Main Endeavour Field
The Main Endeavour Field (MEF) was found in 1984 and first reported to the scientific community in 1986. It was discovered by accident while conducting a cruise in the area (William Wilcock, personal communication). The field is situated along the western wall of the central valley of the Endeavour rift. The vents occupy an area over 350 m long and almost 180 m wide in a chaotic series of lava flows and fault scarps (Delaney et al, 1992).
The MEF is the most active of the five known hydrothermal vent fields on the Endeavour Segment. It contains over 15 large vent structures, some of which rise over 20 meters above the sea floor (Delaney et al, 1992). One vent generated fluids with temperatures of over 400 C, or four times the boiling point of water at sea level (Wilcock, personal communication). These structures are in large part controlled by normal faults in the floor of the central valley of the Endeavour rift. These faults provide conduits which allow hot fluids from deep within the Earth to rise to the surface (Delaney et al, 1992).
Hydrothermal vent structures at MEF are composed primarily of sulfides and silicates. These minerals are formed as metals and sulfur precipitates out of the hydrothermal fluid upon contact with cold seawater. The sulfide structures are typically steep sided, with several actively venting chimneys. Delaney et al did not find much evidence for collapsed chimneys or talus, implying that these large vent structures are not simply rubble piles but grew by direct mineralization (Delaney et al, 1992). The temperature of fluids emanating from these structures is sensitive both to tides and nearby seismic activity (Johnson et al, 2000).
Another feature of the MEF is what Delaney termed ‘flanges.’ These are shelves which extend from the vertical sides of the vent structures and are typically covered in tube worms and other biology. Beneath these flanges are pools of shimmering, superheated fluid trapped against the rock by their own buoyancy. Such pools provide an alternate route for hydrothermal fluids and also a growth mechanism for the sulfide structures (Delaney et al, 1992). They appear reflective because of the extreme density difference between the 300+ C vent fluids and the 1.8 C seawater (Delaney et al, 1992).