卤水演化过程的氯同位素示踪模拟实验研究

In non-traditional isotopic systems, chlorine isotope has its own characteristics. Chlorine ions are abundant in bine because of its high solubility in water, so it can provides important information during brine evolution.Due to using the variation of chlorine isotopic composition to retrieve brine evolution lacking of confirming by related theories and experiments, experiments of chlorine isotopic fractionation during the evaporation of brine are designed, which are conducted to simulate the concentration-desalination-concentration and mixing of brines, the replenishment condition of these experiments is different. Precipitate and brine samples will be collected during the experiments, and the δ37Cl values of the samples will be determined using an improved thermal ionization mass spectrometry procedure for precise measurement of chlorine isotopes based on Cs2Cl+. Chlorine isotopic data in combination with hydrochemical and mineralogical data will be uesd to study the variation characteristics of the δ37Cl values of the samples and their response mechanism to the concentration-desalination-concentration and mixing of brines, and analyze the sensitivity of the response, discuss the suitability of using the variation of chlorine isotopic composition to retrieve brine evolution, further, explore a model retrieve brine evolution with the variation characteristics of the δ37Cl values of the precipitate and coexisting brine. At last, it draws up to modify the model based on theδ37Cl values in deposited saline minerals in the core samples from saline Qarhan Lake.

在"非传统稳定同位素"体系中，氯同位素有其自身特点，由于氯是一种易溶元素，氯离子是卤水中的主要离子，故其能够提供卤水演化的重要信息。本项申请针对利用氯同位素变化反演卤水演化过程缺失相关的理论和实验数据支持，设计了在控制补给条件下的卤水蒸发过程氯同位素分馏实验，重点进行自然界卤水浓缩-淡化-浓缩和混合等演化过程的实验模拟，通过基于检测Cs2Cl+的高精度正热电离质谱法测定样品氯同位素比值，结合实验过程中精确测定的水化学和矿物学数据，研究卤水和盐类沉积δ37Cl值对卤水浓缩-淡化-浓缩和混合过程的响应，分析其敏感性，讨论利用氯同位素组成变化示踪古卤水演化的可行性，进而探索通过卤水和盐类沉积δ37Cl值的变化特征反演卤水演化过程的模式，最后通过察尔汗盐湖钻孔岩芯的氯同位素研究对模式进行完善。

本项目针对利用氯同位素变化反演卤水演化过程缺失相关的理论和实验数据支持，设计了在控制补给条件下的卤水蒸发过程氯同位素分馏实验，重点进行自然界卤水浓缩-淡化和混合等演化过程的实验模拟，研究卤水和盐类沉积δ37Cl值对卤水浓缩-淡化和混合过程的响应，分析其敏感性，讨论利用氯同位素组成变化示踪古卤水演化的可行性，进而探索通过卤水和盐类沉积δ37Cl值的变化特征反演卤水演化过程的模式。首先以我国青海湖湖水代表典型的大陆湖盆水体，通过大体积湖水的蒸发实验获取卤水，进而开展了卤水演化过程的氯同位素示踪模拟实验研究，发现：1、 随着水体体积浓缩-稀释的演化过程，对应的卤水和盐类沉积δ37Cl 值具有降低-增高的同步响应趋势，即从实验角度证明了可以从δ37Cl 值检出古气候变化的波动性。这对于阐明利用氯同位素示踪盐湖形成演化和某些盐类沉积的机理非常重要。2、发现淡化过程的氯同位素效应主要受盐类和水体之间的同位素分馏控制，河流带来的外源氯同位素效应并不显著。3、在水体演化早阶段，我们发现了氯同位素已经发生了显著分馏，改变了以往我们对水体氯同位素演化的认识，这是首次在实验中观测到这一特殊现象。同时我们对钻孔岩芯样品的研究发现：盐类沉积δ37Cl值的升高往往指示了古盐湖水的淡化过程，对应了更湿润的古气候的条件，δ37Cl值的降低往往指示了古盐湖水的蒸发浓缩过程，对应了更干旱的古气候的条件。这与前期进行的室内实验的结果是一致的。