Tahalra volcanic field

Tamanrasset lies east-northeast from the field. Cinder cones, lava domes, lava flows and maars form the field, which covers a surface of 1,800 square kilometres (690 sq mi)[1] elongated west to east.[2] There are about 132 individual vents[1] in the area measuring 30 by 80 kilometres (19 mi × 50 mi).[3]

Tahalra is part of a province of volcanic fields in the Hoggar, which has been active since the Mesozoic.[3] Seismic tomography has shown the existence of low-velocity mantle beneath the Tahalra and Atakor volcanic fields, sign of the presence of recent volcanism.[4]

The basement beneath the field consists of rocks of Precambrian age, mostly metamorphic rocks and plutons[1] which are part of a mobile belt at the margin of the West African Craton. Parts of the basement are covered with Paleozoic rocks.[3]

The field has erupted basalt, basanite, rhyolite and trachyte.[1] They contain amphibole, clinopyroxene, magnetite and olivine phenocrysts.[3] Patterns in trace element composition and isotope ratios imply that the magmas either developed from variable starting material or from metasomatized mantle.[5]

Volcanic activity started in the Miocene and led to the development of a lava plateau up to 100 metres (330 ft) thick.[3] Eruptions continued in the Pliocene and the Pleistocene,[1] forming many individual vents.[3] Maars and cones in the northern part of the field are of Pleistocene and Holocene age (Paleolithic to Neolithic[3]).[1]