地学前缘 ›› 2018, Vol. 25 ›› Issue (4): 65-75.DOI: 10.13745/j.esf.sf.2018.6.28

• 岩（矿）石、地层特征及地质意义 • 上一篇    下一篇

柴西南翼山构造上新统狮子沟组混积岩地球化学特征及物源指示意义

于冬冬，张永生，邢恩袁，王琳霖，李凯，黄囿霖   

  • 收稿日期:2018-01-04 修回日期:2018-04-15 出版日期:2018-07-15 发布日期:2018-07-15
  • 作者简介:于冬冬(1989—)，男，博士研究生，主要从事盐类矿床与油气地质研究。E-mail：radon1203@163.com
  • 基金资助:
    国家重点研发计划项目(2017YFC0602806)；中国地质调查局地质调查工作项目(121201103000150012)

Geochemical characteristics and provenance implication of mixed rocks from the Pliocene Shizigou Formation in the Nanyishan structure of the western Qaidam Basin.

YU Dongdong,ZHANG Yongsheng,XING Enyuan,WANG Linlin,LI Kai,HUANG Youlin   

  1. 1. MLR Key Laboratory of Saline Lake Resources and Environments, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China
    2. School of Earth Sciences and Resources, China University of Geosciences(Beijing), Beijing 100083, China
    3. Research Institute of Exploration and Development, PetroChina Qinghai Oilfield Company, Dunhuang 736202, China
  • Received:2018-01-04 Revised:2018-04-15 Online:2018-07-15 Published:2018-07-15

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摘要： 柴西地区南翼山构造上新统混积岩中含有大量盐类矿物，其物源分析对盐矿物质来源研究有一定的参考价值。本文在野外观察和镜下鉴定的基础上，对南翼山构造上新统狮子沟组混积岩的地球化学特征进行了分析，并结合周缘造山带花岗岩的稀土元素数据，探讨了混积岩中陆源碎屑的物质来源。结果显示：南翼山构造狮子沟组混积岩中碎屑矿物、碳酸盐矿物和黏土矿物呈均匀混合的状态，元素含量与矿物组分密切相关，除Ca、Na、Sr元素外，其余元素含量普遍低于上地壳平均含量，其中CaO和Na2O受碳酸盐和石盐形成影响，不能用于判别构造背景，而Sc、Th、Zr、Hf等微量元素和稀土元素较完整地保留了源岩的地球化学信息，可用于源区构造背景的判别及物源示踪，同时稀土元素配分模式一致性较好，表明混积岩中陆源碎屑具有相同的物源特征。稀土元素配分模式、LaThSc、ThScZr/10、La/ThHf图解以及Al2O3/TiO2比值共同指示南翼山混积岩的陆源碎屑组分来源于大陆岛弧背景下的长英质火成岩，通过与周缘造山带花岗岩稀土配分模式对比，推断晚志留世和晚二叠世花岗岩是混积岩中陆源碎屑和盐类矿物的主要源岩，南部的祁漫塔格是主要的物源区，且西部的阿尔金南段也有部分物源贡献。

关键词: 混积岩, 地球化学, 构造背景, 物源, 南翼山构造, 柴达木西部

Abstract:  The Pliocene mixed rocks contain large amounts of salt minerals in the Nanyishan structure of the western Qaidam Basin, and their provenance analyses can be valuable in finding the origin of the salt minerals. Based on field observation and microscopic identification, we analyzed the geochemical characteristics of mixed rocks from the Pliocene Shizigou Formation in the Nanyishan structure. Combined with rare earth element (REE) characteristics of granites from the surrounding orogenic belts, we discussed the provenance of terrigenous clastics in mixed rocks. The results showed that the detrital, carbonate and clay minerals in mixed rocks were homogeneously mixed, and the elemental contents of the rocks were closely related to the mineral composition. Except for Ca, Na, and Sr, the mixed rocks had generally lower mineral contents than those of the upper continental crust. Considering that CaO and Na2O are affected by the formation of carbonate and halite, Ca and Na are not suitable for identifying tectonic settings. In contrast, trace elements and REE such as Sc, Th, Co, Zr and Hf, retain mostly the geochemical information of source rocks and therefore can be used to evaluate the tectonic settings of the source area for provenance analysis. The REE patterns showed good consistency, indicating the terrigenous clastics of mixed rocks have the same provenance characteristics. Together with LaThSc, ThScZr/10, La/ThHf diagrams and Al2O3/TiO2 ratio, our data suggest that the terrigenous clastics components of mixed rocks were derived from the felsic igneous rocks of continental island arc. In comparison with REE patterns in granites from the surrounding orogenic belts, we consider the Late Silurian and Late Permian granites to be the main source rocks for terrigenous clastics and salt minerals in the mixed rock. In addition, we hypothesize that the south part of the study area, Qimantag, is the main source area, and South Altyn Tagh in the west also takes part in the sedimentary source recharge.

Key words: mixed rocks, geochemistry, tectonic setting, provenance, Nanyishan structure, western Qaidam Basin

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