赣中南城加里东期花岗闪长岩成因:来自LA-ICP-MS锆石U-Pb年代学及岩石地球化学的制约

Genesis of Caledonian granodiorite in Nancheng,central Jiangxi:constraints from LA-ICP-MS zircon U-Pb geochronology and geochemistry

赣中南城地区出露一套加里东期花岗闪长岩,通过对该套花岗岩进行LA-ICP-MS锆石U-Pb测年,获得其成岩年龄为413.8±2.3 Ma,属加里东晚期岩浆活动的产物。岩石富碱(Na2O+K2O在6.46%~6.62%)、贫硅(SiO2在67.81%~68.42%)、贫钙(CaO在3.94%~4.07%)、贫镁(MgO在0.63%~0.65%),具有强过铝质性质和低钾(拉斑)系列特征。稀土总量较低(∑REE=47.39×10^-6~68.11×10^-6),轻稀土富集明显((La/Yb)N=12.97~27.24),REE配分曲线具有明显的右倾特征,Eu正异常明显(δEu=2.15~3.66),亏损Ba、Nb、Ta等元素,富集Rb、Sr、Th、U、Pb,具有高Sr低Yb型花岗岩特征。岩浆来源具有壳幔混合特点,与加里东晚期赣中南古陆大部分花岗岩形成的大地构造背景差异性较大,可能与赣中南古陆该时期大地构造属性不均一有关。

A set of Caledonian granodiorite is exposed in the Nancheng area from the central Jiangxi.Based on the LA-ICP-MS zircon U-Pb dating technique,the diagenetic age of the granite is 413.8±2.3 Ma,which is the magmatite in the late Caledonian period.The rocks are alkali-rich(Na2O+K2O=6.46%-6.62%),silicon-poor(SiO2=67.81%-68.42%),calcium-poor(CaO=3.94%-4.07%),and magnesium-poor(MgO=0.63%-0.65%),with strong over-aluminium properties and low potassium-tholeiite features.The REE distribution curve is a right-dumping curve,Eu positive anomaly is obvious(δEu=2.15-3.66),and elements,such as Ba,Nb,and Ta,are depleted,and Rb,Sr,Th,U,and Pb are enriched.∑REE is low(∑REE=47.39×10^-6-68.11×10^-6),LREE is enriched((La/Yb)N=12.97-27.24).They are high Sr and low Yb type granites.The magma source has the characteristics of crust and mantle mixing.Compared with most of the late Caledonian granites in the ancient land of the central-south Jiangxi,the geotectonic background of study area is very different.It may be related to the heterogeneity of the tectonic attributes of the ancient land in central-south Jiangxi.