April 21, 2017 @ 12:00 pm - 12:50 pm CDT
Departmental Research in Earth Science
Who: Sahand Hajimirza & Laura Carter
When: Noon, Friday, April 21, 2017
Where: Room 100, KWGL
Hajimirza: “Predicting homogenous bubble nucleation rate in rhyolitic eruptions”
Classical nucleation theory has been used to infer magma decompression rates during volcanic eruptions from bubble number density in pyroclasts. We have tested the accuracy of such predictions against a suite of homogeneous bubble nucleation experiments in rhyolitic melt and found discrepancies between observed and predicted bubble number densities of up to four orders of magnitude. We hypothesize that this is due to the curvature dependence of surface tension for the nucleating bubble. To test this hypothesis, we first performed a suite of decompression-nucleation experiments in rhyolitic melt and subsequently numerical modeling of bubble nucleation during the experiments. By minimizing the discrepancy between observed and predicted bubble number densities for all experiments, we obtain a supersaturation-dependent correction to the macroscopically measured surface tension. This correction provides a significant improvement in the predictability of homogeneous bubble nucleation rate in rhyolitic melts and, hence, our ability to constrain magma decompression rates from pyroclast bubble number densities.
Carter: “Release of CO2 from Crustal Carbonates by Magmatic Intrusion”
Carbonates deposited on the Earth’s crust represent a significant reservoir of carbon sequestration. However, they can decarbonate when temperatures surpass their stability, when hydrothermal fluids react chemically to form skarns, and when intruding melts assimilate the surrounding carbonate rock. Thus it is important to the carbon cycle and long-term climate change that we understand the addition of crustal carbon to the atmosphere through these high temperature processes. Experiments control intrinsic variables of these reactions, including temperature, pressure and composition of both intruding magma and carbonate country rock. Results indicate that hotter, shallower, and less evlolved magmas devolatilize more limestone (CaCO3). Dolomite (MgCa(CO3)2), though, is less thermally stable than limestone at constant pressure. Unlike limestone, which is broken down at the magma-country rock interface, dolomite may decarbonate more distally, simply within the aureole that the magmatic heat penetrates. Therefore, the combined effect of thermal decarbonation and magmatic assimilation may cause the release of higher amounts of CO2 into the atmosphere from dolomite-bearing magmatic systems.