新疆木吉盆地鲕状泉华微观结构、地球化学特征及成因探讨  

Microstructure,geochemical and genesis of coated grains in the Muji Basin,Xinjiang

作　　者：陈兆杰 宋旭东 孙淼 余会明 郭晓萌 尹雪 宋庆伟 CHEN Zhaojie;SONG Xudong;SUN Miao;YU Huiming;GUO Xiaomeng;YIN Xue;SONG Qingwei(No.1 Hydrogeology&Engineering Geology Exploration Team of Xinjiang Geology&Mineral Bureau,Vrümqi,830091,Xinjiang;College of Ecology and Environment,Xinjiang University,Vrümqi 830017,Xinjiang;China Geological Environmental Monitoring Institute,Beijing 100081;Xinjiang Geological Engineering Co.,Ltd,Vrümqi 830002,Xinjiang)

机构地区：[1]新疆地矿局第一水文工程地质大队,新疆乌鲁木齐830091 [2]新疆大学生态与环境学院,新疆乌鲁木齐830017 [3]中国地质环境监测院,北京100081 [4]新疆地质工程有限公司,新疆乌鲁木齐830091

出　　处：《第四纪研究》2023年第1期173-186,共14页Quaternary Sciences

基　　金：中国地质调查局“全国地质遗迹立典调查与评价”项目(批准号:DD20221771)资助。

摘　　要：泉华作为地表或地下水中碳酸钙的陆上沉积,其内部微层结构和地球化学特征具有揭示区域环境变化的重要作用。新疆阿克陶县木吉盆地的鲕状泉华包覆颗粒是内陆干旱-半干旱气候区高寒山地环境产出的冷水沉积产物,沉积过程相较于湿润-半湿润气候区同类泉华具有控制因素上的特殊性。在野外地质调查的基础上,对其进行了细致的微观结构观察和化学组成研究,以期为此类泉华成因机制的完善,以及包覆颗粒生长发育过程与区域环境变化关系的探讨提供限定。研究发现,木吉盆地周边地层中发育的碳酸盐岩是泉华发育的物质基础,“两山夹一盆”的地貌特征和盆地内全新世活动断裂的存在为泉华的形成提供了良好的地形地貌以及构造条件。微观结构观察和化学组分分析显示,鲕状包覆颗粒发育由泥晶和亮晶纹层构成的外壳层,两者均由低镁方解石组成,但微量、稀土元素组成差异显著,泥晶纹层的Mg/Ca(0.02~0.04)和ΣLREE/ΣHREE比值(1.75~9.98)以及稀土元素(ΣREE=0.33×10^(-6)~2.96×10^(-6))和Sr(188×10^(-6)~1640×10^(-6))、Ba(8.95×10^(-6)~123.00×10^(-6))等微量元素含量相对亮晶纹层(Mg/Ca=0.01~0.02,ΣLREE/ΣHREE=0.93~5.43,ΣREE=0.05×10^(-6)~0.82×10^(-6),Sr=157×10^(-6)~285×10^(-6),Ba=5.17×10^(-6)~29.50×10^(-6))更高。综合包覆颗粒微观结构、化学成分以及区域气候变化和地下水补给特征认为,木吉鲕状包覆颗粒的成因类型为核形石,颗粒纹层构造的发育是季节交替导致气候条件周期性波动的结果:在降水和冰雪融水少的干冷气候环境下,地下水补给不足,具有较高微量和稀土元素含量的泥晶方解石发生沉淀,藻类生物捕获粘附泥晶方解石形成泥晶纹层;亮晶纹层形成于气候温湿季节,地下水补给充足,水流在包覆颗粒周围绕流过程中直接在泥晶纹层或岩屑外围发生CaCO3沉淀和生长。Sinter is the subaerial deposition of carbonate in the groundwater or surface water,and its internal micro-layer structure and geochemical characteristics play an important role in revealing the regional environmental changes.The coated grains in the Muji Basin,Akto County,Xinjiang Uygur Autonomous Region,are cold-water tufa produced in the alpine mountain environment(loction at 38°59'50"N,74°30'23"E)of the semi-arid and arid climatic zones.The controlling factors of its deposition process are obviously different from those in semi-humid and humid climatic zones.In order to provide a limit for the formation mechanism of these coated grains,and the relationship between the formation process of coated grains and regional environmental changes,a systematic and detailed investigation of field geological survey,detailed microstructure observation and chemical composition analysis were carried out in this paper.It is found that the geomorphological characteristics of"two mountains clip a basin"and the Holocene active faults in the study area are good for the formation of tufa.The coated grains developed cortex composed of micrite ring layers and sparite ring layers.Both of them are composed of low-magnesium calcites,but the compositions of trace and rare earth elements are significantly different.The micrite ring layers have high Mg/Ca(0.02~0.04)andΣLREE/ΣHREE(1.75~9.98)ratios,and high rare earth elements(ΣREE=0.33×10^(-6)~2.96×10^(-6)),Sr(188×10^(-6)~1640×10^(-6))and Ba(8.95×10^(-6)~123.00×10^(-6))contents.Compared to micrite ring layers,the sparite ring layers show lower Mg/Ca(0.01~0.02)andΣLREE/ΣHREE(0.93~5.43)ratios.Rare earth elements(ΣREE=0.05×10^(-6)~0.82×10^(-6)),Sr(157×10^(-6)~285×10^(-6))and Ba(5.17×10^(-6)~29.50×10^(-6))contents are also lower than those in the micrite ring layers.Based on the microstructure and chemical composition of coated grains,and regional climate change and groundwater recharge characteristics of the Muji Basin,it is concluded that the Muji Holocene coated grains a

关 键 词：鲕状包覆颗粒 泉华 纹层 元素组成 木吉盆地 

分 类 号：P595[天文地球—地球化学]