The brittle-ductile deformation of rocks forms the foundation of structural geology, engineering geology and petroleum geology. Although brittle-ductile deformation structures and their evolutionary processes have been extensively investigated at macroscopic and microscopic scales, a reliable discrimination model remains elusive at the nanoscale. To establish distinctive nanostructural models for brittle-ductile deformations, this study combines the scanning electron microscopy analysis of thin shells within brittle-ductile shear zones with high-temperature and high-pressure experimental simulations. The brittle and ductile thin shell models exhibit markedly different structures. The models reveal a tripartite architecture in brittle thin shells: a vice-surface on top layer; a middle layer comprising individual spherical nanoparticles, nanoparticle aggregates and multi-aggregate nanoparticles; a basal substrate layer. In contrast, the ductile thin shell does not have a vice-surface on top layer or a basal substrate layer and its nanostructures are characterized by fibrous, chain-ball and schistose nanoparticles with their associated aggregate structures. Applying the space-for-time assumption, the evolution of thin shells in the shear zone was reconstructed, demonstrating that the brittle-ductile-viscous transition drives nanoparticle transformations through granularization - alienation - reuniting - reproduction sequences. This work extends the discrimination model of brittle-ductile deformation from the microscopic scale to the nanoscale.

Studies on matrix-related pores from the nanometer to the micrometer scale in shales have made considerable progress in recent decades. However, nanoscale pores and cracks developed in the shear thin layers have not been systematically discussed. In this work, interlayer shear slip occurring in shales are observed through practical examples. The results show that the shear thin layer constructed by nanograin coating is widely distributed on superimposed shear slip planes. Usually, the development of the shear thin layer undergoes viscoelastic-rheological-embrittling deformation stages, and the nanograin texture assembled in the shear thin layer can demonstrate three pore and crack structure types. Based on the mechanical analysis concerning nanoscale cohesion force, it is identified that, as long as force remains a state, the shear thin layer must bear a nanoscale pore and crack character. Furthermore, the shale gas reservoir effect of the nanoscale pore and crack is simply discussed. Obviously, the adsorbed gas effect of the nanograin itself has a larger nanoscale size and surface functionality than those of kerogen and clay particles in the shales; three structure types of the nanoscale pore and crack can act as given controlling factors of storage and permeability for the free gas. Both the matrix-related pores and the three pore and crack structures have an intimate connection with respect to each other in the genetic mechanism and temporal-spatial evolution. This work has important theoretical implications for supplementing the pore and crack classification of shale. Moreover, it makes a significant contribution to shale gas exploration and development.