Internal structural variations in a debris-avalanche deposit from ancestral Mount Shasta, California, USA
Internal structural variations in a debris-avalanche deposit from ancestral Mount Shasta, California, USA
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美国加利福尼亚州沙斯塔祖先山的碎片雪崩沉积物的内部结构变化
DOI：
10.1007/bf01087673
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发表时间：
1986
影响因子：
3.5
通讯作者：
H. Glicken
中科院分区：
文献类型：
--
作者：
T. Ui;H. Glicken
为了研究流动和侵位机制，测量了来自祖先沙斯塔山的碎片雪崩存款的内部结构的各种参数（每个暴露中块相的大小和百分比，锯齿状裂缝的数量和宽度，以及基质相中圆形碎屑的数量）。确定了三种类型的连贯块体：块状或角砾状熔岩流或圆顶块体、层状火山岩沉积块体和偶然物质块体，通常来自沙斯塔山谷下面的沉积单元。三个最大的层状火山岩块的平均最大尺寸为220米，熔岩块的平均最大尺寸为110米。这种差异可能反映了层状火山岩物质块体的塑性变形;块状或角砾状火山岩块体发生了脆性变形，并可能分裂成几个较小的块体。存款中的块体比新西兰埃格蒙特山的Punjuhu碎屑雪崩存款大一个数量级，崩塌高度高1100米，尽管破裂程度大致相同。这表明沙斯塔源材料破碎程度较低，或者在祖先沙斯塔山伴随的任何爆炸强度较小。沙斯塔碎片雪崩存款覆盖了封闭盆地的底部;盆地的侧翼可能阻碍了锯齿状裂缝的张开以及伸展和变形块体的形成，例如Pungarehu碎片雪崩存款。
Various parameters of the internal structure of a debris-avalanche deposit from ancestral Mount Shasta (size and percentage of block facies in each exposure, number and width of jigsaw cracks, and number of rounded clasts in matrix facies) were measured in order to study flow and emplacement mechanisms. Three types of coherent blocks were identified: blocks of massive or brecciated lava flows or domes, blocks of layered volcaniclastic deposits, and blocks of accidental material, typically from sedimentary units underlying Shasta Valley. The mean maximum dimension of the three largest blocks of layered volcaniclastic material is 220 m, and that of the lava blocks, 110 m. This difference may reflect plastic deformation of blocks of layered volcaniclastic material; blocks of massive or brecciated volcanic rock deformated brittly and may have split into several smaller blocks. The blocks in the deposit are one order of magnitude larger, and the height of collapse 1100 m higher, than the Pungarehu debris-avalanche deposit at Mount Egmont, New Zealand, although the degree of fracturing is about the same.This suggests either that the Shasta source material was less broken, or that the intensity of any accompanying explosion was smaller at ancestral Mount Shasta. The Shasta debris-avalanche deposit covered the floor of a closed basin; the flanks of the basin may have retarded the opening of jigsaw cracks and the formation of stretched and deformed blocks such as those of the Pungarehu debris-avalanche deposit.