向安平, 陈毓川, 佘宏全, 李光明, 李应栩. 内蒙古东乌旗葛根敖包石英闪长岩岩体年代学、地球化学及其地质意义[J]. 地质通报, 2019, 38(9): 1469-1483.
    引用本文: 向安平, 陈毓川, 佘宏全, 李光明, 李应栩. 内蒙古东乌旗葛根敖包石英闪长岩岩体年代学、地球化学及其地质意义[J]. 地质通报, 2019, 38(9): 1469-1483.
    XIANG Anping, CHEN Yuchuan, SHE Hongquan, LI Guangming, LI Yingxu. Chronology and geochemical characteristics of quartz diorite in Gegen' aobao, Dong Ujimqin Banner, Inner Mongolia, and its geological significance[J]. Geological Bulletin of China, 2019, 38(9): 1469-1483.
    Citation: XIANG Anping, CHEN Yuchuan, SHE Hongquan, LI Guangming, LI Yingxu. Chronology and geochemical characteristics of quartz diorite in Gegen' aobao, Dong Ujimqin Banner, Inner Mongolia, and its geological significance[J]. Geological Bulletin of China, 2019, 38(9): 1469-1483.

    内蒙古东乌旗葛根敖包石英闪长岩岩体年代学、地球化学及其地质意义

    Chronology and geochemical characteristics of quartz diorite in Gegen' aobao, Dong Ujimqin Banner, Inner Mongolia, and its geological significance

    • 摘要: 内蒙古东乌旗地区新近发现的葛根敖包铅锌矿,成矿与赋矿岩体石英闪长岩关系密切,对石英闪长岩进行系统的LAICP-MS锆石U-Pb定年及锆石Hf同位素分析,并对石英闪长岩进行主量、微量和稀土元素分析。锆石U-Pb定年结果显示,石英闪长岩2个样品的锆石U-Pb年龄分别为299±1Ma和301±1Ma,均为晚石炭世。岩石主量、微量及稀土元素分析显示,石英闪长岩具有典型的富硅、富碱特征,Na2O/K2O值为1.14~1.93,平均1.39,明显富钠高钾,属高钾钙碱性系列;铝饱和指数A/CNK值为0.79~0.95,为准铝质或铝不饱和花岗岩类;轻、重稀土元素分馏显著,球粒陨石标准化稀土元素配分模式表现为明显的右倾,显示岩浆源区可能有石榴子石残留;并有微弱负Eu异常,δEu=0.80~0.91,δCe=0.89~0.96,均靠近1,指示源区无斜长石残留;同时具低Sr、高Yb特征;并指示高场强元素U、La、Nd、Zr相对富集,而Th、Nb、Sr、P、Ti相对亏损,且大离子亲石元素Rb、Ba、K相对富集,Nb/Ta值低,指示岩浆源区可能为幔源为主。锆石Hf同位素分析显示,εHf(t)值全部为正值,+10.8~+13.6(全部大于10,较高),TDM2介于440~629Ma之间,相对集中,明显大于其锆石U-Pb年龄,其年轻的TDM2年龄和较高的εHf(t)值表明,岩浆中有相当大的幔源物质的贡献。结合区域构造演化,认为葛根敖包石英闪长岩岩浆源区可能为亏损地幔物质部分熔融并在上升过程中受到少量壳源物质的混染,为活动陆缘弧环境的产物。

       

      Abstract: The newly found Gegen'aobao lead-zinc deposit is within the quartz diorite. Because the exploration is insufficient, the metal resources are unclear. As a newly found deposit, there is no previous research data, and hence systematic isotope dating must be done to determine the age of metallogenesis for the deposit. The U-Pb dating shows that the quartz diorite has the ages of 299±1~301±1Ma. Major element geochemistry shows that the quartz diorite is characterized by high SiO2 and K2O, whereas trace element geochemistry shows that the quartz diorite is a "right-inclined" shape in the chondrite-normalized REE patterns. The rocks are rich in large ion lithophile elements (K, Rb, Ba) and LREEs and depleted in high field strength elements (Th, Nb, Sr, P, Ti) and HREE, with the loss of high field strength elements (HFSEs) such as Th, Nb, P and Ti. The quartz diorite is of high-K calc-alkaline series and has a little negative Eu anomaly (Eu/Eu*=0.80~0.91), with low A/CNK (0.79~0.95). These characteristics shows that the Gegenaobao quartz diorite is mantle source granite. The in situ zircon Hf isotopic data are in agreement with U-Pb age data of zircon grains, and the 176Hf/177Hf isotopic ratio of the quartz diorite is 0.282906~0.282984, with εHf(t) values >0, indicating that the source region of the quartz diorite magma was depleted mantle or newly created lower continental crust beneath the study area. Based on geochemistry, isotopes and regional tectonic evolution history, the authors hold that the quartz diorite was derived from a depleted mantle, which was probably related to an active continental margin arc environment.

       

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