The dynamics of melt and shear localization in partially molten aggregates

Katz, Richard F.; Spiegelman, Marc; Holtzman, B. K.

doi:10.1038/nature05039

Cited by 274 publications

(308 citation statements)

References 23 publications

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“…A stronger effect may be achieved with anisotropic melt percolation. Melt channels are known to form in response to mantle shear and are expected to be angled toward a ridge axis in the areas where the rate of horizontal mantle flow away from the ridge axis decreases with depth [Holtzman et al, 2003;Katz et al, 2006]. This sense of shear is expected to develop due to mantle flow driven passively by plate-spreading and would be further enhanced by northward flow of plume material toward the GSC.…”

Section: Incompatible Element Concentrations Along the Galápagos Sprementioning

confidence: 99%

Patterns in Galápagos Magmatism Arising from the Upper Mantle Dynamics of Plume‐Ridge Interaction

Ito

Bianco

2014

The Galápagos

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Section: Incompatible Element Concentrations Along the Galápagos Sprementioning

confidence: 99%

Patterns in Galápagos Magmatism Arising from the Upper Mantle Dynamics of Plume‐Ridge Interaction

Ito

Bianco

2014

The Galápagos

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“…Most simulations did, of course, predict a high-porosity decompaction channel at the base of the lithosphere, but this feature is independent of the mechanical instability associated with porosity bands [Sparks and Parmentier, 1991]. Emergence of porosity bands in simulations of experimental conditions by Katz et al [2006] were sensitive to the amplitude of the initial noise that was introduced; simulations described above contained no initial noise. To test the importance of initial noise for porosity band emergence in MOR models, I ran the two simulations shown in Figure 13.…”

Section: On the Absence Of Porosity/shear Bandsmentioning

confidence: 99%

“…Experimental [e.g., Holtzman et al, 2003;King et al, 2010] and theoretical [e.g., Stevenson, 1989;Spiegelman, 2003;Katz et al, 2006] studies have shown that partially molten mantle materials subject to shear can develop bands of locally increased porosity and deformation. These rheologically weak bands tend to emerge at a particular angle to the shear plane under simple shear deformation.…”

Section: On the Absence Of Porosity/shear Bandsmentioning

confidence: 99%

“…Various studies have shown that the spacing of porosity bands arising from mechanical instability is expected to be less than or equal to the compaction length [e.g., Spiegelman, 2003]. Numerical models performed by Katz et al [2006] suggest that within this range, it is the wavenumber spectrum of initial noise that controls the spacing of bands. The simulations presented in Figure 13 use an initial noise field with spectral power at scales smaller than the compaction length, and hence should enable growth of porosity bands at that scale.…”

Section: On the Absence Of Porosity/shear Bandsmentioning

confidence: 99%

“…These rheologically weak bands tend to emerge at a particular angle to the shear plane under simple shear deformation. Katz et al [2006] proposed that they might provide a mechanism for melt focusing to the ridge axis. Butler [2009] showed that simulations that account .…”

Section: On the Absence Of Porosity/shear Bandsmentioning

confidence: 99%

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Porosity‐driven convection and asymmetry beneath mid‐ocean ridges

Katz

2010

Geochem Geophys Geosyst

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[1] Seismic tomography of the asthenosphere beneath mid-ocean ridges has produced images of wave speed and anisotropy that are asymmetric across the ridge axis. These features have been interpreted as resulting from an asymmetric distribution of upwelling and melting. Using computational models of coupled magma/mantle dynamics beneath mid-ocean ridges, I show that such asymmetry should be expected if buoyancy forces contribute to mantle upwelling beneath ridges. The sole source of buoyancy considered here is the dynamic retention of less dense magma within the pores of the mantle matrix. Through a scaling analysis and comparison with a suite of simulations, I derive a quantitative prediction of the contribution of such buoyancy to upwelling; this prediction of convective vigor is based on parameters that, for the Earth, can be constrained through natural observations and experiments. I show how the width of the melting region and the crustal thickness, as well as the susceptibility to asymmetric upwelling, are related to convective vigor. I consider three causes of symmetry breaking: gradients in mantle potential temperature and composition and ridge migration. I also report that in numerical experiments performed for this study, the fluid dynamical instability associated with porosity/shear band formation is not observed to occur.

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Compaction around a rigid, circular inclusion in partially molten rock

et al. 2014

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Conservation laws that describe the behavior of partially molten mantle rock have been established for several decades, but the associated rheology remains poorly understood. Constraints on the rheology may be obtained from recently published experiments involving deformation of partially molten rock around a rigid, spherical inclusion. These experiments give rise to patterns of melt segregation that exhibit the competing effects of pressure shadows and melt‐rich bands. Such patterns provide an opportunity to infer rheological parameters through comparison with models based on the conservation laws and constitutive relations that hypothetically govern the system. To this end, we have developed software tools to simulate finite strain, two‐phase flow around a circular inclusion in a configuration that mirrors the experiments. Simulations indicate that the evolution of porosity is predominantly controlled by the porosity‐weakening exponent of the shear viscosity and the poorly known bulk viscosity. In two‐dimensional simulations presented here, we find that the balance of pressure shadows and melt‐rich bands observed in experiments only occurs for bulk‐to‐shear viscosity ratio of less than about five. However, the evolution of porosity in simulations with such low bulk viscosity exceeds physical bounds at unrealistically small strain due to the unchecked, exponential growth of the porosity variations. Processes that limit or balance porosity localization should be incorporated in the formulation of the model to produce results that are consistent with the porosity evolution in experiments.

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The dynamics of melt and shear localization in partially molten aggregates

Cited by 274 publications

References 23 publications

Patterns in Galápagos Magmatism Arising from the Upper Mantle Dynamics of Plume‐Ridge Interaction

Patterns in Galápagos Magmatism Arising from the Upper Mantle Dynamics of Plume‐Ridge Interaction

Porosity‐driven convection and asymmetry beneath mid‐ocean ridges

Compaction around a rigid, circular inclusion in partially molten rock

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