Evolution of Rift Systems and Their Fault Networks in Response to Surface Processes

Abstract

Continental rifting is responsible for the generation of major sedimentary basins, both during rift inception and during the formation of rifted continental margins. Geophysical and field studies revealed that rifts feature complex networks of normal faults but the factors controlling fault network properties and their evolution are still matter of debate. Here, we employ high‐resolution 2D geodynamic models (ASPECT) including two‐way coupling to a surface processes (SP) code (FastScape) to conduct 12 models of major rift types that are exposed to various degrees of erosion and sedimentation. We further present a novel quantitative fault analysis toolbox (Fatbox), which allows us to isolate fault growth patterns, the number of faults, and their length and displacement throughout rift history. Our analysis reveals that rift fault networks may evolve through five major phases: (a) distributed deformation and coalescence, (b) fault system growth, (c) fault system decline and basinward localization, (d) rift migration, and (e) breakup. These phases can be correlated to distinct rifted margin domains. Models of asymmetric rifting suggest rift migration is facilitated through both ductile and brittle deformation within a weak exhumation channel that rotates subhorizontally and remains active at low angles. In sedimentation‐starved settings, this channel satisfies the conditions for serpentinization. We find that SP are not only able to enhance strain localization and to increase fault longevity but that they also reduce the total length of the fault system, prolong rift phases and delay continental breakup.

Punctuated propagation of a corrugated extensional detachment offshore Ireland

“…We do not exclude that the end of low‐angle faults activity may be related to a limit to the relationship between fault offset and serpentinization (Boddupalli et al, 2022). But in agreement with observations (Lymer et al, 2019) and numerical modelling (Neuharth et al, 2022) at the Galicia margin and at the P detachment, we suggest that low‐angle faults locked‐up when they moved further away from the locus of extension, such as illustrated in our model (Figure 6c,d).…”

“…The potential mantle temperature for the southern segments of the Porcupine Basin where the PMR developed (Figure 1a), southwest of the study area, have been suggested to range from 1290° to 1450°C (Calvès et al, 2012), which may be too hot for mantle serpentinization whose maximum temperature is debated but may be between 350°C (Bickert et al, 2020) and 600°C (Lavier & Manatschal, 2006). However, mantle temperature during rifting of the northern magma‐poor segment where the P detachment developed is not defined, and recent numerical modelling indicates that serpentinization can occur in hyper‐extended, magma‐poor rift segments with low syn‐rift sedimentation (Liu et al, 2022; Neuharth et al, 2022), such as in the study area. Serpentinization also occurs at MORs where the extensional systems mix both tectonic spreading and magmatic accretion (Escartin et al, 2017; Haughton et al, 2019; Peirce et al, 2020).…”

“…Low‐angle corrugated extensional detachments are commonly believed to represent the inactive part of a steep fault that has undergone extreme flexural back‐rotation; the inactive shallow fault maintaining continuity with the active steep fault (Buck, 1988; Choi et al, 2013; Deng et al, 2020; Escartin et al, 2017; Mizera et al, 2019; Olive et al, 2019; Reston, 2018; Smith et al, 2014; Webber et al, 2020; Ye et al, 2022). Despite the general acceptance of this model, the linkage between steep and shallow parts of detachments has never been directly observed and the back rotation of detachment faults from high to low angles has been inferred from indirect observations, including: palaeomagnetic measures of extreme footwall rotation (MacLeod et al, 2009; Morris et al, 2009), seismic imaging of shallow detachments (Reston & Ranero, 2011), numerical simulations (Buck, 1988; Choi et al, 2013; Liu et al, 2022; Neuharth et al, 2022) and P‐wave velocity models associated with microseismicity monitoring at MOR detachments (deMartin et al, 2007; Parnell‐Turner et al, 2020). For instance, microearthquake data from two oceanic detachments and associated corrugated low‐angle domes at 13°20′N and 13°30′N along the Mid‐Atlantic Ridge (MAR), show a band of seismicity dipping at ca.…”

Stratigraphic record of continental breakup, offshore NW Australia—Discussion

“…We acknowledge that the approach presented in Reeve et al ( 2022) may have been driven by mathematical models suggesting regional stratigraphic unconformities as representative of the geodynamic processes causing continental breakup. There are several examples of these models in the recent literature (Korchinski et al, 2021;Neuharth et al, 2022;Pérez-Gussinyé et al, 2020). Such models are often formulated assuming sedimentation rates that are relatively constant across and along continental margins, and sediment sources that are homogeneous in nature.…”

Mandyoc: A finite element code to simulate thermochemical convection in parallel

“…Additionally, the current version incorporates surface processes, imposing rates of erosion and sedimentation on the top of the free surface (Silva & Sacek, 2022). Recently, other thermomechanical codes available for the scientific community incorporated the interaction with surface processes (e.g., Beucher & Huismans, 2020;Neuharth et al, 2022) taking into account the simulation of fluvial and hillslope processes. In the present version of Mandyoc, only predefined erosion/sedimentation rate (variable in space and time) is possible.…”