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[SCG54-P05] Spatial distribution of apatite fission-track ages on the Cretaceous granites of the southern part of Ou Backbone Range: insights into the doming uplift of a volcanic arc
Keywords:Thermochronology, Northeast Japan Arc, Fission-track method , Volcanic arc, Ou Backbone Range, Uplift/denudation history
To understand geoscientific phenomena (e.g., magmatism, seismicity, and, orogenesis) that occur actively along plate subduction zones at the Earth's surface, a quantitative approach plays a key role in uplift/subsidence and denudation on various timescales to reveal the mechanism of strain release and accumulation. This study focuses on volcanic arcs, commonly identified in arc-trench systems, and aims to elucidate the vertical deformation history (uplift/denudation history) associated with the formation and development of the volcanic arc. The time scale of such deformations should be approximately 1–10 Myr. (e.g., Kaizuka, 1998, Univ. Tokyo Press). Thermochronology is thus considered effective for reconstructing the deformation process because of encompassing such a time range. In this study, we target the Northeast Japan Arc (NEJA) as an island arc which is supposed to have typical topographies, and attempt to estimate the mountain building process of the Ou Backbone Range (hereinafter, OBR) located in the central axis of the NEJA as a volcanic arc, based on thermochronology.
We have applied low-temperatures (<300°C) thermochronometric approaches, mainly the apatite fission track and apatite (U-Th)/He (AFT and AHe, respectively) methods, to estimate the uplift of each island arc components (i.e., fore-arc, volcanic arc, back-arc) in the NEJA. The uplift and denudation processes of each unit are gradually becoming clear by means of thermochronometric data (Sueoka et al., 2017, EPS; Fukuda et al., 2019, JAES:X; Fukuda et al., 2020, EPS). Based on previous geomorphologic and geologic studies, the OBR has been uplifted rapidly, mainly due to the east-west compressive stress since the end of the Neogene to the Quaternary (e.g., Sato, 1994, JGR; Nakajima, 2013, INTECH; Yoshida et al. 2014, Geol. Soc. Lon.). In addition, two major uplift models for the OBR were proposed; (1) the tilting pop-up model caused by reverse fault movement on both sides of the foot of the mountain (Nakajima 2013, INTECH), and (2) the doming uplift model in which plastic deformation of the crust propagates into a brittle zone (Hasegawa et al., 2005, Tectonophys.). According to our recent investigations, a combination of numerical results using a slope development model (Hirano, 1968, J. Geosci., Osaka City Univ.) with dense thermochronological data (Fukuda et al., 2019, FTNL; Fukuda 2020DT) at intervals of 1 to several km has provided support for a doming uplift model in the southern OBR. (Hirano, 1968, J. Geosci. Osaka City Univ.). The expansion of thermochronological data and the construction of a detailed uplift model are still desirable. As recent progress, a similar methodology has been applied to the northern part of the OBR. Consequently, no clear trend of ages in spatial distribution was inferred (Fukuda et al., 2021, JpGU), inducing a different spatial trend in contrast to one of the southern part. In this presentation, regarding the spatial distribution of ca. 20 AHe ages (39.1–1.5 Ma) and ca. 10 AFT ages (29.8–4.4 Ma) obtained so far in the southern part of the OBR, we attempted to obtain new AFT age data for blank areas where no ages were reported in order to develop a detailed uplift model.
AFT dating was performed using the automated FT measurement instruments (Trackscan Plus Professional) to count FTs, and the laser ablation-inductively coupled plasma mass spectrometer (Analyte G2+iCAP-TQ) for measuring uranium concentrations. As a result, about 10 new AFT ages were obtained in the southern part of the OBR, ranging from a few tens to a few Ma. These results are consistent with the previously reported AFT ages and suggest that the ages of a few Ma may reflect uplift and denudation associated with east-west strong compressive stress since 3–2 Ma. It is noteworthy that the youngest AFT age of 1.6 Ma was obtained near the summit, further supporting the spatial trend of the doming uplift. As future prospects, we plan to apply the AHe method and the inverse thermal modeling based on the FT length distribution to unmeasured locations. We will also investigate the mechanism of the doming uplift model by comparison to volcanic arcs in other regions.
Acknowledgments: This study was supported by the Grant-in-Aid for scientific research (KAKENHI) on innovative areas No. 26109003, and for scientific research (C) No.21K03730.
We have applied low-temperatures (<300°C) thermochronometric approaches, mainly the apatite fission track and apatite (U-Th)/He (AFT and AHe, respectively) methods, to estimate the uplift of each island arc components (i.e., fore-arc, volcanic arc, back-arc) in the NEJA. The uplift and denudation processes of each unit are gradually becoming clear by means of thermochronometric data (Sueoka et al., 2017, EPS; Fukuda et al., 2019, JAES:X; Fukuda et al., 2020, EPS). Based on previous geomorphologic and geologic studies, the OBR has been uplifted rapidly, mainly due to the east-west compressive stress since the end of the Neogene to the Quaternary (e.g., Sato, 1994, JGR; Nakajima, 2013, INTECH; Yoshida et al. 2014, Geol. Soc. Lon.). In addition, two major uplift models for the OBR were proposed; (1) the tilting pop-up model caused by reverse fault movement on both sides of the foot of the mountain (Nakajima 2013, INTECH), and (2) the doming uplift model in which plastic deformation of the crust propagates into a brittle zone (Hasegawa et al., 2005, Tectonophys.). According to our recent investigations, a combination of numerical results using a slope development model (Hirano, 1968, J. Geosci., Osaka City Univ.) with dense thermochronological data (Fukuda et al., 2019, FTNL; Fukuda 2020DT) at intervals of 1 to several km has provided support for a doming uplift model in the southern OBR. (Hirano, 1968, J. Geosci. Osaka City Univ.). The expansion of thermochronological data and the construction of a detailed uplift model are still desirable. As recent progress, a similar methodology has been applied to the northern part of the OBR. Consequently, no clear trend of ages in spatial distribution was inferred (Fukuda et al., 2021, JpGU), inducing a different spatial trend in contrast to one of the southern part. In this presentation, regarding the spatial distribution of ca. 20 AHe ages (39.1–1.5 Ma) and ca. 10 AFT ages (29.8–4.4 Ma) obtained so far in the southern part of the OBR, we attempted to obtain new AFT age data for blank areas where no ages were reported in order to develop a detailed uplift model.
AFT dating was performed using the automated FT measurement instruments (Trackscan Plus Professional) to count FTs, and the laser ablation-inductively coupled plasma mass spectrometer (Analyte G2+iCAP-TQ) for measuring uranium concentrations. As a result, about 10 new AFT ages were obtained in the southern part of the OBR, ranging from a few tens to a few Ma. These results are consistent with the previously reported AFT ages and suggest that the ages of a few Ma may reflect uplift and denudation associated with east-west strong compressive stress since 3–2 Ma. It is noteworthy that the youngest AFT age of 1.6 Ma was obtained near the summit, further supporting the spatial trend of the doming uplift. As future prospects, we plan to apply the AHe method and the inverse thermal modeling based on the FT length distribution to unmeasured locations. We will also investigate the mechanism of the doming uplift model by comparison to volcanic arcs in other regions.
Acknowledgments: This study was supported by the Grant-in-Aid for scientific research (KAKENHI) on innovative areas No. 26109003, and for scientific research (C) No.21K03730.