Comparing intrarift and border fault structure in the Malawi Rift: Implications for normal fault growth

Carpenter, Manon; Williams, Jack N.; Fagereng, Åke; Wedmore, L. N. J.; Biggs, Juliet; Mphepo, Felix; Mdala, Hassan; Dulanya, Zuze; Manda, Blackwell

doi:10.1016/j.jsg.2022.104761

Cited by 6 publications

(1 citation statement)

References 109 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The Malawi Rift is considered juvenile as there is no surface expression of magmatism, the faults (although long) have relatively minor displacements of no more than a few kilometers (Carpenter et al., 2022; Ebinger et al., 1987; Mortimer et al., 2016; Ojo et al., 2022), and the total stretching is estimated at less than 10% (Sun et al., 2021). South of Lake Malawi, relatively well‐exposed fault zones have damage zones that are typically less than 120 m thick, well below global trends for their length and indicating a very early stage of faulting (Carpenter et al., 2022; Williams et al., 2022a). Crustal thickness is typically in the range of 38–42 km, but there is evidence for localized crustal thinning by up to a few kilometers in the center of the Rift (Hopper et al., 2020; Wang et al., 2019).…”

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

Self Cite

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