Multiscale numerical modelling of boundary stress conditions durino oblique rifting in the western Ross Sea, Antartica: implications for the time evolution of permeability anisotropy

Recently available structural, stratigraphical, and AFT thermochronological data pointed out the occurrence of a strong right-lateral oblique component during the progression of rifting in the western Ross Sea. In particular, structural data in fault damage zones describe a non-coaxial, partitioned transtensional evolutionary pathway. Availability of subsidiary fault/fracture data in fault damage zones provides robust constraints to the state of stress during fault activity and, consequently, on the orientation of fracture sets characterised by the best dilational conditions. Fault-fracture patterns in damage zones are influenced by a number of parameters that include:(1) their orientation with respect to the total stress field along the shear zone, that in turn results from the interplay between the stress field produced by fault motion (kinematic stress) and the regional stress field (dynamic stress); (2) the frictional properties within the shear zone and their spatial variability; (3) the contemporary growth and interaction among multiple subsidiary fault surfaces; (4) the rock type; (5) the depth at which faulting occurs; (6) the pore fluid pressure; (7) the strain rate; (8) the structural inheritance. These parameters have been implemented in a numerical-analytical (FRAPtre) tool specifically designed to simulate fracture fabrics in fault damage zones as a function of master fault geometry and kinematics, and of the boundary stress conditions. In this contribution we use the structural architecture (subsidiary faults) in fault damage zones along the western Ross Sea shoulder to get inferences on the state of stress during rifting and on its impact on the location and orientation of dilational fractures. The western shoulder of the Ross Sea is made up by Cambrian-Ordovician granitic rocks where Cenozoic exhumed fault zones are exposed. The persistency of similar rock types all along the rift shoulder allows to neglect the role exerted by mechanical stratigraphy and structural inheritance on the fracture patterns within fault zones. Availability of mafic dyke intrusions within many fault zones provides further constraints on the best dilational fracture orientation and its evolution through time. All these features make the western shoulder of the Ross Sea the proper site for testing numerical predictions on fault zone permeability conditions during oblique rifting. Such a geodynamic framework provides promising play conditions in hydrocarbon exploration.