Earth and Space Science Open Archive PosterOpen AccessYou are viewing the latest version by default [v1]Multi-OSL-thermochronometry using deep borehole core for thermal history over 0.1 Myr in Rokko MountainsAuthorsManabuOgataiDGeorginaKingFredericHermanRyujiYamadaKentaroOmuraShigeruSueokaiDSee all authors Manabu OgataiDCorresponding Author• Submitting AuthorJapan Atomic Energy AgencyiDhttps://orcid.org/0000-0003-1440-6127view email addressThe email was not providedcopy email addressGeorgina KingUniversity of Lausanneview email addressThe email was not providedcopy email addressFrederic HermanUniversity of Lausanneview email addressThe email was not providedcopy email addressRyuji YamadaNational Research Institute for Earth Science and Disaster Preventionview email addressThe email was not providedcopy email addressKentaro OmuraNational Research Institute for Earth Science and Disaster Preventionview email addressThe email was not providedcopy email addressShigeru SueokaiDJapan Atomic Energy AgencyiDhttps://orcid.org/0000-0002-5264-2713view email addressThe email was not providedcopy email address
Abstract The C retaceous T oki granitic pluton of the T ono district, central J apan was emplaced in the E ast A sian continental margin at about 70 Ma. The T oki 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 T oki 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 T oki granitic pluton and was related to the regional denudation of the T ono district. The age–elevation relationships ( AER s) of the T oki 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 HeFT y 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 AER s and AFT inverse calculations represents the following exhumation history of the T oki 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 T ono district, which contains the T oki granite, underwent slow denudation at a rate of less than 0.16 ±0.04 mm/year within the E ast A sian continental margin before the J apan S ea opening at 25–15 Ma and then within the S outhwest J apan A rc after the J apan S ea opening, which is in good agreement with representative denudation rates obtained in low‐relief hill and plain fields.
The impact of Quaternary climate change on landscape evolution, and more specifically the timing of incision of the overdeepened Alpine valleys, remains difficult to quantify with existing thermochronometric methods. Thermochronometers are used to determine rates of rock cooling, however most techniques are insensitive to temperature changes <60 °C that occur within the last kms of Earth’s crust. Recording cooling rates within this temperature range is essential if the impact of glacial-interglacial cycles on rock exhumation is to be resolved.Electron spin resonance (ESR) thermochronometry applied to quartz minerals has the potential to span this thermal (and temporal) gap. We are developing this method by building upon previous studies (e.g. Scherrer, 1993) with the ultimate aim of constraining the timing of incision of the Rhône valley. Preliminary data from the Japanese Alps (King et al., 2020) indicate that ESR thermochronometry could resolve rates of <1 mm/yr over Quaternary timescales.To determine a rock cooling history using ESR thermochronometry, signal accumulation and signal thermal loss must be robustly determined within the laboratory. We have collected a series of geological samples including rocks from boreholes that have known isothermal histories to investigate the potential of this technique. Our objective is to use the latter rocks to confirm the validity of our laboratory measurements and data-fitting/numerical models. Specifically, we have investigated known-thermal history samples from the MIZ1 borehole (Japan) and the KTB borehole (Germany) as well as samples from Sion in the Western European Alps.Preliminary data reveal that the ESR dose response and thermal decay of different quartz samples is highly variable. Whereas the Al-centre of some samples exhibits linear dose response to laboratory irradiation up to 15 kGy, the Al-centre of other samples exhibits exponential, or double-exponential growth and saturates at doses of 3-4 kGy. The Ti-centre of most samples is well described by a single saturating exponential function, however samples from the MIZ1 borehole exhibit pronounced sub-linearity in the low-dose response region. Furthermore, whereas for some samples the Al-centre is less thermally stable than the Ti-centre, for other samples the inverse is observed. These observations suggest that a uniform measurement protocol and data-fitting approach may not be appropriate for quartz ESR data.Inversion of two KTB samples yielded temperatures within uncertainty of borehole temperature, however results for the MIZ1 borehole are more variable and can only recover temperature at best within ~10%. Investigations into the cause of the poor results for the MIZ1 borehole are ongoing (i.e. measurement protocol, data-fitting/numerical model) and will be discussed. Preliminary data from Sion are promising and reveal consistent cooling rates. Scherer, T., Agel, A., and Hafner S. S.: Determination of uplift rates using ESR investigations of quartz, KTB Rep. 93-2. Kontinentales Tiefbohrprogram der Bundesrepublic Deutschland Niedersächs. Landesamt Bodenforsch., Hannover, 121–124, 1993.King, G.E., Tsukamoto, S., Herman, F., Biswas, R.H., Sueoka, S., Tagami, T. Electron spin resonance (ESR) thermochronometry of the Hida range of the Japanese Alps: validation and future potential. Geochronology 2, no. 1 (2020): 1-15.   
Zircon U-Pb dating was carried out on granitic rocks from plutons in the Taiheizan Complex in Akita Prefecture, NE Japan. Two granodiorites from the Main Intrusive Rocks yielded weighted mean 206Pb/238U dates of 103.4±1.0 Ma and 115.6±1.1 Ma (1SE). Three porphyrygranite from the Young Intrusive Rocks yielded weighted mean 206Pb/238U dates of 11.4±0.1 Ma, 4.7±Ma, and 4.8±0.1 Ma (1SE). The older and younger dates can be interpreted as the ages of early and later stages of granitic intrusion at the sampling locations. The Pliocene U-Pb dates suggest that the Nibetsu Body in the Young Intrusive Rocks is one of the youngest granitic plutons currently exposed on Earth.
Abstract Solidification pressures and ages of mafic microgranular enclaves (MMEs) and their host granite were determined and compared based on Al‐in‐hornblende geobarometry and U–Pb zircon dating in two sample localities in the Kurobegawa Granite. In sample KRG19‐A03 from the middle unit of the pluton, the MME and the host granite yielded 0.18 ± 0.03 to 0.24 ± 0.04 GPa and 0.16 ± 0.03 to 0.23 ± 0.04 GPa, respectively. The MME and the host granite of sample KRG19‐B08b from the lower unit, respectively, yielded 0.12 ± 0.02 to 0.21 ± 0.03 GPa and 0.13 ± 0.02 to 0.18 ± 0.03 GPa. In each sample locality, the estimated solidification pressures of the MME and its host granite overlap. The weighted mean ages were calculated as 0.775 ± 0.045 Ma and 0.831 ± 0.055 Ma for the MME and the host granite of KRG19‐A03, respectively. The MME and the host granite of KRG19‐B08b, respectively, yielded 0.672 ± 0.033 Ma and 0.735 ± 0.042 Ma. The ages for MMEs tend to be younger than the host granites, although they overlap within uncertainty. Zircon commonly occurs as the matrix minerals in both lithologies, meanwhile, zircon also occurs as early phases in plagioclase cores only in the host granites. Such differences in mode of occurrence of zircon suggest that the age variation reflects the differences in timing of zircon crystallization between the lithologies. Therefore, the MMEs record the same solidification pressures as the host granites and better represent the final solidification timing of the pluton. From these data of the MMEs, an average exhumation rate of each sample locality was estimated as 7.1–14.5 mm/year (KRG19‐A03) and 5.5–14.4 mm/year (KRG19‐B08b). These exhumation rates are much larger than that of the ca. 5.6–5.2 Ma Shiaidani Granodiorite (0.93–2.5 mm/year), implying that drastic change of the exhumation rate took place between ca. 5.2 Ma and ca. 0.83 Ma.
<p>The exhumation of bedrock is controlled by the interplay between tectonics, surface processes and climate. The highest exhumation rates of cm/yr are recorded in zones of highly active tectonic convergence such as the southern Alps of New Zealand or Himalayan syntaxes, where high rock uplift rates combine with very active surface processes. Here, we use a combination of different thermochronometric systems, and notably trapped-charge thermochronometery, to show that such rates also occur in the Hida Range, Japanese Alps. Our results imply that cm/yr rates of exhumation may be more common than previously thought.</p><p>The Hida Range is the most northern and most extensive of the Japanese Alps, and reaches elevations of up to 3000 m a.s.l. The Hida Range is thought to have uplifted in the last 3 Myr in response to E-W compression and magmatism. Our study focuses on samples from the Kurobe gorge, which is one of the steepest gorges in Japan. Previous work has shown that exhumation rates in this region are exceptionally high, as documented by the exposure of the ~0.8 Ma Kurobe granite (Ito et al., 2013) in the gorge. We combined 12 new zircon (U-Th/He) ages and 11 new OSL-thermochronometry ages together with existing thermochronometric data to investigate the late Pleistocene exhumation of this region.</p><p>We found that exhumation rates increased to ~10 mm/yr within the past 300 kyr, likely in response to river base-level fall that increased channel steepness due to climatically controlled eustatic changes. Our thermochronometry data allow the development of time-series of exhumation rate changes at the timescale of glacial-interglacial cycles and show a four-fold increase in baseline rates over the past ~65 kyr. This increase in exhumation rate is likely explained by knickpoint propagation due to a combination of very high precipitation rates, climatic change, sea-level fall, range-front faulting and moderate rock uplift. Our data show that in regions with horizontal convergence, coupling between climate, surface processes and tectonics can exert a significant effect on rates of exhumation.</p><p><strong>References</strong></p><p>Ito, H., Yamada, R., Tamura, A., Arai, S., Horie, K., Hokada T., 2013. Earth&#8217;s youngest exposed granite and its tectonic implications: the 10-0.8 Ma Kurobegawa Granite. Scientific Reports 3: 1306.</p><p>&#160;</p>
Phase relation in the NaAlSiO 4 -SiO 2 -H 2 O system for the hydrothermal precipitation of jadeite, albite, natrolite, and analcime in jadeitite of the Itoigawa-Omi area, Japan ･････････････････････････････････････････Atsushi GOTO, Keitaro KUNUGIZA, Hiroshi MIYAJIMA ･･････ 271 Chemical composition of fluid inclusions in the Yorii jadeite-quartz rocks from the Kanto Mountains, Japan ･･････････････････････Mayuko FUKUYAMA, Tatsuhiko KAWAMOTO, Masatsugu OGASAWARA ･･････ 281 Cathodoluminescence petrography of P-type jadeitites from the New Idria serpentinite body, California
Abstract Fission track (FT), (U‐Th)/He (He), and U‐Pb data were used to identify the denudation history of the Akaishi Range, central Japan. The northern Akaishi Range is bounded on the east by the Itoigawa‐Shizuoka Tectonic Line Fault Zone (ISTL‐FZ). The thermochronometric ages progressively decrease with the decreasing distance to the ISTL‐FZ. Thermokinematic calculations suggest that the age pattern observed can be explained by 5–7.5 mm/yr reverse slip on the ISTL‐FZ that dips 34–45° west and soles onto detachment at 20–22.5 km depth. By assuming the same geometry and slip rate of the fault, the bedrock uplift rates and denudation rates are estimated at ~4 mm/yr. Thus, the uplift and denudation style of the northern Akaishi Range is well explained as a simple tilted thrust block that has been exhumed along the listric ISTL‐FZ. On the other hand, considering both the difference in apatite FT age and the active fault distribution, the southern Akaishi Range might be different in uplift origin and timing, although the difference in apatite FT ages between them may be attributable to the chlorine content variation in apatite. The inferred total denudation is larger than several kilometers and likely exceeds 10 km since the beginning of the northern Akaishi Range uplift, suggesting that the low‐relief surfaces on the ridges and the relatively constant elevations of the summits reflect postuplift denudation rather than preexisting low‐relief landforms.
