摘要
滇西芒市地区石板村黑云母二长花岗岩分布于芒市粱河县南部勐养村—芒市石板村一带,主要由黑云母二长花岗岩组成.石板村黑云母二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.为了限定该地区中生代岩浆事件的准确时间,本文对该黑云母二长花岗岩进行了LA-ICP-MS锆石U-Pb定年.测定结果显示,石板村黑云母二长花岗岩的锆石U-Pb年龄加权平均值为125.60±1.0Ma.表明该花岗岩体的形成时代属于早白垩世.岩石地球化学研究表明,该区早白垩世黑云母二长花岗岩具有高SiO2（70.70％～76.14％）,高碱（K20＋ Na20=7.35％～9.00％）,中—高钾（K20/Na20=1.12～2.37）的特征.铝饱和指数（A/CNK）为0.67～1.17,岩石属钾玄岩—高钾钙碱性过铝—强过铝S型花岗岩.岩石总体上富集大离子亲石元素Rb、Th、U、Nd、Sm和Pb等,明显亏损高场强元素Nb、Ce、Sr、Eu、Zr、Hf等.稀土元素总量（ΣREE）为80.55×10-6～362.85×10-6,平均为171.97×10-6,稀土元素配分曲线呈右倾型,LaN/YbN介于5.11 ～18.80之间,δEu=0.28～1.08,显示弱到中等程度的负铕异常,具有较明显的轻稀土富集,重稀土亏损的特征.根据地球化学特征和微量元素构造判别图解判别结果表明,该花岗岩是以含粘土的变质杂砂岩部分熔融形成的,岩浆可能来源于本区中—新元古代高黎贡山群为代表的地壳物质的部分熔融.是一种典型的壳源成因类型,具后碰撞花岗岩特征,形成于板块间从挤压体制向拉张体制转变的后碰撞构造环境.冈底斯—滕冲构造带早白垩世构造岩浆事件与羌塘—保山板块与冈底斯—腾冲板块之间俯冲、碰撞、成弧造山作用密切相关.早白垩世花岗岩体的发现及其形成时代的厘定,为进一步探讨腾冲地块构造演化提供了新证据.
The Shibancun biotite monzo-granites in the Mengyang Village of Lianghe county — Shiban Village,Mangshi County,are located in the Tengchong Block,western Yunnan.The Shibancun biotite monzo-granites are mainly composed of biotitic monzogranites.Most of the Lianghe granites is from the original Gaoligong Group disintegration by the author through the 1：50000 regional geological mapping.To limit the precise age of the Cenozoic magmatic mineralization in the Mangshi area,the Lianghe granites have been analyzed using LA-ICP-MS zircon U-Pb techniques and geochemical methods.The zircon LA-ICP-MS dating indicates that the biotite monzogranites was emplanced at 125.60 ± 1.0Ma.The granite is formed in the Early Cretaceous.Geochemical data show that the Lianghe granites are k black to high-K calc-alkaline and peraluminous to strongly peraluminous series,characterized by high content of SiO2 （70.70% ～ 76.14%）,the medium to high K（K20/Na20 =1.12 ～ 2.37）and peraluminous ratio（A/CNK） =0.67 ～ 1.17）.ACF plot indicate that the Lianghe granites are S type granites.Lianghe granites are also enriched in Rb、Th、U、Nd、Sm and Pb,but strongly depleted in Nb、Ce、Sr、Eu、Zr and Hf.The REE content is between80.55 × 10-6and 362.85 × 10-6,average 171.97 × 10-6,with （La/Yb） N ratios of 5.11 ～ 18.80 and δEu of =0.28 ～ 1.08.REE diagram shows rightward incline and obvious negative Eu abnormity.The intrusion is remarkably characterized by enriched LREE and depleted HREE.The chondritenormalized REE patterns show negative Eu anomalies.Magma source is probably rising and emplacement of partially melt granitic magma dominated by greywacke,which is typical of crustal genesis.The biotite monzogranite was derived from partial melting of the Mesoproterozoic metamorphosed basement （Gaoligong Group）. According to geochemistry and the trace element discrimination diagrams for tectonic interpretation,the the Cenozoic granitoids are considered to be of the post-collision type formed in a transitional tectonic setting from the compressional system to the tensional system.The Gangdese—Tengchong block tectono-magmatic orogenesis was intimately related to the closure and subduction and collide orogenesis of between the Qiangtang—baoshan plate and Gangdese—Tengchong massif.The determination of the Lianghe granites＇ s crystallization and origin provides new evidence for the Cenozoic tectonic evolution of the Tengchong massif.
出处
《地质论评》
CAS
CSCD
北大核心
2014年第6期1425-1436,共12页
Geological Review
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"(编号1212010784007)的成果
关键词
早白垩世花岗岩
锆石U-PB定年
地球化学
构造意义
腾冲地块
滇西
the Early Cretaceous granites
zircon U-Pb dating
geochemistry
tectonic implications
Tengchong block
western Yunnan
