A physical experiment shows that shortening applied to existing diapirs
and minibasins produces anomalous structural styles that are unlike
those of more typical foldbelts. Strong minibasins remain largely
undeformed while weak diapirs localize contractional strain. Short
diapirs form the cores to folds and thrusted folds, whereas tall diapirs
are squeezed and often welded, commonly leading to the extrusion of
allochthonous material. Key features of the model are observed in
real examples. In the northern Gulf of Mexico passive margin, minibasins
were originally separated by a polygonal pattern of deep salt ridges,
with diapirs located at ridge intersections. Gravity spreading resulted
in squeezed diapirs (and associated allochthonous salt) connected
by variably oriented contractional, extensional, and strike-slip structures.
In the Flinders Ranges convergent-margin foldbelt of South Australia,
preexisting diapirs were squeezed, welded, and thrusted, with anticlines
plunging away in multiple directions, so that minibasins are surrounded
by highly variable structures. A different geometry is observed in
La Popa Basin, Mexico, where squeezing of a linear salt wall produced
a vertical weld with diapirs at the terminations, rather than the
culmination. In all areas, foldbelt geometries are strongly influenced
by the preestablished salt-minibasin architecture.