MT约束的青藏高原东南缘上地幔热结构研究——以兰坪—贵阳剖面为例

青藏高原东南缘是青藏高原软弱物质运移的关键位置,研究其深部结构有助于理解青藏高原的扩张机制.本文利用穿过青藏高原东南缘的一条起始于兰坪—思茅块体,穿过川滇菱形块体,终止于华南块体的长约750 km的大地电磁测深（MT）剖面的电阻率结构,基于上地幔矿物和熔融体温度与电导率的关系,获得了研究区上地幔温度结构与熔融百分比分布.结果表明,采用随深度变化的含水熔融上地幔矿物组分模型才能合理地获得整个上地幔温度;上地幔全岩含水量约4.69（40 km深度）~0.13 wt%（150 km深度）,矿物熔融百分比约0~1.4%之间,并在70 km深度附近出现了较明显的局部熔融带;上地幔温度位于400~1300℃之间,随深度加深而逐渐增加;70 km以浅的温度表现出相对强烈的横向变化,且川滇和兰坪—思茅块体的上地幔温度和矿物熔融百分比的深度平均值明显高于华南块体.

Uppermantle thermal structure in the southeastern margin of the Tibetan Plateau inferred from MT: A case study on Lanping-Guiyang section

The southeastern margin of the Tibetan Plateau is the key position for the migration of soft material, and it is necessary to study its deep structure to understand the expansion mechanism of the Tibetan Plateau. In this dissertation, based on the relationship between the temperature and conductivity of upper mantle minerals and melts, the resistivity structure of a 750 km long magnetotelluric sounding (MT) profile across the southeast edge of the Tibetan Plateau, starting from the Lanping-Simao block, passing through the Sichuan-Yunnan block and terminating in the South China block, is used to obtain the upper mantle temperature structure and melting percentage distribution model in the study area. The results show that the whole upper mantle temperature can be reasonably obtained only by using the mineral composition model of water bearing melting upper mantle that varies with depth; the whole rock water content in weight percentage in the upper mantle is about 4.69 (40 km depth)~0.13 wt% (150 km depth), the mineral melting percentage is about 0~1.4%, and there is an obvious local melting zone near 70 km depth; the temperature of the upper mantle increases with the depth, usually between 400~1300℃; the temperature above 70 km shows a relatively strong lateral variations trend, and the average values of upper mantle temperature and mineral melting percentage of Sichuan-Yunnan and Lanping-Simao blocks are significantly higher than those of South China block.