Abstract The spectrum of responses exhibited by upper plates to changes in the subduction zone geometry remains poorly constrained. In the Paleogene, the central Andes in southern Peru potentially experienced an episode of flat or shallow-angle subduction. Presented here are new geochronologic, thermochronologic, basin subsidence backstripping analysis, and 2D flexural modeling results. These are synthesized with existing records on the temporal variation of the volcanic arc position, basin fill chronostratigraphy, deformation style and location, and geophysical constraints on lithospheric architecture to investigate how this segment of the Andes developed during a proposed ancient modification to the subduction zone dip. Basin chronostratigraphy confirms persistent contribution from volcanic arc products during the Eocene–Miocene, arguing against complete cessation of arc magmatism. Sediment accumulation was pulsed and generally more rapid during the late Eocene–Oligocene event. The subsidence curve is generally concave-up, atypical for a foreland basin situated within the compressional central Andes. The tectonic subsidence magnitude observed from backstripping analysis is at least 1 km less than the magnitude of subsidence predicted by 2D flexural model results. This suggests a component of basin uplift, potentially as a dynamic response to subduction shallowing, may have opposed flexural subsidence that was driven by crustal thickening and topographic loading. New geo- and thermochronologic results constrain the timing of Late Triassic pluton emplacement, and initial unroofing that predates the proposed timing of flat or shallow-angle subduction. This new timing suggests initial deformation, with mixed thin- and thick-skinned deformation style, in the Eastern Cordillera may be linked to reactivation of inherited structures rather than inboard deformation advance as a response to subduction flattening. The lack of basement-cored uplifts, preservation of mantle lithosphere beneath this segment of the central Andes, and volcanic arc patterns argue against the occurrence of a flat slab event. Instead, these results point to a shallow-angle subduction event and highlight the diverse behaviors of Cordilleran margins affected by variable subduction zone geometry and upper plates with inherited crustal heterogeneities.

中文翻译：

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从秘鲁南部安第斯山脉中部的新生代沉积和变形记录诊断古代浅角俯冲事件

摘要 上板块对俯冲带几何结构变化的反应谱仍然缺乏约束。在古近纪，秘鲁南部安第斯山脉中部可能经历了平角或浅角俯冲事件。这里展示的是新的地质年代学、热年代学、盆地沉降反剥分析和二维弯曲建模结果。这些与关于火山弧位置的时间变化、盆地填充年代地层学、变形方式和位置以及岩石圈结构的地球物理约束的现有记录相结合，以研究安第斯山脉的这一部分在对俯冲带倾角进行古老改造期间是如何发展的. 盆地年代地层学证实了始新世-中新世火山弧产物的持续贡献，反对弧岩浆活动完全停止。在晚始新世-渐新世事件期间，沉积物积累是脉冲式的并且通常更快。沉降曲线通常是上凹的，这对于位于压缩性安第斯山脉中部的前陆盆地来说是不典型的。从反剥分析中观察到的构造沉降幅度至少比二维弯曲模型结果预测的沉降幅度小 1 公里。这表明盆地隆升的一个组成部分，可能是对俯冲变浅的动态响应，可能与由地壳增厚和地形载荷驱动的弯曲沉降相反。新的地质年代学和热年代学结果限制了晚三叠世岩体侵位的时间，以及在提出的平角或浅角俯冲时间之前的初始开顶时间。这个新的时间表明，东部山脉中的初始变形，具有混合的薄皮和厚皮变形风格，可能与继承结构的重新激活有关，而不是作为对俯冲平坦化的反应的内侧变形推进。缺乏基底岩心隆起、在安第斯山脉中部的这一部分下地幔岩石圈的保存以及火山弧模式都反对平板事件的发生。相反，这些结果指向一个浅角俯冲事件，并突出了受可变俯冲带几何形状和具有继承地壳异质性的上板块影响的科迪勒拉边缘的不同行为。在东科迪勒拉可能与继承结构的重新激活有关，而不是作为对俯冲平坦化的反应的内侧变形推进。缺乏基底岩心隆起、在安第斯山脉中部的这一部分下地幔岩石圈的保存以及火山弧模式都反对平板事件的发生。相反，这些结果指向一个浅角俯冲事件，并突出了受可变俯冲带几何形状和具有继承地壳异质性的上板块影响的科迪勒拉边缘的不同行为。在东科迪勒拉可能与继承结构的重新激活有关，而不是作为对俯冲平坦化的反应的内侧变形推进。缺乏基底岩心隆起、在安第斯山脉中部的这一部分下地幔岩石圈的保存以及火山弧模式与平板事件的发生相矛盾。相反，这些结果指向一个浅角俯冲事件，并突出了受可变俯冲带几何形状和具有继承地壳异质性的上板块影响的科迪勒拉边缘的不同行为。