Thermal/exhumation histories of the late Neogene plutons in the Tanigawa-dake area, central Japan, based on multi-thermochronometries

<p>Granites are formed generally at a crustal depth of a few to tens kilometers. Therefore, exposure of young granite intrusions can be evidence of an extremely rapid rock uplift and exhumation. Most of the known granites younger than ~5 Ma have been found along convergent plate boundaries in the world, including the Japan arc [1,2,3]. Quantifying the exhumation rates and deformation dynamics of young granite can provide unique insights in mountain forming processes and crustal deformation. Here we provide new constraints on the Tanigawa-dake area, where intrusive young granites are exposed, located in the back arc of the Northeast Japan subduction: a complex zone of active tectonics and volcanism.</p> <p>The lithology of the Tanigawa-dake is mainly composed of Cretaceous to Paleogene granites (e.g., Minakami quartzdiorite: ~109.4 Ma [4]) and Pliocene Tanigawa-dake granites (Akayu, Tanigawa and Makihata bodies). The Tanigawa and Makihata bodies were estimated to have intruded at ~4.0&#8211;3.2 Ma by zircon U-Pb dating [4] and cooled to ~280&#8211;400 &#176;C at ~3.9&#8211;2.9 Ma [5,6,7] by biotite K-Ar and zircon fission-track dates. In this study, we performed (1) zircon U-Pb dating for unmeasured localities of the Tanigawa-dake Pliocene granites to reveal their more detailed intrusive history and (2) zircon and apatite (U-Th)/He dating (AHe, ZHe), whose Tc are 160&#8211;200&#8451; and 55&#8211;80&#8451; respectively, to obtain the thermal/exhumation histories at the shallow crust. Consequently, we obtained zircon U-Pb ages of ~6.0&#8211;3.2 Ma along with [4], ZHe ages of ~3.1&#8211;1.3 Ma, and AHe ages of ~3.3&#8211;1.2 Ma for the Tanigawa-dake granites and AHe age of ~2.4 Ma for the Minakami quartzdiorite. The zircon U-Pb dates indicate that the three bodies of the Tanigawa-dake granites intruded at different timings, ~6.0-5.5 Ma, ~4.0 Ma and ~3.3-3.2 Ma. The exhumation rates were calculated from the cooling rates between Tc of AHe and surface temperature (10 &#176;C), ranging at ~0.3&#8211;0.8 mm/yr for the Minakami quartzdiorite, the Makihata body, and the western side of the Tanigawa body and ~0.8&#8211;1.4 mm/yr for the eastern side of Tanigawa body. By comparing the exhumation rates to those of the Tanzawa mountain [8] and the Northeast Japan arc [9], the Tanigawa-dake area is suggested to exhume at rate comparable to these active crustal movement regions, such as an arc-arc collision zone (Tanzawa mountain) and strain concentrated zone (Ou Backbone range).</p> <p>References [1] Harayama (1992) Geology, 20, 657-660, [2] Ito et al. (2013) Sci. Rep. 3:1306, [3] Tani et al. (2010) Geology, 38, 215-218, [4] Minami et al. (2021) EPS. 73:231, [5] Ohira and Honda (1999) FTNL, 12, 61-63, [6] Kawano et al. (1992) Jour. Geol. Soc. Japan, 87, 221-225 [7] Sato (2016) Bull. Gunma. Mus. Nat. His., 20, 85-104, [8] Yamada & Tagami (2008) Jour. Geophys. Res., 113, B03402, [9] Sueoka et al. (2017) EPS. 69:79.</p>