Metasomatism and deformation of block-in-matrix structures in Syros: The role of inheritance and fluid-rock interactions along the subduction interface

The behavior of fluids at the subduction plate interface and their chemical rheological impacts remain poorly constrained. Based on detailed fieldwork, petrographic geochemical analyses thermobarometry, present study documents an example a block-in-matrix ‘mélange’ metasomatized along (Kampos-Lia mélange zone, Cycladic Blueschists, Syros island). We show that this particular zone is preserved fragment discontinuous oceanic domain associated with Pindos basin, which underwent dominant exhumation-related deformation top to east shearing. A large part structure inherited from initial intraoceanic setting should not be considered as tectonic ‘mélange’. Through exhaustive, meter-scale mapping nature blocks matrix we metasomatism dominantly occurs contact between metavolcanic layers serpentinite, diffusion Ca metavolcanics Mg in opposite direction. Most (mafic carbonate) are only partly digested contrary ultramafic has been largely forms tremolite-chlorite-talc schist, i.e. ‘hybrid’ rock intermediate composition. Geochemical data demonstrate metasomatic element mobilization (e.g. Li, B, U, LILE REE) varies scale unit, suggesting complex evolution fluid composition kilometer scale. suggest intruded Kampos subunit was derived subducting slab caused enrichment (Rb, K, Na, Ba, Eu), MREE HREE. Mineralogical P-T constraints indicate hybridization occurred during exhumation, ~ 1 GPa, well after peak burial detachment (~ 2 GPa). Due absence major mixing scarce preservation prograde reactions, may representative fore-arc processes depths 35 km. Deeper hypothesized produce potential source for arc magmas studied examples. However, by changing mineralogy matrix, changes properties could thus manipulate rheology influence exhumation processes.