青藏高原中部2.8Ma以来的化学风化与环境演化的湖泊沉积记录

Chemical Weathering and Environmental Change Records of the Last 2.8 Ma in the Central Tibetan Plateau

对采自青藏高原中部错鄂湖泊钻孔近 2 0 0m以上深处、形成于 2 .8Ma以来的沉积岩岩芯中Sr ,Rb ,Zr含量变化及Rb/Sr ,Zr/Rb比进行了研究 ,并结合其岩性、粒度、粘土矿物组成 ,分析了该地区 2 .8Ma来化学风化的相对强度和古环境演化过程。研究表明 ,2 .8Ma来青藏高原中部的环境经历了 3个演化阶段 :在深约 197～ 170m(2 .8～ 2 .5Ma)岩性段 ,低Sr含量 ,高Rb/Sr和Zr/Rb比揭示的是较弱的化学风化过程 ,反映了与当时强烈的高原隆升运动有关 ;在约 170～ 38.5m(约 2 .5～ 0 .8Ma)段 ,高Sr含量 ,低Rb/Sr和Zr/Rb比记录的是该流域较强的化学风化阶段 ,与高原在稳定期中部总体处于温湿或凉湿的环境下的结论吻合 ;在 38.5～ 0m(约 0 .8～ 0Ma)段 ,总体Sr含量处于相对低值 ,Rb/Sr比相对较高 ,化学风化相对较弱 ,表明高原中部处于较寒冷的环境之中 ,高原整体已隆升到 4 0 0

In this paper, we provide a high-resolution vertical distribution of Sr, Rb, Zr, Rb/Sr and Zr/Rb ratios in sediments from the lake of Co Ngoin, Central Tibetan Plateau. Combined with the lithological properties, grain size and clay mineralogy, we discuss the chemical weathering process recorded in lake sediments and reconstruct the history of the weathering intensity and paleoclimatic change in the last 2.8 Ma. The sedimentary records indicate that this region experienced three environmental evolution stages: in the core depth of 197～170 m (about 2.8～2.5 Ma), the lower Sr content, higher Rb/Sr and Zr/Rb ratios indicate a strong tectonic uplift movement with a weaker intensity of chemical weathering; in the core depth of 170～38.5 m (between 2.5 and 0.8 Ma), the higher Sr content, lower Rb/Sr and Zr/Rb ratios reflect a tectonically relatively stable epoch, with a warm/cool and wet plateau climate; in the depth of 38.5～0 m (about 0.8～0 Ma), the relatively lower Sr content, higher Rb/Sr and Zr/Rb ratios record relatively lower intensity of chemical weathering, caused by a cold climatic period. The plateau was uplifted to above 4000 m above sea-level.