Early Paleozoic Blueschist from the Schist of Skookum Gulch, Eastern Klamath Mountains, Northern California

Abstract

Late Ordovician blueschist from the schist of Skookum Gulch, eastern Klamath Mountains, California, is the oldest known blueschist in California and one of the oldest in North America. Lawsonite-bearing glaucophane schist occurs as lenses intimately interlayered with chlorite schist, quartz-albite schist, and dolomite marble. Detailed investigation of a portion of the Skookum Gulch schist demonstrates that these rock types share a common deformational and metamorphic history. The first deformation occurred during blueschist metamorphism and produced similar-style isoclinal folds and an axial-planar foliation. During subsequent deformations, parallel-style open to tight folds and local kink bands deformed foliation but produced no recognizable recrystallization. Major and selected trace elements, analyzed by XRF for 12 samples of mafic schist, show that the protoliths were broadly basaltic in composition ($$SiO_{2} mostly ranges from 46 to 53 wt \%$$) and that ocean-floor basalt affinities are suggested by...