前寒武纪地球动力学(Ⅳ):前板块体制

Precambrian geodynamics(Ⅳ):Pre-plate regime

前寒武纪地球动力学关注地球45.6-5.43亿年期间的沉积、岩浆、变质、变形、地幔和岩石圈的动力学机制,是永恒的地球科学前沿研究内容。现今研究积累表明：早前寒武纪构造还难以完全用板块构造理论给予说明,板块构造起源的时间虽然可能因地而异,但主流认识是27-21亿年期间,华北克拉通也是如此。板块构造出现之前的前板块构造体制也业已提出了多种认识：地幔柱理论、地幔翻转、重力构造、小板块构造等,其中重力构造被认为主要发生在冥古宙的地球层圈分异阶段,尤其是45.4-44.5亿年间地核形成和地幔的岩浆海阶段。迄今,对于地壳层次的卵形构造成因,也有8种模式之多：底辟构造、中下地壳流动构造、水平渠道流、多期褶皱叠加构造、变形分解构造、龟裂-拗沉俯冲构造、卵形构造的多层Top-down流变构造、岩基侵入-挠曲分解构造等,它们皆可出现在挤压、伸展、走滑构造背景下。无论是板块构造还是前板块构造阶段,全球构造过程似乎都是Top-down机制。

Precambrian geodynamics focuses on kinetics mechanism of sedimentation, magmatic, metamorphic and deformation, mantle and lithosphere of the Earth during 4.56 - 0. 543 Ga, being the eternal frontier and research focus of Earth Science. The present-day study shows that the early Precambrian tectonics is difficult to adopt the theory of plate tectonics to be interpreted reasonably; origin time of plate tectonics through the Earth history may vary at various positions, but the mainstream understanding is that the plate tectonics regime occurred during 2. 7 2. 1 Ga, and so is the North China Craton. The pre-plate regimes appearing before plate tectonics has been proposed, including many kinds of understanding： mantle plume, mantle overturn, gravitational tectonics, and platelets, of which the gravitational tectonics was considered at the stage of layering or stratification on the Earth in the Hadean, especially 4.54 - 4.45 Ga of the core formation and mantle magma ocean. So far, for the origin of oval structures of crustal levels, there are 8 original models： diapirism, middle-lower crust flow, horizontal channel flow, polyphase fold superposition, deformation partitioning, cracking-sag subduction, multilayer top-down rheological flow and batholith intrusion-derived buckling-partitioning, they all can appear under extension, compression and strike slipping backgrounds. No matter what both plate tectonics and pre-plate regimes, global tectonic process seems to he top-down mechanism.