Numerical simulations of brine migration by topographically driven recharge

Abstract

The migration of abnormally warm, saline water through the Appalachian basin and North American midcontinent in Paleozoic time has been inferred from fluid inclusion studies, remagnetizations, and widespread potassic alteration. A time‐dependent numerical model of fluid, heat and solute transport is used to evaluate the viability of topographically driven recharge as a mechanism for brine migration. The model represents a wedge‐shaped sedimentary basin 400 km long by 6 km deep (maximum) with a basal aquifer 500 to 750 m thick overlain by a homogeneous aquitard. Temperature predicted by model simulations is found to be inconsistent with constraints inferred from fluid inclusion studies, unless average heat flow values greater than about 100 mW/m2 are used. Model simulations also lead to predictions of low heat flow and subsurface temperature in recharge zones that are generally not observed in modern orogenic zones. The initial solute content of pore waters in the model basin is flushed out by fresh water entering in the recharge zone before fluid velocities high enough to produce significant warming of the discharge zone can develop. Model simulations with source terms reveal that basin sediments can provide enough solute to maintain hot, hypersaline brine migration for about 1 m.y., at most. High fluid velocity in the basal aquifer is required to carry heat to the basin margins, but the higher the fluid velocity, the more quickly the basin's supply of solute is exhausted. Consideration of these constraints implies that topographically driven recharge may be an effective mechanism to explain regional brine migration only if flow is focused from regional scale recharge zones into more spatially restricted discharge zones.

Late Dolomitization in Basinal Limestones of the Southern Apennines Fold and Thrust Belt (Italy)

“…Originally, this model was introduced to explain the peculiar vuggy dolomites, often displaying zebra textures and saddle-shaped crystals, associated with many MVT-type mineralizations of North America (Jackson and Beales, 1967;Anderson and Macqueen, 1982;Machel et al, 1996). It is presently debated whether the large scale circulation of fluids is triggered by tectonic charge or by the hydraulic head induced by regional topography (Garven and Freeze, 1984;Oliver, 1986;Bethke and Marshak, 1990;Deming and Nunn, 1991;Ge and Garven, 1994;Morrow, 1998). Whatever the origin of the fluid-flow, the dolostone bodies are generally found in the undeformed foreland at the front of the fold and thrust belt and may be associated with deep-seated, sub-vertical normal faults (Taylor and Sibley, 1986;Hurley and Budros, 1990;Berger and Davies, 1999;Wendte et al, 2009;Lavoie and Chi, 2010;Shah et al, 2010), although several examples of dolomites formed within the fold and thrust belts itself also exist ( Qing and Mountjoy, 1994;Swennen et al, 2003;Vandeginste et al, 2005).…”

Field identification of groundwater flow systems and hydraulic traps in drainage basins using a geophysical method

“…Based on qualitative analysis, Tóth [1980Tóth [ , 1999 proposed that transported matter could accumulate in hydraulic traps. Studies by various researchers [Baskov, 1987;Deming, 1992;Deming and Nunn, 1991;Garven and Freeze, 1984;Garven et al, 1993;Person et al, 1996] show that the Mississippi Valley type ore deposits are the result of mobilization, transport, and accumulation of metal ions by groundwater, and the loci of accumulation and deposition are below the ancient groundwater discharge centers, which correspond to the basin-bottom hydraulic traps. Despite its importance, the hydraulic trap has not yet been physically detected in natural groundwater basins.…”

Problems with applying topographically driven flow to genesis of the Upper Mississippi Valley zinc-lead district and to fluid flow in the Illinois Basin

“…The abundance of iron-rich (mannatitic) sphalerite (Heyl, 1983) and the alteration of clays in the ore zones (Heyl and others, 1964) also suggest temperatures near 200°C. The maximum temperature obtainable by topographically driven flow from the Pascola arch is, however, only 120°C (Bethke, 1986), and an analysis by Deming and Nunn (1991) suggests that the maximum temperature is even less. Thus, the model lacks the required intensity of heat, and the quantity of heat may also be lacking.…”

“…Furthermore, dissolution of that much salt would have left indications that would not go unnoticed. In the model of Garven and others (1993), the mountains are uplifted instantaneously; thus the model does not address the problem noted by Deming and Nunn (1991) that salt would be flushed from the basin before flow was fast enough to efficiently transport heat. As with flow from the Pascola arch, bromine-chlorine ratios of pore waters hi the basin indicate that the basin was not flushed, an indication contrary to topographically driven flow.…”

“…Hence, they have been leached of elements needed for the ores. Deming and Nunn (1991) pointed out that, as the topography rose on the edge of a basin, fluids would begin to flow slowly and then more rapidly over time as relief increased. They also pointed out that initial flow rates were insufficient to efficiently transport heat to the basin's margins but did transport salt Their calculations indicate that, by the time flow rates were optimal to transport heat, the salt supply of a typical basin was likely to have been exhausted.…”