Partitioning of rare earth and high field strength elements between titanite and phonolitic liquid

Abstract

We present the results of a LA-ICPMS study of titanites and associated glasses from the mixed-magma phonolitic Fasnia Member of the Diego Hernández Formation, Tenerife, Canary Islands. We employ a method of identifying equilibrium mineral-melt pairs from natural samples using REE contents and a linear form of the lattice strain model equation (Blundy and Wood, 1994), where the Young's modulus (E M ) for the 7-fold coordinated site is an output variable. For felsic magmas that contain crystals potentially derived from a variety of environments within the system, this approach is more rigorous than the use of solely textural criteria such as mineral-glass proximity.We then estimate titanite/melt partition coefficients for Y, Zr, Nb, REE, Hf, Ta, U and Th. In common with prior studies, we find that middle REE partition more strongly into titanite than either light or heavy REE, and that REE partitioning behavior in titanite is reasonably predicted by the lattice strain model. Titanite also fractionates Y from Ho, Zr from Hf, and Nb from Ta. Comparison with experimental data indicates that melt structure effects on partitioning are significant, most particularly in very highly polymerized melts. We use the data to estimate 7-fold coordination radii for trivalent Pr, Nd, Ho, Tm and Lu, and to make approximate predictions of titanite/melt partitioning of Ra, Ac and Pa. Interpolation of data for heavy REE does not predict the behavior of Y, indicating that factors other than charge and radius are involved in partitioning. Variations in Y/Ho induced by magmatic processes appear to be negatively correlated with temperature, and are expected to be greatest in near-minimum melts.

Remelting of cumulates as a process for producing chemical zoning in silicic tuffs: A comparison of cool, wet and hot, dry rhyolitic magma systems

“…Mineral assemblages are given in Table 1. Both phonolitic units contain titanite, which has high mineral/melt partition coefficients for REE, Nb and Ta (Olin and Wolff, 2012;Wörner et al, 1983); in contrast, clinopyroxene is the only phase in the Green Tuff with high partition coefficients for REE (Neave et al, 2012). Maximum water contents for these units are in the same range as the rhyolitic examples above, indicating that the most highly differentiated portions were at, or close to, saturation (Harms and Schmincke, 2000;Lanzo et al, 2013;Olin and Wolff, 2010).…”

“…1A), is ascribed to zircon. In the phonolites, REE behavior is dominated by titanite, which has very high mineral/melt partition coefficients for REE and exhibits a preference for middle REE over both light and heavy REE (Olin and Wolff, 2012;Wörner et al, 1983). Strong fractionation of Nb from Ta is also due to titanite.…”

The age and petrogenesis of alkaline magmatism in the Ampasindava Peninsula and Nosy Be archipelago, northern Madagascar

“…Similar patterns in trachyte-syenite-phonolite samples have been already shown (e.g., Bobaomby, Melluso et al 2007a;Massif d'Ambre, Cucciniello et al 2011b;Gharyan, Libya, Lustrino et al 2012;Ischia, Italy, Melluso et al 2014). The concave REE pattern is likely related to removal of small amounts of titanite (~1 %) (e.g., Olin and Wolff 2012;Lustrino et al 2012).…”

Petrogenesis of Cenozoic volcanic rocks in the NW sector of the Gharyan volcanic field, Libya

“…Within Boynton, 1984) REE patterns for Gharyan volcanic rocks. Average of REE partition coefficients for titanite (Olin and Wolff, 2012) are also shown. the limits of this approach, the provenance of the partial melt is supposed at the base of the lithospheric mantle because of the coexistence of spinel and garnet, and the presence of amphibole in the source (e.g., le Roex et al, 2001;Melluso and Morra, 2000;Melluso et al, 2007).…”

“…As it is well known, the removal of small amounts of titanite during the differentiation of silicate melts is expected to significantly decrease the MREE concentrations relative to LREE and HREE in the residual melts (e.g. D La =21-29, D Tb =51-79, D Lu =10-17; e.g., Olin and Wolff, 2012). Indeed, the geochemical changes in the transition from benmoreites to the most mafic trachytes can be explained by subtraction of small amounts (~1%) of titanite (Supplementary Table 13).…”