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- Petrographic and geochemical features of Mouriscas Orthogneisses: contribution to Ossa-Morena Zone geodynamical modelPublication . Henriques, S.B.A.; Ribeiro, Maria Luísa; Moreira, Maria Eugénia Dias; Guimarães, FernandaABSTRACT: A preliminary study presents a set of variscan granitoids, which intruded the Ossa Morena Zone (OMZ), at the Arraiolos-Pavia region. Field, petrographic and geochemical characterization defines the bases for a general classification of the Ossa Morena Zone granitoids, similar to that of Central Iberian Zone (CIZ). The obtained data pointed out the occurrence of enormous volumes of basic and intermediated compositions. Granitoids containing biotite, amphibole and calcic plagioclase, granitoids are frequent, showing particular features of the OMZ, relatively to the CIZ. Geochemical data indicate sub-alkaline sequences and different magmatic sources, from mantle and crust. These sequences have reached different stages of magmatic evolution. The most evolved melts are enriched in alkalis gave compositions for the alkaline field in the TAS diagram (alkali feldspar granite). These evolved rocks have the Al2O3 values of granites.
- Island-Arc signature in amphibolites from the boundary between the Ossa Morena Zone and the Central Iberian Zone in Central Portugal [Poster]Publication . Henriques, S.B.A.; Neiva, A.M.R.; Ribeiro, Maria Luísa; Dunning, G. R.
- Evolution of a Neoproterozoic suture in the Iberian Massif, Central Portugal: New U-Pb ages of igneous and metamorphic events at the contact between the Ossa Morena Zone and Central Iberian ZonePublication . Henriques, S.B.A.; Neiva, A.M.R.; Ribeiro, Maria Luísa; Dunning, G. R.; Tajcmanová, L.ABSTRACT: A Neoproterozoic suture is exposed at the contact between the Ossa Morena Zone and the Central Iberian Zone, in the Iberian Massif (Central Portugal), the westernmost segment of the European Variscides. Although, the Cadomian magmatic and tectonometamorphic events have been previously documented, their timing is still poorly constrained, particularly in the inner zones of the suture. We used geochronological (ID-TIMS U-Pb) data to establish the sequence of events, isotopic (Rb-Sr, Sm-Nd) data to characterize the magmatic sources and thermodynamic modelling to determine the maximum P-T conditions attained during the Cadomian metamorphism. The first event, in the future Ossa Morena Zone, is the onset of island arc magmatism represented mainly by tholeiites with a MORB signature. Their igneous crystallization age is unknown, but they are older than ca. 539 Ma. This magmatic activity was accompanied by deposition of fine-grained sediments in a Neoproterozoic basin. The second event is the evolution of the Cadomian magmatic arc in different stages. The earliest magmatic stage occurs at ca. 692 Ma, which is the oldest igneous age known in the Ossa Morena Zone. It is followed by the generation of subalkaline and peraluminous protoliths at ca. 569 Ma, with the isotopic signature of old crustal sources. The final phase of the arc magmatism (ca. 548-544 Ma) involved mainly partial melting of continental crust. The range of the main magmatic activity must have been between ca. 569 Ma and ca. 544 Ma as mentioned for other areas in the Ossa Morena Zone. A major metamorphic event, recorded in metamorphic monazite, zircon and titanite at ca. 540 Ma, attained upper amphibolite facies conditions close to the transition to granulite facies (7-8 kbar and 640-660 degrees C). It represents the continental arc accretion of the Ossa Morena Zone with the Iberian Autochthon passive margin (future Central Iberian Zone). The Early Ordovician rocks (ca. 483-477 Ma) were generated from depleted and juvenile sources. These rocks are strongly deformed and with melting features, display metamorphism at amphibolite facies conditions. They are interpreted as related with the Rheic Ocean.
- Evolution of a Neoproterozoic suture in the Iberian Massif, Central Portugal: igneous and metamorphic events at the Ossa Morena Zone/Central Iberian Zone boundaryPublication . Neiva, A.M.R.; Dunning, G. R.; Tajčmanová, Lucie; Henriques, S.B.A.ABSTRACT: The existence of the late Neoproterozoic supercontinent Pannotia (ca. 650-540 Ma) is controversial. Several proxies for supercontinent assembly and break-up have been recognized. Global orogeny and granitoid magmatism, detrital zircon and monazite age peaks and extreme conditions of metamorphism are some of the proxies pointed out for supercontinent assembly. The amalgamation of Pannotia was accompanied by the Pan African-Cadomian-Baikalian orogeny that generated several collisional belts. We present a sequence of magmatic and tectonometamorphic events for the Cadomian belt that can be interpreted as proxies of supercontinent assembly.
- Thick-skinned inter-plate and intra-plate tectonics in NW and SW IberiaPublication . Ribeiro, António; Romão, José; Henriques, S.B.A.; Dunning, G. R.; Ribeiro, Maria Luísa; Neiva, A.M.R.; Munhá, José; Pereira, Eurico; Castro, PauloNa área de Abrantes (Zona Ossa Morena), o extremo NW da Zona de Cisalhamento de Tomar-Badajoz-Córdoba termina contra a Zona de Cisalhamento Porto-Tomar-Ferreira do Alentejo. Mantos de carreamento de soco Cadomiano foram transportados para NE durante a orogenia Varisca; granulitos de pressão intermédia/baixa contrastam com associações cadomianas de alta pressão na zona axial da ZCTBC, devido à presença de uma sutura Cadomiana. O sistema intraplacas de mantos de soco da ZOM é conectado via a paleotransformante PTFA com os mantos de soco do sistema interplacas da sutura transportada do NW Ibérico.
- Património Geológico Cadomiano da região de AbrantesPublication . Henriques, S.B.A.; Alves, Paulo; Machado, SusanaSUMMARY: A well preserved Cadomian basement crops out at the contact between the Ossa Morena Zone and the Central Iberia Zone near Abrantes area. The magmatic and metamorphic activity recorded in this area indicates the existence of a long‐lived continental arc (ca. 692–540Ma) with coeval felsic and mafic magmatism and a final collisional event (ca. 540 Ma). This sequence of events, as well as several tectonic and metamorphic features and well‐preserved outcrops of diverse lithologies provides unique conditions for observing and characterize the Cadomian basement. The Geological Heritage from this area has high scientific and didactic relevance, which permit to interpret the past of the Earth.
- Petrology and Geochemistry of Recent Lavas from Santo Antão (Cape Verde Islands)Publication . Henriques, S.B.A.; Munhá, José; Silva, L. Celestino da; Mendes, M. H.ABSTRACT: Santo Antão Island is the northernmost island of the Cape Verde Archipelago that is located in the Atlantic Ocean between 17º 13’N-14º 48’N and 22º 42’W-25º 22’W. The genesis of this Archipelago is explained by the activity of a hot-spot, which began 25 My ago. The main stratigraphic sequences of Santo Antão island (Silva et al., 1994; 2004) have been dated by Plesner et al. (2003) and comprise, from base to top, the “Complexo Eruptivo Antigo” (7.57 ± 0.56 My) the “Formação Conglomerático-Brechóide”, the “Formação Eruptiva Principal” (3.24 ± 0.89 to 0.22 ± 0.03 My) (which is overlain by a white phonolitic deposit pumice) and the “Formação Eruptiva do Tope de Coroa” (0.17 ± 0.02 My to 0.09 ± 0.03 My). The “Complexo Eruptivo Antigo” includes chiefly basaltic flows. The “Formação Conglomerático-Brechóide” is a sedimentary unit formed during an intensive erosion period and was followed by an important volcanic event, represented by the “Formação Eruptiva Principal”, comprising nephelinitic, phonolitic, tephritic and basanitic lava flows. The “Formação Eruptiva do Tope de Coroa”, the most recent unit of the island, was divided (Silva et al. 2004) into three sub-units (figure 1): “Sequência Antiga”, “Sequência Intermédia” and “Sequência Superior”. The “Sequência Antiga” is composed by phonolitic and nephelinitic flows and scorias, the “Sequência Intermédia” comprises basaltic flows and scorias and the “Sequência Superior” includes basaltic, phonolitic and nephelinitic flows and scorias. Santo Antão recent lavas are silica undersaturated (carrying abundant feldspathoids, particularly hauyne), alkaline and considerably evolved (Mg#=13-53 wt%, Ni=0-252 ppm, Cr=0-434 ppm). They display a strong enrichment in incompatible trace elements, suggesting that their primary magmas were produced by low degrees of partial melting, from a heterogeneous, metassomatized, source (including residual garnet and phlogopite), with a significant HIMU component.
- Assessment of metal and metalloid contamination in soils trough compositional data: the old Mortórios uranium mine area, central PortugalPublication . Neiva, A.M.R.; Albuquerque, M.T.D.; Antunes, I. Margarida H. Ribeiro; Carvalho, P.C.S.; Santos, A. C. T.; Boente, C.; Cunha, Pedro Proença e; Henriques, S.B.A.; Pato, R. L.ABSTRACT: Soils from the old Mortórios uranium mine area were studied to look for contamination, as they are close to two villages, up to 3 km away, and used for agriculture. They are mainly contaminated in U and As and constitute an ecological threat. This study attempts to outline the degree to which soils have been affected by the old mining activities through the computation of significant hot clusters, Traditional geostatistical approaches commonly use raw data (concentrations) accepting that the analyzed elements represent the soil’s entirety. However, in geochemical studies these elements are just a fraction of the total soil composition. Thus, considering compositional data is pivotal. The spatial characterization, considering raw and compositional data together, allowed a broad discussion about not only the concentrations’ spatial distribution, but also a better understanding on the possibility of trends of “relative enrichment” and, furthermore an insight in U and As fate. The highest proportions (compositional data) on U (up to 33%), As (up to 35%) and Th (up to 13%) are reached in the south-southeast segment. However, the highest concentrations (raw data) occur in north and northwest of the studied area, pointing out to a “relative enrichment” toward the south-southeast zone. The Mondego Sul area is mainly contaminated in U and As, but also in Co, Cu, Pb and Sb. The Mortórios area is less contaminated than the Mondego Sul area.
- Neoproterozoic magmatism and metamorphism at the northern margin of Gondwana : Ossa Morena/Central Iberian zone boundary (Central Portugal)Publication . Henriques, S.B.A.; Neiva, A.M.R.; Ribeiro, Maria Luísa; Dunning, G. R.; Tajcmanová, L.
- Caracterização petrográfica e geoquímica dos magmatitos da região do Sardoal, Abrantes, e seu enquadramento geodinâmicoPublication . Henriques, S.B.A.; Ribeiro, Maria Luísa; Moreira, M. E.Os magmatitos do Sardoal estão inseridos na Unidade dos Ortognaisses de Mouriscas, considerada de idade proterozóica. Apresentam intercalações mesocratas, com estruturação idêntica à dos gnaisses e intercalações máficas com diferente estruturação. Os Gnaisses do Sardoal exibem deformação variável, desde texturas com foliação milonítica a texturas metaígneas. Correspondem a rochas ácidas, sub-alcalinas, com assinaturas geoquímicas características de ambiente de arco continental. As Rochas Intercaladas apresentam foliação bem desenvolvida, composição básica (as máficas) e intermédia (as mesocratas) e assinaturas geoquímicas indicativas de diferentes fontes. Sugere-se que as Rochas Intercaladas correspondam a termos de sequências sub-alcalinas de diferente natureza - as intermédias relacionadas com ambiente de arco continental e as máficas, ou inseridas em ambiente do mesmo tipo ou de intraplaca continental. Estes dados permitiram correlacionar as rochas desta região com o arco vulcânico já definido no NE da ZOM e que deverá estar relacionado com o fecho da orogenia cadomiana.
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