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Description
This study has the objective to better constrain the role played by thermal erosion by turbulent lava in the formation of large channels on Mars and the Moon. On Mars, a rigorous one-dimensional model was used to test whether lava might have excavated the Athabasca Valles outflow channel. Calculated erosion depths are much lower than the measured depths of the channel, and suggest a limited role played by thermal erosion in excavating it. On the Moon, the investigation focused on the outer and inner sinuous rilles of Vallis Schröteri. At this site, erosional features cannot be explained by one- and two-dimensional models. The first 3-D model of thermal erosion by turbulent lava on the Moon was created to relate the spatial distribution of erosion rates over the bed and banks of a channel with changes in fluid- and thermodynamic parameters. The turbulence model chosen for each steady-state simulation is the Shear Stress Transport (SST) k-ω model and OpenFOAM is the Computational Fluid Dynamics software used. At the 150-km-long, 4-km-wide, and up-to 700-m-deep outer rille, I aimed to determine maximum erosion rates at/near the lava source and rille segments 1-km-long and 4-km-wide were chosen for the simulations. By adopting the obtained maximum erosion rates of 1 m/day, lava might have taken ~2 years to excavate the 700-m-deep depression. These fast erosion rates were unlikely maintained downstream of the lava source unless lava flowed in a tube. Besides, observational evidence suggests that tectonics and constructional processes likely contributed to rille development. On these grounds, thermal or thermo-mechanical erosion might have contributed to rille formation at a later stage. At the Vallis Schröteri inner rille, 1-km-long and 160-m-wide meandering channels were chosen. In one scenario, lava loses heat by radiation, in the other flows in a tube. Using the calculated (and conservative) erosion rate of 50 cm/day, it would have taken ~6 months for the 90-m deep inner rille to be excavated. A mechanism of secondary flow circulation analogous to that found in meandering rivers potentially explains meander generation. At each bend, downstream and cross-stream velocity variations lead to local temperature/ erosion enhancements.
ContributorsCataldo, Vincenzo (Author) / Williams, David A (Thesis advisor) / Clarke, Amanda B (Thesis advisor) / Schmeeckle, Mark W (Committee member) / Robinson, Mark S (Committee member) / Burt, Donald M (Committee member) / Arizona State University (Publisher)
Created2022
Description
A novel technique for measuring heavy trace elements in geologic materials with secondary ion mass spectrometry (SIMS) is presented. This technique combines moderate levels of mass resolving power (MRP) with energy filtering in order to remove molecular ion interferences while maintaining enough sensitivity to measure trace elements. The technique was evaluated by measuring a set of heavy chalcophilic elements in two sets of doped glasses similar in composition to rhyolites and basalts, respectively. The normalized count rates of Cu, As, Se, Br, and Te were plotted against concentrations to test that the signal increased linearly with concentration. The signal from any residual molecular ion interferences (e.g. ²⁹Si³⁰Si¹⁶O on ⁷⁵As) represented apparent concentrations ≤ 1 μg/g for most of the chalcophiles in rhyolitic matrices and between 1 and 10 μg/g in basaltic compositions. This technique was then applied to two suites of melt inclusions from the Bandelier Tuff: Ti-rich, primitive and Ti-poor, evolved rhyolitic compositions. The results showed that Ti-rich inclusions contained ~30 μg/g Cu and ~3 μg/g As while the Ti-poor inclusions contained near background Cu and ~6 μg/g As. Additionally, two of the Ti-rich inclusions contained > 5 μg/g of Sb and Te, well above background. Other elements were at or near background. This suggests certain chalcophilic elements may be helpful in unraveling processes relating to diversity of magma sources in large eruptions. Additionally, an unrelated experiment is presented demonstrating changes in the matrix effect on SIMS counts when normalizing against ³⁰Si⁺ versus ²⁸Si²⁺. If one uses doubly charged silicon as a reference, (common when using large-geometry SIMS instruments to study the light elements Li - C) it is important that the standards closely match the major element chemistry of the unknown.
ContributorsCarlson, Eric Norton (Author) / Hervig, Richard L (Thesis advisor) / Roggensack, Kurt (Committee member) / Burt, Donald M (Committee member) / Arizona State University (Publisher)
Created2021