Cratonic upper-mantle beneath the central Slave Province
Date
1998
Authors
MacKenzie, Jason Millard
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Abstract
The composition of the upper mantle lithosphere beneath the Archean Slave Province has been estimated by combining mineral chemical and petrographic data from mantle xenoliths entrained in the Torrie kimberlite pipe located in the central Slave Province. Coarse- and granuloblastic-, and porphyroclastic- textured peridotite xenoliths are the dominate rock type and yield equilibration temperatures ranging between 850-135° C. Thermobarometry requires a minimum lithospheric thickness of approximately 180 km during the late Cretaceous-early Paleocene. The distribution of pressures and temperatures of equilibration for the xenoliths lie on a calculated 42 mWm-2 paleogeotherm, ~ 11 mWm-2 lower than the present heat flow measured at Yellowknife. Some samples show a complex thermal evolution. The higher heat flow measured at Yellowknife is a result of highly radiogenic rocks near the surface. The Mg# [Mg/(Mg+Fe)] of olivine in peridotites varies from 0.906-0.938 with an average of 0.920. The Torrie xenolith suite show variable degrees of serpentinization and/or carbonation with the rim compositions of many clinopyroxene grains showing Ca enrichment although overall, the xenoliths are homogeneous at all scales. The Torrie xenoliths are rich in orthopyroxene similar to other low temperature (<1100°C) peridotites from southern Africa. Estimates of bulk rock composition based on mineral chemical and modal data reveal a negative correlation between Si and Fe, similar to peridotite xenoliths from Udachnaya (Boyd et al., 1997). Similarities between xenoliths from the Torrie kimberlite and comparable xenoliths from locations around the globe suggest that the lithosphere beneath the Slave craton has experienced a evolution similar to other cratons globally.