Abstract

A Paleocene to Eocene(?) mafic sequence of igneous rocks on Knight Island and a Cretaceous mafic and ultramafic sequence of the Resurrection Peninsula in coastal southern Alaska are characterized by pillow basalts, sheeted dikes, and gabbro intrusions. At both localities, pillow basalts are interbedded with flysch, and the gabbros intrude both the sheeted dikes and the immediately overlying sedimentary rocks. At the Resurrection Peninsula, small bodies of serpentinized dunite are present in the gabbro, and overlying low-grade metasedimentary rocks and mafic tuffs are interbedded with sedimentary rocks. At Knight Island the sheeted dikes intrude Paleocene and Eocene(?) sedimentary rocks. These igneous rocks have petrographic features similar to those of oceanic tholeiites and have some of the characteristics of ophiolites. They apparently were formed near the continental margin, because both sequences intrude and are interlayered with flysch. We believe the igneous rocks were intruded along faults (perhaps leaky transform faults) of ocean floor that happened to be near the continental margin; the faults were oriented parallel to the depositional strike and subsequent deformational strike of the Valdez(?) and Orca Groups.

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