今天是2018年10月18日

南阿尔金陆块科克萨依新元古代花岗岩成因及地质意义

DOI:10.3799/dqkx.2018.720

作者:陈红杰,吴才来,雷敏,郭文峰,张昕,郑坤,高栋,吴迪

联系地址:中国地质科学院地质研究所,中国地质调查局大陆动力学研究中心,北京 100037

摘要:南阿尔金陆块是阿尔金造山带的重要组成部分.大量新元古代花岗岩出露于南阿尔金亚干布阳-帕夏拉依裆-科克萨依一带.这些花岗岩记录了与Rodinia超大陆汇聚有关的动力学信息,因此对其进行研究有利于对阿尔金造山带演化历史的认识和理解.选取了科克萨依花岗岩岩体进行了岩相学、地球化学、锆石U-Pb年代学和Hf同位素组成的研究.研究结果表明:(1)科克萨依二长花岗岩的主要矿物有:石英、钾长石、斜长石、黑云母和白云母;花岗岩的锆石U-Pb年龄为947~945 Ma.(2)地球化学特征显示,岩石具有高SiO2(71.54%~74.69%)、高Na2O+K2O(6.33%~7.40%),低CaO(1.59%~2.00%),低MgO(0.43%~0.61%)和TiO2(0.25%~0.37%)的特征,相对富钾,K2O/Na2O比值为1.02~1.71,A/CNK在1.10~1.14之间,属高钾钙碱性系列的过铝质花岗岩.富集Rb、Th、K、La等元素,亏损Nb、Ta、P、Ti等元素;轻稀土富集而重稀土亏损,具有明显的负Eu异常.(3)锆石ε Hf( t )为-4.09~+3.87之间,二阶段模式年龄t DM2为1.6~2.0 Ga.这些特征表明科克萨依二长花岗岩是古老地壳富长石贫黏土的(变)杂砂岩部分熔融形成的S型花岗岩.结合相邻地区新元古代花岗岩类的地球化学、同位素特征及阿尔金区域构造资料,认为科克萨依二长花岗岩形成于新元古代时期,是碰撞造山环境下的产物,是Rodinia超大陆汇聚碰撞过程的响应.

关键字:花岗岩;地球化学;U-Pb年代学;Hf同位素特征;南阿尔金陆块.

Petrogenesis and Implications for Neoproterozoic Granites in Kekesayi Area, South Altyn Continent

Author:Chen Hongjie, Wu Cailai, Lei Min, Guo Wenfeng, Zhang Xin, Zheng Kun, Gao Dong, Wu Di

Author Address:Centre for Continental Dynamics, China Geological Survey, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China

Abstract:The South Altyn continental block is an important geological unit of the Altyn Tagh orogenic belt. Numerous Neoproterozoic granites outcrops in the South Altyn continental block, and are mainly located in Paxialayidang-Yaganbuyang-Kekesayi area. These granites provide indispensable dynamics information of the Rodinia supercontinent aggregation in Neoproterozoic. Therefore, the study of granites can help us to understand the formation and evolution history of the Altyn Tagh orogenic belt. In this paper, Kekesayi granitic pluton was studied by means of petrography, geochemistry, zircon U-Pb chronology and Hf isotopic analyses. The results are as follows. (1) Main minerals of Kekesayi monzonitic granite are: quartz+K-feldspar+plagioclase+biotite+muscovite. Zircon U-Pb dating shows that the granite was emplaced in 947-945 Ma. (2) Geochemistry characteristics show high SiO2 (71.54%-74.69%), K2O+Na2O (6.33%-7.40%) contents and low CaO(1.59%-2.00%), MgO (0.43%-0.61%) and TiO2 (0.25%-0.37%) contents, with K2O/Na2O ratios of 1.02-1.71 and A/CNK ratios of 1.10-1.14, showing a typical high-K calc-alkaline series with peraluminous features. Meanwhile, the granite is also enriched in Rb, K, Th and La, and depleted in Nb, Ta, Sr and Ba, with negative Eu anormalies and relative enrichment in LREE. (3)ε Hf( t ) values range from -4.09 to +3.87 while two-stage model ages ( t DM2 ) vary in 1.6-2.0 Ga. It is argued that the Kekesayi monzonitic granites were derived from partial melting of the meta-grey wackes of Late Paleoproterozoic to Early Mesoproterozoic ancient crustal materials. In combination with other Neoproterozoic granite features, the petrogenesis and isotopic geochronology indicate that the Kekesayi monzonitic granite was formed in collisional orogeny setting and may have been triggered by the assemblage of Rodinia supercontinent in Neoproterozoic.

Keyword:granite; geochemistry; U-Pb chronology; Hf isotopic characteristics; South Altyn continent.

 

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作者简介:陈红杰(1985-),男,博士研究生,矿物学、岩石学、矿床学专业.ORCID: 0000-0002-4274-9410. E-mail: chenhongjie525@126.com

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