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A triple S-shaped compositional profile in a Karoo dolerite sill - evidence of concurrent multiple fractionation processes

Cawthorn, RG, Chistyakova, SY, Latypov, RM, Kamenetsky, VS ORCID: 0000-0002-2734-8790 and Danyushevsky, LV ORCID: 0000-0003-4050-6850 2017 , 'A triple S-shaped compositional profile in a Karoo dolerite sill - evidence of concurrent multiple fractionation processes' , Geology, vol. 45, no. 7 , pp. 603-606 , doi: 10.1130/G38917.1.

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Abstract

Thick dolerite sills show a range of vertical geochemical variation trends attributable to various processes during slow crystallization. We have identified chemical parameters in a 169-m-thick sill from the Karoo igneous province in South Africa that define three different lower crossover levels (maximum or minimum concentrations) creating S-shaped variation trends. The crossover level for wholerock MgO is at 20 m height (due to mechanical sorting of olivine); the anorthite content of plagioclase is at 52 m (due to addition of primitive magma); and that of the incompatible trace elements is at 75 m (due to different proportions of early formed grains to trapped liquid). Each process can operate independently and concurrently, leading to their maximum effects occurring at different levels in the intrusion. The independence of these processes and the triple S-shaped geochemical profiles have not been recognized before in any mafic-ultramafic sills.

Item Type: Article
Authors/Creators:Cawthorn, RG and Chistyakova, SY and Latypov, RM and Kamenetsky, VS and Danyushevsky, LV
Keywords: dolerite, fractionation, Karoo, igneous, compositional profile, plagioclase
Journal or Publication Title: Geology
Publisher: Geological Soc America
ISSN: 0091-7613
DOI / ID Number: 10.1130/G38917.1
Copyright Information:

Copyright 2017 Geological Society of America

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