Info for my new quiz
So far, my new quiz, "Metamorphism: the story of a changed rock," has had very few plays. It was suggested to me that perhaps it was too hard. So, I provide a brief introduction to metamorphism that should help...
If you start reading about metamorphism-- and not the "shale goes to slate" "sandstone goes to quartzite" variety-- you will quicky encounter the idea of metamorphic facies. I would give it the following "working definition":
Metamorphic Facies-- The set of minerals that form in a rocks of different chemical compositions in a specific range of pressure-temperature conditions.
Notice that this is something different from metamorphic rock names. Slate, phyllite, schist, gneiss, marble, and so on, may reflect something about the mineralogy of a rock, but primarily describe the texture.
There are more or less three series (facies given in order of increasing temperature):
Low pressure/high temperature -- Zeolite, prehnite-pumpellyite, and some others
Medium pressure/medium temperature-- Greenschist, amphibolite, granulite
High pressure/low temperature-- Blueschist, eclogite
The zeolite and prehnite-pumpellyite facies are low temperature and low pressure. The higher temperature low pressure/high temperature series is not that well understood.
The medium pressure/medium temperature series is common in mountain belts. You can treat it as synonymous with "Barrovian metamorphism."
The high pressure/low temperature series occurs in the subducting slab of a subduction zone.
That should help with the tectonic environment of metamorphism questions...I hope....!
If you start reading about metamorphism-- and not the "shale goes to slate" "sandstone goes to quartzite" variety-- you will quicky encounter the idea of metamorphic facies. I would give it the following "working definition":
Metamorphic Facies-- The set of minerals that form in a rocks of different chemical compositions in a specific range of pressure-temperature conditions.
Notice that this is something different from metamorphic rock names. Slate, phyllite, schist, gneiss, marble, and so on, may reflect something about the mineralogy of a rock, but primarily describe the texture.
There are more or less three series (facies given in order of increasing temperature):
Low pressure/high temperature -- Zeolite, prehnite-pumpellyite, and some others
Medium pressure/medium temperature-- Greenschist, amphibolite, granulite
High pressure/low temperature-- Blueschist, eclogite
The zeolite and prehnite-pumpellyite facies are low temperature and low pressure. The higher temperature low pressure/high temperature series is not that well understood.
The medium pressure/medium temperature series is common in mountain belts. You can treat it as synonymous with "Barrovian metamorphism."
The high pressure/low temperature series occurs in the subducting slab of a subduction zone.
That should help with the tectonic environment of metamorphism questions...I hope....!
1 Comment:
Good God, you're a boring woman...
By Flynn_17, Aug 25 06 3:29 PM