THE ROLE OF GROUNDWATER IN GEOLOGIC PROCESSES

Historically, interest in groundwater and other subsurface fluids was confined to a few specific disciplines in the earth sciences, notably groundwater hydrology, soil physics, engineering geology, petroleum geology, and petroleum engineering.  These disciplines tended to be “applied” in nature, with practitioners concentrating on the immediate and practical problems of water supply, water quality, mine dewatering, deformation under structural loads, and the location and recovery of fluid hydrocarbons.  This situation has changed over the past few decades.  Hydrogeologists and geologists are now actively modeling the role of groundwater and other subsurface fluids in such fundamental geologic processes as crustal heat transfer, ore deposition, hydrocarbon migration, earthquakes, tectonic deformation, diagenesis, and metamorphism.  This talk will emphasize (1) the role of fluid properties (Fig. 1) in governing fluid flow and heat transfer at the mid-ocean ridge and (2) the coupling between fluid pressure, seismicity, and crustal permeability (Fig. 2).

References cited: Ingebritsen, S.E., Geiger, S., Hurwitz, S., and Driesner, T., 2010, Numerical simulation of magmatic hydrothermal systems:  Reviews of Geophysics, in press.

Ingebritsen, S.E., and Manning, C.E., 2002, Diffuse fluid flux through orogenic belts:  Implications for the world ocean:  Proceedings of the National Academy of Sciences USA, v. 99, p. 9,113-9,116.

Ingebritsen, S.E., and Manning, C.E., 2010, Permeability of the continental crust:  Dynamic variations inferred from seismicity and metamorphism:  Geofluids, v. 10, in press.

Manning, C.E., and Ingebritsen, S.E., 1999, Permeability of the continental crust:  The implications of geothermal data and metamorphic systems:  Reviews of Geophysics, v. 37, p. 127-150.

 

Fig. 1 – Phase diagrams for temperature-pressure-composition coordinates, showing relations between the pure H₂O system (middle) and two important binary systems, H₂O-CO₂ (left) and H₂O-NaCl (right).  The boiling curve of H₂O (blue) ends in the H₂O critical point (374^oC, 220.6 bar) and separates liquid at high pressures from vapor at low pressures.  In the system H₂O-CO₂ (left), there is a large volume (rather than a single boiling curve) occupied by an aqueous, liquid-like fluid coexisting with a carbonic fluid that may be vapor- or liquid-like, depending on pressure.  This region closes towards higher temperatures, where only a single-phase fluid exists.  In the system H₂O-NaCl (right), however, the region of two-phase liquid + vapor coexistence becomes larger with increasing temperature.  From Ingebritsen and others (2010).

Fig. 2 –Evidence for relatively high crustal-scale permeabilities showing (a) power-law fit to data and (b) data below 12.5 kilometers depth fitted with a constant value.  Upper curve in both (a) and (b) is the best-fit to geothermal-metamorphic data (Manning and Ingebritsen, 1999; Ingebritsen and Manning, 2002).  “High-permeability” data points are midpoints in reported ranges in k and z for a given locality; error bars depict the full permissible range and are not Gaussian errors.  Solid circles = hypocenter migration; open circles = fault-zone metamorphism; solid squares = focused metamorphic heating; open squares = anthropogenic seismicity.  From Ingebritsen and Manning (2010).