Pt/Pd and Pd/Ir ratios in mantle-derived magmas: A possible role for mantle metasomatism

Maier, Wolfgang D. ORCID: https://orcid.org/0000-0002-8654-6658 and Barnes, J. 2004. Pt/Pd and Pd/Ir ratios in mantle-derived magmas: A possible role for mantle metasomatism. South African Journal of Geology 107 (3) , pp. 333-340. 10.2113/107.3.333

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Abstract

We compare concentrations of Pt, Pd, and Ir in mantle-derived magmas, ranging from tholeiitic basalts to komatiitic basalts, komatiites, and various alkaline magmas, and in oceanic and continental settings. The alkaline magmas tend to have higher Pt/Pd ratios, but lower Pd/Ir ratios than most of the other magmas. We suggest this is attributable to different melting conditions in the mantle. Under relatively “dry” melting conditions applicable to tholeiites and komatiites, Pt-alloys and Os-Ir-Ru-Rh-enriched monosulfide solid solution (Mss) behave in a refractory manner, resulting in sub-chondritic Pt/Pd and super-chondritic Pd/Ir. Under fluid-rich melting regimes in metasomatised lithospheric mantle sources that may be applicable to the generation of many alkaline magmas, the alloys/mss are more fusible, resulting in PGE ratios closer to chondrite. Bushveld magmas and some continental flood basalts also have relatively high Pt/Pd ratios and may thus contain a component of the metasomatised sub-continental lithospheric mantle. Komatiites have relatively low Pt/Pd suggesting that they are derived from a dry mantle source.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Earth and Environmental Sciences
Subjects:	Q Science > QE Geology
Publisher:	Geological Society of South Africa
ISSN:	1012-0750
Last Modified:	25 Oct 2022 08:59
URI:	https://orca.cardiff.ac.uk/id/eprint/56729

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