Trace element diffusion and kinetic fractionation in wet rhyolitic melt

Holycross, Megan; Watson, E. Bruce

doi:10.1016/j.gca.2018.04.006

Cited by 26 publications

(15 citation statements)

References 53 publications

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“…6). We note that our measured Zr diffusivity in natural tholeiitic basalt is comparable to those of synthetic haplobasalt (LaTourrette et al 1996) and synthetic basalt (Holycross and Watson 2016), close to the line 1:1 on Figure 6, suggesting a good fit between the experiments for dry basaltic systems and the theoretical model for the basaltic systems. Additionally, other experimental data (except for those of Koepke and Behrens 2001) broadly spread along the line 1:1.…”

Section: Zr Diffusivity and Zircon Solubility In Silicate Meltssupporting

confidence: 82%

“…The use of zircon as a petrogenetic tool requires knowledge of the stability field of this mineral, in addition to quantification of solubility limits and crystallization/dissolution rates at relevant P-T conditions and fields of melt composition. Experimental work to determine zircon solubility, dissolution rates and diffusion coefficients of Zr in silicate liquids began in the early 1980's, but was concentrated on felsic and intermediate compositions of variable H 2 O contents at high temperatures and pressures (Watson 1982;Harrison and Watson 1983;Ellison and Hess 1986;Baker and Watson 1988;Baker et al 2002;LaTourrette et al 1996;Nakamura and Kushiro 1998;Mungall et al 1999; Koepke and Behrens 2001;Lundstrom 2003;Watson et al 2006;Rubatto and Hermann 2007;Behrens and Hahn 2009;Burnham and Berry 2012;Boehnke et al 2013;Zhang and Xu 2016;Holycross andWatson 2016, 2018;Shao et al 2018;Borisov and Aranovich 2019). In contrast, there are few experimental studies on basaltic systems, an exception be-ing the study of Dickinson and Hess (1982) on lunar systems, and more recent studies of synthetic terrestrial basaltic melts (Boehnke et al 2013;Holycross and Watson 2016;Shao et al 2018;Borisov and Aranovich 2019) and dunites (Anfilogov et al 2015).…”

Section: Introductionmentioning

confidence: 99%

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Zircon survival in shallow asthenosphere and deep lithosphere

Borisova

Bindeman

Toplis

et al. 2020

American Mineralogist

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Zircon (ZrSiO4) is the most frequently used geochronometer of terrestrial and extraterrestrial processes. To shed light on question of zircon survival in the Earth's shallow asthenosphere, high-temperature experiments of zircon dissolution in natural mid-ocean ridge basaltic (MORB) and synthetic haplobasaltic melts have been performed at temperatures of 1250–1300 °C and pressures from 0.1 MPa to 0.7 GPa. Zirconium measurements were made in situ by electron probe microanalyses (EPMA) at high current. Taking into account secondary fluorescence effects in zircon-glass pairs during EPMA, a zirconium diffusion coefficient of 2.87E-08 cm2/s was determined at 1300 °C and 0.5 GPa. When applied to the question of zircon survival in asthenospheric melts of tholeiitic basalt composition, the data are used to infer that typical 100 mm zircon crystals dissolve rapidly (~10 h) and congruently upon reaction with basaltic melt at pressures of 0.2–0.7 GPa. We observed incongruent (to crystal ZrO2 and SiO2 in melt) dissolution of zircon in natural mid-ocean ridge the basaltic melt at low pressures <0.2 GPa and in the haplobasaltic melt at 0.7 GPa pressure. Our experimental data raise questions about the origin of zircon crystals in mafic and ultramafic rocks, in particular, in shallow oceanic asthenosphere and deep lithosphere, as well as the meaning of the zircon-based ages estimated from these minerals. The origin of zircon in shallow (ultra-) mafic chambers is likely related to the crystallization of intercumulus liquid. Large zircon megacrysts in kimberlites, peridotites, alkali basalts, and carbonatite magmas suggest fast transport and short interaction durations between zircon and melt. The origin of zircon megacrysts is likely related to metasomatic addition of Zr into the mantle as an episode of mantle melting should eliminate them on geologically short timescales.

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Section: Zr Diffusivity and Zircon Solubility In Silicate Meltssupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Zircon survival in shallow asthenosphere and deep lithosphere

Borisova

Bindeman

Toplis

et al. 2020

American Mineralogist

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“…The assumption of a homogeneous melt for Zr in the Rayleigh distillation model may seem to be problematic, because its diffusivity (D) of Zr is low in the melt (42,43) and kinetic isotope fractionation may take place in the diffusive boundary melt layer near zircon (44). Since light isotopes diffuse faster, they may lead to the observed isotopically light cores of zircon.…”

Section: Significance Of Internal Zr Isotope Zoning In Single Zircon mentioning

confidence: 99%

Significant Zr isotope variations in single zircon grains recording magma evolution history

Guo

Wang

Wen

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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Zircons widely occur in magmatic rocks and often display internal zonation finely recording the magmatic history. Here, we presented in situ high-precision (2SD <0.15‰ for δ94Zr) and high–spatial-resolution (20 µm) stable Zr isotope compositions of magmatic zircons in a suite of calc-alkaline plutonic rocks from the juvenile part of the Gangdese arc, southern Tibet. These zircon grains are internally zoned with Zr isotopically light cores and increasingly heavier rims. Our data suggest the preferential incorporation of lighter Zr isotopes in zircon from the melt, which would drive the residual melt to heavier values. The Rayleigh distillation model can well explain the observed internal zoning in single zircon grains, and the best-fit models gave average zircon–melt fractionation factors for each sample ranging from 0.99955 to 0.99988. The average fractionation factors are positively correlated with the median Ti-in-zircon temperatures, indicating a strong temperature dependence of Zr isotopic fractionation. The results demonstrate that in situ Zr isotope analyses would be another powerful contribution to the geochemical toolbox related to zircon. The findings of this study solve the fundamental issue on how zircon fractionates Zr isotopes in calc-alkaline magmas, the major type of magmas that led to forming continental crust over time. The results also show the great potential of stable Zr isotopes in tracing magmatic thermal and chemical evolution and thus possibly continental crustal differentiation.

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“…If Ce is considered to be one of the fast‐moving elements during chemical diffusion (viz. LREE are the fast moving elements during chemical diffusion, Holycross & Watson, 2018), the plots of Ce versus CaO and K 2 O suggest that the compositions of the high‐Ti basalts/picrites could have evolved from low‐Ti basalts/picrites through chemical diffusion (Figure S7a,b). Plots of SiO 2 versus Na 2 O are more complex (Figure 10d), but suggest diffusion of Na 2 O into the low‐SiO 2 felsic volcanic member during magma mixing (cf.…”

Section: Discussionmentioning

confidence: 98%

“…Eichelberger, 1978; Whalen & Currie, 1984). Only diffusion of selective elements can take place between the two juxtaposing silicate melts, depending either on concentration gradients of elements and their diffusion rates (i.e., from high to low concentration called downhill diffusion), or elements can move from low to high concentration (uphill diffusion) to maintain electrical charge balance between the melts in the late stage of diffusion process (Bindeman & Davis, 1999; Holycross & Watson, 2018; Mollo, Misiti, & Scarlato, 2010; Watson, 1982; Watson & Jurewicz, 1984). Furthermore, trace elements are more sensitive to the chemical diffusion rather than bi, tri‐and tetravalent major ions (Bindeman & Davis, 1999).…”

Section: Discussionmentioning

confidence: 99%

Geochemical evidence of mixing between A‐type rhyolites and basalts from Southern Lebombo, South Africa: Implications for evolution of the Northern Karoo Igneous Province

et al. 2020

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The ~183 Ma Karoo Continental Flood Basalt (CFB), southern Africa, formed during a period of major crustal extension prior to Gondwana breakup. To explain the ‘lithospheric contamination’ observed in its whole‐rock chemical and isotopic data various models have been proposed, such as different subcontinental lithospheric mantle (SCLM) sources or interaction between a mantle plume and SCLM or subducted material. A re‐assessment of data in the literature from the Northern Karoo Province, combined with new petrographic, whole‐rock chemical and Sr‐Nd isotopic data of basaltic and dacite/trachydacite samples from the southern Lebombo suggest that chemical diffusion between low‐Ti basaltic/picritic magmas and high‐SiO2 rhyolite parent melt may have caused this ‘lithospheric contamination’. Such slow chemical diffusion, which is posited to have developed during formation of this CFB, can explain the bimodal Karoo basalt‐rhyolite association, the wide variation in SiO2 content (~62–78 wt%) in the dacite/rhyolites, and variable 87Sr/86Sr (183 Ma) and ɛNd (183 Ma) isotope ratios of the Karoo picrites and basalts (0.7037 to 0.7102; 3.58 to −33.52, respectively) and dacites/rhyolites (0.7032 to 0.7152; 0.44 to −17.19). The intermediate incompatible trace element and isotopic compositions of the Karoo high‐Ti basalt/picrite suggest that these rocks could have evolved by magma mixing through chemical diffusion. Our geochemical model for the northern Karoo CFB province involves existence of a voluminous hot (>1,000°C) low‐Ti basaltic magma chamber with remnant picritic melts at shallow crustal depth (~4 km) during major crustal extension. Magma storage was relatively protracted, resulting in significant volumes of partial melt of the surrounding granitoids of the Kaapvaal Craton under relatively anhydrous condition, leading to generation of A‐type high‐SiO2 rhyolite parent magma at pressure of ~1.5 kbar and temperature of ~930°C. This was followed by chemical diffusion of selected elements [LREE, HFSE, and some LILE (K, Rb, Ba, Pb)] and self‐diffusion of Sr and Nd isotopes in these two melts, which generated the observed litho‐type variations in Karoo CFB.

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Trace element diffusion and kinetic fractionation in wet rhyolitic melt

Cited by 26 publications

References 53 publications

Zircon survival in shallow asthenosphere and deep lithosphere

Zircon survival in shallow asthenosphere and deep lithosphere

Significant Zr isotope variations in single zircon grains recording magma evolution history

Geochemical evidence of mixing between A‐type rhyolites and basalts from Southern Lebombo, South Africa: Implications for evolution of the Northern Karoo Igneous Province

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