Implications for strain accommodation in an oblique subduction zone: new paleomagnetic and geologic data from the central Aleutian arc, Alaska

Abstract

Oblique subduction results in partitioning of strain into arc-normal and arc-parallel components, and a complex pattern of upper plate deformation. Although partitioning of strain is observed in areas of oblique subduction around the world, the kinematics of strain accommodation are poorly understood. This is particularly true in the Aleutian arc because of a paucity of geologic and geophysical data. In the Aleutian arc, models previously proposed for forearc deformation have been characterized by clockwise rotation and westward translation of discrete tectonic blocks. This study utilizes two separate datasets to help constrain these mechanisms. The first step utilizes new high-resolution multibeam sonar data that provides a first detailed look at deformational structures on the seafloor. The second step is to examine the validity of paleomagnetic data previously collected from the arc, by re-measuring samples with improved methods. The multibeam sonar data reveal dense deformational patterns on the seafloor that suggest considerable diffuse strain between block boundaries. Remeasured paleomagnetic samples produce results that are similar to previous findings, but with reduced error bars and improved resolution. Younger rocks indicate little rotation, while samples from Amchtika Island indicate greater rotation than expected.