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Geosciences LibreTexts

7: Metamorphism and Metamorphic Rocks (Exercises)

Q7.1 How long did it take

It might have taken in the order of 20 to 25 million years for these garnets to form, but even more time is needed than that to produce the rock because we have to account for the sedimentary process and then burial and lithification and then deeper burial to reach metamorphic environment – several tens of millions more years.

Q7.2 Naming metamorphic rocks

Rock Description Name
A rock with visible minerals of mica and with small crystals of andalusite. The mica crystals are consistently parallel to one another. Schist or (preferably) Mica-andalusite schist
A very hard rock with a granular appearance and a glassy lustre. There is no evidence of foliation. Probably quartzite
A fine-grained rock that splits into wavy sheets. The surfaces of the sheets have a sheen to them. Phyllite
A rock that is dominated by aligned crystals of amphibole. Amphibolite

Q7.3 Metamorphic Rocks in Areas with Higher Geothermal Gradients

Metamorphic Rock Type Depth (km)
Slate 2 to 5
Phyllite 5 to 8
Schist 8 to 12
Gneiss 12 to 17
Migmatite 17 to 25

Q7.4 Scottish Metamorphic Zones

Metamorphic zones in southern Scotland [SE]

Q7.5 Contact metamorphism and metasomatism

Contact metamorphic rocks: a: hornfels, b: marble, c: quartzite

Contact metamorphic rocks [SE]