Geology, Age, and Tectonic Setting of the Cretaceous Sliderock Mountain Volcano,Montana

摘要

Sliderock Mountain volcano is an Upper Cretaceous stratovolcano located along thesouthern margin of the Crazy Mountains Basin in south-central Montana. The volcano is part of an extensive northwest-trending volcanic field that lies astride the folds and faults of the Nye-Bowler lineament. The volcano consists mostly of volcaniclastic strata, although basaltic andesite lava flows are also present. The Sliderock Mountain volcano represents one of the easternmost manifestations of Late Cretaceous magmatic activity and, except for rocks of the Boulder batholith and cogenetic Elkhorn Mountains Volcanics 160 km to the northwest, is rare in south-central Montana. Compositional diversity within components of the volcano appears to reflect evolution via about 50 percent fractional crystallization involving clinopyroxene and plagioclase.