Roger P. Denlinger M. R. Fisk K. J. Howard G. L. Taghon Kim D. Klitgord James S. McClain G. R. McMurray J. C. Wiltshire Peter A. Rona 1990 <div id="abstract-1" class="section abstract"><p id="p-1">The first hydrothermal field on the northern Gorda Ridge, the Sea Cliff hydrothermal field, was discovered and geologic controls of hydrothermal activity in the rift valley were investigated on a dive series using the DSV <i>Sea Cliff</i>. The Sea Cliff hydrothermal field was discovered where predicted at the intersection of axis-oblique and axis-parallel faults at the south end of a linear ridge at mid-depth (2700 m) on the east wall. Preliminary mapping and sampling of the field reveal: a setting nested on nearly sediment-free fault blocks 300 m above the rift valley floor 2.6 km from the axis; a spectrum of venting types from seeps to black smokers; high conductive heat flow estimated to be equivalent to the convective flux of multiple black smokers through areas of the sea floor sealed by a caprock of elastic breccia primarily derived from basalt with siliceous cement and barite pore fillings; and a vent biota with Juan de Fuca Ridge affinites. These findings demonstrate the importance of off-axis hydrothermal activity and the role of the intersection of tectonic lineations in controlling hydrothermal sites at sea-floor spreading centers.</p></div> application/pdf 10.1130/0091-7613(1990)018<0493:MOAHAO>2.3.CO;2 en Geological Society of America Major off-axis hydrothermal activity on the northern Gorda Ridge article