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田上 高広*; 長谷部 徳子*; 末岡 茂
no journal, ,
Recent progress of low-temperature thermochronology enables to analyze uplift-exhumation-cooling histories of the island-arc mountains with good confidence. This is particularly fruitful for studying the topographic evolution of the Japan Arc, because many of the Japanese mountains are started to uplift in recent time (e.g., late Pliocene to Quaternary) after an extended period of tectonic quiescence, and hence the resultant amount of total denudation is relatively small. The utility of the approach was first demonstrated by elucidating the uplift-exhumation-cooling process for some of the Japan Alps, in which average topographic changes of the tilted mountain block were quantitatively reconstructed by low-temperature thermochronology. Such analyses also allow to estimate the background paleo-depth of neo-tectonic faulting episodes. In this presentation, we highlight recent and ongoing important thermochronological research in and around the Japan Arc. In addition, we will promote the Thermo2025 conference and introduce its preliminary plans. The International Conference on Thermochronology has been held biyearly around the world and the International Standing Committee on Thermochronology (ISCT) determined that the 19th conference (Thermo2025) will be held in Kanazawa, Japan, on September 14-20th, 2025 (https://isct.sedoo.fr/meetings-2/). Then, the local organizing committee, including the authors, have promoted the preparation of the conference in partnership with the domestic geoscience societies and international thermochronological communities. Pre-registration of Thermo2025 is now being accepted at the website (https://smartconf.jp/content/thermo2025). Those who are interested in the conference can soon receive the announcements by pre-registration.
南 沙樹*; 末岡 茂; 福田 将眞; Malatesta, L.*; 河上 哲生*; 東野 文子*; 梶田 侑弥*; 田上 高広*
no journal, ,
The Tanigawa-dake area, in the southern end of the Northeast Japan arc, hosts such granites of late Miocene to Pliocene ages ranging from 6.0-5.5 Ma, ca 4.0 Ma to 3.3-3.2 Ma (zircon U-Pb). Previous studies also reported zircon (U-Th)/He dates (ZHe) of 3.3-1.4 Ma and apatite (U-Th-Sm)/He (AHe) dates of 2.8-1.0 Ma for these young granites and the Cretaceous granites. Exhumation rates of 0.3-1.7 mm/yr were estimated by AHe dates and assumption of constant geothermal gradients of 40-60 K/km. However, the AHe dates might reflect initial cooling phase of the young plutons as well as cooling derived from exhumation, potentially leading to an overestimation of exhumation rates in the Tanigawa-dake area. This study aims to constrain a more reliable exhumation history. We applied two methods for the youngest pluton (ca 3.3 Ma): (1) Al-in-Hbl geobarometry to estimate the emplacement depth and (2) 1D numerical simulation of geothermal structure based on heat advection-diffusion-production equation to explore the best cooling/exhumation histories consistent with the reported zircon U-Pb age, ZHe and AHe dates. As a result of Al-in-Hbl geobarometry, solidification pressures of 0.9-2.6 kbar were estimated. Emplacement depths derived from these pressures are 3.4-9.5 km. Exhumation rates were calculated to be 1.0-2.9 mm/yr for the youngest pluton, assuming an intrusive age of ca 3.3 Ma. In the 1D heat advection-diffusion-generation model, the best exhumation rates are ca 1.2 mm/yr and the best emplacement depth is ca 4.0 km. Comparing with the exhumation rate estimated from the AHe age of ca 1.0 Ma in the same pluton, the exhumation rates by geobarometry are equal to or higher than the rate by AHe date. Similarly, the modeled rate fits with the exhumation rate by AHe age. This indicates that the initial cooling was finished by the time of the AHe date for ca 3 Ma pluton, i.e., the previous geothermal structure in this area had relaxed to the current one.
Malatesta, L.*; 末岡 茂; 片岡 香子*; 小松 哲也; 塚本 すみ子*; Bruhat, L.*; Olive, J.-A.*
no journal, ,
On January 1st 2024, a Mw 7.6 earthquake shook the Noto Peninsula on the Sea of Japan coast of Central Japan. A large number of landslides and rockfalls dissected the road network. Liquefaction damaged infrastructure up to 150 km away from the epicenter. Meter-scale coseismic uplift modified the northern shoreline with displacement of the coastline by up to 200 m seaward discernible on SAR and aerial image data. At the time of abstract submission, we only have limited preliminary observations. It appears that the Noto Earthquake ruptured the same or adjacent fault to the May 5 2023 Mw 6.5 earthquake and was in the vicinity of the March 25 2007 Mw 6.9 Noto earthquake. Coseismic displacement measured geodetically shows uplift of up to +3-4 m (SAR) in the northwest of the peninsula, and +1.06 m (GPS) in the main town of Wajima-shi. The uplift magnitude decreases gradually to the SE. The uplift is near zero (SAR) or -0.3 m (GPS) on Noto Island 30 km to the south of the town of Wajima. Surface deformation goes back to near zero (GPS) a further 20 km to the south. The coseismic deformation pattern broadly reflects the deformation recorded in the Noto landscape. Long-term moderate rock uplift in the north gives way to a complex history of long-term slow uplift around Noto Island that likely includes sustained episodes of subsidence, highlighted by its sinuous "drowned" coastline. Along the western shore, marine terraces presumed to be 120 ka (last Interglacial) show a gradient in elevation also decreasing to the south. In the north, the newly emerged platform does not have a higher marine terrace counterpart. This may reflect the relationship between high wave power and moderate rock uplift resulting in the long-term retreat of the coastline and erosion of any terrace. The Noto Peninsula also holds widespread evidence of drainage reorganization that would reflect varying boundary conditions, in particular rock uplift, in deeper time beyond 100s ka.