Resolving Micrometre‐Scale Zircon Growth in Silicic Systems by 7 μm LA ‐ MC ‐ ICP ‐ MS U‐Pb Dating: Linking Petrology and Geochronology in Silicic Volcanic and Granitic Rocks from Victoria, Australia

We present a systematic evaluation of high spatial‐resolution zircon U‐Pb dating using a Thermo Scientific Neoma multi‐collector ICP‐MS coupled to a Resolution 193 nm excimer laser, operated at 7–15 μm spot diameters under routine high‐throughput production conditions. Performance was assessed during extended measurement sessions comprising 300–400 analyses per run, with reference materials interspersed among unknowns. Three configurations were tested: 15 μm (8 Hz, 15 s), 7 μm (8 Hz, 12 s) and 7 μm (6 Hz, 9 s). Zircon reference materials (Plešovice, 91500, BB) were used to evaluate precision, accuracy, repeatability and down‐hole fractionation (DHF). At 15 μm, individual 206 Pb/ 238 U uncertainties were typically 0.5–1% (2 s ), with intermediate measurement precision better than 0.5% (2 s ). DHF was smooth and repeatable, adequately modelled by linear or polynomial corrections. At 7 μm (8 Hz, 12 s), 206 Pb/ 238 U measurement repeatability precision for single spots of 0.5–1% was routinely achieved, overlapping with the best reported ≤ 10 μm LA‐(MC)‐ICP‐MS performance. Reduced ablated mass (≤ 1 ng zircon), however, increased counting‐statistical noise and DHF sensitivity. This primarily affects 207 Pb/ 206 Pb precision in Phanerozoic zircons, where low radiogenic 207 Pb yielded single‐spot uncertainties > 5% and intermediate measurement precision of 8–10% RSD. Lower repetition rates further reduced ion yield, increasing 206 Pb/ 238 U uncertainties to 1.5–3% while improving depth control for ultra‐thin domains. Application to Devonian silicic rocks from western Victoria demonstrates the geological value of 7–15 μm analyses. Small‐spot data resolve Late Silurian–Early Devonian inherited cores (438–398 Ma) within younger Middle Devonian overgrowths, revealing widespread crustal inheritance not detectable with conventional 25–35 μm spots. These results indicate repeated entrainment of zircon derived from deep‐crustal magmatism associated with the Benambran and Bindian orogenies, supporting a model of prolonged Devonian crustal reworking and magma recycling in the Lachlan Orogen.