A Fluid-Dynamical Study of Crystal Settling in Convecting Magmas

Martin, Dawn Lundy; Nokes, Roger

doi:10.1093/petrology/30.6.1471

Cited by 157 publications

(113 citation statements)

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“…The gravity currents in our experiments are turbulent but, as noted by Martin & Nokes (1998, 1989, the turbulence becomes negligible close to the boundary because both the normal and tangential velocities are zero on the boundary. We do not know if the turbulence has the same energy and spectrum across the valley, nor whether the sedimentation velocity entering the non-turbulent boundary is necessarily vertical, nor whether the non-turbulent boundary has the same thickness across the valley.…”

Section: Box Model For the V-shaped Valleysupporting

confidence: 62%

“…The deposit across the V-shaped valley, for any position along the valley, is much larger in the central part of the valley compared to the flanks. We find that the results can be described with remarkable accuracy by a box model which uses a generalization of the mass deposit equation of Martin & Nokes (1988, 1989 to take account of the geometry of the valley. The experiments are described in § 2.…”

Section: Introductionmentioning

confidence: 92%

“…Studies of such currents flowing in horizontal tanks with flat bottoms have been carried out by Bonnecaze, Huppert & Lister (1993) for constant volume currents, and by Garcia (1994) and Altinakar, Graf & Hopfinger (1996) for constant flux currents. Bonnecaze et al (1993) compared their experiments with calculations based on a two-layer fluid model together with an equation due to Martin & Nokes (1988, 1989 which describes the loss of particulate matter in a turbulent flow. The agreement between the experimental and numerical results for the variation of the length of the current with time was, however, very good.…”

Section: Introductionmentioning

confidence: 99%

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Particulate gravity currents along V-shaped valleys

et al. 2009

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This paper extends previous studies of saline gravity currents at high Reynolds number flowing along a tank with a V-shaped valley. We use experiments and a box model to determine the primary features of the flow. The particulate gravity currents were initiated by releasing a fixed volume of fluid consisting of pure water mixed with silicon carbide particles from a lock at one end of the tank. The resulting motion and deposit pattern differ significantly from those for the propagation of a particulate gravity current along a flat-bottomed tank. The front of the current, seen from above, is approximately parabolic (with axis parallel to the flow direction) in contrast to the current in a flat-bottomed tank where it is nearly a straight line perpendicular to the flow. This feature mimics the results for pure saline currents. When seen in profile the currents do not have a clearly defined raised head, which is a feature of the flat-bottomed currents. The mass deposited per unit area varies nearly monotonically with respect to distance down the tank, again in contrast to the case of the flat-bottomed tank. The exceptions to this are the two experiments which have the highest ratio of lock height to length. The mass deposited per unit area across the V-shaped valley is much larger in the central part of the valley than it is on the flanks for any position along the valley. We find that the results can be described with remarkable accuracy by a box model using a generalization of the equation for sedimentation from a turbulent medium due to Martin and Nokes. Our results further show that the factor used in the deposition rate equation which is commonly assumed to be 1 should be smaller, typically 0.7. IntroductionGravity currents in nature usually flow over complex terrain which can include valleys, basins, changes of slope and obstacles which may completely or partially block the flow (for a convenient and comprehensive discussion of field observations of gravity currents, and the associated experimental work, the review of Kneller & Buckee (2000) is extremely useful). Most experimental work has focused on gravity currents flowing in tanks designed so that the flow is close to two-dimensional. The simplest of these tanks are flat bottomed (Simpson 1997 provides a comprehensive description of experiments using these tanks). The effect of obstacles in the form of ridges on the flow and deposit of particulate matter has also been studied (Rottman, †

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Section: Box Model For the V-shaped Valleysupporting

confidence: 62%

Section: Introductionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

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Particulate gravity currents along V-shaped valleys

et al. 2009

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“…This convection is generated from a cold thermal boundary layer at the upper contact, transports cooled magma away from the roof, and crystals may be nucleated and grown in the reservoir interior. These crystals settle at the bottom, even in the presence of convection, because convective velocities vanish at the base of the chamber and hence cannot maintain crystals in suspension (Martin and Nokes, 1988). A final possibility is that crystals grow from undercooled melt coming from the roof or side-walls.…”

Section: Crystallization In a Thermal Boundary Layermentioning

confidence: 99%

The production of chemically stratified and adcumulate plutonic igneous rocks

Tait

Jaupart

1996

Mineral. mag.

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We review recent advances on the physical principles of crystallization in multicomponent systems, and use them to provide a framework for interpreting petrological and geochemical observations from igneous intrusions. The thermal structure of crystallizing boundary layers imposes strong constraints on the chemical and mineralogical compositions of the solid that can form from a given melt. The thermal problem is largely independent of the chemical composition of the melt, and sets the course of crystallization. A key problem to understand is the temperature of the solidification front (which we take to mean that point at which the last drop of liquid solidifies) particularly in the geologically relevant case in which the temperature at the cold boundary is below the eutectic temperature. Focussing on the solidification front rather than on the liquidus is a valuable perspective. Adcumulus growth requires specific conditions and much can be learned from trying to understand how these can develop from given starting conditions. We discuss the physical reasons and field evidence Ibr the existence of mushy layers, where solid fraction and temperature vary by large amounts. In such regions of the magma chamber, thermodynamic equilibrium is nearly achieved locally and, for a given temperature, this specifies the composition of the interstitial melt. Thus, in a magma chamber, the whole liquid line of descent is present simultaneously. Compositional convection is likely to set in, and this exchange between the interior of the mushy layer and the main reservoir leads to a chemically stratified solid, and to adcumulus growth. The contribution of crystal settling to the floor cumulates is evaluated as a function of the magnitude of convective heat flux through the roof. It is shown that crystal settling is unlikely to overwhelm in-situ nucleation and growth at the floor.

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“…Bursik & Woods 1996). The suspending turbulent current is considered well mixed with no fluid phase loss, and the concentration decreases owing to particles settling through a basal viscous sub-layer (Martin & Nokes 1989).…”

Section: Introductionmentioning

confidence: 99%

A two-layer approach to modelling the transformation of dilute pyroclastic currents into dense pyroclastic flows

2010

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Most models of volcanic ash flows assume that the flow is either dilute or dense, with dynamics dominated by fluid turbulence or particle collisions, respectively. However, most naturally occurring flows feature both of these end members. To this end, a two-layer model for the formation of dense pyroclastic basal flows from dilute, collapsing volcanic eruption columns is presented. Depth-averaged, constant temperature, continuum conservation equations to describe the collapsing dilute current are derived. A dense basal flow is then considered to form at the base of this current owing to sedimentation of particles and is modelled as a granular avalanche of constant density. We present results which show that the two-layer model can predict much larger maximum runouts than would be expected from single-layer models, based on either dilute or dense conditions, as the dilute surge can outrun the dense granular flow, or vice versa, depending on conditions.

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A Fluid-Dynamical Study of Crystal Settling in Convecting Magmas

Cited by 157 publications

References 0 publications

Particulate gravity currents along V-shaped valleys

Particulate gravity currents along V-shaped valleys

The production of chemically stratified and adcumulate plutonic igneous rocks

A two-layer approach to modelling the transformation of dilute pyroclastic currents into dense pyroclastic flows

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