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Carbonate–silicate liquid immiscibility in the mantle propels kimberlite magma ascent

Citation

Kamenetsky, VS and Yaxley, GM, Carbonate-silicate liquid immiscibility in the mantle propels kimberlite magma ascent, Geochimica et Cosmochimica Acta, 158 pp. 48-56. ISSN 0016-7037 (2015) [Refereed Article]

Copyright Statement

Copyright 2015 Elsevier Ltd.

DOI: doi:10.1016/j.gca.2015.03.004

Abstract

Kimberlite is a rare volcanic rock renowned as the major host of diamonds and originated at the base of the subcontinental lithospheric mantle. Although kimberlite magmas are dense in crystals and deeply-derived rock fragments, they ascend to the surface extremely rapidly, enabling diamonds to survive. The unique physical properties of kimberlite magmas depend on the specific compositions of their parental melts that, in absence of historical eruptions and due to pervasive alteration of kimberlite rocks, remain highly debatable. We explain exceptionally rapid ascent of kimberlite magma from mantle depths by combining empirical data on the essentially carbonatite composition of the kimberlite primary melts and experimental evidence on interaction of the carbonate liquids with mantle minerals. Our experimental study shows that orthopyroxene is completely dissolved in a Na2CO3 melt at 2.0–5.0 GPa and 1000–1200 °C. The dissolution of orthopyroxene results in homogeneous silicate–carbonate melt at 5.0 GPa and 1200 °C, and is followed by unmixing of carbonate and carbonated silicate melts and formation of stable magmatic emulsion at lower pressures and temperatures. The dispersed silicate melt has a significant capacity for storing a carbonate component in the deep mantle (13 wt% CO2 at 2.0 GPa). We envisage that this component reaches saturation and is gradually released as CO2 bubbles, as the silicate melt globules are transported upwards through the lithosphere by the carbonatite magma. The globules of unmixed, CO2-rich silicate melt are continuously produced upon further reaction between the natrocarbonatite melt and mantle peridotite. On decompression the dispersed silicate melt phase ensures a continuous supply of CO2 bubbles that decrease density and increase buoyancy and promote rapid ascent of the magmatic emulsion.

Item Details

Item Type:Refereed Article
Research Division:Earth Sciences
Research Group:Geology
Research Field:Igneous and Metamorphic Petrology
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Earth Sciences
Author:Kamenetsky, VS (Professor Vadim Kamenetsky)
ID Code:100295
Year Published:2015
Funding Support:Australian Research Council (DP130100257)
Web of Science® Times Cited:22
Deposited By:Earth Sciences
Deposited On:2015-05-09
Last Modified:2016-05-25
Downloads:0

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