High-angle reverse faults, fluid-pressure cycling, and mesothermal gold-quartz deposits

Sibson, Richard H.; Robert, François; Poulsen, K H

doi:10.1130/0091-7613(1988)016<0551:harffp>2.3.co;2

Cited by 1,084 publications

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“…Because a friction law is valid only for compressive effective normal stresses, (5) yields a limit angle o/max = arctan(1/•) above which slip on reverse faults cannot occur without supralithostatic fluid pressure [Sibson et al, 1988]. In what follows, we limit consideration to compressive effective vertical stresses; our value o/= 30 ø is less than O/max for all the reasonable friction coefficients below unity.…”

Section: Try -P (5) A-p--1 +7•'mentioning

confidence: 99%

Effects of normal stress variations on frictional stability of a fluid‐infiltrated fault

Chambon

Rudnicki²

2001

J. Geophys. Res.

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Abstract. This paper extends the spring-slider model of Segall and Rice [ 1995] for dilating fluid-infiltrated faults to include geometry-induced normal stress variations. Because of the coupling between normal and shear stresses on a dipping plane the shear stress drop accompanying slip is associated with a decrease in normal stress for reverse faulting and with an increase for normal faulting. This coupling stabilizes frictional sliding on normal faults and destabilizes it on reverse faults. When a fluid phase is present, these normal stress variations during slip events also trigger, through poroelastic coupling, compensating pore pressure changes: stabilizing pressure decreases for reverse geometry and destabilizing increases for normal geometry. Fault stability is quantitatively studied using two parameters: the critical spring stiffness kcr separating the stable and unstable slip domains and, when numerical simulations exhibit stick-slip cycles, the stress drop during the slip phases At. As expected, geometric coupling is found to reduce kcr and Ar for normal faults (in comparison with Segal! and Rice's [1995] strike-slip geometry) and to increase these parameters for reverse faults. Poroelastic coupling shows opposite consequences. The combined effect of shear-induced dilatancy and poroelastic coupling is stabilizing for reverse geometry but can be either stabilizing or destabilizing for normal geometry, depending on the dilatancy magnitude. Nevertheless, the stability differences between the types of faults are primarily controlled by the geometric coupling between shear and normal stresses: For all the parameters we investigated, normal faults exhibit lower stress drops (and critical stiffnesses) than reverse faults. Finally, extrema appearing in the graphs featuring A r or kcr versus the diffusion rate demonstrate that the influence of the fluid effects is not maximum in the undrained case. Surprisingly, their influence is maximum at a point intermediate between the drained and undrained limits, when the diffusion time is roughly equal to the frictional relaxation time associated with stick phases. This phenomenon is presumably caused by subtle second-order mechanisms involving the instantaneous pore pressure changes induced by the poroelastic coupling in response to instantaneous friction changes and the interseismic pressure recovery process.

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Section: Try -P (5) A-p--1 +7•'mentioning

confidence: 99%

Effects of normal stress variations on frictional stability of a fluid‐infiltrated fault

Chambon

Rudnicki²

2001

J. Geophys. Res.

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“…However, hydraulic activation of brittle failure also exerts a profound influence on fluid migration in epithermal environments, which typically are associated with extensional (transtensional) tectonics (Sillitoe and Hedenquist, 2003). In these settings, very small increases in pressure may result in fluid flow through mixed-mode meshes of faults and fractures (Sibson, 2003), perhaps explaining the prevalence of seismic swarm activity in active environments (Rowland and Simmons, 2012;Sibson, 2003;Sibson et al, 1988). However, although we consider fault-valve behavior important at all scales in all tectonically active fluid regimes, we focus on the analysis of the suction pump mechanism because of its geometrical simplicity for demonstrating the effect of seismically-triggered pressure drops on gold precipitation.…”

Section: Accepted M Manuscriptmentioning

confidence: 99%

“…The fault-valve mechanism also may occur in hydrothermal systems, but unlike the suction pump, it is driven by pore fluid overpressure (Sibson et al, 1988). This mechanism is generally considered in the context of orogenic gold deposits, in which unfavorably oriented reverse faults are activated by substantial increases in fluid pressure, optimizing conditions for gold deposition across fault-valves (Sibson and Scott, 1998).…”

Section: Accepted M Manuscriptmentioning

confidence: 99%

“…External forcing such as earthquakes can have a profound impact on metal solubility, triggering physical and chemical changes in ore fluids that can enhance the precipitation process by phase separation (Rowland and Simmons, 2012;Sibson et al, 1988). This is particularly relevant in shallow crustal settings where porphyry copper and epithermal gold deposits form as a result of phase separation or boiling of a single-phase fluid.…”

Section: Introductionmentioning

confidence: 99%

“…In the epithermal environment, in particular, precipitation of gold and/or silver may occur in association with gentle boiling, where fluid enthalpy is sufficiently high to produce a small vapor fraction upon ascent, or with flash vaporization forced by a transient pressure drop that converts most of the original liquid into a low density vapor phase (Moncada et al, 2012;Simmons et al, 2005;Weatherley and Henley, 2013). There is abundant evidence in the literature documenting that both permeability and gold precipitation are strongly affected by pressure changes triggered by earthquakes (Rowland and Simmons, 2012;Sibson et al, 1988;Weatherley and Henley, A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT 2013). Furthermore, studies have inferred that flash vaporization of gold-rich fluids in dilational jogs during an earthquake can result in the rapid co-deposition of silica to form gold-enriched quartz veins (Moncada et al, 2012;Sibson, 1987;Weatherley and Henley, 2013).…”

Section: Introductionmentioning

confidence: 99%

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The optimal windows for seismically-enhanced gold precipitation in the epithermal environment

Sánchez-Alfaro

Reich

Driesner

et al. 2016

Ore Geology Reviews

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Epithermal gold (Au) deposits result from the combination of a sustained flux of metalrich fluids and an efficient precipitation mechanism. Earthquakes may trigger gold precipitation A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPTby rapid loss of fluid pressure but their efficiency and time-integrated contribution to gold endowment are poorly constrained. In order to quantify the feedbacks between earthquake-driven fracturing and gold precipitation in the shallow crust, we studied the gold-rich fluids in the active Tolhuaca geothermal system, located in the highly seismic Southern Andes of Chile. We conditions -may significantly enhance gold precipitation rates in the shallow crust and lead to overall increases in metal endowment over time.

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Mechanisms of explosive volcanism on Mercury: Implications from its global distribution and morphology

Thomas

Rothery

Conway

et al. 2014

J. Geophys. Res. Planets

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The identification of widespread pyroclastic vents and deposits on Mercury has important implications for the planet's bulk volatile content and thermal evolution. However, the significance of pyroclastic volcanism for Mercury depends on the mechanisms by which the eruptions occurred. Using images acquired by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft, we have identified 150 sites where endogenic pits are surrounded by a relatively bright and red diffuse-edged spectral anomaly, a configuration previously used to identify sites of explosive volcanism. We find that these sites cluster at the margins of impact basins and along regional tectonic structural trends. Locally, pits and deposits are usually associated with zones of weakness within impact craters and/or with the surface expressions of individual thrust faults. Additionally, we use images and stereo-derived topographic data to show that pyroclastic deposits are dispersed up to 130 km from their source vent and commonly have either no relief or low circumpit relief within a wider, thinner deposit. These eruptions were therefore likely driven by a relatively high concentration of volatiles, consistent with volatile concentration in a shallow magma chamber prior to eruption. The colocation of sites of explosive volcanism with near-surface faults and crater-related fractures is likely a result of such structures acting as conduits for volatile and/or magma release from shallow reservoirs, with volatile overpressure in these reservoirs a key trigger for eruption in at least some cases. Our findings suggest that widespread, long-lived explosive volcanism on Mercury has been facilitated by the interplay between impact cratering, tectonic structures, and magmatic fractionation.

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High-angle reverse faults, fluid-pressure cycling, and mesothermal gold-quartz deposits

Cited by 1,084 publications

References 0 publications

Effects of normal stress variations on frictional stability of a fluid‐infiltrated fault

Effects of normal stress variations on frictional stability of a fluid‐infiltrated fault

The optimal windows for seismically-enhanced gold precipitation in the epithermal environment

Mechanisms of explosive volcanism on Mercury: Implications from its global distribution and morphology

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