Skip to Main Content
Book Chapter

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

By
R. St J. Lambert
R. St J. Lambert
Search for other works by this author on:
I. K. Marsh
I. K. Marsh
Search for other works by this author on:
V. E. Chamberlain
V. E. Chamberlain
Search for other works by this author on:
Published:
January 01, 1989

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 SiO2, 76.1 percent; Al2O3, 12.5 percent; FeO(T), 1.7 percent; MgO, 0.6 percent; CaO, 0.4 percent; Na2O, 2 percent; K2O, 6 percent; and TiO2, 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 km3, comparable in size to the Idaho Batholith to ~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.

You do not currently have access to this article.

Figures & Tables

Contents

GSA Special Papers

Volcanism and Tectonism in the Columbia River Flood-Basalt Province

Stephen P. Reidel
Stephen P. Reidel
Search for other works by this author on:
Peter R. Hooper
Peter R. Hooper
Search for other works by this author on:
Geological Society of America
Volume
239
ISBN print:
9780813722399
Publication date:
January 01, 1989

References

Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal