The role of detachment faulting in the genesis of oceanic felsic melts

Oceanic detachments are deep-rooted, long-lived, plate-scale structures and serve as fluid conduits introducing water into the oceanic lithosphere, impacting plate rheology and potentially inducing oceanic crustal melting. However, the extent and mechanisms of fluid ingress and crustal melting during detachment faulting remains poorly constrained. Here we examine felsic veins from the Atlantis Bank oceanic core complex, Southwest Indian Ridge, to elucidate oceanic detachment controls on crustal melting. We suggest that the felsic veins are products of strong fractionation of either primitive basalts or magmas generated by hydrous melting of gabbros (i.e., anatectic melts). The anatectic felsic veins are proximal to the fault plane, suggesting that detachment fault facilitated high-temperature (750–900 °C) seawater infiltration into deep oceanic crusts. Our findings highlight the essential role of detachment faulting played in the fluid ingress and melting of oceanic crust, bearing implications for chemical and heat exchange between seawater and oceanic lithosphere. Oceanic detachment faulting modulates the extent of hydrous melting of deep oceanic crusts, forming diverse felsic melts, according to geochemical and petrological data from felsic veins in the Atlantic Bank oceanic core complex in the Southwest Indian Ridge.