Thermochemical Modification of the Upper Mantle Beneath the Northern Malawi Rift Constrained From Shear Velocity Imaging

Accardo, N. J.; Gaherty, J. B.; Shillington, D. J.; Hopper, Emily; Nyblade, A.; Ebinger, C. J.; Scholz, Christopher A.; Chindandali, P. R. N.; Wambura‐Ferdinand, R.; Mbogoni, G. J.; Russell, Joshua; Holtzman, B. K.; Havlin, C.; Class, C.

doi:10.1029/2019gc008843

Cited by 23 publications

(20 citation statements)

References 104 publications

(196 reference statements)

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“…The injection of magma into the lithosphere is an important factor in the process of continental rift initiation since magma can greatly reduce the strength of thick lithosphere and facilitates rifting (Bastow et al., 2011; Buck, 2006; Kendall et al., 2005; Kendall & Lithgow‐Bertelloni, 2016; Schmeling & Wallner, 2012; Wallner & Schmeling, 2016). Recent seismic tomography models developed for the RVP and the northern Malawi Rift indicate that the lithosphere beneath the Malawi Rift may have been weakened prior to rifting (Accardo et al., 2020; Grijalva et al., 2018; Yu et al., 2020). Southward flow of the upwelling sublithospheric mantle beneath the RVP (Figure 8b) toward the Malawi Rift possibly leads to thermal erosion of the base of the lithosphere, thereby enabling localization of extension in the Malawi Rift (Njinju, Atekwana, et al., 2019).…”

Section: Discussionmentioning

confidence: 99%

Lithospheric Control of Melt Generation Beneath the Rungwe Volcanic Province, East Africa: Implications for a Plume Source

Njinju

Stamps

Neumiller³

et al. 2021

JGR Solid Earth

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Melt intrusions into the lithospheric mantle and crust during extensional tectonics play a key role in weakening the lithosphere during magma-assisting rifting. Magma-assisted continental rifting involves magmatic intrusions that are sourced from melt generated in the sublithospheric mantle beneath the rift axis, which developed when mantle potential temperatures are higher than average (i.e., McKenzie & Bickle, 1988). The source of melt generation in the sublithospheric mantle beneath rifts has been proposed to originate from thermal perturbations due to plumes (e.g.,

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Section: Discussionmentioning

confidence: 99%

Lithospheric Control of Melt Generation Beneath the Rungwe Volcanic Province, East Africa: Implications for a Plume Source

Njinju

Stamps

Neumiller³

et al. 2021

JGR Solid Earth

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“…The Rungwe Volcanic Province is a late Cenozoic extrusive system that includes the Rungwe volcano, which erupted in the Holocene (Fontijn et al, 2010) and has an active magmatic-hydrothermal system at depth (de Moor, 2013). It is underlain by a prominent low-velocity zone in the upper mantle (Accardo et al, 2017(Accardo et al, , 2020Grijalva et al, 2018).…”

Section: Research Papermentioning

confidence: 99%

Intrarift fault fabric, segmentation, and basin evolution of the Lake Malawi (Nyasa) Rift, East Africa

et al. 2020

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The Lake Malawi (Nyasa) Rift, in the East African Rift System (EARS), is an ideal modern analogue for the study of extensional tectonic systems in low strain rate settings. The seismically active rift contains the 700-m-deep Lake Malawi, one of the world’s oldest and largest freshwater lakes with one of the most diverse endemic faunal assemblages on Earth. Modern and reprocessed legacy multichannel seismic-reflection data are constrained by velocity information from a wide-angle seismic experiment to evaluate variability in extension, segmentation, and timing of fault development along the 550-km-long rift zone. Fault geometries and patterns of synrift sediment fills show that the Lake Malawi Rift is composed of three asymmetric rift segments, with intervening accommodation zone morphologies controlled by the degree of overlap between segment border faults. Most extension occurs on the basin border faults, and broadly distributed extension is only observed at one accommodation zone, where no border fault overlap is observed. Structural restorations indicate a weakly extended rift system (~7 km), with diminishing values of extension and thinner rift fill from north to south, suggesting a progressively younger rift to the south. There is no evidence of diking, sill injection, or extrusives within the synrift fill of the Lake Malawi Rift, although the volcanic load of the Rungwe magmatic system north of the lake and related subsidence may explain the presence of anomalously thick synrift fill in the northernmost part of the lake. The thickest synrift depocenters (~5.5 km) are confined to narrow 10- to 20-km-wide zones adjacent to each rift segment border fault, indicating concentration of strain on border faults rather than intrarift faults. Intrarift structures control axial sediment delivery in the North and Central rift segments, focusing sediment into confined areas resulting in localized overpressure and shale diapirs. The asymmetric, basement-controlled relief was established early in rift development. When overprinted with frequent high-amplitude hydroclimate fluctuations, which are well documented for this basin, the resulting highly variable landscape and lake morphometry through time likely impacted the diverse endemic faunas that evolved within the basin. New seismic-reflection data, augmented by wide-angle seismic data and age constraints from drill core, offer the most highly resolved 3D view to date of latest Cenozoic extensional deformation in East Africa and provide a foundation for hazards analysis, resource assessments, and constraining deformation in a low strain rate, magma-poor active rift.

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“…Shear-wave velocity profiles for each cell in the grid were obtained by inverting the phase velocity dispersion curves following the method of , as implemented by Accardo et al (2020). The inversion of dispersion curves for velocity can be sensitive to the initial velocity model, so a suite of 100 3-layer starting models for each cell was developed using a Monte Carlo approach applied to a limited parameter space (Table S1).…”

Section: Inversion For Shear-wave Velocitiesmentioning

confidence: 99%

Shear‐Wave Velocity Structure of the Southern African Upper Mantle: Implications for Craton Structure and Plateau Uplift

White-Gaynor

Nyblade

Durrheim

et al. 2021

Geophysical Research Letters

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We present a 3D shear‐wave velocity model of the southern African upper mantle developed using 30–200 s period Rayleigh waves recorded on regional seismic networks spanning the subcontinent. The model shows high velocities (∼4.7–4.8 km/s) at depths of 50–250 km beneath the Archean nucleus and several surrounding Paleoproterozoic and Mesoproterozoic terranes, placing the margin of the greater Kalahari Craton along the southern boundary of the Damara Belt and the eastern boundaries of the Gariep and Namaqua‐Natal belts. At depths ≥250 km, there is little difference in velocities beneath the craton and off‐craton regions, suggesting that the cratonic lithosphere extends to depths of about 200–250 km. Upper mantle velocities beneath uplifted areas of southern Africa are higher than the global average and significantly higher than beneath eastern Africa, indicating there that is little thermal modification of the upper mantle present today beneath the Southern African Plateau.

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Thermochemical Modification of the Upper Mantle Beneath the Northern Malawi Rift Constrained From Shear Velocity Imaging

Abstract: This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as

Cited by 23 publications

References 104 publications

Lithospheric Control of Melt Generation Beneath the Rungwe Volcanic Province, East Africa: Implications for a Plume Source

Lithospheric Control of Melt Generation Beneath the Rungwe Volcanic Province, East Africa: Implications for a Plume Source

Intrarift fault fabric, segmentation, and basin evolution of the Lake Malawi (Nyasa) Rift, East Africa

Shear‐Wave Velocity Structure of the Southern African Upper Mantle: Implications for Craton Structure and Plateau Uplift

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