青海可可西里盐湖水化学及硼同位素地球化学特征

摘要

本文主要依据2009—2010年间的考察对可可西里地区盐湖进行了水化学及硼同位素分布特征研究。结果表明，除前人发现的5个盐湖外，可可西里东部新发现的多秀湖、茶错、布查湖和果木错玛德日4个湖泊也属于盐湖；勒斜武担湖为氯化物型盐湖，其余8个盐湖均为硫酸盐型盐湖；盐湖及周围水体皆富集 B、Li 元素，形成以盐湖为中心的含量高值区，且 B-Li 元素对显示出协同消长关系，表明在该地区这两种元素的物质来源、搬运条件及富集环境具有相似性；正热电离质谱法测量结果显示，本区盐湖δ11B 值的变化范围在+4.77‰~+12.52‰之间，远低于海水δ11B值，证明这些盐湖均属陆相成因，与前人对青藏高原地区盐湖成因的研究结果相一致；勒斜武担湖和布查盐湖北部均出露有大量泉水，水化学分析和硼同位素分析数据表明，勒斜武担湖和布查盐湖分别与各自周围的泉水具有同源性，认为这些泉水是这两个盐湖的主要物质来源；根据区域地质构造特征和硼同位素地球化学数据，可判断出新青峰喷泉中的硼主要来自于深部火山岩溶滤。%A study of the hydrochemical characteristics and boron isotope distribution of salt lakes in Hoh Xil region was conducted on the basis of the survey in 2009 and 2010. Besides the Mingjing Lake, Xijinwulan Lake, Lexiewudan Lake, Salt Lake and Cangcuo Lake discovered earlier, the Duoxiu Lake, Chacuo Lake, Bucha Lake and Guomucuomaderi Lake are all salt lakes discovered recently, whose salinities are equal to or higher than 50 g/L. These discoveries have brought the total number of salt lakes in this region to 9. Except for the Lexiewudan salt lake, which is of the chloride type, the remaining 8 salt lakes are of the sulfate type; the boron and lithium are both abundant in the lake water and surrounding waters, and B-Li elements indicate a collaborative growth and decline relationship, suggesting that the material sources, migration conditions and enrichment environment of B is similar to characteristics of Li in this area. The results of Positive Thermal Ionization Mass Spectrometry measurements show thatδ11B values are in the range of +4.77‰~+12.52‰, by far lower than the values of seawater, implying that these salt lakes belong to terrigenous nature, which is consistent with the results of previous research on these areas. There are a large number of springs exposed on the northern bank of the Lexiewudan salt lake and Bucha salt lake, and the springs are the primary material sources of these two lakes according to hydrochemical and boron isotopic analysis. The regional tectonic features and boron isotope geochemistry characteristics reveal that the boron element in the Xinqingfeng hot spring is mainly from lixiviation of volcanic rocks in the depth.