Hydrothermal fluid flow associated to the extensional evolution of the Adriatic rifted margin: Insights from the pre- to post-rift sedimentary sequence (SE Switzerland,N ITALY)

This paper investigates the hydrothermal fluid circulation that was linked to the extensional evolution of the Adriatic rifted margin during the Jurassic opening of the Alpine Tethys. Remnants of this rifted margin are spectacularly preserved in SE Switzerland and N Italy. Five study areas were chosen ranging from the former proximal to the most distal part of the margin. We demonstrate an intimate link between Jurassic extensional tectonics and fluid activity affecting the pre- to early post-rift sedimentary sequences. Nature, composition and origin of fluids are constrained by a multidisciplinary approach based on field observations and including geochemical (O-C, Sr, He isotopes, U-Pb datings, fluid inclusion microthermometry) and petrological methods. Several fluid-related diagenetic products and processes such as dolomitization, veining, hydraulic brecciation, and silicification can be recognized. It appears that different paleogeographic settings and different stratigraphic levels document distinct phases of fluid activity. The fluids reached temperatures of up to 150°C near paleo-seafloor. They were enriched in ¹⁸O, had high ⁸⁷Sr/⁸⁶Sr and low ³He/⁴He ratios, documenting a strong interaction between seawater and a granitic basement. Many lines of evidence point to the occurrence of over-pressured fluids and long-lasting fluid circulation due to fault-valve mechanisms and high thermal gradients. Two main stages with different fluid chemistry can be recognized: (1) a carbonate-rich stage that developed during the stretching phases and was linked to high-angle normal faulting, and (2) a silica-rich stage occurring during late rift exhumation of crustal and mantle rocks in the distal domains in the presence of detachment faults and high thermal gradients. This paper provides, for the first time, a large and robust characterization of fluid–rock interactions occurring during rifting along an almost complete section across a magma-poor rifted margin.     

Reinterpretation of Tractus Fossae region as an asymmetric rift system on Mars

The Tractus Fossae region of Mars is a wide area dominated by grabens, normal faults and pit crater chains. In this work, based on previous studies on the area and the new interpretation of topographic data and morphological units based on images as a geologic framework we present a new insight on the origin of the graben structures as well as on the processes associated with the formation of the volcanic features. Here we propose a new model for this region, on the basis of new measurements of graben extension and geological interpretations, together with a reinterpretation of the stratigraphy and the geologic history of the area. Finally, it is postulated that this region underwent a tectonic regime analog to an asymmetric rift system on Earth.     

Geochemistry and petrology of the jequie granulitic complex (Brazil): an archean basement complex

The Jequie granulitic complex is part of the extensive high-grade metamorphic terrain located within the Sao Francisco craton of northeastern Brazil. Some Jequie rocks appear to have been formed in the middle Archean ( 3.1 Ga) from preexisting sialic crust. The dominant mineral composition of these rocks is quartz-microcline-plagioclase-hyperstene and occurs over an extensive area ( 2,000 km²).Scattered enrichment of normal granites with many minor elements (e.g. Rb, Y, Zr, Nb, Ba, REE), and the non-depletion of other elements (e.g. Cs, U), normally considered mobile during granulite facies metamorphism, must lead either to the reconsideration of regional metasomatism subsequent to granulite facies metamorphism, or at least raise some doubts about common wisdom concerning the distribution of heat-producing elements at depth. The region includes large-scale thrust structures, which could play a part in influencing high-level emplacement of the rocks and their regional metasomatism and structures.     

Phytoplankton community in the tropical lake of Lagoa Santa (Brazil): Conditions favoring a persistent bloom of Cylindrospermopsis raciborskii

This study presents data on seasonal changes of the phytoplanktonic community of a small tropical lake, Lagoa Santa, in the Brazilian cerrado. Temporal variation in the community structure was small and we observed a permanent dominance of the cyanobacteria Cylindrospermopsis raciborskii. This dominance could be associated to the stability of several environmental conditions. Especially water temperature, always within the optimal growth range for C. raciborskii, and the constant mixed water column may have been important factors driving to the long term dominance of this species in the lake. Remarkable seasonal variation in rainfall, as well as the occasional and non-seasonal variation in nutrient concentrations, were important to explain changes in environmental and biological variables, but were not related to the dominance of C. raciborskii. Pearson's correlation and PCA could just in part explain the stable dominance of this cyanobacterium. Meteorological and chemical factors seem to have no clear control on the variability of the phytoplankton dynamics in Lagoa Santa. The weak relationship between C. raciborskii abundance and environmental variables points to additional intrinsic factors associated to this species that may be important in structuring the phytoplankton assemblage.     

Timeline analysis and wavelet multiscale analysis of the AKARI All-Sky Survey at 90 μm

We present a careful analysis of the point-source detection limit of the AKARI All-Sky Survey in the WIDE-S 90-μm band near the North Ecliptic Pole (NEP). Timeline analysis is used to detect IRAS ( Infrared Astronomy Satellite ) sources and then a conversion factor is derived to transform the peak timeline signal to the interpolated 90-μm flux of a source. Combined with a robust noise measurement, the point-source flux detection limit at signal-to-noise ratio  (S/N) > 5  for a single detector row is  1.1 ± 0.1 Jy  which corresponds to a point-source detection limit of the survey of ∼0.4 Jy.
Wavelet transform offers a multiscale representation of the Time Series Data ( tsd ). We calculate the continuous wavelet transform of the tsd and then search for significant wavelet coefficients considered as potential source detections. To discriminate real sources from spurious or moving objects, only sources with confirmation are selected. In our multiscale analysis, IRAS sources selected above 4σ can be identified as the only real sources at the Point Source Scales. We also investigate the correlation between the non- IRAS sources detected in timeline analysis and cirrus emission using wavelet transform and contour plots of wavelet power spectrum. It is shown that the non- IRAS sources are most likely to be caused by excessive noise over a large range of spatial scales rather than real extended structures such as cirrus clouds.