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?
Callan Bentley is Associate Professor of Geology at Piedmont Virginia Community College in Charlottesville, Virginia. He is a Fellow of the Geological Society of America. For his work on this blog, the National Association of Geoscience Teachers recognized him with the James Shea Award. He has also won the Outstanding Faculty Award from the State Council on Higher Education in Virginia, and the Biggs Award for Excellence in Geoscience Teaching from the Geoscience Education Division of the Geological Society of America. In previous years, Callan served as a contributing editor at EARTH magazine, President of the Geological Society of Washington and President the Geo2YC division of NAGT.
Highly fragmented “basaltic” dykes, with little or no remelting and considerable displacement ?
I am e-mailing you a few examples from the BC coast.
CG
It looks like a basic dismembered dyke inside the granite. A kind of extreme boudinage It looks like a basic dike dismembered inside the granite. A kind of extreme boudinage affecting the least competent part of the granite.
Yes, it is possible because the granite is already consolidated, although it has a great deformation capacity and apparently the basic dike is more refractory.