Kinematics of the Chugach metamorphic complex, southern Alaska: Plate geometry in the north Pacific margin during the Late Cretaceous to Eocene

Abstract

The Paleogene plate geometry of the north Pacific margin is poorly constrained because all of the plates involved, except the trailing Pacific plate, have been subducted. However, the kinematic history of the Chugach metamorphic complex in southern Alaska constrains plate configurations because of its link to ridge-subduction. We synthesize recent regional mapping of the complex, finite strain data, and geochronology to show that progressive deformation records the Paleogene triple junction interaction occurred over a period of less than 2 m.y. across ∼350 km of the margin. We document that 140-190 km of distributed dextral shear occurred across the complex during the latest phase of deformation in the complex. This analysis suggests dextral motion of at least 70-95 mm/yr which can account for most, or all, of the margin parallel plate motion during a brief period of the Eocene. We use these results to compare and evaluate possible plate configurations based on older and newer plate motion models. Using modern plate motion models it is difficult to reconcile a Kula-Farallon ridge-subduction model with the available data, but our preferred plate geometry model involving a Kula-Resurrection ridge provides a reasonable explanation for our observations. © 2012. American Geophysical Union. All Rights Reserved.