A Study on the Plate Tectonics in the Early Earth Period Based on the Core-Magma Angular Momentum Exchange

By using a dynamical approach of core-magma angular momentum exchange, this study theoretically explains the continental formation and plate drift as well as main mountain uplifts in the early Earth period. The present mantle and lithosphere were the partial part of magma fluid layer (mantle currents) before and after the Earth’s crust formation. Thus, a theory is presented regarding the driving forces of plate drift, in the form of planetary scale mantle currents. The origin of mantle currents is traced back to the formation of the solar system. It is assumed that small particles (nebula matter) orbiting the Sun assembled, and a molten sphere of primordial Earth with different minerals evenly distributed throughout the total mass came into existence. Subsequently, a process called planetary differentiation took place, as the core and mantle currents (magma layer) started separating. This will inevitably cause the Earth to spin faster, and it is presumed that the inner core first gained angular velocity, thereby spinning faster than the material found at a shallower depth. The time interval of the angular momentum exchange between the core and the magma should have lasted for at least 0.1 - 0.2 billion years. Planetary scale vertical and horizontal circulations of mantle currents took place, and angular momentum exchange was realized through the vertical component. The horizontal part of the mantle currents, near the bottom of the lithosphere, became a real force to drive continental split and plate drift. The acceleration and deceleration of the core compared with the mantle currents then caused different flow directions in the two hemispheres. When the inner core rotates faster from west to east, upper mantle currents will tend to flow westwards and towards the two poles. Surface lighter materials converged towards the two poles so that two continental polar crust caps appeared when the magma surface was cooling. This caused two original supercontinents to form about 4.54 billion years ago, while an original oceanic zone formed in the tropics. The uneven latitudinal variation of crustal thickness did lead to thermal differences within the mantle currents. This caused the core-magma angular momentum exchange. Deceleration of the core will cause two flow vectors, northwesterly in the Northern Hemisphere and southwesterly in the Southern Hemisphere. The history of plate drift is then driven by the motion of upper mantle currents. A distinct Equatorial Convergence Zone of magma flow which developed early in Earth’s history, gave way to the Intertropical Convergence Zone, serving as a border for the magma fluids and continents from the two hemispheres. A possible mechanism for the formation of the Himalayans is the maximum shear stress created by an orthogonal convergence or collision between two continental plates driven by the upper mantle currents.

The progressive onset and evolution of Precambrian subduction and plate tectonics

The regime of plate tectonics on early Earth is one of the fundamental problems in Earth sciences.Precambrian era takes the majority(ca.88%)of Earth’s history and thus plays a key role in understanding the onset of plate tectonics and the mechanism,distribution and process of Precambrian subduction zones.This paper presents a review on the progresses of subduction and subduction zones in different stages of Precambrian era,and sorts out some key issues and fields that merits further attention.We suggest that there was progressive onset and evolution of subduction and plate tectonics from Archean to Proterozoic eras.We emphasize the importance of comprehensive studies on subduction mechanism,metamorphic type,plate tectonics regime,the compositional evolution of continental crust,and petrogenesis of diverse granitoids formed in the Archean.It is proposed that innovative analytical techniques,big data,experimental petrology and numerical geodynamic modeling will facilitate future studies of Precambrian subduction zones.