豫西崤山后河岩体的地球化学及锆石稀土元素特征

摘要

豫西崤山北部内生金属成矿作用较弱,仅有几个规模较小的Au矿床.对崤山北部燕山期酸性小岩体开展岩石成因研究,不仅可对深部动力学过程进行限定,而且为区域找矿思路的转变提供依据.为此,对崤山北部的后河岩体全岩样品进行了主量元素、微量元素、稀土元素及锆石稀土元素成分分析.后河岩体具有高硅、富碱高钾、贫镁低钙的特征,岩体样品投点在SiO2-K2O图解中落入钾玄岩系列,A/CNK值介于1.04～1.26之间.后河岩体的稀土配分模式具有右倾平滑、轻稀土富集、重稀土亏损的特征,(La/Yb)N范围为30.95 ～49.38,无明显Eu异常.后河岩体富集Rb和Th,具有明显的Nb、Ta、P和Ti负异常,高Sr,低Y、Yb,属于埃达克岩.后河岩体是加厚大陆下地壳的部分熔融形成的,部分熔融源区的残余相矿物包括石榴石和金红石,岩浆演化过程中没有经历明显的斜长石结晶分异作用.后河岩体锆石稀土元素具有轻稀土亏损、重稀土富集、Ce正异常及无明显Eu异常的特征,锆石的形成温度介于624 ～701℃之间,后河锆石/熔体体系中重稀土元素分配系数变化证明了深部岩浆(流体)混合作用的存在.后河岩体是早白垩世崤山北部岩石圈拆沉作用的产物,这有利于成矿流体和埃达克质岩浆快速上升,其周缘出露申家窑Au矿床及岩体自身明显的Au、Ag、Cu、Mo及W高含量异常均表明后河具有较大的成矿潜力,它应当是崤山北部的找矿靶区之一.%The endogenetic mineralization in north Xiaoshan Mountain is weak,and only several Au deposits were found.The petrogenesis of small Yanshanian igneous complexes in north Xiaoshan Mountain is useful to limit the deep geodynamic process,and it is an important evidence to change exploration ideal.In this paper,major and trace elements analytical results of whole rock samples and zircon REEs from Houhe complex were reported.Houhe complex is characterized by higher SiO2 content and alkali enrichment in K2O,lower MgO and CaO content.Compositional spots of Houhe complex fell into shoshonitic series in SiO2-K2O diagram.A/CNK ratios of Houhe complex are from 1.04 to 1.26.In chondrite-normalized REE pattern diagram,Houhe complex samples have shown the characteristics of LREE enrichment and HREE depletion without obvious Eu anomaly.The (La/Yb)N ratios of Houhe complex are from 30.95 to 49.38.In spider diagram,the enrichment of Rb,Th,and depletion of Nb,Ta,P and Ti are displayed.Samples of Houhe complex are higher in Sr,and lower in Y and Yb,which indicates that it is adakite.Houhe complex is originated from partial melting of the thickened lower crust,and its residual phases of partial melting source include garnet and rutile.There is no obviously compositional effect of plagioclase fractional crystallization in the process of Houhe granitic magma evolution.Rare earth element content of zircon in Houhe complex has shown the characteristics of LREE depletion,HREE enrichment with Ce positive anomaly and no obvious Eu anomaly.The formation temperature of zircon is from 624 to 701 C.In zircon/melts system of Houhe complex,the change of partition coefficients for HREE is a result of magma (fluids) mixing.Houhe complex is product of regional lithosphere delamination in Early Cretaceous;deep fluids and adakitic magma can ascend rapidly in this process.The occurrence of Shenjiayao Au deposits around Houhe complex and the enrichment of Au,Ag,Cu,Mo and W in Houhe complex indicate that it has mineralization potential,and it should be regarded as one of exploration targets in north Xiaoshan Mountain.