PALEOMAGNETISM OF SMALL FORE-ARC INTRUSIVE BODIES ASSOCIATED WITH THE PALEOCENE KODIAK BATHOLITH

The late Paleocene Kodiak Batholith forms a ~100 km NE-SW striking belt that spans most of Kodiak Island, Alaska. Smaller plutonic bodies of similar age and composition are located to the southeast of the main outcrop belt of the Kodiak Batholith, separated by the Contact Fault. It has been proposed that the plutons were the product of slab-window related igneous activity. Farris (2010) examined the relationship between ages of the main Kodiak Batholith and the smaller plutonic bodies to the southeast. He found that the age of the Kodiak Batholith decreases from ~60Ma- ~58.4 Ma from SW to NE along the strike of the pluton, and that the ages of the smaller plutonic bodies SE of the main batholith are older (60 to 63 Ma). The differences in age were attributed by Farris (2010) to either significant sinistral strike-slip along the Contact Fault, or to significant shortening accommodated by a proposed series of thrust faults within the accretionary complex of the Paleocene Ghost Rocks. As an initial investigation of the kinematics predicted by either of these models, we conducted a pilot paleomagnetic study of the plutonic rocks exposed in the SE belt. One pluton was sampled at Alitak Bay and the other was the Pasagshak Pluton. Alternating field demagnetization revealed that these rocks have well-defined magnetizations. The preliminary mean direction for the Pasagshak Pluton (D = 252, I = -23) is significantly different than an expected direction for Kodiak Island during the Paleocene. This discordance could be produced by a significant southwestern tilt, a combination of 30-40 degrees of CW rotation and a modest amount of tilt, or magnetization at more southerly latitude. While a more robust comparison would need to include paleomagnetic data from the main body of the Kodiak Batholith, our results do suggest that neither the CW rotation, nor the top to SW tilt inferred for the Pasagshak Pluton would be consistent with the kinematic models proposed by Farris 2010.