Fig. 6
From: Relict subduction initiation along a passive margin in the northwest Indian Ocean
Conceptual model of intra-oceanic subduction initiation. The cartoon shows general evolution of SI (modified after Metcalf and Shervais71). a SI nucleates at a lithospheric weakness, e.g. a transform fault, which separates older, colder, denser lithosphere from younger, warmer, buoyant lithosphere31,41,47,48,50. b Incipient sinking of the older lithosphere instigates seafloor spreading in the proto-forearc. Partial melting of fertile, MORB-like mantle produces forearc basalts (FAB). c Based on observed distinct geochemical imprints in LB, SI appears to have been aborted during Stage 2. A slab rollback faster than the plate convergence results in extension on the upper plate and ultimate termination of slab pull66. Extraction of FAB leaves a depleted MORB mantle (DMM), which is subsequently tapped during Stage 2 with culmination of boninites (BON) or Boninite-like rocks. Subduction, if continued past Stage 2 would have lead to production of a magmatic arc as observed in the Izu–Bonin Marianas and other intra-oceanic arc systems41,47,48
