Exploration of Intraoceanic Arc Seafloor Hydrothermal Systems: What do we Know?

Abstract:

Surveying since 1997 of submarine arc volcanoes for their hydrothermal venting has revealed a world of remarkable spectacle, including ‘lakes’ of molten sulfur, chimneys expelling liquid CO₂, spectacular eruptions on the seafloor and never before seen animals. Surveys encompassing hydrothermal systems of the Mariana and Kermadec arcs especially, have meant these systems can be put into context with respect to global seafloor hydrothermal venting. For example, the ~6,900 km of intraoceanic arcs in the world equates to hydrothermal emissions equal to ~10% of that from the 60,000 km of mid-ocean ridges with a similar incidence of venting. In concert with surface ship-based surveys focused on bathymetric, geophysical and water column studies, expeditions utlizing manned submersibles (e.g., Shinkai 6500, Pisces V) and ROVs (e.g., ROPOS, Jason II, Kiel 6000) have provided vital rock, mineral, animal and vent fluid samples from these seafloor systems. The recent introduction of AUVs (e.g., Sentry) has provided information at a scale that is relevant to the study of volcanic and structural processes, ore deposit formation, and vent-related habitats.

Intraoceanic arc volcanoes and their corresponding hydrothermal systems can occur atop cones, inside calderas and combinations thereof, and range in depth from near surface to ~2000 m below sea level. A compilation of information encompassing more than 50 volcanoes has enabled their associated hydrothermal systems to be categorized into three broad types: volcanic, magmatic-hydrothermal, and water/rock interaction. Volcanic systems (~5%) are in various stages of eruption and are dominated by the expulsion of gases. Magmatic-hydrothermal systems are a continuation of volcanic systems and represent the most common type (~75%) observed on the seafloor. They are also dominated by the discharge of magmatic gases (esp. CO₂ and SO₂) that interact with seawater near the seafloor, forming strong acids, sulfate and elemental sulfur. Water/rock systems (~20%) expel less gas but more metals and are commonly associated with Cu-Zn-Au-rich mineralization, locally forming 7-m-high chimneys. Drilling of Brothers volcano by IODP will provide insight into the 3^rd dimension of the volcanic architecture and distribution of metals and metalloids throughout this edifice.