OPHIOLITIC ROCKS OF THE EASTERN ELK OUTLIER OF THE WESTERN KLAMATH TERRANE, SOUTHWESTERN OREGON

The Elk outlier (EO) of the western Klamath terrane (WKT) lies ~ 50 km west and northwest of the main belt of the WKT. In the EO, the Jurassic Galice Formation is intruded by the 145 Ma Pearse Peak pluton and unconformably overlain by the Cretaceous Myrtle Group. In the WKT, the Galice rests on the 164-Ma Josephine ophiolite (JO) and the Rogue Formation, but in the EO, basement to the Galice is not recognized. Giaramita and Harper tentatively correlated a newly discovered sheeted dike complex in the western EO with the Josephine ophiolite. New field work in the eastern part of the Elk outlier, ~ 20 km east of the sheeted dike complex, reveals previously unreported ophiolitic rock units adjacent to and within a few km of the Iron Mountain peridotite to the west and sheared serpentinite of the Coquille River Fault zone to the east. Cumulate peridotite contains poikilitic pyroxene crystals 2 cm in diameter. A unit of gabbro cut by diabasic dikes reveals well preserved chilled margins in the dikes. A quarry exposes abundant basaltic pillows cut by a highly epidositized sheeted dike complex. Cr-vs-Y and Ti-vs-V plots of XRF data from quarry samples reveal that two dikes and a pillow are similar to the early dikes and lower pillows of the JO, and a third dike matches late JO dikes. A pillow from a different quarry geochemically matches pillows from the western EO and has high total iron and Ti similar to the upper pillows of the JO. Late Aalenian to early Aptian radiolarians (ca. 175.6 to 112 Ma) are present in a 5-m-thick section of red ribbon chert (reported by Diller, 1903) in Johnson Creek. Red chert is also present as inter-pillow matrix, but as yet has yielded no datable micro-fossils. The ophiolitic rock units are isolated from each other by sheared serpentinite suggesting a tectonically fragmented ophiolite. A mélange unit in the eastern EO contains blocks of diorite, sheared gabbro, and andesite porphyry encased in sheared serpentinite. The low-elevation, uncharacteristically gentle topography, and the range of block types suggest that the mélange is correlative with the mélange we recently described in the western part of the EO. The new work strengthens the correlation of ophiolitic rocks in the EO with the Josephine ophiolite of the WKT and suggests the possibility that ophiolitic rocks are basement to the Galice in the Elk outlier of the western Klamath terrane.