Widespread recent volcanic rocks occur across the Cordillera landward of the current/recent volcanic arc Mexico to Alaska and most other subduction backarcs. We conclude that most are produced by partial melt in the upper asthenosphere where two conditions are met: (1) thin lithosphere, shallow hot asthenosphere. Most of the Cordillera is uniformly hot with thin lithosphere such that the hot asthenosphere extends up to a sufficiently shallow depth to intersects the wet solidus; (2) wet upper asthenosphere. There is substantial water in the upper asthenosphere that reduces the solidus sufficiently for partial melting. We integrate geochemical analyses that constrain the partial melt source temperature and depth, seismic velocities that define the upper mantle temperature and partial melt zones, and seismic receiver functions that define the lithosphere-asthenosphere boundary (LAB). Geochemical data for the Canadian Cordillera are integrated with data from the western United States. Upper mantle xenoliths indicate a dry strong lithosphere, <50 ppm H₂O. A wet asthenosphere source, >250 ppm, is indicated by the volcanics, facilitating small-scale convection. Geochemical equilibration averages ∼1,350°C, at ∼65 km. Receiver functions also define the LAB at ∼65 km for the western Cordillera, deeper in the eastern US Cordillera, and asthenosphere tomography velocities indicate ∼1,350°C. Low velocities above ∼150 km suggest a few percent partial melt that percolates upward and ponds at the base of the lithosphere until enough accumulates to locally penetrate upward. The 65-km depth may be controlled by the spinel-garnet phase transition. Mechanisms are discussed for the spatial distribution of recent volcanics.

中文翻译：

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北美山脉新近纪火山活动的地球物理和地球化学约束

最近广泛分布的火山岩遍布墨西哥当前/最近的火山弧的山脉山脉，一直延伸到阿拉斯加和大多数其他俯冲背弧。我们得出的结论是，大部分是由满足两个条件的软流圈上层部分融化所产生的：（1）岩石圈薄，热软流圈层较浅。大部分山脉都是均匀的，岩石圈薄而热，因此软流软层延伸到足够浅的深度以与湿的固相线相交。（2）湿软流域上空。在软流圈上层有大量的水，足以减少固相线以部分熔化。我们整合了限制部​​分熔体温度和深度的地球化学分析，定义了上地幔温度和部分熔体带的地震速度，以及定义岩石圈-软流圈边界（LAB）的地震接收器功能。加拿大山脉的地球化学数据已与美国西部的数据整合在一起。上地幔异岩指示干燥坚硬的岩石圈，<50 ppm H₂ O.湿软流源，> 250 ppm时，由火山岩指示的，便于小型对流。地球化学平均平衡温度约为6550 km，约为1350°C。接收器功能还在西部山脉，美国东部山脉的更深处定义了约65 km的LAB，并且软流层的层析速度表明约为1350°C。约150 km以上的低速表明部分熔体向上渗透，并积聚在岩石圈底部，直到有足够的积累以局部向上渗透为止。尖晶石-石榴石相变可以控制65 km的深度。讨论了近期火山的空间分布机制。