Can Electromagnetic Surveys Image Deep Crystalline Basement Flow Systems in Extensional Terrains?

Crystalline basement rocks are rocks composed of crystalized minerals. These basement rocks formed early in the history of the Earth and are typically buried under younger rocks and sediment. These rocks are commonly viewed as impermeable with little or no water flowing through them. However, faults or cracks in crystalline basement rocks can permit fluid flow. This study uses state-of-the-art instruments to image the subsurface at depths to nearly 10 km below the ground surface in New Mexico. The study examines if and when fluid flow occurs in basement rocks in a tectonically active region. The outcomes and understanding gained with this investigation can help quantify the age and amount of brackish water that resides within deep basement rocks in the western USA. This research is relevant to water resource managers and nuclear waste management agencies. The project includes training for both graduate and undergraduate students in the fields of hydrology and geophysics, supports an early-career faculty member, and supports a research team at a Hispanic-serving institution.

The primary goal of this project is to develop a novel framework to explore deep groundwater flow systems in extensional terrains by integrating fluid flow and transport models, magnetotelluric (MT) and time domain electromagnetic (TDEM) geophysical surveys, geochemical and isotopic tracers, temperature profile data, and outcrop-scale measurements of fracture apertures. Typically, hydrogeologists view the crystalline basement rocks as impermeable. On the other hand, geothermal explorationists acknowledge that discrete fault zones within the basement rocks can be permeable but little attention has been devoted to the source of the fluids feeding the fault zones. This study offers a compelling paradigm in which the crystalline basement in tectonically active regions can have a relatively high bulk permeability, serving as a major conveyor for water, solutes, and energy. Using the Rio Grande rift as a test bed, this project combines geophysical (electromagnetic), geochemical, and field observations with advanced numerical models to explore the flow and transport characteristics of these deep hydrologic systems to unprecedented depths. The outcomes and understanding gained with this effort will help quantify the volumes, salinity, residence times, and genesis of brackish water within deep aquifers in the western USA - an unconventional resource with the potential to offset the deficit of water and energy in arid environments. The project leverages infrastructure and equipment acquired as part of New Mexico EPSCoR Energize New Mexico.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.