中国西天山古生代岩浆岩时空架构、源区特征及构造背景  

Spatial and Temporal Framework,Evolution of Magma Sources,and Tectonic Settings of Paleozoic Magmatic Rocks in West Tianshan,China

作　　者：黄河[1] 王涛[1] 童英[1] 张建军[1] 王朝阳 HUANG He;WANG Tao;TONG Ying;ZHANG Jianjun;WANG Chaoyang(Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China)

机构地区：[1]中国地质科学院地质研究所,北京100037

出　　处：《西北地质》2024年第6期25-43,共19页Northwestern Geology

基　　金：中国地质调查局项目“中生代松辽盆地周缘复合造山带岩浆演化及成矿效应专题地质调查”(DD20230213);国家重点研发计划课题“增生造山带典型地区三维岩石圈物质架构的示踪方法”(2019YFA0708601)联合资助。

摘　　要：中亚造山带是全球最大、最典型的增生造山带,是全球显生宙陆壳生长最显著的地区之一。在中亚造山带形成过程中,伴随古亚洲洋的闭合,以及不同性质构造块体的拼贴碰撞,形成了巨量的岩浆岩。笔者以中亚造山带西段西天山出露的古生代岩浆岩为研究对象,系统总结了岩浆岩的时空格架、成因类型、源区特征和构造背景等特征。区内岩浆岩主要形成于3个阶段:寒武纪早期—中泥盆世早期(497~388 Ma)、晚泥盆世—早石炭世(375~323 Ma)、晚石炭世—中二叠世(322~263 Ma)。第一阶段和第二阶段的侵入岩组合主要为钙碱性I型花岗岩,以及具有“岛弧”地球化学特征的中、基性岩石,部分岩体具有埃达克质岩石的性质,并发育少量A型花岗岩。晚石炭世—中二叠世花岗岩等侵入岩以多样性的成分为特征,包括“正常的”钙碱性I型花岗岩、埃达克质岩石、A型花岗岩,以及局部出露的S型花岗岩,基性岩石中也出现较多具洋岛玄武岩特征的辉长岩和玄武岩。结合其他地质证据,笔者认为寒武纪早期—中泥盆世早期、晚泥盆世—早石炭世岩浆岩形成于与古亚洲洋洋分支洋盆俯冲有关的构造环境中,且岩浆活动的迁移和地球化学成分演化趋势均揭示俯冲过程中发生了多次从前进型、低角度俯冲到后撤型、高角度俯冲的转化。西天山南北洋盆的最终闭合均发生在晚石炭世。在南侧,古南天山洋的闭合跟随着大陆板块之间的“硬碰撞”。而在北侧,伊犁地块和中天山地块北缘与一不成熟/新生岛弧发生了“软碰撞”。就地壳演化的方式而言,基于Hf同位素资料所揭示的长英质岩浆岩源区物质演化,识别出西天山地区在在古生代交替发生大陆地壳物质再循环(continental reworking)和大陆生长(continental growth)。在俯冲阶段,大洋板片后撤(回卷)占据了主导性地位,导致了微陆块中增生造山作The Central Asian Orogenic Belt(CAOB)is Earth's largest and most representative accretionary belt and records the most extensive growth and reworking of the continental crust.Accompanying the closure of the giant Paleo-Asian Ocean and the amalgamation of tectonic blocks in the CAOB regime,with different origins and evolutionary histories,voluminous magmatic rocks were formed.This study focuses on Paleozoic magmatic rocks exposed in West Tianshan and systemically summarizes the spatiotemporal frameworks,genetic types,evolution of their magma sources in space and time,and tectonic settings of these rocks.Paleozoic magmatic rocks in West Tianshan were mainly formed at three stages,i.e.,Early Cambrian to Middle Devonian(~479 to~388 Ma),Late Devonian to Early Carboniferous(~375 to~372 Ma),and Late Carboniferous to Middle Permian(~322 to~263 Ma).Magmatic rocks formed at the first and second stages are mainly of calc-alkaline Itype granite and intermediate and mafic rocks with"arc-like"geochemical fingerprints,with a few rocks bearing"adakite-like"features;a few A-type granites are also found.By contrast,Late Carboniferous to Middle Permian magmatic rocks show a diversity in rock types,including calc-alkaline I-type,adakite-like,and A-type felsic rocks,with a few locally exposed S-type granites;OIB-like mafic rocks formed in this period,such as gabbros and basalts,occur locally.In combination with other geological evidence,this study proposes that Early Cambrian to early Middle Devonian and Late Devonian to Early Carboniferous magmatic activities took place in convergent continental margin settings,which were associated with the subduction of branches of the Paleo-Asian Ocean.Besides,both magmatic migration and secular changes in geochemical proxies indicate the transition from advancing low-angle to retreating high-angle subduction.The final closure of oceanic basins plausibly occurred in the Late Carboniferous.Following the closure of the South Tianshan Ocean,a"hard"collision with the arriving Tarim Craton occurred;by

关 键 词：中亚造山带 西天山 古生代 岩浆岩 地壳生长 

分 类 号：P618.13[天文地球—矿床学]