粤东秀才堂铝质A型花岗岩体LA-ICPMS锆石U-Pb年龄及其地质意义

LA-ICP-MS zircon U-Pb dating and its geological significance of Xiucaitang aluminous A-type granite batholith, Easthern Guangdong Province

秀才堂岩体位于潮州—普宁断裂带南东侧,主体岩性为中粒晶洞花岗岩与细粒斑状晶洞花岗岩;LA-ICPMS锆石U-Pb定年结果为94.8±2.9 Ma、94.7±3.6 Ma,属于燕山晚期岩浆活动产物。岩体具有富硅(SiO_2平均为75.6%)、准铝(A/CNK值平均为0.997)、钾大于钠(K_2O/Na_2O值平均为1.087),贫镁、铁、钙的特征。岩体富集大离子元素Rb、Th,明显亏损Ba、Sr、Y,且具有较高的Rb/Sr(平均为6.24)和高的Rb/Nb值(平均为30.76),稳定的碱度率(AR变化于4.0~4.46)和里特曼指数(2.12~2.56),轻、重稀土之间分馏明显,配分模式呈水平型,Eu中等亏损,发育晶洞构造等。主量与微量元素地球化学数据显示具有铝质A型花岗岩特征,其形成于地壳伸展减薄背景下,由幔源岩浆底侵导致下地壳熔融而成。

The Xiucaitang granite batholith is located at South-East of Chaozhou-Puning fault zone, the main lithology is medium-grain miarolitic granites with fine-grained porphyritic miarolitic granites,LA-ICPMS zircon U-Pb dating yields ages of 94.8±2.9 Ma and 94.7±3.6 Ma, suggesting its formation in the Late Yanshanian period. This granite is characterized by high silicon（ average SiO2=75.6 wt%）, subaluminous（average A/CNK=0.997） and potassium higher than sodium（average K2O/Na2O = 1.087） and lowmagnesium, iron, and calcium. It is also enriched in Rb,Th, but depleted in Ba, Sr and Y, with high Rb/Sr values（average of 6.24） and high Rb/Nb values（average of 30.76）,stable alkalinity ratio（AR changes from 4.0 - 4.46） and Rittmann index（2.12 - 2.56）, its light and heavy rare earth elements are well fractionated, having flat chondrite-normalized REE patterns with clear Eu depletion and the characteristics of miarolitic structure. Geochemical data of major and trace element show the characteristics of aluminous A-type granites for the Xiucaitang granitie. It is formed in the background of crustal extension and thinning, which is caused by the underplating of mantle magma resulted in the melting of the lower crust.