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, fluid-rock interaction, and inputs from deeply-derived volatiles. Although it is known that these factors create diverse niches for chemotrophic microbial life, little data exists from continental arcs, especially distal to active volcanoes. The Peruvian Andes are ideal to explore such relationships as there are abundant hot spring locations that span multiple geologic and tectonic settings. We report new water, gas, and microbiology data from 14 thermal springs along a transect from flat-slab to steep-slab subduction in southern Peru. A diverse range of water and gas geochemical results form the foundation for characterizing the controls on the composition of bacterial and archaeal 16S rRNA gene assemblages. Springs are slightly acidic (pH 5.3 to 6.8), 17–81 °C, and have HCO₃^- and Cl^- from 69–1,751 mg/L and 81–30,000 mg/L, respectively. Additionally, springs contain redox sensitive constituents such as ferrous iron (0.54–28 mg/L), arsenic (0.01–23 mg/L), dissolved O₂ (0.1–8 mg/L), CH₄ (0.5–6 mg/L), and H₂ (75–3837 nM). Gibbs Free Energy calculations for representative redox reactions indicate conditions favorable for chemotrophic microbial metabolism. Our results show the presence of known thermophiles and other chemolithotrophs. Microbial communities are diverse with 11 bacteria phyla (including 25 bacterial classes) and two archaea phyla. Proteobacteria phyla are in 13 springs, including two springs that contain Zetaproteobacteria. Novel microbes, <97% ID match to previously characterized strains, are present in all springs. Three distinct geochemical groups are identified through Principle Component Analysis (PCA), and nonmetric multidimensional scaling (NMDS) is used to compare microbial community between springs. Based on these statistical treatments, relationships emerge between spring geochemistry, microbial community composition, and geologic setting. For example, in the back-arc of the Altiplano, springs with correlated temperature, H₂, CH₄, As, and CO₂ have similar microbial community compositions. These contrast to springs located above the flat slab, suggesting that transitions in tectonic setting may also influence the interplay of geochemistry and geomicrobiology.