To post an event in the JSG Events calendar, send details (talk title, series, date, start and end time, location, contact) to the representative for the unit hosting the talk:
Bureau of Economic Geology: Valerie Siewert
Department of Geological Sciences: Lyndsey Turner
Institute for Geophysics: Nancy Hard
Dean’s Office/CIEEP/EER/Other: Submit a ticket
Informal weekly presentations by UTIG students and researchers. Bring your lunch!
Watch live.
Title: The Asthenosphere, Mantle Convection, and the Dynamics of Plate Tectonics
Abstract: Since the discovery of plate tectonics it has been suspected, but never fully demonstrated, that a low-viscosity layer beneath the plates (i.e., the asthenosphere) may play a central role in facilitating their motions.This idea has cast a significant shadow not only on Earth dynamics but also on comparative planetology - in particular on Earth-Venus comparisons. We review constraints on the structure and viscosity of the asthenosphere that are provided by geoid and post glacial rebound studies. We also review previous numerical simulations that highlighted the potentially key role that a rheologically weak asthenosphere, interacting with plates above, could play in maintaining plate tectonics on Earth. We then present new models that expand explorations into the defining characteristics of the asthenosphere and its role for the mantle convection and plate tectonics. The collective works leads us to suggest a geodynamic definition of the asthenosphere that breaks from the traditional view that the principal role of the asthenosphere, for plate tectonics, is to provide basal lubrication for plates.
Learn more about Dr. Lenardic
Host: Thorsten Becker
Informal weekly presentations by UTIG students and researchers. Bring your lunch!
Watch live.
Title: The Wibbly Wobbly Moon: The Rotational Dynamics of the Moon Over Time.
Abstract: The spins of planets and moons are not constant with time; they change in response to both external and internal forces on a variety of spatial and temporal scales. These changes can have important consequences for the geology of a planet, including stirring up the core dynamo, generating tectonic stresses in the crust, and altering the stability of water and other volatile ices across the planet's surface. Beyond the Earth, the Moon is the only other solar system body where we have been able to constrain multiple aspects of its rotational history. In this seminar, I will present a variety of new results detailing our investigations into the Moon's rotational dynamics over time: from long-term true polar wander due due to mantle convection, to chaotic tumbling due to giant impacts. While I will focus on the Moon, these dynamical processes are incredibly general, and I will touch on some prospects for future analogous studies of Mercury, Venus, Mars, and the icy worlds.
Learn more about Dr. Keane.
Host: Duncan Young
Informal weekly presentations by UTIG students and researchers. Bring your lunch!
Watch live.
Title: Shaping slow-spreading seafloor with detachment faults
Abstract: While seafloor formed at intermediate- and fast-spreading mid-ocean ridges shows little variability in the along-axis direction, the morphology of slow-spread seafloor is inherently three-dimensional. Within tens of km along a slow ridge segment, the landscape can change from regularly-spaced basaltic hills bounded by short-offset faults to dome-shaped exposures of mantle units capped by a large-offset detachment. Because most previous modeling efforts have been confined to 2-D cross-axis sections, the mechanics of the along-axis transition between these two distinct modes of seafloor spreading is largely unknown. In a broader sense, the link between the sub-seafloor geometry / extent of a detachment fault and its expression at the seafloor remains contentious. I will address these questions through a combination of bathymetric analysis, 3-D thermo-mechanical modeling, and simple mechanical modeling. In the first part of the presentation, I will show that the along-axis extent and overall shape of detachment fault footwalls directly reflect along-axis gradients in the amount of magma supplied to the ridge axis. In the second part of the talk, I will discuss the way seafloor-shaping processes (e.g., mass wasting) continuously rework detachment fault footwalls and complicate the tectonic interpretation of bathymetry. Together, these efforts greatly improve our ability to interpret seafloor morphology in terms of underlying geodynamic processes.
Learn more about Dr. Olive.
Host: Luc Lavier
Informal weekly presentations by UTIG students and researchers. Bring your lunch!
Watch Live
Title: Deep crustal evolution, continental deformation, and the roots of faults from seismology and xenoliths
Abstract: I will present two studies that combine seismic and xenolith data to investigate continental assembly, evolution of deep crustal structure, and deformation along faults and their ductile roots of the North American continent.
The first study uses EarthScope and pre-existing active source seismic data and xenolith studies to map the distribution of high-velocity lower crust, indicating mafic or garnet-bearing material, across the U.S. and assess its relationship to proposed emplacement and loss mechanisms such as under- and intraplating, collision, extension, heating, cooling, hydration, and delamination. Thin layers of high-velocity crust related to regional processes are found scattered throughout the continent. Thicker layers in large areas are found in the central and eastern U.S. in areas with thick crust, bounded roughly by the Rocky Mountain Front, which cuts across Proterozoic assembly provinces. Hence, the modern north-south first-order contrast in structure may reflect garnet growth with aging of continental crust in much of the central and eastern U.S., while conditions in the western U.S. are unfavorable for growth and maintenance of thick layers of high-velocity garnet-bearing lower crust. We find areas with differences between the seismically defined Moho and the petrological crust-mantle boundary.
The second project combines laboratory data from xenoliths and anisotropic receiver functions to map fault zones and shear zones in the lithosphere. We developed a method to image contrasts in azimuthal anisotropy, dipping rock fabric, and dipping isotropic contrasts based on azimuthally varying conversions in receiver functions. Unlike shear wave splitting, azimuthally varying P to S conversions provide a large-amplitude, robustly observable signal even for small (few percent) contrasts in anisotropy in thin (few km) shear zones and provide depth resolution. Strikes from receiver functions typically align with surface fault traces in tectonically active regions, with depths of the converters extending into the ductile regime. Interpretation of observed seismic anisotropy requires knowledge of underlying symmetry systems, which are not well determined for the crust. We analyze a compilation of whole rock elasticity tensors from ultrasound and microstructural laboratory measurements. Our collection contradicts the commonly made assumption of elliptical hexagonal anisotropy; we observe that crustal anisotropy deviates from the elliptical case with increasing strength of anisotropy, which changes inferred anisotropy amplitudes and orientations in receiver function and surface wave studies. Our observations suggest that reactivation of inherited structures may play a significant role in present day deformation.
Learn more about Dr. Schulte-Pelkum.
Host: Thorsten Becker
s Mars the next step in human exploration of the solar system? What would it take to live and work on the red planet, and what will future explorers need to know in order to survive Martian extremes? Join Dr. Joseph Levy on a journey of endurance and exploration from Earth’s remotest outposts to the surface of Mars.
Special appearance by Dr. Jeannette J. Epps, NASA Astronaut. Attendees may meet Dr. Epps as well explore hands-on activities and demonstrations related to space exploration, engineering, astronomy and more as part of Cool Activities from 5:30 - 6:40 p.m.
