【作者】 陈雪；

【导师】 梁琛岳；

【作者基本信息】 吉林大学 ， 地质学， 2025， 硕士

【摘要】 太古宙晚期(距今30-25亿年前)是大陆地壳和地球动力学过程发生重大变革的时期。华北克拉通(NCC)发育有代表性的太古宙地质记录,包括玄武岩、奥长花岗岩-英云闪长岩-花岗闪长岩(TTG)片麻岩和富钾花岗质岩石,其对于探究新太古代大陆地壳的形成与演化至关重要。辽西地区位于华北克拉通北部,保存了丰富的新太古代地质记录,本文基于细致的岩石学、锆石U-Pb年代学、全岩地球化学以及EBSD组构等,对辽西地区新太古代镁铁质岩石和长英质岩石进行详细研究,以期为理解新太古代晚期地壳形成、演化及其地球动力学机制提供依据。取得以下研究进展:辽西凌海地区镁铁质岩石形成于2549–2531 Ma;TTG片麻岩系列形成于2526–2509 Ma;富钾花岗岩的形成经历了两个阶段,强片麻状花岗岩形成于2514–2512 Ma,弱片麻状至块状的花岗岩形成于2508–2501 Ma,随后侵入形成2477–2474 Ma的煌斑岩脉,但这些岩石均经历了2.49 Ga的区域变质作用。镁铁质岩石来源于超镁铁质岩石圈地幔的部分熔融,形成过程中受到了地壳物质的混染以及俯冲流体交代作用的影响;TTG片麻岩具有过铝质钙碱性花岗岩特征,是由岩浆弧根部加厚地壳的石榴石角闪岩部分熔融形成的;富钾花岗岩属于弱过铝质钾玄岩系列的S型花岗岩,起源于上地壳变质泥质岩的部分熔融。镁铁质岩石和长英质岩石的Hf模式年龄,确定了辽西凌海地区在2.8–2.7 Ga发生了显著的地壳增生事件。典型深熔单元的宏微观构造与EBSD组构特征揭示,辽西凌海地区花岗质岩石深熔作用发生于高温(700℃)中压(0.4～1.0 GPa)环境下,长石普遍发育CPO极密,主要受位错蠕变控制。其中,TTG片麻岩来自于分异的熔体由构造薄弱带上升,属演化熔浆,具有异地岩浆花岗岩特点,代表下地壳的部分熔融,此阶段斜长石发育(010)[100]滑移系。富钾花岗岩形成位置相对较浅,为新太古代末期地壳改造过程中熔体聚集区,具有原地型混合花岗岩特点,代表中上地壳部分熔融,此阶段钾长石发育(001)[100]滑移系。综合区域研究成果,提出了辽西地区新太古代晚期经历了从中洋脊(N-MORB系列)到洋内岛弧(玻安岩系列),再到安第斯型活动大陆边缘(adakite系列和高铝TTG系列),并最终进入伸展构造阶段(富钾花岗岩系列)的地壳动力学演化过程。更多还原

【Abstract】 The late Archean(3.0-2.5 Ga)marks a significant transformation in the continental crust and geodynamic processes.Representative Archean records in the North China Craton(NCC),such as basaltic rocks,trondhjemite-tonalite-granodiorite(TTG)gneisses and K-rich granites,are essential for understanding Archean continental crust formation.The Western Liaoning(WLN)in northern NCC preserves valuable Neoarchean geological records.This study employs petrology,Zircon U-Pb geochronology,whole-rock geochemistry and EBSD fabric analysis to investigate Neoarchean mafic and felsic rocks in WLN,providing insights into late Neoarchean crustal formation,evolution,and geodynamic mechanisms.Zircon U-Pb geochronology reveals that the mafic rocks formed between 2549 and2531 Ma,the TTG gneiss series between 2526 and 2509 Ma.The K-rich granites underwent two formation stages:the older strongly gneissic granites(2514-2512 Ma)and the younger weakly gneissic to massive granites(2508-2501 Ma),followed by the intrusion of lamprophyre dikes(2477-2474 Ma).All these rocks underwent regional metamorphism at 2.49 Ga.Whole-rock geochemical results indicate that the basaltic series rocks are derived from partial melting of the ultramafic lithospheric mantle,influenced by crustal contamination and metasomatic exchange of subduction fluids.TTG gneisses are classified as peraluminous calc-alkaline granites,generated by the partial melting of garnet amphibolites in thickened arc roots.The K-rich granites belong to the weakly peraluminous shoshonite-series are S-type granites,originated from partial melting of upper crustal metamorphic argillaccous rocks.This study also identifies a crustal growth episode in WLN between 2.8 and 2.7 Ga,through a comprehensive analysis of Hf model ages of mafic and felsic rocks.Detailed macro-and microstructural analyses of typical anatexic units in the Linghai area,combined with EBSD fabric analysis,reveal that granite anatexis occurred at high-temperature(700℃)and medium-pressure(0.4-1.0 GPa)conditions,with widespread CPO maxima in feldspar controlled by dislocation creep.Specifically,the TTG gneisses originated from differentiated melts ascending through tectonic weak zones,representing evolved magmas with allochthonous characteristics due to lower crustal partial melting,where plagioclase developed(010)[100]slip systems.The K-rich granites formed at relatively shallow depths,representing melt accumulation zones during late Neoarchean crustal reworking,displaying autochthonous hybrid granite characteristics related to middle-upper crustal partial melting,and featuring K-feldspar with(001)[100]slip systems.Late Neoarchean geodynamic evolution in WLN involved a transition from mid-ocean ridge(N-MORB-type)to intra-oceanic island arc(boninite-type),then to Andean-type active continental margin(adakite-and high-alumina TTG-type),and ultimately to an extensional tectonic phase(the K-rich granite-type).Collectively,WLN preserves a complex geodynamic history of crust-mantle interactions related to subduction during the late Neoarchean.更多还原