Relations of cinder cones to the magmatic evolution of Mount Mazama,Crater Lake National Park,Oregon |
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| Institution: | 1. Institute of Volcanology and Seismology, Russia;2. CODES, University of Tasmania, Hobart, Australia;3. Portland State University, Portland, OR, USA;4. University of Oregon, Eugene, OR, USA;5. University of Queensland, Australia;1. Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK;2. Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, USA;1. School of Earth and Environmental Sciences, The University of Manchester, UK;2. School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA;3. Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Pisa, Italy;1. Leon Charney School of Marine Sciences, Department of Marine Geosciences, University of Haifa, Israel;2. Wheaton Archaeology Museum, Wheaton College, USA |
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| Abstract: | Cinder cones at Crater Lake are composed of high-alumina basaltic to andesitic scoria and lavas. The Williams Crater Complex, a basaltic cinder cone with andesitic to dacitic lava flows, stands on the western edge of the caldera, against an andesite flow from Mount Mazama. Bombs erupted from Williams Crater contain cores of banded andesite and dacite, similar to those erupted during the climatic eruption of Mount Mazama.Major- and trace-element variations exhibit an increase in incompatible elements and a decrease in compatible elements, consistent with crystal fractionation of olivine, plagioclase, clinopyroxene, orthopyroxene, and magnetite. LREE patterns in the rocks are irregular; each successive basalt is enriched in LREE relative to the preceding andesite.Compositional variations in the magmas of the cinder cones suggest that three magmatic processes were involved, partial melting, fractional crystallization, and magma mixing. Partial melting of more than one source produced primary basaltic magma(s). Subsequent mixing and fractional crystallization produced the more differentiated basaltic to andesitic magmas. |
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