江西九岭杂岩体中黑云母花岗闪长岩年龄及对扬子和华夏板块碰撞拼合时间限定

Biotite granodiorite age of Jiuling complex in Jiangxi Province and its limitation on the collision and splicing time of the Yangtze and Cathay plates

为探讨赣北地区九岭岩体的岩浆成因和构造属性,本文选取作为九岭岩基重要组成部分的大湖塘黑云母花岗闪长岩进行了年代学、地球化学及锆石Lu-Hf同位素研究。LA-ICP-MS锆石U-Pb定年结果表明黑云母花岗闪长岩形成于(835.6±1.5)Ma,属于钾-高钾钙碱性过铝质花岗岩系列,具有典型的S型花岗岩的特点,其形成与中元古界双桥山群的熔融密切相关。锆石ε_(Hf)(t)主要为正值(2.8~8.2),表明形成花岗岩的岩浆来源于元古宙地壳物质的再循环。大湖塘黑云母花岗闪长岩形成的构造环境背景很可能是同碰撞向后碰撞转换的阶段,结合前人研究,我们认为扬子板块和华夏板块碰撞拼合的时间上限应为835 Ma左右。

In order to explore the magmatic origin and tectonic setting of the Jiuling pluton in northern Jiangxi,a combined study of geochronology,geochemistry and zircon Lu-Hf isotope was carried out for the Dahutang biotite granodiorite.LA-ICP-MS zircon U-Pb dating of biotite granodiorite suggests it was formed at(835.6±1.5)Ma.Geochemistry analysis shows it belongs to the series of potassium-high potassium calcium alkaline peraluminous granite.It has the typical characteristics of S-type granite and it was derived from the melting of the Neoproterozoic Shuangqiaoshan Group.The positive zirconε_(Hf)(t)value(2.8-8.2)suggests that the magma forming the granite was originated from the recycling of Proterozoic crustal material.The Dahutang biotite granodiorite was formed in a tectonic background of transition stage from syn-collision to post-collision.Combining with previous studies,it is inferred that that the upper time limit of collision between the Yangtze and Cathaysia plate should be about 835 Ma.