There are various natural types of thrust sheets in thinskin thrustbelts. Their development, driving mechanisms and internal deformation differ. However, there are various natural kinematic transitions between these thrust sheet types, driven by continuous shortening, changes in controlling rheologies or potential internal deformation of various types of structures.

Fault-propagation fold

When the stress path of the rock section loaded by burial and tectonic stress intersects the faulting instability envelope synchronously with the folding instability envelope (as discussed in the previous chapter), the deformation results in fault-propagation folding. Faultpropagation fold development should be rather rare, considering the statistical chance of the stress path intersecting both instability envelopes at the same time. However, there are numerous case studies in the literature of fault-propagation folds from thrustbelts around the world. Fairly recently Mitra (2002b), following earlier suggestions by Morley (1994), Mitra (1997) and Storti et al. (1997), provided the most likely explanation for this anomaly. Faulted detachment folds roughly resemble fault-propagation folds, which in regions with poorer quality data could lead to their misinterpretation and interchange, as he documents in several cases from the Albanide thrustbelt, the Wyoming thrustbelt, the Papua New Guinea thrustbelt and the Mississippi Fan thrustbelt in the Gulf of Mexico.

Fault-propagation folds develop by a mechanism described by the flexural-slip model (Suppe and Medwedeff, 1984; Suppe, 1985; Jamison, 1987), which is shown in Fig. 4.1.