Spatial distribution of the apatite fission‐track ages in the Toki granite, central Japan: Exhumation rate of a Cretaceous pluton emplaced in the East Asian continental margin

Abstract

The Cretaceous Toki granitic pluton of the Tono district, central Japan was emplaced in the East Asian continental margin at about 70 Ma. The Toki granite has apatite fission‐track (AFT) ages ranging from 52.1 ±2.8 Ma to 37.1 ±3.6 Ma (number of measurements, n = 33); this indicates the three‐dimensional thermal evolution during the pluton's low‐temperature history (temperature in the AFT partial annealing zone: 60–120 °C). The majority of the Toki granite has a spatial distribution of older ages in the shallower parts and younger ages in the deeper parts, representing that the shallower regions arrived (were exhumed) at the AFT closure depth earlier than the deeper regions. Such a cooling pattern was predominantly constrained by the exhumation of the Toki granitic pluton and was related to the regional denudation of the Tono district. The age–elevation relationships (AERs) of the Toki granite indicate a fast exhumation rate of about 0.16 ±0.04 mm/year between 50 Ma and 40 Ma. The AFT inverse calculation using HeFTy program gives time‐temperature paths (t–T paths), suggesting that the pluton experienced continuous slow cooling without massive reheating since about 40 Ma until the present day. A combination of the AERs and AFT inverse calculations represents the following exhumation history of the Toki granite: (i) the fast exhumation at a rate of 0.16 ±0.04 mm/year between 50 Ma and 40 Ma; (ii) slow exhumation at less than 0.16 ±0.04 mm/year after 40 Ma; and (iii) exposure at the surface prior to 30–20 Ma. The Tono district, which contains the Toki granite, underwent slow denudation at a rate of less than 0.16 ±0.04 mm/year within the East Asian continental margin before the Japan Sea opening at 25–15 Ma and then within the Southwest Japan Arc after the Japan Sea opening, which is in good agreement with representative denudation rates obtained in low‐relief hill and plain fields.

Rapid Exhumation of Earth's Youngest Exposed Granites Driven by Subduction of an Oceanic Arc

“…Terrestrial in situ cosmogenic nuclides Hasebe et al, 2000;Ito & Tanaka, 1999;Kamp & Takemura, 1993;Sueoka et al, 2012Sueoka et al, , 2017Tagami & Shibata, 1993;Yamada & Harayama, 1999;Yamada & Tagami, 2008;Yuguchi et al, 2011Yuguchi et al, , 2017and this study. Terrestrial in situ cosmogenic nuclides Hasebe et al, 2000;Ito & Tanaka, 1999;Kamp & Takemura, 1993;Sueoka et al, 2012Sueoka et al, , 2017Tagami & Shibata, 1993;Yamada & Harayama, 1999;Yamada & Tagami, 2008;Yuguchi et al, 2011Yuguchi et al, , 2017and this study.…”

“…Terrestrial in situ cosmogenic nuclides There is a clear zone of high exhumation that is centered on the Hida Mountain Range (HMR). Data are compiled from Hasebe et al, 2000;Ito & Tanaka, 1999;Kamp & Takemura, 1993;Sueoka et al, 2012Sueoka et al, , 2017Tagami & Shibata, 1993;Yamada & Harayama, 1999;Yamada & Tagami, 2008;Yuguchi et al, 2011Yuguchi et al, , 2017and this study. (b) Simplified map of the major tectonic structures of central Japan (Yamamoto et al, 2009).…”

Genesis and development processes of fractures in granite: Petrographic indicators of hydrothermal alteration

“…The Toki granite underwent exhumation during the period between ca. 50 Ma and the present [ 42 ]. The intersection of the t-T path and temporal condition of 50 Ma yields about 100–200°C.…”

Mass transfer associated with chloritization in the hydrothermal alteration process of granitic pluton

“…The Toki granite has a whole-rock Rb-Sr isochron age of 72.3 ± 3.9 Ma (Shibata and Ishihara, 1979), a monazite chemical Th-U-total Pb isochron (CHIME) age of 68.3 ± 1.8 Ma (Suzuki and Adachi, 1998), zircon U-Pb ages of 74.7 ± 4.2 to 70.4 ± 1.7 Ma (Yuguchi et al, 2016), a hornblende K-Ar age of 74.3 ± 3.7 Ma (Yuguchi et al, 2011A), biotite K-Ar ages of 78.5 ± 3.9 to 59.7 ± 1.5 Ma (N = 33: Yuguchi et al, 2011A), zircon fission-track (ZFT) ages of 75.6 ± 3.3 to 52.8 ± 2.6 Ma (N = 44: Yuguchi et al, 2011A), and apatite fission-track (AFT) ages ranging from 52.1 ± 2.8 to 37.1 ± 3.6 Ma (N = 33: Yuguchi et al, 2017). Based on the phase relationships, Yamasaki and Umeda (2012) estimated that the emplacement depth of granitic magma was about 5-7 km below the surface.…”