Stress space: striated faults, deformation twins, and their constraints on paleostress

Stress space is used to illustrate a discussion of the range of stress tensors theoretically compatible with striated faults, and with deformation twinning. Other than friction laws, each of the main constraints placed on stress by such data specifies the magnitude of a component of traction. Being linear in elements of the stress tensor, such a constraint by each datum is represented in stress space by a hyperplane. Comparison at each level of constraint (orientation, sense of shear, assumption of critical ratio or value of shear stress for faulting/twinning) is made for a single datum, followed by consideration of sets of data, and stress tensor reduction. At no level of constraint are striated faults and deformation twins equivalent. Fault data cannot constrain absolute values of stress components. Data for untwinned crystals within twinned/untwinned sets provide the fullest limit to values of deviatoric stresses. Paleostress estimates from twinned/untwinned data are generally preferable to those from striated faults.