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Some aspects of the geochemistry of high-temperature peridotites and megacrysts from the Jagersfontein kimberlite pipe, South Africa
Bibliography: pages 188-203.
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| Format: | Thesis |
| Language: | English |
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Department of Geological Sciences
2016
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| _version_ | 1867613246040571904 |
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| access_status_str | Open Access |
| author | Hops, Jennifer Jane |
| author2 | Gurney, John J |
| author_browse | Gurney, John J Hops, Jennifer Jane |
| author_facet | Gurney, John J Hops, Jennifer Jane |
| author_sort | Hops, Jennifer Jane |
| collection | Thesis |
| description | Bibliography: pages 188-203. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/22415 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:33:05.164Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2016 |
| publishDateRange | 2016 |
| publishDateSort | 2016 |
| 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:11427/22415 Some aspects of the geochemistry of high-temperature peridotites and megacrysts from the Jagersfontein kimberlite pipe, South Africa Hops, Jennifer Jane Gurney, John J Geological Sciences Geochemistry Bibliography: pages 188-203. The Jagersfontein kimberlite contains an abundance of both deformed high-temperature peridotites and Cr-poor megacrysts. The Cr-poor megacryst suite is represented by olivine, orthopyroxene, clinopyroxene and garnet. The megacrysts show features which are unique to Jagersfontein, a particularly notable feature being the absence of ilmenite and ilmenite-silicate intergrowths. Major element and REE compositions of the Cr-poor megacryst suite are consistent with a magmatic fractionation sequence. ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios of the Cr-poor clinopyroxene megacrysts indicate a source similar to that of non-DUPAL ocean island basalts. Deformed peridotites at Jagersfontein have high calculated temperatures of equilibration (1132-1361°C), which are slightly lower but which overlap with those of the Cr-poor megacryst suite. Both the high-temperature peridotites and the Cr-poor megacrysts yield similar pressures of equilibration (51±2 kbar), indicating their association with a thermal perturbation and supporting a close spatial association between them. Olivine and pyroxenes in the high-temperature peridotites appear homogeneous, but compositional gradients were observed in several garnet porphyroclasts. These garnets show rim enrichments in TiO₂ and Na₂O. This zonation in the garnets is evidence for enrichment of the deformed peridotites shortly before kimberlite eruption. This enrichment is likely to be due to interaction with the megacryst magma. In addition, the high-temperature peridotites show a general enrichment in Fe, Ti, Na and Al with decreasing Ca/(Ca+Mg). Such features support a magmatic aureole model, in that temperature and degree of enrichment might be expected to increase with proximity to the megacryst magma body. ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios of clinopyroxene separates from the high-temperature peridotites are similar to those from oceanic peridotites. Modal abundances and olivine forsterite contents of the high-temperature peridotites are consistent with an origin as residues of partial melting events involving basalt formation. It is suggested that partial melting events, in the upper mantle beneath Jagersfontein, resulted in the formation of a depleted protolith which underplated the base of the Archaean lithosphere. This depleted protolith was subsequently enriched by interaction with the Cr-poor megacryst magma just prior to kimberlite eruption. The high-temperature peridotites therefore represent samples from the base of the lithosphere rather than from the convecting asthenosphere. 2016-11-02T09:07:59Z 2016-11-02T09:07:59Z 1989 Doctoral Thesis Doctoral PhD http://hdl.handle.net/11427/22415 eng application/pdf Department of Geological Sciences Faculty of Science University of Cape Town |
| spellingShingle | Geological Sciences Geochemistry Hops, Jennifer Jane Some aspects of the geochemistry of high-temperature peridotites and megacrysts from the Jagersfontein kimberlite pipe, South Africa |
| thesis_degree_str | Doctoral |
| title | Some aspects of the geochemistry of high-temperature peridotites and megacrysts from the Jagersfontein kimberlite pipe, South Africa |
| title_full | Some aspects of the geochemistry of high-temperature peridotites and megacrysts from the Jagersfontein kimberlite pipe, South Africa |
| title_fullStr | Some aspects of the geochemistry of high-temperature peridotites and megacrysts from the Jagersfontein kimberlite pipe, South Africa |
| title_full_unstemmed | Some aspects of the geochemistry of high-temperature peridotites and megacrysts from the Jagersfontein kimberlite pipe, South Africa |
| title_short | Some aspects of the geochemistry of high-temperature peridotites and megacrysts from the Jagersfontein kimberlite pipe, South Africa |
| title_sort | some aspects of the geochemistry of high temperature peridotites and megacrysts from the jagersfontein kimberlite pipe south africa |
| topic | Geological Sciences Geochemistry |
| url | http://hdl.handle.net/11427/22415 |
| work_keys_str_mv | AT hopsjenniferjane someaspectsofthegeochemistryofhightemperatureperidotitesandmegacrystsfromthejagersfonteinkimberlitepipesouthafrica |