Migration of widespread long-lived volcanism across the Galápagos Volcanic Province: Evidence for a broad hotspot melting anomaly?

The well-studied Galápagos Archipelago is a small part of the much larger Galápagos Volcanic Province (GVP) consisting of the Cocos, Carnegie, Coiba and Malpelo aseismic ridges and related seamount provinces. Although these aseismic ridges and seamounts dominate the morphology of the region, little is known about their origin due to a lack of direct age and geochemical information. In order to establish how well the GVP fits with the predictions of the ‘standard’ fixed hotspot and mantle plume hypotheses we conducted a first reconnaissance dredge/grab sampling of submerged regions of the GVP. We present here 40Ar/39Ar ages for many of these new basement samples and evaluate their implications for the various models put forward to explain the origin of the GVP. Correlating new and published sample-site ages with distance from the western side of the Galápagos Islands show that volcanism has not progressed in narrow, time-progressive lines of seamounts and ridges as predicted by the conventional fixed hotspot and mantle plume hypothesis. Rather, volcanism apparently migrated time-progressively across the GVP in broad regions of long-lived and possibly concurrent volcanism. We propose that the most viable explanation for these observations is that the GVP is the product of Cocos and Nazca plate motions across a broad hotspot melt anomaly. The complex spreading history of the Cocos–Nazca spreading centre likely controlled the relative distribution of GVP volcanism between the Cocos and Nazca plates while creating lithosphere of variable age/thickness across the region. While the notion of a broad Galápagos hotspot melting anomaly linked to a complex regional tectonic history requires significant testing it nevertheless highlights the need to test alternative mantle upwelling shapes and sizes compared to the widely accepted notion of a narrow continuous long-lived Galápagos mantle plume conduit defined by the size and location of a Galápagos island.