Regional Metamorphic Isograds

Have you ever wanted to traverse the regional metamorphic isograds, from biotite up through sillimanite grade and beyond? Well, a drive from Loveland up to Estes Park offers that opportunity. Prof. Bill Braddock and his students at the University of Colorado mapped the different metamorphic zones in pelitic rocks in this part of the northern Front Range. The map below starts in low-grade, greenschist facies (pink) on the east and advances through the garnet zone (blue), staurolite zone (orange), and into the sillimanite zone (green), before crossing into the microcline zone near the granitic batholith.

Map showing the different metamorphic grades traversed by Highway 34 between Loveland and Estes Park.