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Titre du document / Document title

In situ formation of welded tuff-like textures in the carapace of a voluminous silicic lava flow, Owyhee County, SW Idaho

Auteur(s) / Author(s)

MANLEY C. R. (1) ;

Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)

(1) Department of Geology, Box 871404, Arizona State University, Tempe, Arizona 85287-1404, ETATS-UNIS

Résumé / Abstract

The Badlands rhyolite, on the Owyhee Plateau of southwestern Idaho, can be demonstrated to be a large lava flow on the basis of its geometry of large and small flow lobes, its well-exposed near-vent features, and its response to pre-existing topography. However, samples of the dense upper vitrophyre of the unit reveal a range of annealed fragmental textures, including material which closely resembles the compressed, welded glass shards which are characteristic of ignimbrites. Formation of these tuff-like textures involved processes probably common to emplacement of most silicic lava flow units. Decompression upon extrusion causes inflation of pumice at the surface of the lava flow; some of this pumice is subsequently comminuted, producing loose bubble-wall shards, bits of pumice, chips of dense glass, and fragments of phenocrysts. This debris sifts down around loose blocks and into open fractures deeper in the flow, where it can be reheated, compressed, and annealed to varying degrees. The end result is a dense vitrophyre layer (beneath the true upper, non-welded carapace breccia) which can be extremely texturally heterogeneous, with areas of flowfoliated lava occurring very near lava which in many aspects looks like welded ignimbrite, complete with flattened pumices. Identical textures in other silicic units have been cited by previous workers as evidence that those units erupted as pyroclastic flows which then underwent sufficient rheomorphism to create a flowfoliated rock which otherwise appears to be lava. The textures described herein indicate that lava flows can come to mimic rheomorphic ignimbrites, at least at scales ranging from thin sections to outcrops. Voluminous silicic units with scattered fragmental textures, but with otherwise lava-like features, are probably true effusive lava flows.

Revue / Journal Title

Bulletin of volcanology    ISSN  0258-8900   CODEN BUVOEW 

Source / Source

1996, vol. 57, no8, pp. 672-686 (42 ref.)

Langue / Language

Anglais

Editeur / Publisher

Springer, Heidelberg, ALLEMAGNE  (1986) (Revue)

Mots-clés anglais / English Keywords

tuff

;

welded tuff

;

textures

;

lava flows

;

Owyhee County

;

Idaho

;

rhyolites

;

geometry

;

vitrophyre

;

paleorelief

;

emplacement

;

pumice

;

volcanic glass

;

heterogeneity

;

phenocrysts

;

thermal annealing

;

fractures

;

volcanic breccia

;

ignimbrite

;

rheomorphism

;

petrography

;

electron microscopy

;

SEM data

;

volcanic rocks

;

igneous rocks

;

United States

;

North America

;

Mots-clés français / French Keywords

Tuf volcanique

;

Tuf soudé

;

Texture

;

Coulée lave

;

Comté Owyhee

;

Idaho

;

Rhyolite

;

Géométrie

;

Vitrophyre

;

Paléorelief

;

Mise en place

;

Ponce

;

Verre volcanique

;

Hétérogénéité

;

Phénocristal

;

Recuit thermique

;

Fracture

;

Brèche volcanique

;

Ignimbrite

;

Rhéomorphisme

;

Pétrographie

;

Microscopie électronique

;

Donnée MEB

;

Coulée pyroclastique

;

Echarde verre

;

Décompression

;

Plateau Owyhee

;

Mont Juniper

;

Rhyolite Badlands

;

Roche volcanique

;

Roche ignée

;

Etats Unis

;

Amérique du Nord

;

Mots-clés espagnols / Spanish Keywords

Toba volcánica

;

Textura

;

Colada lava

;

Condado Owyhee

;

Idaho

;

Riolita

;

Geometría

;

Paleorelieve

;

Emplazamiento

;

Piedra pómez

;

Vidrio volcánico

;

Heterogeneidad

;

Fenocristal

;

Fractura

;

Brecha volcánica

;

Ignimbrita

;

Reomorfismo

;

Petrografía

;

Microscopía electrónica

;

Dato MEB

;

Roca volcánica

;

Roca ignea

;

Estados Unidos

;

America del norte

;

Localisation / Location

INIST-CNRS, Cote INIST : 2715, 35400006056858.0070

Nº notice refdoc (ud4) : 3141878



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