How Does the Orientation of a Preexisting Basement Weakness Influence Fault Development During Renewed Rifting? Insights From Three‐Dimensional Discrete Element Modeling

Deng, Chao; Gawthorpe, Robert L.; Fossen, Haakon; Finch, Emma

doi:10.1029/2017tc004776

Cited by 35 publications

(40 citation statements)

References 92 publications

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“…Our models build on previous work that showed how obliquity influences rift geometries at crustal to outcrop scale. Discrete element models by Deng et al (2018) show how fracture patterns at the surface are affected by a pre-existing weakness. Based on analog models, Withjack and Jamison (1986) predict maximum extension direction at oblique rifts (which is perpendicular to orientation of early en-échelon fractures) is a function of the angle between rift trend and displacement of the rift walls.…”

Section: Discussion Analog Modelsmentioning

confidence: 99%

The Effect of Obliquity of Slip in Normal Faults on Distribution of Open Fractures

et al. 2019

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Close to surface, cohesive rocks fail in extension, which results in open fractures that can be several tens of meters wide, so-called massively dilatant faults. These open fractures make fault slip analysis in rifts challenging, as kinematic markers are absent. Faults in rifts often have oblique slip kinematics; however, how the amount of obliquity is expressed in the surface structure of massively dilatant faults remains enigmatic. Furthermore, the structures of oblique dilatant faults at depth is largely unconstrained. To understand the subsurface structures we need to understand how different obliquities of slip influence the surface structures and the corresponding structures at depth. We present analog models of oblique massively dilatant faults using different cohesive materials in a sandbox with adjustable basement fault slip obliquity from 0 • to 90 •. Experiments with different mean stress and material cohesion were run. Using photogrammetric 3D models, we document the final stage of the experiments and investigate selected faults by excavation. We show that fault geometry and dilatancy changes systematically with angle of obliquity. Connected open fractures occur along the entire fault to a depth of 6-8 cm, and as isolated patches down to the base of the experiments. Using the scaling relationship of our models implies that transition from mode-1 to shear fracturing occurs at depths of 250-450 m in nature. Our experiments show the failure mode transition is a complex zone and open voids may still exist at depths of at least 1 km. We apply our results to the dilatant faults in Iceland. We show that the relationship between angle of obliquity and average graben width determined on faults on Iceland matches experimental results. Similarly, fracture orientation with respect to fault obliquity as observed on Iceland and in our experiments is quantitatively comparable. Our results allow evaluation of the structure of massively dilatant faults at depth, where these are not accessible for direct study. Our finding of a complex failure mode transition zone has consequences for our understanding of fracture formation, but also influences our interpretation of fluid flow in rift systems such as magma ascent or flux of hydrothermal waters.

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Section: Discussion Analog Modelsmentioning

confidence: 99%

The Effect of Obliquity of Slip in Normal Faults on Distribution of Open Fractures

et al. 2019

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“…Fournier and Petit, 2007;Philippon et al, 2015;Brune, 2016;Zwaan and Schreurs, 2017;Ammann et al, 2017), but is opposite to the convention used in almost as many articles (e.g. Tron and Brun, 1991;Teyssier et al, 1995;Clifton and Schlische, 2001;Deng et al, 2018). 5…”

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confidence: 79%

Oblique rifting: the rule, not the exception

Brune¹,

Williams²,

Müller³

2018

Preprint

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Abstract. Movements of tectonic plates often induce oblique deformation at divergent plate boundaries. This is in striking contrast with traditional conceptual models of rifting and rifted margin formation, which often assume 2D deformation 10 where the rift velocity is oriented perpendicular to the plate boundary. Here we quantify the validity of this assumption by analysing the kinematics of major continent-scale rift systems in a global plate tectonic reconstruction from the onset of Pangea breakup until present-day. We evaluate rift obliquity by joint examination of relative extension velocity and local rift trend using the script-based plate reconstruction software pyGPlates. Our results show that the global mean rift obliquity amounts to 34° with a standard deviation of 24°, using the convention that the angle of obliquity is spanned by extension 15 direction and rift trend normal. We find that more than ~70% of all rift segments exceeded an obliquity of 20° demonstrating that oblique rifting should be considered the rule, not the exception. In many cases, rift obliquity and extension velocity increase during rift evolution (e.g. Australia-Antarctica, Gulf of California, South Atlantic, India-Antarctica), which suggests an underlying geodynamic correlation via obliquity-dependent rift strength. Oblique rifting produces 3D stress and strain fields that cannot be accounted for in simplified 2D plane strain analysis. We therefore highlight the importance of 3D 20 approaches in modelling, surveying, and interpretation of most rift segments on Earth where oblique rifting is the dominant mode of deformation.

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“…Strain migration along individual fault systems is common, typically reflecting fault growth by segment linkage, rheological differences in the deforming host rock, and/or the presence of pre-existing structures (e.g., Cowie et al, 2000;McLeod et al, 2000McLeod et al, , 2002Young et al, 2001;Walsh et al, 2003;Soliva et al, 2006;Putz-Perrier & Sanderson, 2008;Tomasso et al, 2008;Nixon et al, 2014;Whipp et al, 2014;Duffy et al, 2015;. Segment linkage and pre-existing structures played a role in the growth of several fault systems (e.g., segment linkage at Eider Fault System, Figure 6a-b; see also McLeod et al, 2002).…”

Section: Temporal and Spatial Changes In The Basin-scale Distributionmentioning

confidence: 99%

“…Numerical and physical models of rift development, which simulate the formation of upper-crustal deformation, do not, however, commonly consider how strain behaves in three dimensions. This often reflects the limited spatial and temporal resolution of such models, which allows them to only predict the patterns of strain migration in two dimensions (e.g., towards or away from the rift axis) (e.g., McClay, 1990;Cowie et al, 2000;Huismans et al, 2001;Behn et al, 2002;Ziegler & Cloetingh, 2004;Nagel & Buck, 2007;Naliboff et al, 2017). However, observations from individual faults or fault systems (i.e.…”

Section: Introductionmentioning

confidence: 99%

“…a kinematically linked group of fault segments that are several km to tens of km long) suggest that the overall accumulation of rift-related strain can be rather complex in three dimensions due to, for example, fault segment interaction and/or the composition and structure of the upper-crust (e.g. Cowie et al, 2000;Walsh et al, 2003;Soliva et al, 2006;Putz-Perrier & Sanderson, 2008;Nixon et al, 2014;Whipp et al, 2014;Duffy et al, 2015;. Recent studies of relatively young (<5 Myr old), still-active rifts (e.g., Gulf of Corinth Rift, Bell et al, 2009;Ford et al, 2013;Nixon et al, 2016) and inactive rifts (e.g., southern South African extensional system, Paton, 2006; northern North Sea, Claringbould et al, 2017) suggest that the initial phase of upper-crustal stretching is distributed across a wide zone.…”

Section: Introductionmentioning

confidence: 99%

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Pre-breakup extension in the northern North Sea defined by complex strain partitioning and heterogeneous extension rates

Claringbould¹,

Bell²,

Jackson³

et al. 2019

Preprint

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The early stages of continental rifting are accommodated by the growth of upper-crustal normal fault systems that are distributed relatively evenly across the rift width. Numerous fault systems define fault arrays, the kinematics of which are poorly understood due to a lack of regional studies drawing on high-quality subsurface data. Here we investigate the long-term (~150 Myr) growth of a rift-related fault array in the East Shetland Basin, northern North Sea, using a regionally extensive subsurface dataset comprising 2D and 3D seismic reflection surveys and 107 boreholes. We show that rift-related strain during the pre-Triassic-to-Middle Triassic was originally distributed across several sub-basins. The Middle-to-Late Triassic saw a decrease in extension rate (~14 m/Myr) as strain localized in the western part of the basin. Early Jurassic strain initially migrated eastwards, before becoming more diffuse during the main, Middle-to-Late Jurassic rift phase. The highest extension rates (~89 m/Myr) corresponded with the main rift event in the East Shetland Basin, before focusing of strain within the rift axis and ultimate abandonment of the East Shetland Basin in the Early Cretaceous. We also demonstrate marked spatial variations in timing and magnitude of slip along-strike of major fault systems during this protracted rift event. Our results imply that strain migration patterns and extension rates during the initial, pre-breakup phase of continental rifting may be more complex than previously thought; this reflects temporal and spatial changes in both thermal and mechanical properties of the lithosphere, in addition to varying extension rates.

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How Does the Orientation of a Preexisting Basement Weakness Influence Fault Development During Renewed Rifting? Insights From Three‐Dimensional Discrete Element Modeling

Cited by 35 publications

References 92 publications

The Effect of Obliquity of Slip in Normal Faults on Distribution of Open Fractures

The Effect of Obliquity of Slip in Normal Faults on Distribution of Open Fractures

Oblique rifting: the rule, not the exception

Pre-breakup extension in the northern North Sea defined by complex strain partitioning and heterogeneous extension rates

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