中亚盆地钾盐矿床盐类矿物Rb-Sr同位素体系研究及其意义  

Rb-Sr systematics of salt minerals in potash deposits of the Central Asia Basin and their significance

作　　者：沈立建[1] 刘成林[1] 焦鹏程[1] 王春连[1] 曹养同[1] SHEN Li-jian;LIU Cheng-lin;JIAO Peng-cheng;WANG Chun-lian;CAO Yang-tong(MLR Key Laboratory Metallogeny and Mineral Resource Assessment,Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China)

机构地区：[1]中国地质科学院矿产资源研究所成矿作用与资源评价重点实验室,北京100037

出　　处：《岩石矿物学杂志》2021年第1期99-108,共10页Acta Petrologica et Mineralogica

基　　金：国家自然科学基金项目(41802111);中央级公益性科研院所基本科研业务费专项(KK2005,KK2016);地质调查局地质矿产调查评价专项项目(DD20190606);国家重点基础研究发展计划(973)项目(2011CB403007);“十二五”科技支撑课题(2011BAB06B06)。

摘　　要：中亚盆地钾盐矿床的形成时代目前被限定为晚侏罗世至早白垩世,较为宽泛。盐类矿物沉积之后若未被改造,可测定其形成时代;若被改造则可利用同位素测年研究其沉积后作用。为了得到中亚盆地钾盐矿床的形成时代和/或了解盐类矿物受到的后期改造过程,利用Rb-Sr同位素定年对矿床中的盐类矿物进行了测定。结果表明,无法形成可靠的Rb-Sr等时线,说明钾盐矿床中盐类矿物在形成以后Rb-Sr体系并未保持封闭;钾盐样品模式年龄介于9~4 Ma之间,岩盐样品模式年龄约为190~170 Ma。岩盐Rb含量低,积累的放射性87Sr较少,而钾盐Rb含量高,积累的放射性87Sr较多。后期受到外来流体或者光卤石结合水的作用,盐类矿物发生溶解,重结晶后造成岩盐中87Sr/86Sr值升高而钾盐87Sr/86Sr值降低。结合世界上其它钾盐矿床的Rb-Sr测年结果,认为盐类矿物并不适合研究其成矿时代,但可用来揭示钾盐盆地的变质作用过程和水文演化历史。The formation age of potash deposits in Central Asia Basin was constrained roughly from Late Jurassic to Early Cretaceous. The formation age of salt minerals could be determined if they have not been altered since deposition. Otherwise,the isotopic dating results could only indicate their postdepositional process. To obtain the formation age of the Central Asia Basin potash deposits and/or understand the post-depositional alterations of salt minerals,the authors performed rubidium-strontium( Rb-Sr) isotopic dating on these salt minerals. The result shows that there is no reliable Rb-Sr isochron,indicating that these salt minerals have not kept closed after their formation.The Rb-Sr model ages of the potash minerals and rock salts range from approximately 9 to 4 Ma and 190 to 170 Ma,respectively. This result seems to have been caused by dissolution and recrystallization by extraneous or decomposition of carnallite fluids. The potash salts accumulated more radiogenic87 Sr than the rock salts,because the potash salts contained more Rb than the rock salts. The dissolution and recrystallization of the potash and rock salts resulted in decreasing of87 Sr/86 Sr ratios in the potash salts,but increasing of87 Sr/86 Sr ratios in the rock salts. Although dating of salt minerals in other potash deposits of the world indicates that salt minerals are not suitable for dating the formation age of potash deposits,radiogenic isotopes of salt minerals can be used to constrain the metamorphic and hydrologic history of potash basins.

关 键 词：中亚盆地 钾盐矿床 盐类矿物 RB-SR定年 

分 类 号：P619.211[天文地球—矿床学] P597[天文地球—地质学]