滇西南澜沧江结合带北段云县花岗岩的地质特征及形成环境  

Geological characteristics and tectonic setting of Yunxian granite in the northern part of South Lancangjiang convergent margin, Western Yunnan Province

作　　者：刘德利[1] 刘继顺[1] 张彩华[1] 周余国[1] 

机构地区：[1]中南大学地学与环境工程学院,湖南长沙410083

出　　处：《岩石矿物学杂志》2008年第1期23-31,共9页Acta Petrologica et Mineralogica

基　　金：国家自然科学基金资助项目(40072032);云南省省院省校合作项目(2003UDBEA00Q021)

摘　　要：滇西南澜沧江结合带云县花岗岩体的岩石类型主要为黑云二长花岗岩，SiO2含量平均为68．57％，K2O／Na2O值平均为1．67，相对富钾，岩石属高钾钙碱性系列，岩石酸、碱度低于同类岩石平均值，而镁铁组分高于平均值，显示岩石偏中性，与同碰撞构造环境形成的花岗岩特征类似。Al2O3含量较高，平均为13．66％，A／CNK平均为1．1，呈铝过饱和，CIPW计算结果均出现标准矿物刚玉分子（〉1％）。岩石总体上相对富集大离子亲石元素，亏损高场强元素。稀土元素总量较高，平均为240．75×10^-6，轻稀土元素富集，重稀土元素亏损，（La/Yb）N为8．88～9．41，分异不是很大，Eu为中等负异常，8Eu为0．52～0．57。经多种相关图解判别，岩石属S型花岗岩，其构造环境相当于大陆碰撞花岗岩类（CCG）。锆石颗粒U-Pb测年结果显示，源岩的形成年龄最晚是晋宁期（〉778Ma），岩体主体形成于华力西晚期－印支期。其中岩浆成因锆石样品的^206pb／^238U和^207Pb／^235U年龄分别为49Ma和61Ma，反映在云县岩体中可能存在喜马拉雅期岩浆活动。Yunxian granite in South Lancangjiang convergent margin comprises mainly diorite monzonite granite and belongs to the potassium-rich calc-alkali series, with SiO2 being 68.57 % and K2O/Na2O 1.67 on average. The acidity and alkalinity of the rock are lower than the average values of the same kind of rocks, and its mafic ingredient is higher than the average value, suggesting that the rock is somewhat intermediate and similar to the syn-collision type granite. Yunxian granite is peraluminous, with Al2O3 being 13.66% and A/CNK 1.1 on average and the corundum molecule more than 1% according to CIPW. The rocks are on the whole relatively rich in LILE but poor in HFSE and shows moderate negative Eu anomalies with 3Eu being 0.52-0.57, ∑REE 240.75 × 10^- 6 on average and （La/Yb）N 8.88 - 9.41. According to geochemical characteristics and related discrimination diagrams, it is suggested that Yunxian granite should be of S type and its tectonic setting corresponds to CCG. The results of zircon U-Pb dating show that the formation period of the source rocks must not have been later than the Jinningian （ 〉778 Ma）, with the main formation periods being from late Hercynian to Indosinian. Two ages of ^206pb/^238U and ^207pb/^235U of the genetically magmatic zircon are 49 Ma and 61 Ma, which indicate the probable existence of Himalayan magmatic activity in Yunxian granite.

关 键 词：滇西云县 花岗岩 构造环境 锆石U-PB年龄 

分 类 号：P588.121[天文地球—岩石学] P618.510.2[天文地球—地质学]