Oxygen isotope geochemistry of the silicic volcanic rocks of the Etendeka-Parana province: Source constraints

Oxygen isotope ratios of pyroxene phenocrysts in the silicic volcanic rocks from the Cretaceous Etendeka-Parana flood basalt province (Namibia, South America) are believed to reflect the delta18O values of the original magmas. We recognize a high delta18O value type (delta18O pyroxene ~+102) found i...

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Bibliographic Details
Published in:Geology (Boulder) 1990-11, Vol.18 (11), p.1119-1121
Main Authors: Harris, Chris, Whittingham, Andrew M, Milner, Simon C, Armstrong, Richard A
Format: Article
Language:English
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Summary:Oxygen isotope ratios of pyroxene phenocrysts in the silicic volcanic rocks from the Cretaceous Etendeka-Parana flood basalt province (Namibia, South America) are believed to reflect the delta18O values of the original magmas. We recognize a high delta18O value type (delta18O pyroxene ~+102) found in the south of both regions, and a low delta18O value type (delta18O pyroxene ~ +6.52) 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 delta18O 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 delta18O) and Archean lower crust (low delta18O).
ISSN:0091-7613
DOI:10.1130/0091-7613(1990)0182.3.CO;2