Plagioclase and biotite compositions tracing granite genesis and evolution: insights from two syntectonic granitoids from Aguiar da Beira (N Portugal)

The Aguiar da Beira area (N Portugal) is located within the Central-Iberian Zone (CIZ) of the Iberian Variscan Belt. It is mainly composed by granitoids emplaced during (syntectonic) or slightly after (late- to post-tectonic) the last ductile deformation event of the Variscan orogeny (D3). From the petrological and geochemical point of view, the syntectonic granitoids from the CIZ can be included into two genetically distinct suites: (a) calc-alkaline granodiorites and biotite granites, and (b) strongly peraluminous leucogranites and two-mica granites. In the Aguiar da Beira area, the first group is represented by a small intrusion of a medium- to coarse-grained porphyritc biotite granodiorite-granite, emplaced 322 Ma ago, characterized by a slightly peraluminous and moderately evolved composition. The second group comprises a NW-SE elongated pluton of a strongly peraluminous and highly evolved medium- to fine-grained muscovite-biotite granite (317 Ma), showing occasionally a gneissic foliation concordant with the D3 variscan structures. Based on geochemical and Sr-Nd and 18O isotopic data, the biotite granodiorite-granite melt is interpreted either as the result of partial melting of heterogeneous lower crustal materials, or as the product of mixing of mantle derived magmas and lower crustal felsic anatectic melts. In contrast, the muscovite-biotite gneissic granite magma appears to have been exclusively generated by partial melting of upper crustal metasediments and suffered a subsequent evolution dominantly controlled by fractional crystallization processes. Plagioclase and biotite major and trace element compositions can be used to constrain the origin and evolution of the two granitoids and provide strong evidence in support of the proposed petrogenetic models. In the biotite granodiorite-granite, the plagioclase is characterized by a wide compositional range (An20-33), high Sr (749 – 869 ppm) and Ba (32 – 351 ppm) contents and a Sr discontinuous zonation pattern, whilst the biotite shows high TiO2 (2.92 – 3.30 wt%), Ba (407 – 589 ppm), V (214 – 234 ppm), and low Al2O3 (16.83 – 18.03 wt%), Li (335 – 367 ppm), Zn (262 – 279 ppm) and Fet/(Fet + Mg) (0.54 – 0.55) contents. These data confirm the typical calc-alkaline affinity of this intrusion and reveal that these phase minerals crystallized under disequilibrium conditions. In contrast, the plagioclase from the muscovite-biotite granite displays a narrower compositional range (An1-7), unzoned or normally zoned compositional patterns and lower Sr (19 – 33 ppm) and Ba (1.1 – 2.0 ppm) contents, reflecting the highly evolved character of this intrusion and near equilibrium crystallization conditions. The biotite crystals from the muscovite-biotite granite plot in the field of the alumino-potassic series in the AlVI versus Mg diagram (Nachit et al., 1983), supporting a major contribution of metasedimentary rocks for the genesis of this magma. Their AlVI contents increase with decreasing Mg suggesting an important role for fractional crystallization processes during magmatic evolution. The range of AlVI and Fet/(Fet + Mg) values (AlVI: 0.482 – 0.487; Fet/(Fet + Mg): 0.72 – 0.83) displayed by the biotites show that the muscovite-biotite granite crystallized from a reduced magma (low O2), which is consistent with its inferred sedimentary provenance

Different meanings for cummingtonite-hornblende association in plutonic rocks (Iberian Massif, Portugal)

Cummingtonite-grunerite series is frequently related with metamorphism or volcanic environments but rarely described as belonging to a plutonic assemblage [1]. Recently, in Iberian Massif (Portugal), there have been several references [2,3,4,5] of this Fe-Mg amphibole intimately associated with Ca amphiboles (mainly hornblende) on plutonic rocks. Different textural relations between two amphibole types have been argued to for a primary (igneous) or subsolidus metamorphic origin for Fe-Mg amphibole. Cummingtonite-grunerite (Cum, hereafter all abbreviation from [6]) from gabbros and diorites Carrascal Massif (Central Iberian Zone) occurs as tiny exsolution lamellae within a dominant hornblende (Hbl) crystal. Their textural occurrence agrees with the subsolidus growth of the Fe-Mg amphibole reflecting the equation Hbl+ Qtz= Cum + An + H2O [7]. Nevertheless, on Hospitais tonalite (Ossa-Morena Zone) Cum occur as euhedral to subhedral cores usually mantled by Hbl. Although seldom described in literature, Cum on Hospitais tonalite was interpreted as an igneous crystallizing early phase. As a consequence of the high water content of calc-alkaline magmas, the Fe-Mg amphibole should reflect the equation Opx+H2O = Cum+Mag+SiO2+H2 [8]. The similarity between Mg # on Cum and Hbl from tonalitic rocks suggests an equilibrium crystallizing assemblage as pointed by Wones and Gilbert [9] for a hypabyssal igneous suite. Considering that the Cum spectrum analyses from both occurrences exhibited a clear overlap; Carrascal gabbro-dorites (Mg#: 0.49-0.64; Al2O3: 0.7-2.37%; TiO2: 0.01-0.37%) and Hospitais tonalite (Mg#: 0.43-0.53; Al2O3: 1.22-2.44 %; TiO2; 0.05-0.27%), textural relations should be the main (only?) tool to decipher between igneous vs metamorphic growth. More detailed petrographic studies on plutonic rocks from Iberian Massif are needed to ascertain the petrogenetic significance of the association Cum-Hbl

Avaliação de serviços de ecossistema de conservação do solo associados a processos erosivos

Estudos recentes mostram a necessidade de incorporar os conceitos de serviços de ecossistema e de sistemas sócio-ecológicos nos processos de planeamento e gestão dos espaços naturais. Esta necessidade reflete não só a importância dos ecossistemas, e dos serviços que lhes estão associados, para o sucesso dos processos de planeamento, mas também a relevância da implementação de estudos interdisciplinares que acrescentem conhecimento na avaliação das interações entre Homem e Natureza. Neste contexto, foram desenvolvidos um conjunto de trabalhos que pretendem, em zonas bastante distintas em termos climáticos e de ocupação e gestão do solo (i.e. Alto‐Minho [NO de Portugal] e Portel [SE de Portugal]), mostrar a aplicação e a importância da avaliação de serviços de ecossistema para a condução dos processos de planeamento local, definição de estratégias de gestão da terra e definição de políticas de investimento e regulamentação das atividades em espaço rural. A utilização de técnicas de detecção remota, assim como de um modelo conceptual orientado à identificação e quantificação de serviços de ecossistema associados à proteção do solo,permitem-­‐nos inferir por um lado, quais as estratégias de gestão da terra mais adequadas à provisão deste serviço, identificando assim limiares de gestão adequados, e por outro, quais as necessidades de planeamento e regulamentação à escala regional. Sendo o solo o elemento central do desenvolvimento local e regional, os resultados obtidos evidenciam o valor dos serviços de ecossistema associados à proteção do solo e a necessidade de definir novos planos e estratégias de gestão da terra que contribuam para a mitigação dos riscos associados à erosão do solo não só à escala local, como à escala regional

Composição bromatológica de silagens de híbridos de sorgo cultivados em diferentes densidades de plantas.

Avaliou-se a composição bromatológica das silagens de dois híbridos de sorgo, AG-2005 (duplo propósito) e VOLUMAX (forrageiro), cultivados nos espaçamentos de 0,50; 0,75 e 1,00 m, resultando nas densidades de 140.000; 186.666 e 280.000 plantas por ha, respectivamente. A silagem do híbrido AG-2005 apresentou matéria seca (MS) superior no espaçamento de 1,00 m e foi mais elevada ao da silagem de VOLUMAX em todos os espaçamentos. A proteína bruta (PB) elevou-se com a redução dos espaçamentos (6,6; 6,8 e 8%, respectivamente), com maior valor médio no AG-2005 (7,7 vs 6,5%). A fibra em detergente neutro (FDN) foi menor no AG-2005 (59,25 vs 62,3%) e no espaçamento 0,75 m. Para fibra em detergente ácido (FDA) ocorreu diferença entre os dois híbridos no espaçamento 0,5 m, sendo de 33,5 e 39,3 %, respectivamente, para o AG-2005 e VOLUMAX. O EE apresentou diferença significativa (P < 0,05) entre os dois híbridos no espaçamento 0,75 m, sendo maior no AG-2005 (2,05 vs 1,61%). Conclui-se que o híbrido AG-2005 é mais recomendado para ensilagem, pois a sua silagem apresenta características qualitativas melhores que do VOLUMAX. O espaçamento de 0,5 m é o mais indicado no plantio dos híbridos, pois melhora a composição química das silagens. Chemical composition of silage sorghum hybrids grown at different densities. AbstractT - The objective of the experiment was to evaluate the nutritive value of silages from two sorghum hybrids, AG-2005 (double purpose) and VOLUMAX (forage) cultivated with different row spacings (0.50 m; 0.75 m and 1.00 m), resulting in 140,000; 186,666 e 280,000 plants per ha, respectively. Dry matter content of AG-2005 silage was higher for 1 m row spacing, and was higher than for VOLUMAX silage in all row spacings. Crude protein increased as the row spacing was reduced (6.6; 6.8 and 8%, respectively), with higher average value for AG-2005 (7.7 vs 6.5%). Neutral detergent fiber was lower for AG-2005 (59.25 vs 62.3%) and for .75 m spacing. Acid detergent fiber differed between hybrids in .5 m row spacing, being 33.5 and 39.3%, respectively, for AG-2005 and VOLUMAX. Ether extract was significantly different between hybrids in .5 m row spacing, being higher for AG-2005 (2.05 vs 1.61%). The use of AG-2005 is recommended for silage production due to its better qualitative characteristics than the VOLUMAX. The .5 m row spacing is recommended for both hybrids, since it improves the chemical composition of the silages

Geochemistry of the Rio Espinharas hybrid complex, northeastern Brazil

The Rio Espinharas pluton, northeastern Brazil, belongs to the shoshonitic series and consists mainly of syenogranite, quartz-monzonite and porphyritic quartz-monzonite, but diorite, quartz-monzodiorite, quartz-syenite and microsyenogranite also occur containing microgranular enclaves, except for the diorite. Most variation diagrams of rocks, amphiboles, biotites and allanites show linear trends, but K, Zr, Sr and Ba of rocks display curved scattered trends. The rocks ranging from diorite to syenogranite define a pseudo-errorchron and have similar REE patterns. Syenogranite and microsyenogranite are derived from two distinct pulses of granite magma with initial 87Sr/86Sr ratio of 0.7083±0.0003 and 0.7104±0.0007, respectively. Modelling of major and trace elements shows that the syenogranite evolved by fractional crystallization of plagioclase, microcline, edenite, biotite and titanite, whereas quartz-monzonite, porphyritic quartz-monzonite, quartz-monzodiorite and quartz-syenite resulted from simple mixing between an upper mantle-derived dioritic magma and the upper crust-derived syenogranite magma. Dioritic enclaves are globules of a mafic magma from the upper mantle.http://www.sciencedirect.com/science/article/B6V6J-46X86NR-5/1/0e5ce1dcc0c8fe91ebd680e6f2ac523