李运冬. 南秦岭桐柏地区程湾花岗岩LA-MC-ICP-MS锆石U-Pb年龄及地球化学特征[J]. 地质通报, 2018, 37(7): 1213-1225.
    引用本文: 李运冬. 南秦岭桐柏地区程湾花岗岩LA-MC-ICP-MS锆石U-Pb年龄及地球化学特征[J]. 地质通报, 2018, 37(7): 1213-1225.
    LI Yundong. LA-MC-ICP-MS zircon U-Pb age and geochemical characteristics of the Chengwan granite in Tongbai area, South Qinling[J]. Geological Bulletin of China, 2018, 37(7): 1213-1225.
    Citation: LI Yundong. LA-MC-ICP-MS zircon U-Pb age and geochemical characteristics of the Chengwan granite in Tongbai area, South Qinling[J]. Geological Bulletin of China, 2018, 37(7): 1213-1225.

    南秦岭桐柏地区程湾花岗岩LA-MC-ICP-MS锆石U-Pb年龄及地球化学特征

    LA-MC-ICP-MS zircon U-Pb age and geochemical characteristics of the Chengwan granite in Tongbai area, South Qinling

    • 摘要: 程湾花岗岩位于南秦岭桐柏地区,岩性主要为片麻状(黑云母)正长花岗岩,岩石地球化学成分显示其高硅、富碱、贫镁、低磷和低钛的特征,A/CNK=0.99~1.40,平均为1.17,为高钾钙碱性系列过铝质岩石,稀土元素配分曲线总体表现为右倾斜的"海鸥式",具有负Eu异常(δEu=0.11~0.81,平均0.46)。岩石富集高场强元素Zr、Th、Hf和Rb、K,强烈亏损Ba、Sr、P、Ti,10000Ga/Al值在2.84~3.63之间,计算锆石饱和温度为817~879℃,属于A2型花岗岩。正长花岗岩LA-MC-ICP-MS锆石U-Pb测年结果表明,其206Pb/238U年龄加权平均值为793.0±4.1Ma,表明岩体形成于新元古代青白口纪晚期,而非前人认为的早古生代,其形成与Rodinia超大陆的裂解有关,且形成于裂解的初期阶段。桐柏地区当时仍为扬子大陆北缘的南秦岭,在新元古代中-晚期(825~611Ma)整体上处于陆内裂解的构造体制。

       

      Abstract: The Chengwan granite is located in Tongbai area, South Qinling. The lithology is mainly granulite (biotite) syenite granite. Lithochemical analysis shows that it has high SiO2, high alkali, poor MgO and low TiO2, and A/CNK=0.99~1.40, with an average of 1.17, thus belonging to the high-K calc-alkaline series. Chondrite-normalized REE patterns of the Chenwang granite are characterized by right-inclined "seagull"with Eu anomalies (δEu=0.11~0.81, 0.46 on average). The rock is characterized by enrichment of HFSE (Zr, Th, Hf), Rb, K, and strong depletion of Ba, Sr, P and Ti. The values of 10000Ga/Al range from 2.84 to 3.63. Zircon saturation temperatures range from 817~879℃. All these features suggest that the Chengwan granite belongs to A2-type granite. LA-MC-ICP-MS U-Pb dating yielded a weighted mean 206Pb/238U age of 793.0±4.1Ma for the zircon from syenogranite, indicating that the Chengwan granite was formed in the late Neoproterozoic Qingbaikouan period rather than previously considered Early Paleozoic. Its formation was related to the breakup of Rodinia supercontinent, and was formed in the early stage of breakup. The South Qinling still belonged to the northern margin of the Yangtze continental margin in Tongbai area, globally belonging to continental cleavage at the middle to late stage of the Neoproterozoic (about 825Ma to 611Ma).

       

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