September 11, 2020
3:00pm in Online
Adam Simon from University of Michigan
The Formation of Iron Oxide - Apatite (IOA) and  Iron Oxide - Copper - Gold (IOCG) Mineral Deposits: Implications for Sustainable Development

Abstract: There are more than one billion people on Earth who lack access to electricity and other forms of energy infrastructure. This reality for citizens of the less developed world restricts, and in most cases eliminates, their access to modern education, healthcare and economic empowerment that has accompanied the growth of the middle class throughout the developed world. Reducing global poverty, achieving gender equality, reducing birthrates, increasing democracy, and decreasing domestic violence, among many other cultural, economic, political and social challenges depends critically on building energy infrastructure in the developing world and transitioning the built energy environment of the developed world to one that ultimately relies on renewable energy resources.  This requires mining the resources to make said infrastructure the reality for our global society. In this talk, I will review our historic use of resources, discuss the current supply, and make the case that geologists serve a critical role in ensuring a sustainable supply of the resources to satisfy future consumption. I will focus on two mineral deposit types that provide metals such as iron, which is the main component of steel and the backbone of our built environment; copper, which allows the distribution of electricity; gold, which is a conductor in all modern technology; and rare earth metals, which are used to make magnets that make possible our smartphones, televisions, lasers, rechargeable batteries, hard drives and a plethora of medical imaging devices.

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September 18, 2020
3:00pm in Online
Victor Tsai from Brown University
Understanding High-Frequency Earthquake Ground Motion

Abstract: Why do earthquakes damage buildings? Many buildings are damaged most heavily by fast, jerky ground motion rather than the longer duration rolling motions that contain most of the earthquake energy. Despite the importance of these fast, jerky motions, most frictional models for earthquakes generally underpredict how strong they are, even when heterogeneous friction and realistic roughness are accounted for. In this talk, I discuss an alternative hypothesis that collisions of structures as they attempt to slide past each other during an earthquake may also create jerky ground motion. Interestingly, the ground motion from collisions depends mostly on the size of the structures and does not depend on stresses within the Earth and thus gives a very different interpretation of what causes the most damaging ground motions. When incorporated with standard frictional models, the collision model explains various observations that are otherwise difficult to explain, including why some earthquakes appear to be identical in time but with larger amplitudes, why faults that have had many earthquakes have less damaging ground motions, and why earthquake damage is observed to occur more uniformly than previously predicted.

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September 25, 2020
3:00pm in Online
Zach Eilon from UCSB
Probing the Pacific mantle with Ocean Bottom Seismology

Abstract: Despite decades of study, numerous aspects of the oceanic plates, which cover >65% of our planet, remain unclear. These include the cooling regime and shape of the depth-age curve, widespread off-axis, non-plume volcanism, strong anisotropic fabrics with varying depth patterns, and gravity lineations spanning a range of plate ages. This surprising (to many) level of ignorance is largely because geophysical study of the oceanic lithosphere and asthenosphere has mostly been limited to fuzzy imaging from basin-crossing phases and remote sensing. Broadband Ocean Bottom Seismic (OBS) deployments offer new opportunities to peer into the oceanic mantle with high-resolution local constraints. The Pacific OBS Research into Convecting Asthenosphere (Pacific ORCA) experiment involved deployment of an 500x500 km2, 30-station OBS array in the central Pacific Ocean on ~40Ma seafloor northeast of the Marquesas Islands. I will present (for the first time!) analysis the seismic data collected by these OBS instruments. Early results include: P-s receiver function images that reveal an unexpected intra-lithospheric seismic discontinuity, profiles of shear velocity and anisotropy derived from surface waves, and preliminary differential travel time P-wave tomography that hints at mantle velocity anomalies consistent with small scale convection cells beneath the plate. 

October 9, 2020
3:00pm in Online
Meenakshi Wadhwa from ASU
From Dust to Planets: Tracing the History of the Early Solar System via Evidence of Short-lived Radionuclides in Meteorites

Abstract: Meteorites and their components represent some of the earliest-formed materials in our Solar System. As such, geochemical and isotopic studies of these materials can provide great insights into the conditions and processes in the solar nebula, as well as the subsequent evolution resulting in the formation of planetesimals and planets. In this talk, I will focus on the evidence for the former presence of short-lived radionuclides (SLRs; i.e., radionuclides with half-lives significantly shorter than the age of the Solar System, such that they are considered “extinct” at the present time) in meteoritic materials. I will discuss how the inferred abundances and distributions of these SLRs in a variety of meteorites can help to constrain the astrophysical environment in which our Sun was formed and the time scales for the accretion and differentiation of rocky bodies, such as the asteroid 4Vesta, in our Solar System.

October 23, 2020
3:00pm in Online
Kirsten Siebach from Rice University
Source-to-Sink Processes in Gale Crater: Investigating Sedimentary Rocks on the Red Planet

Abstract: Since landing on the floor of Gale crater in August 2012, the Mars Science Laboratory Curiosity rover has explored over 400 m of basin-fill stratigraphy primarily consisting of fluvio-deltaic deposits and lacustrine mudstones. These sedimentary rocks are historical archives, recording an integrated history of past surface and sub-surface environments. We utilize a “source-to-sink” framework for interpreting the geochemistry of sedimentary rocks observed by Curiosity; this recognizes that the rocks represent an integrated history of detrital source particles, affected by weathering, transport, and sorting processes, and then lithified with chemical sediments and cements, and potentially physically and chemically altered by diagenetic processes. I will present how we have been using modeling, field analogs, and laboratory work to detangle these influences to constrain the magmatic systems around Gale, the paleoclimate during sediment deposition, sorting processes during transport, and lithification and diagenetic processes. These constraints help us better understand the type and duration of habitable environments above and below the surface.

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October 30, 2020
3:00pm in Online
Miquela Ingalls from Penn State
P/Ca in Carbonates as a Proxy for Alkalinity and Phosphate Levels

Abstract: Understanding mechanisms, rates, and drivers of past carbonate formation provides insight into the chemical evolution of Earth’s oceans and atmosphere. We paired geological observations with elemental and isotope geochemistry to test potential proxies for calcium-to-alkalinity ratios (Ca:ALK). Across diverse carbonate facies from Pleistocene closed-basin lakes in Owens Valley, CA, we observed less d44/40Ca variation than theoretically predicted (>0.75‰) for the very low Ca:ALK in these systems. Carbonate clumped isotope disequilibria implied rapid carbonate growth—kinetic isotope effects, combined with the diverse carbonate minerals present, complicated the interpretation of d44/40Ca as a paleo-alkalinity proxy. In contrast, we observed that the high phosphate concentrations are recorded by shoreline and lake bottom carbonates formed in eleven Pleistocene lakes at orders of magnitude greater concentrations than in marine carbonates. Because the maximum phosphate content of water depends on Ca:ALK, we propose that carbonate P/Ca can inform phosphate levels and thereby Ca:ALK of aqueous environments in the carbonate record.

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November 13, 2020
3:00pm in Online
Jacob Lowenstern from Volcano Disaster Assistance Program and USGS
Some thoughts on volcanoes, their eruptions, and how we can best mitigate their negative impacts

Abstract: We will explore aspects of volcano monitoring, forecasting, and risk mitigation, with specific focus on the realities of our current understanding of volcanoes and magmatic systems.  As we wander through this topic, we'll think about how volcano observatories operate, the equipment they use, their responsibilities, and the challenges they face in providing useful information to decision makers.  We will also touch upon some of the factors that determine successful outcomes  during volcanic crises.  Specific discussion of a few volcanic systems (Yellowstone, the Aleutians, Agung) and geothermal systems (Krafla) will help illuminate the discussion.

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November 20, 2020
3:00pm in Online
Lars Hansen from University of Minnesota
From mega-annum to microseconds: the role of crystal dislocations in the dynamics of the solid earth

Abstract: Large-scale geodynamic processes in the solid Earth often depend intimately on small-scale defects within the constituent minerals. These processes span a wide range of time scales and include convection in the upper mantle, flexure of the lithosphere, glacial isostatic adjustment, postseismic creep, and frictional sliding on faults during earthquakes. Here I describe the influence of dislocations, a particular type of crystal defect, on this range of processes within upper-mantle rocks. The role of dislocations across these timescales is elucidated by a series of laboratory experiments including synchrotron-based experiments to measure yield stress and strain hardening, high-temperature uniaxial tests to investigate anelasticity, and dynamic indentation using ball-drop experiments to assess mineral strength at extreme strain rates. These different experimental approaches are linked through the dynamics of dislocations. The resulting model of dislocation-based deformation resolves conflicts among previous geophysical observations and provides a series of new predictions about the mechanical properties of rocks at both slow and fast timescales not typically accessible in the laboratory. 


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

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