滇西芒市地区钾长花岗岩的成因及构造背景:岩石地球化学和锆石U-Pb同位素年代学证据  

Petrogenesis and tectonic setting of the K-feldspar granites in Mangshi area, western Yunnan: Evidence from petro-geochemistry and zircon U-Pb isotope chronology

作　　者：邹光富[1] 毛英 邹鑫[3] 毛琼[4] 罗滨[4] 林仕良[1] 丛峰[1] 李再会[1] 谢韬[1] 

机构地区：[1]成都地质矿产研究所,四川成都610082 [2]成都岩矿分析测试中心,四川成都610081 [3]北京大学心理学系,北京100871 [4]华北油田勘探开发研究院,河北任丘062552

出　　处：《中国地质》2013年第5期1421-1432,共12页Geology in China

基　　金：中国地质调查局项目"云南1︰5万梁河县;江东;帕底幅区域地质调查项目"(1212010784007)资助

摘　　要：腾冲地块芒市地区钾长花岗岩分布于芒市北部五叉路乡核桃洼、江东乡杨家寨和轩岗乡南约村一带,主要由钾长花岗岩组成.芒市地区钾长花岗岩大部分是作者通过1∶5万区域地质填图,从原高黎贡山群中解体出来的.为了限定该地区岩浆事件的准确时间,本文对该区钾长花岗岩进行了LA-ICP-MS锆石U-Pb定年和地球化学研究.测得芒市地区钾长花岗岩中锆石的206pb/238U年龄加权平均值为（60.8±0.8） Ma,其形成时代属于古近纪.该区钾长花岗岩具有高SiO2（67.97％～80.62％）、高碱（K2O＋Na2O =5.08％～8.79％）、中-高钾（K2O/Na2O=1.11～17.80）、低P2O5含量（0.01％0.15％）的特征.铝饱和指数（A/CNK）介于1.03～2.31之间,岩石属钾玄岩-高钾钙碱性过铝质-强过铝质S型花岗岩.岩石总体上富集大离子亲石元素Rb、Th、U、Ta、La、Pb、Nd、Sm、Gd等,明显亏损高场强元素Ba、Nb、Ce、Sr、Zr、Hf、Eu等.稀土元素总量（ΣREE）为56×10-6～323×10-6,平均为183×10-6,稀土元素配分曲线呈右倾型,LaN/YbN为1.58～41.60,δ Eu=0.18～0.71,显示弱到中等程度的负铕异常,具有明显的轻稀土富集,重稀土亏损的特征.地球化学研究表明,该花岗岩是以含粘土的变质杂砂岩和粘土岩部分熔融形成的,岩浆可能来源于本区中晚元古代高黎贡山群为代表的地壳物质的部分熔融.是典型壳源成因类型,具岛弧型同碰撞花岗岩特征.该区古近纪钾长花岗岩的形成表明,在60.8 Ma以前,雅鲁藏布江—密支那洋已关闭,印度板块与冈底斯—腾冲板块之间的俯冲、碰撞作用已经发生,并处于岩浆弧形成阶段,为印度板块与冈底斯—腾冲板块之间俯冲、碰撞、成弧造山构造岩浆活动的响应.古近纪钾长花岗岩形成时代及其构造环境的厘定,为进一步探讨腾冲地块构造演化提供了新证据.Located in Tengchong block of western Mangshi are mainly composed of K-feldspar granites. Yunnan, the Paleocene K-feldspar granites in northern Most of the Mangshi K-feldspar granites resulted from the disintegration of original Gaoligong Group, as evidenced limit the age of the K-feldspar magrnatic mineralization 1：50000 regional geological mapping. To precisely Mangshi area, the authors analyzed the granites by using LA-ICP-MS zircon U-Pb technique and geochemical methods. The zircon LA-ICP-MS dating indicates that the K-feldspar granites was emplaced at （60.8___0.8） Ma. The granite mass was formed in the Paleocene period. Geochemical data show that the Lianghe granites are K basaltic, high-K calc-alkaline and peraluminous to strongly peraluminous series, characterized by high content of SiO2 （67.97%-80.62%）, high content of K20＋ Na20 （5.08%~8.79%）, medium to high K（K20/Na20=1.11~17.80）, and lower content of P205 （0.01%~0.15%） with peraluminous ratio （A/CNK） being 1.03-2.31. ACF plot indicates that the granites are S type granites. Mangshi granites are also enriched in Rb, Th, U, Ta, La, Pb, Nd, Sm and Gd,but strongly depleted in Ba, Nb, Ce, Sr, Zr, Eu and Hf. The R_EE content is between 56.42~10-6 and 322.91~10-6, 183.15x10-6 on average, with （La/Yb）N ratios being 1.58-41.60 and 6 Eu being 0.18-0.71. REE diagram shows right inclination and obvious negative Eu anomalies. The intrusion is remarkably characterized by enriched LR.EE and depleted HREE. The chondrite-normalized REE patterns show negative Eu anomalies. Magma source was probably derived from the emplacement of partially melted granitic magma dominated by greywacke and claystone, which is typical of crustal genesis. The K-feldspar granite was derived from partial meking of the Mid-Proterozoic metamorphosed basement （Gaoligong Group）. According to geochemistry and the trace element discrimination diagrams for tectonic interpretation, the Paleocene K-feldspar granites are considered to be of the island arc and syn-coll

关 键 词：古近纪钾长花岗岩 锆石U-PB定年 地球化学 构造意义 腾冲地块 滇西 

分 类 号：P588.12[天文地球—岩石学] P597.3[天文地球—地质学]