Modelling melting and melt segregation by two-phase flow: new insights into the dynamics of magmatic systems in the continental crust

Schmeling, Harro; Marquart, Gabriele; Weinberg, Roberto F.; Wallner, Herbert

doi:10.1093/gji/ggz029

Cited by 31 publications

(123 citation statements)

References 97 publications

Supporting

Mentioning

116

Contrasting

Unclassified

Order By: Relevance

“…The equations are solved on a 201 × 201 grid by finite differences (FDs) using the code FDCON (e.g., Schmeling et al, 2019). Resolution tests have been made with grids varying from 101 × 101 to 401 × 401.…”

Section: Methods and Model Setupmentioning

confidence: 99%

See 1 more Smart Citation

The effect of effective rock viscosity on 2-D magmatic porosity waves

2019

Self Cite

View full text Add to dashboard Cite

Abstract. In source regions of magmatic systems the temperature is above solidus, and melt ascent is assumed to occur predominantly by two-phase flow, which includes a fluid phase (melt) and a porous deformable matrix. Since McKenzie (1984) introduced equations for two-phase flow, numerous solutions have been studied, one of which predicts the emergence of solitary porosity waves. By now most analytical and numerical solutions for these waves used strongly simplified models for the shear- and bulk viscosity of the matrix, significantly overestimating the viscosity or completely neglecting the porosity dependence of the bulk viscosity. Schmeling et al. (2012) suggested viscosity laws in which the viscosity decreases very rapidly for small melt fractions. They are incorporated into a 2-D finite difference mantle convection code with two-phase flow (FDCON) to study the ascent of solitary porosity waves. The models show that, starting with a Gaussian-shaped wave, they rapidly evolve into a solitary wave with similar shape and a certain amplitude. Despite the strongly weaker rheologies compared to previous viscosity laws, the effects on dispersion curves and wave shape are only moderate as long as the background porosity is fairly small. The models are still in good agreement with semi-analytic solutions which neglect the shear stress term in the melt segregation equation. However, for higher background porosities and wave amplitudes associated with a viscosity decrease of 50 % or more, the phase velocity and the width of the waves are significantly decreased. Our models show that melt ascent by solitary waves is still a viable mechanism even for more realistic matrix viscosities.

show abstract

Section: Methods and Model Setupmentioning

confidence: 99%

“…The mathematical formulation of differential movement between solid matrix and melt basically builds on that described in Schmeling (2000) and Schmeling et al (2019) and is applied here to a porosity wave. We solve the equations for mass and momentum conservation for melt and solid.…”

Section: Governing Equationsmentioning

confidence: 99%

The effect of effective rock viscosity on 2-D magmatic porosity waves

2019

Self Cite

View full text Add to dashboard Cite

show abstract

“…We can also quantify the average depletion within the diapir (

\overset{F}{true} = \frac{\int italicFd normalΩ}{\int d normalΩ}

) through time, where Ω represents the total area of the diapir. With an impermeable boundary, the average depletion is equivalent to the average porosity (

\overset{ϕ}{true} = \frac{\int italicϕd normalΩ}{\int d normalΩ}

) (see Appendix A in Schmeling et al, ). The shorter and colder ascent path followed by the 3.7‐km diapir (case CL12.8_I_R3.7) results in a maximum average depletion of only ~6% (green line in Figure a).…”

Section: Resultsmentioning

confidence: 99%

“…For the majority of our calculations we set the top of the diapir to be an impermeable boundary. Although the momentum equations (equations (1) and (2)) are valid only when melt flows within a continuous permeable solid matrix (Hier-Majumder et al, 2006;McKenzie, 1984;Schmeling et al, 2019;Zhu et al, 2011), we allow the porosity to exceed the disaggregation threshold (typically~20-40%), but never increase above 100%. This treatment allows us to explore the total melt fraction in the system (e.g., Katz & Weatherley, 2012).…”

Section: Nondimensionalization Scaling and Parametersmentioning

confidence: 99%

Melt Segregation and Depletion During Ascent of Buoyant Diapirs in Subduction Zones

et al. 2020

View full text Add to dashboard Cite

Cold, low‐density diapirs arising from hydrated mantle and/or subducted sediments on the top of subducting slabs have been invoked to transport key chemical signatures to the source region of arc magmas. However, to date there have been few quantitative models to constrain melting in such diapirs. Here we use a two‐phase Darcy‐Stokes‐energy model to investigate thermal evolution, melting, and depletion in a buoyant sediment diapir ascending through the mantle wedge. Using a simplified 2‐D circular geometry, we investigate diapir evolution in three scenarios with increasing complexity. In the first two scenarios we consider instantaneous heating of a diapir by thermal diffusion with and without the effect of the latent heat of melting. Then, these simplified calculations are compared to numerical simulations that include melting, melt segregation, and the influence of depletion on the sediment solidus along pressure‐temperature‐time (P‐T‐t) paths appropriate for ascent through the mantle wedge. The high boundary temperature induces a rim of high porosity, into which new melts are focused and then migrate upward. The rim thus acts like an annulus melt channel, while the effect of depletion buffers additional melt production. Solid matrix flow combined with recrystallization of melt pooled near the top of the diapir can result in large gradients in depletion across the diapir. These large depletion gradients can either be preserved if the diapir leaks melt during ascent, or rehomogenized in a sealed diapir. Overall our numerical simulations predict less melt production than the simplified thermal diffusion calculations. Specifically, we show that diapirs whose ascent paths favor melting beneath the volcanic arc will undergo no more than ~40–50% total melting.

show abstract

“…Ранее в ряде работ [Polyansky et al, 2009[Polyansky et al, , 2010[Polyansky et al, , 2016[Polyansky et al, , 2017 использовалась модель порционного (batch) плавления вещества гранитной коры, в которой доля расплава (степень плавления) остается постоянной. Характерной формой при этом механизме плавления являются магматические диапиры [Schmeling et al, 2019]. В качестве примера приведен результат моделирования процесса формирования термального ареала вокруг гранитоидного диапира, возникшего над базитовым магматическим источником тепла в основании коры (рис.…”

Section: Discussionunclassified

The Role of Magmatic Heat Sources in the Formation of Regional and Contact Metamorphic Areas in West Sangilen (Tuva, Russia)

Полянский

Kargopolov

Изох

et al. 2019

Geodin. tektonofiz.

View full text Add to dashboard Cite

The tectonomagmatic evolution of the Sangilen massif has been described in detail in numerous publications, but little attention was given to heat sources related to the HT/LP metamorphism. Modeling of the magma transport to the upper‐crust levels in West Sangilen shows that the NT/LP metamorphism is related to gabbromonodiorite intrusions. This article is focused on the thermo‐mechanical modeling of melting and lifting of melts in the crust, taking into account the density interfaces. The model of the Erzin granitoid massif shows that in case of fractional melting, the magma ascent mechanism is fundamentally different, as opposed to diapir upwelling – percolation take place along a magmatic channel or a system of channels. An estimated rate of diapiric rise in the crust amounts to 0.8 cm/yr, which is more than an order of magnitude lower than the rate of melt migration in case of fractional melting (25 cm/yr). In our models, a metamorphic thermal ‘anticline’ develops in stages that differ, probably, due to the modes of crust melting: batch melting occurs at the first stage, and fractional melting takes place at the second stage. It is probable that the change of melting modes from melting conditions in a ‘closed’ system to fractional melting conditions in ‘open’ systems is determined by tectonic factors. For the Sangilen massif, we have estimated the degrees of melting in the granulite, granite, and sedimentary‐metamorphic layers of the crust (6, 15, and 5 vol. %, respectively).

show abstract

Modelling melting and melt segregation by two-phase flow: new insights into the dynamics of magmatic systems in the continental crust

Cited by 31 publications

References 97 publications

The effect of effective rock viscosity on 2-D magmatic porosity waves

The effect of effective rock viscosity on 2-D magmatic porosity waves

Melt Segregation and Depletion During Ascent of Buoyant Diapirs in Subduction Zones

The Role of Magmatic Heat Sources in the Formation of Regional and Contact Metamorphic Areas in West Sangilen (Tuva, Russia)

Contact Info

Product

Resources

About