辽宁北票地区江沟山岩体锆石U-Pb年代学和地球化学

U-Pb ZIRCON GEOCHRONOLOGY AND GEOCHEMISTRY OF JIANGGOUSHAN INTRUSION IN BEIPIAO AREA,LIAONING,CHINA

辽宁北票地区江沟山岩体主要岩性为二长花岗岩,属高钾钙碱性岩系.SiO2含量高(71.4%～73.78%),富碱并相对富Na2O(Na2O/K2O平均为1.17),Mg#较低(平均为0.18).岩石的铝饱和指数(A/CNK)较高(1.09～1.24),为过铝质岩石.标准矿物中普遍出现刚玉分子(1.36～3.01),应属S型花岗岩特点.稀土总量较低(平均为96.99×10-6),轻、重稀土分馏明显((La/Yb)N=6.27～32.88),有中等程度的负铕异常(0.77～0.87).在微量元素蜘蛛网图上,强烈富集大离子亲石元素(如Rb、Ba),高场强元素(如Ti)强烈亏损.在R1-R2图解中,江沟山岩体投影在同碰撞环境.该岩体锆石U-Pb年龄加权平均分别为239±2 Ma和233±4 Ma,表明该岩体为三叠纪侵位.前人研究发现,本区西部有中三叠世(229.2～237.5 Ma)侵入的S型花岗岩体,认为是西伯利亚板块与华北板块碰撞的产物.本文结论与之完全一致,从而为两大板块边缘大陆岩石圈演化提供了新的依据.

The Jianggoushan intrusive body in Beipiao area,Liaoning Province,mainly monzogranite,belongs to high-potash calc-alkalic series.It is characterized by high SiO2（71.4%-73.78%）,rich alkali and relative high Na2O（（Na2O/K2O = 1.17）,with low Mg#（averagely 0.18） and high A/CNK（1.09-1.14）.Normative minerals commonly include corundum（1.36-3.01）.These data prove that the intrusion is of S-type granite.The rocks have relative low abundance of REE（average 96.99×10^-6） with variable differentiation between LREE and HREE and medium negative Eu anomalies（δEu = 0.77-0.87）.The rocks are enriched in LILE（Rb,Ba） but depleted in HFSE（Ti）.The Jianggoushan intrusion formed in syn-collision environment according to R1-R2 diagram.The U-Pb isotopic ages of zircon from two samples are 239±2 Ma and 233±4 Ma,respectively,suggesting an emplacement during Triassic.Previous study shows that the S-type granite of Middle Triassic（229.2-237.5 Ma） in the west of the area is from the collision of Siberia plate and North China plate.This paper agrees with the previous study and provides new information for the research on the evolution of continental lithosphere in the plate＇s margins.