Abstract Aseismic ridges are variably broad linear topographic features built by submarine volcanic activity that are thicker and more buoyant than the surrounding oceanic crust. Together with oceanic plateaus they constitute a non-trivial ∼30% of the oceanic floor. As such, aseismic ridge subduction significantly affects subduction dynamics as well as deformation of the overriding plate. Indeed, it is considered to exert major controls on volcanic activity, the generation of juvenile Earth's crust and the formation of porphyry Cu-Au deposits. Previous studies claimed that magma chemistry changes associated with aseismic ridge subduction are mainly due to source processes, such as melting of the subducting ridge, melting of the edges of the oceanic plate following slab tear, or subduction erosion of the continental margin with subsequent partial melting of the scraped and subducted continental material. Here we explore the role of the subducted aseismic Carnegie ridge on modulating frontal arc magma chemistry in the Ecuadorian-southernmost Colombian frontal arc. We show symmetric changes of several geochemical indices (Th, Nd, Sm, Nb, Th/La, Ba/Th) and evolutionary paths (Na2O-SiO2 correlations) in frontal volcanic arc rocks with respect to the equatorial latitude, which coincides with the projection of the crest of the subducting Carnegie ridge at the frontal arc. We explore the systematic along-arc changes of these geochemical indices through geochemical modelling using a Monte Carlo approach, and conclude that the trends are controlled to a significant extent by intracrustal processes. In particular we argue that magmatic systems associated with the central part of the Ecuadorian volcanic arc evolve through fractionation, partial melting of crustal rocks and mixing, at average greater depths than those in the northern and southern sides. We speculate about possible links between the systematic along-arc geochemical changes and the subduction of the Carnegie ridge. Our findings highlight a new facet of the controls that are exerted by the overriding plate on the geochemical variability of arc magmas.

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抗震脊俯冲对锋弧岩浆地球化学的影响

摘要 抗震脊是由海底火山活动形成的宽度不等的线状地形特征，比周围的大洋地壳更厚、更有浮力。它们与大洋高原一起构成了重要的~30% 的洋底。因此，抗震脊俯冲显着影响俯冲动力学以及上覆板块的变形。事实上，它被认为对火山活动、新生地壳的生成和斑岩铜金矿床的形成起到了主要控制作用。先前的研究声称，与抗震脊俯冲相关的岩浆化学变化主要是由于源过程造成的，例如俯冲脊的融化，板块撕裂后大洋板块边缘的融化，或大陆边缘的俯冲侵蚀，随后被刮削和俯冲的大陆物质部分熔化。在这里，我们探讨了俯冲地震卡内基脊在调节厄瓜多尔-最南端哥伦比亚锋弧锋弧岩浆化学中的作用。我们显示了锋面火山弧岩中几个地球化学指数（Th、Nd、Sm、Nb、Th/La、Ba/Th）和演化路径（Na2O-SiO2 相关性）相对于赤道纬度的对称变化，这与赤道纬度一致。俯冲卡内基海脊的波峰在锋弧处的投影。我们通过使用蒙特卡罗方法的地球化学建模探索了这些地球化学指数的系统沿弧变化，并得出结论，这些趋势在很大程度上受地壳内过程的控制。特别是，我们认为与厄瓜多尔火山弧中部相关的岩浆系统通过分馏、地壳岩石的部分熔融和混合演化，其平均深度比北侧和南侧的深。我们推测系统性沿弧地球化学变化与卡内基海脊俯冲之间可能存在联系。我们的研究结果突出了覆盖板块对弧形岩浆地球化学变化的控制的一个新方面。我们推测系统性沿弧地球化学变化与卡内基海脊俯冲之间可能存在联系。我们的研究结果突出了覆盖板块对弧形岩浆地球化学变化的控制的一个新方面。我们推测系统性沿弧地球化学变化与卡内基海脊俯冲之间可能存在联系。我们的研究结果突出了覆盖板块对弧形岩浆地球化学变化的控制的一个新方面。