北祁连干沙鄂博矿区碱性岩锆石U- Pb年龄、Hf同位素及岩石地球化学特征
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甘肃省地质调查院,中国地质大学(武汉)地球科学学院,成都理工大学地球科学学院,成都理工大学地球科学学院,成都理工大学地球科学学院,成都理工大学地球科学学院,成都理工大学地球科学学院

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国家自然科学(41372094)


U- Pb Ages, Hf Isotopic Composition and Geochemistry of Alkaline Complex from the Ganshaebo REE Deposit in North Qilian Mountains, China
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Geological Survey of Gansu Province,Faculty of Earth Science,China University of Geosciences(Wuhan),College of Earth Science,Chengdu University of Technology,College of Earth Science, Chengdu University of Technology,College of Earth Science,Chengdu University of Technology,College of Earth Science,Chengdu University of Technology,College of Earth Science,Chengdu University of Technology

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    摘要:

    干沙鄂博稀土矿床位于北祁连造山带中段,是祁连成矿带内最大的稀土矿床。矿体产于早泥盆世碱性岩体及其围岩接触带内。为了查明含矿碱性岩体侵位时代、岩石成因和源区性质,本文开展了岩石学、锆石U- Pb定年、锆石Hf同位素及岩石地球化学研究。结果表明碱性岩体由霓辉正长岩、霓辉正长斑岩、石英正长斑岩和花岗斑岩组成,侵入于毛藏寺花岗闪长岩中。该岩体LA- ICPMS锆石U- Pb年龄为409.7±5.8Ma,εHf(t)值变化于-0.15~+2.34之间,平均1.03,tDM2(Hf)为1.2~1.1 Ga。岩石主量元素SiO2介于59.1%~68.5%之间,具高钾(Na2O/K2O =0.35~0.85),富碱质(K2O+Na2O=7.91%~11.09%)、贫CaO(2.90%~8.17%)、MgO(0.21%~1.30%)的特征,属钾玄质系列碱性岩;岩石强烈富集轻稀土元素和大离子亲石元素(如Rb、Ba、Sr、U 和Pb等),亏损重稀土元素和高场强元素(如Nb、Ta和Ti),弱负Eu异常(δEu为0.7 ~ 0.8),以及轻稀土富集的右倾型稀土元素配分模式,具A型花岗岩岩石地球化学特征。结合区域构造演化,认为干沙鄂博矿区碱性岩形成于造山后伸展环境,为晚奥陶世北祁连洋闭合后,于早泥盆世发生区域性拉张作用,诱发碱性岩浆侵入和与其共生稀土矿体的形成。

    Abstract:

    The Ganshanebo REE deposit located in the middle sector of the North Qilian orogenic belt is the largest REE deposit in the North Qilian metallogenic belt. The orebodies are mainly hosted within the Early Devonian alkaline complex and the contact zone between the complex and country rocks. In order to confirm the intrusive age, lithogenesis and magma source characteristic of the alkaline complex, this study carried out zircon U- Pb dating, Hf isotopic and petrogeochemical analysis. The results show that the alkaline complex is composed of aegirine syenite, aegirine syenite porphyry, quartz syenitic porphyry and granite porphyry, and intruded into the Maozangsi granitiods. LA- ICPMS U- Pb zircon dating yielded an age of 409.7±5.8Ma, with a εHf(t) range of -0.15~+2.34m (average 1.03) and a tDM2(Hf) range of 1.2~1.1Ga. The major elements of alkaline complex are characterized by rich potassium (Na2O/K2O=0.35~0.85), high alkaline (K2O+Na2O=7.91%~11.09%) and low CaO (2.90% ~ 8.17%) and MgO (0.21%~1.30%), suggesting the complex belongs to potassic alkaline series rocks. High contents of rare earth elements (REE), and enrichment in Large Ion Lithophile Elements (LILE; Rb, Ba, Sr, U, etc), depletion in high field strength elements (HFSE, Nb, Ta and Ti), weak negative Eu anomalies (δEu=0.7~0.8), and LREEenriched, right- inclined REE distribution patterns suggest the geochemical characteristics of A- type rock suites. In combination with the regional geological feature and geodynamic settings, it can concluded that the alkaline complex formed in the post- orogenic tectonic setting and was the product of the intrusion of alkaline complex, which was triggered by the large- scale lithospheric extension starting at early Devonian after the closure of the North Qilian Ocean.

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黄增保,郑建平,李葆华,董晓燕,付太宇,许龙,高昆丽.2018.北祁连干沙鄂博矿区碱性岩锆石U- Pb年龄、Hf同位素及岩石地球化学特征[J].地质学报,92(12):2420-2436.
HUANG Zengbao, ZHENG Jianping, LI Baohua, DONG Xiaoyan, FU Taiyu, XU Long, GAO Kunli.2018. U- Pb Ages, Hf Isotopic Composition and Geochemistry of Alkaline Complex from the Ganshaebo REE Deposit in North Qilian Mountains, China[J]. Acta Geologica Sinica,92(12):2420-2436.

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  • 收稿日期:2017-12-04
  • 最后修改日期:2017-12-30
  • 录用日期:2018-11-20
  • 在线发布日期: 2018-11-20
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