Cooling history of the St. Elias syntaxis, southeast Alaska, revealed by geochronology and thermochronology of cobble-sized glacial detritus

Falkowski, S. , Enkelmann, E., Drost, K., Pfänder, J. A., Stübner, K. and Ehlers, T. A. (2016) Cooling history of the St. Elias syntaxis, southeast Alaska, revealed by geochronology and thermochronology of cobble-sized glacial detritus. Tectonics, 35(2), pp. 447-468. (doi: 10.1002/2015tc004086)

Abstract

We investigate the spatiotemporal evolution of exhumation in the ice-covered St. Elias syntaxis area, southeast Alaska, using multiple thermochronometers and geochronometers from cobble-sized glacial detritus. Multiple thermochronometers reveal the cooling histories from 500 to 60°C of 27 glacially transported cobbles from the two largest catchments of the syntaxis. Cobble lithologies and 21 zircon U-Pb ages (~277–31 Ma) were examined to determine sample provenance. Furthermore, eight amphibole and seven biotite 40Ar/39Ar ages (~276–16 Ma and ~50–42 Ma, respectively), four zircon and six apatite (U-Th)/He ages (~35–4.8 Ma and ~4.2–0.6 Ma, respectively), and four apatite fission track ages (~17–1.6 Ma) were used to reconstruct the individual cobble cooling histories. An additional four bedrock samples from the Fairweather Range yielded three biotite 40Ar/39Ar ages between ~42 and 5 Ma. A compilation of published bedrock and new cobble cooling histories from the St. Elias Mountains and Fairweather Range reveals the regional Cenozoic cooling and exhumation history, emphasizing the position of the St. Elias syntaxis as a transitional zone between transpression and subduction settings. The new cobble and bedrock data indicate an onset of rapid exhumation at ~5 Ma that was limited in duration (2–3 Myr) and amount (~10 km) in the syntaxial region. This study also demonstrates the usefulness of cobbles for revealing thermal histories of otherwise inaccessible regions as cobble analysis combines advantages of bedrock and detrital thermochronology.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Falkowski, Dr Sarah and Ehlers, Professor Todd A.
• Authors: Falkowski, S., Enkelmann, E., Drost, K., Pfänder, J. A., Stübner, K., and Ehlers, T. A.
• College/School: College of Science and Engineering > School of Geographical and Earth Sciences
• Journal Name: Tectonics
• Publisher: Wiley for the American Geophysical Union
• ISSN: 0278-7407