Abstract
AbstractCrystal‐plastic deformation is one of the main mechanisms that can accommodate large amounts of strain within the lithosphere. Despite the requirement of understanding dislocation nucleation and arrangement, the only accepted method for direct observation of dislocations in geological materials so far is transmission electron microscopy. Herein, we present a study using a combination of electron channelling contrast imaging (ECCI) and electron backscatter diffraction (EBSD) to visualize and analyse crystal defects in pyrite deforming close to the crystal plastic to brittle transition zone. Structures in focus include (a) dislocation nucleation at crack‐tips and (b) the reactivation of mode I cracks accompanied by the nucleation of dislocations and crystal‐plastic behaviour resulting in the development of complex dislocation structures and low‐angle grain boundaries. EBSD maps reveal an increase in misorientation towards micro‐cracks, consistent with a greater dislocation density along cracks observed by ECCI.
Highlights
In geological materials, the presence and multiplication of dislocations is indispensable to accommodate larger amounts of strain by continuous creep processes, possibly controlling large‐scale tectonic processes
The direct observation of crystal defects has been so far restricted to transmission electron microscopy (TEM), limiting observations to the size of a thin foil (Hirsch et al, 1960)
Bleeker suggests that the near‐surface environment where Au deposition is concentrated has a high pressure and temperature gradient and a low confining pressure, which allow for the dilation and opening of vein systems
Summary
The presence and multiplication of dislocations is indispensable to accommodate larger amounts of strain by continuous creep processes, possibly controlling large‐scale tectonic processes. We use electron channelling contrast imaging (ECCI), partly under controlled diffraction conditions, to analyse crystal defects in pyrite. The exact hydrothermal events or processes that caused veining at the Detour Lake deposit remain poorly understood, we assume they are consistent with the orogenic gold deposit forming model proposed by Bleeker (2015). In this model, Bleeker suggests that the near‐surface environment where Au deposition is concentrated has a high pressure and temperature gradient and a low confining pressure, which allow for the dilation and opening of vein systems. The inversion of the main fault zones, in this case, the SLDZ, from extensional to thrust creates an ideal deep‐reaching fluid conduit for the advection of Au‐bearing hydrothermal fluids (Bleeker, 2015)
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