[MIS11-06] Overview of IODP Exp. 376: hydrothermal systems and submarine eruption processes of Brothers volcano, Kermadec Arc
Keywords:IODP, submarine volcanism, hydrothermal
Recovered core material consists primarily of dacitic volcaniclastics (breccia) and lavas, affected by pervasive and complex alteration. We show that the extent of alteration reflects primary lithological porosity and the contrasting spatial and temporal contributions of seawater, hydrothermal fluid and magmatic fluid. Our findings suggest a two-step model for the origins of metal-rich volcanogenic massive sulphide deposits that is linked to caldera formation (de Ronde et al, 2019). In this model, initial hydrothermal activity of the pre-caldera volcano is dominated by magmatic gases and hypersaline brines. The gases mix with seawater as they ascend to the seafloor, while the dense hypersaline brines remain in the subsurface. Following caldera collapse, seawater is able to infiltrate the volcano through fault-controlled permeability, where it interacts with wall rock and the sequestered hypersaline brines before finally transporting their associated metals back to the seafloor where it forms Cu-Zn-Au-rich chimneys at the caldera rim. This two-step process may be common at submarine arc volcanoes that host volcanogenic massive sulphide deposits, and provides a mechanism for efficiently concentrating mineralisation at or near the seafloor. Future work will focus on identifying the volcanic eruption processes that are able to produce a submarine caldera at water depths of more than 1300 m, where hydrostatic pressure may modify eruption styles by limiting the amount of degassing and bubble growth that is possible during magma ascent.
de Ronde, Humphris, Höfig, Reyes, and the IODP Expedition 376 Scientists (2019) Critical role of caldera collapse in the formation of seafloor mineralization: The case of Brothers volcano. Geology, v.47, p.762-766