Abstract
The Paleogene Sitkalidak and Ghost Rocks Formations, along the southeastern side of the Kodiak Islands, respectively comprise the youngest and second youngest deep-sea deposits exposed adjacent to the eastern Aleutian Trench. The Paleocene Ghost Rocks Formation consists of a trench and/or trench slope turbidite sequence with interstratified oceanic basalts and andesites which were deformed and intruded by tonolitic plutons by 60 Ma. The Eocene Sitkalidak Formation comprises a trench slope and trench-filling fan sequence, lacking lavas and plutons, but petrographically correlative to the Aleutian abyssal fan. Regional metamorphism to prehnite-pumpellite and zeolite facies with maximum temperatures of 200 to 240°C and 100 to 125°C, respectively, characterize the G ost Rocks and Sitkalidak Formations. Offscraped parts of the Ghost Rocks Formation exhibit more intense deformation than the comparable obductively offscraped unit of the Sitkalidak Formation. The near-trench volcanism and plutonism, and regional metamorphism of the Ghost Rocks Formation is most simply explained by interaction with the Kula-Farallon Ridge, which plate reconstructions place near Kodiak 60 Ma. The Eocene progradation of sediment from the Kodiak area to the Aleutian abyssal fan requires a filled trench and probably reflects a reduction in convergence rate. Both the Paleocene demise of the Kula-Farallon Ridge and any Eocene northward motion of the Alaska Peninsula would have reduced the convergence rate beneath the Kodiak region during progradation of the Aleutian abyssal fan. Obductive offscraping of the Sitkalidak Formation is consistent with slow convergence beneath a prograding fan sequence. Cessation of siliciclastic turbidite accumulation on the Aleutian byssal fan about 30 Ma suggests an increase in the convergence rate and/or decrease in sediment influx at this time. End_of_Article - Last_Page 960------------
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