Micron- to nanoscale characterisation and U-Pb geochronology of zircon from granites of the Samphire Pluton, South Australia

摘要: Abstract Zircons from three distinct granites within the Samphire Pluton, South Australia, are characterised at micron- to nanoscale. Sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon dating generated 207Pb/206Pb weighted average ages of 1586 ± 9.3 Ma, 1583.2 ± 8.5 Ma and 1578 ± 9.5 Ma, respectively. Although zircons all display evidence hydrothermal overprinting, this is most strongly expressed in a distinct, red-colored granite referred here as Granite C. Alteration variation concentrations HREE + Y, Th Pb, whereby grain margins relatively enriched these elements both Zr Si depleted. Altered cores have high U contents relative margins, which appreciably poorer element, whereas crosscutting microfractures. Coupled with enrichment non-formula marked disturbance U-Th-Pb isotope ratios, nanoscale observations Pb-bearing nanoparticles (galena?) implying mobility Pb other elements, nanofractures structural defects demonstrate that C has undergone multi-stage alteration impacting upon accurate dating. Importantly, implications for analogous systems elsewhere, our results confirm open system behaviour Hiltaba Suite zircon. SHRIMP geochronology cannot confidently resolve any statistical differences age granites, despite their appearance suggesting they might represent temporally phases larger magmatic system. altered (C), directly underlying Blackbush uranium prospect contain convincing an event triggered remobilisation into cover sequence.