Oral Presentation NCGRT/IAH Australasian Groundwater Conference 2019

Chasing helium: Mantle-to-Surface connections to water quality and Geomicrobiology (254)

Laura Crossey 1
  1. University of New Mexico Main Campus, Albuquerque, NM, USA

Birdsall-Dreiss Distinguished Lecture, 2019. Sponsored by the Hydrogeology Division of the Geological Society of America.

Objectives

The discovery of oceanic black (and white) smokers revolutionized our understanding of mid-ocean ridges and led to the recognition of new organisms and ecosystems resulting from mixing of fluids. Continental smokers, defined here to include a broad range of carbonic springs, hot springs, and fumaroles that vent mantle-derived fluids in continental settings, exhibit many of the same processes of heat and mass transfer and ecosystem niche differentiation.

Design and Methodology

The application of noble gas geochemistry (specifically helium isotope (3He/4He) analyses) indicates widespread mantle degassing in perhaps unexpected tectonic locales: including the western U.S.A., Great Artesian basin of Australia, Western Desert of Egypt, and the Tibetan Plateau (Crossey et al., 2013 and 2016; Karlstrom et al., 2013).

Original data and results 

Our work shows that variations in the mantle helium component measured in groundwaters correlate best with low seismic-velocity domains in the upper mantle and with abrupt lateral contrasts in mantle velocity rather than crustal parameters such as strain rate, proximity to volcanoes, crustal velocity, or composition. Microbial community analyses applied to several of these areas indicate that these springs can host novel microorganisms. Our work yielded the first published occurrence of chemolithoautotrophic Zetaproteobacteria in a continental setting (Crossey et al., 2016; Love et al., 2017).

Conclusion

These observations lead to two linked hypotheses. 1) that mantle-derived volatiles transit through conduits in extending continental lithosphere preferentially above and at the edges of mantle low velocity domains. 2) Elevated concentrations of CO2 and other constituents ultimately derived from mantle volatiles drive water–rock interactions and heterogeneous fluid mixing that help structure diverse and distinctive microbial communities. This recognition of the small volume but chemically potent “lower world” contributions to groundwater systems has implications for topics as diverse as tectonics, fluid conduits, water quality, and microbial ecosystems. 

  1. Crossey, L.J., Karlstrom, K.E., Schmandt, B., Crow, R., Colman, D., Cron, B., Takacs-Vesbach, T.D., Dahm, C., Northup, D.E., Hilton, D.R., Ricketts, J.R., Lowry, A.R., 2016, Continental smokers couple mantle degassing and unique microbiology within continents: Earth and Planetary Science Letters, v. 435, p. 22-30, http://dx.doi.org/10.1016/j.epsl.2015.11.039.
  2. Crossey, L. J., Priestley S. C., Shand P., Karlstrom K. E., Love A. J., Keppel M., 2013. Source and origin of western GAB spring water. Allocating Water and Maintaining Springs in the Great Artesian Basin, Groundwater Discharge of the Western Great Artesian Basin. Canberra: National Water Commission. Volume 3, p. 11-33.
  3. Love, A.J., Shand, P., Fulton, S., Wohling, D., Karlstrom, K.E., Crossey, L., Rousseau-Gueutin, P. and Priestley, S.C., 2017. A Reappraisal of the Hydrogeology of the Western Margin of the Great Artesian Basin: Chemistry, Isotopes and Groundwater Flow. Procedia Earth and Planetary Science, v. 17, p.428-431.
  4. Karlstrom, K.E., Crossey, L.C., Hilton, D.R., and Barry, P.H., 2013, Active mantle degassing above the Aspen Anomaly of Colorado: Mantle to surface interconnections and implications for neotectonics of the Rocky Mountains: Geology, v. 41, no. 4, p. 495-498, doi:10.1130/G34007.1.