Time scales of crystal mixing in magma mushes

Schleicher, J.; Bergantz, George W.; Breidenthal, Robert E.; Burgisser, Alain

doi:10.1002/2015gl067372

Cited by 50 publications

(56 citation statements)

References 70 publications

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“…8a, b, d) and stepped (Fig. 8c) profiles cannot be conclusively assessed, although it could be related to different mixing regimes within tur- bulent flow fields (e.g., Misiti et al, 2009;Bergantz et al, 2015;Schleicher et al, 2016). The prevalent occurrence of multi-banded and the anomalous profiles among PP crystals may suggest a higher frequency of proto-lp magma injection(s) associated with slightly different efficiency of the turbulent mixing shortly before eruption.…”

Section: A Working Model For Crystal Zoning and Mixing Dynamicsmentioning

confidence: 93%

“…The PP and EP record a complex history with compositional zoning that reflects crystallisation in a further distinct melt domain in addition to the high-Mg# proto-lp magma, and the low-Mg# proto-hp magma, namely a transient intermediate-Mg# magma recording the homogenisation, via turbulent mixing (e.g., Misiti et al, 2009;Schleicher et al, 2016) and crystallisation, of the proto-lp magma within the proto-hp magma.…”

Section: A Working Model For Crystal Zoning and Mixing Dynamicsmentioning

confidence: 99%

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Rapid mixing and short storage timescale in the magma dynamics of a steady-state volcano

Petrone

Braschi

Francalanci

et al. 2018

Earth and Planetary Science Letters

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Steady-state volcanic activity implies equilibrium between the rate of magma replenishment and eruption of compositionally homogeneous magmas, lasting for tens to thousands of years in an open conduit system. The Present-day activity of Stromboli volcano (Aeolian Islands, Southern Italy) has long been recognised as typical of a steady-state volcano, with a shallow magmatic reservoir (highly porphyritic or hp-magma) continuously refilled by more mafic magma (with low phenocryst content or lp-magma) at a constant rate and accompanied by mixing, crystallisation and eruption. Our aim is to clarify the timescale and dynamics of the plumbing system at the establishment of the Present-day steady-state activity (<1.2 ka) to pinpoint the onset of the steady-state regime. We investigated the Post-Pizzo (PP) pyroclastic sequence (∼1.7-1.5 ka) and one of the Early Paroxysms (EP) of the Present-day activity, focusing on the clinopyroxene population. Whole rock and clinopyroxene compositional variation among the PP and EP magmas is consistent with the time progression of the Stromboli system towards more mafic and lower 87 Sr/ 86 Sr compositions, pointing to the chemical and isotopic signature of the Present-day activity. Clinopyroxenes from both PP and EP record a complex history with compositional zoning that reflects growth in three different melt domains: a high-Mg# proto-lp recharging magma, a low-Mg# proto-hp resident magma, and a transient intermediate-Mg# magma. These are the result of complex turbulent flow fields and mixing regimes produced by repeated injections of the proto-lp magma in the shallow proto-hp magma reservoir. During the PP period the magmatic system was already able to regain the pre-input proto-hp composition, gradually changing toward a less evolved signature after the injection(s) of the more mafic proto-lp magma, owing to efficient (days to a few years) stirring and melt homogenisation (i.e., homogenisation time < residence time).Based upon Fe-Mg diffusion in clinopyroxene the total residence time during PP and EP periods, from the arrival of the mafic magma in the shallow system until the eruption, ranges from 1 to ∼50 years. Longer residence times (up to 150 years) have been recorded in the initial phase of the PP sequence, possibly testifying to the transition from a closed-to the open-conduit, steady-state regime of the Present-day activity. Some clinopyroxenes from the PP recorded the mafic triggering event of the feeding proto-lp magma occurring within few months to a few days before eruption. Remarkably, other clinopyroxene portions crystallised and captured the rapid timescales (a few days) of the on-going mixing and homogenisation process between the proto-lp and the proto-hp magmas leading to the eruption. The modelling of clinopyroxene zoning events at Stromboli provides evidence for growth and storage in three different melt domains, and sets robust constraints on their residence time from lp-magma recharge(s) to eruption, along with the timescales of melt homogenisation and triggerin...

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Section: A Working Model For Crystal Zoning and Mixing Dynamicsmentioning

confidence: 93%

Section: A Working Model For Crystal Zoning and Mixing Dynamicsmentioning

confidence: 99%

Rapid mixing and short storage timescale in the magma dynamics of a steady-state volcano

Petrone

Braschi

Francalanci

et al. 2018

Earth and Planetary Science Letters

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“…To develop and exemplify some relevant concepts of hydrogranular processes, we employ our previously published discrete element method (DEM) simulations [ Bergantz et al ., ; Schleicher et al ., ] (please see Text S1 in the supporting information for a full elaboration of the theory and numerical implementation and Movie S1 in the supporting information), the nomenclature is defined in Table . None of these previous works have described the stresses and corresponding microstructures as we do here.…”

Section: Numerical Experiments Of Hydrogranular Processesmentioning

confidence: 99%

“…Dimensionless time is defined as

t^{*} = ((), \frac{U_{0}}{H_{0}}) t

where U 0 is the velocity of the incoming crystal‐free magma and H 0 is the thickness of the mush. The fluid mechanics and mixing associated with this process have been described elsewhere [ Bergantz et al ., ; Schleicher et al ., ]; our focus here is on the hydrogranular microphysics. The input of new magma is held steady until t* = 1.65 at which time it is shut‐off and the fluidized magma collapses.…”

Section: Numerical Experiments Of Hydrogranular Processesmentioning

confidence: 99%

On the kinematics and dynamics of crystal‐rich systems

2017

Self Cite

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Partially molten rocks, often called a mush, are examples of a hydrogranular mixture where the dynamics are controlled by both fluid and crystal‐crystal interactions. An obstacle to progress in understanding high‐temperature hydrogranular systems has been the lack of adequate levels of description of microphysical processes. Here we rationalize the hydrogranular kinematic and dynamic states by applying the concept of particle (crystal) force chains. We exemplify this with discrete‐element computational fluid dynamic simulations of the intrusion of a basaltic melt into an olivine‐basalt mush, where crystal‐scale force chains, crystal transport, and melt mixing are resolved. To describe the microscale kinematics of the system, we introduce the coordination number and the fabric tensors of particle contacts and forces. We quantify the changing contact and force fabric anisotropy, coaxiality, and the connectedness of the mush, under dynamic conditions. To describe the dynamics, particle and fluid characteristic response times are derived. These are used to define local and bulk Stokes numbers, and viscous and inertia numbers, which quantify the multiphase coupling under crystal‐rich conditions. We employ the Sommerfeld number, which describes the importance of crystal‐melt lubrication, with a viscous number to illustrate the dynamic regimes of crystal‐rich magmas. We show that the notion of mechanical “lock up” is not uniquely identified with a particular crystal volume fraction and that distinct mechanical behaviors can emerge simultaneously within a crystal‐rich system. We also posit that this framework describes magmatic fabrics and processes which “unlock” a crystal mush prior to eruption or mixing.

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“…While variability in disaggregation efficiency may represent lateral variations in mush and cumulate petrology at depth, dynamic processes may have also been important. However, evaluating the controls on mush disaggregation efficiency is beyond the scope of this study, and may be approached better using numerical approaches (e.g., Bergantz et al 2015;Schleicher et al 2016). …”

Section: Mush Disaggregationmentioning

confidence: 99%

Continuous mush disaggregation during the long-lasting Laki fissure eruption, Iceland

Neave

Buisman

Maclennan

2017

American Mineralogist

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Plagioclase textures were investigated in the products of the voluminous 1783-1784 CE Laki eruption from the Eastern Volcanic Zone (EVZ) of Iceland to establish whether mush disaggregation occurred solely at the onset of the eight-month eruption or throughout its whole duration. Phase proportions and plagioclase size distributions were determined using standard optical and manual techniques as well as automated approaches based on Quantitative Evaluation of Minerals by SCANing electron microscopy (QEMSCAN). Based on optical microscopy and the explicit combination of textural and compositional information in QEMSCAN images, plagioclase crystals were divided into two populations: small (<0.5 mm long), high-aspect ratio (length/width >4) microcrysts with low-anorthite (0.5 mm long), low-aspect ratio (length/width = 2-3) macrocrysts with high-anorthite (An 84 -An 92 ) cores. Small microcrysts grew from their carrier liquid during the final phase of pre-eruptive crystallization while large macrocrysts, which are out of geochemical equilibrium with their carrier liquids, were entrained from crystal mushes. Changes in phase proportions and plagioclase size distributions between eruptive episodes demonstrate that macrocryst entrainment efficiency varied substantially during the eruption; material erupted in later episodes contain proportionally more mush-derived material. Using stereologically corrected plagioclase size distributions, we estimate that the pre-eruptive residence times of microcrysts in the Laki carrier liquid were probably of the order of 2-20 days. Because microcryst crystallization was concurrent with macrocryst rim growth, these day-to-week residence times also indicate that macrocryst entrainment occurred on much shorter timescales than the eruption's eight-month duration. In line with constraints from independent geochronometers, macrocryst entrainment and mush disaggregation thus appears to have continued throughout the eruption. Magmas were assembled on an episode by episode basis, and the volume of eruptible magma in the plumbing system at any given time was probably closer to 1-2 km 3 than the final erupted volume of 15.1 km 3 .

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Time scales of crystal mixing in magma mushes

Cited by 50 publications

References 70 publications

Rapid mixing and short storage timescale in the magma dynamics of a steady-state volcano

Rapid mixing and short storage timescale in the magma dynamics of a steady-state volcano

On the kinematics and dynamics of crystal‐rich systems

Continuous mush disaggregation during the long-lasting Laki fissure eruption, Iceland

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