Geological characteristics and eruption cycle partition of jurassic volcanic rocks from Northern Abagaqi, Inner Mongolia

The Northern Abagaqi is located in the northwest of the suture belt between Erlian and Hegenshan Plate that is part of the accretion zone of late paleozoic continental margin on the southeast continental margin of the Siberian Plate. The volcanic magma activity is frequent and volcanic rocks are widely distributed from the late paleozoic to the middle cenozoic. Based on 1 : 50 000 regional geological mapping of the actual geological section and a detailed research on Northern Abagaqi, the Baiyingaolao Formation(J3b) of jurassic rock, was given a intermediate-acid lava and pyroclastic rock priority and its lithologic structure was of bottom-up eruption rhythmicity. According to the rock assemblage and characteristics, the rock reflected its continental volcanic building. The Baiyingaolao Formation volcanic rocks had an acidic volcanic eruption cycle, on account of the facies that could be divided into five eruption rhythms, and each rhythm magma composition was of mainly rhyolitic volcanic rock, and its bottom was often of the dacitic or andesitic volcanic rock. Their erupting facies were more numerous than their flowing facies, showing that the period of volcanic activity was stronger. They reflected the flowing-erupting and erupting facies in turn and had weak-to-strong anti-rhythmic features.