AAPG Foundation 2019 Grants-in-Aid Projects

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Connections between hydrothermal system geochemistry and microbiology: Traversing tectonic boundaries in the south-central Peruvian Andes

Abstract

Hot springs in continental arcs exhibit varied geochemistry reflecting tectono-magmatic influences, extent of fluid-rock interaction, and inputs from deeply-derived volatiles that create diverse niches for chemotrophic microbial life. Microbial community composition should reflect aspects of spring geochemistry. This linkage is well documented in continental magmatic hydrothermal systems and marine hydrothermal vents, but little is known of how tectonic setting specifically influences the geomicrobiology of hot springs. Likewise, the composition of microbial communities in continental, non-magmatic hydrothermal systems remains an outstanding question. Our characterization of spring geomicrobiology will advance the understanding of linkages between gradients in geochemistry and tectono-magmatic setting. I hypothesize that the nutrients available to support microbial metabolism are controlled by the region’s tectono-magmatic setting which will be reflected in the geochemistry of the spring waters. The Peruvian Andes are a novel location to explore such relationships as there are abundant hot springs that span multiple tectonic settings. Water, gas, and microbiology samples were collected at 14 springs along a transect from flat-slab to steep-slab subduction in south-central Peru. Preliminary results reveal a chemically and thermally diverse group of springs. The geochemistry, including the redox speciation of key compounds, will be compared to the homology of 16S rRNA gene sequences to previously characterized strains in order to elucidate chemical and geographic patterns amongst the spring microbial communities. Hydrocarbon systems in arc settings have a range of thermal and chemical gradients that impact their quality and longevity. Since microbes are sensitive to thermal gradients and availability of electron donors, such as hydrocarbons, they are biomarkers that can provide insight into the evolution of hydrocarbon systems. This work bridges a gap in our understanding of continental hydrothermal systems, adding a characterization of microbiology in systems not associated with magmatism. By integrating geochemistry and microbiology, we can evaluate thermal maturation and biological moderation of a resource in a given system. This is significant because microbes are present in and modify most environments on Earth. We will gain an understanding of how geochemistry varies relative to tectono-magmatic influences, shaping composition and putative function of spring microbial communities.