北祁连东段早古生代洋壳俯冲作用记录——来自晚奥陶世高镁埃达克岩的证据  

A record of Early Paleozoic subduction of oceanic crust in the eastern part of the North Qilian Mountains:Evidence from the Late Ordovician high⁃Mg adakites

作　　者：赵少卿[1] 海连富 孙永亮 梅超 母彩霞 魏向成 徐清海 郭蓉 ZHAO Shao-qing;HAI Lian-fu;SUN Yong-liang;MEI Chao;MU Cai-xia;WEI Xiang-cheng;XU Qing-hai;GUO Rong(School of Geosciences,Yangtze University,Wuhan 430100,China;Mineral Geological Survey Institute of Ningxia Hui Autonomous Region,Yinchuan 750021,China;Institute of Mineral Geology of Ningxia Hui Autonomous Region,Yinchuan 750021,China;Faculty of Earth Resources,China University of Geosciences(Wuhan),Wuhan 430074,China)

机构地区：[1]长江大学地球科学学院,湖北武汉430100 [2]宁夏回族自治区矿产地质调查院,宁夏银川750021 [3]宁夏回族自治区矿产地质研究所,宁夏银川750021 [4]中国地质大学(武汉)资源学院,湖北武汉430074

出　　处：《岩石矿物学杂志》2023年第4期465-482,共18页Acta Petrologica et Mineralogica

基　　金：宁夏回族自治区重点研发计划项目(2021BEG03003);宁夏回族自治区自然科学基金项目(2021AAC03447)。

摘　　要：具有特殊成因机制的埃达克质岩石是探究深部岩浆动力学过程与区域构造演化的重要岩石探针之一。本文对北祁连造山带东段宁夏南华山地区出露的石洼里花岗岩进行了系统的锆石U⁃Pb年龄、主量-微量元素及锆石原位Hf同位素分析,以探讨其岩石成因及地球动力学意义。LA⁃ICP⁃MS锆石U⁃Pb定年结果表明石洼里花岗岩侵位年龄为452±4 Ma,为晚奥陶世岩浆活动的产物。岩石具有较高的SiO_(2)(68.60%~71.42%)、Al_(2)O_(3)(14.95%~15.75%)和Na_(2)O(5.06%~5.79%)含量,较低的K_(2)O(2.23%~3.10%)、MgO(0.91%~1.73%)含量和较高的Mg^(#)值(55~59),属弱过铝质钙碱性系列岩石;岩石具有高Ba(1025×10^(-6)~1250×10^(-6))、Sr(324×10^(-6)~577×10^(-6))和低Y(6.99×10^(-6)~7.69×10^(-6))、Yb(0.65×10^(-6)~0.71×10^(-6))含量,较高的Sr/Y(45~79)和(La/Yb)_(N)(17~31)值,且无明显Eu负异常。锆石εHf(t)值相对较高,变化范围为+0.5~+15.5。主量-微量元素及同位素分析结果表明石洼里花岗岩具有高镁埃达克岩的典型特征,可能是在30~40 km深度的岛弧基性下地壳部分熔融的产物,其源区中可能存在早古生代的新生地壳。结合区内蛇绿岩、高压变质岩、弧岩浆岩的研究成果,笔者认为受北祁连原特提斯洋北向俯冲影响,石洼里高镁埃达克岩形成于老虎山弧后盆地洋壳在晚奥陶世的南向俯冲过程中。With special genetic mechanisms,adakitic rock is one of the important rock probes for exploring the deep magmatic dynamic process and regional tectonic evolution.In this paper,zircon U⁃Pb age,major and trace elements and zircon in⁃situ Hf isotopes of the Shiwali granite from the eastern part of the North Qilian orogenic belt were sys⁃tematically analyzed to explore its petrogenesis and geodynamics significance.LA⁃ICP⁃MS zircon U⁃Pb dating yields an emplacement age of 452±4 Ma for the Shiwali granite,indicating a product of Late Ordovician magmatic activi⁃ty.Bulk⁃rock analyses show that these rocks contain high SiO_(2)(68.60%~71.42%),Al_(2)O_(3)(14.95%~15.75%)and Na_(2)O(5.06%~5.79%)contents,with low K_(2)O(2.23%~3.10%)and MgO(0.91%~1.73%)contents,and re⁃sultant high Mg^(#)value(55~59),belonging to the weak peraluminous and calc⁃alkaline series of rocks.These rocks have high concentrations of Ba(1025×10^(-6)~1250×10^(-6)),Sr(324×10^(-6)~577×10^(-6))and low Y(6.99×10^(-6)~7.69×10^(-6)),Yb(0.65×10^(-6)~0.71×10^(-6))contents,with high Sr/Y(45~79)and(La/Yb)_(N)(17~31)values,and no significant negative Eu anomalies.TheεHf(t)values of zircons are relatively high,with a range of+0.5 to+15.5.The geochemical and zircon Hf isotopic compositions of the Shiwali granites are similar to that of high⁃Mg ada⁃kites,which may be the product of partial melting of the basic lower crust of the island arc at a depth of 30~40 km,and there may be Early Paleozoic juvenile crust in the source area.Combined with the research results of ophi⁃olites,high⁃pressure metamorphic rocks and arc magmatic rocks in the study area,we suggest that the Shiwali high⁃Mg adakitic granites might be generated during the southward subduction of the oceanic crust in the Laohushan back⁃arc basin in the Late Ordovician,which affected by the northward subduction of the North Qilian Proto⁃Tethys ocean.

关 键 词：高镁埃达克岩 晚奥陶世 洋壳俯冲 原特提斯洋 南华山 石洼里花岗岩 北祁连 

分 类 号：P588.121[天文地球—岩石学] P542[天文地球—地质学]