Magmatic plumbing system of the 3400 BC caldera-forming eruption (Numazawako eruption) of Numazawa volcano as deduced by componentry and whole-rock and mineral compositions of the pyroclastic deposits

DOI Web Site 2 Citations 27 References
  • Masubuchi Yoshiko
    Graduate School of Science and Engineering, University of Toyama Present address: Toyama Science Museum
  • Ishizaki Yasuo
    Graduate School of Science and Engineering, University of Toyama

Bibliographic Information

Other Title
  • 噴出物の構成物組成と本質物質の全岩および鉱物組成から見た沼沢火山のＢＣ３４００カルデラ形成噴火（沼沢湖噴火）のマグマ供給系
  • フンシュツブツ ノ コウセイブツ ソセイ ト ホンシツ ブッシツ ノ ゼン ガン オヨビ コウブツ ソセイ カラ ミタ ショウタク カザン ノ BC3400 カルデラ ケイセイ フンカ ショウタクコ フンカ ノ マグマ キョウキュウケイ

Search this article

Description

The 3400 BC caldera-forming eruption of Numazawa volcano (the Numazawako eruption), NE Japan, began with a cataclysmic pyroclastic flow (phase I) followed by a Plinian eruption, phreatomagmatic eruptions, and a second Plinian eruption (phases II-IV, respectively). Petrological examinations revealed that a variety of juvenile pyroclasts were ejected during the eruption. White pumice (WP) rich in euhedral phenocrysts (64.7–67.1 wt.% SiO2) dominated the juvenile material expelled during the two early eruption phases, suggesting that WP-forming dacitic magma (∼760–840 °C) constituted the main and upper portions of the pre-eruptive magma chamber. Gray pumice, rich in crystal fragments (65.2–66.0 wt.% SiO2), was a minor component of this eruption, produced by the mechanical breakdown of phenocrysts as the WP magma ascended in the conduit. Whole-rock compositions of scoria suggest that two different mafic magmas, a low-Ba type (LBa; < 58 wt.% SiO2, > 964 °C) and a high-Ba (HBa) type (< 56.3 wt.% SiO2, > 1027 °C), were injected separately into the magma chamber. Diffusion profiles of dacite-derived magnetite phenocrysts in black scoria (BS; 58–64.5 wt.% SiO2) show that the Numazawako eruption was triggered by the injection of LBa magma. LBa magma mixed with dacite magma in the chamber and erupted as BS during the two early eruption phases. In contrast, gray scoria (GS; 56.3–59.8 wt.% SiO2) has a distinct chemical composition found only during the two later eruption phases. The abundance and whole-rock composition of GS suggest that injection of HBa magma occurred immediately before or during phase III; the HBa magma mixed with BS-forming magma in the chamber to produce the GS magma. This second magma injection probably resulted in over-pressurization of the chamber, thereby triggering the second Plinian eruption.

Journal

Citations (2)*help

See more

References(27)*help

See more

Keywords

Details 詳細情報について

Report a problem

Back to top