Geochemical investigation of hydrothermal and microbial alteration in modern and ancient seafloor lavas, and the search for extraterrestrial life
Lauren Anderson
Department of EES
Abstract
This geochemical study of 2.7 Ga, hydrothermally altered, greenschist facies metabasalts from the Abitibi Greenstone Belt (AGB) focuses on characterization of Archean seawater-rock interactions and habitats for Archean microbial activity. The AGB contains relatively undeformed mafic to felsic plutons and volcanic flows related to ancient ocean arc construction and arc-arc collision. Pervasive low-pressure metamorphism of these rocks was largely penecontemporaneous with hydrothermal seawater alteration, resulting in replacement of primary minerals and glasses with quartz, chlorite, calcite, epidote, albite and amphiboles. Two sites were selected, both located on the Blake River Block of the Southern Volcanic Zone: one in Rouyn, Québec, containing greenschist facies variolitic pillow and massive basalt flows, and the other in Harker Township, Ontario, containing sub-greenschist facies hyaloclastite and massive basalt flows. The Harker Township site was previously investigated by Bridge (2008), who found microtubules, thought to be ichnofossils left by ancient microbial activity, within previously glassy shards of the middle hyaloclastite unit. Twenty-six samples representing the major volcanic flows from each site are being characterized using a suite of techniques including (1) petrographicanalysis to identify alteration minerals and textures, (2) x-ray fluorescence to determine the major and trace element contents, (3) powder x-ray diffraction to qualitatively determine mineralogy, and (4) measurement of N, O, and C isotope ratios, and N and C concentrations, to determine the extents and characteristics of the hydrothermal alteration. The analytical data will be combined with field observations (summer, 2008) and petrography to characterize early-Earth ocean chemistry, seafloor chemical alteration, and microbial activity representing the evolving Archean biosphere. The results of this study could also have implications for models of chemical cycling in Archean subduction zones and future investigations for life on Mars.
Bio: Lauren D. Anderson. Lehigh University B.S. Geological Sciences (2009) with Applied Mathematics minor. Lehigh University M.S. Geological Sciences, focus in geochemistry (projected 2010)
