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The geochemistry and petrogenesis of the Saltpeterkop carbonatite complex near Sutherland, Northern Cape, South Africa
The Saltpeterkop Carbonatite Complex is a Late Cretaceous (≈76 Ma) volcanic and shallow intrusive magmatic feature located approximately 20 km southeast of Sutherland in the Northern Cape. It is unusual among southern African carbonatite complexes in that it has not been deeply eroded, and retains a...
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| Format: | Thesis |
| Language: | English |
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Department of Geological Sciences
2019
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| _version_ | 1867613285223759872 |
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| access_status_str | Open Access |
| author | Marageni, Manoka |
| author2 | Janney, Philip |
| author_browse | Janney, Philip Marageni, Manoka |
| author_facet | Janney, Philip Marageni, Manoka |
| author_sort | Marageni, Manoka |
| collection | Thesis |
| description | The Saltpeterkop Carbonatite Complex is a Late Cretaceous (≈76 Ma) volcanic and shallow intrusive magmatic feature located approximately 20 km southeast of Sutherland in the Northern Cape. It is unusual among southern African carbonatite complexes in that it has not been deeply eroded, and retains a significant vestige of its original volcanic features. The main geologic expression of the Complex is a ≈1.5 km diameter tuff ring, located on top of prominently updomed and fractured Beaufort Group (Karoo) sediments, that appears to have formed as the result of a major diatreme-type eruption. The volcaniclastic breccias making up the tuff ring have been heavily altered and silicified by hydrothermal activity, and thick (mm to tens of cm) Fe oxide-rich crusts, which appear to represent the alteration products of Fe-rich carbonatites, are common in this area. Outside of the central ring structure are numerous shallow intrusions (dykes, sills and irregular shapes), satellite breccia pipes and pipe-shaped intrusions that host fresh to only moderately altered igneous rocks. The main igneous rock types include (in decreasing order of abundance): carbonatite, potassic trachyte, olivine melilitite and ultramafic lamprophyre. This thesis provides the first detailed petrographic and geochemical description of these rocks (e.g., major and trace elements) and attempts to explain several aspects of their petrogenesis. The olivine melilitites and ultramafic lamprophyres are the most primitive igneous rocks in the complex and have experienced only minor to moderate extents of differentiation, respectively. They apppear to have been derived by low-degrees of partial melting of a carbonated, likely phlogopite-bearing mantle source. The lamprophyres appear to have been derived by melting at shallower depths than the melilitites based on REE constraints. The carbonatites range from relatively primitive to highly differentiated and they form a nearly continuous compositional range with the ultramafic lamprophyres and melilitites. This seems to argue against a major role for liquid immiscibility in their origin. Their REE content (up to 2 wt.% total REE oxides) correlates with their extent of differentiation. The potassic trachytes are plausibly linked to melts of mafic lower continental crust that has been metasomatised by hydrous potassium-rich carbonatitic melts and which have experienced significant fractional crystallization and assimilation of upper crustal sedimentary rocks during emplacement. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/29818 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:33:41.762Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2019 |
| publishDateRange | 2019 |
| publishDateSort | 2019 |
| publisher | Department of Geological Sciences |
| publisherStr | Department of Geological Sciences |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/29818 The geochemistry and petrogenesis of the Saltpeterkop carbonatite complex near Sutherland, Northern Cape, South Africa Marageni, Manoka Janney, Philip Greyling, Lynnette Geological Science Geochemistry The Saltpeterkop Carbonatite Complex is a Late Cretaceous (≈76 Ma) volcanic and shallow intrusive magmatic feature located approximately 20 km southeast of Sutherland in the Northern Cape. It is unusual among southern African carbonatite complexes in that it has not been deeply eroded, and retains a significant vestige of its original volcanic features. The main geologic expression of the Complex is a ≈1.5 km diameter tuff ring, located on top of prominently updomed and fractured Beaufort Group (Karoo) sediments, that appears to have formed as the result of a major diatreme-type eruption. The volcaniclastic breccias making up the tuff ring have been heavily altered and silicified by hydrothermal activity, and thick (mm to tens of cm) Fe oxide-rich crusts, which appear to represent the alteration products of Fe-rich carbonatites, are common in this area. Outside of the central ring structure are numerous shallow intrusions (dykes, sills and irregular shapes), satellite breccia pipes and pipe-shaped intrusions that host fresh to only moderately altered igneous rocks. The main igneous rock types include (in decreasing order of abundance): carbonatite, potassic trachyte, olivine melilitite and ultramafic lamprophyre. This thesis provides the first detailed petrographic and geochemical description of these rocks (e.g., major and trace elements) and attempts to explain several aspects of their petrogenesis. The olivine melilitites and ultramafic lamprophyres are the most primitive igneous rocks in the complex and have experienced only minor to moderate extents of differentiation, respectively. They apppear to have been derived by low-degrees of partial melting of a carbonated, likely phlogopite-bearing mantle source. The lamprophyres appear to have been derived by melting at shallower depths than the melilitites based on REE constraints. The carbonatites range from relatively primitive to highly differentiated and they form a nearly continuous compositional range with the ultramafic lamprophyres and melilitites. This seems to argue against a major role for liquid immiscibility in their origin. Their REE content (up to 2 wt.% total REE oxides) correlates with their extent of differentiation. The potassic trachytes are plausibly linked to melts of mafic lower continental crust that has been metasomatised by hydrous potassium-rich carbonatitic melts and which have experienced significant fractional crystallization and assimilation of upper crustal sedimentary rocks during emplacement. 2019-02-27T11:21:18Z 2019-02-27T11:21:18Z 2018 2019-02-25T12:37:39Z Master Thesis Masters MSc http://hdl.handle.net/11427/29818 eng application/pdf Department of Geological Sciences Faculty of Science University of Cape Town |
| spellingShingle | Geological Science Geochemistry Marageni, Manoka The geochemistry and petrogenesis of the Saltpeterkop carbonatite complex near Sutherland, Northern Cape, South Africa |
| thesis_degree_str | Master's |
| title | The geochemistry and petrogenesis of the Saltpeterkop carbonatite complex near Sutherland, Northern Cape, South Africa |
| title_full | The geochemistry and petrogenesis of the Saltpeterkop carbonatite complex near Sutherland, Northern Cape, South Africa |
| title_fullStr | The geochemistry and petrogenesis of the Saltpeterkop carbonatite complex near Sutherland, Northern Cape, South Africa |
| title_full_unstemmed | The geochemistry and petrogenesis of the Saltpeterkop carbonatite complex near Sutherland, Northern Cape, South Africa |
| title_short | The geochemistry and petrogenesis of the Saltpeterkop carbonatite complex near Sutherland, Northern Cape, South Africa |
| title_sort | geochemistry and petrogenesis of the saltpeterkop carbonatite complex near sutherland northern cape south africa |
| topic | Geological Science Geochemistry |
| url | http://hdl.handle.net/11427/29818 |
| work_keys_str_mv | AT maragenimanoka thegeochemistryandpetrogenesisofthesaltpeterkopcarbonatitecomplexnearsutherlandnortherncapesouthafrica AT maragenimanoka geochemistryandpetrogenesisofthesaltpeterkopcarbonatitecomplexnearsutherlandnortherncapesouthafrica |