大陆的起源  

Origin of continents

作　　者：赵国春[1,2] 张国伟 ZHAO Guochun;ZHANG Guowei(Departmentof Earth Sciences.The Universily of Hong Kong,Pok fulam Road,Hong Kong;State Key Laboratory of Continental Dynamics,De partment of Geology.Northwest University.Northern Taibai Street 229,Xi'an.710069)

机构地区：[1]香港大学地球科学系,中国香港 [2]西北大学地质学系大陆动力学国家重点实验室,西安710029

出　　处：《地质学报》2021年第1期1-19,共19页Acta Geologica Sinica

基　　金：国家自然科学基金重大项目子课题(编号41890831);香港大学基础研究培育项目(编号HKU Seed Fund for Basic Research;201811159089)资助。

摘　　要：太阳系固体星球都有类似的核-幔-壳结构,但唯独人类居住的地球具有长英质组成的大陆壳。太古宙大陆克拉通主要由英云闪长岩(Tonalite)-奥长花岗岩(Trondhjemite)-花岗闪长岩(Granodiorite)为主的TTG深成侵入体变质而成的正片麻岩和由基性-超基性酸性火山岩及少量沉积岩变质的表壳岩(绿岩)组成。已有的资料显示这些太古宙大陆岩石组合起源于大洋壳的部分熔融。大洋壳分为大洋盆地、洋中脊、岛弧和洋底高原(大洋岛)。前两者地壳的平均厚度只有5~10km,不可能成为形成太古宙TTG深成侵入体的场所。因此,长英质大陆或起源于板块构造体制下的岛弧,或起源于地幔柱体制下的洋底高原。板块构造体制下的岛弧模式能够很好地解释太古宙克拉通TTG深成岩的成因,即俯冲大洋板片部分熔融所形成的埃达克岩相当于太古宙高压(高Al2O2)型TTG,而俯冲板片脱水导致地幔楔部分熔融形成的玄武质地壳再次熔融所形成的钙碱性花岗质岩石相当于太古宙低压(低Al2O2)型TTG。然而,板块构造体制下的岛弧模式不能令人满意地解释太古宙绿岩带火山岩组合中缺少大量的安山岩、科马提岩~1600℃高温形成环境、克拉通规模近于同时侵位的TTG岩套、大规模卵形构造样式、代表性的逆时针P-T轨迹变质作用演化等诸多特征。相反,地幔柱洋底高原模式能够合理地解释太古宙绿岩双峰式火山岩组合的成因,即基性的拉斑玄武岩和超基性的科马提岩分别来自地幔柱头部部分熔融和尾柱熔浆,而酸性的英安岩、流纹质英安岩和流纹岩是地幔柱热异常导致的洋底高原底部的部分熔融物。按照地幔柱洋底高原模式,太古宙TTG岩浆是由洋底高原底部玄武质地壳的部分熔融而成,这样能够合理地解释为什么太古宙TTG能够在短时间内巨量产出并在形成时间上没有任何系统变化。地幔柱洋底高原模式�It is well known that all solid planets in the solar system have a core-mantle-crust structure,but a continental crust with a felsic composition is unique to the Earth inhabited by humans.The Archean continental cratons consist mainly of orthogneisses and supracrustals that were metamorphosed from tonalite-trondhjemite-granodiorite(TTG)plutons and mafic-ultramafic volcanic rocks with minor sedimentary rocks,respectively.Available data suggest that these rock assemblages were derived from oceanic crust or its partial melts.The oceanic crust is generally divisible into ocean basin,mid-ocean ridge,island arc and oceanic plateau(ocean island),of which the ocean basin and mid-ocean ridge have an average crustal thickness no more than 5~10 km,which is too thin to generate Archean TTG magmas.Therefore,continents with felsic composition must have been originated either from island arcs under a plate tectonic regime or from oceanic plateaus derived from mantle plume.The formation of Archean TTG rocks can be explained by the island arc model in which the Archean high-pressure-type TTG rocks is considered to have been derived from the partial melting of subducted slabs,whereas the Archean low-pressure-type TTG rocks equivalent to calc-alkaline granitoids were derived from the partial melting of the juvenile basaltic crust which itself formed by the partial melting of the mantle wedge with addition of fluids released from the subducted slabs.However,the island arc model fails to explain the absence of andesites from the Archean greenstone terranes,the presence of komatiites with temperatures of 1600℃,nearly coeval emplacement of TTG plutons on a cratonic scale,dome-and-keel structures and anticlockwise P-T paths involving isobaric cooling that characterize the deformation and metamorphism of Archean continental cratons.In contrast,the mantle-plume oceanic plateau model can reasonably interpret the origin of the bimodal volcanic assemblages in Archean greenstones of which the tholetiites and komatiites were derived from par

关 键 词：大陆 板块构造 岛弧 地幔柱 洋底高原 花岗-绿岩地体 太古宙 

分 类 号：P311[天文地球—固体地球物理学]