Age, composition and thermal history of lower crustal xenoliths from the Artemisia, Ekati and Munn Lake kimberlites of the Slave Craton Open Access
- Other title
Lower crustal xenoliths
- Type of item
- Degree grantor
University of Alberta
- Author or creator
Coombs, Shauna M.
- Supervisor and department
Chacko, Thomas (Earth and Atmospheric Sciences)
- Examining committee member and department
Pearson, Graham (Earth and Atmospheric Sciences)
Heaman, Larry (Earth and Atmospheric Sciences)
Department of Earth and Atmospheric Sciences
- Date accepted
- Graduation date
Master of Science
- Degree level
In this study we present data from three lower crustal xenoliths suites collected in a northeast to southwest transect across the Slave craton. The samples are from the Artemisia kimberlite, located near the Coronation diamond district of the northwestern Slave (Nunavut), the Ekati kimberlite from the central Slave (NWT) and the Munn Lake kimberlite of the southeastern Slave (NWT). Samples from the Artemisia Suite have a range of bulk composition but the majority are granitic to semi-pelitic in composition and comprise Garnet + Plagioclase + Quartz + Rutile ± K-feldspar ± Biotite and significant amounts of retrograde hydrous minerals that likely pseudomorph orthopyroxene. As well, there are accessory grains of zircon and monazite. The garnet in these samples is characterized by relatively low grossular contents. In contrast to the Artemisia xenoliths, the Ekati and Munn Lake samples are garnet-bearing mafic granulites with a primary mineralogy of Garnet + Clinopyroxene + Plagioclase ±Quartz ± Orthopyroxene ± Amphibole ± Rutile ± Ilmenite. Metamorphic conditions of the lower crust as indicated by mineral equilibria are in the 9-12 kbar range of pressures with temperatures of at least 750-800°C. In the northern Slave, Neoarchean metamorphic events are recorded at 2624±11 Ma and 2520 Ma and Paleoproterozoic metamorphic events are recorded at 2415 Ma, 2150 Ma, and 2050 Ma and weakly at 2010 Ma. The ages observed in the Artemisia suite may be showing events not seen on the surface and there is a possible correlation with rocks of the Hottah terrane or mafic dike swarms that affected the Slave craton between 2200 and 2000 Ma. Still younger Paleoproterozoic ages of 1826-1868 Ma may be related to the Wopmay orogen. The Artemisia, Ekati and Munn Lake xenolith suites investigated in this study illustrates the complexity of unravelling the history of the lower crust.
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