Oxygen isotope geochemistry of the silicic volcanic rocks of the Etendeka/Parana province: evidence for two distinct sources

Two rhyolite types can be distinguished in the Etendeka and Parana volcanic provinces on the basis of trace elements, strontium and oxygen isotopes. The high-δ18O type must be crustally-derived, but it is more problematic to asign an origin to the lowδ18O northern rhyolites. One possibility is that the low-δ18O rhyolites are derived from the partial melting of underplated basalt, in which case some crustal contamination is required to have raised the δ18O values in the northern Etendeka rhyolites by up to 1%. A second possibility is that the northern-type rhyolites are partial melts of Rb-depleted Archaean lower crust. The second model has the advantage of having a crustal source for both rhyolite types and does not require two fundamentally different sources to be present at similar depths beneath the northern- and southern-type rhyolites. 1 fig., 5 refs