北秦岭西峡骨头崖花岗岩锆石U-Pb定年、地球化学特征及地质意义  

LA-ICP-MS Zircon U-Pb Dating,Geochemical Features of Gutouya Granite in Xixia County,Northern Qinling Mountains,and Its Geological Implications

作　　者：卢仁 梁涛 

机构地区：[1]河南省有色金属地质勘查总院,郑州450052 [2]河南省有色金属深部找矿勘查技术研究重点实验室,郑州450052

出　　处：《地质论评》2017年第6期1479-1496,共18页Geological Review

基　　金：国家自然科学基金资助项目(批准号:U1504405);河南省基础与前沿技术研究计划(项目编号:162300410065);河南省国土资源厅科技攻关项目(编号:2016-08和2014-06)的成果~~

摘　　要：骨头崖花岗岩位于北秦岭构造带东部,西峡县北部,对其开展岩石成因研究有助于深入认识燕山期北秦岭豫西南段深部构造演化。岩体定年样品(GTY01)为中粒斑状黑云母二长花岗岩,30个锆石测点中有25个测点的U-Pb同位素测定值位于或者接近^(207)Pb/^(235)U–^(206)Pb/^(238)U一致线,23个测点的^(206)Pb/^(238)U年龄介于108.4±0.9Ma^114.3±1.0Ma之间,其加权平均年龄为111.7±0.6Ma(MSWD=1.4),代表了骨头崖花岗岩的形成时代。锆石稀土元素具有轻稀土亏损、重稀土富集、Ce正异常及负Eu异常的特征,形成温度介于626℃~769℃之间,岩体的锆石/熔体中重稀土元素特征表明,其形成过程中经历了岩浆混合作用。骨头崖花岗岩为富硅、碱和贫钙、镁的高钾钙碱性系列。岩体富集Rb、Th和亏损Nb、Ta、Ti。岩体的稀土配分模式具有右倾、轻稀土富集、重稀土亏损和负Eu异常的特征,(Eu值介于0.48~0.60之间,(La/Yb)_N范围为5.82~11.19,源区组成和部分熔融程度控制了骨头崖花岗岩的成分变异。骨头崖花岗岩形成于厚度为~40km的地壳内,其部分熔融源区为角闪岩相,部分熔融残余相主要为角闪石和斜长石。骨头崖花岗岩是岩石圈拆沉作用所触发的岩浆底侵作用的产物,从源区岩石部分熔融到最终上侵固结成岩耗时~15Ma,它是岩石圈拆沉作用滞后的岩浆响应。Objectives： Gutouya granitic body is one of Yanshanian acid intrusions in Xixia County, southwest Henan Province, locaded in northern Qinling Mountains. Petrogenesis and deep process of Gutouya granite are important to recognize Yanshanian tectonic evolution in northern Qinling Mountains.  Methods： Based on detailed observations of Gutouya granitic body in northern Qinling Mountains, we have studied the petrology, geochemistry and chronology of Gutouya intrusion. The geological implications of Gutouya granitic body was discussed. Results：The zircon U-Pb dating method of LA-ICP-MS was used to conform the age of biotite monzonitic granite sample named GTY01 from Gutouya granite. The results of 25 zircon spots in total 30 spots are concordia with 207Pb/235U 206Pb/238U trendline. The 206Pb/238U ages of GTY01 08 and GTY01 15 are 419.3±4.6 Ma and 905.2±20.2 Ma, respectively. The weighted average 206Pb/238U age of 23 zircon spots in youngest age group from 108.4±0.9 Ma to 114.3±1.0 Ma is 111.7±0.6Ma （MSWD=1.4）, which is regarded as the formation age of Gutouya granite. In chondrite normalized REE patterns of zircons in GTY01 sample, the characteristics of LREE depleted, HREE enriched with Ce positive anomaly and Eu negative anomaly are shown. The formation temperature of zircon is from 626℃ to 769℃. In zircon/melts system of Gutouya granite, the change of partition coefficients for HREE is result of magma （fluids） mixing, which agrees with mafic microgranular enclave in Gutouya granite. Gutouya granite is characterized by higher SiO2 and alkali, and lower MgO and CaO. Compositional spots of Gutouya granite fall into high K calc alkaline series in the SiO2—K2O diagram. Samples from Gutouya granite are enriched in large ion lithophile elements and depleted in high field strength elements, which has formed peaks of Rb and Tb, and troughs of Nb, Ta, P and Ti in spider diagram. In chondrite normal

关 键 词：骨头崖花岗岩 U-PB定年 岩浆混合 底侵作用 JL秦岭 豫西南 西峡 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]