Karasugasen Ito san

Petrology and mineral chemistry of the Karasugasen lava dome and associated pyroclastic flow deposits

Yutaka Ito

Introduction

Japan is located at the western side of the Pacific Ring of Fire and situated on top of four major tectonic plates. Volcanic activity occurs along 5 active volcanic arcs which are from N to S the Kurile arc, the NE Japan arc, The Izu Bonin Arc, the SW Japan Arc and the Ryukyu Arc. Many of the active volcanoes of Japan are large stratovolcanoes which produce highly evolved magmas and therefore pose a substantial hazard to people and infrastructures in their vicinity. Japan has faced several volcanic disasters in its past for example from Mt.Tarumae or Mt Asama.

I believe that by understanding the history of a volcano and its past eruptions, one can understand potential future activity which can help to mitigate and prevent future volcanic disasters.

 

Karasugasen lava dome

The Karasugasen lava dome is part of Mt Daisen, a large stratovolcano located in San-in district in the southwest Japan. Volcanism in this area is related to subduction process and occurs due to subduction of the Philippine Sea Plate (Kimura et al., 2014) Magmas of Mt. Daisen have been identified as adakites and interpreted as a result of slab melting. (Morris, 1995; Tamura et al., 2003) The volcanic products are mostly dacite dome lavas, block and ash flows and Plinian tephras (Tsukui, 1984).

Karasugasen(Fig.1) is one of the eruptive centers of Daisen-Hiruzen volcano group which was active from 1Ma to 17ka. (Tsukui et al., 1984; Tamura et al., 2003)

Karasugasen volcanic products are divided into two main categories, derived from karasugasen lava dome. Firstly the Odori pyroclastic fall deposits and secondly, Sasaganaru pyroclastic flow deposits (Fig.2). The Sasaganaru pyroclastic flow deposits are preserved as three distinct lobes along valleys in the southern and southeastern sector of the mountain. Each lobe area is around 2×7㎢. (Yamamoto, 2017)

 

Odori fall pyroclastic material accompanying the main pyroclastic flow deposit is mainly composed of coarse volcanic ash and lapillituff and covers the Aira Tanzawa (AT) tephra. (Tsukui, 1984; Kimura et al., 2005)

Sasaganaru pyroclastic flow deposits show typical block and ash flow facies (Fig. 2) and is composed of a matrix composed of polyhedral essential rocks with poor foaming and fine powder, and an unclear stratified structure and reverse grading are recognized.

Karasugasen lava dome
Karasugasen lava dome
Sasaganaru pyroclastic flow deposits overlain by Higashidaisen ash and Higashidaisen pumice
Sasaganaru pyroclastic flow deposits overlain by Higashidaisen ash and Higashidaisen pumice

Aims

  • To investigate three main lobes of SaF which generated by Karasugasen lava dome then compare with stratigraphy that I made in bachelor thesis in details.
  • To research Odori F and associated deposit with SaF originated from Karasugasen lava dome.
  • To reveal the geochemistry, mineral and glass composition of the SaF using EPMA and XRF to understand the magmatic system of the Karasugasen lava dome.

Method

  • Fieldwork and recording of geological outcrops to understand explosive activity and volcanic history of Karasugasen
  • Stratigraphy and sedimentary description of Karasugasen
  • Petrography of various volcanic products using microscope
  • Geochemical analytic of whole rock major and trace element composition
  • Analytic of mineral and glass chemistry using EPMA
  • Thermodynamic modelling to determine parameters of the magmatic systems during the most recent eruptions of Karasugasen

 

Reference

  • Kimura, Jun-Ichi, James B. Gill, Tomoyuki Kunikiyo, Isaku Osaka, Yusuke Shimoshioiri, Maiko Katakuse, Susumu Kakubuchi, et al. “Diverse Magmatic Effects of Subducting a Hot Slab in SW Japan: Results from Forward Modeling.” Geochemistry, Geophysics, Geosystems 15, no. 3 (March 2014): 691–739. https://doi.org/10.1002/2013GC005132.
  • Kimura, Jun-Ichi, Mamiko Tateno, and Isaku Osaka. “Geology and Geochemistry of Karasugasen Lava Dome, Daisen–Hiruzen Volcano Group, Southwest Japan.” Island Arc 14, no. 2 (2005): 115–136.
  • MORRIS P. A. 1995. Slab melting as an explanation of Quaternary volcanism and aseismicity in southwest Japan. Geology 23, 395–8.
  • Tamura, Y. “Andesites and Dacites from Daisen Volcano, Japan: Partial-to-Total Remelting of an Andesite Magma Body.” Journal of Petrology 44, no.12(December1,2003):2243–60. https://doi.org/10.1093/petrology/egg076.
  • Tsukui, M (1984) Geology of Daisen volcano. J. Geol. Soc. Jpn.90,643-658
  • Takahiro Yamamoto (2017) Quantitative eruption history of Pleistocene Daisen Volcano, SW Japan. Geol. Surv. Japan, vol.68 (1), p.1–16, 12 figs, 3 tables.