Lithospheric Controls on Volcanic Processes in the Northern Galápagos Volcanic Province
Abstract
The Northern Galápagos Volcanic Province (NGVP), located between the Galápagos Archipelago and the Galápagos Spreading Center (GSC), was mapped and sampled during the 2010 MV1007 cruise. The NGVP is densely populated by a set of seamounts that are morphologically diverse, ranging from small, flat-topped cones to elongate, polygenetic structures. Most of the seamounts are arranged in three NW-trending lineaments that intersect the GSC at 20-40 km intervals, the most voluminous of which is the Wolf-Darwin Lineament, which includes Wolf and Darwin Islands as the emergent tips of large submarine volcanoes. Geochemical evidence suggests that the mantle underlying the entire NGVP region is infused with Galápagos plume material that has a limited compositional range compared to other parts of the archipelago. In general, seamounts in the lineaments become larger and increasingly elongate with distance from the GSC. Despite predictions to the contrary (e.g., Morgan, 1978), there are few systematic geochemical or petrologic variations along strike of the lineaments. Furthermore, what patterns that do exist are not consistent across the different lineaments. The exception is Sm/Yb, which increases progressively with distance from the GSC across the NGVP, with the greatest increase occurring in a step-like manner across a NW-trending pseudofault that crosscuts the study area. Given the relatively consistent plume contents of magmas in the NGVP, this observation suggests that lithospheric thickness is the primary control on variations in geochemical compositions in the region, particularly where the lithosphere is older than ~3 Ma. We present melt fraction-depth profiles from rare earth element inversion modeling using INVMEL (McKenzie and O'Nions, 1991) of NGVP samples, in order to quantify and map lithospheric thickness variations in the study area. Applying an empirical relationship of Gibson and Geist (2010) that relates Sm/Yb to seismically determined lithospheric thickness, we use lithospheric thicknesses estimated from our rare earth element modeling to predict regions of higher and lower melt accumulation in the NGVP, with the primary goal of constraining plume-ridge interaction mechanisms. Our results are consistent with a model in which extensional stresses generated by the transform fault at 90°50'W on the GSC cause the NGVP to be under tension, resulting in NW-trending lithospheric fractures that initiate melting of a variably plume-contaminated mantle to produce the seamounts aligned in lineaments parallel to trajectories of least tensile stress.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMDI13A2140H
- Keywords:
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- 1009 GEOCHEMISTRY / Geochemical modeling;
- 1033 GEOCHEMISTRY / Intra-plate processes;
- 8415 VOLCANOLOGY / Intra-plate processes;
- 8416 VOLCANOLOGY / Mid-oceanic ridge processes