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Master of Science (MS)
Brown, Edwin H.
Pevear, David R.
Babcock, R. Scott (Randall Scott)
Metavolcanic and metasedimentary rocks of the Shuksan Metamorphic Suite near Gee Point have been contact metamorphosed by high-temperature emplacement of ultramafic rock. This intrusion occurred at great depth (>25 km) and caused contact temperatures of about 500°C, resulting in epidote-amphibolite facies metamorphism. Minerals of the contact metamorphism are overprinted by mineral assemblages of the regional Shuksan blueschist facies metamorphism. The K/Ar age of the epidote-amphibolites is Jurassic (145-160 m.y.), and thus the age of Shuksan metamorphism is probably younger than Middle Jurassic.
Ultramafic rocks found near Gee Point have been metamorphosed to serpentinites during Shuksan metamorphism and should be considered part of the Shuksan Metamorphic Suite.
Shuksan blueschist facies metamorphism and the Gee Point epidote-amphibolite facies metamorphism probably occurred within a subduction zone. A tectonic model is proposed in which high-temperature ultramafic rock fills fractures and faults in a subducted plate, causing local contact metamorphism.
Comparison of metamorphic relations at Gee Point with rocks of the Franciscan Complex suggests that Franciscan eclogites may also result from contact metamorphism caused by ultramafic intrusions.
Shuksan blueschist facies
Western Washington University
Skagit County (Wash.)
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Wilson, Daniel L., "The Origin of Serpentinites Associated with the Shuksan Metamorphic Suite Near Gee Point, Washington" (1978). WWU Graduate School Collection. 779.