Calderas of the San Juan volcanic field, southwestern Colorado

Aeolian dust in Colorado Plateau soils: Nutrient inputs and recent change in source

“…1) are also possible. Areas of igneous rock terrain, and their drainages, that might produce felsic aeolian dust at the margins of the Colorado Plateau include the San Juan volcanic field in southwestern Colorado (35) and the Marysvale volcanic field in southwestern Utah (36). Regional felsic sources outside the plateau include the Mojave, Sonoran, and Great Basin deserts, which are generally upwind from the study area (ref.…”

Mount Belknap and Red Hills calderas and associated rocks, Marysvale volcanic field, west-central Utah

“…In comparison with other calderas (Smith and Bailey, 1968;Steven and Lipman, 1976) the Mount Belknap caldera shows few if any ofthe later stages in the typical cauldron development cycle. The complex mixture of lava flows and ash-flow tuff filling the caldera is in contrast to more simple cauldron fills in other areas, where thick prisms of ash-flow tuff similar in composition to related tuffs in the outflow sheet filled the subsided area during or shortly after collapse.…”

“…Whereas the general model of ash-flow eruption and caldera development (Ratte and Steven, 1964;Smith and Bailey, 1968;Lipman, 1975;Steven and Lipman, 1976;Bailey and others, 1976) was applied to studies of both areas, the results were quite different. Minor differences in timing and conditions of eruption led to strongly contrasting volcanic accumulations and structures; depth and configuration of the source magma chambers may have had a major controlling influence.…”

Net Acid Production, Acid Neutralizing Capacity, and Associated Mineralogical and Geochemical Characteristics of Animas River Watershed Igneous Rocks Near Silverton, Colorado

“…Mid-Tertiary volcanism in the San Juan Mountains began between 35 and 30 Ma with the eruption and deposition of voluminous intermediate-composition (52-63 percent SiO 2 ) lava flows, flow breccias, volcaniclastics, minor mafic tuffs, and abundant mudflows of the San Juan Formation (Lipman and others, 1973;Steven and Lipman, 1976). From 30 to 23 Ma, multiple calderas formed and related volcanic units were deposited throughout the San Juan volcanic field (Lanphere, 1988;Lipman and others, 1997;Bove and others, 2001).…”