Analog modeling of divergent and convergent transfer zones in listric normal fault systems

Transfer zones are common features in passive margins such as the Gulf of Mexico, where deformation between adjacent listric normal faults is accommodated by the formation of complex secondary fault systems. Two common types of transfer zones are (1) convergent, with the main faults dipping toward each other, and (2) divergent, with the main faults dipping away from each other. Analog clay models are developed for both convergent and divergent transfer zones with the faults approaching each other, offset by 90°, and overlapping each other. During extension, the structures initiate as symmetric grabens and later transform into asymmetric half grabens. The main fault and associated synthetic faults form a narrow zone of deformation, whereas the antithetic faults develop into a broader zone constituting evenly spaced discrete fault segments. Orientations, lengths, densities, and sizes of connected fault clusters vary with the type of transfer zone, structural position relative to the fault offsets, and total extension. The experiments show that the antithetic faults in convergent transfer zones and synthetic faults in divergent transfer zones tend to be more consistent in orientation and connect easily. Synthetic faults in convergent transfer zones and antithetic faults in divergent transfer zones change orientation along strike toward the transfer zone. Fault connectivity in approaching transfer zones is generally higher than in normal offset or overlapping configurations. The analog models provide important insights on the geometry of fault patterns and possible fluid-migration pathways within transfer zones.