285-5 Unlocking the Elusive Stories of Sulfides: Using EBSD to Characterize Previously Hidden Microstructures

Session: Rock Deformation and the Dynamics of Mountain Building: A Session Honoring the Scientific Contributions of John P. Platt, Part II

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Mineral microstructures harbor a treasure trove of information. Grain geometries, shape- and crystallographic preferred orientations, and intragranular features such as misorientations and subgrains yield insights into deformation mechanisms, rheology, kinematic vorticity, strain geometry, and even the differential stress and temperature during deformation. In addition, mineral microstructures provide crucial context for the interpretation of mineral trace element chemistry, yielding valuable information on the thermochemical conditions of mineral formation (or deformation). The micro-scale structure of minerals thus holds clues to the macro-scale processes that govern global tectonics.  

Over the past decades, the work of John Platt on microstructures in quartz, feldspar and even ice - particularly his work on the evolution of stress and rheology in natural shear zones, rheological flow laws, and links between microstructures and subduction zone phenomena like slow slip and tremor - has greatly contributed to this dynamic field of research. Rock-forming silicates, however, are not the only minerals with interesting microstructural tales to tell… and recently, the use of EBSD to map microstructures in visually opaque sulfide (and oxide) minerals has opened up a whole new world of stories.

In this presentation, I will showcase some of the research being done using sulfide microstructures imaged by EBSD, along with some of my recent work looking at how sulfides respond to deformation and metamorphism, and what effect this has on sulfide-hosted critical- and precious metals. Highlights include how integrating sulfide microstructure with trace element chemistry in a deformed base metal deposit provided evidence for the introduction of additional cobalt during deformation and metamorphism; how pyrrhotite can accommodate strain by dislocation creep and subgrain-rotation recrystallization at greenschist facies conditions, whereas pyrite is largely brittle; and how the dynamic recrystallization of sphalerite influences the distribution of critical metals like germanium, gallium, and indium. Overall, these projects demonstrate how John’s illustrious career in science has provided a solid foundation for research far outside his immediate fields.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-6070

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