Understanding alkaline magmatism via cumulate xenoliths, Fogo, Cape Verde Islands

Understanding alkaline magmatism via cumulate xenoliths, Fogo, Cape Verde Islands

Fogo island (Cape Verdes) is an ideal natural laboratory in which to study the origin and evolution of alkaline magmatism, which ranges from basanite to phonolite. We have already collected and analysed a wide range of pristine lavas, investigated older carbonatites in the underlying seamount, and analysed numerous cumulate xenoliths found within Fogo’s eruptive products. Recently, we identified a deposit of numerous blocks of igneous rocks which were erupted during phreatomagmatic activity that occurred concurrently with the large volcano collapse of Fogo. These blocks are composed of coarse-grained, pre-existing plutonic rocks from beneath the shield-stage lava pile. We have made thin sections of these blocks, and shown that they are composed of pyroxene, amphibole, biotite, apatite, titanite and hauyne. Many have pristine igneous textures, indicating cumulate processes from alkaline magmas that ponded in magma reservoirs beneath the volcano. We plan for the student to spend 8 weeks (full-time) undertaking investigations of these rocks, using a wide variety of modern petrographic and mineralogical techniques, and to record and analyse the mineralogy of the constituent minerals in all the samples by electron microprobe at Birkbeck. Analyses of trace elements in the minerals will be undertaken by LA-ICP-MS at Birkbeck/UCL. The student will then discuss and interpret the results with members of the supervisory team and their PhD students, in order to understand (1) the sequence of crystallisation of the plutonic blocks, (2) the relationship of the blocks to already-analysed xenoliths, and (3) the relationship to phenocrysts in the lavas (also already analysed).

Working pattern: This project is lab-based so the student will need to be in Birkbeck twice a week on average, with the option for working from home or in the department on other days. We can offer flexible working, for example by scheduling lab days in blocks and allowing evening and weekend working, please contact us to discuss your requirements.

Eligibility: The student must be studying geology, planetary sciences or a closely related subject, with a strong background and interest in igneous petrology and mineralogy. Please provide evidence of this in your application.

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