Extreme exhumation along a volcanic arc exposed the world's youngest pluton in the Japanese Alps

火山弧に沿った極端な削剥によって日本アルプスの世界で最も若い深成岩体は露出した

末岡 茂   ; 河上 哲生*; 鈴木 康太*; 鏡味 沙耶   ; 横山 立憲   ; 芝崎 文一郎*; 長田 充弘*; 山崎 あゆ*; 東野 文子*; King, G. E.*; 塚本 すみ子*; Herman, F.*; 田上 高広*

Sueoka, Shigeru; Kawakami, Tetsuo*; Suzuki, Kota*; Kagami, Saya; Yokoyama, Tatsunori; Shibazaki, Bunichiro*; Nagata, Mitsuhiro*; Yamazaki, Ayu*; Higashino, Fumiko*; King, G. E.*; Tsukamoto, Sumiko*; Herman, F.*; Tagami, Takahiro*

Geothermobarometry and zircon U-Pb geochronology reveal an episode of extreme exhumation in the Kurobe area of central Japan, characterized by the exposure of the world's youngest known granite, the middle Pleistocene Kurobegawa Granite. Our results indicate rapid exhumation rates of 7.5-10.2 mm/yr since 0.8 Ma. These exceptionally high rates, among the highest reported globally over orogenic timescales, demonstrate that extremely rapid crustal unroofing, long studied in continental collision zones, is not restricted to those settings and can also occur in subduction-zone volcanic arcs. Three-dimensional tectonic modeling suggests that this localized exhumation reflects focused deformation within high geothermal-gradient zones along the volcanic arc, combined with late Quaternary horizontal shortening. We infer that thermal structure associated with arc magmatism plays a critical role in enhancing exhumation efficiency. These observations highlight that, in subduction-zone orogens, processes linked to magmatism and slab-derived fluids - important components of subduction-zone tectonics - may significantly contribute to long-term mountain building, complementing more traditional mechanisms of mechanical deformation such as faulting and folding, which have been primarily established in studies of continental collision zones.