西藏南木林普洛岗岩体锆石定年和Hf同位素特征及其地质意义  

LA-ICP-MS Dating and Hf Isotopic Analysis of the Zircon from the Puluogang Granite in Namulin County,Tibet,and Its Geological Significance

作　　者：丛源[1] 肖克炎[1] 翟庆国[2] 董庆吉[3] 

机构地区：[1]中国地质科学院矿产资源研究所,北京100037 [2]中国地质科学院地质研究所,北京100037 [3]中国地质调查局,北京100037

出　　处：《吉林大学学报（地球科学版）》2012年第6期1783-1795,共13页Journal of Jilin University：Earth Science Edition

基　　金：国家自然科学基金面上项目(41072167)

摘　　要：对冈底斯中段南木林县普洛岗乡花岗岩岩体进行了原位锆石LA-ICP-MS U-Pb定年和Hf同位素分析。2个花岗岩样品加权平均年龄分别为(44.3±1.1)和(44.5±1.1)Ma,代表该岩体的岩浆结晶年龄为始新世。岩石地球化学资料显示,花岗岩SiO2质量分数为60.53%～65.28%,K2O+Na2O质量分数为6.53%～7.98%,Al2O3质量分数为15.52%～16.13%,铝饱和指数为0.86～0.91,属于准铝质高钾钙碱性系列花岗岩类。花岗岩轻稀土元素相对较富集,具有明显的Eu负异常,微量元素中亏损Nb、Ta、Ti和富集Rb、Th、U、Pb。锆石Hf同位素初始比值εHf(t)值为8.8～11.1,176 Hf/177 Hf为0.282 994～0.283 060,Hf同位素地壳模式年龄为422～557Ma,反映了其岩浆来源于新生地壳物质的部分熔融。普洛岗乡花岗岩的形成与新特提斯洋向北俯冲、俯冲板片折返断离有关。LA-ICP-MS U-Pb dating and Hf isotope compositions of the zircon from granite at Puluogang Town,Namulin County,in the middle Gangdese belt,Tibet,have been studied.LA-ICP-MS U-Pb dating of zircons form two granite samples yielded weighted mean ages of（44.3±1.1） Ma and（44.5±1.1） Ma,representing crystallization age of the granite.Geochemical data show that these samples belong to high-K calc-alkaline series,with SiO2 contents of 60.53%-65.28%,total alkali（K2O＋Na2O） contents of 6.53%-7.98%,Al2O3 contents of 15.52%-16.13%,and A/CNK values of 0.86-0.91.The granitic samples are characterized by enrichment of the light REE,clearly negative Eu anomaly,enriched in Rb,Th,U and Pb,and depleted in Nb,Ta and Ti.Two granite samples have high zircon εHf（t） values of 8.8-11.1,and 176Hf/177Hf values of 0.282 994-0.283 060,with Hf crustal model ages of 422-557 Ma.These geological data indicate that partial melting of newly crustal materials has contributed to the magma origin of the granite.Therefore,we can draw a conclusion that the granitic pluton were probably formed by the northward subduction of new Tethys and slab rollback and break-off.

关 键 词：冈底斯 花岗岩 锆石LA-ICP-MSU-PB定年 HF同位素 地球化学 

分 类 号：P588.12[天文地球—岩石学]