11:45 AM - 12:00 PM
[SCG47-03] Toward the reconstruction of the uplift style of a volcanic arc: Insights from apatite fission-track thermochronometry of granitoids in the northern part of the Ou Backbone Range
Keywords:Low-temperature thermochronology, Volcanic arc, Ou Backbone Range, Fission-track method, Uplift/denudation
In arc-trench systems, volcanisms, earthquakes, and orogenesis actively occur derived from the plate subduction. In principle, these deformations can be comprehended by estimating material properties and forces (Fukahata et al., 2019, Chigaku Zassi). However, to estimate responsibilities of crust (i.e., material property), and especially, stresses (i.e., force) are interactable issues, thus, we attempt to estimate stresses as a causal parameter, based on observed deformations under certain hypotheses or constraints such as responsibilities. Volcanic arcs are commonly identified in arc-trench systems, which are supposed to be formed by partial melting of crust due to dehydration of slab and heating of mantle wedges (e.g., Nakajima, 2016, Volc.). On the other hand, the quantitative development of vertical deformations (uplift/denudation) coinciding a volcanic arc formation has been poorly understood so far.
The Northeast (NE) Japan Arc is characterized by typical topographies of an island arc, where the Ou Backbone Range (OBR) is obviously located along the center as a volcanic arc. The formation process of the OBR has been investigated based on stratigraphy (Nakajima, 2013, INTECH), volcanic geology (Yoshida et al., 2013, Geol. Soc. Lon.), and structural geology (Sato, 1994, JGR). Those studies suggested the OBR was supposed to be uplifted rapidly, mainly because of the E-W compressive stress since the Quaternary, however, uplift/denudation histories of the OBR were not uncovered quantitatively. Developments of thermochronology in three decades enabled to quantitatively reconstruct uplift/denudation histories even for low relief mountains like in Japan Islands (Sueoka et al., 2016, Geosci. Front.). Thus, thermochronologic studies have been recently conducted in the NE Japan Arc based on low-temperature thermochronometers, such as apatite fission-track (AFT) (Fukuda et al., 2019, JAES:X) and (U-Th)/He (Sueoka et al., 2017, EPS; Fukuda et al., 2020, EPS) methods. As the latest one, Fukuda et al. (submitted) preformed AFT and apatite (U-Th)/He thermochronometric mapping at intervals of 1-few km across the southern part of the OBR. This study proposed that the OBR has possibly been uplifted in domal on geologic timescales. Hence, such implications of uplift style of the OBR in a typical island arc are expected to provide the deformation model for a general volcanic arc distributed in plate subduction boundaries as well as tectonic histories in the NE Japan Arc. For elucidating the mountain building process of the OBR on the 106 yrs. timescale, this study has conducted AFT mapping along the E-W traverses of the northern part of the OBR as a low-temperature thermochronometer (Tc of 90-120°C: Ketcham et al., 1999, Am. Mineral.), also attempting to quantitatively constrain the uplift model based on the spatial pattern of obtained AFT ages across the OBR.
We newly conducted AFT dating for 7 localities of the Cretaceous-Miocene granitoids collected from the northern part of the OBR. The number of FTs and the U contents in apatites were determined by FT automated counting system (TrackScan Plus Professional) and laser ablation-inductively coupled plasma-mass spectrometer (Analyte G2: ArF 193nm excimer laser + Agilent 7700x: ICP-QMS), respectively, housed in Tono Geoscience Center, JAEA. These samples yielded AFT ages of the range of few tens to several Ma, implying that consistent with AFT data of previous study (Fukuda et al., submitted). Moreover, such younger ages of several Ma probably reflected uplift/denudation by the recent E-W compressive stress accelerated since 6.5 Ma or 3-2 Ma (e.g., Nakajima, 2013). In this presentation, we will discuss the spatial pattern of AFT ages across the northern part of the OBR, and the uplift model of the overall OBR by integrated with previously reported ages in the south.
The Northeast (NE) Japan Arc is characterized by typical topographies of an island arc, where the Ou Backbone Range (OBR) is obviously located along the center as a volcanic arc. The formation process of the OBR has been investigated based on stratigraphy (Nakajima, 2013, INTECH), volcanic geology (Yoshida et al., 2013, Geol. Soc. Lon.), and structural geology (Sato, 1994, JGR). Those studies suggested the OBR was supposed to be uplifted rapidly, mainly because of the E-W compressive stress since the Quaternary, however, uplift/denudation histories of the OBR were not uncovered quantitatively. Developments of thermochronology in three decades enabled to quantitatively reconstruct uplift/denudation histories even for low relief mountains like in Japan Islands (Sueoka et al., 2016, Geosci. Front.). Thus, thermochronologic studies have been recently conducted in the NE Japan Arc based on low-temperature thermochronometers, such as apatite fission-track (AFT) (Fukuda et al., 2019, JAES:X) and (U-Th)/He (Sueoka et al., 2017, EPS; Fukuda et al., 2020, EPS) methods. As the latest one, Fukuda et al. (submitted) preformed AFT and apatite (U-Th)/He thermochronometric mapping at intervals of 1-few km across the southern part of the OBR. This study proposed that the OBR has possibly been uplifted in domal on geologic timescales. Hence, such implications of uplift style of the OBR in a typical island arc are expected to provide the deformation model for a general volcanic arc distributed in plate subduction boundaries as well as tectonic histories in the NE Japan Arc. For elucidating the mountain building process of the OBR on the 106 yrs. timescale, this study has conducted AFT mapping along the E-W traverses of the northern part of the OBR as a low-temperature thermochronometer (Tc of 90-120°C: Ketcham et al., 1999, Am. Mineral.), also attempting to quantitatively constrain the uplift model based on the spatial pattern of obtained AFT ages across the OBR.
We newly conducted AFT dating for 7 localities of the Cretaceous-Miocene granitoids collected from the northern part of the OBR. The number of FTs and the U contents in apatites were determined by FT automated counting system (TrackScan Plus Professional) and laser ablation-inductively coupled plasma-mass spectrometer (Analyte G2: ArF 193nm excimer laser + Agilent 7700x: ICP-QMS), respectively, housed in Tono Geoscience Center, JAEA. These samples yielded AFT ages of the range of few tens to several Ma, implying that consistent with AFT data of previous study (Fukuda et al., submitted). Moreover, such younger ages of several Ma probably reflected uplift/denudation by the recent E-W compressive stress accelerated since 6.5 Ma or 3-2 Ma (e.g., Nakajima, 2013). In this presentation, we will discuss the spatial pattern of AFT ages across the northern part of the OBR, and the uplift model of the overall OBR by integrated with previously reported ages in the south.