赣南遂川晚侏罗世幕式花岗质岩浆活动:年代学、地球化学和Lu-Hf同位素约束  

Late Jurassic episodic granitic magmatism in Suichuan,southern Jiangxi:Constraints from chronology,geochemistry and Lu-Hf isotope

作　　者：刘高峰 王连训[3] 罗春林 熊清华 楼法生 卢先锋 刘永旭 LIU GaoFeng;WANG LianXun;LUO ChunLin;XIONG QingHua;LOU FaSheng;LU XianFeng;and LIU YongXu(Basic Geological Survey Institute of Jiangxi Geological Survey Institute,Nanchang 330030,China;Nonferrous Geology and Mineral Exploration and Development Institute of Jiangxi,Nanchang 330030,China;School of Earth Sciences,China University of Geosciences(Wuhan),Wuhan 430074,China;Jiangxi Geological Survey Institute,Nanchang 330009,China)

机构地区：[1]江西省地质调查勘查院基础地质调查所,南昌330030 [2]江西有色地质矿产勘查开发院,南昌330030 [3]中国地质大学(武汉)地球科学学院,武汉430074 [4]江西省地质调查勘查院,南昌330009

出　　处：《岩石学报》2023年第8期2489-2510,共22页Acta Petrologica Sinica

基　　金：中国地质调查局地质调查项目(1212011120812)资助。

摘　　要：赣南遂川县晚侏罗世花岗岩体由弹前单元与紫阳单元组成。弹前单元主要岩石类型为细粒黑云母花岗岩(g1)和粗粒黑云母二长花岗岩(g2);紫阳单元为中粗粒黑云母二长花岗岩(g3)、细粒含斑黑云母二长花岗岩(g4)和中细粒黑云母二长花岗岩(g5)。这些花岗岩具有相似的矿物组合及地球化学特征,均不含角闪石、白云母、堇青石、石榴石等矿物,斜长石An值为20~30;具有较高的SiO_(2)(70.6%~78.6%)、Al_(2)O_(3)(12.2%~14.3%)、K_(2)O(4.34%~6.04%)含量与FeOT/MgO比值(3.95~13.5)、A/CNK比值(1.01~2.12),饱和温度(742~820℃)、DI值(86~95),较低的P_(2)O_(5)(0.002%~0.14%)含量;稀土元素中Eu元素负异常明显;微量元素中富集Rb、Th、U、Ta、Nd,亏损Ba、Nb、Sr、Zr等元素,属于高分异I型花岗岩。尽管岩石类型和岩石地球化学特征相近,锆石U-Pb定年结果及野外接触关系显示两单元形成于不同阶段,弹前单元为155.4~152.2Ma,紫阳单元为148.7Ma。锆石Lu-Hf同位素也指示二者具有不同的岩浆源区,前者εHf(t)为-10.9~-19.5,平均为-14.2;后者εHf(t)为-8.50~-11.2,平均为-10.0。这些特征显示该岩体为晚侏罗世幕式多期次岩浆活动的产物,其母岩浆主要为古老地壳熔融产物,并混合了少量地幔组分,在岩浆上升侵位过程中经历了明显的AFC过程。由此本文认为遂川花岗岩形成于后碰撞的构造环境,是由华南板块局部岩石圈拉张减薄导致岩石圈地幔物质上涌热驱动同熔地壳所形成。The Late Jurassic granite pluton in Suichuan County,southern Jiangxi Province,is mainly composed of the Danqian and Ziyang units.The main rock types in the Danqian unit are fine-grained biotite granites(g 1)and coarse-grained biotite monzonite(g 2),while those in the Ziyang unit are mainly medium-to coarse-grained biotite monzogranite(g 3),porphyritic monzonitic granite(g 4)and medium-to fine-grained biotite monzogranite(g 5).These granites have similar mineral assemblages and geochemical characteristics.To be more concretely,the studied samples are absent of muscovite,cordierite and garnet in their mineral assemblages,and have relatively low plagioclase An values(20~30),high SiO 2(70.6%~78.6%),Al_(2)O_(3)(12.2%~14.3%)and K 2O(4.34%~6.04%),and low P 2O 5(0.002~0.14%)contents,variable FeO T/MgO(3.95~13.4)and A/CNK(1.01~2.12)values.Furthermore,these rocks are also characterized by high magma temperatures(742~820℃)and DI values(86~95),and their standardized rare earth element distribution curves show negative Eu anomalies.The whole-rock trace element compositions are enriched in Rb,Th,U,Ta and Nd,but depleted in Ba,Nb,Sr and Zr,suggesting that they are highly-fractionated I-type granite.Although the rock types and geochemical compositions of the two units are similar,their zircon U-Pb ages and field contact relationships show that they were formed in different stages:the Danqian unit was formed at 155.4~152.2Ma,while the Ziyang unit at~148.7Ma.Zircon Lu-Hf isotopes of the rocks in these two units also indicate that they have a slightly different source:the former has zirconεHf(t)values between-10.9~-19.5(averaged at-14.2),while the latter has zirconεHf(t)values of-8.50~-11.2(averaged at-10.0).These features indicate that the Suichuan pluton is the product of episodic multistage magmatic activities in the Late Jurassic,whose parent magma is mainly sourced from partial melt of an ancient crust mixed with a few mantle components.This magma experienced an obvious AFC process during its ascending emplacement.Thus,we

关 键 词：赣南遂川 高分异I型花岗岩 锆石U-PB年龄 LU-HF同位素 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]