Fluid inclusion induced hardening: nanoscale evidence from naturally deformed pyrite

Abstract

The interaction of trace elements, fluids and crystal defects plays a vital role in a crystalline material’s response to an applied stress. Fluid inclusions are typically known to facilitate crystal-plastic deformation in minerals. Herein we discuss a model of fluid hardening, whereby dislocations are pinned at fluid inclusions during crystal-plastic deformation, initiating pipe diffusion of trace elements from the fluid inclusions into crystal defects that leads to their stabilization and local hardening. We derive this hypothesis from atom probe tomography data of naturally deformed pyrite, combined with electron backscatter diffraction mapping, electron channelling contrast imaging and scanning transmission electron microscopy. The 2D and 3D micro- to nanoscale structural and chemical data reveal nanoscale fluid inclusions enriched in As, O, Na and K that are linked by As-enriched dislocations. Our efforts advance the understanding of the interplay between nanostructures and impurities during relatively low temperature deformation, which yields insight into the larger scale mass transfer processes on Earth.