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Titre du document / Document title

Crystallization and welding variations in a widespread ignimbrite sheet; the Rattlesnake Tuff, eastern oregon, USA

Auteur(s) / Author(s)

STRICK M. J. (1) ; GRUNDER A. L. ;

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

(1) GEOMAR, Abt. Vulkanologie petrologie, 24148 Keil, ALLEMAGNE

Résumé / Abstract

The 7.05 Ma Rattlesnake Tuff covers ca. 9000 km2, but the reconstructed original coverage was between 30000 and 40000 km2. Thicknesses are remarkably uniform, ranging between 15 and 30 m for the most complete sections. Only 13% of the area is covered with tuff thicker than 30 m, to a maximum of 70 m. The present day estimated tuff volume is 130 km3 and the reconstructed magma volume of the outflow is 280 km2 DRE (dense rock equivalent). The source area of the tuff is inferred to be in the western Harney Basin, near the center of the tuff distribution, based mainly on a radial exponential decrease in average pumice size, and is consistent with a general radial decrease in welding and degree of post-emplacement crystallization. Rheomorphic tuff is found to a radius of 40-60 km from the inferred source. Four facies of welding and four of post-emplacement crystallization are distinguishable. They are: nonwelded, incipiently welded, partially welded and densely welded zones; and vapor phase, pervasively devitrified, spherulite and lithophysae zones. The vapor phase, pervasively devitrified and lithophysae zones are divided into macroscopically distinguishable subzones. At constant thickness (20 ± 3 m), and over a distance of 1-3 km, nonrheomorphic sections can vary between two extremes: (a) entirely vitric sections grading from nonwelded to incipiently welded; and (b) highly zoned sections. Highly zoned sections have a basal non- to densely welded vitric tuff overlain by a spherulite zone that grades upward through a lithophysae-dominated zone to a zone of pervasive devitrification, which, in turn, is overlain by a zone of vapor-phase crystallization and is capped by partially welded vitric tuff. A three-dimensional welding and crystallization model has been developed based on integrating local and regional variations of 85 measured sections. Strong local variations are interpreted to be the result of threshold-governed welding and crystallization controlled by residence time above a critical temperature, which is achieved through differences in thickness and accumulation rate

Revue / Journal Title

Bulletin of volcanology    ISSN  0258-8900   CODEN BUVOEW 

Source / Source

1995, vol. 57, no3, pp. 151-169 (61 ref.)

Langue / Language

Anglais

Editeur / Publisher

Springer, Heidelberg, ALLEMAGNE  (1986) (Revue)

Mots-clés anglais / English Keywords

Oregon

;

welded tuff

;

ignimbrite

;

crystallization

;

upper Miocene

;

volume

;

pumice

;

granulometry

;

lithofacies

;

devitrification

;

spherulites

;

zoning

;

three-dimensional models

;

spatial variations

;

residence time

;

tridymite

;

framework silicates, silica minerals

;

absolute age

;

Ar-40/Ar-39

;

isopach maps

;

tuff

;

pyroclastics

;

flame structures

;

deformation

;

United States

;

North America

;

volcanic rocks

;

igneous rocks

;

Neogene

;

Tertiary

;

Mots-clés français / French Keywords

Oregon

;

Tuf soudé

;

Ignimbrite

;

Cristallisation

;

Miocène sup

;

Volume

;

Ponce

;

Granulométrie

;

Lithofaciès

;

Dévitrification

;

Sphérolite

;

Zonalité

;

Modèle 3 dimensions

;

Variation spatiale

;

Temps résidence

;

Tridymite

;

Groupe silice minéral

;

Datation

;

Ar 40-Ar 39

;

Isopaque

;

Tuf volcanique

;

Pyroclastique

;

Structure flammée

;

Déformation

;

Tuf Rattlesnake

;

Rhéomorphisme

;

Phase vapeur

;

Lithophyse

;

Texture vitroclastique

;

Etats Unis

;

Amérique du Nord

;

Roche volcanique

;

Roche ignée

;

Néogène

;

Tertiaire

;

Mots-clés espagnols / Spanish Keywords

Oregon

;

Ignimbrita

;

Cristalización

;

Mioceno sup

;

Volumen

;

Piedra pómez

;

Granulometría

;

Litofácies

;

Desvitrificación

;

Esferolito

;

Zonalidad

;

Modelo 3 dimensiones

;

Variación espacial

;

Tridimita

;

Fechado

;

Mapa isopacas

;

Toba volcánica

;

Piroclástico

;

Estructura en llama

;

Estados Unidos

;

America del norte

;

Roca volcánica

;

Roca ignea

;

Neógeno

;

Terciario

;

Localisation / Location

INIST-CNRS, Cote INIST : 2715, 35400005149845.0010

Nº notice refdoc (ud4) : 3563666



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