西藏羌塘南缘早白垩世普让岩体的锆石U-Pb年龄和地球化学特征及其地质意义  

Zircon U-Pb Age and Geochemical Features of the Early Cretaceous Purang Pluton on the Southern Margin of Qiangtang,Xizang(Tibet),and Their Geological Implications

作　　者：黄瀚霄[1] 龚福志 李光明[1] 刘洪[1] 陈华安[1] 祝向平[1] 肖万峰[3] 

机构地区：[1]中国地质调查局成都地质调查中心,成都610081 [2]西藏自治区地质矿产勘查开发局第二地质大队,拉萨850000 [3]河南省地质调查院,郑州450001

出　　处：《地质论评》2016年第3期569-584,共16页Geological Review

基　　金：国家重点基础研究发展计划项目(编号:2011CB403105);中国地质调查项目(编号:DD20160026)的成果~~

摘　　要：普让岩体位于西藏羌塘南缘多龙矿集区西北部,岩体的岩石类型组合为石英二长岩—二长岩—二长闪长岩,侵位于三叠纪日干配错群灰岩中,并形成矽卡岩型磁铁矿。石英二长岩LA-ICP-MS的锆石^(206)Pb/^(238)U加权平均年龄为116±2Ma(MSWD=6.5),与该带上的多龙含矿斑岩成岩年龄基本一致。普让岩体不含白云母,且标准矿物中富含透辉石,具有较高的Al_2O_3,较低的Ti O_2,富集大离子亲石元素(LILE),亏损高场强元素(HFSE)和重稀土元素(HREE),显示Nb和Ta的负异常,具有明显的岛弧型岩石的地球化学特征,属于准铝质I型花岗岩。与多龙含矿斑岩相比,普让岩体具有相似的ε_(Nd)(t)值(-7.22^-6.81),n(^(87)Sr)/n(^(86)Sr)i值(0.707525~0.708243)和古老的Nd的模式年龄(1.29~1.63Ga)。研究表明:普让岩体可能是在班公湖—怒江洋壳北向俯冲的背景下,下地壳重熔,且在上升的过程中经历了分离结晶和地壳混染作用下形成的。多龙外围的岩浆岩带不仅具有寻找斑岩铜矿的潜力,也是形成和寻找的矽卡岩型多金属矿的有利地区。Objectives： The Purang Pluton is located in the south margin of Qiangtang,Xizang（ Tibet）,consisting of Quartz monzonite,monzonite and monzodiorite. It intruded the limestone of the Triassic Riganpeiqun Group,accompanying with skarn-type magnetite mineralization. The study of the pluton is scare. Our research mainly focuses on the formation age and the petrogenesis of quartz monzonite in the Purang area. In addition,here we also discuss its metallogenic significance.Methods：Based on detailed observations of the occurrences of Purang pluton in the field,we have studied the chronology,petrology,geochemistry and related mineralization of this pluton. In order to understand its affinity,we have studied the petrology and elemental geochemistry; Together with the geochronologic and Sr—Nd isotopic studies,the formation age and the petrogenesis of this rock have been well constrained. In compary with the coeval Duolong ore-bearing porphyry in the same tectonic unit,we have discussed the metallogenic significance of the Purang intrusion.Results：The LA-ICP-MS U-Pb dating yields a weighted average age of 116 ± 2 Ma（ MSWD = 6. 5） for the Quartz monzonite,consistent with that of the Duolong ore-bearing porphyry. The Purang pluton is muscovite absent and diopside- rich with high Al_2O_3 but low TiO_2contents. It is also enriched in large ion lithophile elements（LILE）,depleted in high field-strength elements（ HFSE） and heavy rare earth elements（ HREE）,with pronounced negative anomalies of Nb and Ta. These features are similar to those of the island arc. Accordingly,the rock is classified to I type granite. In compary with the Duolong ore-bearing porphyry,the Purang granite have similar initial ε_（Nd）（- 7. 22 ^- 6. 81） and n（^（87）Sr） / n（^（86）Sr） as well as the old model Nd age（1. 29 ~ 1. 63 Ga）.Conclusions：This study suggests that the Purang granite should be emplaced in a subduction setting related to the north-toward subducting of the Bangong Lake—Nujiang River ocea

关 键 词：年代学 地球化学 岛弧 找矿意义 羌塘南缘 西藏 

分 类 号：P597.3[天文地球—地球化学] P534.53[天文地球—地质学]