东秦岭神林花岗岩的锆石U-Pb定年、地球化学特征及构造背景  

Zircon U-Pb age,geochemical features of the Shenlin granite,eastern Qinling Orogenic Belt,and its implications for tectonic settings

作　　者：梁涛 卢仁 刘小丽 LIANG Tao;LU Ren;LIU Xiaoli(General Institute of Non-ferrous Metals Geological Exploration of Henan Province,Zhengzhou,450052;Key Laboratory of Deep Ore-prospecting technology Research for Non-ferrous Metals of Henan Province,Zhengzhou,450052)

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》2021年第5期1245-1262,共18页Geological Review

基　　金：国家自然科学基金资助项目(编号:U1504405);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：神林花岗岩能够为反演东秦岭燕山期区域构造演化提供新的制约。它的主体岩性为斑状黑云母二长花岗岩,其锆石LA-ICP-MS U-Pb同位素定年结果为130.6±0.7 Ma。神林花岗岩样品具有高硅富碱和贫镁低钙的特征,属于高钾钙碱性系列,以准铝质—弱过铝质为主。它们富集大离子亲石元素(如Rb、Th和K)和亏损高场强元素(如Nb、Ta和Ti),具有轻稀土富集、重稀土亏损的特征,其(La/Yb)N范围为17.6~22.2,δEu值为0.59~0.72。在LaN—(La/Yb)N图解中,神林花岗岩样品显示正相关关系,表明是源区组成和部分熔融作用控制其成分变异。神林花岗岩样品显示了高Sr、低Y和Yb的特征,Sr/Y值为24.3~37.9,属于高锶低钇中酸性岩(adakite,有人音译为埃达克岩)。神林花岗岩形成于加厚大陆下地壳的部分熔融,其源区深度大于50 km,部分熔融源区残余相包括石榴子石、金红石和角闪石,无或者少量的斜长石。神林花岗岩锆石具有轻稀土亏损、重稀土富集、Ce正异常的特征,锆石的形成温度介于624~701℃之间,重稀土元素分配系数与年龄的变化特征表明神林花岗岩经历了深部岩浆/流体的注入与混合,这与暗色微粒包体所揭示的神林花岗岩深部成岩过程相吻合。混合活化后的岩浆/流体体系沿区域深大断裂上侵,在其次级断裂带内的断裂交汇处就位成岩。神林花岗岩形成于东秦岭陆(板)内造山阶段,是约131 Ma区域岩石圈拆沉作用的岩浆响应。Objectives:The Shenlin granite is located in the eastern Qinling Orogenic Belt,which emplaced in Yanshanian.The Shenlin granite provides us an opportunity to revealing the tectonic evolution history in the eastern Qinling Orogenic Belt during Yanshanian.Methods:Based on detailed field observations of the Shenlin granite in the eastern Qinling Orogenic Belt,we have studied the petrology,geochemistry and chronology of the Shenlin granite.The petrogenesis and deep tectonic implications of the Shenlin granite was discussed.Results:The zircon LA-ICP-MS U-Pb dating was used to constrain the formation age of the Shenlin granite.The 27 of 30 zircon spots of the Shenlin granite yield a n(206Pb)/n(238U) age of 130.6±0.7 Ma (MSWD=2.1).The Shenlin granite are characterized by higher in Si O_(2)and alkali,and lower in MgO and CaO contents.The Shenlin granite belong to high-K calc-alkaline series in the SiO_(2)—K2O diagram,and metaluminous to weakly peraluminous with A/CNK ratios of 0.99~1.03.The Shenlin granite samples are enriched in large ion lithophile elements (e.g.,Rb,Th and K) and depleted in high field-strength elements (e.g.,Nb,Ta and Ti).In chondrite-normalized rare earth element (REE) patterns,the Shenlin granite samples exhibit light rare earth element (LREE) enrichment and heavy rare earth element (HREE) depletion withδEu values of 0.59~0.72.The linear trend of the Shenlin granite samples in LaN—(La/Yb)Ndiagram has suggested that the compositional change is controlled mainly by source and degree of partial melting.The Shenlin granite samples are with high Sr,and low Y and Yb contents,with the Sr/Y ratios of 24.3~37.9 that is indicative of adakite affinity.The Shenlin granite is originated from partial melting of the thickened lower crust with thickness>50 km,and its residual phases include garnet,rutile and amphibolite,and minor plagioclase.In chondrite-normalized REE patterns of zircons,the characteristics of LREE-depleted,HREE-enriched with Ce positive anomaly are shown,and the zircon formation temperature

关 键 词：神林花岗岩 U-PB定年 锆石稀土元素 岩浆混合 岩石圈拆沉 东秦岭 

分 类 号：P548[天文地球—构造地质学] P588.121[天文地球—地质学]