Fig. 7: Cartoons depicting subduction initiation and the slab dehydration/melting processes.
From: Boron isotopes in boninites document rapid changes in slab inputs during subduction initiation
The model starts at a hypothetical transform fault at the boundary between the proto-Philippine Sea Plate and Pacific plate69. a Shallow angle convergence of the Pacific plate beneath the proto-Philippine Sea Plate resulted in accretion of Pacific sediments and upper crust. The lower crust experienced higher temperature metasomatism resulting in higher overall δ11B. b Decompression melting in response to slab rollback, producing forearc basalt (FAB). c low-silica boninite (LSB) genesis, depleted FAB mantle source metasomatized by lower crust melting components. d high-silica boninite (HSB) genesis, with an ultra-depleted mantle wedge after LSB extraction further metasomatized by hydrous fluids from a mixed ocean crust source + sediment.
