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    豫西崤山龙卧沟岩体锆石U-Pb年代学、地球化学特征及地质意义

    Geochronology and geochemical features of Longwogou granite in Xiaoshan Mountain, western Henan Province, and their geological implications

    • 摘要: 提要:豫西崤山北部出露一系列中酸性小岩体,为探讨其成因、深部动力学背景及成矿潜力,对其中之一的龙卧沟岩体进行了锆石定年和地球化学成分分析研究。龙卧沟岩体的岩性为斑状黑云母二长花岗岩,发育钾长石巨斑晶。LA-ICP-MS锆石206Pb/238U年龄为(128±1)Ma,岩体形成时代为早白垩世。龙卧沟岩体具有高硅、富碱高钾、贫镁低钙的特征,属于高钾钙碱性系列,A/CNK值介于1.00~1.11,岩石学和地球化学特征表明其属于富钾钙碱性花岗岩类(KCG)。龙卧沟岩体的稀土配分模式具有轻稀土富集、重稀土亏损的特征,(La/Yb)N范围为18.55~26.92,无明显Eu异常,微量元素蛛网图中Rb和Th富集,具有明显的Nb-Ta负异常。龙卧沟岩体高Sr、低Y,具有埃达克岩属性,它是加厚大陆下地壳的部分熔融形成的,部分熔融源区残余相矿物包括石榴石、金红石和角闪石。崤山北部地区在早白垩世经历了岩石圈拆沉作用,是对中国东部中生代岩石圈巨大减薄的地质响应之一。龙卧沟岩体形成时代位于东秦岭地区广泛而强烈的成岩成矿作用时限内,且其显示了Au、Ag、Mo和W明显异常,表明龙卧沟岩体(含隐伏部分)具有较大的成矿潜力。

       

      Abstract: Abstract:In order to study petrogenesis, geodynamics and mineralization potential of small intermediate-acid igneous bodies in north Xiaoshan Mountain, the authors determined the age and geochemical compositions of Longwogou granite body, which is one of these igneous bodies. Longwogou body is composed of porphyritic biotite monzonitic granite with extensively distributed K-feldspar megacrysts. 206Pb/238U ages of 30 zircons by LA-ICP-MS method are from 125 Ma to 132 Ma, and the weighted average age is (128±1) Ma. Longwogou granite is characterized by higher SiO2 and alkali, enrichment of K2O, and lower MgO and CaO. Compositional spots of Longwogou granite fall into high-K calc-alkaline series in the SiO2?K2O diagram. A/CNK ratios of Longwogou granite are from 1.00 to 1.11. According to the petrologic and geochemical features of Longwogou granite, it belongs to K-rich calc-alkaline granite (KCG). In chondrite-normalized REE patterns, Longwogou granite samples have shown the characteristics of LREE-enrichment and HREE depletion without obvious Eu anomaly. The (La/Yb)N ratios of Longwogou granite are from 18.55 to 26.92. In spider diagram, the enrichment of Rb, Th, and trough of Nb and Ta are displayed. Samples of Longwogou granite have higher Sr and lower Y, and the Sr/Y ratios are in the range of 30.8-60.8, suggesting that Longwogou granite is adakitic granite. Longwogou granite originated from partial melting of the thickened lower crust, and its residual phases of partial melting source included garnet, rutile and hornblende. North Xiaoshan Mountain area underwent lithosphere delamination in early Cretaceous, and it was one of geological responses to huge lithosphere thinning of eastern China in Mesozoic. The formation age of Longwogou body falls into the time interval of extensive and intensive endogenetic mineralization in east Qinling orogen belt. Samples from Longwogou body display obvious enrichment of Au, Ag, Mo and W. It is considered that Longwogou granite and its concealed part have large mineralization potential.

       

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