Crustal Source for a Syenite Complex in the High-grade Eastern Ghats Belt, India: Sm-Nd Isotopic Evidence

Several plutonic alkaline complexes have been reported from the high-grade Eastern Ghats belt, India and these are thought to have been derived from the mantle. The field features of the syenite complex around Rairakhol in Orissa indicate progressive deformation during emplacement and could be related to the latest deformation/folding in the host granulitic country rocks. Presence of some mafic granulite xenoliths could suggest a crustal source for this syenite complex.Negative epsilon value is a strong indication of crustal source. The long crustal residence ages and ¹⁴³Nd/¹⁴⁴Nd values less than 0.5120, definitely indicate a crustal source.     

Summer sea surface temperature fronts and elevated chlorophyll-a in the entrance to Spencer Gulf,South Australia

Historical and recent oceanographic cruise data, MODIS chlorophyll-a satellite data, and an analytical model are used to examine SST fronts in the entrance to Spencer Gulf, South Australia. The fronts (2–3 °C) due to the contrast between warm Spencer Gulf waters and cooler waters of the continental shelf are readily observable on satellite imagery. Three water masses: cool, fresh upwelled shelf water; warm, salty Great Australian Bight water; and very warm and salty Spencer Gulf bottom water occupy the area. In consequence a summer density minimum is formed at the entrance to Spencer Gulf. The analytical model predicts that this thermohaline structure sets up an ageostrophic circulation, which favours upwelling in the central portion of the entrance. This is confirmed by the satellite data which show an increased chlorophyll-a concentration in the vicinity of the upwelling.     

A review of the tectonic evolution of the Sunsás belt,SW Amazonian Craton

The Sunsás–Aguapeí province (1.20–0.95 Ga), SW Amazonian Craton, is a key area to study the heterogeneous effects of collisional events with Laurentia, which shows evidence of the Grenvillian and Sunsás orogens. The Sunsás orogen, characterized by an allochthonous collisional-type belt (1.11–1.00 Ga), is the youngest and southwesternmost of the events recorded along the cratonic fringe. Its evolution occurred after a period of long quiescence and erosion of the already cratonized provinces (>1.30 Ga), that led to sedimentation of the Sunsás and Vibosi groups in a passive margin setting. The passive margin stage was roughly contemporary with intraplate tectonics that produced the Nova Brasilândia proto-oceanic basin (<1.21 Ga), the reactivation of the Ji-Paraná shear zone network (1.18–1.12 Ga) and a system of aborted rifts that evolved to the Huanchaca–Aguapeí basin (1.17–1.15 Ga). The Sunsás belt is comprised by the metamorphosed Sunsás and Vibosi sequences, the Rincón del Tigre mafic–ultramafic sill and granitic intrusive suites. The latter rocks yield ε_Nd(t) signatures (?0.5 to ?4.5) and geochemistry (S, I, A-types) suggesting their origin associated with a continental arc setting. The Sunsás belt evolution is marked by “tectonic fronts” with sinistral offsets that was active from c. 1.08 to 1.05 Ga, along the southern edge of the Paraguá microcontinent where K/Ar ages (1.27–1.34 Ga) and the Huanchaca–Aguapeí flat-lying cover attest to the earliest tectonic stability at the time of the orogen. The Sunsás dynamics is coeval with inboard crustal shortening, transpression and magmatism in the Nova Brasilândia belt (1.13–1.00 Ga). Conversely, the Aguapeí aulacogen (0.96–0.91 Ga) and nearby shear zones (0.93–0.91 Ga) are the late tectonic offshoots over the cratonic margin. The post-tectonic to anorogenic stages took place after ca. 1.00 Ga, evidenced by the occurrences of intra-plate A-type granites, pegmatites, mafic dikes and sills, as well as of graben basins. Integrated interpretation of the available data related to the Sunsás orogen supports the idea that the main nucleus of Rodinia incorporated the terrains forming the SW corner of Amazonia and most of the Grenvillian margin, as a result of two independent collisional events, as indicated in the Amazon region by the Ji-Paraná shear zone event and the Sunsás belt, respectively.     

Contribution to the ground-based follow-up of the Gaia space mission

The Gaia Space Mission [Mignard, F., 2005. The three-dimensional universe with Gaia. ESA/SP-576; Perryman, M., 2005. The three-dimensional universe with Gaia. ESA/SP-576] will observe several transient events as supernovae, microlensing, gamma ray bursts and new Solar System objects. The satellite, due to its scanning law, will detect these events but will not be able to monitor them. So, to take these events into consideration and to perform further studies it is necessary to follow them with Earth-based observations. These observations could be efficiently done by a ground-based network of well-equipped telescopes scattered in both hemispheres.Here we focus our attention at the new Solar System objects to be discovered and observed by the Gaia satellite [Mignard, F., 2002. Observations of Solar System objects by Gaia I. Detection of NEOS. Astron. Astrophys. 393, 727] mainly asteroids, NEOs and comets. A dedicated ground-based network of telescopes as proposed by Thuillot [2005. The three-dimensional universe with Gaia. ESA/SP-576] will allow to monitor those events, to avoid losing them and to perform a quick characterization of some physical properties which will be important for the identification of these objects in further measurements by Gaia.We present in this paper, the beginning of the organization of a Latin-American ground-based network of telescopes and observers joining several institutions in Argentina, Bolivia, Brazil and other Latin-American countries aiming to contribute to the follow-up of Gaia science alerts for Solar System objects.     

Assessing coastal benthic macrofauna community condition using best professional judgement - Developing consensus across North America and Europe

Benthic indices are typically developed independently by habitat, making their incorporation into large geographic scale assessments potentially problematic because of scaling inequities. A potential solution is to establish common scaling using expert best professional judgment (BPJ). To test if experts from different geographies agree on condition assessment, sixteen experts from four regions in USA and Europe were provided species-abundance data for twelve sites per region. They ranked samples from best to worst condition and classified samples into four condition (quality) categories. Site rankings were highly correlated among experts, regardless of whether they were assessing samples from their home region. There was also good agreement on condition category, though agreement was better for samples at extremes of the disturbance gradient. The absence of regional bias suggests that expert judgment is a viable means for establishing a uniform scale to calibrate indices consistently across geographic regions.     

A SIMPLE DEVICE TO MONITOR SEDIMENT YIELD FROM GULLY EROSION

1INTRODUCTION Gully erosion has been investigated by many researchers throughout the world.Their studies have focused on how the process evolves and on a better understanding of the sub-processes that take place in gully erosion(Small and Clark,1982;Morgan,1986;Hasset and Banwart,1992;Boardman and Favis-Mortlock,1993;Selby,1993;Goudie and Viles,1997;Guerra and Favis-Mortlock,1998;Favis-Mortlock and Guerra,1999,2000;Figueiredo,2003;Garcia and Guerra,2003).Soil properties,rainfall re…     

Mafic dykes at the southwestern margin of Eastern Ghats belt: Evidence of rifting and collision

The southwestern margin of the Eastern Ghats Belt characteristically exposes mafic dykes intruding massif-type charnockites. Dykes of olivine basalt of alkaline composition have characteristic trace element signatures comparable with Ocean Island Basalt (OIB). Most importantly strong positive Nb anomaly and low values of Zr/Nb ratio are consistent with OIB source of the mafic dykes. K-Ar isotopic data indicate two cooling ages at 740 and 530 Ma. The Pan-African thermal event could be related to reactivation of major shear zones and represented by leuco-granite vein along minor shear bands. And 740 Ma cooling age may indicate the low grade metamorphic imprints, noted in some of the dykes. Although no intrusion age could be determined from the present dataset, it could be constrained by some age data of the host charnockite gneiss and Alkaline rocks of the adjacent Prakasam Province. Assuming an intrusion age of ∼1.3Ga, Sr-Nd isotopic composition of the dykes indicate that they preserved time-integrated LREE enrichment. In view of the chemical signatures of OIB source, the mafic dykes could as well be related to continental rifting, around 1.3Ga, which may have been initiated by intra-plate volcanism.     

A GCSS Boundary-Layer Cloud Model Intercomparison Study Of The First Astex Lagrangian Experiment

Three single-column models (all with an explicit liquid water budget and compara-tively high vertical resolution) and three two-dimensional eddy-resolving models (including one with bin-resolved microphysics) are compared with observations from the first ASTEX Lagrangian experiment. This intercomparison was a part of the second GCSS boundary-layer cloud modelling workshop in August 1995.In the air column tracked during the first ASTEX Lagrangian experiment, a shallow subtropical drizzling stratocumulus-capped marine boundary layer deepens after two days into a cumulus capped boundary layer with patchy stratocumulus. The models are forced with time varying boundary conditions at the sea-surface and the capping inversion to simulate the changing environment of the air column.The models all predict the observed deepening and decoupling of the boundary layer quite well, with cumulus cloud evolution and thinning of the overlying stratocumulus. Thus these models all appear capable of predicting transitions between cloud and boundary-layer types with some skill. The models also produce realistic drizzle rates, but there are substantial quantitative differences in the cloud cover and liquid water path between models. The differences between the eddy-resolving model results are nearly as large as between the single column model results. The eddy resolving models give a more detailed picture of the boundary-layer evolution than the single-column models, but are still sensitive to the choice of microphysical and radiative parameterizations, sub-grid-scale turbulence models, and probably model resolution and dimensionality. One important example of the differences seen in these parameterizations is the absorption of solar radiation in a specified cloud layer, which varied by a factor of four between the model radiation parameterizations.