Development of the Nyika Plateau, Malawi: A Long Lived Paleo‐Surface or a Contemporary Feature of the East African Rift?

Abstract

Northern Malawi's Nyika Plateau is a 3,700 km2 large, highly elevated (∼2,500 m) plateau located at the western margin of the Miocene‐Recent Malawi rift and the confluence of multiple Proterozoic orogenic belts. Neighboring asthenospheric upwelling in the Rungwe Volcanic Province, associated with the active East African Rift, has created similar topographic highs, leading some to speculate that the formation of Nyika could be related. Here, we present new low‐temperature data using apatite fission track, apatite (U‐Th‐Sm)/He and zircon (U‐Th)/He thermochronology to constrain the upper crustal thermal history of the Nyika region since the Devonian. The data suggest that Nyika was an isolated feature since at least the Permo‐Triassic, well before more recent rifting in Malawi, and may have developed as a horst between two large Karoo grabens, the Henga‐Ruhuhu and the North Rukuru to the southeast and northwest, respectively. Similarities between the thermal histories of Nyika and the currently separated Livingstone Plateau to the east allow for the possibility that these may have been connected in a contiguous highland prior to the formation of the intervening Neogene Malawi rift. Thermal history models for exposed Precambrian basement samples adjacent to Nyika, and once buried beneath the neighboring Karoo basins, indicate that up to 3.4 km of Permo‐Triassic section has since been eroded, with samples along the plateau not indicating burial of Karoo‐type sediment at this time. Most recent cooling histories suggest that the plateau surface continued to denude at varying degrees from the Cretaceous and reached near‐surface temperatures in the Late Paleogene‐Neogene.

Heterogeneous Strain Distribution in the Malawi (Nyasa) Rift, East Africa: Implications for Rifting in Magma‐Poor, Multi‐Segment Rift Systems

“…Accardo et al (2018) observe an extensive deep zone of material with P-wave velocities intermediate between sediment and crust (3.75-4.5 km/s) that crosscuts the rift at this accommodation zone between the North and Central Basins and extends into the center of the Central Basin; these observations provide the first direct evidence that an earlier rift package may underlie the present phase of EARS-related deformation. This observation is supported by similar trends in low-temperature thermochronology data from either side of the lake (McMillan et al, 2022). It is not clear if these ancient structures provide a mechanistic control on strain partitioning between border and intrarift faults within the Lake Malawi Rift.…”

Spatio‐Temporal Variations in Sediment Delivery as a Response to Rapid Quaternary Climate Change in the Lake Malawi Rift, East Africa

“…However, precipitation is not the only driver of the elevated erosion rates, as the greatest precipitation rates occur farther north across the Songwe catchment, which has lower average erosion rates than the N. Rumphi and N. Rukuru. Both these catchments instead drain the Nyika plateau, a 3,700 km 2 highly elevated (∼2,500 m) region which formed as a response to Karoo rifting during the Late‐Paleozoic (Dixey, 1937a, 1937c; McMillan et al., 2022). This elevated region of topography (Figures 1 and 6) results in greater relief, higher average slopes and smaller catchment area (∼800–2,000 km 2 ) compared to the other catchments across the rift.…”

Metamorphic Inheritance, Lower‐Crustal Earthquakes, and Continental Rifting

“…Subsequent to the Pan‐African transpression, continental‐scale Karoo rifting that occurred primarily in the Permian‐Triassic and culminated with the Jurassic Gondwana break‐up led to the formation of several NE‐SW trending sedimentary basins in Malawi (Figure 1; Castaing, 1991; Catuneanu et al., 2005). These sedimentary basins are confined to upper‐crustal depths with Karoo sediments in Malawi reaching thicknesses of up to 3 km (Castaing, 1991; Geological Survey of Malawi, 1966), although this may be an under‐estimate as significant thicknesses of Karoo sediments may have been eroded (McMillan et al., 2022). Although preserved in the topography and sedimentary record, faults defining the main NE‐SW trending Karoo basins of Malawi show little sign of current tectonic reactivation (Figure 1a; Castaing, 1991).…”