Browsing by Author "Pereira, M. Francisco"
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- Chroniberia : the ongoing development of a geochronological GIS database of IberiaPublication . Lopes, C.; Ferreira, A.; Chichorro, Martim; Pereira, M. Francisco; Almeida, J. A.; Solá, A. Rita
- Deciphering a multi-event in a non-complex set of detrital zircon U-Pb ages from Carboniferous graywackes of SW IberiaPublication . Ferreira, A.; Lopes, C.; Chichorro, Martim; Pereira, M. Francisco; Solá, A. RitaThe determination of U–Pb ages from detrital zircons of sedimentary rocks using LA-ICP-MS has been widely used for the purpose of provenance analysis. One problem that frequently arises is finding a population that appears to be non-complex despite several perceptible age peaks in its spectrum. These peaks are qualitatively defined by means of relative probability diagrams, or PDFs, but it is difficult to quantify their statistical significance relative to a zircon forming multi-event. Thus, can a multi-event in a non-complex set of detrital zircon U–Pb ages be deciphered and characterized? The aim of this study is to attempt to provide an answer to this question by means of statistical analysis. Its objectives are: a) to determine the best minimum number of zircon age populations (peaks), BmPs, b) for the characterization of each peak in terms of age and event duration; c) to compare the results obtained from two datasets showing similar zircon ages; and d) to demonstrate the usefulness of deciphering these BmPs. First, cluster analysis is carried out, aimed at grouping zircon ages into a set of consistent clusters. A Gaussian Kernel function is then fitted to each cluster and summed to obtain a theoretical PDFm (modeled probability density function). Finally, the selected modeled PDFm (that built on the BmPs) is that which reports the lowest number of peaks for which the difference as compared with the original gPDF (global probability density function) is equal to or below 5%. Deciphered BmP peaks can be characterized and used for characterizing and providing an understanding of related event(s). A geological interpretation, based on the results obtained, is attempted. This includes a robust measure for maximum age of deposition for both Cabrela and Mértola graywackes.
- Deciphering a multipeak event in a noncomplex set of detrital zircon U-Pb agesPublication . Ferreira, A.; Lopes, C.; Chichorro, Martim; Pereira, M. Francisco; Solá, A. Rita
- Early Cambrian granitoids of North Gondwana margin in the transition from a convergent setting to intra-continental rifting (Ossa-Morena Zone, SW Iberia)Publication . Sánchez-García, Teresa; Pereira, M. Francisco; Bellido, F.; Chichorro, Martim; Silva, J. Brandão; Valverde-Vaquero, Pablo; Pin, Ch.; Solá, A. RitaTwo distinct Cambrian magmatic pulses are recognized in the Ossa-Morena Zone (SW Iberia): an early rift-(ER) and a main rift-related event. This Cambrian magmatism is related to intra-continental rifting of North Gondwana that is thought to have culminated in the opening of the Rheic Ocean in Lower Ordovician times. New data of whole-rock geochemistry (19 samples), Sm–Nd–Sr isotopes (4 samples) and ID–TIMS U–Pb zircon geochronology (1 sample) of the Early Cambrian ER plutonic rocks of the Ossa-Morena Zone are presented in this contribution. The ER granitoids (Barreiros, Barquete, Calera, Salvatierra de los Barros and Tablada granitoid Massifs) are mostly peraluminous granites. The Sm–Nd isotopic data show moderate negative eNdt values ranging from -3.5 to +0.1 and TDM ages greatly in excess of emplacement ages. Most ER granitoids are crustal melts. However, a subset of samples shows a transitional anorogenic alkaline tendency, together with more primitive isotopic signatures, documenting the participation of lower crust or mantle-derived sources and suggesting a local transient advanced stage of rifting. The Barreiros granitoid is intrusive into the Ediacaran basement of the Ossa-Morena Zone (Série Negra succession) and has yielded a crystallization age of 524.7 ± 0.8 Ma consistent with other ages of ER magmatic pulse. This age: (1) constrains the age of the metamorphism developed in the Ediacaran back-arc basins before the intrusion of granites and (2) defines the time of the transition from the Ediacaran convergent setting to the Lower Cambrian intra-continental rifting in North Gondwana.
- Intra-crustal recycling and crustal-mantle interactions in North Gondwana revealed by oxygen isotopic composition of Neoproterozoic to Ordovician zircons from SW Iberia rocksPublication . Chichorro, Martim; Solá, A. Rita; Pereira, M. Francisco; Sánchez-García, Teresa; Ferreira, A.; Silva, J. Brandão; Armstrong, R.
- Provenance analysis of Lower Palaeozoic siliciclastic rocks of the Southwestern Iberia (Ossa-Morena Zone) : distal shelf deposition on the North Gondwana passive marginPublication . Pereira, M. Francisco; Chichorro, Martim; Lopes, C.; Solá, A. Rita; Silva, J. Brandão; Hofmann, Mandy; Linnemann, Ulf
- Provenance analysis of the Late Ediacaran basins from Southwestern Iberia (Série Negra Succession and Beiras Group) : evidence for a common Neoproterozoic evolutionPublication . Chichorro, Martim; Solá, A. Rita; Pereira, M. Francisco; Hofmann, Mandy; Linnemann, Ulf; Gerdes, Axel; Medina, Jorge; Lopes, L.; Silva, J. Brandão
- Provenance of Cambrian-Ordovician siliciclastic rocks of the Southwestern Iberia : insights to the evolution of the North Gondwana marginPublication . Solá, A. Rita; Chichorro, Martim; Pereira, M. Francisco; Hofmann, Mandy; Linnemann, Ulf; Gerdes, Axel; Medina, Jorge; Lopes, L.; Silva, J. Brandão