Basalt alteration and its consequences

My thesis explores the geochemical consequences of basalt alteration in three distinct Earth environments using reactive transport modelling coupled to geochemical analyses. The weathering of basalt creates unique chemical environments that can drive carbonate mineral precipitation and other secondary mineral formation. The extreme reactivity of basalt, with very fast weathering rates relative to other surface rocks, means that there is great interest in understanding the impact of basalt alteration on the chemistry and secondary mineralisation of different environments. This thesis sets out to explore this. First, I examine basalt alteration at the Earth’s surface in the context of an ultramafic chromite-bearing ore body. Chromium is an environmental toxin in its oxidised state, Cr(VI), due to its water solubility. In contrast, its reduced form, Cr(III), is both less toxic and less soluble. During weathering, Cr(III) in chromite ore oxidises to Cr(VI). I investigate the chromium contamination resulting from the weathering of the ultramafic ore body, particu- larly assessing the extent to which microbially mediated iron reduction contributes reductants to this system. Secondly, I investigate basalt alteration at the mid-ocean ridge, where seawater convec- tion induced by proximity to magma leads to the alteration of basalt through water-rock in- teraction. I assess the consequences of this alteration for the global sulfur cycle; specifically with respect to anhydrite, which precipitates directly from seawater upon heating. I explore how past variations in ocean chemistry may have affected both the amount and the depth of anhydrite precipitation and speculate on the ultimate fate of this precipitated anhydrite. In the final chapter, I study basalt alteration in the context of enhanced rock weathering, where basalt serves as a source of alkalinity and cations to facilitate soil carbonation when used as an agricultural amendment. These investigations were conducted in laboratory-based flow reactor experiments. Specifically, I explore how the incorporation of commonly avail- able mineral products (slag and gypsum) mixed with basalt affects soil carbonation effi- ciency, comparing these mixtures to the outcomes obtained when using basalt alone.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2025

Author dc:creator

• Fotherby, Angus

Advisor dc:contributor.advisor

• Turchyn, Alexandra

• basalt
• alteration
• weathering
• chromium
• hydrothermal
• carbon capture

Licence

• https://www.repository.cam.ac.uk/bitstreams/cbd82fd2-2882-4944-aeed-c16b5479d45b/download
• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

Author Identifier

0000-0002-0470-6743

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/397970