The Mesoproterozoic Nampula Subdomain in southern Malawi: Completing the story from Mozambique

Thomas, Robert J.; Fullgraf, Thomas; Macey, P.H.; Boger, Steven D.; Hölttä, Pentti; Lach, Philippe; Roux, Petrus le; Dombola, Kondwani; Zammit, Carol

doi:10.1016/j.jafrearsci.2022.104667

Cited by 5 publications

(9 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Strong crustal blocks beneath a RIZ, either crustal-scale or only in the lower-crust, can inhibit rapid propagation of a rift tip (Van Wijk and Blackman, 2005;Le Pourhiet et al, 2018). However, this is not likely to be the case in our study area as basement geologic maps (e.g., Bingen et al, 2009;Fritz et al, 2013;Thomas et al, 2022) and large-scale basement metamorphic fabric trends (Kolawole et al, 2021a(Kolawole et al, , 2022 of the region do not show the presence of a discrete basement block separating the southern Malawi Rift from the Lower-Shire Graben. However, numerical models show that significant activation of rift stalling by lower crustal rheological blocks is in fact, most significantly activated when there is compressive tectonic loading ahead of the propagating rift tip (Le Pourhiet et al, 2018).…”

Section: Controls Of Rift Interaction Zone Geometry On Early Vs Delay...mentioning

confidence: 75%

“…The graben is bounded to the west by the Nsanje Fault, and to the east by the Ndidi Fault (Figure 3a). Both the Nsanje and Ndindi border faults crosscut the large-scale NE-trending metamorphic fabrics of the host Precambrian basement (Bloomfield, 1958;Kolawole et al, 2022;Thomas et al, 2022), indicating a lack of large-scale basement inheritance on border fault development. Geologic maps show widespread coverage of Quaternary sediments across the entire graben, deposited in the Ndindi Marsh and floodplains of the Shire River (Figure 3b; Bloomfield, 1958;Choubert et al, 1988).…”

Section: Rift Structure and Tectonic Historymentioning

confidence: 99%

“…Graben to the Nsanje Graben occurs at the NE-trending Lurio Shear Zone, an exhumed ductile shear zone separating the Unango and Nampula terranes of the Precambrian Southern Irumide Belt (Figure S1; Fritz et al, 2013;Kolawole et al, 2022;Thomas et al, 2022). The Middle-Shire RIZ defines an overlapping oblique RIZ geometry in which the NNE/N-trending Malawi Rift is propagating into the NE shoulder of the NW-trending Lower-Shire Graben, whereas the Nsanje RIZ is a tip-to-tip oblique RIZ in which the Lower-Shire Graben has propagated into the northern tip of the N-trending Nsanje Graben (Figure 3a).…”

Section: The Middle-shire and Nsanje Rift Interaction Zonesmentioning

confidence: 99%

See 2 more Smart Citations

Rapid Versus Delayed Linkage and Coalescence of Propagating Rift Tips

Kolawole¹,

Xue²,

Dulanya³

2023

Preprint

View full text Add to dashboard Cite

The tectonic interaction, linkage, and coalescence of propagating isolated rift segments create a through-going along-axis rift floor without which a continental break-up axis cannot develop.However, prior to linkage, interacting rift segments are separated by a topographic basement-high (rift interaction zone, RIZ) which is progressively dismembered and down-thrown by the lateral propagation of rift tip faulting and their hanging wall subsidence. Here, we explore the evolution of the Middle-Shire and Nsanje RIZs located along three slowly extending (~2.2 mm/yr) contiguous propagating rift segments: the southern Malawi Rift, Lower-Shire Graben, and the Nsanje Graben, East Africa. The Middle-Shire RIZ is an overlapping-oblique RIZ in which the NNE/N-trending Malawi Rift is propagating into the shoulder of the NW-trending Lower-Shire Graben, whereas the Nsanje RIZ is a tip-to-tip oblique RIZ in which the Lower-Shire Graben has propagated into the tip of the N-trending Nsanje Graben. These rift zones provide non-volcanic natural examples to explore tectonic strain localization on rift tips and syn-rift RIZ surface processes. We use a landscape evolution model with implemented fault displacement fields of two contiguous RIZs with contrasting geometries, to simulate their geomorphic evolution, and apply a static stress model to evaluate the stress transfer patterns during RIZ evolution. The model results successfully reproduce natural observations in the study area, in which, with progressive extension and tip growth, the Middle-Shire RIZ maintains minor basement down-throw and an unequilibrated axial stream profile, which contrasts the widespread basement burial and equilibrated axial stream profile across the Nsanje RIZ.Modeled static stress distribution predict compounding stress concentrations at tip-to-tip RIZs, favoring brittle strain localization and rift coalescence, and stress relaxation at overlapping oblique RIZs, favoring stalled rift coalescence. We argue that RIZ geometry strongly influences the pace of rift coalescence by modulating the spatial distribution of tectonic stresses necessary to promote riftlinking deformation and the associated surface processes.

show abstract

Section: Controls Of Rift Interaction Zone Geometry On Early Vs Delay...mentioning

confidence: 75%

Section: Rift Structure and Tectonic Historymentioning

confidence: 99%

Section: The Middle-shire and Nsanje Rift Interaction Zonesmentioning

confidence: 99%

See 1 more Smart Citation

Rapid Versus Delayed Linkage and Coalescence of Propagating Rift Tips

Kolawole¹,

Xue²,

Dulanya³

2023

Preprint

View full text Add to dashboard Cite

show abstract

“…Northern Malawi is underlain by Ubendian-Usagaran-aged metamorphic and magmatic rocks that experienced low-to high-P granulite-facies metamorphic conditions (750-850°C at 0.5 GPa to ∼880°C at 1 GPa) at c. 2.0 Ga (Ring et al, 1997). Central and southern Malawi is underlain by rocks that likely experienced deformation and metamorphism related to both c. 1.05 Ga Irumide and c. 580-550 Ma Pan-African Mozambique Belt events (Fritz et al, 2013;Thomas et al, 2022;Tsunogae et al, 2021). In a regional reconstruction, Fritz et al (2013) suggest that the crust west of Lake Malawi is dominated by Irumide rocks that acted as a relatively rigid indentor and only experienced minor to moderate reworking in the Pan-African.…”

Section: Geological Historymentioning

confidence: 99%

“…1.05 Ga Irumide and c . 580–550 Ma Pan‐African Mozambique Belt events (Fritz et al., 2013; Thomas et al., 2022; Tsunogae et al., 2021). In a regional reconstruction, Fritz et al.…”

Section: Regional Geology Tectonics and Thermal Structurementioning

confidence: 99%

Metamorphic Inheritance, Lower‐Crustal Earthquakes, and Continental Rifting

Fagereng,

Diener,

Tulley

et al. 2024

Geochem Geophys Geosyst

View full text Add to dashboard Cite

The Malawi Rift is localized within Precambrian amphibolite‐granulite facies metamorphic belts, bounded by up to 150 km long border faults, and generates earthquakes throughout ∼40 km thick crust. Rift‐related faults are inferred to exploit pre‐existing weaknesses that allow rifting of otherwise dry and strong crust. It is unclear what these weaknesses are, and how localization into weak zones can be reconciled with strength required for lower crustal seismicity. We present results of mineral equilibria modeling, which indicate that Proterozoic metamorphism generated dry crust dominated by a quartz‐feldspar assemblage that is metastable at current conditions. For rift propagation to be possible at current cool thermal gradients and in mechanically strong, dry quartzofeldspathic rocks, mid‐ to lower‐crustal strain must be localized into relatively weak, inherited shear zones that deform primarily by aseismic, viscous creep. These shear zones are embedded within high‐strength crust, and interaction between creeping shear zones and enveloped or surrounding rocks may locally increase stress and trigger frictional, seismic slip at mid‐ to lower‐crustal depths. Over time, this interaction may produce a fracture network that allows infiltration of fluids. We therefore suggest that during rifting of previously deformed and metamorphosed crust, major faults are most likely to grow from below, with their location and orientation prescribed by underlying inherited viscous shear zones. In this case, fluids may infiltrate and locally weaken metastable lower crust, including allowing time‐dependent fluid‐driven seismicity and local partial melting, but length‐scales of this weakening is limited by the scale of the permeability network.

show abstract

On the Timescales of Border Fault Growth: Pleistocene Slip Acceleration and Lateral Border Fault Propagation in the Lower Shire Graben, East Africa

Dulanya,

Kolawole,

Gallen

et al. 2024

Tectonics

View full text Add to dashboard Cite

Normal fault systems may grow by the lateral propagation of segments, yet little is known about the timescales over which this may occur and the implications for rift propagation. Footwall bedrock river networks provide a means to delineate the recent fault displacement patterns since erosional landscapes are sensitive recorders of rock uplift histories. Here, we analyze river profiles and map knickpoints in the Ruo River network and several adjacent rivers draining the footwalls of the en‐echelon Thyolo‐Muona‐Camacho border fault system of the Lower Shire Graben, southern East African Rift System. Using parameters calibrated in previous studies, we estimate the knickpoint initiation times and use linear river profile inversions to understand footwall uplift histories. Abrupt increases in bedrock river channel steepness indices approaching the faults suggest a recent acceleration in fault slip rates. Linear inversion of the bedrock river profiles reveals that footwall uplift rates accelerated from ∼0.1 to 0.3 mm/yr at ∼2–3 Ma in the Thyolo‐Muona footwalls. Later, at ∼0.75–1.0 Myr, farther southeast, the Camacho footwall river profiles show an increase in rock uplift rate from ∼0.05 to 0.2 mm/yr, but this signal decays moving southeast. Modern uplift rates along the Thyolo‐Muona section attain 0.33–0.56 mm/yr, and Camacho 0.19–0.29 mm/yr. We propose that within <2 Myr timescale, the border fault grew by an initial (Early Pleistocene) accelerated slip and hard linkage of the already‐nucleated segments, later followed by the southeastward lateral propagation of the system toward the adjacent rift, the Nsanje Graben.

show abstract

The Mesoproterozoic Nampula Subdomain in southern Malawi: Completing the story from Mozambique

Cited by 5 publications

References 25 publications

Rapid Versus Delayed Linkage and Coalescence of Propagating Rift Tips

Rapid Versus Delayed Linkage and Coalescence of Propagating Rift Tips

Metamorphic Inheritance, Lower‐Crustal Earthquakes, and Continental Rifting

On the Timescales of Border Fault Growth: Pleistocene Slip Acceleration and Lateral Border Fault Propagation in the Lower Shire Graben, East Africa

Contact Info

Product

Resources

About