Other
Scientific paper
Feb 1985
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985e%26psl..72..163d&link_type=abstract
Earth and Planetary Science Letters, Volume 72, Issue 2-3, p. 163-174.
Other
20
Scientific paper
Oxygen, Sr and Nd isotopic compositions for 29 volcanic samples from the Lesser Antilles are reported. These span a considerable range in δ18O, from values similar to those of mantle-derived lavas (δ18O = +6.6), to δ18O = +14.0. Although the highest δ18O results are obtained from evolved andesites and dacites, there is no clear correlation between δ18O and SiO2. An attempt is made to eliminate the effects of varying magma chemistry on δ18O (through differentiation) by normalising to the chemical index of Garlick [1]. This enables the effects on δ18O of processes other than magmatic fractionation to be more clearly assessed. It is concluded that the range in δ18O values measured cannot result from hydrothermal interaction or weathering alone, although limited alteration of a few samples may be responsible for some scatter in the oxygen isotope data. When δ18O is plotted against radiogenic isotopic compositions, well correlated trends are observed. δ18O increases with increasing 87Sr/86Sr and decreasing 143Nd/144Nd. Such behaviour is consistent with the contamination of mantle-derived magmas by variable amounts of an ancient crustal component. The shapes of mixing curves defining this process suggest that contamination occurs largely within the arc crust. Constraints from geochemical and geophysical data suggest that a terrigenous sediment, intercalated within the arc crust, is assimilated. However, subsequent fractional crystallisation at more shallow levels in the crust has obscured any chemical trends which might have resulted from combined assimilation-fractional crystallisation. Furthermore, it is suggested that the mantle-derived magma has already undergone source contamination by the introduction of a ``slab-derived fluid'' into the overlying mantle wedge.
Present address: Department of Geology, Southern Methodist University, Dallas, TX 75275, U.S.A.
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