Diffusive fractionation of trace elements in basaltic melt

Holycross, Megan; Watson, E. Bruce

doi:10.1007/s00410-016-1289-x

Cited by 22 publications

(10 citation statements)

References 37 publications

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“…However, the currently available dataset still lacks diffusivity data for many elements, especially for natural melt compositions. For example, the first data of rare earth elements (REE) diffusion coefficients in basalt were just recently provided by Holycross and Watson (2016). Effects of dissolved water on diffusion in magmas are poorly constrained, and investigations on hydrous magmas are often focused on silicic compositions (Watson, 1979;Watson, 1981;Watson, 1983, 1984;Rapp and Watson, 1986;Baker, 1991;Watson, 1994;Baker et al, 2002;Mungall et al, 1999).…”

Section: Introductionmentioning

confidence: 99%

Diffusive exchange of trace elements between alkaline melts: Implications for element fractionation and timescale estimations during magma mixing

González-García

Petrelli

Behrens

et al. 2018

Geochimica et Cosmochimica Acta

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The diffusive exchange of 30 trace elements (Cs, Nb) during the interaction of natural mafic and silicic alkaline melts was experimentally studied at conditions relevant to shallow magmatic systems. In detail, a set of 12 diffusion couple experiments have been performed between natural shoshonitic and rhyolitic melts from the Vulcano Island (Aeolian archipelago, Italy) at a temperature of 1200 °C, pressures from 50 to 500 MPa, and water contents ranging from nominally dry to ca. 2 wt. %. Concentration-distance profiles, measured by Laser Ablation ICP-MS, highlight different behaviours, and trace elements were divided into two groups: (1) elements with normal diffusion profiles (13 elements, mainly low field strength and transition elements), and (2) elements showing uphill diffusion (17 elements including Y, Zr, Nb, Pb and rare earth elements, except Eu). For the elements showing normal diffusion profiles, chemical diffusion coefficients were estimated using a concentrationdependent evaluation method, and values are given at four intermediate compositions (SiO2 equal to 58, 62, 66 and 70 wt. %, respectively). A general coupling of diffusion coefficients to silica diffusivity is observed, and variations in systematics are observed between mafic and silicic compositions. Results show that water plays a decisive role on diffusive rates in the studied conditions, producing an enhancement between 0.4 and 0.7 log units per 1 wt.% of added H2O. Particularly notable is the behaviour of the trivalent-only REEs (La to Nd and Gd to Lu), with strong uphill diffusion minima, diminishing from light to heavy REEs. Modelling of REE profiles by a modified effective binary diffusion model indicates that activity gradients induced by the SiO2 concentration contrast are responsible for their development, inducing a transient partitioning of REEs towards the shoshonitic melt. These results indicate thatdiffusive fractionation of trace elements is possible during magma mixing events, especially in the more silicic melts, and that the presence of water in such events can lead to enhanced Watson. Furthermore, diffusion studies using natural rock compositions, that are potentially more relevant for geological applications, are scarce in the literature (e.g. Baker, 1990; Lundstrom, 2006).Recently, González-García et al. (2017) reported results on the diffusive exchange of major elements in shoshonite-rhyolite couples. Here we use the same set of experiments to investigate the trace element diffusion in natural silicate melt compositions at physical conditions relevant for subvolcanic magmatic systems. Our primary objectives are: (1) to investigate the diffusive behaviours of trace elements in the presence of strong compositional gradients, linking the results to major element diffusivity; and (2) to assess the influence of water on trace element diffusivities. The implications of this study for element fractionation during mixing of magmas and timescale estimations of related geological processes are discussed.

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Section: Introductionmentioning

confidence: 99%

Diffusive exchange of trace elements between alkaline melts: Implications for element fractionation and timescale estimations during magma mixing

González-García

Petrelli

Behrens

et al. 2018

Geochimica et Cosmochimica Acta

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“…As water is added to silicate liquid, OH -molecules break bridging oxygen bonds, decreasing melt viscosity and increasing cation diffusivities (e.g., Watson, 1979Watson, , 1981Zhang et al, 2003 and many others). The rapid diffusion of Li in hydrous, highly silicic melts implies that any gradients in total Li in rhyolite magma systems will be quickly homogenised while other trace element concentration gradients may persist (Holycross and Watson, 2016a).…”

Section: Lithium Diffusion Coefficients In Wet Rhyolitic Meltmentioning

confidence: 99%

“…7 Li diffusion coefficients obtained from least-squares fits to measured LA-ICP-MS profiles were kept constant while the diffusivity of 6 Li was varied so that the output of the 7 Li/ 6 Li model profile best matched the 7 Li/ 6 Li SIMS profile, as evaluated by obtaining the smallest χ 2 parameter for each ratio profile (Holycross and Watson, 2016b).…”

Section: Lithium Isotope Fractionation In Wet Rhyolitic Meltmentioning

confidence: 99%

Diffusive fractionation of Li isotopes in wet, silicic melts

Holycross¹,

Watson²,

Richter³

et al. 2018

Geochem. Persp. Let.

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The discovery of large lithium isotopic gradients in geologic media has motivated recent work examining the kinetic fractionation of Li isotopes in silicate materials. Here, piston-cylinder experiments were used to determine Li diffusivities in rhyolitic melts containing ~6 wt. % H 2 O at 1 GPa pressure and 790-875 ºC. Lithium transport in wet rhyolitic melt is almost an order of magnitude faster than diffusion in dry obsidian glass over the investigated temperature range. Li isotope profiles collected by ion microprobe show that the kinetic exponent β = 0.228 for diffusive fractionation of Li isotopes in wet rhyolite. This value is very close to β = 0.215 determined by Richter et al. (2003) for Li isotope diffusion in a dry basalt-rhyolite couple at 1350 °C. The similarity of the two values indicates little or no dependence of β Li in silicate melts on either temperature or melt composition. The new data confirm a very high potential for diffusive fractionation of 6 Li from 7 Li and can be confidently used to model deviations in δ 7 Li to determine the time-temperature histories of natural rhyolite samples.

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“…To be more specific, EPMA analyses of core-rim transect across the cpx grain revealed no major or minor element zonation (Fig. 4a; Table S9), especially for slow diffusing cations, Al 3+ and Ti 4+ , indicating steady state cpx growth without the development of a diffusive boundary layer (Holycross and Watson 2016;2018). Moreover, the random analyses of major element in glass also revealed no detectable variations outside of analytical errors (Fig.…”

Section: Equilibrium Partitioning and Henry's Law Behaviormentioning

confidence: 95%

Crystal vs. melt compositional effects on the partitioning of the first-row transition and high field strength elements between clinopyroxene and silicic, alkaline, aluminous melts

He,

Li,

Hou

et al. 2023

American Mineralogist

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The first-row transition element (FRTE) and high field strength element (HFSE) systematics are powerful tools for tracking the source and evolution of mantle-derived magmas. Clinopyroxene is generally considered a key fractionating mineral controlling the partitioning of trace elements between melt and residual solid during mantle melting.Although partitioning of FRTE and HFSE between clinopyroxene and basaltic melts has been well studied, experimental constraints on their partitioning behaviors in the presence of siliceous, aluminous and alkali-rich melts are still lacking. Here we present clinopyroxene-silicic melt (67-69 wt% SiO2) partitioning experiments at 1 bar pressure and 1070-1100 °C for Co, Mn, Ni, Cu, Zn, Fe, Sc, Cr, V, Ti, Zr, Hf, Nb, and Ta. Run products consist of diopsidic clinopyroxene coexisting with various melt compositions with non-bridging oxygen to tetrahedral cation ratio (NBO/T) ranging from 0.10 to 0.22.Using our new partition coefficients (Ds) and combining literature data we assess some of the effects of crystal chemistry and the melt composition on the partitioning of FRTE and HFSE in this simple system.We show that partitioning of FRTE varies from mildly incompatible (e.g., D = ~0.1−1 for V, Cu, and Zn) to highly compatible (e.g., D > 10 for Cr and Ni), with highest compatibilities observed for Ni (DNi = 13−34). The partitioning of HFSE varies from highly incompatible (D = 0.01−0.08) for Nb and Ta to mildly incompatible (D = 0.18−0.82) for Zr, Hf, and Ti. Our measured clinopyroxene-melt Ds are consistent with the theoretical predictions of the lattice strain model. Ds data for most tri-, tetra-, and pentavalent elements tend to increase with increasing tetrahedrally-coordinated Al 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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Diffusive fractionation of trace elements in basaltic melt

Cited by 22 publications

References 37 publications

Diffusive exchange of trace elements between alkaline melts: Implications for element fractionation and timescale estimations during magma mixing

Diffusive exchange of trace elements between alkaline melts: Implications for element fractionation and timescale estimations during magma mixing

Diffusive fractionation of Li isotopes in wet, silicic melts

Crystal vs. melt compositional effects on the partitioning of the first-row transition and high field strength elements between clinopyroxene and silicic, alkaline, aluminous melts

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