Mechanical controls on fluid flow during regional metamorphism: some numerical models

Abstract

The control of fluid flow by plastic deformation during metamorphism is critical to our understanding of metamorphic processes. Various geological observations and field studies demonstrate the consequences of fluid flow control by deformation, so that the concept appears to be accepted, at least for small-scale systems (for example faults and vein systems). However, the concept appears to be less well recognized at regional scales. Considered here are examples of simple, conceptual models based on fully coupled mechanical-fluid flow concepts; they include deformation of a section of fluid-saturated crust containing a block or a layer of material of different properties from its surrounds. In particular, rheological and permeability contrasts between rock types during deformation associated with regional metamorphism are sufficient to control the form of fluid flow over the range of a few kilometres. Low contrasts and small strains allow pervasive fluid flow, whereas greater contrasts and increasing strains cause focusing of the flow. Such focusing is generally associated with localization of the deformation, especially for a strongly dilatant elastic-plastic material. However, a rate of fluid flow much greater than the rate of deformation may result in pervasive flow, although for most models pervasive flow is difficult to attain over regional distances. Furthermore, lateral and downward fluid flow may occur, demonstrated here by simple models for folding and for deformation of regions containing plutons. Therefore, such modelling may be used as a means of testing the various hypotheses concerning the volumes of fluid predicted to have passed through some rock volumes. Numerical models of the future will become increasingly complex and powerful, allowing greater coupling of thermal, mechanical, chemical and fluid flow effects, and based more on the physical processes involved. Combined field and laboratory studies will provide correspondingly greater understanding and will permit the determination of the timing of fluid flow and structural controls on fluid flow patterns.

Mechanical links between erosion and metamorphism in Nanga Parbat, Pakistan Himalaya

“…Stress rates in post-yield flow are governed by a non-associated flow law that is a function of local strain rates. Solution of the mechanical equations in three dimensions is accomplished via a velocity based, Lagrangian formulation (ITASCA; Cundall and Board, 1988) and others, 1990; Upton and others, 1995;Ord and Oliver, 1997;Upton, 1998;Koons and others, 1998) and use an explicit finite-difference solution for elastic and plastic materials. The equations of motion are solved at the grid nodes for spatial and velocity derivatives discretized between nodes over constant strain rate tetrahedral elements.…”

Coupled Models of Brittle-plastic Deformation and Fluid Flow: Approaches, Methods, and Application to Mesoproterozoic Mineralisation at Mount Isa, Australia

“…Compaction is often observed in underconsolidated sediments and sandstones (Aydin and Johnson 1983;Fisher and Knipe 1998;Sheldon et al 2006), while dilation is more likely in crystalline and metamorphic rocks, particularly at the onset of deformation and at low confining pressure (e.g. Edmond and Paterson 1972;Fischer and Paterson 1989;Hobbs et al 1990;Ord 1990;Ord and Oliver 1997;Zhang et al 1994;Paterson and Wong 2005). Deformation induced volume change can either be expressed by a modification of the porosity and permeability of a continuous rock volume, or by the generation of a fracture-rock discontinuum.…”

Numerical Modeling of Coupled Geodynamical Processes and Its Role in Facilitating Predictive Ore Discovery: An Example from Tongling, China

“…There are several commercially available numerical codes, such as FLAC (Fast Lagrangian Analysis of Continua) (Cundall and Soard, 1988;Coetzee et al, 1995), UDEC (Universal Distinct Element Code) (Lemos et al, 1985;Starfield and Cundall, 1988) and FIDAP (Fluid Dynamic Analysis Package) (Fluid Dynamics International, 1997), which have been successfully used for modeling of coupled mechano-hydrological (MH), mechano-thermo-hydrological (MTH) or thermo-hydro-chemical (THC) problems in the tectonic and metallogenic systems (e.g., Ord and Oliver, 1997;Oliver et al, 2001;Jiang et al, 1997;Gow et al, 2002;Ord et al, 2002;Sorjonen-Ward et al, 2002). In our research, we have adopted the FLAC to simulate the deformation and fluid flow during syn-deformational cooling of intrusion.…”