Connections Between Hydrothermal System Geochemistry and Microbiology: Traversing Tectonic Boundaries in the South-Central Peruvian Andes

Hot springs in continental arcs exhibit varied geochemistry reflecting tectono-magmatic influences, depth and extent of fluid-rock interaction, and inputs from deeply-derived volatiles. This setting creates diverse niches supporting chemotrophic microbial communities. Little is known of how tectonic setting specifically influences the geochemical and microbiological composition of hot springs. The Peruvian Andes are an ideal location to explore such linkages as there are abundant accessible hot springs that span multiple tectonic settings. Water, gas, and microbiology samples were collected at 14 springs located along a NE - SW transect spanning the transition from flat-slab to steep-slab subduction in south-central Peru. The traverse included the flat-slab segment above the Nazca Ridge trace, the transition into the back arc and Altiplano Plateau, and ended near the axis of active arc-magmatism. Springs ranged from 17-81°C, with a specific conductance of 1.3 to 85.8 mS, and exhibited a narrow range in pH (5.3-6.8). Alkalinity (as HCO₃^-) and Cl^- range from 69-1751 and 81-30,000 mg/L, respectively. Field measurements detected ferrous iron (0.54-28 mg/L) in 12 of 14 springs, and sulfide (93 mg/L) in one spring. Compositional end members include hot, CO₂-rich, saline springs; cool, CO₂-rich, saline springs; and cool, low-salinity springs. In between these end members, springs vary significantly in temperature, ferrous iron content, dissolved CO₂, and salinity. Forthcoming planktonic and benthic microbial community data is hypothesized to reflect this geochemical variation owing to the link between microbial metabolism and the available geochemical species, nutrients, in thermal fluids. Our results will improve the understanding of how hydrothermal geochemistry varies in relation to tectono-magmatic influences, and how the microbiology is linked to and ultimately influences this variation.