Convective fluid flow through heterogeneous country rocks during contact metamorphism

Abstract

Abstract. Geochemical and petrologic data from contact aureoles consistently document fluid focusing through small-scale permeable structures. We use stochastic representations of permeability in a series of transient numerical simulations to assess how such smallscale rock heterogeneities influence kilometer-scale fluid convection around a shallow crustal pluton. The sensitivity study considers different permeability scenarios by varying statistical characteristics of the permeability distribution (mean, variance, and spatial correlation). Large-scale convective flow patterns in heterogeneous contact aureoles are shown to deviate significantly from equivalent homogeneous aureoles in ways that cannot be predicted without detailed mapping of the permeability field. Fluid focused through displacements as large as 170 ø occur only when average permeability is 10 -25 m 2 and can be detected using isotopic or petrologic thermometry. These temperature deviations reflect local permeability heterogeneities and could be useful in identifying high-permeability paleochannels. These results also imply, however, that temperature profiles taken from only one portion of a heterogeneous contact aureole may not be regionally representative or used to infer the overall advective-conductive thermal structure of the large-scale hydrothermal system.

Estimating the local paleo-fluid flow velocity: New textural method and application to metasomatism

“…Their results point to significant time-integrated fluxes (5000 -300 mol/cm²) consistent with the order of magnitude published in previous studies (Ferry, 1994a). Thermal and hydrological numerical models constitute another approach to constrain the direction and amount of fluid flow (Norton and Knight, 1977;Hanson et al, 1993;Gerdes et al, 1998;Cui et al, 2001;Oliver et al, 2006). In some case, good agreement is found between predictions from numerical models and studies based on mineralogical and stable isotope data (e.g.…”

“…For active regional metamorphism, a Darcy velocity of 10 -11 m/s is considered to be an average value . Hydrothermal numerical models of contact or regional metamorphism, predict Darcy velocities ranging from 10 -8 m/s to 10 -11 m/s (Oliver et al, 2006;Gerdes et al, 1998;Cook et al, 1997). In this work, the calculated velocity at grain scale is much higher, about 10 -3 to 10 -4 m/s.…”

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

“…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.…”

Fluid focusing and its link to vertical morphological zonation at the Dajishan vein-type tungsten deposit, South China

“…Previous studies using convection-type models have shown the significant impact of anisotropy on flow patterns and heat transfer (Dutrow et al, 2001;Gerdes et al, 1998;Hurwitz et al, 2002Hurwitz et al, , 2003López and Smith, 1996;Rosenberg et al, 1993).…”