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Field mapping and structural analysis indicate that the Snowcamp remnant of the Coast Range ophiolite, in the vicinity of Game Lake, southwest Oregon, was thrust to the northeast over mafic phyllonite and amphibolite correlated with the Chetco complex. The contact between the upper ophiolitic and lower mafic sections is marked by a ∼5- to 10-m-thick serpentinite unit and paralleled by mylonitic foliations in the lower mafic section. Syndeformational tonalites intrude the lower plate. The fabric-forming metamorphic mineral assemblages (amphibolite facies) in the mafic section suggest a temperature range of ∼550–600+ °C and medium pressure, whereas quantitative thermobarometry indicates 615–720 °C and 3.5–6 kb (11.5–20 km depth). A mylonitic greenschist-facies mineral assemblage in phyllonites below the thrust overprints the amphibolite-facies fabric, indicating that thrusting continued during cooling. The 40Ar/39Ar analyses indicate that thrusting and syntectonic intrusion occurred by at least 154.2 ± 2.0 and 149.1 ± 0.4 Ma, respectively.

The character of this thrust strongly resembles that of the Madstone Cabin thrust that emplaced the Josephine ophiolite over the Rogue–Chetco arc complex. The proposed correlation between the two faults implies that either the Snowcamp remnant of the Coast Range ophiolite has undergone a similar emplacement history as the Josephine ophiolite or that the ophiolitic rocks near Game Lake may be an outlier of the Josephine ophiolite juxtaposed by postemplacement faulting against a Coast Range remnant around Snowcamp Mountain to the south.

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