The Role of Viscous Particle Segregation in Forming Chromite Layers from Slumped Crystal Slurries: Insights from Analogue Experiments

Forien, Mélanie; Tremblay, Jonathan; Barnes, Sarah‐Jane; Burgisser, Alain; Pagé, Philippe

doi:10.1093/petrology/egv060

Cited by 43 publications

(17 citation statements)

References 93 publications

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“…Magmas expelled into the Marginal Zone surrounding the RLS, referred to as the B1 magmas37, resemble model mixtures of 75% liquid and 25% solids, whereas the weighted average composition of the UG2 pyroxenites from our results matches that of a model mixture of 25% liquid and 75% solids (Figs 7 and 8). Eales et al 38 performed a modelling exercise using alphaMELTS and similar choices of magma and contaminant, envisioning formation of mushes, that resulted from crustal contamination of komatiite in the conduit, which later settled at the base of a magma chamber; analogue models have demonstrated that layering within individual units could be developed due to slurry flow along the base of a magma body45. We concur with some aspects of these recent proposals but propose that the mixture of melt and crystals produced by wholesale crustal assimilation in the deeper magmatic conduits was then, as suggested by Mitchell and Scoon78, emplaced through narrow sills rather than at the base of a large open magma chamber and acquired its layering by slurry flow during transport.…”

Section: Discussionmentioning

confidence: 99%

“…We call attention to the flame structures illustrated in Fig. 3 and note that larger-scale gravitational instability of this nature, combined with shearing along the base of a sill undergoing slurry flow45, could generate sheath folds that would, in cross-section, resemble the complex lamination and interdigitation of chromitite and anorthosite for which the UG1 Unit is renowned (Fig. 5).…”

Section: Discussionmentioning

confidence: 99%

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U–Pb geochronology documents out-of-sequence emplacement of ultramafic layers in the Bushveld Igneous Complex of South Africa

Mungall

Kamo

McQuade³

2016

Nat Commun

138

124

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Layered intrusions represent part of the plumbing systems that deliver vast quantities of magma through the Earth's crust during the formation of large igneous provinces, which disrupt global ecosystems and host most of the Earth's endowment of Pt, Ni and Cr deposits. The Rustenburg Layered Suite of the enormous Bushveld Igneous Complex of South Africa has been presumed to have formed by deposition of crystals at the floor of a subterranean sea of magma several km deep and hundreds of km wide called a magma chamber. Here we show, using U–Pb isotopic dating of zircon and baddeleyite, that individual chromitite layers of the Rustenburg Layered Suite formed within a stack of discrete sheet-like intrusions emplaced and solidified as separate bodies beneath older layers. Our U–Pb ages and modelling necessitate reassessment of the genesis of layered intrusions and their ore deposits, and challenge even the venerable concept of the magma chamber itself.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

U–Pb geochronology documents out-of-sequence emplacement of ultramafic layers in the Bushveld Igneous Complex of South Africa

Mungall

Kamo

McQuade³

2016

Nat Commun

138

124

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“…See the supporting information for methods and values used to plot data fields. Calculation details in supporting information [Androvandi et al, 2011;Caricchi et al, 2008Caricchi et al, , 2014Castruccio et al, 2010;Champallier et al, 2008;Cimarelli et al, 2011;Coetzee and Els, 2009;Dufek and Bergantz, 2005;Forien et al, 2011Forien et al, , 2015Girard and Stix, 2009;Grossmann and Lohse, 2001;Jellinek and DePaolo, 2003;Le Mével et al, 2016;Okumura et al, 2016Okumura et al, , 2015Parks et al, 2012;Petrelli et al, 2016;Pistone et al, 2012Pistone et al, , 2015Rutherford, 2008;Walker et al, 1999].…”

Section: 1002/2017jb014218mentioning

confidence: 99%

On the kinematics and dynamics of crystal‐rich systems

2017

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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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“…based on density and shape) during lateral flow, with flow scales on the order of tens to hundreds of metres. Experimental studies by Forien et al (2015) demonstrated the practical application of such a process.…”

Section: Constraints On Mineralization Modelsmentioning

confidence: 95%

Igneous Rock Associations 23. The Bushveld Complex, South Africa: New Insights and Paradigms

Prevec

2019

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The Role of Viscous Particle Segregation in Forming Chromite Layers from Slumped Crystal Slurries: Insights from Analogue Experiments

Cited by 43 publications

References 93 publications

U–Pb geochronology documents out-of-sequence emplacement of ultramafic layers in the Bushveld Igneous Complex of South Africa

U–Pb geochronology documents out-of-sequence emplacement of ultramafic layers in the Bushveld Igneous Complex of South Africa

On the kinematics and dynamics of crystal‐rich systems

Igneous Rock Associations 23. The Bushveld Complex, South Africa: New Insights and Paradigms

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