Analytical and numerical models of hydrothermal fluid flow at fault intersections

Abstract

Fault intersections are the locus of hot spring activity and Carlin‐type gold mineralization within the Basin and Range, USA. Analytical and numerical solutions to Stokes equation suggest that peak fluid velocities at fault intersections increase between 20% and 47% when fracture apertures have identical widths but increase by only about 1% and 8% when aperture widths vary by a factor of 2. This suggests that fault zone intersections must have enlarged apertures. Three‐dimensional finite element models that consider intersecting 10‐ to 20‐m wide fault planes resulted in hot spring activity being preferentially located at fault zone intersections when fault zones were assigned identical permeabilities. We found that the onset of convection at the intersections of the fault zones occurred in our hydrothermal model over a narrow permeability range between 5 × 10−13 and 7 × 10−13 m2. Relatively high vertical fluid velocities (0.3–3 m year−1) extended away from the fault intersections for about 0.5–1.5 km. For the boundary conditions and fault plane dimensions used, peak discharge temperatures of 112°C at the water table occurred with an intermediate fault zone permeability of 5 × 10−13 m2. When fault plane permeability differed by a factor of 2 or more, the locus of hot spring activity shifted away from the intersections. However, increasing the permeability at the core of the fault plane intersection by 40% shifted the discharge back to the intersections. When aquifer units were assigned a permeability value equal to those of the fault planes, convective rolls developed that extend about 3 km laterally along the fault plane and into the adjacent aquifer.

Fault-Related Controls on Upward Hydrothermal Flow: An Integrated Geological Study of the Têt Fault System, Eastern Pyrénées (France)

“…However, the Têt Valley reliefs are higher, basins are smaller or even inexistent, and geometry is asymmetrical. other similar studies [41,78], whereas McKenna and Blackwell indicate a maximum velocity value of 3.7 × 10 −10 m/s, generally too low to disturb significantly a thermal field (see the detailed numerical models by López and Smith [78], where significant distortion of the thermal field is obtained for velocity around 10 −7 m/s). In our numerical scheme being identical as in other studies [79,80] where other benchmark tests were performed [81,82], we validate our benchmark test of the Dixie Valley hydrothermal system.…”

“…Subsidiary NW-SE brittle faults ( Figure 2) concentrate similarly oriented fractures in their damage zones. Intersections of the Têt fault and the NW-SE faults damage zones enhance fracture connections and favor the formation of efficient drains for fluids rising [1,14,41] (Figure 10). The temperature-dependence of fluid density induces a buoyancy force allowing hydrothermal fluids to upflow using the highly fractured Têt fault damage zone and subsequently causing isotherm uplift ( Figure 10).…”

“…Damage zones have a strong influence on fault permeability, depending on fractures aperture, density, connectivity, and cementation [35][36][37][38]. These properties may vary along fault according to the fault architecture, that is, intersections of fractured damage zones [39][40][41] or fault segmentation [37,42,43]. The fault constitution and the fracture network also evolve with time, as potential mineralized fluids may corrode or seal permeable structures, respectively, enhancing or reducing the permeability.…”

3-D numerical modelling of the influence of pre-existing faults and boundary conditions on the distribution of deformation: Example of North-Western Ghana

“…Our numerical models show that highstrain zones focus along and in between both faults A and B. The highest uplifted point is close to the intersection region which may focus fluids flow (Lawley et al, 2013), the peak fluid velocities increase 20-47% when the fault zone intersections enlarge apertures only about 1-8% (Person et al, 2012). Large localized deformation appears at the two faults' intersection zone and along faults using the free-remeshing surface boundary condition.…”

Structural controls on karstic conduits in a collisional orogen (Sierra de las Nieves, Betic Cordillera, S Spain)

“…In particular, some of the high-dipping to sub-vertical conduits are localized along linked fault intersection zones mostly at the extensional quadrants. Focused fluid flow at fault intersections has been documented in hydrothermal settings by field (Craw, 2000;Tripp and Vearncombe, 2004) and numerical studies (Person et al, 2012). In the case of rainfall in karstic environments, fault intersection focuses water infiltration mostly coming from runoff, potentially forming sub-vertical cave conduits within the vadose zone.…”