"Ten Stories" – The Latest Edition of Earth's "Biography" (7) "Subduction" and "Plate Movement"

Why do the continents on Earth drift and move? The dynamic mechanism of continental drift is related to two sub-forces of the Earth's rotation: the tidal force of westward drift and the force of detachment pointing to the equator. Lighter silicon-aluminum continental blocks float above heavier viscous silicon-magnesium layers, and due to tidal and decanting forces, the pan-continents rupture and separate from the silicon-magnesium layer, while making large-scale horizontal drifts westward and toward the equator, and moving nearby. This is one statement, two forces.

There is also an important role, which is "convection". The lower mantle material rises due to heat expansion, and the upper mantle material decreases due to low temperature, condensation contraction, and high density. Both form a closed circular flow. In the early stages of convection, after the rising mantle reaches the central continent (if there were continents at that time), it splits into two strands and flows in opposite directions, tearing the continent apart, causing the dividing continental masses to drift with the mantle flow, and between the cracked massifs to form oceans.

If the troposphere appears below the continent, the rise of mantle magma will drive the continental block to rupture along the rift valley. And the two parts of the separated block will move to both sides at a uniform speed. When the edge of the continent meets the mantle flow, due to the density and volume of the oceanic crust, it will bend downward and sink with the downcurrent. The ridge rift valley belt is the mantle gushing out belt. Driven by this, the seabed has been expanding. 1-2.25 cm/year in the Atlantic Ocean, 1-2.22 cm/year in the Indian Ocean, 1-1.49 cm/year in the Pacific Ocean.

From the creation of the Earth, this "convection" caused the eruption of the mantle, which flows to both sides and then cools the downward subduction movement, divided into the following stages:

1. Hot subduction. That is, the young mantle plates subduct towards both sides of the mid-ocean ridge. At this time, the movement of the plates did not start. For according to the current view, the plate movement is not dragged by the mantle circulation, not pulled apart by the open middle ridge of the ocean. 90% of the plate movement comes from the subduction of the plates. Plate insertion into the mantle is the beginning of plate movement. When the heat is subducted, the plates are in a state of upward gushing. At this time, the state of the Earth's continents is affected by the mantle column pattern. 3 billion years ago.

2. The Earth is "medieval". 1.7 billion years ago, when the plate subducted to its highest point and was about to flow to both sides, the movement of the earth's plates entered a silent and inactive state, that is, the "Middle Ages" of the earth.

3. Cold subduction. 750 million years ago, the mantle flow entered the cold subduction stage, the subducted plate fell back, inserted into the depths of the mantle, and the metamorphic effect of high pressure and ultra-high pressure occurred. The early movement of the Earth basically began during this period. Later, the Yanshan movement, the Himalayan movement, was also a reaction to the subduction of the cold mantle.

3 billion years, 1.7 billion years, 750 million years ago. The Earth has experienced such a process of plate movement caused by mantle convection. At present, we are throwing in the stage of the "cold dive" of this movement, and some inevitable occurrences are happening.

4. Collision. In subduction zones, i.e. the confluence of plates, which may be between oceanic plates or the confluence of oceanic and continental lithospheres, "continental hyperplasia" caused by collisions arises. Therefore, some experts say that the subduction zone is a processing plant for continental proliferation. Includes important island arc areas. These movements were also essential to have a huge impact on the geological landscape of the continental interior. Including orogeny.

5. Plate insertion, return to the mantle. The plate is processed as a processing product, and after processing the new continent, the remaining scrap will be reinserted back into the mantle. But the problem is far from simple. A portion of the plates can be returned to the lower layer of the mantle, the d'' layer at the junction of the nuclear mantle, where they accumulate to form a "plate graveyard". There is also a part that will remain stuck in the Middle Mantle interface. This part, if a catastrophic fall time occurs, will lead to an upwelling of the high temperature of the lower mantle, causing a lot of serious volcanic activity.

In short, new mantle pillars may be re-emerging at these locations in this subduction zone. A new round of continental layout will begin. The cycle of this rotation is 600-800 million years.