A dynamic atlas of interference patterns in superimposed, opposite sense ductile shear zones

• Published in: Journal of structural geology 2022-12, Vol.165, p.104739, Article 104739
• Main Authors: Finch, M.A., Bons, P.D., Weinberg, R.F., Llorens, M.G., Griera, A., Gomez-Rivas, E.
• Format: Article
• Language: English
• Subjects: Inversion; Microstructures; Numerical modelling; Opposite shear sense; Reactivation; Shear zone; Shear zone interference patterns
• ISSN: 0191-8141; 1873-1201
• DOI: 10.1016/j.jsg.2022.104739

Ductile shear zones that reactivate a coplanar shear zone with opposite shear sense are known from a variety of tectonic environments. Recognition of reactivation requires understanding the interference patterns that form when microstructures produced in the first event (D1) are modified by the second event (D2). We use numerical modelling to demonstrate the effect of D1 structures on the development of shear zone interference patterns during a coplanar, opposite sense D2 ductile shearing event. Seven models were generated from increasing D1 dextral simple shear strains (γdextral = 2–14) and we then superimposed D2 sinistral shearing (γsinistral = 10). The interference patterns produced are highly variable with geometric relationships between weak layers and strong lithons determining deformation style. Shear zones with high D1 strain can more easily accommodate D2 strain because more strain is localised into long, weak phase C planes, which are readily inverted and reused during sinistral shear. Interference structures in models and naturally deformed rocks include rotated σ-clasts, folded D1 S planes, disharmonic and hook folds, and cuspate layers of weak phase. We present a dynamic atlas of interference patterns produced due to overprinting shear zones to facilitate identification of these zones in nature. •Overprinting of D1 shear by opposite sense, coplanar D2 creates interference patterns.•Interference patterns vary over short length and time scales.•High strain during D1 makes transposition to D2 structures quicker.•Low strain during D1 results in a large decrease in strain localisation at the start of D2.•Interference patterns in models are similar to those in naturally deformed rocks.