Evaluation of detrital thermochronology for quantification of glacial catchment denudation and sediment mixing

- Detrital dating provides an age distribution that presents sediments eroded in the catchment.
- Sampling the ice-cored terminal moraine is an alternative to the pro-glacial outwash material.
- Detrital thermochronometry discovers the youngest ages of rocks inaccessible under the glacier.
- Thermochronometric record provided by sand-size and cobble-size glacial material is similar.

Thermochronometric methods have been applied successfully on bedrock samples as well as detrital material to study exhumation processes in mountain belts. The access to exposed bedrock can be a limiting factor in remote and rugged mountainous regions, or areas covered by ice. The analysis of detrital material provides an integrated signal of rock cooling from sediment source areas in a catchment. One advantage of detrital thermochronology is that the source areas can include regions that are inaccessible for bedrock dating, such as beneath glaciers. In this study we investigate the suitability of various detrital thermochronometer sampling approaches at the glacier terminus including sediments from the pro-glacial fluvial outwash, the ice-cored terminal moraine, and older moraines. Specifically we analyzed the detrital apatite fission track ages of sand-size material collected from the Tiedemann and Scimitar Glaciers that drain the eastern and northern flanks of Mt. Waddington British Columbia, Canada, respectively. We present 935 new apatite fission-track ages and compare the grain-age distributions of the various detrital sites among each other and with published bedrock ages from the Tiedemann Glacier catchment. We show that detrital apatite fission-track thermochronometry is a viable and powerful tool to obtain a robust cooling age distribution of a catchment or region that can elucidate age populations originating from those parts of the catchment that are covered by ice and therefore remain undetected by bedrock studies. We also show that sampling the ice-cored terminal moraine is an alternative sampling approach to the pro-glacial river sediments that provides cooling age distributions representative of the sediments sourced by the entire catchment including sub-glacially eroded material. Finally, samples collected from the modern glacial systems and terminal moraines of different ages are compared to assess temporal variations in the distribution of glacial erosion over the Late Holocene.