江西乐安县咸口花岗岩体的锆石LA-ICP-MS定年及构造意义
Acta Geologica Sinica(2015)
Abstract
江西乐安县咸口花岗岩体主要由中粗粒巨斑状黑云二长花岗岩、中粗粒少斑黑云二长花岗岩组成,另有较多细粒碱长花岗岩脉,总体呈偏心式环套状分布.锆石LA-ICP-MS U-Pb年龄分别为230±4Ma、235±3Ma和235±3Ma,形成于中三叠世.岩石具有高硅(SiO2 =70.35%~76.89%),富碱(Na2O+K2O=6.77%~11.40%),弱过铝—强过铝(A/CNK=1.00~1.18,平均1.07)的特征.主体花岗岩富集稀土元素[∑REE=(121.52~383.33)×10-6]和高场强元素(Y、Zr、Nb等),晚期强分异并受流体作用的细粒碱长花岗岩稀土含量低[∑REE=(25.85~43.75)×10-6].具有S型—铝质A型过渡型花岗岩的特征.(37Sr/86 Sr)i为0.7082~0.7120,εNd(t)值介于-7.07~8.10之间,平均值为-7.48,t2DM为1585~1669Ma,平均1618Ma,显示其物源以地壳物质为主,混有地幔组份,钾长石Pb同位素组成也显示壳幔混源的特征.提出咸口岩体形成于后造山的构造环境.
MoreKey words
Indosinian,the Xiankou granitoid,S-type and aluminous A-type,zircon LA-ICP-MS U-Pb dating,South China,post-orogenic
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