Date of Award
Doctor of Philosophy (PhD)
Hydrous magnesium silicates form primarily from the interaction of seawater with the oceanic lithosphere and are drawn down into the mantle by subducting slabs at convergent margins. It is thought that they hold an important control over several aspects of the subduction multisystem, with implications for many different subduction zone processes. In particular, the hydrous magnesium silicates serpentine and talc exhibit unusual rheological and anisotropic properties. To explore the effects of these minerals on global subduction zones, we conducted three separate studies on talc (Mg3Si4O10(OH)2) and two of the serpentine group minerals (Mg3Si2O5(OH)4), lizardite and antigorite. Firstly, to understand the impact of antigorite – a mineral which is extremely anisotropic to S-waves – on seismic anisotropy, an electron backscatter diffraction study was performed on a set of antigorite-bearing samples from Kohistan, Pakistan. Deformed antigorite samples, which exhibited a high degree of crystallographic alignment, were shown to be strongly anisotropic to the passage of S-waves and could help to explain some of the complexity in observations of S-wave anisotropy at the surface. Secondly, to investigate the influence of talc on fault systems a set of torsional experiments (1 GPa and 450-500 C) and nanomechanical tests (25 C) were performed on natural talc specimens. Scanning Transmission Electron Microscopy revealed microstructures similar to much lower pressure talc deformation – indicating a consistency in deformation mechanisms across a range of conditions – as well as the development of nanoporosity which could allow fluids to migrate through fault zones even at relatively high pressures. Finally, a series of high temperature nanoindentation tests were conducted on natural, polycrystalline samples of lizardite and antigorite. Indentation hardnesses for both serpentine minerals (antigorite: 5.7-6.7 GPa, lizardite: 2.3-2.6 GPa) are much lower than olivine under the same conditions (13.1-14.9 GPa), while room temperature tests on talc reveal it to be weakest with a hardness of 0.6 GPa. The weakness of all three of these minerals may make them viable candidates for the facilitation of subduction initiation.
Chair and Committee
Philip A. Skemer
Douglas Wiens, Michael Krawczynski, Paul Byrne, Rohan Mishra,
Horn, Charis Madeleine, "Deformation of Hydrous Magnesium Silicates in Subduction Zone Environments" (2023). Arts & Sciences Electronic Theses and Dissertations. 2857.
Available for download on Sunday, April 13, 2025