Rock Cycle

2 February 2017

Rock cycle is the cycle of rock transformation which affects all rocks. The cycle involves all parts of the crust. When the rocks are subducted into the asthenosphere due to compression, the rocks melt into magma. The melting of rocks intensifies the pressure in the asthenosphere. Cracks develop. When cracks extend downward and reach the magma, the pressure of magma is released.

Magma then extrudes out of the crust along the cracks to the earth’s surface. It results in vulcanicity. Magma cools and solidifies to form igneous rocks when rises nearer to or above the earth surface.During the cooling process, crystallization takes place in magma or lava forming minerals. The accumulation of minerals forms igneous rock. When the processes of vulcanicity, cooling and solidification of magma take place in the crust, the rocks formed are called intrusive igneous rocks. Igneous rocks that are formed deep underground are called plutonic rocks and hypabyssal rocks are formed at intermediate depth below the earth surface.

Rock Cycle Essay Example

When the processes of vulcanicity, cooling and solidification of lava take place on the earth surface, extrusive igneous or volcanic rocks are formed.Any rocks exposed on the land surface are subject to exogenetic processes. They include commonly denudation (weathering, erosion, transportation) and deposition. With the help of denudation agents, rocks are broken down and brought downslope. Rocks formed deep underground may also be exposed eventually after the overlying rocks are removed by denudation. Weathering, physical, chemical or biological, disintegrates or decomposes larger rocks into smaller fragments or sediments which are then eroded away from their original location.When energy for transportation or erosion is lost, deposition takes place and sediments accumulate.

Layers of sediments pile up by sedimentation. The rock fragments and grains are squeezed tightly during the process of compaction. Water in the spore spaces between the grains contains dissolved minerals like silica. It helps glue the grains together. After compaction and cementation, loose sediments are transformed into solid rocks by lithification. The rocks formed are called sedimentary rocks. Sedimentary rocks can be formed chemically, organically and mechanically.

For chemically formed sedimentary rocks, evaporation and precipitation of chemicals or minerals are involved. For organically formed sedimentary rocks, burying and compressing of dead living organisms are involved. For mechanically formed sedimentary rocks, sorting process is often associated during deposition. Due to great heat, when sedimentary is melted, rocks become magma again and it may cools and solidifies to form igneous rocks. Under great heat with melting or great pressure, igneous or sedimentary rocks could be metamorphosed by thermal metamorphism or dynamic metamorphism to form metamorphic rocks.Rising magma intruding into rock layers provide great heat to melt crystals which are then recrystallized into new rocks by thermal metamorphism. Internal stress accumulates along a fault or in a fold results in high pressure to make the mineral crystals in rocks realign to form new metamorphic rocks by dynamic / regional metamorphism, such rocks are usually foliated in structure.

When rocks subduct into the asthenosphere, metamorphic rocks are melted to become magma and form igneous rocks or they are exposed for exogenetic processes to form sedimentary rocks. With plate movements, vulcanicity occurs, the rock cycle continues.Metamorphism at destructive boundary Source:Plate Tecctonics: An Introduction| Geologyrock, http://www. geologyrocks. co. uk/tutorials/plate_tectonics_introduction Along the destructive plate boundary, plates move towards each other due to the sinking subcrustal convection current of magma in the asthenosphere. By compressional force, subduction zone is formed when the collision involves an ocean plate.

? Compressional force also results in folding and faulting. When great pressure is produced within the crust, along the reverse fault or between the plates, it may result in dynamic metamorphism.Rocks are flattened and the minerals inside are aligned towards the plan of flattening. This creates the foliated structure in the resultant metamorphic rocks. For instance, slate (fine grained foliated metamorphic rock) transformed from shale, mudstone or siltstone (mechanically-formed secondary rocks). The intrusive vulcanicity or friction caused by crustal movement produce great heat. The zone where such heat is in contact with the surrounding rocks is called an aureole.

The high temperature melts the rock crystals and they recrystallize into metamorphic rocks.

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