Garnet Valley Act 93 Agreement

The plagioclase of two leucogabbronorites containing andraditary shell xenoccis described in 2007 is within the upper limit of the zone (6·7‰). No correlation is observed between δ18O values and modal plagioclase or its anortrit content. The lower micronutrient concentrations in the plagioklas of the dark anorthosite sequence are well in line with the bulk anorthosite data of Drüppel et al. (2007) and indicate fractionation from homogeneous fusion with a relatively primitive trace element composition. The decrease in the concentration of Sr in medium-grained plagioclases appears to be controlled exclusively by plagiocla fractionation (Fig. 6). 6) indicates simultaneous fractionation of fe-ti oxides. The early crystallization of olivine, resulting from its presence as an inclusion in cumulative plagioclase, probably increased the concentration of trace elements in the cast iron, but did not result in characteristic enrichments or depletions observable in other phases. The composition of oxygen isotopes and trace elements of the plagioclase and intercumulu phases also limits the timing of crust contamination. The composition of the oxygen isotopes of unchanged plagioclases systematically changes from the most primitive dark anorthosites containing olivine to white anorthosites containing pyroxenes and confirms a pattern of more marked contamination of crusts in the petrogenesis of the latter (fig. 9a).

The higher δ18O values of cumulus plagioclase, as well as the trace element compositions of the corresponding fluids (fig.