Browsing by Author "Oliveira, J. T."
Now showing 1 - 3 of 3
Results Per Page
Sort Options
- Detrital zircon geochronology of the Carboniferous Baixo Alentejo Flysch Group (South Portugal); constraints on the provenance and geodynamic evolution of the South Portuguese ZonePublication . Rodrigues, B.; Chew, Dave; Jorge, R. C. G. S.; Fernandes, Paulo; Veiga-Pires, C.; Oliveira, J. T.U–Pb detrital zircon data from the Baixo Alentejo Flysch Group in the South Portuguese Zone show significant age differences between formations. The Visean Mértola Formation and Serpukhovian to early Bashkirian Mira Formation are dominated by zircons in the 316–388Ma age range, whereas the late Bashkirian to late Moscovian Brejeira Formation is dominated by zircons with an age range of 498–687Ma. Detrital zircons spanning an age range of 0.9–1.1Ga are present in the Brejeira Formation but are absent in the Mértola and Mira formations. Detrital zircon ages of the Mértola and Mira formations indicate provenance from an extra-basinal source (Ossa–Morena Zone) with a minor intra-basinal contribution (South Portuguese Zone). The abundant presence of detrital zircon with age ranges of 500–750 and 0.9–1.1Ga in the Brejeira Formation suggests a sediment source from the Avalon–Meguma terranes with limited recycling from the SW Portugal Domain. The different inferred source areas for the Baixo Alentejo Flysch Group formations are attributed to the presence of a forebulge that was formed in Mid-Visean times during the foreland phase of the South Portuguese Zone. The forebulge acted as a physical barrier separating sub-basins that accumulated the Mértola–Mira and Brejeira sediments respectively.
- Idades U-Pb de zircões detríticos do Grupo do Flysch do Baixo Alentejo, Zona Sul PortuguesaPublication . Rodrigues, B.; Chew, Dave; Jorge, R. C. G. S.; Fernandes, Paulo; Veiga-Pires, C.; Oliveira, J. T.Foram obtidas idades U-Pb através de ablação a lazer de zircões detríticos das formações do Grupo do Flysch do Baixo Alentejo. As idades obtidas sugerem uma proveniência sedimentar, no caso das formações de Mértola e Mira, com o envolvimento de uma componente detrítica intrabasinal (Zona Sul Portuguesa) e de áreas fontes associadas ao bordo sul da Zona da Ossa Morena. No caso da Formação de Brejeira as idades sugerem um envolvimento de áreas fontes correlacionáveis com o terreno Avalonia/Meguma assim como de sedimentos reciclados oriundos do Domínio Sul Português.
- Reply to Discussion on 'Detrital zircon geochronology of the Carboniferous Baixo Alentejo Flysch Group (South Portugal); constraints on the provenance and geodynamic evolution of the South Portuguese Zone', Journal of the Geological Society, 172, 294-308Publication . Rodrigues, B.; Chew, D. M.; Jorge, R. C. G. S.; Fernandes, Paulo; Veiga-Pires, C.; Oliveira, J. T.We would like to thank Pereira (2015) for his interest in our work and appreciate the opportunity to clarify some aspects of the Rodrigues et al. (2015) study. Here we dispute several fundamental assertions made in the discussion of our original paper. (1) Pereira (2015) states, based on the U–Pb detrital zircon data of Pereira et al. (2012a, 2014), that the turbidites of the Mértola (late Visean) and the Mira (Serpukhovian to early Bashkirian) formations of the Baixo Alentejo Flysch Group of the South Portuguese Zone (Fig. 1b), were ‘mainly derived from a source terrane dominated by zircon populations of Middle–Late Devonian ages (c. 393–359 Ma) that are absent in the Ossa–Morena Zone’ and that this detrital zircon population forms 37.7% of all detrital zircons of these two formations. However, a large population of zircons of Middle–Late Devonian age was not found in the Rodrigues et al. (2015) study. The Mértola Formation (sample FM1; table 1 of Rodrigues et al. 2015) is clearly dominated by one population whose zircon ages range between 388 and 326 Ma, with this group representing 68% of all ages obtained. This population shows a peak at 336 Ma (middle Visean).