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January 18, 2018
3:00pm in PLS 1140
Megan Newcombe from Columbia University
Eruptions: the final countdown
January 26, 2018
3:00pm in PLS 1140
Colin Jackson from Smithsonian Institution
Early episodes of high-pressure core formation preserved in plume mantle
February 9, 2018
3:00pm in PLS 1140
Patrick Boehnke from University of Chicago
Getting more out of geochemical data: Models for the Hadean to the Pleistocene
February 16, 2018
3:00pm in PLS 1140
Natalia Solomatova from Ecole Normale Supérieure de Lyon
Investigating iron's spin crossover behavior in lower-mantle minerals and its effect on phase stability using experimental and computational methods
February 23, 2018
3:00pm in PLS 1140
Jin Liu from Stanford University
Deep Earth volatile cycles: When water meets iron at the core-mantle boundary
February 26, 2018
3:00pm in PLS 1140
Sarah Slotznick from University of California, Berkeley
Magnetism as a lens into redox conditions in Precambrian environments with early eukaryotes
March 16, 2018
3:00pm in PLS 1140
Jeffrey Plescia from The Johns Hopkins University, Applied Physics Laboratory
The Chesapeake Bay Impact Structure

Abstract: The Chesapeake Bay Impact Structure lies hidden beneath the Delmarva Peninsula and the Chesapeake Bay. It is one of the best-preserved impact structures on Earth, largely because it was immediately buried after the impact occurred 35 Ma. At the time of the impact, the area lay off the eastern coast of North America in a continental shelf marine environment; the target consisting of largely unlithified marine sediments overlying crystalline basement. The structure has a diameter of 85 km with a unique deformation pattern of annular listric faulting of the sediments along a decollement at the sediment / crystalline boundary surrounding a deep crater excavated into the crystalline basement. The presence of some type of geologic anomaly in the area has been recognized since the 1950s when an unusually briny aquifer was discovered. It was not for another 30-40 years until an impact origin was confirmed.

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March 30, 2018
3:00pm in PLS 1140
Helen Janiszewski from Department of Terrestrial Magnetism, Carnegie Institution for Science
Amphibious seismic structure of the Cascadia subduction zone

Abstract: A new onshore-offshore seismic dataset from the Cascadia subduction zone is used to characterize mantle lithosphere structure from the ridge to the volcanic arc, and plate interface structure offshore within the seismogenic zone. The Cascadia Initiative covered the Juan de Fuca plate offshore the northwest coast of the United States with an ocean bottom seismometer (OBS) array for four years; this was complemented by a simultaneous onshore seismic array. Data recorded by this array allows the unprecedented imaging of an entire tectonic plate from its creation at the ridge through subduction initiation and back beyond the volcanic arc along the entire strike of the Cascadia subduction zone. Higher frequency active source seismic data also provides constraints on the crustal structure along the plate interface offshore. Major findings include that thermal oceanic plate cooling models do not explain the velocities observed beneath the Juan de Fuca plate, that slow velocities in the forearc appear to be more prevalent in areas modeled to have experienced high slip in past Cascadia megathrust earthquakes, and along arc variations in phase velocity reflect variations in volumetric magma storage and heat input.

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April 6, 2018
3:00pm in PLS 1140
Mark Harrison from UCLA
A New Paradigm for Early Earth

Abstract: The ubiquity of origin myths among human societies suggests that our species has an innate need to explain how Earth formed and came to its present state. The controls on myth fabrication include the limitations of the available historical record and the technological capability of the culture in question. Despite our impressive technology and a western cultural bias to watery origins, when the scientific community encountered the limits of its historical record – there are no known rocks older than 4 billion years, it chose the paradigm of a desiccated, continent-free wasteland in which surface petrogenesis was largely due to bollide impact into a basaltic substrate and called it the “Hadean” (hellish time). But the story emerging from geochemical investigations of >4 billion year old Jack Hills zircons is of their formation in water-rich granites under relatively low geothermal gradients. These results have been interpreted as reflecting chemical weathering and sediment cycling in the presence of both liquid water and plate boundary interactions shortly after Earth formed. Given general agreement that life could not have emerged until liquid water appeared at or near the Earth’s surface, a significant implication is that our planet may have been habitable as much as 500 million years earlier than previously thought. Indeed, recent C isotopic evidence obtained from inclusions in Hadean zircons is consistent with life having emerged by 4.1 Ga, or several hundred million years earlier that the hypothesized lunar cataclysm. Perhaps the most remarkable feature of these observations drawn from ancient zircons is that none were predicted from theory. Rather, generations of models essentially innocent of observational constraints fed the longstanding paradigm. What compelled the scientific community to develop its own origin myth – of a hellish beginning – in the absence of direct evidence? While science is clearly distinguished from mythology by its emphasis on verification, its practitioners may be as subject to the same existential need for explanations as any primitive society.

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April 13, 2018
3:00pm in PLS 1140
Benjamin Andrews from Smithsonian Institution
Experimental dilute pyroclastic density currents

Abstract: Pyroclastic density currents (PDCs) present substantial hazards to life and property, and can rapidly alter the landscape. Detailed study of these currents in nature, however, is challenging because of the currents’ size, hazards, and (un)predictability. The Smithsonian Institution’s Experimental Volcanology Laboratory allows for study of the dilute endmember of PDCs, so-called “pyroclastic surges,” through scaled laboratory experiments. Temperature measurements, 2D velocity fields, 4D scans of currents, and maps of the resulting deposits provide insights into parameters controlling the runout, liftoff, and general behavior of PDCs, and how those parameters can be inferred from direct observation of natural currents or the deposits they leave behind.

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April 20, 2018
3:00pm in PLS 1140
Lynnae Quick from Center for Earth and Planetary Studies, Smithsonian National Air and Space Museum
Cryovolcanism in the Solar System and the Formation of Cryovolcanic Domes on Europa

Abstract: In addition to altering the surfaces of the terrestrial planets, volcanic processes have also modified the surfaces of the icy worlds in our solar system. Spacecraft imagery of these bodies has revealed evidence of cryovolcanism, during which briny, aqueous solutions, and volatiles such as water vapor and carbon dioxide, are erupted. Voyager 2 and Cassini imaged geyser-like eruptions in the south polar regions of Triton and Enceladus, respectively. Imagery from the Galileo spacecraft and recent Hubble detections of putative geyser-like plumes on Europa suggest that volcanic processes may be currently occurring on the smallest Galilean satellite. Ground-based studies and imagery from NASA’s New Horizons and Dawn spacecrafts suggest that cryovolcanism may have also occurred on large Kuiper Belt Objects such as Pluto and Charon, and possibly on dwarf planet Ceres. In this talk, I will review the current state of knowledge of cryovolcanism in our solar system and present new research results which suggest that a subset of domes on Jupiter’s moon Europa may have been emplaced via cryovolcanic processes. I will also review the merits of cryovolcanism as an exchange process, and implications for habitability on worlds where it is active. Finally, I will introduce the goals and objectives of NASA’s Europa’s Clipper Mission, which will search for ongoing activity at Europa.

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April 27, 2018
3:00pm in PLS 1140
Anaïs Bardyn from Department of Terrestrial Magnetism, Carnegie Institution for Science
The dust of comet 67P/Churyumov-Gerasimenko

Abstract: After a 10-year journey, the European spacecraft Rosetta arrived at comet 67P/Churyumov-Gerasimenko (67P) on August 6, 2014. In order to conduct intensive research for 26 months, a total of 21 instruments were on board the Rosetta orbiter and the Philae lander. The mass spectrometer named COSIMA (Cometary Secondary Ion Mass Analyzer) was one of the orbiter instrument and was designed to collect cometary dust particles ejected from 67P nucleus, imaged them and analyzed in situ their composition. I will present the Rosetta space mission, as well as results from the COSIMA instrument regarding the organic content of the cometary dust particles.

The coordinator for the Colloquium Series is Dr. Nicholas Schmerr. You can contact him at nschmerr@umd.edu.