Ancient melt depletion overprinted by young carbonatitic metasomatism in the New Zealand lithospheric mantle

Spinel facies dunite, harzburgite, lherzolite and wehrlite mantle xenoliths from a cluster of Miocene volcanoes in southern New Zealand preserve evidence of the complex evolution of the underlying continental mantle lithosphere. Spinel Cr# records melt extraction with some values indicative of near...

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Bibliographic Details
Published in:Contributions to mineralogy and petrology 2014, Vol.167 (1), p.1, Article 963
Main Authors: Scott, J. M., Hodgkinson, A., Palin, J. M., Waight, T. E., Van der Meer, Q. H. A., Cooper, A. F.
Format: Article
Language:English
Subjects:
Cretaceous
Earth
Earth and Environmental Science
Earth Sciences
Eocene
Geochemistry
Geology
Inclusions
Lithosphere
Mantle
Mineral Resources
Mineralogy
Miocene
Original Paper
Petrology
Phosphate minerals
Phosphate rock
Rifting
Rocks, Igneous
Spinel group
Volcanoes
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Summary:Spinel facies dunite, harzburgite, lherzolite and wehrlite mantle xenoliths from a cluster of Miocene volcanoes in southern New Zealand preserve evidence of the complex evolution of the underlying continental mantle lithosphere. Spinel Cr# records melt extraction with some values indicative of near complete removal of clinopyroxene. LREE-enriched, low Ti/Eu and low Al 2 O 3 clinopyroxene and rare F-, LREE-rich apatite indicates subsequent interaction between peridotite and a metasomatising carbonatitic melt. The clearest metasomatic signature occurs in the formerly highly depleted samples because there was little or no pre-existing clinopyroxene to dilute the carbonatite signature. For the same reason, the isotopic character of the metasomatising agent is best observed in the formerly highly depleted peridotites ( 87 Sr/ 86 Sr = 0.7028–0.7031; 143 Nd/ 144 Nd = 0.5129; 206 Pb/ 204 Pb = 20.2–20.3). These isotope ratios are very close to, but slightly less radiogenic than, the HIMU end-member mantle reservoir. Nd isotope data imply carbonatite metasomatism occurred within the last several hundred million years, with ubiquitous pyroxene core-to-rim Al diffusion zoning indicating that it must pre-date cooling of the lithospheric mantle following Late Cretaceous–Eocene rifting of Zealandia from Gondwana. Metasomatism was significantly younger than ancient Re-depletion ages of ~2 Ga and shows that decoupling of peridotite isotope systems has occurred.
ISSN:0010-7999
1432-0967
DOI:10.1007/s00410-014-0963-0