The effect of sodium and titanium on crystal-melt partitioning of trace elements

Rare earth elements are commonly assumed to substitute only for Ca in clinopyroxene because of the similarity of ionic radii for REE 3+ and Ca 2+ in 8-fold coordination. The assumption is valid for Mg-rich clinopyroxenes for which observed mineral/melt partition coefficients are readily predicted by the lattice strain model for substitution onto a single site (e.g. Wood and Blundy, 1997). We show that natural Fe-rich pyroxenes in both silica-undersaturated and -oversaturated magmatic systems deviate from this behavior. Salites (Mg# 48 to 59) in phonolites from Tenerife, ferrohedenbergites (Mg# 14.2 to 16.2) from the rhyolitic Bandelier Tuff, and ferroaugites (Mg# 9.6 to 32) from the rhyolitic Rattlesnake Tuff have higher heavy REE contents than predicted by single-site substitution. The ionic radius of Fe 2+ in 6-fold coordination is substantially greater than that of Mg 2+ , hence we propose that, in Fe-rich clinopyroxenes, heavy REE are significantly partitioned between 8-fold Ca sites and 6-fold Fe-Mg sites such that Yb and Lu exist dominantly in 6-fold coordination. We also outline a REE-based method of identifying pyroxene-melt pairs in systems with multiple liquid and crystal populations, based upon the assumption that LREE and MREE reside exclusively in 8-fold coordination in pyroxene.Contrary to expectations, interpolation of mineral/melt partition coefficient data for heavy REE does not predict the behavior of Y. We speculate that mass fractionation effects play a role in mineral/melt lithophile trace element partitioning that is detectable among pairs of isovalent elements with near-identical radii, such as Y-Ho, Zr-Hf, and Nb-Ta.

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“…Those for the FM Na-salites are lower due to the influence of Na, a result also found experimentally by Bennett et al (2004).…”

Section: Identification Of Pyroxene-glass Pairssupporting

confidence: 81%

Rare earth and high field strength element partitioning between iron-rich clinopyroxenes and felsic liquids

Olin

Wolff

2010

Contrib Mineral Petrol

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“…Thermodynamic data derived by the lattice strain model indicate that the 278 influence of P on D i can be considered negligible at pressures lower than 500 MPa (Blundy and 279 . It could be argued that REE partitioning is also sensitive to sodium in clinopyroxene, 280 which in turn varies with pressure (Blundy et al, 1995;Bennett et al, 2004). However, the control 281 of Na + on D REE is dominant only at mantle pressures (≥ 3 GPa) where sodium concentration (Na 2 O 282 = 2.2-13.5 wt.%; data from Klemme et al, 2002;Bennett et al, 2004;Marks et al, 2004) is one to 283 Table 1S).…”

Section: Sample Description 170 171mentioning

confidence: 99%

“…It could be argued that REE partitioning is also sensitive to sodium in clinopyroxene, 280 which in turn varies with pressure (Blundy et al, 1995;Bennett et al, 2004). However, the control 281 of Na + on D REE is dominant only at mantle pressures (≥ 3 GPa) where sodium concentration (Na 2 O 282 = 2.2-13.5 wt.%; data from Klemme et al, 2002;Bennett et al, 2004;Marks et al, 2004) is one to 283 Table 1S). Therefore, in terms of physical parameters, temperature is likely the most important 285 variable that can influence D i at the crystallization conditions of magmas.…”

Section: Sample Description 170 171mentioning

confidence: 99%

“…(Table 4S and (Fig. 6a), although this parameter may not provide a comprehensive description of melt 379 structure at a level relevant to trace element partitioning (e.g., Bennett et al, 2004 It is apparent that the uncertainty measured for the recalibrated equations (11) and (12) is 536 reasonably low due to the restricted bounds of the calibration dataset that, in turn, closely describe 537 the crystallization conditions and compositions of magmas at Campi Flegrei ( Fig. 1 and Table 1S).…”

Section: Sample Description 170 171mentioning

confidence: 99%

“…Subsequently, this assumption has since 364 been found to be an oversimplification (Wood and (Fig. 6a), although this parameter may not provide a comprehensive description of melt 379 structure at a level relevant to trace element partitioning (e.g., Bennett et al, 2004 …”

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confidence: 99%

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Trace element partitioning between clinopyroxene and trachy-phonolitic melts: A case study from the Campanian Ignimbrite (Campi Flegrei, Italy)

Mollo

Forni

Bachmann

et al. 2016

Lithos

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms The partitioning of trace elements between crystals and melts provides an important petrogenetic 29 tool for understanding magmatic processes. We present trace element partition coefficients 30 measured between clinopyroxene phenocrysts and trachy-phonolitic magmas at the Campi Flegrei 31 (Italy), whose late Quaternary volcanism has been characterized by two major caldera-forming 32 events (Campanian Ignimbrite at ~39 ka, and the Neapolitan Yellow Tuff at ~15 ka). Our data 33 indicate that the increase of trivalent rare earth elements and yttrium into the crystal lattice M2 site 34 is facilitated by the charge-balancing substitution of Si 4+ with Al 3+ on the tetrahedral site. Higher 35 concentrations of tetravalent and pentavalent high field strength elements on the M1 site are also 36 measured when the average charge on this site is increased by the substitution of divalent cations by 37Al vi . In contrast, due to these charge balance requirements, divalent transitional elements become 38 less compatible within the crystal lattice. On the basis of the lattice strain theory, we document that 39 the incorporation of rare earth elements and yttrium in clinopyroxene is influenced by both 40 compositional and physical parameters. Data from this study allow to update existing partitioning 41 equations for rare earth elements in order to construct a self-consistent model for trachy-phonolitic 42 magmas based on the lattice strain theory. The application of this model to natural products from 43 the Campanian Ignimbrite, the largest caldera-forming eruption at the Campi Flegrei, reveals that 44 the complex rare earth element pattern recorded by the eruptive products can be successfully 45 described by the stepwise fractional crystallization of clinopyroxene and feldspar where the 46 clinopyroxene-melt partition coefficient changes progressively as a function of the physicochemical 47 conditions of the system. 48 49

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Parameterizations of calcic clinopyroxene—Melt trace element partition coefficients

Bédard

2014

Geochem Geophys Geosyst

119

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Cpx/liquid D for the rare earth elements were fit to the lattice strain model to derive fits that can reproduce the cpx/ liquid D REE profile shapes (REE 5 rare earth elements). These fits indicate that cpx/liquid D REE for melts more evolved than picritic basalts cannot be modeled assuming that all REE are in octahedral coordination in a single M2 site, but also require sixfold partitioning into an M1 site for Lu-Yb-Tm-Er.

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The effect of sodium and titanium on crystal-melt partitioning of trace elements

Cited by 71 publications

References 44 publications

Rare earth and high field strength element partitioning between iron-rich clinopyroxenes and felsic liquids

Rare earth and high field strength element partitioning between iron-rich clinopyroxenes and felsic liquids

Trace element partitioning between clinopyroxene and trachy-phonolitic melts: A case study from the Campanian Ignimbrite (Campi Flegrei, Italy)

Parameterizations of calcic clinopyroxene—Melt trace element partition coefficients

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