The Cascade arc (western North America) is the world’s youngest continental arc, and because the down-going Juan de Fuca plate is young, it is also the hottest end member among subduction zones worldwide. We present evidence that the arc initiated <5 m.y. after accretion of the Siletzia oceanic terrane terminated the earlier subduction system and caused the northern portion of the Farallon slab to break off. Cascade magmatism began ca. 46 Ma with a new trench outboard of Siletzia, a reconfiguration commonly attributed to a seaward jump of the subduction zone. However, the presence of young buoyant oceanic lithosphere that would have resisted being forced into the mantle and the very rapid reestablishment of arc magmatism are hard to reconcile with initiation of a new subduction zone by this process. We propose an alternative mechanism in which the arc was reestablished as the intact southern portion of Farallon slab migrated northward from California (United States), converting a transform margin to a convergent one. This model utilizes plate reconstructions, petrology, mantle tomography, and geochronology to explain how subduction was initiated in a setting where the slab was young and hot and why the earliest Cascade magmatism occurred toward the middle rather than an end of the arc.

中文翻译：

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级联弧的启动

喀斯喀特弧（北美西部）是世界上最年轻的大陆弧，由于下降的胡安德富卡板块很年轻，它也是全球俯冲带中最热的端元。我们提供的证据表明，在 Siletzia 海洋地体的吸积终止了早期俯冲系统并导致法拉隆板块北部部分断裂之后，弧开始了<5米。梯级岩浆作用开始于大约。 46 Ma 在 Siletzia 外侧出现了一个新的海沟，这种重新配置通常归因于俯冲带的向海跳跃。然而，年轻的浮力海洋岩石圈的存在将抵制被迫进入地幔，并且弧岩浆作用的快速重建很难与该过程中新俯冲带的启动相协调。我们提出了一种替代机制，当法拉隆板块完整的南部部分从美国加利福尼亚州向北迁移时，弧被重建，将变换裕度转换为收敛裕度。该模型利用板块重建、岩石学、地幔断层扫描和地质年代学来解释俯冲作用是如何在板块年轻且炎热的环境中开始的，以及为什么最早的喀斯喀特岩浆活动发生在弧的中部而不是末端。