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Faculty of Graduate Studies

Hannah Robutka

  • B.Sc. Hons. (University of Calgary, 2021)
Notice of the Final Oral Examination for the Degree of Master of Science

Topic

Tracking the Evolution of Fe Mineralogy at the Main Endeavour Field using Magnetics

School of Earth and Ocean Sciences

Date & location

  • August 13, 2026
  • 9:00 A.M.
  • Bob Wright Centre, Room A202

Examining Committee

Supervisory Committee

  • Dr. Laurence Coogan, School of Earth and Ocean Sciences, University of Victoria (Supervisor)
  • Dr. Jay Cullen, School of Earth and Ocean Sciences, UVic (Member)
  • Dr. Sarah Slotznick, Department of Earth Sciences, Dartmouth College (Outside Member)

External Examiner

  • Dr. Ioan Lascu, Department of Mineral Sciences, Smithsonian Institute

Chair of Oral Examination

  • Dr. Tim Pelton, Department of Curriculum and Instruction, UVic

Abstract

High-temperature hydrothermal vent fluids at mid-ocean ridges, rich in Fe2+, rapidly precipitate Fe-rich minerals upon mixing with seawater, forming a particle-rich plume. The mineralogy, grain size, and stability of these particles control their dispersal and preservation, ultimately influencing hydrothermal contributions to ocean Fe cycling. However, the processes controlling the evolution of hydrothermal particles in the near-field region remain incompletely constrained.

In this study, magnetic and geochemical analyses of samples from the plume, sediment traps and sediment cores from the Endeavour Segment, Juan de Fuca Ridge, NE Pacific are used to assess mineralogical and chemical transformations near the axis. Both datasets show a systematic decrease in hydrothermal influence with distance off-axis, consistent with progressive sedimentation and dilution by detrital material. Deviations from simple two-component mixing suggest particle transport is also governed by the differing behaviour of individual mineral phases. Magnetic measurements are consistent with the presence of magnetite, pyrrhotite, goethite, and a low-temperature ordering phase, with distinct distributions among plume, sediment trap, and sediment core samples. Two magnetite populations, distinguished by Verwey transition temperatures, are interpreted as hydrothermal and detrital in origin. Pyrrhotite, identified by the Besnus transition, is present in the plume and sediment trap samples up to 3 km off-axis, with increased reversibility of the Besnus transition suggesting smaller pyrrhotite grains with distance. Pyrrhotite is absent in more distal sediments, though elevated chalcophile elements (e.g. Cu, Pb) persist in sediments at least 9 km off-axis, indicating continued transport of hydrothermal sulfides in the plume beyond 3 km. Magnetic data are consistent with the presence of goethite in all sampling locations with an apparent change in grain size or lower abundance in distal sediments. These data are interpreted as recording differential settling and dissolution of sulfide minerals during dispersal. Analysis of a near-field sediment core (2.5 km off-axis) demonstrates early diagenetic alteration, including rapid dissolution of pyrrhotite in the upper oxic sediment column, then preferential dissolution of oxidized magnetite across the redox transition, and later authigenic precipitation of magnetite at depth. Together, these data demonstrate that the evolution of hydrothermal particles in the near-field region is controlled by the differing behaviour of individual mineral phases during transport, and preservation in the sediments is impacted by both early and long-term diagenetic processes which modify hydrothermal particles after deposition.

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