滇西澜沧岩群钠长浅粒岩锆石U-Pb测年、Hf同位素组成及构造意义  

U-Pb dating of zircon, Hf isotope composition and tectonic significance of the albite-leptite of the Lancang Group in the Shuangjiang area of western Yunnan,China

作　　者：韩文文 彭智敏[2] 张辑 关俊雷[2] 胡金锋 刘云鹤 HAN Wenwen;PENG Zhimin;ZHANG Ji;GUAN Junlei;HU Jingfeng;LIU Yunhe(Institute No.280,CNNC,Guanghan,Sichuan,618300;Chengdu Institute of Geology Mineral Resources,China Geological Survey,Chengdu,610081)

机构地区：[1]核工业二八〇研究所,四川广汉618300 [2]中国地质调查局成都地质调查中心,成都610081

出　　处：《地质学报》2020年第4期1282-1294,共13页Acta Geologica Sinica

基　　金：中国地质调查局项目(DD20160016、DD2016013639);中国核工业地质局项目(201807、201922)资助的成果。

摘　　要：澜沧岩群位于滇西"三江"地区的昌宁-孟连结合带,是研究特提斯造山带重要组成部分。本文对双江地区出露的钠长浅粒岩进行锆石U-Pb定年、Hf同位素及岩石地球化学分析,讨论了岩石的成因和形成时代,以及大地构造演化。利用LA-ICP-MS对钠长浅粒岩中具有典型岩浆震荡环带的锆石U-Pb定年,获得了206Pb/238U加权平均年龄为476.5±1.6Ma,形成时代为早奥陶世(O1)。Hf同位素原位分析获得锆石εHf(t)值为-5.6^-2.2,TDMc年龄为1591~1802Ma,表面源区物质形成于早元古代晚期-中元古早期古老地壳物质的部分熔融。岩石地球化学分析,钠长浅粒岩的原岩为花岗闪长岩,具有高硅SiO2=67.89%~68.91%、富铝Al2O3=14.48%~15.14%、高钾钙碱性过铝质S型花岗岩特征;轻稀土富集,整体呈"右"倾型;δEu值介于0.60~0.64之间,呈现强Eu负异常,表明斜长石从岩浆中结晶分离。分析认为,钠长浅粒岩的原岩应特为昌宁-孟连特提斯洋在弧-陆碰撞阶段形成的岛弧花岗岩,与奥陶纪惠民岩组火山岩具有相同的大地构造背景;随着特提斯洋俯冲消减进入陆内挤压阶段,岛弧花岗岩呈俯冲增生杂岩拼贴到昌宁-孟连结合带与临沧花岗岩带之间,组成了澜沧岩群构造岩片。The Lancang group, an important part of the Tethys orogenic belt, is located in the Changning-Menglian combined belt in the Sanjiang area of western Yunnan, China. In this paper, we have conducted zircon U-Pb dating, Hf isotope analyses and petrogeochemistry of albite-leptite to determine the genesis, chronology, and geotectonic evolution of the rocks in the Shuangjiang area. The detrital zircons with strongly oscillatory zoning employed for dating are of magmatic origin from albite-leptite. The U-Pb date, weighted average of 206Pb/238U, is 476.5±1.6 Ma, which is Early Ordovician(O1). The εHf(t) from the in-situ analysis of Hf isotopes is-5.6^-2.2 and the TDMc Age is 1591~1802 Ma indicating that the materials in the source area were formed by partial melting of ancient crustal materials from the terminal Early-Proterozoic to the early Middle-Proterozoic. According to petrogeochemical analysis, the original rock of albite-leptite is granitic diorite which is a peraluminous S-type granite with high SiO2=67.89%~68.91%, aluminum-rich Al2O3=14.48%~15.14% and high potassium calc-alkaline. The characteristics i.e. enrichment in LREE, the overall tilt to "right", δEu(0.60~0.64)and strong negative Eu, indicated that plagioclase has separated from the magma. The analysis shows that the original rock of albite-leptite is island-arc granite, which formed in the continent-arc collision stage around Changning-Menglian Tethys, has the same tectonic background as the volcanic rocks of the Huimin Formation in the Ordovician. As Tethys entered intracontinental subduction-grinding stage, the island-arc granite is a subduction accretionary complex, between the Changning-Menglian combined belts and the Lincang Batholith, forming tectonic sheet of the Lancang group.

关 键 词：滇西双江地区 澜沧岩群 锆石U-Pb年龄 HF同位素 昌宁-孟连结合带 岛弧花岗岩 

分 类 号：P597[天文地球—地球化学] P588[天文地球—地质学]