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40Ar/39Ar ages in mantle xenolith phlogopites: determining the ages of multiple lithospheric mantle events and diatreme ascent rates in southern Africa and Malaita, Solomon Islands

By
Jo-Anne Wartho
Jo-Anne Wartho
Department of Applied Geology, Curtin UniversityGPO Box U1987, Perth, WA 6845, AustraliaJ-A.wartho@curtin.edu.au
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Simon P. Kelley
Simon P. Kelley
Department of Earth Sciences, Open UniversityWalton Hall, Milton Keynes, MK7 6AA, UK
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Published:
January 01, 2003

Abstract

Kimberlites are extraordinary natural phenomena, ascending through the Earth’s lithosphere, entraining xenoliths, to erupt at the surface within hours to days of their inception deep within the lithospheric mantle. With the realization that some Ar/Ar phlogopite grain core ages may be indicative of geological events, we have undertaken high spatial resolution Ar/Ar dating of phlogopites in xenoliths and megacrysts from Kimberley, Monastery and Letseng in southern Africa, and Malaita, in the Solomon Islands, to est whether other mantle phlogopite cores may yield meaningful ages.

Modelling of Ar diffusive loss profiles from phlogopite grain boundaries to cores provides information on both the eruption age and the duration of outgassing within the kimberlite magma, and hence yields estimates on diatreme ascent rates. The ascent durations are very similar for all of the southern African pipes studied, yielding durations of 0.9–6.9 days, assuming an average kimberlite magma temperature of 1000 °C. These can be compared to estimates from phlogopite xenoliths from Siberian diamond-bearing kimberlites yielding ascent durations of 2–15 hours (assuming the same magma temperature).

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Contents

Geological Society, London, Special Publications

Geochronology: Linking the Isotopic Record with Petrology and Textures

D. Vance
D. Vance
Royal HollowayUniversity of London, UK
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W. Müller
W. Müller
The Australian National UniversityAustralia
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I. M. Villa
I. M. Villa
University of BernSwitzerland
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Geological Society of London
Volume
220
ISBN electronic:
9781862394681
Publication date:
January 01, 2003

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