Hydrothermal systems and mineralization of volcanic arcs: Comparison of West Pacific and Mediterranean arcs

Introduction Hydrothermal systems and their associated metal deposits have been studied at oceanic spreading centers since the late 1970s when they were first discovered. More recently, those studies have been extended to subduction zone hydrothermal systems including active volcanic arcs and back-arc environments. Oceanic spreading centers compose a global ridge system where new ocean crust is formed (divergent boundary) and extends for about 64,000 kilometres (km). Volcanic arc hydrothermal systems form where ocean crust is consumed by subduction (convergent boundary) which creates a chain of volcanoes, both submarine and subaerial, and back-arc spreading in some arc systems (Fig. 1); these two together add another 25,000 km to the zone of global volcanism and hydrothermal activity. Back-arc basins generally form via seafloor spreading, similar to that at oceanic ridges. Recent studies have concentrated on hydrothermal systems in West Pacific and Mediterranean Sea volcanic arc and back-arc basin subduction systems and associated mineral deposits, which range from high-temperature sulphide-sulphate deposits, lowtointermediate temperature sulfur and silica deposits, and low-temperature iron-oxide and manganese-oxide deposits (e.g., Alfieris et al., 2013; Dando et al., 1999; Hein et al., 2000, 2008, 2013; Kilias et al., 2001; Petersen et al., 2013). Here we provide a brief background on hydrothermal systems and then compare Pacific and Mediterranean hydrothermal volcanic arc deposits.