Physical Sciences and Mathematics Commons^™

General Geology And Geochemistry Of Metamorphosed Proterozoic Mafic Dikes And Sills, Tobacco Root Mountains, Montana, John B. Brady, Heidi K. Mohlman, Caroline Harris, Sarah K. Carmichael, Lisa J. Jacob, Wilfredo R. Chaparro

Geosciences: Faculty Publications

Just over two billion years ago, basaltic magma intruded rocks of the Pony– Middle Mountain Metamorphic Suite and the Indian Creek Metamorphic Suite that now crop out in the Tobacco Root Mountains of Montana near the northwestern margin of the Wyoming province. Numerous examples can be found of mafic dikes that crosscut layering and gneissic banding, demonstrating that the host rocks were metamorphosed to form the gneissic texture prior to intrusion of the dikes. Although many of the intrusions appear to be sills that followed compositional layering, close inspection reveals low-angle discordance in nearly every case, consistent with rotation of …