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American Mineralogist

Journal of Earth and Planetary Materials

Ed. by Baker, Don / Xu, Hongwu / Swainson, Ian


IMPACT FACTOR 2017: 2.645

CiteScore 2017: 2.31

SCImago Journal Rank (SJR) 2017: 1.440
Source Normalized Impact per Paper (SNIP) 2017: 1.059

Online
ISSN
1945-3027
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Volume 89, Issue 10

Issues

Metasomatic formation of kosmochlor-bearing diopside in peridotite xenoliths from North Island, New Zealand

Kei Ikehata / Shoji Arai
Published Online: 2015-03-28 | DOI: https://doi.org/10.2138/am-2004-1006

Abstract

Pale green Cr- and Na-rich diopside (kosmochlor-bearing diopside) was observed in anhydrous Group I mantle xenoliths hosted by Pliocene-Quaternary hawaiite from the Ngatutura volcanic field of the North Island, New Zealand. The diopside is characterized by high Cr2O3 (up to 5.87 wt%) and Na2O (up to 3.31 wt%) and low Al2O3 (1.09 wt%, on average), and contains the highest kosmochlor component (up to 18 mol%) known for diopsides in spinel peridotite xenoliths. It also contains high REE concentrations and is slightly enriched in LREE relative to HREE. The kosmochlor-bearing diopside commonly forms rims around chromian spinel and replaces secondary Al-poor (<0.57 wt% Al2O3) and Si-rich (~58.1 wt% SiO2) orthopyroxene crystallized from slab-derived fluid/melt at the expense of olivine. The kosmochlor-bearing diopside may have been formed through metasomatism by an Na-bearing carbonatite melt, which selectively reacted with orthopyroxene and can carry a large amount of rare-earth elements. Cr-rich spinel in refractory peridotites that had been formed in an arc setting is a prerequisite for genesis of this kind of kosmochlor-bearing diopside upon carbonatite metasomatism. The carbonatite melt from the deeper part penetrated the mantle wedge, which had been at a supra-subduction zone setting until 15 Ma, due to the absence of slab cover at an intraplate setting (~10 Ma) in the North Island.

About the article

Received: 2003-10-26

Accepted: 2004-05-08

Published Online: 2015-03-28

Published in Print: 2004-10-01


Citation Information: American Mineralogist, Volume 89, Issue 10, Pages 1396–1404, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am-2004-1006.

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© 2015 by Walter de Gruyter Berlin/Boston.

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