Effect of metamorphism on apatite U-Pb systematics: a case study across metamorphic grade in the Anmatjira Range, Central Australia

Abstract

Apatite is a common accessory mineral in igneous, sedimentary and metamorphic rocks and can be used to extract thermochronological information at a range of temperature systems. The apatite U-Pb technique has recently been developed (1) and has the potential to become a viable alternative to more traditional U-Pb dating techniques (e.g. zircon, monazite), particularly since apatite saturates at lower SiO2 concentrations than e.g. zircon. However, compared to zircon and monazite, the effect of metamorphism on U-Pb systematics in apatite is yet to be fully understood and thus, apatite remains under-represented in e.g. provenance studies. This study investigates the effect of prograde metamorphism on the apatite U-Pb clock and trace element diffusion using a case study in the Anmatjira Range, central Australia. The NW trending Anmatjira Range located within the larger broadly E-W trending Arunta region comprises of metamorphosed sedimentary rocks and granitoids that have undergone multiple metamorphic and deformational events since the Paleoproterozoic. Differential exhumation and deformation has been recorded throughout the Anmatjira Range and has been associated with four tectonic episodes. The Strangways Event from 1740-1690 Ma, the Liebig Orogney from ca. 1640 Ma, the Chewings Event from ca. 1590-1550 Ma and finally the Alice Springs Orogeny from ca. 450-300Ma. The consequence of differential exhumation across the Anmatijira range is a regional metamorphic field gradient ranging from greenschist facies in the NW to granulite facies in the SE. Six samples from a large, single granitic intrusion were taken across the metamorphic isograds, aiming to pinpoint the metamorphic boundary conditions to which the apatite U-Pb system retains its primary (igneous) apatite ages and to investigate how the U-Pb system and different trace elements in apatite respond to differential metamorphic conditions. Furthermore, six metapelites were sampled in close vicinity to the granite samples to be modelled and to identify precise local Pressure-Temperature conditions. The full datasets is yet to be fully interpreted and will be presented, for the first time, during the conference.