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热液硬石膏流体包裹体的显微测温实验研究——石膏子晶的形成对盐度和均-温度测量的影响

ISSN号：1006-7493
期刊名称：《高校地质学报》
时间：0
分类：P599[天文地球—地球化学;天文地球—地质学]
作者机构：[1]中国科学院广州地球化学研究所,广州510640, [2]中国科学院研究生院,北京100049
相关基金：国家自然科学基金重点项目（40532011）;国家自然科学基金（40403004;40473032）

关键词：热液硬石膏, 流体包裹体, 石膏, 显微测温, hydrothermal anhydrite, fluid inclusion, gypsum, microthermometry

中文摘要：

硬石膏是海底热液多金属硫化物矿床中常见的少数几种透明矿物之一，是流体包裹体研究的主要对象。对Juande Fuca洋脊Endeavour段的黑烟囱样品中硬石膏流体包裹体的显微观察发现包裹体内含有石膏子晶。显微测温研究也发现包裹体冷冻到-50℃后，再放置12tb时，通常会发育新的石膏子晶。通过反复测定石膏子晶生成前后冰点的变化，发现石膏的生成使得冰点大幅降低，相应地提高残留流体的盐度（上升0、32％～1．6％NaCl eq．）。流体包裹体中石膏生成是硬石膏水化和硬石膏溶解造成溶液过饱和沉淀石膏共同作用的结果，其中硬石膏水化起了主要作用，溶液过饱和沉淀石膏为硬石膏水化提供了有利条件。冷冻条件下和威储藏时间越长，硬石膏水化对盐度的影响越大。加热包裹体到130℃能使石膏分解，释放出所结合的水分子，恢复包裹体的原始盐度。而石膏的生成对均一温度的测量没有影响。

英文摘要：

Hydrothermal anhydrite [CaSO4] is a good host for primary and secondary fluid inclusions. It is also potentially a problematic host for stretching of inclusions, partial dissolution and precipitation of anhydrite, and formation of gypsum from reaction of anhydrite with the trapped aqueous fluid. Microthermometric experiments on liquid/vapor inclusions in anhydrite from Juan de Fuca Ridge show that new daughter crystals, identified to be the low-temperature hydrate gypsum [CaSO4·2H2O], commonly develop during freezing experiments （-50℃）. This phenomenon has been recognized for over 20 years, but its occurrence and significance to the determination of inclusion salinities are not widely appreciated. There is growing evidence that hydration of the host anhydrite may significantly lower the ice melting temperature and increase the salinity of the residual inclusion fluid. The present study shows that the salinities of inclusions increase largely after gypsum formed in liquid/vapor inclusions （salinities increase 0.32 to 1.6% NaC1 eq.）. We propose that gypsum is the product of both anhydrite hydration and supersaturation with respect to gypsum, but mainly owing to the former. Heating inclusions to decompose gypsum results in the release of bound water, restoring the inclusions to their original salinities. So when gypsum formation occurs during freezing experiments, it needs to be dehydrated periodically through heating to about 130℃. These processes could have no impacts on the real homogenization temperatures of inclusions.

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