The role of mixing processes in andesite genesis - deep sediment recycling versus shallow crustal contamination
Final Report Abstract
The sampling of Methana and Aegina yielded a suite of andesitic to dactitic volcanic rocks and basaltic to andesitic enclaves that allows us the study of the generation and evolution of calc-alkaline magmas in continental areas. The composition of Fo-rich olivine and their Crspinel inclusions in the lavas indicates that the mantle beneath the western Aegean Arc was strongly depleted but re-enriched by a sedimentary slab component, most likely from carbonate-rich subducted sediments. The O isotope composition of the primitive olivine suggests a significant sediment contribution up to 6.5% to the Methana primary magmas prior to assimilation of sediments during the passage through the continental crust. Thus, the detailed study of olivine can provide important data on the mantle wedge for magmas that were strongly altered by assimilation processes. The detailed petrological and geochemical study of the andesitic to dacitic lavas indicates the complex history of the Methana magmas with stagnation, fractional crystallization, assimilation and mixing occurring during the ascent of the magmas through the crust. Our results indicate that while fractional crystallization occurs at different depths in the crust starting at the Moho, the assimilation is strongest in the metasediments of the upper crust whereas little assimilation is observed in the more mafic melts. Thus, although the temperatures of the crustal rocks and the magmas are highest in the lower crust, the abundance of fusible material in the upper crust may have a strong effect on the assimilation processes.
Publications
- 2017. The origin of evolved volcanic rocks in Methana, Greece. Goldschmidt Conference 2017, Paris
Schönhofen, M., Wölki, D., Haase, K., and Beier, C.
- 2018. Evidence for melting of subducting carbonate-rich sediments in the western Aegean Arc. Chemical Geology 483, 463-473
Woelki, D., Haase, K.M., Schoenhofen, M.V., Beier, C., Regelous, M., Krumm, S.H., and Günther, T.
(See online at https://doi.org/10.1016/j.chemgeo.2018.03.014)
