Early Paleozoic blueschist from the schist of Skookum Gulch, eastern Klamath Mountains, northern California

Journal Article · Fri May 01 00:00:00 EDT 1992 · Journal of Geology; (United States)

DOI:https://doi.org/10.1086/629635· OSTI ID:7003930

Cotkin, S J ^[1]; Cotkin, M L ^[2]; Armstrong, R L ^[3]

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1. Univ. of Arkansas, Fayetteville (United States)
2. Univ. of Wisconsin, Madison (United States)
3. Univ. of British Columbia, Vancouver (Canada)

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. A phengite Rb-Sr date of 447 {plus minus} 9 Ma (Late Ordovician) is statistically indistinguishable from previously published K-Ar dates and is interpreted as the time of blueschist-facies metamorphism. Mineral separates from one rock yield a date of 353 {plus minus} 18 Ma, suggesting resetting during a Devonian to Early Mississippian thermal event. The schist of Skookum Gulch is a critical component of the Middle Ordovician to Early Silurian Callahan event, which included volcanism, plutonism, metamorphism, deformation, and sedimentation and occurred in response to collisional tectonics. Paleontological and provenance information indicate that the Callahan event occurred relatively close to the North American continental margin. In this regard, features produced by the Callahan event record the earliest period of Phanerozoic plate convergence recognized within the US Cordillera.

• OSTI ID: 7003930
• Journal Information: Journal of Geology; (United States), Vol. 100:3; ISSN 0022-1376
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CALIFORNIA
GEOLOGIC FORMATIONS
ISOTOPE DATING
PETROGENESIS
GEOLOGIC HISTORY
METAMORPHISM
MINERALOGY
ORDOVICIAN PERIOD
PETROLOGY
PLATE TECTONICS
SCHISTS
SILURIAN PERIOD
AGE ESTIMATION
DEVELOPED COUNTRIES
GEOLOGIC AGES
GEOLOGY
METAMORPHIC ROCKS
NORTH AMERICA
PALEOZOIC ERA
ROCKS
TECTONICS
USA
580000* - Geosciences