摘要
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。(87Sr/86Sr)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。
The Xiankou ring complex in Leman county, Jiangxi province is mainly composed of the huge-grained phenocysts-bearing biotite monzonitic granite externally and small-grained phenocysts-bearing biotite monzonitic granite internally, which is penetrated by the fine-grained alaskite dykes. LA-ICP-MS U-Pb zircon ages are obtained for huge-grained phenocysts-bearing, small-grained phenocysts-bearing biotite monzonitic granite and alaskite with weighted ages of 230±4Ma, 235±3Ma and 235±3Ma respectively, All the rocks are characterized by relatively high silicon （SiO2 =70.35%-76. 89%）, alkali （Na20＋Ke0-- 6.77-11.40%） and the weak to strong peraluminium values （A/CNK=1. 00-1. 18, an average of 1.07）. The plutons have high concentrations of rare earth elements [FREE= （121.52-383.33） X 10-8] and high field strength elements （Y, Zr, Nb, etc. ）, but the later dikes own low REE EZREE=（25.85- 43.75） ）〈 10-6values. The rocks are characterized by genesis type between S-type and aluminous A-type granite. （87Sr/8Sr）i=0. 7082-0. 7120,eNd（t）-7.07-8. 10, mean value is --7.48, t2DM=1585-- 1669Ma, and mean value is 1618Ma. It suggest that the magma sources are mainly composed of old crustal rocks and involve some portions of mantle materials. The lead-isotope evolution for K-feldspar also indicate that are mixed mantle-crustal derived, we propose that the Xiankou granitoid produced in post-orogenic tectonic setting.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2015年第1期83-98,共16页
Acta Geologica Sinica
基金
国土资源地质大调查项目(1212011120836,1212011220248)
国家自然科学基金项目(41172063)
核资源与环境教育部重点实验室开放基金项目资助
