Vitrophyre clast breccia (Nez Perce Creek Flow, ~152 ka; Firehole Canyon roadcut, Yellowstone, Wyoming, USA) 6 : 無料・フリー素材/写真
Vitrophyre clast breccia (Nez Perce Creek Flow, ~152 ka; Firehole Canyon roadcut, Yellowstone, Wyoming, USA) 6 / James St. John
| ライセンス | クリエイティブ・コモンズ 表示 2.1 |
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| 説明 | Vitrophyre clast breccia in the Pleistocene of Wyoming, USA.This remarkable outcrop is part of a rhyolite lava flow that erupted in the Yellowstone Caldera during the last Ice Age (Pleistocene). Yellowstone itself is an enormous hotspot volcano - it has semi-regular, giant ash eruptions every 600,000 to 650,000 years or so. After Yellowstone's last mega-eruption and caldera collapse (at ~640 ka), relatively minor volcanic activity occurred in the caldera. Most of this consisted of rhyolite lava flow volcanism, but some basalt lava flow volcanism also took place.The outcrop seen here is part of the Nez Perce Creek Flow (Middle Pleistocene, ~152 ka) at its westernmost margin. This lava flow is well exposed in a series of roadcuts along Firehole Canyon Drive in Yellowstone National Park. Rocks there include gray rhyolites, finely-fractured obsidian, and rhyolite breccias having obsidian clasts (seen here).The gray material is rhyolite & the dark fragments are small to moderately large clasts consisting of felsic vitrophyre (= glassy rhyolite) that have small whitish crystals (feldspar and other minerals) plus small spherulites. Brecciation is a common process as rhyolite lava flows advance (see, for example, Christiansen & Hutchinson, 1987, p. 169).Stratigraphy: Nez Perce Creek Flow, Central Plateau Member, Plateau Rhyolite, upper Middle Pleistocene, ~152 ka (148-160 ka)Locality: roadcut on eastern side of Firehole Canyon Drive, eastern side of the Firehole River Canyon, western Yellowstone National Park, northwestern Wyoming, USA---------------Reference cited:Christiansen & Hutchinson (1987) - Rhyolite-basalt volcanism of the Yellowstone Plateau and hydrothermal activity of Yellowstone National Park, Wyoming. Geological Society of American Centennial Field Guide, Rocky Mountain Section, pp. 165-172. |
| 撮影日 | 2015-07-08 12:26:02 |
| 撮影者 | James St. John |
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