Coastal & Marine Geology InfoBank
Our Mapping Systems
The USGS and Science Education
USGS Fact Sheets
ground penetrating radar
Comment: 16:48 - 17:34 (00:46)
Source: Annenberg/CPB Resources - Earth Revealed - 18. Metamorphic Rocks
Keywords: "James Sadd", "metamorphic facies", basalt, metamorphism, temperature, pressure, composition, mineral, "metamorphic rock", amphibole, "amphibolite facies"
Our transcription: As basalt is metamorphosed to different combinations of temperature and pressure, its mineral composition changes as the rock re-equilibrates to its new condition.
These zones on the chart are called "metamorphic facies," and each facies is defined by the formation during metamorphism of a particular mineral or mineral assemblage.
For example, this is a metamorphosed basalt containing the mineral "amphibole."
Amphibole forms at a temperature between 450 and 700 degrees centigrade and at a pressure corresponding to a depth of at least six kilometers.
So this metamorphosed basalt would plot here on a chart in the amphibolite facies.
Geology School Keywords