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Subduction Initiation And Early Evolution Of The Easton Metamorphic Suite, Northwest Cascades, Washington, Jeremy L. Cordova, Sean R. Mulcahy, Elizabeth R. Schermer, Laura E. Webb

Geology Faculty Publications

The Easton metamorphic suite, in the northwest Cascades of Washington State, preserves an inverted metamorphic sequence with ultramafic rocks underlain by amphibolite and high-temperature blueschist juxtaposed above low-temperature blueschists. The sequence is interpreted as a metamorphic sole and younger accreted rocks that formed during and after the initiation of Farallon plate subduction beneath North America in Jurassic time. Two high-temperature deformation events are recorded in the metamorphic sole at ∼10 kbar and ∼760 °C to 590 °C between >167 and 164 Ma. High-temperature blueschist partly overprints the amphibolite but may have accreted separately at ∼530 °C between ca. 165 and …