General transpression and transtension

Abstract

In this work, a triclinic transpression and transtension model is presented in which the coaxial part of the flow is general, including both constriction and flattening as well as pure shear. The results show that, for both transtension and transpression, the different combinations of the variables that control the model allow obtaining finite strain ellipsoids in all fields of the deformation diagram, including prolate and oblate ellipsoids. It is mainly the ζ angle between the simple-shearing direction and the extrusion (transpression) or sinking (transtension) direction, together with the value of the vorticity, and the characteristics of the coaxial part of the flow, which controls the shape of the finite strain ellipsoid in each case. The orientations of the principal axes (X, Y, Z) of the finite strain ellipsoids show a wide variation, also dependent on ζ. The model has been applied to natural examples, improving the knowledge of their kinematic evolution and tectonic interpretation.