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1

Synsedimentary deformation and thrusting on the eatern margin of the Barberton Greenstone belt, Swaziland  

NASA Astrophysics Data System (ADS)

Mapping on the eastern margin of the 3.6 to 3.3 Ga Barberton Greenstone Belt NW Swaziland has revealed a tectonic complex which is more than 5 km thick. The area consists of fault bound units made up of three lithological associations. Some of these were affected by four phases of deformation. Fold structures, foliations, and lineations are associated with the deformation. Sedimentation, geological structures, and evolutionary history of the area are explained.

Lamb, S. H.

2

Accretionary history of the Archean Barberton Greenstone Belt (3.55-3.22 Ga), southern Africa  

NASA Technical Reports Server (NTRS)

The 3.55-3.22 Ga Barberton Greenstone Belt, South Africa and Swaziland, and surrounding coeval plutons can be divided into four tectono-stratigraphic blocks that become younger toward the northwest. Each block formed through early mafic to ultramafic volcanism (Onverwacht Group), probably in oceanic extensional, island, or plateau settings. Volcanism was followed by magmatic quiescence and deposition of fine-grained sediments, possibly in an intraplate setting. Late evolution involved underplating of the mafic crust by tonalitic intrusions along a subduction-related magmatic arc, yielding a thickened, buoyant protocontinental block. The growth of larger continental domains occurred both through magmatic accretion, as new protocontinental blocks developed along the margins of older blocks, and when previously separate blocks were amalgamated through tectonic accretion. Evolution of the Barberton Belt may reflect an Early Archean plate tectonic cycle that characterized a world with few or no large, stabilized blocks of sialic crust.

Lowe, D. R.

1994-01-01

3

Accretionary history of the Archean Barberton Greenstone Belt (3.55-3.22 Ga), southern Africa  

NASA Astrophysics Data System (ADS)

The 3.55-3.22 Ga Barberton Greenstone Belt, South Africa and Swaziland, and surrounding coeval plutons can be divided into four tectono-stratigraphic blocks that become younger toward the north west. Each block formed through early mafic to ultramafic volcanism (Onverwacht Group), probably in oceanic extensional, island, or plateau settings. Volcanism was followed by magmatic quiescence and deposition of fine-grained sediments, possibly in an intraplate setting. Late evolution involved underplating of the mafic rust by tonalitic intrusions along a subduction-related magmatic arc, yielding a thickened, buoyant protocontinental block. The growth of larger continental domains occurred both through magmatic accretion, as new protocontinental blocks developed along the margins of older blocks, and when previously separate blocks were amalgamated through tectonic accretion. Evolution of the Barber-ton Belt may reflect an Early Archean plate tectonic cycle that characterized a world with few or no large, stabilized blocks of sialic crust.

Lowe, Donald R.

1994-12-01

4

Single zircon dating constraining the maximum age of the Barberton Greenstone Belt, southern Africa  

NASA Astrophysics Data System (ADS)

One of the central issues in early Precambrian crustal evolution is the age and genetic relationship between greenstone belt supracrustal assemblages and nearby high-grade gneiss terranes. The crucial question, in most cases, is which of the two is older. We report zircon ages, using the new single grain evaporation technique, from a metaquartzite and a felsic volcanic flow of the Onverwacht Group in the Barberton greenstone belt (BGB), South Africa and Swaziland, that constrain the age of this basal part of the greenstone sequence between 3451 ± 15 and 3438 ± 6 Ma. This is almost 100 Ma younger than previous age estimates assigned to the Onverwacht and agrees well with recent Sm-Nd, Pb-Pb and zircon ion-microprobe dating. Tonalitic orthogneisses of the Ancient Gneiss Complex (AGC) adjacent to the BGB have ages up to 3644 ± 4 Ma and are thus demonstrably older than the greenstones; also, they cannot be derived from them by partial melting as has been proposed previously. This age relationship as well as the presence of metaquartzites and thrust slices of pregreenstone tonalite in the Onverwacht tectonic sequence rule out an entirely oceanic evolution for the early history of the BGB and suggest that continental crust was either below or nearby.

KröNer, Alfred; Todt, Wolfgang

1988-12-01

5

Growth of early archaean crust in the ancient Gneiss complex of Swaziland and adjacent Barberton Greenstone Belt, Southern Africa  

NASA Technical Reports Server (NTRS)

The relationship between early Archean greenstones and high grade gneisses in the Ancient Gneiss Complex of Swaziland and the neighboring Barberton greenstone belt in Southern Africa is discussed. New high precision zircon analyses reveal a complex history in individual zircons from tonalitic orthogneisses, with ages as old as 3644 + 4 Ma. This suggests the presence of continental crust prior to the formation of the supracrustal rocks of the Barberton greenstone belt, which have been previously considered the earliest rocks in the area. The author suggested that these data are incompatible with the intraoceanic settings that have been widely accepted for this terrane, and favors either a marginal basin or rift environment. By using the detailed age information obtained from zircons in combination with Ar-40 and Ar-39 and paleomagnetic measurements, the author estimated that plate velocities for this part of Africa craton were about 10 to 70 mm/yr, during the period 3.4 to 2.5 Ga. This is not incompatible with the idea that Archean plate velocities may have been similiar to those of today.

Kroener, A.; Compston, W.; Tegtmeyer, A.; Milisenda, C.; Liew, T. C.

1988-01-01

6

Growth of early archaean crust in the ancient Gneiss complex of Swaziland and adjacent Barberton Greenstone Belt, Southern Africa  

NASA Astrophysics Data System (ADS)

The relationship between early Archean greenstones and high grade gneisses in the Ancient Gneiss Complex of Swaziland and the neighboring Barberton greenstone belt in Southern Africa is discussed. New high precision zircon analyses reveal a complex history in individual zircons from tonalitic orthogneisses, with ages as old as 3644 + 4 Ma. This suggests the presence of continental crust prior to the formation of the supracrustal rocks of the Barberton greenstone belt, which have been previously considered the earliest rocks in the area. The author suggested that these data are incompatible with the intraoceanic settings that have been widely accepted for this terrane, and favors either a marginal basin or rift environment. By using the detailed age information obtained from zircons in combination with Ar-40 and Ar-39 and paleomagnetic measurements, the author estimated that plate velocities for this part of Africa craton were about 10 to 70 mm/yr, during the period 3.4 to 2.5 Ga. This is not incompatible with the idea that Archean plate velocities may have been similiar to those of today.

Kroener, A.; Compston, W.; Tegtmeyer, A.; Milisenda, C.; Liew, T. C.

7

Palaeoarchean Barite Deposits in the Barberton Greenstone Belt: Origin and Links to Early Microbial Life  

NASA Astrophysics Data System (ADS)

Barite deposits are considered important for identifying microbial S cycling in Archean rocks since they can provide information about S isotopes in coexisting sulfate and sulfide minerals. However the degree to which barite and pyrite in metasedimentary rocks are related remains unclear. In this study we have investigated the origin of barite and pyrite in four main horizons seen in both outcrop and fresh drill core material from the Lower Mapepe formation (3.26 to 3.23 Ga), Barberton Greenstone Belt, South Africa. Host rocks include shales, cherts, tuffs and conglomerates that are variably silicified and/or affected by carbonate alteration. The high-energy depositional environment of the host rocks, mineralogical textures, barite chemistry and the occurrence of feldspars from the rarely-found celsian-hyalophane-orthoclase series suggest a seafloor exhalative origin for the barite. In contrast pyrite is closely associated with cherts and dolomitic units where rare earth element and Y data support a marine influence. Pyrite chemistry (Co/Ni= 0.1-1, Se/S <5 x 10- 5) also indicates a low temperature sedimentary origin. Multiple S isotope data (32S, 33S, 34S, determined by SIMS) for pyrite indicates a number of arrays with limited ?34S fractionation at constant ?33S associated with individual syn-sedimentary microcrystalline pyrite layers. Isolated euhedral pyrites in massive chert and barite rich units show much more scatter and larger degrees of ?33S variation (-1 to +4 ). Our results are consistent with models invoking microbial mass dependent fractionation of a heterogeneous elemental sulfur source derived from atmospheric photolysis. The sulfate reservoir can also be linked to photolysis but there is no clear relationship between the barite and pyrite S isotope data, suggesting that microbial (or abiotic) sulfate reduction was absent at this time or that the basinal sulfate concentration must have remained significantly lower than the mM level prior to barite precipitation.

Mason, P. R.; Peters, A.; Nijman, W.; Reimer, T. O.; Whitehouse, M. J.

2008-12-01

8

Thermal history of the 3.5 3.2 Ga Onverwacht and Fig Tree Groups, Barberton greenstone belt, South Africa, inferred by Raman microspectroscopy of carbonaceous material  

Microsoft Academic Search

Raman spectra of carbonaceous material were collected in situ from samples of cherts of the Onverwacht and Fig Tree Groups in the central Barberton greenstone belt. The spectra feature two dominant peaks characteristic of disordered carbon: the D peak at ˜1310 cm-1 and the O peak at 1580 1600 cm-1. D peak positions and relative peak intensities and areas indicate

Michael M. Tice; Benjamin C. Bostick; Donald R. Lowe

2004-01-01

9

Study of Carbonaceous Material in cherts from Barberton Greenstone Belt and the Astrobiological Implications.  

NASA Astrophysics Data System (ADS)

Carbonaceous matter is present in chert deposits of Barberton Greenstone Belt (BGB), South Africa. This is a famous place in the world for its Archean geology, wich represents around 3.5 billion years of earth's history. Therefore this area provides us the opportunity to study and understand an important part history of our planet, and also allow to compare with the geological history of other planets in our solar system [1]. Raman micro-spectroscopy has proved to be a very important and non-destructive powerful tool for distinguish micro-sized particles of C-polymorphs, as it is very sensitive to the nature of carbon bonding [2]. The connection between the Raman characterization of these carbonaceous phases with ancient biogenic activity it's of special interest. Cherts of BGB have been interpreted as precipitates or diagenetic replacements of preexisting sedimentary and pyroclastic deposits in a silica saturated Archean ocean [3]. Several layered Samples of cherts from BGB utility for the present study were collected during the expedition carried out in August 2010 sponsored by CNES and ESA. A detailed Raman spectral analysis of carbon C-C vibrations has been performed in the first (1200-1800 cm-1) and second (2500-3200 cm-1) order regions [4]. The results show important changes in the G-D bands in the layered structure of chert. Additionally a UPLC-ESI-QTOF-MS was carried out trying to introduce new insight in the Raman interpretation of the bands and in the possible assignments to particular molecular groups which could be related with biotic or abiotic origin of the carbonaceous material. Among the tentative compounds obtained from UPLC-ESI-QTOF-MS study it is worth to mention hydroxy-lycopene and the hydroxyl derivative of ?-carotene (i.e. ?-cryptoxanthin), which are carotenoids produced by cyanobacteria. These results are consistent with the presence of 22-Hopanol and Tetrahymanol, which are characteristic hopanoids of photosynthetic cyanobacteria and have been found in 2.7 billion year old rocks in Pilbara (Australia) [5]. The chromatographic behavior and exact mass coincidence of the m/z values found in this study give support, at least partially, the identification proposed.

Rull, F.; Venegas, G.; Montero, O.; Medina, J.

2012-04-01

10

Single zircon dating constraining the maximum age of the barberton greenstone belt, Southern Africa  

Microsoft Academic Search

One of the central issues in early Precambrian crustal evolution is the age and genetic relationship between greenstone belt supracrustal assemblages and nearby high-grade gneiss terranes. The crucial question, in most cases, is which of the two is older. We report zircon ages, using the new single grain evaporation technique, from a metaquartzite and a felsic volcanic flow of the

Alfred Kröner; Wolfgang Todt

1988-01-01

11

High but balanced sedimentation and subsidence rates (Moodies Group, Barberton Greenstone Belt), followed by basin collapse: Implication for Archaean tectonics  

NASA Astrophysics Data System (ADS)

Archaean tectonophysical models distinguish between thick, rigid and thin, mobile crust; from these the major mechanisms and rates for continental growth are derived. Archaean sedimentary rocks, preserved in metamorphosed and highly deformed greenstone belts, can contribute to constrain these models by estimating subsidence rates, derived from the combination of facies changes and precise age dates. Largely siliciclastic strata of the Moodies Group form the topmost unit of the Barberton Supergroup of the Barberton Greenstone Belt (BGB), South Africa, represent one of the world's oldest unmetamorphosed quartz-rich sedimentary sequences, and reach ca. 3500m thick (Lowe and Byerly, 2007). Large parts of the Moodies Group were deposited in apparent sedimentary continuity in alluvial, fluvial, shoreline and shallow-marine environments (e.g., Eriksson, 1979; Heubeck and Lowe, 1994). Distinctive sources and variations in facies indicate that Moodies deposition occurred at times in several basins. In several now tectonically separated regions, a regional basaltic lava (unit MdL of Anhaeusser, 1968) separates a lower unit (ca. 2000m thick and possibly representing an extensional setting) from an upper unit (ca. 1500m thick and characterized by progressive unconformities, rapidly changing facies, thicknesses, and sandstone petrographic composition). Single zircons separated from a felsic air-fall tuff of the middle Moodies Group and immediately overlying the basaltic lava in the Saddleback Syncline were dated on the Stanford-USGS SHRIMP RG. Out of 24 dated grains, two near-concordant groups have mean ages of 3230,6+-6,1Ma (2?; n=9) and 3519+-7 Ma (2?; n=9), respectively. We interpret the former age as representing the depositional age of the tuff, the latter as representing inherited zircons from underlying Onverwacht-age basement. The interpreted depositional age of the Moodies tuff is indistinguishable from numerous similar ages from felsic and dacitic volcanics at the top of the underlying Fig Tree Group (Schoongezicht Fm.; Byerly et al., 1996), implying that ca. 2000m of Moodies sandstones and subordinate siltstones and conglomerates were deposited in not more than a few (0-6) Ma. Their comparatively low degree of facies variation and lithological change implies a balance between rates of sediment supply and of subsidence, creating thick stacked units. Ferruginous shales and thin BIFs of the upper Moodies Group suggest that background 'Fig-Tree-style' sedimentation continued during Moodies time but was mostly overwhelmed by the apparently brief but massive influx of medium- to coarse-grained quartzose sediment. Because two progressive unconformities, marking Moodies basin uplift and onset of renewed overall BGB shortening, occur only 50 m above this dated unit, they are likely of a similar age and imply that dominant NW-SE-directed shortening in the BGB began shortly after 3230+-6 Ma. The combination of these new data with published information thus suggest that the Moodies Basin formed after 3225+-6 Ma (i.e., at the earliest at 3231) but was already largely filled and began to be deformed by 3231+-6 (i.e., at the latest by 3225). Moodies deposition thus happened geologically nearly instantaneously following the end of Fig Tree volcanism, took very little time and deposited large volumes of sediments on a rapidly subsiding basement just prior to large-scale BGB deformation. REFERENCES Byerly, G.R., Kroner, A., Lowe, D.R., Todt W., Walsh, M.M., 1996, Prolonged magmatism and time constraints for sediment deposition in the early Archean Barberton greenstone belt: Evidence from the Upper Onverwacht and Fig Tree groups: Precambrian Research, 78, p. 125-138. Eriksson, K.A., 1979, Marginal marine depositional processes from the Archaean Moodies Group, Barberton Mountain Land, South Africa: Evidence and significance: Precambrian Res., 8, p. 153-182. Heubeck, C. and Lowe, D.R., 1994, Depositional and tectonic setting of the Archaean Moodies Group, Barberton Greenstone Belt, South Africa: Precambrian Res., 68, p. 257-290. Lowe, D.R.,

Heubeck, Christoph; Lowe, Donald R.; Byerly, Gary R.

2010-05-01

12

Thermal history of the 3.5 3.2 Ga Onverwacht and Fig Tree Groups, Barberton greenstone belt, South Africa, inferred by Raman microspectroscopy of carbonaceous material  

NASA Astrophysics Data System (ADS)

Raman spectra of carbonaceous material were collected in situ from samples of cherts of the Onverwacht and Fig Tree Groups in the central Barberton greenstone belt. The spectra feature two dominant peaks characteristic of disordered carbon: the D peak at ˜1310 cm-1 and the O peak at 1580 1600 cm-1. D peak positions and relative peak intensities and areas indicate that all samples have been altered to lower greenschist facies or above. No correlation was observed between maximum temperature and stratigraphic position or degree of hydrothermal alteration, implying that metamorphism in the central Barberton greenstone belt was regional and unaccompanied by the flow of large quantities of hydrothermal fluids. Samples from the Marble Bar Chert of the Pilbara block, Western Australia, have been heated to the same extent as samples from Barberton. This study demonstrates the use of Raman spectra of carbonaceous material as a sensitive geothermometer for low-temperature metamorphic facies. This application could also be used to establish the antiquity of putative microfossils from metamorphic terranes.

Tice, Michael M.; Bostick, Benjamin C.; Lowe, Donald R.

2004-01-01

13

Microfacies of mappable Archean biomats, Moodies Group, Barberton Greenstone Belt, South Africa  

NASA Astrophysics Data System (ADS)

The ca. 3.22 Ga-old Moodies Group, Barberton Mountain Land, South Africa, arguably includes the world's oldest regionally mappable biofacies. There, abundant smooth, wavy, domal or cuspate, interwoven or parallel-stratified laminae of isotopically light kerogen (Noffke et al. 2006) in shallow-water or coastal environments show a microtopography of several cm, deform cohesively, trap and bind grains, and were surficially rapidly silicified. In order to investigate the microfacies and habitat of these extensive biomats, we measured stratigraphic sections, sampled for petrography and composition, and documented sedimentary structures throughout. Seven stratigraphic sections allow the reconstruction of a coastal depositional system with an thickness of approx. 240 m along an > 11 km long outcrop belt. The system can be subdivided in (from base to top deepening) terrestrial coastal, low-angle shoreline, subtidal and shoreface facies. Biomats are most densely (mm- to cm-) spaced in the shoreface unit whereas they are least common in the basal terrestrial unit in which single-pebble trains and thin gravel conglomerates occur. Biomats (mean 4 mm thick) reach their greatest individual thickness (up to 0,8 cm) and dominate the spectrum of sedimentary structures in the subtidal unit where they form black, internally laminated chert bands. Most chert bands overlie lenses of elongate, well-sorted, coarse-grained sandstone but are in turn sharply overlain by medium- and fine-grained sandstone, suggesting cyclic current activity. Clustered or regularly spaced (sub-)vertical fluid escape structures penetrate and ductily deform densely spaced interwoven biomats. They occur most widely in the shoreface facies, show a mean height of 49 cm, are commonly offset horizontally, and reach up to 230 cm. The margins of several shallow (max. 1 m deep) and up to 8 m wide channels erosively truncate wrinkled biomats of the terrestrial coastal facies. Channel fill includes dominant medium- to coarse-grained sand and subordinate palm-sized planar (apparently brittle) biomat fragments mixed with granule and pebble lag at the channel base. Channel dimensions and erosivity may suggest a subaerial setting and imply that biomat growth either predated a temporary base-level drop or grew on land, presumably in a flat coastal setting. The micromorphology, large lateral extent, and depositional architecture of the biomats indicate a well-developed, adaptable, resistant microbial ecosystem along a medium-energy coast and offer a remarkable window in the conditions under which early life on Earth developed.

Gamper, Antonia; Heubeck, Christoph; Ohnemueller, Frank; Walsh, Maud

2010-05-01

14

A basin on an unstable ground: Correlation of the Middle Archaean Moodies Basin, Barberton Greenstone Belt, South Africa  

NASA Astrophysics Data System (ADS)

The 3.22 Ga-old Moodies Group, representing the uppermost part of the Barberton Supergroup of the Barberton Greenstone Belt (BGB), is the oldest well-exposed, relatively unmetamorphosed, quartz-rich sedimentary unit on Earth. Moodies facies (north of the Inyoka Fault) were thought to be largely of alluvial, fluvial, deltaic or shallow-marine origin (Anhaeusser, 1976; Eriksson, 1980; Heubeck and Lowe, 1994) and in its upper part syndeformational. However, units can only locally be correlated, and the understanding of the interplay between Moodies sedimentation and deformation is thus limited. We mapped and measured Moodies units in the northern BGB. They partly consist of extensive turbiditic deepwater deposits, including graded bedding, flame structures, and slumped beds, interbedded with jaspilites. These contrast with shallow-water environments, south-facing progressive unconformities and overlying alluvial-fan conglomerates along the northern margin of the Saddleback Syncline further south. The palaeogeographic setting in which late BGB deformation was initiated therefore appears complex and cannot be readily explained by a simple southward-directed shortening event. In order to constrain Moodies basin setting before and during late-Moodies basin collapse, we correlated ~15 measured sections in the northern and central BGB. Most units below the Moodies Lava (MdL, ca. 3230.6+-6 Ma) can be correlated throughout although facies variations are apparent. Above the Moodies Lava, coarse-grained units can only be correlated through the Eureka Syncline and the Moodies Hills Block but not with the Saddleback Syncline. Fine-grained and jaspilitic units can be correlated throughout the northern BGB. Moodies below-wavebase deposition occurred largely north of the Saddleback Fault. The observations are consistent with a pronounced basin compartmentalization event following the eruption of the MdL which appeared to have blanketed most of the Moodies basin(s) in middle Moodies time and immediately predates the initiation of basin shortening. Basin compartmentalization was likely due to the movement along a group of major faults (Sheba, Haki, Barbrook, Saddleback Faults) between the present Saddleback and Eureka Synclines, creating at least two subbasins in late Moodies time. Even though sediment provenance thus became localized, intensive Archaean weathering likely contributed to generate petrographically similar quartz-rich sandstones in fault-bounded minibasins. The late-Moodies minibasins may have become connected occasionally, allowing concurrent deposition of thin BIFs. A similar phase of movement along the major transcurrent Inyoka Fault may be responsible for the distinct petrographic character of Moodies sandstones south of that fault.

Ohnemueller, Frank; Heubeck, Christoph; Kirstein, Jens; Gamper, Antonia

2010-05-01

15

Microfacies of mappable Archean biomats, Moodies Group, Barberton Greenstone Belt, South Africa  

Microsoft Academic Search

The ca. 3.22 Ga-old Moodies Group, Barberton Mountain Land, South Africa, arguably includes the world's oldest regionally mappable biofacies. There, abundant smooth, wavy, domal or cuspate, interwoven or parallel-stratified laminae of isotopically light kerogen (Noffke et al. 2006) in shallow-water or coastal environments show a microtopography of several cm, deform cohesively, trap and bind grains, and were surficially rapidly silicified.

Antonia Gamper; Christoph Heubeck; Frank Ohnemueller; Maud Walsh

2010-01-01

16

The rheological behavior of fracture-filling cherts: example from Barite Valley dikes, Barberton greenstone Belt, South Africa.  

NASA Astrophysics Data System (ADS)

A 100m-thick complex of black carbonaceous chert dikes marks the transition from the Mendon to Mapepe Formations (3260 Ma) in the Barberton Greenstone Belt, South Africa. Fracturing was intense in this area, as shown by the profusion and width of the chert dikes (ca. 1m on average) and by the abundance of completely shattered rocks. Similar structures occur in many greenstones worldwide. Here we investigate (1) the origin of the dikes and (2) the nature of the material that precipitated to form the fracture-filling chert. The dike-and-sill organization of the plumbing system and the upward narrowing of some of the large veins indicate that at least part of the fluid originated at depth and migrated upward. Abundant angular fragments of silicified country rock are suspended and uniformly distributed within the larger dikes. Jigsaw-fit structures and confined bursting textures indicate that hydraulic fracturing was at the origin of the fractures, a particularity attributed to the confinement of the hydrothermal system below an impermeable cape of chert. The location of the dikes beneath an impact spherule bed leads us to propose that the hydrothermal circulation was related to the impact. The present site may have been located at the external margin of a large crater. The geometry of the dikes and the petrography of the cherts indicate that the fluid that invaded the fractures was thixotropic. The injection of black chert into extremely fine fractures is evidence oflow viscosity at the time of injection while the lack of closure of larger veins below eroded country blocks and the suspension of fragments in a chert matrix provides evidence of high viscosity soon thereafter. The inference is that the viscosity of the injected fluid increased from low to high as the fluid velocity decreased. Such rheological behavior is characteristic of media composed of solid and colloidal particles suspended in a fluid. The presence of abundant clay-sized particles of silica, carbonaceous matter and phyllosilicates, the high proportion of siliceous matrix and the capacity of colloidal silica to form cohesive 3D networks, accounts for the viscosity increase and thixotropic behavior of the fluid that filled the veins. Stirring and shearing of the fluid as it was injected imparted a low viscosity by decreasing internal particle interactions; then, as the flow rate declined, the fluid became highly viscous as the inter-particulate bonds were reconstituted. The gelation of the chert was rapid, probably within a day after it was injected, and the structure persisted for several months to years under low temperature conditions (T<200°C) before fractures were sealed and the chert indurated.

Ledevin, Morgane; Arndt, Nicholas; Simionovici, Alexandre

2014-05-01

17

The rheological behavior of fracture-filling cherts: example of Barite Valley dikes, Barberton Greenstone Belt, South Africa  

NASA Astrophysics Data System (ADS)

A 100 m-thick complex of near-vertical carbonaceous chert dikes marks the transition from the Mendon to Mapepe Formations (3260 Ma) in the Barberton Greenstone Belt, South Africa. Fracturing was intense in this area, as shown by the profusion and width of the dikes (ca. 1 m on average) and by the abundance of completely shattered rocks. The dike-and-sill organization of the fracture network and the upward narrowing of some of the large veins indicate that at least part of the fluid originated at depth and migrated upward in this hydrothermal plumbing system. Abundant angular fragments of silicified country rock are suspended and uniformly distributed within the larger dikes. Jigsaw-fit structures and confined bursting textures indicate that hydraulic fracturing was at the origin of the veins. The confinement of the dike system beneath an impact spherule bed suggests that the hydrothermal circulations were triggered by the impact and located at the external margin of a large crater. From the geometry of the dikes and the petrography of the cherts, we infer that the fluid that invaded the fractures was thixotropic. On one hand, the injection of black chert into extremely fine fractures is evidence for low viscosity at the time of injection; on the other hand, the lack of closure of larger veins and the suspension of large fragments in a chert matrix provide evidence of high viscosity soon thereafter. The inference is that the viscosity of the injected fluid increased from low to high as the fluid velocity decreased. Such rheological behavior is characteristic of media composed of solid and colloidal particles suspended in a liquid. The presence of abundant clay-sized, rounded particles of silica, carbonaceous matter and clay minerals, the high proportion of siliceous matrix and the capacity of colloidal silica to form cohesive 3-D networks through gelation, account for the viscosity increase and thixotropic behavior of the fluid that filled the veins. Stirring and shearing of the siliceous mush as it was injected imparted a low viscosity by decreasing internal particle interactions; then, as the flow rate declined, the fluid became highly viscous as the inter-particulate bonds (siloxane bonds, Si-O-Si) were reconstituted. The gelation of the chert was rapid and the structure persisted at low temperature (T < 200 °C) before fractures were sealed and chert indurated.

Ledevin, M.; Arndt, N.; Simionovici, A.

2014-05-01

18

Carbonaceous cherts of the Barberton Greenstone Belt, South Africa: Isotopic, chemical and structural characteristics of individual microstructures  

NASA Astrophysics Data System (ADS)

Carbonaceous matter occurring in chert deposits of the 3.4-3.2 Ga old Barberton Greenstone Belt (BGB), South Africa, has experienced low grade regional metamorphism and variable degrees of local hydrothermal alteration. Here a detailed study is presented of in situ analysis of carbonaceous particles by LRS (laser Raman spectroscopy) and SIMS (secondary ion mass spectrometry), reporting degree of structural disorder, carbon isotope ratio and nitrogen-to-carbon ratio. This combination of in situ analytical tools is used to interpret the ? 13C values of only the best preserved carbonaceous remains, enabling the rejection of non-indigenous (unmetamorphosed) material as well as the exclusion of strongly hydrothermally altered carbonaceous particles. Raman spectroscopy confirmed that all carbonaceous cherts studied here have experienced a regional sub- to lower-greenschist facies metamorphic event. Although this identifies these organics as indigenous to the cherts, it is inferred from petrographic observations that hydrothermal alteration has caused small scale migration and re-deposition of organics. This suggest that morphological interpretation of these carbonaceous particles, and in general of putative microfossils or microlaminae in hydrothermally altered early Archean cherts, should be made with caution. A chert in the Hooggenoeg Formation, which is older than and has been hydrothermally altered by a volcanic event 3445 Ma ago, contains strongly altered carbonaceous particles with a uniform N/C-ratio of 0.001 and a range of ? 13C that is shifted from its original value. Cherts of the Kromberg Formation post-date this volcanic event, and contain carbonaceous particles with a N/C-ratio between 0.002 and 0.006. Both the Buck Reef Chert and the Footbridge Chert of the Kromberg Formation have retained fairly well-preserved ? 13C values, with ranges from -34‰ to -24‰ and -40‰ to -32 ‰, respectively. Abiologic reactions associated with hydrothermal serpentinization of ultramafic crust (such as Fischer-Tropsch synthesis) were an unlikely source for carbonaceous material in these cherts. The carbonaceous matter in these cherts has all the characteristics of metamorphosed biologic material.

van Zuilen, Mark A.; Chaussidon, Marc; Rollion-Bard, Claire; Marty, Bernard

2007-02-01

19

REE geochemistry of 3.2 Ga BIF from the Mapepe Formation, Barberton Greenstone Belt, South Africa  

NASA Astrophysics Data System (ADS)

Banded iron formations (BIFs) are chemical sediments interbedded with Fe- and Si-rich layers, characteristically present in the early history of the Earth. A popular hypothesis for the formation of BIFs postulates that dissolved oxygen produced by photosynthesizers such as cyanobacteria oxidized dissolved ferrous Fe supplied by submarine hydrothermal activities. During precipitation of Fe-oxide minerals, phosphorus and rare earth elements (REEs) were most likely adsorbed on their surface. Therefore, chemical compositions of REEs that adsorbed onto Fe-oxide have useful information on the seawater chemistry at the time of deposition. Especially, information on the redox state of seawater and the extent of the contribution of hydrothermal activity during BIF deposition are expected to have been recorded. Occurrence of BIF has been traditionally tied to the chemical evolution of the atmosphere. Rise of atmospheric oxygen, or as known as GOE (Great Oxidation Event: e.g., Holland, 1994), has been widely believed to have occurred at around 2.4 Ga ago. Contrary, however, some studies have suggested that such oxygenation could have occurred much earlier (e.g., Hoashi et al., 2009). In this study, we used 3.2 Ga old BIF from the Mapepe Formation at the bottom of the Fig Tree Group of the Swaziland Supergroup in the northeastern part of the Barberton Greenstone Belt, South Africa. We aimed to constrain the marine environment, and by inference atmospheric environment, at the time of BIF deposition from REE geochemistry. Major elements and REE compositions of 37 samples were measured using XRF and ICP-MS, respectively. Samples with less than 1.0 wt% Al2O3 are considered to be "pure" BIFs with minimal amount of continental contamination, and are expected to have inherited marine REE signatures. Abundance of REE normalized by C1 chondrite for the analyzed samples commonly exhibits positive Eu anomaly and LREE

Yahagi, T. R.; Yamaguchi, K. E.; Haraguchi, S.; Sano, R.; Teraji, S.; Kiyokawa, S.; Ikehara, M.; Ito, T.

2012-12-01

20

Exceptional preservation of aragonite in a circa 3.3 billion year old microbial mat from the Barberton greenstone belt, South Africa  

NASA Astrophysics Data System (ADS)

Exceptional preservation of aragonite in a circa 3.3 billion year old microbial mat from the Barberton greenstone belt, South Africa Frances Westall, Barbara Cavalazzi, Laurence Lemelle, Yves Marrocchi, Jean-Noël Rouzaud, Alexandre Simionovici, Murielle Salomé, Smail Mostefaoui, Caroline Andreazza, Frédéric Foucher, Jan Toporski, Andrea Jauss, Volker Thiel, Axel Hofmann, Anders Meibom, François Robert Aragonite occurs as a biologically-formed mineral precipitate within modern calcifying microbial mats. It is, however, rarely preserved in the geological record because, as one of the least stable polymorphs of calcium carbonate, it readily converts to calcite in present environmental conditions at the Earth's surface. In an in situ investigation at the micro- to nanometer-scale, we show that 5-10 nm sized nanocrystals of aragonite are preserved within the organic framework of a partially calcified microbial mat from the ~ 3.3 billion year-old Josefsdal Chert in the Barberton greenstone belt, South Africa. Transformation of the aragonite to calcite was blocked by a combination of chemical inhibitors within the crystal lattice, organic molecules coating the nanocrystals and, in particular, to the precocious permeation of the mat by hydrothermal silica. Apart from its exceptional preservation for 3.3 billion years, the identification of aragonite in the Josefsdal microbial mat is the earliest evidence for in situ calcification of a microbial mat. Furthermore, the indications of associated sulphur-reducing bacteria (SRB) activity with calcification strongly support a photosynthetic origin for the mat. This is the most direct evidence for photosynthesis in early Archaean rocks.

Westall, Frances; Cavalazzi, Barbara; Lemelle, Laurence; Marrochhi, Yves; Rouzaud, Jean-Noel; Simionovici, Alexandre; Andreazza, Caroline; Foucher, Frédéric; Thiel, Volker; Hofmann, Axel

2010-05-01

21

Investigating traces of early life in the oldest tectono-sedimentary basin of the 3.5 - 3.1 Ga Barberton greenstone belt, South Africa  

NASA Astrophysics Data System (ADS)

The ca. 3.5 - 3.1 Ga Barberton greenstone belt (BGB) in the Kaapvaal Craton of South Africa, contains some of the world's best preserved sequences of volcano-sedimentary and mafic-ultramafic rocks representative of the Paleoarchean. These rocks provide a unique opportunity to investigate dynamic environments and possible evidence for life on the young Earth. Evidence for early microbial life has been argued to be preserved in silicified marine sediments (cherts) and subseafloor pillow lavas of the upper Onverwacht Group of the BGB. This study will focus on the ca. 3.472 - 3.334 Ga Hooggenoeg, Noisy and Kromberg Formations argued to contain textural, geochemical and isotopic evidence for the oldest traces of subseafloor life on Earth. These include filamentous titanite microtextures as candidate 'ichnofossils', X-ray maps of carbon linings associated with these microtextures and negative carbon stable isotope ratios in Archean pillow lava rims (Furnes et al., 2004, 2008; Banerjee et al., 2006). Based on previously reported similarity between these titanite microtextures and partially mineralized microtubes found in altered in-situ oceanic crust, a complex 'bioalteration' model has been proposed, involving microbial-mediated alteration of basaltic glass. Despite numerous claims for the exceptional preservation of early subseafloor alteration in the proposed 'Biomarker' type-section, constraints on the nature and timing of low-temperature alteration are not available for the Hooggenoeg Formation. In this talk, new field and petrological data from the mafic-ultramafic Kromberg, volcano-sedimentary Noisy, and dominantly mafic Hooggenoeg Formations in the southeastern part of the Onverwacht Group anticline are presented. Thermodynamic modelling provides the first metamorphic constraints on low-temperature alteration conditions preserved in the Hooggenoeg pillow metabasites. This includes a new quantitative microscale mapping approach that characterizes metamorphic temperature and redox conditions surrounding the candidate titanite biotextures. New carbon stable isotope data from pillow cores and rims are presented. U-Pb dating of the alteration in the pillow metabasites determined by laser-ablation ICP-MS, places new constraints on the timing of alteration locally in parts of the pillow lava sequence. A U-Pb detrital zircon provenance study of clastic sediments in the Noisy formation that unconformably overlies the Hooggenoeg pillow lavas, provides evidence for the earliest tectono-sedimentary basin in the BGB at ca. 3.432 Ga (Grosch et al., 2011). Petrological characterization of altered and deformed mafic-ultramafic rocks of the structurally overlying Kromberg type-section indicates a mid-Archean convergent margin setting at 3.23 Ga, similar to modern-day ophiolite terrains. On the basis of SIMS sulfur isotope data, it is proposed that sulfur-metabolizing bacteria and possibly methanogenic microbes may have thrived in the shallow-marine subsurface of this tectono-sedimentary basin as early as ca. 3.432 Ga (Grosch & Mcloughlin, 2013). Collectively, the new field mapping and petrological data allows for a better understanding of the early geologic evolution of the Barberton greenstone belt and the potential habitats that may once have been available for early life. The candidate titanite biotextures are thus placed in better metamorphic and geological context. As such their syngenicity and biogenicity are evaluated particularly in light of an early 'bioalteration' subseafloor model.

Grosch, Eugene

2014-05-01

22

Physics of crustal fracturing and chert dike formation triggered by asteroid impact, ˜3.26 Ga, Barberton greenstone belt, South Africa  

NASA Astrophysics Data System (ADS)

asteroid impacts, reflected in the presence of spherule beds in the 3.2-3.5 Ga Barberton greenstone belt (BGB), South Africa, generated extreme seismic waves. Spherule bed S2 provides a field example. It locally lies at the contact between the Onverwacht and Fig Tree Groups in the BGB, which formed as a result of the impact of asteroid (possibly 50 km diameter). Scaling calculations indicate that very strong seismic waves traveled several crater diameters from the impact site, where they widely damaged Onverwacht rocks over much of the BGB. Lithified sediments near the top of the Onverwacht Group failed with opening-mode fractures. The underlying volcanic sequence then failed with normal faults and opening-mode fractures. Surficial unlithified sediments liquefied and behaved as a fluid. These liquefied sediments and some impact-produced spherules-filled near-surface fractures, today represented by swarms of chert dikes. Strong impact-related tsunamis then swept the seafloor. P waves and Rayleigh waves from the impact greatly exceeded the amplitudes of typical earthquake waves. The duration of extreme shaking was also far longer, probably hundreds of seconds, than that from strong earthquakes. Dynamic strains of ˜10-3 occurred from the surface and downward throughout the lithosphere. Shaking weakened the Onverwacht volcanic edifice and the surface layers locally moved downhill from gravity accommodated by faults and open-mode fractures. Coast-parallel opening-mode fractures on the fore-arc coast of Chile, formed as a result of megathrust events, are the closest modern analogs. It is even conceivable that dynamic stresses throughout the lithosphere initiated subduction beneath the Onverwacht rocks.

Sleep, Norman H.; Lowe, Donald R.

2014-04-01

23

3.2 Ga ocean sedimentary sequence in the Komati section of the Mapepe Formation in the Barberton Greenstone Belt, South Africa  

NASA Astrophysics Data System (ADS)

The Mapepe Formation (Heinrich,1980) is the lowermost part of the Fig Tree Group in the Barberton Greenstone Belt, and single zircon U-Pb dating suggests its sedimentary age of 3260 to 3230 Ma (Kroner et al. 1991). Our study area (Komati section) is located along the Komati River near the border to Swaziland. This section preserved more than 300m-long continuous outcrop and consists of well-stratified sedimentary sequence with bedded chert and shale. We performed 1/100 scale detailed geologic mapping to identify stratigraphic continuity. The Komati section is divided into 6 units (B1-, B2-, C-, D1-, D2- and E-unit) bounded by deformed zones. Thickness of each unit is 6.8m, 45m, 22.8m, 19m, 5.7m and 23m, respectively. Total thickness of the studied section reaches 128m. The studied section may be divided into the following four rock types. 1) black shale: It consists of massive type, laminated type that has 50?m size quartz lamina and gradational type that changes its color from black to red-brown. 2) red-brown (ferruginous) shale; (3) white chert (massive); (4) red chert: It consists of laminated type that has magnetite lamina and podded type that changes its color from white to red with sharp boundary and partly with podded structure. In all secions, grading from black to red-ferruginous shales are observed. The Corg contents of black shale from all units are ranging from 0.01 to 8.96 wt.%, with an average of 1.73 wt.% (n=204) and delta13C show -38.92~-19.83 per mil. The B2 and D1 units show large (>15 per mil) shifit in delta13C values within 10m section from -21.48 to -37,34 per mill and from -23.43 to -38.92 per mil respectively. These organics date not identified at 3.2-3.1 Ga Dixon Island-Cleaverville sequence (Kiyokawa et al., 2012). Magnetic susceptibility data indicate that Fe content is increasing upward in each unit. Therefore, such repeated upward lowering in the C isotope compositions and increase in Fe contents suggest repetition of increasing influence of hydrothermal input and associated changes in microbial community or metabolism.

Teraji, S.; Kiyokawa, S.; Ito, T.; Yamaguchi, K. E.; Ikehara, M.

2012-12-01

24

Carbonaceous matter and putative microfossils of the mid-Archean Kromberg type-section re-visited, Barberton Greenstone Belt, South Africa  

NASA Astrophysics Data System (ADS)

Silicified seafloor sediments of the Kromberg Formation from the Onverwacht Group of the Barberton greenstone belt (BGB), South Africa, have been argued to contain some of the world's oldest preserved carbonaceous microfossils. Previous studies of these cherts have reported filamentous, spheroidal and ellipsoidal microfossils in thin-section (Walsh 1992); and bacteriomorph like structures in HF-etched samples (Westall et al. 2001). These microtextural studies however, lack supporting in-situ geochemical data, and are hampered to some degree by re-mobilisation of the carbonaceous matter (Van Zuilen et al. 2007). In light of these concerns, and ongoing debates surrounding carbonaceous remains in other Archean cherts (e.g., W Australia), further in-situ data from the Kromberg is required to positively identify carbonaceous matter of biogenic origin. New data will also help to address outstanding questions regarding the relative contribution of benthic versus planktonic microorganisms, and the putative microbial metabolisms involved. This study focuses on surface samples and drill core from the Barberton Scientific Drilling Programme, (BSDP, Grosch et al. 2009) from the southeastern limb of the Onverwacht anticline of the BGB. We sampled the Footbridge chert and a second chert horizon in drill core KD1 of the BSDP in the upper Kromberg Fm; and surface outcrops of two black cherts from the lower Kromberg Fm. Sedimentological logging reveals horizons rich in volcaniclastics with interbedded finely laminated grey-black chert, also intrusive black cherts, and sulphide rich horizons. The TOC of the sampled cherts is 1.24 to 5.40 wt%. Preliminary bulk carbon isotope values range from ?13C -21.1 to -35.3o values that are consistent with organic matter produced by anoxygenic photosynthesis. Microfabrics preserved in the Kromberg cherts include, primary wispy-laminated carbonaceous films suggesting compaction of early carbonaceous laminae. Also large composite carbonaceous grains >30 ?m across recording wave-motion on the seafloor. Secondary fabrics include hydrothermal veins containing remobilized carbon and sometimes sulphides, also void-filling silica spherulites coated in carbonaceous matter. A novel fabric discovered in the lower Kromberg chert is silicified carbonaceous fragments with plastic deformation that are morphologically comparable to microtextures reported from the 3.416 Ga Buck Reef Chert (Tice and Lowe 2004) interpreted to be deformed microbial mat fragments. These fabrics are currently being studied by raman spectroscopy to assess the effects of taphonomic processes and metamorphic alteration on this potential biosignature. In-situ sulphur isotope measurements by SIMS on sulphides associated with primary carbonaceous fabrics of the Footbridge chert found a narrow range in ?34SCDTvalues of -6.00 to + 1.50 o and positive ?33S values up to +2.50 o suggesting the involvement of atmospheric sulphur aerosols, but do not strongly support either microbial sulphate reduction or disproportionation (Grosch and McLoughlin 2013). The geochemical evidence for microbial processes must therefore be further tested in the Kromberg cherts to build upon the bulk carbon isotope data that is consistent with, but alone not diagnostic of, microbial processes. In summary, this new survey of carbonaceous cherts from the Kromberg type section has identified well-preserved candidate microbial microfabrics that will be the target of ongoing high resolution in-situ geochemical and ultrastructure analysis.

McLoughlin, Nicola; Grosch, Eugene

2014-05-01

25

A petrological study of Paleoarchean rocks of the Onverwacht Group: New insights into the geologic evolution of the Barberton Greenstone Belt, South Africa  

NASA Astrophysics Data System (ADS)

This study presents a multi-disciplinary petrological approach applied to surface samples and a total of 800 m of scientific drill core that furthers our understanding of the geologic evolution of the ca. 3.5 to 3.2 Ga Onverwacht Group of the Barberton greenstone belt (BGB), South Africa. Detrital zircon grains in coarse (diamictite) to fine-grained clastic sedimentary rocks of the Noisy formation (drill core KD2a) that unconformably overlies the volcanic ca. 3472 Ma Hooggenoeg Formation, are investigated by laser ablation LA-ICP-MS to constrain their 207Pb/206Pb ages for depositional age and provenance. A wide range in 207Pb/206Pb ages between ca. 3600 and 3430 Ma is reported, corresponding to surrounding TTG plutons and the ca.3667-3223 Ma Ancient Gneiss Complex. The youngest detrital zircon grain identified has an age of 3432 ± 10 Ma. Given the short time interval for a major change in geologic environment between ca. 3472 Ma and ca. 3432 Ma, it is argued here, that the Noisy formation is the earliest tectonic basin in the BGB, which developed during major tectonic uplift at ca. 3432 Ma. In the overlying ca. 3334 Ma Kromberg type-section, application of a chlorite thermodynamic multi-equilibrium calculation, dioctahedral mica hydration-temperature curve and pseudosection modelling, indicates a wide range in metamorphic conditions from sub-greenschist to the uppermost greenschist facies across the Kromberg type-section. A central mylonitic fuchsite-bearing zone, referred to as the Kromberg Section Mylonites, records at least two metamorphic events: a high-T, low-P (420 ± 30oC, < 3kbar) metamorphism, and a lower-T event (T = 240-350oC, P = 2.9 ± 0.15kbar) related to retrograde metamorphism. An inverted metamorphic field gradient is documented beneath the KSM suggesting thrust repetition of the Kromberg sequence over the clastic rocks of the Noisy formation at ca. 3.2 Ga. This study also presents the first SIMS multiple sulfur isotope dataset on sulfides from the BGB and is used to test current models of mid-Archean biogeochemical sulfur cycling. In-situ ?34SCDT and ?33S values of volcanic, detrital, diagenetic and hydrothermal pyrite of the Kromberg and Noisy Formations are presented. The Kromberg cherts and mafic-ultramafic hydrothermal vein pyrites exhibit ?33S of -0.20 to +2.50‰, and ?34SCDT from -6.00 to +1.50‰ recording mixing between atmospheric sulfur and hydrothermal magmatic fluids. The Noisy sedimentary sequence contains detrital and diagenetic pyrites with a significant variation in ?33S of -0.62 to +1.4‰ and ?34SCDT between -7.00 and +12.6‰ in the upper turbidite unit, to more narrow isotopic ranges with magmatic-atmospheric values in the underlying polymictitic diamictite. A sedimentary quartz-pyrite vein in the diamictite records the largest range and most negative ?34SCDT values so far reported from an Archean terrain (?34SCDT = -55.04 to +27.46‰), and suggests shallow-level boiling and hydrogen release into early (ca. 3432 Ma) tectonic sedimentary basins during sulfide precipitation and a new possible environment for early microbial life.

Grosch, E. G.; Mcloughlin, N.; Abu-Alam, T. S.; Vidal, O.

2012-12-01

26

Implications of a 3.472-3.333 Gyr-old subaerial microbial mat from the Barberton greenstone belt, South Africa for the UV environmental conditions on the early Earth.  

PubMed

Modelling suggests that the UV radiation environment of the early Earth, with DNA weighted irradiances of about three orders of magnitude greater than those at present, was hostile to life forms at the surface, unless they lived in specific protected habitats. However, we present empirical evidence that challenges this commonly held view. We describe a well-developed microbial mat that formed on the surface of volcanic littoral sediments in an evaporitic environment in a 3.5-3.3Ga-old formation from the Barberton greenstone belt. Using a multiscale, multidisciplinary approach designed to strongly test the biogenicity of potential microbial structures, we show that the mat was constructed under flowing water by 0.25 microm filaments that produced copious quantities of extracellular polymeric substances, representing probably anoxygenic photosynthesizers. Associated with the mat is a small colony of rods-vibroids that probably represent sulphur-reducing bacteria. An embedded suite of evaporite minerals and desiccation cracks in the surface of the mat demonstrates that it was periodically exposed to the air in an evaporitic environment. We conclude that DNA-damaging UV radiation fluxes at the surface of the Earth at this period must either have been low (absorbed by CO2, H2O, a thin organic haze from photo-dissociated CH4, or SO2 from volcanic outgassing; scattered by volcanic, and periodically, meteorite dust, as well as by the upper layers of the microbial mat) and/or that the micro-organisms exhibited efficient gene repair/survival strategies. PMID:17008224

Westall, Frances; de Ronde, Cornel E J; Southam, Gordon; Grassineau, Nathalie; Colas, Maggy; Cockell, Charles; Lammer, Helmut

2006-10-29

27

Implications of a 3.472-3.333 Gyr-old subaerial microbial mat from the Barberton greenstone belt, South Africa for the UV environmental conditions on the early Earth  

PubMed Central

Modelling suggests that the UV radiation environment of the early Earth, with DNA weighted irradiances of about three orders of magnitude greater than those at present, was hostile to life forms at the surface, unless they lived in specific protected habitats. However, we present empirical evidence that challenges this commonly held view. We describe a well-developed microbial mat that formed on the surface of volcanic littoral sediments in an evaporitic environment in a 3.5–3.3?Ga-old formation from the Barberton greenstone belt. Using a multiscale, multidisciplinary approach designed to strongly test the biogenicity of potential microbial structures, we show that the mat was constructed under flowing water by 0.25??m filaments that produced copious quantities of extracellular polymeric substances, representing probably anoxygenic photosynthesizers. Associated with the mat is a small colony of rods–vibroids that probably represent sulphur-reducing bacteria. An embedded suite of evaporite minerals and desiccation cracks in the surface of the mat demonstrates that it was periodically exposed to the air in an evaporitic environment. We conclude that DNA-damaging UV radiation fluxes at the surface of the Earth at this period must either have been low (absorbed by CO2, H2O, a thin organic haze from photo-dissociated CH4, or SO2 from volcanic outgassing; scattered by volcanic, and periodically, meteorite dust, as well as by the upper layers of the microbial mat) and/or that the micro-organisms exhibited efficient gene repair/survival strategies.

Westall, Frances; de Ronde, Cornel E.J; Southam, Gordon; Grassineau, Nathalie; Colas, Maggy; Cockell, Charles; Lammer, Helmut

2006-01-01

28

Evidence of low temperature fractionation of silicon in Archean cherts: SIMS Si and O isotope measurements of 3.42-3.26 Ga banded carbonaceous cherts from the Onverwacht Group, Barberton Greenstone Belt, South Africa  

NASA Astrophysics Data System (ADS)

The striking abundance of chert in Early Archean sedimentary successions highlights a major difference between younger Archean and Proterozoic successions, engendering a number of questions regarding the behavior of the Earth's early silica cycle. Though previously applied largely for the purpose of paleothermometry, Si isotopes are emerging as a new tool for understanding mass flux and mechanisms of silica concentration, precipitation, diagenesis, and metamorphism. In addition, most previous studies lack a detailed petrographic context, laboring under the assumption that the cherts are isotopically homogeneous on a centimeter scale. We present a new suite of high resolution SIMS Si and O isotope ratio data from banded carbonaceous chert from the Onverwacht Group of the Barberton Greenstone Belt, South Africa - collected from the 3.42 Ga Buck Reef Chert and 3.33-3.26 Ga Mendon Formation. These materials contain several distinct silica phases, including carbonaceous bands (with or without well-defined grains), pure chert bands, early cavity filling cements, and later quartz-filled veins, which provide for isotopic comparisons between different textures. ?30Si values from all samples span a range of almost 7‰, from -3.38 to +3.42, with an overall mean of 0.36, median of 0.46, and standard deviation of 0.87. Within individual samples, isotope ratio data displays systematic texture-specific ?30Si variations both between phases and within phases. The observed variations occur on a ~100?m scale and likely reflect isotopically distinct fluids from which different silica phases originated, in addition to fractionation during precipitation. To constrain the causes of the silicon isotope trends, we made 18O/16O measurements on spots placed just adjacent to measured Si spots. SIMS ?18O values are generally 18O-depleted and fall in a range consistent with previously published data from bulk gas source mass spectrometry. Measurements from all samples span a range of ~6‰, from 16.39 to 22.22, but each individual sample has a smaller range of only 2-3‰. One sample shows clear ?18O differentiation between carbonaceous bands and pure chert bands, which is also consistent with previously published data from Onverwacht banded carbonaceous cherts. Importantly, ?18O values do not correlate with corresponding ?30Si points, suggesting that although diagenetic fluids have altered these rocks, the Si isotope ratios were largely rock-buffered and record fractionations incurred during primary and early diagenetic processes. Altogether these results suggest that there were conspicuous low temperature processes fractionating silicon isotopes in Early Archean marine basins—behavior that probably precludes the simple interpretation of Si isotope data from sedimentary cherts as a paleothermometer.

Stefurak, E. J.; Fischer, W. W.; Lowe, D. R.

2012-12-01

29

Trace element model studies of Nyanzian greenstone belts, western Kenya  

Microsoft Academic Search

The Archean greenstone belts of the Nyanzian System in western Kenya are composed principally of andesite with minor tholeiitic basalt and siliceous volcanics. The Nyanzian tholeiite is an intermediate-K tholeiite with a flat REE pattern. There are two chemically-distinct andesites: a low-K andesite (Andesite I) and a high-K andesite (Andesite II). The REE pattern of the Andesite II is enriched

Philip A. Davis Jr.; Kent C. Condie

1977-01-01

30

Archaean greenstone belts: A structaral test of tectonic hypothesis  

NASA Astrophysics Data System (ADS)

Tectonic hypotheses for Archaean greenstone belts are tested against structural data from the Agnew belt, Western Australia. This belt shows the following critical features: (1) A sialic infrastructure, formed by semi-concordant tonalitic intrusions, was present before tectonism began. (2) An early deformation formed recumbent folds and a flat-lying schistosity; a second deformation formed major upright folds and steep ductile shear zones that outline the present tectonic belt. Neither deformation caused major disruptions in the stratigraphy. Both were accompanied by metamorph ism under upper greenschist to amphibolite facies conditions and low pressure. (3) The belt is bounded on either side by tonalitic gneiss of unknown age, emplaced along steep shear zones. Comparison with Phanerozoic orogenic belts representing a subduction complex, a collisional suture zone, and a collapsed marginal basin, indicates that the belt was not formed in any of these plate-tectonic environments. The second deformation in the belt resulted from regional crustal distortion, accomplished by right-lateral ductile wrenching along major N- to NNW-trending shear zones. Associated en-echelon buckle folding formed large granite-cored anticlines and tight synclines. The detailed structural pattern is not consistent with a diapiric origin for these folds. The ductile wrench faults may have been related to mantle flow patterns in a manner analogous to modern transform faults.

Platt, J. P.

1980-05-01

31

Sedimentology of archean greenstone belts: Signatures of tectonic evolution  

NASA Astrophysics Data System (ADS)

Stratigraphic styles in Archean greenstone belts are compared to those of modern and Phanerozoic depositional basins in order to test the conformity of tectonic style through time. Six lithological associations in greenstone belts are recognized: (1) mafic-ultramafic volcanic, (2) calc-alkaline volcanic, (3) bimodal volcanic, (4) quartz arenite-iron-formation or carbonate, (5) conglomerate-wacke and (6) conglomerate-arenite. Examples of the associations are described from the Kaapvaal, Superior and Zimbabwe Provinces and the Pilbara Block. Each association differs only slightly between the four regions, thereby emphasizing a common tectonostratigraphic theme. Sedimentary rocks are a minor component of the mafic-ultramafic volcanic association. They were deposited in two types of volcanic-basin environments: one similar to barred lagoons and bays around oceanic volcanic islands, and the other similar to sediment-starved platforms adjacent to coalesced volcanoes in inter-arc, intra-arc and back-are basins. In contrast, sedimentary rocks in the calc-alkaline volcanic association comprise thick wedges of epiclastic and volcaniclastic detritus deposited in elongate sedimentary basins, and thick wedges of pyroclastic and volcaniclastic detritus deposited adjacent to volcanic centers. Sedimentary facies were identical to those of forearc-trench and marine volcanoplutonic-arc settings. Chemogenic lithofacies in both volcanic associations were deposited in shallow to deep-marine waters, although shallow-water profiles were selectively preserved in some terrains. Sedimentary rocks of the bimodal volcanic association are thick wedges of siliciclastic and volcaniclastic deposits interbedded with subaerial to submarine erupted flows of komatiite, basalt, and rhyolite. Depositional environments ranged from braid-plain and braid-delta to coastal marine and submarine fan. Starved-basin deposits include banded iron-formation and sulfidic black shale. The association is identical to that of cratonic extensional basins in arc-continent and intracontinental rifts. Sedimentary rocks of the quartz arenite-iron-formation or carbonate association onlap weathered basement or bimodal-volcanic association rocks. Depositional environments were either transitional from fluvial to siliciclastic and carbonate marginal-marine to offshore pelagic-hemipelagic, or from inshore intrabasinal-clastic and volcaniclastic to offshore pelagic-hemipelagic. Siliciclastic deposits are supermature. Two tectonic sites are represented: those with siliciclastic facies represent continent-adjacent syn- to post-rift stable shelves and those dominated by banded iron-formation, with volcaniclastic deposits, represent arc-adjacent post-rift stable shelves. Sedimentary rocks of the conglomerate-wacke association are represented by thick wedges of siliciclastic or volcaniclastic sandstone, with minor volcanic components. These were deposited in braid-plain, braid-delta and submarine-fan environments within elongate sedimentary basins. Coastal-plain and pelagic basin facies are also present. Siliciclastic detritus was derived from syndepositional, magmatic and metasedimentary thrust-belts. Two stratigraphic styles are preserved: one that records a flysch-like stage of deep- to marginal-marine environments, and the other that records a molasse-like stage of marginal-marine to fluvial environments. The association is identical to that of compressional-foreland basins of arc-continent collisional and compressional-arc tectonic affinities. The conglomerate-arenite association is preserved in elongate structural basins that transgress crustal components and all other supracrustal units. It is dominated by thick wedges of siliciclastic sandstone, although bimodal volcanic and volcaniclastic rocks can also be present. Depositional environments ranged from talus and alluvial fan, and braid-plain to either lacustrine or coastal marine. Local basin margins often show lateral offsets from source terrains and vertically skewed facies patterns. Longitudinal facies geometries are typical. T

Eriksson, K. A.; Krapez, B.; Fralick, P. W.

1994-10-01

32

Sulfide Mineralization In The Marble Bar Greenstone Belt Around Mount Edger Batholith, Pilbara Craton, Western Australia  

Microsoft Academic Search

Pilbara Craton is one of the most important regions in the world to understand the evolution of early Earth, because the geological history is well preserved through the metamorphism of low grade. Pilbara Craton, Western Australia, consists of two different tectonic components formed 3.6 and 2.8 Ga; an older Archean granite occupying the east Pilbara and greenstone belt. In the

S. Kitazono; M. Nedachi; S. Taguchi

2004-01-01

33

The Finlayson Lake Greenstone Belt, Superior Province, Canada: A Structural Perspective  

NASA Astrophysics Data System (ADS)

Archean greenstone belts are key to understanding the evolution and tectonic framework of the oldest preserved continental fragments in the Earth's stable cratons. Detailed structural studies of Archean greenstone belts are needed in the literature. We present a detailed structural study of the 2.931 - 3.003 Ga Finlayson Lake greenstone belt, which is located in the south-central Wabigoon Subprovince of the Superior Province in Canada. The Finlayson belt is situated between three TTG gneiss domes of similar ages: the 3.002 Ga Marmion gneiss; the 2.982 Ma Eye-Dashwa gneiss; and the 2.936 Ga Hardtack gneiss. Although greenstone belts globally show unique features and we do not assume that the Finlayson belt is a general class for all other greenstone belts, we aim to produce a structural framework and deformational history that is wholly supported by field data. Previous work documented tectonic foliation and way-up indicators with variable lithological and chronological boundary interpretations (Stone and Kamineni 1992, Stone 2008). The dominant fabric that we see throughout the Finlayson belt is a strong flattening foliation trending between 044o and 080o with approximately vertical dip. No clear gradation in the intensity of foliation has been observed across the belt and zones of lesser and stronger foliation intensity are intercalated. All lithological boundaries and structural features in the Finlayson belt (except those on the far western margin) lie approximately parallel to the eastern boundary with the Marmion gneiss. Transects across the belt reveal no discrete sutures, meso-scale folds or faults. Way-up indicators from pillow basalts remain generally consistent, although the western and central portion of the belt are oppositely facing and are also distinguished by their petrography. The prevalent metamorphic grade in the Finlayson belt is lower amphibolite facies with peak epidote-hornblende mineralogy preserved. Peak metamorphism is coeval with the formation of the dominant structural fabric. Retrograde chlorite partially replaces amphibole grains in the interior of the belt, whereas completely retrogressed chlorite schists are found on the eastern margin. Post-kinematic euhedral epidote overprints the foliation fabric, typically replacing titanite grains and including excess titanium as rutile. Late-stage quartz-carbonate veins fill brittle fractures that crosscut the foliation fabric and retrograde assemblages. The veins are predominantly emplaced parallel to the foliation fabric and are also mutually crosscutting. Post-veining dykes are typically undeformed, but folded dykes are observed in the central portion of the belt with a shortening axis approximately parallel to the foliation fabric. Using mapped transects across the Finlayson belt, defining deformational crosscutting relations and way-up reversals, we hope to tie in the structural details together with petrographical observations and metamorphic history. This will provide valuable insight into the evolution and structural reconstruction of the Mesoarchean Finlayson Lake greenstone belt within the framework of Archean terranes.

Backeberg, N. R.; Rowe, C. D.

2012-12-01

34

Boninites from the Neoarchaean Gadwal Greenstone belt, Eastern Dharwar Craton, India: implications for Archaean subduction processes  

NASA Astrophysics Data System (ADS)

Boninites are rare in Archaean arcs all over the world whilst there are some reports from the Phanerozoic convergent margins. In this paper, boninites are reported for the first time from an Archaean greenstone belt of India, which have not been reported from any other Indian greenstone belt as yet. The greenstone belts of western Dharwar Craton are characterized by high-Mg basalts and komatiites whereas in the greenstone belts of eastern Dharwar Craton boninites represent the high-Mg lavas. These boninites are characterized by (1) high MgO (12-24 wt.%), (2) enriched in transition elements such as Ni (423-1184 ppm), Cr (943-2765 ppm), (3) low TiO 2 (0.22-0.36 wt.%), (4) high Al 2O 3/TiO 2 ratio (29-50), (5) Gd/Yb n less than one, (6) slight enrichment in LREE, depletion in MREE compared to LREE and HREE resulting in U-shaped REE patterns, (7) negative Nb, Ta, Zr, Hf, Ti and V anomalies despite the depletion in MREE. These characteristics differentiate them from deep mantle plume-related magmas. These boninites are compositionally similar to those found in modern and fossil island arcs from intraoceanic subduction settings and provide evidence to propose that two-stage melting of the Archaean mantle wedge generated this type of high-Mg magma. The other high-Mg type magma (komatiitic suite) found in the greenstone belts of western Dharwar Craton has an enriched deep mantle plume source and its dry melting whereas boninites are generated by wet melting of the refractory depleted mantle wedge under high temperature and fluid pressure generated by dehydration of the slab. The geological setting, HFSE and REE data show that possibly the 2.7-Ga peak of geological activity had transitional characteristics between those of Paleoarchaean and Phanerozoic. High thermal and fluid flux is inferred to generate these Mg-enriched and MREE-, HFSE-, LFSE-depleted suite. This discovery of boninites from Gadwal greenstone belt indicate that even in Archaean, subduction of small, young and hot oceanic plates produced magmatic assemblage resembling to those of some of the Cenozoic subduction complexes.

Manikyamba, C.; Naqvi, S. M.; Subba Rao, D. V.; Ram Mohan, M.; Khanna, Tarun C.; Rao, T. G.; Reddy, G. L. N.

2005-01-01

35

Rb-Sr dating of the pegmatites from the Kolmozero-Voronya greenstone belt (kola peninsula)  

NASA Astrophysics Data System (ADS)

The Kolmozero-Voronya greenstone belt is situated in the north-eastern part of the Kola Peninsula. The aim of investigation was to establish an age of the REE pegmatite with spodumene, which occurs in the greenstone belt. Four samples of whole rock, spodumene, apatite, and muscovite were taken for Rb-Sr dating of the REE pegmatite. The age obtained on these samples is about 1,9 Ga. The rocks have undergone an alteration due to thermal and hydrothermal processes, and a pressure change during the crystallization, and their Rb-Sr system was disturbed. U-Pb zircon age determined for the same rock ranges within 1,8-2,0 Ga (Kudryashov N.M., in press). Available isotope data allow concluding the following: - REE pegmatites of one of the largest lithium and cesium deposits in Russia have been first dated, and their Rb-Sr age is estimated to be approximately 1,9 Ga; - The formation of the pegmatite is presumably associated with the emplacement of muskovite-tourmaline granites into sedimentary-volcanic rocks at a final stage of the belt evolution; - Obtained results indicate apparently the Proterozoic time of formation of the pegmatites in the Kolmozero-Voronya greenstone belt. The pegmatite with an age of 1,8-1,9 Ga known in a large Sweden -Finnish belt, which are confined to the Svecofennian mobile belt and associated with post-orogenic microcline granite, and also the pegmatite field of the Varutresk-Kluntarna area (Sweden), which age is determined to vary within the interval of 1,775-1,900 Ga can be considered as possible analogues of the pegmatites under the study.

Serov, Pavel

2003-04-01

36

Structural evolution of the Warrawoona Greenstone Belt and adjoining granitoid complexes, Pilbara Craton, Australia: implications for Archaean tectonic processes  

Microsoft Academic Search

The Pilbara granite–greenstone terrain (3.6–2.8 Ga), Australia, is quoted as the key area formed by passive, gravity-driven solid-state diapirism. But, contrasting views have been reported recently, which led us to re-examine the key area: the Warrawoona Greenstone Belt and the adjoining Mt Edgar and Corunna Downs Granitoid Complexes. We found: (i) an asymmetric, non-synclinal distribution of metamorphic grade and deformation

A Kloppenburg; S. H White; T. E Zegers

2001-01-01

37

Rank statistical analysis of nickel sulphide resources of the Norseman-Wiluna Greenstone Belt, Western Australia  

NASA Astrophysics Data System (ADS)

Estimating the undiscovered mineral resources of a terrane is a challenging, yet essential, task in mineral exploration. We apply Zipf's law rank statistical analysis to estimate the undiscovered nickel sulphide resources in the Norseman-Wiluna Greenstone Belt, Western Australia. The analysis suggests that about 3.0 to 10.0 Mt of nickel sulphide resources are yet to be discovered in this belt, compared to the currently known total nickel sulphide endowment of 10.8 Mt. This undiscovered nickel sulphide endowment is likely to be hosted by incompletely delineated deposits and undiscovered deposits in less explored komatiites in the belt. Using the more detailed data subset of the Kambalda domain, this study manipulates Zipf's law to estimate the sizes of undiscovered deposits, in addition to the domain's total nickel sulphide endowment estimate. Importantly, regression analysis shows that the gradient of the line of best fit through the logarithmic rank-size plot for the detailed Kambalda data subset is -1. This gradient, which is the key Zipf's law constant k, has the value of -0.92 for the Norseman-Wiluna Greenstone Belt which is collectively less mature than the Kambalda domain. This result corroborates the use of k = -1 in Zipf's law predictive analyses of mineral resources for deposit populations for which the value of k = -1 has not yet been attained due to exploration immaturity.

Mamuse, Antony; Guj, Pietro

2011-03-01

38

Sulfide Mineralization In The Marble Bar Greenstone Belt Around Mount Edger Batholith, Pilbara Craton, Western Australia  

NASA Astrophysics Data System (ADS)

Pilbara Craton is one of the most important regions in the world to understand the evolution of early Earth, because the geological history is well preserved through the metamorphism of low grade. Pilbara Craton, Western Australia, consists of two different tectonic components formed 3.6 and 2.8 Ga; an older Archean granite occupying the east Pilbara and greenstone belt. In the east Pilbara, the most conspicuous structures are broad domal granitoid complex separated by narrow synformal greenstone belts, and a model of continuous lithostratigraphy in the greenstones in which the dominant structures were produced by multi-stage granitoid diapirism. The Marble Bar greenstone belt is distributed around the Mount Edgar of granitoid pluton, and numerous hydrothermal gold veins are distributed in the greenstone near the boundary of pluton. Also base-metal veins and volcanogenic sedimentary type deposits are located in the same area. In this study, we examined the hydrothermal mineralization observed in the core samples of the Marble Bar greenstone belt, drilled at the Salgash area by the Archean Biosphere Drilling Project (ABDP). The Salgash drill hole is composed of tuff breccias with numerous fragments of black shale of 100 m in thickness, alternation of sandstone and shale of 40 m in thickness, basaltic lava and tuff of 30 m in thickness, and shale and sandstone of 110m in thickness with some sills of basalt and ultramafic rock. The rocks had been metamorphosed, and the grade is near the boundary between green schist and amphibolite facies. Low REE content (43 to 88 ppm), low La/Yb ratio (6.3 to 14.3), and high Eu/Eu* ratio (0.9 to 1.3) of the volcanic rocks are ordinal as the basaltic rock in Archean greenstone belts. On the other hand, these rocks show extremely high values of Cr (1500ppm), Ni (700ppm), Co (70 ppm), and Zn (600 ppm). The C isotopic ratios of carbonate in the volcanic rocks are around -3.8 permil. The clastic sediment sandstone and black shale show similar features, although the absolute values are slightly different. These data suggest that the clastic sediments had been delivered mainly from the volcanic rocks. The C isotopic ratios of organic carbon in the black shale are from -26 to -30 permil, which implies the activity of bacteria. Horizontal veins are often recognized in the clastic sediments, and are composed of quartz, calcite, sphalerite, pyrite, arsenopyrite, pyrrhotite and chalcopyrite. The C isotopic ratios of vein carbonates are from -4.6 to -5.2 permil. The S isotopic ratios of sulfide minerals are concentrated from -1.5 to +0.9 permil. The quartz and calcite veins which are 10 cm in maximal diameter run through the sediment rock. The homogenization temperature of fluid inclusion ranges from 150 to 250 degree with the average of about 200 degree centigrade which concludes well with metamorphic grade, suggesting the origin of metamorphism. The fluid is composed of H2O, CO2, CH4 and C, those constituents seem to reflect the characteristic environments of early Earth, which differ from the accretional material of Phanerozoic, suggesting different tectonic circumstance.

Kitazono, S.; Nedachi, M.; Taguchi, S.

2004-12-01

39

Geochemistry of the Archean Kam Group, Yellowknife Greenstone Belt, Slave Province, Canada.  

PubMed

The geochemistry and isotope systematics of Archean greenstone belts provide important constraints on the origin of the volcanic rocks and tectonic models for the evolution of Archean cratons. The Kam Group is a approximately 10-km-thick pile of submarine, tholeiitic mafic, and subordinate felsic volcanic rocks erupted between 2712 and 2701 Ma that forms the bulk of the Yellowknife greenstone belt in the dominantly granite-metasedimentary Slave Province. Mafic rocks range from Normal-mid-ocean range basalt-like basalts to slightly light-rare-earth-element-enriched (LREE-enriched) but Nb-depleted basaltic andesites and andesites, whereas dacitic to rhyodacitic felsic rocks are strongly LREE-enriched and highly depleted in Nb. The varepsilonTNd range from +5 to -3 in the mafic to intermediate rocks and from 0 to -5.5 in the felsic rocks. The varepsilonTNd decreases with increasing La/Sm, SiO2 and decreasing Nb/La, suggesting that as the mafic magmas evolved they were contaminated by older basement rocks. Gneissic granitoids >2.9 Ga in age, found at the base of the Kam Group, have varepsilonTNd between -6 and -9 and are excellent candidates for the contaminant. The geochemical and isotopic data, combined with the submarine eruptive setting and field evidence for existing continental basement, support a continental margin rift model for the Kam Group. Similar geochemical-isotopic studies are required on other Slave greenstone belts in order to test evolutionary models for the Slave Province. PMID:10736269

Cousens

2000-03-01

40

Succession of structural events in the Goren greenstone belt (Burkina Faso): Implications for West African tectonics  

NASA Astrophysics Data System (ADS)

Ten years after field investigations in the SE Goren greenstone belt (GGB) of Burkina Faso by the Sanmatenga J.V., sponsored field studies conducted in 2007 have significantly enhanced structural datasets. The studies in 2007 were conducted across an expanded area of the GGB that included both southwestern and northeastern domains, and portions of the Pissila batholith to the west of the GGB. A revision of tectonic models proposed by Hein et al. [Hein, K.A.A., Morel, V., Kagoné, O., Kiemde, F., Mayes, K., 2004. Birimian lithological succession and structural evolution in the Goren Segment of the Boromo-Goren Greenstone Belt, Burkina Faso. Journal of African Earth Sciences 39, 1-23] is now possible. Three deformation events characterise the Goren greenstone belt. The deformation, D1 (previously D3) resulted in the formation of NW to NNW-trending steeply-dipping dextral-reverse shear zones folds and a penetrative S1-C schistosity that formed during a period of NE-SW shortening. The event is termed the Tangaean Event because it can be correlated across NE Burkina Faso in the Boromo, Bouroum, Yalago and Oudalan-Gorouol greenstone belts. The deformation, D2 (previously D2) resulted in the progressive development of NNE to NE-trending macroscopic to mesoscopic folds and a penetrative axial planar cleavage (S2), which was followed by the formation of dextral- and sinistral-reverse shears and a pervasive schistosity (S2-C). The first-order crustal-scale Sabce Shear Zone, which traverses the northern portion of the study area, is associated with macroscopic anticlockwise drag rotation of NW to NNW-trending D1 shears and folds: (the macroscopic fold was previously classified as D1). D2 in the GGB corresponds with the Eburnean Orogeny at 2130-1980 Ma, as described by [Feybesse, J.-L., Billa, M., Guerrot, C., Duguey, E., Lescuyer, J.-L, Milesi, J.-P., Bouchot, V., 2006, The paleoproterozoic Ghanian province: geodynamic model and ore controls, including regional stress modelling. Precambrian Research, 149-196]. The deformation D3 (previously D4) is recognised throughout the GGB. It is characterised by the formation of kinks and chevron folds (F3), or crenulation cleavage (S3) that are hosted by narrow WNW-trending shear zones. These formed during a period of north-south shortening termed the Wabo-Tampelse Event that post-dates the Eburnean Orogeny.

Hein, Kim A. A.

2010-02-01

41

Origin and global tectonic significance of Early Archean cherts from the Marble Bar greenstone belt, Pilbara Craton, Western Australia  

Microsoft Academic Search

Five sections of bedded chert in mafic-ultramafic rocks of the Archean Warrawoona Group in the Marble Bar greenstone belt, Pilbara Craton, were analyzed in order to understand their depositional environment and to provide some constraints on Early Archean tectonics. The sections are divisible into two types based on their field occurrence, mineralogy and geochemistry; thicker ones (A and B) that

Yasuhiro Kato; Kentaro Nakamura

2003-01-01

42

Oxygen isotope ratios of Archean plutonic zircons from granite–greenstone belts of the Superior Province: indicator of magmatic source  

Microsoft Academic Search

Zircons commonly preserve primary magmatic oxygen isotope ratios even through high grade metamorphic events unlike quartz which more readily loses its primary ?18O value by subsolidus exchange. Intrusive bodies from the Superior Province, Canada have an average ?18O(Zircon) of 5.8±0.6‰ (n=59 rocks). Those from granite–greenstone belts have an average ?18O(Zrc)=5.8±0.6‰ (n=55), in contrast to those from metasedimentary belts that average

Elizabeth M King; John W Valley; Don W Davis; Garth R Edwards

1998-01-01

43

Tectonic evolution of the Oudalan-Gorouol greenstone belt in NE Burkina Faso and Niger, West African craton  

Microsoft Academic Search

The Oudalan-Gorouol Greenstone Belt (OGGB) forms part of the Palaeoproterozoic as the Baoulé-Mossi domain of the West African Craton (WAC) and hosts gold deposits at Essakane, Gossey, Korizena, and Falagountou in NE Burkina Faso, and Kossa goldfield in Niger. The Birimian supracrustal sequences in the OGGB are dominated by meta-volcanoclastic greywacke intercalated meta-conglomerate, siltstone and shale, carbonate (dolomite) and volcanic

Asinne Tshibubudze; Kim A. A. Hein

2010-01-01

44

Archaean lode gold mineralisation in banded iron formation at the Kalahari Goldridge deposit, Kraaipan Greenstone Belt, South Africa  

Microsoft Academic Search

The Kalahari Goldridge Mine is located within the Archaean Kraaipan Greenstone Belt, about 60 km southwest of Mafikeng in the North West Province, South Africa. The ore body thickness varies from 15 to 45 m along a strike length of about 1.5 km within approximately N–S striking banded iron formation (BIF). The stratabound ore body is hosted primarily by BIF, which consists of

Napoleon Q. Hammond; John M. Moore

2006-01-01

45

3-D imaging of the Central Lapland Greenstone Belt using magnetotelluric and seismic data  

NASA Astrophysics Data System (ADS)

New broadband magnetotelluric (MT) data were acquired in the Central Lapland Greenstone Belt (CLGB) area, northern Finland, during the field campaigns in 2009 and 2010. The measurements belong to an ongoing project at the Geological Survey of Finland. The project intends to create the target- and regional scale 3-D models of the CLGB area using potential field, seismic and electromagnetic data. The survey area is located in the western and northern parts of the CLGB that is one of the largest Proterozoic greenstone belts in the world. In the north and west, the survey area is bordered by Proterozoic granitic rocks and intrusions. The CLGB consists of a Palaeoproterozoic (2.5 - 1.97 Ga) volcanic and sedimentary cover that was deposited on the Archaean (> 2.5 Ga) basement. The Kittilä Group greenstones, which form the core of the CLGB, are suggested representing an allochtonous unit, is bound by tectonic contacts with older units surrounding it (Hanski, 1997). The collected MT dataset consists of the data from 80 sites with the frequency range of 300 - 0.002 Hz and the site spacing of 500 m - 4 km. At the first stage, the MT data were analyzed along a number of crossing 2-D lines. MT parameters were also examined as maps, because the central part of the survey area forms a magnetotelluric array. A regional electrical dimensionality and strike were studied with invariants and various decomposition techniques. Regional electrical dimensionality proved to be mainly 2-D and 3-D except for some northern MT sites in resistive granite-hosted regions, which fulfilled criteria for 1-D interpretation. Smooth 2-D conductivity models were obtained by inverting the determinant of the impedance tensor (Siripunvaraporn & Egbert, 2000; Pedersen & Engels, 2005) and TE- and TM- data jointly using the nonlinear conjugate gradient algorithm of Rodi & Mackie (2001). Model resistivities range from 0.1 Ohm-m to greater than 20 000 Ohm-m in the survey area. The highest conductivities are related to N-S elongated graphite- and sulfide-bearing schists of the CLGB, which are visible also in the airborne electromagnetic data of the study area. Results show that these conductors have the deep roots of about 5 - 10 km. The highest resistivities emerge from granite intrusions that are located in the northern part of the study area. In the west, the resistivity of the CLGB is much higher with no indications of high-conductivity anomalies in the uppermost 40 km. However, in the westernmost part of the study area, a conductivity contrast is observed at the depth of about 10 km possibly indicating the contact zone of the two cratons of the Fennoscandian Shield, i.e. the Karelian and the Norbotten cratons (Lahtinen et al., 2005). 2-D inversion models are presented together with seismic data from the Finnish Reflection Experiment (FIRE) along the CMP-lines 4A and B. In the eastern and central parts of the study area, conductivity anomalies are usually associated with dipping reflectors, whereas such a relationship is not evident in the western part of the study area.

Lahti, I.; Korja, T.; Smirnov, M.; Vaittinen, K.; Sandgren, E.; Niiranen, T.; Nykänen, V.

2012-04-01

46

The geology and mineralisation at the Golden Pride gold deposit, Nzega Greenstone Belt, Tanzania  

NASA Astrophysics Data System (ADS)

The Golden Pride gold deposit (˜3 Moz) is located in the central part of the Nzega Greenstone Belt at the southern margin of the Lake Victoria Goldfields in Tanzania. It represents an inferred Late Archaean, orogenic gold deposit and is hosted in intensely deformed meta-sedimentary rocks in the hanging wall of the approximately E-W striking Golden Pride Shear Zone. The hanging-wall sequence also includes felsic (quartz porphyritic) to mafic (lamprophyric) intrusions, as well as banded iron formations. Hydrothermal alteration phases associated with mineralisation are dominated by sericite and chlorite. Two main ore types can be distinguished, chlorite and silica ore, both occupying dilational sites and structural intersections in the hanging wall of the main shear zone. Sulphide minerals in both ore types include pyrrhotite, arsenopyrite, pyrite and accessory sphalerite, galena, sulphosalts and Ni-Co-Bi sulphides. Gold and tellurides are late in the paragenetic sequence and associated with a secondary phase of pyrrhotite deposition. Sulphur isotope compositions range from -6 to 7 per mil and are interpreted to reflect contributions from two distinct sources to the mineralising fluids in the Golden Pride gold deposit. A redox change, potentially induced by the intrusion of mafic melts, together with structural elements in the hanging wall of the Golden Pride Shear Zone, are interpreted to be the main controls on gold mineralisation in this deposit.

Vos, I. M. A.; Bierlein, F. P.; Standing, J. S.; Davidson, G.

2009-10-01

47

2D-3C high-resolution seismic data from the Abitibi Greenstone Belt, Canada  

NASA Astrophysics Data System (ADS)

One high-resolution seismic profile acquired as part of a 3-component (three orthogonal seismometers) regional seismic reflection survey within the southern Abitibi greenstone belt was investigated in more detail using tomography and by processing all three components. Several high-resolution lines had targeted the Porcupine-Destor deformation zone, a zone proximal to the large gold deposits of the Timmins mining camp, and revealed by the new seismic data to be a composite of early fold structures and late transpressive fault arrays that host quartz-vein gold. Processing of the horizontal-component data assumed that seismic waves were converted from P-waves to S-waves between Vibrator source and receivers; S-wave static corrections proved especially important. Radial-component sections showed most features observed previously on vertical-component sections, but some amplitudes became enhanced, others reduced. The transverse-component stack demonstrated that a few structures are 3-D or contain significant seismic anisotropy. Two dimensional, P- and S-wave travel-time tomography analysis using data from the 10-km-long linear receiver array revealed low-resolution (> 200 m) physical property variations, possibly related to mineralization in near-surface structures of the Porcupine-Destor deformation zone; these variations were especially apparent using Poisson's ratio.

Snyder, David B.; Cary, Peter; Salisbury, Matt

2009-07-01

48

Os Isotopic Composition of Late-Archean Komatiites From Alexo in the Abitibi Greenstone Belt, Canada  

NASA Astrophysics Data System (ADS)

We have examined the Re-Os isotope systematics and major and trace element characteristics of a suite of komatiitic flows from Alexo area in the Abitibi greenstone belt. The objective of this study was to determine the initial Os isotopic composition of the late-Archean mantle source(s) of these rocks. Most of the samples have high Os concentrations and low Re/Os ratios. Moreover, some of these rocks have high Cr concentrations, and, therefore, direct determination of initial Os isotopic composition from primary chromites is possible. The Re-Os isochron results for whole rocks and chromites yield an age of 2760 +/- 79 Ma. This age is in general agreement with Pb-Pb and Sm-Nd isochron ages of 2690 +/- 15 Ma and 2752 +/- 87 Ma, respectively (Dupre et. al., 1984). The initial Os isotopic composition (187Os/188Os(I) = 0.1081 +/- 0.0016) obtained from this isochron is essentially chondritic (? Os = -0.5 +/- 1.5). Our results, therefore, suggest an absence of any large-scale heterogeneity in initial Os isotopic composition of the mantle source(s) of these komatiites. Duplicate analyses of a differentiated (Mg# 0.66) and yet presumably cogenetic basaltic komatiite (187Re/188Os > 8.14 and Os < 0.46 ppb) yield relatively radiogenic initial ? Os values of +15.9 and +12.6. Such radiogenic initial isotopic compositions in an otherwise chondritic association may indicate: [1] open-system behavior due to hydrothermal alteration and low-grade metamorphism and/or [2] crustal contamination. The latter interpretation is consistent with recently studied komatiites and associated magmatic ores from this area (Lahaye et. al., 2001).

Gangopadhyay, A.; Walker, R. J.

2001-12-01

49

Mass and magnetic properties for 3D geological and geophysical modelling of the southern Agnew–Wiluna Greenstone Belt and Leinster nickel deposits, Western Australia  

Microsoft Academic Search

Physical property measurements provide a critical link between geological observations and geophysical measurements and modelling. To enhance the reliability of gravity and magnetic modelling in the Yilgarn Craton's Agnew–Wiluna Greenstone Belt, mass and magnetic properties were analysed on 157 new rock samples and combined with an existing corporate database of field measurements. The new samples include sulfide ore, serpentinised and

N. C. Williams

2009-01-01

50

An Archaean tectonic model of the Dharwar craton, southern India: the origin of the Holenarasipur greenstone belt (Hussan district, Karnataka) and reinterpretation of the Sargur-Dharwar relationship  

Microsoft Academic Search

The occurrence of the Holenarasipur greenstone belt is explained by accretionary process at a trench. A sequence of amphibolite (MORB), chert, and banded iron formation associated with komatiitic amphibolite (oceanic island material) is an Archaean analogue to the modern oceanic crust grown through the migration from an active ridge to a trench. At a trench, slices of such a sequence

K. Kunugiza; Y. Kato; T. Kano; Y. Takaba; I. Kuruma; T. Sohma

1996-01-01

51

Sediment provenance in the Palaeoproterozoic Rio Itapicuru greenstone belt, Brazil, indicates deposition on arc settings with a hidden 2.17-2.25 Ga substrate  

NASA Astrophysics Data System (ADS)

A study of sediment provenance and tectonic setting was carried out for the first time on metasedimentary rocks of the Rio Itapicuru greenstone belt, Serrinha Block, São Francisco craton, Brazil, using a combination of LA-ICP-MS zircon U-Pb geochronology, whole-rock geochemistry and Sm-Nd isotope data. The protoliths of the studied phyllites, micaschists and biotite gneisses were classified mostly as mudstones and impure sandstones, i.e. shales and greywackes. The chemical index of alteration (CIA) ranges from 39 to 70 indicating moderate chemical weathering in source areas. Intermediate and felsic rocks (granite, granodiorite, rhyolite and andesite) are the likely main source rocks, and less often mafic rocks (basalt and gabbro). The depleted-mantle Nd model ages (TDM), most in the range 2.0-2.2 Ga, and the positive ?Nd values for the proposed deposition time (ca. 2115 Ma) suggest source rocks mainly in the greenstone belt. The U-Pb data on detrital zircon grains of four samples yielded 207Pb/206Pb age mostly in the timespan 2125-2237 Ma, with age populations clustering at 2164 ± 4 Ma and 2209 ± 4 Ma, and minor outliers at ca. 2112 Ma, 2270 Ma, and 2415 Ma. The results indicated that the metasedimentary rocks of the Rio Itapicuru greenstone belt have source areas mainly in Palaeoproteroic terranes such as the Rio Itapicuru and Rio Capim greenstone belts. The zircon populations between 2.17 Ga and 2.24 Ga are not found in the Serrinha block, thus requiring sources that are not known in the region. Diagrams of tectonic setting suggest that the sediments may have been deposited on continental island arc. Our data support a model in which basalts and arc granites of the Rio Itapicuru greenstone belt were accreted onto an unknown continental or arc margin and the entire pile collided with, and were thrust onto a microcontinent represented by the adjacent Archaean basement complex.

Grisolia, Maria Fernanda P.; Oliveira, Elson P.

2012-10-01

52

The 3.26–3.24 Ga Barberton asteroid impact cluster: Tests of tectonic and magmatic consequences, Pilbara Craton, Western Australia  

Microsoft Academic Search

The location in the Barberton Greenstone Belt (Kaapvaal Craton) of ?3.26–3.24 Ga asteroid impact ejecta units at, and immediately above, a sharp break between a >12 km-thick mafic–ultramafic volcanic crust (Onverwacht Group ?3.55–3.26 Ga, including the ?3.298>3.258 Ga Mendon Formation) and a turbidite–felsic volcanic rift-facies association (Fig Tree Group ?3.258–3.225 Ga), potentially represents the first documented example of cause–effect relations

Andrew Glikson; John Vickers

2006-01-01

53

Characterization and component tracing of Banded Iron Formations deposited during the ~2.7 Ga superplume event: An example from the Tati Greenstone Belt, Northeastern Botswana  

Microsoft Academic Search

Major and trace element, samarium (Sm)-neodymium (Nd) and lead (Pb) isotopic analyses of individual mesobands of five Banded Iron Formations (BIFs) and associated metavolcanic and metasedimentary rocks from the Neoarchean Tati Greenstone Belt (TGB, Northeastern Botswana) were conducted in order to characterize and determine the source(s) and depositional environment(s) of these chemical sediments and to compare their features with other

L. N. Døssing; R. Frei; H. Stendal; R. B. Mapeo

2008-01-01

54

Characterization of enriched lithospheric mantle components in ?2.7 Ga Banded Iron Formations: An example from the Tati Greenstone Belt, Northeastern Botswana  

Microsoft Academic Search

Major and trace element, samarium (Sm)–neodymium (Nd) and lead (Pb) isotopic analyses of individual mesobands of five Banded Iron Formations (BIFs) and associated volcanic and sedimentary rocks from the Neoarchean Tati Greenstone Belt (TGB, Northeastern Botswana) were conducted in order to characterize the source(s) and depositional environment(s). Rare earth element (REE)–yttrium (Y) patterns of individual BIF mesobands show features characteristic

Lasse N. Døssing; Robert Frei; Henrik Stendal; Read B. M. Mapeo

2009-01-01

55

Oldest reliable Ar-40/Ar-39 ages for terrestrial rocks Barberton Mountain komatiites  

NASA Astrophysics Data System (ADS)

The first Ar-40/Ar-39 ages for komatiites and komatiitic basalts from the Barberton Mountain Greenstone Belt on the Transvaal-Swaziland border in southern Africa are reported. Both rock types display remarkable argon retentivity. While some variation is found among the samples, the best argon age estimate for the time of metamorphism is in the 3450-3490 Myr range. This age is only slightly less than that found in komatiites from the same area by Sm-Nd dating. The results show that the principal pervasive greenschist metamorphism in the area must have occurred within 100 Myr of the eruption of the komatiite. These results represent by far the oldest reliable ages obtained for terrestrial rocks using the K-Ar system.

Lopez Martinez, M.; York, D.; Hall, C. M.; Hanes, J. A.

1984-01-01

56

The volcanology of komatiites as deduced from field relationships in the Norseman-Wiluna greenstone belt, Western Australia  

NASA Astrophysics Data System (ADS)

Komatiites in the western part of the Norseman-Wiluna greenstone belt in the Yilgarn Block of Western Australia display a wide variety of volcanic facies, ranging from very thin differentiated Munro Township-type flow units through to very thick olivine-rich cumulate flow units containing high proportions of adcumulate dunite. Cumulate flow units have been mapped in detail in the Agnew-Wiluna segment of the Norseman-Wiluna Greenstone Belt. In the Yakabindie and Mt. Keith areas, thick lenticular bodies of olivine adcumulate are flanked and overlain by thinner sheet-like sequences of finer grained olivine orthocumulates. They show fine-scale internal layering, broad-scale cryptic layering and upper fractionated sequences containing harrisites, pyroxene bearing cumulates and in some cases gabbroic derivatives. Low grade disseminated sulphide mineralisation occurs within the dunite lenses. In the stratigraphically equivalent Kathleen East area adcumulate dunite grades laterally into olivine orthocumulates and spinifex textured flows. A similar relationship is also seen further south, where the Perseverance ultramafic complex consists of a thick central dunite lens flanked on one side by thin fine grained orthocumulate sequences and on the other by intercalated orthocumulates and spinifex textured flows. These field relationships indicate an extrusive origin for the adcumulate dunite bodies. The Walter Williams Formation, in the west-central part of the Norseman-Wiluna Belt, is a very large cumulate flow unit 150 km long and 30 km wide in presently exposed extent. It consists of a central sheet-like body of adcumulate dunite, underlain and overlain by olivine orthocumulates. The adcumulate sheet is everywhere capped by a distinctive thin layer of olivine harrisite. At its northernmost extent, the flow unit consists of cyclically layered olivine and pyroxene bearing cumulates capped by gabbros, dolerites and pyroxene spinifex-textured material, interpreted as a periodically replenished lava lake sequence. Both the lenticular dunite bodies of the Agnew-Wiluna Belt and the sheet-like dunite body of the Walter Williams Formation are interpreted as crystallisation products of very large submarine komatiite lava flows which erupted and flowed at very high rates. The adcumulate dunites are interpreted as the products of in situ crystallisation at low degrees of supercooling at the top of upward and inward accreting crystal piles at the bases of the flows. Flanking and overlying olivine orthocumulates reflect higher rates of heat loss at the site of crystallisation due to lower lava flow rates. Field evidence from Perseverance, and the general geometry of the dunite lenses, suggest that the lenses formed within large thermal erosion channels developed by turbulent lava rivers flowing over low-melting felsic volcanic substrates. The textural range exhibited by komatiites can be integrated into a comprehensive model for the geometry of large komatiite flow fields formed by rapid extrusion. Dunite sheets form close to the eruption sites, and dunite lenses as a result of channellisation further away from the vent, or close to the vent in the situation where the substrate is non-refractory and thermal erosion can take place readily. Kambalda-type volcanic facies develop in more distal environments where lava emplacement is channellised and episodic, and Munro-type flow units represent small scale lava tubes formed at low flow rates on the distal flanks of major eruptions, or close to the vent of very small ones. Waning eruption rates leads to proximal facies being overridden by distal ones, a common observation in komatiite sequences. The size of thermal erosion channels requires very rapid eruption rates comparable to those in Phanerozoic flood basalt terrains.

Hill, R. E. T.; Barnes, S. J.; Gole, M. J.; Dowling, S. E.

1995-01-01

57

A glimpse of Earth's primordial crust: The Nuvvuagittuq greenstone belt as a vestige of mafic Hadean oceanic crust  

NASA Astrophysics Data System (ADS)

Investigation of Earth’s primitive crust is biased towards felsic rocks because they contain zircons that provide robust geochronological constraints. Felsic rocks, however, cannot be derived directly from the mantle thus the first crust had to be mafic in composition. Obtaining precise ages on old mafic rocks is however difficult due to their lack of zircon and the metamorphic overprinting they have suffered. 143Nd and 142Nd analyses on the Nuvvuagittuq greenstone belt suggests that its mafic components formed more than 4 billion years ago and that the dominant lithology of the belt, known as the “faux-amphibolite”, represents the only relict of Hadean crust formed at ~4.3 Ga. Its protolith is interpreted to be mafic volcanic rocks and volcanic pyroclastic deposits. The faux-amphibolite can be divided into three distinct geochemical group stratigraphically superimposed. The faux-amphibolite at the base of the sequence is tholeiitic with a composition indicating derivation of primary melts from an undepleted mantle and fractionation under dry conditions. Towards the top of the volcanic sequence, the faux-amphibolites are characterized by higher Al/Ti ratios. They appear to have fractionated under elevated water pressure and are geochemically similar to modern boninite and calc-alkaline volcanic rocks. A new series of faux-amphibolite was analysed for 142Nd isotopic composition. 21 samples have deficits in 142Nd ranging from -7 to -18 ppm compared to the terrestrial standard. These deficits have now been confirmed by measurements of the same samples at ETH (Roth et al., GCA, A886, 2010). A 146Sm-142Nd isochron constructed for all faux-amphibolite yields an age of 4368 +72-142 Ma (n=30). A line fit only to the faux-amphibolite compositional group that shows the widest range in LREE enrichment, including corresponding co-genetic ultramafic sills gives a 146Sm-142Nd age of 4381 +67-123 Ma (n=21). The Hadean age for the faux-amphibolite is supported by a 4079 ± 110 Ma (n=15) 147Sm-143Nd age for intruding gabbro sills. The supracrustal sequence has been highly metamorphosed with isotopic data suggesting metamorphic events at circa 3.8 Ga and 3.1 Ga with the last significant heating event recorded at ~2.65 Ga in Sm-Nd data for garnets from the faux-amphibolite. This supports a mafic composition for Earth’s primitive crust with a compositional transition from tholeitic to boninitic and calc-alkaline volcanic rocks. The presence of pillow basalts supports a subaqueous eruption for at least a portion of the province. The Nuvvuagittuq faux-amphibolite shares some chemical characteristics with the 3.8 Ga Garbenschiefer unit of the Isua greenstone belt in SW Greenland. Both the Garbenschiefer and the faux-amphibolite are chemically similar to modern-day suprasubduction volcanic arc lavas suggesting that modern plate tectonic regime already may have been established on Earth by the Hadean/Eoarchean. Regardless of the tectonic regime, the similarities between the 3.8 Ga Garbenschiefer and the Nuvvuagittuq 4.3 Ga faux-amphibolite suggest that their chemical features are perhaps characteristic of Earth’s early mafic crust.

O'Neil, J.; Carlson, R. W.

2010-12-01

58

Age constraints on felsic intrusions, metamorphism and gold mineralisation in the Palaeoproterozoic Rio Itapicuru greenstone belt, NE Bahia State, Brazil  

USGS Publications Warehouse

U-Pb sensitive high resolution ion microprobe mass spectrometer (SHRIMP) ages of zircon, monazite and xenotime crystals from felsic intrusive rocks from the Rio Itapicuru greenstone belt show two development stages between 2,152 and 2,130 Ma, and between 2,130 and 2,080 Ma. The older intrusions yielded ages of 2,152??6 Ma in monazite crystals and 2,155??9 Ma in zircon crystals derived from the Trilhado granodiorite, and ages of 2,130??7 Ma and 2,128??8 Ma in zircon crystals derived from the Teofila??ndia tonalite. The emplacement age of the syntectonic Ambro??sio dome as indicated by a 2,080??2-Ma xenotime age for a granite dyke probably marks the end of the felsic magmatism. This age shows good agreement with the Ar-Ar plateau age of 2,080??5 Ma obtained in hornblendes from an amphibolite and with a U-Pb SHRIMP age of 2,076??10 Ma in detrital zircon crystals from a quartzite, interpreted as the age of the peak of the metamorphism. The predominance of inherited zircons in the syntectonic Ambro??sio dome suggests that the basement of the supracrustal rocks was composed of Archaean continental crust with components of 2,937??16, 3,111??13 and 3,162??13 Ma. Ar-Ar plateau ages of 2,050??4 Ma and 2,054??2 Ma on hydrothermal muscovite samples from the Fazenda Brasileiro gold deposit are interpreted as minimum ages for gold mineralisation and close to the true age of gold deposition. The Ar-Ar data indicate that the mineralisation must have occurred less than 30 million years after the peak of the metamorphism, or episodically between 2,080 Ma and 2,050 Ma, during uplift and exhumation of the orogen. ?? Springer-Verlag 2006.

Mello, E. F.; Xavier, R. P.; McNaughton, N. J.; Hagemann, S. G.; Fletcher, I.; Snee, L.

2006-01-01

59

The Key Tuffite, Matagami Camp, Abitibi Greenstone Belt, Canada: petrogenesis and implications for VMS formation and exploration  

NASA Astrophysics Data System (ADS)

The Key Tuffite is a stratigraphic marker unit for most of the zinc-rich volcanogenic massive sulfide deposits of the Matagami Camp in the Abitibi Greenstone Belt. This 2- to 6-m-thick unit was previously interpreted as a mixture of ash fall (andesitic to rhyolitic tuffaceous components) and volcanogenic massive sulfide (VMS)-related chemical seafloor precipitate (exhalative component). Previous attempts to develop geochemical exploration vectoring tools using metal content within the Key Tuffite were mostly inconclusive due to the complex nature of the Key Tuffite unit and a poor understanding of its composition, origin and relationship with the VMS-forming hydrothermal systems. Detailed mapping and thorough lithogeochemistry of the Key Tuffite in the vicinity of the Perseverance and Bracemac-McLeod deposits indicate that the Key Tuffite is a homogeneous calc-alkaline, andesitic tuff that was deposited before the VMS deposits were formed. The unit is mostly devoid of exhalative component, but it is strongly hydrothermally altered close to orebodies. This is characterized by a strong proximal chloritization and a distal sericitization, which grades laterally into the unaltered Key Tuffite. Neither the Key Tuffite nor the ore was formed by seafloor exhalative processes for the two studied deposits. This probably explains why previously proposed exploration models based on metal scavenging proved unsuccessful and suggests that a re-evaluation of the exhalative model should be done at the scale of the mining camp. However, as shown in this study, hydrothermal alteration can be used to vector towards ore along the Key Tuffite.

Genna, Dominique; Gaboury, Damien; Roy, Gilles

2014-04-01

60

Evidence of water degassing during emplacement and crystallization of 2.7 Ga komatiites from the Agnew-Wiluna greenstone belt, Western Australia  

NASA Astrophysics Data System (ADS)

Komatiites are ancient volcanic rocks, mostly over 2.7 billion years old, which formed through >30% partial melting of the mantle. This study addresses the crucial relationship between volcanology and physical manifestation of primary magmatic water content in komatiites of the Agnew-Wiluna greenstone belt, Western Australia, and documents the degassing processes that occurred during the emplacement and crystallization of these magmas. The Agnew-Wiluna greenstone belt of Western Australia contains three co-genetic komatiite units that (1) display laterally variable volcanological features, including thick cumulates and spinifex-textured units, and (2) were emplaced as both lava flows and intrusions at various locations. Komatiite sills up to 500 m thick contain widespread occurrence of hydromagmatic amphibole in orthocumulate- and mesocumulate-textured rocks, which contain ca. 40-50 wt% MgO and <3 wt% TiO2. Conversely, komatiite flows do not contain any volatile-bearing mineral phases: ~150-m-thick flows only contain vesicles, amygdales and segregation structures, whereas <5-10-m-thick flows lack any textural and petrographic evidence of primary volatile contents. The main results of this study demonstrate that komatiites from the Agnew-Wiluna greenstone belt, irrespective of their initial water content, have degassed upon emplacement, flow and crystallization. More importantly, data show that komatiite flows most likely degassed more water than komatiite intrusions. Komatiite degassing may have indirectly influenced numerous physical and chemical parameters of the water from the primordial oceans and hence indirectly contributed to the creation of a complex zonation at the interface between water and seafloor.

Fiorentini, M. L.; Beresford, S. W.; Stone, W. E.; Deloule, E.

2012-07-01

61

Early Proterozoic (2.0 GA) Phosphorites from Pechenga Greenstone Belt and Their Origin  

NASA Technical Reports Server (NTRS)

The period of 2500-2000 Ma is heralded by several other hallmark events, including onset and decline of the greatest positive excursion of Beta13Ccarb (Lomagundi-Jatuli Paradox), development of a significant seawater sulphate reservoir, abundant deposition of anomalously organic matter (OM)-rich sediments, the oldest known significant petroleum deposits (Shunga Event), and the appearance of first known marine phosphorites at 2000 Ma as reported here. They occur as numerous rounded, soft-deformed, clasts in fine-pebble intra-formational conglomerates, forming two separate c. 200 m-thick turbidite fans within the 1000 m-thick OM- and sulphide-rich turbiditic greywackes of the Pilgujaervi Formation in the Pechenga Greenstrone Belt, NW Russia. Carbonate-fluorapatite is the main mineral in the phosphorite clasts. OM, framboidal and micronodular pyrite as well as inclusions of quartz and chlorite are additional components. Many clasts show microlayering with a variable degree of soft-deformation, implying that they were derived from non-lithified, bedded phosphorites. Numerous samples revealed diverse microbial microstructures interpreted as cyanobacterial mats consisting of filamentous (1-3 micrometer in diameter, 20 micrometers in length), coccoidal (0.8-1.0 micrometers) and ellipsoidal or rod-shaped microfossils (0.8 micrometers in diameter, around 2 micrometers in length) which morphologically resemble modern Microcoleus and Syphonophycus, Thiocapsa, and Rhabdoderma, respectively, reported from alkaline or saline environments. No principle differences have been found between microfossils described from Cambrian and Phanerozoic and the 2000 Ma phosphorites. The sequence of the early Palaeoproterozoic events which point to a significant oxidation of the hydrosphere, now including formation of phosphorites and change in the phosphorous cycle, mimics the sequence which was repeated once again at the Neoproterozoic-Cambrian transition, implying that oxidation of the terrestrial atmosphere-hydrosphere system experienced an irregular cyclic development.

Rozanov, A. Yu.; Astafieva, M. M.; Melezhik, V. A.; Hoover, R. B.; Lepland, I.

2007-01-01

62

Chemical characterization of earth’s most ancient clastic metasediments from the Isua Greenstone Belt, southern West Greenland  

NASA Astrophysics Data System (ADS)

New and published major and trace element abundances of clastic metasediments (mainly garnet-biotite-plagioclase schists) from the ˜3.8 Ga Isua Greenstone Belt (IGB), southern West Greenland, are used in an attempt to identify the compositional characteristics of the protoliths of these sediments. Compositionally, the metasediments are heterogeneous with enrichment of LREE (La/Sm chond = 1.1-3.9) and variable enrichment and depletion of HREE (Gd/Yb chond = 0.8-4.3). Chondrite-normalized Eu is also variable, spanning a range from relative Eu depletion to enrichment (Eu/Eu* = 0.6-1.3). A series of geochemical and geological criteria provides conclusive evidence for a sedimentary origin, in disagreement with some previous studies that questioned the presence of genuine clastic metasediments. In particular, trace element systematics of IGB metasediments show strong resemblance to other well-documented Archaean clastic sediments, and are consistent with a provenance consisting of ultramafic, mafic and felsic igneous rocks. Two schists, identified as metasomatized mafic igneous rocks from petrographic and field evidence, show distinct compositional differences to the metasediments. Major element systematics document incipient-to-moderate source weathering in the majority of metasediments, while signs of secondary K-addition are rare. Detailed inspection of Eu/Eu*, Fe 2O 3 and CIW (chemical index of weathering) relationships reveals that elevated iron contents (when compared to averages for continental crust) and strong relative enrichment in Eu may be due to precipitation of marine Fe-oxyhydroxides during deposition or diagenesis on the seafloor. Some of the IGB metasediments have yielded anomalous 142Nd and 182W isotopic compositions that were respectively interpreted in terms of early mantle differentiation processes and the presence of a meteorite component. Alternatively, W and possibly Nd isotopes could have been affected by thermal neutron capture on the Hadean surface. The latter process was tested in this study by analysis of Sm isotope compositions, which serve as an effective monitor for neutron capture effects. As no anomalous variation from terrestrial values was detected, we infer that isotope systematics (including 182W and 142Nd) of IGB metasediments were not affected by neutron capture, but reflect decay of radioactive parent isotopes.

Bolhar, Robert; Kamber, Balz S.; Moorbath, Stephen; Whitehouse, Martin J.; Collerson, Kenneth D.

2005-03-01

63

Early Archean spherule beds of possible impact origin from Barberton, South Africa: A detailed mineralogical and geochemical study  

NASA Astrophysics Data System (ADS)

The Barberton Greenstone belt is a 3.5- to 3.2-Ga-old formation situated in the Swaziland Supergroup near Barberton, northeast Transvaal, South Africa. The belt includes a lower, predominantly volcanic sequence, and an upper sedimentary sequence (e.g., the Fig Tree Group). Within this upper sedimentary sequence, Lowe and Byerly identified a series of different beds of spherules with diameters of around 0.5-2 mm. Lowe and Byerly and Lowe et al. have interpreted these spherules to be condensates of rock vapor produced by large meteorite impacts in the early Archean. We have collected a series of samples from drill cores from the Mt. Morgan and Princeton sections near Barberton, as well as samples taken from underground exposures in the Sheba and Agnes mines. These samples seem much better preserved than the surface samples described by Lowe and Byerly and Lowe et al. Over a scale of just under 30 cm, several well-defined spherule beds are visible, interspaced with shales and/or layers of banded iron formation. Some spherules have clearly been deposited on top of a sedimentary unit because the shale layer shows indentions from the overlying spherules. Although fresher than the surface samples (e.g., spherule bed S-2), there is abundant evidence for extensive alteration, presumably by hydrothermal processes. In some sections of the cores sulfide mineralization is common. For our mineralogical and petrographical studies we have prepared detailed thin sections of all core and underground samples (as well as some surface samples from the S-2 layer for comparison). For geochemical work, layers with thicknesses in the order of 1-5 mm were separated from selected core and underground samples. The chemical analyses are being performed using neutron activation analysis in order to obtain data for about 35 trace elements in each sample. Major elements are being determined by XRF and plasma spectrometry. To clarify the history of the sulfide mineralization, sulfur isotopic compositions are being determined.

Koeberl, Christian; Reimold, Wolf Uwe; Boer, Rudolf H.

1992-12-01

64

Diverse metal sources of Archaean gold deposits: evidence from in situ lead-isotope analysis of individual grains of galena and altaite in the Ross and Kirkland Lake deposits, Abitibi Greenstone belt, Canada  

Microsoft Academic Search

Lead isotope compositions for individual grains of galena and altaite (PbTe) were determined in situ using a secondary ion mass spectrometer (SIMS). Galena was collected from the Ross deposit and altaite from the Kirkland Lake (KL) deposits in the southern Abitibi greenstone belt, Superior Province of Canada. The samples from KL are more radiogenic than those from the Ross deposit.

Keiko Hattori

1993-01-01

65

Geochronology of the Archaean Kolmozero-Voron'ya Greenstone Belt: U-Pb dating of zircon, titanite, tourmaline and tantalite (Kola Region, North-Eastern BAltic Shield)  

NASA Astrophysics Data System (ADS)

The Archaean Kolmozero-Voron’ya greenstone belt is one of the most ancient geological structures of the Kola Peninsula. It is located between Upper Archaean terrains: Murmansk, Central Kola and Keivy. Within the Kolmozero-Voron'ya greenstone belt there are rare metal (Li, Cs with accessory Nb, Ta, and Be), Cu, Mo, and Au deposits. All rocks were metamorphosed under amphibolite facies conditions and intruded by granodiorites, plagiomicrocline and tourmaline granites and pegmatite veins. Four suites are distinguished within the belt: lower terrigenous formation, komatiite-tholeite, basalt-andesite-dacite and upper terrigenous formation. The U-Pb age of 2925±6 Ma on magmatic zircon was obtained for leucogabbro of differentiated gabbro-anorthosite massif Patchemvarak, situated at the boundary between volcanic-sedimentary units and granitoids of the Murmansk block. This age is the oldest for gabbro-anorthosites of the Kola Peninsula. Sm-Nd age of komatiites is ca. 2.87 Ga (Vrevsky, 1996). U-Pb age of zircon from biotite schist, which belongs to acid volcanites is 2865+/-5 Ma. Quartz porphyries, which are considered to be an intrusive vein analogous of acid volcanites has an age of 2828+/-8 Ma, that marks the final stage of the belt development. Dating of titanite from ovoid plagioamphibolites yielded an U-Pb age of 2595+/-20 Ma that probably is connected with the closure of the U-Pb isotopic titanite system during the regional metamorphism. The Porosozero granodioritic complex with an age of 2733+/-6 Ma is located between granites of the Murmansk domain, migmatites and gneisses of the Central Kola terrain and the Keivy alkaline granites. Tourmaline granites are found all over the Kolmozero-Voron’ya belt occurring among volcanogenic-sedimentary rocks of the belt. Their Pb-Pb age of 2520+/-70 Ma appears to denote the tourmaline crystallization at a post-magmatic stage of the complex formation. U-Pb zircon age from rare metal pegmatites is 1.9-1.8 Ga. Zircons from pegmatites are represented mostly by crystals with disturbed structure as a result of fluid influence that put certain restrictions on its use as a geochronometer of crystallization process [Alviola, et al. 2001]. By this reason we measured U-Pb age of tantalite. U-Pb age of tantalite from rare-metal pegmatites is ca 2.5 Ga, coeval with the age of tourmaline granites, which could be a source for pegmatites. This age determines the time of rare metal pegmatite crystallization, while zircon age of 1.9-1.8 Ga reflects the time of U-Pb zircon system disturbance under the influence of hydrothermal and metasomatic processes. Thus, several stages can be distinguished in the evolution of the Archaean Kolmozero-Voron’ya greenstone belt: protoocean with komatiite-toleite magmatism (3.0-2.9 Ga); volcanic arc with andesite-rhyolite magmatism (2.9-2.8 Ga); regional metamorphism and granitization with melting of granodiorite-granite magmas (2.7-2.6 Ga); regressive metamorphism and potassium metasomatism with the formation of tourmaline and microcline granites and rare-metal pegmatites within and outside the belt 2.5 Ga. The work is supported by RFBR grants 01-05-65451 and 00-05-72032

Kudryashov, N.; Gavrilenko, B.; Apanasevich, E.

2003-04-01

66

Unravelling the Maggie Hays and Emily Ann nickel sulphide deposits via a multidisciplinary study of the Archaean Lake Johnston Greenstone Belt, Yilgarn Craton, Western Australia.  

NASA Astrophysics Data System (ADS)

In order to better understand the architecture and structural evolution of the Archaean Lake Johnston Greenstone Belt and predict, the distribution of remobilized magmatic ultramafic nickel-sulphide mineralization in the belt, a multidisciplinary study has been carried out on the central area of the greenstone belt around the Maggie Hays and Emily Ann nickel-sulphide deposits. The nickel-sulphide deposits are hosted in a sequence of amphibolite facies rocks, severely affected by metamorphic and magmatic events. Geochronology, structural and metamorphic petrology and 3D geological modelling have been undertaken. Through a common georeferencing using Geomodeller 3D modelling software, all available data (geological map, interpretative cross-sections, drill hole and structural information) have been integrated into a 3D model to constrain the thickness of the lithologies and their geometry. Applying the THERMOCALC software coupled to the analysis of textural relationships between the main metamorphic phases, the peak P-T conditions were estimated from garnet rims and matrix minerals. The P-T evolution was deduced from garnet core compositions. The U-Pb SHRIMP method on monazite was utilized to constrain the time parameter of the P-T-t path. Two major thermal events have been inferred from the field relationships. The D1 event was part of regional metamorphism associated with a strong NNE-SSW shortening. The D1 event is associated with the development of kilometre-scale recumbent folds currently preserved at the Emily Ann Ni-deposit during top-to-the-NNE transport. A 2634 +/- 4.6 Ma SHRIMP age of folded dykes in the deposit provides an upper age limit on the D1 event. During this first event, massive nickel sulphides were mechanically remobilized into major fold hinges. The D2 event was associated with peak metamorphic temperatures, and was linked to the emplacement of the granite intrusions into the belt. The D2 event is characterized in the field by an intense top-to-the-SSE shearing. This deformation has substantially remobilized the massive nickel sulphide ore. Garnet-bearing pegmatitic intrusions that cross cut the ductile fabrics associated with peak metamorphism are common at the Maggie Hays deposit, and provide a lower U-Pb SHRIMP age constraint on the D2 event of 2631 +/- 2.9 Ma. The intense shearing observed occurred at upper amphibolite facies, and is inferred to be a key component of massive sulphide remobilization. The studied samples reached metamorphic peak conditions of 596-678 +/- 65 °C and 5-7 +/-2.1 kbars during D2. The combination of different applied approaches is helping to build a better understanding of stratigraphic and structural relationships in the greenstone belt and is helping to develop new exploration targets. Key words: Yilgarn craton, SHRIMP U-Pb dating, metamorphic petrology, 3D modelling.

Joly, A.; Miller, J.; Stott, C.; McCuaig, T.; Duguet, M.

2008-12-01

67

Hydrogen and Carbon Isotope Ratios in the Archean Pilbara Greenstone Belt: Contraints on the Mechanisms of Oxygen Buildup in the Atmosphere  

NASA Astrophysics Data System (ADS)

Hydrogen and carbon isotope ratios of secondary phases formed during seafloor hydrothermal alteration provide constraints on important reservoirs affected by oxygen build-up in the atmosphere. We determined hydrogen and carbon isotope ratios from the well-preserved, ~3.5 Gyr Pilbara greenstone belt to constrain:1) whether hydrogen loss is a viable mechanism for changing the oxidation state of the Archean atmosphere and the lithosphere and 2) the relative proportions of the inorganic carbon (carbonates) and the reduced carbon reservoir. The hydrogen isotope values on greenstones (from the core of the North Pole dome to the base of the Fortescue Group) and granites (from the North Pole, Shaw, Mt Edgar and Coruna Downs batholiths) exhibit the following ranges: -84 < ?D < -22 (mean -64; 33 analyses) and -36 < ?D < -87 (mean -66; 17 analyses), respectively. A single Fortescue (Late Archean) basalt gave a ?D value of -34. The secondary calcite in the greenstones exhibits the following range: -3.7 < ?13C < 1.7 (mean -0.4; 79 determinations). The hydrogen isotope ratio of the ocean is extremely sensitive to hydrogen loss because of the large (several hundred per mil) negative fractionation between hydrogen gas and water vapor. These results indicate that if hydrogen loss affected the oxidation state of the early atmosphere, it should have happened before 3.5 Gyr and not be delayed until the Archean to Proterozoic transition; i.e. the Archean ?D values are indistinguishable from Phanerozoic values. Because of its retrograde solubility and the relative insensitivity of the ?13C value of precipitated secondary carbonate to temperature, the ?13C values of hydrothermal calcite in pillow lavas are proxies for the carbon isotope ratio of the inorganic carbonate reservoir sampled by the ancient ocean. The secondary calcite ?13C values are remarkably similar to values measured on similar calcites from Tertiary and Mesozoic oceans indicating that a complementary 13C-depleted reservoir comparable in size to the present one existed by 3.5 Gyr.

Gregory, R. T.; Richards, I. J.; Ferguson, K. M.

2005-12-01

68

Environmental arsenic contamination and its health effects in a historic gold mining area of the Mangalur greenstone belt of Northeastern Karnataka, India  

PubMed Central

This report summarizes recent findings of environmental arsenic (As) contamination and the consequent health effects in a community located near historic gold mining activities in the Mangalur greenstone belt of Karnataka, India. Arsenic contents in water, hair, nail, soil and food were measured by FI-HG-AAS. Elemental analyses of soils were determined by ICP-MS (inductively coupled plasma-mass spectrometry). Of 59 tube-well water samples, 79% had As above 10 ?g L?1 (maximum 303 ?g L?1). Of 12 topsoil samples, six were found to contain As greater than 2000 mg kg?1 possibly indicating the impact of mine tailings on the area. All hair and nail samples collected from 171 residents contained elevated As. Arsenical skin lesions were observed among 58.6% of a total 181 screened individuals. Histopathological analysis of puncture biopsies of suspected arsenical dermatological symptoms confirmed the diagnosis in 3 out of 4 patients. Based on the time-course of arsenic-like symptoms reported by the community as well as the presence of overt arsenicosis, it is hypothesized that the primary route of exposure in the study area was via contaminated groundwater; however, the identified high As content in residential soil could also be a significant source of As exposure via ingestion. Additional studies are required to determine the extent as well as the relative contribution of geologic and anthropogenic factors in environmental As contamination in the region. This study report is to our knowledge one of the first to describe overt arsenicosis in this region of Karnataka, India as well as more broadly an area with underlying greenstone geology and historic mining activity.

Chakraborti, Dipankar; Rahman, Mohammad Mahmudur; Murrill, Matthew; Das, Reshmi; Siddayya; Patil, S.G.; Sarkar, Atanu; Dadapeer, H.J.; Yendigeri, Saeed; Ahmed, Rishad; Das, Kusal K.

2014-01-01

69

Source heterogeneity for the major components of ? 3.7 Ga Banded Iron Formations (Isua Greenstone Belt, Western Greenland): Tracing the nature of interacting water masses in BIF formation  

Microsoft Academic Search

We report trace element, samarium (Sm)–neodymium (Nd) and lead (Pb) isotopic data for individual micro-and mesobands of the Earth's oldest Banded Iron Formation (BIF) from the ?3.7–3.8 Ga Isua Greenstone Belt (IGB, West Greenland) in an attempt to contribute to the characterization of the depositional environment and to the understanding of depositional mechanisms of these earliest chemical sediments. Rare earth element

Robert Frei; Ali Polat

2007-01-01

70

Gold mineralization in the Mazowe area, Harare-Bindura-Shamva greenstone belt, Zimbabwe: II. Genetic relationships deduced from mineralogical, fluid inclusion and stable isotope studies, and the Sm-Nd isotopic composition of scheelites  

Microsoft Academic Search

In the Mazowe area some 40?km NW of Harare in Zimbabwe, gold mineralization is hosted in a variety of lithologies of the\\u000a Archean Harare-Bindura-Shamva greenstone belt, in structures related to the late Archean regional D2\\/3 event. Conspicuous\\u000a mineralzogical differences exist between the mines; the mainly granodiorite-hosted workings at Mazowe mine are on pyrite-rich\\u000a reefs, mines of the Bernheim group have

T. Oberthür; T. G. Blenkinsop; U. F. Hein; M. Höppner; A. Höhndorf; T. W. Weiser

2000-01-01

71

Internal stratigraphic architecture of the komatiitic dunite-hosted MKD5 disseminated nickel sulfide deposit, Mount Keith Domain, Agnew-Wiluna Greenstone Belt, Western Australia  

NASA Astrophysics Data System (ADS)

The MKD5 nickel deposit is hosted by the Mount Keith Ultramafic Complex (MKUC), a dunite body of komatiitic affinity located in the Agnew-Wiluna Greenstone Belt, Western Australia. The internal architecture of the MKUC comprises seven distinct internal units that range from extreme adcumulate dunite to relatively fractionated pyroxenitic and gabbroic horizons. The MKUC is divided into three packages of units. The main adcumulate domain (MAD), which is situated in the lower portion of the complex, contains the bulk of disseminated nickel sulfide and is dominated by coarse adcumulate olivine textures. Overlying the MAD is an upper fractionated zone, which is dominated by mesocumulate-to-orthocumulate peridotite with domains containing oikocrystic pyroxenite and gabbroic lenses. An aerially restricted unit comprising texturally and chemically distinct olivine cumulate rocks is known as the western mineralized zone (WMZ). The fractionation trend between the MAD and UPZ indicates a westerly facing for the MKUC, conformable with the bounding stratigraphy. In the MKUC, truncation of some of the uppermost internal stratigraphic units by the hangingwall contact indicates that the unit has undergone structural modification since its emplacement and suggests that a proportion of the upper section has been removed by faulting. Furthermore, vertical and lateral textural transitions within the internal stratigraphy suggest that the MKUC (excluding the WMZ) was emplaced from an essentially continuous magma flow, with the MAD representing the period of highest magma flux and the major constructional period of emplacement. Conversely, the WMZ is interpreted to represent a later pulse of ultramafic magma, emplaced stratigraphically above the main MKUC. Comparison of the MKUC with other komatiitic dunites from both within the Agnew-Wiluna Greenstone Belt and worldwide indicates that despite apparent geometrical differences between lens and sheet komatiitic dunites, a broad facies architecture can be defined. We suggest that the differences in geometry are related to differing degrees of flow localization within dunitic units and are a function of both differences in the thermal characteristics and the degree of litho-facies heterogeneity of the enclosing lithologies.

Rosengren, N. M.; Grguric, B. A.; Beresford, S. W.; Fiorentini, M. L.; Cas, R. A. F.

2007-11-01

72

Using the Abitibi Greenstone Belt to understand Martian hydrothermal systems and the potential for biosignature preservation in high temperature aqueous environments  

NASA Astrophysics Data System (ADS)

Impact and magmatic driven hydrothermal systems have long been postulated to exist on Mars. Recent observations of high-temperature mineral associations, e.g., smectite-chlorite-carbonate-serpentine, provide evidence consistent with the presence of hydrothermal environments in the ancient Martian rock record. In light of these discoveries, it is instructive to examine fossil hydrothermal systems on Earth to better understand the conditions under which putative Martian hydrothermal mineral assemblages may have formed. Such investigations may prove to be important in the era of Mars Sample Return, as we possess little scientific understanding of the biosignature preservation potential of ancient terrestrial hydrothermal systems. Motivated by these issues, the Agouron Institute organized a Geobiology Field School in July, 2011 to study the 2.7 Ga Abitibi greenstone belt in Ontario, CA. The Abitibi hosts world-renowned economic volcanogenic massive sulfide mineral deposits, and is characterized by a rich suite of lithologies emplaced predominantly in sub-oceanic settings, including komatiites, basalts, and rhyolitic volcanic rocks and banded iron formation, most of which have been hydrothermally altered, remineralized, and tectonically deformed under greenschist facies conditions. During a 10-day excursion to the Abitibi, guided by the Ontario Geological Survey, our team examined these assemblages, performed in-situ analyses using field portable active mid-IR and reflectance VIS-NIR spectrometers, an X-ray diffractometer, and an X-ray fluorescence spectrometer to inform an extensive sampling campaign. These samples have been returned to our laboratories for in-depth analysis. We will report on the outcome of our field campaign and discuss the unique opportunity provided by examination of the Abitibi to compare and contrast the effects of hydrothermal alteration and mineralization on an ocean planet with an active biosphere to a planet where the presence of large, long-lived water bodies and biology remain open questions.

Hurowitz, J. A.; Abelson, J.; Allwood, A.; Anderson, R. B.; Atkinson, B.; Beaty, D.; Bristow, T. F.; Ehlmann, B. L.; Eigenbrode, J. L.; Grotzinger, J. P.; Hand, K. P.; Halevy, I.; Knoll, A.; McCleese, D. J.; Milliken, R.; Russell, M.; Stolper, D. A.; Stolper, E. M.; Tosca, N. J.

2011-12-01

73

Thermomechanical erosion at the Alexo Mine, Abitibi greenstone belt, Ontario: implications for the genesis of komatiite-associated Ni-Cu-(PGE) mineralization  

NASA Astrophysics Data System (ADS)

The archetypical komatiite-hosted Alexo Ni-Cu-(PGE) deposit occurs in the 2,720-2,710-Ma Kidd-Munro Assemblage of the western Abitibi greenstone belt in Dundonald Township, Ontario. Detailed mapping of a 200-m long glacially polished outcrop provides unequivocal evidence that the host komatiite flow thermomechanically eroded footwall andesites: (1) the contact between komatiite and andesite is very sharp but delicately scalloped, marked by a <1-cm-thick selvedge of black aphanitic komatiite and clearly transgresses pillow structures and interpillow breccias in the andesite without any evidence of a regolith, shearing, or folding, producing multiple nested embayments on scales from hundreds of meters to a few centimeters; (2) the andesites have been contact metamorphosed and altered along the entire length of the outcrop and the degree of metamorphism/alteration is thicker and more intense around embayments; (3) xenoliths of andesite in komatiite are more common within embayments; (4) komatiitic dikes penetrate downward into underlying andesites, primarily along the lateral margins of embayments; and (5) many of the dikes and marginal rocks exhibit geochemical evidence of contamination. This physical and geochemical evidence for thermomechanical erosion, combined with S isotopic evidence for a major component of non-magmatic country-rock S in the ores, provides additional support for the roles of thermomechanical erosion and incorporation of country-rock S in the genesis of komatiite-associated Ni-Cu-(PGE) deposits. The detailed mapping also reveals that the stratigraphy of the ore zone is considerably more complex than previously reported, indicating that the sulfides were emplaced in several stages, confirming the dynamic nature of the ore emplacement process in komatiite-associated Ni-Cu-(PGE) deposits.

Houlé, Michel G.; Lesher, C. Michael; Davis, Paul C.

2012-01-01

74

Early Cambrian Post-collisional volcanosedimentary Rey Bouba greenstone belt in northern Cameroun: LA-MC-ICP-MS U-Pb geochronology and implications for the geodynamic evolution of the Central African Fold Belt (CAFB).  

NASA Astrophysics Data System (ADS)

The Rey Bouba Greenstone Belt (RBGB) is a greenschist volcanosedimentary basin representing the youngest accretion event that characterized the geodynamic evolution of the CAFB of Northern Cameroon. LA-MC-ICP-MS U-Pb detrital zircon data indicate that both older PP to MP and younger NP to Early Cambrian sources from ca 2000 to ca 540 Ma, with main provenance being zircon grains from Cryogenian igneous rocks (between ca 850 and ca 650 Ma) were involved in the formation of the RBGB basin. Considering the age of metamorphism inferred from high pressure granulites at ca 600 Ma within the CAFB of northern Cameroon as the most direct evidence for the timing of continental collision, we conclude that the deformation associated with migmatites and post-collisional granites which fed the Rey Bouba basin mostly with NP zircon lasts until post 540 Ma, in correlation with the final amalgamation of the Gondwana Supercontinent during Latest Neoproterozoic-Earliest Cambrian. Therefore, the RBGB may represent the youngest post-collisional metavolcanosedimentary basin within the CAFB.

Bouyo, Merlain

2014-05-01

75

Intra-sill magmatic evolution in the Cummings Complex, Abitibi greenstone belt: Tholeiitic to calc-alkaline magmatism recorded in an Archaean subvolcanic conduit system  

NASA Astrophysics Data System (ADS)

The stratigraphy of the Abitibi greenstone belt in the Chibougamau area (southern Superior Province, Québec), is dominated by 2 cycles of mafic-felsic metavolcanic and metasedimentary rocks constituting the Roy Group, which is riddled by metagabbroic sills (25%). The Doré Lake Complex (DLC, 2728 Ma) is emplaced into the lower Roy Group. The Cummings Complex sills (2717 Ma) were injected between the Bruneau member and Blondeau Formations of the 2nd Roy Group cycle. The sills of the Cummings Complex (Roberge, Ventures and Bourbeau Sills) contain metaperidotite, metapyroxenite, metagabbro and metagranophyric facies. The trace element contents of melts in equilibrium with these metacumulate rocks were calculated and are compared to Roy Group lavas to clarify the regional magmatic history. Many DLC model melts have fractionated trace element profiles, with LILE-LREE-enrichment, HREE-depletion, and negative Nb-Ta-anomalies suggesting that the DLC formed largely from calc-alkaline melts extracted from garnet-bearing residues. The DLC is coeval with, and shows geochemical resemblances to Waconichi Formation tuffs (the felsic cap of the 1st Roy Group cycle), suggesting it could represent the Waconichi's shallow magma chamber. Meta-anorthosite rafts from the para-autochtonous zone of the Grenville province yield model melts closely resembling those of the DLC and are correlated on this basis. Most Roy Group sills yield model melts with trace element patterns typical of Archaean tholeiites, suggesting they fed the regionally-dominant tholeiitic volcanic plain lavas of the Roy Group. Models for the Cummings Complex imply that it contained two types of magma. Model melts from the Roberge Sill have strongly fractionated calc-alkaline-like trace element patterns, while those of the Ventures and Bourbeau Sills are mostly flat, N-MORB-normalized tholeiitic-like patterns that cannot be derived from the Roberge Sill melts by fractional crystallization. The Roberge Sill must have a separate magmatic stem, and represents the feeder system for a calc-alkaline volcano, possibly represented in part by Blondeau Formation rhyolites, andesites and basalts? If this is correct, the Roberge may be older than the Ventures and Bourbeau Sills, which would have fed the tholeiitic base of a third magmatic cycle, since eroded.

Bédard, Jean H.; Leclerc, François; Harris, Lyal B.; Goulet, Normand

2009-07-01

76

Pb, Sr and Nd isotope systematics of metavolcanic rocks of the Hutti greenstone belt, Eastern Dharwar craton: Constraints on age, duration of volcanism and evolution of mantle sources during Late Archean  

NASA Astrophysics Data System (ADS)

The Hutti greenstone belt, hosting major gold mines, is made up of tholeiitic basalts, felsic volcanic rocks and sediments metamorphosed to amphibolite facies and surrounded by granitoid rocks, predominantly of granodiorite in composition. The granitoid rocks show intrusive contact relationship at places along the eastern and northern margins of the belt while such relationships could not be observed along the western margin as it is covered by soil. The tholeiitic basalts have flat to moderately LREE-enriched chondrite normalized REE patterns and show depletion in Nb relative to MORB. The Hutti metabasalts define a collinear array in the Rb-Sr isotope evolution diagram with a slope corresponding to an age of 2706 ± 130 Ma. The higher uncertainty is due to scatter caused by mobility of Rb and Sr during metamorphism and low temperature hydrothermal alteration. In the 206Pb/ 204Pb vs. 207Pb/ 204Pb diagram the metabasalts define a collinear array corresponding to an age of 2637 ± 150 Ma with significant scatter indicating that Pb was also mobilized by the post-crystallization alteration processes. The Sm-Nd isotope system in the Hutti metabasalts has been least disturbed giving an isochron age of 2662 ± 81 Ma which is suggested as the age of formation of their precursors. Combined with the published U-Pb SHRIMP ages on zircons from the felsic volcanic rocks it is inferred that the Hutti greenstone belt formed over a period of ?86 Ma. The major greenstone belts of the eastern Dharwar craton have evolved coevally at ca. 2700 Ma ago and are older than the surrounding granitoid rocks. The metabasalts have ?Nd values of +1.4 to +3.0 and ?Sr values of -23.4 to +2.0 and plot close to the mantle array. They were derived from long-term LREE depleted mantle source. The felsic volcanic rocks have ?Nd values of -1.3 and -1.4 and ?Sr values of -30.6 and +89.3, respectively. Their magmas were derived from older continental crustal sources.

Anand, R.; Balakrishnan, S.

2010-07-01

77

Multiple sulfur and carbon isotope composition of the Mesoarchean Manjeri and Cheshire Formations (Belingwe Greenstone Belt, Zimbabwe): a window on the sulfur and carbon Mesoarchean biogeochemistry  

NASA Astrophysics Data System (ADS)

In order to bring further insights into the biogeochemical conditions prevailing during the dampendown Mesoarchean Mass Independant Fractionation of Sulfur (MIF-S) attributed to changes in atmospheric and/or oceanic geochemistry, we report the results of a detailed carbon (12C, 13C) and multiple sulfur (32S, 33S, 34S) isotopic study through the ~2.7 Ga Manjeri and ~2.65 Ga Cheshire Formations (Belingwe Greenstone Belt, Zimbabwe). The studied rocks consist of low-grade metamorphic (sub-greenschist facies) black shales, laminated limestones, and stromatolites. In the Manjeri Fm. the stromatolites are a minor part of the succession, which mostly show organic rich black shales associated with sulfide-rich layers. In contrast, the Cheshire Fm. shows well preserved stromatolites and black shales. Organic ?13C values of the Manjeri Formation show a wide range of ?13Corg between -16.2 and -35.4‰ (average of -30.3 ± 6.0‰), while the Cheshire formation show a narrow range of isotopic composition of -41.3 ± 3.5‰. TOC (wt. %) vary from 0.06 to 3.31 (average of 1.28) and from 0.02 to 1.05 (average of 0.18) for the Manjeri and Cheshire Fm., respectively. The remarkable difference of carbon isotope signatures between these two formations argue for the occurrence of different biomass likely reflecting different metabolic pathways, including photosynthesis, methanogenesis and methanotrophy. The Manjeri Fm. ?34S values of sedimentary sulfides (Acid Volatile Sulfur and Chromium Reducible Sulfur) vary between -15.15 and 2.37‰ (average -1.71 ± 4.76‰) and show very small and mostly negative MIF-S varying from -0.58 to 0.87‰ (average 0.02 ± 0.43‰). The Cheshire Fm. is isotopically distinct with ?34S values ranging from -2.11 to 2.39‰ (average 0.25 ± 1.08‰) and show near zero but consistently positive ?33S anomalies between 0.14 and 1.17 ‰ (average 0.56 ± 0.29‰). Sulfides S contents (wt. %) vary from 0.06 to 3.31 (average of 1.28) and from 0.02 to 1.05 (average of 0.18) for the Manjeri and Cheshire Fm., respectively. The sulfur and carbon isotopes signature recorded here likely reflect different environmental conditions and ecosystem between the Cheshire and Manjeri Fm. Low ?13Corg values in the Cheshire Fm. suggest a strong influence of methanogenesis/methanotrphy metabolisms, while the large range of Manjeri Fm. ?34S could reflect the operation of Sulfureta metabolisms (Grassineau et al., 2001). Moreover, the consistent differences in multiple sulfur isotopes systematic recorded between these two Formations suggest different atmospheric conditions (e.g. CO2/CH4 ratio and organic haze thickness) resulting in different pattern of photochemical fractionation of S isotopes. Grassineau N.V. et al., Antiquity of the biological sulphur cycle: Evidence from 2.7Ga rocks of the Belingwe Belt, Zimbabwe, Proceedings of the Royal Society of London, B, 268, (2001), 113-9.

Thomazo, C.; Strauss, H.; Grassineau, N.; Nisbet, E. G.

2010-12-01

78

Geochemistry of the NeoArchaean high-Mg basalts, boninites and adakites from the Kushtagi Hungund greenstone belt of the Eastern Dharwar Craton (EDC); implications for the tectonic setting  

NASA Astrophysics Data System (ADS)

Volcanic rocks of the Kushtagi-Hungund greenstone belt from the Eastern Dharwar Craton (EDC) show extreme diversity due to the presence of high-Mg, high Fe-, high Mg-Fe basalts, high Mg-dacites and andesites (boninitic affinities), and sodic-plagioclase-quartz rich felsic rocks (adakites with Na 2O (˜4-6 wt.%). The adakites ( Drummond and Defant, 1990; Martin, 1999) and high-Mg-dacites-andesites are being reported for the first time from greenstone belts of the Dharwar craton. Trace elements in these different types of volcanic rocks have distinct characteristics. For example, the basalts have (1) Al 2O 3/TiO 2 ˜16 (PM value of 17), (2) (La/Yb) N˜1-3, (3) low order negative anomalies of Nb/Nb*, Zr/Zr*, Hf/Hf* and Ti/Ti*, (4) Zr/Nb ˜4-10 and (5) Ce/Nb ˜3-4. Two samples of andesites having Mg-enrichment and Al 2O 3/TiO 2 ratios of 31-35 are interpreted to have boninitic affinities. Other dacites and andesites are characterized by (1) high-Mg (8-10 wt.%), (2) high Al 2O 3/TiO 2=22-27, (3) Zr/Nb=8-14, (4) (La/Yb) N ˜2-7, (5) negative Nb/Nb*, Zr/Zr*, Hf/Hf* and Ti/Ti* anomalies and (6) Sc/Lu=67-172. The adakites are characterized by (1) a narrow range of SiO 2 (67-70 wt.%), (2) enriched Na 2O (4-6 wt.%) with very high Na 2O/K 2O (2.5-7.7), (3) Low Mg# (0.38-0.48), (4) high (La/Yb) N (13-31) with fractionated patterns, no Eu anomaly and (Gd/Yb) N=2-4, (5) very high Al 2O 3/TiO 2 (50-80) and (6) enriched Ni, Cr and Co (total 50 ppm). These adakites resemble 3.0 Ga tonalite-trondhjemite gneisses of the Dharwar craton, which are interpreted as products of partial melting of the basaltic slab. The available data suggests that partial melting of the different mantle and slab sources generated this collage of compositionally different rocks within an island arc setting.

Naqvi, S. M.; Khan, R. M. K.; Manikyamba, C.; Mohan, M. Ram; Khanna, Tarun C.

2006-06-01

79

Magnesian andesites, Nb-enriched basalt-andesites, and adakites from late-Archean 2.7 Ga Wawa greenstone belts, Superior Province, Canada: implications for late Archean subduction zone petrogenetic processes  

NASA Astrophysics Data System (ADS)

Magnesian andesites (MA) occur with 'normal' tholeiitic to calc-alkaline basalt-andesite suites in four greenstone belts of the 2.7 Ga Wawa subprovince, Canada. Collectively, the magnesian andesites span ranges of SiO2=56-64 wt%, Mg-number=0.64-0.50, with Cr and Ni contents of 531-106 and 230-21 ppm, respectively. Relative to 'normal' andesites, the magnesian andesites form distinct trends on variation diagrams, with relatively high Th and LREE contents, uniform Yb over a range of MgO, more fractionated HREE, and lower Nb/Thpm and Nb/Lapm ratios. Niobium-enriched basalts and andesites (NEBA; Nb=7-16 ppm), and an Al-enriched rhyolite (adakite) suite are associated in space and time with the magnesian andesites. Nb-enriched basalts and andesites are characterized by high TiO2, P2O5, Th, and Zr contents, variably high Zr/Hf (36-44) ratios, and more fractionated HREE (Gd/Ybcn=1.3-4.1) compared to the 'normal' tholeiitic to calc-alkaline basalt-andesite suites. The adakite suite has the high Al (Al2O3=16-18 wt%), high La/Ybcn (21-43), and low Yb (0.4-1.2 ppm) of Archean tonalite-trondhjemite-granodiorite (TTG) suites and Cenozoic adakites, indicative of liquids derived mainly from slab melting. The basalt-andesite suites are not characterized by normal tholeiitic or calc-alkaline fractionation trends of major or trace elements. Rather, compositional trends can be accounted for by some combination of fractional crystallization and variable degrees of metasomatism of the source of basalt and/or andesites by adakitic liquids. The occurrence of magnesian andesites, Nb-enriched basalts/andesites, and adakites has been described from certain Phanerozoic arcs featuring shallow subduction of young and/or hot oceanic lithosphere. Adakites likely represent slab melts, magnesian andesites the product of hybridization of adakite liquids with mantle peridotite, and Nb-enriched basalts/andesites melts of the residue from hybridization. Geological similarities between the late-Archean Wawa greenstone belts and certain Cenozoic transpressional orogens with the MA-NEBA-adakite association suggest that subduction of young, hot oceanic lithosphere may have played an important role in the production of this arc-related association in the late Archean.

Polat, A.; Kerrich, R.

2001-02-01

80

The 3.26-3.24 Ga Barberton asteroid impact cluster: Tests of tectonic and magmatic consequences, Pilbara Craton, Western Australia  

NASA Astrophysics Data System (ADS)

The location in the Barberton Greenstone Belt (Kaapvaal Craton) of ˜3.26-3.24 Ga asteroid impact ejecta units at, and immediately above, a sharp break between a > 12 km-thick mafic-ultramafic volcanic crust (Onverwacht Group ˜3.55-3.26 Ga, including the ˜3.298 > 3.258 Ga Mendon Formation) and a turbidite-felsic volcanic rift-facies association (Fig Tree Group ˜3.258-3.225 Ga), potentially represents the first documented example of cause-effect relations between extraterrestrial bombardment and major tectonic and igneous events [D.R. Lowe, G.R. Byerly, F. Asaro, F.T. Kyte, Geological and geochemical record of 3400 Ma old terrestrial meteorite impacts, Science 245 (1989) 959-962; D.R. Lowe, G.R. Byerly, F.T. Kyte, A. Shukolyukov, F. Asaro, A. Krull, Spherule beds 3.47-3.34 Ga-old in the Barberton greenstone belt, South Africa: a record of large meteorite impacts and their influence on early crustal and biological evolution, Astrobiology 3 (2003) 7-48; A.Y. Glikson, The astronomical connection of terrestrial evolution: crustal effects of post-3.8 Ga mega-impact clusters and evidence for major 3.2 ± 0.1 Ga bombardment of the Earth-Moon system, J. Geodyn. 32 (2001) 205-229]. Here we correlate this boundary with a contemporaneous break and peak magmatic and faulting events in the Pilbara Craton, represented by the truncation of a 3.255-3.235 Ga-old volcanic sequence (Sulphur Springs Group—SSG) by a turbidite-banded iron formation-felsic volcanic association (Pincunah Hill Formation, basal Gorge Creek Group). These events are accompanied by ˜3.252-3.235 Ga granitoids (Cleland plutonic suite). The top of the komatiite-tholeiite-rhyolite sequence of the SSG is associated with a marker chert defined at 3.238 ± 3-3.235 ± 3 Ga, abruptly overlain by an olistostrome consisting of mega-clasts of felsic volcanics, chert and siltstone up to 250 × 150 m-large, intercalated with siliciclastic sedimentary rocks and felsic volcanics (Pincunah Hill Formation-basal Gorge Creek Group-GCG [R. M. Hill, Stratigraphy, structure and alteration of hanging wall sedimentary rocks at the Sulphur Springs volcanogenic massive sulphide (VMS) prospect, east Pilbara Craton, Western Australia. B.Sc Hon. Thesis, University of Western Australia (1997) 67 pp.; M.J. Van Kranendonk, A.H. Hickman, R.H. Smithies, D.R. Nelson, Geology and tectonic evolution of the Archaean north Pilbara terrain, Pilbara Craton, Western Australia, Econ. Geol. 97 (2002) 695-732; M.J. Van Kranendonk, Geology of the North Shaw 1 : 100 000 Sheet. Geological Survey Western Australia 1 : 100 000 Geological Series (2000) 86 pp., R. Buick, C.A.W. Brauhart, P. Morant, J.R. Thornett, J.G. Maniew, J.G. Archibald, M.G. Doepel, I.R. Fletcher, A.L. Pickard, J.B. Smith, M.B. Barley, N.J. McNaughton, D.I. Groves, Geochronology and stratigraphic relations of the Sulphur Springs Group and Strelley Granite: a temporally distinct igneous province in the Archaean Pilbara Craton, Australia, Precambrian Res. 114 (2002) 87-120]). The structure and scale of the olistostrome, not seen elsewhere in the Pilbara Craton, is interpreted in terms of intense faulting and rifting, supported by topographic relief represented by deep incision of overlying arenites (Corboy Formation) into underlying units [M.J. Van Kranendonk, Geology of the North Shaw 1 : 100 000 Sheet. Geological Survey Western Australia 1 : 100 000 Geological Series (2000) 86 pp.]. The age overlaps between (1) 3.255 ± 4-3.235 ± 3 Ga peak igneous activity represented by the SSG and the Cleland plutonic suite (Pilbara Craton) and the 3.258 ± 3 Ga S2 Barberton impact unit, and (2) 3.235 ± 3 Ga top SSG break and associated faulting and the 3.243 ± 4 S3-S4 Barberton impact units may not be accidental. Should correlations between the Barberton S2-S4 impact units and magmatic and tectonic events in the Pilbara Craton be confirmed, they would imply impact-triggered reactivation of mantle convection, crustal anatexis, faulting and strong vertical movements in Archaean granite-greenstone terrains associated with large asteroid impacts, c

Glikson, Andrew; Vickers, John

2006-01-01

81

PGE-Re concentrations in carbonaceous siltstones from the Barberton Drilling Project: Sources and processes  

NASA Astrophysics Data System (ADS)

The emergence, diversification and disappearance of Earth's life forms are closely tied to the redox state of the oceans, and the sources and sinks of metabolically cycled metals. It is generally accepted that the early terrestrial atmosphere contained extremely low levels of free oxygen [1]. While a significant change to atmospheric oxygen levels has been constrained to ca. 2.45 Ga ago, the details of the complex prior redox evolution of the oceans and atmosphere, and their influence on continental weathering, are still blurry [1]. Among the trace metals that have been applied to this problem, Re and the platinum-group elements (PGE) have variable redox chemistry that has been successfully exploited to identify detrital vs. hydrogenous sources and the presence of oxic vs. suboxic or euxinic conditions both in young and ancient sediments, including predominantly outcrop samples from the Barberton Greenstone Belt (BGB) [2,3]. As 187Re decays to 187Os, the Re-Os isotope system can additionally be used to date the deposition of carbonaceous shales through construction of isochrons and obtain the initial Os isotope composition, which is a tracer for continental input of radiogenic Os [4]. The sampling approach here was to choose 8+ samples from narrow intervals (?1 m, to avoid initial Os isotope heterogeneity) from the Barberton Drilling Project (two depths in core BARB5/Fig Tree Group and one interval in core BARB3/Buck Reef Chert. We are currently finalising institution of the sample preparation and analytical techniques, involving (1) high-pressure asher digestion and (2) low-temperature leaching of presumably hydrogenous, acid-soluble components of spiked samples, followed by solvent extraction of Os and cation exchange column chromatography to isolate PGE-Re from the residue, further purification with BPHA and measurement of Ru-Pd-Ir-Pt by ICPMS and of Re-Os by MC-ICPMS. Preliminary tests with the SDO-1 standard have revealed that concentrations of Ir and Pt in low-T dissolutions are indistinguishable from those in high-T dissolutions within the uncertainty, implying that these elements are contained fully in the hydrogenous component. In contrast, Re concentrations in the low-T digest are significantly lower (by 8%), indicating some control by the detrital component in a Phanerozoic shale. Prior work [3] has shown that PGE-Re abundance patterns of BGB sediments resemble those of komatiites, indicating an ultramafic, detrital source. Given the age of the BGB (3.5 - 3.2 Ga) and the absence of oxidative weathering, we expect to see low concentrations and no resolvable difference between the two digestion approaches that would be attributable to the variable redox behavior of Re and PGE. We aim to present results showing whether any short-scale changes occur in the sources and processes of PGE-Re incorporation into the sediment, and to eventually obtain robust Re-Os isotope constraints. [1] Canfield (2005) Annu. Rev. Earth Planet. Sci. 33:1-36; [2] Lee et al. (2003) Geochim. Cosmochim. Acta 67: 655-670; [3] Siebert et al. (2005) Geochim. Cosmochim. Acta 69: 1787-1801; [4] Kendall et al. (2009) Geol. Soc. London Spec. Publ. 326: 85-107

Rammensee, Philipp; Aulbach, Sonja

2014-05-01

82

GEOLOGIA E PETROLOGIA MAGNÉTICA DOS DIQUES DA ÁREA DE BANNACH, TERRENO GRANITO-GREENSTONE DE RIO MARIA, SUDESTE DO PARÁ  

Microsoft Academic Search

In the Bannach area, southeastern Pará state, diabasic, andesitic, dacitic and rhyolitic dykes swarms are found. These dykes crosscut the Archaean units (Rio Maria Granodiorite, Mogno Trondhjemite, greenstone-belts) and locally the Paleoproterozoic Bannach anorogenic granite of the Rio Maria Granite-Greenstone Terrane (TGGRM), southeastern portion of the Central Amazonian province, eastern edge of the Amazonian craton. The values of magnetic susceptibility

Ana Tayla Rodrigues Ferreira; José de Arimatéia; Costa de Almeida; Roberto Dall' Agnol

83

Diverse metal sources of Archaean gold deposits: evidence from in situ lead-isotope analysis of individual grains of galena and altaite in the Ross and Kirkland Lake deposits, Abitibi Greenstone belt, Canada  

NASA Astrophysics Data System (ADS)

Lead isotope compositions for individual grains of galena and altaite (PbTe) were determined in situ using a secondary ion mass spectrometer (SIMS). Galena was collected from the Ross deposit and altaite from the Kirkland Lake (KL) deposits in the southern Abitibi greenstone belt, Superior Province of Canada. The samples from KL are more radiogenic than those from the Ross deposit. Isotopic compositions vary significantly between different grains in each deposit and form broad linear arrays in 207Pb/204Pb-206Pb/204Pb and 208Pb/204Pb-206Pb/204Pb diagrams. The linear arrays of Pb-isotope data are attributed to mixing of Pb from different sources. At least two sources are required for individual deposits: one with low U/Pb and Th/Pb ratios and the other with high ratios. Lead minerals occurring with Au are less radiogenic than those that are not obviously associated with Au, suggesting that Au was supplied from low U/Pb sources such as sulphides or older ultramafic-mafic rocks. While most data are consistent with the derivation from local rocks, highly radiogenic Pb with relatively low 207Pb/206Pb ratios recorded at KL require post-Archaean mineralization or derivation of the Pb from an unusual crustal source with low ?. The latter interpretation is favored because of the lack of textural evidence and because it is difficult to dissolve and precipitate altaite at low temperatures. The presence of a Pb reservoir with low ? is also inferred from the data of Archaean banded iron formations and volcanogenic massive sulphide deposits. Different isotopic patterns of the two deposits suggest different sources of metals in the two deposits. While this conclusion does not reject the derivation of fluids from the lower crust or mantle, the data are not in accord with conceptual models invoking a common source reservoir for metals. The study suggests that fluids, which may have a common origin, leached metals and other constituents from the upper crustal rocks during their ascent. The proposed model, different origins for different constituents, explains much of the conflicting evidence presented by Archaean Au deposits, including provinciality of mineralogy and relatively uniform fluid inclusion and C-isotope data from many Au deposits.

Hattori, Keiko

1993-02-01

84

Controls on the emplacement and genesis of the MKD5 and Sarah's Find Ni Cu PGE deposits, Mount Keith, Agnew Wiluna Greenstone Belt, Western Australia  

NASA Astrophysics Data System (ADS)

The Mount Keith (MKD5) nickel sulfide deposit is one of the largest komatiite-hosted nickel sulfide deposits in the world; it is hosted by a distinctive spinifex-free, cumulate-rich, ultramafic horizon/unit termed the Mount Keith Ultramafic (MKU). The Mount Keith Ultramafic shows significant variation along its lateral extent. The internal architecture is made up of adcumulate-textured pods and lenses, which are flanked by thinner meso- and orthocumulate-textured units, overlain by pyroxenitic and gabbroic horizons. The lateral and vertical changes in the geometry and internal architecture reflect variations in the lithological association and emplacement conditions along the strike extent of the belt. The chilled margins of the Mount Keith Ultramafic unit contain ˜1,200 ppm Ni. Olivine cumulates average ˜2,500 3,500 ppm Ni, with few exceptions (Ni > 4,500 ppm) reflecting occurrence of minor nickel sulfides, whereas pyroxenites and gabbros generally contain, respectively, ˜1,500 2,000 and ˜100 1,000 ppm Ni. Olivine cumulates generally contain low Cr concentrations (<2,500 ppm Cr), with the rare presence of chromite-rich intervals containing anomalously high values (>5,000 ppm Cr). The internal stratigraphy of the Mount Keith Ultramafic unit may be subdivided into two groups based on rare earth element distribution. The chilled margins and the internal units of the Main Adcumulate domain display LREE-enriched patterns [(La/Sm) n > 1 3] and negative Eu, Hf, Zr, Nb, and Ti anomalies. The internal units in the Western Mineralized Zone generally display flat chondrite-normalized REE patterns and only minor negative Nb anomalies. The pattern of platinum-group element (PGE) distribution varies greatly along the strike extent of the Mount Keith Ultramafic unit. The chilled margins display relatively low absolute concentrations [PGE (excl. Os) ˜16 ppb] and relatively fractionated patterns, with subchondritic Pt/Pd ratios (˜1.5), and superchondritic Pd/Ir ratios (˜3). The PGE trends in the thick adcumulate-textured pods containing widespread nickel sulfide mineralization display positive correlation with sulfide abundance, whereas fractionated pyroxenites and gabbros in the thinner domains display highly depleted PGE concentrations and generally show compatible PGE trends. The nickel sulfide ore typology and style vary greatly along the strike extension of the Mount Keith Ultramafic unit. Basal massive nickel sulfide mineralization (e.g., Sarah’s Find) occurs in the thinner meso- and orthocumulate-textured units, whereas stratabound disseminated nickel sulfide mineralization (e.g., MKD5 Ni Deposit) is hosted in the adcumulate-textured pods. We hypothesize that the very low PGE content of the initial liquid of the Mount Keith Ultramafic unit indicates that the initial magma pulse that penetrated through the dacite host-rock had already equilibrated with sulfides at depth and/or carried entrained immiscible sulfide blebs. We argue that upon emplacement, the intruding magma experienced a significant thermal shock at the contact with water-saturated volcaniclastic breccias. The sudden chilling would have increased the viscosity of the magma, possibly to the point where it was no longer able to sustain the suspension of the immiscible sulfide liquid. As a result, the sulfide blebs coalesced and formed the basal massive sulfide nickel sulfide mineralization at the base of the sill (i.e., Sarah’s Find). Prolonged focused high volume magma flow within the sill resulted in the emplacement of a thick, lens-shaped accumulation of olivine adcumulate. Local variations in intensive parameters other than crustal assimilation (e.g., T, fO2, fS2) may be principally responsible for sulfide supersaturation and controlled the local distribution of stratabound disseminated nickel sulfide mineralization (e.g., MKD5 Ni Deposit), generally localized within the core of the thicker dunite lenses.

Fiorentini, M. L.; Rosengren, N.; Beresford, S. W.; Grguric, B.; Barley, M. E.

2007-11-01

85

Deciphering Earth's Deep History: Drilling in Africa's Oldest Greenstone Belt  

Microsoft Academic Search

Earth's early evolution and the conditions under which life first emerged are highly controversial topics. Did Venus-type tectonics dominate the early Earth, with vast landscapes of hot spot volcanoes belching lava and gases into a tenuous carbon dioxide\\/methane-rich atmosphere, or was plate tectonics already in operation? Debates rage about when water first became dominant across Earth's surface, the temperatures and

Eugene G. Grosch; Nicola McLoughlin; Maarten de Wit; Harald Furnes

2009-01-01

86

Magnetic susceptibility, magnetic mineralogy and magnetic fabrics in a late Archean granitoid-gneiss belt  

Microsoft Academic Search

The Opatica belt is a late Archean granitoid-gneiss terrane situated within the northern Abitibi Subprovince, along the northern margin of the Abitibi greenstone belt, Quebec. This belt is composed of several suites of tonalite-granodiorite- granite composition, variably deformed under epidote-amphibolite to upper-amphibolite grade conditions. Specimens from 87 sampling sites within the Opatica belt show a wide range in variation of

K. Benn; P. Rochette; J. L. Bouchez; K. Hattori

1993-01-01

87

Greenstone: A Comprehensive Open-Source Digital Library Software System  

Microsoft Academic Search

This paper describes the Greenstone digital library software, a comprehensive, open-source system for the construction and presentation of information collections. Collections built with Greenstone offer effective full-text searching and metadata-based browsing facilities that are attractive and easy to use. Moreover, they are easily maintainable and can be augmented and rebuilt entirely automatically. The system is extensible: software \\

Ian H. Witten; Rodger J. McNab; Stefan J. Boddie; David Bainbridge

1999-01-01

88

Greenstone: a comprehensive open-source digital library software system  

Microsoft Academic Search

This paper describes the Greenstone digital library software, a comprehensive, open-source system for the construction and presentation of information collections. Collections built with Greenstone offer effective full-text searching and metadata-based browsing facilities that are attractive and easy to use. Moreover, they are easily maintainable and can be augmented and rebuilt entirely automatically. The system is extensible: software \\

Ian H. Witten; Stefan J. Boddie; David Bainbridge; Rodger J. McNab

2000-01-01

89

The origin of carbonaceous matter in pre-3.0 Ga greenstone terrains: A review and new evidence from the 3.42 Ga Buck Reef Chert  

NASA Astrophysics Data System (ADS)

The geological record of carbonaceous matter from at least 3.5 Ga to the end of the Precambrian is fundamentally continuous in terms of carbonaceous matter structure, composition, environments of deposition/preservation, and abundance in host rocks. No abiotic processes are currently known to be capable of producing continuity in all four of these properties. Although this broad view of the geological record does not prove that life had arisen by 3.5 Ga, the end of the early Archean, it suggests a working hypothesis: most if not all carbonaceous matter present in rocks older than 3.0 Ga was produced by living organisms. This hypothesis must be tested by studies of specific early geological units designed to explore the form, distribution, and origin of enclosed carbonaceous matter. The carbonaceous, environmentally diverse 3416 Ma Buck Reef Chert (BRC) of the Barberton greenstone belt, South Africa, provides an opportunity for such a study. Upward facies progressions in the BRC reflect deposition in environments ranging from shallow marine evaporitic brine ponds to a storm- and wave-active shelf to a deep, low-energy basinal setting below storm wave base. Abundances and ratios of Al 2O 3, Zr, TiO 2, and Cr track inputs of various types of volcaniclastic and terrigenous clastic materials. In particular, Zr/Al 2O 3 and Zr serve as proxies for concentration of windblown dust and, indirectly, as proxies for sedimentation rate. Cu, Zn, Ni, and FeO were concentrated in the most slowly deposited transitional and basinal sediments, inconsistent with a hydrothermal setting but consistent with a normal marine setting. The distribution of microfacies defined by associations and layering of clastic, ferruginous, and carbonaceous grains correlates with facies transitions. Fine carbonaceous laminations, which occur only in shallow platform settings, represent photosynthetic microbial mats. These were ripped up and the debris widely redistributed in shallow and deep water by waves and storms. The isotopic composition of carbonaceous matter ranges from - 35‰ to - 30‰ in shallow-water settings and to - 20‰ in deep-water units. The heavier ?13C in deep-water carbonaceous matter is thought to reflect microbial processing, possibly by fermentation and methanogenesis, of organic matter originally produced in shallow water. Hydrothermal origins for BRC carbonaceous matter are clearly excluded by the inferred depositional setting of the rocks as a whole, an inference supported by field, petrographic, and geochemical analysis. We suggest that the biological model proposed here for BRC carbonaceous matter is the best currently available. The hypothesis that "at least some carbonaceous matter present in rocks older than 3.0 Ga was produced by living organisms" should be regarded as likely until extraordinary contradictory evidence is presented.

Tice, Michael M.; Lowe, Donald R.

2006-06-01

90

Age and tectonic setting of Late Archean greenstone-gneiss terrain in Henan Province, China, as revealed by single-grain zircon dating  

Microsoft Academic Search

We report precise U-Pb zircon ages for single grains of a metarhyodacite from the Late Archean Dengfeng greenstone belt in Henan Province, China, near the southern margin of the North China craton. Most grains belong to an igneous population whose U-Pb isotopic systematics define a straight line intersecting concordia at 2512 ±12Ma, and this is interpreted as the time of

Alfred Kröner; William Compston; Zhang Guo-Wei; Guo An-Lin; Wolfgang Todt

1988-01-01

91

Geochemistry and petrology of greenstones from the Erdenetsogt formation, central Mongolia: New evidence for a middle Paleozoic mantle plume  

NASA Astrophysics Data System (ADS)

This research presents evidence of the plume-related formation of greenstones from the Erdenetsogt Formation (EF) hosted by Tsetserleg terrane of middle Paleozoic Hangay-Hentey accretionary complex, which is central part of the Central Asian Orogenic Belt (CAOB). Our new data can support middle Paleozoic evolution of plume-related magmatism of the paleo-oceanic plate and its accretionary processes, which significantly contributed to the continental growth of CAOB. EF is mainly made up of intensively deformed oceanic plate stratigraphy such as radiolarian/ribbon chert, red and green quartzites (metachert), fine to medium-grained sandstone, siltstone with minor amount of limestone, and some basaltic greenstones which have been discovered lately during geological mapping in the south Hangay region. The upper unit of this formation was dated by late Devonian conodonts from the chert. However, the chemistry of greenstones in this region has not been studied yet except brief study by Orolmaa (2008). The studied samples include metabasalts, dolerites, microgabbros, and occasional meta-picrites with mostly subophitic, intersertal, and partly intergranular textures. The common assembledge of phenocrysts is clinopyroxene (well-preserved in all greenstones) and plagioclase (replaced by albite). Also completely altered olivine containing relict Cr-spinel observed from metapicrite and porphyritic metabasalt. The composition of the primary clinopyroxene (augite) and Cr-spinel were analyzed by electron microprobe and bulk rock major and trace elements by XRF. On the basis of Ca +Na vs. Ti and Ca vs. Ti+Cr discrimination diagrams, clinopyroxenes display tholeiitic magma type and non-orogenic affinity. The relict spinels are 20-250 ?m in size. The Al2O3 wt.% vs. TiO2 wt.% variation of the spinels corresponds to the transitional affinity of OIB and MORB. The Cr and Mg numbers of the spinels show very limited values ranging from 55 to 68 and from 0.3 to 0.6, respectively, and implies highly depleted (high melting degree) magma compare with MORB, and more identical to spinel from Hawaiian tholeiitic basalts. From those facts, it is concluded that the Cr-spinel of greenstones may have been derived from a mantle plume source. Furthermore, notable exceptions of the Hangay greenstones are very low ratios of Nb/Zr and Zr/Y (0.05-0.08 and 0.2-0.5, respectively), whereas Hentey basalts show HIMU characteristic (Tsukada, 2006). The greenstones are slightly enriched in LREE and TiO2 (1.6-2.2 wt.%). We suggest that greenstones in Erdenetsogt formation may have been formed as plume-related oceanic island (hotspot or oceanic plateau) within paleo-oceanic plate located between the Siberian and the North China Cratons, and then accreted to the active continental margin of Siberian Craton during middle to late Paleozoic. This setting is analogous to the present southwest Pacific realm. Keywords: Hangay-Hentey accretionary complex, Erdenetsogt Formation, greenstones, clinopyroxene, Cr-spinel, mantle plume

Ganbat, E.; Ishiwatari, A.; Demberel, O.

2012-12-01

92

Barberton drilling project - Buck Reef Chert core BARB3  

NASA Astrophysics Data System (ADS)

As part of the ICDP-sponsored Barberton drilling project a single drill core (BARB3) with a total length of 899 m was obtained from the c. 3.4 Ga old Buck Reef Chert (BRC). The BRC is an unusually thick (up to 350 m) sequence of predominantly black-and-white banded chert and banded ferruginous chert that are steeply dipping. It overlies a shallow intrusive to extrusive sequence of dacitic volcanic rocks of the Hooggenoeg Formation and is separated from ultramafic lapillistone of the Kromberg Formation by a >150 m thick ultramafic sill. Drilling commenced in the ultramafic sill at an angle of c. 45° and c. 200 m of serpentinized peridotite were intersected. The remaining c. 700 m of the core include a great variety of chert lithofacies and minor intrusive mafic to intermediate igneous rocks. The base of the BRC was not intersected. Geophysical logging was done up to a depth of 847 m and included acoustic televiewer, gamma ray, resistivity, magnetic field and caliper logs. Stratigraphic and geophysical logs will be presented that will form the basis of follow-up studies on the BARB3 core. Abundance of organic matter, sulphides and Fe-bearing carbonates in specific intervals or associated with specific facies of the chert succession reflect changes in the oceanic, environmental and/or hydrothermal conditions in a shallow marine early Archaean setting. Evaluating the different processes will require a combined sedimentological, mineralogical, and geochemical approach that will provide insights into the habitat of early life, geochemical cycles and marine/hydrothermal conditions.

Hofmann, Axel; Karykowski, Bartosz; Mason, Paul; Chunnet, Gordon; Arndt, Nick

2013-04-01

93

Burial and exhumation during Archean sagduction in the East Pilbara Granite-Greenstone Terrane  

NASA Astrophysics Data System (ADS)

Archean granitic domes and intervening volcano-sedimentary basins are commonly interpreted as the product of “sagduction”, a process involving the gravitational sinking of surficial greenstone cover sequences into narrow belts and the coeval exhumation of deeper granitic crust into broad domes. Alternatives to the sagduction model that can account for the regional dome and basin pattern include fold interferences and extensional metamorphic core complexes. In order to provide quantitative constraints on the pressure-temperature-time (P-T-t) evolution experienced by greenstone-granite pairs we investigate the Warrawoona greenstone belt and adjacent Mount Edgar granitoid dome the East Pilbara craton (Western Australia). We adopt a multidisciplinary approach that includes structural, metamorphic, geochronological and numerical investigation of the 3.5-3.2 Ga Mount Edgar high-grade metamorphic rocks. Garnet-bearing metasediments and metabasalts collected along the SW and SE rims of the Mount Edgar Dome show higher pressure but lower temperature of equilibration (9-11 kbar and 450-550 °C) than enclaves collected in the core of the dome (6-7 kbar and 650-750 °C). In situ oxygen isotope analysis and U-Pb dating of zircons from the enclave indicate a metasedimentary origin (?18O˜+13‰) for the protoliths and a metamorphic age of 3311.9±4.9 Ma. In addition, monazites included in garnet from the SW dome margin yield an age of 3443.4±4.5 Ma. These monazites suggest the existence of an older metamorphic cycle and imply a polymetamorphic evolution of the unit. The P-T-t data support fast, gravity-driven tectonics, wherein sedimentary rocks were buried to lower crustal conditions, metamorphosed and exhumed back to the surface during a cycle lasting only a few million years. Forward thermo-mechanical modeling confirms the P-T-t evolutions deduced from thermobarometry and geochronology. Our model shows a large range of possible apparent geothermal gradients during sagduction, including low apparent geothermal gradients that are similar to those proposed for Archean and modern subduction.

François, C.; Philippot, P.; Rey, P.; Rubatto, D.

2014-06-01

94

Archean sedimentation and tectonics in southern Africa  

NASA Technical Reports Server (NTRS)

Sequences in the Barberton Mountain Land greenstone belt (southern Africa) were examined to determine the nature of the sedimentary rocks, their tectonic implications, and their bearing on the present large-scale structural condition of the belt. Also assessed was whether there was evidence for a significant component of shallow-water-deposited sedimentary rocks in the parent materials of the Limpopo belt. The nature of a largehigh strain zone on the southern margin of the central Limpopo belt was examined.

Kidd, W. S. F.

1984-01-01

95

Sedimentologic and tectonic aspects of the Archean Limpopo belt  

SciTech Connect

There are marked lithic differences between the central Limpopo belt and other well-studied Archean high-grade and greenstone-granitoid terranes, in particular the presence, in thick sections of supracrustals including approx. 15% of each of 1) carbonate and calc-silicate rocks and 2) pure metaquartzite, often fuchsite-bearing, with the lithic character of quartz arenite, not metachert. Isotopic ages suggest these sediments are 3.3-3.5 Ga old. The sequence and distribution of lithic, plutonic, metamorphic, and structural events in the Limpopo belt resembles that in younger orogens where there has been rifting of continental lithosphere, deposition of sediments at an Atlantic-type margin, then convergence and collision with another continental block. The southern margin of the central Limpopo belt is a wide (20 km) zone of vertically-dipping, horizontally-lineated mylonites, clearly representing the deeper ductile levels of a major strike-slip fault. This fault resembles large strike-slip systems that allow tectonic escape during collision in young orogenic belts. The authors conclude that continental fragments large enough to provide a substrate for significant platform arenite and carbonate sedimentation existed by 3.3-3.5 Ga, and that Tibetan-Himalayan style collisional tectonics greater than or equal to 2.6 Ga ago accounts for the large-scale relationships between the Limpopo belt and the adjacent Archean greenstone-granitoid terrane cratons. By inference, other more fragmentary Archean gneissic terranes may have once been part of such collisional zones.

Erikkson, K.A.; Kidd, W.S.F.

1985-01-01

96

Archean greenstone-tonalite duality: Thermochemical mantle convection models or plate tectonics in the early Earth global dynamics?  

NASA Astrophysics Data System (ADS)

Mantle convection and plate tectonics are one system, because oceanic plates are cold upper thermal boundary layers of the convection cells. As a corollary, Phanerozoic-style of plate tectonics or more likely a different version of it (i.e. a larger number of slowly moving plates, or similar number of faster plates) is expected to have operated in the hotter, vigorously convecting early Earth. Despite the recent advances in understanding the origin of Archean greenstone-granitoid terranes, the question regarding the operation of plate tectonics in the early Earth remains still controversial. Numerical model outputs for the Archean Earth range from predominantly shallow to flat subduction between 4.0 and 2.5 Ga and well-established steep subduction since 2.5 Ga [Abbott, D., Drury, R., Smith, W.H.F., 1994. Flat to steep transition in subduction style. Geology 22, 937-940], to no plate tectonics but rather foundering of 1000 km sectors of basaltic crust, then "resurfaced" by upper asthenospheric mantle basaltic melts that generate the observed duality of basalts and tonalities [van Thienen, P., van den Berg, A.P., Vlaar, N.J., 2004a. Production and recycling of oceanic crust in the early earth. Tectonophysics 386, 41-65; van Thienen, P., Van den Berg, A.P., Vlaar, N.J., 2004b. On the formation of continental silicic melts in thermochemical mantle convection models: implications for early Earth. Tectonophysics 394, 111-124]. These model outputs can be tested against the geological record. Greenstone belt volcanics are composites of komatiite-basalt plateau sequences erupted from deep mantle plumes and bimodal basalt-dacite sequences having the geochemical signatures of convergent margins; i.e. horizontally imbricated plateau and island arc crust. Greenstone belts from 3.8 to 2.5 Ga include volcanic types reported from Cenozoic convergent margins including: boninites; arc picrites; and the association of adakites-Mg andesites- and Nb-enriched basalts. Archean cratons were intruded by voluminous norites from the Neoarchean through Proterozoic; norites are accounted for by melting of subduction metasomatized Archean continental lithospheric mantle (CLM). Deep CLM defines Archean cratons; it extends to ˜ 350 km, includes the diamond facies, and xenoliths signify a composition of the buoyant, refractory, residue of plume melting, a natural consequence of imbricated plateau-arc crust. Voluminous tonalites of Archean greenstone-granitoid terranes show a secular trend of increasing Mg#, Cr, Ni consistent with slab melts hybridizing with thicker mantle wedge as subduction angle steepens. Strike-slip faults of 1000 km scale; diachronous accretion of distinct tectonostratigraphic terranes; and broad Cordilleran-type orogens featuring multiple sutures, and oceanward migration of arcs, in the Archean Superior and Yilgarn cratons, are in common with the Altaid and Phanerozoic Cordilleran orogens. There is increasing geological evidence of the supercontinent cycle operating back to ˜ 2.7 Ga: Kenorland or Ur ˜ 2.7-2.4 Ga; Columbia ˜ 1.6-1.4 Ga; Rodinia ˜ 1100-750 Ma; and Pangea ˜ 230 Ma. High-resolution seismic reflection profiling of Archean terranes reveals a prevalence of low angle structures, and evidence for paleo-subduction zones. Collectively, the geological-geochemical-seismic records endorse the operation of plate tectonics since the early Archean.

Kerrich, Robert; Polat, Ali

2006-03-01

97

Earth's Archean Impact Record In The ICDP Drilling "Barberton Mountain Land".  

NASA Astrophysics Data System (ADS)

The marine meta-sedimentary successions in the "Barberton Mountain Land" are formed by Archean volcanic and sedimentary rocks including the oldest known impact ejecta layers on Earth. The chemical signature (high iridium concentrations, chromium isotopic ratios) of some of these up to tens of cm thick Archean spherule layers advocate that these ejecta deposits represent mainly extraterrestrial material [1]. These ejecta layers contain millimetre sized spherules that are larger and accumulated thicker layers compared to any impact ejecta layer known from Phanerozoic sediments, including the global ejecta layer of the Chicxulub impact catering event terminating the Mesozoic era of Earth's history [2]. The Archean spherule layers are interpreted as products of large impacts by 20 to >100 km diameter objects [3, 4]. Identifying traces of mega-impacts in Earth's ancient history could be of relevance for the evolution of atmosphere, biosphere, and parts of the Earth's crust during that time. In addition, recognizing global stratigraphic marker horizons is highly valuable for inter-correlating sedimentary successions between Archean cratons [5]. However estimates regarding size of the impact event and correlations between the different outcrops in the Barberton mountain land are complicated by post depositional alterations of the tectonically deformed sediments [6, 7]. The relatively fresh samples recovered from below the water table during the 2011-2012 ICDP drilling "Barberton Mountain Land" are promising samples to investigate and to discriminate primary and secondary features of these rare rocks. We plan to conduct 1) petrographic, micro-chemical and mineralogical characterization of the impact ejecta layers, 2) bulk chemical analyses of major and trace elements, and 3) LAICP- MS elemental mapping of platinum group element (PGE) distributions. and elemental analyses of moderately siderophile elements. This aims at 1) characterization of the ejecta layers, 2) identification of the phases hosting the extraterrestrial PGE signature, 3) discrimination of the primary geological evidence of the impact event from those characteristics that resulted from syn- and post-sedimentary alteration. Acknowledgement: Financial support by the DFG - RE 528/14-1. References: [1] Lowe D. R. et al. (2003) Astrobiology 3, 7-47. [2] Simonson B. M. and Harnik P. (2000) Geology 28, 975-978. [3] Lowe D. R. and Byerly G. R. (1986) Geology 14, 83-86. [4] Melosh H. J. and Vickery A. M. (1991) Nature 350, 494-497. [5] Byerly G. R. et al. (2002) Science 297, 1325-1327. [6] Reimold W. U. et al. (2000) Impacts and the Early Earth. Eds.: Gilmour I., Koeberl C. Lecture Notes in Earth Sciences 91, Springer-Verlag, Berlin, pp.117-180. [7] Hofmann A. et al. (2006) GSA Special Paper 405, 33 - 56.

Fritz, Jörg; Schmitt, Ralf-Thomas; Reimold, Uwe; Koeberl, Christian; Mc Donald, Ian; Hofmann, Axel; Luais, Beatrice

2013-04-01

98

Early Proterozoic (2.04 GA) phosphorites of Pechenga Greenstone Belt and their origin  

NASA Astrophysics Data System (ADS)

No principal differences have been found between microfossils described from Cambrian and Phanerozoic and the 2000 Ma phosphorites. Numerous samples revealed diverse microbial microstructures interpreted as cyanobacterial mats consisting of filamentous (1-3 ?m in diameter, 20 ?m in length), coccoidal (0.8-1.0 ?m) and ellipsoidal or rod-shaped microfossils (0.8 ?m in diameter, around 2 ?m in length) which morphologically resemble modern Microcoleus and Siphonophycus, Thiocapsa, and Rhabdoderma, respectively, reported from alkaline or saline environments. The sequence of the early Palaeoproterozoic events which point to a significant oxidation of the hydrosphere, including the formation of phosphorites and changes in the phosphorous cycle, mimics the sequence which was repeated at the Neoproterozoic-Cambrian transition, implying that oxidation of the terrestrial atmosphere-hydrosphere system experienced an irregular cyclic development.

Rozanov, Alexei Yu.; Astafieva, Marina M.; Hoover, Richard B.

2007-10-01

99

Early Proterozoic (2.04 GA) Phoshorites of Pechenga Greenstone Belt and Their Origin  

NASA Technical Reports Server (NTRS)

No principal differences have been found between microfossils described from Cambrian and Phanerozoic and the 2000 Ma phosphorites. Numerous samples revealed diverse microbial microstructures interpreted as cyanobacterial mats consisting of filamentous (1-3 microns in diameter, 20 microns in length), coccoidal (0.8-1.0 microns) and ellipsoidal or rod-shaped microfossils (0.8 microns in diameter, around 2 microns in length) which morphologically resemble modern Microcoleus and Siphonophycus, Thiocapsa, and Rhabdoderma, respectively, reported from alkali ne or saline environment_ The sequence of the early Palaeoproterozoic events which point to a significant oxidation of the hydrosphere, including the formation of phosphorites and changes in the phosphorous cycle, mimics the sequence which was repeated at the Neoproterozoic-Cembrian transition, implying that oxidation of the terrestrial atmosphere-hydrosphere system experienced an irregular cyclic development.

Rozanov, Alexei Yu.; Astafieva, Marina M.; Hoover, Richard B.

2007-01-01

100

Asteroid impact ejecta units overlain by iron-rich sediments in 3.5–2.4 Ga terrains, Pilbara and Kaapvaal cratons: Accidental or cause–effect relationships?  

Microsoft Academic Search

The significance of temporal and spatial associations between asteroid\\/comet impact ejecta units and overlying iron-rich sediments, including banded iron-formation (BIF), jaspilite and ferruginous shale, observed in the Pilbara Craton, Western Australia and the Barberton Greenstone Belt (BGB), Kaapvaal Craton, South Africa, is considered. Such associations include (1) 3470.1±1.9 Ma impact spherule units and tsunami-type breccia overlain by jaspilite in the Antarctic

Andrew Glikson

2006-01-01

101

Laterally bendable belt conveyor  

SciTech Connect

An endless, laterally flexible and bendable belt conveyor particularly adapted for coal mining applications in facilitating the transport of the extracted coal up- or downslope and around corners in a continuous manner is disclosed. The conveying means includes a flat rubber belt reinforced along the middle portion thereof along which the major portion of the belt tension is directed so as to cause rotation of the tubular shaped belt when trammed around lateral turns thus preventing excessive belt bulging distortion between adjacent belt supports which would inhibit belt transport. Pretension induced into the fabric reinforced flat rubber belt by conventional belt take-up means supports the load conveyed when the belt conveyor is making laterial turns. The carrying and return portions of the belt are supported and formed into a tubular shape by a plurality of shapers positioned along its length. Each shaper is supported from above by a monorail and includes clusters of idler rolles which support the belt. Additional cluster rollers in each shaper permit the belt supporting roller clusters to rotate in response to the belt's operating tension imposed upon the cluster rollers by induced lateral belt friction forces. The freely rotating roller clusters thus permit the belt to twist on lateral curves without damage to itself while precluding escape of the conveyed material by effectively enclosing it in the tube-shaped, inner belt transport length.

Peterson, W.J.

1985-07-02

102

Laterally bendable belt conveyor  

SciTech Connect

An endless, laterally flexible and bendable belt conveyor particularly adapted for coal mining applications in facilitating the transport of the extracted coal up- or downslope and around corners in a continuous manner is disclosed. The conveying means includes a flat rubber belt reinforced along the middle portion thereof along which the major portion of the belt tension is directed so as to cause rotation of the tubular shaped belt when trammed around lateral turns thus preventing excessive belt bulging distortion between adjacent belt supports which would inhibit belt transport. Pretension induced into the fabric reinforced flat rubber belt by conventional belt take-up means supports the load conveyed when the belt conveyor is making lateral turns. The carrying and return portions of the belt are supported and formed into a tubular shape by a plurality of shapers positioned along its length. Each shaper is supported from above by a monorail and includes clusters of idler rollers which support the belt. Additional cluster rollers in each shaper permit the belt supporting roller clusters to rotate in response to the belt's operating tension imposed upon the cluster rollers by induced lateral belt friction forces. The freely rotating roller clusters thus permit the belt to twist on lateral curves without damage to itself while precluding escape of the conveyed material by effectively enclosing it in the tube-shaped, inner belt transport length.

Peterson, W.J.

1982-09-24

103

Laterally bendable belt conveyor  

DOEpatents

An endless, laterally flexible and bendable belt conveyor particularly adapted for coal mining applications in facilitating the transport of the extracted coal up- or downslope and around corners in a continuous manner is disclosed. The conveying means includes a flat rubber belt reinforced along the middle portion thereof along which the major portion of the belt tension is directed so as to cause rotation of the tubular shaped belt when trammed around lateral turns thus preventing excessive belt bulging distortion between adjacent belt supports which would inhibit belt transport. Pretension induced into the fabric reinforced flat rubber belt by conventional belt take-up means supports the load conveyed when the belt conveyor is making lateral turns. The carrying and return portions of the belt are supported and formed into a tubular shape by a plurality of shapers positioned along its length. Each shaper is supported from above by a monorail and includes clusters of idler rollers which support the belt. Additional cluster rollers in each shaper permit the belt supporting roller clusters to rotate in response to the belt's operating tension imposed upon the cluster rollers by induced lateral belt friction forces. The freely rotating roller clusters thus permit the belt to twist on lateral curves without damage to itself while precluding escape of the conveyed material by effectively enclosing it in the tube-shaped, inner belt transport length.

Peterson, William J. (Coraopolis, PA)

1985-01-01

104

TTGs in the making: Natural evidence from Inyoni shear zone (Barberton, South Africa)  

NASA Astrophysics Data System (ADS)

Despite the consensus that TTGs, the main constituents of the Archaean continental crust worldwide, originated by partial melting of garnet-bearing amphibolites, natural evidence is scarce. A large variety of Archaean amphibole-rich rocks, including migmatitic amphibolites and hornblende-rich cumulates, was exhumed as a tectonic melange in the Inyoni shear zone (ISZ) near Barberton (South Africa), likely at the time of emplacement of the 3.2 Ga Nelshoogte-Badplaas plutons. This unique collection provides the opportunity to investigate partial melting of garnet-amphibolites, as well as the differentiation processes occurring in the TTG magmas en route to the surface. The ISZ migmatitic amphibolites are characterized by quartz-plagioclase leucosomes in equilibrium with garnet, amphibole, titanite ± epidote. Garnet compositions are characterized by high almandine and grossular contents. Actually, the leucosomes and neosomes likely lost part of their melt component and mesosomes may have been also modified towards restite-rich compositions due to melt segregation. Restite-bearing rocks are very iron-rich according to their high contents in garnet. Besides, the Mg-rich compositions of the hornblende cumulates and their REE distribution patterns resemble those of the nearby TT (tonalite-trondhjemite) plutons. Thermobarometric estimates from the ISZ migmatitic rocks cluster in the range 720-800 °C and 1.1-1.2 GPa for the melting reaction and the derived geothermal gradient is ca 17-22 °C/km. These conditions are consistent with either water-present melting or, more likely, water-absent epidote-dehydration melting. Such a geothermal gradient is therefore assigned to the genesis of large volumes of medium-pressure TTG magmas, that will likely form at greater depth. Unmelted garnet-bearing amphibolites correspond to slightly lower conditions. The magmatic cumulates crystallized at ca 0.6 GPa. The cumulate rocks evidence that the TTG parental magmas en route to the surface experienced fractional crystallization of a large amount of amphibole before crystallizing as tonalite-trondhjemite plutons at slightly shallower depths (ca 0.5 GPa).

Nédélec, A.; Chevrel, M. O.; Moyen, J. F.; Ganne, J.; Fabre, S.

2012-11-01

105

Belt Repair System and Method.  

National Technical Information Service (NTIS)

A belt repair system and method is used to repair a broken belt, such as a drive belt. The belt repair system includes one or more belt couplers having first and second body portions with belt engaging members. The body portions of each belt coupler exten...

P. E. Moody

1997-01-01

106

Ophiolites and oceanic plateau remnants (greenstones) in Japan and Far East Russia  

NASA Astrophysics Data System (ADS)

In Japan, an older ophiolite thrust onto younger ophiolite with tectonic intercalation of accreted oceanic sediments (chert, limestone, shale and sandstone forming _gocean plate stratigraphy_h deposited on the basaltic basement) or their high-P/T metamorphosed varieties. For example, the Yakuno ophiolite (SW Japan) of early Permian igneous age and supra-subduction zone (SSZ) origin (Ichiyama & Ishiwatari, Island Arc, 13, 157-) is tectonically underlain by the Ultra-Tamba nappe (chert, shale, sandstone) accreted in Late Permian, which is further underlain by the Tamba nappes (greenstone, chert, limestone, shale and sandstone) accreted in Jurassic. Major occurrence of the greenstones (mainly Permian) in the Upper Tamba nappe (consisting of 3 sub-nappes) is more than 1 km thick intact sheet of >200 km extension forming the structurally basal part of each sub-nappe, originated in an oceanic edifice composed of pillow lava, massive lava, hyaloclastite and dikes (_gBasal TypEh). Another minor occurrence is greenstone fragments of a few cm to 100 m size in the muddy matrix (_gMixed TypEh), constituting structurally upper part of each sub-nappe. The Basal Type greenstones show uniform E-MORB affinity, but the Mixed Type ones show diverse features such as N-MORB, OIT and OIA. This clear correlation between the occurrence of greenstones and their chemistries suggests the accretion of thick crust of oceanic plateau (E-MORB) to make Basal Type greenstones and the accretion of thin normal oceanic crust (N-MORB) with disseminated small seamounts (OIT and OIA) to make Mixed Type greenstones (Koizumi & Ishiwatari, Island Arc, in submission.). We discovered HFSE-rich picrite (meimechite) sills and hyaloclastites as well as ferropicrite and picritic ferrobasalt dikes emplaced in the Basal Type greenstones and its chert-dolomite cover of Late Permian age. Zr/Y and Ti/Al signatures of these ultramafic volcanic rocks are intermediate between Polynesian picrites and Siberian meimechites, suggesting their origin by deep (4-5 GPa) partial melting of a superplume (Ichiyama & Ishiwatari, 2005; CMP, 149, 373-; Lithos, in submission.). The Yakuno ophiolite and the Tamba greenstone thus represent coeval but unrelated SSZ and oceanic magmatisms, respectively, in the same Permian time. The Jurassic superplume-related volcanic rocks are also reported from Hokkaido (Japan) and Sakhalin (Russia), and Jurassic meimechite lavas and related Alaskan-type zoned ultramafic plutons are reported from Primorye (Russia), but their age of accretion is also Late Jurassic. The Jurassic ophiolites in Hokkaido and Sakhalin are characterized by unusually depleted harzburgite (Spinel Cr#80-90), indicating very high degree of melting (Ishiwatari et al. GSL Spec. Publ. 218, 597-). These facts suggests that the superplume was placed beneath the subduction zone (Ishiwatari & Ichiyama, 2004; Int. Geol. Rev., 46, 316-), and facilitated plate convergence and SSZ magmatism. This study provides a new evidence for Permian oceanic superplume magmatism that is coeval with Siberian and Emeishan LIPs, and postulates possibility of superplume-SSZ interaction in Jurassic NW Pacific margin.

Ishiwatari, A.; Ichiyama, Y.; Koizumi, K.

2005-12-01

107

Dynamic characteristics of conveyor belts  

Microsoft Academic Search

The dynamic characteristics of a belt conveyor are determined to a large extent by the properties of the belt. This paper describes experiments designed to establish the dynamic properties of belting material. The dynamic elastic modulus, viscous damping and rheological constants of the belt were measured. Several properties were studied as a function of the tensile loading on the belt.

You-fu HOU; Qing-rui MENG

2008-01-01

108

Filamentous microfossils from the 3,500-Myr-old Onverwacht Group, Barberton Mountain Land, South Africa  

NASA Astrophysics Data System (ADS)

The Swaziland Supergroup, Barberton Mountain Land, South Africa, has long been regarded as a promising location for the Earth's oldest fossils because it includes some of the most ancient well-preserved sedimentary rocks, many of which contain carbonaceous matter. Although there have been numerous reports of microfossils from Swaziland Group rocks1-7, the biogenicity of most of the structures has been questioned8-10. Although some of the organic spheroids are probably biogenic10,11, the best early Archaean simple spheroids are generally regarded as `possible microfossils'10 because organic spheroids may form abiotically in several ways12. The discovery of less-simple biological morphologies is therefore important in establishing the existence of early life forms in the early Archaean. Uniformly-sized curving filaments, especially tubular ones, are difficult to explain as anything other than the fossil remains of filamentous organisms. Here we report the discovery of numerous filaments from two different stratigraphical positions in the 3,500-Myr-old Onverwacht Group of the Swaziland Supergroup. Their morphologies and abundance provide convincing evidence for the existence of bacteria- or cyanobacteria-like organisms on the Earth during the early Archaean. This supports recent reports of similar filamentous microfossils from 3,500-Myr-old rocks from Western Australia13.

Walsh, Maud M.; Lowe, Donald R.

1985-04-01

109

To Belt or Not To Belt?  

ERIC Educational Resources Information Center

The National Highway Traffic Transportation Safety Administration (NHTSA) is in the midst of the first school-bus crash tests in more than 10 years. Its report is expected in June 2000, and those on both sides of the seat-belt debate are waiting to see what NHTSA will recommend on passenger restraints in large school buses. A sidebar lists sources…

Vail, Kathleen

1999-01-01

110

Precambrian Cratons and Fold-Belts in Brazil: Overview  

NASA Astrophysics Data System (ADS)

The main Precambrian terrains recognized in Brazil comprise the Amazonian, São Francisco and Rio de la Plata cratons, surrounded by Neoproterozoic Brasiliano fold belts, making up the Borborema, Mantiqueira and Tocantins provinces. The Amazonian craton comprises an Archean core, surrounded by Paleoproterozoic terrains (Maroni-Itacaiunas, Ventuari-Tapajós, Rio Negro-Juruena), which southwestwards give way to the Mesoproterozoic Rondoniano-San Ignacio and Sunsas belts, the latter thought to be related to the Grenville belt of North America. The São Francisco craton comprises several Archean blocks (Gavião, Serrinha, Jequié) amalgamated by the Paleoproterozoic high-grade Itabuna-Salvador-Curaçá orogen. The Rio de la Plata craton, largely covered by Phanerozoic strata, is made of Paleoproterozoic basement gneiss and several Paleoproterozoic greenstone belts. Other cratonic blocks are hidden below large Phanerozoic basins, like the Paranapanema and Parnaíba blocks below the Paraná and Parnaíba basins, respectively. Several smaller Archean/Paleoproterozoic blocks appear within the Brasiliano provinces: some were strongly reworked during the Neoproterozoic orogenic events (São José do Campestre, Pernambuco-Alagoas, Goiás, Guanhães, Juiz de Fora, Curitiba), others were only marginally affected (São Luiz, Rio Apa, Luís Alves). The Brasiliano provinces are the result of Neoproterozoic to early Paleozoic orogenic events within the framework of West Gondwana amalgamation. The Mantiqueira Province extends from eastern Brazil to southern Uruguay and includes the Araçuaí, Ribeira and Dom Feliciano fold belts, bordering the São Francisco, Paranapanema and Rio de la Plata cratons and surrounding the Luís Alves craton. The Tocantins province in central Brazil includes the Araguaia, Paraguay and Brasília fold belts, the former bordering the Amazonian craton, the second bordering both the southern Amazonian craton and the Rio Apa block, and the last established on the western border of the São Francisco craton and on the northeastern margin of the Paranapanema block. Deep seismic refraction and other geophysical and geological studies were able to discriminate several crust compartments within the Brasília belt, like the juvenile Goiás magmatic arc, the Archean/Paleoproterozoic Goiás massif, and the external belt zone, as distinguished from the São Francisco craton. The Borborema Province in northeast Brazil is a complex array of Neoproterozoic fold belts (Médio Coreaú, Seridó, Sergipana, Riacho do Pontal, Rio Preto) between the São Luiz and São Francisco cratons, partially covering different crustal blocks (NW Ceará, Ceará Central, Rio Grande do Norte, Pernambuco-Alagoas) separated by large crustal-scale, strike-slip lineaments (Transbrasiliano, Senador Pompeu, Orós, Porta Alegre, Patos, Pernambuco, etc.). Basement of the crustal blocks is mainly Paleoproterozoic in age, but may include Archean cores (São José do Campestre, Grangeiro, Troia). South of the Patos lineament, Mesoproterozoic gneiss, granite and supracrustal belts are recorded in the Transversal domain, in the Pernambuco-Alagoas massif and in the Sergipano and Riacho do Pontal fold belts. Geophysical studies (MT sounding, gravity, seismology, deep seismic refraction, etc.) are underway in order to understand crustal structure and evolution of the province.

Fuck, R.

2008-05-01

111

Characterization of fluids associated with gold mineralization and with regional high-temperature retrogression of granulites in the Limpopo belt, South Africa  

NASA Astrophysics Data System (ADS)

The Hout River Shear Zone forms the terrane boundary between the granite-greenstone terrane of the Kaapvaal craton and the granulite terrane of the Limpopo belt. It dips steeply northward and flattens to the south and was responsible for allowing hot granulites to spread up and over the cooler greenstone terrane. This shear zone acted as a conduit for deep-seated infiltrating fluids into still hot granulites in the hangingwall producing a regional retrograde orthoamphibole isograd and an associated zone of rehydrated granulites. Thermodynamic constraints on the composition of fluids involved in retrograde anthophyllite formation in pelitic granulites on the isograd, supported by the results of a fluid inclusion study and by direct textural evidence in which olivine in closely associated ultramafic granulites has been partially replaced by hypersthene and magnesite, suggest that the hydrating fluid contained at least 70 mol% CO 2 and that this fluid infiltrated at P-Tconditions of about 620°C and 6 kbar pressure. The ?S13C values of CO 2 extracted from magnesite vary between -5.5 and 6.0%. and suggests a deep-seated (possibly mantle) source for the CO 2-rich retrograde fluid. Fluid inclusion studies from two lode-gold deposits (Osprey and Louis Moore) in the same high-grade area, and three deposits from the immediately adjacent Sutherland greenstone belt (Fumani, Klein Letaba, and Birthday) at the northern edge of the Kaapvaal Craton, show that CO 2-rich fluids with similar characteristics were also associated with epigenetic gold mineralization. All of the ore bodies are located within EW-trending northward dipping, ductile shear zones with an oblique to reverse sense of movement. These relationships suggest that there is a direct link between the source of fluids involved in gold mineralization, the fluids that formed the zone of rehydration in the Southern Marginal Zone of the Limpopo belt, and southward verging faulting during the exhumation of the granulite terrane at about 2670 Ma.

Van Reenen, D. D.; Pretorius, A. I.; Roering, C.

1994-02-01

112

Seat Belt Fact Sheet  

MedlinePLUS

... of Emergency Physicians (ACEP) advocates for adoption and enforcement of primary safety belt laws. Emergency physicians see ... use is significantly higher in states with primary enforcement laws compared to those with secondary enforcement laws. ...

113

Belt conveyor apparatus  

DOEpatents

A belt conveyor apparatus according to this invention defines a conveyance path including a first pulley and at least a second pulley. An endless belt member is adapted for continuous travel about the pulleys and comprises a lower portion which engages the pulleys and an integral upper portion adapted to receive objects therein at a first location on said conveyance path and transport the objects to a second location for discharge. The upper belt portion includes an opposed pair of longitudinally disposed crest-like members, biased towards each other in a substantially abutting relationship. The crest-like members define therebetween a continuous, normally biased closed, channel along the upper belt portion. Means are disposed at the first and second locations and operatively associated with the belt member for urging the normally biased together crest-like members apart in order to provide access to the continuous channel whereby objects can be received into, or discharged from the channel. Motors are in communication with the conveyance path for effecting the travel of the endless belt member about the conveyance path. The conveyance path can be configured to include travel through two or more elevations and one or more directional changes in order to convey objects above, below and/or around existing structures.

Oakley, David J. (Richland, WA); Bogart, Rex L. (Kennewick, WA)

1987-01-01

114

Effect of water on the composition of partial melts of greenstone and amphibolite.  

PubMed

Closed-system partial melts of hydrated, metamorphosed arc basalts and andesites (greenstones and amphibolites), where only water structurally bound in metamorphic minerals is available for melting (dehydration melting), are generally water-undersaturated, coexist with plagioclase-rich, anhydrous restites, and have compositions like island arc tonalites. In contrast, water-saturated melting at water pressures of 3 kilobars yields strongly peraluminous, low iron melts that coexist with an amphibolebearing, plagioclase-poor restite. These melt compositions are unlike those of most natural silicic rocks. Thus, dehydration melting over a range of pressures in the crust of island arcs is a plausible mechanism for the petrogenesis of islands arc tonalite, whereas water-saturated melting at pressure of 3 kilobars and above is not. PMID:17835350

Beard, J S; Lofgren, G E

1989-04-14

115

GEOLOGIA E GEOCRONOLOGIA DOS GRANITÓIDES ARQUEANOS DA REGIÃO DE XINGUARA-PA E SUAS IMPLICAÇÕES NA EVOLUÇÃO DO TERRENO GRANITO-GREENSTONE DE RIO MARIA, CRÁTON AMAZÔNICO  

Microsoft Academic Search

GEOLOGY AND GEOCHRONOLOGY OF ARCHEAN GRANITOIDS OF THE XINGUARA REGION: IMPLICATIONS FOR THE EVOLUTION OF THE RIO MARIA GRANITE-GREENSTONE TERRANE, AMAZONIAN CRATON The Xinguara area, located in the Rio Maria Granite-Greenstone Terrain - Pará, is composed of several Archaean granitoids. Structures and fa bric elements visible at outcrop and microscopic scales, and zircon Pb-Pb ages suggest that these granitoids were

ALBANO ANTONIO DA; SILVA LEITE; ROBERTO DALL' AGNOL; MOACIR JOSÉ BUENANO; FERNANDO JACQUES ALTHOFF

116

Radiation belt probes launched  

NASA Astrophysics Data System (ADS)

Storms on Earth delayed by only a few days the launch of NASA's Radiation Belt Storm Probes (RBSP), which blasted off on 30 August for a 2-year tour to explore the Van Allen radiation belts. The two satellites will help scientists learn about the processes that affect electrons and ions in the donut-shaped belts and how the belts change in the context of geomagnetic storms. “The information collected from these probes will benefit the public by allowing us to better protect our satellites and understand how space weather affects communications and technology on Earth,” said John Grunsfeld, associate administrator for NASA's Science Mission Directorate. Each probe carries an identical suite of instruments, including an Energetic Particle, Composition, and Thermal Plasma Suite; Electric and Magnetic Field Instrument Suite and Integrated Science; Electric Field and Waves Suite; Radiation Belt Storm Probes Ion Composition Experiment; and Relativistic Proton Spectrometer. RBSP is part of NASA's Living With a Star program and is managed for NASA by the Johns Hopkins University's Applied Physics Laboratory. For more information, see http://rbsp.jhuapl.edu.

Showstack, Randy

2012-09-01

117

Aluminum depletion in komatiites and garnet fractionation in the early Archean mantle: Hafnium isotopic constraints  

SciTech Connect

Hafnium isotopic compositions were measured in Al-depleted and Al-enriched komatiites from the 3,450 Ma old Barberton greenstone belt, southern Africa. All samples have initial {var epsilon}{sub Hf} values close to zero. Such values are at variance with the strongly negative or positive values that should be observed if these rocks came from old garnet-depleted or garnet-enriched layers, such as may have formed during the solidification of an ancient terrestrial magma ocean. The garnet fractionation observed in komatiites probably took place during the melting event.

Gruau, G. (Max Planck Institut fuer Chemie, Mainz (West Germany) Universite de Rennes (France)); Chauvel, C.; Arndt, N.T. (Max Planck Institut fuer Chemie, Mainz (West Germany)); Cornichet, J. (Universite de Rennes (France))

1990-11-01

118

An Archean Geomagnetic Reversal in the Kaap Valley Pluton, South Africa  

PubMed

The Kaap Valley pluton in South Africa is a tonalite intrusion associated with the Archean Barberton Greenstone Belt. Antipodal paleomagnetic directions determined from the central and marginal parts of the pluton record a geomagnetic reversal that occurred as the pluton cooled. The age of the reversal is constrained by an 40Ar/39Ar plateau age from hornblende at 3214 +/- 4 million years, making it the oldest known reversal. The data presented here suggest that Earth has had a reversing, perhaps dipolar, magnetic field since at least 3.2 billion years ago. PMID:8688075

Layer; Kroner; McWilliams

1996-08-16

119

The Radiation Belt Storm Probes  

NASA Video Gallery

The Radiation Belt Storm Probe mission (RBSP) will explore the Van Allen Radiation Belts in the Earth's magnetosphere. The charge particles in these regions can be hazardous to both spacecraft and ...

120

Moving Belt Radiator technology issues  

NASA Technical Reports Server (NTRS)

Development of the Moving Belt Radiator (MBR) as an advanced space radiator concept is discussed. The relative merits of Solid Belt (SBR) Liquid Belt (LBR), and Hybrid Belt (HBR) Radiators are described. Analytical and experimental efforts related to the dynamics of a rotating belt in microgravity are reviewed. The development of methods for transferring heat to the moving belt is discussed, and the results from several experimental investigations are summarized. Limited efforts related to the belt deployment and stowage, and to fabrication of a hybrid belt, are also discussed. Life limiting factors such as seal wear and micrometeroid resistance are identified. The results from various MBR point design studies for several power levels are compared with advanced Heat Pipe Radiator technology. MBR designs are shown to compare favorable at both 300 and 1000 K temperature levels. However, additional effort will be required to resolve critical technology issues and to demonstrate the advantage of MBR systems.

White, K. Alan, III

1988-01-01

121

Moving belt radiator development status  

NASA Technical Reports Server (NTRS)

Development of the Moving Belt Radiator (MBR) as an advanced space radiator concept is discussed. The ralative merits of Solid Belt (SBR), Liquid Belt (LBR), and Hybrid Belt (HBR) Radiators are described. Analytical and experimental efforts related to the dynamics of a rotating belt in microgravity are reviewed. The development of methods for transferring heat to the moving belt is discussed, and the results from several experimental investigations are summarized. Limited efforts related to the belt deployment and stowage, and to fabrication of a hybrid belt, are also discussed. Life limiting factors such as seal wear and micrometeroid resistance are identified. The results from various MBR point design studies for several power levels are compared with advanced Heat Pipe Radiator technology. MBR designs are shown to compare favorable at both 300 and 1000 K temperature levels. However, additional effort will be required to resolve critical technology issues and to demonstrate the advantage of MBR systems.

White, K. Alan

1988-01-01

122

Safety Belt Use in 2003.  

National Technical Information Service (NTIS)

The National Occupant Protection Use Survey (NOPUS) is an observational survey of safety belt use that began in 1994 and has been used by the National Highway Traffic Safety Administration (NHTSA) to measure the nations belt use. Unlike telephone surveys ...

D. Glassbrenner

2003-01-01

123

Archaean tectonic processes: a case for horizontal shortening in the North Pilbara Granite-Greenstone Terrane, Western Australia  

Microsoft Academic Search

The Archaean Pilbara granitoid-greenstone terrane (GGT) has been the focus of numerous studies on Archaean geology, especially the classic dome-and-basin area around Marble Bar in the east Pilbara. This area has been used as evidence for different tectonic processes, i.e. that vertical tectonics or diapirism was a cause for Archaean deformation. This paper provides evidence to support regional horizontal (plate-interaction)

Richard S. Blewett

2002-01-01

124

Normal Belt Capstan Assembly.  

National Technical Information Service (NTIS)

A normal belt capstan assembly for arrays towed by vessels includes a drive wheel mounted on the vessel and adapted to deploy and discharge an array. The drive wheel has a continuous groove throughout an outer edge thereof with opposed rims on either side...

V. J. Marolda

2006-01-01

125

Radiation belts of Jupiter  

Microsoft Academic Search

Pioneer 10 courted relativistic electrons throughout the magnetosphere ; of Jupiter, with the greatest fluxes being inside 20 Jupiter radii. The peak ; flux of electrons with energy greater than 50 MeV was 1.3 x 107 per square ; centimeter per second at the innermost penetration of the radiation belts. ; (auth);

R. W. Fillius; C. E. McIlwain

1974-01-01

126

The levantine amber belt  

NASA Astrophysics Data System (ADS)

Amber, a fossil resin, is found in Early Cretaceous sanstones and fine clastics in Lebanon, Jordan, and Israel. The term "Levantine amber belt" is coined for this amber-containing sediment belt. The amber occurs as small nodules of various colors and frequently contains inclusions of macro- and microorganisms. The Lebanese amber contains Lepidoptera and the amber from southern Israel is rich in fungal remains. The source of the amber, based on geochemical and palynological evidence, is assumed to be from a conifer belonging to the Araucariaceae. The resins were produced by trees growing in a tropical near shore environment. The amber was transported into small swamps and was preserved there together with lignite. Later reworking of those deposits resulted in redeposition of the amber in oxidized sandstones.

Nissenbaum, A.; Horowitz, A.

1992-02-01

127

Deconstructing the conveyor belt.  

PubMed

For the past several decades, oceanographers have embraced the dominant paradigm that the ocean's meridional overturning circulation operates like a conveyor belt, transporting cold waters equatorward at depth and warm waters poleward at the surface. Within this paradigm, the conveyor, driven by changes in deepwater production at high latitudes, moves deep waters and their attendant properties continuously along western boundary currents and returns surface waters unimpeded to deepwater formation sites. A number of studies conducted over the past few years have challenged this paradigm by revealing the vital role of the ocean's eddy and wind fields in establishing the structure and variability of the ocean's overturning. Here, we review those studies and discuss how they have collectively changed our view of the simple conveyor-belt model. PMID:20558705

Lozier, M Susan

2010-06-18

128

Orinoco Oil Belt  

SciTech Connect

The program for development and exploitation of the Orinoco Oil Belt in Venezuela is discussed. The reservoir characteristics and properties are enumerated, and an exploitation methodology is presented. The results of investigation in the area confirm the existence of large volumes of hydrocarbons with characteristics similar to other Venezuelan heavy crude oil fields. Research programs are being initiated to optimize recovery from the Orinoco area ranging from adaptation of existing technology to new technologic developments.

Not Available

1981-05-03

129

Lap belt injuries in children.  

PubMed

The use of adult seat belts without booster seats in young children may lead to severe abdominal, lumbar or cervical spine and head and neck injuries. We describe four characteristic cases of lap belt injuries presenting to a tertiary children's hospital over the past year in addition to a review of the current literature. These four cases of spinal cord injury, resulting in significant long-term morbidity in the two survivors and death in one child, arose as a result of lap belt injury. These complex injuries are caused by rapid deceleration characteristic of high impact crashes, resulting in sudden flexion of the upper body around the fixed lap belt, and consequent compression of the abdominal viscera between the lap belt and spine. This report highlights the dangers of using lap belts only without shoulder straps. Age-appropriate child restraint in cars will prevent these injuries. PMID:20845604

McGrath, N; Fitzpatrick, P; Okafor, I; Ryan, S; Hensey, O; Nicholson, A J

2010-01-01

130

Intrusive rocks and tectono-metamorphic evolution of the Mako Paleoproterozoic belt (Eastern Senegal, West Africa)  

NASA Astrophysics Data System (ADS)

The Kedougou Kenieba Inlier (KKI) (Paleoproterozoic of Eastern Senegal) is a portion of the West African Craton (WAC) containing a granite-greenstone terrain that experienced three distinct periods of magmatic activity, peaking at 2200, 2160-2130 and 2100-2070 Ma. In the Inlier, Paleoproterozoic granitoids and large-scale transcurrent shear zones are spatially associated, suggesting a genetic link between magma bodies and shear zones. Granitic intrusions are associated with all the volcanic episodes and phases of deformation, and have been used to constrain the age of many of these events. Our structural data and deformation sequence indicate that the Mako Greenstone Belt and the adjacent granitoid complexes have undergone a multi-phase evolutionary history that is spread over a prolonged period. The available geochronological data and field studies allowed classification of the granitoids of the KKI into four generations GI, GII, GIII and GIV. The current data suggest that the oldest rocks in the KKI, the Badon granites (2198 ± 2 Ma) and the tonalitic gneisses from Tonkouto (2200-2198 Ma) (GI), could be correlated with an early Birimian magmatic event. The gneisses, crystallized at depth, record the earliest deformation and in contrast to other tonalites, do not appear to have intruded volcanic rocks. The second manifestation of magmatism was intrusion of mafic diorite - the Gabbro Sandikounda Layered Igneous Complex type (GII) and development of the Laminia Kaourou Plutonic Complex (LKPC) (2160-2130 Ma). These bodies pre-date or are sometimes synchronous with a major deformational episode, and may, therefore, have formed very early in convergent Birimian orogenesis. The third major peak of magmatic activity occurred after the above major episode with the development of the oval shaped Diombalou and Bouroumbourou plutons (GIII). The orientation of these plutons parallel to the regional strike of the schistosity indicates structural control on granite emplacement. Eburnean magmatism was terminated in the Mako Belt following compressional Eburnean deformation, with the emplacement of the Tinkoto, Mamakono plutons (GIV) in the east of the complex and continued in the Dialé-Daléma supergroup with the syntectonic emplacement of the Saraya batholith. Garnitiferous granites of crustal derivation were emplaced in the final period of extensional activity around 2080 Ma. Field observations suggest the early plutons of the complex granitic (Kakadian) batholith intruded during convergent deformation whereas later igneous activity accompanied regional orogen-parallel extension, followed by exhumation. In the Mako Belt, thickening of the crust was proposed to have caused heating and the 'apparent diapiric rise' of the Diombalou and Bouroumbourou plutons.

Gueye, Mamadou; Ngom, Papa Malick; Diène, Mouhamadane; Thiam, Yaouba; Siegesmund, Siegfried; Wemmer, Klaus; Pawlig, Sabine

2008-02-01

131

[Problems with the seat belt].  

PubMed

The greater number of auto-accident victims treated during the observation period had not been using seat belts. Injuries characteristic of belt-usage were also noted. Although there was no significant difference between the two groups in number of injuries, the unbuckled passengers were consistently more seriously injured. In contrast to other studies, fractures of the extremities were more common in the unprotected group. Serious head injuries and head injuries on the whole were more numerous when seat belts were not fastened. The front and rear seat passengers without belts were found to be equally endangered. PMID:4090088

Weyer, F

1985-12-01

132

Gould Belt Origin  

NASA Astrophysics Data System (ADS)

Using archive VLA data and recent observations on the Karl G. Jansky Very Large Array it is worked on a semi-automatic python/CASA code to select, reduce and plot several young stars belonging to the Ophiuchus core. This code mean to help to select observations made along the 30 years of the VLA done in the selected area with the wide configurations A and B, and in the X and C band, to determine their position and compare it with the most recent ones. In this way it is possible to determinate their proper motion with very high precision. It is presented the phases of the process and our first results worked on three well know stars: S1, DoAr 21 and VLA1623. This is the tip of a bigger work that includes Taurus molecular cloud and other important recent star formation regions belonging to the Gould Belt. Our goal is to support the most suitable among several theories about Gould Belt origin or provide a new one taking in count the dynamics of those regions.

Rivera, Leticia; Loinard, Laurent; Dzib, Sergio

2013-07-01

133

Geography of the asteroid belt  

NASA Technical Reports Server (NTRS)

The CSM classification serves as the starting point on the geography of the asteroid belt. Raw data on asteroid types are corrected for observational biases (against dark objects, for instance) to derive the distribution of types throughout the belt. Recent work on family members indicates that dynamical families have a true physical relationship, presumably indicating common origin in the breakup of a parent asteroid.

Zellner, B. H.

1978-01-01

134

The Kuiper Belt Legacy Project  

Microsoft Academic Search

To advance our understanding of the Kuiper belt, the region of the solar system extending beyond 30 AU, we have identified three core issues: [i] Well-determined orbital elements of trans-Neptunian objects (TNOs) are essential for providing an accurate view of the Kuiper belt's physical properties such as dynamics, formation, and structure; [ii] A program of dedicated recovery observations of TNOs

Joel Parker; Brett Gladman; J. J. Kavelaars; Jean-Marc Petit; Lynn Allen; Allyson Bieryla

2006-01-01

135

Archean sedimentary styles and early crustal evolution  

NASA Astrophysics Data System (ADS)

The distinctions between and implications of early and late Archean sedimentary styles are presented. Early Archean greenstone belts, such as the Barberton of South Africa and those in the eastern Pilbar Block of Australia are characterized by fresh or slightly reworked pyroclastic debris, orthochemical sediments such as carbonates, evaporites, and silica, and biogenic deposits including cherts and stromatolitic units. Terrigenous deposits are rare, and it is suggested that early Archean sediments were deposited on shallow simatic platforms, with little or no components derived from sialic sources. In contrast, late Archean greenstone belts in the Canadian Shield and the Yilgarn Block of Australia contain coarse terrigenous clastic rocks including conglomerate, sandstone, and shale derived largely from sialic basement. Deposition appears to have taken place in deepwater, tectonically unstable environments. These observations are interpreted to indicate that the early Archean greenstone belts formed as anorogenic, shallow water, simatic platforms, with little or no underlying or adjacent continental crust, an environment similar to modern oceanic islands formed over hot spots.

Lowe, D. R.

136

Investigation of a new type charging belt  

SciTech Connect

There are many desirable characteristics for an electrostatic accelerator charging belt. An attempt has been made to find a belt that improves on these properties over the stock belt. Results of the search, procurement, and 1,500 hours of operational experience with a substantially different belt are reported.

Jones, N.L. [Oak Ridge National Lab., TN (United States). Accelerator Based Atomic Physics

1994-12-31

137

Platinum-group element alloy inclusions in chromites from Archaean mafic-ultramafic units: evidence from the Abitibi and the Agnew-Wiluna Greenstone Belts  

Microsoft Academic Search

Summary The paper investigates the role of primary magmatic phases in the fractionation and concentration of PGE in Archaean mafic and ultramafic systems. The composition of chromites and olivines in sulphur-poor (S?200?ppb) reflect the presence of PGM. Chromites from Fred’s Flow komatiitic basalt contain Ir-rich clusters, whereas Pt enrichments (>370?ppb) in Boston Creek ferropicritic basalt reflect the presence of Pt-rich

M. L. Fiorentini; W. E. Stone; S. W. Beresford; M. E. Barley

2004-01-01

138

Oxidized and reduced mineral assemblages in greenstone belt rocks of the St. Ives gold camp, Western Australia: vectors to high-grade ore bodies in Archaean gold deposits?  

NASA Astrophysics Data System (ADS)

Hydrothermal sulfide-oxide-gold mineral assemblages in gold deposits in the Archaean St. Ives gold camp in Western Australia indicate extremely variable redox conditions during hydrothermal alteration and gold mineralization in space and time. Reduced alteration assemblages (pyrrhotite-pyrite) occur in deposits in the southwest of the camp (e.g., Argo, Junction deposits) and moderately to strongly oxidized assemblages (magnetite-pyrite, hematite-pyrite) occur in deposits in the Central Corridor in the northeast (e.g., North Orchin, Revenge deposits). Reduced mineral assemblages flank the Central Corridor of oxidized deposits and, locally, cut across it along E-W trending faults. Oxidized mineral assemblages in the Central Corridor are focused on gravity lows which are interpreted to reflect abundant felsic porphyritic intrusions at about 1,000 m below present surface. Hydrothermal magnetite predates and is synchronous with early phases of gold-associated albite-carbonate-pyrite-biotite-chlorite hydrothermal alteration. Later-stage, gold-associated pyrite is in equilibrium with hematite. The spatial distribution and temporal sequence of iron sulfides and oxides with gold indicate the presence of at least two spatially restricted but broadly synchronous hydrothermal fluids with contrasting redox states. Sulfur isotope constraints support the argument that the different mineral assemblages reflect differences in redox conditions. The ? 34S values for pyrite for the St. Ives gold camp range between -8.4‰ and +5.1‰ with the negative values occurring in oxidized magnetite-rich domains and slightly negative or positive values occurring in reduced, pyrrhotitic domains. Preliminary spatial and paragenetic analysis of the distribution of iron sulfides and oxides in the St. Ives camp suggests that gold grades are highest where the redox state of the hydrothermal alteration assemblages switches from relatively reduced pyrrhotite-pyrite to relatively oxidized magnetite-pyrite and hematite-pyrite both in space and time. Gold deposition is inferred to have occurred where fluids of contrasting redox state mixed.

Neumayr, Peter; Walshe, John; Hagemann, Steffen; Petersen, Klaus; Roache, Anthony; Frikken, Peter; Horn, Leo; Halley, Scott

2008-03-01

139

Previously Undetected Radiation Belt Revealed  

NASA Video Gallery

Since their discovery over 50 years ago, the Earth'??s Van Allen radiation belts have been considered to consist of two distinct zones of trapped, highly energetic charged particles. Observations f...

140

Chaos on the conveyor belt  

NASA Astrophysics Data System (ADS)

The dynamics of a spring-block train placed on a moving conveyor belt is investigated both by simple experiments and computer simulations. The first block is connected by a spring to an external static point and, due to the dragging effect of the belt, the blocks undergo complex stick-slip dynamics. A qualitative agreement with the experimental results can be achieved only by taking into account the spatial inhomogeneity of the friction force on the belt's surface, modeled as noise. As a function of the velocity of the conveyor belt and the noise strength, the system exhibits complex, self-organized critical, sometimes chaotic, dynamics and phase transition-like behavior. Noise-induced chaos and intermittency is also observed. Simulations suggest that the maximum complexity of the dynamical states is achieved for a relatively small number of blocks (around five).

Sándor, Bulcsú; Járai-Szabó, Ferenc; Tél, Tamás; Néda, Zoltán

2013-04-01

141

Calculating Belt Velocity and Horsepower  

NSDL National Science Digital Library

In this Flash-based interactive object by James Bourassa and John Rosz from Fox Valley Technical College, learners are given the RPM, the pulley diameter, and the force, and proceed to calculate belt velocity and horsepower.

Bourassa, James; Rosz, John

2008-10-23

142

Liquid Belt Radiator Design Study.  

National Technical Information Service (NTIS)

The Liquid Belt Radiator (LBR) is an advanced concept developed to meet the needs of anticipated future space missions. A previous study documented the advantages of this concept as a lightweight, easily deployable alternative to present day space heat re...

W. P. Teagan K. F. Fitzgerald

1986-01-01

143

Belt conveyors for bulk materials. 6th ed.  

SciTech Connect

The 16 chapters are entitled: Belt conveyor general applications economics; Design considerations; Characteristics and conveyability of bulk materials; Capacities, belt widths and speeds; Belt conveyor idlers; Belt tension and power engineering; Belt selection; Pulleys and shafts; Curves; Steep angle conveying; Belt cleaners and accessories; Transfer points; Conveyor motor drives and controls; Operation, maintenance and safety; Belt takeups; and Emerging technologies. 6 apps.

NONE

2007-07-01

144

Dynamic melting of the Precambrian mantle: evidence from rare earth elements of the amphibolites from the Nellore-Khammam Schist Belt, South India  

NASA Astrophysics Data System (ADS)

The Nellore-Khammam Schist Belt (NKSB) in South India is a Precambrian greenstone belt sited between the Eastern Ghats Mobile Belt (EGMB) to the east and the Cratonic region to the west. The belt contains amphibolites, granite gneisses and metasediments including banded iron formations. Amphibolites occurring as dykes, sills and lenses—in and around an Archaean layered complex—form the focus of the present study. The amphibolites are tholeiitic in composition and are compositionally similar to Fe-rich mafic rocks of greenstone belts elsewhere. The NKSB tholeiites show highly variable incompatible trace element abundances for similar Mg#s, relatively constant compatible element concentrations, and uniform incompatible element ratios. Chondrite-normalized REE patterns of the tholeiites range from strongly LREE depleted ((La/Yb) N = 0.19) to LREE enriched ((La/Yb) N = 6.95). Constant (La/Ce) N ratios but variable (La/Yb) N values are characteristic geochemical traits of the tholeiites; the latter has resulted in crossing REE patterns especially at the HREE segment. Even for the most LREE depleted samples, the (La/Ce) N ratios are > 1 and are similar to those of the LREE enriched samples. There is a systematic decrease in FeOt, K2O and P2O5, as well as Ce and other incompatible elements from the LREE enriched to the depleted samples without any variation in the incompatible element ratios and Mg#s. Neither batch and fractional melting, nor magma chamber processes can account for the non-correlation between the LREE enrichment and HREE concentrations. We suggest that dynamic melting of the upper mantle is responsible for these geochemical peculiarities of the NKSB tholeiites. Polybaric dynamic melting within a single mantle column with variable mineralogy is the likely mechanism for the derivation of NKSB tholeiitic melts. It is possible that the NKSB tholeiites are derived from a source with higher FeO/MgO than that of present day ridge basalts.

Vijaya Kumar, K.; Narsimha Reddy, M.; Leelanandam, C.

2006-08-01

145

Antiquity of the biological sulphur cycle: evidence from sulphur and carbon isotopes in 2700 million-year-old rocks of the Belingwe Belt, Zimbabwe.  

PubMed

Sulphur and carbon isotopic analyses on small samples of kerogens and sulphide minerals from biogenic and non-biogenic sediments of the 2.7 x 10(9) years(Ga)-old Belingwe Greenstone Belt (Zimbabwe) imply that a complex biological sulphur cycle was in operation. Sulphur isotopic compositions display a wider range of biological fractionation than hitherto reported from the Archaean. Carbon isotopic values in kerogen record fractionations characteristic of rubisco activity methanogenesis and methylotrophy and possibly anoxygenic photosynthesis. Carbon and sulphur isotopic fractionations have been interpreted in terms of metabolic processes in 2.7 Ga prokaryote mat communities, and indicate the operation of a diverse array of metabolic processes. The results are consistent with models of early molecular evolution derived from ribosomal RNA. PMID:11209879

Grassineau, N V; Nisbet, E G; Bickle, M J; Fowler, C M; Lowry, D; Mattey, D P; Abell, P; Martin, A

2001-01-22

146

Antiquity of the biological sulphur cycle: evidence from sulphur and carbon isotopes in 2700 million-year-old rocks of the Belingwe Belt, Zimbabwe.  

PubMed Central

Sulphur and carbon isotopic analyses on small samples of kerogens and sulphide minerals from biogenic and non-biogenic sediments of the 2.7 x 10(9) years(Ga)-old Belingwe Greenstone Belt (Zimbabwe) imply that a complex biological sulphur cycle was in operation. Sulphur isotopic compositions display a wider range of biological fractionation than hitherto reported from the Archaean. Carbon isotopic values in kerogen record fractionations characteristic of rubisco activity methanogenesis and methylotrophy and possibly anoxygenic photosynthesis. Carbon and sulphur isotopic fractionations have been interpreted in terms of metabolic processes in 2.7 Ga prokaryote mat communities, and indicate the operation of a diverse array of metabolic processes. The results are consistent with models of early molecular evolution derived from ribosomal RNA.

Grassineau, N V; Nisbet, E G; Bickle, M J; Fowler, C M; Lowry, D; Mattey, D P; Abell, P; Martin, A

2001-01-01

147

Applications of radiation belt research  

NASA Astrophysics Data System (ADS)

When Arthur Clark and John Pierce proposed geosynchronous and low-Earth-orbiting (GEO and LEO) communications satellites, respectively, they did not envision that the environment in which their concepts would fly would be anything but benign. Discovery of the Van Allen radiation belts in 1958 fundamentally altered understanding of Earth's near-space environment and its impacts on technologies. Indeed, the first commercial telecommunications satellite, Telstar 1, in LEO, failed some 6 months after launch (10 July 1962) due to trapped radiation that had been enhanced from the Starfish Prime high-altitude nuclear test on the day prior to launch. Today radiation trapped in the geomagnetic field, as well as solar energetic particles that can access the magnetosphere, forms critical constraints on the design and operations of satellite systems. These considerations were important factors in the planning of the AGU Chapman Conference on radiation belts that was hosted in July 2011 by the Memorial University of Newfoundland in St. John's, Canada (see "Chapman Conference on Radiation Belts and the Inner Magnetosphere," page 4). The conference presentations, discussions, and hallway conversations illuminated current understanding of Earth's radiation belts and critical issues remaining. Certainly, fundamental understanding of radiation belt origins remains elusive. The relative roles of adiabatic processes, geomagnetic storm injections, and wave heating, among other considerations, are central topics of intense debate and of competing modeling regimes by numerous active groups.

Lanzerotti, Louis J.

2011-10-01

148

Trends in PVC conveyor belting  

SciTech Connect

The development of mechanical systems of extraction at the coal face necessitated the introduction of efficient methods of mineral transportation in deep-mining operations. The most popular system is the belt conveyor. Originally PVC was being evaluated as a rubber substitute, as in its liquid form it appeared to offer an easier route to fabric coating and impregnation for conveyor belt applications. However, it was not until 1950, when over 200 miners lost their lives due to an underground fire being spread by combustible rubber conveyor belts, that the full significance of the properties of PVC were appreciated. Following this tragedy, an intensive development program to produce a substitute for rubber was initiated. It had to have similar operational characteristics as rubber while incorporating the safety features of resistance to flame propagation and build-up of static electrical charges. It became evident that PVC could be compounded to realize these requirements and belting manufacturers immediately started to produce a new generation of belts based on the previouly proven mechanical characteristics of multiply fabrics, but substituting PVC for the rubber content. The advantages of PVC are discussed.

Hopwood, J.E.

1984-03-01

149

Effects of vehicle seat and belt geometry on belt fit for children with and without belt positioning booster seats.  

PubMed

A laboratory study was conducted to quantify the effects of belt-positioning boosters on lap and shoulder belt fit. Postures and belt fit were measured for forty-four boys and girls ages 5-12 in four highback boosters, one backless booster, and on a vehicle seat without a booster. Belt anchorage locations were varied over a wide range. Seat cushion angle, seat back angle, and seat cushion length were varied in the no-booster conditions. All boosters produced better mean lap belt fit than was observed in the no-booster condition, but the differences among boosters were relatively large. With one midrange belt configuration, the lap belt was not fully below the anterior-superior iliac spine (ASIS) landmark on the front of the pelvis for 89% of children in one booster, and 75% of children failed to achieve that level of belt fit in another. In contrast, the lap belt was fully below the ASIS for all but two children in the best-performing booster. Child body size had a statistically significant but relatively small effect on lap belt fit. The largest children sitting without a booster had approximately the same lap belt fit as the smallest children experienced in the worst-performing booster. Increasing lap belt angle relative to horizontal produced significantly better lap belt fit in the no-booster condition, but the boosters isolated the children from the effects of lap belt angles. Reducing seat cushion length in the no-booster condition improved lap belt fit but changing cushion angle did not. Belt upper anchorage (D-ring) location had a strong effect on shoulder belt fit in conditions without shoulder belt routing from the booster. Unexpectedly, the worst average shoulder belt fit was observed in one highback booster with a poorly positioned shoulder belt routing clip. The shoulder belt was routed more outboard, on average, with a backless booster than without a booster, but raising the child also amplified the effect of D-ring location, such that children were more likely to experience poor shoulder belt fit due to outboard and forward D-ring locations when sitting on the booster. Taller children experienced more-outboard shoulder belt fit in conditions without shoulder belt routing by the booster and in the one booster with poor shoulder belt routing. Adjustable shoulder belt routing on three of the highback boosters effectively eliminated stature effects, providing approximately the same shoulder belt fit for all children. Seat back angle did not have a significant effect on shoulder belt fit. The results of this study have broad applicability toward the improvement of occupant restraints for children The data show substantial effects of booster design on belt fit, particularly the effects of alternative lap and torso belt routing approaches. The data quantify the critical importance of belt anchorage location for child belt fit, providing an important foundation for efforts to optimize belt geometry for children. PMID:22703990

Reed, Matthew P; Ebert-Hamilton, Sheila M; Klinich, Kathleen D; Manary, Miriam A; Rupp, Jonathan D

2013-01-01

150

A Chaos Conveyor Belt  

NASA Astrophysics Data System (ADS)

A critical question for the habitability of Europa remains: how does the ice shell work? The detection of shallow subsurface lenses below Europa’s chaos implies that the ice shell is recycled rapidly and that Europa may be currently active. While this is not the first time liquid water has been implicated for Europa, the location of these features combined with new perspective on their dynamics frames the question in a new way. Melt lenses are intriguing potential habitats. Moreover, their formation requires the existence of impurities within the upper ice shell that may be sources of energy for microorganisms. Geomorphic evidence also exists for hydraulic redistribution of fluids both vertically and horizontally through pores and fractures. This process, observed in terrestrial ice shelves, may preserve liquid water within the ice matrix over many kilometers from the source. Horizontal transport of material may produce interconnectivity between distinct regions of Europa, thus preserving habitable conditions within the ice over a longer duration. At a surface age of 40-90 Myr, with 25-50% covered by chaos terrain, Europa's resurfacing rate is very high and water likely plays a significant role. Because of the vigor of overturn implied by this new work, it is likely that surface and subsurface materials are well-mixed within the largest and deepest lenses, providing a mechanism for bringing oxidants and other surface contaminants to the deeper ice shell where it can reach the ocean by convective or compositional effects. The timescales over which large lenses refreeze are large compared to the timescales for vertical transport, while the timescales for smaller lenses are comparable to or shorter than convective timescales. Moreover, marine ice accretion at the bottom of the ice shell may be contributing to a compositional buoyancy engine that would change the makeup of the ice shell. From this point of view, we evaluate the habitability of Europa’s ice and ocean in light of active processes that may form a “chaos conveyor belt” that drives material exchange on Europa.

Schmidt, Britney E.

2013-10-01

151

Dynamics of Radiation Belt Particles  

NASA Astrophysics Data System (ADS)

This paper reviews basic concepts of particle dynamics underlying theoretical aspect of radiation belt modeling and data analysis. We outline the theory of adiabatic invariants of quasiperiodic Hamiltonian systems and derive the invariants of particle motion trapped in the radiation belts. We discuss how the nonlinearity of resonant interaction of particles with small-amplitude plasma waves, ubiquitous across the inner magnetosphere, can make particle motion stochastic. Long-term evolution of a stochastic system can be described by the Fokker-Plank (diffusion) equation. We derive the kinetic equation of particle diffusion in the invariant space and discuss its limitations and associated challenges which need to be addressed in forthcoming radiation belt models and data analysis.

Ukhorskiy, A. Y.; Sitnov, M. I.

2013-11-01

152

Proton Spectrometer Belt Research (PSBR)  

NASA Astrophysics Data System (ADS)

The Proton Spectrometer Belt Research (PSBR) program will place Relativistic Proton Spectrometer (RPS) instrumentation on board the Radiation Belt Storm Probes spacecraft and is to measure the inner Van Allen belt protons with energies from 50 MeV to 2 GeV. Presently, the intensity of trapped protons with energies beyond about 150 MeV is not well known and thought to be underestimated in existing specification models. Such protons are known to pose a number of hazards to astronauts and spacecraft; including total ionizing dose, displacement damage, single event effects, and nuclear activation. This instrument will address a priority highly ranked by the scientific and technical community and will extend the measurement capability of this mission to a range beyond that originally planned.

Groves, C.; Selesnick, R. S.; Mazur, J. E.; Blake, J. B.; Clemmons, J. H.; O'Brien, T. P.; Friesen, L. M.; Katz, N.; Kolasinski, W. A.; Looper, M. D.

2006-12-01

153

Geologic evolution of the Serrinha nucleus granite–greenstone terrane (NE Bahia, Brazil) constrained by U–Pb single zircon geochronology  

Microsoft Academic Search

U–Pb single zircon crystallization ages were determined using TIMS and sensitive high resolution ion microprobe (SHRIMP) on samples of granitoid rocks exposed in the Serrinha nucleus granite–greenstone terrane, in NE Brazil. Our data show that the granitoid plutons can be divided into three distinct groups. Group 1 consists of Mesoarchaean (3.2–2.9Ga) gneisses and N-S elongated TTG (Tonalite-Trondhjemite-Granodiorite) plutons with gneissic

D. C. Rios; D. W. Davis; H. Conceição; W. J. Davis; M. L. S. Rosa; A. P. Dickin

2009-01-01

154

Structural evolution of the Marble Bar Domain, Pilbara granite-greenstone terrain, Australia: the role of Archaean mid-crustal detachments  

Microsoft Academic Search

The eastern Pilbara granite-greenstone terrain in Western Australia contains rocks that are largely Early to Mid Archaean in age, from ca 3.6 to 2.9 Ga. The area has been stable since 2.77 Ga and as such provides an opportunity to study the tectonic processes that were involved in the earliest part of the Earth’s development. Was (some form of) plate

A. Kloppenburg

2003-01-01

155

CDC Vital Signs: Adult Seat Belt Use in the US  

MedlinePLUS

... belts in 2008 if all states had primary enforcement seat belt laws achieved 88% use.* Motor vehicle ... wear a seat belt on every trip. Primary enforcement seat belt laws make a big difference in ...

156

46 CFR 169.723 - Safety belts.  

Code of Federal Regulations, 2010 CFR

...and Equipment § 169.723 Safety belts. Each vessel must carry a harness type safety belt conforming to Offshore Racing Council (ORC) standards for each person on watch or required to work the vessel in heavy...

2009-10-01

157

46 CFR 169.723 - Safety belts.  

Code of Federal Regulations, 2013 CFR

...and Equipment § 169.723 Safety belts. Each vessel must carry a harness type safety belt conforming to Offshore Racing Council (ORC) standards for each person on watch or required to work the vessel in heavy...

2013-10-01

158

46 CFR 169.723 - Safety belts.  

Code of Federal Regulations, 2010 CFR

...and Equipment § 169.723 Safety belts. Each vessel must carry a harness type safety belt conforming to Offshore Racing Council (ORC) standards for each person on watch or required to work the vessel in heavy...

2010-10-01

159

Grinding Glass Disks On A Belt Sander  

NASA Technical Reports Server (NTRS)

Small machine attached to table-top belt sander makes possible to use belt sander to grind glass disk quickly to specified diameter within tolerance of about plus or minus 0.002 in. Intended to be used in place of production-shop glass grinder. Held on driveshaft by vacuum, glass disk rotated while periphery ground by continuous sanding belt.

Lyons, James J., III

1995-01-01

160

Mountain Belts and the New Global Tectonics  

Microsoft Academic Search

Analysis of the sedimentary, volcanic, structural, and metamorphic chronology in mountain belts, and consideration of the implications of the new global tectonics (plate tectonics), strongly indicate that mountain belts are a consequence of plate evolution. It is proposed that mountain belts develop by the deformation and metamorphism of the sedimentary and volcanic assemblages of Atlantic-type continental margins. These assemblages result

John F. Dewey; John M. Bird

1970-01-01

161

Proton Spectrometer Belt Research (PSBR)  

Microsoft Academic Search

The National Reconnaissance Office (NRO), NASA, the Air Force Research Laboratory (AFRL), the Aerospace Corporation, the Los Alamos National Laboratory (LANL) and the Naval Research Laboratory (NRL) have jointly formed the Proton Spectrometer Belt Research (PSBR) program to meet two primary objectives: to measure the high-energy proton spectrum by placing the Relativistic Proton Spectrometer (RPS) instrument on board the Radiation

D. Dyers; J. Mazur; P. O'Brien; G. Ginet; G. Reeves

2008-01-01

162

Camshaft timing belt reliability modelling  

Microsoft Academic Search

This paper presents a generic approach to life prediction modelling for automotive components, which aims to establish a correlation between the degradation mechanism, the real world customer usage profile and rig life testing. The approach is illustrated with the development of a life model for the camshaft-timing belt, for which tooth shear fatigue mechanism leads to the common cause failure

Ioan F. Campean; Andrew J. Day; S. Wright

2001-01-01

163

Seat Belt Sign and Its Significance  

PubMed Central

Safety belts are the most important safety system in motor vehicles and when worn intend to prevent serious injuries. However, in unusual circumstances (high velocity motor vehicle collisions) these safety measures (seat belts) can be the source and cause of serious injuries. The seat belt syndrome was first described as early by Garrett and Braunste in but the term “seat belt sign” was discussed by Doersch and Dozier. Medical personnel's involved in emergency care of trauma patients should be aware of seat belt sign and there should a higher index of suspicion to rule out underlying organ injuries.

Agrawal, Amit; Inamadar, Praveenkumar Ishwarappa; Subrahmanyam, Bhattara Vishweswar

2013-01-01

164

Zircon age data from a Greenstone of the archaean Yilgarn Block, Australia: Mid proterozoic heating or uplift?  

NASA Astrophysics Data System (ADS)

A new age determination has been made on the Greenstones of the Agnew-Jones Creek Area, Western Australia by use of the Zircon U-Pb dating procedure. Late stage granophyre from the differentiated Kathleen Valley doleritic sill provided zircons which are otherwise unobtainable from mafic rock suites. An upper intercept age of 2,795 + 38 Ma, extends the known length of the otherwise tightly established, late Archaean tectonic cycle at Agnew from 250 Ma to 320 Ma. A lower intercept of age 1,345 ± 153 Ma is interpreted to record either a hitherto unknown very low temperature heating, or a hitherto unknown tectonic, uplift and cover removal, in the mid-Proterozoic. The existance of a postulated ancient unconformity of craton size dimensions may be being confirmed and dated. Apart from some inconclusive olivine and pyroxene Rb-Sr isotopic data from 190km to the west, the only evidence known that could support either possibility is found outside the Yilgarn Block itself. Minor perturbations to a simple two-stage discordia pattern imply further small amounts of lead loss at later times. Studies of this nature could eventually provide information on the later history of stabilized cratons.

Cooper, J. A.; Dong, Y. B.

1983-06-01

165

The rolling of metal belts  

Microsoft Academic Search

A now method of producing thin-walled seamless metal belts is discussed. The method incorporates the principles of float-rolling (CBS rolling), whereby metal strip is pinched between a small diameter floating roll and two large diameter back-up rolls which rotate with different peripheral speeds. Whereas in conventional rolling reduction may be controlled by regulating the roll gap opening, in float-rolling reduction

J. M. STUART

1973-01-01

166

Investigation of Moving Belt Radiator Technology Issues  

NASA Technical Reports Server (NTRS)

The development of an advanced spacecraft radiator technology is reported. The moving belt radiator is a thermal radiator concept with the promise of lower specific mass (per kW rejected) than that afforded by existing technologies. The results of a parametric study to estimate radiator mass for future space power systems is presented. It is shown that this technology can be scaled up to 200 MW for higher rejection temperatures. Several aspects of the design concept are discussed, including the dynamics of a large rotating belt in microgravity. The results of a computer code developed to model the belt dynamics are presented. A series of one-g experiments to investigate the dynamics of small belts is described. A comprehensive test program to investigate belt dynamics in microgravity aboard the NASA KC-135 aircraft is discussed. It was found that the desired circular shape can readily be achieved in microgravity. It is also shown that a rotating belt is stable when subjected to simulated attitude control maneuvers. Heat exchanger design is also investigated. Several sealing concepts were examined experimentally, and are discussed. Overall heat transfer coefficients to the rotating belt are presented. Material properties for various belt materials, including screen meshes, are also presented. The results presented in this report indicate that the moving belt radiator concept is technically feasible.

Teagan, W. Peter; Aguilar, Jerry L.

1994-01-01

167

Pediatric lap belt injuries: care and prevention.  

PubMed

Motor vehicle collisions are the leading cause of death from injury during childhood. As children outgrow their toddler car seats, they are often restrained by two-point lap belts, which are fashioned for adult body proportions. Those children restrained by two-point lap belts are at risk for intraabdominal and spinal injury during an auto collision. This article explores the mechanisms of injury and identification of "lap belt syndrome." Aspects of nursing care and prevention strategies will be discussed. A case study illustrates and summarizes the cogent aspects of lap belt related injury and child/family care. PMID:9369730

Shoemaker, B L; Ose, M

1997-01-01

168

Drive Alive: Teen Seat Belt Survey Program  

PubMed Central

Objective: To increase teen seat belt use among drivers at a rural high school by implementing the Drive Alive Pilot Program (DAPP), a theory-driven intervention built on highway safety best practices. Methods: The first component of the program was 20 observational teen seat belt surveys conducted by volunteer students in a high school parking lot over a 38-month period before and after the month-long intervention. The survey results were published in the newspaper. The second component was the use of incentives, such as gift cards, to promote teen seat belt use. The third component involved disincentives, such as increased police patrol and school policies. The fourth component was a programmatic intervention that focused on education and media coverage of the DAPP program. Results: Eleven pre-intervention surveys and nine post-intervention surveys were conducted before and after the intervention. The pre- and post-intervention seat belt usage showed significant differences (p<0.0001). The average pre-intervention seat belt usage rate was 51.2%, while the average post-intervention rate was 74.5%. This represents a percentage point increase of 23.3 in seat belt use after the DAPP intervention. Conclusion: Based on seat belt observational surveys, the DAPP was effective in increasing seat belt use among rural high school teenagers. Utilizing a theory-based program that builds on existing best practices can increase the observed seat belt usage among rural high school students.

Burkett, Katie M.; Davidson, Steve; Cotton, Carol; Barlament, James; Loftin, Laurel; Stephens, James; Dunbar, Martin; Butterfield, Ryan

2010-01-01

169

Use of seat belt and enforcement of seat belt laws in pakistan.  

PubMed

Objectives: Traffic crashes are a leading cause of deaths and injuries in Pakistan. The World Health Organization (WHO) estimates that approximately 30,131 people die in road crashes annually on Pakistani roads (WHO 2013). The use of seat belts can be effective in reducing road crash fatalities in Pakistan but under existing seat belt laws, seat belt use is mandatory only for drivers and is limited to specific vehicles and roads. Primarily, this study was aimed to measure seat belt use rates among Pakistani vehicle occupants. It was meant to investigate the factors influencing the compliance behavior of seat belt use among vehicle drivers. The second objective was to gauge the enforcement of seat belt laws and their effectiveness in Pakistan. Methods: A first ever national survey was conducted for the systematic recording of seat belt use rates among Pakistani drivers and front passengers on 5 different kinds of roads. Factors influencing compliance with seat belt use were gauged through a questionnaire for 5 different kinds of roads. Commitment level of different traffic police organizations to enforce seat belt laws was also measured through their previous year's enforcement data. Results: Average seat belt use rates were 20% with the highest on motorways (53%) and the lowest on rural roads (5%). Unawareness of the law/usefulness, seat belt not fitted, discomfort, forgetfulness, low speed, and careless attitude were major reasons for noncompliance with seat belt laws among Pakistani drivers. Seat belt use rates were directly proportional to law enforcement strength and the National Highways and Motorways Police (NH&MP) showed maximum enforcement on M-2. There is a dire need to revise existing seat belt laws in order to raise seat belt use rates in Pakistan. PMID:24433015

Klair, Ashfaq Ahmad; Arfan, Muhammad

2014-10-01

170

47. INTERIOR VIEW, DETAIL OF CONVEYOR BELT SYSTEM SYSTEM WITH ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

47. INTERIOR VIEW, DETAIL OF CONVEYOR BELT SYSTEM SYSTEM WITH BACK BELT DROPPING HARDENED NAILS ON THE FRONT BELT TO BE TEMPERED; MOTION STOPPED - LaBelle Iron Works, Thirtieth & Wood Streets, Wheeling, Ohio County, WV

171

Exploring the Earth's Radiation Belts  

NASA Astrophysics Data System (ADS)

We present the outreach efforts of the MAARBLE (Monitoring, Analyzing and Assessing Radiation Belt Loss and Energization) project, intended to provide the general public with simplified information concerning the scientific objectives of the project, its focus and its expected outcomes. MAARBLE involves monitoring of the geospace environment through space and ground-based observations, in order to understand various aspects of the radiation belts (torus-shaped regions encircling the Earth, in which high-energy charged particles are trapped by the geomagnetic field), which have direct impact on human endeavors in space (spacecraft and astronauts exposure). The public outreach website of MAARBLE, besides regular updates with relevant news, also employs a variety of multimedia (image and video galleries) and impressive sounds of space (characteristic sounds such as whistlers or tweeks) related to very low and ultra low frequency (VLF/ULF) electromagnetic waves. It also provides links to some of the most interesting relevant educational activities, including those at partner institutions such as the Institute of Geophysics and Planetary Physics at UCLA, the University of Alberta, the Swedish Institute of Space Physics and the Institute of Atmospheric Physics of the Academy of Sciences of the Czech Republic.

Daglis, I. A.; Anastasiadis, A.; Chatzichristou, E. T.; Ropokis, G.; Giannakis, O.

2012-09-01

172

36 CFR 1004.15 - Safety belts.  

Code of Federal Regulations, 2013 CFR

...Presidio Trust will have the safety belt or child restraint system properly fastened at...vehicle is in motion. The safety belt and child restraint system will conform to applicable...section does not apply to an occupant in a seat that was not originally equipped by...

2013-07-01

173

36 CFR 4.15 - Safety belts.  

Code of Federal Regulations, 2013 CFR

...a park area will have the safety belt or child restraint system properly fastened at...vehicle is in motion. The safety belt and child restraint system will conform to applicable...section does not apply to an occupant in a seat that was not originally equipped...

2013-07-01

174

Conveyor belt entry fire hazards and control  

Microsoft Academic Search

A fire in a coal mine conveyor belt entry represent a major safety and health risk to miners. Fighting belt entry fires can be a commanding effort. If there is a failure of one aspect in the fire fighting needs such as a dissimilar hose-valve connection, then it can result in the inability to extinguish a fire. Fire incident data

H. Verakis; M. Hockenberry

2008-01-01

175

Understanding Quaternions and the Dirac Belt Trick  

ERIC Educational Resources Information Center

The Dirac belt trick is often employed in physics classrooms to show that a 2n rotation is not topologically equivalent to the absence of rotation whereas a 4n rotation is, mirroring a key property of quaternions and their isomorphic cousins, spinors. The belt trick can leave the student wondering if a real understanding of quaternions and spinors…

Staley, Mark

2010-01-01

176

Great Ocean Conveyor Belt: Part II  

NSDL National Science Digital Library

This podcast features the Great Ocean Conveyor Belt and potential impact of an increase in fresh water (from melting sea ice the Arctic) entering the North Atlantic. It includes interviews with two scientists and discusses the impact of changes in the Great Ocean Conveyor Belt on the climate in Northern Europe over the course of a century.

Domain, Wgbh T.

177

Situational characteristics of safety belt use.  

PubMed

Past research concerning the use and nonuse of safety belts has tended to stereotype users and nonusers as distinct entities on the basis of a single observed situation. The thought processes underlying the reasons given by drivers for using or not using seat belts have not been explored. The purpose of this study was to observe belt use by a group of drivers and describe factors contributing to their use or nonuse as defined by the drivers themselves. In-depth interviews were undertaken with 239 drivers whose safety belt wearing behavior was observed in specific city or highway driving locations. Vehicle license numbers, gender, and age group of selected drivers were used to retrieve driver records and insurance policy data. Open-ended questions were asked concerning their reasons for use or nonuse and their attitudes towards safety belts and other types of traffic safety countermeasures. Driver attitudes, characteristics, and records were compared between observed safety belt user and nonuser groups to validate variables predicting use or nonuse. Respondents' descriptions of the social and personal context of their choice to use or not use safety belts provide a broader view of seat belt wearing that suggests implications for planning future enforcement and education programs. PMID:2331287

Fockler, S K; Cooper, P J

1990-04-01

178

Seat Belts on School Buses: Some Considerations.  

ERIC Educational Resources Information Center

A representative of the National Highway Traffic Safety Administration weighs advantages and discusses issues associated with installing seat belts in school buses. Federal regulations and research findings are considered. A list of guideline questions for school districts planning to install seat belts is included. (PP)

Soule, David

1982-01-01

179

A shell model for tyre belt vibrations  

Microsoft Academic Search

We present a new formulation for the prediction of tyre belt vibrations in the frequency range 0–500Hz. Our representation includes the effects of belt width, curvature and anisotropy, and also explicitly models the tyre sidewalls. Many of the associated numerical parameters are fixed by physical considerations; the remainder require empirical input. A systematic and general approach to this problem is

C. Lecomte; W. R. Graham; M. Dale

2010-01-01

180

Investigation of a Moving Belt Radiator.  

National Technical Information Service (NTIS)

Effort is presented on the continuing research program of the moving belt radiator, a novel concept for the rejection of waste heat in space. The primary concern remaining in this program is the in-flight dynamic simulation of the belt radiator. The track...

1966-01-01

181

DESIGN AND OPERATION OF BELT FILTER PRESSES  

EPA Science Inventory

Because early models of belt filter presses (developed from technology associated with the manufacture of paper) performed poorly, improved design and operation procedures for these presses were studied. Belt filter presses form part of a sludge dewatering system, and in terms of...

182

Inner Radiation Belt Dynamics and Climatology  

NASA Astrophysics Data System (ADS)

We present preliminary results of inner belt proton data assimilation using an augmented version of the Selesnick et al. Inner Zone Model (SIZM). By varying modeled physics parameters and solar particle injection parameters to generate many ensembles of the inner belt, then optimizing the ensemble weights according to inner belt observations from SAMPEX/PET at LEO and HEO/DOS at high altitude, we obtain the best-fit state of the inner belt. We need to fully sample the range of solar proton injection sources among the ensemble members to ensure reasonable agreement between the model ensembles and observations. Once this is accomplished, we find the method is fairly robust. We will demonstrate the data assimilation by presenting an extended interval of solar proton injections and losses, illustrating how these short-term dynamics dominate long-term inner belt climatology.

Guild, T. B.; O'Brien, P. P.; Looper, M. D.

2012-12-01

183

Kuiper Belt Albedoes and Densities  

NASA Astrophysics Data System (ADS)

Spitzer measurements of the thermal emission of Kuiper Belt Objects (KBOs) have shown that a number of them have surprisingly high albedos, and that in general the range of albedoes is very large, from a few percent to nearly 100%!. These results are important to combine with spectra of the reflected light and help determine the surface properties. Models for the collisional and chemical evolution, and the dust production in the Kuiper Belt, depend on this information. For two binary KBOs, the measurements also indicate shockingly low densities, of order 1 g/cm3. These densities push to the limit interior models for these objects, since the KBOs are too large for 'porosity' to account for the low densities: at least in their core regions, gravity should have crushed the material into a solid mass. Thus, the proportion of high density material in them must be kept relatively small to be compatible with the data. The two results indicate the potential for Spitzer thermal measurements to have a major impact on our understanding of the Kuiper Belt. We propose to consolidate these surprising findings by improving the signal to noise on three KBOs previously measured in the MIPS GTO program, but where the current data are insufficient to determine the properties of the objects well. Two of the targets (1997 CS 29 and Typhon) are binaries, and hence can test whether the small densities are fairly typical. Expanding the sample with well-determined densities from two to four can have a lot of leverage on assuring us that the low densities are not for peculiar, exceptional objects. The other one (1996 TL 66) is a case where a high-confidence albedo can be obtained with a modest additional investment of time. It is one of a small number of 'inner classical' KBOs that can be observed well with Spitzer. There are indications of systematic trends in albedo with orbital radius for KBOs and Centaurs, and increasing the size of samples in under-represented classes is important to test this result.

Rieke, George; Stansberry, John

2007-05-01

184

Origin of the asteroid belt  

NASA Technical Reports Server (NTRS)

Earlier and current concepts relevant to the origin of the asteroid belt are discussed and are considered in the framework of the solar system origin. Numerical and analytical solutions of the dynamical theory of planetesimal accumulation are characterized by bifurcations into runaway and nonrunaway solutions, and it is emphasized that the differences in time scales resulting from runaway and nonrunaway growth can be more important than conventional time scale differences determined by heliocentric distances. It is concluded that, in principle, it is possible to combine new calculations with previous work to formulate a theory of the asteroidal accumulation consistent with the meteoritic record and with work on the formation of terrestrial planets. Problems remaining to be addressed before a mature theory can be formulated are discussed.

Wetherill, George W.

1989-01-01

185

Nomenclature in the Kuiper Belt  

NASA Astrophysics Data System (ADS)

The Kuiper Belt has a rich dynamical structure. Discussion of this structure and the orbital properties of individual objects (versus others) requires subdivision the orbital parameter space into dynamical classes. The derivation for the terminology now used in the outer Solar System (cf. chapter on nomenclature in the Solar System Beyond Neptune book, Univ. of Arizona Press) is given. This nomenclature is a mix of clear dynamical divisions (for example, resonant versus non-resonant objects) and arbitrary cuts in parameter space in both the stable and unstable regimes. However, all of the divisions are precise so that measurable orbital parameters uniquely determine the dynamical class of the object. The utility of the system from the theoretical and observational perspective will be discussed.

Gladman, Brett

2008-09-01

186

Changes in Death and Injury Associated with Safety Belt Laws, 1985-1987.  

National Technical Information Service (NTIS)

Contents: Safety belt use laws; Safety belt usage trends; Details of belt usage in North Carolina; Change in fatalities associated with safety belt laws; Change in injuries associated with safety belt laws.

B. J. Campbell J. R. Stewart F. A. Campbell

1988-01-01

187

Collisions in the Kuiper belt  

NASA Astrophysics Data System (ADS)

For most of the 15 year history of observations of Kuiper belt objects, it has been speculated that impacts must have played a major role in shaping the physical and chemical characteristics of these objects, yet little direct evidence of the effects of such impacts has been seen. The past 18 months, however, have seen an explosion of major new discoveries giving some of the first insights into the influence of this critical process. From a diversity of observations we have been led to the hypotheses that: 1 satellite-forming impacts must have been common in the Kuiper belt; 2 such impacts led to significant chemical modification; and 3 the outcomes of these impacts are sufficiently predictable that we can now find and study these impact-derived systems by the chemical and physical attributes of both the satellites and the primaries. If our picture is correct, we now have in hand for the first time a set of incredibly powerful tools to study the frequency and outcome of collisions in the outer solar system. Here we propose three linked projects that would answer questions critical to the multiple prongs of our hypothesis. In these projects we will study the chemical effects of collisions through spectrophotometric observations of collisionally formed satellites and through the search for additional satellites around primaries with potential impact signatures, and we will study the physical effects of impacts through the examination of tidal evolution in proposed impact systems. The intensive HST program that we propose here will allow us to fully test our new hypotheses and will provide the ability to obtain the first extensive insights into outer solar system impact processes.;

Brown, Michael

2007-07-01

188

Collisional evolution of the early asteroid belt  

NASA Astrophysics Data System (ADS)

We present numerical results obtained by a simulation of the collisional process between asteroids and scattered comets from the Uranus-Neptune zone. This mechanism allows the use of single exponent incremental size distributions for the initial belt reaching a final distribution that matches the observed population very well. Since the cometary bombardment was extremely efficient removing mass from the primordial asteroid belt in a very short time, we always obtained belts with total masses less than 0.001 M ? after ? 2×10 7 yrs. This result allows processes with an important initial mass preserving Vestas basaltic crust.

Gil-Hutton, Ricardo; Brunini, Adrián

1999-04-01

189

Electric filter with movable belt electrode  

DOEpatents

A method and apparatus for removing airborne contaminants entrained in a gas or airstream includes an electric filter characterized by a movable endless belt electrode, a grounded electrode, and a filter medium sandwiched therebetween. Inclusion of the movable, endless belt electrode provides the driving force for advancing the filter medium through the filter, and reduces frictional drag on the filter medium, thereby permitting a wide choice of filter medium materials. Additionally, the belt electrode includes a plurality of pleats in order to provide maximum surface area on which to collect airborne contaminants.

Bergman, Werner (Pleasanton, CA)

1983-01-01

190

A morphologic study of Venus Ridge belts  

NASA Technical Reports Server (NTRS)

Ridge belts, first identified in the Venera 15/16 images are distinguished as linear regions of concentrated, parallel to anastomosing, ridges. They are tens to several hundreds of km wide, hundreds to over one thousand km long, and composed of individual ridges 5 to 20 km wide and up to 200 km long. The ridges appear symmetrical in the radar images and are either directly adjacent to each other or separated by mottled plains. Cross-strike lineaments, visible as dark or bright lines, are common within the ridge belts, and some truncate individual ridges. In places the ridge belt may be offset by these lineaments, but such offset is rarely consistent across the ridge belt. Once the mode of formation of these ridge belts is understood, their distribution and orientation will help to constrain the homogeneity and orientation of the stresses over the period of ridge belt formation. The look direction for the Venera system was to the west, so ridges appear as pairs of bright and dark lineaments, with the bright line to the east of the dark. The term ridge was used in a general sense to refer to a linear rise. The use of this term is restricted to rises which have a sharp transition from bright to dark at the crest, and are 5 to 15 km wide. These ridges are either continuous or discontinuous. The continuous ridges are over 30 km long and form coherent ridge belts, while the discontinuous ridges are less than 30 km long and do not form a coherent ridge belt. The continuous ridges were divided into 3 components: (1) Anastomosing ridges, in which the individual ridges are sinuous and often meet and cross at small angles, are the most common component; (2) The parallel ridge component also consists of well defined ridges, often with plains separating the individual ridges, but the ridges are more linear and rarely intersect one another; and (3) Parallel ridged plains are composed of indistinct ridges, some of which do not have a distinctive bright-dark pattern. The nature of deformation within the ridge belts is complex and not fully understood at present. Some belts show distinct signs of compression, while others have symmetrical patterns expected in extensional environments. Thus the ridge belts may have formed by more than one style of deformation; some may be extensional, while others are compressional. All the ridge belts are being systematically mapped, especially for symmetrical relationships.

Frank, S. L.; Head, James W.

1989-01-01

191

Escherynes: Novel carbon allotropes with belt shapes  

NASA Astrophysics Data System (ADS)

A new family of belt-shaped carbon structures, called Escherynes, is theoretically proposed using the octadehydro annulene (ODA) skeleton as a building block. Several ODA rings are fused together and cyclized to form belt-structures. Two isomeric forms of the Escherynes are considered, Hückel and Möbius. We demonstrate that these compounds have thermodynamical and kinetic stabilities comparable to fullerenes. Density functional calculations of the structures revealed: (i) that Escherynes are relatively stable molecules, (ii) they have high affinity for lithium, (iii) large Möbius Escherynes (>60 atoms) are as stable as Hückel belts, and (iv) Möbius Escherynes display remarkable optical activity.

Estrada, Ernesto; Simón-Manso, Yamil

2012-10-01

192

Electric filter with movable belt electrode  

DOEpatents

A method and apparatus for removing airborne contaminants entrained in a gas or airstream includes an electric filter characterized by a movable endless belt electrode, a grounded electrode, and a filter medium sandwiched there between. Inclusion of the movable, endless belt electrode provides the driving force for advancing the filter medium through the filter, and reduces frictional drag on the filter medium, thereby permitting a wide choice of filter medium materials. Additionally, the belt electrode includes a plurality of pleats in order to provide maximum surface area on which to collect airborne contaminants. 4 figs.

Bergman, W.

1983-09-20

193

Petrology and geochemistry of granites from the Archæan terrain north of Lake Victoria, western Kenya  

Microsoft Academic Search

The Neoarchæan greenstone belt of western Kenya forms part of the Tanzania Craton of East Africa. Two groups of supracrustal rock sequences are recognised in this greenstone belt, namely a dominantly volcanic supergroup (the Nyanzian) and a dominantly sedimentary one (the Kavirondian); this is typical of many other Neoarchæan greenstone belts. The Nyanzian volcanics include mafic lavas (rarely ultramafic) which

Norbert Opiyo-Akech; John Tarney; M. Hoshino

1999-01-01

194

Controls on thrust belt curvature, Wyoming-Idaho thrust belt  

SciTech Connect

Structural curvature in the northern part of the Wyoming-Idaho thrust belt (WITB) may be the result of either along-strike variations in pre-thrust stratigraphy or a buttress which physically concentrated shortening, or possibly both. Most thrust sheets of the WITB strike northward and were translated eastward, but in the Snake River Range (SRR) (the northernmost range in the WITB), structural strike curves from northward to nearly westward. Structural cross sections of the SRR are generally drawn in a radial pattern creating a volumetric imbalance in regional palinspastic restorations. Stratigraphic separation diagrams of major, through-going thrust faults in the SRR show extensive cut off in upper Paleozoic strata. New measured sections of upper Paleozoic stratigraphy at locations in several major thrust sheets of the WITB and in the foreland, new structural cross sections and mapping, and existing paleomagnetic data are used in a new interpretation of the origin of structural curvature in the WITB. Published paleomagnetic data require counterclockwise rotation of frontal thrust sheets along the northern boundary of the WITB, but no rotation of eastward-translated thrust sheets farther south along most of the WITB. Evidence for both a pre-existing west-trending depositional margin and rotation of frontal thrust sheets suggests that buttressing and modification of structural strike occurred along an oblique ramp where differences in stratigraphic thickness and possible pre-existing fault partitioning of the Paleozoic strata are localized.

Montgomery, J.M. Jr. (Univ. of Kentucky, Lexington, KY (United States). Dept. of Geological Sciences)

1993-04-01

195

Increasing Automobile Seat Belt Use: An Intervention Emphasizing Risk Susceptibility  

Microsoft Academic Search

A seat belt promotion program was based on the previous finding (Weinstein, 1984) that many people fail to take their seat belt use into account when thinking about their risk of being injured in an automobile accident. The goal of the program was to increase belt use by making the link between belt use and personal risk more salient. The

Neil D. Weinstein; Paul Dallas Grubb; James S. Vautier

1986-01-01

196

Web belt load measuring instrument has excellent stability  

NASA Technical Reports Server (NTRS)

Web belt system measures belt or strap load. It is partially disassembled and installed on an existing belt without cutting or re-threading the belt. A strain gage, installed on one of the support beams, eliminates errors due to uneven loading.

Walker, R. R.

1967-01-01

197

30 CFR 57.14203 - Application of belt dressing.  

Code of Federal Regulations, 2010 CFR

...2010-07-01 2010-07-01 false Application of belt dressing. 57.14203 Section 57.14203 Mineral Resources...Procedures § 57.14203 Application of belt dressing. Belt dressings shall not be applied manually while belts...

2010-07-01

198

30 CFR 56.14203 - Application of belt dressing.  

Code of Federal Regulations, 2010 CFR

...2009-07-01 2009-07-01 false Application of belt dressing. 56.14203 Section 56.14203 Mineral Resources...Procedures § 56.14203 Application of belt dressing. Belt dressings shall not be applied manually while belts...

2009-07-01

199

Sm-Nd age and isotopic systematics of the bimodal suite, ancient gneiss complex, Swaziland  

USGS Publications Warehouse

Studies of the development and stabilization of the Archaean crust often focus on the relative temporal relationships between the metamorphosed basaltic to ultramafic volcanic units (greenstone belts) and the sialic gneiss terrains that make up the oldest sections of the terrestrial crust. At the heart of this interest are the questions of the processes responsible for crust formation in the Archaean and whether or not the various units of an Archaean crustal section represent new additions to the crust from the mantle or are products of the reprocessing of even older crustal materials. One area where this controversy has been particularly pronounced is the Archaean crustal section of south-west Africa1-6. The oldest rocks in the Kaapvaal craton consist of the Onverwacht Group of mafic to ultramafic metavolcanics of the Barberton greenstone belt and a grey-gneiss complex termed the ancient gneiss complex (AGC) of Swaziland. We report here the results of a whole-rock Sm-Nd isotopic study of the AGC and the implications these data may have for crustal evolution in the Kaapvaal craton. ?? 1983 Nature Publishing Group.

Carlson, R. W.; Hunter, D. R.; Barker, F.

1983-01-01

200

Albedos in the Kuiper belt  

NASA Astrophysics Data System (ADS)

I have focused my research on the visual geometric albedos of transneptunian objects (TNOs), how the albedo varies with dynamical class, and whether or not it is correlated to orbital parameters. TNOs are among the least-processed objects in the solar system. By studying them, we can learn about the conditions in the solar system: the density of matter in the protoplanetary disk, the composition of different primordial regions, planetary migration, stirring of the disk, stellar close encounters, collision histories, binary capture, and space weathering. What we learn about how our solar system evolved also can be applied to debris disks surrounding other stars. Using infrared images from the Multiband Imaging Photometer for Spitzer (MIPS) on the Spitzer Space Telescope ( SST ), I measured the thermal flux in two different wavelength bands for sixteen transneptunian objects with point-spread function (PSF) fitting photometry. I converted the measurements to monochromatic flux densities at 23.68 mm and 71.42 mm. Next, I fit the Standard Thermal Model (STM), employing a linear function for the phase integral and Monte Carlo simulations, to the flux measurements and the absolute visual magnitude for each object in order to constrain its albedo and radius. Fitting a thermal model to infrared thermal radiation measurements resolves the ambiguity found with visual reflected radiation between a small object with a high albedo and a large object with a low albedo as they would have different temperatures. Once accurate albedos and radii are determined, they can be applied to size and mass distributions of the Kuiper belt. The sample was constructed from new targets and those previously published in the work of Stansberry et al. (2008), Grundy et al. (2005), and Grundy et al. (2009). A correlation was found between albedo and inclination for Classical Kuiper belt objects (KBOs) not including inner Classicals. The dynamically cold Classicals have higher albedos than hot Classicals. The albedos of the two populations are drawn from different parent distributions if one assumes an inclination break between them of 2.4° to 8.8°. It has already been shown that cold Classicals and hot Classicals differ in color, magnitude, and binary fraction. The high albedos of cold Classicals extend support for orbital dynamic theories that involve different formation regions, methods of transport, or surface alterations for the hot and cold Classical KBO populations. In addition, the high albedos found for cold Classical KBOs reduce the estimate for the total mass in this region by almost an order of magnitude.

Brucker, Melissa J.

201

Safety Belt Laws and Disparities in Safety Belt Use Among US High-School Drivers  

PubMed Central

Objectives. We compared reported safety belt use, for both drivers and passengers, among teenagers with learner’s permits, provisional licenses, and unrestricted licenses in states with primary or secondary enforcement of safety belt laws. Methods. Our data source was the 2006 National Young Driver Survey, which included a national representative sample of 3126 high-school drivers. We used multivariate, log-linear regression analyses to assess associations between safety belt laws and belt use. Results. Teenaged drivers were 12% less likely to wear a safety belt as drivers and 15% less likely to wear one as passengers in states with a secondary safety belt law than in states with a primary law. The apparent reduction in belt use among teenagers as they progressed from learner to unrestricted license holder occurred in only secondary enforcement states. Groups reporting particularly low use included African American drivers, rural residents, academically challenged students, and those driving pickup trucks. Conclusions. The results provided further evidence for enactment of primary enforcement provisions in safety belt laws because primary laws are associated with higher safety belt use rates and lower crash-related injuries and mortality.

Winston, Flaura K.; Durbin, Dennis R.

2012-01-01

202

A repair of a charging belt  

SciTech Connect

Accelerator charging belts are expensive, and sometimes delicate items. A means of repair of the rubber coating has been found that, when applied properly, should give extended lifetime to these items at minimal cost. 3 refs.

Jones, N.L.

1989-01-01

203

Emission products from combustion of conveyor belts  

SciTech Connect

A series of experiments were undertaken by the Bureau of Mines to determine the emission products of several types of conveyor belting and other combustible materials found in mines. These experiments were conducted under intermediate scale, stimulated mine conditions to determine smoke characteristics and gas concentrations. From these determinations, heat-release rates, particle sizes, obscuration rates, combustion yields, and production constants were calculated. Three types of belts were investigated: chloroprene, also known as neoprene (NP); polyvinyl chloride (PVC); and styrene-butadiene rubber (SBR). The belts were designated as ignitable or self-extinguishing depending on the length of the burning time and the subsequent combustion products. These conveyor belt combustion results are compared with previous analyses of wood, transformer fluid, and coal fires. Together they form a data base by which findings from future experiments with other mine combustibles can be compared.

Egan, M.R.

1988-01-01

204

Electron Flux of Radiation Belts Animation  

NASA Video Gallery

This animation shows meridional (from north-south) plane projections of the REPT-A and REPT-B electron flux values. The animation first shows the expected two-belt Van Allen zone structure; from Se...

205

Radiation Belt Storm Probe (RBSP) Mission  

NASA Technical Reports Server (NTRS)

Scheduled to launch in May 2012, NASA's dual spacecraft Living With a Star Radiation Belt Storm Probe mission carries the field and particle instrumentation needed to determine the processes that produce enhancements in radiation belt ion and electron fluxes, the dominant mechanisms that cause the loss of relativistic electrons, and the manner by which the ring current and other geomagnetic phenomena affect radiation belt behavior. The two spacecraft will operate in low-inclination elliptical lapping orbits around the Earth, within and immediately exterior to the Van Allen radiation belts. During course of their two year primary mission, they will cover the full range of local times, measuring both AC and DC electric and magnetic fields to 10kHz, as well as ions from 50 eV to 1 GeV and electrons with energies ranging from 50 eV to 10 MeV.

Sibeck, D. G.; Fox, N.; Grebowsky, J. M.; Mauk, B. H.

2009-01-01

206

Planetary science: Archaeology of the asteroid belt  

NASA Astrophysics Data System (ADS)

The size of asteroids in the Solar System's main asteroid belt may help constrain one of the least-understood aspects of planet formation - the transition from pebble-sized dust balls to mountain-sized planetesimals.

Chambers, John

2009-08-01

207

Radiation Belt and Plasma Model Requirements  

NASA Technical Reports Server (NTRS)

Contents include the following: Radiation belt and plasma model environment. Environment hazards for systems and humans. Need for new models. How models are used. Model requirements. How can space weather community help?

Barth, Janet L.

2005-01-01

208

Congressional panel makes recommendations on belt safety  

SciTech Connect

The Mine Improvement and New Emergency Response Act of 2006 (MINER Act) called for a Technical Study Panel to present a review and make recommendations on the use of belt air and the composition and fire retardant properties of belt materials in underground coal mining. In October 2007 the Panel released 20 recommendations publicly. These are presented in the article. Many recommendations encouraged the MSHA to enforce existing laws of maintenance and fire protection or example more vigorously. Maybe the biggest change recommended was that the industry should adopt the Belt Evaluation Laboratory Test (BELT) standard proposed in 1992. Another important recommendation was one that would help eliminate hazards associated with point feeding. 1 photo.

Fiscor, S.

2007-12-15

209

Visualization of Radiation Belts from REPT Data  

NASA Video Gallery

This visualization, created using actual data from the Relativistic Electron-Proton Telescopes (REPT) on NASAâ??s Van Allen Probes, clearly shows the emergence of new third belt and second slot reg...

210

Requiring Belt Use as Part of a School Parking Permit Program: Does It Increase Students' Belt Use?  

Microsoft Academic Search

Objective: Teenagers have very high motor vehicle crash rates, and their use of seat belts is generally lower than that of adults. A potential school-based strategy to increase teenagers' belt use is a policy making parking privileges contingent on belt use by student drivers and their passengers. This study evaluated the effects of implementing a school belt policy.Methods: The effects

Anne T. McCartt; Lori L. Geary; Mark G. Solomon

2005-01-01

211

Earth's radiation belts. Environmental research papers  

SciTech Connect

This report develops radiation belt transport theory from physical principles and compares the results with experimental data. It also provides an easy reference to the present empirical radiation flux models with some simple application techniques given. Specialized topics include shell-splitting, effects of wave-particle interactions, the ring current, geosynchronous environment, nuclear detonations and radiation effects. Heavy ions are specifically highlighted as a significant component of the radiation belts.

Spjeldvik, W.N.; Rothwell, P.L.

1983-09-20

212

Data assimilation of radiation belt electrons  

Microsoft Academic Search

We present results from a data-assimilation of radiation belt electrons and investigate the effect of the radial diffusion and the amplitude of the plasmashpheric hiss. In the data-assimilation, we use our 1-D radial diffusion model [Miyoshi et al., 2003, JGR] which includes various physical processes of the radiation belts such as radial diffusion, Coulomb collisions, and wave-particle interactions. We assimilate

Y. Miyoshi; G. Ueno; V. Jordanova; G. Reeves; T. Goka

2006-01-01

213

Electrical resistivity survey for groundwater investigations and shallow subsurface evaluation of the basaltic-greenstone formation of the urban Bulawayo aquifer  

NASA Astrophysics Data System (ADS)

Electrical resistivity surveying methods have been widely used to determine the thickness and resistivity of layered media for the purpose of assessing groundwater potential and siting boreholes in fractured unconfined aquifers. Traditionally, this has been done using one-dimensional (1D) vertical electrical sounding (VES) surveys. However, 1D VES surveys only model layered structures of the subsurface and do not provide comprehensive information for interpreting the structure and extent of subsurface hydro-geological features. As such the incorporation of two-dimensional (2D) geophysical techniques for groundwater prospecting has often been used to provide a more detailed interpretation of the subsurface hydro-geological features from which potential sites for successful borehole location are identified. In this study, 2D electrical resistivity tomography was combined with 1D VES to produce a subsurface resistivity model for assessing the availability of groundwater in the basaltic-greenstone formation of the Matsheumhlope well field in Bulawayo, Zimbabwe. Low resistivity readings (<50 ?m) towards the central region of the study area suggest a high groundwater potential, while high resistivities (>500 ?m) around the western margin of the study area suggests a low groundwater potential. 2D electrical resistivity surveys provide a more detailed subsurface structure and may assist in identifying the configuration of possible fractures which could conduct groundwater into the shallow subsurface of study area. It is concluded that 2D electrical resistivity methods is an effective tool for assessing the availability of groundwater in the highly weathered and fractured basaltic greenstone rocks. The methods provided a more precise hydro-geophysical model for the study area compared to the traditional VES. Results from this study are useful for technical groundwater management as they clearly identified suitable borehole locations for long term groundwater prospecting.

Muchingami, Innocent; Hlatywayo, D. J.; Nel, J. M.; Chuma, C.

214

Geochemical and isotopic constraints on the genesis of the Permian ferropicritic rocks from the Mino Tamba belt, SW Japan  

NASA Astrophysics Data System (ADS)

The Permian ferropicrite and picritic ferrobasalt occur in the Jurassic accretionary complexes of the Mino-Tamba belt as dikes intruded into the basaltic volcanic rocks. They are characterized by high MgO (11-27 wt.%), FeO* (16-20 wt.%) and HFSE (Nb = 24-86 ppm and Zr = 103-399 ppm) contents. Mineralogical and petrolographical evidences indicate that their unusual iron-rich nature is apparently magmatic in origin. The incompatible element contents and ratios indicate that the picritic ferrobasalt has close genetic kinship with the previously reported HFSE-rich, but iron-poor picrites, and that they were produced by the low degrees of partial melting of HFSE-enriched source material at high pressures (4-5 GPa). On the other hand, the ferropicrite may have been produced by the same degree of partial melting at a lower pressure, and subsequent olivine accumulation. The Sr and Nd isotopic signatures ( 87Sr/ 86Sr (i) = 0.70266 to 0.70329 and ?Nd (i) = + 5.7 to + 7.7) of these picritic and ferropicritic rocks are nearly constant and are equivalent to those of HIMU rocks, which require involvement of subducted oceanic crust material into their source region. Nevertheless, the ferropicritic melt cannot have been generated from the iron-poor picrite melt by crystal fractionation. Compared to the compositions of the melts obtained by some melting experiments, production of the unusual ferropicritic melts requires addition of an unreasonable amount of recycled basaltic component into the source mantle peridotite or partial melting at extremely high pressures. A possible source material for the ferropicrite is the mixture of the recycled Fe- and Ti-rich basalt (and/or gabbro) and mantle peridotite. Such a ferrobasalt occurs in the present ocean floor and also in some peridotite massifs as Fe- and Ti-rich eclogite bodies. The ferropicritic magma may have been derived from the Permian, deep mantle plume in an oceanic setting. The occurrence of the ferropicritic rocks and the HFSE-rich, iron-poor picrite in the Mino-Tamba belt implies that the greenstone-limestone-chert complexes in the Mino-Tamba belt may be fragments of an oceanic plateau formed by the Permian superplume activities in paleo-Pacific ocean and subsequently accreted to a continental margin through subduction process in the Jurassic time.

Ichiyama, Yuji; Ishiwatari, Akira; Hirahara, Yuka; Shuto, Kenji

2006-06-01

215

Federal Motor Vehicle Safety Standard No. 209 (Seat Belt Assemblies). Daal Seat Belts.  

National Technical Information Service (NTIS)

The report contains the test data, results and conclusions of tests performed on one set of twelve (12) Type 1 seat belt assemblies for compliance to Federal Motor Vehicle Safety Standard No. 209. This set of seat belts without retractors was subjected to...

1970-01-01

216

Thoracic response and injury with belt, driver side airbag, and force limited belt restraint systems  

Microsoft Academic Search

The performance of belt, airbag, and force limited belt restraint systems for the driver were compared using frontal sled tests. Nine human cadaver and six dummy sled tests were conducted at 56 km\\/h using a test buck representing a mid-size vehicle. Subject instrumentation included upper and lower chestbands to measure local thoracic deformations and sternal and spinal accelerometers to record

J. R. Crandall; C. R. Bass; W. D. Pikey; H. J. Miller; J. Sikorski; M. Wilkins

1996-01-01

217

Asteroid Belt Constraints on Giant Planets Evolution  

NASA Astrophysics Data System (ADS)

We investigate the dynamical evolution of the asteroid belt during the planetesimal-driven migration of the giant planets. We assume that giant planet migration happened after the primordial depletion/excitation of the asteroid belt, which occurred during terrestrial planet formation. This is a requirement of models that link giant planet migration to the origin of the Late Heavy Bombardment. During the migration of Jupiter and Saturn the secular resonances nu6 and nu16 sweep through the asteroid belt. These secular resonances cause large-amplitude responses in the eccentricities and inclinations of the asteroids if the amplitude of the g6 and s6 modes in Jupiter are similar to the current ones. The final structure of the asteroid belt depends sensitively on the migration speed of Jupiter and Saturn. Our numerical simulations show the current orbital distribution of the asteroid belt can be reproduced if the e-folding time for the migration is shorter than 1 Myr. This is much shorter than traditional results on planetesimal-driven migration; even in the Nice model, which has the fastest possible migration because the entire planetesimal disc is destabilised at once, the shortest measured time is approximately 5 Myr. As a remedy to this problem we propose a 'jumping Jupiter' scenario, which is a subset of the admissible solutions of the Nice model, in which encounters between an ice giant and Jupiter, without ejection of the former, cause the latter to migrate away from Saturn much faster than caused solely by encounters with planetesimals. The jumping Jupiter scenario leads to the secular resonances quickly sweeping through most of the asteroid belt, thereby only depleting the inner belt.

Morbidelli, Alessandro; Brasser, R.; Tsiganis, K.; Gomes, R.; Levison, H.

2009-09-01

218

IDENTIFYING COLLISIONAL FAMILIES IN THE KUIPER BELT  

SciTech Connect

The identification and characterization of numerous collisional families-clusters of bodies with a common collisional origin-in the asteroid belt has added greatly to the understanding of asteroid belt formation and evolution. More recent study has also led to an appreciation of physical processes that had previously been neglected (e.g., the Yarkovsky effect). Collisions have certainly played an important role in the evolution of the Kuiper Belt as well, though only one collisional family has been identified in that region to date, around the dwarf planet Haumea. In this paper, we combine insights into collisional families from numerical simulations with the current observational constraints on the dynamical structure of the Kuiper Belt to investigate the ideal sizes and locations for identifying collisional families. We find that larger progenitors (r {approx} 500 km) result in more easily identifiable families, given the difficulty in identifying fragments of smaller progenitors in magnitude-limited surveys, despite their larger spread and less frequent occurrence. However, even these families do not stand out well from the background. Identifying families as statistical overdensities is much easier than characterizing families by distinguishing individual members from interlopers. Such identification seems promising, provided the background population is well known. In either case, families will also be much easier to study where the background population is small, i.e., at high inclinations. Overall, our results indicate that entirely different techniques for identifying families will be needed for the Kuiper Belt, and we provide some suggestions.

Marcus, Robert A.; Ragozzine, Darin; Murray-Clay, Ruth A.; Holman, Matthew J., E-mail: rmarcus@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)

2011-05-20

219

How long solar proton radiation belts exists?  

NASA Astrophysics Data System (ADS)

Solar protons of 1-5 MeV range were trapped during recovery phases of the strong magnetic storms on October 2003, July and November 2004 and after additional acceleration remain in the proton radiation belts for a long time. Using measurements of the low-altitude polar satel-lites CORONAS-F, SERVIS-1 and TATJANA-UNIVERSITETSKY we found, that enhanced proton flux of the 15 MeV energy remains about half a year at L=3-5, and about one year protons with 1 MeV energy. Additional 1 MeV proton belt at L=1.8-2.2 existed continuously from October 2003 at least to December 2006. Extrapolation of the measurements to the pre-vious 11-year cycles shows that solar proton contribution to the proton radiation belt of 1-5 MeV energy range may be important for the half of the solar cycle time.

Lazutin, Leonid; Logachev, Yurii; Muravjeva, E.

220

A Contact Binary in the Kuiper Belt?  

NASA Astrophysics Data System (ADS)

2001 QG298 is the first known Kuiper Belt object and only the third minor planet with a radius > 25 km to display a lightcurve with a range in excess of 1 magnitude. The large light variation, relatively long double-peaked period and absence of rotational color change argue against explanations due to albedo markings or elongation due to high angular momentum. Instead, we suggest that 2001 QG298 may be a very close or contact binary similar in structure to what has been independently proposed for the Trojan asteroid 624 Hektor. By correcting for the effects of projection, we estimate that the fraction of similar objects in the Kuiper Belt is at least ˜10% to 20% with the true fraction probably much higher. A high abundance of close and contact binaries is expected in some scenarios for the evolution of binary Kuiper Belt objects. These results are now published in the Astronomical Journal (Sheppard and Jewitt, 2004, AJ, 127, 3023).

Sheppard, S. S.; Jewitt, D.

2004-11-01

221

The double-belt outer radiation belt during CME- and CIR-driven geomagnetic storms  

NASA Astrophysics Data System (ADS)

We have identified eight events with double-belt structure in the outer radiation belt from 110 coronal mass ejection (CME) driven magnetic storms and 223 corotating interaction regions (CIR) driven storms during 1994 to 2003 based on the SAMPEX data sets. Among them, three cases are related to CME-driven magnetic storms and five cases are related CIR-driven storms. All double-belt structure events in the outer radiation belt are found during the recovery phase of a magnetic storm for both CME- and CIR-related events—they usually start to form within 3-4 days after the onset of the magnetic storm. The preconditions needed to form a double-belt structure, for all the CME-related events, are found to be high solar wind dynamic pressure (Pdy) and southward interplanetary magnetic field Bz; nevertheless, for the CIR-related events, they are found to be associated with high-speed stream with southward interplanetary magnetic field, which is enhanced by a suitably orientated By component.It is further found that the flux distributions of the double-belt structure can be fitted well with a simply exponential decay function of L?. Based on the radiation belt content index, the proportion of the total number of 1.5-6.0 MeV electrons inside the position of maximum fluxes to that outside the maximum fluxes keeps rising during the double-belt period, which implies that the acceleration mainly occurs at regions inside the location of maximum fluxes. We suggest that the plasmapause and the strong wave-particle interactions with VLF and ULF waves near it play an important role in the development of the double-belt structures.

Yuan, Chongjing; Zong, Qiugang

2013-10-01

222

A shell model for tyre belt vibrations  

NASA Astrophysics Data System (ADS)

We present a new formulation for the prediction of tyre belt vibrations in the frequency range 0-500 Hz. Our representation includes the effects of belt width, curvature and anisotropy, and also explicitly models the tyre sidewalls. Many of the associated numerical parameters are fixed by physical considerations; the remainder require empirical input. A systematic and general approach to this problem is developed, and illustrated for the specific example of a Goodyear Wrangler tyre. The resulting predictions for the radial response to radial forcing show good correspondence with experiment up to 300 Hz, and satisfactory agreement up to 1 kHz.

Lecomte, C.; Graham, W. R.; Dale, M.

2010-05-01

223

The Kerala Khondalite Belt (KKB) of Southern India: An ensialic mobile belt  

NASA Technical Reports Server (NTRS)

The Proterozoic Kerala Khondalite belt of the Southern Indian Shield is described, a belt dominated by granulite grade (750 C, 5 to 6 kbar) supracrustal rocks whose protoliths included arkoses and shales with cratonic provenances. Rare earth elements and other geochemical signatures suggest a granitic source for these metasediments, possibly the spatially associated charnockite massifs. The presence of intercalated mafic gneisses, interpreted as basalts, implies a cratonic rift basin rather than a foreland basin setting. It was argued that the Kerala, as well as other early Proterozoic mobile belts formed during abortive continental rifting without major additions of new crust.

Chacko, Thomas; Meen, James K.; Kumar, G. R. Ravindra; Rogers, John J. W.

1988-01-01

224

Growth of early Archaean crust in the Ancient Gneiss Complex of Swaziland as revealed by single zircon dating  

NASA Astrophysics Data System (ADS)

We present new single grain zircon ages derived from ion microprobe and evaporation analysis for rocks of the Ancient Gneiss Complex (AGC) of Swaziland, southern Africa, that enable us to document a more extended history of early Archaean crustal growth in the eastern Kaapvaal craton than previously documented. The oldest rocks appear to be strongly flattened tonalitic-trondhjemitic orthogneisses dated as 3644 ± 4 Ma (Compston and Kröner, 1988) which are in faulted contact with rocks of the Barberton Greenstone Belt (BGB) in an AGC enclave in northwest Swaziland and which also record subsequent thermal-metamorphic-plutonic events at ? 3580, 3500, 3430, 3200 and 3000 Ma. These rocks are tectonically interbanded with ? 3200 Ma old granodiorites and K-rich leucogranites, thereby providing evidence for a severe and important post-3.2 Ga deformation event that is also inferred for ? 3500 to 3200 Ma old tonalitic to trondhjemitic gneisses in the AGC of northeast Swaziland. In central Swaziland zircons from the oldest tonalitic gneiss of the AGC have an age of 3560 Ma whereas younger additions of granitoid, which also intrude the Dwalile greenstone enclave in the AGC, record ages of ? 3450-3460 Ma. Intense ductile deformation has repeatedly obliterated original intrusive contacts so that preserved field relationships often cannot resolve the above chronology. Chemical and whole-rock isotopic data are consistent with derivation of some AGC gneisses from mantle sources and thus imply very short crustal residence times for their granitoid precursors, but this is not generally true for the entire AGC. We suggest that at least some gneisses resulted from intracrustal melting, perhaps during crustal thickening events as recorded in granulite parageneses within the AGC. Documentation of 3.5 Ga or older granitoid crust in all major regions of the AGC now exposed suggests the presence of continental terrains of up to at least 100 km in diameter before the Barberton greenstone succession was deposited. The combined geochronologic and structural/metamorphic data for the AGC and BGB reveal a complex history of growth and deformation for the eastern Kaapvaal craton that lasted for at least 600 Ma from 3.64 to about 3 Ga ago. The magmatic and tectonic evolution of the AGC was broadly similar to that of the BGB and suggests that early Archaean greenstone and gneiss terrains were coeval but formed and evolved in different settings and at different crustal levels. Our age data and the structural/metamorphic evolution of the eastern Kaapvaal craton are compatible with models suggesting crustal growth through vertical magmatic underplating and early crustal thickening, uplift and erosion as a result of tectonic interleaving due to repeated horizontal shortening.

Kröner, A.; Compston, W.; Williams, I. S.

1989-04-01

225

Seat Belts, Air Bags May Save Your Kidneys  

MedlinePLUS

... on this page, please enable JavaScript. Seat Belts, Air Bags May Save Your Kidneys Car safety devices reduce ... Vehicle Safety FRIDAY, May 16, 2014 (HealthDay News) -- Air bags and seat belts help protect the kidneys from ...

226

Radiation Belt Environment model: Application to space weather nowcasting  

Microsoft Academic Search

(1) A data-driven physical model of the energetic electrons in the Earth's radiation belts, called the Radiation Belt Environment (RBE) model, has been developed to understand Earth's radiation belt dynamics and to predict the radiation conditions found there. This model calculates radiation belt electron fluxes from 10 keV to 6 MeV in the inner magnetosphere. It takes into account the

Mei-Ching Fok; Richard B. Horne; Nigel P. Meredith; Sarah A. Glauert

2008-01-01

227

Radiation Belt Environment model: Application to space weather nowcasting  

Microsoft Academic Search

A data-driven physical model of the energetic electrons in the Earth's radiation belts, called the Radiation Belt Environment (RBE) model, has been developed to understand Earth's radiation belt dynamics and to predict the radiation conditions found there. This model calculates radiation belt electron fluxes from 10 keV to 6 MeV in the inner magnetosphere. It takes into account the realistic,

Mei-Ching Fok; Richard B. Horne; Nigel P. Meredith; Sarah A. Glauert

2008-01-01

228

Suppression of fire on underground coal mine conveyer belts  

Microsoft Academic Search

The program involves the evaluation of means for suppressing fires on underground coal mine conveyor belts. Full-scale conveyor belt fire tests were conducted to determine the requirements of automatically actuated water sprinkler, high expansion foam, and multipurpose dry powder extinguishing systems, and of various fire detection devices, necessary to adequately protect underground belt heads. The program included the development of

1974-01-01

229

Zero-relative-velocity belt skimmer. Final report  

Microsoft Academic Search

In the approach to high speed (4 to 10 knots) oil recovery discussed here, oil is collected from the water's surface due to a zero relative velocity (ZRV) between a moving belt and the oil layer. A loosely tensioned sorbent belt floats like a blanket on the water imbibing oil for a 40-foot contact length before the belt is withdrawn

R. R. Ayres; K. L. Bickham; J. P. Fraser; P. E. Titus

1975-01-01

230

Direct Observation of Safety Belt Use in Michigan, Fall 1994.  

National Technical Information Service (NTIS)

Results of a direct observation survey of safety belt use in Michigan for fall of 1994 are reported. Belt use was estimated separately for each vehicle type. Within each vehicle type, belt use by gender, age, road type, day of week, and time of day was es...

D. W. Eby F. M. Streff C. Christoff

1994-01-01

231

Do Seat Belt Laws Drive Up Insurance Premiums?  

Microsoft Academic Search

If you have to wear a seat belt when you drive, are you safer? Intuitively, it may seem that the answer is yes. After all, if you are wearing a seat belt and get in an accident, you are half as likely to die, and 62% of fatal accident victims were not wearing seat belts at the time of accident.

George Posner

2012-01-01

232

Charging belt noise in a Van de Graaff accelerator  

SciTech Connect

With the aid of a Fast Fourier Transformer (FFT) spectrum analyzer it has been possible to decompose Van de Graaff terminal voltage noise into components that can be related to various properties of the charging belt. One consequence has been the elimination of the fundamental belt frequency component by a novel belt charge transfer device. 18 figs.

Trainor, T.A.

1988-01-01

233

Abrasiveness properties assessment of coated abrasives for precision belt grinding  

Microsoft Academic Search

This paper addresses a study to achieve a method of assessment of coated abrasives for precision belt grinding based on the identification of the prevailing relationships between the changing features of fixed grains on flexible coated belts and grinding performance. A set of parameters was defined which describe the aluminium oxide resin-bonded belt characteristics including active grits density, cutting edge

S. Mezghani; M. El Mansori

2008-01-01

234

Mean motion resonances. [of asteroid belt structure  

NASA Technical Reports Server (NTRS)

Recent research on the resonant structure of the asteroid belt is reviewed. The resonant mechanism is discussed, and analytical models for the study of mean motion resonances are examined. Numerical averaging methods and mapping methods are considered. It is shown how fresh insight can be obtained by means of a new semianalytical approach.

Froeschle, CL.; Greenberg, R.

1989-01-01

235

Glauconite from the precambrian belt series, Montana  

USGS Publications Warehouse

Glauconite from the upper part of the Missoula Group of the Belt Series, Flathead County, Montana, has been dated at 1070 million years by potassium-argon and rubidium-strontium analyses. This is the first glauconite of Precambrian age reported in North America.

Gulbrandsen, R. A.; Goldich, S. S.; Thomas, H. H.

1963-01-01

236

Hidden Mass in the Asteroid Belt  

Microsoft Academic Search

The total mass of the asteroid belt is estimated from an analysis of the motions of the major planets by processing high precision measurements of ranging to the landers Viking-1, Viking-2, and Pathfinder (1976–1997). Modeling of the perturbing accelerations of the major planets accounts for individual contributions of 300 minor planets; the total contribution of all remaining small asteroids is

G. A. Krasinsky; E. V. Pitjeva; M. V. Vasilyev; E. I. Yagudina

2002-01-01

237

Glauconite from the Precambrian Belt Series, Montana.  

PubMed

Glauconite from the upper part of the Missoula Group of the Belt Series, Flathead County, Montana, has been dated at 1070 million years by potassium-argon and rubidium-strontium analyses. This is the first glauconite of Precambrian age reported in North America. PMID:17815800

Gulbrandsen, R A; Goldich, S S; Thomas, H H

1963-04-26

238

School Buses & Seat Belts: A Discussion.  

ERIC Educational Resources Information Center

Safety belts are not installed in school buses for several reasons. School buses are constructed differently from automobiles in terms of (1) the locations of doors and instrument panels relative to passengers, (2) outer construction, (3) seat design and padding, and (4) visibility on the road. Under current regulations, bus seats are constructed…

Alaska State Dept. of Education, Juneau.

239

Belts and Chains. FOS: Fundamentals of Service.  

ERIC Educational Resources Information Center

This manual on belts and chain drives is one of a series of power mechanics texts and visual aids on theory, of operation, diagnosis, and repair of automotive and off-the-road agricultural and construction equipment. Materials provide basic information and illustrations for use by vocational students and teachers as well as shop servicemen and…

John Deere Co., Moline, IL.

240

Radiation Belts Throughout the Solar System  

NASA Astrophysics Data System (ADS)

The several preceding decades of deep space missions have demonstrated that the generation of planetary radiation belts is a universal phenomenon. All strongly magnetized planets show well developed radiation regions, specifically Earth, Jupiter, Saturn, Uranus, and Neptune. The similarities occur despite the tremendous differences between the planets in size, levels of magnetization, external environments, and most importantly, in the fundamental processes that power them. Some planets like Jupiter are powered overwhelmingly by planetary rotation, much like astrophysical pulsars, whereas others, like Earth and probably Uranus, are powered externally by the interplanetary environment. Uranus is a particularly interesting case in that despite the peculiarities engendered by its ecliptic equatorial spin axis orientation, its magnetosphere shows dynamical behavior similar to that of Earth as well as radiation belt populations and associated wave emissions that are perhaps more intense than expected based on Earth-derived theories. Here I review the similarities and differences between the radiation regions of radiation belts throughout the solar system. I discuss the value of the comparative approach to radiation belt physics as one that allows critical factors to be evaluated in environments that are divorced from the special complex conditions that prevail in any one environment, such as those at Earth.

Mauk, B. H.

2008-12-01

241

Experiences with a Poly-C belt  

Microsoft Academic Search

A Poly-C belt installed in the Budapest 5 MV vertical Van de Graaff accelerator in January 1986 has been used for 3700 working hours. Its performance and the circumstances of its use are discussed and summarized in this report.

P. Kostka; E. Klopfer; G. Bürger; J. Roosz

1988-01-01

242

Research on an Active Seat Belt System  

NASA Astrophysics Data System (ADS)

In a car crash, permanent injury can be avoided if deformation of an occupant's rib cage is maintained within the allowable value. In order to realize this condition, the occupant's seat belt tension must be instantaneously adjusted by a feedback control system. In this study, a seat belt tension control system based on the active shock control system is proposed. The semi-active control law used is derived from the sliding mode control method. One advantage of this proposed system is that it does not require a large power actuator because the seat belt tension is controlled by a brake mechanism. The effectiveness is confirmed by numerical simulation using general parameters of a human thorax and a passenger car in a collision scenario with a wall at a velocity of 100 km/h. The feasibility is then confirmed with a control experiment using a scale model of about 1/10 scale. The relative displacement of the thorax model approaches the allowable value smoothly along the control reference and settles near this value. Thus, the proposed seat belt tension control system design is established.

Kawashima, Takeshi

243

Global resonance in the Jovian radiation belts  

SciTech Connect

The oscillation regimes of cyclotron stability in the Jovian radiation belts are analyzed. It is shown that the eigenfrequencies of oscillations in the outer magnetosphere of Jupiter are independent of the magnetic shell L and coincide with the angular rotational velocity. The theoretical results are used to explain Pioneer observations of 10-hour modulation in the energetic electron flux of Jupiter. 7 references.

Bespalov, P.A.

1985-02-01

244

Measurements of the Jovian radiation belts  

Microsoft Academic Search

The University of California at San Diego trapped radiation detector measured proton and electron fluxes, angular distributions, and energy spectra throughout the Pioneer 10 flyby of Jupiter last December. Here the instrumentation and calibrations are described, and good values for particle fluxes in the inner and outer regions are presented. The major features of the Jovian radiation belts are described,

R. W. Fillius; C. E. McIlwain

1974-01-01

245

Trapped radiation belts of Saturn - First look  

Microsoft Academic Search

Data on the magnetosphere of Saturn obtained with the trapped radiation detector package on board the Pioneer 11 spacecraft is reported. Radiation belt profiles determined by the trapped radiation detectors on Pioneer 10 and 11 indicate that Saturn's magnetosphere is intermediate in size between those of the earth and Jupiter, with particle intensities similar to those of the earth. The

W. Fillius; W. H. Ip; C. E. McIlwain

1980-01-01

246

Exploration for uranium deposits, Grants mineral belt  

Microsoft Academic Search

Uranium ore deposits in the Grants mineral belt, New Mexico, occur in fluvial sandstones in the Morrison Formation (Jurassic). Uranium mineralization is concentrated by a dark-gray to black substance that has been identified as humate, which is derived from decaying vegetation. Black ore is truncated by overlying sandstone in at least three ore deposits, documenting an early age for mineralization.

Fitch

1980-01-01

247

International survey of seat belt use exemptions  

PubMed Central

Background Substantial evidence of seatbelt efficacy has been shown by several studies, and it is widely recommended that motor vehicle occupants use properly fitted seat belts. However, some (but a heretofore unknown number of) countries with national seat belt laws permit various exemptions which may lower use rates. The aim of this study was to survey the variety of exemptions to national seat belt laws. Methods This investigation relied on identifying respondents from national traffic safety agencies, other governmental and non?governmental organizations, Internet searches, personal contacts, and other sources. Questionnaires were deployed through a web based survey supplemented by email and postal versions. Results Responses were received from 30 countries of which 28 (93.7%) had a national seat belt law. About two thirds (63.7%) of the 28 national laws applied to both front and back seat passengers. The leading exemption types included vehicles made before a certain year (n?=?13), antique vehicles (n?=?12), military vehicles (n?=?11), buses (n?=?9), and emergency vehicles (n?=?8). Most responding countries reported one or more specific categories of individuals as exempt including those with medical exemptions (n?=?20), taxi drivers (n?=?11), police (n?=?9), emergency medical personnel (n?=?8), physically disabled people (n?=?6), and pregnant women (n?=?6). Out of 26 responses to the question regarding current level of enforcement, 42.3% felt enforcement was “very good or good” and 57.7% characterized it as “fair or poor”. Conclusions This study represents one of the largest international traffic law surveys reported. Most national seatbelt laws offer perilous exemptions to a broad array of vehicle types and road user groups. These findings, coupled with concern over the level of enforcement in the majority of countries surveyed, suggest that international road safety efforts have a long way to go to improve coverage and enforcement of national seat belt laws.

Weiss, H; Sirin, H; Levine, J A; Sauber, E

2006-01-01

248

Neptune's Migration into a Hot Kuiper Belt  

NASA Astrophysics Data System (ADS)

The abundance of Kuiper Belt Objects (KBOs) at Neptune's 3:2 resonance has been interpreted as evidence of Neptune's outward migration. However recent reports of several KBOs inhabiting Neptune's more distant higher order resonances, namely, the 7:3 and 5:2 (which are located at 53 and 55 AU) represent something of a puzzle because previous simulations of Neptune's migration into a dynamically cold Kuiper Belt did not reveal any resonance capture at the 7:3 and 5:2. One possible explanation for these objects is given in Chiang et al (2003), who show that capture by the 5:2 is indeed possible when Neptune migrates into a previously stirred-up, or "hot" Kuiper Belt. We have investigated this scenario further by performing a suite of simulations of Neptune's migration into a hot Kuiper Belt. These simulations obtain endstates that resemble the observed Kuiper Belt if the KBO's have initial eccentricities and sin(i) of ˜0.1 prior to the onset of planet migration. In this case, the high capture probabilities of the familiar 2:1 and 3:2 resonances are reduced by only a factor of ˜2, while the more distant high-order resonances such as the 9:4, 7:3, 5:2, and the 3:1, become effective at capturing KBOs and pumping their eccentricities up to e ˜0.4. Note that these latter resonances are located at semimajor axes 52 < a < 64 AU, and that resonance capture inserts many of these eccentric KBOs into the domain of the Scattered Disk. Consequently, resonance capture by these weak resonances might also account for many members of the so-called 'extended Scattered Disk' (described by Gladman et al 2002) comprised of distant, eccentric KBOs having high perihelion distances exceeding 38 AU.

Hahn, J. M.; Malhotra, R.

2003-05-01

249

The effects of nighttime seat belt enforcement on seat belt use by tavern patrons: a preliminary analysis.  

PubMed Central

The purpose of this study was to determine the effects of police enforcement and the use of signs and posters in promoting seat belt use by nighttime tavern patrons. Ten taverns in two cities served as sites. Data were collected on the nighttime seat belt use of tavern patrons and daytime citywide seat belt use. Results indicated that the intervention increased nighttime seat belt use by tavern patrons. Daytime seat belt use increased in one city and remained at a high level in the other following the intervention. Because previous research has shown that tavern patrons are overrepresented in the impaired driving population, and that seat belt use decreases the likelihood of serious injury or death, results of this study suggest that enforcement of seat belt use could reduce casualties resulting from impaired driving.

Malenfant, J E; Van Houten, R

1988-01-01

250

A belted kingfisher flies above KSC  

NASA Technical Reports Server (NTRS)

A belted kingfisher soars over the Merritt Island National Wildlife Refuge, which shares a boundary with Kennedy Space Center. The pigeon-sized, blue-gray male is identified by the blue-gray breast band; females show a chestnut belly band. The belted kingfisher ranges throughout the United States and Canada, wintering south to Panama and the West Indies. They dive into the water for fish and may also take crabs, crayfish, salamanders, lizards, mice and insects. The 92,000-acre refuge is a habitat for more than 310 species of birds, 25 mammals, 117 fishes and 65 amphibians and reptiles. The marshes and open water of the refuge also provide wintering areas for 23 species of migratory waterfowl, as well as a year-round home for great blue herons, great egrets, wood storks, cormorants, brown pelicans and other species of marsh and shore birds.

1999-01-01

251

Compositional structure of the asteroid belt  

Microsoft Academic Search

A variety of observations, mainly albedos derived from 10 and 20 micron radiometry and eight-filter broadband spectrophotometry, were used to show that the asteroid belt is highly structured in composition. The bias-corrected distribution from 1.8 to 5.2 A.U. of the previously defined compositional types C,S,E,R, and M, plus type D and the newly described types F and P, are reported

J. Gradie; E. Tedesco

1982-01-01

252

Geochronologic studies in the Grants mineral belt  

Microsoft Academic Search

Geologic observation coupled with radiometric age dating can be used to assess ages of ore formation and, in some cases, ages of sedimentation in the Grants mineral belt. Rb-Sr studies indicate the earliest mineralization is trend ore at Ambrosia Lake and Smith Lake, dated at 139 +- 9.5 m.y. This date is similar to that for barren-rock montmorillonite from the

Brookins

1980-01-01

253

Meningococcal carriage in the African meningitis belt.  

PubMed

A meningococcal serogroup A polysaccharide/tetanus toxoid conjugate vaccine (PsA-TT) (MenAfriVac(™) ) is being deployed in countries of the African meningitis belt. Experience with other polysaccharide/protein conjugate vaccines has shown that an important part of their success has been their ability to prevent the acquisition of pharyngeal carriage and hence to stop transmission and induce herd immunity. If PsA-TT is to achieve the goal of preventing epidemics, it must be able to prevent the acquisition of pharyngeal carriage as well as invasive meningococcal disease and whether PsA-TT can prevent pharyngeal carriage needs to be determined. To address this issue, a consortium (the African Meningococcal Carriage (MenAfriCar) consortium) was established in 2009 to investigate the pattern of meningococcal carriage in countries of the African meningitis belt prior to and after the introduction of PsA-TT. This article describes how the consortium was established, its objectives and the standardised field and laboratory methods that were used to achieve these objectives. The experience of the MenAfriCar consortium will help in planning future studies on the epidemiology of meningococcal carriage in countries of the African meningitis belt and elsewhere. PMID:23682910

2013-08-01

254

Rapid rebuilding of the outer radiation belt  

NASA Astrophysics Data System (ADS)

Recent observations by the radiation monitor (RDM) on the spacecraft Akebono have shown several cases of >2.5 MeV radiation belt electron enhancements occurring on timescales of less than a few hours. Similar enhancements are also seen in detectors on board the NOAA/POES and TWINS 1 satellites. These intervals are shorter than typical radial diffusion or wave-particle interactions can account for. We choose two so-called “rapid rebuilding” events that occur during high speed streams (4 September 2008 and 22 July 2009) and simulated them with the Space Weather Modeling Framework configured with global magnetosphere, radiation belt, ring current, and ionosphere electrodynamics model. Our simulations produce a weaker and delayed dipolarization as compared to observations, but the associated inductive electric field in the simulations is still strong enough to rapidly transport and accelerate MeV electrons resulting in an energetic electron flux enhancement that is somewhat weaker than is observed. Nevertheless, the calculated flux enhancement and dipolarization is found to be qualitatively consistent with the observations. Taken together, the modeling results and observations support the conclusion that storm-time dipolarization events in the magnetospheric magnetic field result in strong radial transport and energization of radiation belt electrons.

Glocer, A.; Fok, M.-C.; Nagai, T.; Tóth, G.; Guild, T.; Blake, J.

2011-09-01

255

The atmospheric implications of radiation belt remediation  

NASA Astrophysics Data System (ADS)

High altitude nuclear explosions (HANEs) and geomagnetic storms can produce large scale injections of relativistic particles into the inner radiation belts. It is recognised that these large increases in >1 MeV trapped electron fluxes can shorten the operational lifetime of low Earth orbiting satellites, threatening a large, valuable population. Therefore, studies are being undertaken to bring about practical human control of the radiation belts, termed "Radiation Belt Remediation" (RBR). Here we consider the upper atmospheric consequences of an RBR system operating over either 1 or 10 days. The RBR-forced neutral chemistry changes, leading to NOx enhancements and Ox depletions, are significant during the timescale of the precipitation but are generally not long-lasting. The magnitudes, time-scales, and altitudes of these changes are no more significant than those observed during large solar proton events. In contrast, RBR-operation will lead to unusually intense HF blackouts for about the first half of the operation time, producing large scale disruptions to radio communication and navigation systems. While the neutral atmosphere changes are not particularly important, HF disruptions could be an important area for policy makers to consider, particularly for the remediation of natural injections.

Rodger, C. J.; Clilverd, M. A.; Ulich, Th.; Verronen, P. T.; Turunen, E.; Thomson, N. R.

2006-08-01

256

Meningococcal carriage in the African meningitis belt  

PubMed Central

Summary A meningococcal serogroup A polysaccharide/tetanus toxoid conjugate vaccine (PsA-TT) (MenAfriVac™) is being deployed in countries of the African meningitis belt. Experience with other polysaccharide/protein conjugate vaccines has shown that an important part of their success has been their ability to prevent the acquisition of pharyngeal carriage and hence to stop transmission and induce herd immunity. If PsA-TT is to achieve the goal of preventing epidemics, it must be able to prevent the acquisition of pharyngeal carriage as well as invasive meningococcal disease and whether PsA-TT can prevent pharyngeal carriage needs to be determined. To address this issue, a consortium (The African Meningococcal Carriage Consortium) (MenAfriCar) was established in 2009 to investigate the pattern of meningococcal carriage in countries of the African meningitis belt prior to and after the introduction of PsA-TT. This paper describes how the consortium was established, its objectives and the standardised field and laboratory methods that were used to achieve these objectives. The experience of the MenAfriCar Consortium will help in planning future studies on the epidemiology of meningococcal carriage in countries of the African meningitis belt and elsewhere.

2014-01-01

257

Are the main belt comets, comets?  

NASA Astrophysics Data System (ADS)

We present the visible spectrum of asteroid-comet transition object 133P/Elst-Pizarro (7968), the first member of the new population of objects called Main Belt Comets (Hsieh & Jewitt 2006). The spectrum was obtained with the 4.2m William Herschel Telescope at the “Roque de los Muchachos” observatory. The orbital elements of 133P place it within the Themis collisional family, but the observed cometary activity during it last 3 perihelion passages also suggest a possible origin in the trans-Neptunian belt or the Oort Cloud, the known sources of comets. We found a clear similarity between our spectrum of 133P and those of other members of the Themis family such as 62 Erato, and a strong contrast with those of cometary nuclei, such as 162P/Siding-Spring. This spectral comparison leads us to conclude that 133P is unlikely to have a cometary origin. This conclusion is strengthened by spectral similarities with activated near-Earth asteroid 3200 Phaethon, and suggest that there are activated asteroids in the near-Earth asteroid and main belt populations with similar surface properties.

Licandro, Javier; Campins, Humberto

258

Rapid Rebuilding of the Outer Radiation Belt  

NASA Technical Reports Server (NTRS)

Recent observations by the radiation monitor (RDM) on the spacecraft Akebono have shown several cases of greater than 2.5 MeV radiation belt electron enhancements occurring on timescales of less than a few hours. Similar enhancements are also seen in detectors on board the NOAA/POES and TWINS 1 satellites. These intervals are shorter than typical radial diffusion or wave-particle interactions can account for. We choose two so-called "rapid rebuilding" events that occur during high speed streams (4 September 2008 and 22 July 2009) and simulated them with the Space Weather Modeling Framework configured with global magnetosphere, radiation belt, ring current, and ionosphere electrodynamics model. Our simulations produce a weaker and delayed dipolarization as compared to observations, but the associated inductive electric field in the simulations is still strong enough to rapidly transport and accelerate MeV electrons resulting in an energetic electron flux enhancement that is somewhat weaker than is observed. Nevertheless, the calculated flux enhancement and dipolarization is found to be qualitatively consistent with the observations. Taken together, the modeling results and observations support the conclusion that storm-time dipolarization events in the magnetospheric magnetic field result in strong radial transport and energization of radiation belt electrons.

Glocer, A.; Fok, M.-C.; Nagai, T.; Toth, G.; Guild, T.; Bkake, J.

2011-01-01

259

CHAOTIC DIFFUSION OF RESONANT KUIPER BELT OBJECTS  

SciTech Connect

We carried out extensive numerical orbit integrations to probe the long-term chaotic dynamics of the two strongest mean-motion resonances of Neptune in the Kuiper Belt, the 3:2 (Plutinos) and 2:1 (Twotinos). Our primary results include a computation of the relative volumes of phase space characterized by large- and small-resonance libration amplitudes, and maps of resonance stability measured by mean chaotic diffusion rate. We find that Neptune's 2:1 resonance has weaker overall long-term stability than the 3:2-only {approx}15% of Twotinos are projected to survive for 4 Gyr, compared to {approx}27% of Plutinos, based on an extrapolation from our 1-Gyr integrations. We find that Pluto has only a modest effect, causing a {approx}4% decrease in the Plutino population that survives to 4 Gyr. Given current observational estimates, and assuming an initial distribution of particles proportional to the local phase-space volume in the resonance, we conclude that the primordial populations of Plutinos and Twotinos formerly made up more than half the population of the classical and resonant Kuiper Belt. We also conclude that Twotinos were originally nearly as numerous as Plutinos; this is consistent with predictions from early models of smooth giant planet migration and resonance sweeping of the Kuiper Belt and provides a useful constraint for more detailed models.

Tiscareno, Matthew S. [Department of Astronomy, Cornell University, Ithaca, NY 14853 (United States); Malhotra, Renu [Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 (United States)], E-mail: matthewt@astro.cornell.edu

2009-09-15

260

Surface testing and evaluation of the conveyor belt service machine  

SciTech Connect

In underground room-and-pillar mining methods, the sectional conveyor belts are extended or retracted periodically to maintain shuttle car tramming distance to a minimum. A conventional conveyor belt extension or retraction is a heavy, arduous job that, if mechanized, has the potential to improve productivity and safety. This book presents a Bureau of Mines conveyor belt service machine (CBSM) reduced the burden of heavy work of this activity and mechanize it. The CBSM is a self-contained, battery-powered, rubber-tired vehicle capable of handling, storing, and transporting conveyor belting, wire rope, and associated belt structures in seams as low as 48 in. Belt extensions and retractions are accomplished by moving the tailpiece of a belt conveyor with the CBSM to the next position while dispensing or retrieving the belt, wire rope, and associated belt structures. The CBSM improves the belt extensions and retractions by making them easier and faster, and it utilizes fewer workers. The CBSM was surface tested at the Bureau's Mining Equipment Test Facility to evaluate its performance and reliability. Modifications were made to the CBSM to correct deficiencies found during surface testing.

Jaspal, J.S.; Miller, L.F.

1988-01-01

261

Radiation Belts of Antiparticles in Planetary Magnetospheres  

NASA Astrophysics Data System (ADS)

The Earth's radiation belts could be populated, besides with electrons and protons, also by antiparticles, such as positrons (Basilova et al., 1982) and antiprotons (pbar). Positrons are born in the decay of pions that are directly produced in nuclear reactions of trapped relativistic inner zone protons with the residual atmosphere at altitudes in the range of about 500 to 3000 km over the Earth's surface. Antiprotons are born by high energy (E > 6 GeV) cosmic rays in p+p - p+p+p+ pbar and in p+p - p+p+n+nbar reactions. The trapping and storage of these charged anti-particles in the magnetosphere result in radiation belts similar to the classical Van Allen belts of protons and electrons. We describe the mathematical techniques used for numerical simulation of the trapped positron and antiproton belt fluxes. The pion and antiproton yields were simulated on the basis of the Russian nuclear reaction computer code MSDM, a Multy Stage Dynamical Model, Monte Carlo code, (i.e., Dementyev and Sobolevsky, 1999). For estimates of positron flux there we have accounted for ionisation, bremsstrahlung, and synchrotron energy losses. The resulting numerical estimates show that the positron flux with energy >100 MeV trapped into the radiation belt at L=1.2 is of the order ~1000 m-2 s-1 sr-1, and that it is very sensitive to the shape of the trapped proton spectrum. This confined positron flux is found to be greater than that albedo, not trapped, mixed electron/positron flux of about 50 m-2 s-1 sr-1 produced by CR in the same region at the top of the geomagnetic field line at L=1.2. As we show in report, this albedo flux also consists mostly of positrons. The trapped antiproton fluxes produced by CR in the Earth's upper rarified atmosphere were calculated in the energy range from 10 MeV to several GeV. In the simulations we included a mathematic consideration of the radial diffusion process, both an inner and an outer antiproton source, losses of particles due to ionization process, annihilation, and nuclear interactions with the ambient matter. We have found that the Earth's antiproton belt possesses about 6-60 times larger antiproton fluxes compared to the galactic fluxes in interplanetary space during minimum and maximum solar activity at all energies in confinement zone. The radiation belt antiproton fluxes are spread into a wider L-shell range than its generation location around L=1.2. This is due to diffusion processes, and it demonstrates that radial diffusion as a relatively significant process for antimatter, even in the inner magnetosphere. Antimatter accumulated in the magnetospheres of solar system bodies may be of significance for space travel. It could be used as a propulsion for space missions to the outer planets and beyond. Antimatter has an energy density more than ten orders of magnitude higher than the best chemical propellants currently used in rocket systems. References: Basilova, R. N., A.A. Gusev, G.I. Pugacheva , Geom. and Aeronom. V. 22, p. 671-673, 1982.Chen, J., T. Dementyev, A.V., Sobolevsky, N.M. Radiation Measurements, 30, 553, 1999.

Pugacheva, G. I.; Gusev, A. A.; Jayanthi, U. B.; Martin, I. M.; Spjeldvik, W. N.

2007-05-01

262

Normative misperceptions of peer seat belt use among high school students and their relationship to personal seat belt use.  

PubMed

Objectives: This research examined gender-specific perceptions of peer seat belt use norms among high school students and their relationship with one's own seat belt use. We expected that students would underestimate the seat belt use of their peers and that these perceptions would be positively associated with their own seat belt use. Methods: High school students from 4 schools (N = 3348; 52% male) completed measures assessing perceived seat belt use and personal seat belt use. Results: Findings demonstrated that students perceived that others engaged in less seat belt use than they do and that perceived norms were positively associated with one's own seat belt use. Conclusions: Peer influences are a strong predictor of behavior, especially among adolescents. Ironically, adolescents' behaviors are often influenced by inaccurate perceptions of their peers. This research establishes the presence of a misperception related to seat belt use and suggests that misperception is associated with own behaviors. This research provides a foundation for social norms-based interventions designed to increase seat belt use by correcting normative misperceptions among adolescents. PMID:24628560

Litt, Dana M; Lewis, Melissa A; Linkenbach, Jeffrey W; Lande, Gary; Neighbors, Clayton

2014-10-01

263

Phyllosilicate absorption features in main-belt and outer-belt asteroid reflectance spectra  

NASA Technical Reports Server (NTRS)

Absorption features having depths up to 5 percent are identified in high-quality, high-resolution reflectance spectra of 16 dark asteroids in the main belt and in the Cybele and Hilda groups. Analogs among the CM2 carbonaceous chondrite meteorites exist for some of these asteroids, suggesting that these absorptions are due to iron oxides in phyllosilicates formed on the asteroidal surfaces by aqueous alteration processes. Spectra of ten additional asteroids, located beyond the outer edge of the main belt, show no discernible absorption features, suggesting that aqueous alteration did not always operate at these heliocentric distances.

Vilas, Faith; Gaffey, Michael J.

1989-01-01

264

A population of comets in the main asteroid belt.  

PubMed

Comets are icy bodies that sublimate and become active when close to the Sun. They are believed to originate in two cold reservoirs beyond the orbit of Neptune: the Kuiper Belt (equilibrium temperatures of approximately 40 kelvin) and the Oort Cloud (approximately 10 kelvin). We present optical data showing the existence of a population of comets originating in a third reservoir: the main asteroid belt. The main-belt comets are unlike the Kuiper Belt and Oort Cloud comets in that they likely formed where they currently reside and may be collisionally activated. The existence of the main-belt comets lends new support to the idea that main-belt objects could be a major source of terrestrial water. PMID:16556801

Hsieh, Henry H; Jewitt, David

2006-04-28

265

ViRBO, The Virtual Radiation Belt Observatory  

Microsoft Academic Search

The Virtual Radiation Belt Observatory (ViRBO) has synthesized a large collection of data and tools relevant to radiation belt science including instrument data, scientist-contributed model data, and analysis software. Instrument data from the SAMPEX, GOES, POES, LANL GEO, Polar, and GPS satellites are all available from a common interface. Scientist-contributed model data include that of the radiation belt content index,

R. S. Weigel; E. Kihn; D. N. Baker; R. Friedel; J. Green; S. Bourdarie; J. Faden; M. Zhizhin

2007-01-01

266

Simulation model of wax diffusion and cleaning in printer belts  

Microsoft Academic Search

A belt that transports toner is one of the vital components of a printer. Since toner is fused to the paper at a high temperature,\\u000a wax releases from the paper and penetrates into the rubber top layer of the belt. When the rubber becomes saturated with wax,\\u000a the wax remains on top of the belt. The formed layer of wax

S. J. L. van Eijndhoven; D. P. Siregar; T. Siebers

2012-01-01

267

New compounds will help coal operators comply with BELT standards  

SciTech Connect

US coal producers will soon have a new set of conveyor belting standards, which are currently proposed as a rulemaking by the Mine Safety and Health Administration (MSHA), to bring higher levels of resistance to propagation of fire by a secondary source. The new test being put into effect is known as a Belt Evaluation Laboratory Test (BELT). The article, submitted by Fenner Dunlop, discusses the company's testing procedures and the development of conveyors to comply with regulations. 2 photos.

NONE

2009-04-15

268

State of the art in radiation belt research  

NASA Astrophysics Data System (ADS)

AGU Chapman Conference on Dynamics of the Earth's Radiation Belts and Inner Magnetosphere; St. John's, Newfoundland and Labrador, Canada, 17-22 July 2011 Earth's radiation belts were discovered by James Van Allen and colleagues in 1958 using data from the Explorer I satellite. Since then, the Van Allen belts have been under extensive theoretical and experimental investigation. Because highly energetic (relativistic) electrons generated in the outer radiation zone during geomagnetically disturbed times can damage orbiting satellites, Earth's radiation belts are regarded as a serious space weather hazard. The emerging science of space weather has fueled a resurgence of interest in radiation belt physics in the past 10 years. This will culminate in 2012 with the launch of NASA's Radiation Belt Storm Probes (RBSP) twin satellite mission, which will make in situ measurements of the radiation belts. Shortly after 2012 are also planned launches of the Japanese Energization and Radiation in Geospace (ERG) satellite and the Russian mission RESONANCE, both designed to probe Earth's radiation belts. Thus, 2012-2013 promises to be an exciting and pivotal period in radiation belt science.

Summers, Danny; Mann, Ian R.; Baker, Daniel N.

2011-12-01

269

Rogue Asteroids in the Inner Main Asteroid Belt  

NASA Astrophysics Data System (ADS)

Very red featureless asteroids (spectroscopic D-types) are common among Jupiter Trojans, Hildas, and the outer main belt, and are thought to have formed in the outer solar system. Dynamical models of planetary migration and orbital drift by the Yarkovsky effect predict these D-types could have been transported as close to the sun as the middle main belt, but not closer. We detect D-types in the inner main belt, where they are not expected, through follow-up observations of 13 D-type candidates as determined by SDSS colors. Near-infrared spectroscopic measurements were taken using SpeX on the IRTF. Known inner belt D-types range in diameter from roughly 7 to 30 kilometers. Based on these detections we estimate there are ˜100 inner belt D-types with diameters between 2.5 and 20km. The total mass of inner belt D-types is 4x10^16kg which represents 0.01% of the mass of the inner belt (note Vesta alone accounts for 2/3 of the inner belt mass). Dynamical models have yet to show how D-types could penetrate into the inner reaches of the Main Belt.

DeMeo, Francesca E.; Binzel, R. P.; Carry, B.; Moskovitz, N.; Polishook, D.

2014-01-01

270

Magnetic refrigeration apparatus with belt of ferro or paramagnetic material  

DOEpatents

A magnetic refrigerator operating in the 12 to 77 K range utilizes a belt which carries ferromagnetic or paramagnetic material and which is disposed in a loop which passes through the center of a solenoidal magnet to achieve cooling. The magnetic material carried by the belt, which can be blocks in frames of a linked belt, can be a mixture of substances with different Curie temperatures arranged such that the Curie temperatures progressively increase from one edge of the belt to the other. This magnetic refrigerator can be used to cool and liquefy hydrogen or other fluids.

Barclay, J.A.; Stewart, W.F.; Henke, M.D.; Kalash, K.E.

1986-04-03

271

The Overthrust Belt of Western North America  

SciTech Connect

The Overthrust Belt extends for 5000 mi (8000 km) from the Brooks Range in Alaska to the Sierra Madre Oriental in Mexico. It consists of northeastward vergent thrust and fold structures involving late Precambrian to early Tertiary sedimentary section. These sediments represent deposition off the western rift margin, formed in late Precambrian time, of the North American Precambrian craton. The northeastward thrusting continued throughout the Mesozoic as a response to the convergence of the East Pacific Plate with the North American Plate. This convergence resulted in subduction beneath the North American Plate except at the northwest end (the Brooks Range) where the result was obduction. Convergence ceased when the west edge of the East Pacific Plate reached the subduction zone. The sedimentary section involved in the Thrust Belt contains good Devonian to Cretaceous hydrocarbon source rocks, and Ordovician to traps related to the thrusting (simple thrust sheets, imbricate thrust sheets, folded thrust sheets, step anticlines, footwall cutoffs, footwall anticlines, etc.). Field methods involved in exploration for hydrocarbons include field geological mapping, remote sensing (aerial photography and Landsat imagery), various seismic refraction and seismic reflection techniques (including modern detailed three dimension surveys) and potential field methods such as gravity and magnetic surveying. Studies of the field data include paleontology, source rock and hydrocarbon migration studies, structural and stratigraphic analyses, and the processing of geophysical data. This work has succeeded in two major areas: the Western Canadian Rocky Mountain Foothills, a major gas province producing mainly from Paleozoic reservoirs; and the Wyoming-Idaho-Utah portion of the thrust belt, also a major gas producer from Paleozoic reservoirs and, in addition, a major oil producer from the Jurassic Nugget Sandstone.

Verrall, P.

1993-02-01

272

The origin of Jupiter's outer radiation belt  

NASA Astrophysics Data System (ADS)

The intense inner radiation belt at Jupiter (>50 MeV at 1.5 RJ) is generally accepted to be created by radial diffusion of electrons from further away from the planet. However, this requires a source with energies that exceed 1 MeV outside the orbit of the moon Io at 5.9 RJ, which has never been explained satisfactorily. Here we test the hypothesis that this source population could be formed from a very soft energy spectrum, by particle injection processes and resonant electron acceleration via whistler mode chorus waves. We use the British Antarctic Survey Radiation Belt Model to calculate the change in the electron flux between 6.5 and 15 RJ; these are the first simulations at Jupiter combining wave particle interactions and radial diffusion. The resulting electron flux at 100 keV and 1 MeV lies very close to the Galileo Interim Radiation Electron model spectrum after 1 and 10 days, respectively. The primary driver for the increase in the flux is cyclotron resonant acceleration by chorus waves. A peak in phase space density forms such that inside L?9 radial diffusion transports electrons toward Jupiter, but outside L?9 radial diffusion acts away from the planet. The results are insensitive to the softness of the initial energy spectrum but do depend on the value of the flux at the minimum energy boundary. We conclude by suggesting that the source population for the inner radiation belt at Jupiter could indeed be formed by wave-particle interactions.

Woodfield, E. E.; Horne, R. B.; Glauert, S. A.; Menietti, J. D.; Shprits, Y. Y.

2014-05-01

273

An Evaluation Study of a CALL Application: With BELT or without BELT  

ERIC Educational Resources Information Center

The present study tried to evaluate the 6th grade students' attitudes towards the use of a CALL program which is called BELT Success used in English language learning course in a private school, the relationship to students' attitudes to their English language proficiency level, and finally teachers` experiences and opinions towards the use of…

Genc, Humeyra

2012-01-01

274

The Radiation Belt Storm Probes Mission: Advancing Our Understanding of the Earth's Radiation Belts  

NASA Technical Reports Server (NTRS)

We describe NASA's Radiation Belt Storm Probe (RBSP) mission, whose primary science objective is to understand, ideally to the point of predictability, the dynamics of relativistic electrons and penetrating ions in the Earth's radiation belts resulting from variable solar activity. The overarching scientific questions addressed include: 1. the physical processes that produce radiation belt enhancement events, 2. the dominant mechanisms for relativistic electron loss, and 3. how the ring current and other geomagnetic processes affect radiation belt behavior. The RBSP mission comprises two spacecraft which will be launched during Fall 2012 into low inclination lapping equatorial orbits. The orbit periods are about 9 hours, with perigee altitudes and apogee radial distances of 600 km and 5.8 RE respectively. During the two-year primary mission, the spacecraft orbits precess once around the Earth and lap each other twice in each local time quadrant. The spacecraft are each equipped with identical comprehensive instrumentation packages to measure, electrons, ions and wave electric and magnetic fields. We provide an overview of the RBSP mission, onboard instrumentation and science prospects and invite scientific collaboration.

Sibeck, David; Kanekal, Shrikanth; Kessel, Ramona; Fox, Nicola; Mauk, Barry

2012-01-01

275

Anatomy of an intracratonic fold belt: Examples from the southwestern Palmyride fold belt in central Syria  

SciTech Connect

The Palmyride fold belt, a 400 {times} 100 km, NE-trending, transpressive belt in central Syria, represents the late Mesozoic and Cenozoic inversion of a linear intracratonic basin. The southwestern Palmyrides are characterized by short wavelength (2-5 km) folds separated by small intermontane basins. To elucidate the subsurface structure, a three-dimensional model, based mainly on about 450 km of two-dimensional seismic reflection data, was generated using a LandMark{reg sign} graphics workstation. The new model includes many features not identified in outcrop. Short, NW-trending transcurrent, or transfer, faults link the short, en echelon NE-trending thrust faults and blind thrusts of the Palmyrides. Varying structural styles are observed within the southwestern part of the belt. In one instance the structure of Mesozoic and Cenozoic rocks mimics that in deeper Paleozoic rocks; elsewhere, a strong discordance between Paleozoic and Mesozoic rocks appears to be related to the development of a regional detachment in Triassic rocks at about 4 km depth. Shortening the southwestern palmyrides totals about 20-25 km, based on palinspastic restoration of a balanced cross section across the belt. Seismic stratigraphy constrains the timing of at least three distinct episodes of Palmyride shortening: Late Cretaceous, middle Eocene, and Miocene to present. All three episodes were penecontemporaneous with specific tectonic events along the northern Arabian plate boundaries.

Chaimov, T.A.; Barazangi, M.; Best, J.A. (Cornell Univ., Ithaca, NY (United States)); Al-Saad, D.; Sawaf, T.; Gebran, A. (Syrian Petroleum Co., Damascus (Syria))

1991-03-01

276

Dust bands in the asteroid belt  

NASA Technical Reports Server (NTRS)

This paper describes the original IRAS observations leading to the discovery of the three dust bands in the asteroid belt and the analysis of data. Special attention is given to an analytical model of the dust band torus and to theories concerning the origin of the dust bands, with special attention given to the collisional equilibrium (asteroid family), the nonequilibrium (random collision), and the comet hypotheses of dust-band origin. It is noted that neither the equilibrium nor nonequilibrium models, as currently formulated, present a complete picture of the IRAS dust-band observations.

Sykes, Mark V.; Greenberg, Richard; Dermott, Stanley F.; Nicholson, Philip D.; Burns, Joseph A.

1989-01-01

277

Period Determination of Six Main Belt Asteroids  

NASA Astrophysics Data System (ADS)

Observations of six main-belt asteroids (MBA) produced lightcurve parameters of: 487 Venetia, P = 13.34 ± 0.01 h, A = 0.20 mag; 684 Hildburg, P = 15.89 ± 0.01 h, A = 0.22 mag; 772 Tanete, P = 8.629 ± 0.001 h, A = 0.18 mag.; 1181 Lilith, P = 15.04 ± 0.01 h, A = 0.11 mag.; 1246 Chaka, P = 25.44 ± 0.01 h, A = 0.25 mag.; and 2834 Christy Carol, P = 12.79 ± 0.01 h, A = 0.39 mag.

Ferrero, Andrea

2014-07-01

278

Aircraft radial-belted tire evaluation  

NASA Technical Reports Server (NTRS)

An overview is given of the ongoing joint NASA/FAA/Industry Surface Traction And Radial Tire (START) Program being conducted at NASA Langley's Aircraft Landing Dynamics Facility (ALDF). The START Program involves tests using three different tire sizes to evaluate tire rolling resistance, braking, and cornering performance throughout the aircraft ground operational speed range for both dry and wet runway surfaces. Preliminary results from recent 40 x 14 size bias-ply, radial-belted, and H-type aircraft tire tests are discussed. The paper concludes with a summary of the current program status and planned ALDF test schedule.

Yager, Thomas J.; Stubbs, Sandy M.; Davis, Pamela A.

1990-01-01

279

Effectiveness of primary enforcement safety belt laws and enhanced enforcement of safety belt laws: A summary of the Guide to Community Preventive Services systematic reviews  

Microsoft Academic Search

Background: The use of safety belts is the single most effective means of reducing fatal and nonfatal injuries in motor-vehicle crashes. This paper summarizes the systematic reviews of two interventions to increase safety belt use: primary enforcement safety belt laws and enhanced enforcement of safety belt laws. The reviews were previously published in the American Journal of Preventive Medicine. Methods:

Ruth A. Shults; James L. Nichols; Tho Bella Dinh-Zarr; David A. Sleet; Randy W. Elder

2004-01-01

280

Pattern of seat belt wearing in Nanjing, China  

PubMed Central

Objective To describe the patterns of seat belt wearing in Nanjing, China for drivers, front seat passengers, and rear occupants of motor vehicles. Design Roadside observational study. Setting Four sites in central and northern Nanjing during daylight hours over 1 week in April 2005. Subjects Drivers and passengers of 17?147 cars, taxis, goods vans, and pickups, which traveled in the inside traffic lane. Main outcome measures Percentage seat belt wearing for each of seating position, age/sex, time of day, vehicle type, day of week. Results The rate of seat belt wearing was significantly higher in drivers (67.3%, 95% CI 66.6 to 68.0) than front seat passengers (18.9%, 95% CI, 18.0 to 19.8). It was negligible for second front seat passengers (2.6%, 95% CI 0.3 to 4.9) and rear seat passengers (0.5%, 95% CI 0.3 to 0.7). Belt tampering, such that protection would be reduced in the event of a crash, was observed for 18.5% of taxi drivers. Drivers were most likely to wear seat belts in cars and vans and at a city roundabout; front seat passengers were most likely to wear seat belts in non?taxi vehicles, during the evening rush hour, if the driver was wearing a belt, and on the local north road. Drivers were least likely to wear a belt in the early morning, in pickups and taxis, on Tuesday (or the following week), and on the local north road; front seat passengers were least likely to wear a belt in taxis and if the driver was not wearing a belt. Conclusions Rates of seat belt wearing by passengers were low despite national legislation and provincial regulations coming into effect several months before the survey. Combined education and enforcement are necessary accompaniments to legislation.

Routley, V; Ozanne-Smith, J; Li, D; Hu, X; Wang, P; Qin, Y

2007-01-01

281

30 CFR 14.22 - Test for flame resistance of conveyor belts.  

Code of Federal Regulations, 2010 CFR

... 2009-07-01 false Test for flame resistance of conveyor belts. 14...PRODUCTS REQUIREMENTS FOR THE APPROVAL OF FLAME-RESISTANT CONVEYOR BELTS Technical Requirements § 14.22 Test for flame resistance of conveyor belts....

2009-07-01

282

Dust bands in the asteroid belt  

SciTech Connect

The Infrared Astronomical Satellite (IRAS) discovered three bands of dust: one above, below, and approximately in the plane of the ecliptic. These bands are located in the asteroid belt and are believed to arise from collisional activity. Debris from an asteroid collision, over time, fills a torus having peaks in particle number density near its inner and outer corners, corresponding to the locus of perihelia and aphelia, respectively. As a consequence of this geometry, such a swarm should produce two pairs of bands that straddle the ecliptic - a perihelion band pair and an aphelion band pair (which generally overlap along the line of sight from earth). Indeed, processing of the IRAS data now resolves the band structure into at least three such band pairs, with indications of several more pairs distributed over a large range of ecliptic latitudes. Some of these bands appear to be associated with major Hirayama asteroid families, while others are not. Possible origins of the observed dust bands include: (1) the gradual comminution of the asteroid belts as a whole, in which the local dust population is maximum where the concentration of asteroids is greatest (e.g. families); (2) one or a few large random asteroid collisions enhancing the local population of small debris, which in turn is comminuted into dust; and (3) the disintegration of one or more large comets. Dust bands are not necessarily constant features of the solar system.

Sykes, M.; Greenberg, R.; Dermott, S.; Nicholson, P.; Burns, J.

1989-09-08

283

Fading of Jupiter's South Equatorial Belt  

NASA Technical Reports Server (NTRS)

One of Jupiter's most dominant features, the South Equatorial Belt, has historically gone through a "fading" cycle. The usual dark, brownish clouds turn white, and after a period of time, the region returns to its normal color. Understanding this phenomenon, the latest occurring in 2010, will increase our knowledge of planetary atmospheres. Using the near infrared camera, NSFCAM2, at NASA's Infrared Telescope Facility in Hawaii, images were taken of Jupiter accompanied by data describing the circumstances of each observation. These images are then processed and reduced through an IDL program. By scanning the central meridian of the planet, graphs were produced plotting the average values across the central meridian, which are used to find variations in the region of interest. Calculations using Albert4, a FORTRAN program that calculates the upwelling reflected sunlight from a designated cloud model, can be used to determine the effects of a model atmosphere due to various absorption, scattering, and emission processes. Spectra that were produced show ammonia bands in the South Equatorial Belt. So far, we can deduce from this information that an upwelling of ammonia particles caused a cloud layer to cover up the region. Further investigations using Albert4 and other models will help us to constrain better the chemical make up of the cloud and its location in the atmosphere.

Sola, Michael A.; Orton, Glenn; Baines, Kevin; Yanamandra-Fisher, Padma

2011-01-01

284

Exploration for uranium deposits, Grants mineral belt  

SciTech Connect

Uranium ore deposits in the Grants mineral belt, New Mexico, occur in fluvial sandstones in the Morrison Formation (Jurassic). Uranium mineralization is concentrated by a dark-gray to black substance that has been identified as humate, which is derived from decaying vegetation. Black ore is truncated by overlying sandstone in at least three ore deposits, documenting an early age for mineralization. Ore deposits in the Grants mineral belt vary greatly in size and shape, tend to occur in clusters, and often present difficult drill targets. Current exploration is largely a matter of drilling in stages to distinguish favorable from unfavorable ground on a wide spacing, to seek mineralization in favorable ground, and to conduct close-spaced drilling in mineralized areas. Criteria for favorability differ among exploration groups but generally include 1) presence of a host sandstone, 2) anomalous mineralization, 3) color of the host rock, 4) presence of carbonaceous matter, and 5) position of the area relative to mineralized trends. A description of the drilling sequence, from ore discovery to the development of a mine at the Johnny M deposit (in the east part of the Ambrosia Lake district), exemplifies the problem of predicting where orebodies may occur. A study of the drill data at the Johnny M indicates the uranium ore is not related to specific geologic features other than humate, which is commonly associated with coalified plant fragments in mudstone-rich parts of the host sandstone.

Fitch, D.C.

1980-01-01

285

The fossilized size distribution of the main asteroid belt  

Microsoft Academic Search

Planet formation models suggest the primordial main belt experienced a short but intense period of collisional evolution shortly after the formation of planetary embryos. This period is believed to have lasted until Jupiter reached its full size, when dynamical processes (e.g., sweeping resonances, excitation via planetary embryos) ejected most planetesimals from the main belt zone. The few planetesimals left behind

William F. Bottke; Daniel D. Durda; D. Nesvorn'y; Robert Jedicke; Alessandro Morbidelli; D. Vokrouhlick'y; Hal Levison

2005-01-01

286

The Magnetic Field of a Model Radiation Belt, Numerically Computed  

Microsoft Academic Search

The magnetic field of a model ring-current belt encircling the earth symmetri- cally is numerically calculated, to a first approximation, for a particular model belt already discussed by Akasou and Chapman (1961a). They calculated the first approximation to the field only for points in the equatorial plane. The whole distribution of the field is here dis- cussed, and for a

Syuh-Ichi Akasofu; Joseph C. Cain; Sydney Chapman

1961-01-01

287

Effectiveness of Automatic Shoulder Belt Systems in Motor Vehicle Crashes  

Microsoft Academic Search

Context Approximately 10 million cars with automatic shoulder belt systems are cur- rently in use in the United States. However, reports on the effectiveness of such re- straints have yielded conflicting results. Objective To determine the effectiveness of automatic shoulder belt systems in re- ducing the risk of injury and death among front-seat passenger vehicle occupants. Design, Setting, and Subjects

Frederick P. Rivara; Thomas D. Koepsell; David C. Grossman; Charles Mock

2000-01-01

288

Policy Implications from an Evaluation of Seat Belt Use Regulation.  

ERIC Educational Resources Information Center

Effects of Ohio's mandatory seat belt law on seat belt use, number of car accidents, and number of fatal and severe injuries were evaluated for January 1982 through March 1988. The monthly average number of accident victims was 2,002. Implications for public policy formulation and implementation are discussed. (SLD)

Desai, Anand; You, Min-Bong

1992-01-01

289

Teaching Taekwondo in Physical Education: Incorporating the Color Belt System  

ERIC Educational Resources Information Center

Taekwondo is an excellent lifetime physical activity that provides both physical and mental benefits to its participants. The color belt system may be creatively used in physical education to encourage improvement in all learning domains. This article provides information on incorporating the color belt system into physical education, and provides…

Oh, Hyun-Ju; Hannon, James C.; Banks, Aaron

2006-01-01

290

Control strategy of disc braking systems for downward belt conveyors  

Microsoft Academic Search

Reliability of braking systems is a key requirement to ensure the safety of in using downward belt conveyor brakes. By analyzing and comparing three commonly used braking velocity curves, we conclude that the Harrison curve is the best. Given the characteristics of a downward belt conveyor, we studied the control in a closed-loop velocity, a conventional PID method and an

Youfu Hou; Fangwei Xie; Fei Huang

2011-01-01

291

An Evaluation of the Seat Belt Education Campaign.  

ERIC Educational Resources Information Center

A seat belt education campaign conducted in Canada to dispel myths surrounding seat belts and promote a better understanding of their functions was evaluated. Two telephone surveys, each comprised of 4,000 respondents, were conducted. The first was done immediately before the campaign and the second immediately succeeding the campaign. Also, a…

Rochon, James

292

Multiple heliospheric current sheets and coronal streamer belt dynamics  

Microsoft Academic Search

The authors offer a new interpretation of the structure of the coronal streamer belt, offering a reinterpretation of satellite observations. They argue that the multiple directional discontinuities observed by satellites crossing the belt are the signature of a network of current sheets which are the result of an array of streamers originating in the corona. The random nature of these

N. U. Crooker; G. L. Siscoe; S. Shodhan; D. F. Webb; J. T. Gosling; E. J. Smith

1993-01-01

293

Fuzzy PI control design for an industrial weigh belt feeder  

Microsoft Academic Search

An industrial weigh belt feeder is used to transport solid materials into a manufacturing process at a constant feedrate. It exhibits nonlinear behavior because of motor friction, saturation, and quantization noise in the sensors, which makes standard autotuning methods difficult to implement. The paper proposes and experimentally demonstrates two types of fuzzy logic controllers for an industrial weigh belt feeder.

Yanan Zhao

2003-01-01

294

Loss Prevention through Safety Belt Use: A Handbook for Managers.  

ERIC Educational Resources Information Center

This handbook is designed to help managers address safety belt usage issues through a cost-effective and direct approach--establishing an employee safety belt program. The handbook offers a hands-on guide for conducting the program and provides for implementation at all levels. The handbook contains cost information, a program overview, policy and…

National Highway Traffic Safety Administration (DOT), Washington, DC.

295

New horizons: a Pluto-Kuiper belt mission  

Microsoft Academic Search

New Horizons is the mission that NASA has selected to explore the Pluto-Charon binary planet system and other objects in the Kuiper Belt. The mission plan calls for a launch in January 2006 with an arrival at Pluto-Charon as early as 2015, and for a flyby of one or more Kuiper Belt objects by 2021.. The spacecraft will carry four

A. Stern; A. Cheng

2002-01-01

296

Increasing Safety Belt Use by High Risk Drivers.  

National Technical Information Service (NTIS)

The objectives of the study were to: (1) identify groups of non-belt users who are most likely to become involved in highway crashes; and (2) develop and test communication programs designed to increase safety belt use by one or more of these groups. The ...

R. D. Blomberg E. W. Bishop J. M. Edwards

1991-01-01

297

30 CFR 75.1403-5 - Criteria-Belt conveyors.  

Code of Federal Regulations, 2013 CFR

...along all belt conveyors used to transport men, and such controls should be readily...scheduled mantrips should be stopped while men are loading or unloading. (c...least 36 inches of side clearance where men board or leave such belt conveyors....

2013-07-01

298

Fatality risk for belted drivers versus car mass.  

PubMed

This study was performed to determine how the likelihood of a belted driver being killed in a single car crash depends on the mass of the car. This was done by applying the pedestrian fatality exposure approach to the subset of fatalities in the Fatal Accident Reporting System (FARS) for which the driver was coded as using a shoulder belt and/or a lap belt. Combining the 1975 through 1982 data provided a sufficiently large population of belted drivers to perform the analysis. In the exposure approach used, the number of car drivers killed in single car crashes is divided by the number of nonoccupant fatalities (pedestrians or motorcyclists) associated with the same group of cars. The ratio is interpreted to reflect the physical effect of car mass, essentially independent of driver behavior effects. In the present application, car mass effects for belted drivers were determined by considering the number of belted drivers killed divided by the number of nonoccupants killed in crashes involving cars whose drivers were coded in the FARS files as being belted. Because the belt use of surviving drivers is, to some extent, self-reported, it is considered that the data given in the report should be not used to estimate the effectiveness of seat belts in preventing fatalities. The results are presented as graphical and analytical comparisons of fatality likelihood versus car mass for belted and unbelted drivers. It is concluded that the effect of car mass on relative driver fatality likelihood is essentially the same for belted and unbelted drivers (for example, the present analysis gives that a belted driver in a 900 kg car is 2.3 times as likely to be killed in a single car crash as is the belted driver in an 1800 kg car. The corresponding ratio determined here for unbelted drivers is 2.4). As a consequence of this conclusion, the relative effectiveness of seat belts in preventing driver fatalities is similar for cars of different masses. PMID:4096791

Evans, L

1985-06-01

299

Neptune's Eccentricity and the Nature of the Kuiper Belt  

NASA Technical Reports Server (NTRS)

The small eccentricity of Neptune may be a direct consequence of apsidal wave interaction with the trans-Neptune population of debris called the Kuiper belt. The Kuiper belt is subject to resonant perturbations from Neptune, so that the transport of angular momentum by density waves can result in orbital evolution of Neptune as well as changes in the structure of the Kuiper belt. In particular, for a belt eroded out to the vicinity of Neptune's 2:1 resonance at about 48 astronomical units, Neptune's eccentricity can damp to its current value over the age of the solar system if the belt contains slightly more than an earth mass of material out to about 75 astronomical units.

Ward, William R.; Hahn, Joseph M.

1998-01-01

300

The Effects of Nighttime Seat Belt Enforcement on Seat Belt Use by Tavern Patrons: A Preliminary Analysis.  

ERIC Educational Resources Information Center

Nighttime seat belt use by patrons of 10 taverns in two Canadian cities increased following an intervention consisting of police enforcement and the use of signs and posters. Separate observations of daytime seat belt use noted an increase in one city and maintenance at a high level in the other. (JW)

Malenfant, J. E. Louis; Van Houten, Ron

1988-01-01

301

Studying the Saturn Inner Radiation Belt  

NASA Astrophysics Data System (ADS)

In 2004 the MIMI/INCA detector onboard the Cassini spacecraft measured the significant flux of the energetic neutral atoms (ENA) coming from the area between the D-ring and the Saturn's atmosphere, what brought up the idea of the possible existence of the innermost radiation belt in this narrow gap. In the present study we estimate the possible sources for this radiation belt, assuming the two main processes: the double charge exchange of the ENAs, coming from the middle magnetosphere, what can bring the keV ions to the region of our interest, and the interaction of the Galactic Cosmic Rays (GCR) with the Saturn's atmosphere and rings, which due to CRAND process can produce the keV-MeV ions or electrons in the region. Both of these possible sources are possible to evaluate using the charged particle tracer. In our group we developed such charged particle tracer, which works in all different modes (Newton-Lorentz full equation of motion, guiding center or bounce averaged approximations), and allows using the different magnetic field models (from simple dipole magnetic field till complex realistic magnetic field model like Khurana model of Saturn's magnetosphere) for both forward and backward tracing simulations. This charged particle tracer was validated using the comparison of the simulation results and observations during several flybys of Cassini by icy moons of Saturn. Using the particle tracer we can calculate the access of GCRs to the atmosphere and rings of the planet and evaluate the filtering of the GCR spectrum that hits the atmosphere from the direction of the Saturn's main rings. Also we can investigate different non-dipolar effects which possible can change the Stroemer cutoff rigidities of GCRs, especially for the high-latitude atmosphere, which maps magnetically in the outer magnetosphere. We can also estimate the production of secondaries as well (and also from the multiple impacts of these secondaries on the rings or atmosphere) and evaluate the energy spectrum of neutrons, the decay of which leads to the production of final CRAND elements in the inner Saturnian radiation belts. Using this complex simulation we are going to predict the fluxes of energetic ions and electrons, which particle detector MIMI/LEMMS onboard the Cassini can measure during the so-called "proximal" orbits in 2017, when the Cassini spacecraft will pass directly through this diverse and enigmatic region extremely close to the planet.

Kotova, A.; Roussos, E.; Krupp, N.; Dandouras, I.

2013-09-01

302

Plains tectonism on Venus: The deformation belts of Lavinia Planitia  

NASA Technical Reports Server (NTRS)

High-resolution radar images from the Magellan spacecraft have revealed the first details of the morphology of the Lavinia Planitia region of Venus. A number of geologic units can be distinguished, including volcanic plains units with a range of ages. Transecting these plains over much of the Lavinia region are two types of generally orthogonal features that we interpret to be compressional wrinkle ridges and extensional grooves. The dominant tectonic features of Lavinia are broad elevated belts of intense deformation that transect the plains with complex geometry. They are many tens to a few hundred kilometers wide, as much as 1000 km long, and elevated hundreds of meters above the surrounding plains. Two classes of deformation belts are seen in the Lavinia region. 'Ridge belts' are composed of parallel ridges, each a few hundred meters in elevation, that we interpret to be folds. Typical fold spacings are 5-10 km. 'Fracture belts' are dominated instead by intense faulting, with faults in some instances paired to form narrow grabens. There is also some evidence for modest amounts of horizontal shear distributed across both ridge and fracture belts. Crosscutting relationships among the belts show there to be a range in belt ages. In western Lavinia, in particular, many ridge and fracture belts appear to bear a relationship to the much smaller wrinkle ridges and grooves on the surrounding plains: ridge morphology tends to dominate belts that lie more nearly parallel to local plains wrinkle ridges, and fracture morphology tends to dominate belts that lie more nearly parallel to local plains grooves. We use simple models to explore the formation of ridge and fracture belts. We show that convective motions in the mantle can couple to the crust to cause horizontal stresses of a magnitude sufficient to induce the formation of deformation belts like those observed in Lavinia. We also use the small-scale wavelengths of deformation observed within individual ridge belts to place an approximate lower limit on the venusian thermal gradient in the Lavinia region at the time of deformation.

Squyres, Steven W.; Jankowski, David G.; Simons, Mark; Solomon, Sean C.; Hager, Bradford H.; Mcgill, George E.

1993-01-01

303

Main Belt Asteroids: Present and Future Inventory  

NASA Astrophysics Data System (ADS)

It is difficult to derive a precise inventory of the asteroids present in the main belt. This is due to the fact that a large fraction of the existing bodies have not been detected due to their faint apparent magnitudes. On the other hand, recent advances in asteroid science allow us to make more reliable estimates of the magnitude at which the available sample is nearly complete, and on the real trend of the underlying asteroid size distribution. The very important role played by asteroid families is extensively analyzed and discussed. Family members appear to dominate the asteroid population at small sizes, as impressively shown by some quantitative predictions of what will be the appearance of the asteroid inventory in the future. The importance of this conclusion from the point of view the asteroid collisional evolution is also discussed.

Zappala, V.; Cellino, A.

304

Primordial Ices In The Kuiper Belt  

NASA Astrophysics Data System (ADS)

We have undertaken a comprehensive near-infrared (NIR) photometric survey of Kuiper Belt Objects (KBOs) to locate primordial ices. Optical surveys provide very little constraint on ices, which are mostly featureless in the visible region. Thus, we have employed custom medium-width bandpass NIR filters that allow us to divide the KBOs into water, methane and neutral surface types. Our custom bandpass NIR filters provide a factor of 10 sensitivity increase over previous NIR photometric works. In contrast, standard JHK bandpasses are not optimized to detect volatile ices. We have manufactured and installed our custom filters in the Gemini North (8.1 meter diameter) NIRI imager as well as the Magellan (6.5 meter diameter) PANIC imager. When completed, we will have surveyed most known KBOs brighter than a visual magnitude of 22, over 100 objects. We present the observing methodology and first results from the survey.

Trujillo, Chadwick A.; Sheppard, S. S.; Schaller, E. L.

2009-09-01

305

What Drives the Global Conveyer Belt?  

NSDL National Science Digital Library

In this laboratory activity, students observe what happens when a fluid of one density is placed in a fluid of a different density. The fluids are salt water and fresh water, cold water and warm water. They generalize their results to describe what occurs in the world's oceans to drive the global conveyor belt pattern of ocean currents. There is an option to conduct an investigation taking quantitative measurements, which requires an immersible thermometer and a heat source. Assessment suggestions are included. The investigation is found in the teacher's guide accompanying the textbook, Climate Change, part of Global System Science (GSS), an interdisciplinary course for high school students that emphasizes how scientists from a wide variety of fields work together to understand significant problems of global impact.

306

NASA's Radiation Belt Storm Probe Mission  

NASA Technical Reports Server (NTRS)

NASA's Radiation Belt Storm Probe (RBSP) mission, comprising two identically-instrumented spacecraft, is scheduled for launch in May 2012. In addition to identifying and quantifying the processes responsible for energizing, transporting, and removing energetic particles from the Earth's Van Allen radiation, the mission will determine the characteristics of the ring current and its effect upon the magnetosphere as a whole. The distances separating the two RBSP spacecraft will vary as they move along their 1000 km altitude x 5.8 RE geocentric orbits in order to enable the spacecraft to separate spatial from temporal effects, measure gradients that help identify particle sources, and determine the spatial extent of a wide array of phenomena. This talk explores the scientific objectives of the mission and the manner by which the mission has been tailored to achieve them.

Sibeck, David G.

2011-01-01

307

Dynamical Maps of the Inner Asteroid Belt  

NASA Astrophysics Data System (ADS)

We construct the dynamic portrait of the inner asteroidal belt using the information about the distribution of the test particles, which were initially placed on a perfectly rectangular grid of initial conditions, after 4.2 Myr of gravitational interactions with the Sun and five planets, from Mars to Neptune. Using the Spectral Analysis Method introduced by Michtchenko et al. (2002), we illustrate the asteroidal behaviour on the dynamical maps. We superpose over the maps the information on the proper elements and proper frequencies of the real objects, extracted from the database AstDyS (Milani & Kneževi? 1994; Kneževi? & Milani 2003). The comparison of the maps with the distribution of the real objects allows us to detect possible dynamical mechanisms acting in the domain under study: these mechanisms are related to mean-motion and secular resonances. Their long-lasting action, overlaying with the Yarkovsky effect, may explain many observed features of the distribution of the asteroids.

Michtchenko, Tatiana A.; Lazzaro, Daniela; Carvano, Jorge M.; Ferraz-Mello, Sylvio

308

The Foundations of Radiation Belt Research  

NASA Astrophysics Data System (ADS)

The United States undertook the launching of an artificial Earth satellite as part of its contribution to the International Geophysical Year. The Vanguard program was established to meet that commitment, and it developed a launch vehicle, ground station network, and suite of scientific payloads, including the cosmic ray experiment proposed by James A. Van Allen. Although Vanguard eventually exceeded all of its pre-stated goals, the preemptive launches of Sputniks I and II by the Soviets in October and November 1957 spurred the U.S. into a frenzy of activity, resulting in the launches of Explorers I and III in January and March of 1958. The data from those two satellites quickly revealed the lower boundary of an unexpected region of high intensity radiation trapped in the Earth's magnetic field. The original announcement in May 1958 stated that the radiation was probably composed of either protons or electrons, and that, if electrons, it was probably bremsstrahlung formed in the satellite shell. Immediately following that announcement, approval was received for what became Explorer IV, whose announced purpose was to follow up on the new discovery. Another reason for the satellite, unmentioned at the time, was its inclusion as a component of the highly classified Argos program, a covert military program to test whether the detonation of nuclear devices at high altitude would inject measurable numbers of charged particles into durable trajectories in the Earth's magnetic field. Our team at Iowa produced the satellites under the oversight of, and with assistance by, the Army Ballistic Missile Agency in Huntsville, and with the contributions of key hardware from several other government laboratories. The project was completed in the unbelievably short period of seventy-seven days from approval to launch. Launched into a higher-inclination orbit than the earlier Explorers, Explorer IV confirmed the discovery and greatly expanded our understanding of the natural phenomenon. It also provided the first hint that there were two distinct radiation belts, although that conclusion was not reached until later. Although that new information was quickly announced, the results of the high altitude nuclear detonations were kept secret until well into 1959. They clearly revealed the charged particle shells created by the Argos nuclear detonations. The next major step in mapping and understanding the high-intensity radiation involved the launch of deep space probes Pioneers III and IV in December 1958 and March 1959. Although both launches fell short in their primary objective, to reach the moon, they traveled far enough from the Earth to fully meet the needs of the scientific experiment. They very clearly showed the two-radiation belt structure, and mapped its extent. They also showed the probable effect of a magnetic storm on 25 February, thus indicating the direct influence of solar activity on the outer belt. By the end of 1959, the existence of the Van Allen Radiation Belts and their general structure were solidly established, early information about the composition of the radiation was appearing in print, and energetic work was under way to understand the physics of the processes involved.

Ludwig, G. H.

2008-12-01

309

Ambient tremors in a collisional orogenic belt  

NASA Astrophysics Data System (ADS)

tectonic tremors have been regarded as an observation tied to interconnected fluids at depth, which have been well documented in worldwide subduction zones and transform faults but not in a collisional mountain belt. In this study we explore the general features of collisional tremors in Taiwan and discuss the possible generation mechanism. In the 4 year data, we find 231 ambient tremor episodes with durations ranging from 5 to 30 min. In addition to a coseismic slip-induced stress change from nearby major earthquake, increased tremor rate is also highly correlated with the active, normal faulting earthquake swarms at the shallower depth. Both the tremor and earthquake swarm activities are confined in a small, area where the high attenuation, high thermal anomaly, the boundary between high and low resistivity, and localized veins on the surfaces distributed, suggesting the involvement of fluids from metamorphic dehydration within the orogen.

Chuang, Lindsay Yuling; Chen, Kate Huihsuan; Wech, Aaron; Byrne, Timothy; Peng, Wei

2014-03-01

310

The Relative Sizes of Kuiper Belt Binaries  

NASA Astrophysics Data System (ADS)

Nearly 40 binary and multiple systems are now known in the Kuiper Belt. Most of these consist of similar-sized components; for some it is problematic to define a primary and a secondary. Systems with faint companions do exist. In the Pluto system, the most extreme example known, the two newly identified satellites are approximately 9 magnitudes fainter than Pluto. Observational bias favors the detection of bright secondaries, especially in low or modest S/N observations, a common occurrence in the observation of transneptunian objects. Because of this bias, it has not been clear whether the apparent preference for similar-sized components in binaries is real or an observational artifact. In the last year we have made very deep observations of 61 Centaurs and TNOs using the Hubble Space Telescope High Resolution Camera. These observations have 3-sigma detection limits of visual magnitude 27.5 or fainter. This is the first large data set capable of assessing the relative frequency of symmetric (similar brightness) and asymmetric (large brightness differences) binaries. Our data show a clear and significant preference for companions that have a 1 magnitude or smaller difference compared to the primary. This result confirms the qualitative prediction of the chaos-assisted model for binary formation (Astakhov et al. 2005, MRAS 360, 401) and supports the contention that most of the bound systems in the Kuiper Belt formed via mutual capture. Asymmetric systems may, in contrast, be the result of collisional formation as is postulated for the Pluto system (Stern et al. 2006, Nature, 439, 946). Based on observations made with the NASA/ESA Hubble Space Telescope program #10514. Support for program #10514 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Noll, Keith S.; Grundy, W. M.; Levison, H. F.; Stephens, D. C.

2006-09-01

311

Giant Kuiper Belt Object (20000) Varuna  

NASA Astrophysics Data System (ADS)

Through a concerted observational campaign using optical and submillimeter telescopes on Mauna Kea, we have determined the size, albedo, color, rotation period, and sky-plane projected axis ratio of Kuiper Belt Object (20000) Varuna. We find a large (diameter = 900+/-140 km), elongated (axis ratio 1.5:1) and dark object (red albedo 0.07(+0.03/-0.02)) with a uniformly reddish surface (V-R = 0.64 +/-0.01) in a state of rapid rotation (period P = 6.3442+/-0.0002 hr). The large size, short period and elongated shape suggest that Varuna is rotationally distorted. If so, the best fitting Jacobi ellipsoid equilibrium model yields a bulk density of only 1000 kg/m-3. Given that water and denser, refractory materials must be present in cosmic proportions, this low bulk density requires an internal void space (porosity) of 10% to 30%. Varuna may be a rotationally distorted rubble pile, with a weak and porous internal constitution due to fracturing by ancient impacts. The high specific angular momentum implied by our observations and recent detections of several binary trans-Neptunian objects both point to an early, intense collisional epoch in which large trans-Neptunian objects were 100 times more abundant than now. This epoch presumably coincided with the termination of the growth phase in the Kuiper Belt. Work supported by the National Science Foundation. Jewitt, D., Aussel, H., and Evans, A. (2001). Nature, 411, 446-447. Jewitt, D. and Sheppard, S. (2002). Astronomical Journal, 123, 2110-2120.

Jewitt, D.; Sheppard, S.; Aussel, H.

2002-09-01

312

Evolutionary Models of Main Belt Comets  

NASA Astrophysics Data System (ADS)

The discovery of the new class of objects, known as Main Belt Comets (MBCs), raises several questions regarding their structure, composition and origin. Whether MBCs were formed in their present location or captured from more distant regions during the early bombardment era is still debated; either way, they have spent most of their lifetimes in the main belt, which has been considered too hot for ice to survive for any length of time. The low conductivity of porous cometary material suggests, however, that ice may be retained in the interior of MBCs, despite continual insolation. We show results of long-term evolutionary calculations for a model representing MBC 133P/Elst-Pizarro, considering different mixtures of ices and dust. The main conclusion is that crystalline water ice may survive at depths of 50-150m, but other volatiles will be completely lost. We then show results of a parameter study addressing the ice survival question by means of long-term evolution calculations for a range of initial parameters: radii between 150m and 2.5km, two different density values, and two different orbits. We find that small bodies (< 600m in radius) may completely lose the ice over the age of the Solar System, especially if the density is low and they are relatively close to the Sun. By contrast, in larger bodies (a few km in size) that may have been captured or collisionally formed only 100 Myr ago, ice may be found at depths of only 10m. Such bodies could be easily activated by collisions to exhibit cometary activity. Finally, we investigate the effect of spin and latitude on the depth at which ice may be found and show that near the poles ice may survive quite close to the surface.

Prialnik, Dina; Sarid, G.; Meech, K.; Assis, A.

2012-01-01

313

Road traffic noise attenuation by belts of trees  

NASA Astrophysics Data System (ADS)

Measurements were made at a number of sites of road traffic noise propagating through belts of trees and bushes and above grass-covered ground, respectively. The belt widths were between 3 and 25 m. The distance from the road to the front of the belts also varied from site to site. The microphones were placed 1·5 m above the ground. A comparison between attenuations obtained, expressed as differences in equivalent constant A-weighted sound pressure levels, LAeq, showed no significantly higher attenuation values for propagation through belts of trees than for propagation above grass-covered ground. Only in the frequency range above 2 kHz were attenuations significantly higher through the belts of trees and bushes. The belts of trees selected consisted mainly of deciduous trees and bushes between 5 and 10 years of age. Such types and widths are representative of what could often be used in normal urban situations in an attempt to provide practical noise reduction. According to the results of this investigation, however, these do not significantly reduce LAeq 1·5 m above the ground. Planting of belts of trees and bushes between roads and dwellings might influence the environmental quality of residential areas due to nonacoustic factors or reduce nuisance due to spectral changes not affecting LAeq. This has not been investigated.

Kragh, J.

1981-01-01

314

Untangling complex processes within Earth's radiation belts with the Radiation Belt Storm Probes (RBSP) mission  

NASA Astrophysics Data System (ADS)

Progress towards developing a predictive understanding of Earth's dynamic radiation belts requires that we: 1) better understand individual transport and energization mechanisms, and 2) better understand how these mechanisms act together to yield the complex behaviors that are observed. An example of the former imperative is to understand the extent to which non-linearities modify the role that whistler mode waves play in exchanging energy with and scattering radiation belt electrons. However, the latter imperative represents a greater challenge. What is the relationship between processes that supply electron source populations and those that generate the Ultra Low Frequency waves that can help transport those particles? What is the role of substorm injections in creating or modifying the global electric fields that transport and redistribute the injected plasma populations? How dependent is the wave activity that energizes radiation belt electrons on the global electric field that creates the conditions for wave generation? Two characteristics of the Radiation Belt Storm Probes (RBSP) mission will enable researchers to address these interdependent mechanisms. First, the payload complement is unusually comprehensive, measuring all of the particle (electrons, ions, ion composition), fields (E and B), and wave distributions (dE and dB) needed to address the most critical science questions. However, the ability of the two RBSP spacecraft to make multiple, identical, and simultaneous measurements over a wide range of spatial scales is even more critical. RBSP comprises two spacecraft making in situ measurements for at least 2 years in nearly the same highly elliptical, low inclination orbits (1.1 x 5.8 RE, 10 degrees). The orbits are slightly different so that 1 spacecraft laps the other spacecraft about every 2.5 months, allowing separation of spatial from temporal affects over spatial scales ranging from ~0.1 to 5 RE. Here we discuss how the unique capabilities of the RBSP mission, when combined with a multiplicity of other serendipitous assets, will resolve the interdependent mechanisms that determine the complex behavior of the radiation belts.

Mauk, B. H.; Fox, N. J.; Sibeck, D. G.; Kanekal, S. G.; Kessel, R.

2011-12-01

315

The Fossilized Size Distribution of the Main Asteroid Belt  

NASA Astrophysics Data System (ADS)

The main asteroid belt evolved into its current state via two processes: dynamical depletion and collisional evolution. During the planet formation epoch, the primordial main belt (PMB) contained several Earth masses of material, enough to allow the asteroids to accrete on relatively short timescales (e.g., Weidenschilling 1977). The present-day main belt, however, only contains 5e-4 Earth masses of material (Petit et al. 2002). To explain this mass loss, we suggest the PMB evolved in the following manner: Planetesimals and planetary embryos accreted (and differentiated) in the PMB during the first few Myr of the solar system. Gravitational perturbations from these embryos dynamically stirred the main belt, enough to initiate fragmentation. When Jupiter reached its full size, some 10 Myr after the solar system's birth, its perturbations, together with those of the embryos, dynamically depleted the main belt region of > 99% of its bodies. Much of this material was sent to high (e,i) orbits, where it continued to pummel the surviving main belt bodies at high impact velocities for more than 100 Myr. While some differentiated bodies in the PMB were disrupted, most were instead scattered; only small fragments from this population remain. This period of comminution and dynamical evolution in the PMB created, among other things, the main belt's wavy size-frequency distribution, such that it can be considered a "fossil" from this violent early epoch. From this time forward, however, relatively little collisional evolution has taken place in the main belt, consistent with the surprising paucity of prominent asteroid families. We will show that the constraints provided by asteroid families and the shape of the main belt size distribution are essential to obtaining a unique solution from our model's initial conditions. We also use our model results to solve for the asteroid disruption scaling law Q*D, a critical function needed in all planet formation codes that include fragmentation between rocky planetesimals.

Bottke, W. F.; Durda, D.; Nesvorny, D.; Jedicke, R.; Morbidelli, A.

2004-05-01

316

Kuiper Belt Objects Along the Pluto-Express Path  

NASA Technical Reports Server (NTRS)

The science objective of this work is to identify objects in the Kuiper Belt which will, in the 5 years following Pluto encounter, be close to the flight path of NASA's Pluto Express. Our hope is that we will find a Kuiper Belt object or objects close enough that a spacecraft flyby will be possible. If we find a suitable object, the science yield of Pluto Express will be substantially enhanced. The density of objects in the Kuiper Belt is such that we are reasonably likely to find an object close enough to the flight path that on-board gas thrusters can effect a close encounter.

Jewitt, David (Principal Investigator)

1997-01-01

317

Reassessing the biogenicity of Earth's oldest trace fossil with implications for biosignatures in the search for early life  

PubMed Central

Microtextures in metavolcanic pillow lavas from the Barberton greenstone belt of South Africa have been argued to represent Earth’s oldest trace fossil, preserving evidence for microbial life in the Paleoarchean subseafloor. In this study we present new in situ U–Pb age, metamorphic, and morphological data on these titanite microtextures from fresh drill cores intercepting the type locality. A filamentous microtexture representing a candidate biosignature yields a U–Pb titanite age of 2.819 ± 0.2 Ga. In the same drill core hornfelsic-textured titanite discovered adjacent to a local mafic sill records an indistinguishable U–Pb age of 2.913 ± 0.31 Ga, overlapping with the estimated age of intrusion. Quantitative microscale compositional mapping, combined with chlorite thermodynamic modeling, reveals that the titanite filaments are best developed in relatively low-temperature microdomains of the chlorite matrix. We find that the microtextures exhibit a morphological continuum that bears no similarity to candidate biotextures found in the modern oceanic crust. These new findings indicate that the titanite formed during late Archean ca. 2.9 Ga thermal contact metamorphism and not in an early ca. 3.45 Ga subseafloor environment. We therefore question the syngenicity and biogenicity of these purported trace fossils. It is argued herein that the titanite microtextures are more likely abiotic porphyroblasts of thermal contact metamorphic origin that record late-stage retrograde cooling in the pillow lava country rock. A full characterization of low-temperature metamorphic events and alternative biosignatures in greenstone belt pillow lavas is thus required before candidate traces of life can be confirmed in Archean subseafloor environments.

Grosch, Eugene G.; McLoughlin, Nicola

2014-01-01

318

Reassessing the biogenicity of Earth's oldest trace fossil with implications for biosignatures in the search for early life.  

PubMed

Microtextures in metavolcanic pillow lavas from the Barberton greenstone belt of South Africa have been argued to represent Earth's oldest trace fossil, preserving evidence for microbial life in the Paleoarchean subseafloor. In this study we present new in situ U-Pb age, metamorphic, and morphological data on these titanite microtextures from fresh drill cores intercepting the type locality. A filamentous microtexture representing a candidate biosignature yields a U-Pb titanite age of 2.819 ± 0.2 Ga. In the same drill core hornfelsic-textured titanite discovered adjacent to a local mafic sill records an indistinguishable U-Pb age of 2.913 ± 0.31 Ga, overlapping with the estimated age of intrusion. Quantitative microscale compositional mapping, combined with chlorite thermodynamic modeling, reveals that the titanite filaments are best developed in relatively low-temperature microdomains of the chlorite matrix. We find that the microtextures exhibit a morphological continuum that bears no similarity to candidate biotextures found in the modern oceanic crust. These new findings indicate that the titanite formed during late Archean ca. 2.9 Ga thermal contact metamorphism and not in an early ca. 3.45 Ga subseafloor environment. We therefore question the syngenicity and biogenicity of these purported trace fossils. It is argued herein that the titanite microtextures are more likely abiotic porphyroblasts of thermal contact metamorphic origin that record late-stage retrograde cooling in the pillow lava country rock. A full characterization of low-temperature metamorphic events and alternative biosignatures in greenstone belt pillow lavas is thus required before candidate traces of life can be confirmed in Archean subseafloor environments. PMID:24912193

Grosch, Eugene G; McLoughlin, Nicola

2014-06-10

319

The color of the Kuiper belt Core  

NASA Astrophysics Data System (ADS)

Recent dynamical analyses of the Kuiper belt have introduced a rigorous classification scheme, determined the mean orbital plane, and identified "Core" and "Halo" populations as a function of inclination with respect to this plane (Elliot, J.L., Kern, S.D., Clancy, K.B., Gulbis, A.A.S., Millis, R.L., Buie, M.W., Wasserman, L.H., Chiang, E.I., Jordan, A.B., Trilling, D.E., Meech, K.J., 2005. Astron. J. 129, 1117-1162). Here, we use new observations and existing data to investigate the colors of Kuiper belt objects (KBOs) within this framework. With respect to the bulk KBO color distribution (all objects for which we have B-V and V-R colors; median B-R=1.56), we find that the population of objects classified following (Elliot, J.L., Kern, S.D., Clancy, K.B., Gulbis, A.A.S., Millis, R.L., Buie, M.W., Wasserman, L.H., Chiang, E.I., Jordan, A.B., Trilling, D.E., Meech, K.J., 2005. Astron. J. 129, 1117-1162) as Classical tends to be red ( B-R>1.56) while the Scattered Near population is mostly neutral ( B-R<1.56). Colors of Scattered Extended and Resonant objects are consistent with the bulk distribution. Separating objects into specific resonances demonstrates that the color of the Resonant sample is dominated by KBOs in the 3:2 resonance, which is consistent with previous findings. Unlike the objects in the 3:2 resonance, however, the majority of objects in the 5:2 resonance are neutral and all but one of the objects in the 4:3, 5:3, 7:4, 2:1, and 7:3 resonances are red. In particular, the objects in the 7:4 resonance are remarkably red. We find that the colors of KBOs in the Core (low-inclination) and Halo (high-inclination) are statistically different, with Core objects being primarily red and Halo objects having a slight tendency to be neutral. Notably, virtually all of the non-Resonant Core objects are red. This combination of low inclination, unperturbed orbits and red colors in the Core may be indicative of a relic grouping of objects.

Gulbis, Amanda A. S.; Elliot, J. L.; Kane, Julia F.

2006-07-01

320

Continuing scearch for a new type charging belt  

SciTech Connect

The EN Tandem accelerator at Oak Ridge National Laboratory (ORNL) operates to support a varied program of atomic physics research. As such, the demands on the accelerator often require a range of operation from {approximately}0.38 to 7.0 MV on the terminal, with low ripple and long term steady state operation. The standard charging belts obtained from the manufacture have generally given acceptable performance, but it is reasonable that modem manufacturing techniques and materials could increase belt lifetimes and improve accelerator performance, particularly voltage ripple. A new belt of significantly different construction from that of the conventional belts was specified, purchased, and installed in 1993. After 2800 hours of use at voltages from 0.38 to 5.8 MV, it was removed from the accelerator in early August 1995.

Jones, N.L.

1995-12-31

321

30 CFR 75.350 - Belt air course ventilation.  

Code of Federal Regulations, 2013 CFR

...Effective December 31, 2009, the air velocity in the belt entry must be at least...district manager may approve lower velocities in the ventilation plan based on specific mine conditions. Air velocities must be compatible with all...

2013-07-01

322

76. Credit FM. Detail showing belts running from water wheel ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

76. Credit FM. Detail showing belts running from water wheel to governor and from water wheel to tachometer (foreground). - Battle Creek Hydroelectric System, Battle Creek & Tributaries, Red Bluff, Tehama County, CA

323

30 CFR 57.15005 - Safety belts and lines.  

Code of Federal Regulations, 2013 CFR

...2013-07-01 2013-07-01 false Safety belts and lines. 57.15005 Section 57.15005 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH...

2013-07-01

324

Design Study of Flat Belt CVT for Electric Vehicles.  

National Technical Information Service (NTIS)

A continuously variable transmission (CVT) was studied, using a novel flat belt pulley arrangement which couples the high speed output shaft of an energy storage flywheel to the drive train of an electric vehicle. A specific CVT arrangement was recommende...

E. L. Kumm

1980-01-01

325

30 CFR 57.4263 - Underground belt conveyors.  

Code of Federal Regulations, 2013 CFR

...STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Fire Prevention and Control Firefighting Equipment § 57... Underground belt conveyors. Fire protection shall be provided...shall be made for extinguishing fires along the beltline. Fire...

2013-07-01

326

Bunkhouse basement interior showing storage area and a conveyor belt ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Bunkhouse basement interior showing storage area and a conveyor belt (circa 1936) used to unload dry goods into the basement through an opening on the east side of the bunkhouse. - Sespe Ranch, Bunkhouse, 2896 Telegraph Road, Fillmore, Ventura County, CA

327

45. INTERIOR VIEW SHOWING CONVEYOR BELT SYSTEM WHICH CONVEY THE ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

45. INTERIOR VIEW SHOWING CONVEYOR BELT SYSTEM WHICH CONVEY THE HARDENED NAILS TO THE DRAWBACK TUBE FOR TEMPERING; MOTIONED STOPPED - LaBelle Iron Works, Thirtieth & Wood Streets, Wheeling, Ohio County, WV

328

Nanomaterial modifications on conductivity of coal conveyer belt  

SciTech Connect

By analyzing the macro electrical properties and the microscopic structure from SEM of nanomaterials modified mine transmission belt samples. The influences of the filling process of inorganic nano particle-filled rubber and PVC polymer on the physical properties of coal transmission belt is reviewed, as well as PTC and NTC effect on the stability of the physical properties and stability of materials. Influence of nano-materials and polymer materials for rubber and temperature changes in the plastic filled refining process. Crosslinker and major filler changes in the amount and filled plastic chain time on the conductivity of coal conveyer belt is studied. Influence of cure temperature. Cure time on the mechanical performance is studied. The microscopic mechanism of macro conductivity change of conveyer belt is discussed.

Zhang, J.C.; Zhang, Y.G.; Wang, T.T.; Yang, L.F.; Liu, S.M.; Yang, D.H.; Zhang, M.; Gao, X. [Zhongyuan University of Technology, Zhengzhou (China)

2008-08-15

329

56. Rock Belt Line, Transfer Building, date unknown Historic Photograph, ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

56. Rock Belt Line, Transfer Building, date unknown Historic Photograph, Photographer Unknown; Collection of William Everett, Jr.(Wilkes-Barre, PA), photocopy by Joseph E.B. Elliot - Huber Coal Breaker, 101 South Main Street, Ashley, Luzerne County, PA

330

Jupiter's radiation belt ions - A comparison of theory and observation  

NASA Technical Reports Server (NTRS)

Radial profiles are constructed for the Jovian radiation belt flux-tube content Y-asterisk from the reported phase-space density of energetic particles obtained from Voyager 1 data over the range L = 6 to L = 9. These experimental profiles are compared with theoretical solutions for Y-asterisk from an interchange-diffusion model of the coupled radiation belt and Iogenic ion populations. Subject to certain limitations of the Voyager 1 data, the model solutions are found to be consistent with the data for a variety of input parameters. Model solutions are also found corresponding to radiation belt ions that are expected to be mainly responsible for the auroral energy input. Comparison of the present theoretical profiles with the data implies that the energetic radiation belt ions should have a peak loss rate within a factor of three of that for strong diffusion scattering.

Summers, Danny; Thorne, Richard M.; Mei, YI

1989-01-01

331

The IRBEM library -- open source tools for radiation belt modeling  

NASA Astrophysics Data System (ADS)

The COSPAR Panel on Radiation Belt Models sponsors an open-source library of software routines for radiation belt modeling, the International Radiation Belt Models (IRBEM) library (irbem.sf.net). Descended from the ONERA-DESP library, the IRBEM library contains primarily Fortran routines for magnetic field model evaluation and tracing, coordinate transforms, orbit propagation, radiation models, and neutral atmosphere models. The library can be accessed from several popular languages via a dynamic linked library (DLL) interface. Extra capabilities that have not been integrated into the library are provided for computing particle diffusion coefficients, training and evaluating neural networks, evaluating instrument response functions, inverting particle measurements from data channels to flux spectra, fast nearest-neighbors look-ups, and sharing structured data between high level languages. The IRBEM library continues to grow to meet the changing needs of radiation belt researchers.

O'Brien, P. P.; Bourdarie, S.

2012-12-01

332

Small Main-Belt Asteroid Spectroscopic Survey: Initial Results  

Microsoft Academic Search

The spectral characterization of small asteroids is important for understanding the evolution of their compositional and mineralogical properties. We report the results of a CCD spectroscopic survey of small main-belt asteroids which we call the Small Main-belt Asteroid Spectroscopic Survey (SMASS). Spectra of 316 asteroids were obtained, with wavelength coverage ranging from 4000 to 10000 Å (0.4 to 1 ?m).

Shui Xu; Richard P. Binzel; Thomas H. Burbine; Schelte J. Bus

1995-01-01

333

A modular radiation-belt electron flux model  

Microsoft Academic Search

We present a time-dependent model for the energetic electron flux in Earth's radiation belts developed from measurements by several spacecraft in the radiation belts (POLAR, SAMPEX, Akebono, HEO, and GOES) and the solar wind (ACE, WIND). The flux is a function of L shell (1-11), particle energy (0.8-6.4 MeV) and time. A different module is developed for each one of

D. Vassiliadis; D. N. Baker; S. F. Fung; S. G. Kanekal; E. J. Rigler; R. S. Selesnick; R. S. Weigel

2006-01-01

334

“Abomination”—Life as a Bible Belt Gay  

Microsoft Academic Search

Drawing on observation, autoethnography, and audio-taped interviews, this article explores the religious backgrounds and experiences of Bible Belt gays. In the Bible Belt, Christianity is not confined to Sunday worship. Christian crosses, messages, paraphernalia, music, news, and attitudes permeate everyday settings. Consequently, Christian fundamentalist dogma about homosexuality—that homosexuals are bad, diseased, perverse, sinful, other, and inferior—is cumulatively bolstered within a

Bernadette Barton

2010-01-01

335

Castalia: A European Mission to a Main Belt Comet  

NASA Astrophysics Data System (ADS)

Main Belt Comets (MBCs) are a newly found population in the main asteroid belt. A spacecraft mission to MBCs can provide key insights into the formation and evolution of the planetary system and the early evolution of Earth. The scientific key questions of the mission, its instrumentation and mission profile is studied with the goal to prepare for future mission calls of international space agencies.

Boehnhardt, H.

2013-09-01

336

Kuiper Belt Objects Along the Pluto Express Path  

NASA Technical Reports Server (NTRS)

The objective of this proposal was to mount a ground-based search for Kuiper Belt objects near the trajectory of the NASA Pluto Express spacecraft. The high density of Kuiper Belt objects established from work on Mauna Kea makes it probable that one or more bodies can be visited by Pluto Express after its encounter with Pluto. The work was funded during its first year through NASA HQ. The second year was funded through Goddard. The third year was never funded.

Jewitt, David

1999-01-01

337

Folded-belts - petroleum systems of Northern South America  

SciTech Connect

A series of seismic reflection profiles allow to document the styles, timing and relevant characteristics to the petroleum systems associated with the folded belts along northern South America. These mountain systems are responsible for the partial destruction of the thin Cretaceous Atlantic type passive margin, and as the northern source of sediments for the Tertiary Venezuelan foredeeps. The passive margin is only preserved at the far-east limit of the Eastern Venezuela Basin, east of the Orinoco Delta. This margin became progressively deformed to the West, where a Neogene segment of a thin-skin south-vergent folded belt is reported as the Eastern Serrania del Interior, which is in turn coupled to the evolution of the Maturin Foredeep. Westwardly, the Late Paleogene-Early Neogene Guarico Foredeep is tied to the emplacement of a basement involved folded belt, the Western Serrania del Interior. West of the El Baul High, a two stage folded belt is coupled to the Barinas Foredeep. A first phase corresponds to the Eocene south vergent Lara Nappes, and a satellite Foredeep due to the north-vergent emplacement of the basement involved Late Neogene Merida Andes. Farther west, the Apure-Llanos sub-basin is developed from an Early Paleogene basement-involved folded belt, modified to its present configuration by a Neogene reactivation of the east-vergent Eastern Cordillera of Colombia. These folded belts have unique conditions defining the petroleum systems but always had been related to the Late Cretaceous source rocks.

Audemard, F.P. [PDVSA, Caracas (Venezuela)

1996-08-01

338

Emission products from combustion of conveyor belts. Information Circular/1988  

SciTech Connect

A series of experiments was undertaken by the Bureau of Mines to determine the emission products of several types of conveyor belting and other combustible materials found in mines. These experiments were conducted under intermediate-scale, simulated mine conditions to determine smoke characteristics and gas concentrations. From these determinations, heat-release rates, particle sizes, obscuration rates, combustion yields, and production constants were calculated. Three types of belts were investigated: chloroprene, also known as neoprene (NP); polyvinyl chloride (PVC); and styrene-butadiene rubber (SBR). The belts were designated as ignitable or self-extinguishing depending on the length of the burning time and the subsequent combustion products. Under these experimental conditions, the SBR belts were the easiest to ignite. The PVC and NP belts tended to self-extinguish within a few minutes after ignition, but were still capable of maintaining a brief flaming period. These conveyor belt combustion results are compared with previous analyses of wood, transformer fluid, and coal fires. Together they form a data base by which findings from future experiments with other mine combustibles can be compared.

Egan, M.R.

1988-01-01

339

Collisional velocities and rates in resonant planetesimal belts  

NASA Astrophysics Data System (ADS)

We consider a belt of small bodies (planetesimals, asteroids, dust particles) around a star, captured in one of the external or 1:1 mean-motion resonances with a massive perturber (protoplanet, planet). The objects in the belt collide with each other. Combining methods of celestial mechanics and statistical physics, we calculate mean collisional velocities and mean collisional rates, averaged over the belt. The results are compared to collisional velocities and rates in a similar, but non-resonant belt, as predicted by the particle-in-a-box method. It is found that the effect of the resonant lock on the velocities is rather small, while on the rates more substantial. At low to moderate eccentricities and libration amplitudes of tens of degrees, which are typical of many astrophysical applications, the collisional rates between objects in an external resonance are by about a factor of two higher than those in a similar belt of objects not locked in a resonance. For Trojans under the same conditions, the collisional rates may be enhanced by up to an order of magnitude. The collisional rates increase with the decreasing libration amplitude of the resonant argument, depend on the eccentricity distribution of objects, and vary from one resonance to another. Our results imply, in particular, shorter collisional lifetimes of resonant Kuiper belt objects in the solar system and higher efficiency of dust production by resonant planetesimals in debris disks around other stars.

Queck, Martina; Krivov, Alexander V.; Srem?evi?, Miodrag; Thébault, Philippe

2007-11-01

340

Tectonic setting of the Kolar Schist Belt, Karnataka, India  

NASA Technical Reports Server (NTRS)

The tectonic setting of the Kolar Schist Belt and why the belt may represent a late Archean suture was discussed. The isotopic and chronological evidence that suggest diverse origins of the various packages of supracrustal rocks within the schist belt and the two gneiss terrains adjoining the belt were summarized. The eastern and western amphibolites were derived from sources at similar depths in the mantle (probably at similar ages, ca. 2.7 Ga), but these sources had distinct trace element compositions and histories. A distinctive feature of these differences was shown by the differences between the east and west amphibolites on a Ce vs. Nd diagram. In the gneisses the age and isotopic evidence suggest that the two terranes had distinct histories until after 2520 Ma and by 2420 Ma (Ar-40/Ar-39 age of muscovite in the sheared margin of the schist belt). Based on these data, the schist belt probably represents the site of accretion of diverse fragments (terrains) to the margin of the craton in the latest Archean, possibly as an Archean analog to the Phanerozoic North American Cordillera.

Hanson, G. N.; Krogstad, E. J.; Rajamani, V.

1988-01-01

341

Non-Linear Vibration of Power Transmission Belts  

NASA Astrophysics Data System (ADS)

Non-linear vibration of a prototypical power transmission belt system, which is excited by pulleys having slight eccentricity, is investigated through experimental and analytical methods. Laboratory measurements demonstrate the role of non-linearity in setting the belt's response, particularly in the near-resonance region, and at high running speeds. The belt is coated with a retroreflective medium so as to improve displacement and velocity measurements made through non-contact laser interferometry. A frequency crossing diagram relates the belt's speed-dependent excitation and natural frequencies, and is shown to be useful for identifying those speeds at which resonance is expected. Distinctive jump and hysteresis phenomena in the near-resonant response are observed experimentally, and are also studied with a model that includes non-linear stretching of the belt. In that regard, a modal perturbation solution is developed in the context of the asymptotic method of Krylov, Bogoliubov and Mitropolsky for a general, continuous, non-autonomous, gyroscopic system with weakly non-linear stiffness. The solution is subsequently specialized to the belt vibration problem at hand. Near- and exact-resonant response amplitudes are predicted by the perturbation method, and they are compared with those obtained by laboratory tests and by direct numerical simulation of the non-linear model.

Moon, J.; Wickert, J. A.

1997-03-01

342

Repeal of the Massachusetts seat belt law.  

PubMed Central

In November 1986, the Massachusetts mandatory seat belt use law repealed in a referendum by a 53 per cent to 47 per cent vote. In an anonymous random digit telephone survey of 1,046 adults in Massachusetts in summer 1986, while the law was in effect, 61 per cent of respondents had said they would vote in favor of the law. A post-repeal follow-up of 80 per cent of these persons revealed initial supporters and opponents of the law were equally likely to vote, but 15 per cent of the summer supporters switched their opinions and voted for repeal, compared to only 4 per cent of summer opponents who switched. In addition, a separate survey of 167 households that had refused to answer the summer survey indicated that survey nonrespondents were more likely to vote against the law than for it. Those opposing the law saw it as an infringement on personal liberty and believed it was not effective in reducing injury and death.

Hingson, R; Levenson, S M; Heeren, T; Mangione, T; Rodgers, C; Schiavone, T; Hertz, R P; Schiavonnet, T

1988-01-01

343

Spectroscopy of Kuiper Belt Objects and Centaurs  

NASA Astrophysics Data System (ADS)

Due to their faintness, only a small fraction of the Kuiper Belt Objects (KBOs) and Centaurs discovered so far have been studied by spectroscopy. The spectra acquired have revealed a large variety of spectral shapes. Very few of them present absorptions. Only water ice (for a few Centaurs and KBOs) and methane (for the KBO 50000 Quaoar) have been identified unambiguously at the surface of these primitive bodies. Some weak features are found in the near infrared (for the KBO 26375 (1999DE9)) as well as in the visible (for the KBOs 47932 (2000 GN171), 38628 Huya, and 2003 AZ84) that are tentatively assigned to the presence of hydrated silicates. Other features (a narrow one due to methanol ice - or ice of a similar compound -, and a broad one that could be due to olivine) appear only in spectra of the Centaur 5145 Pholus. A few objects have heterogeneous surfaces revealed by differences in spectra recorded for different rotational phases. We will review the spectroscopic investigations and modelling attempts made so far, and see what can be deduced from them. We will then evaluate the needs for additional spectral data and laboratory data to optimize the scientific return of the observations that have been carried out. Some concluding remarks on object selections for future spectroscopic investigations and target selections for space exploration will be made.

de Bergh, C.; Barucci, A.; Doressoundiram, A.; Dotto, E.

344

Trapped radiation belts of saturn: first look.  

PubMed

Pioneer 11 has made the first exploration of the magnetosphere and trapped radiation belts of Saturn. Saturn's magnetosphere is intermediate in size between Earth's and Jupiter's, with trapped particle intensities comparable to Earth's. The outer region of Saturn's magnetosphere contains lower energy radiation and is variable with time; the inner region contains higher energy particles. The pitch angle distributions show a remarkable variety of field-aligned and locally mirroring configurations. The moons and especially the rings of Saturn are effective absorbers of trapped particles; underneath the rings, the trapped radiation is completely absorbed. We confirm the discovery of a new ring, called the F ring, a new division, the Pioneer division, and a moon, called 1979 S 2. The latter has probably been seen from Earth. There may be evidence for more bodies like 1979 S 2, but at this stage the interpretation of the data is ambiguous. Using particle diffusion rates, we estimate that the cross-sectional area of the F ring is > 7 x 10(13) square centimeters and that the opacity is > 10(-5). Cosmic-ray albedo neutron decay should be looked into as a source of energetic particles in the inner magnetosphere of Saturn. PMID:17833553

Fillius, W; Ip, W H; McIlwain, C E

1980-01-25

345

Cretaceous biostratigraphy in the Wyoming thrust belt.  

USGS Publications Warehouse

In the Cretaceous section of the thrust belt, fossils are especially useful for dating and correlating repetitive facies of different ages in structurally complex terrain. The biostratigraphic zonation for the region is based on megafossils (chiefly ammonites) , which permit accurate dating and correlation of outcrop sections, and which have been calibrated with the radiometric time scale for the Western Interior. Molluscan and vertebrate zone fossils are difficult to obtain from the subsurface, however, and ammonites are restricted to rocks of marine origin. Palynomorphs (plant microfossils) have proven to be the most valuable fossils in the subsurface because they can be recovered from drill cuttings. Palynomorphs also are found in both marine and nonmarine rocks and can be used for correlation between facies. Stratigraphic ranges of selected Cretaceous marine and nonmarine palynomorphs in previously designated reference sections in Fossil Basin, Wyoming are correlated with the occurrence of ammonites and other zone fossils in the same sections. These correlations can be related to known isotopic ages, and they contribute to the calibration of palynomorph ranges in the Cretaceous of the Western Interior. -from Authors

Nichols, D. J.; Jacobson, S. R.

1982-01-01

346

Active asteroids: mystery in the Main Belt  

NASA Astrophysics Data System (ADS)

Classically, comets from the outer solar system (beyond the orbit of Neptune), are expected to be icy, and thus active near the Sun, while asteroids in the inner solar system (interior to the orbit of Jupiter) are expected to be relatively ice-deficient, and thus inert. Studies of anomalous objects, most recently 133P/Elst-Pizarro, challenge this classical picture, however, and suggest that either (1) subsurface ice can in fact be preserved over billions of years in small bodies in the inner solar system but still be close enough to the surface to be excavated by an impact by another body, or (2) non-gravitational dynamical evolution (primarily driven by asymmetrical outgassing) of icy bodies from the outer solar system can drive these cometary bodies onto thoroughly asteroid-like orbits, erasing all dynamical signs of their trans-Neptunian origins in the process. The question thus boils down to whether occasionally sublimating icy bodies on stable asteroid-like orbits in the inner solar system, particularly in the main asteroid belt, may in fact be native to the region or whether they must necessarily be recent arrivals.

Hsieh, Henry H.; Jewitt, David

347

Trapped radiation belts of Saturn: first look  

SciTech Connect

Pioneer 11 made the first exploration of the magnetosphere and trapped radiation belts of Saturn. Saturn's magnetosphere is intermediate in size between Earth's and Jupiter's, with trapped particle intensities comparable to Earth's. The outer region of Saturn's magnetosphere contains lower energy radiation and is variable with time; the inner region contains higher-energy particles. The pitch angle distributions show a remarkable variety of field-aligned and locally mirroring configurations. The moons and especially the rings of Saturn are effective absorbers of trapped particles; underneath the rings, the trapped radiation is completely absorbed. The discovery of a new ring, called the F ring, a new division, the Pioneer division, and a moon, called 1979 S 2, is confirmed. The latter has probably been seen from Earth. There may be evidence for more bodies like 1979 S 2, but at this stage the interpretation of the data is ambiguous. Estimates that the cross-sectional area of the F ring is >7 x 10/sup 13/ square centimeters and that the opacity is >10/sup -5/ were obtained with the aid of particle diffusion rates. Cosmic-ray albedo neutron decay should be looked into as a source of energetic particles in the inner magnetosphere of Saturn. 7 figures, 2 tables.

Fillius, W. (Univ. of California, San Diego); Ip, W.H.; McIlwain, C.E.

1980-01-25

348

Dynamic picture of the main asteroid belt  

NASA Astrophysics Data System (ADS)

Using the Spectral Analysis Method introduced by Michtchenko et al. (2002), we construct a dynamic portrait of the main asteroid belt. For this task, we use information extracted from the distribution of test particles (which were initially placed on a perfectly rectangular grid of initial conditions) after 4.2 Myr of gravitational interactions with the Sun and five planets, from Mars to Neptune. We illustrate in detail the asteroidal behavior on the dynamical, averaged and frequency maps. On the maps, we superpose information on the proper elements and proper frequencies of real objects, extracted from the data base, Ast- DyS (http://hamilton.dm.unipi.it/astdys), constructed by Milani and Kneževi? (2003). A comparison of the maps with the distribution of real objects allows us to detect dynamical mechanisms acting in the domain under study. These mechanisms are related to meanmotion and secular resonances. We note that the twoand three-body mean-motion resonances and the secular resonances (strong linear and weaker non-linear) play an important role in the diffusive transportation of the objects and the formation of the clumps which could be misidentified as asteroid families. The longlasting action of the resonances, overlaid with the Yarkovsky effect, may explain many observed features of the density, size and taxonomic distributions of the asteroids.

Michtchenko, T. A.; Lazzaro, D.; Carvano, J. M.; Mothé-Diniz, T.

2011-10-01

349

Magnetoinertial Oscillations of Jupiter's Inner Radiation Belt  

NASA Astrophysics Data System (ADS)

Quasi-periodic 40 minute (QP-40) bursts of both relativistic electrons (energy E~10 MeV) and radio emissions (frequency ?<~700 kHz) from the south Jovian pole were detected by the instrument onboard the Ulysses spacecraft at high jovigraphic latitudes (~30-40 S°). We show here that Jupiter's inner radiation belt (IRB) may oscillate globally with a quasi-period of ~40 minutes or so and propose that, as results of asymmetries and small-scale circumpolar magnetic irregularities/anomalies, a fraction of relativistic electrons normally trapped within the IRB may go astray from a roughly circular zone surrounding the Jovian magnetic pole during certain phases of such IRB magnetoinertial oscillations. The escaped relativistic electrons rapidly convert their transverse motions to (anti)parallel motions along the magnetic field lines by the mirror force. The observed QP-40 radio bursts are closely associated with such QP-40 leaks of relativistic electrons in near-antiparallel motions. Our prediction for QP-40 magnetoinertial oscillations of the IRB can be tested by directly observing variations of IRB decimetric brightness using ground-based radio telescopes, especially upon the arrival of high-speed solar winds at Jupiter. Several relevant aspects of this scenario are also discussed.

Lou, Yu-Qing

2001-02-01

350

Granites of southeast Asian tin belt  

SciTech Connect

The objective of this study is to establish the essential granite geology of the southeast Asian tin belt, distinguishing plutons within batholiths and characterizing them by their component units, field relationships, lithology, texture, petrology, geochemistry, geochronology, and mineral potential. To date, approximately 180 plutons have been recognized and partly or entirely described in the above terms. In addition, four granite provinces have been delineated, each with its own distinctive mineralization pattern. In all provinces, but particularly in the Main Range, granitoids designated as two-phase variants have been recognized where xenocrysts and xenoliths of coarse, primary texture granite are enclosed in and corroded by an invasive, equigranular quartzo-feldspathic matrix. These rocks form an essential part of the granite sequence in all provinces and have probably resulted from the infiltration and disruption of the host granite by late-stage magmatic fluids. Whole-rock geochemistry from peninsular Malaysia shows that the granites from the Main Range and Eastern provinces comprise two contrasted suites, which correspond approximately to the I- and S-type categories advocated by Chappell and White. In addition, individual plutons within batholiths in the two provinces have distinct geochemical parameters. Variation diagrams of plutons having the intrusive sequence primary texture granite-two-phase granite-microgranite show linear trends with increasing SiO/sub 2/, Na/sub 2/O, Rb, W, Sn, and U, and decreasing Sr, Ba, Th, and all other major elements.

Cobbing, E.J.; Mallick, D.I.J.; Pitfield, P.E.J.; Darbyshire, D.P.F.; Teoh, L.H.

1986-07-01

351

Crustal structure across the northern Cordillera, Yukon Territory, from seismic wide-angle studies: Omineca Belt to Intermontane Belt  

Microsoft Academic Search

A seismic refraction - wide-angle reflection experiment shot in 1997 in the southern Yukon Territory crosses the Omineca Belt, which includes the strike-slip Tintina Fault, and terminates within the Intermontane Belt of the northern Canadian Cordillera. Lithospheric structure is interpreted from two-dimensional forward and inverse modelling of traveltimes, combined with forward-amplitude modelling, and from 2.5-dimensional modelling of gravity data. Beneath

Brian Creaser; George Spence

2005-01-01

352

Timescale dependent deformation of orogenic belts?  

NASA Astrophysics Data System (ADS)

The principle aim to link geodetic, paleoseismologic and geologic estimates of fault slip is to extrapolate the respective rates from one timescale to the other to finally predict the recurrence interval of large earthquakes, which threat human habitats. This approach however, is based on two often implicitly made assumptions: a uniform slip distribution through time and space and no changes of the boundary conditions during the time interval of interest. Both assumptions are often hard to verify. A recent study, which analysed an exceptionally complete record of seismic slip for the Wasatch and related faults (Basin and Range province), ranging from 10 yr to 10 Myr suggests that such a link between geodetic and geologic rates might not exist, i.e., that our records of fault displacement may depend on the timescale over which they were measured. This view derives support from results of scaled 2D sandbox experiments, as well as numerical simulations with distinct elements, both of which investigated the effect of boundary conditions such as flexure, mechanic stratigraphy and erosion on the spatio-temporal distribution of deformation within bivergent wedges. We identified three types of processes based on their distinct spatio-temporal distribution of deformation. First, incremental strain and local strain rates are very short-lived are broadly distributed within the bivergent wedge and no temporal pattern could be established. Second, footwall shortcuts and the re-activation of either internal thrusts or of the retro shear-zone are irregularly distributed in time and are thus not predictable either, but last for a longer time interval. Third, the stepwise initiation and propagation of the deformation front is very regular in time, since it depends on the thickness of the incoming layer and on its internal and basal material properties. We consider the propagation of the deformation front as an internal clock of a thrust belt, which is therefore predictable. A deformation front advance cycle requires the longest timescale. Thus, despite known and constant boundary conditions during the simulations, we found only one regular temporal pattern of deformation in a steady active bivergent-wedge. We therefore propose that the structural inventory of an orogenic belt is hierarchically ordered with respect to accumulated slip, in analogy to the discharge pattern in a drainage network. The deformation front would have the highest, a branching splay the lowest order. Since kinematic boundary conditions control deformation front advance, its timing and the related maximum magnitude of finite strain, i.e. throw on the frontal thrust are predictable. However, the number of controlling factors, such as the degree of strain softening, the orientation of faults or fluid flow and resulting cementation of faults, responsible for the reactivation of faults increases with increasing distance from the deformation front. Since it is rarely possible to determine the complete network of forces within a wedge, the reactivation of lower order structures is not predictable in time and space. Two implications for field studies may emerge: A change of the propagation of deformation can only be determined, if at least two accretion cycles are sampled. The link between geodetic, paleoseismologic and geologic fault slip estimates can only be successfully derived if the position of the investigated fault within the hierarchical order has not changed over the time interval of interest.

Hoth, S.; Friedrich, A. M.; Vietor, T.; Hoffmann-Rothe, A.; Kukowski, N.; Oncken, O.

2004-12-01

353

Winds Near Jupiter's Belt-Zone Boundary  

NASA Technical Reports Server (NTRS)

Time Sequence of a belt-zone boundary near Jupiter's equator. These mosaics show Jupiter's appearance at 757 nanometers (near-infrared) and were taken nine hours apart. Images at 757 nanometers show features of Jupiter's primary visible cloud deck.

Jupiter's atmospheric circulation is dominated by alternating jets of east/west (zonal) winds. The bands have different widths and wind speeds but have remained constant as long as telescopes and spacecraft have measured them. A strong eastward jet is made visible as it stretches the clouds just below the center of this mosaic. The maximum wind speed of this jet is 128 meters per second (286 miles per hour). Features on this jet move about one quarter of the width of the mosaic. All the features visible in these mosaics are moving eastward (right).

North is at the top. The mosaic covers latitudes -13 to +3 degrees and is centered at longitude 282 degrees West. The smallest resolved features are tens of kilometers in size. These images were taken on November 5th, 1996, at a range of 1.2 million kilometers by the Solid State Imaging system aboard NASA's Galileo spacecraft.

The Jet Propulsion Laboratory, Pasadena, CA manages the mission for NASA's Office of Space Science, Washington, DC.

This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

1997-01-01

354

Super-Comet or Big Asteroid Belt?  

NASA Technical Reports Server (NTRS)

[figure removed for brevity, see original site] Figure 1: Spectrograph of HD 69830

This graph of data from NASA's Spitzer Space Telescope demonstrates that the dust around a nearby star called HD 69830 (upper line) has a very similar composition to that of Comet Hale-Bopp. Spitzer spotted large amounts of this dust in the inner portion of the HD 69830 system.

The bumps and dips seen in these data, or spectra, represent the 'fingerprints' of various minerals. Spectra are created when an instrument called a spectrograph spreads light out into its basic parts, like a prism turning sunlight into a rainbow. These particular spectra reveal the presence of the silicate mineral called olivine, and more specifically, a type of olivine called forsterite, which is pictured in the inset box. Forsterite is a bright-green gem found on Earth, on the 'Green Sand Beach' of Hawaii among other places; and in space, in comets and asteroids.

Because the dust around HD 69830 has a very similar make-up to that of Comet Hale-Bopp, astronomers speculate that it might be coming from a giant comet nearly the size of Pluto. Such a comet may have been knocked into the inner solar system of HD 69830, where it is now leaving in its wake a trail of evaporated dust.

Nonetheless, astronomers say the odds that Spitzer has caught a 'super-comet' spiraling in toward its star - an unusual and relatively short-lived event - are slim. Instead, they favor the theory that the observed dust is actually the result of asteroids banging together in a massive asteroid belt.

The data of HD 69830's dust were taken by Spitzer's infrared spectrograph. The data of Comet Hale-Bopp were taken by the European Space Agency's Infrared Observatory Satellite. The picture of forsterite comes courtesy of Dr. George Rossman, California Institute of Technology, Pasadena.

2005-01-01

355

Correlates of the belt voice: a broader examination.  

PubMed

The purpose of the present study was to further clarify a definition of belting in physiological and acoustic terms. Twenty professional female singers produced triads ascending by halftone steps from C? to C? and sang the last four measures of a popular Broadway ballad in both legit and belt styles. Vocal source differences between belt and legit singing modes were assessed with respect to closed quotient (CQ) and speed quotient (SQ) computed from the electroglottographic waveform during productions of /ma/ triads covering approximately one octave. Differences in supraglottal configuration were evaluated in terms of the ratio (dB) of the amplitudes of the first and second harmonics of /I/ sustained at the pitch A?(b), as noted in the long-term average spectrum. CQ did not vary significantly as a function of the singing type. SQ, however, decreased monotonically in association with increasing pitch level in both legit and belt singing styles. Belt mode phonations had higher SQ's than those of legit mode phonations at the same pitch. A repeated-measures analysis of variance demonstrated that the data differences associated with both pitch level and with singing mode were significant beyond P < 0.01. Analysis of the relative magnitude of the first and second harmonics showed that the direction of the harmonic ratio varied between styles. In legit singing style, H? was always stronger than H?, but this unidirectionality of amplitude was not characteristic of belt singing, for which the second harmonic had greater amplitude in 25% of the cases. Implications of these results are discussed with regard to a new definition of belting. PMID:20236798

Lebowitz, Amy; Baken, R J

2011-03-01

356

The Fossilized Size Distribution of the Main Asteroid Belt  

NASA Astrophysics Data System (ADS)

At present, we do not understand how the main asteroid belt evolved into its current state. During the planet formation epoch, the primordial main belt (PMB) contained several Earth masses of material, enough to allow the asteroids to accrete on relatively short timescales (e.g., Weidenschilling 1977). The present-day main belt, however, only contains 5e-4 Earth masses of material (Petit et al. 2002). Constraints on this evolution come from (i) the observed fragments of differentiated asteroids, (ii) meteorites collected from numerous differentiated parent bodies, (iii) the presence of ˜ 10 prominent asteroid families, (iv) the "wavy" size-frequency distribution of the main belt, which has been shown to be a by-product of substantial collisional evolution (e.g., Durda et al. 1997), and (v) the still-intact crust of (4) Vesta. To explain the contradictions in the above constraints, we suggest the PMB evolved in this fashion: Planetesimals and planetary embryos accreted (and differentiated) in the PMB during the first few Myr of the solar system. Gravitational perturbations from these embryos dynamically stirred the main belt, enough to initiate fragmentation. When Jupiter reached its full size, some 10 Myr after the solar system's birth, its perturbations, together with those of the embryos, dynamically depleted the main belt region of ˜ 99% of its bodies. Much of this material was sent to high (e,i) orbits, where it continued to pummel the surviving main belt bodies at high impact velocities for more than 100 Myr. While some differentiated bodies in the PMB were disrupted, most were instead scattered; only small fragments from this population remain. This period of comminution and dynamical evolution in the PMB created, among other things, the main belt's wavy size distribution, such that it can be considered a "fossil" from this violent early epoch. From this time forward, however, relatively little collisional evolution has taken place in the main belt, consistent with the surprising paucity of prominent asteroid families. Preliminary modeling results of this scenario and implications will be presented.

Bottke, W. F.; Durda, D.; Nesvorny, D.; Jedicke, R.; Morbidelli, A.

2003-05-01

357

The fossilized size distribution of the main asteroid belt  

NASA Astrophysics Data System (ADS)

Planet formation models suggest the primordial main belt experienced a short but intense period of collisional evolution shortly after the formation of planetary embryos. This period is believed to have lasted until Jupiter reached its full size, when dynamical processes (e.g., sweeping resonances, excitation via planetary embryos) ejected most planetesimals from the main belt zone. The few planetesimals left behind continued to undergo comminution at a reduced rate until the present day. We investigated how this scenario affects the main belt size distribution over Solar System history using a collisional evolution model (CoEM) that accounts for these events. CoEM does not explicitly include results from dynamical models, but instead treats the unknown size of the primordial main belt and the nature/timing of its dynamical depletion using innovative but approximate methods. Model constraints were provided by the observed size frequency distribution of the asteroid belt, the observed population of asteroid families, the cratered surface of differentiated Asteroid (4) Vesta, and the relatively constant crater production rate of the Earth and Moon over the last 3 Gyr. Using CoEM, we solved for both the shape of the initial main belt size distribution after accretion and the asteroid disruption scaling law QD?. In contrast to previous efforts, we find our derived QD? function is very similar to results produced by numerical hydrocode simulations of asteroid impacts. Our best fit results suggest the asteroid belt experienced as much comminution over its early history as it has since it reached its low-mass state approximately 3.9-4.5 Ga. These results suggest the main belt's wavy-shaped size-frequency distribution is a "fossil" from this violent early epoch. We find that most diameter D?120 km asteroids are primordial, with their physical properties likely determined during the accretion epoch. Conversely, most smaller asteroids are byproducts of fragmentation events. The observed changes in the asteroid spin rate and lightcurve distributions near D˜100-120 km are likely to be a byproduct of this difference. Estimates based on our results imply the primordial main belt population (in the form of D<1000 km bodies) was 150-250 times larger than it is today, in agreement with recent dynamical simulations.

Bottke, William F.; Durda, Daniel D.; Nesvorný, David; Jedicke, Robert; Morbidelli, Alessandro; Vokrouhlický, David; Levison, Hal

2005-05-01

358

Structure of possible long-lived asteroid belts  

NASA Astrophysics Data System (ADS)

High-resolution simulations are used to map out the detailed structure of two long-lived stable belts of asteroid orbits in the inner Solar system. The Vulcanoid belt extends from 0.09 to 0.20au, though with a gaps at 0.15 and 0.18au corresponding to de-stabilizing mean motion resonances with Mercury and Venus. As collisional evolution proceeds slower at larger heliocentric distances, km-sized or larger Vulcanoids are most likely to be found in the region between 0.16 and 0.18au. The optimum location to search is at geocentric ecliptic longitudes 9°<=|lg|<=10° and latitudes |?g|<1°. Dynamically speaking, the Earth-Mars belt between 1.08 and 1.28au is a stable repository for asteroids on nearly circular orbits. It is interrupted at 1.21au owing to the 3:4 commensurability with the Earth, while secular resonances with Saturn are troublesome beyond 1.17au. These detailed maps of the fine structure of the belts can be used to plan search methodologies. Strategies for detecting members of the belts are discussed, including the use of infrared wide-field imaging with VISTA, and forthcoming European Space Agency satellite missions such as GAIA and BepiColombo.

Evans, N. W.; Tabachnik, S. A.

2002-06-01

359

Angle stations in or for endless conveyor belts  

DOEpatents

In an angle station for an endless conveyor belt, there are presented to each incoming run of the belt stationary curved guide members (18, 19) of the shape of a major segment of a right-circular cylinder and having in the part-cylindrical portion (16 or 17) thereof rectangular openings (15) arranged in parallel and helical paths and through which project small freely-rotatable rollers (14), the continuously-changing segments of the curved surfaces of which projecting through said openings (15) are in attitude to change the direction of travel of the belt (13) through 90.degree. during passage of the belt about the part-cylindrical portion (16 or 17) of the guide member (18 or 19). The rectangular openings (15) are arranged with their longer edges lengthwise of the diagonals representing the mean of the helix but with those of a plurality of the rows nearest to each end of the part-cylindrical portion (16 or 17) slightly out of axial symmetry with said diagonals, being slightly inclined in a direction about the intersections (40) of the diagonals of the main portion of the openings, to provide a "toe-in" attitude in relation to the line of run of the endless conveyor belt.

Steel, Alan (Glasgow, GB6) [Glasgow, GB6

1987-04-07

360

JOVIAN EARLY BOMBARDMENT: PLANETESIMAL EROSION IN THE INNER ASTEROID BELT  

SciTech Connect

The asteroid belt is an open window on the history of the solar system, as it preserves records of both its formation process and its secular evolution. The progenitors of the present-day asteroids formed in the Solar Nebula almost contemporary to the giant planets. The actual process producing the first generation of asteroids is uncertain, strongly depending on the physical characteristics of the Solar Nebula, and the different scenarios produce very diverse initial size-frequency distributions (SFDs). In this work, we investigate the implications of the formation of Jupiter, plausibly the first giant planet to form, on the evolution of the primordial asteroid belt. The formation of Jupiter triggered a short but intense period of primordial bombardment, previously unaccounted for, which caused an early phase of enhanced collisional evolution in the asteroid belt. Our results indicate that this Jovian Early Bombardment caused the erosion or the disruption of bodies smaller than a threshold size, which strongly depends on the SFD of the primordial planetesimals. If the asteroid belt was dominated by planetesimals less than 100 km in diameter, the primordial bombardment would have caused the erosion of bodies smaller than 200 km in diameter. If the asteroid belt was instead dominated by larger planetesimals, the bombardment would have resulted in the destruction of bodies as big as 500 km.

Turrini, D.; Coradini, A.; Magni, G., E-mail: diego.turrini@ifsi-roma.inaf.it [Istituto di Astrofisica e Planetologia Spaziali, INAF-IAPS, Via Fosso del Cavaliere 100, 00133, Rome (Italy)

2012-05-01

361

Monitoring, Analyzing and Assessing Radiation Belt Loss and Energization  

NASA Astrophysics Data System (ADS)

We present the concept, objectives and expected impact of the MAARBLE (Monitoring, Analyzing and Assessing Radiation Belt Loss and Energization) project, which is being implemented by a consortium of seven institutions (five European, one Canadian and one US) with support from the European Community's Seventh Framework Programme. The MAARBLE project employs multi-spacecraft monitoring of the geospace environment, complemented by ground-based monitoring, in order to analyze and assess the physical mechanisms leading to radiation belt particle energization and loss. Particular attention is paid to the role of ULF/VLF waves. A database containing properties of the waves is being created and will be made available to the scientific community. Based on the wave database, a statistical model of the wave activity dependent on the level of geomagnetic activity, solar wind forcing, and magnetospheric region will be developed. Multi-spacecraft particle measurements will be incorporated into data assimilation tools, leading to new understanding of the causal relationships between ULF/VLF waves and radiation belt dynamics. Data assimilation techniques have been proven as a valuable tool in the field of radiation belts, able to guide 'the best' estimate of the state of a complex system. The MAARBLE (Monitoring, Analyzing and Assessing Radiation Belt Energization and Loss) collaborative research project has received funding from the European Union’s Seventh Framework Programme (FP7-SPACE-2011-1) under grant agreement no. 284520.

Daglis, I.; Balasis, G.; Bourdarie, S.; Horne, R.; Khotyaintsev, Y.; Mann, I.; Santolik, O.; Turner, D.; Anastasiadis, A.; Georgiou, M.; Giannakis, O.; Papadimitriou, C.; Ropokis, G.; Sandberg, I.; Angelopoulos, V.; Glauert, S.; Grison, B., Kersten T.; Kolmasova, I.; Lazaro, D.; Mella, M.; Ozeke, L.; Usanova, M.

2013-09-01

362

HST observations of Kuiper Belt binaries  

NASA Astrophysics Data System (ADS)

We report preliminary results from a Hubble Space Telescope (HST) program designed to characterize the orbital and physical properties of six confirmed KBO binaries [Margot et al. 2003]. Our results show that KBOs in our sample have much smaller sizes and larger albedos than expected, possibly requiring continuous collisional resurfacing and implying a Kuiper Belt that is less massive than previously assumed. Table 1 describes a subset of four KBO binaries that can be clearly resolved only with HST (1999 TC36, 1998 SM165, 2001 QC298, 1997 CQ29). The orbital period P and semi-major axis a yield the total mass of the binary M. Uncertainties listed are three times the formal errors of the fit or 1%, whichever is greater. The primary to secondary radius ratio Rp/R_s is based on flux measurements in HST's F606W filter. We used the absolute magnitudes as reported by JPL's Horizons system, assumed that binary components have identical albedos and densities, and derived the densities corresponding to geometric albedos of 5%, 10%, and 20%. Most KBOs in our sample must have albedos in excess of the radiometric average of 8% [Altenhoff et al., 2004] otherwise their density would be implausibly low. For unit density, the primary radii/geometric albedos are (147 km, 23%), (116 km, 15%), (117 km, 7.6%), and (42 km, 41%). Detection of such small KBOs in the IR/mm is challenging. \\begin{tabular}[h]{rrrrrrrr} & P [days] & a [km] & M [1018 kg]& (Rp)/(R_s) & ? 5 & ? 10 & ? 20 TC& 50.38 ± 0.5 & 7640 ± 460 & 13.9 ± 2.5 & 2.7 & 0.1 & 0.3 & 0.8 SM& 130.1 ± 1 & 11310 ± 110 & 6.78 ± 0.24 & 3.0 & 0.2 & 0.5 & 1.5 QC& 19.23 ± 0.2 & 3690 ± 70 & 10.8 ± 0.7 & 1.2 & 0.5 & 1.5 & 4.3 CQ& 309.2 ± 3 & 8320 ± 240 & 0.48 ± 0.04 & 1.2 & - & 0.1 & 0.3 References Margot, Brown, Trujillo, Sari, HST General Observer Prgm 9746, 2003. Altenhoff, Bertoldi, Menten, A&A 415, 2004.

Margot, J. L.; Brown, M. E.; Trujillo, C. A.; Sari, R.

2004-11-01

363

Radiation Belt Environment Model: Application to Space Weather and Beyond  

NASA Technical Reports Server (NTRS)

Understanding the dynamics and variability of the radiation belts are of great scientific and space weather significance. A physics-based Radiation Belt Environment (RBE) model has been developed to simulate and predict the radiation particle intensities. The RBE model considers the influences from the solar wind, ring current and plasmasphere. It takes into account the particle drift in realistic, time-varying magnetic and electric field, and includes diffusive effects of wave-particle interactions with various wave modes in the magnetosphere. The RBE model has been used to perform event studies and real-time prediction of energetic electron fluxes. In this talk, we will describe the RBE model equation, inputs and capabilities. Recent advancement in space weather application and artificial radiation belt study will be discussed as well.

Fok, Mei-Ching H.

2011-01-01

364

The Size Frequency Distribution of Small Main-Belt Asteroids  

NASA Technical Reports Server (NTRS)

The asteroid size distribution informs us about the formation and composition of the Solar System. We build on our previous work in which we harvest serendipitously observed data of the Taurus region and measure the brightness and size distributions of Main-belt asteroids. This is accomplished with the highly sensitive MIPS 24 micron channel. We expect to catalog 104 asteroids, giving us a statistically significant data set. Results from this investigation will allow us to characterize the total population of small, Main-belt asteroids. Here we will present new results on the completeness of our study; on the presence of size distribution variations with inclination and radial distance in the belt; and early result on other archival fields.

Burt, Brian J.; Trilling, David E.; Hines, Dean C.; Stapelfeldt, Karl R.; Rebull, Luisa M.; Fuentes, Cesar I.; Hulsebus, Alan

2012-01-01

365

Are comets the so called Main Belt comets?  

NASA Astrophysics Data System (ADS)

Main Belt Comets (MBCs) are objects of the main belt with observed sporadic cometary-like activity (Hsieh and Jewitt 2006, Science, 312, 561). The study of asteroids that present sporadic cometary activity is of fundamental importance to address several astronomical problems including the end states of comet nuclei, the abundance of water in main belt asteroids, and its role as a possible source of terrestial water. Up to now three MBCs are known: (7968) Elst-Pizarro, 118401 (1999 RE70) and P/2005 U1 (Read). All of them are members of the Themis family of asteroids. In this work we present new spectroscopic and photometric observations of the three MBCs, compare them with other activated asteroids of the NEO population, other Themis family asteroids, comet nuclei and asteroids in cometary orbits, and discuss their cometary or asteroidal nature.

Licandro, J.; de Léon, J.; Pinilla-Alonso, N.; Campins, H.; Mothé-Diniz, T.; Alvarez-Candal, A.; Fiorenzano, A.

2007-08-01

366

Recent Developments in the Radiation Belt Environment Model  

NASA Technical Reports Server (NTRS)

The fluxes of energetic particles in the radiation belts are found to be strongly controlled by the solar wind conditions. In order to understand and predict the radiation particle intensities, we have developed a physics-based Radiation Belt Environment (RBE) model that considers the influences from the solar wind, ring current and plasmasphere. Recently, an improved calculation of wave-particle interactions has been incorporated. In particular, the model now includes cross diffusion in energy and pitch-angle. We find that the exclusion of cross diffusion could cause significant overestimation of electron flux enhancement during storm recovery. The RBE model is also connected to MHD fields so that the response of the radiation belts to fast variations in the global magnetosphere can be studied.Weare able to reproduce the rapid flux increase during a substorm dipolarization on 4 September 2008. The timing is much shorter than the time scale of wave associated acceleration.

Fok, M.-C.; Glocer, A.; Zheng, Q.; Horne, R. B.; Meredith, N. P.; Albert, J. M.; Nagai, T.

2010-01-01

367

Kinematics of Gould Belt Based on Open Clusters (Bobylev, 2006)  

NASA Astrophysics Data System (ADS)

We have redetermined kinematic parameters of the Gould Belt using currently available data on the motion of nearby young (logt<7.91) open clusters, OB associations, and moving stellar groups. Our modeling shows that the residual velocities reach their maximum values of -4km/s for rotation (in the direction of Galactic rotation) and +4km/s for expansion at a distance from the kinematic center of 300pc. We have taken the following parameters of the Gould Belt center: R0=150pc and l0=128{deg}. The whole structure is shown to move relative to the local standard of rest at a velocity of 10.7+/-0.7km/s in the direction l=274+/-4{deg} and b=-1+/-3{deg}. Using the derived rotation velocity, we have estimated the virial mass of the Gould Belt to be 1.5 million solar masses. (2 data files).

Bobylev, V. V.

2007-10-01

368

Outstanding Scientific Problems on the Earth's Radiation Belts (Invited)  

NASA Astrophysics Data System (ADS)

The original ideas to explain the origin and structure of the Earth’s radiation belts have been relatively successful during quiet geomagnetic activity, but they simply cannot explain the dynamic behaviour of the radiation belts observed during storms and other solar driven disturbances. Over the last few years new evidence suggests that there must be other physical processes that are operating inside the magnetosphere and this has stimulated a wealth of new ideas. In this overview we will focus on some of the outstanding scientific problems that need to be addressed. We will discuss why the radiation belts respond so differently to different geomagnetic storms and fast solar wind streams, the different ways in which electrons could be accelerated to MeV energies, how a radiation belt could be formed within 2 minutes, and what mechanisms could be responsible for the large depletions in electron flux that occur during geomagnetic storms. We will discuss whether large amplitude waves and non-linear wave-particle interactions could be more important than has been considered so far for acceleration and loss. We will also discuss some of the mechanisms that could transport electrons across the radiation belts, including non-diffusive as well as diffusive radial transport and the role of electric fields. We will consider whether these or other mechanisms could explain increases in the electron flux in the slot region. We will discuss some of the ways in which the ring current could affect electron radiation belt dynamics. New satellite missions including RBSP, ERG, RESONANCE, DSX and ORBITALS, are being designed to address these problems. We will comment on the difficulty to find evidence to prove or disprove these physical processes, or rank them in order, and the challenge for modelling studies, which only address a subset of these problems, for years to come.

Horne, R. B.

2010-12-01

369

Searching for Chips of Kuiper Belt Objects in Meteorites  

NASA Technical Reports Server (NTRS)

The Nice model [1&2] describes a scenario whereby the Jovian planets experienced a violent reshuffling event approx.3:9 Ga the giant planets moved, existing small body reservoirs were depleted or eliminated, and new reservoirs were created in particular locations. The Nice model quantitatively explains the orbits of the Jovian planets and Neptune [1], the orbits of bodies in several different small body reservoirs in the outer solar system (e.g., Trojans of Jupiter [2], the Kuiper belt and scattered disk [3], the irregular satellites of the giant planets [4], and the late heavy bombardment on the terrestrial planets approx.3:9 Ga [5]. This model is unique in plausibly explaining all of these phenomena. One issue with the Nice model is that it predicts that transported Kuiper Belt Objects (KBOs) (things looking like D class asteroids) should predominate in the outer asteroid belt, but we know only about 10% of the objects in the outer main asteroid belt appear to be D-class objects [6]. However based upon collisional modeling, Bottke et al. [6] argue that more than 90% of the objects captured in the outer main belt could have been eliminated by impacts if they had been weakly-indurated objects. These disrupted objects should have left behind pieces in the ancient regoliths of other, presumably stronger asteroids. Thus, a derived prediction of the Nice model is that ancient regolith samples (regolith-bearing meteorites) should contain fragments of collisionally-destroyed Kuiper belt objects. In fact KBO pieces might be expected to be present in most ancient regolith- bearing meteorites [7&8].

Zolensky, M. E.; Ohsumi, K.; Briani, G.; Gounelle, M.; Mikouchi, T.; Satake, W.; Kurihara, T.; Weisberg, M. K.; Le, L.

2009-01-01

370

Photometry and Lightcurve Analysis of 7 Main-Belt Asteroids  

NASA Astrophysics Data System (ADS)

We report the synodic periods and lightcurves for three main-belt asteroids and provide lightcurves for four other main-belt asteroids. 676 Melitta has a period of 8.35 ± 0.05 hours, with an amplitude of 0.056 ± 0.026 magnitude; 688 Melanie has a period of 16.10 ± 0.05 hours, and an amplitude of 0.091 ± 0.019 magnitude; 1677 Tycho Brahe has a period of 3.89 ± 0.06 hours, and an amplitude of 0.564 ± 0.011 magnitude.

Violante, Renata; Leake, M. A.

2013-01-01

371

Photometry and Lightcurve Analysis of 7 Main-Belt Asteroids  

NASA Astrophysics Data System (ADS)

We report the synodic periods and lightcurves for three main-belt asteroids and provide lightcurves for four other main-belt asteroids. 676 Melitta has a period of 8.35 ± 0.05 hours, with an amplitude of 0.056 ± 0.026 magnitude; 688 Melanie has a period of 16.10 ± 0.05 hours, and an amplitude of 0.091 ± 0.019 magnitude; 1677 Tycho Brahe has a period of 3.89 ± 0.06 hours, and an amplitude of 0.564 ± 0.011 magnitude.

Violante, R.; Leake, M. A.

2012-12-01

372

Mission Overview for the Radiation Belt Storm Probes Mission  

NASA Astrophysics Data System (ADS)

Provided here is an overview of Radiation Belt Storm Probes (RBSP) mission design. The driving mission and science requirements are presented, and the unique engineering challenges of operating in Earth's radiation belts are discussed in detail. The implementation of both the space and ground segments are presented, including a discussion of the challenges inherent with operating multiple observatories concurrently and working with a distributed network of science operation centers. An overview of the launch vehicle and the overall mission design will be presented, and the plan for space weather data broadcast will be introduced.

Stratton, J. M.; Harvey, R. J.; Heyler, G. A.

2013-11-01

373

Structural evolution of the Kolar Schist Belt, South India  

NASA Technical Reports Server (NTRS)

The structural evolution of the Kolar Schist Belt was discussed. Evidence was described from structures in the ferrigenous quartzite within the schist belt for two periods of nearly coaxial isoclinal folding attributable to E-W compression. This folding was followed by collapse of the F sub 1/F sub 2 folds, forming open F sub 3 folds with NNE-SSW axes. Finally, a period of N-S shortening caused a broad warping of the earlier N-S trending fold axes. There is evidence within the gneisses for shearing produced by similar, nearly E-W compression.

Mukhopahyay, Dilip K.

1988-01-01

374

VIR, the imaging spectrometer for the asteroid belt exploration.  

NASA Astrophysics Data System (ADS)

We describe the journey Dawn mission to the asteroid belt. The objective of Dawn is to explore backward in time via its observations of the primitive bodies, Vesta and Ceres. Dawn is the ninth mission in NASA's Discovery Program and is the first interplanetary mission that will orbit two solar system bodies: the massive main belt asteroid Vesta and the dwarf planet Ceres. Dawn is the first science mission to use ion propulsion. The spacecraft carries three scientific instruments: two redundant cameras, a visible and infrared spectrometer, named VIR, and a gamma ray and neutron spectrometer.

De Sanctis, M. C.; Coradini, A.; Ammannito, E.; Capria, M. T.; Fonte, S.

375

Leaching of S, Cu, and Fe from disseminated Ni-(Fe)-(Cu) sulphide ore during serpentinization of dunite host rocks at Mount Keith, Agnew-Wiluna belt, Western Australia  

NASA Astrophysics Data System (ADS)

Komatiite-hosted disseminated Ni sulphide deposits in the Agnew-Wiluna greenstone belt occur both above and below the olivine isograd that was imposed on the greenstone sequence during the M2 metamorphic/deformation event. Deposits in the northern and central part of the belt and that are located below the isograd (Mount Keith, Honeymoon Well and West Jordan) have complex sulphide mineralogy and strongly zoned sulphide assemblages. These range from least-altered assemblages of pentlandite-pyrrhotite-chalcopyrite±pyrite to altered assemblages of pentlandite±chalcopyrite, pentlandite-heazlewoodite (or millerite), heazlewoodite (or millerite), and rarely to heazlewoodite-native Ni. Deposits to the south and that are above of the olivine isograd (Six Mile, Goliath North) are dominated by less complex magmatic assemblages with a lower proportion of weakly altered pentlandite±chalcopyrite assemblages. More altered assemblages are uncommon in these deposits and occur as isolated patches around the periphery of the deposits. The sulphide zonation is reflected by whole-rock reductions in S, Cu, Fe and Zn, whereas Ni, Pt and Pd and, with some exceptions, Co are conservative. The leaching of S, Cu, Fe and Zn from sulphide assemblages and the whole rock was initiated by highly reduced conditions that were produced during low fluid/rock ratio serpentinization. Consumption of H2O resulted in Cl, a component of the fluid, being concentrated sufficiently to stabilise iowaite as part of lizardite-rich assemblages. Once the rate of olivine hydration reactions declined and during and after expansion and associated fracturing of the ultramafic sequence allowed higher fluid access, a more fluid-dominated environment formed and new carbonate-bearing fluid gained access to varying extents to the ultramafic rock sequence. This drove Cl from iowaite (to form pyroaurite) and caused the sulphide assemblages to be altered from the original magmatic assemblages and compositions to those stable at the prevailing fO2 and fS2 conditions. Mass transfer was made possible via metal chloride complexes and H2S with fluids driven by deformation associated with the M2 metamorphism. Disseminated deposits in higher metamorphic grade terrains where olivine was stable during peak metamorphism did not undergo the metasomatism seen in the deposits in areas of lower metamorphic grade. Some minor leaching of S, Fe and Cu occurred around the periphery of the deposits during early, pre-M2 peak metamorphism, but once olivine stability was reached the driving force for the series of leaching reactions was exhausted. The effect of this process on the original magmatic sulphides is to induce significant variability in texture, mineralogy and bulk composition and to markedly reduce the Fe and S contents of the sulphide fraction (in extreme cases to zero for both elements), and to reduce the volume of the sulphide fraction per unit of Ni. These changes impact unfavourably on Ni sulphide recoveries and metallurgical characteristics of these Ni ores.

Gole, Martin J.

2014-04-01

376

Surface testing and evaluation of the conveyor-belt service machine. Information Circular/1988  

SciTech Connect

The Bureau of Mines developed a conveyor-belt service machine (CBSM) through a research contract with Tractor MBA. The CBSM is a self-contained, battery-powered, rubber-tired vehicle capable of handling, storing, and transporting conveyor belting, wire rope, and associated belt structures in seams as low as 48 in. Belt extensions and retractions are accomplished by moving the tailpiece of a belt conveyor with the CBSM to the next position while dispensing or retrieving the belt, wire rope, and associated belt structures. The CBSM improves the belt extensions and retractions by making them easier and faster, and it utilizes fewer workers. The CBSM was surface tested at the Bureau's Mining Equipment Test Facility to evaluate its performance and reliability. Modifications were made to the CBSM to correct deficiencies found during surface testing.

Jaspal, J.S.; Miller, L.F.

1987-12-30

377

Identifying Information that Promotes Belt-Positioning Booster Use Volume I: Summary and Findings.  

National Technical Information Service (NTIS)

Many parents with low educational attainment prematurely graduate their children to seat belt restraint rather than use belt-positioning booster seats. This study aimed to identify interventions that promoted booster seat use among this population. Focus ...

D. C. Erkoboni F. K. Winston

2008-01-01

378

Identifying Information that Promotes Belt-Positioning Booster Use Volume II: Appendices.  

National Technical Information Service (NTIS)

Many parents with low educational attainment prematurely graduate their children to seat belt restraint rather than use belt-positioning booster seats. This study aimed to identify interventions that promoted booster seat use among this population. Focus ...

D. C. Erkoboni F. K. Winston

2008-01-01

379

Safety Belt Usage Rates at High Schools and Colleges in Rhode Island.  

National Technical Information Service (NTIS)

This report presents the implementation, analysis, and results of a model seat belt survey targeting Rhode Island high school and college students. This study was conducted to gather baseline information on seat belt usage patterns and characteristics, ca...

D. J. Berman J. Schaffran A. Fong

2004-01-01

380

A Kinematic Comparison of Split-belt and Single-belt Treadmill Walking and the Effects of Accommodation  

PubMed Central

INTRODUCTION Instrumented treadmills are becoming increasingly more common in gait laboratories. Instrumented side-split treadmills allow the collection of forces under each foot during walking. However, there may be a tendency to increase the base of support when walking on these treadmills, influencing other frontal plane mechanics as well. Therefore, the purpose of this study was to examine the effect of walking on a side-split instrumented treadmill on base of gait and frontal plane kinematics of the lower extremity. METHODS Twenty subjects walked on both a split and a single-belt treadmill. Base of gait and frontal plane kinematic angles and variability data were recorded. A one-way ANOVA was used to determine differences between the single and split-belt conditions at baseline and following a 10 minute accommodation on the split-belt. The relationships between the change in base of gait and change in each kinematic variable were also determined. RESULTS On average, the base of gait was 3.7 cm wider on the split-belt treadmill with a 4 mm gap between belts. No significant differences were observed in the mean values of lower extremity kinematics or kinematic variability at baseline or following the 10 minute accommodation. However, the increase in base of gait was significantly related to a decrease in peak knee and hip adduction angles. CONCLUSION The 4 mm gap between the treadmill belts significantly increased the mean base of gait in all subjects. This did not alter mean frontal plane kinematics. However, as base of gait increased, the tendency towards hip and knee abduction also increased.

Altman, Allison R.; Reisman, Darcy S.; Higginson, Jill S.; Davis, Irene S.

2011-01-01

381

Explorers 1 and 3 - The Discovery and Early History of the Earth's Radiation Belts  

NSDL National Science Digital Library

The first of 6 linked web pages on how the inner radiation belt was discovered in 1958 by Van Allen, on the type of instrument used (Geiger counter), on the belt's explanation based on neutron albedo, on radiation belts created by nuclear bombs and on the discovery of the outer belt. This resource is nonmathematical and short; a longer exposition (with references) is also available.

Stern, David

2005-01-04

382

Metamorphism of the Palaeoproterozoic Magondi mobile belt north of Karoi, Zimbabwe  

Microsoft Academic Search

The Palaeoproterozoic Magondi mobile belt flanks the Zimbabwe Archaean Craton to the northwest. The belt is composed of metamorphosed sedimentary, volcanic and volcaniclastic rocks associated with quartzofeldspathic gneisses intruded by granitoids, some charnockitic, in the high-grade part of the belt. The belt is metamorphosed from low-grade greenschist-facies in the south and middle to upper amphibolite-facies in the north. Granulite-facies rocks

Hubert Munyanyiwa; Pieter Maaskant

1998-01-01

383

Seat Belt and Child Seat Use in Lipetskaya Oblast, Russia: Frequencies, Attitudes, and Perceptions  

Microsoft Academic Search

Objective: Despite the importance of understanding seat belt use patterns among drivers and passengers for the purpose of direct interventions or monitoring improvements, no study has described wearing rates for all seat positions in Russia. This study describes observed seat belt use and knowledge, attitudes, and perceptions of seat belt use in Lipetskaya Oblast, Russia.Methods: An observational study on the

Sai Ma; Nhan Tran; Vladimir E. Klyavin; Francesco Zambon; Kristin W. Hatcher; Adnan A. Hyder

2012-01-01

384

Long-Term Benefits of Prompts to Use Safety Belts among Drivers Exiting Senior Communities  

ERIC Educational Resources Information Center

Senior drivers are vulnerable to automobile crashes and subsequent injury and death. Safety belts reduce health risks associated with auto crashes. Therefore, it is important to encourage senior drivers to wear safety belts while driving. Using a repeated baseline design (AAB), we previously reported that motivating signs boosted safety belt usage…

Cox, Cory D.; Cox, Brian S.; Cox, Daniel J.

2005-01-01

385

The research on the detection method of belt deviation by video in coal mine  

Microsoft Academic Search

Belt deviation is the most common failure during the operation of belt conveyor, and may cause tremendous harmfulness. In order to improve the intelligence of traditional video monitoring system of belt in coal mine, according to the deficiency of traditional system, we deeply studied various types of edge detection algorithm, and proposed an improved algorithm to achieve the edge extraction

Zhu Aichun; Hua Gang; Wang Yongxing

2011-01-01

386

The Research and Design of the Belt Grinder which Based on PLC  

Microsoft Academic Search

The main introduction is the PLC and the touching screen which to control a new type of belt grinder, narrates its working principle, simultaneously introduces its design of the hardware and the software. This new type of belt grinding, which uses PLC as the control system core, and use the frequency converter to achieve the speed of the belt stepless

Huiqiang Wang; Jianjun Cui; Ying Zheng; Minying Hu

2009-01-01

387

Measurement and monitoring of electrocardiogram belt tension in premature infants for assessment of respiratory function  

Microsoft Academic Search

BACKGROUND: Monitoring of the electrocardiogram (ECG) in premature infants with conventional adhesive-backed electrodes can harm their sensitive skin. Use of an electrode belt prevents skin irritation, but the effect of belt pressure on respiratory function is unknown. A strain gauge sensor is described which measures applied belt tension. METHOD: The device frame was comprised of an aluminum housing and slide

Edward J Ciaccio; Mark Hiatt; Thomas Hegyi; Gary M Drzewiecki

2007-01-01

388

The Radiation Belt Storm Probes (RBSP): Using A Fundamental Physics Mission to Support Practical Applications  

Microsoft Academic Search

This presentation provides an overview of the Living With a Star (LWS) Radiation Belt Storm Probes (RBSP) mission and its planned contributions to space weather activities. The RBSP mission targets Earth's space radiation belts that comprise multiple components of high energy, penetrating charged particles. These belts are hazardous to spacecraft and astronauts alike and are controlled by dynamic processes that

N. J. Fox; B. H. Mauk; M. Weiss; R. J. Barnes; R. Kessel; D. G. Sibeck

2010-01-01

389

Long-term Benefits of Prompts to Use Safety Belts among Drivers Exiting Senior Communities  

Microsoft Academic Search

Senior drivers are vulnerable to automobile crashes and subsequent injury and death. Safety belts reduce health risks associated with auto crashes. Therefore, it is important to encourage senior drivers to wear safety belts while driving. Using a repeated baseline design (AAB), we previously reported that motivating signs boosted safety belt usage by drivers exiting senior communities from baseline (72% and

CORY D. COX; BRIAN S. COX; Daniel J Cox

2005-01-01

390

Experimental Study of Flame Spread on Conveyor Belts in a Small-Scale Tunnel.  

National Technical Information Service (NTIS)

This paper presents experimental results for conveyor belt flame spread from tests conducted in a small-scale tunnel. The purpose of this study is to investigate the effects of belt type, ventilation velocity, belt surface-to-roof distance and ignition so...

C. D. Litton L. Yuan

2008-01-01

391

Plate tectonic model for the Carboniferous evolution of the New England Fold Belt  

Microsoft Academic Search

The New England Fold Belt forms the easternmost, youngest part of the Tasman Fold Belt System. For much of Late Palaeozoic time, it was a convergent plate margin at the edge of the Australian continent. At present, the New England Fold Belt is separated into the Yarrol Province in the north and the New England Province in the south by

C. G. Murray; C. L. Fergusson; P. G. Flood; W. G. Whitaker; R. J. Korsch

1987-01-01

392

23 CFR Appendix A to Part 1340 - State Seat Belt Use Survey Reporting Form  

Code of Federal Regulations, 2013 CFR

...2013-04-01 false State Seat Belt Use Survey Reporting Form A Appendix A to Part...UNIFORM CRITERIA FOR STATE OBSERVATIONAL SURVEYS OF SEAT BELT USE Pt. 1340, App. A...A to Part 1340âState Seat Belt Use Survey Reporting Form PART A: To be...

2013-04-01

393

The APIES microsatellite mission to explore the asteroid belt  

NASA Astrophysics Data System (ADS)

APIES (Asteroid Population Investigation &Exploration Swarm) is a mission developed by EADS Astrium in response to a European Space Agency (ESA) Call for Ideas for "swarm" missions, based on the utilisation of a large number of spacecraft working cooperatively to achieve the mission objectives. The APIES baseline concept is centred on a "swarm" of 19 BElt Explorer (BEE) identical microsatellites, weighting less than 45 kg each, including their scientific payload, visiting over 100 Main Belt asteroids in multiple flybys. The BEEs are carried to the asteroid belt by a Hub and Interplanetary VEhicle (HIVE), a conventional spacecraft launched with a Soyuz-Fregat rocket, using solar electric propulsion for the transfer to the asteroid belt and acting as communication hub and control centre for the mission after the swarm deployment. Using the latest advances in systems miniaturization, propulsion, onboard autonomy and communications, the APIES mission can achieve its ambitious goal within the framework of a standard ESA mission, representing a novel mission concept example, whose feasibility is essentially linked to the use of microsatellite technology, enabling the achievement of science objectives unattainable with conventional spacecraft.

D'Arrigo, P.; Santandrea, S.

2004-11-01

394

The lightcurve of main-belt asteroid 774 Armor  

NASA Astrophysics Data System (ADS)

Observations spanning more than two months reveal the synodic period of the main-belt asteroid 774 Armor to be 25.162±0.002hr with an amplitude of 0.37±0.02mag. This study affirmed the importance of both collaboration and having data from widely separated locations.

Warner, Brian D.; Higgins, David; Bennett, Thomas; Fauerbach, Michael

2006-12-01

395

Effective Conveyor Belt Inspection for Improved Mining Productivity  

SciTech Connect

This document details progress on the project entitled ''Effective Conveyor Belt Inspection for Improved Mining Productivity'' during the period from November 15, 2004 to May 14, 2004. Highlights include fabrication of an improved LED lightbar, fabrication of a line-scan sensor head for the Smart-Camera based prototype, and development of prototype vulcanized splice detection algorithms.

Chris Fromme

2006-06-01

396

Origins of The Paleolandslide of Tarapaca (north Chile, Andean Belt)  

Microsoft Academic Search

Landslides are an important and potentially rate-limiting process in the topographic evolution of active orogens like the Andean Belt. Various processes are responsi- ble for triggering landslides, including hillslope baselevel lowering, seismic events (Keefer, 1999); climate changes (Coriminas and Moya, 1999), anthropic effects (Sah and Mazari, 1998) and each of these triggers may be spatially heterogeneous in strength and effectiveness.

J. Darrozes; L. Pinto; J. Ingles; J.-C. Soula; E. Maire; P. Courjault-Radé; G. Hérail

2002-01-01

397

Lightcurve Analysis of Main-belt Binary System 3905 Doppler  

NASA Astrophysics Data System (ADS)

Photometric observations of the main-belt asteroid 3905 Doppler over eight nights in 2013 revealed for the first time that it is a synchronous binary system. A synodic period of 50.8 ± 0.1 hours was derived from the data.

Hayes-Gehrke, Melissa N.; Maroulis, Michael; Bartek, Alec; Garcia, Eric; Greenebaum, Robert; Basile, Terence; Lee, Seong Min; Bent, Brady; Oliver, Nick; Koester, Kenneth; Franco, Lorenzo

2014-04-01

398

A Population of Comets in the Main Asteroid Belt  

Microsoft Academic Search

Comets are icy bodies that sublimate and become active when close to the Sun. They are believed to originate in two cold reservoirs beyond the orbit of Neptune: the Kuiper Belt (equilibrium temperatures of ~40 kelvin) and the Oort Cloud (~10 kelvin). We present optical data showing the existence of a population of comets originating in a third reservoir: the

Henry H. Hsieh; David Jewitt

2006-01-01

399

Dynamical lifetimes of objects injected into asteroid belt resonances  

Microsoft Academic Search

Numerical simulations of particles placed in orbital resonances in the main asteroid belt show that the typical dynamical lifetimes of objects that could become near-Earth asteroids or meteorites are only a few million years, with the majority destroyed by being transferred to Jupiter-crossing orbits or being driven into the sun. Particles that fortu- itously migrate to the terrestrial planet region

B. J. Gladman; Fabbio Migliorini; Alessandro Morbidelli; Vincenzo Zappala; Patrick Michel; Alberto Cellino; Christiane Froeschle; H. F. Levison; Mark Bailey; Martin Duncan

1997-01-01

400

Crystalline water ice on the Kuiper belt object (50000) Quaoar  

NASA Astrophysics Data System (ADS)

The Kuiper belt is a disk-like structure consisting of solid bodies orbiting the Sun beyond Neptune. It is the source of the short-period comets and the likely repository of the Solar System's most primitive materials. Surface temperatures in the belt are low (~ 50K), suggesting that ices trapped at formation should have been preserved over the age of the Solar System. Unfortunately, most Kuiper belt objects are too faint for meaningful compositional study, even with the largest available telescopes. Water ice has been reported in a handful of objects, but most appear spectrally featureless. Here we report near-infrared observations of the large Kuiper belt object (50000) Quaoar, which reveal the presence of crystalline water ice and ammonia hydrate. Crystallinity indicates that the ice has been heated to at least 110K. Both ammonia hydrate and crystalline water ice should be destroyed by energetic particle irradiation on a timescale of about 107yr. We conclude that Quaoar has been recently resurfaced, either by impact exposure of previously buried (shielded) ices or by cryovolcanic outgassing, or by a combination of these processes.

Jewitt, David C.; Luu, Jane

2004-12-01

401

OORT-Cloud and Kuiper-Belt Comets.  

National Technical Information Service (NTIS)

This paper follows the broadly accepted theory that Oort-Cloud Comets originated in the Solar Nebula in the general region where the major planets, Jupiter and Saturn, were formed while the Kuiper-Belt Comets originated farther out where the temperatures ...

F. L. Whipple

1998-01-01

402

Kuiper Belt dust in the inner and outer Solar System  

Microsoft Academic Search

The dust produced in the Kuiper Belt (KB) spreads throughout the Solar System forming a dust disk. We have numerically modelled the dynamical evolution of KB dust grains using a modified symplectic integrator which resolves close planetary encounters and includes solar wind and radiation forces. We report here a selection of results from our modeling efforts. (1) We find that

A. Moro-Martin; R. Malhotra

2002-01-01

403

Towards initial mass functions for asteroids and Kuiper Belt Objects  

Microsoft Academic Search

Our goal is to understand primary accretion of the first planetesimals. Some examples are seen today in the asteroid belt, providing the parent bodies for the primitive meteorites. The primitive meteorite record suggests that sizeable planetesimals formed over a period longer than a million years, each of which being composed entirely of an unusual, but homogeneous, mixture of millimeter-size particles.

Jeffrey N. Cuzzi; Robert C. Hogan; William F. Bottke

2010-01-01

404

Evaluating the North Carolina safety belt wearing law.  

PubMed

The North Carolina Seat Belt Law required an evaluation of the effectiveness of the act with a report of the findings to the Legislature three years after the law went into effect. This paper addresses changes in statewide belt usage and in occupant injury associated with that law. Observational data collected bimonthly from a probability sample of 72 sites stratified by geographic region, rural/urban location, road type, and time of day show that belt use rose from a baseline rate of 25% to a warning ticket phase rate of 45%. Belt use then reached 78% upon enforcement and is now nearly 64%. Time series analysis showed that statistically significant reductions in percentages of moderate and serious injuries occurred at the beginning of both the warning ticket and the enforcement phases. Forecasts of injuries and deaths were also developed from the time series models and were compared with observed totals. Warning tickets brought about a modest 5.4% reduction in serious injuries; fatalities among occupants covered by the law showed no change. In contrast, the subsequent enforcement phase saw a reduction of 11.6% in fatalities and 14.6% in serious or worse injuries. This represents an estimated annual savings of 131 lives and over 2,300 serious injuries in North Carolina during the 18 months following onset of enforcement. PMID:2393468

Reinfurt, D W; Campbell, B J; Stewart, J R; Stutts, J C

1990-06-01

405

Smoking, Sociodemographic Determinants, and Stress in the Alabama Black Belt  

ERIC Educational Resources Information Center

Purpose: In the Alabama Black Belt, poverty is high, and the educational level is low. Studies have found increased tobacco use among individuals exposed to high levels of stress. Few studies have been conducted in this region to measure smoking status, its sociodemographic determinants, and how smoking status relates to stressful environmental…

Shuaib, Faisal; Foushee, H. R.; Ehiri, John; Bagchi, Suparna; Baumann, Angela; Kohler, Connie

2011-01-01

406

8. POWERHOUSE, LOWER LEVEL, LEFT, GOVERNOR DRIVE MOTOR WITH BELT ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

8. POWERHOUSE, LOWER LEVEL, LEFT, GOVERNOR DRIVE MOTOR WITH BELT ON RIGHT, HYDRAULIC PUMP WITH RESERVOIR TANK, STEAM HEAT PIPES ON BACK WALL LOOKING NORTHEAST - Dayville Mills Hydroelectric Facility, Powerhouse, North side of Route 101, .5 mile west of Route 395, Killingly Center, Windham County, CT