藏南上地壳低速高导层的性质与分布:来自热水流体活动的证据  

Characteristic and Distribution of the Partial Melting Layers in the Upper Crust: Evidence from Active Hydrothermal Fluid in the South Tibet

作　　者：李振清[1] 侯增谦[1] 聂凤军[1] 孟祥金[1] 

机构地区：[1]中国地质科学院矿产资源研究所,北京100037

出　　处：《地质学报》2005年第1期68-77,共10页Acta Geologica Sinica

基　　金：国家重点基础研究规划 973项目 (编号 2 0 0 2 CB412 60 6);国家自然科学基金项目 (编号 40 3 0 2 0 2 8)资助的成果

摘　　要：沿亚东—谷露裂谷带实施的一系列地球物理探测发现了一组地震亮点。结合其他地球物理探测剖面的资料 ,认为藏南上地壳中存在一个低速高导层 ,这些地震亮点处于这个低速高导层中。人们对这些亮点和低速高导层有两种不同的解释和认识 :一种认为是含盐的超临界流体 ;而另一种认为是地壳中的部分熔融层。由于目前缺少有效的手段和方法 ,对这个低速高导层的性质和分布范围仍只是推测。本文从藏南强烈活动的热水流体系统着手 ,尝试从另一个角度探讨这些地震亮点和低速高导层的性质。通过对热泉气体的 He同位素组成和热水的地球化学特征研究以及前人对温度场的模拟表明 ,该低速高导层的性质为硅酸盐岩浆熔体 ,不是以水为主的流体 ,这就为部分熔融层的存在提供了佐证。本文进一步讨论了该部分熔融层对热泉流体系统的驱动热机作用 ,并根据热泉流体的温度场限定了此部分熔融层的空间分布范围。During the process for carrying out of a series of geophysical probe, a suit of were observed along the Yadong—Gulou rift valley zone. Combining with data from other geophysical sections, a low velocity-high conductivity layer was recognized in the upper crust in the southern Tibet. These seismic bright spots do lie in the low velocity-high conductivity layer. For these bright spots and the low velocity-high conductivity layer, there are still two kinds of understandings and opinions: one is saliferous supercritical fluid; the other is partial melting layer of the upper crust. Due to lack of effective means and methods, their characteristic and distribution were still guessed. Based on the research on the violent hydrothermal activity of the south Tibet, this paper made an attempt to discuss the characteristic of these bright spots and low velocity-high conductivity layer from other point. The research on helium isotope composition of hot spring's gas, geochemical characteristic of spring water, and former modeling for temperature field suggest that the low velocity-high conductivity layer was composed of rather silicate magma than water fluid. Theses research provide new evidences for exist of the partial melting layers. What's more, this paper discusses how the partial melting layer driving the active hydrothermal system to circulate and flow, At last, and restrict the spatial distribution of the partial melting layer based on the distribution of hot springs and temperature field.

关 键 词：高导层 部分熔融 上地壳 流体活动 地球物理探测 地震 裂谷 自热 超临界流体 熔体 

分 类 号：P542[天文地球—构造地质学]