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杨泽黎,王树庆,胡晓佳,赵华雷,李承东,辛后田,孙立新.内蒙古吉尔嘎郎图早古生代岩体成因——年代学、地球化学及Nd-Hf同位素制约[J].地质通报,2017,(8):1369-1384.
内蒙古吉尔嘎郎图早古生代岩体成因——年代学、地球化学及Nd-Hf同位素制约    点此下载全文
杨泽黎  王树庆  胡晓佳  赵华雷  李承东  辛后田  孙立新
天津地质矿产研究所, 天津 300170
基金项目:中国地质调查局项目《二连-东乌旗成矿带西乌旗和白乃庙地区地质矿产调查》(编号:DD20160041)、《华北重大岩浆事件及其成矿作用和构造背景综合研究》(编号:1212014121079)、《兴蒙造山带中段古生代花岗岩的组成、性质、时代和成矿作用研究》(编号:1212011121079)
DOI:
摘要:
      兴蒙造山带北缘断续分布的早古生代岩浆岩带,对古生代构造格局恢复及造山带演化研究具有重要意义。阿巴嘎旗北部吉尔嘎郎图岩体位于该岩浆岩带中段,为带内最大的早古生代复式侵入体。LA-ICP-MS锆石U-Pb定年表明,吉尔嘎郎图岩体早期花岗闪长岩单元成岩年龄为455.0~495.6Ma。在主量元素组成上,岩体SiO2含量中等(59.49%~68.22%),贫铁、镁,K2O/Na2O值(0.64~0.85)小于1,A/CNK=0.96~1.09,整体具有亚碱、弱过铝特征。稀土及微量元素方面,岩体富Cs、Rb、Th、U、Pb,亏损Ba、Sr、P及高场强元素Nb、Ta等,稀土元素总量中等,具有弱负Eu异常(δEu=0.52~0.82)。Sr-Nd-Hf同位素分析结果显示,岩体具有亏损的同位素组成,(87Sr/86Sr)i=0.7053~0.7034,εNdt)=0.39~4.29,2件Hf同位素样品εHft)均为正值,分别为εHft)=7.6~10.8和εHft)=3.7~7.9。岩石地球化学、年代学及Sr-Nd-Hf同位素综合分析表明,吉尔嘎郎图岩体是早古生代古亚洲洋沿苏左旗-锡林浩特一线向北俯冲背景下,遭受了俯冲板片析出流体交代作用影响的新生下地壳部分熔融的产物,后期由于弧后拉张、贺根山洋盆打开与主体岛弧带分离,最终随着古亚洲洋的整体闭合,形成了与俯冲带彼此分隔的格局。
关键词:早古生代  锆石U-Pb定年  Nd-Hf同位素  岛弧岩浆岩  兴蒙造山带  新生地壳
Petrogenesis of the Early Paleozoic Jiergalangtu pluton in Inner Mongolia:Constraints from geochronology, geochemistry and Nd-Hf isotopes    Download Fulltext
YANG Zeli  WANG Shuqing  HU Xiaojia  ZHAO HuaLei  LI Chengdong  XIN Houtian  SUN Lixin
Tianjin Institute of Geology and Mineral Resources, Tianjin 300170, China
Fund Project:
Abstract:
      Early Paleozoic granites are distributed on the northern margin of Xingmeng orogenic belt discretely, and the genesis of these granites has important implications for the reconstruction of regional Paleozoic tectonic setting and orogenic evolution. Jier-galangtu pluton outcropped in northern Abag Banner and located in the middle of the early Paleozoic granite belt is the biggest com-posite pluton in the granite belt. Zircon LA-ICP-MS U-Pb dating shows that the early stage of the pluton was emplaced during 455.0~495.6Ma. Geochemically, the Jiergalangtu granites show moderate SiO2 values (59.49%~68.22%) and depletion of magnesium and iron, with K2O/Na2O ratios less than 1 (0.64~0.85) and A/CNK values being 0.96~1.09; in addition, most of the samples present subalkaline and weak per-aluminous signature. The trace element data of these rocks display enrichment of Cs, Rb, Th, U, Pb and depletion of Ba, Sr, P and HFSE such as Nb, Ta, the pluton exhibits indistinct negative europium anomalies(δEu=0.04~0.25) with moderate total REE content. Jiergalangtu pluton shows depleted isotopic compositions, (87Sr/86Sr)i=0.7053~0.7034, εNd(t)=0.39~4.29, and both samples for Hf isotopic analysis have positive εHf(t) values, being 7.6~10.8 and 3.7~7.9 respectively. Integrated geochemical, geochronology and Sr-Nd-Hf isotopic data suggest that the Jiergalangtu granites were generated in early Paleozoic and resulted from the subduction of Paleo-Asian Ocean along Sunid-Xilinhot. The granites were formed by partial melting of juvenile crust which was modified by subduction slab fluids. The back-arc extension and opening of Hegenshan Ocean possibly resulted in the separation of Jiergalagntu pluton from predominant Sunid-Xilinhot island arc. Along with the closure of Paleo-Asian Ocean, the pluton ultimately occurred on the northern margin of Xingmeng orogenic belt and was separated from the subduction zone by He-genshan ophiolite complex.
Keywords:Early Paleozoic  zircon U-Pb dating  Nd-Hf isotopic compositions  arc magmatic rocks  Xingmeng orogeny  juve-nile crust
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