Abstract The Neoproterozoic Anti-Atlas belt (Morocco) is a key segment in tracing the history of the northern margin of the West African craton (WAC) from Rodinia breakup to Gondwana assembly. In order to constrain geodynamic events related to rifting and convergence and their stratigraphic records, a radiometric study was carried out on the volcano-sedimentary Tachdamt and Bleida Formations. The volcaniclastic deposits of Tachdamt Fm. yield an age of ca. 883 Ma and provide a new constraint for the timing of the subaqueous volcanic eruption and the initiation of rifting in the Anti-Atlas. This age is ~100 my older than the previous age of 788 ± 10 Ma obtained from Rb/Sr isotope dating (Clauer, 1976). Available zircon data from the interbedded clastic deposits from Tachdamt Fm. indicate major shifts in provenance during the rifting with sediments sourced from the WAC and a nearby Grenvillian terrane. Detrital zircon ages from metasiltstones of Bleida Fm. set a maximum depositional age at ca. 700 Ma. The age spectra discloses a major shift in sediment input with provenance from the WAC, Grenvillian terrane and an arc-related terrane (ca. 770–700 Ma) lying along the Anti-Atlas margin. The newly obtained results combined with existing radiometric data allowed the refinement of the stratigraphic and geotectonic framework of the pre-Pan-African strata in the WAC. The Early Tonian syn-rift volcanism has much in common with similar events in other cratons and provides a stratigraphic record for incipient Rodinia breakup. The overlying Bleida Fm. deposited in a peripheral foreland basin chronicles the Cryogenian arrival of the ca. 770–700 Ma Bou Azzer-Siroua arc-related terrane at the Anti-Atlas margin, and correlates with initial accretion in West Gondwana. The new results indicate that the Grenvillian detrital input in the Anti-Atlas during both geodynamic stages points toward a possible Mesoproterozoic terrane existing along the western margin of the WAC.

中文翻译：

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西非克拉通北缘早期托尼阶裂谷和低温弧地体-大陆汇聚的时间限制：来自泛非反阿特拉斯带（摩洛哥）的 SHRIMP 和 LA-ICP-MS 锆石年代学的见解

摘要 新元古代反阿特拉斯带（摩洛哥）是追溯西非克拉通（WAC）北缘从罗迪尼亚破裂到冈瓦纳大陆组装历史的关键部分。为了限制与裂谷和辐合及其地层记录有关的地球动力学事件，对火山沉积的 Tachdamt 和 Bleida 组进行了辐射测量研究。Tachdamt Fm 火山碎屑沉积。产生大约的年龄。883 Ma，并为水下火山爆发的时间和反阿特拉斯裂谷的开始提供了新的约束。这个年龄比从 Rb/Sr 同位素测年获得的前一个年龄 788 ± 10 Ma（Clauer，1976）大 100 岁。来自 Tachdamt Fm 夹层碎屑沉积物的可用锆石数据。表明在裂谷期间，来自 WAC 和附近 Grenvillian 地体的沉积物的来源发生了重大变化。来自 Bleida Fm 变质粉砂岩的碎屑锆石年龄。将最大沉积年龄设置为大约。700 马。年龄谱揭示了沉积物输入的重大变化，其来源来自 WAC、Grenvillian 地体和位于反阿特拉斯边缘的弧相关地体（约 770-700 Ma）。新获得的结果与现有的辐射测量数据相结合，可以改进 WAC 中前泛非地层的地层和大地构造框架。托尼阶早期同裂谷火山活动与其他克拉通中的类似事件有很多共同之处，并提供了罗迪尼亚早期破裂的地层记录。上覆的 Bleida Fm。沉积在外围的前陆盆地记载了大约低温纪的到来。770-700 Ma Bou Azzer-Siroua 弧形地体在 Anti-Atlas 边缘，与西冈瓦纳的初始增生相关。新的结果表明，在两个地球动力学阶段，反阿特拉斯的 Grenvillian 碎屑输入指向可能存在于 WAC 西缘的中元古代地体。