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Monogenetic volcanism and small volcanoes in the San Francisco volcanic field, Arizona, USA

Nancy Riggs1, Michael Ort1, Claire Sotelo1, Eloise Andry2, Wendell Duffield1

  • Affiliations: 1School of Earth and Sustainability, Northern Arizona University, Flagstaff, AZ, USA 2Department of Geology, Williams College, MA, USA

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 18

  • Programme No: 3.7.25

  • Theme 3 > Session 7

Abstract

The San Francisco volcanic field, southwestern USA, hosts over 600 volcanoes within ~5000 km2, ranging from small monogenetic cones to large composite volcanoes and in age from ca. 6 Ma to ca. 1085 CE. Government Prairie vent is a breached benmoreitic scoria cone and lava flow. A rhyolite dome fills the crater and dacite lava flowed from the cone's side. Xenoliths/crysts in the dome demonstrate magma mingling. An initial Strombolian event at Red Mountain was followed by partial cone collapse that included the vent area. Eruptive style changed to Hawaiian, producing extensive clastogenic lava. Post-eruptive phreatic explosions removed part of the unbreached side of the cone. Earliest deposits at Colton Crater are scoria and xenolith-bearing spatter. Phreatomagmatic explosions were caused by interaction of the feeder dike system with water, and caused collapse of part of the spatter rampart. SP Crater is a 'simple' Strombolian scoria cone with a lava flow that has bodies of vent-facies rocks, indicating rafting of the cone during eruption. Earliest phases produced spiky, vesicular tephra and poorly vesicular tephra was deposited after breaching as the cone rebuilt. A second lava flow filled in lower areas of the original flow. Strawberry Crater is a breached cone. Three lava flows and facies within the cone document rafting and destabilization of the crater walls as well as changes in chemistry. A trachydacite dome was emplaced in the latest stages. Cones in the field illustrate some of the many forms of eruptions and hazards possible in a mafic monogenetic system.