Interactions between propagating rotational rifts and linear rheological heterogeneities: Insights from three‐dimensional laboratory experiments

Abstract

The lateral propagation of rifts is a consequence of the relative divergence of lithospheric plates about a pole of rotation. Modern and ancient examples of rifts are known to overprint preexisting linear anisotropies in the crust and lithosphere, such as lithospheric boundaries, crustal sutures, and thermal anomalies. Here we investigate how propagating rifts interact with preexisting structures by using three‐dimensional analogue experiments with rotational extensional boundary conditions and variably oriented linear weak zones in the lithospheric mantle. When linear weaknesses are oriented at low angles to the rift axis, early strain localization occurs in narrow domains, which merge at later stages, resulting in continental breakup by unzipping. Strong strain partitioning is observed when the linear heterogeneity is oriented at high angles with respect to the rift axis. In these experiments, early subparallel V‐shaped basins propagate toward the pole of rotation until they are abandoned and strain is transferred entirely to structures developed in the vicinity of the strongly oblique weak lithosphere zone boundary. The experimental results are characterized in terms of their evolution, patterns of strain localization, and surface topography as a function of the lithospheric heterogeneity obliquity angle. Comparison of the experiments to ancient and modern examples in nature may help to elucidate the common but still poorly understood process of propagating rift‐lithospheric heterogeneity interaction.

Perspectives on Continental Rifting Processes From Spatiotemporal Patterns of Faulting and Magmatism in the Rio Grande Rift, USA

“…Physiographic characteristics (e.g., narrow or wide grabens, asymmetric or symmetric faulting, voluminous volcanism vs. lack of magmatism, and/or changes in graben trend/strike) within continental rifts are partially attributed to differences in extensional accommodation mechanisms, which in rift systems, can be either faulting, magmatism, or a combination of the two (e.g., Buck, 2004;Ebinger et al, 2013;Lavecchia et al, 2017;Molnar et al, 2017;Muirhead et al, 2016;Reyners et al, 2007). The RGR is a >1,000-km-long continental rift that extends from potentially as far south as the Big Bend area on the Texas-Mexico Border (e.g., Muehlberger et al, 1978;Nakai et al, 2017;van Wijk et al, 2018), through New Mexico to central Colorado (Figure 2; Kelley et al, 1992;Knepper, 1974;Limbach, 1975), and possibly as far north as southern Wyoming, USA (e.g., Cosca et al, 2014;Kellogg, 1999;Leonard et al, 2002;Naeser et al, 2002;Nakai et al, 2017).…”

“…Rifting was primarily synchronous along the length of the RGR (Chapin & Cather, 1994;Landman & Flowers, 2013;Ricketts et al, 2016). Typical models supporting synchronous rifting include either block rotation or oblique strain (Figure 1; Ebinger et al, 1984;Brown & Golombek, 1986;Ebinger, 1989;Nelson et al, 1992;McClay et al, 2002;Kreemer et al, 2010;Busby, 2013;Molnar et al, 2017;Lavecchia et al, 2017;Brune et al, 2017). Additionally, interbasin synrift sedimentation and thermochronometry data from the rift flanks have been invoked to support a model of synchronous rift initiation (Chapin & Cather, 1994;Ingersoll, 2001;Landman & Flowers, 2013;Ricketts et al, 2015).…”

“…Additionally, the mechanisms that accommodate extension may be controlled by crustal and lithospheric properties such as strength, thickness, preexisting weakness, inherited structure, composition, and/or rates of extension (e.g., Brun, 1999;Buck, 1991;Corti, 2012;Fletcher et al, 2018). As such, there are numerous expressions of rifting, for example, rifts can be wide, narrow, magma dominated, have large basin-bounding faults, numerous intrabasin faults, or en echelon geometries (e.g., Brune et al, 2017;Ebinger, 1989;Ebinger et al, 1984;McClay et al, 2002;Molnar et al, 2017;Nelson et al, 1992), emphasizing the roles that faulting and magmatism can have on the geometry and extension accommodation of a rift system (Figure 1; e.g., Buck, 2004;Ebinger, 2005;Buck, 2006;Corti, 2009).…”

Controls of inherited lithospheric heterogeneity on rift linkage: Numerical and analog models of interaction between the Kenyan and Ethiopian rifts across the Turkana depression

“…In this case the mantle beneath the central rift is so weak that it governs the necking process and forces crustal localization to bend right laterally into the central segment. This case is reminiscent to recent analog models of propagating rotational rifts interacting with linear rheological heterogeneities cutting the rift at moderate and high obliquity [ Molnar et al , ]. If the rheological configuration of the central domain is very similar to the rift valleys to the north and south, the model virtually does not notice the inherited heterogeneity and straight linkage (Type 5) occurs.…”

Oblique rifting: the rule, not the exception

“…This is mainly due to rift variability in general, which arises from tectonic inheritance Morley, 5 2016;Hodge et al, 2018;Phillips et al, 2018), or from along-strike changes in rheology, crustal configuration, temperature and rift velocity (e.g. Sippel et al, 2017;Molnar et al, 2017;Brune, et al, 2017b;Mondy et al, 2017).…”