Abstract The upper portion of the Huichapan Ignimbrite (UHI), central Mexico, is a non-welded massive ignimbrite characterized by large and well-developed fines-poor elutriation pipes. We conclude that the most important pipe-forming process in the Huichapan Ignimbrite was deposition-triggered aggregative-type segregation, and this process is enhanced by positive pore-pressure feedback during the rapid settling of the pyroclastic material. In experiments, pumice concentration zones and elutriation pipes have been formed in separated portions of the deposits. Contrary to the experimental results, in the UHI both pumice concentration zones and elutriation pipes have been observed alongside one another within the deposit. We interpret this association to have formed during time periods of unusually high deposition rate within a long-lived, sustained pyroclastic density current system. Elutriation pipes were formed because of low shearing and vertical channeling of gases, and the pumice concentration zones formed because of pumice segregation during hindered settling. Nevertheless, the deposition rate was so high that the segregated pumice was “frozen” before it could bypass, within the deposit, right next to the elutriation pipes. We present a classification scheme of five types of elutriation pipes based on our field observations in the UHI and a review of field and experimental work from other authors: 1) tubular pipes; 2) irregular tubular pipes; 3) anastomosing pipes; 4) pinch-out pipes; 5) deflected pipes. Irregular tubular pipes are the most common in the volcanic geological record and they form because of deposition-triggered aggregative-type segregation and/or post-depositional upward fluid flow. Likely, anastomosing elutriation pipes are a unique product of deposition-triggered aggregative-type segregation. A comparison between the lower and upper portion of the Huichapan Ignimbrite leads to the conclusion that deposition-triggered pipe formation is enhanced by poor sorting, low shearing, and presence of large clasts (>−5Φ, 32 mm). Pipe-free ignimbrites in the volcanic geological record likely come from relatively better-sorted dispersions with few coarse clasts, but more importantly, strong shearing during deposition may be the main processes that diminish pipe formation.

中文翻译：

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ignimbrites 中的淘析管：基于墨西哥 Huichapan Ignimbrite 的概念分析

摘要 墨西哥中部Huichapan Ignimbrite (UHI)的上部是一个非焊接的块状凝灰岩，其特征是大而发育良好的细粉-贫淘析管。我们得出结论，在辉茶盘火凝灰岩中最重要的管道形成过程是沉积触发的聚集型偏析，并且在火山碎屑材料的快速沉降过程中，正孔隙压力反馈增强了该过程。在实验中，在沉积物的分离部分形成了浮石浓缩区和淘析管。与实验结果相反，在 UHI 中，浮石浓缩区和淘析管在沉积物中并排观察到。我们将这种关联解释为是在长期存在的异常高沉积率的时间段内形成的，持续火山碎屑密度电流系统。气体的低剪切和垂直窜流形成淘析管，受阻沉降过程中浮石偏析形成浮石浓集区。然而，沉积速率如此之高，以至于分离出的浮石在它可以绕过沉积物内，就在淘析管旁边之前就被“冻结”了。根据我们在 UHI 的现场观察以及其他作者的现场和实验工作回顾，我们提出了五种类型的淘析管的分类方案：1）管状管；2) 不规则管状管道；3) 吻合管；4) 夹断管；5) 偏转管道。不规则管状管道在火山地质记录中最常见，它们的形成是由于沉积触发的聚集型偏析和/或沉积后向上的流体流动。很可能，吻合淘析管是沉积触发的聚集型分离的独特产物。比较灰查盘火凝灰岩下部和上部的结论是，不良分选、低剪切和大碎屑（>-5Φ，32 毫米）的存在增强了沉积触发的管道形成。火山地质记录中的无管道熔凝灰岩可能来自分类相对较好的分散体，几乎没有粗碎屑，但更重要的是，沉积过程中的强剪切可能是减少管道形成的主要过程。吻合淘析管是沉积触发聚集型离析的独特产品。比较灰查盘火凝灰岩下部和上部的结论是，不良分选、低剪切和大碎屑（>-5Φ，32 毫米）的存在增强了沉积触发的管道形成。火山地质记录中的无管道熔凝灰岩可能来自分类相对较好的分散体，几乎没有粗碎屑，但更重要的是，沉积过程中的强剪切可能是减少管道形成的主要过程。吻合淘析管是沉积触发聚集型离析的独特产品。比较灰查盘火凝灰岩下部和上部的结论是，不良分选、低剪切和大碎屑（>-5Φ，32 毫米）的存在增强了沉积触发的管道形成。火山地质记录中的无管道熔凝灰岩可能来自分类相对较好的分散体，几乎没有粗碎屑，但更重要的是，沉积过程中的强剪切可能是减少管道形成的主要过程。和大碎屑的存在（>-5Φ，32 毫米）。火山地质记录中的无管道熔凝灰岩可能来自分类相对较好的分散体，几乎没有粗碎屑，但更重要的是，沉积过程中的强剪切可能是减少管道形成的主要过程。和大碎屑的存在（>-5Φ，32 毫米）。火山地质记录中的无管道熔凝灰岩可能来自分类相对较好的分散体，几乎没有粗碎屑，但更重要的是，沉积过程中的强剪切可能是减少管道形成的主要过程。