Melt residence and percolation in silicate matrices.
Understanding fluid behavior is essential for a wide range of geological settings.
For instance, estimating melt volumes in low-velocity zones requires a clear understanding of the shape distribution of melt and any preferred orientation of melt pockets. Additionally, immiscible fluids are present in magmas generated in subduction zones, as well as under the pressures and temperatures relevant to core formation in small planetary bodies. The manner in which these fluids interact and travel relative to each other in such environments has significant implications for processes like ore deposit formation and planetary differentiation. However, it remains unclear how immiscible fluids segregate based on factors such as wettability, density, fluid fraction, and matrix geometry.
Core formation in small planetary bodies
Meteorites offer a unique "window" into planetary interiors, providing valuable insights into the evolution of the early solar system and the processes of planetary differentiation. Iron meteorites, in particular, present an exceptional opportunity to study core formation processes. The diversity in chemical compositions observed among different iron meteorite groups suggests complex accretion and differentiation histories of their parent bodies. Understanding core-mantle segregation processes under various accretionary conditions can shed light on the range of chemical compositions recorded in meteorites. While planets may undergo different segregation processes depending on their heat sources and thermal evolution, differentiation through percolation is likely the dominant process in smaller planetary bodies when heated to temperatures sufficient to melt their metallic components.
To explore this, I conducted piston-cylinder and multi-anvil experiments to investigate the percolation behavior of immiscible fluids in a multi-light element system. Specifically, I determined the chemical composition of immiscible liquids in the Fe-Ni-Si-S-C system and analyzed how temperature and pressure influence percolation behavior through texture analysis.
*Poster presentation at 2018 Lunar and Planetary Science Conference, Houston, TX
Carbon mobility in subduction zones.
The carbon flux between Earth's interior reservoirs remains a longstanding puzzle in geoscience. Carbonates, which make up a significant portion of subducting sediment, play a critical role in influencing arc volcanism and mantle carbon concentrations. Despite numerous experimental studies, the precise mechanisms governing how carbonates are recycled back into arc magmas or delivered to the mantle remain unclear.
In my research, I conducted high-pressure, high-temperature multi-anvil experiments to investigate the wettability of a newly proposed amorphous phase of calcium carbonate within an olivine matrix. In porous matrices, fluids are typically transported through interconnected networks of pores along grain boundaries. The efficiency with which this amorphous phase percolates through such networks under subduction zone conditions depends on the solid-liquid dihedral angle of the system. My experiments revealed a thermally induced development of a melt-like fabric in the aggregate and a low dihedral angle, indicating that the amorphous phase should readily form an interconnected network, independent of melt volume. Due to its low density, amorphous CaCO₃ could buoyantly percolate into the overlying mantle wedge.
[Image] Left column: BSE images of CaCO₃ in an olivine matrix. Right column: Ca maps showing the texture evolution of CaCO₃.
*Oral presentation at 2018 American Geophysical Union conference, Washington, DC
High-Speed 3D Imaging of Multiphase Systems
Experimental petrology allows petrologists to capture and "freeze" kinetic processes within samples under specific pressure and temperature conditions. However, this approach provides only a "snapshot" of fluid migration, requiring us to infer the movement and behavior of fluids through texture analysis, as direct observation within our experimental equipment is not possible. To overcome this limitation, analog experiments offer an alternative method for studying fluid migration.
To better understand how non-wetting immiscible liquids travel through granular media, I collaborated with my colleague Julie Oppenheimer. By utilizing Swept Confocally Aligned Planar Excitation (SCAPE) microscopy, we were able to capture this process at the microscopic level. In Oppenheimer et al. (2021)*, we demonstrate the significant influence of pore, throat, and droplet size on the velocity of non-wetting droplets.
*Oppenheimer, J., Patel, K., Lindoo, A., Hillman, E. M. C., & Lev, E., 2021. High‐Speed 3D Imaging of Multiphase Systems: Applying SCAPE Microscopy to Analogue Experiments in Volcanology and Earth Sciences. Geochemistry, Geophysics, Geosystems, e2020GC009410.
P and S wave propagation in experimental magmas.
Seismic velocities are significantly influenced by pressure, temperature, and melt volume. Myriad seismic studies have estimated melt volume by referring to Gassmann’s relations based only on a granite matrix and rhyolitic melt. However, without taking into account compositional effects and the geometric details of pore space, more constrained determinations of melt fraction in storage regions cannot occur. As more tomographic data becomes available through large-scale seismic experiments, it is important references from mineral physics keep pace. In situ analog experiments using mono-mineral (olivine or alumina) matrices have been conducted with very small degrees (0-4 vol.%) of basaltic melt and larger amounts (0-50 vol.%) of more evolved compositions. However, these data could be improved by measuring velocities in a multi-mineral matrix and melt compositions expected in magma storage regions. In order to estimate melt volume in low-velocity zones, it is essential to understand the shape distribution of melt and any preferred orientation of the melt pockets.
To understand how moderate amounts (5-20 vol%) of melt influence seismic velocities, I successfully procured beamtime at Argonne National Laboratory’s Advanced Photon Source to carry out in situ ultrasonic experiments in the Large Volume Press at GSECARS. The experiments involved X-ray diffraction, X-ray radiography and ultrasonic measurements.
Elastic waves generated by each electrical pulse to the transducer are reflected and transmitted at the buffer rod/sample interface. The transmitted portion reverberates inside the sample, resulting in a series of 'sample' echoes following the buffer rod echo.
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