Temporal clustering of fissural eruption across multiple segments within the Ethiopian Rift

Peer reviewed: TrueAcknowledgements: We thank the RiftVolc community for thoughtful interactions over many meetings. We thank staff of the Institute of Geophysics, Space Science and Astronomy and Department of Earth Science at Addis Ababa University, Ethiopia for support during fieldwork. Radiocarbon dating was performed by the Beta Analytic Laboratory (Florida, US). We acknowledge skillful analytical assistance from Andy Milton, Matthew Cooper and Agnes Michalik (University of Southampton) and Tom Knott (University of Leicester). We would like to thank the reviewers Francesco Mazzarini and Gabriel Ureta and the editor Karoly Nemeth for their constructive comments that improve the manuscript.Magmatic continental rifts show evidence that discrete rift segments experience episodic intrusive and eruptive events, more commonly termed rifting episodes. However, whether multiple rifting episodes across adjacent rift segments are clustered in time is not well understood. To address this issue, we conduct new radiocarbon dating that constrains the timing of the most recent rifting episode at the Boset magmatic segment of the northern Ethiopian rift, and combine this with historical dating of similar rifting events in the adjacent magmatic segments. New radiocarbon dates of multiple charcoal samples from the base of the most recent fissural lava at the Boset Volcanic Complex indicate that it likely occurred between 1812 and 1919 CE. These dates are similar to those from historical accounts of fissural eruption from the neighbouring Kone (∼1810 CE), and Fantale (∼1770 to 1808 CE) magmatic segments. We conduct new analysis of major and trace element compositions from these historical fissural lavas, as well as from a fresh-looking lava flow from Beru cone near to Kone volcano. The results of the geochemistry from these flows of all three magmatic segments show compositions that vary in the basalt and trachybasalt fields, with sufficient variation to rule out them having erupted from a single dike intrusion episode. This, combined with the scatter in dates from the radiocarbon analysis and historical accounts, along with the location of each eruption in a discrete and spatially offset magmatic segment, favours an interpretation of each magmatic segment experiencing separate rifting episodes but with these being clustered in time. Mechanisms to explain the clustering of rifting episodes are more speculative but could include stress transfer from dike intrusion and deep crustal hydraulic connection in the plumbing system of multiple segments.</jats:p

Manipulação, Tradução Literária e Identidade Nacional

La polémica en torno a las Lettres portugaises originó una contienda literaria entre Portugal y Francia durante más de dos siglos. Publicada en Francia en 1669 como una traducción de cinco cartas de amor anónimas de una religiosa portuguesa escritas a un militar francés, esta obra fue reivindicada por ambos países. Para Portugal, la traducción de esta obra significó, durante el llamado “Siglo del Nacionalismo Portugués (1870-1975)”, la recuperación de un patrimonio literario necesario para la identidad nacional. Este trabajo discurre sobre la utilización ideológica de la traducción literaria al servicio de la Nación y señala el empobrecimiento de la producción literaria (casi exclusivamente propagandística) en un Portugal excesivamente ensimismado, nostálgico de su pasado de gran imperio mundial y consumido en la revalorización nacional

Evolution of the Alu-Dalafilla and Borale volcanoes, Afar, Ethiopia

The Danakil depression in the Afar region of Ethiopia marks the change from subaerial continental rifting to seafloor spreading further north in the Red Sea [1]. Extension and volcanism in this incipient spreading centre is localised to the ~70-km-long, 20-km-wide active Erta Ale volcanic segment (EAVS), with multiple volcanic centres consisting of a combination of fissures, shield volcanoes and stratovolcanoes [2]. This study aims to better understand the nature of interaction between three volcanoes with the EAVS (Alu, Dalafilla and Borale) while also investigating their evolution during the transition from continental to oceanic crustal production.Here we combine results of mapping, using remote sensing, and geochemical analysis of Alu, Dalafilla and Borale in the northern half of the EAVS. Multispectral images were used to create a high-resolution map and establish a relative chronology of lava flows. Our results show that the majority of flows are sourced from a combination of scoria cones and fissures, representing in total 15 phases of volcanism within four major eruptive stages.The first stage represents large-scale fissure volcanism comprising basaltic phases that erupted in a submarine environment. Stage two involves basaltic fissure volcanism centred around the Alu dome. The third stage is dominated by trachy-andesite to rhyolitic (SiO2 of 59-70%) volcanism sourced from the volcanic edifices of Alu, Dalafilla and Borale. The fourth and final stage is characterised by a resumption of small-scale basaltic/trachybasalt (SiO2 of 49-55%) fissure eruptions.Geochemical modelling indicates a paucity of crustal assimilation and mixing within the sub-volcanic magmatic system. Spatial analysis of volcanic cones and fissures within the area indicate the presence of a cone sheet and ring faults. The fissures are likely fed by sills connecting the magma source with the volcanic edifices of Alu and Borale. Our results reveal the cyclic nature of both eruption style and composition of major volcanic complexes in rift environments, prior to the onset of seafloor spreading

Quantitative constraints on faulting and fault slip-rates in the northern Main Ethiopian Rift

The Boset magmatic segment (BMS) of the northern Main Ethiopian Rift (MER) is an ideal natural laboratory to investigate the kinematics, interaction, and rates of activity within a fault network in a magma‐rich rift. In this paper we take advantage of the availability of 1) high‐resolution remote sensing data (LiDAR, Aster); 2) absolute age chronology on offset reference surfaces; 3) well‐exposed active normal fault arrays to place new constraints on rift kinematics and strain distribution, and to quantify the architecture and fault slip‐rates at different temporal scales within a magmatic segment. We found that the rift border faults strike ~NE, while the younger faults in the rift segments strike NNE. Analyses of geometric rift parameters show that the axial active part of the rift is transtensional with an increase of the shear component northward. The fault displacement analyses and displacement: length ratios increase towards the segments tips suggesting a significant contribution of fault growth by linkage. In contrast, magmatism is focused on the segment centre and localized to a narrow zone. Estimated fault slip‐rates vary, with rates of up to ~0.37 mm/yr in ~0.3 Ma old rift floor deposits, whereas higher rates of up to ~4.4 mm/yr are observed for faults cutting through ~6 ka lavas. The difference in slip‐rates indicates short term variability or a very active recent episode compared to long‐term low average slip‐rates