5 December 2022

Mafic blocks in Wind River Range granite

Posted by Callan Bentley

Got these photos from a reader, showing outcrops in the northern Wind River range (ESE of Island Lake). The question, inevitably, is are these MMEs (microgranular mafic enclaves) or xenoliths?

They’re fine grained and mafic… but some lithologies of xenolith could be too!

This next set shows what appear to be a bunch of blocks strung out in a line…

This one is shaped like a toaster or a television set:

Note that more pronounced weathering of the mafic blocks, and also how the granite’s fabric wraps around it on at least three sides.

Any thoughts, igneous petrologists?