In the Eastern Cordillera of Peru, observations related to the accretion of the Arequipa Terrane to the Amazon craton are scarce and reactivation of sutures in a backarc basin may make interpretation more difficult. Cambro-Ordovician backarc successions located in proximity to a proposed suture in the Eastern Cordillera of southern Peru were investigated at Umachiri and Ollantaytambo in order to disentangle the early Paleozoic tectonic history of the Arequipa Terrane. At Umachiri, newly identified fossil assemblages in the upper Cambrian Llallahue Formation (Fm) and in the Lower to Middle Ordovician Umachiri Fm constrain the age of these successions and allow correlation of these strata throughout the Central Andes. Using U–Pb geochronology on zircon, we establish that the Ollantaytambo Fm is an upper Carboniferous succession and that the Umachiri Fm instead correlates with the Lower to Middle Ordovician Verónica and San José formations, which form the base of a backarc succession in the Eastern Cordillera of southern Peru that extended into northwestern Argentina. Detrital zircons from the Umachiri Fm display age signatures characteristic of Arequipa basement and contain a prominent 540–510 Ma peak. Precise dating and trace element analysis yielded 539 Ma arc-derived and 522–510 Ma mantle-derived zircons. We infer that a Cambrian backarc system related to deposition of the lower Furongian (~494 Ma) Llallahue Fm developed following ~ 540 Ma Pampean arc magmatism. Closure of the backarc in late Cambrian to Early Ordovician time resulted in regional deformation, uplift, and erosion followed by renewed backarc subsidence in the Ordovician Period. In summary, our results support a new tectonic model of late Neoproterozoic to early Cambrian Pampean collision of an exotic Arequipa Terrane with Amazonia, opening and closing of a Cambrian backarc basin, the presence of parallel Ordovician continental arcs associated with Famatinian subduction, and the opening of an Ordovician–Devonian backarc basin.

在秘鲁东部山脉，与阿雷基帕地带到亚马逊克拉通的增生有关的观测稀少，而在后弧盆地重新缝合线可能使解释变得更加困难。在Umachiri和Ollantaytambo对秘鲁南部东部山脉拟建缝合线附近的坎布罗-奥陶纪后弧演替进行了研究，以弄清阿雷基帕地层的早期古生代构造历史。在Umachiri，上寒武统Llallahue组（Fm）和下奥陶纪Umachiri Fm的新发现的化石组合限制了这些演替的年龄，并使整个安第斯中部这些地层具有相关性。在锆石上使用U–Pb年代学，我们确定Ollantaytambo Fm是上石炭统，而Umachiri Fm则与奥陶纪中下奥陶统和圣何塞地层相关，后者形成了秘鲁南部东山脉山脉向后延伸到阿根廷西北部的弧背演替的基础。 。Umachiri Fm的碎屑锆石显示了阿雷基帕地下室的特征，并具有一个540-510 Ma的突出峰。精确的年代测定和微量元素分析得出了539 Ma弧源和522–510 Ma地幔源锆石。我们推断，与大约540 Ma的潘庞山脉弧岩浆作用有关的寒武纪背弧系统与下部芙蓉系（〜494 Ma）Llallahue Fm的沉积有关。寒武纪晚期至奥陶纪早期，后弧的封闭导致区域变形，隆升，和侵蚀，然后在奥陶纪重新陷落弧后。总而言之，我们的研究结果支持了新元古代晚期至异质的阿雷基帕地貌与亚马逊河的寒武纪庞贝斯碰撞的新构造模型，寒武纪后弧盆地的打开和闭合，与法马汀俯冲有关的平行奥陶纪大陆弧的存在和开放奥陶纪-德文统的后弧盆地。