterwards, extensive deformation is being caused in the crust, including the non-orthogonal disassembly belts and the pressure-rotational tectonic systems. From the distribution pattern of the high-to-low resistance zones we see that the geological processes going on the east Qinghai-Tibet Plateau has a deep mantle roots, which will further develope in the future.