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

journal contribution
posted on 2023-05-19, 06:26 authored by Cawthorn, RG, Chistyakova, SY, Latypov, RM, Vadim Kamenetsky, Leonid Danyushevsky
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.

History

Publication title

Geology

Volume

45

Issue

7

Pagination

603-606

ISSN

0091-7613

Department/School

School of Natural Sciences

Publisher

Geological Soc America

Place of publication

Inc, Po Box 9140, Boulder, USA, Co, 80301-9140

Rights statement

Copyright 2017 Geological Society of America

Repository Status

  • Restricted

Socio-economic Objectives

Expanding knowledge in the earth sciences

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