Browsing by Author "Amaral, Joao Lains"
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- Cadomian/Pan-African consolidation of the Iberian Massif assessed by its detrital and inherited zircon populations: is the similar to 610Ma age peak a persistent Cadomian magmatic inheritance or the key to unravel its Pan-African basement?Publication . Chichorro, Martim; Solá, A. Rita; Santos, Telmo M. Bento Dos; Amaral, Joao LainsABSTRACT: This work assessed the age distribution of Cadomian/Pan-African orogenic events (550-590 and 605-790Ma, respectively) in several zones of Iberian Massif by means of detrital and inherited zircon analysis compilation. Detrital zircon age spectra show that throughout the late Neoproterozoic-to-Early Ordovician era (similar to 120Ma sedimentary record), the main systematic peak occurs at similar to 610Ma, followed by peaks at typical Cadomian ages (similar to 590-550Ma). Inherited zircons incorporated in Cambrian-to-Lower Ordovician igneous rocks show typical Cadomian ages (similar to 590-550Ma) but, once again, a remarkably consistent Pan-African similar to 610Ma peak occurs. In accordance with compiled zircon data and taking into account the evidence of North African peri-cratonic inliers, Ediacaran (similar to 610Ma) zircons incorporated in Paleozoic magmas provide indirect evidence of Pan-African magmatism, suggesting that these magmas and synorogenic sediments are likely to constitute the cryptic stratigraphic infrastructure of most of the Iberian Massif. The main source of similar to 610Ma inherited zircons may be the lateral chrono-equivalents of the Saghro and Bou Salda-M'Gouna Groups (Anti-Atlas, Morocco) and/or coeval igneous rocks from West African Craton or Trans-Sahara Belt, emplaced at a stratigraphic level below the late-Ediacaran sediments of the Ossa Morena Zone and the Central Iberian Zone. Assuming that the Iberian crust is a fragment of the Pan-African orogen, a relative paleoposition situated between the West African Craton and the Trans-Saharan Belt during the Late Neoproterozoic is proposed. The closed-system behaviour of Stenian-Tonian detrital zircon ages in the Trans-Sahara Belt suggests that this mega-cordillera acted as a barrier, in paleogeographic terms, to separating the Sahara Metacraton from Iberia. In Iberia, the opening of the system to Stenian-Tonian detrital zircon during the Ordovician indicates that, at that time, the Trans-Saharan Belt had already become a vast peneplain, which favoured a large drainage system with a long-distance transport mechanism that fed the passive continental margins.
- Detrital zircon similarities and dissimilarities between the Iberian Pyrite Belt, Ossa-Morena Zone and MegumaPublication . Amaral, Joao Lains; Solá, A. Rita; Santos, Telmo M. Bento Dos; Chichorro, MartimABSTRACT: Despite the so-called exotic nature of the South Portuguese Zone relatively to the other major domains of the Iberian Massif of peri-Gondwanan affinity, Devonian detrital rocks of the oldest strata in the Iberian Pyrite Belt have a remarkable resemblance with the Ossa-Morena Zone’s Neoproterozoic-Cambrian rocks and the West Meguma’s Cambrian-Ordovician rocks, presenting the so-called “West African signature”.Using published U-Pb detrital zircon data, we discuss the similarities and dissimilarities between the Iberian Pyrite Belt, Ossa-Morena Zone and West Meguma Terrane through multidimensional scaling, comparing them with other zones of the Iberian Massif, Saxo-Thuringian Zone, Avalonia-Ganderia, and the North African cratonic regions. Our findings show that multidimensional scaling is not entirely effective in displaying the dissimilarities between the peri-Gondwanan terranes due to the background noise caused by the overwhelming number of Cadomian-Panafrican ages. However, it becomes a powerful tool if these ages are filtered. A dominant Meguma-type provenance (Cambro-Ordovician) for the Middle-Upper Devonian rocks of the Iberian Pyrite Belt is demonstrated, mainly attending to their similar Birimian-Eburnean pattern. The possibility of minor contributions from the lower Cambrian rocks of the Ossa-Morena Zone into the Iberian Pyrite Belt quartzites is unlikely, as the latter lack the 1.9Ga peak that characterises the Ossa-Morena Zone sediments. Additionally, the remarkable similarities between Ossa-Morena Zone’s and West Meguma’s detrital rocks strongly suggest a similar paleogeographic setting (but diachronic) for both terrains from the Ediacaran to Lower Ordovician times relative to the North African blocks.
- O magmatismo mais antigo da Faixa Piritosa Ibérica: dados geocronológicos UPb da Jazida do Salgadinho, CercalPublication . Feitoza, L. M.; Santos, Telmo M. Bento Dos; Amaral, Joao Lains; Solá, A. Rita; Tassinari, Colombo C. G.; Basei, M.A.S.; Matos, João Xavier; Albardeiro, Luís; Morais, IgorSUMMARY: New U-Pb geochronological data (SHRIMP/LA-ICP-MS) is presented for zircons of volcanic rocks and dark shales of the Salgadinho deposit, located in Cercal, Iberian Pyrite Belt. Results show that the main magmatic event was placed between 387-392 Ma, indicating the oldest volcanism in the Iberian Pyrite Belt so far. Inherited and detrital zircon ages suggest affinity to Laurussian and Avalonia (s.l.) peri-Gondwanan sources, which provides additional constraints on the paleogeographic positioning of the Iberian Pyrite Belt during the Variscan Cycle.