湖北麻城市四道河地区面理化含榴花岗岩的成因

摘要

Field and laboratory studies show that the foliated garnet-bearing granites from the Sidaohe region were derived from the Paleozoic sedimentary rocks through metamorphism.Geochemical characteristics of the garnet-bearing granites are similar to those of the typical alkali granites,i.e.,rich in silicon ( SiO2 = 75.24% -77.23%),alkali (Na2O +K2O=6.87% -8.84%) and poor in aluminium ( A12O,= 11.00% -12.78%).The rocks are rich in lithophile trace elements (Mb,Ba,Th,U) and poor in HFS elements ( Nb,Ta,Zr,Hf).The rocks are relatively rich in LREE ( XREE = 101.08 ~ 180.1 μg/g,LREE/HREE =3.1 ~6.8) showing moderate negative Eu anomalies.Genetic types and ages of the zircons from garnet-bearing granites demonstrate that they are inherited zircons in sedimentary rocks formed no earlier than Paleozoic.%野外和室内研究结果表明,四道河地区面理化含榴花岗岩由古生代沉积岩变质而成.在元素地球化学特征上,具有与岩浆成因的碱性花岗岩一致的特点:高硅(SiO2=75.24％ ～ 77.23％)、富碱(Na2O+ K2O =6.87％ ～8.84％)、低铝(Al2O3=11.00％ ～ 12.78％)；富Rb、Ba、Th、U等大离子亲石元素和Pb,贫Nb、Ta、Zr、Hf等高场强元素；稀土元素含量较高(ΣREE=101.08～180.1 μg/g),轻稀土元素相对富集(LREE/HREE=3.1 ～ 6.8),铕有中等负异常( δEu=0.30～0.68)；锆石成因类型及定年结果表明,老核(继承锆石)是异地多时代(元古代-古生代),其寄主岩的原岩是沉积岩,时代不会早于古生代.