Inheritance Across the Scales – Assessing the Relative Importance of Crustal and Lithospheric Structures during Rift Evolution

Abstract

Continental lithosphere is a heterogeneous assemblage of different units with variable strength, sutured together by a plethora of structures such as faults, shear zones, and other deformation fabrics. When this pre-existing framework of heterogenous lithosphere is broken apart, by extensional forces, these pre-existing structures and strength contrasts will have a considerable impact on the evolution of the resultant rift basins – a process known as inheritance. Inherited structures vary in scale and nature, ranging from broad zones of deformation fabrics in the upper mantle, to discrete faults in the upper crust. Inherited structures are often envisioned to influence rift evolution by reactivation of the inherited structure by a newly formed fault, yet this may not be the only mechanism in which inherited structures influence rifting. The constraint on how the scale and rheology of an inherited structure influence their effect on rift basins and their “reactivation” mechanism is poorly understood. Furthermore, the timing of when different scales of inheritance influence rift evolution is equally poorly constrained.
In this thesis, a multidisciplinary approach is used to understand how different scales of inheritance vary in their influence on continental rift evolution. Quantitative geomorphology of the Shanxi Rift in North China was used to constrain the rift evolution and analyse it under consideration of inherited structures, both in the upper crust and the deeper mantle. 2D geodynamic modelling of the North China Cenozoic rift systems was employed to better understand the impact of upper mantle structures and lithospheric architecture on rifting style, localisation, and migration. And finally, the interpretation of 2D and 3D seismic data of the Great South Basin, offshore New Zealand was carried out to constrain the temporal dimension of inheritance and contrast the impact of two variable terrane boundaries on rift evolution.
Each chapter illuminates a different aspect of the scale dependence of inheritance, in combination the results show that inherited structures do not necessarily need to reactivate to influence rift evolution. They also show that deeper seated structures in the lower crust or upper mantle are most important during the early localisation of rifting and determine the broader rift orientation. Meanwhile, shallow crustal structures segment individual rift faults at a smaller scale. These shallow crustal structures influence rifting most significantly in later stages during linkage and can sustain fault activity for longer along individual faults. These results not only present major implications for how we interpret the evolution of rift basins but also have practical considerations for seismic hazard assessments of active rifts and economic considerations for fluid flow in rift basins.