地学前缘 ›› 2016, Vol. 23 ›› Issue (2): 206-221.DOI: 10.13745/j.esf.2016.02.020

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柴北缘宗务隆构造带印支期花岗闪长岩地质特征及其构造意义

彭渊,马寅生,刘成林,李宗星,孙娇鹏,邵鹏程   

  1. 1. 中国地质科学院 地质力学研究所, 北京 100081
    2. 中国石油大学(华东) 地球科学与技术学院, 山东 青岛 266555
  • 收稿日期:2015-01-03 修回日期:2015-02-07 出版日期:2016-03-15 发布日期:2016-03-15
  • 通讯作者: 马寅生(1962—)，男，研究员，博士生导师。E-mail：mayinsheng@sohu.com
  • 作者简介:彭渊(1986—)，男，博士研究生，主要从事构造地质、石油地质方面的研究。E-mail:cugb_pengyuan@126.com
  • 基金资助:

    中国地质调查局项目“柴达木盆地油气资源潜力评价”(1212010818054)；中国地质调查局项目“柴达木盆地古生代油气资源调查评价”(1212011120964)

Geological characteristics and tectonic significance of the Indosinian granodiorites from the Zongwulong tectonic belt in North Qaidam.

  • Received:2015-01-03 Revised:2015-02-07 Online:2016-03-15 Published:2016-03-15

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摘要：

为了研究柴北缘宗务隆构造带印支期构造演化特征，选取宗务隆构造带内具代表性的晒勒克郭来花岗闪长岩和察汗诺花岗闪长岩进行了岩石学、年代学与地球化学研究。锆石SHRIMP UPb年代学结果显示，晒勒克郭来花岗闪长岩与察汗诺花岗闪长岩分别形成于(249.2±2.6) Ma、(242.7±1.9) Ma和(243.5±2.4) Ma，为早三叠世，也更加证实柴北缘印支期构造岩浆活动的存在。两岩体均相对富SiO2、Na2O和Al2O3，A/CNK分别为1.02～1.06和1.01～1.05，里特曼指数分别为1.54～1.73和1.07～1.61，属于弱过铝质中钾高钾钙碱性I型花岗岩； K/Rb值平均分别为234和279，分异指数分别为72.95～76.06和64.49～76.42，两岩体原始岩浆结晶分异不充分；LREE/HREE分别为6.83～9.70和3.29～7.40，弱的Eu负异常或正异常；在微量元素原始地幔标准化蛛网图上，两岩体明显富集Rb、U、La、Pb、Sr等大离子亲石元素，亏损Nb、P、Ti等高场强元素；察汗诺花岗闪长岩中发育中基性暗色包体，包体和寄主岩中见斜长石、角闪石等矿物结构和成分不平衡现象，说明其为岩浆混合成因。综上所述，两岩体应为印支期柴北缘活动大陆边缘俯冲碰撞作用导致幔源岩浆底侵与下地壳部分重融形成的壳幔混合岩浆形成的产物。对比柴北缘宗务隆构造带与柴东鄂拉山构造带内岩浆岩地质特征认为，宗务隆构造带的形成可能与西秦岭沿共和坳拉谷强烈斜向碰撞柴达木地块有关。

关键词: 宗务隆构造带, 晒勒克郭来, 察汗诺, 花岗闪长岩, 印支期, 岩浆混合成因, 俯冲碰撞

Abstract:

In order to research the Indosinian tectonic evolution features of the Zongwulong tectonic belt, the studies of petrology, geochronology and geochemistry were conducted for the Shailekeguolai granodiorite samples and Chahannuo granodiorite samples from that area. The results of zircon SHRIMP UPb dating of three samples for the Shailekeguolai granodiorite and Chahannuo granodiorite were 249.2±2.6 Ma, 242.7±1.9 Ma and 243.5±2.4 Ma respectively, which confirmed that the intermediateacidic intrusive rocks of the Zongwulong tectonic belt were formed in the Early and Middle Triassic, and the existence of Indosinian tectonicmagmatic activity in North Qaidam has been proved. The Shailekeguolai granodiorite and Chahannuo granodiorite are weak peraluminous Itype granites of middlehigh potassium calcalkaline series, characterized by high SiO2, high Na2O and high Al2O3, with A/CNK ratio ranging between 1.021.06 and 1.011.05, Rittmann index ranging between 1.541.73 and 1.071.61 respectively. The two granodiorites experienced a relatively insufficient crystallizationdifferentiation process, which is reflected by K/Rb(234 and 279 on average respectively) and DI(72.9576.06 and 64.4976.42 respectively). The rocks show LREE enrichment(LREE/HREE=6.839.70 and 3.297.40 respectively) and weak negative and positive Eu anomalies. The primitive mantle normalized trace element spider diagrams are characterized evidently by positive anomalies of Rb, U, La, Pb, Sr and negative of Nb, P, Ti. Microgranular mafic enclaves(MMEs) are developed in the Chahannuo granodiorite. Compositional and textural disequilibrium between plagioclase and hornblende in the MMEs and host rocks had been found, suggesting a magma mixing origin for the granodiorites. The granodiorites are products of lower crustmantle mixed magma due to the crustal thickening caused by active continental margin subduction and arccontinent collision during the Indosinian period in the North Qaidam. Based on the comparison of geologic features of the magmatites between the Zongwulong tectonic belt in North Qaidam and the Ela mountain tectonic belt in East Qaidam, the formation of the Zongwulong tectonic belt may have a close genetic relationship with the intense oblique collision of West Qinling along the Gonhe aulacogen towards Qaidam blocks.

Key words: Zongwulong tectonic belt, Shailekeguolai, Chahannuo, granodiorite, Indosinian, magmamixing origin, subduction and collision

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