Title

Petrology, Thermobarometry, and Geochemistry of Amphibolites of the Ruby Range, Montana

Presentation Type

Poster

Abstract

The Ruby Range in southwest Montana preserves a record of the tectonic events that occurred >2.5 to 1.7 billion years ago and records the growth and evolution of the North American continent at that time. In particular, metamorphic rocks and deformational structures found in the range preserve evidence for a regional continental collision 1.8 to 1.7 billion years ago, which has been termed the Big Sky orogeny. Garnet amphibolites found in three distinct compositional suites hosted within the Ruby Range contain appropriate mineral assemblages to constrain the peak pressures and temperatures at which the rocks were metamorphosed. Determining the peak pressure and temperature conditions experienced by the amphibolites can be used to determine the grade of metamorphism that occurred during orogenesis. Samples of garnet amphibolites were collected from the Ruby Range for whole rock geochemistry, petrography, and SEM (scanning electron microscope) mineral chemistry analysis. Major and trace element compositional data was obtained for one of the three suites to determine possible protolith rock types and petrogenesis. Mineral chemistry data was also collected with the SEM-EDS (energy dispersive spectroscopy) to use in the calculation of the pressure and temperature conditions for each of the three compositional suites. This information will determine if there is a gradient in peak metamorphic conditions across the range. The information obtained from these rocks can be integrated to gain a better understanding of the origins and characterize the metamorphic event(s) that affected this margin of North America during the Big Sky orogeny.

Category

Physical Sciences

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Apr 17th, 3:00 PM Apr 17th, 4:00 PM

Petrology, Thermobarometry, and Geochemistry of Amphibolites of the Ruby Range, Montana

South UC Ballroom

The Ruby Range in southwest Montana preserves a record of the tectonic events that occurred >2.5 to 1.7 billion years ago and records the growth and evolution of the North American continent at that time. In particular, metamorphic rocks and deformational structures found in the range preserve evidence for a regional continental collision 1.8 to 1.7 billion years ago, which has been termed the Big Sky orogeny. Garnet amphibolites found in three distinct compositional suites hosted within the Ruby Range contain appropriate mineral assemblages to constrain the peak pressures and temperatures at which the rocks were metamorphosed. Determining the peak pressure and temperature conditions experienced by the amphibolites can be used to determine the grade of metamorphism that occurred during orogenesis. Samples of garnet amphibolites were collected from the Ruby Range for whole rock geochemistry, petrography, and SEM (scanning electron microscope) mineral chemistry analysis. Major and trace element compositional data was obtained for one of the three suites to determine possible protolith rock types and petrogenesis. Mineral chemistry data was also collected with the SEM-EDS (energy dispersive spectroscopy) to use in the calculation of the pressure and temperature conditions for each of the three compositional suites. This information will determine if there is a gradient in peak metamorphic conditions across the range. The information obtained from these rocks can be integrated to gain a better understanding of the origins and characterize the metamorphic event(s) that affected this margin of North America during the Big Sky orogeny.