Petrological study of Cenozoic basic lavas and melt inclusions from Northern Victoria Land (Antartica)

This study offers a first view of the petrologic features of basic lavas and melt inclusions (MI) in olivine phenocrysts from Northern Victoria Land (Antartica). Samples were collected during three Italian expeditions with the aim of comparing major element composition and volatile content in the lavas and their mantle sources. Major elements and volatiles (H2O, CO2, S, F and Cl) were analyzed in MI, while major and trace elements were carried out on lavas from three localities, Eldridge Bluff, Shield Nunatak and Handler Ridge. Lavas are olivine-phyric (up to 15 %vol) with minor clinopyroxene and plagioclase in a glassy to microcristalline plagioclase-dominated groundmass; opaque minerals are mostly magnetites and subordinately ilmenites. The great majority of lavas are basanites (42.20-45.02 wt% SiO2 ,with 3.36-4.21 wt% of Na2O+K2O) with Mg# (MgO/(MgO+FeO) mol%, Fe2O3=0.15FeO) ranging from 44.87 to 60.83. Lavas from Handler Ridge are the most primitive. At similar fractionation degree, however two series can be distinguished based on K2O and trace element contents (Rb, Ba, La, Nb and Zr). MI in olivine phenocrysts from Shield Nunatak basanites were analysed. They are comparable to the host lavas but encompasse a wider range in composition (43.68 to 48.73 wt% SiO2, with 2.81-4.55 wt% of Na2O+K2O) and Mg# 49.51 to 74.44). The great majority of olivine in equilibrium with MI are more forsteritic than the enclosing crystal suggesting that MI were trapped from a less evolved magma or, most probaby, that Mg-Fe interdiffusion occurred between olivine and MI after entrapment. Most of MI have H2O content ranging from 0.70 wt% to 1.19 wt% and CO2 from 25 ppm to 341 ppm (H2O/CO2~1). At comparable H2O contents few samples show a remarkable higher CO2 values (1322 ppm to 3905 ppm) with a H2O/CO2 down to 0.8.