 Atis and Gtsain Ridge) from the Late Miocene has been dated at 5.7–4.6 Ma by K-Ar and is the oldest sequence in the region.Late Pliocene activity involved various basaltic lavas (including Lchain Volcano) and subsequently, during the Quaternary, rhyolite and obsidian from the Kotayk centre (Gutansar and Atis 700 ka, then associated fissure volcanoes 550–480 ka).The volcanic activity peaked round 200 ka, when most of the Gegham centres formed from trachyandesitic lavas.