MULTI-SCALE EXPRESSIONS AND MECHANISMS OF STRUCTURAL INHERITANCE IN RIFT BASIN FORMATION AND INVERSION (Invited Presentation)

Structural inheritance describes the influence of pre-existing structures on younger structures. During continental rifting, inheritance can affect rift-related structures at various scales. For example, lithospheric-scale weaknesses can localize or segment rifts, while pre-existing crustal fabrics and faults can experience reactivation or interact with the far-field stress or strain, affecting the orientations, distributions, and growth of faults in cover sequences from basin to outcrop scales.

An example of the multi-scale expressions and mechanisms of structural inheritance is evident in the Gippsland Basin. This basin formed during Jurassic–Cretaceous rifting between Australia and Antarctica and is now located at the eastern end of Australia’s southern margin. Faults in the eastern, offshore part of the Gippsland Basin strike mainly E-W, consistent with the inferred N-S regional paleoextension. In contrast, faults in the western, onshore part strike ENE-WSW. Here, folded and faulted basement rocks have a NNE-SSW structural grain which may have locally re-oriented the far-field strain, resulting in rift-related faults oblique to both the inferred paleoextension direction and basement structures.

Following rifting, the Gippsland Basin experienced regional uplift and inversion. Pervasive NNW-SSE trending joints, conjugate N-S to NNE-SSW and NW-SE strike-slip faults, and reactivated NNE-SSW striking basement faults in outcrop all indicate NNW-SSE maximum horizontal shortening during this phase. Regional-scale expressions of this shortening include basin uplift and reverse reactivation of ENE-WSW striking rift-related faults. The different types and kinematics of shortening-related structures observed at outcrop and regional scales highlight that structural inheritance is scale-dependent.

Advancing our understanding of structural inheritance requires examining its mechanisms and scale dependency across tectonic settings. Insights from such studies can help recognize the influence of pre-existing structures where direct reactivation is not evident, identify the geometric and genetic relationships between deep and shallow structures, and understand fault behavior near pre-existing structures. This knowledge is important for inferring fluid transport pathways in the crust and assessing seismic hazard.