Geology and geochemistry of the Spuhler Peak Metamorphic Suite

The Spuhler Peak Metamorphic Suite consists of a thick sequence of Archean metamorphic rocks, dominated by amphibolite, orthoamphibole-garnet gneiss, and hornblende gneiss and containing minor quantities of quartzite, aluminous schist, quartzofeldspathic gneiss, and meta-ultramafic rocks. Although the Spuhler Peak Metamorphic Suite represents less than 3% of Precambrian exposures in the Tobacco Root Mountains, it has been recognized as a unique suite in the region, due in large part to the unusually abundant amphibolite and the spectacular appearance of the orthoamphibole-garnet gneisses.