PRESSURE-TEMPERATURE EVOLUTION OF METAPELITES WITHIN THE ANACONDA METAMORPHIC CORE COMPLEX, SOUTHWESTERN 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.

Name thesis:degree_name

Master of Science (MS)

Grantor dc:publisher

University of Montana

Year

2008

Author dc:creator

• Haney, Erin

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

Repository record dc:identifier

https://scholarworks.umt.edu/etd/1262

OAI identifier oai:identifier

oai:scholarworks.umt.edu:etd-2281