Competition between 3D structural inheritance and kinematics during rifting: Insights from analogue models

Abstract

The competition between the impact of inherited weaknesses and plate kinematics determines the location and style of deformation during rifting, yet the relative impacts of these ‘internal’ and ‘external’ factors remain poorly understood, especially in 3D. In this study, we used brittle‐viscous analogue models to assess how multiphase rifting, that is changes in plate divergence rate or direction, and the presence and orientation of weaknesses in the competent mantle and crust, influences rift evolution. We find that the combined reactivation of mantle and crustal weaknesses without any kinematic changes already creates complex rift structures. Divergence rates affect the strength of the weak lower crustal layer and hence the degree of mantle‐crustal coupling; slow rifting decreases coupling, so that crustal weaknesses can dominate deformation localisation and surface structures, whereas fast rifting increases coupling and deformation related to mantle weaknesses can have a dominant surface expression. Through a change from slow to fast rifting mantle‐related deformation can overprint structures that previously formed along (differently oriented) crustal weaknesses. Conversely, a change from fast to slow rifting may shift deformation from mantle‐controlled towards crust‐controlled. When changing divergence directions, structures from the first rifting phase may control where subsequent deformation occurs, but only when they are sufficiently well developed. We furthermore place our results in a larger framework of brittle‐viscous rift modelling results from previous experimental studies, showing the importance of general lithospheric layering, divergence rate, the type of deformation in the mantle, and finally upper crustal structural inheritance. The interaction between these parameters can produce a variety of deformation styles that may, however, lead to comparable end products. Therefore, careful investigation of the distribution of strain localisation, and to an equal extent of basin depocenter locations over time is required to properly determine the evolution of complex rift systems, providing an incentive to revisit various natural examples.

Large-to Local-Scale Control of Pre-Existing Structures on Continental Rifting: Examples From the Main Ethiopian Rift, East Africa

“…Furthermore, several works show that many rifts developed in different, successive extensional phases (Whipp et al, 2014;Deng et al, 2017;Phillips et al, 2019;Wu et al, 2020), with normal faults formed during initial extensional events exerting a strong control on the structural architecture developed during the later rifting phases (Bell et al, 2014;Duffy et al, 2015;Henstra et al, 2015Henstra et al, , 2019Deng et al, 2018;Wang et al, 2021). Such a control exerted by early normal faults on structures formed during later extension is also supported by crustal and lithospheric scale analogue models (e.g., Corti et al, 2007;Sokoutis et al, 2007;Autin et al, 2013;Molnar et al, 2017Molnar et al, , 2019Molnar et al, , 2020Zwaan and Schreurs, 2017;Maestrelli et al, 2020;Wang et al, 2021;Zwaan et al, 2021a).…”

A review of structural inheritance in rift basin formation

“…Modelling also gives us the flexibility to examine the influence of various model parameters separately (e.g., rheological layering, obliquity, geometry of inherited weakness) as well as their combined effects (Zwaan et al, 2016(Zwaan et al, , 2021a(Zwaan et al, , 2021bZwaan and Schreurs, 2017). The modelling approach is especially useful for distinguishing between the relative contributions of oblique rift kinematics and inherited structures in shaping rift basins, as each on its own can create a transtensional system, resulting in faults that are oblique to the inferred paleo-extension direction.…”

“…The presence of a high-strength lithospheric mantle in "cold and strong" lithosphere favours the end-member narrow rift (e.g., East African Rift System), while extension of a "hot and weak" lithosphere leads to a wide rift (e.g., Basin and Range province) (see Buck, 1991 andBrun, 1999 for a thorough discussion). Strain distribution in the cover is attributed to the coupling between the brittle and ductile layers in the model, which depends on the applied strain rate as well as the mechanical layering (i.e., thermal structure) of the lithosphere (Kusznir and Park, 1986;Cowie et al, 2005;Wijns et al, 2005;Zwaan et al, 2021b). This distribution determines where basin-bounding faults and accommodation space are created during rifting.…”

“…When weaknesses are present in both the upper crust and lithospheric mantle, their relative contributions to strain localisation are determined by the degree of mechanical coupling between the two layers. This coupling depends on kinematic boundary conditions (e.g., rate of divergence) and the thickness and strength of the intervening, weak lower crust (Zwaan et al, 2021b).…”

“…Models show that discrete and pervasive weaknesses in the brittle upper crust (Brun and Tron, 1993;Bellahsen and Daniel, 2005;Corti et al, 2007;Chattopadhyay and Chakra, 2013;Ghosh et al, 2020;Zwaan and Schreurs, 2020;Zwaan et al, 2021aZwaan et al, , 2021b; see Table 2) undergo frictional reactivation (discussed from a geomechanics perspective in Section 2.3). This reactivation influences the orientations of rift-related faults (i.e., they show geometric similarity with the weaknesses) as well as their kinematics, growth, and linkage.…”