WHOLESALE TRANSFORMATION OF CONTINENTAL CRUST DURING UHP TECTONISM? GARNET GEOCHRONOLOGY OF THE WESTERN GNEISS REGION, NORWAY
Garnet constitutes perhaps the single-most useful vector for answering these outstanding questions about the deformation and transformation of continental margins at UHP conditions because of its presence throughout the WGR, and its ability to record i) PT changes in its composition, ii) deformation in its textures, and iii) history in its age(s). This research uses Sm → Nd decay to date garnets in eight quartzofeldspathic gneisses from both within and outside the UHP/HP boundaries. The garnet ages are expected to be i) c. 950 Ma grains that predate and were unaffected by UHP tectonism, ii) c. 425390 Ma UHP phases, or iii) <390 Ma neoblasts grown during the supra-Barrovian to Buchan metamorphism overprint that occurred during exhumation of the UHP terrane to crustal depths. Accompanied by PT data and detailed petrography, the ages of these eight samples will establish whether continental crust in the WGR transformed to UHP mineralogy and the degree of deformation to the terrane attributed to UHP tectonism.