南秦岭早古生代碱性岩地球化学特征及其成因机制:研究进展与展望  

Geochemistry and petrogenesis of Early Paleozoic alkaline rocks in the South Qinling belt:Research progress and prospects

作　　者：赖绍聪[1] 杨航 张方毅 LAI Shaocong;YANG Hang;ZHANG Fangyi(State Key Laboratory of Continental Dyna mics,Department of Geology,Northwest University,Xi'an Shaanri710069,China;Center of Deep Sea Research,Institute of Oceanology,Chinese Academy of Sciences,Qingdao,Shandong266071,China)

机构地区：[1]大陆动力学国家重点实验室,西北大学地质学系,陕西西安710069 [2]中国科学院海洋研究所深海研究中心,山东青岛266071

出　　处：《地质学报》2024年第3期799-828,共30页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号42172056)资助的成果。

摘　　要：南秦岭地区在早古生代经历了大规模且持续性的碱性岩浆活动,其丰富的碱性岩石记录为探索深部地幔物质组成、壳内岩浆演化过程以及地球动力学演化机制提供了珍贵的地质载体。文章基于团队近期对于区域上典型碱性岩的地球化学分析结果和成因机制探讨,旨在对南秦岭早古生代碱性岩浆的源区和演化过程进行全面地约束。南秦岭早古生代碱性岩石类型主要包括一套成分从碱性玄武质向粗面质变化,呈双峰式分布的碱性火山-侵入岩组合,以及少量与碱性硅酸岩(角闪辉石岩、正长岩)-碳酸岩共生杂岩体。岩相学、年代学和地球化学证据显示这些碱性岩具有相同的地幔源区,其中演化程度较低的镁铁质端元记录了南秦岭早古生代交代岩石圈地幔的部分熔融事件,交代介质主要为硅酸盐熔体。演化程度较高的碱性岩端元(粗面-正长岩、碳酸岩)来源于初始镁铁质组分的岩浆分异过程,其中粗面-正长岩类主要受到以长石和单斜辉石为主的分离结晶作用控制。中生代热液交代过程主要记录在北大巴山东部和武当地块西南缘的早古生代碱性岩体中,热液交代作用促进了碳酸岩杂岩体中稀土元素的富集成矿。副矿物年代学和独居石Nd同位素特征反映了热液可能形成于岩体本身的再活化事件,晚三叠世秦岭地区的造山运动可能对此过程具有促进作用。The South Qinling belt experienced large-scale and continuous alkaline magmatism during the Early Paleozoic.The presence of alkaline rocks in this area offers valuable insights into the deep material composition,magmatic evolution,physicochemical environment,and geodynamic evolution.This article aims to provide a comprehensive understanding of the source area and evolution of early Paleozoic alkaline magmatism in the South Qinling Mountains,based on the team's recent work on the genesis of typical alkaline rocks in the region.The Early Paleozoic alkaline rocks in the South Qinling belt mainly consist of a bimodal suite,transitioning in composition from basaltic to trachytic rocks.Additionally,there area small number of carbonatitesthat coexist with alkaline silicate rocks(amphibole pyroxenites and syenite).Petrographical,chronological,and geochemical evidence suggests that these alkaline rocks share the same mantle source.The mafic rocks indicate partial melting of the mantle in the South Qinling Mountains,where the metasomatic agent ismainly silicate melt.The trachyte/syenite and carbonatite rocks are all derived from magmatic differentiation of the initial mafic component.The trachyte/syenite rocks are controlled by the segregation and crystallization of mainly feldspar and clinopyroxene.Hydrothermal processes are mainly concentrated in the Zhuxi-Zhushan area in the eastern part of the Northern Daba Mountains and the southwestern margin of the Wudang region.In these areas,hydrothermal metasomatism has led to the enrichment of rare earth elements in carbonatite.Geochronology and monazite Nd isotopic signatures suggest that the hydrothermal fluids may have originated from a reactivation event within the rocks themselves,and the Late Triassic orogeny in the Qinling region may have contributed to this process.

关 键 词：早古生代 南秦岭 碱性岩浆事件 源区性质 岩浆分异 

分 类 号：P534.4[天文地球—古生物学与地层学] P588.11[天文地球—地质学] P597.3