The role of apatite fractionation and REE distribution in alkaline rocks from Mt. Etna, Sicily

Abstract

Melt inclusions in olivine and apatite, and REE distribution of apatite were studied in one of the least differentiated members of the oldest alkaline succession of Mt. Etna. Apatite occurs both as microphenocrysts and as inclusions in olivine crystals, even in the most Mg-rich ones (Fo 82 ). In addition phenocrysts and groundmass are composed of plagioclase, clinopyroxene, olivine and magnetite.Apatite is¯uor-apatite, with rather homogeneous major element (measured by electron microprobe, EMP) and REE (measured by laser-ablation microprobe, LAM, and by secondary ion mass spectrometer, SIMS) contents. REE are enriched when compared to the whole rock, with contents in olivine-hosted apatite lower than or the same as those of the microphenocryst cores; these in turn show lower REE values than their edges. Distribution coef®cients, calculated from LAM data of microphenocryst edges and whole rock analyses, are higher for LREE (8±12) than for HREE (5±4).In the SiO 2 vs. P 2 O 5 diagram melt inclusions and whole rock samples de®ne a trend that is consistent with continuous apatite extraction from a``high P'' basalt magma. Finally, whole rock data show LREE/HREE (La/Lu) n enrichment ratios from hawaiites to mugearites ( 1.14), consistent with apatite fractionation, lower than those documented for lavas of the``low P'' type (enrichment ratio 1.34±1.37), where conditions for apatite saturation were not established.

Geochemical behaviour of rare earths in Vitis vinifera grafted onto different rootstocks and growing on several soils

“…The larger LREE partitioning in ET-1 is consistent with the more incompatible nature of these elements that usually allows them to fractionate into intraplate basic magmatic products such as those associated with the Mt. Etna volcanism (Busà et al 2002;Viccaro et al, 2006) and can be observed both in the labile and whole fractions. By contrast, the MREE fractionation in PA soils could be related to their larger Fe-oxyhydroxide and carbonate contents (Bau, 1999;Haley et al, 2004).…”

Plio-Pleistocene intra-plate magmatism from the southern Sulu Arc, Semporna peninsula, Sabah, Borneo: Implications for high-Nb basalt in subduction zones

“…3). The Tawau lavas can be divided 199 into four sub-groups (PP1 to PP4) for which, at any concentration of MgO which could indicate crystallisation of apatite, however, Semporna lavas are more mafic than 213 would be suitable for apatite saturation at these P 2 O 5 concentrations in basalt or alkali basalt 214 (DeLong and Chatelain, 1990; Busà et al, 2002). 215…”

Chemical Composition and Petrogenetic Implications of Apatite in the Khibiny Apatite-Nepheline Deposits (Kola Peninsula)

“…Our study demonstrated that in the cross-section of Rasvumchorr deposit the concentrations of Sr, Ce, and La in apatite systematically increase with the increasing stratigraphic height (Figure 4). In the huge alkaline magmatic chamber of Etna (Italy) volcanic system, the content of REE in apatite also increases with the degree of differentiation [3]. The compositional evolution of the Khibiny apatite reflects the primary fractionation processes in the alkaline magma that differentiated from the bottom to the top of the magma chamber as a result of magmatic convection, coupled with the settling of minerals with different settling velocities.…”

“…Apatite is a common accessory mineral and it has been extensively used to obtain significant genetic information [1][2][3][4]. This mineral is found in virtually all igneous rocks due to expanded crystallization fields.…”