Late miocene adakites and Nb-enriched basalts from Vizcaino Peninsula, Mexico: Indicators of East Pacific Rise subduction below Southern Baja California?

A typical slab melt association was emplaced from 11 to 8 Ma in the Santa C lara volcanic field, Vizcaino Peninsula, Baja California Sur. It includes a dakitic domes and associated pyroclastic Bow deposits, together with lava f lows of niobium-enriched basalts. The tract element and isotopic (Sr-Nd-Pb) signatures of adakites are consistent with melting of altered mid-ocean ri dge basalts, and the sources of the Nb-enriched basalts contain an enriched mantle wedge component. Such associations commonly form at depths of 70-80 km during low-dip subduction of very young oceanic crust. However, the San ta Clara field is relatively close (100 km) to the paleotrench, which sugge sts that the genesis of its adakites and Nb-enriched basalts occurred in a very high thermal regime linked to the subduction of the then-active Guadal upe spreading center of the East Pacific Rise. Our data suggest that the as thenospheric window documented below northern Baja California also develope d beneath the south of the peninsula during the Neogene. This hypothesis is consistent with the spatial distribution and the ages of adkites and magne sian andesites from this region.