地质学报2018，Vol.92Issue(1)：28-40,13.
安徽铜陵焦冲辉石闪长岩体中的两类锆石及其地质意义
Two Types of Zircons from the Jiaochong Pyroxene Diorite Pluton in the Tongling Area of Anhui Province and Their Geological Significance
摘要
Abstract
The zircon grains from the Jiaochong pyroxene diorite pluton in the Tongling area of Anhui Province can be categorized into two types based on the CL images.Type Ⅰ zircon grains are offwhite,show clear oscillatory zoning,and have relatively low concentrations of U,Th,Pb and REE.All these characteristics indicate their magmatic origin.A weighted average 206pb/238U age of 128.5 ±2.1 Ma (MSWD=0.29)yielded in this study may represent the crystallization age of the pluton in a close environment.Combined with the previous published age data,our result indicates there are two periods of magmatic activity.The age data along with the published age of magmatic rock indicate that the Tongling area not only contains the 145～135 Ma magmatic emplacement activity,but also the 134～123 Ma magma activity,which has not been acknowledged but occurred at the same time as volcanic-intrusive rocks in volcanic basins such as the Ningwu basin and Luzong basin.Type Ⅱ zircon grains are greyish black and show unclear oscillatory zoning,and have extremely high concentrations of U,Th,Pb and REE.The type Ⅱ zircon grains are called "high U zircon",and might be influenced by hydrothermal process.The weighted average 206Pb/2338U age of 141.4±2.0 Ma (MSWD=1.06) obtained in this study has no definite geological significance.The two types of zircon grains with two groups of ages occuring in the same pluton verify that if we do not distinguish zircon grains when calculating the weighted average U-Pb age,the results obtained may not be correct or confuse the geological facts.Another significant characteristic of zircon grains from the Jiaochong pyroxene diorite pluton is that the crystal forms of zircon grains are poorly preserved and fragmented,with embayed texture.This indicates that the formation of Jiaochong pluton may have experienced zircon crystallization,corrosion,and the preservation of corrosion morphology.The characteristics of the two types of zircon grains and the U-Pb age from the Jiaochong pyroxene diorite not only record the earlier crystallization and hydrothermal metasomatism of the intermediate-acidic magma,but also reflect the later mafic magma injection and mixing during the diagenetic stage.This reveals the formation of the host rocks has experienced a complicated process:magmatic crystallization →hydrothermal metasomatism →magmatic crystallization →magmatic mixing →magmatic emplacement.关键词
锆石U-Pb年龄/锆石CL图像/锆石微量元素特征/辉石闪长岩/安徽铜陵焦冲Key words
zircon U-Pb age/zircon CL image/trace elements of zircon/pyroxene diorite/Jiaochong district in the city of Tongling/Anhui Province引用本文复制引用
徐晓春,范子良,王蒙,傅仲阳,何俊,谢巧勤..安徽铜陵焦冲辉石闪长岩体中的两类锆石及其地质意义[J].地质学报,2018,92(1):28-40,13.基金项目
本文为国家自然科学基金项目(编号41472066,41672038,40972063)和国家重点研发计划项目之课题(编号2016YFC0600209)联合资助的成果. （编号41472066,41672038,40972063）
