New geochemical data consisting of major and 15 trace element analyses are presented for 41 rocks from three andesitic and associated basaltic rock occurrences in the North Eastern Cape Province. These include the Pronksberg, Belmore and Roodehoek localities. Field evidence suggests that the three andesites were emplaced during the early stages of Karoo volcanicity. Geochemical variations within the Pronksberg and Roodehoek andesite are small, manifesting the undifferentiated nature of the magmas. Variations within the Belmore andesite are interpreted as representing fractionation of orthopyroxene, accompanied by only minor plagioclase fractionation. Differences in trace element concentrations and inter-element ratios between the andesites and associated basalts of the Pronksberg and Belmore volcanic suites precludes the possibility of the two rock types being genetically related. Geochemical differences constrain the possibility of the three andesites being cogenetic. Magmatic processes resulting in their formation are, however, thought to be similar. The differences in chemistry between the Pronksberg Basalt (High K Type) and Pronksberg Basalt (Drumbo Type) are interpreted as representing the combined influence of weathering, the presence of amygdales and the within-flow variations of alkali elements on the Pronksberg Basalt (High K Type). Similarities in petrography and chemistry justifies a correlation of the Pronksberg Basalt (Drumbo Type) with the Drumbo Basalt Member in the Barkly East area. Data for the Drumbo Basalt (This study) in the Barkly East area confirms and complements previously presented data. Normative chemistry and strontium isotope data indicate a process involving crustal assimilation or melting of crustal rocks as being the most likely explanation for the genesis of the Karoo andesites / KMBT_363 / Adobe Acrobat 9.53 Paper Capture Plug-in
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:rhodes/vital:4902 |
| Date | 11 February 2013 |
| Creators | Rumble, Keith Christopher |
| Publisher | Rhodes University, Faculty of Science, Geology |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis, Masters, M.Sc |
| Format | 180 p, pdf |
| Rights | Rumble, Keith Christopher |
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