Tectonic controls on the origin and segmentation of the Cascade Arc, USA
Tectonic controls on the origin and segmentation of the Cascade Arc, USA
复制标题
构造对美国喀斯喀特弧起源和分段的控制
DOI：
10.1007/s00445-022-01611-2
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发表时间：
2022
影响因子：
3.5
通讯作者：
Grunder, Anita L.
中科院分区：
文献类型：
--
作者：
Humphreys, Eugene D.;Grunder, Anita L.
俯冲洋岩石圈上方的岩浆响应从弱到强，从窄带到广布。小而年轻的喀斯喀特弧，骑在构造活跃的北美板块的边缘，几乎表达了整个火山活动范围。这允许异常好的检查电弧起始和早期生长。本文回顾了与火山活动有关的火山岩浆活动从开始到现在的构造控制作用，并对构造应力应变对火山活动的影响作了新的思考。Cascade Arc是在Siletzia海洋高原在~ 50 Ma结束了一个平板俯冲时期后的吸积而形成的。这（1）在北方弧的大部分区域（华盛顿和俄勒冈州下方）引发了下沉板片俯冲，（2）使更靠南的俯冲平板（内华达州下方）滚回加州。随着被遗弃的平板破碎并沉没在俄勒冈州和华盛顿之下，整个美国西北部都发生了剧烈的扩张和火山活动;在内华达州，俯冲的平板滚回加州。喀斯喀特弧的早期迹象在~ 45 Ma时就很明显了，而祖先喀斯喀特弧在~ 35 Ma时就已经很好地建立起来。因此，从约55-35 Ma的俯冲相关的岩浆活动演变从近amagmatic区域耀斑，以明确建立火山弧在两个不同的构造背景。现代Cascades结构开始约7马时，太平洋板块运动的变化造成部分夹带的塞拉利昂内华达州/克拉马斯块。该地块向北和向西推挤俄勒冈州海岸山脉地块，将弧分为三段：南部伸展弧、中部过渡弧和北方挤压弧。延伸增强了南部弧的镁铁质火山活动，促进玄武岩减压熔体从亏损地幔（低钾拉斑玄武岩），是subequal的体积俯冲熔融钙碱性玄武岩。挤压限制了北部的火山活动;火山活动主要是俯冲的，板内玄武岩簇集在主弧火山附近。过渡的中央弧容纳右旋剪切变形，导致广泛的火山弧与分布的玄武岩喷口的不同亲和力和没有明确的弧轴。
The magmatic response above subducting ocean lithosphere can range from weak to vigorous and from a narrow zone to widely distributed. The small and young Cascade Arc, riding on the margin of the tectonically active North American plate, has expressed nearly this entire range of volcanic activity. This allows an unusually good examination of arc initiation and early growth. We review the tectonic controls of Cascade-related magmatism from its inception to the present, with new considerations on the influences of tectonic stress and strain on volcanic activity. The Cascade Arc was created after accretion of the Siletzia oceanic plateau at ~ 50 Ma ended a period of flat-slab subduction. This (1) initiated dipping-slab subduction beneath most of the northern arc (beneath Washington and Oregon) and (2) enabled the more southerly subducting flat slab (beneath Nevada) to roll back toward California. As the abandoned flat slab fragmented and foundered beneath Oregon and Washington, vigorous extension and volcanism ensued throughout the northwest USA; in Nevada the subducting flat slab rolled back toward California. Early signs of the Cascade Arc were evident by ~ 45 Ma and the ancestral Cascade Arc was well established by ~ 35 Ma. Thus, from ~ 55–35 Ma subduction-related magmatism evolved from nearly amagmatic to regional flare-up to a clearly established volcanic arc in two different tectonic settings. The modern Cascades structure initiated ~ 7 Ma when a change in Pacific plate motion caused partial entrainment of the Sierra Nevada/Klamath block. This block pushes north and west on the Oregon Coast Ranges block, breaking the arc into three segments: a southern extensional arc, a central transitional arc, and a northern compressional arc. Extension enhances mafic volcanism in the southern arc, promoting basalt decompression melts from depleted mantle (low-K tholeiites) that are subequal in volume to subduction fluxed calcalkaline basalts. Compression restricts volcanic activity in the north; volcanism is dominantly silicic and intra-plate-like basalts cluster close to the main arc volcanoes. The transitional central arc accommodates dextral shear deformation, resulting in a wide volcanic arc with distributed basaltic vents of diverse affinities and no clear arc axis.
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