INSIGHTS INTO THE EXHUMATION HISTORY OF THE SHUSWAP COMPLEX AT JOSS MOUNTAIN, SOUTHEASTERN CANADIAN CORDILLERA
We reconstructed the PTdt path for Wm- and Bt-bearing schists by combining multiscale structural data with petrology and U-Pb ID-TIMS data to contribute to the reconstruction of the geodynamic evolution of the Shuswap complex. The age of an igneous protolith was constrained at ~ 360 Ma and is consistent with late Devonian magmatism, interpreted as related to a continental arc along the western margin of the paleo-North American plate. PT estimates on equilibrium mineral assemblages from metapelites indicate that the transposition fabric developedat 20 - 30 km depth, under conditions approaching those of a crust thermally relaxed after orogenic thickening. Age data suggest that transposition was probably ongoing at 93 Ma, based on a U-Pb monazite age in schist, and ended by 70 Ma, based on the age of an ST-crosscutting pegmatite. Subsequent near-isothermal decompression resulted in high geothermal gradients consistent with lithospheric thinning, but lower than those of the late LP-HT imprint recorded in the adjacent northwestern TOD. This suggests that the JM rocks were further away from the axis of lithospheric thinning than the northwestern TOD during late thermal relaxation. Possibly they were displaced along the Greenbush Lake shear band zone that contributed to Eocene unroofing of the Shuswap complex.