The Shonkin Sag laccolith (Montana) is a differentiated mafic hypabyssal intrusion that was concordantly emplaced into undeformed sandstones. Erosional processes have produced a cross-section-like exposure of the laccolith, revealing its base, roof, and eastern contact, where it transitions to fringing sills. We present evidence for a multi-pulse emplacement model for the Shonkin Sag laccolith by showing that the rapidly cooled margin of the laccolith and fringing sills preserve features formed during emplacement. These features include internal contacts associated with variably deformed zones at the margin of the laccolith and normal and thrust faults within the surrounding sedimentary rocks. Bulk magnetic susceptibility measurements, anisotropy of magnetic susceptibility and thin section analyses support evidence for strain accumulation in pulses. Thermal models suggest that the pulses emplaced over ~3 years, while total cooling and differentiation of the laccolith to the solidus occurred over ~21 years. From these results, a three-stage emplacement model was determined. The model provides insight into ground deformation and associated hazards caused by the rapid emplacement of shallow magma bodies similar in size to the Shonkin Sag laccolith, such as the 1980 Mt. St. Helens cryptodome and the 2011 Cordón Caulle laccolith.

Shonkin Sag laccolith（蒙大拿州）是一种分化的基性浅层侵入体，它一致地进入未变形的砂岩中。侵蚀过程产生了类似横截面的漆石暴露，揭示了它的底部、屋顶和东部接触，在那里它过渡到边缘的窗台。我们通过显示漆石快速冷却的边缘和边缘基石保留了就位过程中形成的特征，为 Shonkin Sag 石斑岩的多脉冲就位模型提供了证据。这些特征包括与胶石边缘的可变变形带以及周围沉积岩内的正断层和逆冲断层相关的内部接触。大容量磁化率测量，磁化率的各向异性和薄片分析支持脉冲中应变积累的证据。热模型表明脉冲发生在大约 3 年的时间内，而完全冷却和石蜡向固相线的分化发生在大约 21 年。根据这些结果，确定了一个三阶段就位模型。该模型提供了对由与 Shonkin Sag laccolith 大小相似的浅层岩浆体的快速侵位引起的地面变形和相关危害的洞察，例如 1980 Mt. 圣海伦斯隐穹顶和 2011 年的 Cordón Caulle laccolith。该模型提供了对由与 Shonkin Sag laccolith 大小相似的浅层岩浆体的快速侵位引起的地面变形和相关危害的洞察，例如 1980 Mt. 圣海伦斯隐穹顶和 2011 年的 Cordón Caulle laccolith。该模型提供了对由与 Shonkin Sag laccolith 大小相似的浅层岩浆体的快速侵位引起的地面变形和相关危害的洞察，例如 1980 Mt. 圣海伦斯隐穹顶和 2011 年的 Cordón Caulle laccolith。