Chemical diffusion of major components in granitic liquids: Implications for the rates of homogenization of crustal melts

Acosta-Vigil, Antonio; London, David; Morgan, Gareth

doi:10.1016/j.lithos.2012.06.017

Cited by 27 publications

(12 citation statements)

References 70 publications

(156 reference statements)

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“…151 One assessment comes from experiments in which the chemical diffusivity of alkali ions has been measured. Acosta-Vigil et al (2012a) have observed that the diffusivity of Na and K through melts at high temperature (800C, 200 MPa) is essentially instantaneous in response to gradients in their own compositions or to gradients imposed by other cations with which the alkalis interact. Morgan and London (2005) found that the diffusion of Na and K through undercooled granitic melt or glass was instantaneous (i.e., equilibrated with aqueous solution and crystals at least on the scale of minutes) down to 515C at 200 MPa.…”

Section: Numerical Modelingmentioning

confidence: 99%

A Rayleigh model of cesium fractionation in granite-pegmatite systems

London

2022

American Mineralogist

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The K/Cs ratios of K-feldspars from granitic pegmatites are compared to models derived from the Rayleigh equation. The K/Cs and K/Rb ratios of K-feldspars and micas exhibit decreasing values when plotted against their Cs or Rb contents across cogenetic suites of granites and pegmatites, and from margin to core of individual bodies. The trends in elemental ratios conform to Rayleigh fractionation for the crystallization of feldspars and micas from a silicate melt. Within two individual pegmatite bodies, the K/Cs ratio of K-feldspar initially falls more rapidly than the Rayleigh model predicts. That might reflect a local increase in the concentration of Cs relative to K due to the pile-up of incompatible elements in a boundary layer of melt adjacent to the crystal growth front. The addition of an aqueous solution to the Rayleigh model (i.e., the simultaneous crystallization of K-feldspars from melt and from aqueous solution) predicts high and increasing K/Cs ratios of K-feldspars that are not observed in natural rock suites, except when K-feldspars crystallize in miarolitic cavities or when primary K-feldspar recrystallizes to microcline perthite in an open hydrothermal system. In those cases, the Cs content of K-feldspars falls to nil because of the high solubility of Cs in aqueous solution and low compatibility of Cs in K-feldspar. Otherwise, the observed patterns of K/Rb or K/Cs in K-This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America.The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

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Section: Numerical Modelingmentioning

confidence: 99%

A Rayleigh model of cesium fractionation in granite-pegmatite systems

London

2022

American Mineralogist

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“…Whether this melt is homogeneous is another matter. Homogeneity will be determined by the rates of dissolution of minerals in contact with the melt, the rates of diffusive transport of their components through the melt, and whether residual minerals recrystallize (Acosta-Vigil et al, 2012b). These issues are fundamental for fl uid-present melting at high degrees of reaction overstepping.…”

Section: Melting the Crustmentioning

confidence: 99%

Granite: From genesis to emplacement

Brown

2013

Geological Society of America Bulletin

522

219

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At low temperatures (<750 °C at moderate to high crustal pressures), the production of suffi cient melt to reach the melt connectivity transition (~7 vol%), enabling melt drainage, requires an infl ux of aqueous fl uid along structurally controlled pathways or recycling of fl uid via migration of melt and exsolution during crystallization. At higher temperatures, melting occurs by fl uid-absent reactions, particularly hydrate-breakdown reactions involving micas and/or amphibole in the presence of quartz and feldspar. These reactions produce 20-70 vol%, melt according to protolith composition, at temperatures up to 1000 °C. Calculated phase diagrams for pelite are used to illustrate the mineralogical controls on melt production and the consequences of different clockwise pressure-temperature (P-T) paths on melt composition. Preservation of peritectic minerals in residual granulites requires that most of the melt produced was extracted, implying a fl ux of melt through the suprasolidus crust, although some may be trapped during transport, as recorded by composite migmatitegranite complexes. Peritectic minerals may be entrained during melt drainage, consistent with observations from leucosomes in migmatites, and dissolution of these minerals during ascent may be important in the evolution of some crustal magmas. Since siliceous melt wets grains, suprasolidus crust may become porous at only a few volume % melt, as evidenced by microstructures in residual migmatites in which quartz or feldspar pseudomorphs form after melt fi lms and pockets. With increasing melt volume and decreasing effective pressure, assuming the residue is able to deform and compact, the source becomes permeable at the melt connectivity transition. At this threshold, a change from distributed shear-enhanced compaction to localized dilatant shear failure enables melt segregation. The result is a highly permeable vein network that allows transfer of melt to ascent conduits at the initiation of a melt-extraction event. Melt is drained from the anatectic zone via several extraction events, consistent with evidence for incremental construction of plutons from multiple batches of magma. Buoyancy-driven magma ascent occurs via dikes in fractures or via high-permeability zones controlled by tectonic fabrics; the way in which these features relate to compaction and the generation of porosity waves is discussed. Emplacement of laccoliths (horizontal tabular intrusions) and wedge-shaped plutons occurs around the ductile-to-brittle transition zone, whereas steep tabular sheeted and blobby plutons represent back freezing of melt in the ascent conduit or lateral expansion localized by instabilities in the magma-wallrock system, respectively.

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“…4f-h) are suggestive of a small amount of melt spreading along grain boundaries and at triple junctions forming an interconnected network (Beere, 1975;von Bargen & Waff, 1986), rather than in larger segregations such as outcrop-scale leucosome patches or dykes. The presence of a meltfilled grain boundary network in modified rock types facilitated enhanced element mobility by allowing efficient diffusion of major and REEs and volatiles through the melt (Bickle & McKenzie, 1987;Watson, 1991;Acosta-Vigil et al, 2012). This enabled the large-scale scavenging of REE by clinozoisite for example, and homogenization of mineral chemistry at an outcrop scale throughout all modified rocks.…”

Section: Former Presence Of Melt In Hydrated Rocksmentioning

confidence: 99%

“…In contrast to water‐fluxed melting, dehydration melting is associated with: slower reaction and chemical diffusion rates in the melt (Behrens & Nowak, ; Acosta‐Vigil et al ., , ), reactions which increase bulk volume (Clemens & Droop, ), the formation of anhydrous peritectic minerals (e.g. Naney, ; Johnston & Wyllie, ; Gardien et al ., ; Alonso‐Perez et al ., ), a product melt with high viscosity (Holtz et al ., ; Richet et al ., ; Schulze et al ., ) and product melts that generally tend towards granitic compositions, that is, higher K 2 O and lower Al saturation (Conrad et al ., ; Patiño Douce, ; Gardien et al ., ; Acosta‐Vigil et al ., ).…”

Section: Introductionmentioning

confidence: 99%

Local partial melting of the lower crust triggered by hydration through melt–rock interaction: an example from Fiordland, New Zealand

Stuart

Daczko

Piazolo

2016

Journal Metamorphic Geology

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We investigate a low‐strain outcrop of the lower crust, the Pembroke Granulite, exposed in northern Fiordland, New Zealand, which exhibits localized partial melting. Migmatite and associated tschermakite–clinozoisite (TC) gneiss form irregular, elongate bodies that cut a two‐pyroxene–pargasite (PP) gneiss. Gradational boundaries between rock types, and the progressive nature of changes in mineral assemblage, microstructure and chemistry are consistent with the TC gneiss and migmatite representing modified versions of the PP gneiss. Modification is essentially isochemical, where partial modification involves hydration of the assemblage and mineral chemistry changes, and complete modification involves additional recrystallization and in situ partial melt production. Microstructures of quartz and plagioclase, including small dihedral angles, string of beads textures and films surrounding amphibole and garnet grains are consistent with the former presence of melt in modified rock types. The documented rock modification is attributed to melt–rock interaction occurring during porous melt flow of a dominantly externally derived, hydrous silicate melt. Microstructures indicate melt flow occurred along grain boundaries and field relationships show it was focused into channels tens of metres wide, with preference for following the pre‐existing foliation. Melt–rock interaction at the grain scale resulted in hydration and modification of the host PP gneiss, which resulted in localized partial melting. These relationships indicate prograde hydration during localized melt–rock interaction drove migmatization of the lower crust.

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Chemical diffusion of major components in granitic liquids: Implications for the rates of homogenization of crustal melts

Cited by 27 publications

References 70 publications

A Rayleigh model of cesium fractionation in granite-pegmatite systems

A Rayleigh model of cesium fractionation in granite-pegmatite systems

Granite: From genesis to emplacement

Local partial melting of the lower crust triggered by hydration through melt–rock interaction: an example from Fiordland, New Zealand

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