Testing the chemical signature of chaotic magma mixing

Kamal Raj Regmi, Roberto Weinberg, Ian Nicholls

Research output: Contribution to journalArticleResearchpeer-review

2 Citations (Scopus)

Abstract

In this paper recent experimental predictions of the geochemical pattern of rock suites resulting from the mixing of magmas governed by chaotic dynamics are tested. It has been suggested in the past that during chaotic mixing of two magmas, the competition between element diffusion and the stretching and folding of magmas (mixing dynamics), leads to a systematic decrease in correlation between any two elements as the difference in diffusivities between them increases. This hypothesis is tested here using suites of rocks that record magma hybridization and others that record magma fractionation. The prediction is supported by our results, but it is impossible to differentiate between magma suites that have undergone mixing and those that have undergone fractionation. A recent experiment regarding chaotic magma mixing reported an unexpectedly high level of complexity in the distribution of major elements in systems undergoing mixing. This was also tested during the present work and for that we chose hybrid volcanic glass samples from the 1875A.D. eruption of Askja CentralVolcano, Iceland.Amicroprobe analysis carried out on samples from the extrusions and the existing published and unpublished data were collated. It was found that the data clustered into two separate groups: a basaltic one with approximately 50% SiO and a rhyolitic one with approximately 70% SiO with a small number of analyses in between. Each of the two end-member groups covers a relatively narrow range of compositions that can be explained by fractionation. The mixing trends are typically linear as is expected in conventional mixing models. We conclude that the typical linear trends between two end-member magmas, typically interpreted in the literature to indicate magma hybridization, are only well-developed for elements with similar diffusivities or for systems where the two end-members were fully mixed in different proportions in different parts of a magma suite, and that the complex trends expected from chaotic mixing are inferred to be relatively rare in nature.

Original languageEnglish
Pages (from-to)8-16
Number of pages9
JournalHimalayan Geology
Volume37
Issue number1
Publication statusPublished - 1 Jan 2016

Keywords

  • Chaotic mixing
  • Diffusion coefficients
  • Felsic-mafic mixing
  • Fractionation
  • Granite
  • Magma fractionation

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