Extensional Polarity Change in Continental Rifts: Inferences From 3‐D Numerical Modeling and Observations

Abstract

Extensional basins often show along‐strike variability in terms of fault geometries, basement structures, subsidence, and thermal evolution. This is particularly pronounced when extension reactivates preexisting suture zones with opposing dip directions, that is, opposite polarities, which creates wide strike‐slip transfer zones. We have studied this extensional variability by means of thermomechanical lithospheric‐scale 3‐D numerical modeling. We conducted a series of experiments to model the extension of a thick lithosphere simulating a young orogenic area containing segmented suture zones inherited from former opposing subduction polarities, implemented as rheologically weak inclined layers with opposite dips. Numerical experiments demonstrate that the initial subduction sutures are reactivated by two long‐lived lithospheric‐scale detachment faults, which remain active until the onset of oceanic spreading. The opposite polarity of these faults causes their migration toward each other by asymmetric mantle lithosphere extension and thermal accretion. Crustal kinematics shows the formation of extensional detachment faults and high‐offset listric normal faults. These structures undergo gradual tilting during their footwall exhumation, while the rheological weak suture layers are redistributed beneath the crust. The results demonstrate an active interaction along the strike of the system between the two opposite dipping weak zones, where fault segments mechanically interact. During extension, the maximum horizontal fault offset switches the apparent sense of shear in the separating strike‐slip transfer zone. This kinematics explain the rapid change in the sense of shear in major strike‐slip transfer zones or transform faults, such as observed during the extension of the Pannonian back‐arc basin.

Segmentation of Rifts Through Structural Inheritance: Creation of the Davis Strait

“…Indeed, this study is important as it applies well‐established theories regarding mantle lithosphere inheritance (e.g., Bercovici & Ricard, ) to a regional geological feature. Here, a mantle lithosphere structure can generate appropriate deformation related to the Davis Strait and follows a number of previous studies highlighting the importance of the mantle lithosphere in tectonic processes (e.g., Balázs et al, ; Babuška & Plomerová, ; Pysklywec & Beaumont, ; Heron et al, ; Heron et al, ; Heron et al, ; Heron & Pysklywec, ; Hopper & Fischer, ).…”

“…It should be noted that it is indeed unexpected that applying a North Atlantic Craton mantle suture (Figure 3b) in the presence of an extension field that is relevant in velocity and orientation to the Paleogene (Figure 4) would produce appropriate rift dynamics for the Davis Strait system ( Figure 6). However, the study here complements a growing body of work that highlights the potential of the mantle lithosphere to play an important role in tectonic processes (Pysklywec & Beaumont, 2004;Babuška & Plomerová, 2013;Jourdon et al, 2017;Salazar-Mora et al, 2018;Phillips et al, 2018;Balázs et al, 2018;Heron et al, 2019).…”

“…Numerous previous studies have shown the potential for mantle lithosphere structures to control the evolution of shallow tectonics (Balázs et al, 2018;Heron et al, 2019;Jourdon et al, 2017;Pysklywec & Beaumont, 2004;Phillips et al, 2018;Salazar-Mora et al, 2018;Schiffer et al, 2018), highlighting a deep genesis for lithosphere-scale deformation (e.g., Holdsworth et al, 2001;Vauchez et al, 1997). Reactivation of features formed through previous collisional or rifting events (Wilson, 1966) is well established and thought to occur along well-defined, preexisting structures such as faults, shear zones, or lithological contacts (Holdsworth et al, 1997).…”

Oblique rifting: the rule, not the exception

“…The first phases of rifting between Australia and Antarctica began in the Late Jurassic (Powell et al, 1988;Ball et al, 2013) but continental breakup did not begin until the Late Cretaceous and progressed diachronously from west to east. Within this rift system, the signatures of oblique extension have been previously recognized along Australia's southern margin (Willcox and Stagg, 1990;Norvick and Smith, 2001).…”

Thermo-mechanical and stratigraphic numerical forward modelling: recent advances and their joint application in the Pannonian Basin

“…Our setup used in this study (Table I) assumes a 1 000 km wide and 450 km deep section (Figure 1, a (CHOPRA & PATERSON 1984). Similar to previous studies we defined a tilted weak zone in the lithosphere representing a suture inherited from a former subduction episode (BALÁZS et al 2017a(BALÁZS et al , 2018a. It is assumed that such former subduction and collisional phases have resulted in a The divergent velocities are set to zero for the subsequent 11 Myr, simulating the post-rift phase of basin evolution.…”