Computer Science
Scientific paper
Apr 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001e%26psl.186..513p&link_type=abstract
Earth and Planetary Science Letters, Volume 186, Issue 3-4, p. 513-526.
Computer Science
11
Scientific paper
The Re-Os data on Archean komatiites from the Kostomuksha greenstone belt in the Baltic Shield are presented. This greenstone belt has been previously interpreted to represent a former oceanic plateau formed by the emplacement of an ancient plume head [Puchtel et al., Earth Planet. Sci. Lett. 155 (1998) 57-74]. Samples of flowtop breccia, spinifex-textured and cumulate komatiites and a chromite separate, all collected from the core of a 300 m deep diamond drill hole, yielded a Re-Os isochron with an age of 2795+/-40 Ma and an initial 187Os/188Os of 0.1117+/-0.0011 (γ187Os=+3.6+/-1.0). The high positive γ187Os(T) implies that the komatiites were derived from a mantle source with a time-integrated suprachondritic Re/Os ratio. Recycling of oceanic lithosphere to produce the enriched 187Os isotope signature is considered unlikely, as 15-25% crustal component is required to be incorporated into the plume source as early as 3.5-4.3 Ga. Such a substantial proportion of mafic material in the source would likely destroy the major and trace element characteristics of the komatiites. Our tentative interpretation is that the 187Os-enrichment in the Kostomuksha plume represents an outer core signature. If confirmed by the ongoing Pt-Os isotope studies, the results would provide evidence for the existence of whole-mantle convection in the late Archean, and might place constraints on the timing of core differentiation in the early Earth.
Brügmann Gerhard E.
Hofmann Albrecht W.
Puchtel Igor S.
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