イロシンカルデラ内から採取されたコア試料(IrBH-2)の層序とAMS放射性炭素年代  [in Japanese] Stratigraphy and AMS Radiocarbon Dates of Cored Sediments (IrBH-2) from the Irosin Caldera, the Philippines  [in Japanese]

Access this Article

Search this Article

Author(s)

Abstract

 フィリピン,南ルソンのイロシンカルデラ内の地点IrBH-2で深度 50 mまでコア試料を採取し,50 cmごとに堆積物を記載した。深度 7.02~10.40 mから採取した植物片について,およそ1000~1800BPのAMS放射性炭素年代を得た。このコア試料では,ラハールや河川堆積物が多くを占めるが,上部 12 mは主として安山岩質の河川堆積物からなり,ラハール堆積物をわずかに伴う。この層準は,おそらく安山岩質の後カルデラ火山活動に対比できると考えられる。深度 12~50 mまでに12枚の降下テフラと1枚の火砕流堆積物が認められるが,そのなかの5枚の降下テフラは再堆積かもしれない。火山ガラスと斑晶鉱物の屈折率を測定したいくつかの試料は,後カルデラ火山の活動では安山岩質~デイサイト質噴出物が主であり,流紋岩質なものがわずかに伴うことを示唆する。また,流紋岩質降下テフラは,41 cal kBPのイロシン火砕流堆積物と共通した岩石記載的特徴を持ち,両者が同一のマグマに由来する可能性を示唆する。

 Core drilling at Site IrBH-2 within the Irosin caldera in Sorsogon Province, southern Luzon reached a depth of 50 m. Systematic logging and documentation were carried out to describe and interpret the sediments. The accelerator mass spectrometer (AMS) radiocarbon dates obtained from plant fragments at 7.02-10.40-m depth were 1000 to 1800 BP. Lahars and fluvial deposits were the predominant deposits in the core sequence. The upper 12 m consisted mostly of andesitic fluvial and minor lahar deposits. These deposits may be correlated with the reworking of eruptive products from resurgent andesitic volcanism. One pyroclastic flow and 12 fallout deposits, including five possible fallout deposits, were intercalated with reworked sediments at depths of 12-50 m. The refractive index of representative samples indicated that post-caldera eruptions involved mainly andesite to dacite, with minor rhyolite magmas. The rhyolite fallout in the core had similar petrographic characteristics to the 41 cal kBP Irosin ignimbrite, suggesting that the fallout and the ignimbrite were sourced from the same magma.

Journal

  • Journal of Geography (Chigaku Zasshi)

    Journal of Geography (Chigaku Zasshi) 123(5), 751-760, 2014

    Tokyo Geographical Society

Codes

  • NII Article ID (NAID)
    130004707033
  • NII NACSIS-CAT ID (NCID)
    AN00322536
  • Text Lang
    JPN
  • ISSN
    0022-135X
  • NDL Article ID
    025875626
  • NDL Call No.
    Z15-169
  • Data Source
    NDL  J-STAGE 
Page Top