Oxygen isotope and trace element compositions of platiniferous dunite pipes of the Bushveld Complex, South Africa – Signals from a recycled mantle component?

Abstract The composition of magmas proposed as parental to the layered suite of the Bushveld Complex, and some models for the manner of their emplacement, are reviewed briefly. Included are some contributions published in South Africa, with which overseas readers might be less familiar. Emphasis is given to the broader features of the cumulates, and the contradictions raised by whole-rock compositional, Sr-isotopic, and trace-element data that cloud their correlation with proposed parental magmas. It is concluded that the Lower, Critical and Main Zones are the derivatives of only two primary magmatic lineages, while a third was added to residual liquids from which the layered rocks above the Pyroxenite Marker were formed. Excessive amounts of olivine and chromium in the cumulates of the Lower and Lower Critical Zones in the northern sector of the Western Limb can seemingly not be accounted for by the composition and volume of the putative magmas. This is attributed to (1) this sector being a proximal facies located close to the original feeder, and/or (2) crystal-charged magma batches, expelled from a lower magma chamber, being periodically injected into and dispersed within the liquids already in place in the Bushveld chamber. Thus, ongoing changes in the bulk composition of the liquids within the chamber would not be reflected in the rinds of earlier, chilled-facies rocks. The expulsion of significant volumes of liquid residua from the chamber during cumulate deposition is not ruled out.

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Magma addition and possible decoupling of major- and trace-element behaviour in the Bushveld Complex, South Africa

Chemical Geology ◽

10.1016/0009-2541(83)90023-2 ◽

1983 ◽

Vol 39 (3-4) ◽

pp. 335-345 ◽

Cited By ~ 12

Author(s):

R.Grant Cawthorn

Keyword(s):

South Africa ◽

Trace Element ◽

Bushveld Complex

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Recent fluid processes in the Kaapvaal Craton, South Africa: coupled oxygen isotope and trace element disequilibrium in polymict peridotites

Earth and Planetary Science Letters ◽

10.1016/s0012-821x(99)00311-8 ◽

2000 ◽

Vol 176 (1) ◽

pp. 57-72 ◽

Cited By ~ 44

Author(s):

H.-F Zhang ◽

D.P Mattey ◽

N Grassineau ◽

D Lowry ◽

M Brownless ◽

...

Keyword(s):

South Africa ◽

Trace Element ◽

Oxygen Isotope ◽

Kaapvaal Craton

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Trace-element content and partitioning in calcite, dolomite and apatite in carbonatite, Phalaborwa, South Africa

Mineralogical Magazine ◽

10.1180/0026461036750151 ◽

2003 ◽

Vol 67 (5) ◽

pp. 921-930 ◽

Cited By ~ 50

Author(s):

J. B. Dawson ◽

R. W. Hinton

Keyword(s):

South Africa ◽

Trace Element ◽

Oxygen Isotope ◽

Trace Element Content ◽

The Other ◽

Element Content ◽

Isotope Data ◽

Oxygen Isotope Data ◽

Carbon And Oxygen Isotope

AbstractA carbonatite sample from Phalaborwa, South Africa, consists of apatite, magnetite and a calcitedolomite ‘perthite’ which is interpreted as being due to exsolution of dolomite from a high-Mg calcite precursor. Carbon and oxygen isotope data indicate that the carbonates are equilibrated. In situ ionmicroprobe analyses for Fe, Mn, Na, Si, Y, the REEs, Pb, Th and U give the following average concentrations (in ppm) in the sequence apatite, calcite, dolomite: Fe 98, 1680, 8190; Mn 61, 510, 615; Na 1171, 627, 125; Si 368; 1.6, 0.2; Sr 4447, 5418, 2393; Ba 37, 2189, 75; La 1245, 300, 67; Y 121, 50, 5.8; Pb 16, 5.4, 1.4; Th 20, 0.02, 0; U 2.4, 0, 0.01. The concentrations are reasonably uniform in both apatite and dolomite, but in calcite are more variable. Na, Si, Y, the REEs, Pb, Th and U partition into apatite relative to both carbonates (and, hence, the precursor carbonate); KD ap/cc for REE decreases from ∽4 for La to ∽2 for Tm. There is almost equal partitioning of Sr between apatite and calcite. During separation of dolomite from calcite, Sr and Ba partition strongly into calcite and all the other analysed elements, except Fe and Mn, also preferentially enter calcite. The REEs prefer calcite relative to dolomite, and the KD dol/cc is reasonably constant, only varying from 0.23 to 0.17. Sr, Ba and Pb in the carbonates, and their partitioning between the calcite and dolomite, differ from other carbonatite carbonates reported in the literature.

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