Transfer Zones and Transfer Faults in Salt Tectonics

Fort, Xavier¹, J.-P. Brun², F. Chauvel³ (1) Norsk Hydro, Rennes, France (2) University of Rennes 1, France (3) University of Rennes 1, now at ExxonMobil

The term “transfer zone/fault” describes a broad category of structures that accommo­date lateral variations of deformation and strain. They occur at all scales in all types of tec­tonic processes.

In salt tectonic environments, a number of transfer-type structures can be identified and are here illustrated by laboratory experiments and comparison with natural examples in both extension and compression. Experiments show that two main types of causes can be invoked: i) either related to deformation heterogeneities within the sedimentary cover above salt or ii) due to lateral flow variations of the salt layer that are themselves due to lat­eral variations of sedimentary loading, salt thickness variations, inherited basement topog­raphy… The main types of transfer structures range from real localized transfer faults to distributed zones of faulting and block rotation.

The salt provinces of Lower Congo and Kwanza basins on the Angolan passive margin, provide a large spectrum of examples that illustrate the modes of transfer-type deforma­tion. In these areas, gravity driven deformation above salt defines domains of proximal extension and of distal contraction, in the margin slope direction. The development of transfer structures is discussed in terms of progressive deformation within the sedimenta­ry cover and/or of flow variations related to thickness variations of the salt layer in both extension and contraction.