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October 27, 2021
12:00pm in Virtual
Matthew Jerram from Lamont Doherty Earth Observatory
Chromium Stable Isotope Variations in the Early Solar System and Deep Earth

Abstract: Chromium is arguably one of the most important elements for studying high temperature processes. It’s behaviour in processes from condensation of the solar nebula, core formation and magma oceans, through to crustal differentiation, varies depending on physical parameters (i.e. oxygen fugacity, pressure, temperature and composition). The Cr concentration and isotopic composition of bodies throughout the Solar System therefore reflect their evolution.

Initial isotopic interest in Cr resolved around it’s radiogenic and nucleosynthetic isotopic anomalies. With the advent of new mass dependent isotope measurement techniques (e.g. double spikes and a new generation of mass spectrometers), very high precision mass dependent variations have been made possible. Interest continues to grow with the number of studies doubling in the last few years. Recent work has provided further insights into the history of Cr on Earth and throughout the solar system.

November 3, 2021
12:00pm in CHEM 0215
Aubrey Zerkle and Mark Claire from University of St. Andrews
 “Volcanic contributions to Earth’s early atmosphere”- Aubrey Zerkle

"Photochemical modelling insights into oxygen levels before and after the Great Oxidation.”-Mark Claire

Abstract: There will be two talks each lasting 20 minutes.

Aubrey and Mark will also be around the department for the next two weeks, so if meeting with them Wednesday does not work, feel free to send them an email and set up a time to meet at a later date.

November 10, 2021
12:00pm in Virtual
Nicole Nie from Earth and Planets Laboratory
Mechanisms for the Depletion of Moderately Volatile Elements (MVEs) in the Moon and Chondrites

Abstract: Planetary bodies are universally depleted in moderately volatile elements (MVEs) (e.g., K, Rb, Cu, and Zn etc.) compared to the CI chondrites, which represent the bulk solar composition. The reason for this is unclear, but studying the isotopes of MVEs could provide some clues. In the presentation, I will use Rb and K isotopes to constrain the processes that have led to the MVE depletion in the Moon and in carbonaceous chondrites.

November 17, 2021
12:00pm in CHEM 0215
Jan Hellman from University of Maryland
Fractionation and mixing processes in the early Solar System inferred from tellurium isotope variations in chondrites

Abstract: Understanding fractionation and mixing processes in the early Solar System is important because ultimately, they define the chemical characteristics of the planetary building blocks and Earth. For instance, meteoritic and planetary materials are variably depleted in volatile elements compared to the composition of CI chondrites and the Sun. However, the origin of these volatile element fractionations, and how they are related to volatile loss during high-temperature processes within the solar nebula, remains poorly understood. In this presentation, I will use mass-dependent tellurium (Te) isotopic variations in chondrites and terrestrial rocks to constrain the origin of volatile element depletion in the solar nebula, and to gain a better understanding of the nature and origin of the material that was added to Earth after core formation was completed.

December 1, 2021
12:00pm in CHEM 0215
Juliana Troch from Smithsonian
Will it melt? What low-δ18O rhyolites can teach us about crustal melting and assimilation processes

Abstract: Why is this interesting? Silicic magmas play an important role in the formation of continental crust and are responsible for some of the most hazardous volcanic eruptions on the planet. Low-δ18O silicic magmas have been a petrological conundrum as they require significant incorporation of rocks that were hydrothermally altered by meteoric water in the shallow, permeable, and relatively cold upper crust - a region that should generally be unfavorable for the production of large melt volumes. Their genesis is therefore crucial in understanding how silicic magma reservoirs interact with the upper crust, and how they can remain active and produce extensive amounts of silicic magma over timescales of millions of years. In this talk, we will look at how the „meltability“ of hydrothermally altered rocks of various compositions affects the formation of low-δ18O rhyolites in Yellowstone and Iceland. By comparing settings around the world, we will investigate whether there is a common „recipe“ of conditions that promote the generation of low-δ18O silicic magmas. 

December 8, 2021
12:00pm in Virtual
Allie Balter-Kennedy from Lamont Doherty Earth Observatory
Novel cosmogenic-nuclide techniques for assessing ice-sheet stability

Abstract: Recent analytical improvements have opened up the possibility for applying cosmogenic-nuclide methods to bedrock cores in currently deglaciating and even subglacial bedrock and sediment. Not only does this methodology yield information about the duration of bedrock exposure during past warm periods, but also about subglacial erosion rates, a remaining source of uncertainty in glaciological models for which empirical constraints are lacking. 

In this talk, I will present two new methods that expand this emerging toolkit for assessing ice-sheet stability using cosmogenic-nuclide measurements in bedrock cores. First, I will show that a buildup of excess 10Be at depth in rock can be used to assess orbital-scale erosion rates beneath glaciers and ice sheets. Second, I will detail a method for routinely measuring 10Be in pyroxenes, which is useful for addressing ice-sheet change and landscape evolution in regions dominated by mafic lithologies. Together, these methods will expand the possibilities for investigating ice-sheet processes and (in)stability.

The organizer for the lunchtime seminar is Dr. James Dottin. You can contact him at jdottin@umd.edu.