Superplume mantle tracked isotopically the length of Africa from the Indian Ocean to the Red Sea

Seismological findings show a complex scenario of plume upwellings from a deep thermo-chemical anomaly (superplume) beneath the East African Rift System (EARS). It is unclear if these geophysical observations represent a true picture of the superplume and its influence on magmatism along the EARS. Thus, it is essential to find a geochemical tracer to establish where upwellings are connected to the deep-seated thermo-chemical anomaly. Here we identify a unique non-volatile superplume isotopic signature (‘C’) in the youngest (after 10 Ma) phase of widespread EARS rift-related magmatism where it extends into the Indian Ocean and the Red Sea. This is the first sound evidence that the superplume influences the EARS far from the low seismic velocities in the magma-rich northern half. Our finding shows for the first time that superplume mantle exists beneath the rift the length of Africa from the Red Sea to the Indian Ocean offshore southern Mozambique.

Low seismic velocity anomalies reveal a complex scenario of plume upwellings from a deep thermo-chemical anomaly (superplume) in the mantle below the East African Rift, however, geophysical observations alone are insufficient to identify the extent of plume influence on the magmatism along the rift. Here, the authors use Sr-Nd-Pb isotope data to show that superplume mantle underlies the entire rift system, from the Red Sea to the Indian Ocean south of Mozambique.

Detecting gas-rich hydrothermal vents in Ngozi Crater Lake using integrated exploration tools

Gas-rich hydrothermal vents in crater lakes might pose an acute danger to people living nearby due to the risk of limnic eruptions as a result of gas accumulation in the water column. This phenomenon has been reported from several incidents, e.g., the catastrophic Lake Nyos limnic eruption. CO₂ accumulation has been determined from a variety of lakes worldwide, which does not always evolve in the same way as in Lake Nyos and consequently requires a site-specific hazard assessment. This paper discusses the current state of Lake Ngozi in Tanzania and presents an efficient approach how major gas-rich hydrothermal feed zones can be identified based on a multi-disciplinary concept. The concept combines bathymetry, thermal mapping of the lake floor and gas emission studies on the water surface. The approach is fully transferable to other volcanic lakes, and results will help to identify high-risk areas and develop suitable monitoring and risk mitigation measures. Due to the absence of a chemical and thermal stratification of Lake Ngozi the risk of limnic eruptions is rather unlikely at present, but an adapted monitoring concept is strongly advised as sudden CO₂ input into the lake could occur as a result of changes in the magmatic system.

Analysis of temporal diversification of African Cyprinidae (Teleostei, Cypriniformes)

Recent evidence that freshwater fishes diversify faster than marine fishes signifies that the evolutionary history of biodiversity in freshwater system is of particular interest. Here, the evolutionary diversification events of African Cyprinidae, a freshwater fish family with wide geographic distribution, were reconstructed and analysed. The overall diversification rate of African Cyprinidae is 0.08 species per million year (when extinction rate is very high, i.e., ε = 0.9) and 0.11 species per million year (when ε = 0). This overall rate is lower than the rate reported for African Cichlids, suggesting that African freshwaters might be less conducive for a rapid diversification of Cyprinidae. However, the observed diversification events of African Cyprinidae occurred in the last 10 million years. The temporal pattern of these events follows a non-constant episodic birth-death model (Bayes Factor > 28) and the rate-constant model never outperformed any of the non-constant models tested. The fact that most diversification events occurred in the last 10 million years supports the pattern reported for Cyprinidae in other continent, e.g., Asia, perhaps pointing to concomitant diversification globally. However, the diversification events coincided with major geologic and paleo-climatic events in Africa, suggesting that geological and climatic events may have mediated the diversification patterns of Cyprinidae on the continent.

Influence of the balance of the intertropical front on seasonal variations of the isotopic composition in rainfall at Kisiba Masoko (Rungwe Volcanic Province, SW, Tanzania)

Tropical rainfall isotopic composition results from complex processes. The climatological and environmental variability in East Africa increases this complexity. Long rainfall isotope datasets are needed to fill the lack of observations in this region. At Kisiba Masoko, Tanzania, rainfall and rain isotopic composition have been monitored during 6 years. Mean year profiles allow to analyse the seasonal variations. The mean annual rainfall is 2099 mm with a rain-weighted mean composition of -3.2 ‰ for δ¹⁸O and -11.7 ‰ for δ²H. The results are consistent with available data although they present their own specificity. Thus, if the local meteoric water line is δ²H = 8.6 δ¹⁸O + 14.8, two seasonal lines are observed. The seasonality of the isotopic composition in rain and deuterium excess has been compared with precipitating air masses backtracking trajectories to characterize a simple scheme of vapour histories. The three major oceanic sources have two moisture signatures with their own trajectory histories: one originated from the tropical Indian Ocean at the beginning of the rainy season and one from the Austral Ocean at its end. The presented isotopic seasonality depends on the balance of the intertropical front and provides a useful dataset to improve the knowledge about local processes.

Old fossils-young species: evolutionary history of an endemic gastropod assemblage in Lake Malawi

Studies on environmental changes provide important insights into modes of speciation, into the (adaptive) reoccupation of ecological niches and into species turnover. Against this background, we here examine the history of the gastropod genus Lanistes in the African Rift Lake Malawi, guided by four general evolutionary scenarios, and compare it with patterns reported from other endemic Malawian rift taxa. Based on an integrated approach using a mitochondrial DNA phylogeny and a trait-specific molecular clock in combination with insights from the fossil record and palaeoenvironmental data, we demonstrate that the accumulation of extant molecular diversity in the endemic group did not start before approximately 600,000 years ago from a single lineage. Fossils of the genus from the Malawi Rift, however, are over one million years older. We argue that severe drops in the lake level of Lake Malawi in the Pleistocene offer a potential explanation for this pattern. Our results also challenge previously established phylogenetic relationships within the genus by revealing parallel evolution and providing evidence that the endemic Lanistes species are not restricted to the lake proper but are present throughout the Malawi Rift.

Structural Control of Flank Volcanism in Continental Rifts

Many volcanoes emerge from the flank (footwall) of normal faults in continental rift zones. Because such locations are commonly topographically high and exhibit minor compressional structures, the association is enigmatic. A simple flexing plate model shows that deformation of a flexurally supported upper crust during normal faulting generates a dilational strain field in the footwall at the base of the crust. This strain field allows cracking and tapping of preexisting melt.