The geochemical stratigraphy of the volcanic rocks of the Witwatersrand triad in the Klerksdorp area, Transvaal
- Authors: Bowen, Teral Barbara
- Date: 1985 , 2013-03-14
- Subjects: Lava -- South Africa -- Transvaal , Igneous rocks -- South Africa -- Transvaal , Geochemistry -- South Africa -- Transvaal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4932 , http://hdl.handle.net/10962/d1004932 , Lava -- South Africa -- Transvaal , Igneous rocks -- South Africa -- Transvaal , Geochemistry -- South Africa -- Transvaal
- Description: This study lias initiated with the aim of identifying the existence of any geochemical criteria which may be used to distinguish between the various volcanic formations within the Witwatersrand triad. The Witwatersrand triad comprises three sequences: the Dominion Group at the base, the Witwatersrand Supergroup in the middle, and the Ventersdorp Supergroup at the top. It is underlain by Archaean basement rocks, and covered by rocks of the Transvaal sequence. The Dominion Group consists of the sedimentary Rhenosterspruit quartzite Formation at the base, overlain by a bimodal component of the Syferfontein Porphyry succession of lavas. Basaltic lavas are the major component of the Rhenosterhoek Formation, while the overlying Formation consists primarily of dacitic porphyries. Intercalations of one lava type within the other are common, however, so each formation is not the exclusive domain of only one lava type. The Witwatersrand Supergroup, a predominantly argillaceous and arenaceous sequence, contains two narrow volcanic horizons, one of wbich, the Jeppestown Amygdaloid (now Crown Formation), consisting of tholeiitic andesites, occurs in the study area. The overlying Ventersdorp Supergroup has, at its base, the basaltic Klipriviersberg Group, of which four out of six formations are present in the study area, namely, the Alberton, Orkney, Loraine and Edenville Formations. This group is succeeded unconformably by the PIatberg Group, consisting of the sedimentary Kameel doorns Formation, followed by the (informal) Goedgenoeg, Makwassie Quartz Porphyry and Rietgat Formations. The Goedgenoeg and Rietgat Formations are basaltic, whil e the Mawassie rocks range from basaltic to dacitic, the majority being tholeiitic andesites and andesites . The Pniel sequence at the top of the Ventersdorp Supergroup consists of the sedimentary Bothaville Formation, and the Allarridge Formation, the lavas of which are basaltic with some andesitic tendencies. A well-defined geochemical stratigraphy was found to exist. From the eleven volcanic formations examined, nine distinct geochemical units emerged, as the Loraine and Edenville Formations were found to have the same geochemical characteristics, as did the Goedgenoeg and Rietgat Formations. Despite having undergone law-grade greenschist facies metamorphism, very clear variation patterns with height are displayed by the immobile elements Ti, P, Kb, Zr and Y, and the light rare earth elements La, Ce and Nd. In contrast, much scatter was observed in the variation patterns of Na, K, Mn, Ba and Rb. Three techniques were employed to effect discrimination between formations - orthosonal discrimination, interelement and ratio vs ratio plots, and discriminant analysis. Confidence limits placed on normal probability plots served to isolate outlier samples for further examination by the various discrimination techniques. A successful test of the efficacy of the discrimination techniques was afforded when fourteen samples from an unknown succession were positively identified as representative of the Klipriviersberg Group
- Full Text:
- Date Issued: 1985
- Authors: Bowen, Teral Barbara
- Date: 1985 , 2013-03-14
- Subjects: Lava -- South Africa -- Transvaal , Igneous rocks -- South Africa -- Transvaal , Geochemistry -- South Africa -- Transvaal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4932 , http://hdl.handle.net/10962/d1004932 , Lava -- South Africa -- Transvaal , Igneous rocks -- South Africa -- Transvaal , Geochemistry -- South Africa -- Transvaal
- Description: This study lias initiated with the aim of identifying the existence of any geochemical criteria which may be used to distinguish between the various volcanic formations within the Witwatersrand triad. The Witwatersrand triad comprises three sequences: the Dominion Group at the base, the Witwatersrand Supergroup in the middle, and the Ventersdorp Supergroup at the top. It is underlain by Archaean basement rocks, and covered by rocks of the Transvaal sequence. The Dominion Group consists of the sedimentary Rhenosterspruit quartzite Formation at the base, overlain by a bimodal component of the Syferfontein Porphyry succession of lavas. Basaltic lavas are the major component of the Rhenosterhoek Formation, while the overlying Formation consists primarily of dacitic porphyries. Intercalations of one lava type within the other are common, however, so each formation is not the exclusive domain of only one lava type. The Witwatersrand Supergroup, a predominantly argillaceous and arenaceous sequence, contains two narrow volcanic horizons, one of wbich, the Jeppestown Amygdaloid (now Crown Formation), consisting of tholeiitic andesites, occurs in the study area. The overlying Ventersdorp Supergroup has, at its base, the basaltic Klipriviersberg Group, of which four out of six formations are present in the study area, namely, the Alberton, Orkney, Loraine and Edenville Formations. This group is succeeded unconformably by the PIatberg Group, consisting of the sedimentary Kameel doorns Formation, followed by the (informal) Goedgenoeg, Makwassie Quartz Porphyry and Rietgat Formations. The Goedgenoeg and Rietgat Formations are basaltic, whil e the Mawassie rocks range from basaltic to dacitic, the majority being tholeiitic andesites and andesites . The Pniel sequence at the top of the Ventersdorp Supergroup consists of the sedimentary Bothaville Formation, and the Allarridge Formation, the lavas of which are basaltic with some andesitic tendencies. A well-defined geochemical stratigraphy was found to exist. From the eleven volcanic formations examined, nine distinct geochemical units emerged, as the Loraine and Edenville Formations were found to have the same geochemical characteristics, as did the Goedgenoeg and Rietgat Formations. Despite having undergone law-grade greenschist facies metamorphism, very clear variation patterns with height are displayed by the immobile elements Ti, P, Kb, Zr and Y, and the light rare earth elements La, Ce and Nd. In contrast, much scatter was observed in the variation patterns of Na, K, Mn, Ba and Rb. Three techniques were employed to effect discrimination between formations - orthosonal discrimination, interelement and ratio vs ratio plots, and discriminant analysis. Confidence limits placed on normal probability plots served to isolate outlier samples for further examination by the various discrimination techniques. A successful test of the efficacy of the discrimination techniques was afforded when fourteen samples from an unknown succession were positively identified as representative of the Klipriviersberg Group
- Full Text:
- Date Issued: 1985
The petrology of the basalts of the Dordabis Formation in the vicinity of Dordabis in central S.W.A./Namibia|
- Authors: Williams-Jones, Ian Eric
- Date: 1985 , 2013-03-14
- Subjects: Basalt -- Namibia , Petrology -- Namibia , Geochemistry -- Namibia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5062 , http://hdl.handle.net/10962/d1013277
- Description: The late Proterozoic volcanic and sedimentary sequence in the Dordabis area SWA/Namibia has been named the Dordabis Formation and subdivided, on the basis of field, petrological and petrographic evidence, into the Opdam and Bitterwater Members. Relict phases including augite and minor plagioclase only occur in the Bitterwater metalavas, as recrystallisation is complete in the Opdam metal avas. The composition of the relict feldspars ranges from labradorite in the ophitic basalts to oligoclase in the blastoporphyritic metalavas. The feldspars in the Opdam member are albitic in composition (An content 0,0 to 1,7) . Epidote compositions are typical of those occurring in metabasic rocks. Samples with high-iron whole-rock compositions are accompanied by high concentrations of Fe3+ in concomitant epidotes. Sixty three samples were analysed using X-ray fluorescence spectrometry to determine concentrations of major and 16 trace elements. Although greenschist facies metamorphism, metasomatism and shearing have produced scatter in the more mobile element concentrations, variation trends in other elements closely resemble modelled low-pressure fractional crystallisation trends. The Dordabis metalavas are petrologically classified as sub-alkaline, tholeiitic continental basalts. Low K/Rb ratios and low ratios of less incompatible to more incompatible elements probably reflect a source that has either been metasomati ca lly enriched or that has undergone little previous partial melting. Overlapping whole-rock variation trends indicate that the generally more evolved Opdam and primitive tholeiitic Bittenwater lavas are cogenetic. A comparison of the Dordabis Formation with the Sinclair Sequence and the Koras Group shows that their ages, petrology, petrography, associ a ted sedimentary suites and depositional environments are similar. It is concluded that they may possibly be coeval equivalents.
- Full Text:
- Date Issued: 1985
- Authors: Williams-Jones, Ian Eric
- Date: 1985 , 2013-03-14
- Subjects: Basalt -- Namibia , Petrology -- Namibia , Geochemistry -- Namibia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5062 , http://hdl.handle.net/10962/d1013277
- Description: The late Proterozoic volcanic and sedimentary sequence in the Dordabis area SWA/Namibia has been named the Dordabis Formation and subdivided, on the basis of field, petrological and petrographic evidence, into the Opdam and Bitterwater Members. Relict phases including augite and minor plagioclase only occur in the Bitterwater metalavas, as recrystallisation is complete in the Opdam metal avas. The composition of the relict feldspars ranges from labradorite in the ophitic basalts to oligoclase in the blastoporphyritic metalavas. The feldspars in the Opdam member are albitic in composition (An content 0,0 to 1,7) . Epidote compositions are typical of those occurring in metabasic rocks. Samples with high-iron whole-rock compositions are accompanied by high concentrations of Fe3+ in concomitant epidotes. Sixty three samples were analysed using X-ray fluorescence spectrometry to determine concentrations of major and 16 trace elements. Although greenschist facies metamorphism, metasomatism and shearing have produced scatter in the more mobile element concentrations, variation trends in other elements closely resemble modelled low-pressure fractional crystallisation trends. The Dordabis metalavas are petrologically classified as sub-alkaline, tholeiitic continental basalts. Low K/Rb ratios and low ratios of less incompatible to more incompatible elements probably reflect a source that has either been metasomati ca lly enriched or that has undergone little previous partial melting. Overlapping whole-rock variation trends indicate that the generally more evolved Opdam and primitive tholeiitic Bittenwater lavas are cogenetic. A comparison of the Dordabis Formation with the Sinclair Sequence and the Koras Group shows that their ages, petrology, petrography, associ a ted sedimentary suites and depositional environments are similar. It is concluded that they may possibly be coeval equivalents.
- Full Text:
- Date Issued: 1985
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