Once the rocks have formed from the magma that rises and comes to the surface, they can undergo various processes that transform them. On the one hand, they can be pulverized by erosion and, their fragments, give rise to sedimentary rocks. On the other, they may sink - or not have reached the surface - and be transformed by heat and pressure, resulting in metamorphic rocks.
Sedimentary rocks are composed of transformed materials, formed by the accumulation and consolidation of pulverized mineral matter, deposited by erosion.
Sedimentary rocks are classified according to their origin:
The rocks detritic, or fragmentary, they are composed of mineral particles produced by the mechanical disintegration of other rocks and transported, without chemical deterioration, thanks to water. They are transported to larger bodies of water, where they are deposited in layers. Examples: shales and sandstone.
Sedimentary rocks chemical they are formed by chemical sedimentation of materials that have been in solution during their transport phase. In these sedimentation processes the activity of living organisms can also influence, in which case we can talk about biochemical or organic origin. Examples: plaster, anhydrite and limestone.
Metamorphic rocks are those whose original composition and texture have been altered by heat and pressure. This process is called rock metamorphosis. Environments with sufficient heat and pressure to cause metamorphism are frequently found where Earth's tectonic plates are joining. There, the plates that collide with each other, crush the rocks and are heated to great depths by magma.
Rocks can be altered in small areas of contact metamorphism, or in large areas by regional metamorphism.
He contact metamorphism It occurs when a magma intrudes a cooler rock. In the mother or box rock (the coldest) an alteration zone called contact halo is formed. The halo can be divided into several metamorphic zones, since high temperature minerals such as garnet will form near the intrusive while further low-grade minerals such as chlorite will form.
He regional metamorphism It occurs when large regions of the cortex are compressed and deformed. When rivers accumulate sediments on the rocks in sedimentary basins for hundreds of millions of years, the pressure on these rocks increases and the basin slowly sinks. Over time the temperature and pressure in the older lower layers will increase until metamorphism begins.
Another form of regional metamorphism occurs when tectonic plates converge. One plate dips under the other towards the mantle. In these subduction zones, magma is produced that ascends through the crust, causing metamorphism in large regions of the continental crust near the subduction zones.
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