34 Quaternary volcanoes are distributed along a Quaternary NE strike belt in Halaha river and Chaoer river volcanic field. The lava flow, characterized by alkali olivine basalts, cover an area of 400km2. Based on studies on the volcanic field characteristics, in conjunction with geological dating by K-Ar, it is identified that the volcanism occurred in four periods; Early Pleistocene, Middle Pleistocene, Late Pleistocene and Holocene. Basalts of Early Pleistocene, mostly mantled by the later volcanic rocks, are distributed in the margin and valleys of the volcanic field. Middle Pleistocene, the most volcanic active period in this area, witnessed the formation of more than half of Quaternary volcanoes and lava spreading. Moderate volcanism occurred in Late Pleistocene which produced a small amount of volcanic deposits. Volcanic activities are strengthened again in Holocene Period, characterized by strongly explosive explosion, widespread lava flow and well-keeping lava landforms features.%大兴安岭中部哈拉哈河-绰尔河第四纪火山区分布有34座火山,这些火山总体呈北东向带状分布,火山岩分布面积约400 km2,岩性主要为碱性橄榄玄武岩.根据火山地质特征,结合火山岩K-Ar测年结果,哈拉哈河-绰尔河第四纪火山可进一步划分为早、中、晚更新世和全新世4期.早更新世火山岩,由于被后期火山岩覆盖,主要分布于火山区周边和出露在河谷中.中更新世火山活动最强,不论火山数量(27座)还是熔岩流规模都超过该区第四纪火山的一半以上.晚更新世时期火山活动趋弱,火山活动范围缩小,只局限于小范围区域.全新世火山活动又进入新的高峰期,强爆破式喷发和规模宏大的熔岩流,以及保存完好的熔岩流地貌是全新世火山之特点.
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