科研之友
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摘要
Despite the presence of a deep history of continental evolution from Archean to Recent and a wealth of outcrop, existing studies of detrital zircon geochronology in Morocco are limited, focused mostly in the Cambrian and Neoproterozoic Pan-African exposures in the Anti-Atlas belt. We broaden the use of this tool by surveying the detrital zircon geochronology of three stratigraphic units from three distinct Mesozoic terranes: the Tisiren unit of the Maghrebian flysch domain, the Ketama unit of the Intrarif, and the Bou Rached sandstones of the Middle Atlas Mountains. Samples were analyzed for zircon U-Pb ages using laser-ablation inductively coupled plasma mass spectrometry, and zircon fission-track (ZFT) ages were analyzed using the emerging technique of scanning electron microscope high-density fission-track analysis. In total, 259 U-Pb ages are presented, along with 60 ZFT ages. U-Pb ages reveal dominant Pan-African (Cryogenian-Ediacaran) and West African cratonic (Paleoproterozoic) signatures that are typical of northwest Africa. All samples also include significant Mesoproterozoic U-Pb populations that are hitherto unknown in Morocco and scarce in North Africa. Proposed scenarios for the provenance of these zircons include delivery to Morocco from the Amazonian craton or the African Volta basin during Ordovician glaciation and/or delivery from Avalonian terranes during the Variscan orogeny. The Bou Rached sandstones contain a significant Ordovician-Devonian U-Pb population not found in the other samples and are of an age without a viable source currently dated in Morocco. An Avalonian source is likewise suggested for these Ordovician-Devonian ages. The Ketama and Tisiren units have comparable U-Pb ages, but their preliminary ZFT cooling age distributions differ, lending support to the idea that different source regions are required for the two domains.
- 出版日期2015-3
