四国中央部・三波川帯，東赤石超苦鉄質岩体のＰ‐Ｔ‐Ｄ履歴―ウェッジ・マントルカンラン石の沈み込み過程―

• 榎並 正樹

  名古屋大学大学院環境学研究科地球環境科学教室

• 水上 知行

  東京大学大学院理学系研究科附属地殻化学実験施設

書誌事項

タイトル別名

• P-T-D Evolution of the Higashi-akaishi Ultramafic Mass in the Sanbagawa Metamorphic Belt, Central Shikoku, Japan: Subduction of Wedge Mantle Peridotite
• シコク チュウオウブ サンバガワタイ ヒガシアカイシ チョウクテツシツガンタイ ノ P T D リレキ ウェッジ マントル カンランガン ノ シズミ コミ カテイ
• Subduction of Wedge Mantle Peridotite
• ウェッジ・マントルカンラン岩の沈み込み過程

抄録

Garnet-bearing ultramafic rocks including clinopyroxenite, wehrlite, and websterite locally crop out in the Higashi-akaishi peridotite of the Besshi region in the Sanbagawa metamorphic belt. These rock types occur within dunite as lenses, boudins, or layers with a thickness ranging from a few centimeters to 1 meter. The wide and systematic variations of bulk-rock composition and overall layered structure imply that the ultramafic complex originated as a cumulate sequence. Garnet and other major silicates contain rare inclusions of edenitic amphibole, chlorite, and magnetite, implying equilibrium at relatively low T and hydrous conditions during prograde metamorphism. Orthopyroxene coexisting with garnet shows bell-shaped Al zoning with a continuous decrease of Al from the core towards the rim, and its rim records peak metamorphic conditions. Estimated P-T conditions imply a high P/T gradient (> 3.1 GPa/100 °C) from 1.5-2.4 GPa/700-800 °C to 2.9-3.8 GPa/700-810°C during prograde metamorphism. Olivines recrystallized at the high P/T prograde metamorphic stage show a B-type lattice preferred orientation (LPO) with a-axis concentrations normal to the stretching lineation. The presence of B-type LPO indicates that deformation of the prograde metamorphic stage possibly progressed under hydrous and high-stress conditions at the wedge mantle adjacent to the subducted slab. The Higashi-akaishi peridotite is a unique example that well records the prograde evolution of subducted ultramafic rocks.

収録刊行物

• 地学雑誌

  地学雑誌 113 (5), 617-632, 2004

  公益社団法人 東京地学協会

キーワード

• P-T経路
• 超高圧変成作用
• 格子定向配列 (LPO)
• カンラン石
• 超苦鉄質岩
• ウェッジ・マントル
• 沈み込み帯
• 三波川帯

詳細情報

• CRID: 1390001204228869248
• NII論文ID: 10017474143
• NII書誌ID: AN00322536
• DOI: 10.5026/jgeography.113.5_617
• ISSN: 18840884
• ISSN: 0022135X
• NDL書誌ID: 7190061
• Web Site: https://ndlsearch.ndl.go.jp/books/R000000004-I7190061
• 本文言語コード: ja
• データソース種別:
  • JaLC
  • NDL
  • Crossref
  • CiNii Articles
  • KAKEN
• 抄録ライセンスフラグ: 使用不可