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Fused tuff and peperites in south-central Washington

Hans-Ulrich Schmincke
Fused tuff and peperites in south-central Washington
Geological Society of America Bulletin (1967) 78 (3): 319-330


The Pomona Basalt, an extensive tholeiitic lava flow of the Columbia River Basalt, overlies an airfall vitric tuff in south-central Washington. In many places, this tuff was welded at the contact from the heat and pressure of the overlying basalt. Textures and minerals (mainly Na-sanidine and cristobalite) formed in the tuff during and after welding are identical to those of welded ash flow tuffs. Heat conduction from the lava could have accomplished the welding, as shown by calculations, although water vapors greatly aided in heat transfer. Welding was completed prior to deuteric crystallization of the Pomona Basalt. In other places, where the tuff was probably thicker, the Pomona flow burrowed into the tuff, fragmented it, and formed spectacular breccias (peperites). The peperites occur sporadically between outcrops of the un-brecciated Pomona in an area of about 5400 km (super 2) (2100 miles (super 2) ).

ISSN: 0016-7606
EISSN: 1943-2674
Serial Title: Geological Society of America Bulletin
Serial Volume: 78
Serial Issue: 3
Title: Fused tuff and peperites in south-central Washington
Pages: 319-330
Published: 1967
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
Accession Number: 1967-016746
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus., table
N45°30'00" - N49°00'00", W124°45'00" - W116°55'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from Bibliography and Index of North American Geology, U. S. Geological Survey, Reston, VA, United States
Update Code: 1967
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