A magma mixing redox trap that moderates mass transfer of sulphur and metals
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Authors
Fiege, A.
Ruprecht, P.
Simon, A.
Issue Date
2017
Type
Article
Language
Keywords
magma-magma mixing , redox gradient , porphyry Cu-Au ore deposit formation , Fe XANES , dacite , andesite
Alternative Title
Abstract
Mixing and juxtaposition of chemically distinct magmatic systems are key processes for the evolution of Earth's crust. Yet, the physicochemical nature at mixing interfaces remains poorly described, as crystallisation, melting, heat transfer, and diffusion are interconnected and lead to complex mass transfer processes driving unique patterns of element fractionation. Here, we use diffusion couple experiments between felsic and mafic magmas (melt + crystals +/- volatiles) to document the formation of large gradients in oxygen fugacity at the magma-magma mixing interface. Reducing and oxidising boundary layers at the interface develop rapidly and remain in dynamic disequilibrium for days to possibly weeks. We suggest that the observed transient redox gradient is caused by cation transfer across the interface where the required counter flux of electron holes is insufficient to compensate an evolving electron hole gradient. Such boundary layer redox effects may control fractionation of polyvalent and chalcophile elements and moderate, for example, Cu/Au ratios in arc-related porphyry ore deposits.
Description
Citation
Fiege, A., Ruprecht, P., & Simon, A. (2017). A magma mixing redox trap that moderates mass transfer of sulphur and metals. Geochemical Perspectives Letters, 190–199. doi:10.7185/geochemlet.1722
Publisher
Journal
Volume
Issue
PubMed ID
ISSN
2410-339X