The snowball Earth hypothesis states that between ~720-635 Ma Earth underwent glaciations during which the planet was covered completely in ice. Scientists use carbonate deposits, called cap carbonates, which appear atop snowball Earth glacial deposits to mark the end of these glaciations. Cap carbonate deposition is currently thought to have occurred during extreme stages of the chemical weathering (breakdown of rock by chemical reactions) that followed snowball Earth. However, there is insufficient geochemical evidence to confidently determine which stage–extreme, mild, or otherwise–of chemical weathering intensity the carbonates were deposited in. Magnesium, Mg, isotope abundance is useful in tracking chemical weathering events because of magnesium’s sensitivity to chemical weathering intensity. Data collected from rock samples from the Yangtze Formation in South China support the conjecture that chemical weathering was most intense immediately following snowball Earth, but it was not until chemical weathering slowed down that cap carbonates were deposited. This scenario allows time for continental chemical weathering to occur and calcium and magnesium cations to become available for the production of carbonates. To revise the snowball Earth hypothesis with this information, samples from more than one region are needed to apply this timeline globally. I will dissolve rock samples collected from the Amazon Craton in Brazil and study the sample powders using mass spectrometry to collect Mg isotope abundance data. I expect the data collected from these samples to resemble the data collected from the Yangtze Formation cap carbonates. This corroboration will help piece together the puzzle of the Snowball earth timeline.

This research investigates the behavior of magnesium isotopes during the dehydration process of subducting oceanic crust. The aim is to understand how magnesium isotopes behave during the metamorphic process of subducting oceanic crust up to eclogite-facies, and whether potential magnesium isotope heterogeneity in the altered oceanic crust can be retained in the dehydrated residual eclogites. The research utilizes geochemical methods to analyze eclogites from Europe.

Specifically, this project involves the use of a Nu Plasma II multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) to measure Mg isotopes in the rock samples. The samples are weighed and digested first, followed by column chemistry to purify the Mg fractions. The purified Mg fractions are finally measured using MC-ICP-MS to determine their Mg isotope compositions. The data will be interpreted to gain insights into the behavior of magnesium isotopes during the dehydration process of subducting oceanic crust.

Preliminary results reveal significant heterogeneity in the Mg isotope composition of the eclogites. These results have important implications for our understanding of role of oceanic crust recycling in chemical evolution of the Earth's mantle.