INTEGRATING STRUCTURAL ANALYSIS, MONAZITE GEOCHRONOLOGY, AND FORWARD PETROLOGIC MODELING WITHIN THE ATHABASCA GRANULITE TERRANE (SNOWBIRD TECTONIC ZONE): IMPLICATIONS FOR UNDERSTANDING THE LONGEVITY OF P-T LOOPS WITHIN A LOWER CRUSTAL HOT ZONE

Absolute ages of structural fabrics, kinematics, and metamorphic assemblages are critical to understanding the timescales associated with tectonothermal events. The ca. 3.2 Ga Chipman batholith corresponds to the geophysical trace of the Snowbird Tectonic Zone within the western Churchill Province. The batholith contains a NE-striking, steeply dipping tectonic fabric that is syn-kinematic with the Chipman dike swarm. The locally mylonitic fabric is associated with gently plunging upright folding and transposition (in areas of more intense shearing) of the regional Archean magmatic to tectonic layering (S_1C). We employed monazite U-Th-total Pb geochronology to constrain the age and longevity of folding, dextral transpressional shear, and transposition. Diatexites within the Chipman batholith contain abundant monazite, but they typically lack appropriate mineralogy suitable for thermobarometry. However, correlating fabrics between rocks with proper assemblages for thermobarometry to rocks that contain monazite has proven successful at bracketing P-T-t-D paths. Within a low strain diatexite sample, a strong compositional layering contains a subsolidus axial planar mineral alignment parallel to the regional S_2C. Monazite grains within the leucosome contain elliptical Archean cores that are aligned with compositional layering, and low Th rims that grew contemporaneous to the development of S_2C. Three sets of analyses from these low Th rims yield an age of 1900 +/- 3 Ma. Further monazite analyses are currently underway, and results are consistent with the structural evolution in the adjacent northwestern domain, where folding has been determined to have initiated by 1917 +/- 12 Ma, and continued to 1895 +/- 3.2 Ma. Thermobarometry of the syn-kinematic mafic dike swarm yields metamorphic conditions of 1.17 GPa and 825°C. Petrologic modeling is underway to constrain the P-T-t path of the mafic dikes and to evaluate the P-T evolution of the diatexites themselves. Preliminary results suggest that the region represents a crustal-scale hot zone that remained at temperatures exceeding 750°C for ca. 15 my. Subsequent deformation was localized, and persisted for ca 50 my, which was likely the result of the region remaining “weak” due to slow cooling of the lower crust after the cessation of the chipman dike swarm.