| 大别山北缘商城岩体SHRIMP锆石U-Pb年龄、地球化学及地质意义 |
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| 引用本文： | 黄丹峰,卢欣祥,罗照华,宋要武,吕国营.大别山北缘商城岩体SHRIMP锆石U-Pb年龄、地球化学及地质意义[J].地球科学,2019,44(11):3829-3844. |
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| 作者姓名： | 黄丹峰 卢欣祥 罗照华 宋要武 吕国营 |
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| 作者单位： | 1.河南省地质调查院, 河南郑州 450001 |
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| 基金项目： | 河南省自然科学基金项目182300410106国家重点研发计划项目2016YFC0600504-02中国地质调查局项目121201004000160901-18 |
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| 摘 要： | 商城岩体位于大别造山带北淮阳火山岩带中段，被早白垩世金刚台组火山岩不整合覆盖，厘定其侵位时间和成因对于揭示大别造山带晚中生代构造演化具有重要意义.对岩体进行SHRIMP锆石U-Pb测年和岩石地球化学研究，岩体中心相肆顾墩单元巨斑状二长花岗岩15个锆石测点中有13个测点的206Pb/238U年龄加权平均值为130.2±1.7 Ma，代表商城岩体最终就位的时间.商城岩体具有高含量的Al2O3、Sr，高Sr/Y值和低含量的Y、Yb，轻重稀土分馏显著，无Eu异常（δEu=0.90~1.05），发育Nb、Ta负异常，具有埃达克质岩石的地球化学特征.商城岩体3个岩相单元从早到晚长英质矿物结晶压力降低，侵位深度显著变浅，为挤压作用下主动侵位的结果.商城岩体是大别造山带早白垩世岩浆爆发的产物，岩浆起源于加厚下地壳的部分熔融，从商城岩体开始侵位至金刚台组火山岩喷发，该区地壳经历快速的隆升和剥蚀，而这一过程正是两者地球化学属性所反映的加厚下地壳减薄的浅表响应，130 Ma是大别造山带晚中生代构造体制转换的时间.
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| 关 键 词： | 大别山 商城岩体 SHRIMP锆石U-Pb年龄 早白垩世 构造体制转换 地质年代学 |
| 收稿时间： | 2018-12-08 |
Zircon SHRIMP U-Pb Age,Geochemical Characteristics and Geological Implications of Shangcheng Pluton in the Northern Margin of Dabie Mountain |
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| Abstract: | Unconformably overlain by the Early Cretaceous volcanic rocks, the Shangcheng pluton is located in the central segment of the northern Huaiyang tectono-magmatic belt, Dabie orogen. It is of great importance to determine the emplacement age and petrogenesis of this pluton in terms of deciphering the Mesozoic tectonic evolution of the Dabie orogeny. In this paper, it reports the SHRIMP U-Pb zircon ages and whole rock geochemical data. For the central Sigudun unit of the pluton, thirteen zircon analysis spots out of fifteen yield zircon U-Pb ages of 130.2±1.7 Ma, representing the emplacement age of the pluton. The Shangcheng pluton displays high contents of Al2O3 and Sr, as well as high ratios of Sr/Y, and low abundances of Y and Yb, with Nb-Ta negative anomalies and pronounced LREE/HREE, but without obvious Eu anomalies (δEu=0.90~1.05), collectively pointing to an adakite affinity. Three units of Shangcheng pluton, from old to young, display a trend of gradually decreasing crystallization pressures corresponding to shallower emplacement depths step by step, suggesting that formed in an active emplacement background. The Shangcheng pluton results from the Early Cretaceous magmatic flare-up in the Dabie orogeny, and it is originated from the partial melting of the thickened lower crust. From the emplacement of the Shangcheng pluton to the eruption of the Jingangtai volcanics, this region has experienced rapid uplift and denudation. The process is exactly the surface response recorded by those two different geochemical signatures generated through thinning of the thickened lower crust. The 130 Ma is the time of tectonic regime transition of the Dabie orogen during the Mesozoic. |
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