The title of the post comes from a simpler question....
What is the volcanic equivalent of granite?
The quick answer is rhyolite, but we need to understand why.
The main thing we need to start with is that granite is an igneous rock. Igneous rocks are originally born from the cooling of a melt.
If the melt cools below surface, this is an intrusive environment and the rock is considered plutonic.
If the melt makes it to surface, the environment is extrusive and the rock is volcanic.
The key thing to remember is that you can have the same mineral composition in a melt regardless whether it is plutonic or volcanic. The minerals will be the same but they will cool under different condition and the rocks will have different textures.
So...when a melt containing quartz, feldspar and biotite cools and solidifies in an intrusive environment, the rock is a granite. When it form in a volcanic environment, the rock is a rhyolite - same minerals, different environments.
No comments:
Post a Comment