Rocks #1

B. Explain the formation of metamorphic rocks, with reference to examples from Ireland.

There are three forms of rock types which I have studied. These rock types are igneous, sedimentary and metaphoric rocks. Metamorphic rocks are appropriately titled due to their metamorphose origination. Metamorphic rocks are former igneous or sedimentary rocks which have changed form, either chemically or physically due to intense heat and/or pressure caused by plate tectonic movements.

Metamorphose occurs through one of three mediums; thermal, dynamic or regional. Thermal metamorphism is the process by which rocks are forced to change by intense heat; this is usually caused by contact of molten magma, often occurring at the edge of dykes or sills. Quartzite, which is a pale coloured metamorphic rock, is created from the thermal metamorphism of sandstone. An example of a quartzite landform induced by metamorphose in Ireland is Mount Errigal in County Donegal.

Dynamic metamorphose is the changing of rock due to pressures forced by the movement of plates. When two plates collide due to conflicting convection currents extreme pressure is placed along fault lines within the rocks. Fault gouge is a fine sticky powder which the rock is compressed to when placed under such severe and extended strain. Metamorphosis of a dynamic nature can be seen in the Caledonian fold mountains which formed some 400 million years ago when the American and European plates collided. Slate is the product of dynamic metamorphosed shale. Slate can be separated very easily along its layered structure making it ideal for roofing in the construction industry. An Irish example of shale metamorphosed to slate is in Valentia Island in County Kerry.

The third and final stage of metamorphism is regional. This form of metamorphose can transform large areas of rock at once. When plates collide at a destructive plate boundary such as that of an oceanic and continental plate, the heavier plate is forced downward under t...

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