本文为国家自然科学基金项目(编号42472272，42172236)、中国地质调查局项目(编号DD20190570，DD20230053，DD20230355)、河南省自然科学基金项目(编号 252300421472)、有色金属成矿预测与地质环境监测教育部重点实验室开放基金项目(编号2024YSJS01)、河南省战略性金属矿产成矿规律与找矿预测研究项目(编号 2023- 903- XM006)和南阳理工学院交叉科学研究项目(编号 24NGJY014)资助的成果
CHEN Guochao
1) Nanyang Institute of Technology, Nanyang, Henan 473000, China;2) Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring(Central South University), Ministry of Education, Changsha, Hunan 410083, China;3) School of Earth Science and Resources, Chang an University, Xi an, Shaanxi 710054, China北秦岭构造带花岗伟晶岩是我国重要的伟晶岩矿区，花岗伟晶岩的形成时间和岩石成因存在一定争议。本文通过对北秦岭构造带东段官坡地区峡河村花岗伟晶岩和上河村花岗伟晶岩开展岩石学、锆石U- Pb年代学、锆石Hf同位素地球化学及全岩主微量元素地球化学研究，限定北秦岭构造带东段花岗伟晶岩的形成时代，揭示花岗伟晶岩的岩浆来源和岩石成因。LA- ICP- MS锆石U- Pb同位素定年结果显示峡河村花岗伟晶岩和上河村花岗伟晶岩的结晶年龄分别为361~360 Ma和334. 8 Ma。峡河村花岗伟晶岩和上河村花岗伟晶岩含有石榴子石、白云母和电气石，富集SiO2、Na2O和K2O，CaO、TFeO和MgO含量较低，主体呈过铝质。峡河村花岗伟晶岩和上河村花岗伟晶岩轻重稀土元素分异不明显，具较明显的Eu正异常；微量元素富集Rb、Th、Ba、Cs等大离子亲石元素(LILE)，亏损Nb、Ta、Ti等高场强元素(HFSE)，具有低的Nb/Ta和Zr/Hf比值，指示岩浆经历了高度结晶分异作用。峡河村花岗伟晶岩具有较低的εHf(t)值，为11. 7~6. 2；上河村花岗伟晶岩εHf(t)值明显高于峡河村花岗伟晶岩，为4. 9~1. 1。以上结果显示，峡河村花岗伟晶岩为古老地壳部分熔融产物，上河村花岗伟晶岩为新生地壳部分熔融的岩浆在上侵过程中同化混染围岩的结果。北秦岭构造带东段花岗伟晶岩初步可分为北部稀有金属花岗伟晶岩和南部铀花岗伟晶岩。
The granitic pegmatites in the North Qinling tectonic belt represent one of China' s most significant pegmatite areas. However, their formation age and petrogenesis remain subjects of debate.This paper presents LA- ICP- MS zircon U- Pb ages, Hf isotopic data, and geochemical analyses of the Xiahecun and Shanghecun granitic pegmatites in the Guanpo area toconstrain their formation ages, magma sources, petrogenesis, and tectonic setting. LA- ICP- MS zircon U- Pb dating reveals that the Xiahecun and Shanghecun granitic pegmatites crystallized at 361~360 Ma and 334. 8 Ma, respectively. Both pegmatites contain garnet, muscovite, and tourmaline, with high SiO2, Na2O, and K2O contents but low CaO, TFeO, and MgO concentrations, exhibiting a mainly peraluminous composition. They display little fractionation between LREE and HREE and exhibit obvious positive Eu anomalies. The magmas are enriched in large ion lithophile elements (LILEs; e. g. , Rb, Th, Ba, and Cs) but depleted in high field strength elements (HFSE; i. e. , Nb, Ta, and Ti), with low Nb/Ta and Zr/Hf ratios, indicating a high degree of crystallization differentiation. The Xiahecun granitic pegmatite has low εHf values (11. 7 to 6. 2), whereas the Shanghecun granitic pegmatite shows higher εHf values (4. 9 to 1. 1). These findings imply that the Xiahecun granitic pegmatite originated from partial melting of ancient crust, while the Shanghecun granitic pegmatite formed through partial melting of juvenile lower crust, followed by magma assimilation and wall- rock contamination. In the eastern part of the North Qinling tectonic belt, the granitic pegmatites can be divided into two types: northern rare- metal granitic pegmatites and southern uranium- bearing granitic pegmatites.
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