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Another line of research follows up on this, proposing that differences in the densities of newly formed crystals caused separation of crustal rocks; upper crust largely composed of fractionated gabbros and lower crust composed of anorthosites. [13] The overall result of initial crystallisation formed a primordial crust roughly 60 km in depth. [13]
Seafloor spreading, or seafloor spread, is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. History of study
It is estimated that along Earth's mid-ocean ridges every year 2.7 km 2 (1.0 sq mi) of new seafloor is formed by this process. [50] With a crustal thickness of 7 km (4.3 mi), this amounts to about 19 km 3 (4.6 cu mi) of new ocean crust formed every year. [50]
New magma from deep within Earth rises easily through these weak zones and eventually erupts along the crest of the ridges to create new oceanic crust. This process, at first denominated the "conveyer belt hypothesis" and later called seafloor spreading, operating over many millions of years continues to form new ocean floor all across the ...
Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. ... New rock is formed by magma at the mid-ocean ridges, and the ocean floor ...
Consequently, old crust must be destroyed, so opposite a spreading center, there is usually a subduction zone: a trench where an ocean plate is sinking back into the mantle. This constant process of creating a new ocean crust and destroying the old ocean crust means that the oldest ocean crust on Earth today is only about 200 million years old ...
During this process, the rock remains mostly in the solid state, but gradually recrystallizes to a new texture or mineral composition. [1] The protolith may be an igneous, sedimentary, or existing metamorphic rock. Metamorphic rocks make up a large part of the Earth's crust and form 12% of the Earth's land surface. [2]
At mid-ocean ridges, new crust is created by the injection, extrusion, and solidification of magma. After the magma has cooled through the Curie point, ferromagnetism becomes possible and the magnetization direction of magnetic minerals in the newly formed crust orients parallel to the current background geomagnetic field vector.