Mantle plume capture, anchoring, and outflow during Galápagos plume‐ridge interaction

Abstract

AbstractCompositions of basalts erupted between the main zone of Galápagos plume upwelling and adjacent Galápagos Spreading Center (GSC) provide important constraints on dynamic processes involved in transfer of deep‐mantle‐sourced material to mid‐ocean ridges. We examine recent basalts from central and northeast Galápagos including some that have less radiogenic Sr, Nd, and Pb isotopic compositions than plume‐influenced basalts (E‐MORB) from the nearby ridge. We show that the location of E‐MORB, greatest crustal thickness, and elevated topography on the GSC correlates with a confined zone of low‐velocity, high‐temperature mantle connecting the plume stem and ridge at depths of ∼100 km. At this site on the ridge, plume‐driven upwelling involving deep melting of partially dehydrated, recycled ancient oceanic crust, plus plate‐limited shallow melting of anhydrous peridotite, generate E‐MORB and larger amounts of melt than elsewhere on the GSC. The first‐order control on plume stem to ridge flow is rheological rather than gravitational, and strongly influenced by flow regimes initiated when the plume was on axis (>5 Ma). During subsequent northeast ridge migration material upwelling in the plume stem appears to have remained “anchored” to a contact point on the GSC. This deep, confined NE plume stem‐to‐ridge flow occurs via a network of melt channels, embedded within the normal spreading and advection of plume material beneath the Nazca plate, and coincides with locations of historic volcanism. Our observations require a more dynamically complex model than proposed by most studies, which rely on radial solid‐state outflow of heterogeneous plume material to the ridge.