Variation in the composition of apatite through the Merensky cyclic unit in the western Bushveld Complex

摘要: Microprobe analysis of interstitial apatite from a 100-m section through the Merensky reef Bushveld Complex reveals that this stratigraphic marks transition Cl-rich to more F-rich compositions in Critical and Main zones, respectively. Apatite across vary by than 80 mole percent chlorapatite component. The trend decreasing Cl concentration with height is not regular, contents apatites some samples may as much 50 percent. La 2 O 3 Ce tend be enriched melanocratic, orthocumulate parts section. SrO concentrations show an increase position, which opposite observed coexisting cumulus plagioclase.The data are consistent mineralogic textural evidence for influx vapor into has affected Cl/F variations lower portion Bastard unit. This occurred above crystallization temperature (1,000 degrees -1,050 C). It suggested modal variation seen result shifts liquidus field boundaries caused gain or loss volatile components melt.