室生火砕流堆積物の全岩化学組成 : その給源への手掛り  [in Japanese] Bulk rock chemistry of the Muro pyroclastic flow deposit : a clue to its source region  [in Japanese]

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Author(s)

Abstract

The Muro pyroclastic flow deposit (MPFD), distributed in the central part of the Kii peninsula southwest Japan, is composed of rhyolitic welded tuff, representing a single cooling unit. Though the MPFD is a remarkable gigantic igneous unit with the volume of ∼100 km<sup>3</sup>, its source region is still in dispute. To discuss the problem, bulk rock chemical composition of MPFD were determined by XRF and LA-ICP-MS. The samples used in this study scarcely contain exotic materials. The MPFD welded tuffs indicate rhyolitic compositions with SiO<sub>2</sub>=74.0-75.5 wt%. They are characterized by LREE enrichments, large Eu negative anomalies (Eu/Eu<sup>*</sup>=0.30-0.59), and relatively constant chondrite-normalized middle to heavy REE abundances. All the analyzed samples have mole Al<sub>2</sub>O<sub>3</sub>/(CaO+Na<sub>2</sub>O+K<sub>2</sub>O) ratio higher than 1.1. Garnet is ubiquitously included, and some samples contain cordierite. Some of the rhyolitic rocks in the middle Miocene Setouchi Volcanic Rocks, as found in the lowest horizon of the Nijo Group for example, also have peraluminous bulk rock compositions. However, they are discriminated from MPFD by whole rock chemical compositions, in particular depletion in HREE. Actually, major and trace element compositions of MPFD are very close to those of the middle Miocene S-type granitoids in the Outer Zone of southwest Japan. These facts strongly suggest that MPFD was derived from an S-type felsic igneous body in the Outer Zone, travelling more than 20 km.

Journal

  • Japanese Magazine of Mineralogical and Petrological Sciences

    Japanese Magazine of Mineralogical and Petrological Sciences 31(6), 307-317, 2002-11-30

    Japan Association of Mineralogical Sciences

References:  41

Cited by:  8

Codes

  • NII Article ID (NAID)
    130000253637
  • NII NACSIS-CAT ID (NCID)
    AA1146088X
  • Text Lang
    JPN
  • Article Type
    Journal Article
  • ISSN
    1345630X
  • NDL Article ID
    6470855
  • NDL Source Classification
    ZM46(科学技術--地球科学--岩石・鉱物・鉱床)
  • NDL Call No.
    Z15-117
  • Data Source
    CJP  CJPref  NDL  J-STAGE 
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