This is a multi-disciplinary study to address the evolution of the highest coastal mountain range on Earth - the St. Elias Mountains of southern Alaska and northwestern Canada. This orogen has developed over the past few million years as the Yakutat block, a continental-oceanic terrane, has attempted subduction beneath the eastern end of the Aleutian arc-trench system. The ~500 km-long, 150 km-wide St. Elias mountain range is the product of the dynamic balance between rapid uplift induced by crustal convergence and rapid exhumation by a regional system of large, fast-moving temperate glaciers. Most sediments are deposited either on a broad shelf or in deepsea fans and provide a complete record of the tectonic, climatic, erosional, and eustatic events that have accompanied the orogeny.

The overarching goal of the project is to develop a comprehensive model for the St. Elias orogen that accounts for the interaction of regional plate tectonic processes, structural development, and rapid erosion. The focus of the study is on the partitioning of deformation within the system from upper mantle flow to near-surface faulting and exhumation. The study will investigate the geodynamics of oblique collision under a set of conditions that will allow the PIs to address several important and fundamental questions:

- Has intense Quaternary glacial erosion redistributed mass in the orogen sufficiently to change regional deformational patterns, and has focused erosion along deep glacial valleys been sufficient to localize crustal strains? - How is deformation partitioned into lithospheric shortening and uplift versus lateral extrusion of the detached crust, and does intense erosion influence this partitioning? - Is the orogeny driven primarily by subduction of a buoyant oceanic plateau or by collision of a small microcontinental block attached to allochthonous ocean crust?

Addressing these questions has broad implications for understanding the geodynamics of oblique collision in general, the role of different mechanisms in development of far-field orogenic effects, and the control of erosion on development of slip partitioning during oblique convergence. The project also has general implications for how subduction/accretion of small continental terranes versus oceanic plateaus contribute to deformation of the continents, and ultimately the fate of these fragments in construction of the crustal collage which is typical of virtually all continents. Specifically, the P.I.s propose a multidisciplinary approach involving seismologists (subsurface imaging and seismicity), geologists, geodesists, glaciologists, geochronologists, and geodynamic modelers.

National Science Foundation (NSF)
Division of Earth Sciences (EAR)
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Leonard E. Johnson
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Lehigh University
United States
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