Metamorphic Rocks and Processes
Metamorphic rocks form by changes in PRESSURE and TEMPERATURE in a SOLID
STATE.
Pressure: lithostatic (confining) = in all directions, and directed , unequal in direction.
Changes that occur during metamorphism:
Recrystallization
New Mineral Growth
Foliation (alignment of mineral grains)
Changes in mineral structure (polymorphs)
PROTOLITH is the parent rock, pre-metamorphic rock
Some examples of protoliths:
Shale -> Slate
Limestone-> Marble
Quartz Sandstone ->Quartzite
Basalt -> Serpentinite
Increasing metamorphic Grade: generally larger crystals, and different minerals
For Regional Metamorphism
Shale (sed) ->Slate->Phyllite->Schist->Gneiss->Migmatite-> (melting) Igneous Rock
Granite
Index minerals are those that grow under specific P and T conditions to indicate grade.
Some examples: Garnet, Kyanite, Sillmanite, Andalucite
Metamorphic Facies are used as indicators of P and T conditions regardless of rock type
Other types of metamorphism: CONTACT -High T low P (around igneous intrusions),
FAULT-high P low T (around faults)
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Metamorphic Rocks and Processes