Geology and geochemistry of Karasugasen lava dome, Daisen–Hiruzen Volcano Group, southwest Japan

Abstract

The geology and geochemistry of pyroclastic flows and fallout tephras formed during the Karasugasen dome eruption in the Daisen-Hiruzen Volcano Group in southwest Japan have been examined in detail. The Karasugasen lava dome erupted at about 26 ka. The eruption began with a vulcanian ash fall, and this was followed by at least eight block and ash flows and a pumice flow. The block and ash flows were produced by the successive collapses of a growing lava dome. This main eruption phase was followed by an eruption of vulcanian ash falls, and finally ended with a sub-Plinian pumice fall. This eruption sequence is typical of the Daisen Volcano during the last three eruption events, which occurred at 58, 26 and 17 ka. The magma produced during the Karasugasen eruption was a typical adakite, with extremely high Sr/Y ratios and low HREE/LREE ratios compared to normal arc lavas. The chemistry of the Karasugasen lavas is almost identical to other Daisen-Hiruzen lavas that were produced from eruptions over an interval of a million years. The continuous supply of a huge amount of adakitic magma ( > 100 km 3 ) for such a long period suggests a massive homogeneous source material, such as molten Philippine Sea Plate slab. Slab melting is a plausible mechanism for the production of the adakitic lavas at Karasugasen, and hence the Daisen-Hiruzen Volcano Group.

Two types of adakites revealed by 238U-230Th disequilibrium from Daisen Volcano, southwestern Japan

“…The Misen lava dome is less crystalline, with 5-10% plagioclase phenocrysts, and 1-3% phenocrysts of hornblende, biotite, hypersthene, and/or quartz. Kimura et al (2005) and Tamura et al (2000Tamura et al ( , 2003 (Tamura et al, 2000(Tamura et al, , 2003. The isotopic compositions are close to those of bulk earth (Zindler and Hart, 1986).…”

“…1). Daisen is a large composite volcano, more than 120 km 3 in volume, ranging in age from 0.017 to 1.2 Ma, and consisting of several clustered and overlapping lava domes (Kimura et al, 2005;Tamura et al, 2000Tamura et al, , 2003Tsukui, 1984Tsukui, , 1985Tsukui et al, 1985). Samples discussed here were collected from the Karasugasen and Misen lava domes.…”

“…The isotopic compositions are close to those of bulk earth (Zindler and Hart, 1986). Kimura et al (2005) suggested that the Karasugasen dacite were derived from the slab sediment melting based on the isotopic data.…”

“…The abundance and isotope measurements were performed using a MC-ICPMS at ERI (IsoProbe; GV Instruments Ltd., Manchester, U.K.). An Aridus micro-concentric nebulizer (Cetac Technologies, Omaha, U.S.A.) was used to intro- Kimura et al (2005) (Fukuda and Nakai, 2002). In this study we used the following decay constants for calculation of radioactivity ratios: (λ 238 U = 1.551 × 10 -10 yr -1 (Jaffey et al, 1971), λ 230 Th = 9.158 × 10 -6 yr -1 (Cheng et al, 2000), λ 232 Th = 4.945 × 10 -11 yr -1 (Holden, 1990).…”

Effect of subduction components on production of basalts from Tateshina volcano, central Japan: geochemical calculation of dehydration of subducting oceanic crust and partial melting of overlying sediments, and subsequent fluid-mantle interaction

“…However, adakite is unlikely to be found in the Izu -Mariana Arc, as adakite production requires the subduction of a young, hot lithosphere at a slow rate (e.g., Tables 3, 4, and 5. Morris, 1995;Ujike et al, 1999;Kimura et al, 2005). The rare earth element compositions of Tateshina basalts (black line) are compared with those of adakite (gray line) in Figure 6.…”