Monogenetic Near‐Island Seamounts in the Galápagos Archipelago

Rarely have small seamounts on the flanks of hotspot derived ocean-island volcanoes been the targets of sampling, due to sparse high-resolution mapping near ocean islands. In the Galápagos Archipelago, for instance, sampling has primarily targeted the subaerial volcanic edifices, with only a few studies focusing on large-volume submarine features. Sampling restricted to these large volcanic features may present a selection bias, potentially resulting in a skewed view of magmatic and source processes because mature magmatic systems support mixing and volcanic accretion that overprints early magmatic stages. We demonstrate how finer-scale sampling of satellite seamounts surrounding the volcanic islands in the Galápagos can be used to lessen this bias and thus, better constrain the evolution of these volcanoes. Seamounts were targeted in the vicinity of Floreana and Fernandina Islands, and between Santiago and Santa Cruz. In all regions, individual seamounts are typically monogenetic, but each seamount field requires multigenerational magmatic episodes to account for their geochemical variability. This study demonstrates that in the southern and eastern regions the seamounts are characterized by greater geochemical variability than the islands they surround but all three regions have (Sr-Nd-He) isotopic signatures that resemble neighboring islands. Variations in seamount chemistry from alkalic to tholeiitic near Fernandina support the concept that islands along the center of the hotspot track undergo greater mean depths of melting, as predicted by plume theory. Patterns of geochemical and isotopic enrichment of seamounts within each region support fine-scale mantle heterogeneities in the mantle plume sourcing the Galápagos hotspot.