VARIATIONS IN ISOTOPIC COMPOSITIONS OF CHLORINE IN EVAPORATION-CONTROLLED SALT LAKE BRINES OF QAIDAM BASIN, CHINA

摘要

The variations in the isotopic compositions of chlorine in evaporation-controlled saline lake brines were determined by using an improved procedure for precise measurement of chlorine isotopes based on Cs_2Cl~+ ion by thermal ionization mass spectrometry. The results showed that variation in δ~37 Cl values in these evaporation-controlled brines are attributable to evaporation of brine accompanied by the deposition of saline minerals. The isotopic fractionation of chlorine between the deposited saline mineral and the co-existing brine caused the variation of δ37 Cl values in the brine. In general the isotopic fraction- ation of chlorine in nature indicates enrichment of 37~Cl in the solid phase relative to 35~Cl. The reverse isotopic fractionation of chlorine in which 35~Cl is enriched in the solid phase, was observed to some ex- tent during quick deposition under laboratory conditions as well as in nature. The mechanism of isotopic fractionation of chlorine during evaporation deposition was studied.