Title

High-Resolution Surveys Along the Hot Spot–Affected Galapagos Spreading Center: 2. Influence of Magma Supply on Volcanic Morphology

Document Type

Article

Abstract

The Galapagos Spreading Center (GSC) at 89o-95oW exhibits large gradients in magma supply at a relatively constant intermediate spreading rate, making this area an ideal natural laboratory to study the effects of magma supply on volcanism at seafloor spreading ridges. Prior work shows that the GSC develops from axial valley to shallow axial rise and a shallow magma sill, much like a typical fast spreading ridge, as the contribution of the hot spot increases. The volcanic morphology varies with magma supply in a predictable manner that we divide into three terrains based on the characteristic style of volcanic emplacement and edifice construction within each terrain. The volcanic cone terrain comprises most of the GSC and is characterized by prominent volcanic cones within a >1 km wide and >100 m deep axial graben. Approaching the area of maximum mantle plume influence at 91oW, the GSC axis lies along an elevated axial rise split by a <1 km wide and><100 m deep axial>graben, and the style of volcanism shifts to axial volcanic ridge terrain characterized by axis-elongate, low-relief ridges of pillow lava. The lava channel terrain comprises only one segment on either side of the maximum magma supply at 91oW, where sheet lava flows and lava channels are relatively widespread. A general lengthening of seafloor fissures with increasing magma supply suggests a greater tendency toward linear source eruptions, in agreement with the volcanic observations. These results suggest that magma supply rather than magma chamber depth or rate of tectonic extension is the primary influence on lava morphology, hence eruptive processes, at seafloor spreading ridges in general. In both the axial volcanic ridge and lava channel terrains, a single prominent volcanic cone exists within each volcanic segment, suggesting a segment-centered magma focusing.

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