40AR-39AR DATING OF MULTICOMPONENT MAGNETIZATIONS IN THE ARCHEAN SHELLEY LAKE GRANITE, NORTHWESTERN ONTARIO

The Shelley Lake granite yields two paleopoles which could represent either of two scenarios: both poles were acquired early, SL2 at 2.7 Ga and SL1 during metamorphic overprinting near 2.6 Ga; pole SL1 was acquired first on cooling at 2.6 Ga while the SL2 antipole represents a late Proterozoic remagnetization. We chose biotie and K-feldsars from the available cores-biotite to record high temperature ecents and K-feldspars to detect any weak late Proterozoic reheating event. The biotite 40Ar/39Ar age spectrum is flat for 80% of the released Ar, indicating closure to Ar loss at 300oC 2.60 Ga ago. -Authors