Breadcrust bubbles are a previously undescribed pyroclast providing unique insights into post-fragmentation conduit dynamics. We describe these particles from the ca. 7 Ma Rattlesnake Tuff deposits (Oregon, USA) and ca. 15 ka deposits at Laguna del Maule (Chile). The clasts comprise discrete, ∼1-mm-diameter, fully intact hollow spheroids composed of high-silica rhyolite glass with a series of cross-cutting cracks on the shell exterior akin to breadcrust texture on volcanic bombs. We interpret the spheroids as resulting from fragmentation of a thick-walled magmatic foam. As the pyroclasts accelerated up the conduit, breadcrust textures recorded cycles of brittle and ductile deformation to relieve overpressure. We exploit this texture to quantify parameters inaccessible through direct observation including strain accommodation and the time scale necessary for it to accrue. Breadcrust bubbles have additional potential to better describe and quantify the nature of fragmentation and transport conditions in high-silica rhyolite eruptions.

中文翻译：

---

面包壳气泡：记录碎裂后脆性-韧性变形的灰粒

面包壳气泡是以前未描述的火山碎屑，可提供有关碎片后导管动力学的独特见解。我们从ca描述这些粒子。7 Ma Rattlesnake Tuff矿床（美国俄勒冈州）和约。在Laguna del Maule（智利）有15 ka矿床。这些碎片包括直径约1毫米的完整完整的空心球体，这些球体由高硅质流纹岩玻璃组成，在外壳的外部具有一系列横贯的裂纹，类似于火山炸弹上的面包壳结构。我们将椭球体解释为厚壁岩浆泡沫破裂造成的。当破火山岩加速导管时，面包壳质地记录了脆性和延性变形的周期，以缓解过压。我们利用这种纹理来量化通过直接观察无法获得的参数，包括应变适应和产生应变所必需的时间尺度。面包壳气泡具有更好的描述和定量高硅流纹岩喷发中碎裂和运输条件性质的潜力。