Abstract
Petrographic, field, and geochemical evidence from the Rogue and Galice formations in the Klamath Mountains of Oregon indicate that the rocks formed in a calc-alkaline volcanic arc of Jurassic age. The volcanic rocks range from basalt to rhyolite and are predominantly (> 95 %) fragmental in character. They are interlayered with a sequence of volcaniclastic rocks 5-8 km thick. The Rogue and Galice formations are part of a Late Jurassic-Early Cretaceous complex that includes a paired metamorphic belt of lawsonite-bearing schists along the Oregon coast and garnet-bearing amphibolite to the east, faulted against the Rogue and Galice formations. Major-element analyses, plotted on AFM, FeO*/MgO, and alkalis versus silica diagrams, yield ambiguous results when used to infer the magmatic affinities of these weakly metamorphosed rocks. However, abundances of Ti, Cr, Zr, and REE, and clinopyroxene phenocryst compositions in volcanic rocks from the Rogue and Galice Formations are identical to those in volcanic rocks from Holocene calc-alkaline volcanic arcs.
Published Version
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