北秦岭地体东段早白垩世大规模的新生地壳再造:黄花墁岩体地球化学组成和岩石成因  

Early Cretaceous Large-scale Reworking of the Juvenile Crust in North Qinling:Geochemical Composition and Genesis of the Huanghuaman Pluton

作　　者：齐泽秋 于洋 赵静欣 葛东莉 何俊 陈福坤[1] QI Zeqiu;YU Yang;ZHAO Jingxin;GE Dongli;HE Jun;CHEN Fukun(School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,China;Helmholtz-Zentrum für Ozeanforschung Kiel,Wischhofstraße 1-3,24148 Kiel,Germany)

机构地区：[1]中国科学技术大学地球和空间科学学院,合肥230026 [2]Helmholtz-Zentrum für Ozeanforschung Kiel,Wischhofstraße 1-3,24148 Kiel,Germany

出　　处：《高校地质学报》2023年第6期831-846,共16页Geological Journal of China Universities

基　　金：国家自然科学基金(41872049,42172051)资助。

摘　　要：秦岭造山带东段记录了晚侏罗世和早白垩世两期花岗质岩浆作用,作为深部地壳物质组成和结构的岩石探针,二者的岩石地球化学特征具有明显的差异,反映了复杂的岩浆源区物质组成。文章报道出露于北秦岭地体东部黄花墁岩体的元素和Sr-Nd-Pb同位素地球化学组成和锆石U-Pb年龄数据:锆石U-Pb年龄分析显示,主体岩石黑云母二长花岗岩形成于约119~117 Ma之间,岩浆作用规模大、延续时限短。研究区的花岗岩属于弱过铝质高钾钙碱性系列;富集大离子亲石元素和轻稀土元素,亏损高场强元素和重稀土元素,显著的Eu负异常;具有较高的放射性成因铅同位素组成和相对亏损的Nd同位素组成,初始εNd值为-5.7~-4.1,显著区别于北秦岭地体晚侏罗世花岗岩和华北陆块南缘晚中生代花岗岩。这一相对亏损的同位素组成特征相似于同期形成的东段老君山岩体和西段太白岩体,暗示北秦岭地体早白垩世期间经历大规模的新生地壳再造作用。新生地壳物质可能来自北秦岭地体基性地壳岩石或俯冲至其下的扬子陆块/南秦岭地体新元古代地壳岩石。这些早白垩世岩体与北秦岭地体晚侏罗世蟒岭岩体和牧护关岩体存在明显的Nd同位素组成差异,表明下覆的深部地壳物质组成的复杂性造成花岗岩组成的多样性。The eastern Qinling orogen documents two magmatic episodes of granitoids in the Late Jurassic and Early Cretaceous.Their geochemical characteristics,being a petrologic probe for the composition and structure of the deep crust,are distinctly different,pointing to the complex magma sources.In this study,we report zircon U-Pb isotopic ages and whole-rock major and trace element contents and Sr-Nd-Pb isotopic compositions of the Huanghuaman pluton exposed in the eastern section of the North Qinling block.Zircon U-Pb ages indicate that the large-volume biotite monzogranite of the Huanghuaman pluton was emplaced during the 119 Ma to 117 Ma interval.The biotite monzogranites are enriched in large ion lithophile elements and light rare earth elements,but depleted in high field-strength elements and heavy rare earth elements,with significantly negative Eu anomalies and belong to the weakly peraluminous high-K calc-alkaline series.They are characterized by high radiogenic Pb isotopic compositions and relatively depleted Nd isotopic composition with initialεNd values of-5.7 to-4.1.These geochemical characteristics are remarkably different from those of the Late Jurassic granitoids within the North Qinling block and L ate Mesozoic granitoids within the southern margin of the North China block.The relatively depleted Nd isotopic composition of the Huanghuaman pluton is similar to those of the coeval Laojunshan in the eastern section and the Early Cretaceous Taibai granite in the western section of the North Qinling block,s uggesting that this block underwent large-scale reworking of the juvenile crust during the Early Cretaceous.The juvenile crustal materials might be derived from the mafic rocks within the North Qinling block or the subducted Neoproterozoic crustal rocks of the Yangtze and/or South Qinling blocks.These Early Cretaceous granitoids have different Nd isotopic compositions from those of the Late Jurassic Mangling and Muhuguan plutons in the North Qinling block,reflecting the compositional diversity of the grani

关 键 词：北秦岭地体 晚中生代 新生地壳再造 黄花墁岩体 岩石成因 

分 类 号：P581[天文地球—岩石学] P597[天文地球—地质学]