GPS Event Calendar

" Mountain building and mantle convection : Holmes (1931) revisited "

Claudio Faccenna, University of Texas at Austin

Abstract:

Orogeny results from crustal thickening at active margins, and much progress has been made on understanding the associated kinematics. However, the ultimate cause of orogeny is still debated, especially for the case of extreme crustal thickening. Inspired by the seminal work of Holmes (1931), we explore the connections between the style of orogeny and mantle dynamics. We distinguish between two types of orogeny, those that are associated with one-sided, mainly upper mantle subduction, "slab-pull orogeny", and those related to more symmetric, whole mantle convection cells, referred to as "mantle", or "slab-suction orogeny". Only the latter leads to extreme crustal thickening. We propose that mantle orogeny is generated by the penetration of slabs into the lower mantle and the associated change in the length scales of convection. This suggestion is supported by numerical dynamic models which show that upper plate compression is associated with slab penetration into the lower mantle. We explore the geological record to test the validity of such a model for both Cordillera and the Tibetan-Himalayan orogenies and with older Pangea assembly events orogeny. We propose that this Late Paleozoic large-scale compression is likewise related to a change from transient slab ponding in the transition zone to lower mantle subduction. If our model is correct, the geological record of orogeny in continental lithosphere can be used to decipher time-dependent mantle convection, and episodic lower mantle subduction may be causally related to the supercontinental cycle.

Brief Bio:

Claudio Faccenna is a solid Earth Scientist with a broad spectrum of interests around tectonics and geodynamics. Initially trained as a structural geologist, he devoted most of his career on understanding processes that govern subduction, continental deformation and mantle convection over geological timescale. His cross-disciplinary expertise ranges from field-based studies (Mediterranean - Middle East, South America, Antarctica and East-Africa) to modelling.

He is Chair of Structural Geology at UT Austin (2019), before Full Professor at the University of Roma TRE (2011-2019), where he was first Researcher (1994) and then Assistant professor (2001). Author of more than 190 papers, he is serving as Editor of Tectonics and from 2018 EiC for G-Cubed. He is member of the Academia Europaea, and he received Premio Galileo Galilei (2010), prix Viquesnel from the Societé Geologique de France (2013), Stephan Muller medal from EGU (2014), von Humboldt Research award (2015), and Fellow of the AGU (2018).

"Understanding Planetary System Formation Through Astrochemistry"

Ilse Cleeves, University of Virginia

Abstract:

Historically, our understanding of planet formation and the origins of planets' compositions has been largely informed by our Solar System. However, we are just one system, and now with facilities like NASA's Kepler and TESS telescopes, we are discovering a wide variety of planet types and architectures, many of which are unlike our own. In the last five years, the Atacama Large Millimeter/Submillimeter Array has simultaneously revolutionized our understanding of planet formation by imaging disks around young stars at high resolution and with high sensitivity. In this presentation, I will discuss how observations of molecular spectral line emission in protoplanetary disks can shed light on 1) the compositions of future planets; and 2) the key physics governing disk evolution during the first few million years of evolution, to help us move toward a more general picture of planet formation, at home and abroad.

Background:

Ilse Cleeves is an Assistant Professor in the Departments of Astronomy and of Chemistry at the University of Virginia. She arrived at UVa in 2018 after a NASA Hubble Postdoctoral Fellowship at the Harvard-Smithsonian Center for Astrophysics (2015-2018). She obtained her PhD from the University of Michigan in 2015. Recent accolades include being named the 2020 Johnson & Johnson Women in STEM2D Awardee in "Science," a 2019 Packard Fellowship, and named the 2018 AAS Annie Jump Cannon Awardee.

" Deep Mantle Plume beneath the Yellowstone Hotspot? "

Stephen Grand, University of Texas at Austin

Abstract:

The Yellowstone Hotspot, located in western North America, is an intraplate source of magmatism whose origin has been hotly debated. Some argue that a deep mantle plume sourced at the base of the mantle supplies the heat beneath Yellowstone while others claim shallower subduction or lithospheric related processes can explain the anomalous magmatism. We present a new shear wave tomography model for the deep mantle beneath the western United States that was made using the travel times of core waves recorded by the dense USArray seismic network. The model shows a narrow (~350 km diameter) cylindrically shaped slow anomaly that is tilted to the northeast and extends from the Core-Mantle boundary to the surficial position of the Yellowstone Hotspot. We interpret the anomaly as a plume. The tilt of the plume may be due to large scale mantle flow advecting the rising plume. We have run simulations of convection with a rising plume inserted and find for most convection models, the predicted tilt of the plume agrees with the seismic model, supporting our interpretation. The degree of tilt, however, requires a rise time of 80 Ma or longer.

" Understanding the rules of microbiome resilience "

Ashley Shade, Michigan State University

Abstract:

Microbial communities (also called microbiomes) are composed of up to tens of thousands of different types of microbial members. These communities perform functions that are absolutely essential for their ecosystems, from nutrient cycling in the environment, to priming the immune system in a plant or animal host. Many of these functions are supported by the collective community, which is why it is important to consider the microbiome as a system with many interacting parts.

The Shade lab, we want to understand how microbial communities respond to stress so that we can manage them to quickly recover. The capacity to recover quickly and fully from a large stress is called resilience. Understanding the rules of microbiome resilience will help to support healthy outcomes for hosts and environments by stabilizing the essential functions that microbial communities perform. In this seminar, I will discuss our recent research and working conceptual framework for how microbial traits and processes determine a community's resilience. We hypothesize that there are general rules of microbiome resilience that can be usefully applied across different contexts. My lab's research is grounded in ecological framework and focused on building transferable theory, approaches, and knowledge of resilience mechanisms that transcend microbiome hosts and ecosystems.

"TBD"

Caroline Morley, University of Texas at Austin

"The Icy Mid-Latitudes of Mars"

Ali M. Bramson, Professor – Department of Earth, Atmospheric, and Planetary Sciences

Purdue University

Abstract

The distribution and nature of water ice on Mars has important implications for understanding the Martian climate system, as well as evaluating the in-situ resources available for future human exploration and the astrobiological potential of our solar system. I will present the results of several multi-faceted studies to investigate the distribution, properties, and preservation of ice on Mars. I will show how the properties of mid-latitude ice can be constrained using remote sensing observations from imaging and radar systems onboard NASA's Mars Reconnaissance Orbiter, and discuss the importance of these constraints for understanding the planet's climate. I will discuss how I combine these remote sensing datasets with theoretical models of ice stability to understand the evolution and continued preservation of subsurface ice sheets to the present day. I will conclude by presenting how new remote sensing projects, such as the SWIM Project (swim.psi.edu), and analog studies can elucidate ice-related processes occurring on Mars and elsewhere.

"Can We Get to Carbon Neutral Livestock Production?"

Ermias Kebreab, University of California Davis

Abstract:

California is committed to reducing methane emissions by 40% by 2030 (SB 1383) and carbon neutrality by 2045. The livestock industry is responsible for 55% of anthropogenic methane emissions and about 4% of total greenhouse gas emissions in the state. Several options are available or need to be made available if we are going to reach this goal for both methane and total carbon emissions.

"The Early Earth Productivity Paradox"

Michael Kipp, Caltech

Abstract:

Numerous lines of evidence suggest that net primary productivity was considerably lower on the early Earth than it is today. Combined with isotopic evidence for only small changes in fractional organic burial through time, this implies lower-than modern rates of total carbon burial in Precambrian marine sediments. However, other lines of evidence imply that rates of carbon input to Earth's surface reservoir– volcanism and weathering – were higher in Earth's early history than at present. It is well-established that negative feedbacks balance the carbon cycle on million-year timescales, meaning a long-term (>Myr) budget imbalance is implausible. So are we left with a paradox in Earth's early carbon budget?

In this talk I will present literature estimates of carbon fluxes into and out of Earth's surface reservoir through geologic time and attempt to construct a balanced carbon budget through Earth's history. In doing so I will show that in order to accommodate high outgassing rates and low biological productivity in the Precambrian, the burial efficiency of organic carbon in marine sediments must have been higher than it is today by 1-2 orders of magnitude. This is consistent with recent work that has argued for high burial efficiency due to a scarcity of oxidants in Precambrian seawater. We also consider the implications of high burial efficiency for the Archean redox budget, finding that atmospheric anoxia would have been difficult to maintain in a high-burial-efficiency world unless the flux of reductants from the mantle was greater than it is today. This supports recent studies that invoke an increase in mantle redox state in the late Archean as a possible trigger for the Great Oxidation Event.

"TBD"

Darcy McRose, Caltech

"TBD"

Carina Fish, UC Davis

" Investigating the role of thermo-poro-elastic stresses and deformation on induced seismicity "

Kyungjae Im, Caltech

ABSTRACT:
We investigate the influence of thermo- and poro-elastic stresses on induced seismicity in the context of geothermal energy production at Coso and Brawley in California. Coso geothermal field is one of the largest (>250MW at peak) geothermal fields operated for ~30 years, and the Brawley geothermal field is a smaller (~40MW) and shallower geothermal system operated for ~10 years. To model accurate field scale thermo-hydro-mechanical response, we set a permeable reservoir embedded in a large hosting domain using a Tough-FLAC coupled simulator. Additionally, for the Brawley field, a critically stressed normal fault is embedded through the reservoir and host rock, as observed in a previous study. All simulation parameters are determined to reproduce the production, pressure and surface deformation of each field. Both simulations results in comparably rapid poro-elastic stress change over a broad area of reservoir and host, followed by slow but strongly accumulating thermal stress change within localized areas near injection and production zones. The Coso field simulation predicts a cumulative surface subsidence of ~70cm over 30 years and the Brawley simulation predicts surface subsidence of ~20 cm over 10 years across the area generally consistent with the subsidence measured from InSAR. The surface deformations are influenced by both thermo- and poro-elastic stress changes. For the Brawley simulation, surface rupture is observed, which additionally contributes to the surface deformation. Both Brawley and Coso cases show strong Coulomb stress increase within the reservoirs consistent with the dense cloud of observed induced seismicity and a strong Coulomb stress drop in a halo surrounding the depleted reservoir due to the development of compressive circumferential stress. The strongly accumulated Coulomb stress change in the Coso area leads to shear stress depletion, which can explain the lack of aftershocks following the 2019 Ridgecrest earthquakes. In the case of Brawley, a zone of strong positive Coulomb stress change is predicted below the reservoir, due to the stress transfer via aseismic fault reactivation. The model explains the triggering of a Mw5.4 earthquake in 2012 at ~7km depth in that zone.

"TBD"

Surendra Adhikari, JPL

"TBD"

Melissa Sims, Johns Hopkins