Apatite inclusions in zircon: records of porphyry melt evolution

摘要

Igneous apatite is a useful mineral in petrological and ore studies. However, in porphyry environments the modification of apatite compositions through metasomatism is common due to the large volume of circulating fluids. In addition, elements key to tracking magmatic-hydro-thermal processes (e.g. halogens and S) have fast diffusion rates (Cherniak 2010) such that even visibly fresh grains may not preserve a primary igneous composition. In this study we avoid uncertainty through the analysis of fine (<0 urn) apatite inclusions hosted within zircon. We suggest these apatites are shielded from the effects of metasomatism and diffusion, preserving a record of the melt at the time of zircon growth. This approach also means that trace element analyses can be compared to those of the co-existing zircon from which age and temperature (Ferry and Watson 2007) information can be obtained.