Regional Metamorphism

Most regional metamorphism is accompanied by deformation, so these metamorphic rocks will have foliated textures.Regional metamorphism and plate tectonicsRegional metamorphism results from both heat and pressure generated at convergent plate margins during subduction and continental collision.Convergent plate margins with subduction zones when oceanic and continental plate collide, high pressure is produced as the oceanic plate is subducted the result is high pressure, low temperature burial metamorphism and the formation of blueschists further way from the subduction zone, magma is rising from the melting oceanic plate and pressures are lower, so high temperatures, low pressure metamorphism occurs high temperatures lead to the formation of igneous intrusions and metamorphic aureoles Paired metamorphic belts will form at convergen margins with subduction zones. The zone closest to the trench will have high pressure due to compressive stress and low temperature as no magma is rising. The zone further away has high temperature due to rising magma and low pressure.Convergent plate margins continental-continentalFold mountains form at these margins where the Earth's crust is deformed, thickened and there is extensive intrusive igneous activity. The Himalayan mountain range began to form about 50 Ma when India collided with Asia. The Himalayas are still growing as the plates are still moving towards each other. High temperatures and pressures acting over long periods create broad (>100km2) and often complex orogenic belts affected by all grades of regional metamorphism. At the deepest part of the orogenic belt the pressures and temperature will be highest, giving high grade regional metamorphism. Away from the collision zone and higher in the crust the grade of metamorphism will be low.Grades of Regional Metamorphic RocksRegional metamorphism of shale produces the following rocks: low grade: slate medium grade: schist high grade: gneiss Regional metamorphism of orthoquartzite and limestones produces the same products as contact metamorphism - quartzite and marble. Each of these rocks is composed of only one mineral, quartz and calcite. The minerals are equi-dimensional, so they cannot align under pressure.

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