Titanium isotopes as a tracer for the plume or island arc affinity of felsic rocks

Zhengbin Deng*, Marc Chaussidon, Paul Savage, François Robert, Raphaël Pik, Frédéric Moynier

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

71 Citations (Scopus)
1 Downloads (Pure)

Abstract

Indirect evidence for the presence of a felsic continental crust, such as the elevated 49Ti/47Ti ratios in Archean shales, has been used to argue for ongoing subduction at that time and therefore plate tectonics. However, rocks of intermediate to felsic compositions can be produced in both plume and island arc settings. The fact that Ti behaves differently during magma differentiation in these two geological settings might result in contrasting isotopic signatures. Here, we demonstrate that, at a given SiO2 content, evolved plume rocks (tholeiitic) are more isotopically fractionated in Ti than differentiated island arc rocks (mainly calc-alkaline). We also show that the erosion of crustal rocks from whether plumes (mafic in average) or island arcs (intermediate in average) can all produce sediments having quite constant 49Ti/47Ti ratios being 0.1–0.3 per mille heavier than that of the mantle. This suggests that Ti isotopes are not a direct tracer for the SiO2 contents of crustal rocks. Ti isotopes in crustal sediments are still a potential proxy to identify the geodynamical settings for the formation of the crust but only if combined with additional SiO2 information.
Original languageEnglish
Pages (from-to)1132-1135
JournalProceedings of the National Academy of Sciences of the United States of America
Volume116
Issue number4
Early online date3 Jan 2019
DOIs
Publication statusPublished - 22 Jan 2019

Keywords

  • Titanium isotopes
  • Plume
  • Island arc
  • Magma differentiation
  • Plate tectonics

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