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南秦岭地体东江口花岗岩及其基性包体的锆石U-Pb年龄和Hf同位素组成
引用本文:弓虎军,朱赖民,孙博亚,李犇,郭波,王建其.南秦岭地体东江口花岗岩及其基性包体的锆石U-Pb年龄和Hf同位素组成[J].岩石学报,2009,25(11):3029-3042.
作者姓名:弓虎军  朱赖民  孙博亚  李犇  郭波  王建其
作者单位:西北大学地质学系大陆动力学国家重点实验室,西安,710069
基金项目:国家重大基础研究项目课题,国家自然科学基金项目,西北大学大陆动力学国家重点实验室科技部专项项目资助 
摘    要:东江口花岗岩体位于商丹与勉略缝合带之间的南秦岭中部,其中存在大量基性暗色微粒包体.锆石的LA-MCICPMS联机U-Pb年代学分析表明,东江口岩体的形成年龄为223Ma,其包体锆石的结晶年龄为222Ma,与寄主岩体大致同时形成,指示秦岭造山带印支晚期岩石圈构造体制属性从挤压.伸展转变发生在220Ma左右.锆石的Lu-Hf同位素原位分析结果表明,南秦岭晚三叠纪花岗岩是壳幔混合作用的产物,亏损的幔源岩浆与南秦岭(或扬子)的基底地壳物质可能为南秦岭地区晚三叠纪花岗岩的源区物质,它们的形成起因于秦岭造山带在主造山期后发生的岩石圈拆沉作用.大约220Ma开始,南秦岭岩石圈构造应力性质从挤压向伸展构造体制转变,岩石圈发生拆沉作用,地幔软流圈物质上涌并底侵于下地壳,诱发下地壳物质的部分熔融,当岩浆沿构造薄弱带上升过程中,幔源岩浆与寄主岩浆发生成份的交换,两种岩浆混合过程中不完全混溶,最终形成寄主岩体和暗色基性微粒包体.

关 键 词:锆石U-Pb年龄  Hf同位素  包体  南秦岭

Zircon U-Pb ages and Hf isotopic composition of the Dongjiangkou granitic pluton and its mafic enclaves in the South Qiniing terrain
GONG HuJun,ZHU LaiMin,SUN BoYa,LI Ben,GUO Bo,WANG JianQi.Zircon U-Pb ages and Hf isotopic composition of the Dongjiangkou granitic pluton and its mafic enclaves in the South Qiniing terrain[J].Acta Petrologica Sinica,2009,25(11):3029-3042.
Authors:GONG HuJun  ZHU LaiMin  SUN BoYa  LI Ben  GUO Bo  WANG JianQi
Abstract:The Dongjiangkou granitic pluton is exposed in the South Qinling terrain between the Shang-Dan and the Mian-Lue suture zones.This granitic pluton generally contains abundant mafic enclaves of different types.Results of zircon U-Pb dating for a granite and two mafic enclaves by using the LA-MC-ICPMS technique show that the Dongjiangkou granitic pluton crystallized in 223Ma and mafic enclaves formed simultaneously in 222Ma.This magmatism of early Mesozoic constrains the time of tectonic transformation from compression to extension in the Qinling orogenic belt.Hf isotopic composition of zircons obtained by the LA-MC-ICPMS technique suggests that the granitic pluton resulted from a mixing-mingling process between mantle-derived mafic magma and crustal-derived granitic magma.The mafic magma originated likely from depleted mantle,while basement rocks of the South Qinling(or Yangtze)terrain contributed major material source for the granitic pluton.This magmatic activity is attributed to lithospheric delamination during the post-orogenic stage of the Qinling orogenic belt.
Keywords:Zircon U-Pb ages  Hf isotope  Enclaves  South Qinling orogenic belt
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