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SHRIMP U-Pb and U-Pb Laser Ablation Geochronological on Zircons from Monte Santo Alkaline Intrusive Suite, Westhern Araguaia Belt, tocantins State, Brazil

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Journal of Geoscience and Environment Protection 2014年第3期2卷 170-180页

作者： Rúbia Ribeiro Viana Gislaine Amorés Battilani Department of Mineral Resource Federal University of Mato Grosso Cuiabá Brazil

The Monte Santo Alkaline Intrusive Suite (MSAIS) is an association syenite foid, nepheline syenite and syenite, which are intruded in metapelites of the Rio do Coco meta-volcanic-sedimentary Sequence, presenting abundant pegmathoid veins cutting all of them. The ages obtained by Shrimp (1051 ± 22 Ma, 1048 ± 11 Ma) are very close those younger age obtained by U-Pb laser ablation (1056 ± 21), beeing interpreted as crystallization age. These dating reveal also that MSAIS rocks were affected by common succession of younger events below 550 Ma ago, responsible by the later rocky bodies of varying composition occurring in the region, including the alkaline pegmatites hosted in the nepheline syenite of the MSAIS.

关键词： Alkaline Rocks Shrimp Dating tocantins Structural Province Neoproterozoic Brazil

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Geochemistry and Petrography of Alkaline rocks from Monte Santo Alkaline Intrusive Suite, Western Araguaia Belt, tocantins State, Brazil

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Journal of Geoscience and Environment Protection 2014年第3期2卷 72-79页

作者： Rúbia Ribeiro Viana Gislaine Amorés Battilani Department of Mineral Resource Federal University of Mato Grosso Cuiabá Brazil

The Monte Santo Alkaline Intrusive Suite (MSAIS) is an association syenite foid, nepheline syenite and syenite. The MSAIS rocks are intruded in metapelites of the Rio do Coco meta-volcanic-sedi- mentary Sequence and are abundant pegmathoid veins cutting all of them. The mineral paragenesis is represented by aegirina, arfvedsonite, albite and nepheline, crystallized during the initial phase of crystallization. A late magmatic phase show nepheline, perthite, calcite and biotite, and a hydrothermal phase allowed for the formation of cancrinite, sodalite, analcime and natrolita associated with altered nepheline. The geochemical analyses showed metaluminous and medium to high potassium characteristics, being classified as miaskitic rocks, according to agpaicity and the Na + K > 1/6Si indexes. However, the mineralogical assemblage suggests a low to medium agpaitic composition, which can be related to a transition from miaskitic to agpaitic crystallization regime. The rare earth elements showed depletion in heavy rare earth and a strong negative Eu anomaly and enrichments in the some lithophile elements, suggesting a differentiated pattern later, which can be associated to metasomatic alterations.

关键词： Alkaline Rocks tocantins Structural Province Brazil

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Ichthyological Overview and Remarks on Freshwater Fishes from Capim River, Lower Amazon Basin, Brazil

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Open Journal of Ecology 2014年第13期4卷 797-806页

作者： Júlio Cesar Garavello Alexandre Kannebley de Oliveira Department of Ecology and Evolutive Biology Federal University of Sao Carlos Sao Carlos Brazil Department of Environmental Sciences Federal University of Sao Carlos Sao Carlos Brazil

The Capim River drainage should be considered small and thin by comparison with large Amazonian rivers. It rises by confluence of the Surubiú and Ararandeua rivers near 400 m high and their headwaters would be comfortably included in the Dry Emerged Lowland (terra firme) forest area of Sternberg’s Amazonian concept. Because of this reason the freshwater fish fauna of Capim River is comprised mainly by Amazonian fish families found in tributaries also with origin in terra firme areas. The ichthyofauna from the main channel of the poorly sampled Capim River, in the stretch between its confluence with Tauarí River and its mouth at Guamá River, is herein reported by way of rapid assessment. Also broad comparisons were made among freshwater fishes of the Capim with that from tocantins and Guamá rivers. Two rapid access research surveys of collecting ichthyological material were performed in dry and humid periods of the year 1998 comprising the regional hydrologic cycle. The ichthyological diversity showed by the 461 studied specimens includes 79 species probably derived from Guamá and tocantins rivers. These species are distributed between two situations: 1) downstream Capim River, at confluence with Guamá River, where is under tidal waters influence and periodically flooded, and 2) upriver Capim that is less humid and with water rapids, independent from sea hydrologic influence. This fish fauna includes local species common at high areas of the Amazonian Dry Emerged Lowland that are in part shared with that from tocantins River. In view of these observations, we assume that the Capim River freshwater ichthyofauna may reflect diverse origin from the simple transfer of populations from Guamá River, but originate through a more complex process including the past ichthyofauna of the earlier drainages of terra firme forest and their reorganization.

关键词： Neotropical Ichthyofauna Biodiversity tocantins Amazon

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