February 8, 2019
3:00pm in PLS 1140
Nicholas Schmerr from University of Maryland, College Park
Sounding Ice: Exploring For Liquid Water in the Frozen Subsurfaces of Greenland and Europa

Abstract: The polar ice caps of Earth are rapidly melting under the influence of global warming. On the Greenland ice sheet, the resulting melt water is creating many new types of glacial features, including lakes deep beneath the overlying ice, liquid water stored in aquifers in the near surface ice and snow, and stunning aquamarine ponds of melt at the surface. My team and I are investigating the properties and size of these melt pockets using advanced geophysical tools to look through the ice and determine where and how much liquid water is present. We are using this unique Greenland environment to plan for exploring the interior of Europa, Jupiter's icy moon. Our techniques for studying liquid water within the Greenland ice sheet provide crucial inputs for future NASA missions that plan to investigate the properties of the subsurface Europa ocean (and other icy ocean worlds like it) and determine if Europa could potentially harbor life.

February 15, 2019
3:00pm in PLS 1140
Ciaran Harman from Johns Hopkins University
Co-evolution, bedrock weathering, and lateral flow in hillslopes

Abstract: Catchment hydrology has struggled to develop a unified approach to understanding and predicting the internal organization of hillslopes, and the process dynamics that apparently control the delivery of water and solutes to streams. This arguably limits our ability to deliver the kind of predictions needed for water resource planning and regulation the over the long term, and across spatial scales. To address this challenge, perhaps we need to reframe the question entirely: in addition to asking “what is the hydrologic structure of the landscape?” we should also be asking “why is it so?”. How do landscapes develop the hydrologic properties they have? The potential and promise of ‘co-evolution’ or ‘Darwinian hydrology’ has been widely discussed, but there have been limited attempts to address the question directly. Here I will present an attempt to understand how the internal structure of chemically-weathered hillslopes could both control and be controlled by the lateral flow of meteoric water towards adjacent streams. I will present a model that couples hillslope hydraulics and solute transport with a parsimonious model of geochemical weathering and its effect on porosity and permeability. The resulting approximate analytical solutions yield realistic hillslope internal architectures when supplied with realistic geomorphic, geochemical and hydrologic parameter values derived from literature.

February 22, 2019
3:00pm in PLS 1140
David Kring from USRA - Lunar and Planetary Institute
The Discovery of the Chicxulub Crater and Recent Insights from IODP-ICDP Expedition 364

Abstract: The discovery of the Chicxulub impact crater added tremendous credibility to the impact-mass extinction hypothesis.  That discovery led, in turn, to detailed studies of the impact’s environmental effects.  More recently, deep subsurface drilling by IODP and ICDP provided an opportunity to study the formation of the extraordinary ~180 km diameter basin, which shattered the Yucatan Peninsula, causing once immobile granite to flow in excess of a hundred kilometers an hour.  The heat of the impact spawned a vast hydrothermal system that persisted for about a million years.  That hydrothermal system is currently being used as a proxy for Hadean Earth systems that may have hosted Earth’s earliest life.

March 1, 2019
3:10pm in PLS 1140
Linda Gundersen from USGS
Scientific Integrity, Ethics, Diversity, and Sexual Harassment: Why Should You Care?

Abstract: Understanding the values each person brings to the table is key to understanding how ethics, integrity, diversity, and  harassment are connected. Values are critical, they determine decisions we make such as falsifying data or consciously discriminating to out-compete someone. Values also determine our implicit and explicit biases, both scientific and personal. Through these biases we may systematically exclude ideas, people, and practices; weakening the very framework of science. This presentation explores these concepts interactively with the audience through learning, scenarios, and discussion.

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March 15, 2019
3:10pm in PLS 1140
Megan Holycross from Smithsonian
Probing the Earth’s deep oxygen cycle with vanadium

Abstract: The oxidation state of the solid Earth influences, to a first order, the structure of the planet and the chemistry of rocks, ores and volcanic gases; mass transfer of oxygen between terrestrial reservoirs enables a habitable world. The abundance of oxygen in Earth’s upper mantle has increased by nine orders of magnitude since accreation—however, there is considerable debate about both the timing and mechanism of the processes that have oxidized the Earth’s interior, and if these processes are related to the rise of atmospheric O2. The oxidation state of eclogites, the products of basalt metamorphism on subducting slabs, may hold the clues. Here, I’ll present the experimental calibration of a new redox proxy for eclogitic mineral assemblages that utilizes the multivalent trace element vanadium. The new proxy is applied to determine the oxidation state of Archean eclogite xenoliths from Sierra Leone and further constrain the redox evolution of the mantle.

March 29, 2019
3:10pm in PLS 1140
Meredith Townsend from Brown University
How do magma chambers grow? Insights from thermo-mechanical modeling with applications to large silicic caldera systems

Abstract: Magma chambers in Earth’s crust can grow to be hundreds to thousands of cubic kilometers, potentially feeding catastrophic caldera‐forming eruptions. Smaller‐volume chambers are expected to erupt frequently and freeze quickly; a major outstanding question is how magma chambers ever grow to the sizes required to sustain the largest eruptions on Earth. I will present recent results from Townsend et al. 2019 G-cubed, which uses a thermo‐mechanical model to investigate the primary factors that govern the extrusive:intrusive ratio in a chamber, and how this relates to eruption frequency, eruption size, and long‐term chamber growth. The model consists of three fundamental timescales: the magma injection timescale τin, the cooling timescale τcool, and the timescale for viscous relaxation of the crust τrelax. We estimate these timescales using geologic and geophysical data from four volcanoes (Laguna del Maule, Campi Flegrei, Santorini, Aso) to compare them with the model. In each of these systems, τin is much shorter than τcool and slightly shorter than τrelax, conditions that in the model are associated with efficient chamber growth and simultaneous eruption. In addition, the model suggests that the magma chambers underlying these volcanoes are growing at rates between ~10‐4‐10‐2 km3/yr, speeding up over time as the chamber volume increases. We find scaling relationships for eruption frequency and size that suggest that as chambers grow and volatiles exsolve, eruption frequency decreases but eruption size increases. These scaling relationships provide a good match to the eruptive history from the natural systems, suggesting the relationships can be used to constrain chamber growth rates and volatile saturation state from the eruptive history alone.

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April 5, 2019
3:10pm in PLS 1140
Mark Kurz from Woods Hole Oceanographic Institution
Noble gases from the deep earth: evidence from ocean island volcanoes

Abstract: Oceanic basalts are the most voluminous product of mantle melting and provide important information on the structure and evolution of the mantle. Due to their inertness and isotope systematics the noble gases in basaltic glasses are unique tracers for the evolution of the earth's mantle and atmosphere. Unradiogenic helium and neon isotopes in mantle samples are found at only a few ocean islands, such as Hawaii, Iceland and Galapagos, providing unique evidence for primitive/primordial material remaining in the earth's mantle. This talk will provide an overview of the spatial and temporal noble gas isotopic variations in ocean island volcanoes, with an emphasis on Hawaii, Galapagos and Iceland, and implications for the scales of mantle heterogeneity and residence sites of mantle noble gases.

April 19, 2019
3:10pm in PLS 1140
Jessica Warren from University of Delaware
Using fault-zone geology to understand oceanic transform fault seismicity

Abstract: Oceanic transform faults are a major category of plate boundaries, yet the mechanisms accommodating slip across the plate interface are poorly constrained. Some fault segments undergo repeated large earthquakes, while other segments are relatively aseismic yet host deep microseismicity. Rocks recovered from transform faults can be used to constrain the mechanisms of seismic versus aseismic slip through the evidence that they preserve of high-strain deformation. I will present observations of deep fluid flow preserved in these fault rocks, which may drive grain size reduction, metamorphic reactions, and switches in the mechanisms accommodating slip. I will propose that variable hydration along the fault controls the fault rheology, including the depth to the brittle-ductile transition and the occurrence of seismic versus aseismic behavior.

April 26, 2019
3:10pm in PLS 1140
Robert Holder from Johns Hopkins University
Metamorphism and the Evolution of Plate Tectonics

Abstract: At present, Earth’s mantle convection, which facilitates planetary heat loss, is expressed at the surface as plate tectonics. When plate tectonics emerged and how it has evolved through time are two of the most fundamental and provocative questions outstanding in Earth science. Metamorphic rocks, those that have experienced solid-state mineral transformations due to changes in pressure (P) and temperature (T), record periods of burial/exhumation and heating/cooling that reflect the tectonic environments in which they formed. Changes in the global distribution of metamorphic P–T conditions in the continental crust through time reflect secular evolution of Earth’s tectonic processes at convergent plate boundaries. On modern Earth, convergent plate margins are characterized by metamorphic rocks that record a bimodal distribution of apparent thermal gradients (change in temperature with depth, parameterized in this talk as metamorphic T/P), in the form of paired metamorphic belts, which is attributed to metamorphism near to (low T/P) and away from (high T/P) subduction zones. In this talk, I will evaluate the emergence of bimodal metamorphism as a proxy for secular change in plate tectonics using a statistical evaluation of the distributions of metamorphic T/P through time. I will argue that Earth’s modern plate tectonic regime developed gradually since the Neoarchaean Era in conjunction with secular cooling of the mantle and associated changes in the thickness, buoyancy and rheology of oceanic lithosphere, resulting in an evolution in the styles of both subduction and collisional orogenesis.

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The coordinator for the Colloquium Series is Dr. Mong-Han Huang. You can contact him at mhhuang@umd.edu.
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