Nichole Moerhuis

PhD student
University of British Columbia

Magmatic differentiation processes (fractional crystallization, assimilation, magma mixing, silicate immiscibility and volatile transport) are the mechanisms by which a single melt produces a range of igneous rock types, and they are vital for the formation of Layered Intrusions. We have many outstanding questions concerning magmatic differentiation in Layered Intrusions: How long does it takes for these intrusions to cool and crystallize at different scales? How does the melt chemically evolve during late-stage crystallization? As Layered Intrusions commonly form as part of large continental plumbing system connecting mantle melting and surficial flood basalt provinces, what can their timing and chemical evolution tell us about the evolution of Large Igneous Provinces and the occurrence of mass extinction events they are associated with?

To try and answer these questions, my research applies a petrographic, geochemical (trace element geochemistry, Hf isotopes) and geochronological (CA-TIMS U-Pb) tool-box to the Paleocene Skaergaard Intrusion in East Greenland. Skaergaard has been a classic testing ground for magmatic processes since the 1930’s because it cooled and crystallized as a closed-system during magmatism in the North Atlantic Igneous Province and has since become beautifully exposed by glaciation, making it a fantastic natural laboratory to examine magmatic differentiation processes. Whereas the vast majority of prior research into the magmatic evolution of layered intrusions has focused on early forming ‘primocryst’ minerals, my research involves examining highly differentiated interstitial melt pockets of minerals that have crystallized under near-solidus conditions and include a suite of U-Th-Pb bearing accessory minerals such as zircon, apatite and rutile. This enables us to gain new insights into near-solidus processes, and utilize high-precision CA-TIMS U-Pb dating of zircon to resolve magmatic timescales to tens of thousands of years! With high-resolution emplacement and crystallization ages, shallow level magmatism in the East Greenland Flood Basalt plumbing system can be linked to regional events such as the continental breakup of the North Atlantic and potentially to the Paleocene-Eocene Thermal Maximum (PETM).

This PhD research is based at the University of British Columbia and the Pacific Center for Isotopic and Geochemical Research with Drs. James Scoates and Dominique Weis, and in collaboration with Dr. Christian Tegner at Aarhus University, Denmark. CA-TIMS geochronology is undertaken at the Pacific Center for Isotopic and Geochemical Research and Boise State University.

I am from the South Island of New Zealand and my interest in geology began as I explored my beautiful backyard – the Southern Alps. I completed an Bachelor’s Degree in Geology at the University of Otago (New Zealand) with a component of study at Haskoli Islands (University of Iceland) in 2012. As an undergraduate, I focused upon palaeontology and examined Tertiary perturbations in sea level within sedimentary sequences from Central Otago. My MSc thesis (University of Otago, 2013-14) examined the metamorphism, mineralization and deformation of a Paleozoic amphibolite schist (the Onekaka Schist) in northwest Nelson, New Zealand. This project initiated my interest in geochronology and geochemistry as tools to unravel geological processes.