Intracrystalline melt migration in deformed olivine revealed by trace element compositions and polyphase solid inclusions

Abstract. Melt transport mechanisms have an important impact on the chemical composition of percolated host rock and migrating melts. migration is usually assumed to occur at grain boundaries. However, microstructural studies revealed occurrence polyphase inclusions along dislocations, subgrain boundaries microcracks in single mineral grains. The are interpreted as crystallized melt pockets suggesting that melts can migrate within deformed crystals. Intracrystalline diffusive re-equilibration lead significant trace element enrichments when associated with dissolution–precipitation reactions. In this contribution, we study a body replacive troctolites Erro-Tobbio ophiolitic mantle peridotites (Ligurian Alps, Italy). formation olivine-rich troctolite involved extensive impregnation dunitic matrix, i.e. partial dissolution olivine concomitant crystallization interstitial phases. matrix characterized by two distinct textures: (i) coarse olivine, representing relicts pre-existing dunite (olivine1), (ii) fine-grained undeformed product melt–rock interaction process (olivine2). Previous documented decoupling between texture composition, namely enriched compositions olivine1 rather than olivine2, would be expected from process. Notably, olivines correlated elongated 10 µm size (clinopyroxene, Ti-pargasite, chromite) preferentially oriented crystallographic axes. These show irregular contacts no preferred orientation phases composing similar vermicular formed during late-stage reactive troctolite. This suggests investigated did not form exsolutions but input metasomatic fluids percolating through grains closure magmatic system. We infer strongly fractionated volatile-rich were incorporated microfractures led inclusions. presence intracrystalline greatly enhanced evolved olivine1, turn acquiring character neoformed percolation strong geochemical implications efficient minerals rocks.