The behavior of magma as it encounters unconsolidated sediment can be studied in fortuitous exposures of incised volcanic systems to help determine the conditions that control the transport, arrest, or mingling of that magma in the sediment. The Pliocene subaqueous basaltic fissure at 71 Gulch, Idaho, USA contains unusual light-colored glassy mingled clasts that were produced through the incorporation of domains of siliciclastic sands and silts into basalt. These clasts contain textures reflective of melting and mechanical mixing of these sediments with the rising basalt along intrusions at depths > 30 m beneath the pre-eruptive surface and transport into and through a shallow subsurface debris-filled vent. Mingled clasts comprised colorless glass with locally high silica contents and visible swirls of sideromelane along with crystals derived from both the host sediment and the 71 Gulch basalt. The unique combination of textures, minerals, plus major and trace element geochemistry within the geologic context of 71 Gulch points to a two-phase mixing that did not contribute directly to, nor impede, the phreatomagmatic explosions that erupted the mingled clasts.

中文翻译：

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71 峡谷玄武岩岩浆裂隙第 2 部分：来自沉积岩浆混合和融化的异常火山碎屑

岩浆遇到松散沉积物时的行为可以在切开的火山系统的偶然暴露中进行研究，以帮助确定控制沉积物中岩浆运输、滞留或混合的条件。位于美国爱达荷州 71 Gulch 的上新世水下玄武岩裂隙包含不寻常的浅色玻璃状混合碎屑，这些碎屑是通过将硅质碎屑砂和粉砂的区域掺入玄武岩中而产生的。这些碎屑包含的质地反映了这些沉积物与上升的玄武岩在喷发前表面下深度 > 30 m 处沿侵入体的熔化和机械混合，并输送到并穿过浅层地下碎屑填充的喷口。混合碎屑包括具有局部高二氧化硅含量的无色玻璃和可见的铁锰烷漩涡以及来自宿主沉积物和 71 Gulch 玄武岩的晶体。在 71 Gulch 的地质背景下，质地、矿物质以及主要和微量元素地球化学的独特组合表明两相混合既不会直接促成也不会阻碍爆发混合碎屑的潜水岩浆爆炸。