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

J. M. Scott, A. Hodgkinson, J. M. Palin, T. E. Waight, Q. H.A. van der Meer, A. F. Cooper

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54 Citations (Scopus)

Abstract

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 Al2O3 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 (87Sr/86Sr = 0.7028-0.7031; 143Nd/144Nd = 0.5129; 206Pb/204Pb = 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.

Original languageEnglish
Article number963
Pages (from-to)1-17
Number of pages17
JournalContributions to Mineralogy and Petrology
Volume167
Issue number1
DOIs
Publication statusPublished - Jan 2014

Bibliographical note

Funding Information:
Acknowledgments We thank the Foundation for Research, Science and Technology for contract UOOX1004 to JMS; the AUSIMM for a scholarship to AH; the Carlsberg Foundation and Danish Research Council for Nature and Universe for research grants to TEW; A. Riches, C. Perinelli and C. Ballhaus for comments on the text.

Other keywords

  • Carbonatite
  • Mantle metasomatism
  • Peridotite
  • Zealandia

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