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(STFC DTP) The Halogen Budget of Asteroid 4 Vesta


Project Description

Asteroid 4 Vesta is the second largest body in the Asteroid Belt, second to the dwarf planet Ceres. Unlike most asteroids, but similar to Earth, Vesta is differentiated into a silicate crust, mantle and core. The HED meteorites (Howardite-Eucrite-Diogenite) that sample Vesta comprise the largest fraction of achondrites sampled in meteorite collections, making Vesta relatively accessible for the study of planetary-scale magmatic differentiation processes. The HED meteorites are a suite of crustal igneous rocks that likely represent crystallisation from a magma ocean1 and subsequent episodic magmatic intrusion and eruptions (ca. ~4547-4459 Ma2). HEDs are traditionally thought to have crystallised from volatile poor parent magmas3, but recent studies on apatites in eucrites report H2O contents of up to ~2600 ppm and D/H ratios comparable to carbonaceous chondrites, terrestrial basalts and some lunar lithologies4. The HED meteorites thus represent an exciting opportunity to examine the behavior of volatiles during crystallization of a magma ocean, with implications for planetary differentiation.

In this project, an inventory of the noble gases and halogens in eucrite and diogenite meteroites will be carried out. Halogens and noble gases are powerful geochemical tracers of volatile evolution in planetary bodies because they are significantly affected by the physical processes of differentiation and impact events. The key aim of this project is therefore to create a quantitative and empirically-constrained description of volatile behaviour during planetary-scale magmatic differentiation and processing.

Methods and Project Objectives:
• Apply for and acquire meteorites from Museum and Antarctic holdings. The basaltic eucrites and diogenites are particularly advantageous because of the large number of samples in collections, allowing for careful selection of appropriate target materials.
• Undertake careful petrological characterization of the sample suite, including basaltic (cumulate and non-cumulate) eucrites and olivine-rich diogenites. In addition to standard petrography, micro-analysis using the automated mineral mapping software QEMSCAN will yield detailed and high-resolution mineral, chemical and textural information. This will be coupled with mineral chemical data from the electron microprobe, including F/Cl mapping, to assess terrestrial contaminants and aid the identification of host halogen phases.
• Carry out X-ray microtomography (complementing the QEMSCAN analysis) to quantify the distribution of petrological features consistent with volatile exsolution, such as vesicles (there are several moderately vesicular eucrites and diogenites, for example).
• Employ the neutron−irradiation noble gas mass spectrometry (NI−NGMS) technique5, pioneered at the University of Manchester, to measure the halogen abundances of both bulk rocks and mineral separates of Vesta materials.
• Synthesise the petrological observations and datasets from the halogen and noble gas analyses to construct robust petrogenetic models for the behavior of volatile elements during magma fractionation, degassing and solidification on Vesta.

This project will suit a student with interests and some previous experience in petrology and geochemistry from their earlier degree(s).

References

[1] Greenwood, R. C. et al. Earth Planet. Sci. Lett. 390, 165–174 (2014). [2] Zhou, Q. et al. Geochim. Cosmochim. Acta 110, 152–175 (2013). [3] Mittlefehldt, D. W. Chemie der Erde - Geochemistry 75, 155–183 (2015). [4] Sarafian, A. R., Nielsen, S. G., Marschall, H. R., McCubbin, F. M. & Monteleone, B. D. Science 346, 623–626 (2014). [5] Ruziè-Hamilton et al. (2016) Chem. Geol.,437, 77–87.

Related Subjects

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

FTE Category A staff submitted: 42.13

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