Observation of relative timing of deformation, metamorphism, and plutonism in a high-temperature-low-pressure metamorphic belt in the eastern Chugach Mountains of Alaska leads to a model of ridge subduction followed by plate reorganization to account for the abnormally high geothermal gradients in the fore arc. Between 56 and 53 Ma, a change in the direction of the Kula-Farallon spreading halted the previous southward migration of the Kula-Farallon-North American triple junction. This forced the triple junction to migrate back north along the plate margin, enlarging the slab window beneath the accretionary margin. The expanded slab window produced a large-scale thermal manifestation now recognized as the Chugach metamorphic complex. The accretionary complex responded to plate reorganization by orogen-parallel extension associated with oblique subduction of the Kula plate. Contraction began again following passage of the triple junction and subduction of the Farallon plate.

First Page Preview

First page PDF preview
You do not currently have access to this article.