Some Elementary Principles of Polycrystalline Microstructure

Smith, Cyril Stanley

doi:10.1179/095066064790152640

Cited by 214 publications

(37 citation statements)

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“…For large values of ", a small amount of melt will form isolated pockets at four grain junctions if the surface energy of the solid is isotropic. Decreasing " increases the tendency for melt to wet threegrain junctions until, at " = 60 ° or less, an interconnected network will form even for very small amounts of melt (e.g., Smith 1964;von Bargen and Waff 1986). Several studies show that the dihedral angle between sulfide melt and olivine decreases strongly as the oxygen and sulfur content of the sulfide melt increases (Minarik et al 1996;Gaetani and Grove 1999;Rose and Brenan 2001;Terasaki et al 2005).…”

Section: Iiie Transport Of Pb By Advection Of Sulfide Meltmentioning

confidence: 99%

Mantle Pb paradoxes: the sulfide solution

Hart

Gaetani

2006

Contrib Mineral Petrol

115

108

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There is growing evidence that the budget of Pb in mantle peridotites is largely contained in sulfide, and that Pb partitions strongly into sulfide relative to silicate melt. In addition, there is evidence to suggest that diffusion rates of Pb in sulfide (solid or melt) are very fast. Given the possibility that sulfide melt 'wets' sub-solidus mantle silicates, and has very low viscosity, the implications for Pb behavior during mantle melting are profound. There is only sparse experimental data relating to Pb partitioning between sulfide and silicate, and no data on Pb diffusion rates in sulfides. A full understanding of Pb behavior in sulfide may hold the key to several long-standing and important Pb paradoxes and enigmas. The classical Pb isotope paradox arises from the fact that all known mantle reservoirs lie to the right of the Geochron, with no consensus as to the identity of the "balancing" reservoir. We propose that long-term segregation of sulfide (containing Pb) to the core may resolve this paradox.Another Pb paradox arises from the fact that the Ce/Pb ratio of both OIB and MORB is greater than bulk earth, and constant at a value of 25. The constancy of this "canonical ratio" implies similar partition coefficients for Ce and Pb during magmatic processes (Hofmann et al. 1986), whereas most experimental studies show that Pb is more incompatible in silicates than Ce. Retention of Pb in residual mantle sulfide during melting has the potential to bring the bulk partitioning of Ce into equality with Pb if the sulfide melt/silicate melt partition coefficient for Pb has a value of ~ 14. Modeling shows that the Ce/Pb (or Nd/Pb) of such melts will still accurately reflect that of the source, thus enforcing the paradox that OIB and MORB mantles have markedly higher Ce/Pb (and Nd/Pb) than the bulk silicate earth. This implies large deficiencies of Pb in the mantle sources for these basalts. Sulfide may play other important roles during magmagenesis: 1). advective/diffusive sulfide networks may form potent metasomatic agents (in both introducing and obliterating Pb isotopic heterogeneities in the mantle); 2). silicate melt networks may easily exchange Pb with ambient mantle sulfides (by diffusion or assimilation), thus 'sampling' Pb in isotopically heterogeneous mantle domains differently from the silicate-controlled isotope tracer systems (Sr, Nd, Hf), with an apparent 'de-coupling' of these systems.

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Section: Iiie Transport Of Pb By Advection Of Sulfide Meltmentioning

confidence: 99%

Mantle Pb paradoxes: the sulfide solution

Hart

Gaetani

2006

Contrib Mineral Petrol

115

108

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“…It has long been recognized [Smith, 1964;Watson and Brenan, 1987] that fluids in such rocks will be distributed not as thin films along two-grain boundaries, but in "pockets" and along "channels" where three or more grains join. The exact nature of fluid distribution will be dictated by relative interfacial energies of grain boundaries (ff88) and pore walls (ffsf).…”

Section: Fluidmentioning

confidence: 99%

Effect of grain size on the distribution and transport of deep‐seated fluids and melts

Wark

Watson

2000

Geophysical Research Letters

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Abstract. Because permeability increases with the square of the grain size for a given fluid Ëaction, it is commonly assumed that porous flow of fluids and melts is more effective in coarse-grained domains of deep-seated rocks. This relative behavior is accurate, however, only as a description of two systems operating in isolation. We demonstrate that if coarse-and fine-grained domains are in chemical communication, then equilization of pore-wall curvature across the system results in concentration of fluid or melt in domains of finer grain size. Because of this localization of fluid, the permeability of the finer-grained domains will match or exceed that of domains with coarser grains. Fluid focussing due to differences in grain size has potentially important implications for grain-scale transport of metamorphic fluids -including those released from subducting slabs into the sheared mantle wedge -and also for partial melts in the mantle and deep crust.

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“…The initial steady increase in grain size is usually explained by static ('normal') grain growth (Smith, 1964;Alley and others, 1986;Weaire and Rivier, 2009), defined as growth that is only driven by the reduction of free energy of the grain boundaries. The increase in grain size, expressed in mean radius, r, from a starting grain size, r 0 , is usually described by (Anderson, 1986;Glazier and others, 1987;Weygand and others, 1998) …”

Section: Introductionmentioning

confidence: 99%

Competition between grain growth and grain-size reduction in polar ice

Roessiger¹,

Bons²,

Griera

et al. 2011

J. Glaciol.

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ABSTRACT. Static (or 'normal') grain growth, i.e. grain boundary migration driven solely by grain boundary energy, is considered to be an important process in polar ice. Many ice-core studies report a continual increase in average grain size with depth in the upper hundreds of metres of ice sheets, while at deeper levels grain size appears to reach a steady state as a consequence of a balance between grain growth and grain-size reduction by dynamic recrystallization. The growth factor k in the normal grain growth law is important for any process where grain growth plays a role, and it is normally assumed to be a temperature-dependent material property. Here we show, using numerical simulations with the program Elle, that the factor k also incorporates the effect of the microstructure on grain growth. For example, a change in grain-size distribution from normal to log-normal in a thin section is found to correspond to an increase in k by a factor of 3.5.

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Some Elementary Principles of Polycrystalline Microstructure

Cited by 214 publications

References 0 publications

Mantle Pb paradoxes: the sulfide solution

Mantle Pb paradoxes: the sulfide solution

Effect of grain size on the distribution and transport of deep‐seated fluids and melts

Competition between grain growth and grain-size reduction in polar ice

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