Primary carbonatite melt from deeply subducted oceanic crust

M. J. Walter, G. P. Bulanova, L. S. Armstrong, S. Keshav, J. D. Blundy, G. Gudfinnsson, O. T. Lord, A. R. Lennie, S. M. Clark, C. B. Smith, L. Gobbo

Research output: Contribution to journalArticlepeer-review

170 Citations (Scopus)

Abstract

Partial melting in the Earth's mantle plays an important part in generating the geochemical and isotopic diversity observed in volcanic rocks at the surface. Identifying the composition of these primary melts in the mantle is crucial for establishing links between mantle geochemical 'reservoirs' and fundamental geodynamic processes. Mineral inclusions in natural diamonds have provided a unique window into such deep mantle processes. Here we provide experimental and geochemical evidence that silicate mineral inclusions in diamonds from Juina, Brazil, crystallized from primary and evolved carbonatite melts in the mantle transition zone and deep upper mantle. The incompatible trace element abundances calculated for a melt coexisting with a calcium-titanium-silicate perovskite inclusion indicate deep melting of carbonated oceanic crust, probably at transition-zone depths. Further to perovskite, calcic-majorite garnet inclusions record crystallization in the deep upper mantle from an evolved melt that closely resembles estimates of primitive carbonatite on the basis of volcanic rocks. Small-degree melts of subducted crust can be viewed as agents of chemical mass-transfer in the upper mantle and transition zone, leaving a chemical imprint of ocean crust that can possibly endure for billions of years.

Original languageEnglish
Pages (from-to)622-625
Number of pages4
JournalNature
Volume454
Issue number7204
DOIs
Publication statusPublished - 31 Jul 2008

Bibliographical note

Funding Information:
Acknowledgements Diamond samples from Collier 4 were collected by Rio Tinto (Rio Tinto Desenvolvimentos Minerais Ltda) in 1994. We thank Rio Tinto for access to the collection and J. Pickles for technical assistance. This work was supported by an NERC grant to M.J.W. Experiments by L.S.A. at Bayerisches Geoinstitut were supported by the Marie Curie 6th Framework Programme. Synchrotron experiments at Synchrotron Radiation Source, Daresbury Laboratory, UK, and at the Advanced Light Source, Berkeley, USA, were supported by awards to M.J.W. Trace element analyses at the NERC Edinburgh Ion Microprobe Facility were supported by an award to M.J.W.

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