Geology of the Precambrian Metamorphic Rocks Along South Hardscrabble Creek, Wet Mountains, Colorado¹

 

Jeffrey B. Noblett²

 

 

ABSTRACT

 

 

Proterozoic metamorphic rocks exposed along South Hardscrabble Creek are typical of those in the Wet Mountains on the east side of the llse fault, lacking the northeast trending, 1-mi (1.6 km) wavelength folds of rock to the west. They are folded isoclinally implying that this is not a stratigraphic succession, but map units can be described and analyzed.

 

Three major units were recognized: 1) amphibolite, 2) biotite gneiss, and 3) granitic gneiss. Minor rock types include metagabbro and sillimanite-bearing quartzite. The amphibolite and metagabbro have compositions suggesting that they originated as tholeiitic basalts. The biotite gneiss probably had both shale and greywacke protoliths. The mineralogy, textures, and chemistry of the granitic gneisses indicate igneous origin, probably as late tectonic granitic intrusions of crustal derivation.