Understanding the stress evolution of extinct volcanoes can improve efforts to forecast flank eruptions on active systems. Field, petrographic, and seismic data are combined with numerical modeling to investigate the paleo-stress field of New Zealand's Akaroa Volcano, or Akaroa Volcanic Complex. Field mapping identifies 86 radially oriented dikes and seven lava domes found only within a narrow elevation range along Akaroa's erosional crater rim. These observations suggest that crater rim dike emplacement resulted from lateral deflection of vertically ascending intrusions from a centralized magma source, which in turn may have facilitated formation of the lava domes, as well as two scoria cones. We postulate that dike deflection occurred along a stress barrier, as neither a compositional change nor structural boundary are present. We use a finite element model (FEM) simulating Akaroa to test how different factors may have influenced the system's stress state and dike geometry. Elastic, non-flexural (“roller”) model configurations containing a large, oblate, and shallow magma chamber produce stress barriers most conducive to radial dike emplacement along Akaroa's crater rim. These configurations also simulate rapid edifice construction above a preexisting lithospheric “bulge.” Conversely, simulating flexural stresses exerted on the lithosphere by Akaroa's large mass hinder rather than promote radial dike emplacement. Temperature-dependent viscoelastic relaxation promotes gradual increases in stress barrier elevation, though this effect is strongly dependent on magma chamber parameters. These results suggest that Akaroa was constructed rapidly (within ∼100 kyr) prior to crater rim dike emplacement, which occurred throughout the volcano's remaining active lifespan.

中文翻译：

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新西兰阿卡罗阿火山堤坝挠度和侧翼喷发的应力控制

了解死火山的应力演化可以改进预测活动系统侧翼喷发的努力。现场、岩相和地震数据与数值模拟相结合，以研究新西兰阿卡罗阿火山或阿卡罗阿火山复合体的古应力场。实地测绘确定了 86 个径向堤坝和 7 个熔岩穹顶，这些熔岩穹顶仅在阿卡罗阿侵蚀火山口边缘的狭窄海拔范围内发现。这些观察结果表明，火山口边缘堤坝的就位是由于集中岩浆源的垂直上升侵入物的横向偏转，这反过来可能促进了熔岩圆顶以及两个熔渣锥的形成。我们假设堤坝挠度沿应力屏障发生，因为既不存在成分变化也不存在结构边界。我们使用模拟 Akaroa 的有限元模型 (FEM) 来测试不同因素如何影响系统的应力状态和堤坝几何形状。弹性、非弯曲（“滚子”）模型配置包含大型、扁圆形和浅岩浆室，产生的应力屏障最有利于沿阿卡罗阿火山口边缘的径向堤坝就位。这些配置还模拟了在预先存在的岩石圈“凸起”之上的快速大厦建设。相反，模拟由 Akaroa 的大质量施加在岩石圈上的弯曲应力会阻碍而不是促进径向堤坝的就位。温度相关的粘弹性松弛促进应力屏障升高的逐渐增加，尽管这种影响强烈依赖于岩浆房参数。