FAMOUS MORB olivines as diaries of igneous mush processes in ocean ridge plumbing systems

Magma storage and differentiation commonly involve extensive interactions between melts and crystal-rich domains. However, the mechanisms controlling these interactions remain difficult to constrain because erupted lavas and deep plutonic rocks provide complementary but rarely directly connected records of crustal magmatic processes. Here, we integrate petrological and geochemical data from the FAMOUS segment of the Mid-Atlantic Ridge with thermodynamic modelling. Together, these data provide a simple criterion for identifying mid-ocean ridge basalt (MORB) phenocrysts that were inherited from underlying mush zones and subsequently cannibalised by ascending magmas. This process of crystal scavenging documents repeated recycling of mush-derived crystals by ascending melts prior to eruption. It also provides unique snapshots of processes occurring within active mushy reservoirs. Reactive porous flow and diffusive re-equilibration modify both melt and crystal compositions, producing hybrid magmas whose geochemical signatures differ from those of primary mantle melts. These hybrid magmas highlight the key role of melt-mush interactions in mid-ocean ridge basalt (MORB) genesis.