Slab melt metasomatism in subduction zones: insights from the geochemical and isotopic study of magnesian andesites.

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Project objective

The discovery of rocks with geochemical characteristics of slab melts (called adakites) in Ecuador (South America) and in several volcanic arcs around the globe suggests that both partial melts from the basaltic oceanic crust and hydrous fluids can be considered as important metasomatizing agents of the pendotitic mantle wedge. In Ecuador, magnesian andesites are commonly associated with the adakites of the fore-arc, suggesting a strong genetic relation between these rock types. Magnesian andesites share with adakites the typical characteristics of slab melts, but also display strong enrichments in Mg suggesting they interacted with the peridotitic material of the mantle wedge en route to the surface. The presence of both rock types closely associated in time and space in Ecuador reinforces the hypothesis that slab melts could be an important metasomatic agent in subduction zones. We would like to characterize the geochemical and isotopic differences (Sr, Nd, Hf, Pb. Th and CI) existing between both rock types to constrain the derivation of the magnesian andesites from the interaction of slab melts with the mantle. Basically, expected work would consist to show if a shift in isotopic data (or CI concentrations) from typical altered oceanic crust values (for adakites) to mantle values (for magnesian andesites) exists. Also, minerals in magnesian andesites will be investigated as early work (with major elements) has shown that their cores might possess a permanent adakite signature. Results from this study would bring precious informations on past and present process of material transfer from the subducted oceanic lithosphere to the mantle and the continental crust.

Original text from CORDIS.

Participants

• ROYAL HOLLOWAY AND BEDFORD NEW COLLEGE · EghamCoordinatorUnited Kingdom

Links

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