Mapping and chronology are central to understanding spatiotemporal volcanic trends in diverse tectonic settings. The Cascades back arc in northern California (USA) hosts abundant lava flows and normal faults, but tholeiitic basalts older than 200 ka are difficult to discriminate by classic mapping methods. Paleomagnetism and chemistry offer independent means of correlating basalts, including the Tennant, Dry Lake, and Hammond Crossing basalt fields. Paleomagnetic analysis of these chemically similar basalts yield notable overlap, with statistical analysis yielding 7 chances in 1,000,000 that their similar mean remanent directions are random. These basalts also have overlapping ⁴⁰Ar/³⁹Ar ages of 272.5 ± 30.6 ka (Tennant), 305.8 ± 23.9 ka (Dry Lake), and 300.4 ± 15.2 and 322.6 ± 17.4 ka (Hammond Crossing). Chemical and paleomagnetic analyses indicate that these spatially distributed basalts represent simultaneous (<100 yr uncertainty) eruptions, and thus we use 305.5 ± 9.8 ka (weighted mean) as the eruption age. Their vents align on a N25°W trend over a distance of 39 km. Tennant erupted the largest volume (3.55 ± 0.75 km³) at the highest elevation; both factors decay to the south-southeast at Dry Lake (0.75 ± 0.15 km³) and Hammond Crossing (0.15 ± 0.05 km³). We propose vertical magma ascent beneath the Tennant vent area, where the most evolved, high-SiO₂ magma erupted, with lateral dike propagation in the brittle crust. Propagation was near orthogonal to east-west extension (0.3–0.6 mm/yr) along north-northwest–trending normal faults.

中文翻译：

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加利福尼亚北部（美国）的三个广泛的玄武岩同时中更新世喷发：洞察活跃地向后延伸的地壳岩浆运移

测绘和年代学对于了解不同构造环境中的时空火山趋势至关重要。美国加利福尼亚北部的喀斯喀特山脉后弧拥有丰富的熔岩流和正常断层，但是用经典的测绘方法很难区分年龄大于200 ka的生辉玄武岩。古磁性和化学提供了玄武岩相关的独立方法，包括Tennant，Dry Lake和Hammond Crossing玄武岩田。这些化学相似的玄武岩的古磁分析产生显着的重叠，而统计分析则以百万分之七的概率显示它们相似的平均剩余方向是随机的。这些玄武岩也有重叠的⁴⁰ Ar / ³⁹Ar年龄为272.5±30.6 ka（Tennant），305.8±23.9 ka（Dry Lake）和300.4±15.2和322.6±17.4 ka（Hammond Crossing）。化学和古磁性分析表明，这些空间分布的玄武岩代表了同时爆发（不确定性<100年），因此我们使用305.5±9.8 ka（加权平均值）作为喷发年龄。它们的通风孔在39 km的距离上按照N25°W趋势对齐。坦能（Tennant ）在海拔最高处喷出最大体积（3.55±0.75 km ³）；这两个因素都在干湖（0.75±0.15 km ³）和哈蒙德克罗斯（0.​​15±0.05 km ³）处向东南偏南。我们建议在Tennant通风孔区域下方进行垂直岩浆上升，这是发展最快的高SiO ₂岩浆喷发，横向堤坝在脆性地壳中传播。沿北-西北走向的正常断层，其传播与东西向延伸（0.3-0.6 mm / yr）正交。