Determining Source of Anisotropy of Magnetic Susceptibility in the Múlajökull Glacial Till, Iceland
Mentor 1
Julie Bowles
Location
Union Wisconsin Room
Start Date
24-4-2015 10:30 AM
End Date
24-4-2015 11:45 AM
Description
Magnetic susceptibility of an Icelandic glacial till was found to be anisotropic and may suggest a new understanding of the formation of drumlins on glacial fore-fields (Hooyer et al., 2008). Hooyer and Iverson used anisotropy of magnetic susceptibility (AMS), physical alignment of magnetic particles, to infer past deformation on the Mulajokull glacial till. This leads to an induced magnetization that is inferred to be strongest in the direction of alignment and presumed to be linked to shear forces experienced by the till. The objective of this study is to identify which physical and magnetic grain sizes make the greatest contribution to the AMS in order to determine the validity of the AMS data. It is known that titanomagnetite is the primary magnetic mineral in the Mulajokull till (Hooyer et al., 2008) Multiple, randomly-oriented magnetic grains can reside in a single grain of sand, or a single clast, and any anisotropy arising from these aggregates is not due to drumlin formation processes. By contrast, the isolated magnetite grains in the silt size fraction are more likely to be representative of glacial processes. Knowing which physical grain size is making the largest contribution to the AMS is key in understanding the efficiency of using AMS as evidence for past deformation events and may provide insight on the formation of drumlins. Till samples were separated into different grain sizes; silt (2.0 mm). Magnetic properties of each grain-size were then measured to determine their magnetic grain-size and their potential contribution to the AMS signal. AMS measurements were performed on the larger granules and pebbles in order to determine weather or not the magnetic grains in the basaltic clasts have any AMS prior to glacial deformation. It is expected that the silt-sized portion of the glacial till will yield the highest concentration of magnetic grains, and thus be responsible for the AMS in the samples. AMS for an individual pebble (or sand grain) could have developed during original lava flow/cooling but unless one or two pebbles dominate the susceptibility, the AMS of the aggregate till sample still must reflect some glacial process. Concluding which grain size holds the highest concentration of magnetic grains may determine the tenability of using AMS data in the study of drumlin formation.
Determining Source of Anisotropy of Magnetic Susceptibility in the Múlajökull Glacial Till, Iceland
Union Wisconsin Room
Magnetic susceptibility of an Icelandic glacial till was found to be anisotropic and may suggest a new understanding of the formation of drumlins on glacial fore-fields (Hooyer et al., 2008). Hooyer and Iverson used anisotropy of magnetic susceptibility (AMS), physical alignment of magnetic particles, to infer past deformation on the Mulajokull glacial till. This leads to an induced magnetization that is inferred to be strongest in the direction of alignment and presumed to be linked to shear forces experienced by the till. The objective of this study is to identify which physical and magnetic grain sizes make the greatest contribution to the AMS in order to determine the validity of the AMS data. It is known that titanomagnetite is the primary magnetic mineral in the Mulajokull till (Hooyer et al., 2008) Multiple, randomly-oriented magnetic grains can reside in a single grain of sand, or a single clast, and any anisotropy arising from these aggregates is not due to drumlin formation processes. By contrast, the isolated magnetite grains in the silt size fraction are more likely to be representative of glacial processes. Knowing which physical grain size is making the largest contribution to the AMS is key in understanding the efficiency of using AMS as evidence for past deformation events and may provide insight on the formation of drumlins. Till samples were separated into different grain sizes; silt (2.0 mm). Magnetic properties of each grain-size were then measured to determine their magnetic grain-size and their potential contribution to the AMS signal. AMS measurements were performed on the larger granules and pebbles in order to determine weather or not the magnetic grains in the basaltic clasts have any AMS prior to glacial deformation. It is expected that the silt-sized portion of the glacial till will yield the highest concentration of magnetic grains, and thus be responsible for the AMS in the samples. AMS for an individual pebble (or sand grain) could have developed during original lava flow/cooling but unless one or two pebbles dominate the susceptibility, the AMS of the aggregate till sample still must reflect some glacial process. Concluding which grain size holds the highest concentration of magnetic grains may determine the tenability of using AMS data in the study of drumlin formation.
