Mush Regions Research Articles

Theoretical study of solidification phase change heat and mass transfer with thermal resistance and convection subjected to a time-dependent boundary condition

The solidification of phase-change materials (PCMs) is a key process that occurs commonly in materials science and metallurgy, such as in the casting of alloys and energy management systems. There is a lot of literature in this area that assumes the PCMs are in close contact with the heat source or sink. However, a non-freezing wall frequently encloses them in practical situations. This work presents a phase change problem that describes the solidification of a semi-infinite PCM with thermal resistance. We assume that time-dependent heat flux drives the solidification process. The PCM first convert into mush and then into solid, which leads to a three-region problem. The current study accounts for both conduction as well as convection heat transfer mechanisms. Unfortunately, the exact solution to such problems with time-dependent flux-type boundary conditions may not be possible. Thus, there is considerable interest in deriving the analytical solution. The space–time transformation yields the analytical solution to the problem. A numerical example of Al−Cu alloy with 5%Cu is presented to demonstrate the current study. Thermal resistance shows a pronounced impact on the temperature field. Lower thermal resistance offers faster solidification rate. It is found that as the heat transfer constant increases, the rate of propagation of solid–mush and mush–solid interfaces gets enhanced. In addition, the growth of thermal resistance is of linear nature, with variation in the value of Q. The solidified region has higher concentration than the mush region. The current study is applicable to both eutectic systems and solid solution alloys.

Mayotte 2018 eruption likely sourced from a magmatic mush

Despite significant advancements in understanding crustal melt transport, determining the shallow magmatic architecture at any given volcanic system remains a significant challenge with geophysical methods alone. In this study, we present a new conceptual model combining previously studied models for geomechanical magma reservoirs and dyke-shaped conduits. Supplementary to previous work, we include a model for porous mush adjacent to a visco-elastic magma reservoir during the eruption. This addition enables physically consistent magma recharge into the elastic magma reservoir by porous flow instead of employing an arbitrary mantle magma recharge parameterization. We compare our conceptual model with an illustrative test case - the submarine 2018 Mayotte eruption in the Comoros Islands (∼6.55 km3 Bulk Rock Volume, ∼3.5 km water depth, ∼35 km estimated deep magma reservoir). We estimate a magma effusion rate history using a new continuous-time inversion of surface deformation data. A single magma reservoir cannot match the observed eruptive history for any reservoir geometry or crustal and magmatic material properties. However, the presence of a porous mush adjacent to the magma reservoir helps to reconcile the model with the observations. The additional magma flux from the mush region sustains the long eruption at a low effusion rate, as is observed off Mayotte, with a decreasing effusion rate after few months of eruptions and a low persistent effusion rate since then. The mush flow dynamics are a direct consequence of reduced pressure in the magma reservoir during the eruption. Thus, our model provides a parsimonious and physically motivated explanation of the Mayotte eruptive history. Since many historical basaltic eruptions worldwide, such as sometime observed at Piton de la Fournaise, Volcan Arenal, and Laki, have a similar effusion rate history shape as Mayotte, magmatic mushes may be a key component for explaining long-lived basaltic eruptions.

Trachyte-phonolite transition at Dunedin Volcano: Fingerprints of magma plumbing system maturity and mush evolution

Phonolite-trachyte associations are a common feature of alkaline volcanoes in intraplate settings, and their coexistence challenges closed-system magmatic differentiation scenarios. Here we have investigated the mineralogical and petrochemical features of dikes, lavas, pyroclastic deposits, and comagmatic crystal-rich enclaves outcropping at Dunedin Volcano (Otago region, southern New Zealand). These alkaline magmatic products show both highly and mildly alkaline affinities, trending towards phonolitic and trachytic end-members, respectively. Intermediate rocks are phonotephrites + tephriphonolites (highly alkaline series) and mugearites + benmoreites (mildly alkaline series) with a phenocryst assemblage of clinopyroxene + plagioclase ± amphibole formed at low to mid-crustal levels (i.e., ~29–16 km). Phonolites are porphyritic rocks characterized by alkali feldspar ± amphibole ± clinopyroxene. Their whole-rock compositions are highly enriched in incompatible elements, with variable Ba + Sr contents. A weak negative to slightly positive Eu anomaly is also associated with 87Sr/86Sr ratios of 0.7028–0.7031, which are comparable to those of parental magmas. Geochemical models indicate that phonolites originate as interstitial melts that are generated via abundant alkali feldspar crystallization from a shallow crystalline mush (i.e., ~14–5 km). Strong melt differentiation and extraction is testified by crystal-rich enclaves, as remnants of the mush region. On the other hand, trachytes are phenocryst-poor products strongly depleted in Ba + Sr and with a marked negative Eu anomaly. Trachytes are characterized by 87Sr/86Sr ratios of 0.7040–0.7060, which are different from intermediate rocks and phonolites, and trend towards crustal isotopic compositions. Integrated mass balance, trace element, and energy-constrained modeling confirm that trachytes originate from mildly alkaline magmas interacting with the country rock during feldspar fractionation. We interpret the transition from trachyte to phonolite formation and eruption resulting from the maturation of the plumbing system through accumulation, cooling, and degassing of both highly and mildly alkaline magmas.

Decoding multiple zoning patterns in clinopyroxene phenocrysts at Vulcano Island: A record of dynamic crystallization through interconnected reservoirs

Here we document how the different growth features and intracrystalline distributions of both major and trace cations in clinopyroxene phenocrysts are important recorders of the intricate magma dynamics at Vulcano Island (Aeolian Arc, Italy). The compositions of clinopyroxene phenocrysts from products erupted over the last ~54 ka cluster at different degrees of evolution, paralleling the polybaric-polythermal differentiation of mantle-derived mafic magmas into more evolved silicic melts. The hotter lower crust is the most favorable location for the storage of mafic magmas and the early crystallization of diopsidic (Mg#91) clinopyroxene (Pmax ≈ 750 MPa and Tmax ≈ 1220 °C). Diopsidic phenocrysts are depleted in both rare earth elements (REE) and high field strength elements (HFSE) but are enriched in transition elements (TE). The transfer and accumulation of primitive magmas in the colder upper crustal regions lead to the formation of an interconnected series of more differentiated magmatic reservoirs (P ≈ 100–450 MPa and T ≈ 1100–1180 °C) hosting discrete populations of clinopyroxene (Mg#84–85) with a broad spectrum of zonations and dissolution features. Recharge bands in clinopyroxene are markers of multiple inputs of primitive REE-HFSE-poor, TE-rich magmas from depth. Augitic phenocrysts (Mg#82) with strong negative Eu anomaly and REE + HFSE enrichments crystallizes from highly differentiated trachytic and rhyolitic melts stored at very shallow crustal conditions (P ≤ 50 MPa and T ≤ 1100 °C). These silicic reservoirs represent residual melts trapped-extracted from crystal-dominated mush regions in the uppermost part of the plumbing system. The residence time of clinopyroxene increases from ∼0.1 to ∼44 years from basalt to rhyolite, together with an increasing number of recharge bands. The mineral assemblage in more silicic and viscous mush melts is sufficiently resilient to record numerous mafic injections and high degrees of magma mixing, hybridization, and crystallization before eruption. Overall, the compositional zoning pattern of clinopyroxene presents a picture of plumbing system that extends through the crust and is characterized by distributions of melts and crystals which are progressively more evolved and heterogeneous in both space and time.

Mechanisms and patterns of magmatic fluid transport in cooling hydrous intrusions

Volatile outgassing from hydrous magma intrusions emplaced and cooling in the Earth's upper crust is key to a number of geologic processes including volcanic eruptions and ore deposition, yet the physical interactions between production, storage and transport of a magmatic volatile phase within magmatic intrusions and their large-scale thermal evolution have remained elusive. We performed numerical simulations of aqueous volatile transport in generic magma chambers as they crystallize in response to conductive and convective cooling and thereby transition from a crystal - volatile - melt suspension to a mush and eventually to a rigid rock. We used simplified but realistic material properties based on published phase equilibrium experiments, published grain-scale modeling results and general geological constraints.We found that the intrusion depth and water content exert decisive control on the rates and mechanisms of intrusion outgassing. Above a critical volatile content, highly permeable capillary tubes develop in crystal mush regions with intermediate crystal volume fractions (∼ 0.5 to 0.7), and such grain-scale tubes provide rapid intrusion-scale degassing paths. These tubes are located in a ring-like mush region inside the intrusion, allowing strongly lateral flow and focusing towards the top of the intrusion. If the water content of the magma is close to saturation at the time of emplacement (5 to 6 wt% H2O) and the depth of the magma chamber roof is at least 4 km deep, initially distributed breakthrough points may coalesce to a single area of fluid release. Large-scale intrusion geometry determines this location of focused fluid release, and cooling rate and size of the intrusion determine overall fluid flux. Feedbacks between local hydrofracturing and heat advection break up the focused fluid expulsion into many short-lived pulses. These conditions for large-scale fluid focusing favor the formation of porphyry copper deposits, but might also trigger caldera-forming ignimbrite eruptions.

Magma accumulation beneath Santorini volcano, Greece, from P-wave tomography

AbstractDespite multidisciplinary evidence for crustal magma accumulation below Santorini volcano, Greece, the structure and melt content of the shallow magmatic system remain poorly constrained. We use three-dimensional (3-D) velocity models from tomographic inversions of active-source seismic P-wave travel times to identify a pronounced low-velocity anomaly (–21%) from 2.8 km to 5 km depth localized below the northern caldera basin. This anomaly is consistent with depth estimates of pre-eruptive storage and a recent inflation episode, supporting the interpretation of a shallow magma body that causes seismic attenuation and ray bending. A suite of synthetic tests shows that the geometry is well recovered while a range of melt contents (4%–13% to fully molten) are allowable. A thin mush region (2%–7% to 3%–10% melt) extends from the main magma body toward the northeast, observed as low velocities confined by tectono-magmatic lineaments. This anomaly terminates northwest of Kolumbo; little to no melt underlies the seamount from 3 to 5 km depth. These structural constraints suggest that crustal extension and edifice loads control the geometry of magma accumulation and emphasize that the shallow crust remains conducive to melt storage shortly after a caldera-forming eruption.

Valve-like dynamics of gas flow through a packed crystal mush and cyclic strombolian explosions

Strombolian volcanic explosions are commonly attributed to the rise and burst of conduit-filling gas slugs. The magmas associated with strombolian activity, however, are typically not only volatile-rich but also highly crystalline, with mush regions in the shallow plumbing system, where an exsolved volatile phase may also be abundant. Through analogue experiments, we explore a new mechanism to form gas slugs and strombolian explosions. A steady flux of gas is supplied to the base of a particle-rich liquid layer, generating a localised gas intrusion, which initially grows through plastic deformation. Once the pressure in the intrusion overcomes the effective tensile strength of the particle pack, a localised channel opens, allowing gas to propagate upwards. As the pressure in the intrusion falls, the gas pocket collapses. The continued supply of gas leads to the formation of a new intrusion, and the cycle repeats. With higher gas fluxes, continuous channelised gas flow occurs. Highly crystalline shallow portions of basaltic conduits may act as a flow valve, transforming a steady gas flux into a series of discrete gas slugs which cause explosions.

Axisymmetric front tracking model for the investigation of grain structure evolution during directional solidification

A recent numerical investigation by the present authors Battaglioli et al. (2017) had shown that the heat and mass transfer associated with steady-state Bridgman furnace solidification is dependent on advection of sensible and latent heat, and also on the axisymmetric geometry of the crucible. The present work extends the previous one by considering more complex non-steady solidification scenarios, where transient (limited-duration) Bridgman solidification is subsequently combined with a controlled power-down cooling process. A significant advancement with respect to the previous model is the inclusion of a front tracking method for the simulation of columnar growth. In the front tracking method the columnar mush region is demarcated by a series of markers that advance at a growth rate governed by the solutal undercooling at the dendrite tips. A classic micro-segregation law is used to govern the evolution of solid fraction in the columnar mush and the release of latent heat. The inclusion of the front tracking method has provided greater insights into how heat fluxes and thermal conditions can influence the final grain structure. Firstly, we show that by analysing the trajectories of the markers, it is possible to predict the transition from axial columnar growth (directional solidification) to unwanted radial columnar growth due to significant radial heat fluxes in the sample. Secondly, we show that model can simulate an undercooled liquid region ahead of the columnar front where equiaxed grains could possibly nucleate and grow, leading to a columnar to equiaxed transition (CET). Two indirect CET prediction methods from literature have been included to the model to assess the likelihood of a CET occurring in the as-cast grain structure of the alloy. The model was employed to simulate experimental scenarios from literature involving a γ-TiAl alloy where the samples were subjected to different transient cooling conditions in a Bridgman furnace. Examples of axial columnar growth, radial columnar growth, and CET are discussed in detail with elucidation from the model.

Dynamic Magma Systems: Implications for Forecasting Volcanic Activity

Magma systems that supply volcanoes can extend throughout the crust and consist of mush (melt within a crystalline framework) together with ephemeral magma accumulations. Within a crystal-rich mush, slow processes of melt segregation and heat loss alternate with fast processes of destablisation and magma transport. Magma chambers form by two mechanisms: incremental magma intrusion into sub-solidus rocks or the segregation and rapid merging of melt-rich layers within mush regions. Three volcanic states reflect alternations of slow and fast processes: dormancy, unrest and eruption. Monitoring needs to detect processes of melt and fluid movements in the lower and middle crust during destabilisation to improve forecasting.

Numerical investigation on species transport in electroslag remelting dual alloy ingot

A transient three-dimensional (3D) comprehensive model has been developed to investigate the solute transport in electroslag remelting (ESR) dual alloy ingot. The solutions of the mass, momentum, energy, and species conservation equations were simultaneously calculated by the finite volume method, and full coupling of the Joule heating and Lorentz force through the solving Maxwell’s equations. The movement of the metal droplet was described with the volume of fluid (VOF) approach. Besides, the solidification was modeled by using an enthalpy-based technique, where the mushy zone was treated as a porous medium with an anisotropic permeability. A reasonable agreement between the simulation and the experiment was obtained. The results indicate that the colder metal flowing downward washes the solidification front in the process. The solute-poor metal in the pool displaces the solute-rich metal in the mush region. Meanwhile, the solute enrichment promotes the sinking of the liquid. The inward Lorentz force pushes the metal from the periphery to the bottom. The solutes are deposited at the pool bottom. The negative segregation occurs in the lower part and then rises to positive for the two elements. The maximal positive and negative segregation indexes of the carbon and nickel along the vertical centerline of the ESR dual alloy ingot are 0.38 and −0.19, and 0.15 and −0.02, respectively.

Melt evolution and residence in extending crust: Thermal modeling of the crust and crustal magmas

Tectonic extension and magmatism often act in concert to modify the thermal, mechanical, and chemical structure of the crust. Quantifying the effects of extension and magma flux on melting relationships in the crust is fundamental to determining the rate of crustal melting versus fractionation, magma residence time, and the growth of continental crust in rift environments. In order to understand the coupled control of tectonic extension and magma emplacement on crustal thermal evolution, we develop a numerical model that accounts for extension and thermal-petrographic processes in diverse extensional settings. We show that magma flux exerts the primary control on melt generation and tectonic extension amplifies the volume of melt residing in the crustal column. Diking into an extending crust produces hybrid magmas composed of 1) residual melt remaining after partial crystallization of basalt (mantle-derived melt) and 2) melt from partial melting of the crust (crustal melt). In an extending crust, mantle-derived melts are more prevalent than crustal melts across a range of magma fluxes, tectonic extension rates, and magmatic water contents. In most of the conditions, crustal temperatures do not reach their solidus temperatures to initiate partial melting of these igneous lithologies. Energy balance calculations show that the total enthalpy transported by dikes is primarily used for increasing the sensible heat of the cold surrounding crust with little energy contributing to latent heat of melting the crust (maximum crustal melting efficiency is 6%). In the lower crust, an extensive mush region develops for most of the conditions. Upper crustal crystalline mush is produced by continuous emplacement of magma with geologically reasonable flux and extension rates on timescales of 106 yr. Addition of tectonic effects and non-linear melt fraction relationships demonstrates that the magma flux required to sustain partially molten regions in the upper crust is within the range of estimates of magmatic flux in many rifting regions (∼10−4 to 10−3 km3/yr) and at least an order of magnitude lower than previous modeling estimates. Our results demonstrate the importance of tectonics in augmenting melt production, composition, and crustal evolution in active magmatic systems.

Development, mobilisation and eruption of a large crystal-rich rhyolite: The Ongatiti ignimbrite, New Zealand

The Ongatiti ignimbrite (>~500km3 DRE) was erupted at 1.21±0.04Ma from the Mangakino volcanic centre (Taupo Volcanic Zone, New Zealand). The ignimbrite is crystal rich (20–30%), of rhyodacite to low-silica rhyolite composition and lacks any consistent compositional zonation. Pumice whole-rock and glass compositions and crystal rim chemistries imply that the final erupted magma body was, to a first order, homogeneous, with the only variations reflecting crystal:glass proportions in analysed clasts. Crystals from pumices can be divided into two populations based on textural and chemical signatures: those that are inferred to have grown within the final erupted magma body (82% of plagioclase, 88% of orthopyroxene, 17% of amphibole), and those that originated in a chemically heterogeneous mush zone (18% of plagioclase, 12% of orthopyroxene, 83% of amphibole). Crystal-rich microcrystalline clasts, and clots within pumices, provide direct samples of parts of this heterogeneous source region. Amphibole model temperatures and pressures, coupled with in-situ trace element concentrations suggest that the mush region extended to ~15km depth, near the base of the quartzofeldspathic crust and was rich in amphibole. Amphibole plus subordinate plagioclase and orthopyroxene, as well as antecrystic zircon were extracted from the crystal mush and ascended to a final storage region. Model temperatures and pressures from amphibole rims and Fe–Ti oxide model temperatures imply that the final erupted magma body was stored between 770 and 840°C at 4–6km depths. Homogenisation of the magma body occurred through convective stirring accompanying gradually rising temperatures induced by less-evolved magma(s) emplaced at deeper levels. Plagioclase records a steady core-to-rim increase in An content, implying that a gradual heating and/or increase in H2O in the final erupted magma body occurred over some significant period prior to the eruption. No signals of a rapid defrosting or rejuvenation event that could be considered as an eruption trigger are recorded by the crystal phases. The Ongatiti ignimbrite has features both common to, and distinct from crystal rich ‘monotonous intermediates’ and crystal-poor compositionally zoned rhyolites. As such, the Ongatiti ignimbrite demonstrates that ‘monotonous rhyolites’ can also be developed on a large scale.

Upper crustal structure of Newberry Volcano from P‐wave tomography and finite difference waveform modeling

Seismic tomography combined with waveform modeling constrains the dimensions and melt content of a magma body in the upper crust at Newberry Volcano. We obtain a P‐wave tomographic image by combining travel‐time data collected in 2008 on a line of densely spaced seismometers with active‐source data collected in the 1980s. The tomographic analysis resolves a high‐velocity intrusive ring complex surrounding a low‐velocity caldera‐fill zone at depths above 3 km and a broader high‐velocity intrusive complex surrounding a central low‐velocity anomaly at greater depths (3–6 km). This second, upper‐crustal low‐velocity anomaly is poorly resolved and resolution tests indicate that an unrealistically large, low‐velocity body representing ∼60 km3of melt could be consistent with the available travel times. The 2008 data exhibit low amplitude first arrivals and an anomalous secondary P wave phase originating beneath the caldera. Two‐dimensional finite difference waveform modeling through the tomographic velocity model does not reproduce these observations. To reproduce these phases, we predict waveforms for models that include synthetic low‐velocity bodies and test possible magma chamber geometries and properties. Three classes of models produce a transmittedP‐phase consistent with the travel time and amplitude of the observed secondary phase and also match the observed lower amplitude first arrivals. These models represent a graded mush region, a crystal‐suspension region, and a melt sill above a thin mush region. The three possible magma chamber models comprise a much narrower range of melt volumes (1.6–8.0 km3) than could be constrained by travel‐time tomography alone.

In situ investigation of spinodal decomposition in hypermonotectic Al–Bi and Al–Bi–Zn alloys

Spinodal decomposition of hypermonotectic Al–6 wt.%Bi, Al–8 wt.%Bi and Al–6 wt.%Bi–8 wt.%Zn alloys has been investigated using synchrotron radiography. In the case of the 6 and 8 wt.%Bi binary alloys undercoolings of 70 and 110 K, respectively, were required to initiate the L→L1+L2 reaction, which appeared to occur very close to the monotectic reaction temperature. The nucleated L2 droplets were set in collective size-dependent motion by forces coupled to external fields (gravity and imposed temperature gradient) as well as forces arising due to internal fluctuations of the system. With experimental conditions similar to those realized during strip casting of the same materials, it was found that the size-dependant droplet velocity field combined with Stokes drag at the L1–L2 interfaces as well as attractive and repulsive diffusion-coupling between adjacent L2 droplets, yield complex meso- to microscale hydrodynamics. The hydrodynamics are the dominating mechanisms for L2 droplet coagulation, and are accordingly decisive for the final size distribution and geometrical dispersion of the soft Bi-rich component in the cast material. A different decomposition mode was observed in the Al–6 wt.%Bi–8 wt.%Zn ternary alloy, with the L2 droplets undergoing an immiscible–miscible–immiscible transition. In contrast to what was found for the binaries, L2 domains formed at relatively small undercoolings, and very little droplet motion was observed, as all L2 domains nucleated and remained on the crucible walls until they encroached on the monotectic front. At small distances from the monotectic front a Zn-rich solute boundary layer preceding the α-Al, caused the L2 domains to dissolve as Bi–Zn–Al regains complete miscibility upon reaching a critical Zn-concentration. In the shallow mush region behind the monotectic reaction, a high Zn solid solubility and a relatively fast diffusion of Zn in α-Al combine to cause a rapid diminishing Zn concentration in the mush liquid, restoring Bi-immiscibility and consequentially a secondary nucleation of L2 droplets in the mush.

An analysis of convection in a mushy layer with a deformable permeable interface

We study the dynamics of a mushy layer in directional solidification for the case of a thin near-eutectic mush with a deformable and permeable mush–liquid interface. We examine the onset of convection using linear stability analysis, and the weakly nonlinear growth of liquid inclusions that signal the onset of chimneys. This analysis is compared to past analyses in which the mush–liquid interface is replaced by a rigid impermeable lid. We find qualitative agreement between the two models, but the rigid-lid approximation gives substantially different quantitative behaviour.In linear theory, the rigid-lid approximation leads to an over-estimate of the critical Rayleigh number and wavenumber of the instability. The condition for the onset of oscillatory instability is also changed by a factor of about 5 in composition number C. In the weakly nonlinear theory, the location of the onset of liquid inclusions is near the undisturbed front for the free-boundary analysis, whereas it lies at the centre of the mushy layer when the rigid-lid approximation is used. For hexagonal patterns, the boundary between regions of parameter space in which up and down hexagons are stable, shifts as a result of coupling between the liquid and mush regions.

A study of the freezing of binary solutions saturating a porous matrix

The freezing of a binary solution saturating a porous matrix is investigated experimentally and numerically. An aqueous solution of sodium chloride constituted the binary solution. Spherical glass beads constituted the porous matrix. The freezing was initiated at one of the vertical walls of a rectangular cavity. The temperature distribution in the solid, liquid and mush regions were recorded. A mathematical model that considered conduction as the only mode of heat transfer was developed. The predictions of the model were compared with experimental data. In general, as the model were compared with experimental data. In general, as the model ignored natural convection, the predicted temperatures agreed well with the data during early times in the freezing when conduction was the dominant mode of heat transfer. But as freezing progressed the predictions departed from the data and this departure was larger when the initial superheat was high i.e., when the natural convective flow was vigorous and its influence strong on the freezing process.

HYBRID MODEL FOR SOLIDIFICATION AND CONVECTION

A hybrid model for continuum phase-change problems is presented. The hybrid model accounts for flow in regions of concentrated mush, dilute mush, and single-phase liquid. Scale analysis shows that, in dilute mush, the Blake-Kozeny-Carman relation may lead to inaccuracy in the continuum formulation for certain values of the Rayleigh and Darcy numbers. The hybrid model uses arctangent switching functions to switch on the Darcy flow and variable viscosity terms depending on the local value of the fraction solid. Two-dimensional example calculations suggest that the hybrid model more accurately accounts for transport in the dilute mush region.

Numerical modeling of solidification and convection in a viscous pure binary eutectic system

The solidification and convection of the pure binary eutectic silicate system diopside-anorthite (Di-An) is numerically modeled. A mass-weighted enthalpy of fusion is used to account for the second solid phase (An) which crystallizes at the solidus temperature. Variable under-relaxation is used to aid convergence of the momentum equations in our implementation of the SIMPLER algorithm used to solve the two-dimensional continuum conservation equations. Numerical experiments of the solidification of Di80 melt show that a large temperature drop occurs across the solid and mush regions which decreases convective vigor in the liquid. Interesting compositional segregation patterns are produced during the solidification of Di80.