Using oxygen isotopes to trace crustal input into magmas
The degree to which magma inside a magma reservoir exchanges with surrounding crust is crucial for being able to disentangle many of the chemical characteristics that we find in volcanic deposits. And it is important for understanding the long-term thermal evolution of magma reservoirs! Exchange with crustal rocks through melting or assimilation is energy-intensive - you can therefore only add a limited amount of crustal material before a magma reservoir cools and crystallizes and can no longer erupt.
Many of the rhyolitic lavas and ignimbrites along the Yellowstone hotspot track show oxygen isotopic compositions that suggest an extra-ordinary component of hydrothermally altered crustal rocks in these magmas. By combining isotopic analyses with thermal models and partial melting experiments, we were able to better quantify the required interaction of magma with hydrothermally altered wallrock, as well as the physical mechanisms behind this process. This helps us to better understand the generation of silicic melts in Yellowstone, and on-going work now focuses on applying this approach to other settings such as the Krafla volcanic field in Iceland, where magmas with similar oxygen isotopic compositions have been documented.
Many of the rhyolitic lavas and ignimbrites along the Yellowstone hotspot track show oxygen isotopic compositions that suggest an extra-ordinary component of hydrothermally altered crustal rocks in these magmas. By combining isotopic analyses with thermal models and partial melting experiments, we were able to better quantify the required interaction of magma with hydrothermally altered wallrock, as well as the physical mechanisms behind this process. This helps us to better understand the generation of silicic melts in Yellowstone, and on-going work now focuses on applying this approach to other settings such as the Krafla volcanic field in Iceland, where magmas with similar oxygen isotopic compositions have been documented.
The great escape: Volatiles in magma reservoirs
Volatile components in magmas comprise mostly water, with minor addition of carbon dioxide, fluorine, chlorine, sulfur and others. These elements are dissolved in the melt or form bubbles with exsolved magmatic volatile phase, if water concentrations are higher than the saturation limit. The presence of such an exsolved volatile phase plays a key role for the eruption behavior, magma chamber stability and the long-term growth of the magma reservoir. For this project, we couple melt inclusion studies to a numerical magma chambers model in order to investigate the pre-eruptive volatile budget in Yellowstone rhyolites and other case studies. We also investigate the diffusivities and fluid-melt partitioning behaviors of different trace elements in high-temperature high-pressure (800-1100°C/1-2 kbar) experiments, in order to trace their great escape.
Pegmatites as recorders of the magmatic-hydrothermal transition
The magmatic-hydrothermal transition separates regions in the Earth's crust that are dominated by melt from those that are dominated by aqueous fluids. The composition of these fluids ranges from dilute aqueous fluids and vapors to extremely solute-rich dense fluids, brines and supercritical liquids, which play an important role in removing trace elements from magma reservoirs and concentrating them into ore deposits - for example porphyry copper deposits or pegmatites. Pegmatites are particularly fascinating due to their enrichment in critical metals, such as lithium, which plays a key role for renewable energies. In order to find out when and how pegmatite-forming, solute-rich liquids are extracted from their source reservoirs, I couple field observations from pegmatites in the central Damara orogen in Namibia to geochemical and geochronological data. These findings can then be tied to thermomechanical numerical models in order to link chemical data to physical processes, and develop a better understanding for fluid transport in these systems.