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Porosity induced by dislocation dynamics in quartz-rich shear bands of granitic rocks

Abstract : The production of micro-pores is a driving mechanism for fluids to interact with deep environment and influence rock properties. Yet, such a porosity still remains misunderstood to occur in viscous rocks and may be attributed to either grain boundary sliding (GBS), dissolution effects or sub-grain rotation. Here we focus on quartz-rich shear bands across the Naxos western granite (Aegean Sea, Greece), where we document sub-micron pores at quartz boundaries. While most of these pores are observed along grain boundaries, some of them occur at intra-grain boundaries, which excludes dissolution or GBS to produce them, but instead involves the dynamic of dislocations. We then confirm that quartz is dominated by dislocation creep with evidence of a moderate to strong lattice-preferred orientation (LPO) and numerous tilt/twist boundaries, including at the pluton margin where rocks embrittled. These features coincide with (1) randomly oriented 'inclusion' quartz grains along tilt/twist boundaries and (2) a partial dependency of the LPO strength on grain size. Our findings suggest that pores arise from coalescing dislocations at boundaries of rotating sub-grains, providing nucleation sites for new grains to be precipitated during plastic flow. Fluid infiltration, rock embrittlement and related implications are also expected through pores accumulation with increasing strain.
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Submitted on : Tuesday, May 10, 2022 - 2:07:21 PM
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Jacques Précigout, Estelle Ledoux, Laurent Arbaret, Charlotte Spriet. Porosity induced by dislocation dynamics in quartz-rich shear bands of granitic rocks. Scientific Reports, Nature Publishing Group, 2022, 12 (1), pp.6141. ⟨10.1038/s41598-022-10053-x⟩. ⟨hal-03663782⟩



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