Computer Science
Scientific paper
Dec 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986e%26psl..81...29r&link_type=abstract
Earth and Planetary Science Letters, Volume 81, Issue 1, p. 29-45.
Computer Science
46
Scientific paper
The Ronda Ultramafic Complex in southern Spain represents a piece of the Earth's mantle which has been tectonically emplaced into the crust. Nd and Sr isotopic analyses are presented for leached, hand-picked Cr-diopside separates prepared from 15 rock and 18 river sediment samples from Ronda. These results demonstrate that within this small, contiguous body there exists the entire range of Nd isotopic compositions, and much of the range of Sr compositions, found in rocks derived from the sub-oceanic mantle. The sediment cpx samples show that the average isotopic composition of the massif becomes progressively less ``depleted'' moving from SW to NE along the long axis of the massif. The rock cpx samples document 143Nd/144Nd variations from 0.5129 to 0.5126 and 87Sr/86Sr variations from 0.7031 to 0.7039 within a uniform outcrop less than 10 m in extent. Thus, extreme isotopic fluctuations exist over a wide range of wavelengths. Sr and Nd isotopes are generally inversely correlated, forming a trend on a Nd-Sr diagram that sharply crosscuts that of the ``mantle array''.
Many of the 143Nd/144Nd values, and all of the Sm/Nd values, from one section of the massif are lower than that SCV015SCV0 of the bulk earth, implying that this region existed, or was influenced by a component which existed, in a LREE-enriched environment for a significant period of time. Among the sediment cpxs there is a positive correlation between 143Nd/144Nd and 147Sm/144Nd. The rock cpx separates display considerably more scatter. A simple, single-stage differentiation event starting with a uniform mantle source cannot explain these results. At least one episode of mixing with a LREE-enriched component is required. If these results from Ronda are typical of the upper mantle, basalts with different isotopic compositions need not derive from spatially separated mantle sources.
Reisberg Laurie
Zindler Alan
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