长白山天池地区全新世以来火山活动及其特征

长白山火山全新世规模最大的喷发活动发生在公元1199-1200年,即800年前的大爆发,被确定为普林尼或布里尼(Plinian)式喷发。这次大爆发形成体积巨大的、分布广泛的以空中降落堆积物为主的火山喷发碎屑堆积物,在长白山火山周围,远至日本都留下了地质记录。文章辨认并划分了这次大爆发火山碎屑物的成因类型:火山喷发空中降落堆积物(airfalltephra)、火山碎屑流(pyroclasticflow)状堆积物和火山泥流(lahar)堆积物,并且点、面结合,近、远和国内、国外兼顾,分析了这些火山碎屑物的主要特征、分布和相互关系,进而确定这些火山碎屑物分别属于两次普林尼式爆发。第1次(早期)普林尼式爆发称赤峰期,火山喷发模式为:普林尼式喷发柱(赤峰空落浮岩层)-火山碎屑流(长白山火山碎屑流层),随即主要由火山碎屑流诱发火山泥流(二道白河火山泥流层);第2次(晚期)普林尼式爆发称园池期,喷发模式为:普林尼式喷发柱(园池空落浮岩火山灰层)-火山碎屑流(冰场火山碎屑流层)。在层序上将气象站期碱流岩置于800年前大爆发火山碎屑物之下是正确的,其时代为晚更新世-全新世早期。

HOLOCENE VOLCANIC ACTIVITYS AND THEIR FEATURES IN TIANCHI AREA,CHANGBAISHAN MOUNTAINS

The Changbaishan Volcano, a stratovolcano or a gigantic polygenetic volcanic cone, is located at the border between China and North Korea.The historically recorded 1199-1200A.D. eruption is the largest Changbaishan Volcano eruption during the period of Holocene. It can be subdivided into two phases of Plinian eruption; the first is named Chifeng phase and the second Yuanchi phase. The total volume of both the first Plinian fall and the second Plinian fall has been estimated more than 120km3.The eruptive pattern of the Chifeng phase is Plinian column (Chifeng pumice fall deposit)-pyroclastic flow (Changbai pyro-clastic flow deposit)-lahar (Erdaobaihe lahar deposit) which was mainly triggered by pyroclastic flow deposit. The Chifeng pumice fall deposit is characterized by light colour, fine grains and very good sorting. The deposit was spread towards SE direction as a tephra fan whose apex is at the summit of volcano. The Changbai pyroclastic flow deposit is distributed around the volcano as far as 50km from the vent and the area of deposit is about 2 100km2 and the bulk volume of deposit can be estimated over 8km3. The pumice flow deposit is of poor sorting, massive structure, developed graded structure, and gas escaping structure. The Erdaobaihe lahar deposit was accumulated along the Erdaobaihe River and the Songhua River and extended over 300km from the volcano.The eruptive pattern of the Yuanchi phase is Plinian column (Yuanchi pumice and ash fall deposits)-pyroclastic flow ( Bingchang pyroclastic flow deposits) . The Yuanchi pumice and ash fall deposit was blown towards east by the west unidirection wind and the apex of the tephra fan is at the summit of volcano. The deposit with yellow colour is mainly of alternative pumice and ash deposition. The Bingchang pyroclastic flow deposit filled the gorges around the volcano. This kind of deposit can be observed inside the caldera and on the top of the volcano in some places. The bulk volume of the deposit is about 0.5km3. The Bingchang pyroclastic flow deposit appears to be welded tuff, welded breccia and agglutinate with black to purple colour.The Qixiangzhan pantellerite is covered by the airfall tephra produced in this 800aB. P. eruption of the Changbaishan Volcano and the Qixiangzhan pantellerite is reported to be formed in Late Pleistocene-Early Holocene according to the geological occurrence of volcanic rocks and age dating. The view that the airfall tephra produced in 800aB. P. eruption of the Changbaishan Volcano was covered by the Qixiangzhan pantellerite and the Qixiangzhan patellerite was formed in Holocene suggested by Xu Dongman, Zheng Xiangshen and Xu Xiangxi is incorrect.