坦桑尼亚乌本迪造山带Kipili英安岩-流纹岩的年代学、地球化学特征及岩石成因  

Geochronology,geochemistry and petrogenesis of the Kipili dacite-rhyolite in the Ubendian Belt,Tanzania

作　　者：吴兴源 刘晓阳 龚鹏辉 许康康 孙凯 何胜飞 周佐民 贺福清 WU Xingyuan;LIU Xiaoyang;GONG Penghui;XU Kangkang;SUN Kai;HE Shengfei;ZHOU Zuomin;HE Fuqing(Tianjin Center,China Geological Survey,Tianjin,300170;Eastern and Southern Africa Geosciences Cooperation Research Center,CGS,Tianjin,300170)

机构地区：[1]中国地质调查局天津地质调查中心,天津300170 [2]中国地质调查局东部南部非洲地学合作研究中心,天津300170

出　　处：《地质学报》2021年第4期1212-1230,共19页Acta Geologica Sinica

基　　金：中国地质调查局地质调查项目“海上丝绸之路非洲中东部7国矿产资源潜力评价”(编号DD20160108)、“非洲中东部大型铜-钴资源基地评价”(编号DD20190439);商务部援外项目“援赞比亚东北地区航空物探和地质地球化学综合填图”(编号[2015]352)、“援卢旺达地质矿产调查”(编号jsyz20180051)联合资助的成果。

摘　　要：Kate-Kipili火山-侵入岩组合位于乌本迪带西缘与班韦乌卢地块的结合部位,通常被认为代表了造山后阶段的岩浆活动记录。本文对Kipili火山岩进行LA-ICP-MS锆石U-Pb测年的结果显示,3件样品的207Pb/206Pb年龄加权平均值分别为1887.0±8.6Ma、1885.4±8.0Ma和1869.0±8.0Ma,指示其形成于古元古代晚期。全岩地球化学分析表明,Kipili英安岩-流纹岩样品总体表现为高硅、高碱和低钛、低铁、低镁和低磷的特征,属于偏铝质—弱过铝质、高钾钙碱性系列岩石;所有样品均富集轻稀土元素及Rb、Th和K等大离子亲石元素,具中等的负Eu异常,亏损Nb、Ta、P和Ti等高场强元素,Ba、Sr含量变化较大。本文样品具有高的分异指数(DI=94~98)、低的铝饱和指数(A/CNK=0.82~1.10)和刚玉分子数(<1.0%),其斑晶通常仅见黑云母(绿泥石化)、石英和长石,而未出现白云母、石榴子石等富铝矿物,暗示它们属于高分异I型长英质岩石。Kipili火山岩的锆石εHf(t)值变化范围大(-5.42~+2.16)、全岩εNd(t)值为较小的负值(-1.83~+0.11)并具有高的锆饱和温度,Hf-Nd二阶段模式年龄均为古元古代早期—新太古代,表明本文英安岩-流纹岩是古老的下地壳物质遭受幔源基性岩浆底侵发生部分熔融并与之混合后的母岩浆经历高程度分离结晶作用形成的。结合区域上已有的资料,本文认为Kipili火山岩很可能形成于乌本迪造山作用同碰撞到后碰撞过渡阶段的伸展背景。The Kate-Kipili volcano-plutonic complex is located at the junction of the western margin of the Ubendian belt and the Bangweulu block,and is generallyconsidered to represent post-orogenic magmatism of the Ubendian orogeny.The LA-ICP-MS zircon U-Pb dating of three samples has yielded weighted mean 207Pb/206Pb ages of 1887.00±8.6 Ma,1885.4±8.0 Ma and 1869.0±8.0 Ma,respectively,indicating that they were formed during the late Paleoproterozoic.The whole rock major and trace elements analyses show that these dacite-rhyolites are generally characterized by high silica and are alkali-rich,with low contents of TiO2,TFeO,MgO and P2O5,belong to metaluminous-weakly peraluminous and high potassium calc-alkaline rock series.All the samples are enriched in LREEs and large ion lithophile elements(e.g.,Rb,Th and K),with moderate negative Eu anomaly,while depleted in high field strength elements(e.g.,Nb,Ta,P and Ti),as well as the contents of Ba and Sr vary widely.The dacite-rhyolites inthis study have a high differentiation index(DI=94~98),low aluminum saturation index(A/CNK=0.82~1.10)and corundum(<1.0%).In addition,the phenocrysts from the Kipili volcanics are commonly composed of biotite(chloritized),quartz and feldspar,but aluminum-rich mineralsare absent,suggesting that they are of highly differentiated I-type series.A wide range of zirconεHf(t)values(-5.42~+2.16),both negative and positive whole rockεNd(t)values,high zirconium saturation temperature,as well as two-stage Hf-Nd model ages between early Paleoproterozoic and Neoarchean(2.26~2.86 Ga),reveal that these felsic volcanics were derived from partially melted ancient lower crustal rocks which were heated by the underplating of mantle-derived magma,simultaneously with a significant contribution of mantle-derived materials,and then underwent a high degree fractional crystallization.The present results combined with the previous researches in the region,demonstrate that the Kipili volcanic rocks probably erupted during the transition period from syn-collision to pos

关 键 词：乌本迪带 Kate-Kipili火山-侵入岩 古元古代晚期 高分异Ⅰ型长英质火山岩 

分 类 号：P588.14[天文地球—岩石学]