H160-01
To impermeable, and beyond: Expanding conceptual models for the hidden hydrogeosphere

Tuesday, 15 December 2020: 04:00
Virtual
Barbara Sherwood Lollar1, Oliver Warr1, Chris J. Ballentine2, Jesse Dylan Tarnas3, John F Mustard3, Vlada Stamenkovic4, Grant A G Ferguson5, Ji-Hyun Kim6, Mcintosh, Jennifer C6 and Jeffrey McDonnell7, (1)University of Toronto, Department of Earth Sciences, Toronto, ON, Canada, (2)University of Oxford, Department of Earth Sciences, Oxford, United Kingdom, (3)Brown University, Department of Earth, Environmental and Planetary Sciences, Providence, RI, United States, (4)NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States, (5)University of Saskatchewan, Civil, Geological and Environmental Engineering, Saskatoon, SK, Canada, (6)University of Arizona, Hydrology and Atmospheric Sciences, Tucson, AZ, United States, (7)University of Saskatchewan, School of Environment and Sustainability, Global Institute for Water Security, Saskatoon, SK, Canada
Recorded Presentation
Abstract:
The general conceptual model of the hydrological cycle is one where all components eventually return to the Earth’s surface. In this sense the prevailing image of the hydrologic cycle is really a meteoric water cycle (e.g. water in contact with the atmosphere). This is the case even for paleo-meteoric waters (e.g. glacially recharged groundwaters), common around the world, that return to the surface cycle on timescales of thousands of years. But beyond these meteoric waters lies a hidden hydrogeosphere where groundwater and saline fracture fluids exist in the deep crystalline basement rocks that are so often portrayed as an assumed “impermeable boundary” in conventional hydrologic models. Such crystalline rocks account for the vast majority of the terrestrial crust and yet are significantly under-investigated to date. Preliminary estimates suggest the hidden hydrogeosphere accounts for up to 99% of groundwaters below 2 km [1], but the total volumes, age distributions (in some cases shown to be hundreds of millions to > a billion years) [1-3], rates and extent of transport and mixing remain largely unconstrained. This talk explores the controls on the distribution and preservation of these fluids - a largely unknown and uncharted research frontier. These subsurface fracture fluids support a subsurface biomass estimated to rival that of the surface biosphere – and understanding this unseen part of our home planet and the processes controlling the distribution, preservation and geochemical characteristics of deep subsurface fluids and life on this planet is critically needed to inform mission planning for planetary and astrobiological investigation elsewhere in the solar system.

[1]. Warr, O. et al. (2018) Tracing ancient hydrogeological fracture network age and compartmentalisation using noble gases. Geochimica Cosmochimica Acta 222:340-362.

[2]. Holland, G. et al. (2013) Deep fracture fluids isolated in the crust since the Precambrian. Nature 497(7449): 367-360.

[3]. Lippmann-Pipke, J. et al. Neon identifies two billion year old fluid component in Kaapvaal Craton. Chem. Geol. 283, 287–296 (2011).

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