Henry Lickorish - Structural Geology
Calgary, Canada
tel: +1 250 213 2643
Arcuate thrust systems in sand-box experiments: a comparison to the external arc of the western Alps
Lickorish W.H., Bürgisser J., Ford M. and Cobbold P. 2002
Geological Society of America Bulletin, 114, 1089-1107.

In the external Western Alps, two regional structural arcs were generated during Tertiray northwest-directed collision between the Apullian Indentoer and the European passive margin. These arcs, distinguished by their geographic position and their age, are examined by using a new compilation of structural data and comparing these to the results of sand-box analogue experiments. The principal Western Alpine arc comprises two orthogonal, synchronous thrust systems. In the Late Eocene to Early Miocene, major shortening (105kn) was towards the northwest to west-northwest, and minor shortening (11km) was toward the southwest. SHortening in each branch decreased toward the core of the arc. During the Late Miocene and Pliocene, the Jura arc accommodated 35km of northwest directed snortening, while 10.5km of southwest directed shortening was accommodated on the Digne thrust system. SAndbox experiments were used to investigate the role of the motion vector of a rigid rectangular indenter (orthogonal, diagonal, curved or rotational paths) and the mechanical stratigraphy of the foreland in the evolution of upper crustal arcuate systems (e.g. presence of a basal easy-slip [silicone] horizon). Comparison of results with the external Alpine arc suggests that the indenter followed a slightly diagonal path with respect to the European margin from the Eocene to Early Miocene and curved counter-clockwise by 10°-15° in the Middle Miocene. Mechanical stratigraphy experiments support the hypothesis that thick Triassic evaporites played a primary role in the evolution of the Jura arc. The influence of mechanical stratigraphy was most prominent during weak deformation at the external boundaries of the Alpine orogen (Jura fold-and-thrust belt, Digne thrust).