夏林圻.超大陆构造、地幔动力学和岩浆-成矿响应[J].西北地质,2013,46(3):1-38
超大陆构造、地幔动力学和岩浆-成矿响应
Supercontinent Tectonics, Mantle Dynamics and Response of Magmatism and Metallogeny
投稿时间:2013-04-10  
DOI:
中文关键词:  超大陆构造;地幔动力学;超级地幔柱;超级沉降流;岩浆和成矿响应
英文关键词:supercontinent tectonics;mantle dynamics;superplume;super downwelling;response of magmatism and metallogeny
基金项目:中国地质调查局综合研究项目(1212011120133, 12120113014000)
作者单位
夏林圻 中国地质调查局西安地质调查中心, 陕西 西安 710054 
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中文摘要:
      超大陆是地球上全部或近乎全部(> 90%)大陆块的集合。推测最老的超大陆存在于3.0 Ga,称作Ur。由于年龄老,很难检测该超大陆的存在。地球的历史中,似乎曾有2次,所有的陆块被焊合到一起形成一个超大陆。地球历史中第一个真正被黏合在一起的超大陆大概是Columbia超大陆,它形成于1.85 ~1.90 Ga,在大约1.60 Ga开始破裂,于~1.3~1.2 Ga最终裂解。Columbia超大陆之后第二个真正被黏合在一起的超大陆是Rodinia超大陆,它存在于~1 100 Ma 到 540 Ma。Pangea (0.25 Ga)并不是一个真正的超大陆,只是一个很大的大陆块的集合体——准-超大陆。该准-超大陆的南半部(冈瓦纳古陆)有一个离散的历史,北半部(劳亚古陆——即古亚洲)有一个会聚的历史。目前,第三个超大陆还未形成,我们的星球尚处在一个未来真正超大陆(Amasia)的形成途中。超大陆形成和裂离的机制是有争议的话题。对于一些新近概念模型的综合分析表明,地幔动力学对于地球历史中超大陆的会聚和裂解有着重要的控制作用。超大陆的形成过程受超级沉降流的控制。超级沉降流通过如当今在西太平洋所见到的双向俯冲带而发生,它也为地质历史和P-波全地幔层析所认可。超级沉降流就像外太空的黑洞一样呑噬了所有物质,将大陆会聚到一个紧密的集合之中。超大陆的命运受控于超级地幔柱(超级上涌流),后者将大陆集合裂离。随着数字模型技术的进步及计算能力和资源的增强,地幔动力学的数字研究已经在识别地幔结构的地震层析图像方面取得了明显进展,并对地球动力学机制有了更好地理解。固体地球可以被认为是由上地幔中具水平运动的板块构造、下地幔中受垂直运动主宰的地幔柱构造和地幔底部以水平运动为特征的'反-板块构造’所构成。尽管地幔层析开启了进入深部地球的窗口,在增生造山带中被保存的"大洋板块地层"的叠瓦状残骸仍然构成了研究俯冲-增生-碰撞历史(特别是与地球表面古老超大陆聚合有关的俯冲-增生-碰撞历史)的有用的地质学工具。超大陆的动力学也影响着生命的起源和灭绝、地表环境变化以及岩浆作用和成矿作用。与超大陆会聚和裂解相伴的地幔下沉和地幔上涌引起大规模物质和能量的流动,也导致大规模岩浆作用和成矿作用、灾难性的环境变迁,有时甚至造成生物灭绝。当一个上升的地幔柱撞击超大陆的底部时,它所诱发的大陆裂谷化,形成大火成岩省、大规模成矿作用和火山喷发,可能会导致地幔柱的冬天,后果是生物灭绝和长时期的大洋缺氧。因此,与地幔动力学有关的超大陆构造为评估大陆地壳演化和破坏的历史,进行资源评价、了解生命的历史和追踪我们所居住的星球的主要地表环境变迁提供了一把钥匙。
英文摘要:
      Supercontinents are assemblies of all or nearly all (> 90%) of the earth's continental blocks. The oldest supercontinent speculated is the one at 3.0 Ga termed as Ur. It is difficult to test the existence of this supercontinent due to its old age. There appear to have been twice in earth history when all of the continents were fused into one supercontinent. The first truly coherent supercontinent in earth history was probably Columbia, which formed between 1.85 and 1.90 Ga, began to fragment at ~1.6 Ga, and finally broke up at ~1.3-1.2 Ga. Columbia was followed by the second supercontinent Rodinia, which lasted from ~1100 Ma to 540 Ma. The Pangea (0.25 Ga) was not a true supercontinent, but an unusually large assembly of continents making a semi-supercontinent. The southern half (Gondwanaland) of this semi-supercontinent has a dispersion history, and the northern half (Laurasia, i.e. Paleo-Asia) has an amalgamation history. At present, the third supercontinent has not formed yet, and our planet is in midway to make a true supercontinent (Amasia) in the future. The mechanisms of formation and disruption of supercontinents have been two controversial topics. A synthesis of some of the recent conceptual models suggests that mantle dynamics exerted a significant control on the assembly and breakup of supercontinents through the history of the Earth. The formation process of supercontinents is controlled by super downwelling that develops through double-sided subduction zones as seen in present-day western Pacific, and also endorsed by both geologic history and P-wave whole mantle tomography. The super downwelling swallows all material like a black hole in the outer space, pulling together continents into a tight assembly. The fate of supercontinents is managed by superplumes (super-upwelling) which break apart the continental assemblies. With the advancement in numerical modeling techniques as well as the enhancement in computational power and resource, the numerical studies of mantle dynamics have markedly progressed toward the realization of seismic tomography images of mantle structure and a better understanding of geodynamic mechanisms. The solid Earth can be considered to comprise a plate tectonics domain with broadly horizontal motion in the upper mantle, plume tectonics dominated by vertical movements in the lower mantle region and an "anti-plate tectonics" zone characterized by horizontal movements at the bottom of the mantle. Although mantle tomography opens windows into the deep Earth, the imbricated remnants of "ocean plate stratigraphy" preserved in accretionary orogens still constitute useful geological tools to study subduction-accretion-collision history, particularly in relation to the assembly of older supercontinents on the surface of the globe. The dynamics of supercontinents also impact the origin and extinction of life, surface environmental changes as well as magmatism and metallogeny. Massive flow of material and energy was induced by mantle downwelling and upwelling accompanied by supercontinent assembly and breakup, which would also lead to large-scale magmatism and metallogeny, catastrophic environmental changes, sometimes even triggering mass extinction. When a rising mantle plume impinges the base of a supercontinent, the consequent continental rifting, formation of large igneous provinces, large scale metallogeny and volcanic emissions might lead to the initiation of a plume winter, the aftermath of which would be mass extinction and long-term oceanic anoxia. Supercontinent tectonics in relation to mantle dynamics thus provides a key to evaluate the history of evolution and destruction of the continental crust, to carry out the resource assessment, to understand the history of life, and to trace the major surface environmental changes of our planet.
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