CORRELATION OF THE ROGUE VOLCANIC AND CHETCO INTRUSIVE COMPLEX IN THE KLAMATH MOUNTAINS, SW OREGON

The Rogue-Chetco magmatic complex, SW Oregon, is a suite of extrusive and intrusive magmatic rocks in the Klamath Mountains. The Rogue Formation is a low-grade metamorphosed, succession of porphyritic lavas, pyroclastic rocks and volcanogenic sedimentary rocks that have been metamorphosed to epidote + chlorite. The Chetco Complex is a composite plutonic complex that was suggested to be the intrusive equivalent of the Rogue volcanic rocks. This hypothesis is tested using major and trace element bulk rock compositions, and comparison of trace element compositions of augite between intrusive and extrusive samples.

Whole-rock compositions of Rogue Formation lavas indicate that these rocks are tholeiitic basalts extruded in an island arc environment (Leterrier 1981). Augite phenocrysts are well preserved in the rocks. Plagioclase phenocrysts (An_91-72) are commonly altered to sericite.

The Chetco Complex consists of a quartz hornblende gabbro (Red Dog Creek gabbro) and a two-pyroxene gabbro troctolite (York Butte gabbro); both units are intruded by tonalitic dikes. The Red Dog Creek gabbro is characterized by hornblende, biotite, plagioclase (An_50-81), quartz, and rare pyroxene. The York Butte gabbro is predominately hornblende, pyroxene, plagioclase (An_96-91), and rare olivine. Accessory phases are dominated by sulfides, apatite, chlorite, and epidote. Major and trace element whole-rock compositions indicate that the gabbros of the Chetco Complex are derived from high-alumina arc basalt.

Trace element analyses of pyroxene from the Rogue Formation and Chetco Complex are underway and will be reported and compared to test the possible correlation of the two units.