Lunchtime Seminar Schedule

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Abstract: Scattering of seismic waves can reveal subsurface structures, but usually in a piecemeal way focused on specific target areas. We used a manifold learning algorithm, the Sequencer, to simultaneously analyze thousands of seismograms of waves diffracting along the core-mantle boundary and obtain a panoptic view of scattering across the Pacific region. In nearly half of the diffracting waveforms, we detected seismic waves scattered by 3D structures near the core-mantle boundary. The prevalence of these scattered arrivals shows that the region hosts pervasive lateral heterogeneity. Our analysis revealed loud signals due to a plume root beneath Hawaii and a previously unrecognized ultralow-velocity zone beneath the Marquesas islands. These observations illustrate how approaches flexible enough to detect robust patterns with little-to-no user supervision can reveal unique insights into the deep Earth.

Abstract: Continental crust is a major geochemical reservoir whose evolution is tightly linked to the onset of plate tectonics, degassing history, and the budget of heat production within the Earth. Understanding the evolution of continental crust helps to unravel the workings of the Earth system as a whole. In this study, we present a coupled crust-mantle-atmosphere evolution model to explore the constraints of atmospheric argon on crustal evolution. Our model is the first to quantitatively investigate the effects of crustal recycling and reworking on degassing by computing the formation and surface age distributions of continental crust. The thermal history is coupled with the degassing history to ensure a self-consistent evolution of the Earth system. Parameter uncertainties are incorporated by Monte Carlo sampling, and successful results are selected by how closely they can reproduce the present-day and Archean atmospheric argon ratios, Proterozoic and Archean mantle potential temperatures, and the formation and surface age distributions of continental crust. We have collected an ensemble of 104 successful solutions, which suggests that the history of argon degassing favors rapid crustal growth during the early Earth. The highly incompatible nature of K requires a large quantity of early developed felsic crust (>80%), which challenges the popular notion of less than 10% of felsic crust at Archean. The presence of the early felsic crust provides important indications for the thermal regime, surface environment, and the extent of mantle processing during the early Earth.

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Abstract: In order to interpret seismic data, rock physics models are required to make explicit links between observed quantities and physical properties.  Many of our fundamental rock physics models have been formulated with clastic sedimentary rocks in mind.  Today, as our scientific and technological questions expand to address more diverse lithologies, we need to revisit these older models.  I'll be presenting a broadband experimental study of the seismic velocity and attenuation of a single fracture in low porosity rock, which can shed some insight into the future directions of rock physics.

Abstract: In the absence of global plate tectonics, mantle convection and plume-lithosphere interaction are thought to be the main drivers of surface deformation on Venus, resulting in a wealth of volcanoes, coronae, rifts, and mountains that cover the Venusian surface. It remains in question to what extent these surface tectonic and volcanic features reflect the current state of the planet’s interior.
In this seminar talk, Anna will showcase how the mysterious corona structures bear testimony to turbulent processes within Venus. Coronae are large ring-shapes structures with traces of volcanic and tectonic activity, and they feature a wide range of sizes and morphologies. While they are commonly thought to form by plume-lithosphere interactions, the exact processes underlying their development and the reasons for their diverse morphologies are uncertain.
Anna will present a systematic numerical study of plume-lithosphere interaction that links the morphological diversity of large coronae to the lithospheric structure and underlying processes. She will then provide guidance for identifying which coronae on Venus may be active today. Her assessment revealed that at least thirty-seven coronae feature structures that are consistent with ongoing plume activity, providing new evidence for widespread plume activity on the planet.

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Abstract: This talk will focus on small-scale soil interfaces in redox-dynamic systems and their broader environmental impacts spanning different research projects. Dr. Jared Wilmoth has recently joined UMD as a new Assistant Professor in the Department of Environmental Science and Technology (ENST). Current investigations continue to examine the biogeochemistry of redox-dynamic interfaces in soils with an emphasis on the pursuit of using ultrahigh-resolution mass spectrometry (MS) and various geochemical and microbiome characterization techniques, including heavy metal isotope tracing with Mossbauer spectroscopy and meta-omics. His Ph.D. research at the University of Georgia focused on mineral-microbe interactions in redox-oscillating, forest soils of Puerto Rico. He then joined the Biological and Nanoscale Systems Group at Oak Ridge National Laboratory (ORNL) as a postdoc to study environmental microsites using microfluidics and high-performance computer simulations. He most recently completed a second postdoctoral project at Princeton University, with the Princeton Environmental Institute, to study how large methane emissions from wetlands are stimulated by soil redox transitions. His ongoing research seeks to understand the mechanistic linkages between soil organic and mineral chemistry, soil microbiome activity and global climate change using advanced analytical, omics and computational approaches.

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Abstract: Very long period seismic signals (VLPs) are thought to be produced by magma and gas flow through shallow volcano conduits. At Stromboli Volcano, Italy (the type volcano for strombolian explosions) and other basaltic volcanoes worldwide, VLPs have been modeled as gas slug flow through the conduit followed by an explosion when the slug bursts at a free surface. However, these interpretations do not account for variable crystal content. Here we show that the standard 'slug' model does not hold during a period of intense study at Stromboli in 2018. We compare the timing and characteristics between two repeating VLP families and explosions at the surface, as indicated by acoustic data. We argue that VLPs are generated when gas bubbles interact with and move into a semipermeable plug in the uppermost portion of the conduit, which acts as a mechanical filter for gas transport.

Abstract: Geochemists study the composition, structure, processes, evolution, and other aspects of the Earth. In this seminar, Xiaoming will take you to a geochemical adventure focusing on what her group has done over the past five years at UNC and future adventure plans on Earth’s surface and beyond. The main research interests of Liu’s group lie in understanding fundamental questions related to the origin and evolution of Earth using geochemical tools, including but not limited to 1). Chemical weathering and its influence on climate; 2). Evolution of Earth’s surface environments; 3). Fluid-rock interactions and its implications in environmental geochemistry.

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Abstract: Suprasubduction zone (SSZ) ophiolites of the northern Appalachians have provided key constraints on the fundamental tectonic processes responsible for the evolution of the Appalachian Orogen. The central and southern Appalachians, which extend from southern New York to Alabama, also contain numerous ultramafic–mafic bodies that have been interpreted as ophiolite fragments; however, this interpretation is a matter of debate, with the origin(s) of such occurrences also attributed to layered intrusions. These disparate proposed origins have varied potential implications for the magmatic and tectonic evolution of the central and southern Appalachian Orogen, and its relationship with the northern Appalachian Orogen.

In this talk, I will present the results of field observations, petrography, bulk-rock geochemistry and spinel mineral chemistry (see Fig.) for ultramafic portions of the Baltimore Mafic Complex (BMC) in Maryland and southern Pennsylvania. Our data indicate that the BMC comprises SSZ ophiolite fragments, which includes mantle peridotites/serpentinites and the ‘layered ultramafics’ that form the Moho. Interpretation of the BMC as an Iapetus-derived SSZ ophiolite in the central Appalachian Orogen raises the possibility that a broadly coeval suite of ophiolites is preserved along 1000s of kilometers of orogenic strike. I will also discuss these data (and the methodologies utilized) in the context of my broader research, which focuses on understanding the evolution of Earth tectonics during the Archean and Proterozoic Eons.

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Abstract: Meteorites and their components can be used to unravel the history of the early Solar System. Carbonaceous chondrites are meteorites that originated from undifferentiated parent bodies that formed within a few million years of the beginning of the Solar System. These meteorites contain calcium-aluminum-rich inclusions (CAIs), which are the oldest dated solids in the Solar System at ~4.567 billion years old and thus preserve a record of the earliest stage of Solar System formation. The isotopic compositions of CAIs and bulk carbonaceous chondrites can be used to identify the sources of material inherited by the protoplanetary disk, assess the degree of mixing in the disk, evaluate potential genetic relationships between parent bodies, and trace sample origins to either the inner or outer Solar System. In this talk, I will first discuss the Cr and Ti isotopic compositions of CAIs from carbonaceous chondrites and implications for the ingredients inherited by the early Solar System, the characteristics of the CAI-forming region, and the role of CAIs in the preservation of planetary-scale isotopic anomalies. I will then discuss the Cr, Ti, and O isotopic compositions of bulk carbonaceous chondrites and implications for the genetic relationship between the CM and CO chondrite groups. Together, these results provide important constraints on the processes that were occurring during the first few million years of Solar System formation.

Abstract: The history of seawater sulfate sits at the center of any effort to reconstruct Earth's evolving oxidant budget.  To date, however, sulfur and oxygen isotope records from Cenozoic and Cretaceous barite (barium sulfate) offer more complexity than clarity in telling this story.  Here we offer a new hypothesis, whereby the emplacement of large igneous provinces plays a critical, yet punctuated role in marine sulfate budgets.  This idea is constrained with sulfur isotopes records, and testable with the minor oxygen isotope catalog from the exact sample minerals.

Abstract: Mr. Rich Pepino has a long-standing interest in public policy research, especially as related to public health issues in vulnerable communities. For many years, Mr. Pepino has been a lecturer at the University of Pennsylvania, where he teaches Academically Based Community Service (ABCS) courses. His participation in Penn’s ABCS program has directly lead to ongoing funded grants with the Philadelphia (AMS) and Pennsylvania Departments of Health to address lead and other toxic exposures in vulnerable urban communities. The first part of this seminar will be given by Mr. Pepino, focusing on Mitigating the Impacts of Childhood Lead Poisoning in Urban Centers. The talk will be 20 mins and have been given at GSA meeting in October 2020. The second part of the seminar will be given by Hasibe Caballero-Gomez, a summer student on Mr. Pepino's NIEHS grant and currently a senior at Haverford College with a chemistry major. Hasibe is a passionate and talented student. Her research talk on Childhood Lead Poisoning in Philadelphia has been given to US.EPA & ATSDR/CDC and her remarks were well received.