Unveiling the impact of Quaternary climate on mountain erosion; New insights from the Japanese Alps using novel trapped charge thermochronometry

第四紀の気候による山地侵食への影響の解明; 新しい捕獲電子熱年代法による新知見

Kranz-Bartz, M.*; King, G. E.*; Bernard, M.*; Herman, F.*; Wen, X.*; 末岡 茂   ; 塚本 すみ子*; Braun, J.*; 田上 高広*

Kranz-Bartz, M.*; King, G. E.*; Bernard, M.*; Herman, F.*; Wen, X.*; Sueoka, Shigeru; Tsukamoto, Sumiko*; Braun, J.*; Tagami, Takahiro*

The influence of Quaternary climate on mountain topography remains a topic of debate, largely due to the challenges associated with measuring surface processes over the recent geological past. A compelling location to investigate mountain erosion in response to Quaternary climate change is found in the Tateyama Mountains, part of the northern Japanese Alps, due to its distinct geomorphological features. The Japanese Alps uplifted within the last 1-3 million years and have undergone multiple glaciations during the late Quaternary. In this study, we employ novel ultra-low temperature thermochronometres based on the luminescence and electron spin resonance (ESR) from feldspar and quartz, respectively, in combination with inverse modelling to derive rock cooling and exhumation rate histories on timescales of 10-10 years within the Tateyama region. The four luminescence signals have already reached their upper dating limit, indicating maximum exhumation rates of ca. 1-1.5 mm/yr. In contrast, ESR signals from Al and Ti centres provided ESR ages ranging ca. 0.3-1.1 Ma, suggesting that surface processes were active during the Pleistocene. A negative age-elevation relationship reveals a reduction in local relief at the scale of the cirque basin over the past million years. However, a positive age-elevation trend observed in samples from near the mountain summit deviates from this pattern. Inverse modelling shows rock cooling rates ranging 20-80C/Myr, with slightly faster cooling in cirque-floor samples. Thermal kinematic modelling reveals erosion rates of 0.5-1 mm/yr in the cirque basin, which are higher than those observed from periglacial and slope processes in the same area. Our data suggest that Quaternary climate change, coupled with distinct surface processes, has significantly altered the slopes of the Tateyama mountains, leading to a localized decrease in relief within individual cirque basins during the second half of the Quaternary.