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GEOREF RECORD

The occurrence of interstitial granite-glass in all formations of the Columbia River Basalt Group and its petrogenetic implications

Richard St. J. Lambert, I. K. Marsh and V. E. Chamberlain
The occurrence of interstitial granite-glass in all formations of the Columbia River Basalt Group and its petrogenetic implications (in Volcanism and tectonism in the Columbia River flood-basalt province, Stephen P. Reidel (editor) and Peter R. Hooper (editor))
Special Paper - Geological Society of America (1989) 239: 321-332

Abstract

Almost all Columbia River Basalt Group (CRBG) flows contain a residuum that consists of two phases, one chlorophaeite-rich and one a granite-glass. The chlorophaeite includes types that vary from irregular aggregates to polycrystalline spherules and drop-shaped inclusions of two major types occurring totally within the unaltered granite-glass. The granite-glass is usually isotropic but may be cryptocrystalline. The average analysis for our samples from Wanapum Basalt flows is SiO (sub 2) , 76.1 percent; Al (sub 2) O (sub 3) , 12.5 percent; FeO(T), 1.7 percent; MgO, 0.6 percent; CaO, 0.4 percent; Na (sub 2) O, 2 percent; K (sub 2) O, 6 percent; and TiO (sub 2) , 0.7 percent. The modal abundance by volume varies from a trace in the Picture Gorge Basalt and 1 percent in some Imnaha Basalt flows to 10 percent in the Grande Ronde Basalt and as much as 24 percent in the Wanapum Basalt. If segregated and accumulated, this glass could yield a potential potassic granite batholith of about 10,000 km (super 3) , comparable in size to the Idaho Batholith to approximately 1 km depth. This glass is compositionally very similar to some of the Tertiary granites of Syke and to Tertiary rhyolites from east Iceland. Separated glasses contain rare-earth elements (REE) that mimic the whole-rock REE except for a substantial negative Eu anomaly. Cs, Rb, Ba, Hf, and Ta are greatly enriched over the whole-rock composition. The glasses must represent the residual liquid from which the fayalitic olivine, augite, andesine, and magnetite of the Wanapum Basalt ferrobasalts have crystallized. The current petrogenetic theory for North Atlantic Tertiary granite occurrences is by derivation from ferrobasalt by fractional crystallization. The CRBG glasses fit this model, except that in this case the rapid eruption of CRBG has precluded the physical separation of the rhyolite component. Our present theory of direct derivation of CRBG from the mantle without significant crustal contamination thus has the corollary that it is also possible to derive large volumes of granite from that same source, given a suitable fractionation process.


ISSN: 0072-1077
EISSN: 2331-219X
Coden: GSAPAZ
Serial Title: Special Paper - Geological Society of America
Serial Volume: 239
Title: The occurrence of interstitial granite-glass in all formations of the Columbia River Basalt Group and its petrogenetic implications
Title: Volcanism and tectonism in the Columbia River flood-basalt province
Author(s): Lambert, Richard St. J.Marsh, I. K.Chamberlain, V. E.
Author(s): Reidel, Stephen P.editor
Author(s): Hooper, Peter R.editor
Affiliation: Univ. Alberta, Dep. Geol., Edmonton, AB, Canada
Affiliation: Westinghouse Electr. Co., Environ. Div., Richland, WA, United States
Pages: 321-332
Published: 1989
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
ISBN: 0-8137-2239-X
References: 23
Accession Number: 1990-032086
Categories: Geochemistry of rocks, soils, and sedimentsIgneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables
N44°00'00" - N48°30'00", W120°00'00" - W115°00'00"
Secondary Affiliation: Wash. State Univ., USA, United StatesUniv. Idaho, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 1990
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