Full Text Available
Note: Clicking the button above will open the full text document at the original institutional repository in a new window.
Megacryst suite from the Salpeterkop carbonatite complex, Sutherland, Northern Cape, South Africa: an in-depth geochemical study
Presented here are major and trace element, stable (oxygen and hydrogen) and radiogenic (Sr-Nd-Pb) isotope analyses for a Cr-poor megacryst suite from the Salpeterkop complex, South Africa. The clinopyroxene, amphibole, phlogopite and ilmenite megacrysts all appear to be cogenetic, and based on know...
Saved in:
| Main Author: | |
|---|---|
| Other Authors: | |
| Format: | Thesis |
| Language: | English |
| Published: |
Department of Geological Sciences
2021
|
| Subjects: | |
| Tags: |
No Tags, Be the first to tag this record!
|
| _version_ | 1867613261286866944 |
|---|---|
| access_status_str | Open Access |
| author | Peel, Chad |
| author2 | Janney, Philip Edward |
| author_browse | Janney, Philip Edward Peel, Chad |
| author_facet | Janney, Philip Edward Peel, Chad |
| author_sort | Peel, Chad |
| collection | Thesis |
| description | Presented here are major and trace element, stable (oxygen and hydrogen) and radiogenic (Sr-Nd-Pb) isotope analyses for a Cr-poor megacryst suite from the Salpeterkop complex, South Africa. The clinopyroxene, amphibole, phlogopite and ilmenite megacrysts all appear to be cogenetic, and based on known mineral relationships and intergrowths from xenoliths in the complex, the apparent order of mineral crystallisation is as follows: phlogopite → ilmenite → amphibole → clinopyroxene. Megacrysts of amphibole and phlogopite exhibit δD and δ18O values that are aligned with these grains having crystallised from melt originating from the upper mantle. Additionally, the amphibole and phlogopite megacrysts appear have experienced dehydration styled degassing, possibly related to their exhumation. Calculated P-T conditions have the megacrysts crystallising in the lower crust, under conditions ranging from 1 to 1.5 GPa (35 to 45 km depth) and 1000 to 1250 ℃. Calculated REE melts in equilibrium with the megacryst as well as radiogenic isotope results suggest that the Salpeterkop ultramafic lamprophyres are genetically related the the SPKC megacryst suite, however, the calculated parent melt to the megacryst appears to have mixed with a HIMU component. These findings primarily affect higher Mg-number megacrysts, suggesting that this assimilation or mixing occurred during initial stages of crystallisation. Lower Mg-number megacrysts lack the variations noted in their more primitive counterparts and present more tightly defined trends. A model of formation for the megacryst suite of the Salpeterkop complex sees grains having crystallised from an SPKC ultramafic lamprophyre-like melt originating from sublithospheric/asthenospheric conditions. During ascension the melt episodically assimilates material with a HIMU signature. The high Mg-number megacryst population crystallises from this melt at lower crustal depths. Soon after assimilation halts the megacryst parent melt homogenises (or re-homogenises), with grains to crystallise from this melt forming the low-Mg megacryst population. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/32915 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:33:19.547Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2021 |
| publishDateRange | 2021 |
| publishDateSort | 2021 |
| 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:11427/32915 Megacryst suite from the Salpeterkop carbonatite complex, Sutherland, Northern Cape, South Africa: an in-depth geochemical study Peel, Chad Janney, Philip Edward geological sciences Presented here are major and trace element, stable (oxygen and hydrogen) and radiogenic (Sr-Nd-Pb) isotope analyses for a Cr-poor megacryst suite from the Salpeterkop complex, South Africa. The clinopyroxene, amphibole, phlogopite and ilmenite megacrysts all appear to be cogenetic, and based on known mineral relationships and intergrowths from xenoliths in the complex, the apparent order of mineral crystallisation is as follows: phlogopite → ilmenite → amphibole → clinopyroxene. Megacrysts of amphibole and phlogopite exhibit δD and δ18O values that are aligned with these grains having crystallised from melt originating from the upper mantle. Additionally, the amphibole and phlogopite megacrysts appear have experienced dehydration styled degassing, possibly related to their exhumation. Calculated P-T conditions have the megacrysts crystallising in the lower crust, under conditions ranging from 1 to 1.5 GPa (35 to 45 km depth) and 1000 to 1250 ℃. Calculated REE melts in equilibrium with the megacryst as well as radiogenic isotope results suggest that the Salpeterkop ultramafic lamprophyres are genetically related the the SPKC megacryst suite, however, the calculated parent melt to the megacryst appears to have mixed with a HIMU component. These findings primarily affect higher Mg-number megacrysts, suggesting that this assimilation or mixing occurred during initial stages of crystallisation. Lower Mg-number megacrysts lack the variations noted in their more primitive counterparts and present more tightly defined trends. A model of formation for the megacryst suite of the Salpeterkop complex sees grains having crystallised from an SPKC ultramafic lamprophyre-like melt originating from sublithospheric/asthenospheric conditions. During ascension the melt episodically assimilates material with a HIMU signature. The high Mg-number megacryst population crystallises from this melt at lower crustal depths. Soon after assimilation halts the megacryst parent melt homogenises (or re-homogenises), with grains to crystallise from this melt forming the low-Mg megacryst population. 2021-02-22T07:43:56Z 2021-02-22T07:43:56Z 2020 2021-02-22T07:38:06Z Master Thesis Masters MSc http://hdl.handle.net/11427/32915 eng application/pdf Department of Geological Sciences Faculty of Science |
| spellingShingle | geological sciences Peel, Chad Megacryst suite from the Salpeterkop carbonatite complex, Sutherland, Northern Cape, South Africa: an in-depth geochemical study |
| thesis_degree_str | Master's |
| title | Megacryst suite from the Salpeterkop carbonatite complex, Sutherland, Northern Cape, South Africa: an in-depth geochemical study |
| title_full | Megacryst suite from the Salpeterkop carbonatite complex, Sutherland, Northern Cape, South Africa: an in-depth geochemical study |
| title_fullStr | Megacryst suite from the Salpeterkop carbonatite complex, Sutherland, Northern Cape, South Africa: an in-depth geochemical study |
| title_full_unstemmed | Megacryst suite from the Salpeterkop carbonatite complex, Sutherland, Northern Cape, South Africa: an in-depth geochemical study |
| title_short | Megacryst suite from the Salpeterkop carbonatite complex, Sutherland, Northern Cape, South Africa: an in-depth geochemical study |
| title_sort | megacryst suite from the salpeterkop carbonatite complex sutherland northern cape south africa an in depth geochemical study |
| topic | geological sciences |
| url | http://hdl.handle.net/11427/32915 |
| work_keys_str_mv | AT peelchad megacrystsuitefromthesalpeterkopcarbonatitecomplexsutherlandnortherncapesouthafricaanindepthgeochemicalstudy |