Age and thermal history of the Port Mouton Pluton, southwest Nova Scotia: A combined uranium-lead, argon-40/argon-39 age spectrum, and argon-40/argon-39 laserprobe study

New U-Pb data for monazite and titanite, and new {dollar}sp{lcub}40{rcub}{dollar}Ar/{dollar}sp{lcub}39{rcub}{dollar}Ar incremental heating data for muscovite and K-feldspar, coupled with the first reported laserprobe data (total fusion and spot analysis of muscovite) from Meguma Zone plutons, provide clarification of the age and thermal history of the PMP. U-Pb dating of monazite constrains the crystallization age of the main intrusive units to 373 {dollar}pm{dollar} 1 Ma. Magmatic muscovite ages of ca. 373 Ma ({dollar}sp{lcub}40{rcub}{dollar}Ar/{dollar}sp{lcub}39{rcub}{dollar}Ar laserprobe) from undeformed samples suggest rapid postcrystallization cooling. Laserprobe muscovite ages of ca. 360 Ma to 345 Ma (with core ages generally older than rim ages) reflect partial loss of accumulated argon from muscovite between ca. 330-300 Ma. Recrystallized grain margins and core-rim element variation suggest that argon loss from deformed samples occurred by a combination of reaction and deformation mechanisms. Ages of ca. 360-345 Ma from some undeformed samples suggest that other mechanisms may have contributed to argon loss from these samples. Muscovite incremental heating spectra generally yield ages of ca. 360-350 Ma and do not show the apparent age gradients revealed by laserprobe spot fusion snalysis. Total fusion ages from all samples are highly variable, possibly reflecting the complex age gradients preserved within PMP muscovite. The oldest ages recorded in the highest-temperature increments of K-feldspar spectra suggest a distinct argon loss event between ca. 280-260 Ma. A U-Pb titanite age of ca. 260 Ma may record this event. Younger ages recofded in low-temperature increments suggest reheating events at ca. 230-210 Ma and ca. 200 Ma.; This study demonstrates the value of integrated geochronological studies involving several techniques on a variety of minerals in elucidating complex thermal histories. In particular, {dollar}sp{lcub}40{rcub}{dollar}Ar/{dollar}sp{lcub}39{rcub}{dollar}Ar laserprobe studies are more effective than conventional inmmental heating analysis in revealing complex age gradients in minerals from complex geological regions. (Abstract shortened by UMI.)...