摘要
宁芜盆地内分布若干基性侵入岩,这些岩体可以用来分析该区岩浆作用机制,从而了解大陆岩石圈深部过程。选取蒋庙辉长岩体为研究对象,利用LA-ICP-MS微区分析技术测定蒋庙辉长岩的锆石U-Pb年龄及其REE地球化学特征,其中锆石的Th和U的质量分数分别变化于327×10^(-6)~3 531×10^(-6)和601×10^(-6)~5 126×10^(-6),REE元素总量均值为2 049.12×10^(-6),^(206)Pb/^(238) U年龄范围为(120±1)Ma^(128±1)Ma。结果表明,蒋庙辉长岩中的锆石显示出高REE含量,HREE富集,Eu负异常,高Th/U比(0.46~1.11)等特征,为典型岩浆成因,其15点的加权平均年龄为(124.5±1.6)Ma,为早白垩世,燕山晚期。综合研究表明,自晚古生代以来,长江中下游地区经历了三期岩浆活动,而蒋庙辉长岩属于长江中下游地区晚期岩浆活动的产物。从早期到晚期,三期岩浆的起源越来越深,受地壳混染程度逐渐降低,暗示本区拉张程度越来越高。
LA-ICP-MS age data and REE geochemistry of zircons from the Jiangmiao gabbro in the Ningwu basin are presented in the paper and theses data are used to analyze magmatic mecha- nism and study the deep processes of the continental lithosphere from the mafic intrusions. It re- veals that the contents of Th and U of Zircon in Jiangmiao gabbro range from 327×10-6 to 3 531 × 10-6 and 601 × 10.6 to 5 126 × 10.6 , respectively and the average of EREE is 2 049.12 ×10-6. LA-ICP-MS dating ages of 2-6Pb/2asU of zircon range from （120±1） Ma- （1284-1） Ma. The zir- cons from the Jiangmiao gabbro show high Th/U ratios （0.46±1.11） ,characteristic of a common melting source,and yield a U-Pb age of （124.5±1.6） Ma of early Cretaceous period. In addition, these zircons show high REE contents,prominent HREE enrichment and a negative Eu anomaly, also characteristic of a common melting source. On the basis of existing petrology,geochemistry and age dating data,it is considered that there are three stages of magmatic events in the Middle and Lower Yangtze region since the late Mesozoic,and the Jiangmiao gabbro represents the latest stage of magmation. The origin of these three stages of magma becomes deeper and deeper,with a trend of more and more extension in this area.
出处
《矿物岩石》
CAS
CSCD
北大核心
2017年第4期88-94,共7页
Mineralogy and Petrology
基金
国家自然科学基金项目(编号:40672045)
