Rock Cycle Essay

ROCK CYLCE

A rock is a naturally occurring substance or solid material which is composed of one or more minerals. There are three types of rocks namely – Igneous , Metamorphic and Sedimentary rocks. These rock are in a continuous cycle of process whereby they are changed from one type of rocks to another which may be of a different mineral composition. This processes is called Rock cycle. The rock cycle is a process that describes the formation, breakdown, and reformation of a rock as a result of sedimentary, igneous, and metamorphic processes.

The rock cycle can involve changes which may include the changes of a rock to igneous, to sedimentary and to metamorphic. Even though the process is called cycle the rock cycle does not or may not truly

Sedimentary rock can be transformed to igneous rock by the process of melting and solidification. This suggested that the process cycle endlessly from one to the other without proper direction.

There is a more definite rock cycle called Wilson cycle. In this cycle the path follow a certain direction and it does not cycle back on itself completely. To each round of the Wilson cycle it increases the diversity of rocks on the earth, and increases the volume of felsic igneous rocks. The Earth is not just on a rock cycle, it is an evolutionary rock cycle. A simple ideal model of Rock cycle is Tectonic Rock Cycle.

Tectonic Rock Cycle involves different stages in which the cycle are carried out by rocks of different Parent

The descending in the subduction zone begins cold. As it descends heat increases because of the geothermal gradient and friction of subduction and heat lead to Fractional Melting . The initial melt may be mafic,but evolves through time to intermediate (Diorite/Andesite) and felsic (Plagiogranite/Rhyolite) rocks.

Step 3- Generation of high P/high T ecolgite by descent of unmelted oceanic lithosphere which usually takes place above the subduction zone. The oceanic lithosphere which descend into the mantle has now been fractionated twice, once at the oceanic rift center, and now a second time along the subduction zone. It is a sterile residue of ultramafic rock. At the high temperatures and pressures inside the mantle it metamorphoses to eclogite, the first metamorphic rock in the tectonic rock cycle.

Step 4- Generation of lithic rich sediments by weathering of a volcanic arc which is an outcome of the continuing process of subduction. The weathering products of the volcanic are sediments of lithic-rich composition. On deeper weathering, down into coarser igneous rocks . The result is lithic-rich to feldspar-rich sediments deposited in submarine fans surrounding the volcanic arc, the first sedimentary rocks of the tectonic rock