华北陆块南缘泌阳李仙桥花岗岩锆石U-Pb年龄及地球化学特征

Zircon U-Pb Ages and Geochemistry of the Lixianqiao Batholith in Biyang,the Southern Margin of the North China Block

华北陆块南缘李仙桥花岗岩基分布于河南省泌阳县李仙桥-大尖山-贾楼一带,主要岩性为二长花岗岩类,以发育弱片麻理为特征。LA-MC-ICPMS锆石U-Pb年龄资料表明,岩体侵位年龄为131.6~120Ma,属于早白垩世。可划分为3个侵入期次,其中第一期次侵位时间为131Ma左右;第二期次侵位时间为127Ma左右,第三期次侵位时间为120Ma左右。李仙桥花岗岩基具有高硅(w(SiO_2)=70.48%~76.20%)、高碱(w(K_2O+Na_2O)=7.26%~9.55%)、高分异指数(DI=83.90~95.53)的特点,A/CNK平均为1.12,属于高钾钙碱性系列,为过铝质S型花岗岩,富集轻稀土元素、亏损重稀土元素,Eu亏损较为明显(δEu=0.35~0.63),Ba、Sr、P、Ti相对亏损,Rb和高场强元素Th、U、Zr、Hf相对富集。源区岩石成分主要为变质砂屑岩、次为变质泥岩,可能来源于包括太华岩群和秦岭岩群的副变质岩,是地壳部分熔融作用的结果。岩体形成于陆内造山环境下由挤压向伸展的过渡期。

The Lixianqiao batholith of the southern margin of the North China Block is located in Lixianqiao-Dajianshan-Jialou area,Biyang,Henan Province.The main lithology is monzonitic granites,characterized by the development of weak patch.LA-MC-ICPMS zircon U-Pb dating of the Lixianqiao batholith,concordant age of 131.6-120.0 Ma,indicates that the batholith was formed in Early Cretaceous.The batholith can be divided into three invasion periods,of which the first stage emplacement time is about 131 Ma;the second stage emplacement time is about 127 Ma,and the third stage emplacement time is about 120 Ma.The results show that the Lixianqiao batholith is high in silicon（SiO2=70.48%-76.20%）and alkali（K2O＋Na2O=7.26%-9.55%）,high score index（DI=83.90-95.53）,A/CNK average was 1.12.All these charateristics suggest that it belongs to high-K calcium-alkali series and peraluminous S-type granite.The rocks are relatively enriched in LREE and depleted in HFSE,the Eu loss is more obvious（δEu=0.35-0.63）.Ba,Sr,P and Ti are relatively enriched,Rb and HFSE such as Th,U,Zr,Hf are depleted.Source rock composition should be mainly metamorphic psammitolite and secondary metamorphic mudstone,probably from parablastesis that include the Taihua Group and Qinling Group.This should be the result of the partial melting of the crust,This batholith formed the intracontinent orogenic process,were related with extension system substitute extrusion.