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Contributions to Mineralogy and Petrology

, Volume 131, Issue 2–3, pp 111–122 | Cite as

Jadeite, albite and nepheline as inclusions in spinel of chromitite from Hess Deep, equatorial Pacific: their genesis and implications for serpentinite diapir formation

  • Kyoko Matsukage
  • Shoji Arai
Article

Abstract

Polymineralic inclusions which consist of a few grains of diopside, enstatite, jadeite, nepheline, albite, pargasite, phlogopites and olivine were found in chromian spinel in a chromitite pod and in troctolite from Hess Deep, equatorial Pacific. The inclusion mineral suite in chromitite is characterized by Na-Al silicates, such as jadeite, nepheline and albite. Jadeite and nepheline commonly coexist with enstatite, and tend to occur as interstitial grains between subhedral enstatite (or other minerals) and host spinel. Albite, diopside and enstatite occur as equant inclusions. The mafic minerals in the inclusions have similar chemistry to those found in the troctolite and dunite. The modes of occurrence and mineral chemistry of the inclusions are controlled by magmatic precipitation, and subsequent reequilibration due to decrease of temperature in the uppermost mantle. The mafic minerals in spinel inclusions were crystallized from a melt enriched in Cr and some incompatible components formed by melt-mantle interaction process mixed to various extent with subsequently supplied more primary melt. Albite and nepheline could also be formed at the magmatic stage. Jadeite was formed by a subsolidus reaction of albite and nepheline at low temperatures (250–300 °C) at slightly less than 3 kbar. This requires a remarkable temperature decrease, at least locally, of the uppermost mantle and crust. The Hess Deep rocks were formed in the uppermost mantle beneath a spreading-ridge axis at more than 1000 °C, and were transposed outwards from the axis by corner flow. At the off-ridge conditions, the rocks were cooled and serpentinized by circulation of sea water at the mantle depth to form jadeite in chromitite. The serpentinized portion could have risen as a kind of serpentinite diapir through the thin crust up to the ocean floor.

Keywords

Olivine Diopside Nepheline Enstatite Chromian Spinel 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag Berlin Heidelberg 1998

Authors and Affiliations

  • Kyoko Matsukage
    • 1
  • Shoji Arai
    • 1
  1. 1.Department of Earth Science, Kanazawa University, Kakuma-machi, Kanazawa 920-11, Japan Fax: 81-762-64-5746 E-mail: kyokoala@kenroku.ipc.kanazawa-u.ac.jpJP

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