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Unlocking clinopyroxene records of magma and mantle oxygen fugacity


Project Description

Subduction recycles oceanic lithosphere formed at mid-ocean ridges back into the Earth’s convecting mantle, creating much of the deep compositional heterogeneity we now see reflected in the diversity of magmas erupted at mid-ocean ridges and ocean islands. However, current observations from erupted magmas provide conflicting views on whether subduction of hydrothermally altered oceanic lithosphere creates heterogeneity in the oxygen fugacity (i.e. oxidising potential) of the deep mantle. As a consequence, the extent to which variations in mantle oxygen fugacity are coupled to Earth’s tectonically driven deep oxygen cycle remains largely unknown. This is despite mantle oxygen fugacity playing a vital role in controlling the composition of the volcanic gas emissions that mediate atmospheric chemistry over geological timescales. Developing new tools for determining the oxygen fugacity of primitive magmas is therefore a key step towards deciphering how the deep Earth has affected our planet’s ability to create and sustain life through time.

Clinopyroxene is a common mineral in many of Earth’s main magma types and is commonly used as a tool for estimating the pressure and temperature conditions under which magmas are stored. Clinopyroxene incorporates both reduced and oxidised iron species, so it has the potential to be used as a tool for estimating magma oxygen fugacity conditions. However, obtaining robust descriptions of clinopyroxene’s sensitivity to oxygen fugacity has so far proven elusive because little is known about the systematics of iron speciation in clinopyroxene. This project will work towards overcoming this uncertainty by collating and manipulating large and underexploited datasets of clinopyroxene chemistry, and augmenting them with new analyses of natural and/or experimental clinopyroxenes.

The project will involve data manipulation, geochemical microanalysis and, according to the interests and expertise of the student, fieldwork and/or high-temperature experiments. The student will collate and manipulate large datasets in order to evaluate clinopyroxene’s sensitivity to oxygen fugacity. They will use a range of analytical techniques including scanning electron microscopy and electron microprobe analyses to examine clinopyroxene samples formed under different oxygen fugacity conditions. These samples will either be collected during fieldwork in volcanic regions such as Iceland and the Canary Islands or produced in Manchester’s experimental laboratories. There will also be opportunities, subject to additional proposals, to perform in situ spectroscopic analyses of iron speciation in clinopyroxenes at the Diamond Light Source synchrotron facility, and/or undertake a research visit to collaborators at the Leibniz Universität Hannover, Germany, to carry out high-pressure experiments in their pressure vessel lab.

We seek an able and enthusiastic individual with a strong background (MSc, MSci or BSc) in Earth or physical sciences to join our research group. No specific coding or laboratory experience is necessary, but the candidate should have appropriate experience in igneous petrology and optical microscopy and an interest in developing their programming skills. Some knowledge of coding, scanning electron microscopy, electron microprobe analysis and/or experimental petrology would be helpful.

Funding Notes

Tuition Fees: EARTH Band 3: £14,000 for Home students, £31,500 for Overseas students

How good is research at The University of Manchester in Earth Systems and Environmental Sciences?

FTE Category A staff submitted: 42.13

Research output data provided by the Research Excellence Framework (REF)

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