HKDSE Geography/E1/Metamorphic Rocks

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There are two main types of metamorphism:

Dynamic and regional metamorphism[edit]

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[edit]

  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