贺根山缝合带南侧西乌旗哈尔敖包早石炭世二长花岗岩的发现及其构造意义  

Discovery and its tectonic significance of the Early Carboniferous monzogranite from the south of Hegenshan suture zone in Haer,Xiwuqi,Inner Mongolia

作　　者：程天赦 杨文静[2] 张学斌[2] 滕超[1] 杨欣杰 来林[2] 吴荣泽[2] 周长红[2] Cheng Tianshe;Yang Wenjing;Zhang Xuebin;Teng Chao;Yang Xinjie;Lai Lin;Wu Rongze;Zhou Changhong(Cores and Samples Center of Natural Resources,China Geological Survey,Langfang,Hebei 065201;Tianjin Institute of Geological Survey,Tianjin 300191)

机构地区：[1]中国地质调查局自然资源实物地质资料中心,河北廊坊065201 [2]天津市地质调查研究院,天津300191

出　　处：《地质科学》2024年第4期907-924,共18页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：中国地质调查局项目(编号:DD20242250,[2010]矿评01‑19‑01)资助。

摘　　要：内蒙古西乌旗地区新发现的哈尔敖包二长花岗岩体出露于贺根山缝合带南侧,厘定该岩体的形成时代、岩石成因和构造环境对探讨古亚洲洋贺根山洋盆的构造演化具有重要意义。哈尔敖包二长花岗岩LA-ICP-MS锆石U-Pb测年结果为327.7±2.6 Ma,形成于早石炭世,并非前人推测的中二叠世;岩石富硅(SiO_(2)平均值为76.04%)、碱(K_(2)O+Na_(2)O平均值为8.82%)、铝(Al_(2)O_(3)平均值为13.44%)及Rb、Pb、Th、U、Ta、LREE,低镁、铁、锰、钙、钛、磷(P_(2)O_(5)平均值为0.03%)及Sr、Eu、Nb、Ti、HREE,铕负异常较明显(δEu平均值为0.30)。岩石地球化学研究表明,哈尔敖包二长花岗岩显示Ⅰ型花岗岩特征,形成于同碰撞向后造山转换阶段的初始伸展构造环境,Zr/Hf、Nb/Ta比值及岩石分异指数(DI=94.93~96.81)显示岩浆在侵位过程中经历了较强的分异演化。结合区域研究成果,哈尔敖包早石炭世二长花岗岩体的识别与确定,表明西伯利亚板块南缘与锡林浩特微陆块可能在早石炭世早期发生了短暂碰撞造山作用,标示着古亚洲洋贺根山洋盆在早石炭世早期短暂性闭合后,于早石炭世晚期又快速打开并进入俯冲消减阶段,呈现出多旋回演化的特征。The newly recognized monzogranite distributes along the south of Hegenshan suture zone in Haer,Xiwuqi,Inner Mongolia,and its chronology,tectonic setting and genesis has not been studied yet,which is of great significance for studying the geological evolution of the Hegenshan ocean.The LA-ICP-MS zircon U-Pb dating shows that the age of the monzogranite is 327.7±2.6 Ma.The rock has high SiO_(2)(the average value of SiO_(2) is 76.04%),alkali(the average value of K_(2)O+Na_(2)O is 8.82%),Al_(2)O_(3)(the average value of Al2O3 is 13.44%)and low MgO,TFeO,MnO,CaO and P2O5(the average value of P_(2)O_(5) is 0.03%).The Rb,Pb,Th,U,Ta and LREE are relatively enriched,while Sr,Eu,Nb,Ti and HREE are relatively depleted,with obvious Eu anomaly(the average value ofδEu is 0.30).The Zr/Hf,Nb/Ta and rock differentiation index(DI=94.93~96.81)indicate that the magma of Haer monzogranite might have been experienced strong crystallization differentiation during the emplacement,with the characteristics of I-type granite.The lithogeochemistry indicates that the Haer monzogranite has the characteristics of I-type granite,which is preliminarily believed that the monzogranite was formed in an initial extensional tectonic environment during the collisional post orogenic transition stage.Together with regional geologic research results,the identification and determination of the Early Carboniferous Haer monzogranite indicate that collision orogeny may have occurred between the Siberian plate and the Xilinhot microcontinental block during the Early Carboniferous.The Hegenshan ocean experienced brief closure until to the Late Early Carboniferous,and it opened quickly again entering a subduction and subduction stage.The Hegenshan ocean exhibited a feature of multi-cycle evolution.

关 键 词：二长花岗岩 Ⅰ型花岗岩 早石炭世 贺根山洋盆 多旋回演化 贺根山缝合带 

分 类 号：P588.1[天文地球—岩石学]