内蒙古西乌旗早泥盆世Ⅰ型石英闪长岩的发现及其地质意义  

New Discovery of the Middle Devonian I-Type Xiwuqi Quartz Diorite in Inner Mongolia and Its Geological Significance

作　　者：程天赦 杨文静[2] 滕超[1] 张学斌[2] 杨欣杰 来林[2] 吴荣泽[2] 周长红[2] CHENG Tianshe;YANG Wenjing;TENG Chao;ZHANG Xuebin;YANG Xinjie;LAI Lin;WU Rongze;ZHOU Changhong(Cores and Samples Center of Natural Resources,China Geological Survey,Sanhe,Hebei 065201,China;Tianjin Institute of Geological Survey,Tianjin 300191,China)

机构地区：[1]中国地质调查局自然资源实物地质资料中心,河北三河065201 [2]天津市地质调查研究院,天津300191

出　　处：《现代地质》2023年第6期1624-1633,共10页Geoscience

基　　金：中国地质调查局资助项目([2010]矿评01-19-01,DD20221814)

摘　　要：内蒙古西乌旗地区位于贺根山古生代结合带南部,是研究古亚洲洋分支洋贺根山古洋盆演化的重要地区之一。该地区泥盆纪岩浆岩发现较少,对泥盆纪贺根山古洋盆的演化研究不够深入。本文对新发现的西乌旗乌和日楚鲁石英闪长岩进行了岩相学、LA-ICP-MS锆石U-Pb年代学和全岩元素组成研究。结果显示,岩浆锆石^(206)Pb/^(238)U加权平均年龄为(395.8±7.5)Ma(MSWD=1.4,n=8),指示石英闪长岩体形成于早泥盆世。全岩元素组成具有高硅、富钠和偏铝质特征;Rb、Ba、Th、U、Pb和Sr等大离子亲石元素相对富集,Zr、Hf、Nb、Ta和Ti等高场强元素相对亏损;稀土元素总量偏低,轻重稀土元素分馏程度较高,Eu弱负异常。这些特征表明乌和日楚鲁石英闪长岩系I型花岗岩成因;结合Y-Nb和(Y+Nb)-Rb判别图解,反映其形成于与洋板片俯冲有关的火山弧环境。乌和日楚鲁石英闪长岩的发现,指示贺根山古洋盆在早泥盆世时期仍然存在,并可能发生了朝锡林浩特微陆块的南向俯冲消减作用,此认识有别于传统认为的贺根山古洋盆仅存在北向俯冲的观点。The Xiwuqi area,situated in the southern section of the Paleozoic Hegenshan suture zone,is a key tectonic unit for revealing the evolution of the Paleozoic Hegenshan ocean,a branch of the Paleo-Asian Ocean.There are a few Devonian magmatic rocks in this area,and the evolution of the Devonian Hegenshan ocean is not well studied.In the regional geological survey,a quartz diorite body was newly discovered at Uhelchulu and Xiwuqi.Here,we studied the petrography,zircon U-Pb chronology and geochemistry of the quartz diorite samples.LA-ICP-MS zircon U-Pb dating obtained the weighted average^(206)Pb/^(238)U age of 395.8±7.5 Ma(MSWD=1.4,n=8),indicating an Early Devonian pluton emplacement.Geochemistry of the quartz diorite indicates that it is calc-alkaline,characterized by high Si and Na and metaluminous.The pluton is enriched in LILEs(e.g.,Rb,Ba,Th,U,Pb,and Sr)and depleted in HFSEs(e.g.,Zr,Hf,Nb,Ta,and Ti).TheΣREE content is relatively low with moderate LREE/HREE fractionation and weak negative Eu anomalies.Basing on this study and published data,we considered the quartz diorite to be I-type.The Y-Nb and(Y+Nb)-Rb granite discrimination diagrams suggest that the pluton was formed in the volcanic arc setting related to oceanic plate subduction.The discovery of the quartz diorite indicates that the Hegenshan ocean basin probably had existed in the Early Devonian,and it undergone southward subduction beneath the Xilinhot micro-continent.This new finding is different from the conventional understanding that the Hegenshan ocean has only subducted northward.

关 键 词：贺根山泥盆纪古洋盆 洋盆双向俯冲 Ⅰ型花岗岩 火山弧 

分 类 号：P588.1[天文地球—岩石学] P588.115[天文地球—地质学]