What can Fe stable isotopes tell us about magmas?
The majority of the Earth’s crust is formed by magmas, and understanding their production and differentiation is important to interpret the geologic rock record. A powerful tool to investigate magmatic processes is the distribution of the stable isotopes of the major redox-sensitive element in magma...
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| Format: | Book |
| Language: | English |
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Aarhus Universitetsforlag
2017
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| Online Access: | https://pure.au.dk/portal/en/publications/b95ecb62-e4f3-4a0d-acd4-54b641a86f09 http://phd.au.dk/gradschools/scienceandtechnology/newsandevents/show-news/artikel/what-can-fe-stable-isotopes-tell-us-about-magmas/ |
| Summary: | The majority of the Earth’s crust is formed by magmas, and understanding their production and differentiation is important to interpret the geologic rock record. A powerful tool to investigate magmatic processes is the distribution of the stable isotopes of the major redox-sensitive element in magmas, Fe. Fe isotope compositions of magmatic rocks exhibit systematic differences, where the heaviest compositions are found in rhyolites and granites. Understanding of these systematics is complicated by a lack of constraints on Fe isotope fractionation among minerals and liquids under magmatic conditions, and basic knowledge about the complementarity of erupted magmas and crystal loads left behind during the course of magmatic differentiation, as well as, the residues remaining after partial melting within the crust and mantle. This Ph.D. dissertation addresses basic questions about the differentiation of magmas from the perspective of Fe stable isotopes, integrated with petrology, by studying igneous rocks and their constituent phases (minerals and glasses) from the Bushveld Complex, South Africa, Thingmuli, Iceland, Pantelleria, Italy, and the Bishop Tuff, USA. The findings are interpreted in terms of available theory, experiments and forward modeling incorporating petrologic constraints. Mafic cumulate rocks from the Bushveld Complex exhibit resolvable whole rock Fe isotopic variation with modal mineralogy and mineral composition, to a 1st order reflecting partitioning of Fe3+ and Fe2+ between melt and minerals. The isotope composition of mineral phases of Bushveld cumulate rocks is highly variably, and records closure temperatures, modal abundance and inter-mineral textural relations. In contrast, isotope compositions of mafic to intermediate lavas from Thingmuli volcano vary little, while silicic lavas are systematically heavier. Generation of heavy Fe isotope compositions is shown to be strongly affected by the intensive variable governing magmatic differentiation, most importantly, oxygen fugacity, mineral and ... |
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