Architecture, Kinematics, and Exhumation of a Convergent Orogenic Wedge: A Thermochronological Investigation of Tectonic-Climatic Interactions within the Central St. Elias Orogen, Alaska
Berger AL, Spotila JA, Pavlis TL, Enkelmann E, Buscher JT. 2007. Architecture, Kinematics, and Exhumation of a Convergent Orogenic Wedge: A Thermochronological Investigation of Tectonic-Climatic Interactions within the Central St. Elias Orogen, Alaska
The kinematics and architecture of orogenic systems along the leading edges of accreting terranes may be heavily influenced by climate, but little research has been devoted to the long term effects of glacial erosion on orogenesis. In this study, we have used thermochronometry to develop a new architectural model of the St. Elias orogen in southern Alaska, which is one of the best examples of a glaciated orogenic wedge worldwide. Apatite and zircon (U-Th)/He dating illustrate that this orogen consists of a deformational backstop on the leeward flank and a rapidly deforming and eroding, thin-skinned fold and thrust belt on the windward flank. These distinct deformational and thermal domains are separated by a structure beneath the Bagley ice field, which we propose is a backthrust that makes the orogen doublyvergent. Within the orogenic wedge, denudation and deformation are strongly influenced by glacial erosion. Exhumation, at rates of up to 4 mm/yr, is concentrated at a zone along the windward flank, where the glacial equilibrium line intersects the orogenic wedge. The onset of enhanced glaciation following the Mid-Pliocene Warm Interval also coincided with a ten-fold increase in cooling rates within the wedge and a major shift in deformation away from the North American-Yakutat terrane suture (Chugach St. Elias fault). We propose that accelerated denudation redistributed strain along an en echelon array of forethrusts that lie beneath the zone of heaviest glaciation and the backthrust, which in turn truncates the southward-vergent thrusts. This focusing of deformation matches predictions from analytical models of orogenic wedges and implies a high degree of coupling between climate and tectonics in this glacially-dominated orogen.
- Type
- Published Report
- Authors
- Berger, Aaron; Spotila, James; Pavlis, Terry; Enkelmann, Eva; Buscher, Jamie
- Date of Issue
- 2007-06-28
- Units
- WRST
- Keywords
- (U-Th)/He dating, Alaska tectonics, Climate-tectonic coupling, St. Elias orogen, Tectonic-Climatic Interactions, Terrane accretion, Thermochronological Investigation, Thermochronometry, Yakutat