Hydrothermal exploration near the Azores Triple Junction: tectonic control of venting at slow-spreading ridges?

Simultaneous acoustic imaging of the seafloor and detection of particle-rich plumes in the overlying water column have been used to identify and determine the tectonic setting of high-temperature ‘black smoker’ hydrothermal activity along 200 km of the Mid-Atlantic Ridge between 36° and 38°N. Using this approach, we have identified hydrothermal signals at 7 different locations. These results indicate a higher incidence of hydrothermal activity along this section of ridge axis than has been reported elsewhere along slow spreading ridges. Our data show that the majority of hydrothermal sites here are located near to non-transform offsets rather than at the centres of individual ridge segments. We suggest that this intersection of fabrics, associated with ridge discontinuities and the spreading process, is instrumental in focussing hydrothermal flow at these localities. Future strategies of exploration for hydrothermal activity on slow-spreading ridges may need to be revised accordingly.