摘要
华北克拉通岩石圈减薄和破坏机理长期以来存在争议,基于岩石学、岩石地球的化学分析研究突出强调深部过程的重要性。前人提出了两种重要模式:包括以拆沉作用为代表的top-down tectonics模型和以热-机械侵蚀与化学侵蚀,或地幔置换、交代作用的bottom-up tectonics模型。然而,对于这两种模式而言尚存在许多无法合理解释的问题,比如在此深部过程中,区域性岩石圈伸展有多大的贡献?地壳伸展构造是作为深部过程的响应,还是同为岩石圈伸展的产物?本文基于早白垩世东亚地区(尤其是华北克拉通东部地区)伸展构造与岩浆活动的综合分析,揭示出华北克拉通东部不同地区伸展构造变形与岩浆活动之间的时、空和成因关系有一定的差异。但整体上看,岩石圈伸展起着主导作用,控制着岩浆上侵和就位,在拆离断层下盘侵入形成各种规模的花岗质为主的侵入体,或于上盘喷发形成火山-沉积岩盆地。在伸展构造发育的不同阶段,可以有伸展早期、伸展期及伸展期后的岩浆活动。岩浆活动的强度及岩浆源区特点有显著的时空变化。一方面,在同一地区不同演化阶段其源区有很大的差异。表现为主体上是早期以古老下地壳源为主,随着壳/幔伸展作用演化,逐渐向混合源或独立幔源的演化。同时,不同地区岩浆源区的变化规律也显著不同。以胶辽地区为例,胶东整体上是壳幔混合源区对于岩浆演化有重要贡献;而辽东地区具有显著的源区演化特点:从剪切早期古老下地壳源区为主,并伴有幔源物质加入,剪切期古老下地壳为主,到剪切晚期和剪切期后以新生下地壳为主。本文认为岩石圈伸展的壳/幔拆离模型(Parallel Extension Tectonics),可以合理地解释华北克拉通及邻区早白垩世构造-岩浆活动性。在该模型中,遭受伸展的华北克拉通岩石圈发生壳-幔拆离作用。在岩石圈伸展作用期间,地壳层次的拆离作用与岩石圈地幔层次上的拆离作用可以是耦合的或者是解耦的,从而导致华北克拉通岩石圈减薄过程中在地壳尺度上的拆离作用与变质核杂岩的剥露有三种不同的类型:同岩浆活动型伸展(C型:Co-magmatism mode extension)、无岩浆活动型伸展(A型:Amagmatism mode extension)和多阶段混合型(M型:Multi-mode extension)。
The mechanism of lithosphere thinning and destruction of the North China Craton has long been controversial.Two popularly discussed models,i.e.,the top-down tectonics model and the bottom-up model,based on petrological and geochemical studies that stress the importance of deep processes.The former is exemplified by delamination and foundering of thickened lithospheric root,while the later is represented by processes involving thermo-mechanical and chemical erosions,mantle replacement or metasomatism.How the regional lithospheric extension contributed to thinning of the lithosphere remains not well-understood,although tectonic stresses are generally accepted to be one of the major driving forces during cratonic evolution.It is also debatable if the crustal extension is a response to deep processes or both are parallel products of lithospheric extension.This paper demonstrates,based on comprehensive analysis of Early Cretaceous extensional and magmatic activities in East Asia that there are obvious differences in temporal,spatial and genetic relationships between extensional tectonic deformation and magmatic activities in different area,especially in the eastern part of the North China Craton.Extensional tectonic activities predominted over the generation,up-welling and emplacement of syntectonic magmas.At different stages of the tectonic extension,there are early syn-extensional,syn-extensional and post-extensional magmatic activities.The characteristics of magmatic activities and their source attributes vary significantly with time at different tectonic domains.Meanwhile,there are obvious differences in magmatic sources at different stages of tectonic extension in a specific tectonic domain,in spite of a general tendency from mixed sources with dominant ancient crust contributions to separate mantle or crustal sources.Further more,different tectonic domains may have different tendencies of source region variations.Taking the Jiaodong and Liaodong peninsulas at the southeastern North China Craton as an example,mixed sources of ancient crust,juvenile crust and lithospheric mantle have important contributions to magma evolution in the Jiaodong area,but evolving magma sources played key roles in the generation of magmas in the Liaodong Peninsula.The present study suggests that the Early Cretaceous tectono-magmatic activities in the North China Craton and adjacent areas can be reasonably explained by Parallel Extension Tectonics(PET).In the PET model,both crust and mantle detachment occurs in response to regional lithosphere extension.Detachment faulting in the crust and in the lithospheric mantle can be either coupled or decoupled,which may have different tectono-magmatic responses.Three different modes of crustal detachment and exhumation of metamorphic core complexes are shown to have occurred during the Early Cretaceous tectonic extension of the North China Craton:co-magmatim(hot)mode extension,amagmatism(cold)mode extension and multi-mode extension.
作者
刘俊来
倪金龙
陈小宇
Craddock JP
郑媛媛
孙彦琪
季雷
LIU JunLai;NI JinLong;CHEN XiaoYu;CRADDOCK JP;ZHENG YuanYuan;SUN YanQi;JI Lei(State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Beijing 100083,China;College of Earth Sciences and Engineering,Shandong University of Science and Technology,Qingdao 266590,China;Geology Department,Macalester College,Saint Paul,MN 55105,USA)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2020年第8期2331-2343,共13页
Acta Petrologica Sinica
基金
国家自然科学基金项目(41430211)资助.
关键词
岩石圈不均匀伸展
壳幔拆离
同伸展岩浆作用
岩石圈伸展的壳幔拆离模型
华北克拉通
Inhomogeneous tectonic extension
crustal and mantle detachment faulting
syn-extensional magmatic activities
Parallel Extension Tectonics
North China Craton
