In recent decades, most mountain glaciers have been losing mass in response to climate change, and the area of the ablation zone covered by rock debris is expanding. Debris-covered glaciers are expected to have a longer life expectancy than climatically equivalent clean-ice glaciers because supraglacial debris insulates the underlying ice surface and reduces ablation. In order to accurately predict how debris-covered glaciers will evolve under a changing climate it is essential to quantify the processes controlling their behaviour. We used luminescence rock surface burial dating to constrain the englacial transport time of debris within an alpine debris-covered glacier. We collected 24 samples embedded in the ice in the ablation zone of the Miage Glacier, in the Mont-Blanc Massif (Italy). The natural luminescence signal of rock slices was measured from the surface to a depth of ~10 mm using a protocol comprising IRSL50, IRSL225 and OSL125 measurements. Nine of our samples showed a plateau within the first 2 to 3 discs suggesting that the luminescence signal has the potential to be used to date the burial duration of debris. Among them, 5 and 7 samples passed the dose recovery test for the IR50 signal within 10% and 20% of unity respectively. Only 3 samples passed the dose recovery test for the IR225 signal within 10% of unity. After 24h bleaching in the solar simulator, typical residual doses are as high as 20-40% of the natural equivalent dose measured. We obtained preliminary non fading corrected ages for 5 samples in the range from ~0.8 to ~11 ka. Glacier model estimated englacial rock debris transport times are an order of magnitude lower than the oldest ages obtained suggesting either that some clasts were stored on hillslopes or within moraines prior to englacial transport or that calibration issues may have contributed to age overestimation. Further luminescence signal processing quality checks are required to assess the quality of our ages. If ultimately successful, our results, and the application of luminescence rock surface burial dating to englacially transported debris, will enhance understanding of the dynamics of debris-covered glaciers and inform the use of glacier models for debris covered glaciers, which will improve projections of the contribution of mountain glaciers to the sustainability of water resources in vulnerable catchments such as those in High Mountain Asia and South America.
  Constraining the pathways and time scales of englacial sediment transport is of primary importance for both understanding the processes that move sediment through glacierised catchments and quantifying the response of mountain glaciers to climate change. However, sediment transport through glaciers is a more complex process than ice flow and difficult to observe; clasts can be transported englacially and at the ice margins, but also deposited into moraines before being re-entrained into englacial transport. We developed a novel method taking a Lagrangian approach that combines luminescence rock surface burial dating of the time for englacial transport of individual rock debris with ice-dynamical glacier evolution modelling of glacial sediment transport to quantify rates of sediment transport through the Miage Glacier catchment in the Italian Alps. Luminescence rock surface burial dating allows determining the burial duration of rocks after they have been exposed to sunlight, but this method has not previously been applied to englacial clasts. We obtained luminescence ages for seven samples embedded in the ice in the ablation zone of Miage Glacier, with burial ages ranging from 0.2 ± 0.1 ka to 5.0 ± 1.4 ka. Samples collected in the upper part of the ablation zone yield younger ages than samples collected near the terminus. The younger luminescence ages (0.2 ± 0.1 ka and 0.3 ± 0.1 ka) are consistent with expected burial duration based on the present-day glacier velocity. In contrast, older luminescence ages obtained for samples located in the lower part of the ablation zone (1.2 ± 0.1 ka to 5.0 ± 1.4 ka) show that these samples record a longer and more complex burial history, suggesting that these samples were either stored in the headwall area or within moraines for several thousand years before being entrained in the ice. In the Miage catchment, debris could have been stored in a moraine at the junction between the Bionnassay Glacier and the Dome Glacier before being entrained in the Miage glacier. We compare the burial ages of the englacial clasts with simulations of glacial sediment transport using a Lagrangian particle tracking scheme in the glacier model iSOSIA. The model results illustrate the range of englacial and subglacial sediment flow paths through the Miage Glacier and simulate similar durations of englacial transport to those obtained for our luminescence samples.
The incision history of the Three Rivers (Salween, Mekong, and Yangtze) region in the Southeast Tibetan Plateau has been linked to both tectonic and climatic controls. In this study, we report new apatite (U‐Th)/He and fission‐track thermochronology data from the >6,000‐m‐high Kawagebo massif, which forms the edge of the high plateau on the western flank of the steepened knickzone reach of the middle Mekong River valley. Thermal‐history modeling of a thermochronological age‐elevation profile shows rapid cooling since ~1.5 Ma and suggests a mean Quaternary exhumation rate of >1 km/Myr at the valley bottom. The amount of Quaternary exhumation is too high to be caused by fluvial incision alone and requires additional tectonic uplift. Comparing our data from the western flank of the Mekong River valley with published data from the eastern flank shows differential exhumation across the valley in the late Miocene, with the western flank undergoing more exhumation, but relatively uniform exhumation in the Quaternary. We relate rapid exhumation since the late Miocene on the western flank of the Mekong valley and the high topography of the Kawagebo massif to localized tectonic uplift associated with a restraining (left stepping) overstep between the still‐active right‐lateral Parlung and Zhongdian strike‐slip faults. The pattern of river steepness index across the knickzone also indicates that it results from locally focused uplift. Our results demonstrate the importance of detailed thermochronologic studies in this very active region to constrain the complex multiphase tectonic history before invoking any potential climatic forcing of river incision.
Earth and Space Science Open Archive This preprint has been submitted to and is under consideration at Tectonics. ESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary.Learn more about preprints preprintOpen AccessYou are viewing the latest version by default [v1]Exhumation of the Western Cordillera, Ecuador driven by late Miocene subduction of the Carnegie RidgeAuthorsAudreyMargirierManfred R.StreckerPeter WReinersStuart NThomsonIsmaelCasadoSarah W.M.GeorgeAlexandra PatriciaAlvaradoiDSee all authors Audrey MargirierCorresponding Author• Submitting AuthorIDYSTview email addressThe email was not providedcopy email addressManfred R. StreckerUniversity of Potsdamview email addressThe email was not providedcopy email addressPeter W ReinersUniversity of Arizonaview email addressThe email was not providedcopy email addressStuart N ThomsonUniversity of Arizonaview email addressThe email was not providedcopy email addressIsmael CasadoUniversity of Potsdamview email addressThe email was not providedcopy email addressSarah W.M. GeorgeUniversity of Arizonaview email addressThe email was not providedcopy email addressAlexandra Patricia AlvaradoiDIG-EPNiDhttps://orcid.org/0000-0003-4901-8175view email addressThe email was not providedcopy email address
