Ba, Sr and Rb feldspar/melt partitioning in the basanite-phonolite suite from Teide-Pico Viejo volcanic complex, Tenerife.

The behaviour of Group I and II elements during the petrogenesis of felsic igneous rocks is largely controlled by feldspar-liquid relationships and processes. Numerous experimental studies have addressed plagioclase/melt element partitioning, with fewer studies devoted to potassium feldspar, and very few to albite-rich ternary-composition feldspar (An ~ Or < Ab). However, the partition coefficient for Ba is known to increase at least 10-fold through the crystallization sequence sodic plagioclase – anorthoclase – potassium feldspar that is typical of sodic alkaline suites. Consequently, melt Ba concentrations may drop by orders of magnitude along such a liquid line of descent. Feldspars, glasses and whole rocks in such suites may exhibit strong enrichments and depletions in Ba that can be used to track processes of crystal fractionation, cumulate formation, and cumulate recycling.

Here, we review experimental feldspar/melt partitioning data for Ba, Sr and Rb as a function of feldspar composition. Regression of available experimental data offers the basis for expressions that appear to provide a working description for the compositional dependence of partition coefficients for albite-rich compositions. We have applied this model to feldspar and melt compositions of the products of several Holocene eruptions (Pico Viejo C, Pico Viejo H, Teide J2, Lavas Negras, Arenas Blancas, Montaña Rajada and Montaña Reventada) of the basanitic-phonolitic suite of the Teide-Pico Viejo volcanic system (Tenerife, Spain). Comparing feldspar/groundmass pairs obtained by EMPA and LA-ICP-MS analyses with predicted partition coefficients obtained with the models allows us to attribute an antecrystic or xenocrystic origin to some of the feldspars. The results confirm the existence of a distinct population of cumulate feldspars, that had undergone multiple fusion and recrystallization events, in Lavas Negras and Arenas Blancas flows. In addition, the trachytic composition of Montaña Reventada is due to melting of a feldspar-dominated cumulate. Application of these techniques to active magmatic systems will allow us a better understanding of different pre-eruptive processes, and ultimately improve volcanic hazard assessment.

This research was funded by the Intramural CSIC grant MAPCAN (Ref. 202130E083). OD was supported by an FPU grant (FPU18/02572) and a complementary mobility grant (EST19/00297) from the Ministry of Universities of Spain.