Zoned Poikiloblastic Garnets: P-T Paths and Syn-Metamorphic Uplift through 30 km of Structural Depth, Wopmay Orogen, Canada

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Abstract
In the early Proterozoic Wopmay Orogen (Northwest Territories, Canada), the occurrence of garnet-biotite-sillimanite/kyanite-plagioclase-quartz assemblages in pelitic schists at a variety of obliquely exposed structural levels enables the use of calibrated geothermometers and geobarometers through 30 km of composite structural relief. Direct derivation of multipoint P-T paths from single garnets is attained from core-to-rim microprobe analyses of zoned poikiloblastic garnets, which contain biotite, plagioclase, quartz, and less commonly Al2SiO5 inclusions. The documented garnet zoning and the entrapment of the mineral inclusions is compatible with partial-equilibrium growth models. The lack of significant diffusion re-equilibration in the garnet interiors is favored by sample restriction to medium-grade schists and is attested by the preservation of normal-zoning profiles, the lack of garnet diffusion babes around biotite inclusions, the matching composition trends of garnet-core to -rim plagioclase inclusions with those of zoned matrix plagioclase grains, and the systematic variation of the derived P-T data. Only the garnet rims, which are characterized by a reversal of compositional trends and by textural resorption, are interpreted to indicate local post-thermal-peak re-equilibration.

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