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Constraints on the size and temperature of magma batches that constructed the Peninsula pluton, based on the metamorphic record of metasedimentary xenoliths
Thesis (MSc)--Stellenbosch University, 2023.
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Stellenbosch : Stellenbosch University
2023
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| _version_ | 1867613991661993984 |
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| access_status_str | Open Access |
| author | Muller, Jared |
| author2 | Stevens, Gary |
| author_browse | Muller, Jared Stevens, Gary |
| author_facet | Stevens, Gary Muller, Jared |
| author_sort | Muller, Jared |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MSc)--Stellenbosch University, 2023. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/127362 |
| institution | Stellenbosch University (South Africa) |
| language | en_ZA |
| last_indexed | 2026-06-10T12:44:55.985Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2023 |
| publishDateRange | 2023 |
| publishDateSort | 2023 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/127362 Constraints on the size and temperature of magma batches that constructed the Peninsula pluton, based on the metamorphic record of metasedimentary xenoliths Muller, Jared Stevens, Gary Stellenbosch University. Faculty of Science. Dept. of Earth Sciences. Magmas -- Environmental aspects Global temperature changes Igneous rocks -- Inclusions -- South Africa -- Peninsula pluton Malmesbury Group metasediments Metasedimentary xenoliths Granite --Effect of temperature on UCTD Thesis (MSc)--Stellenbosch University, 2023. ENGLISH ABSTRACT: This study aimed to investigate the metamorphic histories of nine greenschist facies xenolith samples from the Malmesbury Group metasediments, which have an estimated age of deposition of approximately 575 to 550 Ma. These samples are hosted in the Peninsula Pluton granitoids (537.8 ± 1.6 Ma to 532.7 ± 1.9 Ma) of the Cape Granite Suite. The goal of the study was to put constraints on the size and temperature of the magma batches that formed the Peninsula Pluton granitoids. To achieve this, various techniques including petrography, field evidence, scanning electron microscopy, phase equilibria modelling using the freeware "Rcrust" and thermal modelling using the freeware "Energy2D" were employed to establish peak metamorphic mineral assemblages and constrain peak metamorphic conditions. The peak metamorphic assemblages for the xenoliths were determined to be quartz + biotite + plagioclase + cordierite ± K-feldspar ± ilmenite ± muscovite. The results of the bulk rock and mineral composition analyses revealed that the metasedimentary xenoliths of this study plot within a normal range of the Malmesbury group sediments and metasediments. Temperatures of formation for the magma batches that constructed the Peninsula Pluton have been noted to be between 800 and 900°C. Ti-in-biotite thermometry was used to constrain the temperature of peak metamorphism for the xenoliths of this study to be in the range of 665 to 725°C. Phase equilibria modelling revealed that the different xenoliths experienced peak temperatures between 530 and 730°C and pressures between 0 and 4.5 kbar. This has important implications for background magma temperature in the pluton and the size and temperature of the magma batches that entrained the xenoliths. Obviously if the magma arrived in the upper crust at ~ 700°C, batches could conceivably be any size. However, there is strong evidence for the Peninsula Pluton magmas having arisen by fluid absent melting involving biotite at >850°C. Two-dimensional conductive thermal modelling was used to explore the ranges of background magma temperature and magma batch sizes and temperatures that would be consistent with the xenoliths recording only amphibolite facies temperatures. The results indicate that the background magma temperature cannot be higher than the maximum temperatures recorded by the xenoliths. Additionally, if the magma batches that sampled the xenoliths and introduced them into the pluton were at 850°C, they could not have been thicker than 1m if intruded as 10m wide sills. Similarly, magma batches arriving at 750°C could not have been thicker than 2m if intruded as 10m wide sills. These size and temperature estimates contribute to the body of evidence supporting the incremental growth model of granitic plutons, as well as providing insight into the size and temperature of magma batches that were assimilated to form the Peninsula Pluton granitoids. The assimilation of these batches, as well as their frequency, can be better understood considering these data. AFRIKAANSE OPSOMMING: Hierdie studie het ten doel gehad om die metamorfiese geskiedenis van nege groen-fasiese xenolitiese monsters van die Malmesbury Group-metasedimente te ondersoek, wat 'n geskatte ouderdom van afsetting van ongeveer 575 tot 550 Ma het. Hierdie monsters word aangebied in die Peninsula Pluton granitoids ( 537.8 ± 1.6 Ma tot 532.7 ± 1.9 Ma ) van die Kaapse Granietsuite. Die doel van die studie was om beperkings te plaas op die grootte en temperatuur van die magma- kolfke wat die Peninsula Pluton-granitoïede gevorm het. Om dit te bereik, verskillende tegnieke, waaronder petrografie, veldbewyse, die skandeer van elektroniese mikroskopie, fase- ewigmodellering met behulp van die freeware "Rcrust" en termiese modellering met behulp van die freeware "Energy2D" is gebruik om piekmetamorfiese minerale samestellings en konstreinpiekmetamorfiese toestande te vestig. Die piekmetamorfiese samestellings vir die xenoliete was vasbeslote om kwarts te wees + biotiet + plagioklas + cordierite ± K-feldspar ± ilmenite ± muscovite. Die resultate van die grootmaat- en minerale komposisie-ontledings het aan die lig gebring dat die metasedimentêre xenoliete van hierdie studie-plot binne 'n normale reeks van die Malmesbury-groep sedimente en metasedimente. Daar is opgemerk dat die temperatuur van die vorming vir die magma-kolfke wat die Peninsula Pluton gebou het, tussen 800 en 900 ° C was. Ti-in-biotiettermometrie is gebruik om die temperatuur van piekmetamorfisme te beperk vir die xenoliete van hierdie studie wat tussen 665 en 725 ° C was. Fase-ewewigsmodellering het aan die lig gebring dat die verskillende xenoliete piektemperature tussen 530 en 730 ° C en druk tussen 0 en 4,5 kbar ervaar het. Dit het belangrike implikasies vir agtergrondmagma-temperatuur in die pluton en die grootte en temperatuur van die magma-kolfke wat die xenoliete behels het. Dit is duidelik dat as die magma in die boonste kors by ~ 700 ° C aangekom het, groepe denkbaar enige grootte kan wees. Daar is egter sterk bewyse dat die Peninsula Pluton magmas ontstaan het deur vloeistof wat afwesig is met biotiet by > 850 ° C. Twee-dimensionele geleidende termiese modellering is gebruik om die reeks agtergrondmagma-temperatuur en magma-lotgroottes en -temperature te ondersoek wat ooreenstem met die xenoliete wat slegs amfibolietfasiesemperature opneem. Die resultate dui daarop dat die agtergrondmagma-temperatuur nie hoër kan wees as die maksimum temperatuur wat deur die xenoliete aangeteken is nie. As die magma-kolfke wat die xenoliete et en dit in die pluton voorgestel het, 850 ° C was, kon hulle nie dikker gewees het as 1 m as hulle as 10 m breë sille ingedring is nie. Op dieselfde manier kon magma-kolfke wat op 750 ° C aankom, nie dikker as 2 m gewees het as 10 m breë sille nie. Hierdie grootte en temperatuurberamings dra by tot die bewys van die inkrementele groeimodel van granitiese plutons, sowel as insig in die grootte en temperatuur van magma-groepe wat geassimileer is om die Peninsula Pluton-korrelitoïede te vorm. Die assimilasie van hierdie groepe, sowel as die frekwensie daarvan, kan beter verstaan word as hierdie data oorweeg word. Masters 2023-03-06T07:59:18Z 2023-05-18T07:18:12Z 2023-03-06T07:59:18Z 2023-05-18T07:18:12Z 2023-03 Thesis http://hdl.handle.net/10019.1/127362 en_ZA Stellenbosch University xxi, 125 pages : illustrations (some color), maps application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Magmas -- Environmental aspects Global temperature changes Igneous rocks -- Inclusions -- South Africa -- Peninsula pluton Malmesbury Group metasediments Metasedimentary xenoliths Granite --Effect of temperature on UCTD Muller, Jared Constraints on the size and temperature of magma batches that constructed the Peninsula pluton, based on the metamorphic record of metasedimentary xenoliths |
| title | Constraints on the size and temperature of magma batches that constructed the Peninsula pluton, based on the metamorphic record of metasedimentary xenoliths |
| title_full | Constraints on the size and temperature of magma batches that constructed the Peninsula pluton, based on the metamorphic record of metasedimentary xenoliths |
| title_fullStr | Constraints on the size and temperature of magma batches that constructed the Peninsula pluton, based on the metamorphic record of metasedimentary xenoliths |
| title_full_unstemmed | Constraints on the size and temperature of magma batches that constructed the Peninsula pluton, based on the metamorphic record of metasedimentary xenoliths |
| title_short | Constraints on the size and temperature of magma batches that constructed the Peninsula pluton, based on the metamorphic record of metasedimentary xenoliths |
| title_sort | constraints on the size and temperature of magma batches that constructed the peninsula pluton based on the metamorphic record of metasedimentary xenoliths |
| topic | Magmas -- Environmental aspects Global temperature changes Igneous rocks -- Inclusions -- South Africa -- Peninsula pluton Malmesbury Group metasediments Metasedimentary xenoliths Granite --Effect of temperature on UCTD |
| url | http://hdl.handle.net/10019.1/127362 |
| work_keys_str_mv | AT mullerjared constraintsonthesizeandtemperatureofmagmabatchesthatconstructedthepeninsulaplutonbasedonthemetamorphicrecordofmetasedimentaryxenoliths |