Abstract
We present the first oxygen fugacity (fO2) profile through the cratonic lithospheric mantle under the Panda kimberlite (Ekati Diamond Mine) in the Lac de Gras kimberlite field, central Slave Craton, northern Canada. Combining this data with new and existing data from garnet peridotite xenoliths from an almost coeval kimberlite (A154-N) at the nearby Diavik Diamond Mine demonstrates that the oxygen fugacity of the Slave cratonic mantle varies by several orders of magnitude as a function of depth and over short lateral distances. The lower part of the diamond-bearing Slave lithosphere (>120–130 km deep) has been oxidized by up to 4 log units in fO2, and this is clearly linked to metasomatic enrichment. Such coupled enrichment and oxidation was likely caused by infiltrating carbonate-bearing, hydrous, silicate melts in the presence of diamond, a process proposed to be critical for “pre-conditioning” deep lithospheric mantle and rendering it suitable for later generation of kimberlites and other SiO2-undersaturated magmas.
Highlights
In the absence of partial melts or fluids, the fO2 of the Earth’s upper mantle is controlled internally by redox sensitive reactions involving Fe-bearing mineral components in spinel, garnet and pyroxenes in which Fe has variable oxidation states
Fresh garnet peridotite xenoliths recovered from the Panda kimberlite on the Ekati Diamond Mine lease and from the A154-North (A154-N) pipe on the nearby Diavik lease were investigated
The two host kimberlites were emplaced at 53.3 ± 0.6 Ma (Panda)[15] and 56.0 ± 0.7 Ma (A154-N)[16], and are located about 30 km apart near the edge of Lac de Gras in the central Slave Craton
Summary
In the absence of partial melts or fluids, the fO2 of the Earth’s upper mantle is controlled internally by redox sensitive reactions involving Fe-bearing mineral components in spinel, garnet and pyroxenes in which Fe has variable oxidation states. Because of the positive molar volume changes of these reactions[2,3,4] fO2 should decrease steadily with increasing pressure (depth) in the upper ≈250 km of the peridotite-dominated mantle. Experimental calibrations of redox controlling reactions in garnet peridotite assemblages[2, 3], coupled with determinations of the Fe3+/∑Fe of garnet from peridotite xenoliths transported by kimberlite magmas to the surface from depths as great as 220 km (~7 GPa), enable determination of the fO2 of the cratonic mantle lithosphere. We have determined the oxygen fugacities recorded by garnet peridotite xenoliths hosted by two nearly coeval and diamondiferous kimberlites from the geographically close Ekati and Diavik mine leases in the central Slave Craton, Canada. No redox data has previously been reported from xenoliths from the Panda kimberlite
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
