10/31/2022 0 Comments Plate boundary![]() Mantle convection simulations with rheologies that generate plate-like behaviour. Start of the Wilson cycle at 3 Ga shown by diamonds from subcontinental mantle. ) 281–294 (Special Paper 440, Geological Society of America, 2008) in When Did Plate Tectonics Begin on Planet Earth? (eds Condie, K. An overview of the geochemistry of Eoarchean to Mesoarchean ultramafic to mafic volcanic rocks, SW Greenland: implications for mantle depletion and petrogenetic processes at subduction zones in the early Earth. ![]() Constraints on Hadean geodynamics from mineral inclusions in >4Ga zircons. ) 1–29 (Special Paper 440, Geological Society of America, 2008) Shirey, S., Kamber, B., Whitehouse, M., Mueller, P. Heterogeneous Hadean hafnium: evidence of continental crust at 4.4 to 4.5 Ga. Initiation and evolution of plate tectonics on Earth: theories and observations. The generation of plate tectonics from mantle convection. ![]() Generation of plate tectonics with two-phase grain-damage and pinning: source–sink model and toroidal flow. Mechanisms for the generation of plate tectonics by two-phase grain-damage and pinning. After plates have developed, continued changes in driving forces, combined with inherited damage and weak zones, promote increased tectonic complexity, such as oblique subduction, strike-slip boundaries that are subparallel to plate motion, and spalling of minor plates.īercovici, D. But for hotter surface conditions, such as those on Venus, accumulation and inheritance of damage is negligible hence only subduction zones survive and plate tectonics does not spread, which corresponds to observations. In the simplest case, for Earth-like conditions, a few successive rotations of the driving pressure field yield relic damaged weak zones that are inherited by the lithospheric flow to form a nearly perfect plate, with passive spreading and strike-slip margins that persist and localize further, even though flow is driven only by subduction. We simulate this process using a grain evolution and damage mechanism with a composite rheology (which is compatible with field and laboratory observations of polycrystalline rocks 1, 2), coupled to an idealized model of pressure-driven lithospheric flow in which a low-pressure zone is equivalent to the suction of convective downwellings. ![]() Here we suggest that when sufficient lithospheric damage (which promotes shear localization and long-lived weak zones) combines with transient mantle flow and migrating proto-subduction, it leads to the accumulation of weak plate boundaries and eventually to fully formed tectonic plates driven by subduction alone. The reason for this time lag is unknown but fundamental to understanding the origin of plate tectonics. The time lag between the first proto-subduction (about 4 billion years ago) and global tectonics (approximately 3 billion years ago) suggests that plates and plate boundaries became widespread over a period of 1 billion years. Transform boundaries do not produce or destroy lithosphere, rather one block of the lithosphere slides horizontally past each other (Wilson, 1965).The initiation of plate tectonics on Earth is a critical event in our planet’s history. Convergent boundaries exist where lithosphere is destroyed, as one plate sinks below the other (e.g., at oceanic trenches). Divergent boundaries occur where new lithosphere is created as the plates move away from each other, as in mid- ocean ridges. As shown in Figure 4, there are three types of plate boundaries. The motion of the rigid plates on the surface of Earth are determined in part by the type of boundaries between the plates. The theory evolved to include the definition of different types of plate boundary motion. His work helped unify the theory of plate tectonics (Wilson,ġ963, 1965). Tuzo Wilson was an early supporter of seafloor spreading and conti- nental drift. The ability to show these earthquakes and volcanoes occur along the plate boundaries helped to support the development of the theory of plate tectonics. ![]() The plate boundaries are marked by a large occurrence of earthquakes and volca- noes. The low strain-rate in the interiors of the plates allow them to transmit stress over large distances, which helps to drive the plates. The plates are defined by rigid, non-deforming sections of lithosphere moving at nearly uniform velocity with weak regions between them. The Earth’s lithosphere, is divided up into different regions that com- prise the tectonic plates. This mobile plate motion is referred to as plate tectonics. Evidence of long-lived, ongoing plate motion on the Earth appears in the magnetic field of the seafloor, seafloor sediment thickness, in the occurrence of earthquakes and even in the appearance of volcano locations. ![]()
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