西秦岭凤太矿集区花岗闪长斑岩脉的成因类型和年龄及其地质意义 |
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关键词:Petro-geochemistry LA-ICP-MS zircon U-Pb ages granitoid porphyry dikes Fengtai ore concentration area West Qinling |
基金项目:国家自然科学基金项目(编号: 41372089);中国地质调查局地质调查项目(编号: 1212011220869);陕西省地质勘查基金项目(编号: 61201304172) |
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Genetic Type and Geochronology of the Granodiorite Porphyry Dikes in the Fengtai Ore Concentration Area, West Qinling Orogen, and Their Geological Significance |
The Fengtai ore concentration area in Shaanxi Province is one of the most important lead-zinc and gold ploymetallic ore concentration areas in the West Qinling orogen. In this paper, two samples were collected from the Kongguan and Jintonggou granodiorite porphyry dikes, which are filled in the NWW–trending Tonglinggou–Jiashangou fault in the north central part of the ore concentration area. LA-ICP-MS dating yielded zircon ages of (230.7±1.8) Ma (MWSD=0.68) and (230.4±1.8) Ma (MSWD=0.27), respectively, suggesting Middle Triassic. Geochemical features are as follows: strong depletion of high field strength elements (HFSE), such as Th, Nb, Ta, P and Ti, with Nb/Ta ratios similar to those of the continental crust; strongly fractionated REE patterns ((La/Yb)N=250.69 and 134.94) and no notable Eu anomalies; the 87Sr/86Sr ratios of the two samples being 0.712833±0.000017 and 0.712365±0.000016. All these data indicate that the magma might have been derived from partial melting of the Neoproterozoic Bikou Group, and there existed garnet with no plagioclase left in the source. The dikes were formed at the beginning of the syn-collision period. By integrating the regional tectonic and magmatic characteristics, the authors hold that tectonic evolution of the ore concentration area can be divided into the subduction stage (±250 Ma), the collision stage (±230 Ma) and the post-collision stage (220–200 Ma). The age of 230 Ma from these two dikes gives an upper time limit of the NWW–trending faults in the ore concentration area, implying they were formed during the middle Triassic, earlier than the NE–trending fractures which were formed during the late Triassic. More and more age data show that the time of deformation, metamorphism, magmatism and mineralization in the Fengtai ore concentration area are all focused on 190–230 Ma, implying they are spatial-temporal coupling with each other, and were formed during the Qinling orogenic process in Indosinian period. |
CHEN Shao-cong,WANG Yi-tian,HU Qiao-qing,ZHANG Juan,WANG Rui-ting,WANG Chang-an,LIU Xie-lu,OUYANG Sheng.2018.Genetic Type and Geochronology of the Granodiorite Porphyry Dikes in the Fengtai Ore Concentration Area, West Qinling Orogen, and Their Geological Significance[J].Acta Geoscientica Sinica,39(1):14-26. |
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