SUBMARINE HYDROTHERMAL VENTING RELATED TO VOLCANIC ARCS

Volcanic arcs that have a submarine component (n=21) include both intra-oceanic and island arcs that combined total almost 22,000 km with ~93%, or just over 20,000 km, occurring in the Pacific region. We estimate the number of volcanoes known to occur along these arcs to be 693, with at least 206 (29%) being submarine. Less than 3% of arc length has been systematically surveyed for seafloor hydrothermal emissions. Submarine hydrothermal venting along these arcs therefore remains overwhelmingly undetected.

Plumes and vent fluids from arc sites are chemically heterogeneous in nature and in some cases highly enriched compared to MOR sites. They include liquid- plus gas-rich to liquid-poor but gas-rich types. Evidence for a magmatic component in arc vent systems is given by the nature and concentrations of various gases and iron.

The Kermadec arc extends for ~1,200 km northeastwards from New Zealand and forms the southern part of the ~2,500-km-long Tonga-Kermadec intra-oceanic arc system. At least 33 volcanoes occur along the Kermadec arc with all but one (Raoul Island) being submarine. The combined NZAPLUME I and II cruises of March 1999 and May 2002, respecitvely, have systematically surveyed ~840 km of the Kermadec arc including 26 major volcanoes and 8 smaller volcanic edifices. Ten of the volcanoes (38%) host active vent fields with Brothers and Healy each hosting two separate sites. In addition, both Curtis and Raoul islands host subaerial geothermal systems. Combined, this equates to a ‘vent field’ every 70 km of arc length. However, our surveys show that venting is not distributed evenly along the Kermadec arc with ‘active’ southern and northern sections hosting vent fields every ~35 km while a stretch of ~520 km of arc in between appears dormant (pending shore-based analyses such as helium isotope ratios) with respect to venting.

If the frequency of venting for the presently surveyed part of the Kermadec arc is projected worldwide for all known submarine arc volcanoes, this equates to 78 hydrothermally active vent sites. Considering the number of sites still to be discovered, this makes submarine arcs a potentially a very rich source of hydrothermal fluids and minerals.