Ben Bond-Lamberty, Pacific Northwest National Laboratory
A 1014 scaling problem: what can soil respiration observations tell us about the global land carbon sink?
February 7, 2025 at 11:00 am (ESJ 0215)
The soil-to-atmosphere flow of CO2 generated by microbes and plant roots is intrinsically linked with the vulnerability of global soils to climate change. Despite this importance, "soil respiration" is one of the least well constrained components of the global carbon cycle, and most of our understanding of it comes from ~1 m2 chamber measurements. How consistent are upscaled estimates with satellite-driven projections of a robust land carbon sink? Why our global soil respiration flux estimates diverging, not converging? This talk will explore the role of open-source data and science in tackling one of the most uncertain parts of the global carbon cycle.
Daniel Segessenman, George Mason University
North America’s Ediacaran Story: A Tale of Global Environmental Change as told by Carbonate Quantity and Carbon Isotope Values
February 14, 2025 at 11:00 am (ESJ 0215)
Strata of the Ediacaran Period record many Earth-life features that distinguish the Neoproterozoic-Phanerozoic transition, including a snowball Earth deglaciation, the oldest known complex macroscopic fossil assemblages, the greatest magnitude negative carbon isotope excursion in the rock record, the last stages of Rodinia’s rifting, and the assembly of Gondwana. However, it is difficult to determine cause and effect relationships between these Ediacaran events, due in part to a relative rarity of sampling locations. Here we focus on quantitative properties of carbonate rock area, volume, geochemistry, and depositional environments from the Ediacaran System of North America. Patterns of carbonate sedimentation and geochemistry are broadly coincident with proposed transgressive/regressive cycles which have been linked to glacioeustacy and global tectonics. Highly negative carbonate carbon isotope values distinguishing the Shuram-Wonoka carbon isotope excursion (SW-CIE) occur against the backdrop of the largest increase in carbonate rock quantity observed in the Ediacaran, which spans nearshore, outer shelf, and slope/basin depositional environments. An increase in the extent of carbonate sedimentation, when combined with existing indications of global marine transgression, increased continental weathering, and evidence of glacially influenced sediments before and after, but not during, the SW-CIE, may indicate that the excursion occurred during an interglacial warm period. A subsequent increase in carbonate rock quantity in the latest Ediacaran, particularly among nearshore environments, coincides with an expansion of biocalcifying taxa, potentially indicating common cause drivers for both the extent of carbonate sedimentation on the continents and macroevolution. Although this analysis does not solve current limitations of Ediacaran geochronology, it does provide new evidence of environmental correlates for several key Ediacaran features and provides a foundation for future hypothesis testing of Earth systems evolution during the dawn of animal life.
Erica Jawin, National Air and Space Museum, Smithsonian Institute
Shattered Fragments: Origins and evolution of asteroid (101955) Bennu and the OSIRIS-REx mission
February 21, 2025 at 11:00 am (ESJ 0215)
NASA's OSIRIS-REx asteroid sample return mission investigated near-Earth asteroid (101955) Bennu and collected over 100 g of rocky material from its surface, after several years spent orbiting the asteroid. In September 2023, the spacecraft safely delivered its sample to Earth. Bennu proved to be a surprising object from the very first images showing an unexpectedly rugged surface, documented active particle ejections, and an extremely weak surface probed during sample collection. This lecture will discuss Bennu’s diverse surface geology and its rubble pile structure, as well as initial perspectives from analysis of the returned sample. The OSIRIS-REx spacecraft is now on its way to a new target, the asteroid (99942) Apophis, following its close approach with Earth in 2029.
Alexander Halliday, Columbia University
Isotopes and the Origin of the Earth
March 7, 2025 at 11:00 am (ESJ 0215)
Earth formed from bodies colliding in a protoplanetary disk, although exactly how, and how fast, are still debated. There exists a range of Giant Impact models for the Moon’s exact origin, all focused on explaining its isotopic similarity to the silicate Earth. Regardless of its origin, the isotopic age of the Moon constrains terrestrial accretionary processes and timescales, providing evidence that the final ~10% of Earth accretion took place between 50 and 120 million years after the start of the Solar System. Within this range, earlier estimates are perhaps more readily reconciled with the remarkable 129Xe and 182W anomalies in the Earth’s mantle. However, fluxes from, or equilibration with, core material has also been advocated as a contributor to some of the W anomalies. There also is considerable uncertainty still about the origins of Earth’s building blocks. While, there is strong isotopic evidence for a dominance of inner solar system feeding zones, the volatile components, such as carbon, nitrogen, water, are more complex. They were not delivered principally in a late veneer as often argued, but rather in many complex stages, that included solar, chondritic and cometary components. A major challenge is to understand how this earliest history segued into an Earth with crustal growth, but isotope geochemistry is also providing new constraints on this.
Patrick Beaudry, Johns Hopkins University
Iron oxidation and sulfur recycling in subduction zones
March 10, 2025 at 2:00 pm (ANS 0408)
Chemical mass transfer in subduction zones is a fundamental aspect of plate tectonics on Earth, driving arc magmatism and the recycling of subducted materials to the surface. The reactive mechanisms between aqueous fluids released by slab dehydration and mantle minerals are not well understood, but are likely associated with redox transfer, which may explain the generally oxidized character of arc magmas. Here I present mass transfer calculations of oxidized slab fluids variably enriched in sulfur and carbon reacting with a mantle mineralogical assemblage using the Deep Earth Water (DEW) model. Fe3+-bearing multi-component phases are considered in DEW calculations for the first time, including Fe-Ti-Cr-Mg-Al oxides as well as silicate components. Fluid-rock reaction heating paths are calculated at fixed pressure (2 and 3 GPa) and temperature increasing from 650 to 950°C. At those subarc conditions, sulfate-bearing complexes are very efficient at oxidizing iron and producing overall oxidized mineral products after reaction with the depleted mantle, whereas carbonate-rich fluids cause only marginal oxidation. Modelled Fe2O3 contents in spinel and clinopyroxene match those of natural data from variably metasomatized xenoliths. Furthermore, despite oxidizing significant quantities of iron, sulfate-saturated fluids remain sulfate-rich owing to very high initial solubilities, implying that the sulfur isotope composition of oxidized slab fluids dominates the sulfur isotope signature of primitive arc magmas. Calculated sulfur solubilities are generally consistent with sulfur concentrations of primitive arc melts inferred from melt inclusion and experimental data. Sulfate-bearing fluids also occur in high-temperature experiments (1200°C and 1 GPa), coexisting with oxidized, H2O- and S-rich primitive basaltic andesite melts. This suggests that sulfur from primitive arc magmas could be transferred to overlying magmatic or hydrothermal systems through fluid transport.
Liam Courtney-Davies, University of Colorado Boulder
Snowballs, Unconformities, BIFs and Beyond: Navigating Proterozoic Rock and Climate Records Using Geochronology
March 14, 2025 at 11:00 am (ESJ 0215)
The Proterozoic Eon (2500 - 541 Ma) comprised drastic periods of upheaval in Earth’s climate and tectonics which altered the course of life on Earth and resulted in unique geologic features and essential mineral resources. Resolving the age and timescales of events and processes which triggered climactic, depositional and erosional changes during this time underpins our knowledge of how Earth evolved into a more habitable planet towards the end of this Eon. This talk will highlight some recent developments in geochronology by applying non-traditional iron oxide geochronometers to investigate the timing of major events during the Proterozoic — and place direct age constraints on the development of the Great Unconformity, the extent of Cryogenian Snowball Earth and link supercontinent cycles to the assembly of giant mineral deposits.
Laura Waters, New Mexico Institute of Mining and Technology
Advances in thermodynamics and experimental petrology towards understanding magmatic systems and critical mineral mobility
March 24, 2025 at 2:00 pm (ANS 0408)
The application of thermodynamics to geological systems has a wide range of uses from interpreting the temperatures and pressures encoded in chemistry of minerals within an erupted magma to modeling and predicting the transport of critical minerals. However, reaction directions and quantities determined for natural systems that are based on thermodynamic models calibrated on pure mineral and melt standard state properties must be checked against experiments to understand how well models reproduce observations from nature. In this two-part talk, I present some recent advances in the subject area of Earth Materials that use experimental petrology to build thermodynamic models for (1) high-silica rhyolites from Valles Caldera, NM, and (2) critical mineral mobility in aqueous fluids. In part 1, we evaluate the intensive variables recorded by minerals in the post-collapse, high-silica rhyolites erupted from Valles Caldera, NM, following the most recent caldera-forming of the Bandelier Tuff (400 km3; 1.2 Ma) using petrology and experiments to understand how magmatic storage conditions changed following a super-eruption. Through this investigation, we found that sanidine composition has an apparent dependence on wt% H2O, suggesting it can be exploited as a new thermodynamic hygrometer. Using our experiments and those from the literature we present a new hygrometer, based on sanidine melt equilibrium. We additionally use kinetic experiments to assess possible mechanisms responsible for producing the crystal-rich, high-silica, post-collapse rhyolite lavas, which are devoid of microlites. Through these kinetic tests, we uncovered a mechanism to grown extremely large crystals (>1mm) in viscous melts over short durations (2-3 weeks). In part 2, I share an isotope dilution technique used in determining the solubility of NdPO4 (monazite-Nd) and DyPO4 (xenotime-Dy) in saline aqueous fluids at supercritical conditions and how these experiments are used to obtain thermodynamic data for REE aqueous species. I use results from our experiments to explain occurrences of xenotime-bearing, monazite-free pegmatites and granites.
The application of thermodynamics to geological systems has a wide range of uses from interpreting the temperatures and pressures encoded in chemistry of minerals within an erupted magma to modeling and predicting the transport of critical minerals. However, reaction directions and quantities determined for natural systems that are based on thermodynamic models calibrated on pure mineral and melt standard state properties must be checked against experiments to understand how well models reproduce observations from nature. In this two-part talk, I present some recent advances in the subject area of Earth Materials that use experimental petrology to build thermodynamic models for (1) high-silica rhyolites from Valles Caldera, NM, and (2) critical mineral mobility in aqueous fluids. In part 1, we evaluate the intensive variables recorded by minerals in the post-collapse, high-silica rhyolites erupted from Valles Caldera, NM, following the most recent caldera-forming of the Bandelier Tuff (400 km3; 1.2 Ma) using petrology and experiments to understand how magmatic storage conditions changed following a super-eruption. Through this investigation, we found that sanidine composition has an apparent dependence on wt% H2O, suggesting it can be exploited as a new thermodynamic hygrometer. Using our experiments and those from the literature we present a new hygrometer, based on sanidine melt equilibrium. We additionally use kinetic experiments to assess possible mechanisms responsible for producing the crystal-rich, high-silica, post-collapse rhyolite lavas, which are devoid of microlites. Through these kinetic tests, we uncovered a mechanism to grown extremely large crystals (>1mm) in viscous melts over short durations (2-3 weeks). In part 2, I share an isotope dilution technique used in determining the solubility of NdPO4 (monazite-Nd) and DyPO4 (xenotime-Dy) in saline aqueous fluids at supercritical conditions and how these experiments are used to obtain thermodynamic data for REE aqueous species. I use results from our experiments to explain occurrences of xenotime-bearing, monazite-free pegmatites and granites.Charlotte Devitre, University of California Berkeley
Quantifying CO2 via Raman Spectroscopy: new frontiers for volatile studies, magma storage depths and rapid petrology
March 28, 2025 at 11:00 am (ESJ 0215)
Nearly 15% of the world’s population lives within ~100 km of an active volcano and explosive eruptions can be devastating to life and human economies. Better understanding the architecture of volcanic plumbing systems and eruptive drivers is essential to interpret signals of unrest, mitigate risks associated with eruptions and identify key processes governing the formation of economically important ore deposits. Volatile species, and in particular CO2 and H2O, play dominant roles in these processes, making them the ideal tools to study them and highlighting the need for accurate and reliable volatile constraints. I will start by discussing methods I have developed to significantly improve the quality of CO2 measurements from melt inclusions, allowing new insights on magma storage, magmatic source characteristics and the origin of high explosivity in mafic magmas from Fogo volcano, Cabo Verde. Then, I will discuss how Raman spectroscopy-based measurements of CO2 in fluid inclusions (small pockets of exsolved fluids trapped in growing crystals) can be used to provide incredibly fast and much more reliable petrological constraints on magma storage depths. For example, in collaboration with Hawaiian volcano observatory, we successfully placed constraints on magma storage for the September 10th , 2023, eruption of Kīlauea within a single day of sample analysis. Owing to these new developments, rapid barometry via petrology can now be used in near-real time to support the construction and validation of magmatic plumbing system models during ongoing volcanic eruptions and aid in understanding potential evolutions in eruptive behaviour not only at Kīlauea but also many of the world’s most active and hazardous mafic volcanic systems (e.g., Iceland, Hawaiʻi,Galápagos, East African Rift, Réunion, Canary Islands, Azores, Cabo Verde).
Colin Jackson, Tulane University
Why is chlorine so concentrated in deep slab fluids?
March 31, 2025 at 2:00 pm (PHY 1201)
Subduction zones are engines for mineralization of economically important elements. The connection between subduction zones and ore genesis relates, in part, to the chlorine-rich nature of arc magma systems. Indeed, it is well-established that chlorine supercharges the ability of aqueous fluids to dissolve a wide range of elements that later precipitate in concentrated forms at various stages within the crust. Chlorine in arc magmas likely results from the reaction of seawater with the lithosphere prior to its subduction and the transport of chlorine (and water) to the region of arc magma genesis during slab descent. We seek to understand the mechanisms for chlorine transport by slabs. The presumptive highly fluid-mobile nature of chlorine suggests that its retention in a continuously dehydrating slab should be difficult, and yet it is clear that chlorine is retained to deep depths. I will present new experiments that constrain the ability of slab minerals to retain chlorine during their descent. Our experiments demonstrate that chlorine remains highly fluid-mobile under applicable conditions. We conclude by arguing that physical trapping of fluids in slabs may be key in enabling the transport of highly-fluid mobile elements to the regions of arc magma genesis and ultimately formation of ore in subduction settings.
The coordinator for the Colloquium Series is Dr. Mengqiang "Mike" Zhu. You can contact him at mqzhu [at] umd [dot] edu.
If you would like to suggest a speaker for a future seminar, click here.