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King, G. E.*; Ahadi, F.*; 末岡 茂; Herman, F.*; Anderson, L.*; Gautheron, C.*; 塚本 すみ子*; Stalder, N.*; Biswas, R.*; Fox, M.*; et al.
Geology, 51(2), p.131 - 135, 2023/02
The exhumation of bedrock is controlled by the interplay between tectonics, surface processes, and climate. The highest exhumation rates of centimeters per year are recorded in zones of highly active tectonic convergence such as the Southern Alps of New Zealand or the Himalayan syntaxes, where high rock uplift rates combine with very active surface processes. Using a combination of different thermochronometric systems including trapped-charge thermochronometry, we show that such rates also occur in the Hida Mountain Range, Japanese Alps. Our results imply that centimeter per year rates of exhumation are more common than previously thought. Our thermochronometry data allow the development of time series of exhumation rate changes at the time scale of glacial-interglacial cycles, which show a fourfold increase in baseline rates to rates of 
10 mm/yr within the past 65 k.y. This increase in exhumation rate is likely explained by knickpoint propagation due to a combination of very high precipitation rates, climatic change, sea-level fall, range-front faulting, and moderate rock uplift. Our data resolve centimeter-scale sub-Quaternary exhumation rate changes, which show that in regions with horizontal convergence, coupling between climate, surface processes, and tectonics can exert a significant and rapid effect on rates of exhumation.
Anderson, L.*; Bartz, M.*; King, G.*; Fox, M.*; Herman, F.*; Stalder, N.*; Biswas, R.*; 末岡 茂; 塚本 すみ子*; Ahadi, F.*; et al.
no journal, ,
Optically stimulated luminescence (OSL) and electron spin resonance (ESR) thermochronometry have the potential to resolve continuous erosion histories from rapidly eroding settings. These thermochronometers are viable over the past few hundred thousand to a million years. These time periods are defined by persistent oscillations between warm and cold states. During the Quaternary, fundamental questions about the relationship between climate and erosion remain unanswered. With further development, the OSL and ESR thermochronometers could answer these questions. To realize this potential new strategies are required to invert low-temperature thermal histories for erosion rates. Here, we explore the use of PeCUBE (Braun, 2003), a three-dimensional finite-element model that simulates heat conduction and advection in the upper crust. As a training dataset we use cooling histories derived from eight samples from the Tateyama region in the Hida Mountains of Japan. The flexibility of PeCUBE allows us to quantify the role of time varying surface temperatures between glacial and interglacial periods. In high-relief settings the three-dimensionality of the topography, for example between valleys and ridges, can substantially perturb rock temperatures. PeCUBE allows us to quantify and remove these confounding topographic effects. We additionally explore the role of changing topographic relief on time varying thermal fields and erosion rates. Lastly, we explore a generous range of model parameters to quantify the sensitivity and robustness of our inversions.
King, G. E.*; Ahadi, F.*; 末岡 茂; Herman, F.*; Anderson, L.*; Gautheron, C.*; 塚本 すみ子*; Stalder, N.*; Biswas, R.*; Fox, M.*; et al.
no journal, ,
The exhumation of bedrock is controlled by the interplay between tectonics, surface processes and climate. The highest exhumation rates of cm/yr are recorded in zones of highly active tectonic convergence. Here, we use a combination of different thermochronometric systems, and notably trapped-charge thermochronometery, to show that such rates also occur in the Hida Range, Japanese Alps. Our results imply that cm/yr rates of exhumation may be more common than previously thought. The Hida Range is the most northern and most extensive of the Japanese Alps, and reaches elevations of up to 3000 m a.s.l. The Hida Range is thought to have uplifted in the last 3 Myr in response to E-W compression and magmatism. Our study focuses on samples from the Kurobe gorge, which is one of the steepest gorges in Japan. Previous work has shown that exhumation rates in this region are exceptionally high, as documented by the exposure of the ~0.8 Ma Kurobe granite in the gorge. We combined 12 new zircon (U-Th/He) ages and 11 new OSL-thermochronometry ages together with existing thermochronometric data to investigate the late Pleistocene exhumation of this region. We found that exhumation rates increased to ~10 mm/yr within the past 300 kyr, likely in response to river base-level fall that increased channel steepness due to climatically controlled eustatic changes. Our data allow the development of time-series of exhumation rate changes at the timescale of glacial-interglacial cycles and show a four-fold increase in baseline rates over the past ~65 kyr. This increase in exhumation rate is likely explained by knickpoint propagation due to a combination of very high precipitation rates, climatic change, sea-level fall, range-front faulting and moderate rock uplift. Our data show that in regions with horizontal convergence, coupling between climate, surface processes and tectonics can exert a significant effect on rates of exhumation.
