Bulk rock chemistry of the Muro pyroclastic flow deposit: A clue to its source region.
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- SHINJOE Hironao
- Tokyo Keizai University
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- ORIHASHI Yuji
- Earthquake Research Institute, University of Tokyo
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- SUMII Tomoaki
- Geological Survey of Japan, AIST
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- NAKAI Shun-ichi
- Earthquake Research Institute, University of Tokyo
Bibliographic Information
- Other Title
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- 室生火砕流堆積物の全岩化学組成 その給源への手掛り
- ムロオ カサイリュウ タイセキブツ ノ ゼン ガン カガク ソセイ ソノ キュウゲン エ ノ テガカリ
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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 km3, 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 SiO2=74.0-75.5 wt%. They are characterized by LREE enrichments, large Eu negative anomalies (Eu/Eu*=0.30-0.59), and relatively constant chondrite-normalized middle to heavy REE abundances. All the analyzed samples have mole Al2O3/(CaO+Na2O+K2O) 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
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- Japanese Magazine of Mineralogical and Petrological Sciences
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Japanese Magazine of Mineralogical and Petrological Sciences 31 (6), 307-317, 2002
Japan Association of Mineralogical Sciences
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Details 詳細情報について
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- CRID
- 1390001206526847360
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- NII Article ID
- 130000253637
- 10012095508
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- NII Book ID
- AA1146088X
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- COI
- 1:CAS:528:DC%2BD3sXivVGktrc%3D
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- ISSN
- 13497979
- 1345630X
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- NDL BIB ID
- 6470855
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- Text Lang
- ja
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- Data Source
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- JaLC
- NDL
- Crossref
- CiNii Articles
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- Abstract License Flag
- Disallowed