滇西北羊拉铜矿矿区花岗岩成因及其构造意义  

Genesis and tectonic significance of granites in the Yangla ore district,northwestern Yunnan Province

作　　者：朱经经[1,2] 胡瑞忠[1] 毕献武[1] 钟宏[1] 陈恒[1,2] 叶雷[3] 龙斐 

机构地区：[1]中国科学院地球化学研究所矿床地球化学国家重点实验室,贵阳550002 [2]中国科学院研究生院,北京100049 [3]有色金属矿产地质调查中心新疆地质调查所,乌鲁木齐830011 [4]云南迪庆矿业开发股份有限责任公司,香格里拉674400

出　　处：《岩石学报》2011年第9期2553-2566,共14页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划项目(2009CB421005);中国科学院重要方向项目(KZCX2-YW-Q04-08;KZCX2-YW-Q04-01)联合资助

摘　　要：羊拉铜矿位于金沙江缝合带中段,贝吾、里农和路农岩体在矿区内从北向南呈线状分布。3个岩体主要岩性为花岗闪长岩,具有相似的地球化学和Sr-Nd同位素组成特征,反映它们可能具有相同岩浆源区。岩体具高的SiO2(64%～73%)、较高的K2O(2.15%～4.05%)和低的P2O5(0.04%～0.11%)含量,δ(里特曼指数)=1.4～2.4,铝饱和指数(摩尔Al2O3/(CaO+Na2O+K2O))为0.92～1.11。同时3个岩体均富集Rb、Th、U、Pb和LREE等元素,显著亏损Nb、Ta、Ti和P等元素。10000Ga/Al比值(1.7～2.1)较典型A型花岗岩偏低,Eu负异常不明显,这些特征表明3个岩体属于准铝-弱过铝质的、高钾钙碱系列I型花岗岩。与区域上大陆地壳物质相比(如临沧黑云母二长花岗岩和川西沙坝麻粒岩),贝吾、里农和路农岩体具有相对低的(87Sr/86Sr)i(0.7078～0.7105)和相对高的εNd(t)(-5.1～-6.7),并具古老的Nd同位素二阶段模式年龄(tDM2=1.5Ga)。结合花岗岩体内部发育大量的同时代的暗色微粒包体(MME),认为岩浆源区存在幔源物质的加入。区域地质背景分析表明,贝吾、里农和路农岩体很可能是在中咱微陆块与昌都-思茅微陆块碰撞的晚期或后碰撞的动力学背景之下,由底侵的幔源基性岩浆及其诱发的中下地壳长英质岩浆在深部岩浆房混合,并经一定程度的分离结晶作用而形成。The Yangla copper deposit is located in the middle zone of Jinshajiang suture zone.The Beiwu,Linong and Lunong granitoids exhibit a linear distribution from north to south in the ore district.The three granitoids have similar compositions of major,trace elements and Sr-Nd isotopes,indicating that they have a common magma source.They do not contain muscovite,and have high concentrations of SiO2（64%~73%）,K2O（2.15%~4.05%） and low P2O5（0.04%~0.11%） content.In addition,they have low δ（（K2O＋Na2O）2/（SiO2-43）;1.4~2.4） and A/CNK（molecular Al2O3/（CaO＋Na2O＋K2O）;0.92~1.11）.The granitoids display significantly negative anomalies of Nb,Ta,Ti and P,obvious enrichment of LREE and Rb,Th,U and Pb.The 10000Ga/Al ratios（1.7~2.1） of those rocks are lower than typical A-type granites.Moreover,considering the slightly negative Eu anomalies,it is suggested that the three granitoids belong to high-K calc-alkaline,metaluminous-slightly peraluminous I-type granites.Compared with the continental crust（i.e.,the Lincang granite and the Shaba granulite）,the granites have lower（87Sr/86Sr）i（0.7078~0.7105） and higher εNd（t）（-5.1^-6.7）,with ancient Nd two-stage model age（tDM2=1.5Ga）.And there occur a number of coeval mafic microgranular enclaves（MMEs） in these granitoids,suggesting that mantle-drived magmas were involved in the source region（see in a separate article）.By combining with comparative analyses of the tectonic settings,we propose a model in which the Beiwu,Linong and Lunong granitoids were generated under a late collisional or post-collisional setting.Decompression induced those mantle-derived magmas underplated and provided the heat for the anatexis of the crust.The hybrid melts（i.e.,mantle-derived and the lower crustal magmas） and subsequent fractional crystallization could be responsible for the formation of the Beiwu,Linong and Lunong granitoids.

关 键 词：I型花岗岩 全岩地球化学 SR-ND同位素 贝吾 里农和路农岩体 壳幔混合 

分 类 号：P588.121[天文地球—岩石学]