Quantifiying deformation and erosion at the Yakutat plate corner (SE Alaska) with integrated thermochronology and numerical modelling
Final Report Abstract
This project aimed to investigate the interaction between the tectonic processes that build mountains and climate-driven erosion processes that destroy mountains. The heavily glaciated St. Elias Mountains (southeast Alaska and southwest Yukon) appear to be an excellent natural laboratory for such investigations because tectonics and erosion is strong. Over million years time the combination of surface uplift and erosion results in exhumation of rocks originating from kilometers deep in the crust. The timing and rates of exhumation can be measured with thermochronology that date the time of rock cooling below certain temperatures. In this project we used a variety of thermochronology methods applied to samples collected across the entire St. Elias Mountains to quantify the spatial and temporal changes in rock exhumation. We found that the exhumation is primarily driven by tectonics, but also correlates with the precipitation pattern that show high erosion and rock exhumation along the wet coastal side, whereby erosion and exhumation is slow on the dry northern side. A very efficient tectonicerosion feedback mechanism developed at the St. Elias syntaxis where stress is concentrated and results in deformation and rock uplift, which is collocated with efficient glacial erosion that together results in localized extreme rapid exhumation. Such feedbacks have been shown to occur in other orogenic syntaxis such as in the eastern and western Himalayas, however the surprising outcome of this study was that the location shifted spatially through time. The feedback mechanism started north of the plate boundary at ~10 Ma, and thus prior to the beginning of alpine glaciation. Through time the focused region of extreme exhumation shifted south, and since ~2 Ma it is centered south of the plate boundary at the syntaxis. The shift in the location is a consequence of the changing rheology of the subducting Yakutat plate due to the extreme high sedimentation rates, combined with intensification of glaciation due to global climate shifts.
Publications
-
2013. An examination of the interplay between glacial processes and exhumation in the St. Elias Range, Alaska. Geosphere 9, no. 2
Headley, R. M.; Enkelmann, E. & Hallet, B.
-
2013. Evaluation of the spatial extend of rapid exhumation in the St. Elias syntaxis region, SE Alaska. JGR-Earth Surface, 118, 1-18
Grabowski, David M.; Enkelmann, Eva & Ehlers, Todd A.
-
2014. Constraining the area of rapid and deep-seated exhumation at the Yakutat plate corner, southeast Alaska. Tectonics 33
Falkowski, Sarah; Enkelmann, Eva & Ehlers, Todd A.
-
2015. Cooperation of tectonic and surface processes produces Earth’s highest coastal mountains. Geophysical Reserach Letters, 42
Enkelmann, Eva; Koons, Peter O.; Pavlis, Terry L.; Hallet, Bernard; Barker, Adam; Elliott, Julie; Garver, John I.; Gulick, Sean P. S.; Headley, Rachel M.; Pavlis, Gary L.; Ridgway, Kenneth D.; Ruppert, Natalia & Van Avendonk, Harm J. A.
-
2015. Evaluation of detrital apatite fission track thermochronology for quantification of glacial catchment denudation and sediment mixing. Chemical Geology, 411, 299-309
Enkelmann, Eva & Ehlers, Todd A.
-
2015. Low-temperature thermochronology of the Yakutat Plate corner, St. Elias Range (Alaska): bridging short-term and long-term deformation. Quaternary Science Review, 113, 23–38
Enkelmann, Eva; Valla, Pierre G. & Champagnac, Jean-Daniel
-
2016. Cooling history of the St. Elias syntaxis, southeast Alaska, revealed by geo- and thermochronology of cobble-size glacial detritus. Tectonics, 35, 447-468
Falkowski, Sarah; Enkelmann, Eva; Drost, Kerstin; Pfänder, Jörg A.; Stübner, Konstanze & Ehlers, Todd A.
-
2016. Upper crustal cooling of the Wrangellia Composite Terrane in the northern St. Elias Mountains, western Canada. Lithosphere, 8, 359–378
Falkowski, Sarah & Enkelmann, Eva
-
2017. Thermochronology in southeast Alaska and southwest Yukon: Implications for North American Plate Response to Terrane Accretion. Earth and Planetary Science Letters, 457, 348–358
Enkelmann, Eva; Piestrzeniewicz, Adam; Falkowski, Sarah; Stübner, Konstanze & Ehlers, Todd A.
