scholarly journals Compositional boundary layers trigger liquid unmixing in a basaltic crystal mush

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Victoria C. Honour ◽  
Marian B. Holness ◽  
Bernard Charlier ◽  
Sandra C. Piazolo ◽  
Olivier Namur ◽  
...  
Keyword(s):  
Boundary Layers ◽  
Liquid Immiscibility ◽  
Atom Probe ◽  
Immiscible Liquid ◽  
Ore Deposits ◽  
Crystal Mush ◽  
Compositional Zoning ◽  
Resolution Imaging ◽  
River Plain ◽  
Crystal Interfaces

Abstract The separation of immiscible liquids has significant implications for magma evolution and the formation of magmatic ore deposits. We combine high-resolution imaging and electron probe microanalysis with the first use of atom probe tomography on tholeiitic basaltic glass from Hawaii, the Snake River Plain, and Iceland, to investigate the onset of unmixing of basaltic liquids into Fe-rich and Si-rich conjugates. We examine the relationships between unmixing and crystal growth, and the evolution of a nanoemulsion in a crystal mush. We identify the previously unrecognised role played by compositional boundary layers in promoting unmixing around growing crystals at melt-crystal interfaces. Our findings have important implications for the formation of immiscible liquid in a crystal mush, the interpretations of compositional zoning in crystals, and the role of liquid immiscibility in controlling magma physical properties.

scholarly journals The Creation and Evolution of Crystal Mush in the Upper Zone of the Rustenburg Layered Suite, Bushveld Complex, South Africa

2019 ◽  
Vol 60 (8) ◽  
pp. 1523-1542 ◽  
Author(s):  
Z Vukmanovic ◽  
M B Holness ◽  
M J Stock ◽  
R J Roberts
Keyword(s):  
South Africa ◽  
Magma Chamber ◽  
Simple Shear ◽  
Bushveld Complex ◽  
Immiscible Liquid ◽  
Textural Analysis ◽  
Crystal Nucleation ◽  
Crystal Mush ◽  
Gravitational Loading ◽  
Crystal Accumulation

Abstract The Upper Zone of the Rustenburg Layered Suite of the Bushveld Complex contains the world’s largest Fe–Ti–V ± P deposit and formed from the last major injection of magma into the chamber. Quantitative textural analysis of Upper Zone rocks was undertaken to constrain the processes operating during mush formation and solidification, focussing on horizons with the greatest density contrast to isolate the effects of gravitational loading. We examined three magnetitite layers, together with their underlying and overlying anorthosites. The similarity of microstructures in anorthosites above and below the dense magnetitite layers suggests that the rocks were not affected by viscous compaction driven by gravitational loading. The magnetitite cumulate layers formed by crystal accumulation from a mobile crystal slurry dominated by the Fe-rich conjugate of an unmixed immiscible liquid. We suggest a new mechanism of crystal nucleation in deforming crystal-rich systems, driven by undercooling caused by cavitation as grains slide past each other during simple shear. We propose that the super-solidus deformation recorded in these rocks was caused by prolonged regional subsidence of the magma chamber at Upper Zone times.

scholarly journals Liquid immiscibility and problems of ore genesis (according to experimental data)

2019 ◽  
Vol 27 (5) ◽  
pp. 577-597
Author(s):  
Yu. B. Shapovalov ◽  
A. R. Kotelnikov ◽  
I. N. Suk ◽  
V. S. Korzhinskaya ◽  
Z. A. Kotelnikova
Keyword(s):  
Partition Coefficients ◽  
Liquid Immiscibility ◽  
Ore Deposits ◽  
Silicate Melt ◽  
Distribution Of Elements ◽  
Ore Minerals ◽  
Silicate Liquids ◽  
L1 And L2 ◽  
Salt Systems ◽  
Alkaline Fluid

The results of an experimental study of phase relations and distribution of elements in silicate melt–salt systems (carbonate, phosphate, fluoride, chloride) melt, silicate melt I–silicate melt II, and also in fluid – magmatic systems in the presence of alkali metal fluorides are presented. Salt extraction of a number of ore elements (Y, REE, Sr, Ba, Ti, Nb, Zr, Ta, W, Mo, Pb) was studied in liquid immiscibility processes in a wide temperature range of 800–1250°С and pressure of 1–5.5 kbar. It is shown that the partition coefficients are sufficient for the concentration of ore elements in the quantity necessary for the genesis of ore deposits. In the fluid-saturated melt of trachyrhyolite, the separation into two silicate liquids has been determined. The partition coefficients of a number of elements (Sr, La, Nb, Fe, Cr, Mo, K, Rb, Cs) between phases L1 and L2 has been obtained. The interaction processes of a heterophase fluid in the granite (quartz)–ore mineral–heterophase fluid (Li, Na, K-fluoride) system were studied at 650–850°C and P = 1 kbar. The formation of the phase of a highly alkaline fluid–saturated silicate melt – Ta and Nb concentrator is shown as a result of the reaction of the fluid with the rock and ore minerals.

Nb-rich baotite in carbonatites and fenites at Haast River, New Zealand

1996 ◽  
Vol 60 (400) ◽  
pp. 473-482 ◽  
Author(s):  
Alan F. Cooper
Keyword(s):  
New Zealand ◽  
Octahedral Site ◽  
Microprobe Analysis ◽  
Liquid Immiscibility ◽  
Dyke Swarm ◽  
Accessory Mineral ◽  
Compositional Zoning ◽  
Octahedral Sites ◽  
Octahedral Substitution

AbstractBaotite occurs as an accessory mineral in carbonatites, fenites, and carbothermal veins associated with a lamprophyre dyke swarm in the Haast River area of south Westland, New Zealand. Carbonatites are petrogenetically evolved, with assemblages dominated by ankerite, siderite and Ba-Sr-REE carbonates. Microprobe analysis indicates baotite compositions more Nb-rich than previously recorded, with compositions close to Ba4[Ti3(Nb,Fe)5]Si4O28Cl. Ti must be partially replaced in both crystallographically-independent octahedral sites. Compositional zoning, and stoichiometric considerations suggest that the dominant octahedral substitution is the same as that described in rutile, namely 3Ti4+ ⇌ 2Nb5+ + Fe2+. Contrary to previous suggestions, Fe in the octahedral site should, therefore, be dominated by Fe2+.The presence of baotite further documents the involvement of halogens in carbonatite magmas. In the New Zealand occurrences it is suggested that the chlorine originates from associated phonolitic magmas and is partitioned into carbonatite during liquid immiscibility.

scholarly journals Silicate Liquid Immiscibility within the Crystal Mush: Late-stage Magmatic Microstructures in the Skaergaard Intrusion, East Greenland

2010 ◽  
Vol 52 (1) ◽  
pp. 175-222 ◽  
Author(s):  
M. B. Holness ◽  
G. Stripp ◽  
M. C. S. Humphreys ◽  
I. V. Veksler ◽  
T. F. D. Nielsen ◽  
...  
Keyword(s):  
Late Stage ◽  
Liquid Immiscibility ◽  
Silicate Liquid ◽  
Crystal Mush ◽  
Skaergaard Intrusion ◽  
East Greenland ◽  
Silicate Liquid Immiscibility

Noble metal nanonugget insolubility in geological sulfide liquids

Geology ◽  
2020 ◽  
Vol 48 (9) ◽  
pp. 939-943 ◽  
Author(s):  
Michael Anenburg ◽  
John A. Mavrogenes
Keyword(s):  
Noble Metal ◽  
Partition Coefficients ◽  
Noble Metals ◽  
Analytical Techniques ◽  
Liquid Immiscibility ◽  
Experimental Methods ◽  
Ore Deposits ◽  
Nanometer Scale ◽  
Clear Liquid ◽  
Planetary Differentiation

Abstract Noble metals (NMs) in Earth’s magmatic systems are thought to be controlled entirely by their strong partitioning to sulfide liquids. This chemical equilibrium is at the root of various models, ranging from NM deposit formation to planetary differentiation. Noble metals commonly occur as sub-micrometer phases known as nanonuggets. However, the assumptions that nanometer-scale thermodynamic equilibrium partitioning is attained and that NM nanonuggets are soluble in sulfide liquids have never been validated. Using novel experimental methods and analytical techniques we show nanometer-scale NM ± Bi phases attached to exterior surfaces of sulfide liquids. Larger phases (≤1 µm) show clear liquid immiscibility textures, in which Fe, Cu, and Ni partition into sulfide liquids whereas NMs partition into bismuthide liquids. Noble metal compositions of sulfides and their associated NM phases vary between adjacent droplets, indicating NM disequilibrium in the system as a whole. We interpret most nanometer-scale NMs contained within sulfides to be insoluble as well, suggesting that previously reported sulfide–silicate partition coefficients are overestimated. Consequently, sulfide liquids likely play a secondary role in the formation of some NM ore deposits.

Layered rhyolite bands in a thick North Mountain Basalt flow: the products of silicate liquid immiscibility?

1992 ◽  
Vol 56 (384) ◽  
pp. 309-318 ◽  
Author(s):  
John D. Greenough ◽  
J. Dostal
Keyword(s):  
Liquid Immiscibility ◽  
Immiscible Liquid ◽  
Chemical Compositions ◽  
Forming Process ◽  
Basalt Flow ◽  
Immiscible Liquids ◽  
Fine Grained ◽  
Mafic Intrusions ◽  
Bulk Chemical ◽  
Rich Liquid

AbstractThe upper 35 m of a thick (≤175 m) Early Jurassic North Mountain Basalt flow at KcKay Head contains 25 cm thick differentiated layers that are separated by 130 cm sections of basalt. The lower layers are mafic, pegmatitic, and contain thin (2 cm), fine-grained 'rhyolite' bands. Evidence that the rhyolite represents a Si-rich immiscible liquid includes: (1) textures such as fiine-grained globules of Ferich pyroxene (once Fe-rich liquid) bordering pegmatite feldspar grains; (2) structureless, microcrystalline, interstitial, polygonal patches of Si-rich minerals and similar areas of Fe-rich stilpnomelane surrounding skeletal Fe-Ti oxide grains, with bulk chemical compositions (to a first approximation), relative proportions and total modat percentages suggesting they were once Si-rich and Fe-rich glasses respectively; (3) basalt and pegmatite compositions (particularly their Fe, and Ti contents) similar to rocks known to contain immiscible liquids; (4) rhyolite major element compositions generally consistent with formation from an immiscible Si-rich liquid; (5) mineral compositions and temperature of pegmatite formation compatible with immiscibility; (6) the inability of mass balance calculations (crystal fractionation) to explain rhyolite formation unless mesostasis stilpnomelane (representing the Fe-rich liquid) is included in the caculations. If, as we suggest, these rocks are the result of immiscibility, they shed light on the incipient formation of granophyres in mafic intrusions and support liquid immiscibility as an important rock-forming process.

scholarly journals Immiscible silicate liquids: K and Fe distribution as a test for chemical equilibrium and insight into the kinetics of magma unmixing

2021 ◽  
Vol 176 (6) ◽  
Author(s):  
Alexander Borisov ◽  
Ilya V. Veksler
Keyword(s):  
Regression Analysis ◽  
Chemical Equilibrium ◽  
Volcanic Rocks ◽  
Experimental Studies ◽  
Liquid Immiscibility ◽  
Immiscible Liquid ◽  
Liquid Droplets ◽  
Liquid Distribution ◽  
Immiscible Liquids ◽  
Element Partitioning

AbstractSilicate liquid immiscibility leading to formation of mixtures of distinct iron-rich and silica-rich liquids is common in basaltic and andesitic magmas at advanced stages of magma evolution. Experimental modeling of the immiscibility has been hampered by kinetic problems and attainment of chemical equilibrium between immiscible liquids in some experimental studies has been questioned. On the basis of symmetric regular solutions model and regression analysis of experimental data on compositions of immiscible liquid pairs, we show that liquid–liquid distribution of network-modifying elements K and Fe is linked to the distribution of network-forming oxides SiO2, Al2O3 and P2O5 by equation: $$\log K_{{\text{d}}}^{{\text{K/Fe}}} = \, 3.796\Delta X_{{{\text{SiO}}_{2} }}^{{{\text{sf}}}} + \, 4.85\Delta X_{{{\text{Al}}_{2} {\text{O}}_{3} }}^{{{\text{sf}}}} + \, 7.235\Delta X_{{{\text{P}}_{2} {\text{O}}_{5} }}^{{{\text{sf}}}} - \, 0.108,$$ log K d K/Fe = 3.796 Δ X SiO 2 sf + 4.85 Δ X Al 2 O 3 sf + 7.235 Δ X P 2 O 5 sf - 0.108 , where $$K_{{\text{d}}}^{{\text{K/Fe}}}$$ K d K/Fe is a ratio of K and Fe mole fractions in the silica-rich (s) and Fe-rich (f) immiscible liquids: $$K_{d}^{{\text{K/Fe}}} = \, \left( {X_{{\text{K}}}^{s} /X_{{\text{K}}}^{f} } \right)/ \, \left( {X_{{{\text{Fe}}}}^{s} /X_{{{\text{Fe}}}}^{f} } \right)$$ K d K/Fe = X K s / X K f / X Fe s / X Fe f and $$\Delta X_{{\text{i}}}^{sf}$$ Δ X i sf is a difference in mole fractions of a network-forming oxide i between the liquids (s) and (f): $$\Delta X_{i}^{sf} = X_{i}^{s} - X_{i}^{f}$$ Δ X i sf = X i s - X i f . We use the equation for testing chemical equilibrium in experiments not included in the regression analysis and compositions of natural immiscible melts found as glasses in volcanic rocks. Departures from equilibrium that the test revealed in crystal-rich multiphase experimental products and in natural volcanic rocks imply kinetic competition between liquid–liquid and crystal–liquid element partitioning. Immiscible liquid droplets in volcanic rocks appear to evolve along a metastable trend due to rapid crystallization. Immiscible liquids may be closer to chemical equilibrium in large intrusions where cooling rates are lower and crystals may be spatially separated from liquids.

Solubility of Monazite-Cheralite and Xenotime in Granitic Melts, and Experimental Evidence of Liquid-Liquid Immiscibility in Concentrating REE

2021 ◽  
Author(s):  
Marieke Van Lichtervelde ◽  
Philippe Goncalves ◽  
Aurélien Eglinger ◽  
Aurélia Colin ◽  
Jean-Marc Montel ◽  
...  
Keyword(s):  
Experimental Data ◽  
Experimental Evidence ◽  
Liquid Immiscibility ◽  
Immiscible Liquid ◽  
Solubility Data ◽  
Positive Correlation ◽  
Natural Systems ◽  
Magmatic Rocks ◽  
Peraluminous Granites ◽  
Water Saturated

Abstract We provide new experimental data of monazite, xenotime and U-Th-bearing cheralite solubility in slightly peralkaline to peraluminous granitic melts using dissolution and reverse (i.e., recrystallisation after dissolution) experiments in water-saturated and flux-bearing (P+F+Li) granitic melts, at 800 °C and 200 MPa. Although a positive correlation between REE solubility and melt peralkalinity is confirmed, monazite solubilities reported here are much lower than the values previously published. We suggest that the presence of elevated phosphorus concentrations in our melts depresses monazite solubility, principally because phosphorus complexes with Al and alkali which normally depolymerise the melt through the formation of non-bridging oxygens. The new solubility data provide an explanation for the very low REE concentrations generally encountered in phosphorus-bearing peraluminous granites and pegmatites. This accounts for the compatibility of REE in peraluminous systems, as the early crystallisation of REE-bearing minerals (mainly monazite and zircon) leads to progressive REE depletion during liquid differentiation. In addition, dissolution and reverse experiments of U-Th-bearing cheralite-monazite display liquid-liquid immiscibility processes in our slightly peralkaline glass. The immiscible liquid forms droplets up to 10 µm in diameter and hosts in average 35 wt.% P2O5, 25-30 wt.% F, 22 wt.% Al2O3, 4 wt.% CaO, 5 wt.% Na2O, 2 wt.% La2O3, and 12 wt.% ThO2+UO2. We believe that the droplets formed during the runs and may have coalesced to larger droplets during quenching. We suggest that liquid-liquid immiscibility is a possible mechanism of REE concentration in highly-fluxed melts and should be considered in natural systems where REE are extremely concentrated (up to thousands of µg/g) in magmatic rocks.

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