摘要
为了更好地了解华北板块北缘东段志留纪-泥盆纪的构造格局和演化过程,本文对吉林省公主岭市附近出露的中志留世-晚泥盆世岩浆岩(放牛沟火山岩和西蟒仗侵入岩)进行了LA-ICP-MS锆石U-Pb年代学、岩石地球化学、锆石Hf同位素和全岩Sr-Nd同位素的研究,探讨了其源区性质及构造背景。测年结果显示,放牛沟火山岩中变安山岩、糜棱岩化变流纹质晶屑凝灰岩和流纹岩形成年龄分别为426±4.8Ma、404±4.5Ma、375.5±4.6Ma,代表岩石的结晶年龄;结合前人测年结果,放牛沟火山岩中包括426~425Ma、~419Ma、404~400Ma、390~384Ma、~375Ma等多期火山事件;放牛沟火山岩构造变形强烈,形成糜棱岩化变质火山岩、构造片岩等,各类岩石之间多为构造接触,实际上是由形成于不同时代、不同构造环境的构造岩片组成。西蟒仗侵入岩中英云闪长质糜棱岩、糜棱岩化黑云母英云闪长岩形成年龄分别为419.5±3.7Ma、424.7±5.9Ma,为中-晚志留世。中-晚志留世岩浆岩(426~419Ma)为一套钙碱性-高钾钙碱性英云闪长岩、花岗闪长岩、安山岩、英安岩、流纹岩及火山碎屑岩组合,侵入岩和火山岩在时间、空间、物源方面具有一致性,属于同源的火山-侵入杂岩;具有正的ε_(Nd)(t)(+1.04~+1.21)和ε_(Hf)(t)(+1.26~+7.85),相对富集Rb、Ba、Th、U、K(LILEs)及轻稀土元素(LREE),并且亏损Nb、Ta、P、Ti(HFSEs),主要源自中-新元古代增生下地壳物质(俯冲板片)的部分熔融,上升过程与地幔和下地壳物质发生了混染,形成于活动大陆边缘环境。早泥盆世变流纹质晶屑凝灰岩富集Rb、Th、U、K,亏损Ba、Nb、Ta、Eu、Sr、P、Ti,表现出铝质A型花岗岩地球化学特征,形成于白乃庙岛弧与华北板块碰撞后的伸展环境;具有正ε_(Nd)(t)(+1.28~+2.70)和ε_(Hf)(t)(+3.18~+7.22),表明其源自中-新元古代增生玄武质下地壳物质的部分熔融,岩浆形成后经历了斜长石、磷灰石、磁铁矿等矿物的分离结晶作用。晚泥盆世糜棱岩化变流纹岩属于钙碱性I型流纹岩;富集Rb、Ba、Th、U、K,亏损Nb、Ta、Sr、P、Ti,具有正ε_(Nd)(t)(+6.08)和ε_(Hf)(t)(+9.63~+13.39),表明其源自新元古代-中寒武世增生玄武质下地壳物质的部分熔融;形成于活动大陆边缘环境,古亚洲洋板块开始南向俯冲。
In order to better understand the Silurian-Devonian tectonic framework and evolution process in the eastern part of the northern margin of the North China Plate,We conducted LA-ICP-MS zircon U-Pb dating,geochemical,zircon Hf isotope and whole rock Sr-Nd isotope analysis on the Middle Silurian-Late Devonian magmatic rocks(Fangniugou volcanic rock and Ximanzhang intrusive rock)near the Gongzhuling City,Jilin Province,with the aim of constraining the tectonic setting of the eastern segment of the northern margin of the North China Plate.The zircon LA-ICP-MS U-Pb ages of the meta-andesite,mylonitized rhyolitic crystal tuff and rhyolite in Fangniugou volcanic rocks are 426±4.8Ma,404±4.5Ma and 375.5±4.6Ma respectively,represents the crystallization age of their protolith.Combined with previous dating results,Fangniugou volcanic rocks include 426~425Ma,~419Ma,404~400Ma,390~384Ma,~375Ma multi-stage volcanic events.Fangniugou volcanic rocks are strong structural deformation,and tectonic contact in the rocks.In fact,they are composed of tectonic fragments formed in different times and different tectonic environments.The formation ages of tonalite mylonite and mylonitized tonalite in the Ximangzhang intrusive rock are 419.5±3.7Ma and 424.7±5.9Ma respectively,representing the crystallization age of tonalite.The Middle-Late Silurian magmatic rocks(426~419Ma)are a set of calc-alkaline to high potassium calc-alkaline tonalite,granodiorite,andesite,dacite,rhyolite and pyroclastic rocks.The intrusive rocks and volcanic rocks are consistent in time,space and provenance,belonging to the homologous volcanic intrusive complex;With positive ε_(Nd)(t)(+1.04~+1.21)and ε_(Hf)(t)(+1.26~+7.85),relatively enriched in Rb,Ba,Th,U,K(LILEs)and light rare earth elements(LREE),and depleted in Nb,Ta,P and Ti(HFSEs),mainly derived from the partial melting of Meso-Neoproterozoic accretionary lower crust materials(subduction plates),which were mixed with mantle and lower crust materials in the ascending process and formed in the active continental margin environment.The Early Devonian metamorphic rhyolitic crystal tuff is enriched in Rb,Th,U,K and depleted in Ba,Nb,Ta,Eu,Sr,P and Ti,showing the geochemical characteristics of aluminous A-type granite,which was formed in the extensional environment after the collision between Bainaimiao island arc and North China Plate;positive ε_(Nd)(t)(+1.28~+2.70)and ε_(Hf)(t)(+3.18~+7.22),indicating that it originated from the partial melting of the Middle Neoproterozoic accretionary basaltic lower crust material.After the formation of magma,minerals such as plagioclase,apatite and magnetite are separated and crystallized.The Late Devonian mylonitized rhyolite belongs to calc-alkaline I-type rhyolite;Enriched Rb,Ba,Th,U,K,depleted Nb,Ta,Sr,P,Ti,with positive ε_(Nd)(t)(+6.08)and ε_(Hf)(t)(+9.63~+13.39),indicating that it originated from the partial melting of Neoproterozoic-Middle Cambrian accretionary basaltic lower crustal material;Formed in the active continental margin environment,the paleo Asian Ocean plate began to subduct southward.
作者
李斌
时溢
杨帆
刘淼
吴振
LI Bin;SHI Yi;YANG Fan;LIU Miao;WU Zhen(Shenyang Center of Geological Survey,China Geological Survey,Shenyang 110034,China;Northeast Geological S&T Innovation Center of China Geological Survey,Shenyang 110034,China;College of Resources and Environment,Jilin Agricultural University,Changchun 130118,China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2022年第8期2364-2396,共33页
Acta Petrologica Sinica
基金
国家自然科学基金项目(41902234)
中国地质调查局项目(DD20190042-04、DD20221632-02)联合资助。
关键词
中亚造山带
华北板块北缘东段
岩浆岩
志留纪
泥盆纪
Central Asian Orogenic Belt
Eastern segment of the northern margin of the North China Plate
Magmatic rock
Silurian
Devonian