地学前缘 ›› 2011, Vol. 18 ›› Issue (2): 180-191.

• 论文 • 上一篇    下一篇

西准噶尔克拉玛依岩体的成因：年代学、岩石学和地球化学证据

贺敬博，陈斌   

  1. 1. 北京大学 地球与空间科学学院； 造山带与地壳演化教育部重点实验室， 北京 100871
    2. 新疆大学 地质与勘察工程学院， 新疆 乌鲁木齐 830046
  • 收稿日期:2011-01-05 修回日期:2011-02-05 出版日期:2011-03-15 发布日期:2011-04-15
  • 作者简介:贺敬博(1987—)，男，硕士研究生，岩石学专业。E-mail：hejingbo@pku.edu.cn
  • 基金资助:

    新疆大学“天山学者”特聘教授启动资金项目；国家自然科学基金项目(40625005，40821002)

 Petrogenesis of Karamay plutons in the west Junggar： Constraints from geochronology， petrology and geochemistry.

  1. 1. Key Laboratory of Orogenic Belts and Crustal Evolution，Ministry of Education； School of Earth and Space Sciences，Peking University，Beijing 100871，China
    2. School of Geology and Exploration Engineering，Xinjiang University，rümqi 830046，China
  • Received:2011-01-05 Revised:2011-02-05 Online:2011-03-15 Published:2011-04-15

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摘要：

西准噶尔地区克拉玛依岩体主要由闪长岩和花岗岩组成，锆石SHRIMP法给出的岩体结晶年龄为（3155±28） Ma，为晚石炭世侵入岩。克拉玛依岩体具岛弧岩石的元素地球化学特征：总体上岩石富钠，A/CNK=057~084，富集LREE，(La/Yb )N=47~61，Eu显示弱负异常(δEu=076~091)，富集大离子亲石元素，亏损高场强元素Nb、Ta，是钙碱性的I型花岗岩。岩体各主要元素随SiO2呈良好的线性变化，表明壳幔岩浆混合作用和/或结晶分异作用在不同类型的岩石成因上起重要作用。岩体中发育闪长质的暗色包体，包体和寄主岩石中都有斜长石、角闪石等矿物结构和成分不平衡的现象，说明包体和寄主岩石之间进行了晶体和化学物质的交换，包体为岩浆混合成因。在同位素特征上，寄主岩石和包体相似，都显示出亏损地幔的特征，ISr(t)=0703 52~0703 88，εNd(t)=69~74。模拟计算表明，古老大陆地壳在准噶尔地区几乎不存在。克拉玛依岩体的成因：碰撞后岩石圈伸展导致软流圈上涌和岩石圈地幔的部分熔融而形成大量玄武岩，后者底侵到下地壳位置引起年轻的下地壳(古生代大洋岛弧玄武岩和洋壳等)部分熔融而形成花岗岩岩浆，之后花岗质熔体与玄武质熔体发生强烈相互作用和岩浆混合，并经过富钙斜长石和辉石、角闪石等铁镁矿物的结晶分异作用形成了克拉玛依岩体。

关键词: 关键词：克拉玛依岩体, 包体, 岩浆混合, NdSr同位素, 西准噶尔

Abstract:

The Karamay plutons from the west Junggar are mainly made up of dioritic to granitic rocks. UPb dating of zircons from a quartz diorite suggests that the pluton was emplaced at 3155±28 Ma (late Carboniferous)，based on the SHRIMP method. The Karamay plutons show geochemical features reminiscent of arc magmas: Narich，A/CNK=057-084，enrichment of LREE((La/Yb)N=47-61) and LILEs with minor negative Eu anomalies (δEu=076-091)，depletion of HFSEs such as Nb and Ta，and being typical of Itype granitoids. Linear trends of SiO2 versus other major elements were observed，suggesting that mixing between mantlederived magma and crustal melts and/or fractional crystallization have played an important role in forming different rock types of the plutons. Microgranular mafic enclaves (MMEs) are common in the plutons. Compositional and textural disequilibrium of plagioclase and hornblende in the MMEs and host rocks was observed，suggesting a mechanical and chemical exchange between the two rock units and also a mixing origin for the MMEs. The host rocks and MMEs are similar in terms of Nd and Sr isotopic compositions，with ISr(t)=070352-070388，εNd(t)=69-74，typical of that of depleted mantle. Isotopic modeling suggests no signs of old continental crust beneath the west Junggar. The petrogenesis of the Karamay plutons can be summarized as below: postcollisional lithospheric extension caused the upwelling of asthenosphere and partial fusion of lithospheric mantle，producing voluminous basaltic magmas，which underplated in，and thus caused the partial melting of the juvenile lower crust(Paleozoic arc series and oceanic crust) and resulted in the formation of granitic magmas;subsequent mixing between the granitic and basaltic magmas gave birth to a hybrid magma，from which the Karamay plutons were formed through significant fractionation of calcic plagioclase and ferromagnesian phases such as pyroxene and hornblende.

Key words:  , Karamay plutons, mafic enclaves, magma mixing, NdSr isotopes, west Junggar

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