Transpression and transtension zones

Abstract

Transpression and transtension are strike-slip deformations that deviate from simple shear because of a component of, respectively, shortening or extension orthogonal to the deformation zone. These three-dimensional non-coaxial strains develop principally in response to obliquely convergent or divergent relative motions across plate boundary and other crustal deformation zones at various scales. The basic constant-volume strain model with a vertical stretch can be modified to allow for volume change, lateral stretch, an oblique simple shear component, heterogeneous strain and steady-state transpression and transtension. The more sophisticated triclinic models may be more realistic but their mathematical complexity may limit their general application when interpreting geological examples. Most transpression zones generate flattening (k < 1) and transtension zones constrictional (k > 1) finite strains, although exceptions can occur in certain situations. Relative plate motion vectors, instantaneous strain (or stress) axes and finite strain axes are all oblique to one another in transpression and transtension zones. Kinematic partitioning of non-coaxial strike-slip and coaxial strains appears to be a characteristic feature of many such zones, especially where the far-field (plate) displacement direction is markedly oblique (<20 ~ to the plate or deformation zone boundary. Complex foliation, lineation and other structural patterns are also expected in such settings, resulting from switching or progressive rotation of finite strain axes. The variation in style and kinematic linkage of transpressional and transtensional structures at different crustal depths is poorly understood at present but may be of central importance to understanding the relationship between deformation in the lithospheric mantle and crust. Existing analyses of obliquely convergent and divergent zones highlight the importance of kinematic boundary conditions and imply that stress may be of secondary importance in controlling the dynamics of deformation in the crust and lithosphere.

Structural history of the Arthur Lineament, northwest Tasmania: An analysis of critical outcrops

“…Based on similarities with examples of shear-related rotation discussed by Ridley and Casey (1989) and Dewey et al (1998), it is suggested that the change in orientation associated with CaD2 described above is the result of a strongly rotational shear component with a north-south stretching direction in the high-strain zone at the core of the Arthur Lineament.…”

Oblique rifting: the rule, not the exception

“…In general terms, oblique deformation takes place whenever a plate boundary exhibits irregular trends (Dewey et al, 1998) and is therefore an obvious ingredient of plate boundary tectonics. However, we speculate that the unexpectedly high percentage of oblique rifts and rifted margins could also reflect the existence of an underlying geodynamic process that influences plate velocities and thereby affects the resulting obliquity distribution.…”

“…al., 2016) and provided insight into the fault evolution during rifting (Ranero and Pérez-Gussinyé, 2010;Brune et al, 2014. The applicability of these concepts and models is often rooted in the assumption that rifts can be understood via plane strain cross-sections orthogonal to the rift trend and that the direction of extension aligns with the orientation of these crosssections. Many rifts and passive margins however involve segments where the extension direction is not perpendicular to the rift strike such that oblique, non-plane strain configurations occur (Sanderson and Marchini, 1984;Dewey et al, 1998). 5 Oblique rift segments differ from classical orthogonal examples in several major aspects: 1) In contrast to orthogonal rifts, the initial phase of oblique rifting is characterized by segmented en-échelon border faults that strike transversely to the rift trend.…”

Strain partitioning in front of an obliquely convergent indenter

“…However, the location of simple shear zones or strike slip faults within the transpressional zone was chosen rather arbitrarily, often in the centre of a zone (Jones and Tanner, 1995;Dewey et al, 1998) or, more rarely, at the margins of transpressional zones (Tikoff and Teyssier, 1994). It is quite evident from the above cited works, that the problem of locations, periodicity and spatial distribution of heterogeneous simple shear dominated zones within the global transpressional system are not yet sufficiently solved.…”

“…In contrast, the amount of strain partitioning in previous models was arbitrarily selected to demonstrate the role of orogen parallel slip on the bulk strain (see, e.g. Dewey et al, 1998).…”