Computer Science
Scientific paper
Mar 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989e%26psl..92..207e&link_type=abstract
Earth and Planetary Science Letters, Volume 92, Issue 2, p. 207-218.
Computer Science
23
Scientific paper
Highly magnesian Jurassic picrite basalts from the Nuanetsi area of southeastern Zimbabwe are close to primary mantle melts, not substantially modified by high level fractionation processes. The lavas display a wide variation in isotope ratios and incompatible trace element abundances, which may be attributed to a heterogeneous mantle source. Sm-Nd isotope results, on samples carefully selected to be thoroughly representative of the chemical variation within the whole suite, reveal a late Proterozoic isochron. One possibility is that this represents a mantle isochron corresponding to the last episode of Sm-Nd fractionation within a lithospheric source. Alternatively, binary mixing might explain the apparent isochron, but there are problems identifying a mantle reservoir with sufficiently high Sm/Nd ratios. In either case a significant role for an ancient sub-crustal lithospheric source is implied. Rb-Sr data do not lie on a well-defined isochron, and probably reflect Rb-Sr fractionation at, or close to, the time of eruption. Pb isotope data are broadly consistent with the late Proterozoic age. The apparent age of the mantle isochron is similar to that of a crust-forming event in the Natal-Namaqualand belt, which may indicate coupled evolution of the continental crust and lithospheric mantle.
Cox K. G.
Ellam Rob M.
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