Magma transfer in the continental crust is a first order problem that needs to be addressed to understand how magmatic systems operate through time and in space. This is particularly important in the case of Large Igneous Provinces in which large volumes of magma have moved from the source to the surface of the Earth in, geologically speaking, relatively short times (approximately 1 million years). Magnetic fabric techniques, such as the Anisotropy of Magnetic Susceptibility method, have been successful in constraining flow geometry and kinematics. However, numerous aspects of this approach are still ambiguous. For example, no satisfactory explanation accounts for cases where the magnetic foliation is parallel to a dike wall and yet the magnetic lineation, which is supposed to mimic the flow direction, is perpendicular to the dike boundary. This research project addresses these issues by combining several independent methods (image analysis, Electron BackScatter Diffraction, Anisotropy of Anhysteretic Remanent Magnetism) to determine the mineral fabric and magma flow parameters. Six controlled experiments specifically investigate differences in magnetic fabrics between feeder and non-feeder dikes, the possible contribution of single domain magnetite grains to Anisotropy of Magnetic Susceptibility and the importance of layering-forming processes in development of mineral fabric. The natural laboratory targeted for the experiments is the Karoo Large Igneous Province in South Africa, a region with well-mapped, exceptional exposures in addition to available continuous borehole cores. The project will be carried out by a U.S. research team from Southern Illinois University, College of Saint Rose, and University of New Mexico in partnership with South African scientists from Rhodes University and the Council for Geoscience.
This study will provide the theoretical background and validation for the technique Anisotropy of Magnetic Susceptibility that is currently the most often used to determine magma flow direction. It will define the boundaries within which the Anisotropy of Magnetic Susceptibility technique could and should be used. The results of this investigation will enable the broader community to apply this technique to many other geological settings with greater confidence regarding the significance of its results. Although the project focuses on one type of magmatic system (silica-poor magmas), it is very likely that the results will have broader applications to silica-rich systems. This research will considerably impact the igneous petrology and volcanic community because magma transfer is still one of the key questions in these disciplines. The project involves extensive graduate and undergraduate participation in international research and makes efforts to broaden participation of underrepresented groups in the Earth Sciences. The NSF Office of International Science and Engineering (Near East and South Asia Program) and the NSF Earth Sciences Division (Tectonics Program and Geophysics Program) are supporting this research.
