Post-subduction volcanism in the Baja California Peninsula, Mexico: The effects of tectonic reconfiguration in volcanic systems

Late Cenozoic volcanism in the Baja California Peninsula records the effects of cessation of subduction at a previously convergent plate margin. Prior to 12.5 Ma the predominant volcanic activity had a calc-alkaline signature, however, after 12.5 Ma during the period of tectonic transition from a convergent to a strike-slip boundary, the style and composition of the magmatic products changed dramatically. It has been proposed that the origin of the post-subduction “anomalous” slab–melt-related magmas (i.e., adakites, niobium-enriched basalts, magnesian andesites) is linked to regional tectonic events such as the subduction of an active ridge, the breakoff of the subducted slab, or the tearing of the stalled slab. Here, we compile already published data on this volcanism and critically examine the tectonic models proposed to explain its origin. An alternative approach, based on a physical model of volcanic systems, suggests that post-subduction volcanism is strongly influenced by more local aspects including the stress field and the tensile strength of the rock overlying the zones where partial melting occurred. This interpretation allows us to reconcile the apparent contradictory observations of the temporal and spatial distributions of post-subduction activity, providing a more adequate explanation of many characteristics of the Baja California post-subduction volcanism.