Low-temperature thermochronology history of the Kyrgyz Range – Western Tien Shan (Kyrgyzstan)

Abstract

Constraining the effect of global climatic changes on earth surface’s processes is crucial to our understanding of landscape evolution. One debated question is the impact of the Late Cenozoic cooling and subsequent Quaternary glaciations on the erosion of mountain ranges.Low-temperature bedrock thermochronology is widely used to measure rock exhumation/erosion rates in mountain ranges across the world. Specifically, the (U-Th)/He system measured in apatite (AHe) can record low temperature (<100 ◦C) cooling histories and thus has the sensibility to detect million-year timescale changes in erosion rates in glaciated regions. The Kyrgyz Range, part of the Tien Shan and situated in northwest Kyrgyzstan, spans east-west over 400 km and present strong glacial features in the northern flank. Previous thermochronology studies in the Kyrgyz Range have identified an increase of exhumation rates over the last 3 Ma which could be the result of enhanced glacial erosion (Bullen et al., 2003; Sobel et al., 2006). Furthermore, a global analysis of published thermochronology data found the Kyrgyz Range as one of the few locations with the potential to record the effect of Quaternary glaciations (Schildgen et al., 2018). In this study, we present new AHe ages for 6 samples collected along a vertical profile in the glacial valley of Ala Archa. Samples cover an elevation difference of 1850m and were collected on granite outcrops. These results will build on the previous thermochronology dataset by Bullen et al., 2003 (3 AHe ages) by adding both lower and higher elevation samples. Future work includes apatite fission track ages for the same vertical profile.