Magma Reservoir and Magmatic Feeding System beneath Hakone Volcano, Central Japan, Revealed by Highly Resolved Velocity Structure

2021 ◽  
Author(s):  
Y. Yukutake ◽  
Y. Abe ◽  
R. Honda ◽  
S. Sakai
Keyword(s):  
Velocity Structure ◽  
Magma Reservoir ◽  
Feeding System ◽  
Central Japan ◽  
Hakone Volcano ◽  
Magmatic Feeding System

scholarly journals P-wave velocity structure in the northern part of the central Japan Basin, Japan Sea with ocean bottom seismometers and airguns

2004 ◽  
Vol 56 (5) ◽  
pp. 501-510 ◽  
Author(s):  
Takeshi Sato ◽  
Masanao Shinohara ◽  
Boris Y. Karp ◽  
Ruslan G. Kulinich ◽  
Nobuhiro Isezaki
Keyword(s):  
Wave Velocity ◽  
Velocity Structure ◽  
Japan Sea ◽  
P Wave ◽  
Ocean Bottom ◽  
Japan Basin ◽  
Central Japan ◽  
P Wave Velocity ◽  
Ocean Bottom Seismometers ◽  
P Wave Velocity Structure

Upper mantle P-wave velocity structure in the Japan region from travel-time studies of deep earthquakes using a new analytical method

1971 ◽  
Vol 61 (6) ◽  
pp. 1549-1570
Author(s):  
K. L. Kaila ◽  
V. G. Krishna ◽  
Hari Narain
Keyword(s):  
Wave Velocity ◽  
Calibration Curve ◽  
Velocity Gradient ◽  
Upper Mantle ◽  
Inflection Point ◽  
Velocity Structure ◽  
P Wave ◽  
Central Japan ◽  
P Wave Velocity ◽  
P Wave Velocity Structure

abstract The upper mantle P-wave velocity structure of the region of Japan has been studied in great detail from travel times of 107 earthquakes with focal depths varying from 40 to 600 km, using a new analytical method given by Kaila (1969). In southwestern Japan the P-wave velocity is found to be 7.88 km/sec at a 40-km depth, and it remains almost constant to a depth of 255 km. For northeastern Japan the velocity, determined as 7.88 km/sec at 40 km, increases linearly with moderate gradient to 8.14 km/sec at a 175-km depth. On the other hand, for central Japan the P-velocity is found to be 7.92 km/sec at a 40-km depth, and increases linearly with a high-velocity gradient to 8.33 km/sec at a depth of 180 km. Then, there is a slight decrease in the velocity gradient, but the velocity still increases linearly to 8.52 km/sec at a depth of 365 km. At this transition depth, there is a first-order velocity discontinuity—the velocity increasing from 8.52 to 9.10 km/sec. Below this depth, velocity again increases linearly from 9.10 to 9.99 km/sec at a depth of 600 km. Probable causes for these lateral-velocity inhomogeneities in the upper mantle of the Japan region are discussed. Graphs have been drawn to show the variation with depth of Δ*, the epicentral distance to the inflection point, (Δ2 − Δ1), ptrue = ∂T/∂Δ and ap = (T − pΔ) at the inflection point, the latter acting as a calibration curve for earthquake focal-depth determination in Japan. Using this calibration curve, focal depths are redetermined for all of the earthquakes under study for central Japan, and the same are compared with the values reported in the International Seismological Summaries.

Time and tempo of melt segregation from a magma mush: evidence from the Takidani pluton (Japan)

2020 ◽  
Author(s):  
Federico Farina ◽  
Daniela Rubatto ◽  
Eva Hartung ◽  
Luca Caricchi
Keyword(s):  
High Precision ◽  
Time Lag ◽  
Magma Reservoir ◽  
Gradual Transition ◽  
Age Difference ◽  
Central Japan ◽  
Melt Extraction ◽  
Zircon Crystallization ◽  
Melt Segregation ◽  
Residual Melt

<p>The Takidani pluton is a Pleistocene intrusion representing a nearly 2 km-thick shallow level magma reservoir located in the Central Japan Alps. The pluton, which is associated with caldera-forming eruptions, is vertically zoned and composed of six distinct lithological units ranging from hornblende-bearing granodiorite to biotite granite, with silica content varying from ca. 65 to 76 wt.%. In its upper part, the intrusion is characterized by the gradual transition between equigranular and porphyritic granodiorites. Textural and geochemical evidence indicates that the porphyritic unit represents a lens of residual melt extracted from the underlying equigranular granodiorite (Hartung et al., 2017).</p><p>The time and tempo of melt extraction is determined using both high precision and high-spatial resolution U-Pb zircon geochronology, performed by CA-ID-TIMS and SIMS respectively. High precision <sup>206</sup>Pb/<sup>238</sup>U zircon ages for the two units are similar, with grains from both rocks exhibiting an age spread as large as 200-300 kyr, from ca. 1.2 to 1.5 Ma. In-situ U-Pb dating obtained by SIMS using a spot size of 20 μm reveal systematic age difference between cores and rims, highlighting two events of zircon crystallization with no substantial difference between the two units. Zircon cores from the porphyritic and equigranular granodiorites give identical ages at ca. 1.45 ± 0.06 Ma. Spot U-Pb ages from magmatic rims range between 1.29 and 1.07 Ma, with a peak of the distribution density at around 1.20 Ma.</p><p>This information, combined with Zr saturation temperatures and phase equilibria modelling, suggests that zircon cores crystallized from the magma reservoir before rheological locking and melt segregation were achieved. The segregation of the interstitial melt from the mush took place in the ca. 250 kyr between the two events of zircon crystallization. The extracted residual melt was depleted in Zr and carried entrained crystals of plagioclase and zircon from the mush. The low Zr content of this melt hindered zircon crystallization that was only possible after a time lag of 250 kyr. The youngest event of zircon crystallization at ca. 1.2 Ma was contemporaneous in the segregated melt and in the underlying mush.</p><p> </p><p>Reference: Hartung, E., Caricchi, L., Floess, D., Wallis, S., Harayama, S., Kouzmanov, K., Chiaradia, M., 2017. Evidence for residual melt extraction in the Takidani Pluton, Central Japan. J. Petrol.58, 763–788.</p>

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