<i>P–T</i>–t Path of Unusual Garnet–Kyanite–Staurolite– Amphibole Schists, Ellesmere Island, Canada—Quartz Inclusion in Garnet Barometry and Monazite Petrochronology

Abstract Garnet–kyanite–staurolite assemblages with large, late porphyroblasts of amphibole form garbenschists in Ordovician volcaniclastic rocks lying immediately south the Pearya terrane on northernmost Ellesmere Island, Canada. The schist, which together carbonate olistoliths makes up Petersen Bay Assemblage (PBA), displays a series parallel isograds that mark an increase metamorphic grade over distance 10 km towards contact Pearya; however, steep, brittle Cenozoic strike-slip fault unknown amount displacement disturbs earlier accretionary relationship. growth, probably due to fluid ingress, is clear evidence disequilibrium conditions garbenschist. In order recover P–T history schists, we construct isochemical phase equilibrium models for nearby garnet–mica schist escaped event and compare results quartz inclusion garnet (QuiG) barometry garbenschist metapelitic schist. Quartz inclusions are confined cores QuiG results, combined Ti-in-biotite garnet–biotite thermometry, delineate prograde path from 480 600°C 0.7 0.9 GPa. This agrees growth zoning deduced X-ray maps spessartine component garnet. peak obtained pseudosection modelling using effective bulk composition intersection rim matrix biotite white mica isopleths metapelite 665°C at ≤0.85 Three generations monazite (I, II III) were identified by textural characterization, geochemical (REE Y concentrations) U–Pb ages measured ion microprobe. Monazite I occurs as rims grew 397 ± 2 Ma (2σ) breakdown allanite. forms overgrowths grains oriented main schistosity yield 385 Ma. III, found only garbenschist, 374 6 Ma, interpreted time during infiltration lower temperature pressure clockwise remained kyanite stability field. These point relatively short (≈12 Myr) Barrovian affected schists PBA. An obvious heat source lacking adjacent terrane, but speculate it was large Devonian plutons—similar 390 Cape Woods granite located 40 across strike fault—that have been excised strike-slip. Arc fragments correlative PBA low grade; they never saw not directly involved accretion.