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Watch seminars by the people doing diamond research around the world

Goldschmidt2021 Plenary Lecture by Sonja Aulbach - P. Gast Medal Lecture
28:36
goldschmidtconf

Goldschmidt2021 Plenary Lecture by Sonja Aulbach - P. Gast Medal Lecture

Chemical geodynamics with eclogite. Mid-ocean ridge basalt (MORB), the melting product of the ambient convecting mantle, subducts at convergent margins. Some of this material returns to the surface as tectonically exhumed or xenolithic “oceanic” eclogite.Oceanic eclogite is a key indicator of past subduction and can also be used to investigate its source in the convecting mantle as far back as ~3 Ga. However, the eclogite record is obscured by seafloor weathering and processing in subduction zones. When samples that were metasomatised or derived from strongly differentiated or cumulate protoliths are excluded, V/Sc and Fe3+/ΣFe in eclogites are robust geochemical proxies of the oxygen fugacity (ƒO2) of the ambient mantle. Both ratios are higher in post-Archaean than in most Archaean eclogites, suggesting a secular increase in the convecting mantle’s ƒO2. The moderately incompatible elements, Ti and Sm, record the melt fraction by which the eclogites’ protoliths formed, and indirectly, the mantle potential temperature (TP). Their abundances increase through time, consistent with cooling, but require TP at 3 Ga only some 100-150°C higher than today. Extremely low 87Sr/86Sr (≤0.7007) in some eclogites suggests moderate depletion of ambient mantle by 3 Ga. These parameters (ƒO2, TP, composition) affect mantle dynamics and melting relations, plate strength and the redox state of volcanic gases, with strong impacts on the evolution of Earth and life.Oxybarometry also shows that after metamorphism, the vast majority of eclogites, including those showing evidence of seafloor weathering (non-mantle δ18O), record ƒO2 lower than both modern MORB and its Archaean equivalent. The low ƒO2 stabilises diamond relative to oxidised carbon species, presenting a pathway for deep carbon recycling, and indicating little oxidising power for deeply subducted oceanic crust.
Ania Bleszynski Jayich - "Quantum Sensing and Imaging with Diamond Spins”
01:03:34
Stanford Physics

Ania Bleszynski Jayich - "Quantum Sensing and Imaging with Diamond Spins”

Stanford University APPLIED PHYSICS/PHYSICS COLLOQUIUM Tuesday, October 8, 2019 4:30 p.m. on campus in Hewlett Teaching Center, Rm. 200 Ania Bleszynski Jayich Dept. of Physics, University of Calif. at Santa Barbara “Quantum Sensing and Imaging with Diamond Spins” Quantum sensors based on optically addressable solid-state spins are powerful tools that offer high sensitivity, nanoscale spatial resolution, and quantitative field information. The nitrogen vacancy (NV) center in diamond is the most advanced such sensor because of its robust, room-temperature coherence and its high sensitivity to a variety of fields: magnetic, electric, thermal, and strain. Here I discuss an NV-based imaging platform where we have incorporated an NV center into a scanning probe microscope and used it to image skyrmions, nanoscale topological spin textures. I also discuss recent experiments that utilize the NV center’s sensitivity to fluctuating magnetic fields to image conductivity with nanoscale spatial resolution. A grand challenge to improving the spatial resolution and magnetic sensitivity of the NV is mitigating surface-induced quantum decoherence, which I will discuss in the second part of this talk. Decoherence at interfaces is a universal problem that affects many quantum technologies, but the microscopic origins are as yet unclear. Our studies guide the ongoing development of quantum control and materials control, pushing towards the ultimate goal of NV-based single nuclear spin imaging.
VKC February 2021 - Nicole Meyer: Diamonds and Their Inclusions From The Koffiefontein Pipe
51:51
Vancouver Kimberlite Cluster

VKC February 2021 - Nicole Meyer: Diamonds and Their Inclusions From The Koffiefontein Pipe

Nicole Meyer (University of Alberta, PhD candidate) presents: "Diamonds and Their Inclusions From The Koffiefontein Pipe Provide Insights Into the Formation and Evolution of the Kaapvaal Craton" Seminar was live on Feb 24, 2021 at 6 PM (PST) hosted by Katherine Landoni and convened by Barbara Scott Smith. Sponsored by SRK Consulting (https://cdn-web-content.srk.com/upload/user/image/SRK%20Diamond%20Group_2020_Spreads20201117125325026.pdf?_ga=2.196734636.1489000300.1613172515-924229164.1553535947). Seminar Abstract: Diamonds and their mineral inclusions preserve mantle processes over space and time. Forming over a protracted period, diamonds also provide snapshots of early craton formation and mantle evolution over much of Earth’s history. The lithosphere beneath Koffiefontein is extremely depleted and is characterised by high-Mg# olivine and low-Ca garnet. In addition to garnet LREE enrichment, Koffiefontein experienced a unique K-Nb-Ta-rich metasomatism event that resulted in new minerals. The lack of clinopyroxene and co-existing garnet-orthopyroxene assemblages lead to the use of the electron microprobe for trace element analysis of Al in olivine. Geothermobarometry indicates that upper mantle diamond formation conditions are 1100-1300 °C and 4-7 GPa. Koffiefontein diamonds have a main δ13C mode for both peridotitic and eclogitic diamonds similar to mantle carbon. Relationships of δ15N-[N] and δ13C-δ15N indicate that nitrogen was derived from subducted sources and suggests that formation of not only eclogitic but also peridotitic diamonds involved fluids derived from altered oceanic crust. Lower mantle diamonds with coexisting ferropericlase and former bridgmanite indicate formation at or below 660 km. The high bulk Mg# of this assemblage is consistent with the diamond substrate originating from the depleted lithospheric mantle portion of an oceanic slab. Diamond formation at Koffiefontein dominantly takes place in depleted peridotite at both lithospheric and lower mantle depths. The δ13C-δ15N systematics suggest the same subducted source for both peridotitic and eclogitic diamonds. Subduction has played an important role in the formation and evolution of the Kaapvaal Craton and subsequent diamond formation.
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