HKDSE Geography/E1/Metamorphic Rocks

There are two main types of metamorphism:

Dynamic and regional metamorphism
Formation:
 * 1) Internal stress accumulates along a fault or fold
 * 2) High pressure forces the minerals to realign to form metamorphic rocks
 * 3) Rocks are flatted and the minerals are aligned towards the plane of flattening
 * 4) A foliated structure is formed

Conditions:
 * Associated with large-scale mountain-building processes (the collision of two continental plates or the subduction of an oceanic plate)
 * High temperature and pressure

Examples:
 * Shale/Mudstone/Siltstone → Slate → Phyllite → Schist → Gneiss
 * Granite → Gneiss

Contact/thermal metamorphism

 * 1) Rising magma intrudes into the rock strata
 * 2) Heat from magma intrusion creates high temperature, which melts and recrystallises the rock crystals into new rock

This is a localised process. The zone of contact between the existing rock and the intrusion - i.e. where the metamorphism takes place - is the aureole. The rocks do not have a foliated structure.

Conditions:
 * High temperature
 * Magma intrusion

Examples:
 * Bituminous coal → Anthracite
 * Sandstone → Quartzite
 * Limestone → Marble