Field investigations have determined 24 Quaternary volcanoes and volcanic rocks with an area of about 600 km 2 in the Nuomin River and Kuile River area in the north of the Greater Hinggan Mountains.In the volcanic field,explosive eruption produced pyroclasts,which constitute volcanic cones,and effusive eruption produced aa,pahoehoe and block lava,which make up lava flows.There are three volcano types here,i.e.,cinder cone,spatter cone,and scutulum type volcano.Multi-vent pyroclastic cones and scutulum type volcanoes characterize this volcanic field.The volcanic features,stratigraphy,and weathering extent,in conjunction with dating data,indicate that the volcanism occurred in four periods:early Pleistocene,middle Pleistocene,late Pleistocene,and Holocene.Basalts of the early Pleistocene dominated by lava flows were distributed in a few valleys.Volcanic products of the middle Pleistocene constitute the main part of the Quaternary volcanic deposits,which indicates the peak season of volcanism.Volcanism in the late Pleistocene and Holocene were constrained in the Bila River valley,products of which make up fresh lava flows and spectacular volcanoes.
