Year of Award


Document Type


Degree Type

Master of Science (MS)

Degree Name


Department or School/College

Department of Geosciences

Committee Chair

Julie Baldwin


Amphibolite Facies, Anaconda, Greyson Formation, Metamorphic Core Complex, NCKFMASH, Phase Diagram, Pressure, Prichard Formation, Pseudosection, Temperature, THERMOCALC


University of Montana


This study shows the complete metamorphic evolution of metapelitic footwall rocks in the Anaconda metamorphic core complex, located in southwestern Montana. Pseudosections were constructed using the computer program THERMOCALC (v. 3.26) in conjunction with the internally consistent dataset of Holland and Powell (1998, version 5.5, updated Nov. 2003) in the model system NCKFMASH (Na2O-CaO-K2O-FeO-MgO-Al2O3- SiO2-H2O). Microprobe data reveals that garnet is very almandine rich and contains very little manganese, thus not requiring MnO as a component in the model system. X-ray mapping of garnet within metapelites indicate only one growth phase. Petrographic analysis in conjunction with pseudosections reveal peak metamorphism occurred at 3.3-5.3 kbars and 590-665°C with an assemblage of biotite + garnet + sillimanite + quartz + plagioclase + muscovite. Chemical composition of garnet, biotite, and plagioclase all verify peak metamorphic conditions on contoured pseudosections. Evolution of footwall rocks occurred along a prograde, clockwise path that was largely stable within sillimanite stability as evidenced by its abundance. These amphibolite facies metapelites equilibrated at or near the solidus.



© Copyright 2008 Erin Haney