September 3, 2021
3:00pm in PLS 1140
Sarah Stamps from Virginia Tech
Clues About the Break-up of the African Continent

Abstract: The African continent is slowly fragmenting along the East African Rift System (EARS) across east Africa. What drives this fragmentation process and how exactly is the Earth's lithosphere moving along the EARS? In this seminar, I present results that shows how the tectonic plates of the EARS are slowly moving and deforming, which causes hazardous seismic and volcanic activity.  Using modern-day, high precision positioning measurements from Global Navigation Satellite Systems (GNSS) and advanced numerical methods, we investigate the physics driving surface motions to understand the driving forces causing the break-up of Africa. We find that deformation is characterized by east-west extension and the major forces driving extension are derived from topography gradients.

September 10, 2021
3:00pm in PLS 1140
Jonathan Tucker from Smithsonian
Linking deep volatile cycles from subduction to eruption

Abstract: The plate tectonic cycling of volatiles like water, halogens, and noble gases between Earth’s interior and exterior has been responsible for maintaining a habitable planetary surface environment for billions of years and is a key control on mantle convection and Earth’s thermal evolution. However, the history and mechanism of volatile exchange is poorly constrained. I will discuss novel observational evidence that deep Earth cycles of water, chlorine, argon, and xenon are linked and preserve seawater provenance throughout mantle circulation and their eventual eruption at mid-ocean ridges. The results imply that subduction of volatiles derived from unfractionated seawater is the major control on the distribution of diverse volatile species in the mantle. I will show that subducted hydrous minerals formed in equilibrium with seawater are incapable of preserving seawater noble gas signatures, requiring hydrous minerals to be formed in closed systems. Furthermore, I will use temporal constraints on xenon subduction to estimate that the water flux into the mantle during the Archean was much lower than modern rate, consistent with slower plate velocities or a change in the nature of convective recycling in the Archean.

September 17, 2021
3:00pm in PLS 1140
Freya George from Johns Hopkins University
From grain-scale records to global volatile cycling: rhythmic garnet zoning and mass transfer during subduction

Abstract: The chemical and isotopic zoning exhibited by many metamorphic minerals serves as a time-resolved record of processes occurring during both mineral growth and periods of diffusive relaxation. Using garnet from high pressure–low temperature metamorphic rocks derived from a global suite of subduction zones, oscillatory zoning—rhythmic cycles of peaks and troughs in element concentration—is shown to be near ubiquitous. Therefore, this zoning likely reflects some fundamental dynamic or petrogenetic process operating during garnet crystallization in these settings of significant mass transfer. Here, oxygen isotopes are used to explore the notion that elemental oscillations are buffered by infiltrating grain boundary fluids. Our results imply that fine-scale elemental and isotopic zoning in garnet is decoupled, and may be driven by distinct processes of dispersal and advection. Data and modeling results presented here also suggest that while local fluid-filled porosities generally behave as closed systems during prograde metamorphism, grain boundaries may be transiently flushed and buffered by large volumes of external fluids without a need for evident fluid channelization structures. Together, these norms and exceptions point to the significant spatiotemporal heterogeneity of these settings, and therefore the continuing opportunities the geological record presents to assess the nature of global volatile cycling.

September 24, 2021
3:00pm in PLS 1140
Delta Merner from Union of Concerned Scientists

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October 8, 2021
3:00pm in PLS 1140
Shreeram Inamdar from University of Delaware
October 22, 2021
3:00pm in PLS 1140
Casey Honnibal from NASA GSFC
October 29, 2021
3:00pm in PLS 1140
November 12, 2021
3:00pm in PLS 1140
Jeff Freymueller from Michigan State University
November 19, 2021
3:00pm in PLS 1140
December 3, 2021
3:00pm in PLS 1140
Anthony Pollington from Los Alamos National Laboratory

The coordinator for the Colloquium Series is Dr. Megan Newcombe. You can contact her at newcombe@umd.edu.

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