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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Experimental and textural investigation of welding: effects of compaction, sintering, and vapor-phase crystallization in the rhyolitic Rattlesnake Tuff
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Experimental and textural investigation of welding: effects of compaction, sintering, and vapor-phase crystallization in the rhyolitic Rattlesnake Tuff

机译：焊接的实验和组织研究：流纹响尾蛇凝灰岩中的压实，烧结和气相结晶的影响

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The abrupt changes in character of variably welded pyroclastic deposits have invited decades of investigation and classification. We conducted two series of experiments using ash from the nonwelded base of the rhyolitic Rattlesnake Tuff of Oregon, USA, to examine conditions of welding. One series of experiments was conducted at atmospheric pressure (1 At) in a muffle furnace with variable run times and temperature and another series was conducted at 5 MPa and 600℃ in a cold seal apparatus with variable run times and water contents. We compared the results to a suite of incipiently to densely welded, natural samples of the Rattlesnake Tuff. Experiments at 1 At required a temperature above 900℃ to produce welding, which is in excess of the estimated preemptive magmatic temperature of the tuff. The experiments also yielded globular clast textures unlike the natural tuff. During the cold-seal experiments, the gold sample capsules collapsed in response to sample densification. Textures and densities that closely mimic the natural suite were produced at 5 MPa, 600℃ and 0.4 wt.% H_2O, over run durations of hours to 2 days. Clast deformation and development of foliation in 2-week runs were greater than in natural samples. Both more and less water reduced the degree of welding at otherwise constant run conditions. For 5 MPa experiments, changes in the degree of foliation of shards and of axial ratios of bubble shards and non-bubble (mainly platy) shards, are consistent with early densification related to compaction and partial rotation of shards into a foliation. Subsequent densification was associated with viscous deformation as indicated by more sintered contacts and deformation of shards. Sintering (local fusion of shard-shard contacts) was increasingly important with longer run times, higher temperatures, and greater pressures. During runs with high water concentrations, sintering was rare and adhesion between clasts was dominated by precipitation of sublimates in pore spaces. A few tenths wt.% H_2O in the rhyolite glass promote the development of welding by sharp reduction of glass viscosity. Large amounts of water inhibit welding by creating surface sublimates that interfere with sintering and may exert fluid pressure counter to lithostatic load if sintering and vapor-phase sublimates seal permeability in the tuff.
机译：可变焊接火山碎屑矿床的特征突然变化，已经引起了数十年的研究和分类。我们使用来自美国俄勒冈州的流纹Rattlesnake Tuff的未焊接基底的灰进行了两个系列的实验，以检查焊接条件。在马弗炉中，在大气压（1 At）下，进行了一系列试验，其运行时间和温度是可变的；在另一台试验中，在5 MPa和600℃的马弗炉中，运行时间和含水量是可变的。我们将结果与一组响尾蛇凝灰岩初生至密集焊接的天然样品进行了比较。在1℃下进行的实验需要900℃以上的温度才能进行焊接，该温度超过了凝灰岩的先发制浆岩浆温度。实验还产生了不同于天然凝灰岩的球形碎屑质地。在冷封实验期间，响应于样品致密化，金样品胶囊塌陷。在数小时至2天的运行时间内，在5 MPa，600℃和0.4 wt。％H_2O的条件下产生了与天然套件非常相似的质地和密度。 2周运行中的碎屑变形和叶面发育比自然样品大。越来越少的水都降低了在其他恒定运行条件下的焊接程度。对于5 MPa实验，碎片的叶化程度以及气泡碎片和非气泡（主要是板状）碎片的轴向比的变化与与压实和碎片旋转成碎片有关的早期致密化是一致的。随后的致密化与粘性变形相关，如更多的烧结接触和碎片变形所表明。随着更长的运行时间，更高的温度和更大的压力，烧结（碎片接触的局部融合）变得越来越重要。在高水浓度的运行过程中，很少发生烧结，并且碎屑之间的粘附主要由孔空间中升华物的沉淀决定。流纹岩玻璃中十分之几的重量百分比的H_2O通过急剧降低玻璃粘度来促进焊接的发展。大量的水会通过形成会干扰烧结的表面升华来抑制焊接，并且如果烧结和气相升华凝灰岩中的密封渗透性，则可能会施加流体压力来抵抗岩石静载荷。

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