摘要
西昆仑造山带发育有大量的早古生代岩浆岩,它们的形成与原特提斯洋俯冲-碰撞密切相关,然而,对于这些岩浆岩的岩石成因和形成的构造背景仍然存在较大的争议。本文对西昆仑造山带早古生代阿喀孜二长岩和赛图拉石英闪长岩岩体开展了详细的矿物学、锆石U-Pb年代学、全岩地球化学和Sr-Nd-Hf-O同位素研究,以探讨这些侵入岩的岩浆源区与成因,揭示原特提斯洋在这一时期的构造演化过程。这两个岩体的LA-ICP-MS锆石U-Pb年龄分别为456±2Ma和452±2Ma,指示它们形成于晚奥陶世。阿喀孜二长岩具有富碱(K_(2)O+Na_(2)O=10.5%~11.8%)、富钾(K_(2)O/Na_(2)O=1.20~1.44)特征,相对低MgO(0.89%~0.97%)、TiO_(2)(0.42%~0.45%)含量,富集Rb、Th、U等大离子亲石元素,且具有较高的全岩锆饱和温度(T_(Zr)=814~862℃),属于钾质碱性岩石。该岩体具有较高的(^(87)Sr/^(86)Sr)_(i)值(0.72057~0.72186),负的全岩ε_(Nd)(t)值(-5.1~-4.5)和负的锆石ε_(Hf)(t)值(-7.6~-3.4),以及较高的锆石δ^(18) O值(5.39‰~7.94‰),表明其源区可能为伸展环境下古老基性下地壳部分熔融。赛图拉石英闪长岩SiO_(2)含量为56.8%~58.6%,全碱(Na_(2)O+K_(2)O)含量为5.75%~6.39%,具有较低的铝饱和指数(A/CNK=0.85~0.89),相对高的MgO含量(2.93%~3.41%)以及Mg^(#)值(~45),为高钾钙碱性系列岩石。它们富集大离子亲石元素(Rb、Ba、Th)和亏损高场强元素(Nb、Ta、Ti),且具有微弱的Eu异常(δEu=0.72~0.77),类似于俯冲带岩浆岩地球化学特征。这些石英闪长岩具有相对高的(^(87)Sr/^(86)Sr)_(i)比值(0.71317~0.71322),负的全岩ε_(Nd)(t)值(-5.6~-5.1)和负的锆石ε_(Hf)(t)值(-7.8~-2.9),与同时期来源于富集地幔的基性岩同位素特征相似,表明赛图拉石英闪长岩岩浆可能是由俯冲板片流体交代的富集地幔楔部分熔融形成,并在岩浆演化的过程中经历了橄榄石、辉石、角闪石、磷灰石和Fe-Ti氧化物等矿物的分离结晶作用。�
The Early Paleozoic magmatic rocks are widespread in the West Kunlun orogenic belt,and their formation is genetically linked to the subduction-collision of the Proto-Tethys Ocean.However,the petrogenesis of these magmatic rocks and their tectonic setting remain controversial.In this paper,we present new zircon U-Pb ages,whole-rock geochemistry,Sr-Nd isotopic and zircon Hf-O isotopic data of the Early Paleozoic Arkarz monzonite and Saitula quartz-diorite in the West Kunlun orogenic belt to reveal their magma sources and explore the evolution process of the Proto-Tethys Ocean.Zircon U-Pb dating reveals that the two plutons are formed during the Late Ordovician,with the ages of 456±2Ma and 452±2Ma,respectively.The Arkarz monzonite samples are characterized by high alkali contents(K_(2)O+Na_(2)O=10.5%~11.8%)with potassium-rich ratios(K_(2)O/Na_(2)O=1.20~1.44),and low MgO(0.89%~0.97%)and TiO_(2)(0.42%~0.45%)contents,demonstrating that they belong to potassic alkaline rocks.Furthermore,they are enriched in large ion lithophile elements(LILEs;Rb,Th,U),and have high zircon saturation temperatures(T_(Zr)=814~862℃).In addition,the monzonites have high(^(87)Sr/^(86)Sr)_(i)(0.72057~0.72186),negative whole-rocksε_(Nd)(t)(-5.1~-4.5)and zirconε_(Hf)(t)(-7.6~-3.4)and high zirconδ^(18) O(5.39‰~7.94‰)values,suggesting that they could be the partial melting products of the ancient mafic lower crust at an extensional setting.The Saitula quartz diorites have SiO_(2) contents of 56.8%~58.6%,total alkali contents of 5.75%~6.39%,with a low aluminum saturation index(A/CNK=0.85~0.89),as well as relatively high MgO contents(2.93%~3.41%)and Mg^(#)values(ca.45),which is consistent with the geochemical features of high potassium calc-alkaline series.Furthermore,they are enriched in large ion lithophile elements(e.g.,Rb,Ba,Th)and light rare earth elements,and depleted in high field strength elements(e.g.,Nb,Ta and Ti),with weak Eu anomalies(Eu/Eu^(*)=0.72~0.77),which is similar to those of magmatic rocks formed in the subduction zon
作者
陶再礼
尹继元
袁超
肖文交
陈文
陈岳龙
王雅美
杨帆
TAO ZaiLi;YIN JiYuan;YUAN Chao;XIAO WenJiao;CHEN Wen;CHEN YueLong;WANG YaMei;YANG Fan(Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;School of Earth Science and Resources,China University of Geosciences,Beijing 100083,China;State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China;Xinjiang Research Center for Mineral Resources,Xinjiang Institute of Ecology and Geography,Chinese Academy of Sciences,Urumqi 830011,China;State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2022年第11期3321-3340,共20页
Acta Petrologica Sinica
基金
国家自然科学基金项目(42127801)
国家重点研发计划项目(2022YFC2903302)
第二次青藏科考项目(2019QZKK0802)
国家自然科学基金项目(41873060、41830216)
中国地质调查项目(DD20221649)
IGCP 662联合资助.
关键词
西昆仑造山带
原特提斯洋
奥陶纪
富集地幔楔
板片回撤
West Kunlun orogenic belt
Proto-Tethys Ocean
Ordovician
Enriched mantle wedge
Slab rollback
