The Resurrection Peninsula Ophiolite, Mélange and Accreted Flysch Belts of Southern Alaska as an Analog for Trench-Forearc Systems in Precambrian Orogens

The Resurrection Peninsula and Knight Island ophiolitic lavas/dikes exhibit both calcalkaline and tholeiitic geochemistry possibly reflecting fractionation from multiple, compositionally diverse parentalmagmas coupled with variable assimilation of flysch metasedimentary rock. Basalts from the Resurrection and Knight Island ophiolites, Ghost Rocks Formation, southern Kenai Peninsula and possibly Valdez/Orca accretionary complex may be related to high-angle subduction of the Kula–Farallon ridge system. Mantle convection beneath the mid-ocean ridge portion permits near-instantaneous melts from shallower, more refractory mantle sources to efficiently mix with melts from deeper, more fertile sources to produce mid-ocean ridge basalts (MORB)-like parental magmas. Ultramafic rocks occur as pods of serpentinized peridotite and pyroxenite in the gabbroic section, and as tectonic blocks in flysch lying in fault contact with the ophiolite, the flysch having been thrust in a west-southwest direction over the ophiolite. Pillow basalts include aphanitic, porphyritic, and hypocrystalline varieties. Subhedral to euhedral plagioclase phenocrysts are enclosed within a fine-grained quenched groundmass or devitrified glass containing abundant needle-like, randomly oriented plagioclase microlites. Some plagioclase phenocrysts are embayed and many crystals are normally zoned. Some show corroded, altered cores, but most are remarkably unaltered.