吉林龙岗龙泉龙湾火山火口基浪堆积物粒度特征及搬运机制分析

Preliminary study on grain size distribution and transportation characteristics of the base-surge deposits near Longquanlongwan volcano crater,Jilin.

龙泉龙湾是射汽岩浆爆发形成的复合式低平火山口湖。龙泉龙湾火山近火口基浪堆积物地层特征为含有火山弹的厚层粗粒—细粒火山砂与薄层细粒火山砂的韵律层,发育气管构造、透镜体构造、下陷构造、U 型下蚀堆积构造和丘状构造等。碎屑粒度中值 Md_φ为-2.8～1.8,分选系数σ_φ为1.38～3.23,整体粒径大、分选差。碎屑成分主要是浮岩碎屑、基岩碎屑和晶屑。本文在火山地层堆积构造和粒度特征研究基础上,通过应用 SFT 分布模式分析发现,龙泉龙湾火山近火口火山碎屑动力学模式主要以牵引为主,其次为弹道和跳跃,悬浮相对较少。

Longquanlongwan is a composite low rimmed volcano formed by phreatomagmatic eruption. The volcanic strata near the crater are characterized by interlaying beds with coarse massive layers and fine thin layers. Many transporting and depositional features are developed in the base-surge deposits, such as lenticular structure, U-shaped channel, sag structure, dune form, climbing-up structure and gas segregation structure. The base-surge deposits are composed with pumices, lithics and crystals, in which the grains are of coarse size and poorly sorted. The median diameter values （Mdφ） are from -2. 8 to 1.8, and the zorting parameters （ σφ ） are from 1.38 to 3.23. The combined analysis of depositional structures and grain size distribution with the Sequence Fragment/Transport （SFT） method suggests that the main transport process of Longquanlongwan basesurge deposits is predominant by traction, accompanied by ballistic ejection, saltation, and suspension.