Abstract
We present new Sr, Th, and O isotopic results on recent olivine tholeiites and quartz tholeiites from the active rift zones in Iceland. Our data show a negative correlation between 87Sr/ 86Sr ratios and δ 18O values, and a positive correlation between ( 230Th/ 232Th) ratios and δ 18O. These covariations of isotopic ratios strongly support the model proposed by Oskarsson et al. (1982) [1]; which involves a mixing of mantle-derived magmas with crustal silicic magmas produced by melting of old hydrothermally altered rocks under central volcanoes. The hybrid magmas have quartz tholeiite compositions. Thus a large part of the Iceland geochemical anomaly is probably inherited from interaction of the primitive magmas (P-type tholeiites) with the Icelandic crust, and the mantle isotopic heterogeneities in the Icelandic “mantle plume” seem to be rather small.
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