Sr-S-K同位素示踪思茅盆地深部富钾盐体的物源

Sr,S and K isotopes to tracing material sources of the deep potassium-bearing salt body in the Simao basin,southwestern China

思茅盆地2350 m以深新发现了累计厚度149 m的富钾盐体。为了厘定其成钾物质来源,本文重点对15件钾石盐岩样品的Sr、K同位素和7件硬石膏岩样品的Sr、S同位素进行了分析。结果显示样品的Sr、S、K同位素均具有海水的特征,说明该盐体的成钾物质来源为海水。^(87)Sr/^(86)Sr值分别与δ^(34)S_(V-CDT)值和δ^(41)K值负相关揭示析盐期存在陆源淡水补给蒸发盆地。淡水补给导致样品的^(87)Sr/^(86)Sr值大于母源海水、δ^(34)S_(V-CDT)和δ^(41)K值小于母源海水。混源模拟计算显示钾石盐岩中淡水补给锶元素的比例为3.3%~29.2%,硬石膏岩中淡水补给锶元素的比例不超过35.2%。淡水补给Sr、S、K元素的量较少,不足以影响我们根据相应的同位素指标对盐体母质来源的识别。本项研究综合应用传统的Sr-S同位素与新兴的K同位素示踪思茅盆地深部富钾盐体的物源,为进一步研究其成因机理提供了可靠的数据支撑。

A deep potassium-bearing salt body is first discovered in the Simao basin and it is characterized by a cumulative thickness of 149 m and burial depths of more than 2350 m.In this study,Sr,K isotope from 15 sylvinites and Sr,S isotope of the 7 anhydrock have to be analyzed by MC-ICP-MS,respectively,and it aims to determine the material sources of the salt body.The results are shown that all of the ~(87)Sr/~(86)Sr ratios,δ~(34)S_(V-CDT) values,and δ~(41)K values indicate that seawater provided potassium sources for this salt body.The ~(87)Sr/~(86)Sr values were negatively correlated with δ~(34)S_(V-CDT) and δ~(41)K values,respectively,which revealed the presence of terrestrial freshwater recharge to the evaporation basin during the precipitation of salt.Freshwater recharge resulted in samples with ~(87)Sr/~(86)Sr values greater than parental seawater and δ~(34)S_(V-CDT) and δ~(41)K values less than parental seawater.Data obtained by simulation calculation of the mixed source suggest that the proportion of strontium in the freshwater supply in the sylvinite ranges from 3.3% to 29.2%,and the proportion of strontium in the freshwater supply in the anhydrock does not exceed 35.2%.The Sr,S,and K isotopes compositions of the samples still hold characteristics of the seawater,because of terrigenous recharge amount is little and does not disturb the identification of parent source.This study integrates the traditional stable isotopes(Sr-S) with the emerging K isotopes to trace the source of deep potassium-bearing salt body in the Simao basin,providing reliable data to further investigate the genesis mechanism.