Geochemistry and provenance of Archean metasedimentary rocks in the southwestern Beartooth Mountains

A thick sequence of Archean metasedimentary rocks is exposed along the southwestern margin of the Beartooth Mountains, Montana.Rock types include quartz-biotite schist, biotite schist, biotite-garnet-staurolite-andalusite schist, iron formation (hornblende-cummingtonite-garnet schist), and dacitic metavolcanic rocks (quartz-muscovite-plagioclase schist).Preliminary chronologic data indicate an age of at least 3200 Ma for these racks (Paul Mueller, pers.comm.).The entire belt is metamorphosed from greenschist to middle amphibolite facies.Peak metamorphic conditions occurred at 550 degrees C and less than 3.8 kilobars.The entire rock package has experienced at least two periods of structural deformation.Early isoclinal folds (F1) are coincident with peak metamorphism (M1).Later open folds (F2) are superimposed on earlier structures.Primary sedimentary structures such as horizontal lamination, graded bedding, cross bedding, wavy bedding, and cut and fill structures are preserved.Analysis of sedimentary structures suggests that the rocks were originally deposited by turbidity currents in an environment similar to the midfan portion of a submarine fan.These data suggest deposition along an active continental margin; geochemical data indicates a provenance with iii