Fijian Tonalites: Enriched mantle to continental crust in an oceanic arc setting
Abstract
Seismic cross sections of some island arcs, such as the Izu arc, have shown a 6-6.5 km/s middle crust consistent with a tonalitic composition and mineralogy. While seismic data do not exist for the remnant arc of Fiji, Viti Levu has one of the largest exposures of Tertiary tonalite plutons in the world. This study uses major and trace elements, Sr-Nd-Pb-Hf isotopes, and zircon data for four tonalite plutons and adjacent dacitic volcanics to decipher potential sources and processes for production of middle crust in island arcs. The data show geochemical variability between and within plutons. K2O ranges from <0.5 to 2% at >70% SiO2. REE patterns vary from LREE enriched like that of continental crust to LREE depleted Each pluton is isotopically unique, but all overlap the Fijian basement and local mantle. No subducted or even crustal-level sediment is required. However, both crust and mantle are enriched and FOZO-like isotopically. Trace element modeling shows that the tonalites can be explained by simple melting models using Fijian basement as source material. This suggests that the production of middle crust could be the result of reworking arc-type crust while preserving enriched mantle features.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.V33B2375D
- Keywords:
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- 1037 GEOCHEMISTRY / Magma genesis and partial melting;
- 8185 TECTONOPHYSICS / Volcanic arcs;
- 8413 VOLCANOLOGY / Subduction zone processes