Abstract The Rif belt (Northern Morocco) forms the western edge of the Alpine-Himalayan orogenic system, resulting from the progressive closure of the Tethys oceanic domain between the Africa and Eurasia plates. The External Rif, topic of this paper, comprises three paleogeographic zones, namely the Prerif, Mesorif and Intrarif, inherited from the zonation of the North-West African paleo-margin from proximal to distal domains, respectively. Its current architecture displays tectonic windows (belonging to the Mesorif) at depth supporting far-travelled thrust-sheets (namely, the Senhadja and Higher Nappes of Mesorif and Intrarif origin, respectively). A puzzling aspect of the Mesorif structure is the coexistence of metamorphic and non-metamorphic units within the tectonic windows and Senhadja Nappes. In particular, the latter presents a chaotic structure, which origin remains under debate. We integrate previous studies and new data (field observations, geological mapping and thermochronology results) to reassess the structure of the External Rif and propose an up-dated interpretation of its Cenozoic evolution. In the Prerif and Mesorif, we highlight a poly-phased tectonic evolution occurring before and after a major unconformity (the “Mesorif Unconformity”). This unconformity seals a pre-Miocene compressional event that we relate to the under-thrusting of the North-African paleo-margin below the Maghrebian Tethys (the former Tethys branch located between South Iberia and North Africa). The MP-LT metamorphism, recorded in the metamorphic tectonic window of the Temsamane Massif, is a direct vestige of this process. After the “Mesorif Unconformity”, i.e. during the Miocene, the regional geodynamics is ruled by the westward translation of the Alboran Domain and the coeval out-of-sequence deformation of the “oceanic” units in front of it (Flyschs and Intrarif Units, the most internal parts of the External Rif). This process directly results from the subduction of the Maghrebian Tethys below the Alboran Domain. The docking of the Intrarif Units against the already exhumed Temsamane Units and Senhadja Nappes generated an uplift and the subsequent detachment of the top of the Intrarif lithostratigraphic pile, forming the Higher Nappes. We show that the chaotic structure of the Senhadja Nappes is only apparent, being mostly inherited from the Mesozoic rifting. Results of apatite fission track, apatite helium dating and thermal modeling from the gabbroic intrusions of the Senhadja Nappes confirm an overburden by the Higher Nappes and their subsequent exhumation during the Upper Miocene. Finally, all these elements are integrated in a coherent model incorporating the External Rif in the geodynamics of the West Mediterranean.

中文翻译：

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中东部外部 Rif 的结构（摩洛哥）；西北非古边缘逆冲作用的多相变形及作用

摘要 Rif 带（摩洛哥北部）形成了高山-喜马拉雅造山系统的西部边缘，是由于特提斯洋域在非洲和欧亚板块之间逐渐闭合而形成的。本文的主题External Rif包括三个古地理带，即Prerif、Mesorif和Intrarif，分别继承自西北非洲古边缘从近端到远端区域的分带。其当前的结构在支持远行的逆冲层（即分别为 Mesorif 和 Intrarif 起源的 Senhadja 和更高的 Nappes）的深度显示构造窗口（属于 Mesorif）。Mesorif 结构的一个令人费解的方面是构造窗口和 Senhadja Nappes 内变质和非变质单元的共存。特别是，后者呈现出一个混乱的结构，其起源仍有争议。我们整合以前的研究和新数据（实地观察、地质测绘和热年代学结果）来重新评估外部 Rif 的结构，并提出对其新生代演化的最新解释。在 Prerif 和 Mesorif 中，我们强调了在主要不整合（“Mesorif 不整合”）前后发生的多相构造演化。这种不整合封闭了一个前中新世挤压事件，我们将其与马格里布特提斯山脉（位于南伊比利亚和北非之间的前特提斯分支）下方的北非古边缘的逆冲事件有关。在 Temsamane 地块的变质构造窗口中记录的 MP-LT 变质作用是这一过程的直接遗迹。在“Mesorif 不整合”之后，即 在中新世期间，区域地球动力学由 Alboran 域的西移和它前面的“海洋”单元（Flyschs 和 Intrarif 单元，外部 Rif 的最内部部分）的同时期乱序变形所支配。 ）。这一过程直接由阿尔博兰域下方的马格里布特提斯俯冲引起。Intrarif Units 与已经挖掘出的 Temsamane Units 和 Senhadja Nappes 的对接产生了隆起，随后 Intrarif 岩石地层桩的顶部脱离，形成了更高的 Nappes。我们表明 Senhadja Nappes 的混沌结构只是显而易见的，主要是从中生代裂谷继承而来。磷灰石裂变径迹结果，来自 Senhadja Nappes 辉长岩侵入体的磷灰石氦测年和热模拟证实了上中新世期间上层推覆岩及其随后的剥露。最后，所有这些元素都被整合到一个连贯的模型中，将外部 Rif 纳入西地中海的地球动力学。