Thermo-tectonic history of the Kisseynew Domain near Sandy Narrows, Saskatchewan
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The Sandy Narrows study area is comprised of mainly 1.86-1.84 Ga Kisseynew Domain marine metaturbidite rocks which represent the uppermost stratigraphic level in the Reindeer Zone. Based on mineralogical changes from west to east, isograds delineating metamorphic and compositional zones are recognized. Zone 1 consists of andalusite-cordierite-staurolite bearing gneisses. Zone 2, on the eastern side of Zone 1, consists of sillimanite-garnet-cordierite-muscovite-biotite gneisses. Zone 3 rocks consist of intercalated garnet-biotite and sillimanite-garnet-cordierite-biotite gneisses. Zone 4 is mineralogically similar to Zone 3, but contains an additional late cross-cutting cordierite-garnet bearing leucosome. Fabric development and collisional tectonics were accompanied by the first metamorphic event (M1), which began pre-D2 but waned before the end of deformation at ~1825 Ma. Growth of andalusite and staurolite is documented in the lower grade area (Zone 1), along with sllimanite, garnet, cordierite, K-feldspar, and melt development in the higher grade zones (Zones 2,3,4). Peak metamorphism is deduced to have occurred prior to 1830 Ma and reached conditions of 720-730 °C at pressures less than 6.5 kbars. Timing is recorded in numerous 1833-1830 Ma zircon ages. A period of retrogression followed, prior to the end of D2, evident by the D2 deformation of replacement minerals. A second metamorphic event (M2) is recognized, broadly coeval with a third deformational event (D3). Metamorphism resulted in growth of andalusite in Zone 1, and garnet, cordierite, sillimanite, and K-feldspar in Zones 2,3, and 4. A second generation of melt also developed; evident cross-cutting the S2 fabric, but is present only within Zone 4. M2 mineral growth texturally overprints the S2 fabric, and is observed oriented parallel to the axial plane of F3 folds. Peak temperatures exceeded that of M1 upwards 741-758 °C with pressures less than 6 kbars. Peak conditions were achieved by 1805 Ma, and were followed by rapid uplift and cooling. M1 metamorphism is attributed to a remnant thermal anomaly associated with back arc basin crust, along with magmatism above southwards subducting Kisseynew oceanic/back arc crust, which resulted from collision of the Sask Craton and the Flin Flon-Glennie Complex. The second metamorphic event may have resulted from subsequent foundering of a Sask Craton detached slab after subduction reversal, which would have allowed influx of hot asthenosphere beneath the Kisseynew, creating a thermal anomaly.