Geochemical Evolution of the Lithospheric Mantle in the West Antarctic Rift System
About Cathleen Doherty
Cathleen Doherty received her B.S. degree in Biology and M.S. degree in Earth Science from Montclair State University. She received two National Science Foundation Graduate STEM Teaching Fellowships while at MSU and Columbia. She is a Ph.D. candidate in Geochemistry and will begin a Postdoctoral Science Fellowship as Lecturer in Discipline in Columbia University’s Frontiers of Science program in July. Her research interests include mantle geochemistry, lithosphere evolution, and deep Earth chemical cycling. She is also passionate about science education and analytical method development in geochemistry.
About the Presentation
With nearly 98% of the continent covered by ice, the geologic history of Antarctica remains enigmatic. Much of our understanding comes from limited rock exposures, seismologic studies, and sedimentary deposits. Mantle xenoliths, pieces of the mantle that have been carried to Earth’s surface through volcanism, provide access into Earth’s deep interior. I use bulk and in-situ mineral major and trace element abundances, integrated with Re-depletion ages and Sr, Nd, and Hf isotopes in mantle xenoliths to investigate the geochemical and dynamic evolution of the lithospheric mantle beneath the West Antarctic Rift System (WARS) in Antarctica. Together, these geochemical “tools” enable us to reconstruct a timeline of geologic events that are obscured on the surface. By studying a present day rifted margin, we gain insight into the current processes that drive plate tectonics. Os isotopes (i.e. Re-depletion ages) reveal widespread Paleoproterozoic (1.7-2.4 Ga) stabilization of the lithosphere and subsequent preservation of ancient mantle domains, suggesting the lithosphere has dynamically thinned in response to rifting. Trace elements reveal the re-enrichment of the lithospheric mantle by carbonatite metasomatism, while time integrated Hf isotopes indicate an ancient metasomatic event. Nd and Sr isotopes are de-coupled from Hf isotopes, and overlap with the Cenozoic rift related magma compositions, supporting the lithospheric mantle’s role in the widespread Cenozoic volcanism.