Minerals Report - International Seabed Authority
Minerals Report - International Seabed Authority Minerals Report - International Seabed Authority
Figure 6: Distributions of hydrothermal activity detected along the central Mid-Atlantic Ridge near the Azores Triple Junction (35°N-40°N) superimposed upon the pseudobathymetry derived from satellite altimetry by Sandwell & Smith [29]. One of these sites has been studied in detail - the Rainbow hydrothermal field, which lists among the few largest massive sulphide deposits yet located in the North Atlantic Ocean (Fouquet et al., 1997). Intriguingly, this deposit is also located in an entirely new geological setting. It does not occur where freshest lava out-pouring have occurred, at the centre of a ridge segment but, instead, is found at the intersection between a segment of ridge axis and the offset or fracture zone that connects that segment of the INTERNATIONAL SEABED AUTHORITY 384
Mid Atlantic Rise crest to the next one (German & Parson, 1998). In fact, of the seven different hydrothermal fields located as part of our Azores hydrothermal study, four including Rainbow were found in this novel geologic setting (Figure 7). Figure 7: Line drawn map of the MAR near the Azores Triple Junction. Locations of detected hydrothermal plume signals and/or active vent sites are shown by coloured circles. Yellow: “conventional” volcanically hosted systems. Orange: novel fault-controlled environments within non-transform ridge discontinuities [7, 9,10]. What is clearly the case, therefore, is that one does not simply require a fresh volcanic eruption (heat source) to establish seafloor hydrothermal circulation. If one includes the Reykjanes Ridge and Azores Triple Junction data in our previous plot, we now find that a range of different vent abundances can arise at constant spreading rate (Figure 8). INTERNATIONAL SEABED AUTHORITY 385
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Mid Atlantic Rise crest to the next one (German & Parson, 1998). In fact, of<br />
the seven different hydrothermal fields located as part of our Azores<br />
hydrothermal study, four including Rainbow were found in this novel<br />
geologic setting (Figure 7).<br />
Figure 7: Line drawn map of the MAR near the Azores Triple Junction. Locations of detected<br />
hydrothermal plume signals and/or active vent sites are shown by coloured circles. Yellow:<br />
“conventional” volcanically hosted systems. Orange: novel fault-controlled environments<br />
within non-transform ridge discontinuities [7, 9,10].<br />
What is clearly the case, therefore, is that one does not simply require a<br />
fresh volcanic eruption (heat source) to establish seafloor hydrothermal<br />
circulation. If one includes the Reykjanes Ridge and Azores Triple Junction<br />
data in our previous plot, we now find that a range of different vent<br />
abundances can arise at constant spreading rate (Figure 8).<br />
INTERNATIONAL SEABED AUTHORITY 385
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