title: Did diamond-bearing orangeites originate from MARID-veined peridotites in the lithospheric mantle?
abstract: Kimberlites and orangeites (previously named Group-II kimberlites) are small-volume igneous rocks occurring in diatremes, sills and dykes. They are the main hosts for diamonds and are of scientific importance because they contain fragments of entrained mantle and crustal rocks, thus providing key information about the subcontinental lithosphere. Orangeites are ultrapotassic, H2O and CO2-rich rocks hosting minerals such as phlogopite, olivine, calcite and apatite. The major, trace element and isotopic compositions of orangeites resemble those of intensely metasomatized mantle of the type represented by MARID (mica-amphibole-rutile-ilmenite-diopside) xenoliths. Here we report new data for two MARID xenoliths from the Bultfontein kimberlite (Kimberley, South Africa) and we show that MARID-veined mantle has mineralogical (carbonate-apatite) and geochemical (Sr-Nd-Hf-O isotopes) characteristics compatible with orangeite melt generation from a MARID-rich source. This interpretation is supported by U-Pb zircon ages in MARID xenoliths from the Kimberley kimberlites, which confirm MARID rock formation before orangeite magmatism in the area.
authors.affiliation: School of Earth Sciences, The University of Melbourne, Parkville, 3010 Victoria, Australia.
authors.forename: Andrea
authors.initials: A
authors.lastname: Giuliani
authors.affiliation: School of Earth Sciences, The University of Melbourne, Parkville, 3010 Victoria, Australia.
authors.forename: David
authors.initials: D
authors.lastname: Phillips
authors.affiliation: School of Earth Sciences, The University of Melbourne, Parkville, 3010 Victoria, Australia.
authors.forename: Jon D
authors.initials: JD
authors.lastname: Woodhead
authors.affiliation: School of Physical Sciences, University of Tasmania, Hobart, 7001 Tasmania, Australia.
authors.forename: Vadim S
authors.initials: VS
authors.lastname: Kamenetsky
authors.affiliation: Centre for Exploration Targeting, Australian Research Council Centre of Excellence for Core to Crust Fluid Systems, School of Earth and Environment, University of Western Australia, Crawley, 6009 Western Australia, Australia.
authors.forename: Marco L
authors.initials: ML
authors.lastname: Fiorentini
authors.affiliation: School of Earth Sciences, The University of Melbourne, Parkville, 3010 Victoria, Australia.
authors.forename: Roland
authors.initials: R
authors.lastname: Maas
authors.affiliation: School of Earth Sciences, The University of Melbourne, Parkville, 3010 Victoria, Australia.
authors.forename: Ashton
authors.initials: A
authors.lastname: Soltys
authors.affiliation: Research School of Earth Sciences, The Australian National University, Acton, 0200 Australian Capital Territory, Australia.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Armstrong