Arc to rift transitional volcanism in the Santa Rosalía Region, Baja California Sur, Mexico

ASL lavas are generated from the partial melting of the sub-arc wedge after extensive slab-derived aqueous fluid metasomatism, followed by extensive calc-alkaline crystal fractionation (±amphibole accumulation) and variable degrees of crustal assimilation. SRD are interpreted to be slab melts that hybridized a significant mantle component. BTB, BBA and CSL rift lavas are the products of moderate degrees of partial melting of an adakite and aqueous fluid metasomatized mantle, with the principal control on melt chemistry being the extent of adakite contamination and degree of partial melting. Clinopyroxene-bearing CSL lavas appear to have undergone varying degrees of mixing with co-eruptive SRD melts.