Classification of refold structures

Structural geology textbooks distinguish among four end members of three-dimensional refold structures established from their two-dimensional interference patterns. Here it is shown that six different end members of three-dimensional refold structures exist. These end members can be described by a reduced direction cosines matrix L*. The classical types 1-3 are extended to have three new counterparts types 0₁-0₃, which are derived by 90° rotation of the superposed fold around its fold axis. The matrix L* can be used to characterize the angles between the two fold generations in a simple triangle plot illustrating the six end members and even any intermediate refold structure.