Microbioestratigrafia do Mesozóico-Cenozóico brasileiro: um passeio pelo tempo

Abstrac

The Borborema Pegmatite Province, NE-Brazil revisited

Considering the internal structure, mineralogical distribution and geochemical data on K-feldspar, white micas, Nb-Taoxides, tourmalines, garnet and spinel, it becomes clear that the pegmatites classified as "heterogeneous" (Johnston 1945) include examples of several types and subtypes of LCT family, Rare Element Class pegmatites if the modern pegmatite classification models of Černý & Ercit 2005 are applied: at least examples of the beryl-columbite, beryl-columbite-phosphate and complex-spodumene,complex-lepidolite (±gemmologic elbaite)and albite (± cassiterite) pegmatite types and subtypes were ntatively identified. The impossibility to determine a granitelinked zoned regional distribution of these types may be the result of the fact that there is no single central source pluton but several smaller granitic intrusions in the province and the zoning around them may overlap each other

Quartz chemistry of granitic pegmatites: Implications for classification, genesis and exploration

Quartz from 254 pegmatites representing eight pegmatite fields and provinces worldwide was investigated by laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) to determine concentrations of trace elements Al, Ti, Li, Ge, B, Be, Rb, Na, K, Ca, P, Ga, Sb, Zn and U. A total of 271 new analyses combined with 535 published LA-ICP-MS quartz chemistry data were evaluated with binary and ternary trace element discrimination plots and principal component analysis (PCA). The classifications applied for discrimination of pegmatite types include the widely applied NYF(Nb-Y-F) - LCT(Li-Cs-Ta) classification and the new RMG (pegmatites derived from residual melts of granite magmatism) - DPA (pegmatites as direct products of anatexis) grouping. Pegmatites of both classifications can be well distinguished via Al-Ti, Al-Li and Al/Ti-Ge/Ti binary trace element plots and the Ti - Al/10 - 10*Ge ternary diagram. PCA applied to Al, Li, Ti, Be, B, Ge and Rb contents in quartz allowed to further distinguish between anatectic DPA-1 (Li-enriched DPA) and granite-pluton-derived RMG-1 (Li-enriched RMG) pegmatites. Some pegmatite fields and provinces (Hagendorf-Pleystein, Oxford County) are distinguishable by region-specific Li, Ge and Al contents. The results imply that the chemistry of pegmatite quartz is mainly controlled by the origin (source rock chemistry) of pegmatite melts and, to a much lesser extent, by the geodynamic setting of the pegmatite fields and provinces. Chemically primitive NYF and DPA-2 type pegmatites contain quartz with the lowest total trace-element contents and lowest internal-pegmatite trace-element variation, making it potentially suitable for high-tech application. Pegmatite quartz containing >30 μgg-1 Li and >100 μgg-1 Al is strongly indicative of economic spodumene/montebrasite mineralization and, thus, serves as a strong Li-mineralization pathfinder mineral. Quartz with >5 μgg-1 B may be a potential indicator for gem-quality tourmaline mineralization.Fil: Müller, Axel. University of Oslo; Noruega. Natural History Museum; Reino UnidoFil: Keyser, William. University of Oslo; NoruegaFil: Simmons, William B.. Maine Mineral And Gem Museum; Estados UnidosFil: Webber, Karen. Maine Mineral And Gem Museum; Estados UnidosFil: Wise, Michael. Smithsonian Institution; Estados UnidosFil: Beurlen, Hartmut. Universidade Federal de Pernambuco; BrasilFil: Garate Olave, Idoia. Universidad del País Vasco; EspañaFil: Roda Robles, Encarnación. Universidad del País Vasco; EspañaFil: Galliski, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentin

Caracterização geoquímica de rochas metamáficas e metaultramáficas da Faixa Pajeú-Paraíba, Província Borborema - NE Brasil

Concordant lenses of high pressure metaultramafic and metamafic rocks are positioned in Paleoproterozoic migmatites and orthogneisses of the Pajeú-Paraíba belt, Borborema Province, northeast Brazil. The geochemical signature of theses eclogites facies rocks points to a tholeiitic basaltic composition related to an island arc evolution. They are probably associated with a enriched mantle source underlying a subduction zone. This mantelic source was melted and further underwent in-situ differentiation, producing as high-MgO as high-FeO-TiO2 rocks. Cumulatic pyroxenites could be residual product of this process. The high-FeO-TiO2 group seems to represent more differentiated member submits to crustal contamination event. Reported positive and negative gravimetric anomalies in these metaultramafic and metamafic rocks occurrence area suggest the presence of possible NE-SW to E-W continental collision zone in the Borborema Province.Rochas metamáficas e metaultramáficas submetidas a metamorfimo de alta pressão ocorrem como lentes concordantes em uma seqüência de migmatitos - ortognaisses de provável idade Paleoproterozóica, na Faixa de Dobramentos Pajeú-Paraíba, Província Borborema, NE do Brasil. As rochas metamáficas possuem composição basáltica toleítica com assinatura geoquímica de arcos oceânicos, provavelmente geradas a partir de uma mesma fonte, um manto enriquecido subjacente a uma zona de subducção, que sofreu diferenciação in-situ gerando rochas com altos teores em MgO deixando um resíduo piroxenítico e um grupo de alto FeO-TiO2 que poderia representar os membros mais diferenciados dessa associação, submetidos a um mais elevado grau de contaminação crustal. A associação dessas rochas com anomalias gravimétricas positivas-negativas sugerem a presença de uma zona de colisão continental com direção geral NE-SW a E-W na Província Borborema

Espectrometria de raios gama de granitos pegmatíticos da Província Pegmatítica da Borborema (PPB), nordeste do Brasil

O presente estudo tem como objetivo a caracterização de granitos pegmatíticos localizados na região sul da Província Pegmatítica da Borborema (PPB) usando dados de aerogamaespectrométricos e de gamaespectrometria terrestre. Medidas gamaespectrométricas terrestres, dosagens radiométricas e determinações químicas por ICP-MS indicaram concentrações de urânio variando entre 0,4 ppm e 7,8 ppm, concentrações de tório entre 0,1 ppm e 21 ppm e concentrações de potássio entre 2% e 5,2%. Com base nessas características, e utilizando imagens dos canais individuais, das razões de canais e da composição ternária dos radioelementos foi possível diferenciar das rochas encaixantes regionais um conjunto de granitos pegmatíticos e também diferenciar quartzitos das regiões norte e sul da área investigada com base nas concentrações mais elevadas de tório (Th) nestes últimos. Dados de gamaespectrometria terrestre de detalhe coletados em um desses granitos pegmatíticos conhecido como granito Galo Branco, revelaram irregularidades na distribuição espacial de radioelementos, sugerindo mudanças de conteúdo e concentração de minerais acessórios durante a diferenciação e cristalização magmática da rocha. Pegmatitos encaixados em quartzitos ao sul do granito Galo Branco foram individualizados com base nas razões eU/eTh e eU/K. Os resultados revelam grande potencial dos métodos para a caracterização e mapeamento geológico de granitos e pegmatitos da PPB.The objective of this study is the characterization of pegmatitic granites located in the southern region of the Borborema Pegmatitic Province (BPP) with aerial and ground gamma ray data. Ground gamma ray data, radiometric and ICP-MS laboratory analysis showed that these granites have uranium concentrations varying between 0.4 ppm and 7.8 ppm, thorium concentrations varying between 0.1 ppm and 21 ppm and potassium concentrations varying between 2% and 5.2%. Based on these radiometric characteristics and using individual, ratios and ternary images of radioelements of aerial gamma ray data it was possible to distinguish from others country rocks a group of granitic pegmatitic bodies and also to individualize quartzitic formations from the northern and southern portions of the area, based on their different thorium (Th) contents. Ground gamma ray data, acquired for one of these pegmatitic granites, called Galo Branco granite, reveals an irregular spatial distribution of radioelements, indicating mineralogical changes in contents and concentrations of accessory minerals during magmatic crystalization. Pegmatites intruding quartzites in the south portion of the granite were also distinguished using eU/eTh and eU/K ratios images. The results indicated the potential of these methods for the characterization and mapping of pegmatitic granites and associated pegmatites of the Borborema Pegmatitic Province (BPP)

Animal Behavior Frozen in Time: Gregarious Behavior of Early Jurassic Lobsters within an Ammonoid Body Chamber

Direct animal behavior can be inferred from the fossil record only in exceptional circumstances. The exceptional mode of preservation of ammonoid shells in the Posidonia Shale (Lower Jurassic, lower Toarcian) of Dotternhausen in southern Germany, with only the organic periostracum preserved, provides an excellent opportunity to observe the contents of the ammonoid body chamber because this periostracum is translucent. Here, we report upon three delicate lobsters preserved within a compressed ammonoid specimen of Harpoceras falciferum. We attempt to explain this gregarious behavior. The three lobsters were studied using standard microscopy under low angle light. The lobsters belong to the extinct family of the Eryonidae; further identification was not possible. The organic material of the three small lobsters is preserved more than halfway into the ammonoid body chamber. The lobsters are closely spaced and are positioned with their tails oriented toward each other. The specimens are interpreted to represent corpses rather than molts. The lobsters probably sought shelter in preparation for molting or against predators such as fish that were present in Dotternhausen. Alternatively, the soft tissue of the ammonoid may have been a source of food that attracted the lobsters, or it may have served as a long-term residency for the lobsters (inquilinism). The lobsters represent the oldest known example of gregariousness amongst lobsters and decapods in the fossil record. Gregarious behavior in lobsters, also known for extant lobsters, thus developed earlier in earth's history than previously known. Moreover, this is one of the oldest known examples of decapod crustaceans preserved within cephalopod shells