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- Geoquímica de soleiras e filões aplito-pegmatíticos graníticos do centro de Portugal : cristalização fraccionada, fluxos e fluídosPublication . Neiva, A.M.R.; Ramos, João Farinha; Silva, Paulo BravoAs soleiras e filões aplito-pegmatíticos graníticos de Arcozelo da Serra, Cabeço dos Poupos (Sabugal) e Gonçalo (Belmonte) podem ser derivados por cristalização fraccionada de quartzo, plagioclase, feldspato potássico e biotite de um magma de granito da área respectiva, o que foi testado por modelização, usando o método de regressão de mínimos quadrados para os elementos maiores e a equação de cristalização fraccionada perfeita para os elementos menores. Há aumento no grau de evolução dos aplito-pegmatitos de Arcozelo da Serra para os de Cabeço dos Poupos e destes para os de Gonçalo, pois há aumento progressivo na quantidade e número de minerais litiníferos. Os aplitopegmatitos graníticos do subtipo lepidolítico são os mais evoluídos e derivam de um maior grau de cristalização fraccionada, sendo os mais ricos em fluxos (H2O, F, P, B) e fluidos. Com o aumento do grau de evolução dos aplitopegmatitos diminui o efeito dos fluxos e fluidos nos teores de Sr e Ba, mas aumentou esse efeito no teor de Rb. A cristalização fraccionada causou aumento nos teores de Rb, Li, F, Sn e Ta nos aplito-pegmatitos graníticos, especialmente nos do subtipo lepidolítico e os fluxos e fluidos influenciaram a cristalização de lepidolite, cassiterite e óxidos de Nb-Ta.
- 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.
- Different meanings for cummingtonite-hornblende association in plutonic rocks, Iberian Massif, Portugal [Poster]Publication . Solá, A. Rita; Moita, Patrícia; Santos, José Francisco; Neiva, A.M.R.; Ribeiro, Maria Luísa
- Mineralogia dos filões aplito-pegmatíticos litiníferos da região de SeguraPublication . Antunes, I. Margarida H. Ribeiro; Neiva, A.M.R.; Silva, M. M. V. G.; Silva, Paulo BravoNa região de Segura, os filões aplito-pegmatíticos litiníferos Variscos intruíram o Complexo Xisto-Grauváquico, Câmbrico. Osfilões pegmatíticos são do tipo REL-Li e incluem-se na família dos pegmatitos LCT. A ocorrência de lepidolite, montebrasite, microlite, cassiterite e minerais do grupo da columbite primários sugerem um elevado grau de diferenciação nestes filões. A montebrasite primária é heterogénea e a lacroixite secundária ocorre nas suas zonas enriquecidas em Na. A cassietrite é zonada com alternância de zonas escuras e zonas claras e possui Mn > Fe, o que é raro. As zonas escuras são fortemente pleocróicas, com zonamento oscilatório, e possuem teores mais elevados de Nb e Ta do que as zonas claras. As inclusões de moscovite, apatite, ferrotapiolite, ixiolite e microlite foram encontradas em ambas as zonas de cassiterite, mas as exsoluções de ferrocolumbite, ferrocolumbite manganífera e manganocolumbite ocorrem nas zonas escuras.
- 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.
- Alguns aplito-pegmatitos graníticos com minerais de Li das regiões centro e norte de PortugalPublication . Neiva, A.M.R.; Ramos, João Farinha; Silva, Paulo Bravo
- Geochemistry of granitic aplite-pegmatite sills and petrogenetic links with granites, Guarda-Belmonte area, central PortugalPublication . Neiva, A.M.R.; Ramos, João FarinhaGranitic amblygonite-subtype and lepidolite-subtype, aplite-pegmatite sills intruded a biotite>muscovite granite (G1). Two other biotite>muscovite granites (G2 and G3) and a muscovite>biotite granite (G4) crop out in the area. Variation diagrams for major and trace elements of the Variscan rocks show fractionation trends for a) G1 and G4; b) G2, G3 and aplite-pegmatite sills. The two series are confirmed by the two trends defined by major elements of primary muscovite. The sills also contain Li-bearing muscovite, which has higher Mn, Li, F and paragonite contents and lower AlVI content than primary muscovite from G2, G3 and sills. All sills have pure albite and P2O5 content of K-feldspar and plagioclase increases in the series G2, G3 and sills. Beryl occurs in all sills, but lepidolite and a nearly pure petalite only occur in lepidolite-subtype sills, which are the most evolved sills. Primary topaz and amblygonite have a similar composition in all sills. Aplite-pegmatite sills contain cassiterite, which shows sequences of alternating darker and lighter zones. The former are richer in (Nb + Ta + Fe + Mn) than the latter. Manganocolumbite is common in all sills, but ferrocolumbite only appears in amblygonite-subtype sills and manganotantalite in lepidolite-subtype sills. The sills richest in Li contain reversely-zoned crystals with a homogeneous microlite core and a heterogeneous uranmicrolite rim. Least squares analysis of major elements shows that granite G3 and amblygonite-subtype and lepidolite-subtype aplite-pegmatite sills can be derived from granite G2 magma by fractional crystallization of quartz, plagioclase, K-feldspar, biotite and ilmenite. Modelling of trace elements shows good results for Sr, but magmatic fluids controlled the Rb and Ba contents of the aplite-pegmatite sills and probably also their Li, F, Sn and Ta contents and crystallization of lepidolite, cassiterite and Nb–Ta oxide mineral assemblage. Schorl from the lepidolite-subtype sills that cut granite G1 has higher Mg/(Mg + Fe) than schorl from metasomatised granite at sill walls and resulted from the mixing of magmatic fluids carrying B and some Fe with a meteoric fluid that has interacted with the host granite G1 and carried Fe and Mg. Schorl and dravite, respectively from metasomatised granite and micaschist at sill walls, were also formed from the mixing processes.
- Geochemistry of granitic aplite-pegmatite veins and sills and their minerals from Cabeço dos Poupos, Sabugal, central PortugalPublication . Neiva, A.M.R.; Silva, Paulo Bravo; Ramos, João Farinha
- 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.
- Geochemistry of minerals, waters and weathering from the Fonte Santa mine area, NE of PortugalPublication . Gomes, Maria Elisa Preto; Antunes, I. Margarida H. Ribeiro; Neiva, A.M.R.; Pacheco, F. A. L.; Silva, Paulo BravoThe quartz veins containing scheelite from Fonte Santa mine area were exploited for W between 1942 and 1982. At the end of November 2006, a flood event damaged the dam land of Fonte Santa mine and metal content of water increased. Fonte Santa mine area cuts the quartzites close to the Fonte Santa muscovite granite. The granite contains quartz, microcline, albite, muscovite, chlorite, columbite-tantalite, volframite, W-ixiolite and ilmenite. The quartz veins contain muscovite, chlorite, tourmaline, scheelite, pyrrhotite, pyrite, sphalerite, chalcopyrite, galena, arsenopyrite, magnetite, jarosite, phosphates of Pb, Fe and AI. The waters related to the Fonte Santa mine are poorly mineralized, with electrical conductivity < 965 ~S / cm, of mixed type or HCO3- and SO42- types. These waters have Fe and Mn contents that forbid to use that for human consumption and agriculture. Sodium, Mg and K water contents are associated with the alteration of albite, chlorite and muscovite of country rock, while Ca is related to the W-bearing quartz veins.