内蒙古乌海桌子山花岗岩的锆石U-Pb年代学、地球化学特征及其地质意义  

Zircon U-Pb Geochronology and Significance of Granites from Zhuozishan Region,Wuhai,Inner Mongolia

作　　者：何泽宇 申俊峰[1] 张善明[1,2] 刘俊 杜佰松[1] HE Zeyu;SHEN Junfeng;ZHANG Shanming;LIU Jun;DU Baisong(School of the Earth Sciences and Resources,China University of Geosciences,Beijing 100083,China;Inner Mongolia Eighth Geological Mineral Exploration Institute,Wuhai,Inner Mongolia 016000,China;School of Earth Resources,China University of Geosciences,Wuhan,Hubei 430074,China)

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]内蒙古第八地质矿产勘查开发院,内蒙古乌海016000 [3]中国地质大学(武汉)资源学院,湖北武汉430074

出　　处：《现代地质》2021年第2期523-534,共12页Geoscience

基　　金：内蒙古自治区地勘基金项目(NMKD2014-10,NMKD2016-06)。

摘　　要：内蒙古乌海桌子山花岗岩体位于鄂尔多斯盆地西缘与阿拉善地块东缘交汇处,主要由正长花岗岩和二长花岗岩组成。锆石LA-ICP-MS U-Pb测年结果显示,正长花岗岩和二长花岗岩的形成年龄分别为(2039±79)Ma和(1866±120)Ma,属古元古代岩浆活动的产物。地球化学特征显示,正长花岗岩与二长花岗岩均属钙碱性岩系列,两者具有富硅、富铝、富钾,而相对贫钛、贫钠、贫钙的特征,且A/CNK值在1.19~1.32之间变化,均属于过铝质花岗岩。两者之间的稀土总量相差较大,其中二长花岗岩的稀土总量(ΣREE)为17.36×10^(-6)~11.704×10^(-6),正长花岗岩的稀土总量(ΣREE)为241.05×10^(-6),但均表现出轻稀土(LREE)明显富集、重稀土(HREE)相对亏损的特点,前者呈明显负Eu异常(Eu/Eu^(*)=0.36),后者呈明显正Eu异常(Eu/Eu^(*)=3.39~4.89),表明正长花岗岩的分离结晶程度更高。在微量元素方面,正长花岗岩表现出富集Th、U、Pb及大离子亲石元素(Rb、K等),相对亏损Ba、Nb、Ti等特征;二长花岗岩表现为富集大离子亲石元素(Rb、Ba、K),亏损Th、Nb、Ta、Ti等高场强元素特点。结合区域地质背景,认为二者为同一岩浆作用时期不同阶段泥质岩石部分熔融的结果,代表了同碰撞阶段的产物,指示桌子山地区在古元古代末期存在两期岩浆事件。结合该区地层产状和接触关系以及矿产分布特征,认为阿拉善地块与鄂尔多斯地块之间在古元古代末期完成了最后一次拼合造山事件。The Zhuozishan granites in Wuhai(Inner Mongolia)are located at the intersection of the western margin of Ordos basin and the eastern margin of Alxa block,and comprise mainly syenogranite and monzogranite.LA-ICP-MS zircon U-Pb dating indicates that the syenogranite and monzogranite were emplaced in(2,039±79)Ma and(1,866±120)Ma,respectively,which are the products of Paleoproterozoic magmatsm.According to geochemical characteristics,the syenogranite and monzogranite are calc-alkaline,and both are rich in Si,Al and Ka,but relatively poor in Ti,Na and Ca.In addition,the granites are peraluminous(A/CNK=1.19-1.32).There is significant total REE difference between the monzogranite(17.36×10^(-6)-11.70×10^(-6))and syenogranite(241.05×10^(-6)).Meanwhile,our data show that LREEs are obviously enriched and HREEs are relatively depleted.The former shows obvious negative Eu anomaly(Eu/Eu^(*)=0.36),and the latter shows obvious positive Eu anomaly(Eu/Eu^(*)=3.39-4.89),indicating that the fractionation degree of syenogranite is higher.In terms of trace elements,syenogranite is characterized by enrichments in Th,U,Pb,and large ion lithophile elements(LILEs,e.g.,Rb,K),but depleted in Ba,Nb,and Ti.Monzogranite is characterized by enrichments in LILEs and depletions in high field strength elements(HFSEs,e.g.,Th,Nb,Ta,and Ti).Considering the regional geological background,these rocks were likely formed by partial melting of argillaceous rocks in different stages of the same magmatic phase,representing the products of the same collision stage.This indicates that there were two magmatic events in the Late Paleoproterozoic Zhuozishan.Considering the contact characteristics of strata and the mineralization distribution characteristics,we infered that the final orogenic event between the Alxa and Ordos blocks was completed by the end Paleoproterozoic.

关 键 词：阿拉善地块 华北克拉通 不整合 锆石U-PB测年 拼合 古元古代 

分 类 号：P618[天文地球—矿床学] P597[天文地球—地质学]