Métamorphisme régional du nord-est de la Sous-province de Pontiac, Abitibi, Québec
|Abstract:||The Pontiac Subprovince is located in the Superior Province, south of the Abitibi Subprovince. The metasedimentary rocks are characterized by a Barrovian metamorphic gradient increasing from north to south from biotite zone, to garnet zone and to staurolite zone. The Pontiac Subprovince interpreted as an accretionary wedge that was tectonically docked to the Abitibi Subprovince during Archean subduction, however, few studies have attempted to characterize its pressure-temperature-time path to test this hypothesis and little is known about the timing relationship between regional metamorphism and the Au mineralization. The regional fabric is defined by an E-W, NW-SE lepidoblastic ductile foliation in which garnet and staurolite porphyroblasts are interpreted to be late- to post-kinematic with the rare occurrence of syn-kinematic staurolite growth. The garnet-biotite Fe-Mg partitioning coefficient geothermometer is not significantly different between the garnet and the staurolite zone. Similarly, Ti in biotite geothermometry does not suggest different temperature of equilibration between the biotite, garnet and staurolite zone. Pressure and temperature (PT) forward thermodynamic modelling with a water saturated pseudosection yielded conditions of 550-600 ⁰C and 5-6 kbar during a prograde, clock-wise P-T path. Lu-Hf dating of garnet from three outcrops within the staurolite zone yielded an age of 2657 +/- 7 Ma that is inferred to be representative of these conditions. The results of this study imply that the Canadian Malartic mineralization event, previously dated at 2664 Ma with Re-Os on molybdenite, is younger or synchronous with the garnet growth condition in the staurolite zone next to the ore body. The age of garnet growth calls into question the accretionary prism tectonic model currently explaining the contact between the Abitibi and Pontiac Subprovinces.|
|Document Type:||Mémoire de maîtrise|
|Open Access Date:||26 September 2018|
|Collection:||Thèses et mémoires|
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