Hydrothermal activity along the slow-spreading Lucky Strike ridge segment (Mid-Atlantic Ridge): Distribution, heatflux, and geological controls

Abstract:

We have reviewed available visual information from the seafloor, and recently acquired microbathymetry for several traverses across the Lucky Strike segment to evaluate the distribution of hydrothermal activity. The Lucky Strike segment hosts three active hydrothermal fields: Capelinhos, Ewan, and the known Main Lucky Strike Hydrothermal Field (MLSHF). Capelinhos is located 1.3 km E of the axis and the MLSHF, and consists of a ~20 m sulfide mound with black smoker vents. Ewan is located ~1.8 km south from the MLSHF along the axial graben, and displays only diffuse flow along and around scarps of collapse structures associated with fault scarps. At the MLSHF we have identified an inactive site, thus broadening the extent of this field.

Heat flux estimates from these new sites are relatively low and correspond to ~10% of the heat flux estimated for the Main field, with an integrated heatflux of 200-1200 MW. Overall, most of the flux (up to 80-90%) is associated with diffuse outflow, with the Ewan site showing solely diffuse flow and Capelinhos mostly focused flow.

Microbathymetry also reveals a large, off-axis (~2.4 km) hydrothermal field, similar to the TAG mound in size, on the flanks of a rifted volcano. The association of these fields to a central volcano, and the absence of indicators of hydrothermal activity along the ridge segment, suggest that sustained hydrothermal activity is maintained by the enhanced melt supply and the associated magma chamber(s) required to build central volcanoes. Hydrothermal outflow zones at the seafloor are systematically controlled by faults, indicating that hydrothermal circulation in the shallow crust exploits permeable fault zones. Central volcanoes are thus associated with long-lived hydrothermal activity, and these sites may play a major role in the distribution and biogeography of vent communities.