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Conflicting Sm-Nd whole rock and U-Pb zircon ages for Archean lavas from Newton Township, Abitibi Belt, Ontario |
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| Authors: | A Cattell TE Krogh NT Arndt |
| Institution: | aMax-Planck-Institut für Chemie, Postfach 3060, D-6500 Mainz F.R.G. bDepartment of Geology, The University, Southampton England cGeochronology Laboratory, Royal Ontario Museum, 100 Queen's Park, Toronto, Ont. M5S 2C6 Canada |
| Abstract: | Archean komatiitic and tholeiitic lavas from Newton Township, Ontario, have a sufficient range of Sm-Nd ratios to define a well-constrained line on the normal 143Nd/144Nd vs. 147Sm/144Nd isochron plot. The data give an isochron age of 2826 ± 64Ma, and an initial εNdof+2.65 ± 0.26. However, U-Pb analysis of zircons from a dacitic volcaniclastic that underlies the komatiite-tholeiite suite give an age of 2697 ± 1.1Ma. There is strong evident that the zircon age is the eruption age, suggesting that the older Sm-Nd age is incorrect and probably results from mixing between isotopically distinct mantle sources. At the time of eruption, the sources had εNd values from about +4.2 to +1.6, indicating that the Archean mantle in this area was markedly heterogeneous and not uniformly depleted. |
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