Geometry of thin-skinned tectonic systems in relation to detachment layer thickness in sedimentary basins

Abstract

Characterizing features of both extensional and compressional thin-skinned systems may be controlled by the thickness of the underlying mobile material. Within extensional fault arrays, detachment layer thickness, in conjunction with detachment dip, controls variations in fault spacing and polarity because rigid blocks are only free to rotate as long as there is enough underlying mobile material to redistribute between the fault block keels. Different styles of extensional fault array range from single polarity arrays with closely spaced faults (thin detachment) to arrays where the fault blocks rotate until the fault blocks separate from one another (thick detachment). Departure from this relationship depends on the amount of internal deformation that can be sustained by the domino fault blocks. Within contractional zones, detachment folds occur where the amount of mobile material can fill the evolving fold core via redistribution; thrusts occur where there is insufficient mobile material to sustain detachment fold growth. The variation in extensional and contractional style that are described here in relation to mobile layer thickness can be combined to give an idealized model of regional variation in structural style in relation to regional variation in stratigraphy. Applying this model to a salt basin, an allochthon in the area of thicknest salt may be characterized by updip raft tectonics and downdip detachment fold belts; this style would be laterally transitional toward areas of thinner or lower net salt to updip domino fault arrays and downdip thrust systems.