Geochemie und Geochronologie des Erongo-Komplexes, Namibia

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Zusammenfassung

The Erongo complex is the largest of the Cretaceous igneous complexes in the Damaraland, Southern Etendeka Province, Namibia. Erongo is made up of a series of mainly silicic volcanic and intrusive units, like many of the Damaraland complexes, but it is unique by virtue of its size and well-preserved igneous sequence silicic magmas as well as tholeiitic and alkaline basalts.The goals of this study were to determine the ages and petrogenetic relationships of the silicic and basic units in the Erongo complex, and to contribute to understanding the magmatic evolution of the Damaraland province. As part of this investigation, Os isotope compositions were determined on basic rocks from the complex, and this is the first study of Os isotopes in the Etendeka Province. The Erongo is built up on a sequence of tholeiitic basaltic lavas which are compositionally equivalent to the Southern Etendeka flood basalts (Tafelberg type) and probably represent erosional remnants of these (see below). The felsic volcanic units at Erongo include two types of rhyodacites and one rhyolite. The most voluminous of these is the Ombu rhyodacite, which has a thickness of up to 500 m and makes up most of the topographic expression of the complex. The Ombu rhyodacite rests directly on the basal tholeiites in the southern and eastern part of the complex, but to the north and west, a second rhyodacite occurs below it, the Erongorus rhyodacite ...
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