Luminescence dating of cobbles buried in moraines from the source area of the Litang River (Konglongluo Valley), eastern Tibetan Plateau

Moraine deposits are difficult to date using conventional luminescence techniques, especially such deposits without glaciofluvial sand lenses incorporated within the feature. Recently developed rock-surface luminescence burial dating has shown the potential for constraining heterogeneous glacial till sediments. However, the wider applicability of the luminescence dating of cobbles obtained from moraine deposits needs to be tested. Thirty-one buried granite cobbles from different generations of terminal moraines of the last deglaciation moraine series in the source area of the Litang River, eastern Tibetan Plateau, were collected. Eight cosmogenic nuclide 10Be exposure ages were generated from eight boulders obtained from the ridges of two moraines, to provide an external age control. A post-IR50 IRSL225 single aliquot regenerative dose (SAR) protocol was applied to measure the luminescence signal from rock slices. The IRSL50 Ln/Tn-depth profiles from 23 cobbles showing surface age plateaus (up to 12 mm), indicating that the material was well-bleached prior to deposition. The depth of the bleaching front is variable between individual cobbles from the same deposit. Three distinct methods were employed to observe and correct for any anomalous fading present. We observe age agreement from different cobbles collected from the same moraine deposits, illustrating the reproducibility at our selected locations. The luminescence ages of burial cobbles (15.5 ± 2.1 ka to 20.0 ± 1.6 ka) align with geomorphic relationships and 10Be exposure ages. Particularly, the age of cobbles from one of the moraines (20.0 ± 1.6 ka) is consistent with independent 10Be exposure ages (18.6 ± 1.2 ka) of boulders from the same moraine. This study demonstrates the applicability of the luminescence dating of moraine deposits, using cobbles, and provides deeper insights of the last deglaciation in the eastern Tibetan Plateau.