Physical Geology lecture outline - Metamorphic rocks

Definition of metamorphism: solid state change in mineral texture or content due to change in pressure, temperature or other conditions (e.g. fluids, deformation) at substantial depth below the surface.

Reference: Con Gillen, 1982, Metamorphic Geology; Allen & Unwin, London, 144 p..

What are processes involved in metamorphism?

• mineral phase change.
• recrystallization.
• metasomatism.

What are factors that influence metamorphism?

Nature of the geothermal gradient?

• computation or estimation of?
• source of heat?
• variation in?

Controls on the 'pressure' (lithostatic) gradient?

Metamorphic paths (from here to there and back again):

• What causes rocks to travel to new crustal positions and experience new P-T conditions?
• How can we work out the changes expected as a rock experiences changing metamorphic conditons with time?
• A map of P-T space and changes.
• Why do we see high P-T mineral assemblages at the earth's surface (i.e. what is the difference between prograde and retrograde paths)?

Important concepts in navigating metamorphic space:

• index minerals.
• metamorphic isograds.
• metamorphic grade -> high vs. low.
• metamorphic facies.

Paired metamorphic belts and tectonic settings for metamorphism;

• variation in temperature at depth from a subduction zone to an arc.
• Japan as an example.

Common metamorphic rock types and textures.

• protoliths of various metamorphic rock types
• foliations, lineations and porphyroblasts and porphyroclasts

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