Influence of preexisting fault fabric on inversion-related deformation: A case study of the inverted Fundy rift basin, southeastern Canada

Preexisting zones of weakness significantly influenced the structural development of the Fundy basin during rifting and subsequent basin inversion. The preexisting fabric, consisting of NE striking faults with gentle dips and east striking faults with steeply dipping upper segments and gently dipping lower segments, formed during Paleozoic and older orogenic activity. During Mesozoic rifting, the preexisting fabric was reactivated, creating a border-fault system composed of linked NE and east striking extensional fault zones with anomalous dips (gentle and steep) compared to those of newly formed normal faults. During inversion, the preexisting fabric was again reactivated as the hanging wall of the composite border-fault system moved NNE relative to the footwall. Inversion was highly oblique on the NE striking fault zones, producing gentle fault-parallel buttress folds and fault-perpendicular detachment folds above the low-angle fault zones. Inversion was moderately oblique on the east striking fault zone, producing relatively tight fault-parallel buttress and detachment folds above the gently dipping lower fault segments and reactivating the steeply dipping upper fault segments as left-lateral strike-slip faults. Thus, inversion-related deformation on the east striking fault zone was partitioned at shallow levels (i.e., partitioned updip). Our work shows that the geometry of preexisting extensional faults and their obliquity relative to the shortening direction profoundly affect deformation style during basin inversion. Namely, the type of inversion-related faults, the type and shape of inversion-related folds, and the distribution of deformation (e.g., updip partitioning) depend, in part, on the geometry of the preexisting extensional faults and the variations in these geometries with depth and along strike.