The dangerous juxtaposition of human populations and active volcanic arcs worldwide makes elucidating the history of explosive eruptions of these arcs a crucial endeavor. The well-preserved Deschutes Formation, which forms part of the Deschutes Basin of central Oregon, USA, contains a distal record of a period of unusually frequent explosive eruptions between 5.45 and 6.25 Ma, which is atypical of the Cascades arc as a whole. However, no previous study has established the chronology, frequency, or total volume of all of the ignimbrites and tephra-fall units exposed within the Formation in order to compare to baseline activity of the arc. We use multivariate statistics on major and trace element compositions of pumice glass to correlate pyroclastic units across the Deschutes Basin, and combine these with recently published ⁴⁰Ar/³⁹Ar dates to establish, for the first time, a detailed and comprehensive tephrochronology of the Deschutes Formation. Our results suggest that at least 78 statistically distinct explosive eruptions occurred between 6.25 and 5.45 Ma. Eruption frequency is not constant throughout the 800 kyr of pyroclastic volcanism; a maximum rate of 1.7 to 3.0 explosive eruptions per 10 kyr occurred between 5.76 and 5.68 Ma and decreased for 340 kyr prior to graben formation. We estimate that the volume for 51 ignimbrite eruptions is 290 to 565 km³ (170 to 280 km³ DRE), assuming an equal westward flow component and a fall:flow ratio of 0.5:1 to 1.9:1. Using a single isopach method, we also estimate that a minimum volume of 110 km³ (45 km³ DRE) was deposited as 27 pumice-fall units which have no correlated ignimbrites. Thus, we estimate that a cumulative pyroclastic volume of 400 to 675 km³ (210 to 330 km³ DRE) was erupted in the central Oregon Cascades during this time. The volumetric rate (2.7 to 4.1 km³/10 kyr, DRE) and average frequency of ignimbrite eruptions (1.0 to 1.5 eruptions/ 10kyr) are more than a factor of ten greater than the Quaternary Cascades arc. Thus, the Deschutes Formation records North America's most recent arc-sourced ignimbrite flare-up. Although smaller in volume than most well-recognized flare-up events, this represents an important category of flare-ups that may be more common in arcs than previously recognized. We hypothesize that a heightened flux of basalt, possibly induced by slab-rollback, was focused beneath the arc and into the shallow crust by minor amounts of crustal extension. This extension allowed for the high flux of basalt to be stored at shallow levels beneath a new arc locus within fertile crust, resulting in an unusually silicic and explosive period of Cascade arc history.

全世界人口与活跃的火山弧并存的危险并存使得阐明这些弧的爆炸性喷发的历史成为一项至关重要的工作。保存完好的Deschutes地层是美国俄勒冈州中部Deschutes盆地的一部分，其远端记录了一段在5.45至6.25 Ma之间异常频繁的爆炸爆发，这是整个喀斯喀特弧的典型现象。但是，以前没有研究确定在地层中暴露的所有火成岩和特菲拉坠落单元的年代，频率或总体积，以便与电弧的基线活动进行比较。我们使用浮石玻璃的主要和微量元素组成的多元统计量来关联整个Deschutes盆地的火山碎屑单元，并将其与最近发表的相结合⁴⁰ Ar / ³⁹ Ar日期首次确定是Deschutes组的详细而全面的年代学。我们的结果表明，在6.25至5.45 Ma之间至少发生了78次统计上不同的爆炸性喷发。在整个800年的火山碎屑火山爆发中，喷发频率不是恒定的。每10年的最大爆发速率为1.7至3.0次爆发，发生在5.76至5.68 Ma之间，并在en石形成之前下降了340年。假定向西流动分量相等，且流量下降比为0.5：1至1.9：1，我们估计51次火成岩喷发的体积为290至565 km ³（170至280 km ³ DRE）。使用单一等值线方法，我们还估计最小体积为110 km ³（45 km ³ DRE）被沉积为27个浮石下降单位，没有相关的火成岩。因此，我们估计这段时间在俄勒冈州中部喀斯喀特火山爆发了400至675 km ³（210至330 km ³ DRE）的累积火山碎屑积。容积率（2.7至4.1 km ³/ 10 Kyr（DRE）和火成岩喷发的平均频率（1.0到1.5喷发/ 10kyr）比四级瀑布弧大十倍。因此，Deschutes编队记录了北美最近的弧源火成岩闪耀。尽管其数量比大多数公认的爆发事件小，但它代表了重要的爆发事件类别，在电弧中可能比以前认识到的更为普遍。我们假设玄武岩的通量增加（可能是由板坯回滚引起的）被少量的地壳伸展集中在弧线下方并进入浅地壳。这种延伸使得高玄武岩通量被储存在肥沃地壳内新的弧形轨迹之下的浅层之下，从而导致了级联弧形历史的异常硅化和爆炸期。