• journal_title：Geology
• Contributor：Chris Harris ; Andrew M. Whittingham ; Simon C. Milner ; Richard A. Armstrong
• Publisher：Geological Society of America
• Date：1990-
• Format：text/html
• Language：en
• Identifier：10.1130/0091-7613(1990)018<1119:OIGOTS>2.3.CO;2
• journal_abbrev：Geology
• issn：0091-7613
• volume：18
• issue：11
• firstpage：1119

Oxygen isotope ratios of pyroxene phenocrysts in the silicic volcanic rocks from the Cretaceous Etendeka-Paraná flood basalt province (Namibia, South America) are believed to reflect the δ¹⁸O values of the original magmas. We recognize a high δ¹⁸O value type (δ¹⁸O pyroxene ∼+10‰) found in the south of both regions, and a low δ¹⁸O value type (δ¹⁸O pyroxene ∼ +6.5‰) found in the north. Other differences between these two rhyolite types include higher concentrations of incompatible elements and lower initial ⁸⁷Sr/⁸⁶Sr ratios in the low δ¹⁸O value type. We suggest that the regional distribution of rhyolite types reflects differences in source composition, which can best be explained if the sources are lower crustal, Late Proterozoic mobile belt material (high δ¹⁸O) and Archean lower crust (low δ¹⁸O).