During continental rifting, strain and magmatism are believed to localize to narrow magmatic segments, while the rift margin is progressively abandoned. We integrate volcanological, geochemical, petrological and seismic data from the Ma’Alalta volcanic field (MVF) near the western margin of Afar, to show that the MVF is an active magmatic segment. Magmatism in MVF initiated with lava flows and large-volume, caldera-forming ignimbrites from a central edifice. However, the most recent magmatic activity shifted towards mafic lava fields, cinder cones and obsidian-rich silicic domes erupted from vents aligned NNW-SSE, defining a ~ 35-km-long magmatic segment. Along the same area, a NNW-SSE alignment of earthquakes was recorded by two local seismic networks (2005–2009 and 2011–2013). The geochemistry of the mafic rocks is similar to those of nearby axial volcanoes. Inferred magma storage depth from mineral geobarometry shows that a shallow, silicic chamber existed at ~ 5-km depth below the stratovolcano, while a stacked plumbing system with at least three magma storage levels between 9 and 24 km depth fed the recent basalts. We interpret the wide set of observations from the MVF as evidence that the area is an active magmatic segment, showing that localised axial extension can be heavily offset towards the rift margin.

在大陆裂谷期间，应变和岩浆作用被认为局限在狭窄的岩浆段，而裂谷边缘被逐渐放弃。我们对来自阿法尔西缘附近的马阿拉塔火山场（MVF）的火山学，地球化学，岩石学和地震数据进行了整合，以表明该MVF是活跃的岩浆段。MVF中的岩浆作用是由熔岩流和来自中央建筑物的大量火山灰形成的火成岩引起的。但是，最近的岩浆活动向着对准NNW-SSE的喷口喷出的镁铁质熔岩田，煤渣锥和富含黑曜石的硅质圆顶，形成了一个约35公里长的岩浆段。在同一地区，两个地方地震网络（2005-2009年和2011-2013年）记录了NNW-SSE地震的准线。镁铁质岩石的地球化学与附近的轴向火山相似。根据矿物地质学推断的岩浆储藏深度表明，在层状火山下方约5 km的深度处存在一个浅的硅质腔，而在9到24 km深度之间至少有3个岩浆储藏水平的堆叠式管道系统为最近的玄武岩提供了能量。我们将来自MVF的大量观测结果解释为该地区是活跃的岩浆段的证据，表明局部轴向伸展可能会严重地向裂谷边缘偏移。