Journal
EARTH AND PLANETARY SCIENCE LETTERS
Volume 283, Issue 1-4, Pages 48-58Publisher
ELSEVIER
DOI: 10.1016/j.epsl.2009.03.023
Keywords
Re-Os isotopes; kimberlite-borne xenolith; eclogite; pyroxenite; sulfide petrology; Slave Craton
Categories
Funding
- NSERC
- Diavik Diamond Mines Inc.
- Macquarie University International Postgraduate Award and Postgraduate Research Fund (SA)
- Kennecott Canada Inc.
- ARC Large and Discovery Grants
- ARC LIEF
- DEST Systemic Infrastructure Grants
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We characterized single sulfides in eclogite and pyroxenite xenoliths from the Diavik kimberlites (central Slave Craton, Canada) with regard to their petrography, major-element composition and Re-Os isotope systematics. Together with trace-element and Re-Os isotope compositions of whole rocks, these data allow identification of the major Re-Os host phases and provide constraints on the origin(s) of sulfides in these samples. The majority of sulfide minerals contain 8 to 28 at.% Ni, with intragranular sulfides having on average significantly lower contents (similar to 6 at.%) than intergranular sulfides (similar to 12 at.%). These high Ni-sulfides are not in equilibrium with an eclogitic assemblage and were likely introduced from a peridotitic source subsequent to eclogite formation. In contrast, their Re-Os abundances and Re/Os ratios (average similar to 825 ppb, 190 ppb and 10, respectively) overlap those of primary eclogitic sulfides. These conflicting compositional characteristics may document open-system disequilibrium processes accompanying the introduction of sulfides into eclogites. The general association of high Os-187/Os-188 with high Re-187/Os-188 of sulfides in three low-temperature eclogite xenoliths suggests that the addition is not young. In contrast, sulfides in a high-temperature eclogite plot on a similar to 90 Ma errorchron with radiogenic initial Os-187/Os-188, perhaps indicative of young introduction of sulfides from a deep enriched source. Sulfides in a single pyroxenite xenolith have Ni, Re and Os contents intermediate between pristine eclogitic and peridotitic sulfides, and correlated Re-Os isotope systematics defining an age of 1.84 +/- 0.14 Ga with a radiogenic Os-187/Os-188, (0.16 +/- 0.01). The age and Os-187/Os-188(i) are identical to those obtained for eclogitic sulfide inclusions in diamonds from Diavik, thus supporting a link between eclogite and pyroxenite formation. Several eclogite and pyroxenite whole rocks show evidence for addition of secondary sulfides, but many plot on Paleoproterozoic Re-Os age arrays - particularly so at low Re/Os - coincident with previously determined ages using Lu-Hf and Pb-Pb techniques. They may represent sulfide-poor varieties that did not suffer secondary sulfide addition and that may be best suited to yielding meaningful Re-Os ages. (C) 2009 Elsevier B.V. All rights reserved.
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