Unravelling Temporal Geochemical Changes in the Miocene Mogan and Fataga group ignimbrite succession on Gran Canaria, Canary Islands, Spain
Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Gran Canaria hosts a long-lived Miocene volcanic caldera system, the Tejeda Caldera, which produced an extensive succession of silicic ignimbrites and lavas (the Miocene Mogan and Fataga formations, > 1400 km3) between 14 and 12 Ma. The ignimbrite succession exhibits temporal geochemical changes in radiogenic isotopes that were first examined by Cousens et al (1990). These changes were originally interpreted to be caused by changing mantle source compositions that fed the Tejeda volcanic system.
Recent work on large silicic caldera systems like Yellowstone employs a record of oxygen isotopes in the erupted products and postulates the progressive assimilation of crustal or older volcanic material into the successive magmas that fed the eminently large scale silicic eruptions (Bindeman et al 2001). This new theory has put forward the idea that crustal assimilation may be more important in such long-lived caldera systems than previously recognised.
The transition from the dominantly trachytic to rhyolitic Mogan group (14 – 13.2 Ma) to the dominantly trachytic to phonolitic Fataga group ignimbrites and lavas (ca 13.2 – 8 Ma) was sampled for oxygen isotopes to test whether temporal changes in the Mogan and Fataga group magmas were caused by crustal assimilation processes or indeed by temporal changes in mantle source composition (e.g. Cousens et al 1990).
Oxygen isotopes show gradually decreasing values up section between 14 and 12 Ma, which confirms that considerable changes occurred in the magmatic supply system through time. Progressively lower δ18O values upsection are consistent with a low δ18O component being added during the magma differentiation but we note that the Strontium isotope ratios decrease at around the same time, while Pb isotopes show correlated excursions too. These observations appear to point towards a mantle source change from the Mogan to Fataga group volcanism, the latter with the lower average δ18O signature. This scenario is more plausible than crustal contamination as we would then expect an increase in strontium isotope ratios rather than an overall decrease. Crustal contamination is nevertheless detected to have played a role during the evolution of the Mogan group, where several units record additional crustal involvement. The overall oxygen-strontium isotope correlations however suggests a change in mantle source and requires change from a mixed source involving EM1, DM and HIMU to a higher proportion of the HIMU component towards the end of Miocene activity. This change was likely a function of the gradual waning of the DM and EM1-like components in the mantle supply column towards end of the Miocene volcanic episode on Gran Canaria.
Place, publisher, year, edition, pages
2014. , 47 p.
Examensarbete vid Institutionen för geovetenskaper, ISSN 1650-6553 ; 274
Ocean islands, explosive volcanism, oxygen isotopes, magmatic processes
IdentifiersURN: urn:nbn:se:uu:diva-218650OAI: oai:DiVA.org:uu-218650DiVA: diva2:696408
Master Programme in Earth Science
Troll, Valentin, Professor
Troll, Valentin, Doctor