U th he dating of apatite a potential thermochronometry Mature fuck with free trial
(U–Th)/He thermochronometric analyses were performed across the southern part of the Northeast Japan Arc for reconstructing the long-term uplift and denudation history in the region.Apatite (U–Th–Sm)/He ages ranged from 64.3 to 1.5 Ma, while zircon (U–Th)/He ages ranged between 39.6 and 11.0 Ma.2013), Kt M Kitakami Mountains, Ab M Abukuma Mountains, As M Asahi Mountains, Id M Iide Mountains, EUR Eurasian plate, PAC Pacific plate, PHS Philippine Sea plate, NAM North American plate The NE and the SW Japan Arcs were formed as a result of opening of the Sea of Japan at 25–15 Ma, although they had originally been parts of the East Asian continental margin (e.g., Otofuji et al. A few studies have been conducted to reveal the uplift and denudation histories of the mountains in the NE Japan Arc, but the available literatures are still somewhat limited.Only a few sets of thermochronometric studies on the back-arc side and the OBR are available (Fig. On the basis of sedimentary facies analyses, three uplift stages were identified in the OBR as (1) surface uplift and regional unconformity (12–9 Ma), (2) differential uplift and compression (6.5–3 Ma), and (3) uplift and intense compression (after ~3 Ma) (Nakajima et al. In addition, uplift stages in the Dewa Hills and the Asahi Mountains on the back-arc side were constrained by analyzing sedimentary facies in the adjacent Shinjo basin, suggesting that the oldest uplift phase of the Asahi Mountains occurred at ~5 Ma and then the Dewa Hills began to uplift over the Pliocene (Moriya et al. By contrast, in the Kitakami and the Abukuma Mountains on the fore-arc side, remnants of uplifted peneplains can be seen at elevations of ~300 to 1200 m (e.g., Nakamura 1963; Koike 1969; Kimura 1994). Together, these imply relatively stable thermal and tectonic conditions over the Cenozoic with recent minor uplift episode(s).(U–Th)/He thermochronometers have relatively low closure temperatures, ~55 to 80 °C for apatite (Flowers et al. 2009) and ~160 to 200 °C for zircon (Guenthner et al.
Clear, non-fractured euhedral grains with average grain radii in a close size range were hand-picked under an Olympus SZX12 binocular microscope, then immersed in ethanol and checked under polarized light to detect and exclude grains with possible inclusions.
2009), e U and grain age should have a positive correlation if the dispersion is derived from radiation damage (cf Fig. Within samples, we adopted grain ages that overlapped with the other grain ages within ±3σ to calculate the weighted mean age of each sample (Table 3; Fig. For A02-ST03, grain ages present a cluster ranging 80–50 Ma, except for one grain yielding an age of ~225 Ma.
However, all of the grain ages belonging to the cluster do not overlap within ±3σ.
1), providing a typical island arc setting (e.g., Minoura and Hasegawa 1992; Yoshida et al. The mountains on the fore-arc side are relatively wide, have gentle slopes, and low-relief surfaces (Fig. The OBR is a narrow and long mountain range wedged between active faults (Fig. Quaternary volcanism is dominant in the OBR and in a few parts of the back-arc side (Fig. The NE Japan Arc generally shows arc-parallel structures, for example, mountain ranges, active faults, and volcanic chains, although across-arc mountains and chains of volcanoes are also observed on the back-arc side (e.g., Tamura et al. FT ages are from Ohira and Honda (1999), Goto (2001) and Ohtani et al. This figure was drawn by using Generic Mapping Tools (GMT) (Wessel and Smith 1991) and 30 arc-second grid of the General Bathymetric Chart of the Oceans (GEBCO).
b Topographic cross-sections across the study area.