我国喜马拉雅山中段地区风化壳类型及其地球化学特征

喜马拉雅山是地球上最高大与最年轻的山脉之一。自第三纪以来,随着海洋历史的完结和不断上升,自然环境发生了巨大变化,尤其第四纪时期,本区古气候的变化更为引人注目。地壳表层岩石在各地质历史时期和高山气候环境下,曾经受过种种不同程度的风化作用,与陆地表面物质重新分异和组合的同时,各种化学元素也相应地发生过迁移和富集。因此,作为特定气候产物的风化壳类型和地球化学内容都是富有特色的。

TYPES OF WEATHERING CRUST AND THEIR GEOCHEMICAL CHARACTERISTICS IN CENTRAL HIMALAYAS, CHINA

On the basis of geological observation and laboratory analysis of some samples of rock and soil from four typical profiles of the weathering crust in Central Himalayas, southern Xizang, the auther of this paper has come to the following conclusions:1. The different types of weathering crust are distributed on various level of the Himalayas on account of the uplift of Himalayas and climatic change during Quaternary.2. Each typical profile of the weathering crust has clearly zonal feature and each zone both in chemical components and in minor element contents differs from each other.3. The distribution and enrichment of chemical elements are closely related to rock types and mineral assemblages of the related weathering crust as well as to the climatic conditions. Under the sub-tropical climatic condition for southern slope of Himalayas, SiO2 was partly lost from the weathering crust in the early stage of its development. The contents of SiO2, Fe2O3 and Al2O3 are higher than those for other three profiles of weathering crust.4. In this four profiles of weathering crust the contents of minor elements appear to be lower. The most strongly concentrated are Ti and Ba. The less enrichment are Zr and V. Moreover, an evident indication of increase of Ti and B from south to north slopes of Himalayas is observed.5. According to the features of distribution of chemical elements, the weathering crust can be divided into two distinct large types, i.e. progressive and retrogressive. In upper profile of retrogressive type of weathering crust Fe+++ is reduced into Fe++ and a great amount of Illite mineral is herein found.6. Under the influence of climatic and environmental changes the different geo-chemical process of weathering is related to different alpine superficial zone.