中国东部全新世火山的镭-钍同位素年代学  

Holocene volcanoes from eastern China:Constraints from Ra/Th isotope disequilibrium

作　　者：邹海波 郭紫佩 樊祺诚[3] 赵勇伟[3] ZOU HaiBo;GUO ZiPei;FAN QiCheng;ZHAO YongWei(Department of Geosciences,Auburn University,Auburn,AL 36830,USA;State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi'An 710069,China;Institute of Geology,China Earthquake Administration,Beijing 100029,China)

机构地区：[1]Department of Geosciences,Auburn University,Auburn,AL 36830 [2]大陆动力学国家重点实验室,西北大学地质系,西安710069 [3]中国地震局地质研究所,北京100029

出　　处：《岩石学报》2020年第7期1945-1952,共8页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41973029)资助。

摘　　要：活火山是指1万年来有过喷发历史的全新世火山。火山的高分辨年代学对火山灾害评估和火山分类具有重要意义。对于缺乏历史记载的全新世火山,直接对火山岩进行同位素定年很困难。本文利用具有高时间分辨率的镭-钍-铀非平衡确定中国东部年轻火山的年龄。根据镭-钍-铀同位素,海南岛的马鞍岭和雷虎岭是全新世火山(马鞍岭:4.3ka;雷虎岭:4.7ka);镜泊湖火山(4.9ka)也是全新世火山;龙岗火山存在晚更新世和全新世活动(7.0ka,15.0ka);大兴安岭阿尔山和诺敏河Ra/Th非平衡消失但230Th/238U非平衡显著,属于晚更新世喷发(阿尔山:63ka;诺敏河:71ka)。海南岛的马鞍岭火山、雷虎岭火山和东北地区的龙岗火山、镜泊湖火山,是4座活火山。至于东北地区的阿尔山和诺敏河火山是否是活火山,有待测试更多样品的Ra/Th同位素。五大连池老黑山和火烧山有历史喷发记录,这与它们都存在显著Ra/Th非平衡一致。五大连池老黑山和火烧山的岩浆滞留年龄分别小于4.2ka和3.2ka,岩浆上升速率>18~23m/y。An active volcano is defined as a volcano that has had at least one eruption in the past 10,000 years during Holocene.Isotope dating of young volcanoes that lack historic eruption records is challenging but is important for volcanic hazard assessment and volcano classifications(active or not).Here we use high-temporal-resolution Ra/Th disequilibrium to evaluate possible Holocene eruptions for young volcanoes from eastern China.According to 226Ra/230Th and 230Th/238U disequilibrium data,Leihuling volcano and Maanling volcano from Hainan Island and Jingpohu from NE China are Holocene volcanoes;Longgang volcano has both Holocene eruptions and Late Pleistocene eruptions;Aershan volcano from Central Daxing'Anling and Nuominhe volcano from northern Daxing'Anling had Ra/Th secular equilibrium but significant 230Th/238U disequilibrium,indicating Late Pleistocene eruptions.Thus,Maanling and Leihuoling from Hainan Island,Longgang and Jingpohu from northeastern China are active volcanoes.Analyses of additional samples for Ra/Th isotopes are needed to evaluate whether or not Aershan and Nuominhe volcanoes are active.The Laoheishan and Huoshaoshan from Wudalianchi had historic eruption record,which is consistent with their significant Ra/Th disequilibrium.The magma residence times are<4.2ka for Laoheishan and<3.2ka for Huoshaoshan with a magma transport velocity of>18~23m/y.

关 键 词：活火山 全新世火山 晚更新世火山 铀系非平衡 镭钍非平衡 

分 类 号：P317[天文地球—固体地球物理学] P597.3[天文地球—地球物理学]