#crenulation

[cordially-stupid]

Hello fellow geology enthusiasts! I've finished my structural class and have now put some of my homework on my redbubble! link is to the socks version >:3 Enjoy!

[fieriframes]

[Crenulation.]

[earthstory]

Kink

The process of metamorphism is not a simple one. Metamorphic rocks are produced in mountain ranges that grow in pulses, with different faults active at different times. As these complex tectonic processes reshape the landscape, the rocks buried deep in the mountain range find their conditions changing constantly.

Foliation in metamorphic rocks is a planar fabric produced in response to stress. As the rocks are squeezed, planar minerals like mica grains orient themselves so that they are aligned perpendicular to the strongest squeezing direction. But, over time as the position of the rock changes and the mountain building event evolves, the stress that created the foliation can change.

This rock has been “crenulated”. There was an original foliation created by metamorphic stresses – the pencil is in the plane of that foliation – but it has been rekinked and bent into folds by a later stress. If the metamorphism had continued, eventually the tips of these kinks would have connected as new minerals grew, in the process developing a completely new foliation and starting to remove evidence of the previous foliation. This process can repeat itself many times in a single metamorphic rock – in fact, this rock from Western Australia is marked as showing F5 and F4 foliations, where the foliation represented by the pen is the 4th metamorphic foliation in the rock and the crenulation is the 5th fabric. Previous events may be recognized in other outcrops or through microscopic analysis techniques.

-JBB

Image credit: http://bit.ly/2hKPEGc

[earthstory]

Check out the fine-scale folding in this metamorphic schist, viewed under thin section