Preliminary report on the significance of magmatic enclaves in adakite genesis at Hakusan volcano, central Japan

Ujike, Osamu; Mashimo, Reina

doi:10.2465/jmps.081011

Cited by 5 publications

(5 citation statements)

References 9 publications

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“…This interpretation is consistent with studies of 3 He/ 4 He ratios and the geochemistry of volcanic rocks [ Sano and Wakita , ; Iio et al ., ; Nakamura et al ., ]. In addition, adakites have been found in central Japan [e.g., Ujike et al ., ; Ujike and Mashimo , ; Nakamura and Iwamori , ]. Adakites have not elucidated the production mechanisms.…”

Section: Discussionmentioning

confidence: 99%

Deep slab dehydration and large‐scale upwelling flow in the upper mantle beneath the Japan Sea

et al. 2015

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We present a three-dimensional P and S wave tomography model beneath the central Japan Sea using arrival time data obtained by long-term ocean bottom seismometer observations. The tomographic model is determined down to over 300 km. The resulting tomographic image has two features in the mantle wedge. First, a remarkable low-velocity region is spread within the shallow part of the mantle wedge beneath the Japan arc with a slight extension beneath the Japan Sea. Second, an inclined low-velocity anomaly exists in the deeper part beneath the Japan Sea and converges to the slab at~300 km depth. Moreover, its anomaly amplitude is distinctly small compared to the shallow part of the low-velocity region. These low-velocity anomalies are interpreted to represent fluids that were dehydrated from the Pacific and Philippine Sea slabs and melt production affected by the fluid. Our observations suggest that the deep dehydration from the Pacific slab is found at a depth of approximately 300 km and large-scale upwelling flow mechanically induced by plate subduction exists beneath the Japan Sea. Our results indicate the importance of the deep heterogeneous mantle wedge structure beneath the Japan Sea with regards to better understanding the magmatism of the subduction dynamics in Japan and the evolution of the opening of the Japan Sea.

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Section: Discussionmentioning

confidence: 99%

Deep slab dehydration and large‐scale upwelling flow in the upper mantle beneath the Japan Sea

et al. 2015

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“…Nakamura et al (2008) pointed out that a relatively large amount of fluids from the Philippine Sea plate contributes to magmatism at Hakusan. Ujike and Mashimo (2009) also suggested that adakitic magmas erupting from Hakusan are affected by fluids from the oceanic crust of the subducting Philippine Sea plate. These results suggest that aqueous fluids originating from the subducting Philippine Sea slab migrate through the upwelling flow and are consequently supplied to the lower crust around the Atotsugawa fault as well as the NKTZ.…”

Section: Deep Origin Of Fluids In the Lower Crustmentioning

confidence: 99%

“…Geochemical analyses of rock samples have suggested lower crustal melting beneath Hakusan (Ujike and Mashimo, 2009) and the existence of a basaltic magma chamber in the lower crust beneath Ontake volcano, located south of Tateyama (Kimura and Yoshida, 1999). Therefore, under the assumption that partial melting occurs in the lower crust, we evaluate aspect ratios and volume fractions of melts beneath the two volcanoes.…”

Section: Low-velocity Zones Beneath Volcanoes On the Bothmentioning

confidence: 99%

Deep crustal structure around the Atotsugawa fault system, central Japan: A weak zone below the seismogenic zone and its role in earthquake generation

et al. 2010

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We carried out travel-time tomography around the Atotsugawa fault in central Japan, using arrival-time data obtained from a dense temporary seismograph network in joint observations by the Japanese University group. The observed velocities beneath the fault are 10-13% lower than those of the assumed host rocks (pyroxene amphibolite and hornblende-pyroxene gabbro) in the lower crust. Because the seismogenic layer is thickest in the central part of the fault, reaching a depth of ∼15 km, we infer that the low-velocity anomaly is caused by aqueous uids. Fluid fractions in the lower crust are estimated to be 2-3% and ∼10%, assuming pyroxene amphibolite and hornblende-pyroxene gabbro, respectively. A distinct low-velocity anomaly is imaged in the central part of the Atotsugawa fault at a depth of 10 km, where seismic activity is very low at the upper 7 km and creeplike movement is observed at the surface. This anomaly is horizontally isolated but vertically connected to the lowvelocity anomaly in the lower crust. We interpreted that abundant aqueous uids supplied from the lower crust are responsible for this anomaly. High pore uid pressure may enhance the stability of frictional slip, resulting in aseismic or episodic slip along the fault.

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“…Hakusan (Ishikawa, Japan; Fig. ) is a composite volcano that is 2702 m high and comprised of three stratovolcanoes: (a) 0.43‐0.32 Ma Kagamuro; (b) 0.14–0.06 Ma Ko‐Hakusan; and, (c) 0.03 Ma Shin‐Hakusan (Ujike & Mashimo ). The lavas of these three volcanoes consist of calc‐alkaline orthopyroxene and hornblende andesite (Wang et al .…”

Section: Study Areamentioning

confidence: 99%

“… A regional map with the locations of the 25 in‐field survey and sampling sites (after Ujike & Mashimo ).…”

Section: Study Areamentioning

confidence: 99%

Magnetic measurements of roadside topsoil pollution in an active volcanic region: Mt. Hakusan, Japan

Kawasaki

Fukushi

Sakai

2018

Water & Environment J

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Environmental magnetic applications to topsoil have proved useful for investigating roadside pollution. However, such magnetic monitoring has been avoided in volcanic regions due to the high magnetic content in volcanic ash. Environmental magnetic studies are reported for the volcanically active Mt. Hakusan National Park in Japan. In‐field magnetic susceptibility measurements along the park's major road show higher magnetic susceptibilities in topsoils within 1.5 m from the roadside. However, laboratory mass susceptibility measurements fail to show a similar susceptibility trend to the field measurements. Based on rock magnetic analyses, the major magnetic mineral is pseudosingle‐ to multidomain (MD) magnetite that is both increased in abundance in MD and oxidized magnetite near the roadside, indicating that passing vehicles are evidently the main pollutant source. Therefore, even in an active volcanic region where magnetic susceptibility may not be an efficient tool, detailed magnetic measurements can provide the basis for the discrimination of roadside pollution.

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Preliminary report on the significance of magmatic enclaves in adakite genesis at Hakusan volcano, central Japan

Cited by 5 publications

References 9 publications

Deep slab dehydration and large‐scale upwelling flow in the upper mantle beneath the Japan Sea

Deep slab dehydration and large‐scale upwelling flow in the upper mantle beneath the Japan Sea

Deep crustal structure around the Atotsugawa fault system, central Japan: A weak zone below the seismogenic zone and its role in earthquake generation

Magnetic measurements of roadside topsoil pollution in an active volcanic region: Mt. Hakusan, Japan

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