Ultra-depleted, shallow cratonic mantle beneath West Greenland: dunitic xenoliths from Ubekendt Ejland

Publication Status is "Submitted" Or "In Press: 
LDEO Publication: 
Publication Type: 
Year of Publication: 
2006
Editor: 
Journal Title: 
Contributions to Mineralogy and Petrology
Journal Date: 
Sep
Place Published: 
Tertiary Title: 
Volume: 
152
Issue: 
3
Pages: 
335-347
Section / Start page: 
Publisher: 
ISBN Number: 
0010-7999
ISSN Number: 
Edition: 
Short Title: 
Accession Number: 
ISI:000239813700006
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Abstract: 

Dunitic xenoliths from late Palaeogene, alkaline basalt flows on Ubekendt Ejland, West Greenland contain olivine with 100 x Mg/(Mg + Fe), or Mg#, between 92.0 and 93.7. Orthopyroxene has very low Al2O3 and CaO contents (0.024-1.639 and 0.062-0.275 wt%, respectively). Spinel has 100 x Cr/(Cr + Al), or Cr#, between 46.98 and 95.67. Clinopyroxene is absent. The osmium isotopic composition of olivine and spinel mineral separates shows a considerable span of Os-187/Os-188 values. The most unradiogenic Os-187/Os-188 value of 0.1046 corresponds to a Re-depletion age of ca. 3.3 Gy, while the most radiogenic value of 0.1336 is higher than present-day chondrite. The Os isotopic composition of the xenoliths is consistent with their origin as restites from a melt extraction event in the Archaean, followed by one or more subsequent metasomatic event(s). The high Cr# in spinel and low modal pyroxene of the Ubekendt Ejland xenoliths are similar to values of some highly depleted mantle peridotites from arc settings. However, highly depleted, arc-related peridotites have higher Cr# in spinel for a given proportion of modal olivine, compared to cratonic xenolith suites from Greenland, which instead form coherent trends with abyssal peridotites, dredged from modern mid-ocean ridges. This suggests that depleted cratonic harzburgites and dunites from shallow lithospheric mantle represent the residue from dry melting in the Archaean.

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074LMTimes Cited:3Cited References Count:50

DOI: 
DOI 10.1007/s00410-006-0109-0