Controls on apatite compositional variations in magmatic rocks: A case study of Mesozoic mafic–felsic intrusions from the eastern North China Craton

Abstract

Compositional variations of apatite are mainly determined by parameters such as partition coefficients and the composition of parental magma. However, the relative importance of these parameters in relation to apatite geochemistry in different lithologies of magmatic rocks is not well constrained. In this study, six Mesozoic (219–154 Ma) mafic–felsic intrusions from the eastern North China Craton, were selected for detailed apatite microanalyses (trace elements and Nd isotopes). Apatite from the studied intrusions has uniform textures in the cathodoluminescence image. They exhibit high abundances of rare earth elements (REE) and are characterized by light REE enriched patterns, indicative of a magmatic origin. Alongside compiled apatite data, these findings suggest that compositional variations of REE + Y in apatite from mafic to felsic magmatic rocks are controlled primarily by elemental partitioning between apatite and melts. The competitive crystallization of other accessory minerals prior to apatite can be responsible for compositional variations of Sr, Pb, Th, and U. New Nd isotope data for apatite are discussed and compared with whole-rock Nd and zircon Hf isotope data for the same sample. The Nd isotopic compositions between the whole-rock and apatite are identical. The integrated dataset provides an alternative interpretation for the isotopic decoupling between apatite Nd and zircon Hf isotope systems. In conclusion, apatite REE concentrations and Nd isotopes have the potential to serve as geological indicators.