基于DEM的中国北方新生代火山锥降解过程研究

摘要

In northern China,there are many Cenozoic volcanic fields,which provide opportunity for the study of volcanic cone degradation.To understand the degradation process of volcanic cone,here we calculated Hco values and Wco values of 40 volcanoes with 30 m-resolution DEM.These volcanic cones are from volcanic fields of Wudalianchi,Chaihe-Arxan,Nuomin River-Kuile River,Ashikule and Datong,and their corresponding geochronological data were collected.Main conclusions of this study include:(1) According to the Hco/Wco-age grouping rules of San Francisco volcanic field,among the 40 volcanoes in five volcanic fields,there are 31volcanic cones complying with the Hco/Wco-age grouping rule.The actual age values of these volcanic cones are well consistent (～ 80％) with the theoretical age values obtained from the grouping analysis.Therefore,the morphological parameter measurement of volcanic cones is reliable to evaluate the volcanic eruption age.(2) The degradation model of volcanic cone shows that the Hco/Wco ratio decreases rapidly at the beginning (within 1Mys),and decreases slowty after 1Mys.The decreasing rate of the Hco/Woo ratio decreases with time.(3) The effect of climatic conditions on the degradation rate of volcanic cone in different areas is discussed.The annual average precipitation in the eastern region is high,the climate is humid and the degradation rate of volcanic cone is higher,while the annual average precipitation in the western region is small,the climate is dry and the volcanic cone degradation rate is lower.The climate effect results in decreasing rate of Hco/Wco in eastern region is higher than that in the west.%中国北方有着众多新生代以来形成的火山群,为研究火山锥降解问题提供了良好条件.文章通过30 m精度DEM统计了来自五大连池、柴河—阿尔山、诺敏河—奎勒河、新疆阿什库勒、大同五个火山群共40座火山的锥体形态学参数Hco与Wco值,并搜集了对应的锥体年代学数据对火山锥的降解过程开展研究.获得的主要认识如下:(1)对火山锥进行了H o/Wco—年龄分组,结果显示在五个火山群中具有实际喷发年龄的40座火山中,符合分组规则的火山锥为31座,火山锥实际年龄值与按照分组规则所得的理论年龄值区间的统计重合率高达80％,充分表明了锥体形态学参数测量对判断火山喷发时代的可信性.(2)火山锥降解模型表明在刚开始的1 Ma内,火山锥Hco/Wco值下降较快,1 Ma以后,火山锥的Hco/Wco值下降变慢,整个火山锥降解过程中Hco/Wco值下降速度随着时间逐渐变慢.(3)通过分析气候条件对不同地区火山锥降解速率的影响表明:东部地区年平均降水量大,气候湿润,火山锥降解速率较高;而西部地区年平均降水量较小,气候干旱,火山锥降解速率较低;这就导致东部地区火山锥Hco/Wco值的下降速率要高于西部地区.