吉南老岭地区早白垩世铝质A型花岗岩的厘定及其构造意义

Confirmation of Aluminous A-Type Granite Emplacement and Its Tectonic Significance during Early Cretaceous in the Laoling Area, South of Jilin Province

主微量元素分析和LA-ICP-MS锆石U-Pb年龄显示吉南老岭地区的头道、老岭、上绿水桥和高台子岩体为一套早白垩世铝质A型花岗岩.主要岩性为钾长花岗岩、晶洞钾长花岗岩、花岗斑岩和花岗岩.LA-ICP-MS锆石U-Pb年龄为121～125Ma.主量元素具有富Si、alk,贫Fe、Mg、Ca、Ti的特征;微量元素亏损Ba、Sr、Ti、Nb、Ta、P,富集K、Rb、Th等不相容元素;稀土元素具有中等到强烈的负铕异常及右倾海鸥型的球粒陨石标准化稀土配分模式.元素地球化学特征表明岩体为铝质A型花岗岩(A/CNK=0.82～1.15,A/NK=1.00～1.28).岩石具有较低的不相容元素Ce/Nb、Y/Nb、Yb/Ta比值,为A1型非造山花岗岩.研究表明吉南老岭地区早白垩世时处于非造山的伸展构造环境,是华北板块东部早白垩世伸展地球动力学背景在吉林南部地区的岩浆活动体现.

Major and trace elements analysis and LA-ICP-MS zircon U-Pb ages show Toudao, Laoling, Shanglvshuiqiao and Gaotaizi plutons are Early Cretaceous aluminum A-type granites in the Laoling area, South of Jilin Province. Plutons mainly consist of k-feldspar granite, miarolitic k-feldspar granite, granite porphyry and granites. The results of LA-ICP-MS dating are （121--125） Ma. The major elements of granitoids are high in St, alk and low in Fe, Mg, Ca, and Ti. Trace elements are en- riched in incompatible elements such as K, Rb, Th and depleted in Ba, Sr, Ti, Nb, Ta, and P. The granitoids have right-wing type of chondrite-normalized REE patterns and moderate negative Eu anomalies. Geochemical features indicate that granitoids are aluminum A-type granites （A/CNK= （0. 82--1.15）, A/NK= （1.00--1.28））. Granitoids with relatively low incompatible element ratio values such as Ce/Nb, Y/Nb and Yb/Ta are Al-type anorogenic granite. The formation of Al-type granite indi- cates Laoling area is in the Anorogenic extensional tectonic setting during Early Cretaceous.