Pb and Nd isotopic study of two archean komatiitic flows from Alexo, Ontario

Details Pb and Nd isotopic study of two archean komatiitic flows from Alexo, Ontario Pb and Nd isotopic study of two archean komatiitic flows from Alexo, Ontario

Oct 1984

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984gecoa..48.1965d&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 48, Issue 10, pp.1965-1972

Computer Science

20

Scientific paper

Isotopic analysis of two Archean komatiitic flows from Alexo, Ontario, gives a Pb-Pb isochron age of 2690 ± 15 Ma and a Sm-Nd isochron age of 2752 ± 87 Ma. These ages agree well with U-Pb zircon ages from underlying and overlying volcanics. The variations in element ratios that define the isochrons were not produced during crystallization of the lavas. The spread in U/Pb was caused by submarine alteration soon after eruption, and the spread in Sm/Nd resulted from (a) differences in the composition of the residue of melting, and (b) contamination of the upper komatiite flow through thermal erosion of the lower flow. The 147 Sm/ 144 Nd ratio of uncontaminated komatiite is 0.25 which reflects the depleted nature of its mantle source. The Th/U ratio of about 3.4 is probably also representative of depleted mantle. The initial Nd of +2.44 ± 0.51 indicates that the mantle depletion took place long before magma formation.

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