マントル起源超塩基性岩の希ガス同位体研究 : 希ガス同位体から見たマントルプロセス

• 松本 拓也

  大阪大学大学院理学研究科宇宙地球科学専攻

書誌事項

タイトル別名

• Nobl gas studies on mantle-derived ultramafic rocks: things that noble gas can tell us about mantle processes
• 2001年度日本地球化学会奨励賞受賞記念論文 マントル起源超塩基性岩の希ガス同位体研究:希ガス同位体から見たマントルプロセス
• 2001ネンド ニホン チキュウ カガクカイ ショウレイショウ ジュショウ キネン ロンブン マントル キゲン チョウエンキセイガン ノ キガス ドウイタイ ケンキュウ キガス ドウイタイ カラ ミタ マントルプロセス

抄録

Elemental and isotopic compositions of noble gases trapped in ultramafic rocks (xenoliths and orogenic peridotites) provide valuable information regarding the processes that affected the terrestrial mantle. Here I present some of the examples we found in fresh suites of xenoliths from southeastern Australia and in orogenic peridotites from Horoman complex in northern Japan. The great majority of SE Australian xenoliths yielded MORB-like ³He/⁴He ratios by crushing gas extraction, indicating that fluids derived from the convecting upper mantle (= MORB source mantle) clearly dominate the continental lithospheric mantle. In contrast, noble gas extraction by stepheating revealed the presence of significantly radiogenic ²¹Ne (and ⁴He to a lesser extend) in crystal structures of U-Th-bearing minerals such as apatite, amphibole and clinopyroxene. The presence of radiogenic noble gas component is clearly a consequence of mantle metasomatism by fluid/melt enriched in incompatible elements. Separation of CO₂ + noble gas-rich fluid from the incompatible-element-rich melt during the ascent would be a plausible explanation for the preservation of mantle source signature in fluid inclusions. This in turn suggests that noble gases in fluid inclusions of ultramafic rocks can be used to infer the source of metasomatic agent which sometimes is difficult to speculate upon. This notion can further be confirmed by the occurrence of plume-like neon in metasomatic apatite in the xenoliths in which the coexisting minerals showed MORB-like noble gases signatures. It was also found in the orogenic peridotites from Horoman complex that they were affected by metasomatic fluids from the dehydrating slab which introduced recycled-atmospheric argon into the mantle wedge. We note that this recycled component could have been stored in mantle wedge for a significant period of time to become part of continental lithospheric mantle. Somewhat lower ⁴⁰Ar/³⁶Ar ratios in xenoliths from the subcontinental mantle might be due to an involvement of a recycled component during the formation of the metasomatizing melt. These observations suggest that the continental lithospheric mantle have multiple noble gas components of distinct origins; a mantle component (both from degassed- and less-degassed-sources), an in situ radiogenic component and a recycled atmospheric component. It was also noted that Kola carbonatites of supposed lower mantle origin also showed some indication of a recycled volatile component. This issue certainly has important implications for bettering our understandings on the origin of noble gas heterogeneity observed in samples from the deeper mantle origin.

収録刊行物

• 地球化学

  地球化学 36 (2), 89-106, 2002

  一般社団法人日本地球化学会

キーワード

• noble gas
• isotope
• mantle
• metasomatism
• ultramafic xenoliths
• orogenic peridotites

詳細情報

• CRID: 1390001205740937856
• NII論文ID: 110008680036
• NII書誌ID: AN00141280
• DOI: 10.14934/chikyukagaku.36.89
• ISSN: 21885923
• ISSN: 03864073
• NDL書誌ID: 6182859
• Web Site: https://ndlsearch.ndl.go.jp/books/R000000004-I6182859
• 本文言語コード: ja
• データソース種別:
  • JaLC
  • NDL
  • CiNii Articles
• 抄録ライセンスフラグ: 使用不可