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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.
南 沙樹*; 末岡 茂; 福田 将眞; Malatesta, L.*; Kohn, B. P.*; 河上 哲生*; 東野 文子*; 梶田 侑弥*; 田上 高広*
no journal, ,
We attempt to constrain a reliable exhumation history for the youngest plutons, central Tanigawa-dake area, using two methods: (1) Al-in-Hbl geobarometry to estimate emplacement depths and (2) 1D numerical simulation to explore the best exhumation/cooling histories that fit the reported zircon U-Pb, zircon and apatite (U-Th)/He (ZHe and AHe) dates. As a result of Al-in-Hbl geobarometry, solidification pressures of 0.9-2.6 kbar were obtained. Emplacement depths of 3.4-9.5 km were estimated from the pressures and a crustal density of 2.7 g/cm
. 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. As a result of the 1D numerical simulation, the best exhumation rate is estimated to be ca. 1.2 mm/yr and the best emplacement depth is ca. 4.0 km. Comparing with the AHe-derived exhumation rate (0.8-1.7 mm/yr) in the same pluton, the geobarometry-derived exhumation rate (1.0-2.9 mm/yr) are comparable or higher. The modeled exhumation rate (1.2 mm/yr) is within the range of the exhumation rates estimated by the AHe age. This indicates that the AHe date of the ca. 3.3 Ma pluton does not reflect the initial cooling but exhumation. Consequently, the exhumation rate calculated from the AHe dates and current geothermal gradient were consistent with those obtained from the combination of geobarometry, zircon U-Pb dating and numerical thermal modeling.
Malatesta, L.*; Huppert, K.*; Weiss, N.-M.*; Asiedu, R.*; Finnegan, N.*; 末岡 茂
no journal, ,
Erosive marine terraces offer a precious record of crustal strain across hundreds of earthquake cycles along subduction zones. The predominant paradigm that terrace steps correctly reflect unique sea level high stands is significantly weakened when considering the continuous work of wave erosion regardless of sea level stand. A better understanding of the actual information encoded in erosive marine terraces hinges on grasping the dominant processes that control their generation and preservation. Here, we exploit a large dataset of 5352 marine terraces of presumed last interglacial high stand age combined a reconstruction of local wave power around the archipelago. We identify three main boundary envelopes to the distribution of presumed MIS 5e terraces when the entire dataset is displayed as a function of their mean elevation and surface area, and attribute it to potential controls: 1) There are no large terraces preserved at low elevation because waves can more easily erode platforms that reside in or near the swash zone, 2) Terrace surface area reaches a maximum around 30 masl before declining again with higher elevation because faster rock uplift rates reduce the time that waves have to erode any given bedrock elevation, 3) The minimum area of terraces increases with elevation because under faster rock uplift, subaerial erosion processes tend to be more efficient and destroy small platforms. Further study of the dataset - in particular accounting for lithology - will provide valuable insights to universal controls on marine terrace creation and preservation.
Malatesta, L.*; Weiss, N.-M.*; 石村 大輔*; Gailleton, B.*; 西村 卓也*; 高橋 直也*; 塚本 すみ子*; 小松 哲也; 岩佐 佳哉*; 末岡 茂; et al.
no journal, ,
本発表では、令和6年能登半島地震において発生した沿岸部の地形変化、特に隆起分布について着目し、それらと更新世の海成段丘群の高度分布との比較から、過去約100万年間の能登半島におけるテクトニクスや変動地形について考察した。
Malatesta, L.*; Huppert, K.*; 末岡 茂; Finnegan, N.*; Asiedu, R.*; Weiss, N.-M.*
no journal, ,
A dataset of over 6000 wave-cut marine terraces of presumed Last Interglacial high-stand age (~120 ka) around the Japan islands provides an unprecedented access to the controls on the generation and preservation of marine terraces. The data is a subset from the Atlas of Marine Terraces later digitized, and carefully corrected and redrawn by ourselves. The terrace dataset is complemented by wave power estimates from NOAA WaveWatch III and bedrock lithology information from the Geological Survey of Japan. Each individual terrace is matched with topographic information, local wave condition, lithology, and local relief. Along the subductions, terraces show an increase in elevation toward the trench reflecting non-recoverable deformation linked to the earthquake cycle. On the back arc side, terrace elevation can vary between ~0 and 150 masl over short distances (
20 km). We can identify the signature of the Niigata-Kobe Tectonic Zone responsible for the small block tilting noted by Ota and Yoshikawa (1978) along the coast of the back arc. Ongoing study of the dataset provides valuable insights to universal controls on marine terrace creation and preservation. We use their elevations as an indicator of relative patterns in rock uplift (precise ages and corresponding sea level stage are rarely available). At the time of abstract submission, we have identified the following: There are no large terraces preserved at low elevation as waves may more easily erode platforms residing in or near the swash zone. Terrace surface area reaches a maximum around 30 masl before declining again with higher elevation because faster rock uplift rates may reduce the time that waves have to erode any given bedrock elevation. The minimum area of terraces increases with elevation as subaerial erosion processes would tend to be more efficient under faster rock uplift. Lithology does not play a first-order role in controlling the distribution of terraces across elevation and wave power.
Malatesta, L.*; Weiss, N.-M.*; 塚本 すみ子*; 末岡 茂; 石村 大輔*; Gailleton, B.*; 西村 卓也*; 高橋 直也*; 片岡 香子*; 小松 哲也; et al.
no journal, ,
On January 1st, 2024, the Mw 7.5 Noto Peninsula earthquake ruptured on a series of coastal offshore reverse faults in the back arc of central Japan. Recent Holocene terraces mapped along the northern coast, where coseismic uplift was greatest on January 1st 2024, suggest that they may be attributable to similar past ruptures. The Peninsula itself is remarkable for its 4767 unique terraces ranging in age from Holocene to 1.02 Ma. We digitized all terraces and recorded the elevation of their landward edge, and derived a rock uplift rate for each based on their age and the corresponding original sea level. The southeast-tilting crustal deformation recorded by the terraces associated with the last two interglacial high stands strongly resembles that caused by the Mw 7.5 earthquake. Older terraces, on the contrary all record a spatially uniform rate of uplift across the Peninsula. We conclude that the faults that caused the most recent earthquake became the dominant structures on the Peninsula over a quarter million year ago. This onset of seismogenic activity informs us about the regional plate tectonics of the area. The boundary separating Eurasia from the North American Plate currently runs south of the Noto Peninsula, linking the cities of Niigata and Kobe along a northeast-striking Tectonic Zone (NKTZ). Immediately east of the Peninsula lies another north-striking Tectonic Line, from Itoigawa to Shizuoka (ISTL). East of the ISTL and north of the NKTZ is the Island of Sado, which terraces also suggest a change in deformation with strong southeast tilting synchronous and similar to Noto. Together, Noto and Sado act as a railroad switch, indicating which of the ISTL or the NKTZ is the active plate boundary. When the ISTL is active, the sites are on different tectonic plates and evolve differently. When the NKTZ takes over, Sado Island becomes part of Eurasia and is more likely to evolve similarly to the Noto Peninsula.