海底“三极”与地表“三极”:动力学关联

Tripole on seafloor and tripole on Earth surface: Dynamic connections

  • 摘要: 地球地表环境3个极端分别为南极、北极和青藏高原,被誉为地表“三极”。本文提出深地动力系统的“三极”,分别为Tuzo、Jason和东南亚环形俯冲系统,这“三极”主体发育于海底之下的深部地幔,因此称为海底“三极”。地表“三极”和海底“三极”统称地圈“六极”,是全球变化(变暖或变冷)、深时地球、深地动力、地球系统、宜居地球等地球科学前沿研究领域难以回避的研究对象,是地球多圈层相互作用的6个纽带和突破口,也是寻求地球系统动力学机制的关键所在。Tuzo和Jason是现今分别位于大西洋、太平洋之下的大型横波低速异常区(LLSVP),它们控制了大火成岩省、微板块的形成和演化,也控制了集中式火山去气作用,进而引起大气循环变化;它们还不断衍生微板块,并将其向北驱散,这些微板块围绕东亚环形俯冲系统不断聚集,导致大量物质深俯冲,促进深部物质循环,同时,在岛弧地带释放大量温室气体,改变地表系统大气环流;板块聚散伴随海陆格局变迁,同时,也改变着全球海峡通道、高原隆升和垮塌,调节着地表流体系统的运行:包括海洋环流和大气环流。冰盖形成与演化也受其控制。海底“三极”也是地史时期超大陆聚散的根本控制因素,而地表系统的百万年内的多尺度周期性变化主要受公转偏心率、地轴斜率和岁差控制,气候变化受热带驱动和冰盖驱动双重控制。总之,尽管早期地球以后逐渐具有地球宜居性,但地圈-生物圈相互作用极其复杂,地圈“六极”研究可作为宜居地球研究的突破口和生长点。

     

    Abstract: The three extreme regions of the Earth’s surface environment, i.e. the Antarctica, Arctic and Qinghai-Tibet Plateau, are known as the " three poles (tripole)” of the surface Earth system. In this paper, the concept of tripole of deep-Earth geodynamic system is proposed, which includes Tuzo, Jason and the Circum-East Asian subduction system. Since the principle parts of the deep-Earth tripole are developed mainly in the deep mantle beneath the seafloor, they are called hereby the seafloor tripole. The surface tripole and the deep tripole collectively consists of the " six poles” of the geosphere, which are the unavoidable research objects in the frontiers of geosciences, such as global change, deep-time Earth, deep-Earth geodynamics, Earth system and habitable Earth. They are the six links and breakthroughs in the multi-spherical interaction of the Earth as well as the key to search for the dynamic mechanism of the Earth system. Tuzo and Jason are Large Low Shear-wave Velocity Provinces (LLSVPs) located under the Atlantic and the Pacific, respectively. They control the formation and evolution of large igneous provinces and micro-plates, as well as centralized volcanic degassing which leads to the changes in atmospheric circulation. They also continuously cause the formation of micro-plates, push them moving northward, and constantly assemble them into the Circum-East Asian subduction system. A large amount of substances are subducted deeply to trigger the deep material circulation. Simultaneously, a large amount of greenhouse gases are released through island arcs, which changes the atmospheric circulation of the surface Earth system. Plate assembly and dispersion together will change the continent-ocean configuration patterns in addition to the global seaways, the uplift and collapse of the plateaus, and further regulate the operation of surface Earth fluid system, including both the ocean circulation and atmospheric circulation. The formation and evolution of ice sheets are also controlled by them. The " three poles” under the seafloor are indeed the fundamental controlling factors of the supercontinent convergence and dispersal in the geological history. The multi-scale periodic changes of the surface Earth system are mainly controlled by the eccentricity of the Earth around the Sun, the obliquity of the Earth axis and the precession. Climate change is driven by both tropical and ice-sheet driving forces. In a word, although the Earth is habitable after the Early Earth, the interaction between the geosphere and biosphere is extremely complex. The study of the geospheric " six poles” is doubtlessly the breakthrough and growth point for the study of habitable Earth.

     

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