Investigating a mantle source for Central Australian high heat producing granites

Abstract

The Arunta Region of Australia is a region of high heat flow, largely attributed to an abundance of heat producing elements. High heat producing Proterozoic granites found in the Anmatjira Range in Central Australia have close spatial relationships with mafic rock units. This paper uses field relations, geochemistry, geochronology and isotopic nature of mafic rocks observed in the Range, as well as the Arunta Region, to investigate a possible mantle source for the generation of a fractionation series including the high heat producing granites. Using U–Pb zircon geochronology the Possum Creek Charnockite and Tyson Creek Granulite were dated at 1795.4 ± 4.9 Ma and 1779.9 ± 4.9 Ma respectively. These data as well as field relationships are used to infer that the mafic rock units were interacting coevally with the granites and were intruded during the same tectonic events, the 1820-1795 Ma Stafford and 1790-1770 Ma Yambah Events. Geochemical results of high Cr and Ni concentrations with low SiO2 contents characterised the rocks as mafic and ratios of LILE and HFSE suggests some form of enrichment of the source. Geochemistry implicates a subduction tectonic setting that produced dehydration metasomatism of the overlying mantle wedge. εNd values of -1.8 to -4.7 infer crustal contamination but coupled with the mafic nature of the units further implies a modified and enriched mantle source. It has been interpreted that a subduction related dehydration metasomatism event occurred to enrich the mantle source region which then interacted with crustally derived melts to form a fractionation series including both mafic rock units sampled in this work as well as the high heat producing granites of interest.