Evolution of the Mozambique Belt in Malawi constrained by granitoid U-Pb, Sm-Nd and Lu-Hf isotopic data

Manda, Blackwell; Cawood, Peter A.; Spencer, Christopher J.; Prave, Anthony R.; Robinson, R. W.

doi:10.1016/j.gr.2018.11.004

Cited by 25 publications

(27 citation statements)

References 41 publications

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“…The metamorphic foliation and migmatitic banding in the Thyolo fault's footwall dips moderately SW. The foliation formed at granulite facies metamorphic conditions coincident with partial melting during a series of collisional events at a convergent continental margin in the Pan-African Orogeny (~710-555 Ma) associated with the amalgamation of Gondwana (Kröner et al, 2001;Johnson et al, 2005;Manda et al, 2019). In the region of the Thyolo fault, the edge of the Unango Terrane is in contact with the basement of the South Irumide Belt, which underwent peak metamorphism between 1.06 and 1.05…”

Section: Tectonic Historymentioning

confidence: 99%

“…Ga (Johnson et al, 2005;Westerhof et al, 2008;Karmakar and Schenk, 2016). The terrane boundaries have been roughly mapped based on exposures within Malawi (Manda et al, 2019), but because younger cover sequences (~330-180 Ma Karooage sedimentary rocks) have obscured the basement, the unit boundaries are largely extrapolated from neighbouring Mozambique, where mapping was supported by geochemical and airborne magnetic data (Bingen et al, 2009;Macey et al, 2010).…”

Section: Tectonic Historymentioning

confidence: 99%

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Structural inheritance and border fault reactivation during active early-stage rifting along the Thyolo fault, Malawi

Wedmore

Williams

Biggs

et al. 2020

Journal of Structural Geology

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Highlights • The Thyolo fault, Malawi, is a rift border fault with a polyphase tectonic history • Satellite and field data confirm recent activity on an 18.6 ± 7.7 m high scarp • The fault is segmented, but scarp height minima do not align with geometry changes • Pre-existing shallow structures control the surface geometry and 0.7 m wide fault core • Fault displacement is affected by viscous reactivation along a terrane boundary

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Section: Tectonic Historymentioning

confidence: 99%

Section: Tectonic Historymentioning

confidence: 99%

Structural inheritance and border fault reactivation during active early-stage rifting along the Thyolo fault, Malawi

Wedmore

Williams

Biggs

et al. 2020

Journal of Structural Geology

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“…The topography of the Zomba Graben is influenced by the structure and composition of the basement complex, which comprises Proterozoic metamorphic rocks of the Southern Irumide Belt and subsequent intrusions (Figure ; Manda et al, ). At the regional scale, the rift follows the strike of the Southern Irumide foliation (Figure f).…”

Section: Tectonic and Geological Settingmentioning

confidence: 99%

Active Fault Scarps in Southern Malawi and Their Implications for the Distribution of Strain in Incipient Continental Rifts

et al. 2020

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The distribution of deformation during the early stages of continental rifting is an important constraint on our understanding of continental breakup. Incipient rifting in East Africa has been considered to be dominated by slip along rift border faults, with a subsequent transition to focused extension on axial segments in thinned crust and/or with active magmatism. Here, we study high-resolution satellite data of the Zomba Graben in southern Malawi, an amagmatic rift whose topography is dominated by the west-dipping Zomba fault. We document evidence for five subparallel fault scarps between 13 and 51 km long spaced~10-15 km apart. The scarps consist of up to five segments between 4 and 18 km long, separated by minima in scarp height and river knickpoints. The maximum height of each fault scarp ranges from 9.5 ± 4.2 m to 35.3 ± 14.6 m, with the highest scarp measured on the intrabasin Chingale Step fault. We estimate that the scarps were formed by multiple earthquakes of up to M w 7.1 and represent a previously unrecognized seismic hazard. Our calculations show that 55 ± 24% of extensional strain is accommodated across intrabasin faults within the~50 km wide rift. This demonstrates that a significant proportion of displacement can occur on intrabasin faults during early-stage rifting, even in thick continental lithosphere with no evidence for magmatic fluids.Plain Language Summary When continents begin to stretch, earthquakes occur on faults that incrementally accumulate slip to eventually form a rift valley. To estimate the hazard posed by these earthquakes, it is important to understand where these faults are located and how much stretching they each accommodate. We analyze faults in the Zomba Graben, a young rift in southern Malawi, using high-resolution satellite data. Steep scarps indicate that recent earthquakes have occurred at both the edges and in the middle of the rift valley. Pronounced activity in the rift middle is thought to require a thinned rigid outer layer of the Earth or mechanically unfavorable faults at the rift edge. Neither of these factors have been observed in southern Malawi. We suggest that the distribution of active faults, and hence of earthquakes, is likely controlled by weaknesses in the middle and lower parts of the Earth's crust.

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“…Southern Malawi lies at a complex intersection of orogenic belts that formed during the Pan African Orogeny (~800-450 Ma) and possibly earlier Irumide age deformation (~1,020-950 Ma) as the African continent gradually amalgamated during the Proterozoic, and which imparted amphibolitegranulite facies metamorphic fabrics (mineral segregations and alignments) within the rift's basement rocks (Figs. 1 and 2;Andreoli, 1984;Fritz et al, 2013;Fullgraf et al, 2017;Kröner et al, 2001;Manda et al, 2019). Within the Phanerozoic (540 Ma to present day), Permian-Triassic sediments were deposited in the Lower Shire Graben under NW-SE Karoo extension (Fig.…”

Section: Tectonic History Of Southern Malawimentioning

confidence: 98%

A systems-based approach to parameterise seismic hazard in regions with little historical or instrumental seismicity: The South Malawi Active Fault Database

Williams¹,

Mdala²,

Fagereng³

et al. 2020

Preprint

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Abstract. Seismic hazard is frequently characterised using instrumental seismic records. However, in regions where the instrumental record is short relative to earthquake repeat times, extrapolating it to estimate seismic hazard can misrepresent the probable location, magnitude, and frequency of future large earthquakes. Although paleoseismology can address this challenge, this approach requires certain geomorphic settings and carries large inherent uncertainties. Here, we outline how fault slip rates and recurrence intervals can be estimated through an approach that combines fault geometry, earthquake-scaling relationships, geodetically derived regional strain rates, and geological constraints of regional strain distribution. We then apply this approach to the southern Malawi Rift where, although no on-fault slip rate measurements exist, there are theoretical and observational constraints on how strain is distributed between border and intrabasinal faults. This has led to the development of the South Malawi Active Fault Database (SMAFD), the first database of its kind in the East African Rift System (EARS) and designed so that the outputs can be easily incorporated into Probabilistic Seismic Hazard Analysis. We estimate earthquake magnitudes of MW 5.4–7.2 for individual fault sections in the SMAFD, and MW 6.0–7.8 for whole fault ruptures. These potentially high magnitudes for continental normal faults reflect southern Malawi's 11–140 km long faults and thick (30–35 km) seismogenic crust. However, low slip rates (intermediate estimates 0.05–0.8 mm/yr) imply long recurrence intervals between events: 102–105 years for border faults and 103–106 years for intrabasinal faults. Sensitivity analysis indicates that the large range of these estimates can be reduced most significantly from an improved understanding of the rate and partitioning of rift-extension in southern Malawi, earthquake scaling relationships, and earthquake rupture scenarios. Hence these are critical areas for future research. The SMAFD provides a framework for using geological and geodetic information to characterize seismic hazard in low strain rate settings with few on-fault slip rate measurements, and could be adapted for use elsewhere in the EARS or globally.

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Evolution of the Mozambique Belt in Malawi constrained by granitoid U-Pb, Sm-Nd and Lu-Hf isotopic data

Cited by 25 publications

References 41 publications

Structural inheritance and border fault reactivation during active early-stage rifting along the Thyolo fault, Malawi

Structural inheritance and border fault reactivation during active early-stage rifting along the Thyolo fault, Malawi

Active Fault Scarps in Southern Malawi and Their Implications for the Distribution of Strain in Incipient Continental Rifts

A systems-based approach to parameterise seismic hazard in regions with little historical or instrumental seismicity: The South Malawi Active Fault Database

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