Insights into the effects of oblique extension on continental rift interaction from 3D analogue and numerical models

Abstract

Continental rifts often develop from linkage of distinct rift segments under varying degrees of extension obliquity. These rift segments arise from rift initiation at non-aligned crustal heterogeneities and need to interact to develop a full-scale rift system. Here, we test the effects of 1) oblique extension and 2) initial heterogeneity (seed) offset on continental rift interaction with the use of an improved analogue model setup. X-Ray computer tomography (CT) techniques are used to analyse the 3D models through time and the results are compared with additional numerical models and natural examples. The experimental results reveal that increasing extension obliquity strongly changes rift segment structures from wide rifts in orthogonal settings to narrower rifts with oblique internal structures under oblique extension conditions to narrow strike-slip dominated systems towards the strike-slip domain. We also find that both decreasing seed offset and increasing extension obliquity promote hard linkage of rift segments through the formation of continuous rift boundary faults at the surface. (Initial) soft linkage through the formation of relay ramps is more likely when seed offset increases or extension is more orthogonal. Rather than linking at depth, the rift boundary faults curve around each other at depth and merge towards the surface to form a continuous trough. Orthogonal extension promotes the formation of intra-rift horsts, which may provide hydrocarbon traps in nature.

How oblique extension and structural inheritance influence rift segment interaction: Insights from 4D analog models

“…Data from numerical and analog studies indicate the influence of various parameters on rift interaction, e.g., the presence and geometry of structural heterogeneities, such as fault and shear zones, detachment layers, and magma intrusions that determine what structures develop (Elmohandes, 1981;Naylor et al, 1994;Acocella et al, 1999Acocella et al, , 2005Basile and Brun, 1999;Le Calvez and Vendeville, 2002;McClay et al, 2002;Tentler and Acocella, 2010;Paul and Mitra, 2013;Brune, 2014;Zwaan et al, 2016). Key factors affecting the large-scale evolution of rift interaction structures are the rift offset and the degree of brittle-ductile coupling in the system.…”

“…Key factors affecting the large-scale evolution of rift interaction structures are the rift offset and the degree of brittle-ductile coupling in the system. Larger offsets between rift segments cause TZs to be narrower (Acocella et al, 1999;Dauteuil et al, 2002) or even prevent TZs from developing (Le Calvez and Vendeville, 2002;Allken et al, 2011Allken et al, , 2012Zwaan et al, 2016). However, initial accommodation zones tend to evolve into TZs with increasing deformation ) and higher strain rates increase transfer zone widths (Dauteuil et al, 2002).…”

“…The overlap or underlap of rift segments (see also Figure 2d, 2e, and 2i) can result in a variation of rift interaction zone structures and can cause the formation of microcontinents (Müller et al, 2001;Tentler and Acocella, 2010). In addition, strong brittle-ductile coupling due to either high viscosities in the lower crust or high extension velocities (Brun, 1999;Buiter et al, 2008) causes distributed deformation (wide rifting) and prevents rift segments from developing discrete transfer zones (Allken et al, 2011(Allken et al, , 2012Zwaan et al, 2016).…”

“…Although oblique extension has been studied and modeled extensively with respect to the evolution of continuous rifts (Tron and Brun, 1991;McClay and White, 1995;Clifton and Schlische, 2001;McClay et al, 2002;Brune, 2014;Philippon et al, 2015), its effects on interacting rift segments have largely been neglected to date. In our previous analog modeling study (Zwaan et al, 2016), we did apply various degrees of dextral oblique extension and various seed offsets. The offset was of the "staircase" type (no over-or underlapping seeds), Figure 1.…”

Oblique rifting: the rule, not the exception

“…In this study, however, where we investigate the frequency of oblique rifting, it appears to be useful to draw a line between orthogonal and oblique extension. In simplified model settings, previous studies suggested that qualitative differences in the rifting style emerge when rift obliquity exceeds 15 to 20° (Clifton et al, 2000;Agostini et al, 10 2009;Brune, 2014;Zwaan et al, 2016). Keeping in mind that the specific value is somewhat arbitrary, we will use 20° as the critical obliquity separating orthogonal from oblique rifts.…”