滇西九顶山斑状花岗岩LA-ICP-MS锆石U-Pb定年及地球化学特征  

Zircon U-Pb Geochronology and Geochemistry of Porphyritic Granite in the Jiudingshan area,West Yunnan

作　　者：刀艳[1] 李峰[1] 王蓉[1] 吴静[1] 范柱国[1] 陆世才[1] 

机构地区：[1]昆明理工大学国土资源工程学院,云南昆明650093

出　　处：《地质与勘探》2014年第3期533-542,共10页Geology and Exploration

基　　金：国家危机矿山接替资源勘查项目(编号:20089943);云南省自然科学基金项目(编号:2011FZ035)资助

摘　　要：九顶山斑状花岗岩产于扬子板块西缘与金沙江-哀牢山深大断裂构造带东侧交会部位,是矿区内复式小杂岩体群中出露面积最大的岩体。岩体斑晶含量约占30%,主要由正长石、斜长石、石英和少量的黑云母、角闪石等组成;基质为中细粒的石英、斜长石和正长石等组成,副矿物主要有磷灰石和锆石等。斑状花岗岩中锆石U-Pb年龄为34.7±0.6 Ma,为喜马拉雅早中期(始新世)的产物。斑状花岗岩具有高钾富碱高铝的特征,属碱性-碱钙性,高钾钙碱性系列-钾玄岩系列,大部分落入A型花岗岩区域。斑状花岗岩轻稀土富集、重稀土亏损(La/Yb)N=28.90~42.28,负Eu异常(δEu=0.69~0.93)不明显,富集大离子亲石元素Rb、Ba、U、Th和亏损高场强元素Nb、Ta、Zr、Hf。通过斑状花岗岩地球化学特征、图解判别等的综合研究,认为九顶山斑状花岗岩是壳幔混合成因,形成于青藏高原新生代碰撞造山-造山期后拉张的构造环境。The Jiudingshan porphyritic granite,the largest exposed rock of the Jiudingshan complex,is located at the junction of the west Yangtze plate and the east Ailaoshan-Jinshajiang fault. Megacrysts( 10%) of porphyric granite contain orthoclase,plagioclase,quartz and biotite,and matrix comprises quartz,plagioclase and orthoclase. The accessory mineral assemblages consist of apatite,zircon,and so on. LA-ICP-MS zircon U-Pb dating of 10 zircon grains from Jiudingshan porphyritic granite gives a concordant age of 34. 7 ± 0. 6 Ma,the Eocene. The porphyric granite is petrochemicaly characterized by high potassium,rich alkali and high alumina,belonging to high K calc alkaline series and shoshonite series,which can be classified as Atype granite. The intrusion shows LREE enrichment,HREE depletion,weak negative Eu anomaly( δEu = 0. 69 ~ 0. 93) and a smoothly right-declined REE distribution pattern,enrichment of LILE( Rb,Ba,U,Th) and depletion of HFSE( Nb,Ta,Zr,Hf) with negative Nb and Ta. Geochemical characteristics in discrimination diagrams of porphyritic granite in Jiudingshan indicate that this rock body was mainly derived from a crust source mixed with mantle materials and formed at the Cenozoic syn-collision and post-orogenic stage of the Tibetan plateau in an extensional tectonic setting.

关 键 词：斑状花岗岩 锆石U-PB年龄 地球化学 九顶山 云南 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]