St. Elias Orogen

NASA photograph of southeast Alaska and northwest Canada showing the high relief, rugged topography, and glaciated terrain within the St. Elias orogen Theoreticle cross-section linking glacial erosion and tectonic uplift	ACTIVE TECTONICS, MOUNTAIN BUILDING, AND EROSION RATES IN THE ST. ELIAS OROGEN By: Aaron L.Berger Abstract: The ongoing collision of the Yakutat terrane and the North American plate in southeastern Alaska’s Chugach / St. Elias orogen is a modern analog for the tectonic processes which produced and shaped the Cordilleran during the Mesozoic and Cenozoic. Over the past decade, evidence has mounted that focused erosion within active orogenic belts results in changes in crustal strain initiating the upward advection of hot rocks to replace the eroded material. This coupled process of erosion and tectonic uplift is hypothesized to locally weaken the crust by injecting hot lower viscosity rocks into the shallow crust which results in further strain focusing and erosion in a positive feedback cycle. In an effort to understand the geologic processes shaping the Chugach / St. Elias orogen, the $5,103,000 NSF “STEEP” project will employ geophysics, structural geology, thermochronology, sedimentology, and geomorphology within the vicinity of the Yakutat terrain to gain a crustal scale picture of what processes are shaping this orogen. As part of my dissertation, I will combine low temperature apatite helium thermochronology, tectonic mapping, and geomorphology within the Chugach / St. Elias orogen to study what effect extreme glacial erosion and erosion due to orographic precipitation have on strain partitioning within the crust, active tectonic uplift, and the location of tectonic structures. A better understanding of the link between focused erosion and tectonic processes within active orogens will have profound implications to our understanding of how the lithosphere deforms and also our interpretation of existing structures within inactive orogenic belts. In some cases the location and formation of regional synclines and thrust faults may be the result of localized exhumation and not classic tectonic processes.

NASA photograph of southeast Alaska and northwest Canada showing the high relief, rugged topography, and glaciated terrain within the St. Elias orogen

Theoreticle cross-section linking glacial erosion and tectonic uplift

ACTIVE TECTONICS, MOUNTAIN BUILDING, AND EROSION RATES IN THE ST. ELIAS OROGEN

By: Aaron L.Berger

Abstract:
The ongoing collision of the Yakutat terrane and the North American plate in southeastern Alaska’s Chugach / St. Elias orogen is a modern analog for the tectonic processes which produced and shaped the Cordilleran during the Mesozoic and Cenozoic. Over the past decade, evidence has mounted that focused erosion within active orogenic belts results in changes in crustal strain initiating the upward advection of hot rocks to replace the eroded material. This coupled process of erosion and tectonic uplift is hypothesized to locally weaken the crust by injecting hot lower viscosity rocks into the shallow crust which results in further strain focusing and erosion in a positive feedback cycle. In an effort to understand the geologic processes shaping the Chugach / St. Elias orogen, the $5,103,000 NSF “STEEP” project will employ geophysics, structural geology, thermochronology, sedimentology, and geomorphology within the vicinity of the Yakutat terrain to gain a crustal scale picture of what processes are shaping this orogen. As part of my dissertation, I will combine low temperature apatite helium thermochronology, tectonic mapping, and geomorphology within the Chugach / St. Elias orogen to study what effect extreme glacial erosion and erosion due to orographic precipitation have on strain partitioning within the crust, active tectonic uplift, and the location of tectonic structures. A better understanding of the link between focused erosion and tectonic processes within active orogens will have profound implications to our understanding of how the lithosphere deforms and also our interpretation of existing structures within inactive orogenic belts. In some cases the location and formation of regional synclines and thrust faults may be the result of localized exhumation and not classic tectonic processes.