High strain zones may deform by flow with a triclinic symmetry. This paper describes triclinic flow in a reference frame where Instantaneous Stretching Axes (ISA) are fixed. The operation of triclinic flow is described in two ways: first in terms of flow and the nature of flow eigenvectors and in the second part of the paper in terms of finite strain. In monoclinic flow, at least one of the eigenvectors of the flow coincides with one of the ISA and one or two of the eigenvectors act as attractors of foliation or lineation elements. In triclinic flow some flow eigenvectors are undefined since the two largest eigenvalues (controlling the flow) are imaginary. Imaginary eigenvalues are particularly common at high kinematic vorticity and within flow with deviation of the vorticity vector of more than 20° from one of the ISA. Strong deviation from monoclinic flow is therefore possible, but this will not produce permanent foliations or lineations. For triclinic flow that does produce permanent fabrics, the angle between ISA and the fabric is so small that it is unlikely that it can be recognised in nature. A discussion of the potential application of such results within real shear zones is presented.
- flow kinematics
- shear zones