B. A. Wyatt

University of Cape Town

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Nature of alkali-carbonate fluids in the sub-continental lithospheric mantle

Geology (2012)

Andrea Giuliani Vadim S. Kamenetsky David Phillips Mark A. Kendrick B. A. Wyatt

Research Article| November 01, 2012 Nature of alkali-carbonate fluids in the sub-continental lithospheric mantle A. Giuliani; A. Giuliani 1School of Earth Sciences, University of Melbourne, Parkville, 3010 Victoria, Australia Search for other works by this author on: GSW Google Scholar V.S. Kamenetsky; V.S. Kamenetsky 2ARC Centre of Excellence on Ore Deposits, and School of Earth Sciences, University of Tasmania, Hobart, 7001 Tasmania, Australia Search for other works by this author on: GSW Google Scholar D. Phillips; D. Phillips 1School of Earth Sciences, University of Melbourne, Parkville, 3010 Victoria, Australia Search for other works by this author on: GSW Google Scholar M.A. Kendrick; M.A. Kendrick 1School of Earth Sciences, University of Melbourne, Parkville, 3010 Victoria, Australia3Wyatt Geological Consulting Ltd, 1/3 Westbury Grove, East St. Kilda, 3183 Victoria, Australia Search for other works by this author on: GSW Google Scholar B.A. Wyatt; B.A. Wyatt 3Wyatt Geological Consulting Ltd, 1/3 Westbury Grove, East St. Kilda, 3183 Victoria, Australia Search for other works by this author on: GSW Google Scholar K. Goemann K. Goemann 4Central Science Laboratory, University of Tasmania, Hobart, 7001 Tasmania, Australia Search for other works by this author on: GSW Google Scholar Author and Article Information A. Giuliani 1School of Earth Sciences, University of Melbourne, Parkville, 3010 Victoria, Australia V.S. Kamenetsky 2ARC Centre of Excellence on Ore Deposits, and School of Earth Sciences, University of Tasmania, Hobart, 7001 Tasmania, Australia D. Phillips 1School of Earth Sciences, University of Melbourne, Parkville, 3010 Victoria, Australia M.A. Kendrick 1School of Earth Sciences, University of Melbourne, Parkville, 3010 Victoria, Australia3Wyatt Geological Consulting Ltd, 1/3 Westbury Grove, East St. Kilda, 3183 Victoria, Australia B.A. Wyatt 3Wyatt Geological Consulting Ltd, 1/3 Westbury Grove, East St. Kilda, 3183 Victoria, Australia K. Goemann 4Central Science Laboratory, University of Tasmania, Hobart, 7001 Tasmania, Australia Publisher: Geological Society of America Received: 18 Jan 2012 Revision Received: 16 Apr 2012 Accepted: 23 Jun 2012 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2012 Geological Society of America Geology (2012) 40 (11): 967–970. https://doi.org/10.1130/G33221.1 Article history Received: 18 Jan 2012 Revision Received: 16 Apr 2012 Accepted: 23 Jun 2012 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation A. Giuliani, V.S. Kamenetsky, D. Phillips, M.A. Kendrick, B.A. Wyatt, K. Goemann; Nature of alkali-carbonate fluids in the sub-continental lithospheric mantle. Geology 2012;; 40 (11): 967–970. doi: https://doi.org/10.1130/G33221.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Mantle xenoliths sampled by kimberlite and alkali basalt magmas show a range of metasomatic styles, but direct evidence for the nature of the metasomatising fluids is often elusive. It has been suggested that carbonate-rich melts produced by partial melting of carbonated peridotites and eclogites play an important role in modifying the composition of the lithospheric mantle. These mantle-derived carbonate melts are often inferred to be enriched in alkali elements; however, alkali-rich carbonate fluids have only been reported as micro-inclusions in diamonds and as unique melts involved in the formation of the Udachnaya-East kimberlite (Yakutia, Russia). In this paper we present the first direct evidence for alkali-carbonate melts in the shallow lithospheric mantle (∼110–115 km), above the diamond stability field. These alkali-carbonate melts are preserved in primary multiphase inclusions hosted by large metasomatic ilmenite grains contained in a polymict mantle xenolith from the Bultfontein kimberlite (Kimberley, South Africa). The inclusions host abundant carbonates (magnesite, dolomite, and K-Na-Ca carbonates), kalsilite, phlogopite, K-Na titanates, and phosphates, with lesser amounts of olivine, chlorides, and alkali sulfates. Textural and chemical observations indicate that the alkali-carbonate melt likely derived from primary or precursor kimberlite magmas. Our findings extend the evidence for alkali-carbonate melts/fluids permeating the Earth mantle outside the diamond stability field and provide new insights into the chemical features of previously hypothesized melts. As metasomatism by alkali-rich carbonate melts is often reported to affect mantle xenoliths, and predicted from experimental studies, the fluid type documented here likely represent a major metasomatising agent in the Earth's lithospheric mantle. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Excellence

Northern territory

10.1130/g33221.1

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Citations (94)

Compositional classification of “kimberlitic” and “non-kimberlitic” ilmenite

Lithos (2004)

B. A. Wyatt Mike Baumgartner Eva Anckar Herman Grütter

Ilmenite

Ultramafic rock

Chromite

10.1016/j.lithos.2004.04.025

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Citations (98)

Petrogenesis of Mantle Polymict Breccias: Insights into Mantle Processes Coeval with Kimberlite Magmatism

Journal of Petrology (2014)

Andrea Giuliani David Phillips Vadim S. Kamenetsky Mark A. Kendrick B. A. Wyatt

Mantle polymict breccias sampled by kimberlite magmas are complex mixtures of mantle minerals and rock clasts, cemented together by olivine, phlogopite, orthopyroxene, ilmenite, rutile and sulphides. Because of the kimberlite-like texture (i.e. mineral clasts of diverse origin and composition set in a magmatic matrix) and the large geochemical heterogeneity preserved in polymict breccias, these rocks are believed to derive from primitive or precursor kimberlite magmas. Therefore, the study of such xenoliths can provide constraints on the processes occurring in the mantle during the early stages of kimberlite ascent, and possibly on the composition of kimberlite melts. To constrain the petrogenesis of these unusual rocks, we have studied two samples of polymict breccia from the Bultfontein kimberlite (Kimberley, South Africa) and compared our results with published data for other polymict breccias. The most abundant phase in the matrix of the studied samples is olivine with a narrow range in Mg# (∼88–89), but variable Ni–Mn–Ca contents. Similar compositions are characteristic of magmatic olivine in the Bultfontein and nearby De Beers kimberlites. Orthopyroxene is the dominant phase in the matrix of polymict breccias surrounding clinopyroxene clasts, which, like the other silicate mineral clasts, are highly resorbed. The matrix orthopyroxene exhibits variable compositions, with significant enrichment in Ca, Na, Cr, Sr, Ba and light rare earth elements in the grains adjacent to clinopyroxene. The other main matrix phases (phlogopite, ilmenite and rutile) also display variable compositions. Matrix olivine hosts primary carbonate-rich inclusions similar to those observed in polymict breccia ilmenite. These inclusions were previously interpreted as an alkali-carbonate melt trapped during ilmenite growth. This alkali-carbonate melt may represent the parental melt to the matrix minerals of the polymict breccias. The variable composition of the matrix minerals is attributed to rapid, small-scale (centimetre to millimetre) variations in the melt composition owing to clast dissolution, possibly coupled with wall-rock assimilation, closely followed by fast cooling. Partial digestion of silicate porphyroclasts increased the Si content of the matrix melt, thus allowing crystallization of orthopyroxene. Further arguments in favour of a genetic relationship between polymict breccias and kimberlite magmas are provided by (1) similar Hf isotope compositions of polymict breccia ilmenite and South African kimberlites, (2) overlapping olivine compositions in polymict breccias and the host Bultfontein kimberlite, and (3) the occurrence of alkali-carbonate inclusions in polymict breccia and kimberlite minerals. Polymict breccias are interpreted as failed kimberlite intrusions, which metasomatized the magmatic conduit through which subsequent pulses of kimberlite magmas ascended. These wall-rock interactions would limit reactions between later pulses of kimberlite melt and mantle wall-rocks, thus enhancing the ability of kimberlite magmas to reach the surface.

Breccia

Phlogopite

Petrogenesis

Xenolith

Ilmenite

10.1093/petrology/egu008

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Citations (98)

Ilmenite in Polymict Xenoliths from the Bultfontein and De Beers Mines, South Africa

Developments in petrology (1984)

B. A. Wyatt P. J. LAWLESS

Ilmenite

Phlogopite

Rutile

Xenolith

Metasomatism

Chromite

10.1016/b978-0-444-42274-3.50011-1

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Citations (15)

Alkali-carbonate fluids in the lithospheric mantle

International Kimberlite Conference Extended Abstracts: 2008 (2019)

Andrea Giuliani Vadim S. Kamenetsky David Phillips B. A. Wyatt G. Hutchinson

10.29173/ikc3683

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Citations (0)

Possible Liquid Immiscibility Textures in High-Magnesia Basalts from the Ventersdorp Supergroup, South Africa

The Journal of Geology (1979)

R. Grant Cawthorn James McIver T.S. McCarthy B. A. Wyatt JA Ferguson

The lowermost succession of lavas in the Proterozoic Ventersdorp Supergroup contains light weathering ocelli up to 15 cm in diameter which occur in layers of a darker weathering volcanic material. Some ocelli appear to merge, and discrete light weathering layers may be the ultimate end-stage of this coalescence. Alternatively, coexisting magmas in the neck of the volcano may have been erupted in varying proportions, and turbulence during flow caused spalling of large drops of the lighter weathering material into the other. Several lines of field evidence suggest that two distinct liquids coexisted and were rapidly quenched after eruption. Chemical data for ocelli and matrix are consistent with the hypothesis of liquid immiscibility. The differences in compositions between the coexisting pairs of liquids are small and it is suggested that the original magmas must have been close to the consulute composition.

Supergroup

Coalescence (physics)

10.1086/628395

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Citations (22)

Harzburgite to lherzolite and back again: metasomatic processes in ultramafic xenoliths from the Wesselton kimberlite, Kimberley, South Africa

Contributions to Mineralogy and Petrology (1999)

William L. Griffin S Shee C.G. Ryan Tin Tin Win B. A. Wyatt

Metasomatism

Xenolith

Phlogopite

Ultramafic rock