诸广山南体燕山期花岗岩的锆石SHRIMPU-Pb年龄及其构造意义

摘要

诸广山南体是一个由加里东期、印支期和燕山期花岗岩组成的巨型复式岩体.本文采用高精度的锆石SHRIMP U-Pb法首先对位于诸广山南体东、西部结合部位的长江、赤坑、企岭和茶山等4个岩体进行精确定年,测定结果分别为160 ±2 Ma(MSWD=1.8)、154±1 Ma(MSWD=0.41)、156±2 Ma(MSWD=2.5)和157±3 Ma(MSWD=2.7),反映它们都是燕山早期岩浆活动产物,从而进一步证实中—晚侏罗世之交是南岭地区岩浆活动的高峰时期.结合这些岩体的岩石学特征以及相邻地区地质资料,上述燕山早期花岗岩是在太平洋板块俯冲影响下,使先期印支地块与华南地块碰撞产生的薄弱构造带发生进一步伸展的背景下由位于中、下地壳部位的古老变质沉积岩发生部分熔融的方式形成.%The southern part of the Zhuguang Mountains is a large granitic composite consisting of Caledonian, Indosinian and Yanshanian granites. This paper reports SHRIMP zircon U-Pb dating results for four granites located at the joint area of eastern and western sections of the granitic composite. These four granites, namely Changjiang, Qiling, Chikeng and Chashan, yield ages of 160 ±2 Ma(MSWD = 1. 8) 、156 ±2 Ma( MSWD = 2. 5)、154 ± 1 Ma(MSWD = 0.41) and 157 ±3 Ma (MSWD =2.7) .respectively, which indicates that they are formed during the Early Yanshanian magmatic activity and further verifies that in the Nanling region there was a magmatic activity peak during the period between the Middle and Late Jurassic. The petrological characteristics of these granites and regional geological features support the view that these Early Yanshanian granites were emplaced during the further extension induced by Paleopacific Plate subduction in the vulnerable zone originally generated by the collision between the Indochina Plate and South China Plate in the Indosinian period.