The effect of thermal history on the development of mineral assemblages during infiltration-driven contact metamorphism

Dipple, Gregory M.; Ferry, John M.

doi:10.1007/s004100050194

Cited by 18 publications

(8 citation statements)

References 22 publications

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“…Although advection‐related effects dominate mass transfer at large fluid fluxes, diffusion influences the signal of flow, particularly through the smoothing of chemical and isotopic fronts (e.g. Dipple & Ferry 1996; Fletcher & Hoffman 1974; McCaig et al . 1995).…”

Section: Fluid Flow and Cracksmentioning

confidence: 99%

Mechanisms of fluid flow and fluid–rock interaction in fossil metamorphic hydrothermal systems inferred from vein–wallrock patterns, geometry and microstructure

2001

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Comparison of mass transfer patterns, geometry and microstructures developed within and around veins allows the interpretation of processes of fluid flow during deformation, metamorphism and mineralization. A classification of vein types based on the degree of interaction with wallrock (using petrological, geochemical or isotopic indicators) can be used to identify a range of processes, from closed system behaviour in which the vein mass is derived from local wallrock, through to open system behaviour in which the vein mass is derived externally. Microstructural characteristics, such as wallrock selvages, multiple growth events recorded by vein seams and vein crystal morphology, also help to constrain mass transfer patterns during vein formation. We present a range of processes for vein formation, including: (i) the formation of closed system fibrous veins by dissolution–precipitation creep, including varieties in which tensile failure is not required; (ii) pressure‐ or kinetically dependent closed system segregation veins in which transfer of soluble components from wallrock to vein leaves behind a residual selvage; (iii) similar vein–selvage patterning, but with mass imbalances between vein and wallrock requiring fluid advection through both interconnected fracture networks and in the surrounding permeable rock; and (iv) the proposed formation of veins by fluid ascent in mobile hydrofractures, in which isotopic or chemical disequilibrium within and around the vein suggests that the crack and fluid within it moved essentially as one. The postulate of rapid fluid and mass transfer via such mobile hydrofractures has implications for the release of volatiles from metamorphic terrains. Also, consideration of a broad range of possible vein‐forming mechanisms is highly desirable when dealing with mineral deposits found in deformed, metamorphosed rocks, because closed system veining may produce patterns that, if erroneously recognized as being open systems, could lead to false interpretations of the role of tectonic fracturing in ore genesis.

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Section: Fluid Flow and Cracksmentioning

confidence: 99%

Mechanisms of fluid flow and fluid–rock interaction in fossil metamorphic hydrothermal systems inferred from vein–wallrock patterns, geometry and microstructure

2001

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“…Prograde devolatilization reactions can be driven by heat and/or by chemically disequilibrium fluid (Dipple & Ferry, 1996; Ferry & Gerdes, 1998). Our model results show that heat mainly drives low‐ to medium‐grade reactions, whereas fluid‐driven reactions mainly occur at or after peak temperatures are reached.…”

Section: Coupled Fluid Flow and Reactionsmentioning

confidence: 99%

Reactive flow of mixed CO₂–H₂O fluid and progress of calc‐silicate reactions in contact metamorphic aureoles: insights from two‐dimensional numerical modelling

Cui

Nábělek

Liu

2003

Journal Metamorphic Geology

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Previous models of hydrodynamics in contact metamorphic aureoles assumed flow of aqueous fluids, whereas CO2 and other species are also common fluid components in contact metamorphic aureoles. We investigated flow of mixed CO2–H2O fluid and kinetically controlled progress of calc‐silicate reactions using a two‐dimensional, finite‐element model constrained by the geological relations in the Notch Peak aureole, Utah. Results show that CO2 strongly affects fluid‐flow patterns in contact aureoles. Infiltration of magmatic water into a homogeneous aureole containing CO2–H2O sedimentary fluid facilitates upward, thermally driven flow in the inner aureole and causes downward flow of the relatively dense CO2‐poor fluid in the outer aureole. Metamorphic CO2‐rich fluid tends to promote upward flow in the inner aureole and the progress of devolatilization reactions causes local fluid expulsion at reacting fronts. We also tracked the temporal evolution of P‐T‐XCO2conditions of calc‐silicate reactions. The progress of low‐ to medium‐grade (phlogopite‐ to diopside‐forming) reactions is mainly driven by heat as the CO2 concentration and fluid pressure and temperature increase simultaneously. In contrast, the progress of the high‐grade wollastonite‐forming reaction is mainly driven by infiltration of chemically out‐of‐equilibrium, CO2‐poor fluid during late‐stage heating and early cooling of the inner aureole and thus it is significantly enhanced when magmatic water is involved. CO2‐rich fluid dominates in the inner aureole during early heating, whereas CO2‐poor fluid prevails at or after peak temperature is reached. Low‐grade metamorphic rocks are predicted to record the presence of CO2‐rich fluid, and high‐grade rocks reflect the presence of CO2‐poor fluid, consistent with geological observations in many calc‐silicate aureoles. The distribution of mineral assemblages predicted by our model matches those observed in the Notch Peak aureole.

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“…The absence of corundum (or aluminosilicates) in the deposit requires that the fluid fluxes were insufficient to completely strip all but the immobile elements from the rocks, and/or that large fluid fluxes were not moving along an up‐temperature pathway, which would also have the capacity to deplete silica (e.g. Dipple & Ferry 1991).…”

Section: Discussionmentioning

confidence: 99%

“…The time and distance relationships for a fluid front moving through rock can be related to the rock and fluid properties and chemistry using the general transport equation of Dipple & Ferry (1991), where φ is the porosity, C i is the concentration of component i in the fluid, t is time, v is the Darcy flux, z is the distance along the flow path, and R i is a reaction rate term for component i . This equation ignores the effects of diffusion and dispersion acting on the component being transported.…”

Section: Discussionmentioning

confidence: 99%

“…The fluid/rock ratio (referred to here as water/rock or w/r for consistency with Reed 1997) is used to define many equilibrium dynamic models. The relationship between equilibrium dynamic modelling, reactive transport (a coupling between fluid‐flow and chemical solver codes), and the use of fluid–rock ratios were subjects of extensive debate (Blattner & Lassey 1989; Bickle & Baker 1990; Ferry & Dipple 1991; Dipple & Ferry 1991). For theoretical fluid infiltration through a saturated rock column, models using equilibrium steps should converge on reactive transport models only when the equilibrium steps are infinitesimally small and kinetic effects are ignored.…”

Section: Introductionmentioning

confidence: 99%

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Comparing closed system, flow‐through and fluid infiltration geochemical modelling: examples from K‐alteration in the Ernest Henry Fe‐oxide–Cu–Au system

Cleverley¹,

Oliver²

2005

Geofluids

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Potassic alteration of rocks adjacent to, and within the Ernest Henry Fe-oxide-Cu-Au deposit is used here as a test case to investigate fluid-rock interactions using various equilibrium dynamic geochemical modelling approaches available in the HCh code. Reaction of a simple K-Fe-(Na,Ca) brine (constrained by published fluid inclusion analysis) with an albite-bearing felsic volcanic rock, resulted in predicted assemblages defined by (i) K-feldsparmuscovite-magnetite, (ii) biotite-K-feldspar-magnetite, (iii) biotite-quartz-albite and (iv) albite-biotite-actinolitepyroxene with increasing rock buffering (decreasing log w/r). Models for isothermal-isobaric conditions (450°C and 2500 bars) were compared with models run over a T-P gradient (450 to 200°C and 2500 to 500 bars). Three principal equilibrium dynamic simulation methods have been used: (i) static closed system, where individual steps are independent of all others, (ii) flow-through and flush, where a part of the result is passed as input further along the flow line, and (iii) fluid infiltration models that simulate fluid moving through a rock column. Each type is best suited to a specific geological fluid-rock scenario, with increasing complexity, computation requirements and approximation to different parts of the natural system. Static closed system models can be used to quickly ascertain the broad alteration assemblages related to changes in the water/rock ratio, while flow-through models are better suited to simulating outflow of reacted fluid into fresh rock. The fluid infiltration model can be used to simulate spatially controlled fluid metasomatism of rock, and we show that, given assumptions of porosity relationships and spatial dimensions, this model is a first-order approximation to full reactive transport, without requiring significant computational time. This work presents an overview of the current state of equilibrium dynamic modelling technology using the HCh code with a view to applying these techniques to predictive modelling in exploration for mineral deposits. Application to the Ernest Henry Fe-oxide-Cu-Au deposit demonstrates that isothermal fluid-rock reaction can account for some of the alteration zonation around the deposit.

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The effect of thermal history on the development of mineral assemblages during infiltration-driven contact metamorphism

Cited by 18 publications

References 22 publications

Mechanisms of fluid flow and fluid–rock interaction in fossil metamorphic hydrothermal systems inferred from vein–wallrock patterns, geometry and microstructure

Mechanisms of fluid flow and fluid–rock interaction in fossil metamorphic hydrothermal systems inferred from vein–wallrock patterns, geometry and microstructure

Reactive flow of mixed CO₂–H₂O fluid and progress of calc‐silicate reactions in contact metamorphic aureoles: insights from two‐dimensional numerical modelling

Comparing closed system, flow‐through and fluid infiltration geochemical modelling: examples from K‐alteration in the Ernest Henry Fe‐oxide–Cu–Au system

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The effect of thermal history on the development of mineral assemblages during infiltration-driven contact metamorphism

Cited by 18 publications

References 22 publications

Mechanisms of fluid flow and fluid–rock interaction in fossil metamorphic hydrothermal systems inferred from vein–wallrock patterns, geometry and microstructure

Mechanisms of fluid flow and fluid–rock interaction in fossil metamorphic hydrothermal systems inferred from vein–wallrock patterns, geometry and microstructure

Reactive flow of mixed CO2–H2O fluid and progress of calc‐silicate reactions in contact metamorphic aureoles: insights from two‐dimensional numerical modelling

Comparing closed system, flow‐through and fluid infiltration geochemical modelling: examples from K‐alteration in the Ernest Henry Fe‐oxide–Cu–Au system

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Reactive flow of mixed CO₂–H₂O fluid and progress of calc‐silicate reactions in contact metamorphic aureoles: insights from two‐dimensional numerical modelling