The complex impact structure Serra da Cangalha, Tocantins State, Brazil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Serra da Cangalha is a complex impact structure with a crater diameter of 13,700 m and a central uplift diameter of 5800 m. New findings of shatter cones, planar fractures, feather features, and possible planar deformation features are presented. Several ring-like features that are visible on remote sensing imagery are caused by selective erosion of tilted strata. The target at Serra da Cangalha is composed of Devonian to Permian sedimentary rocks, mainly sandstones that are interlayered with siltstone and claystones. NNE-SSW and WNW-ESE-striking joint sets were present prior to the impact and also overprinted the structure after its formation. As preferred zones of weakness, these joint sets partly controlled the shape of the outer perimeter of the structure and, in particular, affected the deformation within the central uplift. Joints in radial orientation to the impact center did not undergo a change in orientation during tilting of strata when the central uplift was formed. These planes were used as major displacement zones. The asymmetry of the central uplift, with preferred overturning of strata in the northern to western sector, may suggest a moderately oblique impact from a southerly direction. Buckle folding of tilted strata, as well as strata overturning, indicates that the central uplift became gravitationally unstable at the end of crater formation.466875889German Research Foundation (DFG) [Re 528/9-1, Re 528/11-1]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Ph.D. grantGerman Academic Exchange Service (DAAD)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)German Research Foundation (DFG) [Re 528/9-1, Re 528/11-1]FAPESP [2008/53588-7]CNPq [30334/2009-0

The impacts of climate change on the winter water cycle of the western Himalaya

Some 180 million people depend on the Indus River as a key water resource, fed largely by precipitation falling over the western Himalaya. However, the projected response of western Himalayan precipitation to climate change is currently not well constrained: CMIP5 GCMs project a reduced frequency and vorticity of synoptic-scale systems impacting the area, but such systems would exist in a considerably moister atmosphere. In this study, a convection-permitting (4 km horizontal resolution) setup of the Weather Research and Forecasting (WRF) model is used to examine 40 cases of these synoptic-scale systems, known as western disturbances (WDs), as they interact with the western Himalaya. In addition to a present-day control run, three experiments are performed by perturbing the boundary and initial conditions to reflect pre-industrial, RCP4.5 and RCP8.5 background climates respectively. It is found that in spite of the weakening intensity of WDs, net precipitation associated with them in future climate scenarios increases significantly; conversely there is no net change in precipitation between the pre-industrial and control experiments despite a significant conversion of snowfall in the pre-industrial experiment to rainfall in the control experiment, consistent with the changes seen in historical observations. This shift from snowfall to rainfall has profound consequences on water resource management in the Indus Valley, where irrigation is dependent on spring meltwater. Flux decomposition shows that the increase in future precipitation follows directly from the projected moistening of the tropical atmosphere (which increases the moisture flux incident on the western Himalaya by 28%) overpowering the weakened dynamics (which decreases it by 20%). Changes to extreme rainfall events are also examined: it is found that such events may increase significantly in frequency in both future scenarios examined. Two-hour maxima rainfall events that currently occur in 1-in-8 WDs are projected to increase tenfold in frequency in the RCP8.5 scenario; more prolonged (one-week maxima) events are projected to increase fiftyfold

Impact Craters In South America

5199699

GEOLOGICAL MAPPING USING LANDSAT THEMATIC MAPPER IMAGERY IN ALMERIA PROVINCE, SOUTHEAST SPAIN

10350551

Hydrothermal alteration mapping at Bodie, California, using AVIRIS hyperspectral data

AVIRIS data covering the Bodie and neighboring Paramount mining districts, eastern California, were used to map hydrothermal alteration minerals. Two spectral analysis algorithms were used: Spectral Angle Mapper (SAM) and Tricorder. The objective was to compare the performance of the two algorithms where no a priori ground or atmospheric information is available. AVIRIS data were calibrated to apparent surface reflectance using a modified MODTRAN radiative transfer model in conjunction with laboratory and in-flight calibration data. Both algorithms appear to produce satisfactory results for geologic reconnaissance and mapping applications, but Tricorder generally classified more pixels and identified more mineral species than SAM. For some minerals, such as Na-montmorillonite, results from Tricorder and SAM matched reasonably well, but major differences appeared in how to two algorithms classified kaolinite group minerals and ferric oxides. Laboratory spectra of rock samples from five localities were compared to reference spectra of minerals identified by the classification algorithms for corresponding pixels, with the results matching to some extent. (C)Elsevier Science Inc., 199865330931

The role of airborne geophysics for detecting hydrocarbon microseepages and related structural features: The case of Remanso do Fogo, Brazil

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)The first direct indication of hydrocarbon occurrence in Remanso do Fogo area (Minas Gerais State, Brazil) was the existence of microseepages. However. Quaternary sedimentary cover in the area made the identification of new occurrences and associated controlling structures quite difficult. This study investigated the spatial distribution of hydrocarbon related gases in shallower to intrasedimentary depths in Remanso do Fogo area, using airborne gamma-ray spectrometry and magnetic data. The geophysical data were processed using techniques designed to suppress the influence of regional geological signatures. Known and possible new occurrences of microseepages were detected by mapping low residual potassium values and high uranium residual values in relation to potassium, termed as DRAD values, which resulted from the subtraction of potassium from uranium residual values, using a Thorium (Th)-normalizing approach. The validation of these occurrences was done based on. existing gas geochemistry data in the soil. For the magnetic data, the amplitude of the analytic signal, combined with the total horizontal gradient of the subtraction between the 1200- and 400-meter upward continuations, enhanced the northwest- southeast and east west magnetic lineaments, which are partially related to the microseepages and the drainage of the area. The distinction of near-surface and deep signatures also allowed the general identification of intrasedimentary and basement structures, which are potentially controlling the occurrences of seepages in the area.772B35B41Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Targeting key alteration minerals in epithermal deposits in Patagonia, Argentina, using ASTER imagery and principal component analysis

Principal component analysis (PCA) is an image processing technique that has been commonly applied to Landsat Thematic Mapper (TM) data to locate hydrothermal alteration zones related to metallic deposits. With the advent of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), a 14-band multispectral sensor operating onboard the Earth Observation System (EOS)-Terra satellite, the availability of spectral information in the shortwave infrared (SWIR) portion of the electromagnetic spectrum has been greatly increased. This allows detailed spectral characterization of surface targets, particularly of those belonging to the groups of minerals with diagnostic spectral features in this wavelength range, including phyllosilicates ('clay' minerals), sulphates and carbonates, among others. In this study, PCA was applied to ASTER bands covering the SWIR with the objective of mapping the occurrence of mineral endmembers related to an epithermal gold prospect in Patagonia, Argentina. The results illustrate ASTER's ability to provide information on alteration minerals which are valuable for mineral exploration activities and support the role of PCA as a very effective and robust image processing technique for that purpose.24214233424

The first description and confirmation of the Vista Alegre impact structure in the Parana flood basalts of southern Brazil

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)The Vista Alegre structure, centered at 25 degrees 57'S and 52 degrees 41'W, has been recently proposed as a meteorite impact structure. The 9.5 km-diameter structure is located in the Parana state of southern Brazil, within the Parana Basin, which contains one of the largest and most extensive flood basalt provinces on Earth. The Parana flood basalts belong to the Serra Geral Formation and are temporally related to the opening of the South Atlantic Ocean, having been dated at about 133-132 Ma. Tholeiitic basalts dominate the western portion of Parana state, with some minor rhyodacites. Morphologically, Vista Alegre has a prominent circular outline, in the form of an incomplete ring of escarpments, and an inner depression. The presence of a central uplift is not obvious, but it is inferred by the occurrence of deformed sandstone blocks near the center of the structure. These sandstones are possibly related to the Triassic Piramboia Formation and/or to the Cretaceous Botucatu Formation. These units are normally at stratigraphic depths of about 700-800 m below the present surface in this portion of the Parana Basin. The structure appears to be in an advanced erosion stage and its interior is occupied by a soil cover several meters thick, extensively used for agriculture. As a result there are limited outcrops in the interior of the structure, all of polymict breccias, some of them melt-bearing. We report the extensive occurrence of shatter cones, in the form of fine-grained rock clasts within the polymict breccias. The shatter cone-bearing breccias occur at different locations within the structure, separated by several kilometers. The nested shatter cones range in size from about 0.5 to 20 cm for individual cones, and up to half a meter for complete assemblages. The shatter cones formed in fine-grained Parana flood basalt and might be the first examples of shatter cones in such a rock type. In addition, planar deformation features (PDFs) were found in quartz grains within sedimentary rock clasts of the polymict breccia. These findings confirm the impact origin of the Vista Alegre structure.452181194Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)University of ViennaConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPq [306829/2006-1

Reconnaissance geologic mapping in the Tapajos mineral Province, Brazilian Amazon, using spaceborne SAR imagery and airborne geophysics

The Tapajos Mineral Province lies within the Amazonian Craton, northern Brazil, and stands as one of the largest gold-producing provinces of the country. The geology; mapped at 1:250,000 scale, comprises Archean to Phanerozoic rocks, where numerous gold-rich placers of Quaternary alluvium provenance have been exploited and a few primary, deposits are known. No large primary deposit has been discovered thus far in the region. Spaceborne radar imagery (RADARSAT-1 and JERS-1) and airborne geophysics (magnetic and gamma-ray) surveys were used to produce a more complete geological map of a portion of the province and to provide guidelines for targeting potential primary gold mineralization. SAR imagery provided valuable textural information, related to bedrock geology; as well as structural information. Thorium and potassium gamma-ray data were most useful in the identification of lithologic units, allowing the recognition of distinct domains within the basement. Aeromagnetic data helped delineate regional structures. An integrated analysis and interpretation of these datasets allowed the definition of previously unrevealed lithologic domains within the basement, one of which encompasses most of the known primary and placer gold deposits. Furthermore, brittle structures interpreted from SAR and aeromagnetic data showed a spatial correlation with reported primary gold occurrences. These findings, obtained for a small portion of the Tapajos Province, demonstrate the importance of the synergistic use of spaceborne SAR and airborne geophysics for geologic mapping and mineral exploration activities in the entire province and elsewhere in the Amazon, where the geology is poorly known and the mineral potential is high.27666967