- journal_title：Geological Society of America Bulletin
- Contributor：E. H. BROWN ; D. L. WILSON ; RICHARD LEE ARMSTRONG ; J. E. HARAKAL
- Publisher：Geological Society of America
- Date：1982-
- Format：text/html
- Language：en
- Identifier：10.1130/0016-7606(1982)93<1087:PSAARO>2.0.CO;2
- journal_abbrev：Geological Society of America Bulletin
- issn：0016-7606
- volume：93
- issue：11
- firstpage：1087
Part of the Shuksan blueschist terrane, near Iron Mountain and Gee Point, North Cascades, Washington, has associated serpentinite, amphibolite, barroisite schist, blueschist, rare eclogite, and blackwall-type metasomatic rock. Field, petrographic, and microprobe observations indicate that the amphibolite and barroisite schists were metamorphosed in contact with peridotite and suggest that the peridotite may have been a heat source. The serpentinite and associated rocks are structurally concordant with the regional blueschists and have been overprinted by blueschist metamorphism. Isotopic dating gives metamorphic ages of 148 ± 5 to 164 ± 6 m.y. for the amphibolite and barroisite schist and 129 ± 5 m.y. for nearby regional Shuksan blueschists. The origin of the serpentinite + amphibolite + blueschist assemblage is interpreted to be the result of sequential events in a subduction zone. As subduction began, oceanic crustal materials underwent high-temperature metamorphism along the hot ultramafic hanging wall and were converted to amphibolites; materials that were subducted later came in contact with a cooler hanging wall and recrystallized as blueschist. This hypothesis may be applicable to the origin of similar rock associations in the Franciscan terrane and other orogenic belts.