2D and 3D coexisting modes of thermal convection in fractured hydrothermal systems - Implications for transboundary flow in the Lower Yarmouk Gorge |
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| Institution: | 1. Departamento de Geología, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile;2. Centro de Excelencia en Geotermia de los Andes (CEGA), Universidad de Chile, Plaza Ercilla 803, 8370450, Santiago, Chile;3. Dipartimento di Scienze della Terra, Via G. La Pira 4, 50121 Firenze, Italy;4. CNR-IGG Istituto di Geoscienze e Georisorse, Via G. La Pira 4, 50121, Firenze, Italy;5. Servicio Nacional de Geología y Minería, Av. Santa María Chaina 0104, Santiago, Chile;6. Istituto Nazionale Geofisica e Vulcanologia INGV, Sez. di Palermo, Via U. La Malfa 153, 90145 Palermo, Italy;1. Utrecht University, Faculty of Earth Sciences, Budapestlaan 4, 3584CD Utrecht, The Netherlands;2. Repsol Exploración S.A., Mendez Álvaro 44, 28045 Madrid, Spain;3. Eötvös Loránd University, Department of Geophysics and Space Science, Pazmany Peter setany 1/c, 1117 Budapest, Hungary;4. MTA-ELTE Geological, Geophysical and Space Sciences Research Group, Hungarian Academy of Sciences at Eötvös Loránd University, Pazmany Peter setany 1/c, 1117 Budapest, Hungary |
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| Abstract: | Numerical investigations of 2D and 3D modes of large-scale convection in faulted aquifers are presented with the aim to infer possible transport mechanisms supporting the formation of thermal springs through fractured aquicludes. The transient finite elements models are based on idealized structural features that can characterize many hydrothermal systems. The sensitivity analysis of the fault permeability showed that faults cross-cutting the main regional flow direction allow groundwater to be driven laterally by convective forces within the fault planes. Therein thermal waters can either discharge along the fault traces or exit the fault through adjacent permeable aquifers. In the latter case, the resulting flow is helicoidally and transient. The location and the spacing between discharge areas can migrate with time, is not strictly constrained to the damage zones and reflects the wavelength of the multicellular regime in the fault zone.An illustrative example based on simplified structural data of the Lower Yarmouk Gorge (LYG) is presented. The numerical calculations indicate that crossing flow paths result from the coexistence of fault convection, developing for example along NE-SW oriented faults within the Gorge, and additional flow fields. The latter are induced either by topography N S gradients, e.g. perpendicular to the major axe of the Gorge, or by local thermal convection in permeable aquifers below the Eocene aquiclude. Sensitivity analysis of fault hydraulic conductivity (K) and the analytical solutions based on viscous-dependent Rayleigh theory show that K values between 2.3e−7 m/s and 9.3e– 7 m/s (i.e. 7 m/yr and 30 m/yr, respectively) favor coexisting transport processes. The uprising thermal plumes spread over several hundred meters forming clusters of springs, in agreement with observation, and which temperature fall within the measured ranges, i.e. 20 °C−60 °C. To some extent the models also reproduced the transient behavior of the spring temperature. Owing to the idealized nature of the presented models, the numerical results and the associated analytical solution can be applied to study the onset of thermal convection and resulting flow patterns of any fractured hydrothermal basin. |
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| Keywords: | Convection Faults Numerical simulation Rayleigh Viscosity Israel Jordan |
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