Pinch-and-swell structures

Pinch-and-swell structures form in layered, ductile rocks due to layer-parallel extension (Figure 1). Pinch-and-swell structures can only form in rocks whose deformation behaviour is non-linear and, for example, described by a power-law or exponential flow law. In rocks having a linear viscous rheology, pinch-and-swell structures cannot form. Therefore, pinch-and-swell structures provide important information of the palaeorheology, i.e. the rheology of the rock when the pinch-and-swell structure was formed. To better understand pinch-and-swell formation and to be able to better constrain rheology from observed structures we study pinch-and-swell formation with numerical simulations based on the finite element method (Figure 2).

Figure 1: Pinch-and-swell structures in calc-silicate rocks (dark) embedded in marble (Adamello, Italy).


Figure 2: Finite element simulation of pinch-and-swell structures.


Raymond Fletcher
Dani Schmid

Géopolis - CH-1015 Lausanne
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