青藏高原南北地体壳幔热结构差异的大地热流证据

HEAT FLOW EVIDENCE FOR THE DIFFERENTIATED CRUST-MANTLE THERMAL STRUCTURES OF THE NORTHERN AND SOUTHERN TERRANES OF THE QINGHAI-XIZANG PLATEAU

本文首先报道大地热流剖面测量的系统成果,进而分析南北剖面的热流分布特征及其构造热演化意义;在此基础上,结合南北各地体不同的构造变形环境所诱发的深部热作用和放射性生热、摩擦应变生热和深部热流分量等热源组分在配置上的差异,分区论述青藏高原北部、中部和南部3种不同类型的地壳—上地幔热结构。

The average thickness of the crust reaches 70 km in the Qinghai-Xizang Plateau, meanwhile the surface hydrothermal manifestations are widespread over the Himalayan Geothermal Belt. In addition, high heat flow was observed in South-Xizang, and the DSS, gravity and magnetic survey, as well as MTS all unanimously revealed a series of geophysical features of a warm crust. This compatibility of a thick yet warm crust in the Qinghai-Xizang Plateau fully evidenced geophysically has been once again proved by a N-S heat flow profile study, reflecting not only the peculiarity of the crust-mantle thermal structure, but also the close genetic relation between the deep-seated formation process of such a specific thermal structure and the tectono-dymanic environment. Thus, the first step was forwarded towards the study on the unitary thermo- tectonic evolution of the Qinghai-Xizang Plate au. The N-S heat flow profile consists of the following 13 study areas :Pum-uyiong Lake(n = 5, q=91 mW/m2), Yangzhuoyiong Lake(n=4, q=146mW/m2), Luobusha(q=60mW/m2), Northern Suburb of Lhasa(q = 66mW/m2), Maqu(q = 106mW/m2), Yanbajing(q = 108mW/m2), Yangyingxiang(q = 364mW/m2), Ladu-ogang(q=338mW/m2), Naqu(q = 319mW/m2), Lunbula(n = 2, 9 = 140mW/m2), Tuotuohe(q = 47mW/m2), Northern Foothill of Kunlun Mts. (q = 42mW/m2), and Xitieshan(q = 42mW/m2). The heat flow distribution pattern is noted with:(l)heat flow highs in South and lows in North, (2)stable in North and fluctuating in South, and(3)low heat flow belt affiliated to the Yarlung-Za-ngbo Suture Zone of bordering significance among the anomalously high heat flow regions in the south. Based on this pattern and considering the forms and boundary conditions of deformations and the heat source patterns (including shear-heating) of the different terranes, the whole Qinghai-Xizang Plateau can be divided into three parts:( 1 )cold united block of the four old terranes in north with, thick crust-thick lithosphere structure, (2) enormously squized-shortened hot Lhasa-Gangdise Terrane in the middle, accompanied by multi-layered tectonically induced deep thermal activities of thickened crust-thinned lithosphere structure, and( 3 ) overthrust-thichened warm Himalayan Terrane in south, accompanied by magmatic emplacement of anatectic type and crust-originated abnormal thermal structure of shear-heating genesis.