Controls on Early‐Rift Geometry: New Perspectives From the Bilila‐Mtakataka Fault, Malawi

Hodge, Michael; Fagereng, Åke; Biggs, Juliet; Mdala, Hassan

doi:10.1029/2018gl077343

Cited by 51 publications

(143 citation statements)

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“…Geochemistry, Geophysics, Geosystems 2017). Along most of its length, the Bilila-Mtakataka fault consists of a soil-mantled scarp (Hodge et al, 2018;Jackson & Blenkinsop, 1997). However, at Kasinje (Figure 2a), the fault consists of a 3-m thick unit of fractured gneiss that separates footwall and hanging wall hornblende gneisses (Hodge et al, 2018).…”

Section: 1029/2019gc008219mentioning

confidence: 99%

“…Dips of 57°a nd 60°for the Chingale Step and Thyolo faults were derived from field measurements ( Figure 5). The deep structure of the Bilila-Mtakataka fault is best described by two subparallel segments, the longest of which is oriented 156/46 NE (Hodge et al, 2018). By using these averaged strike measurements, we reduce the influence of fault nonplanarity caused by near-surface topographic stresses on our analysis (Norris & Cooper, 1995).…”

Section: The Strike Of the Chingalementioning

confidence: 99%

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How Do Variably Striking Faults Reactivate During Rifting? Insights From Southern Malawi

Williams

Fagereng

Wedmore

et al. 2019

Geochem Geophys Geosyst

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137

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Crustal extension is commonly thought to be accommodated by faults that strike orthogonal and obliquely to the regional trend of the minimum compressive stress (σ3). Activation of oblique faults can, however, be conceptually problematic as under Andersonian faulting, it requires preexisting crustal weaknesses, high fluid pressures, and/or stress rotations. Furthermore, measurements of incremental fault displacements, which are typically used to identify oblique faulting, do not necessarily reflect regional stresses. Here, we assess oblique faulting by calculating the stress ratio (σ3/σ1, where σ1 is the maximum compressive stress), slip tendency, and effective coefficient of friction (μs′) required to reactivate variably striking normal faults under different trends of σ3. We apply this analysis to NW and NNE striking active faults at the southern end of the Malawi Rift, where NE‐SW, ENE‐WSW, E‐W, and SE‐NW σ3 trends have previously been proposed. A uniform σ3 trend is inferred for this region as recent joints sets do not rotate along the rift. With a NE‐SW trending σ3, NW‐striking faults are well oriented, however, NNE‐striking faults require μs′ < 0.6 to reactivate. This is inconsistent with a lack of frictionally weak phyllosilicates detected in the fault zone rocks. With an ENE‐WSW to E‐W trending σ3, all faults can reactivate at μs′ > 0.55. These σ3 trends are also comparable to a focal mechanism stress inversion, regional joint orientations, and previously reported geodetically derived extension directions. We therefore conclude that unlike typical models of oblique rifting, the southern Malawi Rift consists of faults that all strike slightly oblique to σ3.

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Section: 1029/2019gc008219mentioning

confidence: 99%

Section: The Strike Of the Chingalementioning

confidence: 99%

How Do Variably Striking Faults Reactivate During Rifting? Insights From Southern Malawi

Williams

Fagereng

Wedmore

et al. 2019

Geochem Geophys Geosyst

Self Cite

137

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“…We quantify extension velocity using the global kinematic plate reconstruction of Müller et al (2016). This plate model integrates the latest syn-rift reconstructions for the South Atlantic (Heine et al, 2013), North Atlantic (Hosseinpour et al, 2013;Barnett-Moore et al, 2016), Australia-Antarctica separation and India-Antarctica breakup Whittaker et al, 2013;Gibbons et al, 2015), and Gulf of California opening (McQuarrie and Wernicke, 2005), among others ( Fig. 1).…”

Section: Rift Kinematicsmentioning

confidence: 99%

Oblique rifting: the rule, not the exception

2018

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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 2-D deformation 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 the 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 since 230 Ma amounts to 34° with a standard deviation of 24°, using the convention that the angle of obliquity is spanned by extension 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 3-D stress and strain fields that cannot be accounted for in simplified 2-D plane strain analysis. We therefore highlight the importance of 3-D 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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“…However, assessing the influence of preexisting structures on rift faulting is challenging because preexisting features can take many forms (e.g., compositional heterogeneity, variations in crustal or lithospheric thickness, and ancient faults or fabrics) and are often poorly known beneath rifts and ancient rifted margins since they are commonly overprinted. Furthermore, the influence of preexisting structures may be scale dependent (e.g., Kirkpatrick et al, ; Samsu et al, ) and can change with depth and/or time (e.g., Hodge et al, ; Muirhead & Kattenhorn, ; Ring, ). In some cases, preexisting structures appear to have minimal influence (Claringbould et al, ).…”

Section: Introductionmentioning

confidence: 99%

Controls on Rift Faulting in the North Basin of the Malawi (Nyasa) Rift, East Africa

Shillington

Scholz

Chindandali³

et al. 2020

Tectonics

100

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The North Basin of the Malawi Rift is an active, early-stage rift segment that provides the opportunity to quantify cumulative and recent faulting patterns in a young rift, assess contributions of intrarift faults to accommodating rift opening, and examine controls on spatial patterns of faulting. Multichannel seismic reflection data acquired in Lake Malawi (Nyasa) in 2015 together with legacy multichannel seismic data image a system of synthetic intrarift faults within this border-fault-bounded, half-graben basin. A dense wide-angle seismic reflection/refraction dip profile acquired with lake bottom seismometer data constrains sediment velocities that are used to convert fault throws from travel time to depth. Observed extension on intrarift faulting in the northern and central parts of the North Basin is approximately twice what would be predicted for hanging wall flexure, implying that the intrarift faults contribute to basin opening. The cumulative throw on intrarift faults is higher in the northern part of the rift segment than the south and is anticorrelated with throw on the border fault, which is largest in the southern part of the North Basin. This change in faulting coincides with a change in the orientation of the North Basin from a N-S trend in the south to a NNW-SSE trend in the north. We infer that the distribution of extension is influenced by rift orientation with respect to the regional extension direction. Almost all intrarift faults substantially offset late Quaternary synrift sediments, suggesting they are likely active and need to be considered in hazard assessments.

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Controls on Early‐Rift Geometry: New Perspectives From the Bilila‐Mtakataka Fault, Malawi

Cited by 51 publications

References 53 publications

How Do Variably Striking Faults Reactivate During Rifting? Insights From Southern Malawi

How Do Variably Striking Faults Reactivate During Rifting? Insights From Southern Malawi

Oblique rifting: the rule, not the exception

Controls on Rift Faulting in the North Basin of the Malawi (Nyasa) Rift, East Africa

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