Thermal/denudation histories of the late Neogene pluton revealed by multi-thermochronometries and Al-in-Hornblende geobarometry in the Tanigawa-dake area, central Japan

複数の熱年代計と角閃石アルミ地質圧力計により解明された谷川岳地域の新第三紀後期の深成岩体の熱史・削剥史

南 沙樹*; 末岡 茂   ; 福田 将眞   ; 長田 充弘   ; Kohn, B. P.*; 横山 立憲   ; 鏡味 沙耶   ; 河上 哲生*; 東野 文子*; 安邊 啓明   ; 中嶋 徹   ; 梶田 侑弥*; 田上 高広*

Minami, Saki*; Sueoka, Shigeru; Fukuda, Shoma; Nagata, Mitsuhiro; Kohn, B. P.*; Yokoyama, Tatsunori; Kagami, Saya; Kawakami, Tetsuo*; Higashino, Fumiko*; Abe, Noriaki; Nakajima, Toru; Kajita, Yuya*; Tagami, Takahiro*

Granites are generally formed at a crustal depth of several kilometers or deeper. Especially, granites younger than ca 5 Ma are exposed along the plate convergence boundaries, implying very rapid uplift/exhumation rates in the areas. Japanese islands are one of such areas, e.g., the world's youngest Kurobegawa granite (ca 0.8 Ma) is exposed on the Hida mountains. The Tanigawa-dake area is located in the arc-arc junction, where late Neogene Tanigawa-dake granites (zircon U-Pb ages: ca 4.0-3.2 Ma) are exposed. In this study, we performed zircon U-Pb, zircon (U-Th)/He (ZHe) and apatite (U-Th-Sm)/He (AHe) datings for the Tanigawa-dake granites to constrain thermal/denudation histories from the intrusion to exposure. We obtained 6.0-3.2 Ma of zircon U-Pb ages together with the previous work, 3.3-1.4 Ma of ZHe ages and 2.8-1.0 Ma of AHe ages. Zircon U-Pb ages indicated at least three intrusive events for the Tanigawa-dake granites. The AHe ages reflect uplift/denudation rather than thermal disturbance by the intrusions based on time-temperature paths. The denudation rates calculated from AHe ages are 0.3-1.4 mm/yr, comparable with those in other tectonically active regions in Japan, e.g., Tanzawa mountain and Ou back-bone range. The spatial distribution of the denudation rates suggests the Tanigawa-dake region might be symmetrically denudated centering around the west-side of Mt. Tanigawa-dake main ridge. In the presentation, further discussion will be provided with the results of geobarometry, stress analysis and QTQt thermal inversion modeling.