Geodynamic Cycles and Geodynamic Systems of Various Ranks: Their Relationships and Evolution in the Earth's History

摘要

The previously stated ideas of hierarchical geodynamic cyclicity and geodynamics of hierarchically subordinate geospheres are compared in detail. The convective geodynamic system of the first rank (GS-1) that functions throughout the mantle and crust beneath the entire surface of the Earth corresponds to the geodynamic cycle of the first rank (GC-1, or the Wilson cycle). The geodynamic system of the second rank (GS-2) that embraces the mantle and crust only beneath oceans corresponds to the geodynamic cycle of the second rank (GC-2, or the Bertrand cycle). The geodynamic system of the third rank (GS-3) functioning in the tectonosphere (asthenosphere + lithosphere) in zones of elevated heat flow (spreading, subduction, and collision zones) is brought into the line with the geodynamic cycle of the third rank (GC-3, or the Stille cycle). The geodynamic system of the fourth rank (GS-4) that embraces the sedimentary cover of mobile belts corresponds to the geodynamic cycle of the fourth rank (GC-4) (the phase cycle of increasing and decreasing intensity of folding and thrusting). This hierarchy controlled by internal endogenic factors, above all, by the heat flow from the Earth's core and internal sources within the mantle, is supplemented by the geodynamic system of the zeroth rank (GS-0) that embraces the entire Earth and that is controlled by external rotational factors, primarily, the tidal effect of the Moon. The GS-0 is characterized by interference of the permanent westward and meridional (southward and northward, alternately) continental drift in frames of the zeroth geodynamic cycle (GC-0) twice as long as the Wilson cycle (GC-1). An attempt is made to connect cyclicity of various ranks with periodic excitation and waning of convection in a geosphere of the respective rank. The convective geospheres progressively grew downward in the course of geologic history. Only the GS-3 functioned in the Archean, embracing tectonosphere and creating greenstone belts around the gray-gneiss islands with gradual accretion of these belts and the formation of the granite-greenstone continent (Pangea-0). In the Paleoproterozoic, the process spread over the entire upper mantle with switching Rayleigh-Benard polygonal convection expressed in pure form as gran-ulite belts along the polygon perimeters that bounded the protoplatform blocks. The contemporaneous limited convection in the lower mantle (GS-1) led to some divergence of these blocks and formation of minor oceans and their subsequent closure, resulting in the formation of Pangea-1. This tendency developed further in the Mesoproterozoic and completed with the formation of Pangea-2 (Rodinia). Afterward, in the Neogean, the cyclic-hierarchical geodynamics started to work in full as described above.