Evaluating the Role of Glaciation on the Structural Configuration of the Southern Alaska Syntaxis

Purdue University, West Lafayette IN

Investigators

Abstract

The role of glaciation on the tectonic configuration of convergent margins is a first order question that remains largely unanswered. The eastern Gulf of Alaska is arguably the best place on Earth to study the coupling of glacial erosional processes and tectonics. The coastal mountains in this area, the Chugach and St. Elias Ranges, contain the largest non-polar ice fields on earth and are characterized by the most erosive agents on earth, tidewater glaciers, and are part of a wide zone of deformation that forms along the southern Alaska syntaxis. This structural, depositional, and climatic framework of the Gulf of Alaska provide the ideal study area to understand the relationship between glaciation and tectonics. Few places on earth have the extreme exhumation, erosional, and depositional rates that have been documented as in the syntaxial corner. Many recent studies provide evidence for intensified rock uplift in response to focused erosion by glaciers but the structural mechanics that are responsible for the reorganization of the mountain belt are not well understood in Alaska or elsewhere. This project has two basic goals: 1) to refine the structural cross-sections of the region using geologic data and, 2) develop mechanical analog models that account for the role of glacially driven erosion and deposition (amount and location) on the reorganization of deformation along the geologically and geometrically complex plate boundary of the Alaskan margin. Analog modeling will utilize state-of-the-art kinematic analysis to understand the development and evolution of structures. The influence of glaciers in Southern Alaska, and in general, on tectonics is directly related to variations in climate, however, most models for the mechanical development of convergent margins are disconnected from the role of glaciations in mass redistribution and the coupled tectonic response. This modeling study will help to quantify the general mechanical response of Coulomb wedges to highly localized glacial erosion, which occurs on geologically rapid time scales, and more specifically will put constraints on the style and evolution of deformation along the Alaskan convergent margin. This work will help to elucidate both short and long-term response of mountain belts, including changes in uplift and strain patterns, due to rapid loading and unloading, that can occur during periods of rapid climate change. The project has a significant outreach and education component that seeks to increase diversity in the geosciences by working with high school Native American students from rural Alaskan communities.