An alternative kinematic interpretation of Thetis Boundary Shear Zone, Venus: Evidence for strike‐slip ductile duplexes

Abstract

On Venus a 1000‐km‐long, 50‐ to 200‐km‐wide, anastomosing shear zone system (Thetis Boundary Shear Zone (TBSZ)) separates the eastern Ovda and northwestern Thetis Regiones. Previous workers mapped a part of this shear zone and interpreted it as a sinistral strike‐slip shear zone containing an extensional jog. In the present study it is reexamined for a detailed structural and kinematic analysis, and an alternative kinematic interpretation is provided. The TBSZ is divided into western, central, and eastern segments. The western segment is narrow and is oriented in a ENE‐WSW direction. Along its northern boundary the preexisting folds of tessera are cut by the shear zone, and the folds are dragged into parallelism with the shear zone in response to dextral strike‐slip motion. Both the western and central segments contain a pair of conjugate deformation bands (sigmoidal folds and linear ridges), which appear similar to S–C‐like structures of large‐scale ductile shear zones. The acute angle between the S and C bands suggests dextral sense of displacement. The eastern segment forms the northeastern restraining bend of the TBSZ, where the shear zone is characterized by a wide, branching, fan‐like anastomosing shear zone system with well‐developed contractional strike‐slip ductile duplexes. The internal fabric defined by the sigmoidal folds consistently shows dextral sense of displacement. Therefore the TBSZ is a dextral strike‐slip shear zone showing S–C‐like structures and contractional strike‐slip duplexes, similar to the continental‐scale ductile shear zones on Earth.