2023-2024: Volcanology, Geochemistry, and Petrology: Jeff Vervoort

Jeff Vervoort
Washington State University


Professor Vervoort is a leading expert in radiogenic isotope geochemistry and geochronology and has been among the pioneers in applying these tools to understanding the early Earth.  Dr. Vervoort received his Ph.D. from Cornell University (USA) in 1994 and was a research scientist at the University of Arizona for several years before joining the faculty of Geology at Washington State University in 2002.  He became full professor in 2013 and is director of the Radiogenic Isotope and Geochronology Laboratory (RIGL) at Washington State University (USA).  Vervoort has been a visiting Professor at Ecole Normale Superieure de Lyon, (9 months), Université Grenoble Alpes (1 month), Aarhus University, Denmark (4 months), University of Western Australia (3 months), and the Institute de Physique du Globe de Paris (2 months). Professor Vervoort has published 185 peer-reviewed papers and book chapters spanning a wide range of topics in isotope geochemistry and geochronology.  These papers have been cited over 21,000 times with an H-index of 63 (Google Scholar).  He is a Fellow of the American Geophysical Union and the Geological Society of America and has held 25 research and equipment grants from the US National Science Foundation. 

"In my research, I use the Hf and Nd isotope record of the early Earth to help better understand its early differentiation and how this relates to the formation and evolution of Earth’s earliest continental crust. A recent focus of my work is on the integrity of that isotope record: to what extent it has been modified by subsequent metamorphic events and how we can assess whether it faithfully records original isotope compositions.  To answer these questions, I use coupled U-Pb age and Hf isotope analyses of zircon and U-Pb age and Nd isotope analyses of REE-rich phases (monazite, titanite, allanite, etc.) determined simultaneously by the laser ablation split-stream (LASS) method. Our research indicates that the formation of long-lived continental crust and corresponding depletion of the mantle did not occur significantly until after about 3.8 Ga."

Abstract: The Growth of Earth’s Earliest Crust

The creation and growth of Earth’s continents is a topic that has captivated geoscientists—and engendered spirited debate—for decades. Questions about the formation and composition of the first continental crust and when it formed, the mechanisms and sites of crust formation, and how crustal volumes have changed through time have all been vigorously debated in the literature for over 50 years.  One of the main reasons these questions still endure today is the lack of a geologic record from Earth's earliest history.  Only a very small percentage of Earth's preserved crust is older than 3.5 billion years, and there is no intact crust—at least on which geoscientists can agree—that is older than 4 billion years. This leaves the first 500 million years of Earth's history without any physical evidence, absent a few detrital zircon grains in younger sediments. In order to try and understand this earliest Earth history, geochemists have turned to the isotope record preserved in the oldest rocks that do remain. Underlying this approach is the fundamental tenet of geochemistry that extraction of Earth’s crust from the mantle has produced a crust enriched, and a mantle depleted, in incompatible elements.  The long-lived Lu-Hf and Sm-Nd isotope systems have long been used to help understand this process. However, the Hf and Nd isotope records do not yield the same information for Earth’s oldest rocks. Hf isotopes in zircon from juvenile, nominally mantle-derived rocks have initial isotope compositions suggesting that significant development of a depleted mantle reservoir did not begin earlier than ~ 3.8 Ga. In striking contrast, bulk-rock samples have large variations in Nd isotope compositions implying early depleted mantle formation and extraction of significant crustal volumes. A caveat regarding these conflicting datasets, however, is the fact that these oldest rocks have had a long and often complex history and can be potentially compromised by later magmatic and metamorphic disturbances. In addition, the Hf isotope record has been mostly determined on zircon, whereas the Nd isotope record has been determined on bulk rock samples. In total, this raises the question of whether these records represent primary isotopic signatures or if they have been modified by subsequent processes. In this talk I will review the geological and isotope record of Earth's oldest rocks, discuss new analytical approaches that are being used to help us better constrain that isotope record, and summarize what these data tell us about the formation of continental crust on the early Earth.