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; Frederic Moynier

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

Zhengbin Deng ¹ Marc Chaussidon ¹ Paul Savage ² François Robert ³ Raphaël Pik ⁴ Frederic Moynier ^{1, 5}

1 IPGP - Institut de Physique du Globe de Paris

2 University of St Andrews [Scotland]

3 IMPMC - Institut de minéralogie, de physique des matériaux et de cosmochimie

4 CRPG - Centre de Recherches Pétrographiques et Géochimiques

5 IUF - Institut Universitaire de France

Abstract : Indirect evidence for the presence of a felsic continental crust, such as the elevated 49 Ti/ 47 Ti 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 SiO 2 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 49 Ti/ 47 Ti 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 SiO 2 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 SiO 2 information. titanium isotopes | plume | island arc | magma differentiation | plate tectonics

Keywords : plume plate tectonics island arc titanium isotopes magma differentiation

Document type :

Journal articles

Domain :

Sciences of the Universe [physics] / Earth Sciences / Geochemistry

Sciences of the Universe [physics] / Earth Sciences / Tectonics

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