Hot springs host many deeply branching microbes rich in phylogenetic and metabolic diversity. These springs are the surface expression of hydrothermal systems that originate deep in Earth’s crust. Abundance of a given element can vary by more than 5 orders of magnitude between springs. The extreme variability in geochemical compositions observed in such systems is primarily the result of deep water-rock reaction combined with near-surface groundwater mixing and surface input. The composition of these hydrothermal fluids is therefore heavily influenced by the host rock. The igneous regions that host hydrothermal systems range from basaltic to rhyolitic end members, differentiated primarily by silica and cation content that result from where the rocks were formed; the seafloor is typically basaltic, whereas continental crust is predominately rhyolitic. Andesite, an intermediate, can result in subduction zones. Together, these three rock types are the most prevalent hosts for hydrothermal systems on earth and are also the most likely hosts for hot springs on other tectonically active bodies in our solar system. This study characterizes the major and trace element composition of dozens of hot springs in both the Ecuadorian Andes (andesite hosted) and Yellowstone National Park (rhyolite hosted) to establish the range of compositions in hot spring ecosystems and constrain the composition of potential hot springs on other worlds. A comparison of abundance of between the two locations reveals systematic compositional fingerprints. As an example, the andesite springs contain elevated As, Fe, B, and Mo, but are typically lacking in Zn and Al relative to Yellowstone hot springs. The availability of these elements to microbes influences the microbial composition of the hot springs and likely played a role in the trajectory of microbial evolution on Earth.

Host rock influences metal abundance in terrestrial hot springs

2019 Spring National Meeting

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