Please join us on Wednesday, October 2nd, at 2 p.m. for a Geochemistry seminar with Dr. Madeleine Murphy, a new postdoc at Lamont working in Alex Halliday's lab. She recently completed her PhD in geochemistry at the University of St. Andrews under the supervision of Paul Savage, Nick Gardiner, and Tony Prave.
Silicon Isotope Insights into Earth's Ancient Crust and Hydrosphere
Her work focuses on the silicon isotope system, a well-established geochemical tool for tracing processes influenced by the interplay of Earth's present-day crust and hydrosphere. While there is good understanding of stable silicon (Si) isotope systematics for high- and low-temperature processes in the Phanerozoic eon, these are poorly constrained for early Earth processes. Despite this, recent investigations of Si isotopes in Archaean granitoids have linked heavy isotopic signatures to seawater-derived sources, invoking the hydrosphere in forming Earth's earliest continental crust.
Motivated by recent research gaps, her PhD work explored secular crust-hydrosphere interactions by establishing the Si isotope compositions of Archaean granitoids, specifically tonalite-trondhjemite-granodiorites (TTGs), and other ancient lithologies. In this seminar, she will take you on a whistle-stop tour of her PhD thesis by presenting the outcomes of four Si isotope studies on globally diverse, ancient silicate materials. Discuss how Eoarchaean igneous rocks from Greenland were influenced by supracrustal fluids, necessitating a primeval hydrosphere in forming early continents. She will also explore Si isotope behaviour during ancient partial melting from an Archaean migmatite from Ontario and discuss the finding that TTG sources were likely seawater-silicified. Additionally, explain the secular homogenising of Si isotopes in the ancient upper continental crust from global glacial diamictites, supporting craton stabilisation after ~3.0 Ga. Finally, she will show that Archaean–Proterozoic Fennoscandian weathering crusts imply no significant Si isotope trends at the Great Oxidation Event and highlight local controls instead.
In total, she will present a more robust temporal Si isotope record of ancient crustal materials and argue that Si isotopes can provide greater understanding of the connection between Earth's earliest continental materials and the fluids that shaped them.
