The Earth and Planets Laboratory hosts free weekly scientific seminars most Mondays and Thursdays. The popular seminar series covers the broad range of topics studied on our campus and are presented by both guest speakers and Carnegie scientists.
Note: These seminars are designed for a scientific audience and have limited space, so we are not advertising the Zoom links publically. However, you're still welcome to join! Just email Alycia Alexander (adalexander@carnegiescience.
- Monday, September 19, 2022, at 11:00 a.m. (hybrid seminar)
Zachary Torrano, Earth and Planets Laboratory
Title: Isotopic Compositions of Refractory Inclusions in Meteorites: Tracers of Early Solar System Processes
Abstract: Refractory inclusions in carbonaceous chondrites include Ca-Al-rich inclusions (CAIs) that are the oldest dated Solar System solids at 4.567 billion years old, and amoeboid olivine aggregates (AOAs). These refractory inclusions record a snapshot of the earliest history of our Solar System, and by measuring their isotopic compositions we can learn about the nucleosynthetic sources of the initial material present in the nascent Solar System, the isotopic reservoirs
present at this time, and the potential relationships between refractory inclusions and later formed solids. The Cr and Ti isotopic compositions of meteorites have proven to be particularly useful forensic tracers of isotopic reservoirs present in the early Solar System, and the Cr and Ti isotopic compositions of refractory inclusions, therefore, provide new information about the formation environment of these objects and the isotopic evolution of our Solar System.
Host: John Chambers
- Monday, September 19, 2022, at 11:30 a.m. (hybrid seminar)
Samuel Dunning, Earth and Planets Laboratory
Title: Controlling the Formation of Flexible Diamonds
Abstract: Diamond nanothreads, or “flexible diamonds”, are an emerging class of sp3-hybridized carbon nanomaterial, formed through the solid-state polymerization of small unsaturated ring systems. Nanothreads are predicted to combine the flexibility of conventional polymers with the superlative properties of diamond. However, due to the number of viable reaction pathways at high pressure, it is a significant challenge to form chemically homogeneous nanothreads for which the properties and reactivity can be predicted and understood. In this talk, I will describe our work on the use of heteroatom incorporation and intermolecular forces to limit reaction pathways, control nanothread formation, and produce functionalized nanothreads which can be used for controlled post-processing reactions.
Host: Timothy Strobel
- Thursday, September 29, 2022, at 11:00 a.m. (hybrid seminar)
George Cody, Earth and Planets Laboratory
Title: Establishing a molecular understanding of isotopic enrichment and variation in extraterrestrial organic solids contained within Chondritic meteorites
Abstract: Carbonaceous Chondrite meteorites are derived from some of the most primitive (least altered) and earliest (youngest) planetary objects in the Solar System. Chondrites are notable in that they contain a relatively large amount of organic carbon (~ 2 wt %) in the form of a complex insoluble organic macromolecule (referred to as IOM). Nearly 60 years ago it was shown that the IOM has substantial enrichments in deuterium (relative to terrestrial D/H values) which points to some connection with cold (possibly interstellar) chemistry capable of producing some enrichment. Extensive solid state Nuclear Magnetic Resonance (NMR) experiments have revealed that the molecular structure of IOM varies considerably across various chondritic meteorites where such molecular evolution arises from parent body processing during radiogenic heating of the parent planetesimal. However, no systematic relationship between D/H nor 13 C/ 12 C and the degree of molecular evolution is observed for IOM from many chondrites. We have applied D and 1 H NMR (at natural abundance) to IOM samples from two different chondritic meteorites. D NMR enables us to see directly where D resides in IOM at the molecular level. Laboratory experiments on the synthesis of IOM using 1 H, D, and 13 C NMR point to deuterium enrichment arising at the time of IOM synthesis, where the source of deuterium is derived from the water IOM is synthesized in. Combining this insight with a detailed molecular analysis of molecular evolution and D/H variation exhibited in IOM from the Tagish Lake clasts enables us to resolve the combined effects of molecular evolution on variation in IOM’s D/H abundances. If time permits, we will also present evidence for a potential molecular origin for 13 C/ 12 C variation in IOM across chondritic meteorites.
Host: John Chambers
- Monday, October 3, 2022, at 11:00 a.m. (hybrid seminar)
Sarah Penniston-Dorland, University of Maryland
Title: Applying crystal clocks to metamorphic rocks: Using Li isotopes in garnet to constrain fluid flow processes during subduction metamorphism
Abstract: Fluids released within subduction zones affect fundamental Earth processes, including seismicity and the generation of arc magmas, the formation of continental crust, and the geochemical evolution of the mantle. However, very little is understood about processes of fluid transport within subduction zones and the chemistry of these fluids. Bulk-rock variations in Li isotopic compositions (d 7 Li) are observed in fluid-related features in subduction-related metamorphic rocks at the centimeter-scale suggesting a short duration to fluid infiltration events – weeks to centuries. These measurements record a time-integrated record, while in situ measurements in metamorphic minerals can record individual events experienced by the rock. In this study, traverses across garnet crystals in subduction-related eclogite and amphibolite from the Franciscan Complex, CA and the Monviso Ophiolite, Italy were analyzed for Li isotopes. Observed variations in d 7 Li occur within crystals over a scale of a few hundred microns, including troughs of low d 7 Li measurements in the mantle regions of some of the garnets from both localities. In both localities, variations in d 7 Li are associated with evidence for fluid-rock reaction suggesting a role for fluids fluxing through the slab. The unusual trough pattern suggests that diffusion played a role in generating these features, but the nature of diffusion differs between the two localities. Garnets from the Franciscan experienced intracrystalline diffusion of Li on the scale of a few hundred microns, whereas garnets from Monviso recorded diffusion of Li on a centimeter scale, within an intergranular fluid surrounding the garnets. Multiple troughs in some of the Monviso garnets indicate that episodicity of fluid flow events can be discerned. Variability in profiles from the Franciscan garnets suggest that some aspect of the chemistry of the fluids may be responsible for intracrystalline diffusion; likely candidates are either pH or Eh of the fluid. Ongoing work is focusing on investigating garnets from a wide range of natural samples to look for patterns in fluid flow episodicity. Additionally, experiments determining the diffusivity of Li within garnet are being performed in order to quantitatively constrain timescales of intracrystalline diffusion.
Host: Peter van Keken
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