摘要
冈底斯岩浆岩带(以下简称冈底斯带)是新特提斯洋俯冲和印度—亚洲板块碰撞的产物,为典型的复合型大陆岩浆弧,是研究板块增生、大陆地壳生长再造和碰撞造山的天然实验室。大量研究揭示新特提斯洋主要经历了4个重要的演化时期:分别是早期俯冲(>152 Ma)、晚期俯冲(100~65 Ma)、主碰撞(55~40 Ma)和后碰撞伸展期(23 Ma至今)。前人对其开展了大量的工作,并取得了重要的认识和进展,然而关于新特提斯洋的形成和演化以及冈底斯带火成岩岩浆源区的属性、精细的成岩过程等方面仍然存在着激烈的争议。文章首先介绍了冈底斯带的研究历史和大地构造背景,对冈底斯带目前存在的主要科学问题和争议进行了初步梳理,从13个方面进行了论述和总结。初步的梳理给出的启示是:冈底斯带是一个典型的岩浆—构造—成矿—变形变质带,经历了长期、复杂和多阶段的演化过程,而不是简单地拼贴于古老拉萨地体之上的新生大陆岛弧体。主要认识包括:(1)冈底斯岛弧带是研究新特提斯洋俯冲最为理想的场所,记录了新特提斯洋演化的关键信息,是破解新特提斯洋板片初始俯冲时限和板片俯冲方式最佳的研究对象;(2)冈底斯带中不同时代的花岗岩基或岩株可能经历了一个多期次组装累积的过程,今后应运用晶粥体的模型去重新理解冈底斯带花岗质岩石的形成和动力学成岩过程;(3)冈底斯地区地幔的性质沿着走向表现出复杂性,具有地球化学上的不均一性;(4)冈底斯带的火成岩存在同位素上的倒转,这可能暗示冈底斯地区存在老的基底;(5)冈底斯岛弧带在构造上具有明显的掀斜性,表现出东段以下地壳组分为主,中西段以中上地壳组分为主,暗示了冈底斯带自新生代以来经历了一个不均衡的构造抬升和剥露过程;(6)冈底斯带的研究对象仍以火成岩为主,研究方法多限于传统的岩石学和放射性Sr-Nd-Hf同位素手段,而非传统的稳定性同位素(Mg-O-Li-B-Mo)的研究却鲜有报道,并且在研究内容上主要以岩石成因和地质年代学为主,而对火成岩侵位过程和成岩后的构造变形和抬升剥蚀等相关研究则相对薄弱;(7)目前,构造地质学手段在冈底斯带的研究中运用较少,常以岩浆演化来代替构造演化。最后,文章针对目前的研究现状,对冈底斯带未来的研究方向进行了展望。
The Gangdese magmatic belt is the product of the northward subduction of the Neo-Tethys oceanic lithosphere beneath the Lhasa terrane and subsequent India-Asia collision.The Gangdese magmatic arc belongs to the typical continental magmatic belt and is the target area for studying plate accretion,crustal growth and reworking and collisional orogeny.Numerous lines of evidence indicate that the Neo-Tethys oceanic lithosphere experienced four distinct stages of evolution:the early-stage subduction(>152 Ma),late-stage subduction(100 to 65 Ma),main-collisional(55 to 40 Ma),and post-collision extentional stages(23 Ma to present).Multiple studies were carried out in the Gangdese belt and much progress has been made during past decades.However,the formation and evolution of the Neo-Tethys Ocean and magma source of igneous rocks are still debated,especially the detailed petrogenetic dynamic processes.This paper reviews the evolution history and tectonic background,and then summarizes related scientific problems from thirteen aspects.It is shown that the Gangdese magmatic belt is a typical magmatism-tectonism-mineralization-deformational metamorphism belt and experienced multi-stage evolution processes rather than a simple continental magmatic arc aggregated in the Lhasa terrane.The review shows that(1)the Gangdese magmatic belt is a natural laboratory for studying the evolution history of the Neo-Tethys,and provides better constraints on the styles of the subducting slab.(2)The different-stage granitoid stocks and batholiths might be formed by multiple additions and incremental assembly of magmas over a span of millions of years or even longer.Therefore,we should use a mush model to reconstruct petrogenesis and petrogenetic secnarios of granitoid rocks in detail.(3)The mantle nature of the Gangdese region shows complicated features that are characterized by geochemical heterogeneity along the arc strike direction.(4)The reversed isotopes exist in the Gangdese belt,probably indicating an ancient nucleus.(5)The Gangdese belt is tilting and has different crustal compositions that are characterized by lower crustal compositions in the eastern segment and middle-upper crustal compositions in the middle-western segment.Crustal tilting of the Gangdese region suggests a differential and imbalanced exhumation process.(6)At present,numerous studies are focused on igneous rocks with methods mainly including radioactive Sr-Nd-Hf isotopes,whereas non-traditional stable isotopes(Mg-O-Li-B-Mo)are rarely reported.In addition,research topics are mainly associated with petrogenesis and geochronology,but few studies focus on the magma emplacement and post-magmatic deformation and uplifting-denudation processes.(7)Research in structural geology of the area is few and usually tectonic evolution is inferred from magmatic evolution in the Gangdese belt,southern Tibet.Finally,we also provide future prospects based on the current research status of the Gangdese magmatic belt in southern Tibet.
作者
孟元库
袁昊岐
魏友卿
张书凯
刘金庆
MENG Yuanku;YUAN Haoqi;WEI Youqing;ZHANG Shukai;LIU Jinqing(Research Center of Continental Dynamics,College of Earth Science and Engineering,Shandong University of Science and Technology,Qingdao 266590,China)
出处
《高校地质学报》
CAS
CSCD
北大核心
2022年第1期1-31,共31页
Geological Journal of China Universities
基金
国家自然科学基金(41902230)
山东省自然科学基金(青年基金)(ZR2019QD002)
山东省高等学校青创科技支持计划(2019KJH004)联合资助。
关键词
拉萨地体
冈底斯岩浆带
新特提斯洋
岩石地球化学
构造演化
Lhasa terrane
Gangdese magmatic belt
Neo-Tethys Ocean
Petro-geochemistry
tectonic evolution
