Large massive sulfide deposits in a newly discovered active hydrothermal system, The High‐Rise Field, Endeavour Segment, Juan De Fuca Ridge

Abstract

Submersible observations and side‐scan sonar imagery delineate ten large venting sulfide‐sulfate‐silica structures located on an uplifted block of the axial valley floor on the central portion of the Endeavour Segment, Juan de Fuca Ridge. This newly discovered vent field lies 1.8 km north of the main Endeavour vent field. The axial valley, a horst, and faults controlling sulfide deposition trend parallel to the ridge axis. The horst rises 10 to 15 m above the valley floor and offsets a lava lake which extended 500 m in width across the valley. The largest sulfide structures are perched along the major horst‐bounding faults. One structure is the tallest single edifice (45 m) reported in the Pacific Ocean. Smaller, less‐active and inactive sulfide edifices are associated with faulted remnants of the lava lake surface, fissured pressure ridges, and at the edge of collapse pits.Based on the relationship between faults and sulfide structures, the morphology of sulfide edifices, and their venting characteristics, we infer that sulfide structures grow vertically by chimney accumulation and laterally by flange development. Late stage deposition of amorphous silica toughens the large deposits and may be responsible for the unusual size and aspect ratio of Endeavour edifices.