Investigation of Ge and Ga exchange behaviour and Ge isotopic fractionation during subduction zone metamorphism

The relatively small variation of δ74Ge values in metabasites compared to mantle rocks implies that the subducted oceanic crust cannot trigger Ge isotopic heterogeneities in the mantle through fluid-induced metasomatism or recycling in the deep mantle. However, during the late stages of retrogression, migration of oxidising fluids along the crust-mantle wedge may be responsible for a resolvable increase of the δ74Ge value of the mantle wedge along the subduction channel. Besides, the larger range of Ge concentrations and δ74Ge values in the micaschists suggests that recycling of subducted sediments may generate mantle Ge elemental and isotopic heterogeneities.