Dense, vitric, dacitic pyroclasts (dacite lithics) from the 1991 preclimactic explosions of Mt. Pinatubo were analyzed for their vesicular and crystal textures and dissolved H2O and CO2 contents. Micron-scale heterogeneities in groundmass glass volatile contents (0.9 wt% differences in H2O within 500 μm) are observed and argue that parts of the dacite lithics equilibrated at different depths before finally being constructed. Greater vesicularities and larger and greater number densities of vesicles are observed in groundmass glass around phenocrysts compared to groundmass glass away from phenocrysts, similar to textures produced in experiments that sintered bimodal distributions of particles. Furthermore, increasingly greater proportions of stretched and distorted vesicles are observed in lithics from the later explosions, which parallels the increasingly shorter reposes between explosions. Finally, micron-sized crystal fragments are ubiquitous in groundmass glass of all dacite lithics. The textures, together with the variable volatile contents, lead us to propose a model that the dacite lithics formed by rapid and repetitive sintering of ash particles derived from a variety of depths on the conduit walls above the fragmentation level. We speculate that sintering of conduit material produced impermeable layers that retarded gas flow through the conduit, causing pressure to build until the cap failed and the next explosion occurred.

中文翻译：

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在山的前气候喷发期间通过烧结灰颗粒形成致密的火山碎屑。1991年的皮纳图博

来自 1991 年 Mt. 高潮前爆炸的致密、玻璃、英安质火山碎屑（英安岩岩屑）。分析了 Pinatubo 的囊泡和晶体结构以及溶解的 H2O 和 CO2 含量。观察到地块玻璃挥发物含量的微米级异质性（500 μm 内 H2O 的差异为 0.9 wt%），并认为部分英安岩岩屑在最终构建之前在不同深度平衡。与远离斑晶的基质玻璃相比，在斑晶周围的基质玻璃中观察到更大的气泡和更大和更大的囊泡数量密度，类似于在烧结颗粒双峰分布的实验中产生的纹理。此外，在后期爆炸的岩屑中观察到越来越大比例的拉伸和扭曲的囊泡，这与爆炸之间越来越短的休息平行。最后，微米大小的晶体碎片在所有英安岩岩屑的地块玻璃中无处不在。纹理，连同可变的挥发物含量，使我们提出了一个模型，即英安岩岩屑通过快速和重复烧结的灰粒形成，这些灰粒来自管道壁上破碎水平以上的各种深度。我们推测管道材料的烧结产生了不透水层，阻碍了气体通过管道的流动，导致压力增加，直到盖子失效并发生下一次爆炸。引导我们提出一个模型，即英安岩岩屑通过快速和重复烧结的灰粒形成，这些灰粒来自破碎水平以上的导管壁上的各种深度。我们推测管道材料的烧结产生了不透水层，阻碍了气体通过管道的流动，导致压力增加，直到盖子失效并发生下一次爆炸。引导我们提出一个模型，即英安岩岩屑通过快速和重复烧结的灰粒形成，这些灰粒来自破碎水平以上的导管壁上的各种深度。我们推测管道材料的烧结产生了不透水层，阻碍了气体通过管道的流动，导致压力增加，直到盖子失效并发生下一次爆炸。