Most regional metamorphism is accompanied by deformation, so these metamorphic rocks will have foliated textures.

Regional metamorphism and plate tectonics
Regional 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-continental
Fold 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 Rocks
Regional 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.

	Created by siobhan.quirk over 11 years ago

Undergraduate Geology - Part 2 (Metamorphic Processes and Products) Note on Regional Metamorphism, created by siobhan.quirk on 20/05/2013.

Regional Metamorphism