HKDSE Geography/E1/Metamorphic Rocks

There are two main types of metamorphism: Dynamic and regional metamorphism Formation: Internal stress accumulates along a fault or fold High pressure forces the minerals to realign to form metamorphic rocks Rocks are flatted and the minerals are aligned towards the plane of flattening 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 Rising magma intrudes into the rock strata 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