This study is an investigation of the geochronology of Crane Mountain, a previously undated area in the Southern Adirondacks. It intends to refine the timing of magmatic and metamorphic events within the Grenville Province. The region is often characterized by anorthosite-mangerite-charnockite-granite (AMCG) suites with an age of emplacement between 1130 and 1160 Ma. With consideration of these age constraints, this research provides new insights into the zircon modification that occurred at the sampled Crane Mountain. Three granitic gneiss samples (ADK25-1, ADK25-2, and ADK25-4) were processed for U-Pb dating using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS).
Results indicate a complex history for the region with clear modification of zircon after initial crystalisation. Sample ADK25-4 yielded a concordant age of 1050 ± 3 Ma, while ADK25-1 showed a distinct correlation between cathodoluminescence (CL) brightness and age, particularly when only rim data was used, with "bright" domains averaging 1139 ± 13 Ma and "dark" domains averaging 1082.2 ± 7.5 Ma. In contrast, sample ADK25-2 exhibited extreme discordance and ages as young as 263 ± 13 Ma, likely due to lead loss from fluid intrusion and physical weathering or possible Appalachian metamorphism. This pattern is consistent with findings by Lupolescu et al. (2011) in the nearby Great Sacandaga Lake area. Collectively, these findings suggest that the sampled ages reflect Ottawan metamorphism (~1080-1030 Ma) or Appalachian metamorphism (~250-480 Ma) rather than primary AMCG magmatism.