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1

Incipient basin inversion of the Middle Archean Moodies Basin, Barberton Supergroup, Barberton Greenstone Belt, South Africa  

Microsoft Academic Search

The Moodies Group of the Barberton Greenstone Belt is one of the oldest and best-preserved quartz-rich sedimentary sequences on Earth. Its strata, approx. 3 km thick, record an initial extensional setting, followed by a strong shortening pulse which resulted in the dominant large-scale final deformation of the greenstone belt. We investigated the apparently rapid transition from Moodies extensional to compressive

Jens Kirstein; Christoph Heubeck; Wigbert Lippold

2010-01-01

2

Sm-Nd dating of Fig Tree clay minerals of the Barberton greenstone belt, South Africa  

NASA Technical Reports Server (NTRS)

Sm-Nd isotopic data from carbonate-derived clay minerals of the 3.22-3.25 Ga Fig Tree Group, Barberton greenstone belt, South Africa, form a linear array corresponding to an age of 3102 +/- 64 Ma, making these minerals the oldest dated clays on Earth. The obtained age is 120-160 m.y. younger than the depositional age determined by zircon geochronology. Nd model ages for the clays range from approximately 3.39 to 3.44 Ga and almost cover the age variation of the Barberton greenstone belt rocks, consistent with independent evidence that the clay minerals are derived from material of the belt. The combined isotopic and mineralogical data provide evidence for a cryptic thermal overprint in the sediments of the belt. However, the highest temperature reached by the samples since the time of clay-mineral formation was <300 degrees C, lower than virtually any known early Archean supracrustal sequence.

Toulkeridis, T.; Goldstein, S. L.; Clauer, N.; Kroner, A.; Lowe, D. R.

1994-01-01

3

Late syndepositional deformation and detachment tectonics in the Barberton Greenstone Belt, South Africa  

NASA Astrophysics Data System (ADS)

The thick-bedded, competent quartzose sandstones, conglomerates, and siltstones of the Moodies Group (<3,225 Ma) influence structural style in the ˜3.1-3.5 Ga Barberton Greenstone Belt. Moodies Group rocks are folded into a train of tight, subparallel, doubly plunging, overturned synclines separated by narrow, strike-parallel fault zones. Structural analysis along a transect across the central part of the greenstone belt suggests that much of the volcanic-sedimentary greenstone sequence was buckle-folded above a detachment within altered ultramafic rocks located at a depth of 3-6 km. Early development of brittle structures concentrated shortening and displacement near the fold hinges and in the anticlinal fault zones. Penetrative strain during folding was low. The sense of displacement along faults, the original fold vergence, and the provenance of Moodies Group sandstone and conglomerate suggest that tectonic transport was directed toward the interior of the belt from its northwestern and southeastern margins. Orogenic contraction due to folding alone was at least -56% and subsequent ductile shortening strain accounted for an additional contraction of approximately -10%. Buoyant rise of the Kaap Valley Tonalite to the north at approximately 3.22 Ga and lateral intrusions of sheetlike granitic plutons along both sides of the preserved greenstone belt at 3.1 and 3.0 Ga, respectively, imposed significant ductile strain on the greenstone belt margins and obscured or displaced the orogenic hinterlands of the facing fold-and-thrust belts. The syn-and post-Moodies tectonic history of the central Barberton Greenstone Belt involves the formation and deformation of several shortlived alluvial to shallow marine sedimentary basins on unstable "protocontinental" crust. The probable extensional origin of at least some of these basins and their subsequent shortening, buckle folding, and displacement above a subhorizontal detachment emphasizes the dominance of horizontal tectonics in the late-stage deformation of this Archean greenstone belt.

Heubeck, Christoph; Lowe, Donald R.

1994-12-01

4

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

5

Palaeomagnetism of Archaean rocks of the Onverwacht Group, Barberton Greenstone Belt (southern Africa): Evidence for a stable and potentially reversing geomagnetic  

E-print Network

Greenstone Belt (Kaapvaal Craton, southern Africa). Our palaeomagnetic measurements strengthen a recently) in the Kaapvaal Craton of southern Africa and the Pilbara Granite-Greenstone terrain in western Australia, bothPalaeomagnetism of Archaean rocks of the Onverwacht Group, Barberton Greenstone Belt (southern

Utrecht, Universiteit

6

Magnetic Carriers In Archean Cherts from the Barberton Greenstone Belt, South Africa  

NASA Astrophysics Data System (ADS)

The ~3.4 billion-year-old Buck Reef Chert of the Barberton Greenstone Belt, South Africa has been the focus of continued study, especially in regard to the presence of potential biogenic microstructures. Here, we address the nature of magnetic carriers in the Buck Reef Chert and other cherts from the Barberton area. Magnetic properties of bulk samples and magnetic separates have been measured. Scanning Electron Microscope observations of magnetic separates in Scanning Transmission Electron Microscope (STEM) mode reveal cubo-octahedral to quasi-rectangular shaped grains that fall within a stable single domain range. Energy Dispersive Spectrometer (EDS) analysis shows that iron, sulfur, carbon, and oxygen are contained within the magnetic separates. Measurements of magnetic hysteresis properties using a Princeton Measurements Corporation Alternating Gradient Force Magnetometer show that bulk samples have a variety of hysteresis behaviors (including multi-domain, pseudo-single domain and wasp-waisted curves). Preliminary analyses of bulk magnetic susceptibility versus temperature (using a KLY-4S Kappabridge) highlight the tendency for alteration on heating (100-400 °C). Our results to date should be interpreted in terms of the original depositional environment, and the subsequent geologic history. While it is possible that some of the magnetic minerals we have separated and observed using STEM analysis are primary, it is also important to recognize that the host rocks have undergone low grade metamorphism at peak temperatures of 250 to 320 °C. Therefore any depositional sulfides (e.g. greigite) in the originally sulfur rich environment may have been converted to other iron oxides. This may be a common process in Archean cherts. We will discuss attempts to better distinguish primary from secondary magnetic minerals in the Barberton rocks.

Voronov, J.; Tarduno, J. A.; Cottrell, R. D.; Watkeys, M. K.; Hofmann, A.

2008-12-01

7

Flow banding in basaltic pillow lavas from the Early Archean Hooggenoeg Formation, Barberton Greenstone Belt, South Africa  

Microsoft Academic Search

Well-preserved pillow lavas in the uppermost part of the Early Archean volcanic sequence of the Hooggenoeg Formation in the Barberton Greenstone Belt exhibit pronounced flow banding. The banding is defined by mm to several cm thick alternations of pale green and a dark green, conspicuously variolitic variety of aphyric metabasalt. Concentrations of relatively immobile TiO2, Al2O3 and Cr in both

Brian Robins; Nils Rune Sandstå; Harald Furnes; Maarten de Wit

2010-01-01

8

Flow banding in basaltic pillow lavas from the Early Archean Hooggenoeg Formation, Barberton Greenstone Belt, South Africa  

Microsoft Academic Search

Well-preserved pillow lavas in the uppermost part of the Early Archean volcanic sequence of the Hooggenoeg Formation in the\\u000a Barberton Greenstone Belt exhibit pronounced flow banding. The banding is defined by mm to several cm thick alternations of\\u000a pale green and a dark green, conspicuously variolitic variety of aphyric metabasalt. Concentrations of relatively immobile\\u000a TiO2, Al2O3 and Cr in both

Brian Robins; Nils Rune Sandstå; Harald Furnes; Maarten de Wit

2010-01-01

9

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

10

Preliminary Palaeomagnetic Results from ICDP Barberton Greenstone Belt Scientific Drill Cores.  

NASA Astrophysics Data System (ADS)

Four drill cores from the ICDP Barberton Greenstone Belt Scientific Drilling Project have been sampled for palaeomagnetic analysis. Some 350 oriented mini-samples (10mm diameter) were collected from cores BARB1 to BARB 4, allowing units from the Onverwacht (Komatii and Hooggenoeg Formations) and Fig Tree Groups to be studied. Previous work has indicated that rocks from the Noisy and Hooggenoeg Formations have the potential to record a near-primary direction of remanence and suggest the presence of a reversing geomagnetic field of similar magnitude to the recent field at ca. 3.5Ga. Previous paleomagnetic studies carried out on the Komatii Formation have yielded one of the oldest paleomagnetic poles and intensities in the world but these results are even more questionable. So far, no paleomagnetic work has been carried out on the Buck Reef Chert Formation or the Fig Tree Group. This sampling forms part of a larger study aiming, firstly to constrain the reliability of previous results by performing improved field stability tests. A positive fold test would constrain the age of the magnetic signal recorded by the Komatii and Hooggenoeg Formations to older than 3.2 Ga. Confirmation of the presence of a viable and reversing field during the Palaeoarchean would place a strong constraint on processes occurring in the outer core during this time with implications for planetary evolution. Rates of polar wander will also be constrained by the directional findings, shedding some light on mantle convection processes at the time. Preliminary directional work on samples from drill cores will be presented here.

Roberts Artal, Laura; Biggin, Andy; Langereis, Cor; Wilson, Allan; Arndt, Nicholas; Hill, Mimi

2013-04-01

11

Depositional and tectonic setting of the Archean Moodies Group, Barberton Greenstone Belt, South Africa  

NASA Technical Reports Server (NTRS)

The 3.22-3.10 Ga old Moodies Group, uppermost unit of the Swaziland Supergroup in the Barberton Greenstone Belt (BGB), is the oldest exposed, well-preserved quartz-rich sedimentary sequence on earth. It is preserved in structurally separate blocks in a heavily deformed fold-and-thrust belt. North of the Inyoka Fault, Moodies strata reach up to 3700 m in thickness. Detailed mapping, correlation of measured sections, and systematic analysis of paleocurrents show that the lower Moodies Group north of the Inyoka Fault forms a deepening- and fining-upward sequence from a basal alluvial conglomerate through braided fluvial, tidal, and deltaic sandstones to offshore sandy shelf deposits. The basal conglomerate and overlying fluvial facies were derived from the north and include abundant detritus eroded from underlying Fig Tree Group dacitic volcanic rocks. Shoreline-parallel transport and extensive reworking dominate overlying deltaic, tidal, and marine facies. The lithologies and arrangement of Moodies Group facies, sandstone petrology, the unconformable relationship between Moodies strata and older deformed rocks, presence of at least one syndepositional normal fault, and presence of basaltic flow rocks and airfall fall tuffs interbedded with the terrestrial strata collectively suggest that the lower Moodies Group was deposited in one or more intramontane basins in an extensional setting. Thinner Moodies sections south of the Inyoka Fault, generally less than 1000 m thick, may be correlative with the basal Moodies Group north of the Inyoka Fault and were probably deposited in separate basins. A northerly derived, southward-thinning fan-delta conglomerate in the upper part of the Moodies Group in the central BGB overlies lower strata with an angular unconformity. This and associated upper Moodies conglomerates mark the beginning of basin shortening by south- to southeast-directed thrust faulting along the northern margin of the BGB and suggest that the upper Moodies Group was deposited in a foreland basin. Timing, orientation, and style of shortening suggest that this deformation eventually incorporated most of the BGB into a major fold-and-thrust belt.

Heubeck, C.; Lowe, D. R.

1994-01-01

12

Depositional and tectonic setting of the Archean Moodies Group, Barberton Greenstone Belt, South Africa.  

PubMed

The 3.22-3.10 Ga old Moodies Group, uppermost unit of the Swaziland Supergroup in the Barberton Greenstone Belt (BGB), is the oldest exposed, well-preserved quartz-rich sedimentary sequence on earth. It is preserved in structurally separate blocks in a heavily deformed fold-and-thrust belt. North of the Inyoka Fault, Moodies strata reach up to 3700 m in thickness. Detailed mapping, correlation of measured sections, and systematic analysis of paleocurrents show that the lower Moodies Group north of the Inyoka Fault forms a deepening- and fining-upward sequence from a basal alluvial conglomerate through braided fluvial, tidal, and deltaic sandstones to offshore sandy shelf deposits. The basal conglomerate and overlying fluvial facies were derived from the north and include abundant detritus eroded from underlying Fig Tree Group dacitic volcanic rocks. Shoreline-parallel transport and extensive reworking dominate overlying deltaic, tidal, and marine facies. The lithologies and arrangement of Moodies Group facies, sandstone petrology, the unconformable relationship between Moodies strata and older deformed rocks, presence of at least one syndepositional normal fault, and presence of basaltic flow rocks and airfall fall tuffs interbedded with the terrestrial strata collectively suggest that the lower Moodies Group was deposited in one or more intramontane basins in an extensional setting. Thinner Moodies sections south of the Inyoka Fault, generally less than 1000 m thick, may be correlative with the basal Moodies Group north of the Inyoka Fault and were probably deposited in separate basins. A northerly derived, southward-thinning fan-delta conglomerate in the upper part of the Moodies Group in the central BGB overlies lower strata with an angular unconformity. This and associated upper Moodies conglomerates mark the beginning of basin shortening by south- to southeast-directed thrust faulting along the northern margin of the BGB and suggest that the upper Moodies Group was deposited in a foreland basin. Timing, orientation, and style of shortening suggest that this deformation eventually incorporated most of the BGB into a major fold-and-thrust belt. PMID:11539505

Heubeck, C; Lowe, D R

1994-01-01

13

Peering into the Cradle of Life: Scientific Drilling in the Barberton Greenstone Belt, South Africa  

NASA Astrophysics Data System (ADS)

The Barberton Greenstone Belt in South Africa is one of the best-preserved successions of mid-Archean (3.5-3.2 Ga) supracrustal rocks in the world, and a site where conditions and processes at the surface of the Archean Earth can be studied in detail. Despite generally good outcrop, complete field sections are not preserved, and crucial features such as the contacts of lava flows and continuous successions of critical sedimentary rock sequences are not exposed. Through diamond drilling we have obtained continuous sections and relatively unaltered samples from the volcano-sedimentary successions. The sedimentary sequences provide information about erosion and sedimentation on the early Earth, the composition and temperature of Archean seawater, and one possible site where life may have emerged and evolved. Investigation of spherule layers (including impact debris) provide information about the nature and magnitude of meteorite impact on the early Earth. The ultramafic to mafic volcanic rocks provide new insights into volcanic processes, dynamics of the crust and mantle, interaction between oceanic volcanic crust and the hydrosphere and biosphere. The project supported by the International Continental Drilling Program and by scientists from 13 countries in five continents. Drilling started in July 2011 and is expected to finish in February 2012. Regular updates are posted on the ICDP web site < www.icdp-online.org>. By December 2011, two 300m holes in komatiite had been completed. This drilling provided excellent sections through over 60 flows of komatiite or komatiitic basalt, including a thick inflated flow composed of highly magnesian, possibly hydrous komatiite. Drilling was continuing at two sites in sedimentary sequences. The first, at Buck Reef, has yielded over 600 m of banded chert retaining complex sedimentary and diagenetic structures; the second, in the Middle Fig Tree formation, has intersected 350 m of interbanded chert and ferruginous shale. Two additional hole will be completed by March 2012. The distribution of samples and post-drilling research will be coordinated by a steering committee from all member countries and a workshop to decide who does what on the core will be held in South Africa in mid 2012.

Arndt, N. T.; Barberton Drilling Team

2012-04-01

14

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

15

Extensional tectonics during the igneous emplacement of the mafic-ultramafic rocks of the Barberton greenstone belt  

NASA Astrophysics Data System (ADS)

The simatic rocks (Onverwacht Group) of the Barberton greenstone belt are part of the Jamestown ophiolite complex. This ophiolite, together with its thick sedimentary cover occupies a complex thrust belt. Field studies have identified two types of early faults which are entirely confined to the simatic rocks and are deformed by the later thrusts and associated folds. The first type of fault (F1a) is regional and always occurs in the simatic rocks along and parallel to the lower contacts of the ophiolite-related cherts (Middle Marker and equivalent layers). These fault zones have previously been referred to both as flaser-banded gneisses and as weathering horizons. In general the zones range between 1-30m in thickness. Displacements along these zones are difficult to estimate, but may be in the order of 1-100 km. The structures indicate that the faults formed close to horizontal, during extensional shear and were therefore low angle normal faults. F1a zones overlap in age with the formation of the ophiolite complex. The second type of faults (F1b) are vertical brittle-ductile shear zones, which crosscut the complex at variable angles and cannot always be traced from plutonic to overlying extrusive (pillowed) simatic rocks. F1b zones are also apparently of penecontemporaneous origin with the intrusive-extrusive igneous processs. F1b zones may either represent transform fault-type activity or represent root zones (steepened extensions) of F1a zones. Both fault types indicate extensive deformation in the rocks of the greenstone belt prior to compressional overthrust tectonics.

Dewit, M. J.

16

Magnetotelluric measurements across the southern Barberton greenstone belt, South Africa: data improving strategies and 2-D inversion results  

NASA Astrophysics Data System (ADS)

Magnetotelluric (MT) measurements in areas with electromagnetic (EM) noise sources such as electric fences, power and railway lines pose severe challenges to the standard processing procedures. In order to significantly improve the data quality advanced filtering and processing techniques need to be applied. The presented 5-component MT data set from two field campaigns in 2009 and 2010 in the Barberton/Badplaas area, South Africa, was acquired within the framework of the German-South African geo-scientific research initiative Inkaba yeAfrica. Approximately 200 MT sites aligned along six profiles provide a good areal coverage of the southern part of the Barberton Greenstone Belt (BGB). Since it is one of the few remaining well-preserved geological formations from the Archean, it presents an ideal area to study the tectonic evolution and the role of plate tectonics on Early Earth. Comparing the electric properties, the surrounding high and low grade metamorphic rocks are characteristically resistive whereas mineralized shear zones are possible areas of higher electrical conductivity. Mapping their depth extension is a crucial step towards understanding the formation and the evolution of the BGB. Unfortunately, in the measurement area numerous noise sources were active, producing severe spikes and steps in the EM fields. These disturbances mainly affect long periods which are needed for resolving the deepest structures. The Remote Reference technique as well as two filtering techniques are applied to improve the data in different period ranges. Adjusting their parameters for each site is necessary to obtain the best possible results. The improved data set is used for two-dimensional inversion studies for the six profiles applying the RLM2DI algorithm by Rodi and Mackie (2001, implemented in WinGlink). In the models, areas with higher conductivity can be traced beneath known faults throughout the entire array along different profiles. Resistive zones seem to correlate well with plutonic intrusions.

Kutter, S.; Chen, X.; Weckmann, U.

2011-12-01

17

Tourmaline mineralization in the Barberton greenstone belt, South Africa: early Archean metasomatism by evaporite-derived boron.  

PubMed

Tourmaline-rich rocks are common in the low-grade, interior portions of the Barberton greenstone belt of South Africa, where shallow-marine sediments and underlying altered basaltic and komatiitic lavas contain up to 50% tourmaline. The presence of tourmaline-bearing rip-up clasts, intraformational tourmaline pebbles and tourmaline-coated grains indicate that boron mineralization was a low-temperature, surficial process. The association of these lithologies with stromatolites, evaporites, and shallow-water sedimentary structures and the virtual absence of tourmaline in correlative deep-water facies rocks in the greenstone belt strengthens this model. Five tourmaline-bearing lithologic groups (basalts, komatiites, evaporite-bearing sediments, stromatolitic sediments, and quartz veins) are distinguished based on field, petrographic, and geochemical criteria. Individual tourmaline crystals within these lithologies show internal chemical and textural variations that reflect continued growth through intervals of change in bulk-rock and fluid composition accompanying one or more metasomatic events. Large single-crystal variations exist in Fe/Mg, Al/Fe, and alkali-site vacancies. A wide range in tourmaline composition exists in rocks altered from similar protoliths, but tourmalines in sediments and lavas have similar compositional variations. Boron-isotope analyses of the tourmalines suggest that the boron enrichment in these rocks has a major marine evaporitic component. Sediments with gypsum pseudomorphs and lavas altered at low temperatures by shallow-level brines have the highest delta 11B values (+2.2 to -1.9%); lower delta 11B values of late quartz veins (-3.7 to -5.7%) reflect intermediate temperature, hydrothermal remobilization of evaporitic boron. The delta 11B values of tourmaline-rich stromatolitic sediments (-9.8 and -10.5%) are consistent with two-stage boron enrichment, in which earlier marine evaporitic boron was hydrothermally remobilized and vented in shallow-marine or subaerial sites, mineralizing algal stromatolites. The stromatolite-forming algae preferentially may have lived near the sites of hydrothermal discharge in Archean times. PMID:11542207

Byerly, G R; Palmer, M R

1991-05-01

18

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

19

Carbonaceous cherts in the Barberton greenstone belt and their significance for the study of early life in the Archean record.  

PubMed

The 3.5-3.2 Ga old volcano-sedimentary succession of the Barberton greenstone belt (South Africa) is characterized by lithological units that are repeated in a regular manner. Komatiitic, basaltic, and dacitic volcanic and volcaniclastic sequences are capped by zones of silica enrichment, followed by bedded carbonaceous cherts. Stratiform and crosscutting carbonaceous chert veins are common in silica alteration zones and bedded cherts. A detailed field study of several chert horizons and chert veins that range in age from 3.47 to 3.30 Ga revealed the importance of syndepositional hydrothermal activity for their origin. Bedded cherts consist of silicified detrital and tuffaceous sediments that were deposited on the seafloor. Silicification took place at the sediment-water interface as a result of diffuse upflow of low-temperature hydrothermal fluids, which gave rise to the formation of impermeable chert caps. Fluid overpressure resulted in the breaching of the cap rocks at times. Chert veins contain angular host rock fragments, replace wall rocks, and show evidence of multiple vein fillings and in situ brecciation of earlier generations of vein fillings. They represent hydraulic fractures that were initiated by overpressuring of the hydrothermal system. The vein networks were infilled, partly by hydrothermal chert precipitates, and partly by still unconsolidated (not yet silicified) sedimentary material derived from overlying sedimentary horizons. Field, petrographic, isotopic, and trace element evidence indicate that most carbonaceous matter represents sedimentary material that originated by biogenic processes in the Archean oceans and not by hydrothermal processes in the subsurface. PMID:17480166

Hofmann, Axel; Bolhar, Robert

2007-04-01

20

Geochemical and petrological study of Barberton Greenstone Belt cherts (3.2-3.5 Ga), South Africa  

NASA Astrophysics Data System (ADS)

The massive deposition of cherts during Archean time provides important information about conditions on the sea floor during the early history of the Earth. We studied samples from four sites in the Barberton Greenstone Belt (3.2-3.5 Ga), South Africa, including fresh ICDP core samples, to understand their formation. We identified three different origins for cherts: direct precipitation from seawater, precipitation in fractures from silica-rich fluids, and replacement of preexisting rocks (silicification) at or near the surface. To better constrain the various formation processes of cherts, we use a petrological, rheological and geochemical approach: both macro- and micro- structural observations are used to understand early physical behavior of chert, silica precipitation, and silicification processes. Rheological information is obtained by careful field observations: we observe a complex behavior for cherts, with ductile to brittle deformation structures, sometimes both in the same layer, extremely fast diagenetic induration processes, and evidence of an early colloidal silica phase. High-resolution analyses (RAMAN, synchrotron and lab-based X-Ray microfluorescence, cathodoluminescence) are used to link micro-scale element distribution with microstructures, and to understand micro-scale formation processes. These approaches will be complemented by stable isotope (Si and O) and fluid inclusions analyses. Coupling petrological informations and geochemical analyses allow us to define reliable criteria to differentiate the three origins of cherts. When petrological observations show a secondary silicification of previously deposited sediments (e.g. laminations, ripple marks, silicified ashes), samples have trace element patterns with high HREE contents, and strong negative Sr and Li anomalies. In comparison, when cherts seem to be chemically precipitated on the sea floor, patterns show lower HREE and higher LILE contents, with a strong positive Ba anomaly and depletion in Zr and Hf. Some commonly used criteria to identify the origin of fluids, such as Eu positive anomaly as a hydrothermal signal and Y, La and Gd positive anomalies and enrichment in HREE contents as oceanic signals, appear unreliable. We also undertook a petrological and geochemical study of siliceous chemical precipitates in modern volcanic lakes. Comparison of internal structures and chemical signatures of Archean and modern cherts is used to constrain rheological properties, to infer early physico-chemical conditions on the seafloor, and to study fractionation processes during silica transfer from fluid to rock.

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

2011-12-01

21

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

22

Evidence for Microbial Activity in ~3.5 Ga Pillow Basalts From the Barberton Greenstone Belt, South Africa  

NASA Astrophysics Data System (ADS)

We have discovered biosignatures in the formerly glassy rims of pillow lavas from the Mesoarchean Barberton Greenstone Belt (BGB) in South Africa. Over the last decade, bioalteration of basaltic glass in pillow lavas and volcaniclastic rocks has been well documented from in-situ oceanic crust and well-preserved Phanerozoic ophiolites. Much of the debate regarding the biogenicity of purported microfossils of early life centers on the interpretation of the host rocks' protoliths. To date, most protoliths have been interpreted to be of sedimentary origin. Some workers have proposed alternate origins for these substrates, including hydrothermal and even volcanic derivation, to cast doubt on their putative biogenicity. Hence studies documenting evidence for early life have proven to be controversial. Here we document evidence for microbial activity in ~3.5 Ga subaqueous volcanic rocks that represent a new, unambiguous geological setting in the search for early life on Earth. The BGB magmatic sequence is dominated by mafic to ultramafic pillow lavas, sheet flows, and intrusions interpreted to represent 3480- to 3220-million-year-old oceanic crust and island arc assemblages. The BGB pillow lavas are exceptionally well-preserved and represent unequivocal evidence that these rocks were erupted in a subaqueous environment. The formerly glassy rims of the BGB pillow lavas contain micron-sized, microbially generated, tubular structures consisting of titanite. These structures are interpreted to have formed during microbial etching of the originally glassy pillow rims and were subsequently mineralized by titanite during greenschist facies seafloor hydrothermal alteration. Overlapping metamorphic and magmatic dates from the pillow lavas suggest this process occurred soon after eruption of the pillow lavas on the seafloor. X-ray mapping has revealed the presence of carbon along the margins of the tubular structures. Disseminated carbonates within the microbially altered BGB pillow rims have C-isotope values depleted by as much as -16 per mil, which is consistent with microbial oxidation of organic matter. In contrast, the crystalline pillow interiors exhibit C-isotope values bracketed between Archean marine carbonate (~0 per mil) and mantle CO2 (-5 to -7 per mil). On the basis of the observed textural and geochemical signatures we propose that the glassy rims of the BGB pillow lavas hosted microbial life almost 3.5 billion years ago. Remnants of Archean oceanic crust may therefore be one of the most promising places to search for vestiges of early life on Earth.

Muehlenbachs, K.; Banerjee, N. R.; Furnes, H.; Staudigel, H.; de Wit, M.

2004-05-01

23

Texture-specific Si isotope variations in Barberton Greenstone Belt cherts record low temperature fractionations in early Archean seawater  

NASA Astrophysics Data System (ADS)

Sedimentary cherts are unusually abundant in early Archean (pre-3.0 Ga) sequences, suggesting a silica cycle that was profoundly different than the modern system. Previously applied for the purpose of paleothermometry, Si isotopes in ancient cherts can offer broader insight into mass fluxes and mechanisms associated with silica concentration, precipitation, diagenesis, and metamorphism. Early Archean cherts contain a rich suite of sedimentological and petrographic textures that document a history of silica deposition, cementation, silicification, and recrystallization. To add a new layer of insight into the chemistry of early cherts, we have used wavelength-dispersive spectroscopy and then secondary ion mass spectrometry (SIMS) to produce elemental and Si and O isotope ratio data from banded black-and-white cherts from the Onverwacht Group of the Barberton Greenstone Belt, South Africa. This geochemical data is then interpreted in the framework of depositional and diagenetic timing of silica precipitation provided by geological observations. SIMS allows the comparison of Si and O isotope ratios of distinct silica phases, including black carbonaceous chert beds and bands (many including well-defined sedimentary grains), white relatively pure chert bands including primary silica granules, early cavity-filling cements, and later quartz-filled veins. Including all chert types and textures analyzed, the ?30Si dataset spans a range from -4.78‰ to +3.74‰, with overall mean 0.20‰, median 0.51‰, and standard deviation 1.30‰ (n = 1087). Most samples have broadly similar ?30Si distributions, but systematic texture-specific ?30Si differences are observed between white chert bands (mean +0.60‰, n = 750), which contain textures that represent primary and earliest diagenetic silica phases, and later cavity-filling cements (mean -1.41‰, n = 198). We observed variations at a ?100 ?m scale indicating a lack of Si isotope homogenization at this scale during diagenesis and metamorphism, although fractionations during diagenetic phase transformations may have affected certain textures. We interpret these systematic variations to reflect fractionation during silica precipitation as well as isotopically distinct fluids from which later phases originated. SIMS ?18O values fall in a range from 16.39‰ to 23.39‰ (n = 381), similar to previously published data from bulk gas source mass spectrometry of Onverwacht cherts. We observed only limited examples of texture-related variation in ?18O and did not observe correlation of ?18O with ?30Si trends. This is consistent with hypotheses that Si isotope ratios are more resistant to alteration under conditions of rock-buffered diagenesis (Marin-Carbonne et al., 2011). Our results indicate that low temperature processes fractionated silicon isotopes in early Archean marine basins, a behavior that probably precludes the application of chert ?30Si as a robust paleothermometer. The values we observe for facies that sedimentological and petrographic observations indicate formed as primary and earliest diagenetic silica precipitates from seawater are more 30Si-rich than that expected for bulk silicate Earth. This is consistent with the hypothesis that the silicon isotope budget is balanced by the coeval deposition of 30Si-enriched cherts and 30Si-depleted iron formation lithologies. Precipitation of authigenic clay minerals in both terrestrial and marine settings may have also comprised a large 30Si-depleted sink, with the corollary of an important non-carbonate alkalinity sink consuming cations released by silicate weathering.

Stefurak, Elizabeth J. T.; Fischer, Woodward W.; Lowe, Donald R.

2015-02-01

24

Possible and Impossible Sources for Archean Granitoids: Preliminary Results of Melting Experiments on Barberton Greenstone Belt Lithologies at 3-5 Gpa  

NASA Astrophysics Data System (ADS)

An understanding of the relationship between the profuse granitoid batholiths of mid-late Archean granite-greenstone terrains, and the keels of mafic-ultramafic metavolcanics that comprise the greenstone belts is crucial to the development of models for the evolution of Archean continental crust. If the mafic-ultramfic rocks of the greenstone complexes represent Archean oceanic crust, then they also represent possible source materials for the granitoid magmas that engulf them, assuming that plate tectonic boundary processes are valid throughout the Archean. The greenstone belt sequences thus represent hydrated, chemically-altered, mafic-ultramafic secondary crust that can be subducted or otherwise foundered to depths at which partial melting may take place. We present preliminary results of a broader experimental study examining the control of the source bulk composition (hence source mineralogy) on the composition of low-degree partial melts of mafic-ultramafic metavolcanics from the Barberton greenstone belt, South Africa, and simulating processes taking place at the base of tectonically-thickened piles of secondary crust associated with general zones of "plate" convergence and quasi-subduction in the Archean. Melting experiments have thus far been carried out on a basaltic komatiite (CaO/Al2O3 = 1.3, MgO = 11 wt%) and an ultramafic komatiite (MgO = 33 wt% from the Komati Formation, Barberton. Pulverized rock powders were packed in pressure-sealed Au capsules for melting experiments in the multi-anvil apparatus at 3.8 GPa and 1200C. Low-degree melt (10%) of the basaltic komatiite at 3.8 GPa and 1200C contains 55wt% SiO2, but is highly alkaline and SiO2-undersaturated, and coexists with an eclogitic residual assemblage containing rutile. Low-degree melt of the ultramafic komatiite (6-8%) is basaltic and highly enriched in Cr and Ti. Although very different in terms of its major-element composition from typical tonalite-trondhjemite-granodiorite (TTG) granitoids of the mid-late Archean, the trace element characteristics of the low-degree melt of the basaltic komatiite, as determined by ion microprobe, closely mirror those of typical mid-late Archean TTG, with enrichments in large-ion lithophile elements (Sr = 298 ppm, Ba = 814 ppm), strongly fractionated, heavy rare-earth element depleted REE patterns ((La/Yb)n = 19), and negative-anomalies in Nb and Ti. These are features of the characteristic geochemical signature of TTG granitoids, attributable to an origin by partial melting of a rutile-bearing, garnet-amphibolite or eclogitic, metabasaltic source, yet manifest in a melt that, in terms of its major element composition, is fundamentally different from typical TTG. Although low-degree melts of basaltic komatiite possess the trace element characteristics of typical Archean TTG, their major-element compositions differ fundamentally, and thus the source of TTG magmas appears to be variably-enriched, hydrothermally-altered "generic" MORB (i.e., CaO/Al2O3 = 0.4-0.8, MgO = 6-8 wt%).

Rapp, R. P.; Shimizu, N.; de Wit, M. J.

2001-05-01

25

Compositional Grading in an Impact-produced Spherule Bed, Barberton Greenstone Belt, South Africa: A Key to Condensation History of Rock Vapor Clouds  

NASA Technical Reports Server (NTRS)

The chemical and physical processes by which spherules form during the condensation of impact-produced rock vapor clouds are poorly understood. Although efforts have been made to model the processes of spherule formation, there is presently a paucity of field data to constrain the resulting theoretical models. The present study examines the vertical compositional variability in a single early Archean spherule bed in the Barberton Greenstone Belt (BGB), South Africa, in order to better identify the process by which impact vapor clouds condense and spherules form and accumulate. The BGB spherule beds are suitable for this type of study because of their great thickness, often exceeding 25cm of pure spherules, due to the massive sizes of the impactors. Two main problems complicate analysis of vertical compositional variability of graded spherule beds: (1) differential settling of particles in both the vapor and water column due to density and size differences and (2) turbulence within the vapor cloud. The present study compares sections of spherule bed S3 from four different depositional environments in the Barberton Greenstone Belt: (1) The Sheba Mine section (SAF-381) was deposited under fairly low energy conditions in deep water, providing a nice fallout sequence, and also has abundant Ni-rich spinels; (2) Jay's Chert section (SAF-380) was deposited in subaerial to shallow-water conditions with extensive post-depositional reworking by currents. The spherules also have preserved spinels; (3) the Loop Road section (loc. SAF-295; samp. KSA-7) was moderately reworked and has only rare preservation of spinels; and (4) the shallow-water Barite Syncline section (loc. SAF-206; samp KSA-1) has few to no spinels preserved and is not reworked. Although all of the spherule beds have been altered by silica diagenesis and K-metasomatism, most of the compositional differences between these sections appear to reflect their diagenetic histories, possibly related to their differing depositional environments. Sulfate diagenesis in the Barite Syncline and Loop road sections may account for the loss of spinels.

Krull, A. E.; Lowe, D. R.; Byerly, G. R.

2003-01-01

26

Inferred Primary Compositions of Archean Spherules Formed by the Condensation of an Impact-produced Rock Vapor Cloud, Barberton Greenstone Belt, South Africa  

NASA Technical Reports Server (NTRS)

Based on the lunar cratering record, impacts were larger and more frequent on the early Earth than they are today. There is no persevered record of these early terrestrial impacts because rocks of this age have been obliterated by tectonism and erosion. The oldest known evidence of impacts on Earth lies in four beds (S1, S2, S3 and S4) in the Barberton Greenstone Belt (BGB), South Africa, ranging in age from about 3.24 to 3.47 Ga. These beds are composed in large part of sand-sized spherical particles, termed spherules, that are thought to have formed by the condensation of rock vapor clouds ejected above the atmosphere as a result of large impacts. Spherule beds S2 and S3 are both about 20 cm thick where composed entirely of fall-deposited spherules and up to a meter thick where spherules are mixed with locally derived debris. The diameters the bolides have been estimated to be between 20 and 50 km, based on bed thickness, size of the largest spherules, Ir fluence and extraterrestrial Cr.

Krull, A. E.; Lowe, D. R.; Byerly, G. R.

2003-01-01

27

Archean deep-water depositional system: interbedded and banded iron formation and clastic turbidites in the Barberton Greenstone Belt, South Africa  

NASA Astrophysics Data System (ADS)

The 3.23 billion year old sediments in the Barberton greenstone belt, South Africa include some of the world's oldest known deep-water deposits. Unique to this locality are turbidites interbedded with banded iron formation (BIF) and banded ferruginous chert (BFC). This unusual association may provide clues for reconstructing Archean deep-water depositional settings. For our study we examined freshly drilled core in addition to measuring ~500 m of outcrop exposures along road cuts. The stacking pattern follows an overall BIF to BFC to amalgamated turbidite succession, although isolated turbidites do occur throughout the sequence. The turbidites are predominately massive, and capped with thin, normally graded tops that include mud rip-ups, chert plates, and ripples. The lack of internal stratification and the amalgamated character suggests emplacement by surging high-density turbidity currents. Large scours and channels are absent and bedding is tabular: the flows were collapsing with little turbulence reaching the bed. In contrast, field evidence indicates the BIF and BFC most likely precipitated directly out of the water column. Preliminary interpretations indicate the deposits may be related to a pro-deltaic setting. (1) Deltaic systems can generate long-lived, high volume turbidity currents. (2) The contacts between the BIF, BFC, and turbidite successions are gradual and inter-fingered, possibly representing lateral facies relationships similar to modern pro-delta environments. (3) Putative fan delta facies, including amalgamated sandstone and conglomerate, exist stratigraphically updip of the basinal sediments.

Zentner, Danielle; Lowe, Donald

2013-04-01

28

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

29

Implications of in situ calcification for photosynthesis in a ~ 3.3 Ga-old microbial biofilm from the Barberton greenstone belt, South Africa  

NASA Astrophysics Data System (ADS)

Timing the appearance of photosynthetic microorganisms is crucial to understanding the evolution of life on Earth. The ability of the biosphere to use sunlight as a source of energy (photoautotrophy) would have been essential for increasing biomass and for increasing the biogeochemical capacity of all prokaryotes across the range of redox reactions that support life. Typical proxies for photosynthesis in the rock record include features, such as a mat-like, laminated morphology (stratiform, domical, conical) often associated with bulk geochemical signatures, such as calcification, and a fractionated carbon isotope signature. However, to date, in situ, calcification related to photosynthesis has not been demonstrated in the oldest known microbial mats. We here use in situ nanometre-scale techniques to investigate the structural and compositional architecture in a 3.3 billion-year (Ga) old microbial biofilm from the Barberton greenstone belt, thus documenting in situ calcification that was most likely related to anoxygenic photosynthesis. The Josefsdal Chert Microbial Biofilm (JCMB) formed in a littoral (photic) environment. It is characterised by a distinct vertical structural and compositional organisation. The lower part is calcified in situ by aragonite, progressing upwards into uncalcified kerogen characterised by up to 1% sulphur, followed by an upper layer that contains intact filaments at the surface. Crystallites of pseudomorphed pyrite are also associated with the biofilm suggesting calcification related to the activity of heterotrophic sulphur reducing bacteria. In this anoxygenic, nutrient-limited environment, the carbon required by the sulphur reducing bacteria could only have been produced by photoautotrophy. We conclude that the Josfsdal Chert Microbial Biofilm was formed by a consortium of anoxygenic microorganisms, including photosynthesisers and sulphur reducing bacteria.

Westall, Frances; Cavalazzi, Barbara; Lemelle, Laurence; Marrocchi, Yves; Rouzaud, Jean-Noël; Simionovici, Alexandre; Salomé, Murielle; Mostefaoui, Smail; Andreazza, Caroline; Foucher, Frédéric; Toporski, Jan; Jauss, Andrea; Thiel, Volker; Southam, Gordon; MacLean, Lachlan; Wirick, Susan; Hofmann, Axel; Meibom, Anders; Robert, François; Défarge, Christian

2011-10-01

30

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

31

High Resolution Tephra and U/Pb Chronology of the 3.33-3.26 Ga Mendon Formation, Barberton Greenstone Belt, South Africa  

NASA Astrophysics Data System (ADS)

Stratigraphic and geologic interpretations of komatiitic flows and tuffs in the Barberton greenstone belt (BGB) are complicated by structural complexity, facies changes, and temporal repetition of lithofacies. Here we describe new data on the compositions of flows and tuffs and U/Pb ages that correlate existing and proposed new members of the Mendon Formation across the BGB. The Mendon Formation includes from 300 to >1000 m of komatiite, komatiitic tuff, and carbonaceous-to-ferruginous chert that represent the uppermost Onverwacht Group south of the Inyoka Fault. Our new data confirm that the Weltevreden Formation, the uppermost Onverwacht Group north of the Inyoka Fault, is correlative with the upper members of the Mendon Formation. The conformably overlying Fig Tree Group is composed largely of lithic sandstones and dacitic volcaniclastic rocks likely representing uplift and volcanism within a magmatic arc. Thus the Onverwacht to Fig Tree Group transition may represent a profound change from plume to plate tectonics. Recent studies have also demonstrated the importance of large asteroidal impacts near the Onverwacht-Fig Tree contact, two in the Mendon Formation and two in the lower Fig Tree Group spanning a 50 myr interval, suggesting a possible link between impacts and this tectonic transition. The compositional change from komatiitic to dacitic ash is moderately abrupt and near the S2 impact layer. However, at least five felsic ash layers are recognized in the Mendon Formation, and several komatiitic ash layers occur above S2 in the lowest Fig Tree Group. A preliminary compilation of the new data with that of previous studies suggests: 1) the Mendon Formation has an extreme diversity of primary komatiitic compositions, but also includes thin felsic ash layers, 2) no komatiitic flows have been identified in the Fig Tree Group but several komatiitic ash layers occur associated with spherule bed S2, 3) major faults in the south-central BGB isolate sections of the Mendon Formation with correlative komatiitic compositions, but remarkably different thicknesses, and 4) there are at least four impact layers in this short interval.

Decker, N. B.; Stefurak, E. J.; Thompson, M. E.; Lowe, D. R.; Byerly, G. R.

2012-12-01

32

Sulfur isotope mass-independent fractionation in impact deposits of the 3.2 billion-year-old Mapepe Formation, Barberton Greenstone Belt, South Africa  

NASA Astrophysics Data System (ADS)

Theoretical and experimental studies have shown that atmospheric SO2 isotopologue self-shielding effects in the 190-220 nm region of the solar spectrum are the likely cause for mass independent fractionation of sulfur isotopes (S-MIF). The main products of this photochemical reaction - SO3 and S0 - typically define a compositional array of ca. ?33S/?34S = 0.06-0.14. This is at odds with the generally observed trend in Archean sulfides, which broadly defines an array of ca. ?33S/?34S = 0.9. Various explanations have been proposed, including a diminution of ?34S caused by chemical and biogenic mass-dependent fractionation of sulfur isotopes (S-MDF), mixing with photolytic products produced during felsic volcanic events, or partial blocking of the low-wavelength part of the spectrum due to the presence of reduced atmospheric gases or an organic haze. Early in Earth history large meteorite impacts would have ejected dust and gas clouds into the atmosphere that shielded solar radiation and affected global climate. It is thus likely that at certain time intervals of high meteorite flux the atmosphere was significantly perturbed, having an effect on atmospheric photochemistry and possibly leaving anomalous sulfur isotopic signatures in the rock record. Here we describe the sulfur isotopic signatures in sulfides of spherule beds S2, S3 and S4 of the Barberton Greenstone Belt, South Africa. In particular, in spherule bed S3 - and to a lesser extent S4 - a trend of ca. ?33S/?34S = 0.23 is observed that closely follows the expected trend for SO2-photolysis in the 190-220 nm spectral range. This suggests that an impact dust cloud (deposited as spherule beds), which sampled the higher region of the atmosphere, specifically incorporated products of SO2 photolysis in the 190-220 nm range, and blocked photochemical reactions at higher wavelengths (250-330 nm band). By implication, the generally observed Archean trend appears to be the result of mixing of different MIF-S sources arising from a variety of photochemical reactions that took place in the lower part of the atmosphere.

van Zuilen, M. A.; Philippot, P.; Whitehouse, M. J.; Lepland, A.

2014-10-01

33

Palaeomagnetism of Archaean rocks of the Onverwacht Group, Barberton Greenstone Belt (southern Africa): Evidence for a stable and potentially reversing geomagnetic field at ca. 3.5 Ga  

NASA Astrophysics Data System (ADS)

Palaeomagnetic data from the Palaeoarchaean Era (3.2-3.6 Ga) have the potential to provide us with a great deal of information about early conditions within, and processes affecting, the Earth's core, mantle, and surface environment. Here we present new data obtained from some of the oldest palaeomagnetic recorders in the world: igneous and sedimentary rocks from the Onverwacht Group of the Barberton Greenstone Belt (Kaapvaal Craton, southern Africa). Our palaeomagnetic measurements strengthen a recently published positive conglomerate test (Y. Usui, J.A. Tarduno, M. Watkeys, A. Hofmann and R.D. Cottrell, 2009) and our new U-Pb date constrains the conglomerate to older than 3455 ± 8 Ma. The new palaeomagnetic data from other units are nontrivial to interpret and are of uncertain reliability when taken individually; similar, we argue, to all other published palaeomagnetic data of this age. Nonetheless, four poles (two new, two derived from published data) produced from high temperature components of magnetisation recorded in the Komati, Noisy, and Hooggenoeg formations exhibit considerably improved clustering when their directions are corrected for differences in attitude resulting from a large fold structure dated at 3.23 Ga. On the basis of this enhanced consistency in stratigraphic coordinates, the positive conglomerate test, and the absence of any clear indications of their remagnetisation from comparison with younger poles, we argue that these are the most trustworthy palaeomagnetic results yet produced from any rocks of Palaeoarchaean age. When taken in conjunction with published data, the new results present the most compelling evidence to date that the Earth had a stable geomagnetic field at ca. 3.5 Ga in addition to presenting tentative evidence that it was undergoing polarity reversals. The data do not appear to support a claim, made previously from Palaeoarchean palaeomagnetic data from the Pilbara Craton (Y. Suganuma, Y. Hamano, S. Niitsuma, M. Hoashi, T. Hisamitsu, N. Niitsuma, K. Kodama and M. Nedachi, 2006), of extremely rapid latitudinal plate motion during this period. Finally, when compared with similarly aged data from the Pilbara Craton (Western Australia), the new data do not rule out the hypothesis that the two cratons were conjoined at this point in their history in the supercraton Vaalbara.

Biggin, Andrew J.; de Wit, Maarten J.; Langereis, Cor G.; Zegers, Tanja E.; Voûte, Sara; Dekkers, Mark J.; Drost, Kerstin

2011-02-01

34

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

35

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

36

Greenstone Belt Assessment  

NSDL National Science Digital Library

This lab utilizes rock samples and images of rocks found in Greenstone Belts that formed globally during the Precambrian Era. The students examine and describe each of the samples visually using terminology regarding their rock texture and associated features. The students then describe or suggest what the rock properties suggest about the process of formation of the rock and the depositional or geologic environment in which the rock formed. Students then collate the data given the relative ages of the rocks and hypothesize how or where these rock units and features could possibly have formed in this association.

Pamela Nelson

37

Spherule Beds 3.47-3.24 Billion Years Old in the Barberton Greenstone Belt, South Africa: A Record of Large Meteorite Impacts and Their Influence on Early Crustal and Biological Evolution  

NASA Technical Reports Server (NTRS)

Four layers, S1-S4, containing sand-sized spherical particles formed as a result of large meteorite impacts, occur in 3.47-3.24 Ga rocks of the Barberton Greenstone Belt, South Africa. Ir levels in S3 and S4 locally equal or exceed chondritic values but in other sections are at or only slightly above background. Most spherules are inferred to have formed by condensation of impact-produced rock vapor clouds, although some may represent ballistically ejected liquid droplets. Extreme Ir abundances and heterogeneity may reflect element fractionation during spherule formation, hydraulic fractionation during deposition, and/or diagenetic and metasomatic processes. Deposition of S1, S2, and S3 was widely influenced by waves and/or currents interpreted to represent impact-generated tsunamis, and S1 and S2 show multiple graded layers indicating the passage of two or more wave trains. These tsunamis may have promoted mixing within a globally stratified ocean, enriching surface waters in nutrients for biological communities. S2 and S3 mark the transition from the 300-million-year-long Onverwacht stage of predominantly basaltic and komatiitic volcanism to the late orogenic stage of greenstone belt evolution, suggesting that regional and possibly global tectonic reorganization resulted from these large impacts. These beds provide the oldest known direct record of terrestrial impacts and an opportunity to explore their influence on early life, crust, ocean, and atmosphere. The apparent presence of impact clusters at 3.26-3.24 Ga and approx. 2.65-2.5 Ga suggests either spikes in impact rates during the Archean or that the entire Archean was characterized by terrestrial impact rates above those currently estimated from the lunar cratering record.

Lowe, Donald R.; Byerly, Gary R.; Kyte, Frank T.; Shukolyukov, Alexander; Asaro, Frank; Krull, Alexander

2003-01-01

38

Terrestrial Biomarkers for Early Life on Earth as Analogs for Possible Martian Life Forms: Examples of Minerally Replaced Bacteria and Biofilms From the 3.5 - 3.3-Ga Barberton Greenstone Belt, South Africa  

NASA Technical Reports Server (NTRS)

The search for extraterrestrial life and especially martian life hinges on a variety of methods used to identify vestiges of what we could recognize as life, including chemical signatures, morphological fossils, and biogenic precipitates. Although the possibility of extant life on Mars (subsurface) is being considered, most exploration efforts may be directed toward the search for fossil life. Geomorphological evidence points to a warmer and wetter Mars early on in its history, a scenario that encourages comparison with the early Earth. For this reason, study of the early terrestrial life forms and environment in which they lived may provide clues as to how to search for extinct martian life. As a contribution to the early Archean database of terrestrial microfossils, we present new data on morphological fossils from the 3.5-3.3-Ga Barberton greenstone belt (BGB), South Africa. This study underlines the variety of fossil types already present in some of the oldest, best-preserved terrestrial sediments, ranging from minerally replaced bacteria and bacteria molds of vaRious morphologies (coccoid, coccobacillus, bacillus) to minerally replaced biofilm. Biofilm or extracellular polymeric substance (EPS) is produced by bacteria and appears to be more readily fossilisable than bacteria themselves. The BGB fossils occur in shallow water to subaerial sediments interbedded with volcanic lavas, the whole being deposited on oceanic crust. Penecontemporaneous silicification of sediments and volcanics resulted in the chertification of the rocks, which were later subjected to low-grade metamorphism (lower greenschist).

Westall, F.; McKay, D. S.; Gibson, E. K.; deWit, M. J.; Dann, J.; Gerneke, D.; deRonde, C. E. J.

1998-01-01

39

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. PMID:17008224

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

2006-01-01

40

Workshop on Techtonic Evolution of Greenstone Belts  

NASA Technical Reports Server (NTRS)

Topics addressed include: greenstone belt externalities; boundaries; rock terranes; synthesis and destiny; tectonic evolution; rock components and structure; sedimentology; stratigraphy; volcanism; metamorphism; and geophysics.

Dewit, M. J. (editor); Ashwal, Lewis D. (editor)

1986-01-01

41

The Jack Hills greenstone belt, Western Australia  

Microsoft Academic Search

The Jack Hills greenstone belt is situated along the southern margin of the Narryer Terrane in the northwest of the Yilgarn Craton, in fault contact with Archean granitic gneiss and granitic rocks. The belt has endured a long deformation history and the effects of recrystallisation, alteration, and the occurrence of a substantial proportion of lithologically similar metasedimentary rocks makes it

Catherine V. Spaggiari; Robert T. Pidgeon; Simon A. Wilde

2007-01-01

42

The Jamestown Ophiolite Complex, Barberton mountain belt - A section through 3.5 Ga oceanic crust  

NASA Astrophysics Data System (ADS)

The Jamestown Ophiolite Complex of the Barberton greenstone belt, South Africa, is investigated, and the intrusive nature of mafic-ultramafic units from the Komati and Kromberg formations into overlying pillow lavas and sediments is documented. Evidence is presented for multiple intrusive events within the igneous sections, including crosscutting intrusives, multiple injection of magma in the Komati section, and sheeted intrusions in the Kromberg section. The thinness of the Jamestown complex suggests that, locally at least, the ca 3.5 Ga oceanic crust was also thin, consistent with the regionally extensive metasomatic alteration.

de Wit, Maarten J.; Hart, Roger A.; Hart, Rodger J.

43

Chronology of early Archaean granite-greenstone evolution in the Barberton Mountain Land, South Africa, based on precise dating by single zircon evaporation  

NASA Technical Reports Server (NTRS)

Precise Pb-207/Pb-206 single zircon evaporating ages are reported for low-grade felsic metavolcanic rocks within the Onverwacht and Fig Tree Groups of the Barberton Greenstone Belt (BGB), South Africa, as well as for granitoid plutons bordering the belt. Dacitic tuffs of the Hooggenoeg Formation in the upper part of the Onverwacht Group are shown to yield ages between 3445 + or - 3 and 3416 + or - 5 Ma and to contain older crustal components represented by a 3504 + or - 4 Ma old zircon xenocryst. Fig Tree dacitic tuffs and agglomerates have euhedral zircons between 3259 + or - 3 Ma in age which are interpreted to reflect the time of crystallization. The comagmatic relationships between greenstone felsic volcanic units and the surrounding plutonic suites are keynoted. The data adduced show that the Onverwacht and Fig Tree felsic units have distinctly different ages and thus do not constitute a single, tectonically repeated unit as proposed by others. It is argued that conventional multigrain zircon dating may not accurately identify the time of felsic volcanic activity in ancient greenstones, and that the BGB in the Kaapval craton of southern Africa and greenstones in the Pilbara Block of Western Australia may have been part of a larger crustal unit in early Archaean times.

Kruener, Alfred; Byerly, Gary R.; Lowe, Donald R.

1991-01-01

44

Chronology of early Archaean granite-greenstone evolution in the Barberton Mountain Land, South Africa, based on precise dating by single zircon evaporation.  

PubMed

We report precise 207Pb/206Pb single zircon evaporation ages for low-grade felsic metavolcanic rocks within the Onverwacht and Fig Tree Groups of the Barberton Greenstone Belt (BGB), South Africa, and from granitoid plutons bordering the belt. Dacitic tuffs of the Hooggenoeg Formation in the upper part of the Onverwacht Group yield ages between 3445 +/- 3 and 3416 +/- 5 Ma and contain older crustal components represented by a 3504 +/- 4 Ma old zircon xenocryst. Fig Tree dacitic tuffs and agglomerates have euhedral zircons between 3259 +/- 5 and 3225 +/- 3 Ma in age which we interpret to reflect the time of crystallization. A surprisingly complex xenocryst population in one sample documents ages from 3323 +/- 4 to 3522 +/- 4 Ma. We suspect that these xenocrysts were inherited, during the passage of the felsic melts to the surface, from various sources such as greenstones and granitoid rocks now exposed in the form of tonalite-trondhjemite plutons along the southern and western margins of the BGB, and units predating any of the exposed greenstone or intrusive rocks. Several of the granitoids along the southern margin of the belt have zircon populations with ages between 3490 and 3440 Ma. coeval with or slightly older than Onverwacht felsic volcanism, while the Kaap Valley pluton along the northwestern margin of the belt is coeval with Fig Tree dacitic volcanism. These results emphasize the comagmatic relationships between greenstone felsic volcanic units and the surrounding plutonic suites. Some of the volcanic plutonic units contain zircon xenocrysts older than any exposed rocks. These indicate the existence of still older units, possibly stratigraphically lower and older portions of the greenstone sequence itself, older granitoid intrusive rocks, or bodies of older, unrelated crustal material. Our data show that the Onverwacht and Fig Tree felsic units have distinctly different ages and therefore do not represent a single, tectonically repeated unit as proposed by others. Unlike the late Archaean Abitibi greenstone belt in Canada, which formed over about 30 Ma. exposed rocks in the BGB formed over a period of at least 220 Ma. The complex zircon populations encountered in this study imply that conventional multigrain zircon dating may not accurately identify the time of felsic volcanic activity in ancient greenstones. A surprising similarity in rock types, tectonic evolution, and ages of the BGB in the Kaapvaal craton of southern Africa and greenstones in the Pilbara Block of Western Australia suggests that these two terrains may have been part of a larger crustal unit in early Archaean times. PMID:11538384

Krüner, A; Byerly, G R; Lowe, D R

1991-04-01

45

Workshop on the Tectonic Evolution of Greenstone Belts  

NASA Technical Reports Server (NTRS)

The Workshop on the Tectonic Evolution of Greenstone Belts, which is part of the Universities Space Research Association, Lunar and Planetary Institute, of Houston, Texas, met there on Jan. 16-18, 1986. A number of plate tectonic hypotheses have been proposed to explain the origin of Archean and Phanerozoic greenstone/ophiolite terranes. These hypotheses are explored in the abstracts.

1986-01-01

46

Petrography, PGE Contents and Os Isotope Systematics of Barberton CT3 Spherule Layers  

NASA Astrophysics Data System (ADS)

We focus on some spherule layers from the northeastern part of the Barberton Greenstone Belt, South Africa and aim to determine their diagenetic-metamorphic history and to assess their possible impact origin by petrographic and geochemical analyses.

Ozdemir, S.; Schulz, T.; Koeberl, C.; Reimold, W. U.; Mohr-Westheide, T.

2014-09-01

47

A Sm-Nd and Pb isotope study of Archaean greenstone belts in the southern Kaapvaal Craton, South Africa  

NASA Technical Reports Server (NTRS)

An Sm-Nd and Pb study on a wide variety of lithologies in Archaean greenstone belt fragments in the southern Kaapvaal Craton reveals a complex petrogenetic history. The fragments are important because they represent a 350 km transect through the craton south of Barberton to its southern margin. The Commondale greenstone belt yields a precise Sm-Nd age of 3334 + or - 18 Ma on an exceptionally well preserved peridotite suite of komatiitic affinity. The wide range of Sm/Nd from 0.6 to 1.0 is attributed to the unusual occurrence of orthopyroxene in the spinifex-bearing rocks. A considerably younger age of about 3.2 Ga is suggested for the Nondweni greenstone belt close to the southern margin of the craton on the basis of separate Sm-Nd isochrons on individual lithologies ranging from komatiite, through komatiitic basalt and basalt to felsic volcanic rocks. On the basis of the present study the greenstone belts appear to have been emplaced at progressively younger ages toward the southern margin of the craton.

Wilson, A. H.; Carlson, R. W.

1989-01-01

48

Petrography and geochemistry of Mesoarchaean komatiites from the eastern Iron Ore belt, Singhbhum craton, India, and its similarity with 'Barberton type komatiite'  

NASA Astrophysics Data System (ADS)

The Mesoarchaean supracrustals of the Gorumahishani-Badampahar belt, eastern India record sedimentation-volcanism like most other contemporary greenstone belts over the world. The current study reports unambiguous komatiitic rocks from Tua-Dungri hill, Gorumahishani-Badampahar belt, Jharkhand and presents a petrological and geochemical inventory of these very interesting rocks. The Tua-Dungri komatiites are characterised by a well distinguishable cumulate, platy and random spinifex zone. These Tua-Dungri komatiites are rich in SiO2 (47-50 wt%) like Barberton type komatiite or modern day boninite. Their Al depleted nature (Al2O3 = 1.36-2.95 wt%) with very low Al2O3/TiO2 (3.4-6.5) and high CaO/Al2O3 (2-3), high LREE/HREE ratios show further resemblance with the Barberton komatiite. The Tua Dungri komatiite data along with published geochemical, sedimentological and stratigraphic data from the Iron Ore Group of rocks suggest mantle plume activity during the Mesoarchaean on the Singhbhum craton.

Chaudhuri, Trisrota; Mazumder, Rajat; Arima, Makoto

2015-01-01

49

Isotopic age data of single zircons from the Archæan Zukumaland Greenston e Belt, Tanzania  

NASA Astrophysics Data System (ADS)

This study presents precise {U}/{Pb} single zircon age data for three rhyolitic metavolcanic units: one trachyandesitic porphyry, presumably of extrusive origin; one palæosome of a migmatitic gneiss; and one lamprophyric dyke cross-cutting banded iron formation (BIF) of the Upper Nyanzian Supergroup in the Archæan Sukumaland Greenstone Belt, Tanzania. The obtained ages partly contradict the expected field stratigraphical relationships. The isotopic ages of the felsic metavolcanics give a good age bracket for the deposition of the Nyanzian Greenstone Belt units. The older felsic metavolcanics yield ages of 2808±3 Ma and 2780±3 Ma, respectively, whereas the younger felsic metavolcanics provide a minimum age of {2654+15}/{-13 Ma} for the greenstone belt. The porphyritic trachyandesite, intercalated with oxide BIF at Geita, yield an age of 2699±9 Ma and the lamprophyre dyke an age of 2644±3 Ma, respectively. The data for the lamprophyre imposes a maximum age on the Au mineralisation at Geita Mine, since the dyke has been mineralised together with adjacent BIF. The palæosome of a migmatitic gneiss, possibly a basement flanking the greenstone belt to the south at Kahama, has been dated at 2680±3 Ma. Previous models advocating the pre-existing, significantly older, Dodoman basement gneiss within the Archæan Sukumaland Greenstone Belt of northern Tanzania cannot be supported. Emplacement or complete reworking of the granitic protolith coeval with greenstone belt volcanism appears more likely.

Borg, G.; Krogh, T.

1999-08-01

50

Workshop on the Tectonic Evolution of Greenstone Belts (supplement containing abstracts of invited talks and late abstracts)  

NASA Technical Reports Server (NTRS)

Topics addressed include: greenstone belt tectonics, thermal constaints, geological structure, rock components, crustal accretion model, geological evolution, synsedimentary deformation, Archean structures and geological faults.

1986-01-01

51

Bizarre geochemistry of komatiites from the Crixás greenstone belt, Brazil  

NASA Astrophysics Data System (ADS)

Komatiite lava flows in the Crixás greenstone belt, Goiás, Brazil, have textures and volcanic structures typical of Archean komatiites, but are geochemically most unusual. The flows are porphyritic and massive, or layered with spinifex upper parts and olivine cumulate lower parts. MgO contents range from 18 to 40%. In such lavas, only olivine (and minor chromite) can have crystallized, but neither major nor trace elements fall on olivine control lines. In MgO variation diagrams, CaO and Sr fall on lines with slopes steeper than olivine control lines; SiO2, FeO, Na2O, K2O and Y show little systematic variation; Zr shows a large variation that does not correlate with MgO; and Al2O3 decreases markedly with decreasing MgO. The aberrant behaviour is highlighted by the REE (rare earth elements) in spinifex and olivine cumulate layers from three flows: in the spinifex layers, chondrite-normalized REE patterns are hump-shaped with maxima at Nd or Sm ((La/Sm)N=0.6, (Gd/Yb)N=1.6 2.3), whereas cumulate zones in the same flows have steadily sloping patterns, with LREE enriched relative to HREE ((La/Sm)N=1.3, (Gd/Yb)N=1.4). Neither normal magmatic processes acting during emplacement of the komatiites, nor thermal erosion and wall-rock assimilation can explain these effects, and we speculate that elements commonly thought of as “immobile” (e.g. Al, Zr, REE) migrated during hydrothermal alteration or metamorphism. A Pb-Pb whole rock isochron gave an age of 2,728±140 Ma and selected Sm-Nd analyses an apparent isochron age of 2,825±98 Ma (?Nd?0). The Pb-Pb age is believed to be the approximate time of emplacement. Interpretation of the Sm-Nd data is complicated by the evidence of mobility of REE.

Arndt, N. T.; Teixeira, N. A.; White, W. M.

1989-02-01

52

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

Microsoft Academic Search

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

Kim A. A. Hein

2010-01-01

53

THE MURCHISON GREENSTONE BELT, SOUTH AFRICA: ACCRETED1 SLIVERS WITH CONTRASTING METAMORPHIC CONDITIONS2  

E-print Network

1 THE MURCHISON GREENSTONE BELT, SOUTH AFRICA: ACCRETED1 SLIVERS WITH CONTRASTING METAMORPHIC their geotectonic31 implications. The MGB is made of three tectono-metamorphic units: the Silwana Amphibolites, the a greenschist- to lower-amphibolite-facies metamorphism at maximum P--T conditions of 5.639 hal-00691575,version

Boyer, Edmond

54

Evidence for a complex archean deformational history; southwestern Michipicoten Greenstone Belt, Ontario  

NASA Technical Reports Server (NTRS)

The Michipicoten Greenstone Belt extends for about 150 km ENE from the northeastern angle of Lake Superior. In common with many other Archean greenstone belts, it is characterized by generally steep bedding dips and a distribution of major lithologic types suggesting a crudely synclinal structure for the belt as a whole. Detailed mapping and determination of structural sequence demonstrates that the structure is much more complex. The Archean history of the belt includes formation of at least three regionally significant cleavages, kilometer-scale overturning, extensive shearing, and diabase intrusion. Most well defined, mappable 'packages' of sedimentary rocks appear to be bounded by faults. These faults were active relatively early in the structural history of the belt, when extensive overturning also occurred. Steepening of dips, NW-SE shortening, development of steep NE cleavage, and pervasive shearing all postdate the early faulting and the regional overturning, obscuring much of the detail needed to define the geometry of the earlier structures. The results obtained so far suggest, however, that the Michipicoten Greenstone Belt underwent an early stage of thrusting and associated isoclinal folding, probably in a convergent tectonic environment.

Mcgill, George E.; Shrady, Catherine H.

1986-01-01

55

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

56

A crustally contaminated komatiitic dyke–sill–lava complex, Abitibi greenstone belt, Ontario  

Microsoft Academic Search

Detailed field and laboratory studies indicate the Shaw Dome area of the Abitibi greenstone belt, Ontario, contains a lower horizon of intrusive komatiitic rocks (LKH), komatiitic dykes, and an upper horizon of extrusive komatiitic rocks (UKH). The LKH is 500–1000 m thick and consists of undifferentiated dunite (45–50% MgO), laterally equivalent wehrlite (20–50% MgO), and differentiated wehrlite–amphibole gabbro sills. A

M. S. Stone; W. E. Stone

2000-01-01

57

Geochemistry of Precambrian carbonates: II. Archean greenstone belts and Archean sea water.  

PubMed

Carbonate rocks with geological attributes of marine sediments are a minor component of the Archean greenstone belts. Despite their relative scarcity, these rocks are important because they record chemical and isotopic properties of coeval oceans. The greenstones containing such carbonates appear to cluster at approximately 2.8 +/- 0.2 and approximately 3.5 +/- 0.1 Ga ago. The samples for the younger group are from the Abitibi, Yellowknife, Wabigoon (Steep Rock Lake), Michipicoten and Uchi greenstone belts of Canada and the "Upper Greenstones" of Zimbabwe. The older group includes the Swaziland Supergroup of South Africa, Warrawoona Group of Australia and the Sargur marbles of India. Mineralogically, the carbonates of the younger greenstones are mostly limestones and of the older ones, ferroan dolomites (ankerites); the latter with some affinities to hydrothermal carbonates. In mineralized areas with iron ores, the carbonate minerals are siderite +/- ankerite, irrespective of the age of the greenstones. Iron-poor dolomites represent a later phase of carbonate generation, related to post-depositional tectonic faulting. The original mineralogy of limestone sequences appears to have been an Sr-rich aragonite. The Archean carbonates yield near-mantle Sr isotopic values, with (87Sr/86Sr)o of 0.7025 +/- 0.0015 and 0.7031 +/- 0.0008 for younger and older greenstones, respectively. The best preserved samples give delta 13C of +1.5 +/- 1.5% PDB, comparable to their Phanerozoic counterparts. In contrast, the best estimate for delta 18O is -7% PDB. Archean limestones, compared to Phanerozoic examples, are enriched in 16O as well as in Mn2+ and Fe2+, and these differences are not a consequence of post-depositional alteration phenomena. The mineralogical and chemical attributes of Archean carbonates (hence sea water) are consistent with the proposition that the composition of the coeval oceans may have been buffered by a pervasive interaction with the "mantle", that is, with the oceanic crust and the coeval ubiquitous volcanosedimentary piles derived from mantle sources. PMID:11539784

Veizer, J; Hoefs, J; Lowe, D R; Thurston, P C

1989-01-01

58

The taloveis gold deposit in the precambrian Kostomuksha greenstone belt, Karelia  

NASA Astrophysics Data System (ADS)

The Kostomuksha greenstone belt is the main iron district of Karelia. Gold, diamonds, and molybdenum mineralization have been found in this belt over the last two decades. The gold occurrences and deposits pertaining to the gold-sulfide and gold-quartz types were formed at the orogenic stage. The Taloveis deposit and the Faktorny and Berendei ore occurrences are located in the South Kostomuksha area and related to a complex of porphyritic diorite and granite porphyry. The West Ruvinvaara, Niemijarvi, Eastern, and Kurgelampi gold-sulfide and gold-sulfide-quartz occurrences are controlled by metasomatized shear zones and recrystallized sulfide ore hosted in the Shurlovaara and Ruvinvaara formations in the contact aureole of granite of the framework of the greenstone belt near its margin. The gold-arsenopyrite mineralization of the South Kostomuksha open pit is related to shear and metasomatic zones at the contact between the Kostomuksha Formation and helleflinta. Significant concentrations of gold are related to the complex of diorite and granite porphyry and the shear and metasomatic zones formed at the collision stage after emplacement of potassium granite. The small Taloveis deposit is located in the southern portion of the Kostomuksha greenstone belt and related to an intrusion of diorite and granite porphyry dated at 2720 Ma. The gold-sulfide mineral type in beresitized granite is combined with the gold-quartz type in shear zones trending at an azimuth of 20 NNE and coinciding in orientation with shear zones in the Kostomuksha belt. The Au grade varies from 0.5 to 60 g/t.

Kuleshevich, L. V.; Furman, V. N.

2009-02-01

59

U–Pb geochronology of 3810–3630 Ma granitoid rocks south of the Isua greenstone belt, southern West Greenland  

Microsoft Academic Search

The oldest well preserved granitoid rocks on Earth envelope the Isua greenstone belt, southern West Greenland. The timing and nature of geological events that affected granitoid rocks south of the Isua belt (“southern gneisses”) are refined with new mapping and U–Pb geochronology. These results and previous work allow for a detailed comparison between the southern gneisses and similar granitoid rocks

J. L Crowley

2003-01-01

60

Exploring lithological assemblages and structural styles of granite-greenstone belts  

NSDL National Science Digital Library

1. Day 1: End of class Mini lecture (15 minutes) on: a. what greenstone belts are (where in the world, rock assemblages, structures) b. vertical vs. horizontal tectonic models (old arguments and current details). c. Superior Province (one example) introduction 2. Homework and Jigsaw Activity: Looking at "typical" structures within greenstone belts. This assignment asks students to compare papers with folding models vs. thrusting models. One set of papers that provides a good contrast focuses on the Beardmore-Geraldton greenstone belt in the Superior Province, Canada. Students will also use a paper with Lithoprobe seismic data across the Superior Province. a. Folding model: Kehlenbeck, M. M. 1986. Folds and folding in the Beardmore-Geraldton fold belt. Canadian Journal of Earth Sciences (CJES) 23, 158-171. b. Thrusting model: Devaney, J. R. & Williams, H. R. 1989. Evolution of an Archean subprovince boundary: a sedimentological and structural study of part of the Wabigoon-Quetico boundary in northern Ontario. CJES 26 1013-1026. c. Percival, J. A. et al. 2006. Tectonic evolution of the western Superior Province from NATMAP and Lithoprobe studies. CJES 43(7): 1085-1117. Divide the class into 3 "expert" groups and assign one paper to each group. Students need to create an outline of the major structures (faults, folds, both) described and the evidence provided for the structural interpretation. Students should bring two copies of their outline to class. 3. Day 2 Turn in one copy of outline (to be assessed for grade) and meet with the group to create a composite, master outline (30 minutes). Students break up into small groups (one from each "expert" group), discover very different structural style interpretations, and try to determine WHY there are the discrepancies (lack of data, preconceived notions influencing interpretations, etc). The goal of the new group is to prepare each student to write a short paper. Each student is assigned to write a 1-page paper exploring reasons why there are discrepancies between the models. Students are also encouraged to speculate on what other evidence or future research might help resolve the apparent conflict. Students begin paper in class and finish outside of class. 4. Day 3 Students hand in paper (to be graded). Mini lecture/ discussion on key related questions. a. Does either model (folding or faulting) support or negate either vertical or horizontal tectonic models? b. Are there any modern analogues to greenstone belts? If so, what are the differences or limitations to the comparisons (lithological and structural)?

Dyanna Czeck

61

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

62

Gold deposits in the late Archaean Nzega-Igunga greenstone belt, central plateau of tanzania  

SciTech Connect

2.2 m oz of gold have been produced, since 1935, from late Archaean (2480-2740 Ma) greenstone belts of the Central Plateau, Tanzania. North and east of Nzega (4/sup 0/12'S, 3/sup 0/11'E), 18% of the exposed basement, mainly Dodoman schists and granites, consists of metavolcanics and metasediments of the Nyanzian and Kavirondian Series. Four styles of mineralization are observed. 1. Stratabound quartz-gold veins with minor sulfides. Host rocks are quartz porphyry, banded iron formation (BIF), magnetite quartzite, and dense, cherty jasperite at the Sekenke and Canuck mines. The Canuck veins are on strike from BIF's in quartz-eye porphyry of the Igusule Hills. 2. Stratabound, disseminated gold in coarse-grained, crowded feldspar porphyry with lithic fragments and minor pyrite. At Bulangamilwa, the porphyry is conformable with Nyanzian-aged submarine (.) greenstone, volcanic sediment, felsic volcanics, and sericite phyllite. The deposits are on strike with BIF of the Wella Hills, which contains massive sulfide with up to 15% Pb+Zn. 3. Disseminated gold in quartz-albite metasomes in Nyanzian greenstones. At Kirondatal, alteration is associated with alaskites and feldspar porphyry dikes traceable several hundred meters into post-Dodoman diorite porphyry. Gold is with pyrite, arsenopyrite, pyrrhotite, minor chalcopyrite, and sphalerite as well as tourmalinite and silica-cemented breccias. 4. Basal Kavirondian placers in metaconglomerates containing cobbles and boulders of Dodoman and Nyanzian rocks several hundred meters up-section from the stratabound, disseminated mineralization at Bulangamilwa.

Feiss, P.G.; Siyomana, S.

1985-01-01

63

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

64

Generation of early Archaean felsic greenstone volcanic rocks through crustal melting in the Kaapvaal, craton, southern Africa  

NASA Astrophysics Data System (ADS)

High-potassium felsic volcanic rocks interlayered with basalt and komatiite in early Archaean greenstone sequences in the Barberton Greenstone Belt of South Africa and Swaziland, previously considered to be derived from melting of mafic precursors, are shown to be the result of melting of significantly older felsic crust. This is documented by a combination of SHRIMP zircon dating with Hf-in-zircon and whole-rock Lu-Hf and Sm-Nd isotopic data. Zircons from felsic rocks of the oldest Barberton unit, the 3.53 Ga Theespruit Formation, yielded predominantly negative ?-values, whereas whole-rock ?- and ?-data are slightly negative to slightly positive. Similar results were obtained for ca. 3.45 Ga felsic rocks in the Hoeggenoog and Noisy Formations higher up in the greenstone stratigraphy. These data rule out derivation of the felsic units from melting of basaltic precursors and favor a crustal source, most likely of TTG composition. The isotopic data are not compatible with an entirely oceanic origin of the Barberton greenstone sequences and favor a pre-greenstone basement beneath the volcanic rocks. Crustal melting of Eo- to Paleoarchaean lower crust probably generated the felsic volcanic rocks and is likely to have been responsible for gradual stabilization of the Kaapvaal craton.

Kröner, Alfred; Elis Hoffmann, J.; Xie, Hangqiang; Wu, Fuyuan; Münker, Carsten; Hegner, Ernst; Wong, Jean; Wan, Yusheng; Liu, Dunyi

2013-11-01

65

The Archaen volcanic facies in the Migori segment, Nyanza greenstone belt, Kenya: stratigraphy, geochemistry and mineralisation  

NASA Astrophysics Data System (ADS)

The Migori segment is an 80 by 20 km portion of the Nyanza greenstone belt which forms the northern part of the Archean Tanzanian Craton in western Kenya, northern Tanzania and southeastern Uganda. It consists of two volcanic centres, each with central, proximal and distal volcanic facies, comprising the Migori Group, the Macalder and Lolgorien Subgroups, and eleven volcano-sedimentary formations. The centres are separated by a basin of tuffs and greywacke turbidites. The volcanics are bimodal mafic basalt and dolerite ( Zr/Y = 3.8 - 6.5, La N/Yb N = 1.0 - 2.4) , and felsic calc-alkaline dacite-rhyolite ( Zr/Y = 10 - 21, La N/Yb N = 19 - 42 ) and high-K dacite ( Zr/Y = 9 - 16, La N/Yb N = 21 - 22 ). Felsic units form approximately three-fourths of the volcanic stratigraphy. Basalts, calc-alkaline dacites and rhyolites were deposited in a submarine environment, but the voluminous high-K dacites were erupted subaerially. The turbidites contain units of iron-formations. Granitic intrusions are chemically continuous with the high-K dacites. The felsic volcanics are anologous to those found at modern volcanic arc subduction settings involving continental crust. The Macalder Zn?Cu?Au?Ag volcanogenic massive sulphide deposits is in central facies basalts-greywacke-rhyolite. Gold mineralisation occurs in proximal facies tuffs and iron formation, and in oblique and semi-conformable quartz veins. Greenstones in the Nyanza belt are dominated by calc-alkaline felsic volcanics in constrast to the komatiite-tholeiitic basalt volcanism in the Kaapvaal Craton of South Africa, and a mixture of the two types in the Zimbabwe Craton.

Ichang'l, D. W.; MacLean, W. H.

66

Abstract, 2011 Advances in Earth Science Research Conference 2011 Petrogenesis of the Metavolcanic Rocks of the North Caribou Greenstone Belt: Implications for  

E-print Network

deposits including the Musselwhite gold mine, which is hosted by highly deformed and altered are commonly associated with orogenic gold deposits in Archean greenstone belts. The occurrence of biotite a large continuous belt and dismembered during later deformation. The belt contains numerous gold

67

Volcanic Stratigraphy and Lithogeochemistry of the Northern Section of the Lynn Lake Greenstone Belt: Implications for Regional Geodynamics and Metallogenesis  

NASA Astrophysics Data System (ADS)

The MacLellan Au-Ag deposit, located in the Paleoproterozoic Lynn Lake greenstone belt of the Trans-Hudson Orogen, Manitoba, is hosted by a package of plagioclase-amphibole, chlorite-amphibole, and quartz-plagioclase-biotite schists that are considered to be representative of the geodynamic evolution of the northern section of the Lynn Lake greenstone belt. A combination of field and petrographic observations and high-precision trace element chemistry have identified the protoliths to the host rock sequence as transitional aluminous basalt with subordinate picrite and biotite-altered aluminous basalt, respectively. The Th-Nb-La-REE systematics of these rocks are consistent with a rifted continental margin environment. Volcanic rocks with similar Th-Nb-La-REE systematics to those from the MacLellan host rock sequence have been identified throughout the Lynn Lake region. Therefore, it is proposed that the Lynn Lake greenstone belt represents a rifted continental margin and based on this revised geodynamic model, the mineral potential of the belt should be reassessed.

Glendenning, Michael W. P., Jr.

68

Volcanic environments of ore formation in the late Archaean Abitibi greenstone belt of Canada  

SciTech Connect

The tectonic and petrological evolution of the late Archaean Abitibi greenstone belt indicate both emergent and submergent volcanism played a role in its metallogenesis. At approximately 2700 m.y. the southern volcanic zone (SVZ) of the Abitibi belt was dominated by a rift-related tectonic and volcanic evolution in a transcurrent (wrench) fault regime. The tholeiitic and komatiitic magmas and associated differentiated volcanic rocks had access to shallow crustal levels allowing the development of submarine hydrothermal systems and syngenetic Cu-Zn (Noranda type) massive sulfide ore bodies. These deposits formed along a 300 km. axis in submerging, fault bounded, basins. In contrast, the northern volcanic zone (the Chibougamau-Chapais area) formed at 2720 m.y and was characterized by emergent volcanoes emplaced on a continental crust and cored by coeval diorite-tonalite plutons. Mafic magma was inhibited from the crust by fractionated and contaminated magmas. This resulted in the emplacement of hydrous calc-alkaline magmas and associated porphyry-type epigenetic Cu(Au) massive sulfides. Au-lode deposits are predominantly located near major shear-zones in the SVZ. The are forming solutions were released as a result of burial due to wrench faulting. The dynamic regime of the rifted SVZ may have resulted in the syngenetic massive sulfides, the Au-lode deposits, metamorphism and sedimentation being synchronous on a regional scale, whilst on a local scale, Au-lodes superimpose and replace massive sulfides, iron formation and metamorphic isograds.

Ludden, J.N.

1985-01-01

69

Single zircon age constraints on the tectonic juxtaposition of the Archean Abitibi greenstone belt and Pontiac subprovince, Quebec, Canada  

SciTech Connect

Zircons from metasediments and granitoids in the high-grade Lacorne block within the low-grade Archean Abitibi greenstone belt have been dated by single zircon Pb-evaporation technique, yielding {sup 207}Pb/{sup 206}Pb minimum ages. Detrital zircons in the mature clastic metasediments of the Lacorne block display a range of ages from 2,691 {plus minus} 8 Ma to 3,042 {plus minus} 6 Ma. The younger zircon ages thus impose an upper limit for deposition and indicate that the high-grade Lacorne block is not basement to the Abitibi supracrustal sequence (2,747-2,680 Ma). Existence of abundant (69%) older detrital zircons (> 2,750 Ma) suggest in turn that the Abitibi supracrustal rocks are not the source of the Lacorne sediments. Two generations of granitoids occur in the Lacorne block, an early monosodiorite-monzonite-granodiorite-syenite series and a younger S-type garnet-muscovite granite series. This contrasts with granitoid magmatism in the Abitibi greenstone belt which ended at {approximately}2675 Ma. The Pontiac subprovince to the south of the Abitibi greenstone belt shares all of the above features of the Lacorne block, including detrital zircon ages as well as the composition and timing of granitoid magmatism. This is interpreted detrital zircon ages as well as the composition and timing of granitoid magmatism. This is interpreted to indicate that the Lacorne block was originally part of the same tectonic terrane as the Pontiac subprovince. After development of the MMGS magmatism (21,670-2,680 Ma), the Pontiac subprovince locally underthrust the Abitibi greenstone belt, and crustal thickening promoted partial melting of underthrust Pontiac metasediments to form the {approximately}2,644 {plus minus} 13 Ma S-type granites.

Feng, R.; Kerrich, R. (Univ. of Saskatchewan, Saskatoon (Canada))

1991-11-01

70

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

71

Tectonic significance of bimodal volcanism in the Archean Michipicoten greenstone belt, Ontario  

SciTech Connect

In the lower volcanic cycle (2750 Ma old) of the Michipicoten greenstone belt, Ontario, a basal mafic unit (MV1) consisting mainly of basalt-basaltic andesite (49.4-56.4 wt.% SiO/sub 2/, 8.77-12.36 wt.% FeO/sub t/) with enriched ((La/Sm)/sub n/=1.9-2.6, Th=2.0-4.1 ppm, Sr=310-570 ppm) and depleted ((La/Sm)/sub n/=0.55-1.07, Th=0.16-0.71 ppm, Sr<250 ppm) trace element characteristics is locally overlain by a felsic unit (FV1) dominated volumetrically by rhyolite (71.9-79.6 wt.% SiO/sub 2/) and subordinate dacite (62.2-68.8 wt.% SiO/sub 2/). The mafic rocks are pillowed, massive flows and hyaloclastites suggesting subaqueous emplacement, whereas the felsic rocks are dominantly subaerial to shallow subaqueous pyroclastic deposits. The basalts of MV1 are similar chemically to modern tholeiites formed in primitive island arc/marginal basin complexes. In contrast, the rhyolites and dacites of FV1 exhibit the calc-alkaline chemical characteristics and rock associations typical of some continental inner arc volcanics. The juxtaposition of primitive island arc/marginal basin and continental inner arc tectonic settings occurs at the present time in the Tonga-Kermadec-New Zealand island arc. According to this model, MV1 is analogous to the basalt/basaltic andesite-dominated volcanism of the Tonga-kermadec island arc/Lau back-arc basin, whereas FV1 is the equivalent of the voluminous rhyolitic ignimbrites of the Taupo inner arc basin. The model suggests that the lower volcanic cycle of the Michipicoten belt formed on a basement consisting of small blocks of continental crust surrounded by oceanic crust.

Sylvester, P.J.

1985-01-01

72

3.4-Billion-year-old biogenic pyrites from Barberton, South Africa: sulfur isotope evidence  

NASA Technical Reports Server (NTRS)

Laser ablation mass spectroscopy analyses of sulfur isotopic compositions of microscopic-sized grains of pyrite that formed about 3.4 billion years ago in the Barberton Greenstone Belt, South Africa, show that the pyrite formed by bacterial reduction of seawater sulfate. These data imply that by about 3.4 billion years ago sulfate-reducing bacteria had become active, the oceans were rich in sulfate, and the atmosphere contained appreciable amounts (>>10(-13) of the present atmospheric level) of free oxygen.

Ohmoto, H.; Kakegawa, T.; Lowe, D. R.

1993-01-01

73

3.4-Billion-year-old biogenic pyrites from Barberton, South Africa: sulfur isotope evidence.  

PubMed

Laser ablation mass spectroscopy analyses of sulfur isotopic compositions of microscopic-sized grains of pyrite that formed about 3.4 billion years ago in the Barberton Greenstone Belt, South Africa, show that the pyrite formed by bacterial reduction of seawater sulfate. These data imply that by about 3.4 billion years ago sulfate-reducing bacteria had become active, the oceans were rich in sulfate, and the atmosphere contained appreciable amounts (>10(-13) of the present atmospheric level) of free oxygen. PMID:11539502

Ohmoto, H; Kakegawa, T; Lowe, D R

1993-10-22

74

Overview of the Barberton Drilling Project  

NASA Astrophysics Data System (ADS)

The Barberton Greenstone Belt in South Africa is one of the best-preserved successions of mid- Archean (3.5-3.2 Ga) supracrustal rocks in the world, and, as such, a remarkable natural laboratory where conditions and processes at the surface of the Archean Earth can be studied in detail. Volcanic and sedimentary sequences in the belt provide information on the environment in which life emerged and evolved. A drilling project, sponsored by the International Continental Drilling Program (ICDP), and many national funding agencies, was completed in May 2012. More than 3000 m of core from 5 holes at four sites were recovered. At the Tjakastad site, two ca. 300 m holes were drilling through sequences of komatiites and komatiitic basalts. The other three holes targeted sedimentary rocks: the Buck Reef hole sampled over 700m of mainly banded black and white cherts; the Mid Fig Tree hole sampled a sequence of ferruginous charts and mudstones; and the Barite Valley hole samples a more varied sequence including sandstone, shale, cherts and volcaniclastic rocks. The core is stored and has been logged in facilities of the University of the Wirwatersrand. Core logs can be found at tp://www.peeringintobarberton.com/Sites.html . An open call for proposals to work on the core, sent out in November 2012, was answered by over 50 scientists from 12 countries who plan to study the core using techniques ranging from petrography, through major and trace-element analysis, to sophisticated isotopic analysis. A workshop to discuss the drilling project and to view the core is planned at the University of the Witwatersrand in Johannesburg from Mon 18th to Wed the 21st February 2013, followed by a short trip to the Barberton belt to visit the drilling sites.

Arndt, Nicholas T.; Wilson, Allan; Mason, Paul; Hofmann, Axel; Lowe, Don

2013-04-01

75

Isotopic geochronological evidence for the Paleoproterozoic age of gold mineralization in Archean greenstone belts of Karelia, the Baltic Shield  

NASA Astrophysics Data System (ADS)

The Rb-Sr age of metasomatic rocks from four gold deposits and occurrences localized in Archean granite-greenstone belts of the western, central, and southern Karelian Craton of the Baltic Shield has been determined. At the Pedrolampi deposit in central Karelia, the dated Au-bearing beresite and quartz-carbonate veins are located in the shear zone and replace Mesoarchean (˜2.9 Ga) mafic and felsic metavolcanic rocks of the Koikar-Kobozero greenstone belt. At the Taloveis ore occurrence in the Kostomuksha greenstone belt of western Karelia, the dated beresite replaces Neoarchean (˜2.7 Ga) granitoids and is conjugated with quartz veins in the shear zone. At the Faddeinkelja occurrence of southern Karelia, Aubearing beresite in the large tectonic zone, which transects Archean granite and Paleoproterozoic mafic dikes, has been studied. At the Hatunoja occurrence in the Jalonvaara greenstone belt of southwestern Karelia, the studied quartz veins and related gold mineralization are localized in Archean granitoids. The Rb-Sr isochrons based on whole-rock samples and minerals from ore-bearing and metasomatic wall rocks and veins yielded ˜1.7 Ga for all studied objects. This age is interpreted as the time of development of ore-bearing tectonic zones and ore-forming hydrothermal metasomatic alteration. New isotopic data in combination with the results obtained by our precursors allow us to recognize the Paleoproterozoic stage of gold mineralization in the Karelian Craton. This stage was unrelated to the Archean crust formation in the Karelian Block and is a repercussion of the Paleoproterozoic (2.0-1.7 Ga) crust-forming tectonic cycle, which gave rise to the formation of the Svecofennian and Lapland-Kola foldbelts in the framework of the Karelain Craton. The oreforming capability of Paleoproterozoic tectonics in the Archean complexes of the Karelian Craton was probably not great, and its main role consisted in reworking of the Archean gold mineralization of various genetic types, including the inferred orogenic mesothermal gold concentrations.

Larionova, Yu. O.; Samsonov, A. V.; Shatagin, K. N.; Nosova, A. A.

2013-09-01

76

In-situ Fe and S isotope analyses of pyrite from the Lower Mapepe Formation (3.26-3.23 Ga), Barbeton Greenstone Belt, South Africa  

NASA Astrophysics Data System (ADS)

The Archaean oceans differed from today in being anoxic, Fe-rich and S-poor. Despite the low abundance of marine sulfate, significant amounts of sedimentary pyrite are associated with shales and sandstones deposited in Palaeoarchean time. Combined Fe and S isotopes can be used in pyrite to trace element sources as well as pathways of mineral formation and environmental redox processes since they record the changes in redox state in abiotic and biological processes. In this study, Fe and S isotopes were measured in pyrite from sedimentary rocks sampled by diamond drilling in the Lower Mapepe Formation (3.26-3.23 Ga, Lowe, 1999)1 of the Archean Barberton Greenstone Belt, South Africa. We performed in situ Fe and multiple S isotopic analysis by secondary ionization mass spectrometry (SIMS) of single mineral grains. The grain size range from 10 to several hundreds of micrometers. The stratigraphy consists of barite-chert units and barite-free terrigeneous clastic sediments with pyrites occurring in both types of lithologies. The complete range of pyrite ?56Fe data vary from -2.61 to +2.74 ‰ . Most individual pyrite samples showed iron isotopic variability of between 1.0-1.5 ‰, consistent with the range induced by abiotic pyrite precipitation (Guilbaud et al. 2012)2, whilst one sample contained more extreme variability of close to 5 ‰. Clear correlations with multiple S isotopes were not seen in individual samples, but there was a clear shift in average Fe isotope values and mixing trends in multiple S isotopes on going from the barite-free to the barite-rich part of the drill core. Pyrites in barite-free lithologies show slightly more positive ?56Fe value than those in close association with the barite. This suggests different sources of iron in the lower and upper parts of the stratigraphy, with a possible hydrothermal source for the pyrite associated with the barite. The origin of the more negative ?56Fe values (up to -2.61 ‰) is unclear but might result from microbial activity or mixing with a light iron pool. Pyrites with a positive ?56Fe signature could suggest involvement of ?56Fe enriched oxyhydroxides. Our in situ Fe isotope data reveal fractionation, mixing and inherited variability on a scale that would be difficult to resolve using bulk rock analyses. This microscale approach is critical to better constrain iron biogeochemistry in the Mid-Archaean environment. 1 Lowe, D. R., 1999. Geologic evolution of the Barbeton Greenstone Belt and vicinity. Geol. Soc. Am. Spec. Pap. 329, 287-312 2Guilbaud, I.R., Butler, I.B., Ellam, R.M. 2011. Abiotic pyrite formation produces a large Fe isotope fractionation. Science 332, 1528-1551

Galic, Aleksandra; Roerdink, Desiree L.; Mason, Paul. R. D.; Vroon, Pieter. Z.; Whitehouse, Martin. J.; Reimer, Thomas

2013-04-01

77

The Cosmos greenstone succession, Agnew-Wiluna greenstone belt, Yilgarn Craton, Western Australia: Geochemistry of an enriched Neoarchaean volcanic arc succession  

NASA Astrophysics Data System (ADS)

The geodynamic setting of the Neoarchaean Eastern Goldfields Superterrane (EGS) of the Yilgarn Craton is the subject of debate. Some authors propose plume models, while others advocate variants on a subduction accretion model for the origin of mineralised greenstone belt sequences. Felsic volcanism in the Kalgoorlie Terrane, the westernmost terrane of the EGS, is considered to have a tonalite-trondhjemite-granodiorite/dacite (TTG/D) geochemical affinity. The Cosmos greenstone succession, which lies in the Agnew-Wiluna greenstone belt (AWB) of the Kalgoorlie Terrane, contains several komatiite-hosted nickel sulphide deposits, the volcanic footwall to which consists of an intercalated succession of fragmental and coherent rocks ranging in composition from basaltic andesite to rhyolite. Light rare earth elements (LREEs) and large ion-lithophile elements (LILEs) are strongly enriched relative to high field strength elements (HFSEs) across all volcanic units, and the rocks display strong positive Pb and negative Nb anomalies. These geochemical characteristics resemble closely those of modern high-K calc-alkaline to shoshonite continental arc successions. Contrasting REE, LILE and HFSE concentrations, coupled with assimilation-fractional crystallisation (AFC) modelling, shows that the intercalated dacitic and andesitic volcanic rocks within the footwall succession are not co-genetic. Xenocrystic zircons within the felsic volcanic lithologies indicate that some assimilation of older continental crust contributed to the generation of the footwall volcanic sequence. The geochemical characteristics of the Cosmos volcanic succession indicate that parental melts were derived via partial melting of enriched peridotite that had been contaminated by subducted crustal material within the mantle wedge of a subduction zone. In contrast, two younger felsic porphyry intrusions, which cross-cut the volcanic succession, have a distinct TTG/D affinity. Therefore, these intrusions are considered to be generated via partial melting of a subducting slab and are related to local high-Ca granitoid intrusions. The Cosmos volcanic succession represents the first extrusive high-K calc-alkaline to shoshonitic volcanic arc sequence described in the Kalgoorlie Terrane and, coupled with age dating of the stratigraphy, is indicative of formation in a long-lived volcanic arc setting active from 2736 Ma to later than 2724 Ma. The composition and geochemical affinity of the volcanic footwall succession to the Cosmos komatiite-hosted nickel-sulphide deposits contrasts with the majority of felsic volcanic rocks within the AWB and also the wider Kalgoorlie Terrane, suggesting that the overall architecture of this region is more complex than is currently thought. Our conclusions not only have consequences for recent models of the tectonic evolution of the EGS but also contribute to the debate on the operation of plate tectonics during the late Archaean in general. The arc affinity of the Cosmos volcanic succession, containing abundant high-K calc-alkaline andesite lavas, provides further support for the operation of plate tectonics in the Neoarchaean.

de Joux, A.; Thordarson, T.; Fitton, J. G.; Hastie, A. R.

2014-09-01

78

Volcanic-hosted massive sulfide deposits in the Murchison greenstone belt, South Africa  

NASA Astrophysics Data System (ADS)

The Archean Murchison greenstone belt, Limpopo Province, South Africa, represents a rifted epicontinental arc sequence containing the largest volcanic-hosted massive sulfide (VMS) district in Southern Africa. The so-called Cu-Zn line is host to 12 deposits of massive sulfide mineralization including: Maranda J, LCZ, Romotshidi, Mon Desir, Solomons, and Mashawa with a total tonnage of three million metric tons of very high grade Zn, subordinate Cu, and variable Pb and Au ore. The deposits developed during initial phases of highly evolved felsic volcanism between 2,974.8 ± 3.6 and 2,963.2 ± 6.4 Ma and are closely associated with quartz porphyritic rhyolite domes. Elevated heat supply ensured regional hydrothermal convection along the entire rift. Recurrent volcanism resulted in frequent disruption of hydrothermal discharge and relative short-lived episodes of hydrothermal activity, probably responsible for the small size of the deposits. Stable thermal conditions led to the development of mature hydrothermal vent fields from focused fluid discharge and sulfide precipitation within thin layers of felsic volcaniclastic rocks. Two main ore suites occur in the massive sulfide deposits of the “Cu-Zn line”: (1) a low-temperature venting, polymetallic assemblage of Zn, Pb, Sb, As, Cd, Te, Bi, Sn, ±In, ±Au, ±Mo occurring in the pyrite- and sphalerite-dominated ore types and (2) a higher temperature suite of Cu, Ag, Au, Se, In, Co, Ni is associated with chalcopyrite-bearing ores. Sphalerite ore, mineralogy, and geochemical composition attest to hydrothermal activity at relatively low temperatures of ?250 °C for the entire rift, with short-lived pulses of higher temperature upflow, reflected by proportions of Zn-rich versus Cu-rich deposits. Major- and trace-metal composition of the deposits and Pb isotope signatures reflect the highly evolved felsic source rock composition. Geological setting, host rock composition, and metallogenesis share many similarities not only with Archean VMS districts in Canada and Australia but also with recent arc-back-arc systems on the modern seafloor where fragments of continental crust and areas of elevated heat flow are involved in petrogenetic and associated metallogenic processes.

Schwarz-Schampera, Ulrich; Terblanche, Hennie; Oberthür, Thomas

2010-02-01

79

Origin of Peculiar Horizons from the Nuvvuagittuq Greenstone Belt: Testing the Conglomerate Hypothesis  

NASA Astrophysics Data System (ADS)

Earth's earliest rock record is fragmentary, and often distorted by metamorphic changes suffered under great temperatures and pressures. Recent work may, however, have opened the door to more direct examination of the earliest Earth. Measurements of Nd-142 from rocks of the Nuvvuagittuq Greenstone Belt (NGB), N. Quebec yield an apparent 4.28 Ga isochron (O'Neil et al., 2008). These are potentially the oldest rocks on Earth and understanding the protoliths of the rocks of the NGB may help constrain Earth's earliest surface environment. Peculiar horizons of quartz-rich rocks within the NGB have been hypothesized to represent metamorphosed conglomerates. In order to evaluate this hypothesis, we apply a series of consistency tests aimed at observations ranging from the field to microscale. First, we made high-resolution (10m grid) maps of the purported conglomerate horizons, and interpreted the map pattern of these horizons for their conformity with sedimentary contacts. The horizons are continuous throughout the mapped area, and do not cross cut any other lithologies, which is necessary, but not sufficient, evidence for a sedimentary origin. Second, we examined the mineralogy and three-dimensional geometry of the potential clasts in large polished blocks. The potential clasts fall into just two different types: the dominant type is made up primarily of coarse grains of quartz; the second type is distinctly subordinate and is largely made up of fine-grained equigranular quartz and relict plagioclase with minor amounts of biotite. The dominant type can occur as lozenge-shaped pods up to 5 cm thick, while the subordinate type more commonly occurs as thin (<2 cm thick) undulose layers. Neither the mineralogies nor the geometries of the potential clasts offer certain indication of a sedimentary origin, though they are potentially consistent with one. Third, we are comparing the identity and chemistry of trace minerals within the potential clasts to that of the surrounding matrix. Preliminary results suggest that the matrix hosts many zircon, monazite and xenotime neoblasts as well as a variety of sulfide minerals, while most of the trace minerals in the dominant type of potential clasts are euhedral sulfides, with rare chromite-rich regions. Trace zircon and monazite are more common in the subordinate type of potential clasts, with zircon occasionally exhibiting that show a concentric but truncated zonation. And finally, we are also measuring sulfur isotope compositions of sulfides from the potential clasts and from the matrix. The key principle linking these two consistency tests is the presence or absence of mineralogical, mineral chemical, and isotopic heterogeneity.

Kitayama, C.; Thomassot, E.; Wing, B. A.

2009-05-01

80

Making the link between geological and geophysical uncertainty: geodiversity in the Ashanti Greenstone Belt  

NASA Astrophysics Data System (ADS)

The process of 3-D modelling forces the operator to consider data collection and processing error, while simultaneously making assumptions about geology during interpretation, to arrive at the most likely or logical geological scenario. These kinds of ambiguities lead to situations where multiple model realizations can be produced from a single input data set. Decisions are typically made during the modelling process with the aim of reducing the number of possible models, preferably to produce a single geological realization. These types of decisions involve how input data are processed and what data are included, and are always made without complete knowledge of the system under study. This regularly, if not always, results in natural geometries being misrepresented by the model, which can be attributed to uncertainty inherent in the modelling process. Uncertainty is unavoidable in geological modelling as complete knowledge of the natural system is impossible, though we use many techniques to reduce the amount introduced during the modelling process. A common technique used to reduce uncertainty is geophysical forward modelling, and the misfit between the calculated and observed response provides a means to gauge whether changes in model architecture improve or degrade the quality of the model. Unfortunately, geophysical data are ambiguous and provide a non-unique solution, with different model geometries able to produce the same geophysical response. We propose a process whereby multiple models, collectively known as the `model suite', are produced from a single data set that allows an exploration of geological model space. Various `geodiversity' metrics have been developed to characterize geometrical and geophysical aspects of each model. Geodiversity measurements are combined into multivariate analysis to reveal relationships between metrics and define the boundaries of the geological possibility. A previous study using geodiversity metrics on the Gippsland Basin is extended here by including geophysical metrics. We use the Ashanti Greenstone Belt, southwestern Ghana in West Africa, as a case study to assess the usefulness of the technique. A critical assessment of the 3-D model is performed and aspects of the model space are identified that could be of interest to gold explorers.

Lindsay, Mark D.; Perrouty, Stéphane; Jessell, Mark W.; Aillères, Laurent

2013-11-01

81

Spherule Size Distribution in the BARB5 ICDP Drill Core from the Barberton Greenstone Belt, South Africa  

NASA Astrophysics Data System (ADS)

On the four 4 cm thick spherule layers of the ICDP BARB5 drill core grain size analysis has been performed. The grain size statistics do not indicate regular decrease of spherule sizes, so do not represent a single impact bed.

Hoehnel, D.; Mohr-Westheide, T.; Fritz, J.; Reimold, W. U.

2014-09-01

82

Discovering the Carrier Phase of the Extraterrestrial Component in Archean Spherule Layers, Barberton Greenstone Belt, South Africa  

NASA Astrophysics Data System (ADS)

Comprehensive study of sedimentary, petrographic, mineralogical, and geochemical characteristics from a set of new samples of Archean spherule layers in the ICDP Drill Core BARB5 from the Barite Valley.

Mohr-Westheide, T.; Fritz, J.; Reimold, W. U.; Schmitt, R. T.; Hofmann, A.; Koeberl, C.; Luais, B.; Tagle, R.; Salge, T.; Hoehnel, D.

2014-09-01

83

Stratigraphy, sedimentology and physical volcanology of the Henik Group, central Ennadai-Rankin greenstone belt, Northwest Territories, Canada: late Archean paleogeography of the Hearne Province and tectonic implications  

Microsoft Academic Search

Extensive areas of the Hearne and Rae provinces are underlain by Archean metavolcanic and metasedimentary rocks. In the Rae Province, supracrustal sequences with prominent continental to shallow-water quartz arenites have been interpreted by others as rift and passive margin deposits. In the Hearne Province to the southeast, the Ennadai-Rankin greenstone belt is exposed in an area ca. 700 × 200

Lawrence B. Aspler; Jeffrey R. Chiarenzelli

1996-01-01

84

Potential of thermal emissivity for mapping of greenstone rocks and associated granitoids of Hutti Maski Schist belt, Karnataka  

NASA Astrophysics Data System (ADS)

In the present study, different temperature-emissivity separation algorithms were used to derive emissivity images based on processing of ASTER( Advanced spaceborne thermal emission and reflection radiometer) thermal bands. These emissivity images have been compared with each other in terms of geological information for mapping of major rock types in Hutti Maski schist Belt and its associated granitoids. Thermal emissivity images are analyzed conjugately with thermal radiance image, radiant temperature image and albedo image of ASTER bands to understand the potential of thermal emissivity in delineating different rock types of Archaean Greenstone belt. The emissivity images derived using different emissivity extraction algorithms are characterised with poor data dimensionality and signal to noise ratio. Therefore, Inverse MNF false-colour composites(FCC) are derived using bands having better signal to noise(SNR)ratio to enhance the contrast in emissivity. It has been observed that inverse-MNF of emissivity image; which is derived using emissivity-normalisation method is suitable for delineating silica variations in granite and granodioritic gneiss in comparison to other inverse- MNF-emissivity composites derived using other emissivity extraction algorithms(reference channel and alpha residual method). Based on the analysis of ASTER derived emissivity spectra of each rocks, band ratios are derived(band 14/12,band 10/12) and these ratios are used to delineate the rock types based on index based FCC image. This FCC image can be used to delineate granitoids with different silica content. The geological information derived based on processing of ASTER thermal images are further compared with the image analysis products derived using ASTER visible-near-infrared(VNIR) and shortwave infrared(SWIR) bands. It has been observed that delineation of different mafic rocks or greenstone rocks(i.e. separation between chlorite schist and metabasalt) are better in SWIR composites and these composites also provide comparable results with thermal bands in terms of delineation of different types of granitoids.

Guha, A.; Vinod Kumar, K.

2014-11-01

85

Geochemistry and petrogenesis of intrusions at the Golden Pride gold deposit in the Nzega greenstone belt, Tanzania  

NASA Astrophysics Data System (ADS)

The greenstone sequence at Golden Pride gold deposit in Nzega greenstone belt of northern Tanzania is cross-cut by several intrusions whose geochemistry and petrogenesis is unknown. We present major and trace elements geochemistry of the Golden Pride igneous intrusions with the aim of constraining their petrogenesis and their ancient tectonic setting. The Golden Pride intrusions are geochemically categorized into two main rock suites: the granodiorites (which include the porphyries) and the lamprophyres (formerly intermediate intrusions). The granodiorites are characterized by SiO2 contents of 54.5-69.9 wt%, elevated MgO (1.22-3.59 wt%) Cr (up to 54 ppm), Mg# (35-55) pointing to a mantle component in the source. Compared to the TTG and adakites, the granodiorites are characterized by higher K2O (1.52-4.30 wt%), medium HREE (Gd/ErCN = 2.13-3.77) and marked enrichment in Ba and Sr (Ba + Sr = 819-2922 ppm) and are in these respects similar to Archean high Ba-Sr sanukitoids. The rocks in this suite are interpreted to have formed by partial melting of an enriched mantle wedge through two metasomatic events: subduction-related fluids/melts and by metasomatism related to asthenospheric mantle upwelling caused by slab break-off. Compared to the granodiorites, the lamprophyres have higher MgO contents (2.37-3.81 wt%), Cr (60-298 ppm), Co (31-57 ppm) and Mg# (32-40). They also show slight enrichment of the LREE relative to HREE (La/YbCN = 3.3-7.1), moderate Nb-Ti depletion and sub-chondritic Zr/Hf ratios (34-41). These geochemical features are attributed to derivation of the Golden Pride lamprophyres by partial melting of the amphibole-rich metasomatized mantle by slab derived hydrous fluids. Both of the Golden Pride intrusion suites show strong affinity to subduction related magmas and we interpret that the entire greenstone sequence and the associated intrusions at Golden Pride gold deposit formed in a late Archaean convergent margin.

Kwelwa, Shimba; Manya, Shukrani; Vos, Ivo M. A.

2013-10-01

86

Petrogenesis of greenstones from the Mino Tamba belt, SW Japan: Evidence for an accreted Permian oceanic plateau  

NASA Astrophysics Data System (ADS)

Permian greenstones in the Jurassic Mino-Tamba accretionary complex, southwest Japan, are divided into three distinct series on the basis of their geological occurrence, mineralogy, and geochemistry. A low-Ti series (LTS) is associated with Lower Permian chert and limestone, and is the most voluminous of the three series. The LTS shows slightly more enriched geochemical and isotopic characteristics than MORB. A transition series (TS) is mainly associated with Lower Permian chert, and has more enriched geochemical signatures than MORB. Its isotopic characteristics are divided into enriched and depleted types. A high-Ti series (HTS) occurs as sills and hyaloclastites within Middle Permian chert and as dikes intruding the TS. Some HTS rocks have high MgO contents. The HTS is characterized by enrichment in incompatible trace elements and an isotopic composition comparable to HIMU-type basalt. The geochemistry of the voluminous LTS is similar to that of the oceanic basalt series of the Kerguelen plateau, suggesting production by partial melting of a shallow mantle plume head below thick oceanic lithosphere in Early Permian time. We infer that the TS formed simultaneously at the margins of the mantle plume head. In contrast, the HTS may have resulted from partial melting of a deep mantle plume tail in Middle Permian time. Permian greenstones in the Mino-Tamba belt may have thus formed by superplume activity in an intra-oceanic setting. Given the presence of two known contemporary continental flood basalt provinces (Siberia and Emeishan) and some accreted oceanic plateau basalts, the vast magmatism of the Mino-Tamba oceanic plateau suggests a large-scale superplume pulse in Permian time. Accretion of oceanic plateaux may have played an important role in the growth of continental margins and island arcs in Japan and elsewhere in the circum-Pacific region.

Ichiyama, Yuji; Ishiwatari, Akira; Koizumi, Kazuto

2008-01-01

87

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

Microsoft Academic Search

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

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

2009-01-01

88

An Early Shelter for Life on Earth? S and O Isotope Evidence From the Nuvvuagittuq Greenstone Belt, Northeastern Superior Province, Canada  

Microsoft Academic Search

The Nuvvuagittuq Greenstone Belt (NGB,) is one of Earth's oldest Eoarchean volcano-sedimentary suites, and was emplaced prior to 3.75 Ga (Cates and Mojzsis, S.J. 2007), and likely as early as 4.28 Ga (O'Neil et al. 2008). As revealed by recent detailed mapping, the NGB geology is dominated by cummingtonite-bearing amphibolites (formerly called Faux-amphibolite, (O'Neil et al. 2008)) and a series

E. Thomassot; J. O'Neil; D. Francis; P. Cartigny; D. Rumble; B. Wing

2009-01-01

89

EVIDENCE FOR 2.45 GA TECTONISM RECORDED in THE NORTH CARIBOU GREENSTONE BELT, NORTHWESTERN ONTARIO  

E-print Network

Caribou-Totogan Shear Zone (NCTSZ) marks portions of the contact of the belt with the Island Lake Domain the suture zone further along strike to the northwest. The strain in this eastern stretch of the NCGB tends

90

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

91

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

92

Atmospheric record in the Hadean Eon from multiple sulfur isotope measurements in Nuvvuagittuq Greenstone Belt (Nunavik, Quebec).  

PubMed

Mass-independent fractionation of sulfur isotopes (S-MIF) results from photochemical reactions involving short-wavelength UV light. The presence of these anomalies in Archean sediments [(4-2.5 billion years ago, (Ga)] implies that the early atmosphere was free of the appropriate UV absorbers, of which ozone is the most important in the modern atmosphere. Consequently, S-MIF is considered some of the strongest evidence for the lack of free atmospheric oxygen before 2.4 Ga. Although temporal variations in the S-MIF record are thought to depend on changes in the abundances of gas and aerosol species, our limited understanding of photochemical mechanisms complicates interpretation of the S-MIF record in terms of atmospheric composition. Multiple sulfur isotope compositions (?(33)S, ?(34)S, and ?(36)S) of the >3.8 billion-year-old Nuvvuagittuq Greenstone Belt (Ungava peninsula) have been investigated to track the early origins of S-MIF. Anomalous S-isotope compositions (?(33)S up to +2.2‰) confirm a sedimentary origin of sulfide-bearing banded iron and silica-rich formations. Sharp isotopic transitions across sedimentary/igneous lithological boundaries indicate that primary surficial S-isotope compositions have been preserved despite a complicated metamorphic history. Furthermore, Nuvvuagittuq metasediments recorded coupled variations in (33)S/(32)S, (34)S/(32)S, and (36)S/(32)S that are statistically indistinguishable from those identified several times later in the Archean. The recurrence of the same S-isotope pattern at both ends of the Archean Eon is unexpected, given the complex atmospheric, geological, and biological pathways involved in producing and preserving this fractionation. It implies that, within 0.8 billion years of Earth's formation, a common mechanism for S-MIF production was established in the atmosphere. PMID:25561552

Thomassot, Emilie; O'Neil, Jonathan; Francis, Don; Cartigny, Pierre; Wing, Boswell A

2015-01-20

93

Barberton Drilling Project - Barite Valley Core BARB5  

NASA Astrophysics Data System (ADS)

Diamond drilling has recently been completed in the Barberton Greenstone Belt, South Africa in order to obtain fresh, unweathered samples and continuous stratigraphic sections of Palaeoarchean volcanic and sedimentary rocks. The Barberton drilling project, sponsored by ICDP, has multiple aims including investigating the composition and temperature of the early atmosphere and oceans, the presence and activity of early microbial biosphere, the nature of melting in the mantle, and early tectonic processes. Three sections of sedimentary rocks have been obtained including the site BARB5 that is described here. The cores represent diverse chemical and clastic sediments and primary as well as diagenetic sedimentary structures. BARB5 cuts through stratigraphy in the 3.26-3.23 Ga lower Mapepe Formation of the Fig Tree Group in the Barite Valley Syncline. We provide core logs, details of the main lithologies sampled and present preliminary chemostratigraphic data. The core has a total length of 763 m and samples three major units with depth: siltstone, silicified volcaniclasics and laminated carbonaceous shales. The uppermost part of the stratigraphy consists of poorly preserved siltstone with some interbedded heavily weathered and variably silicified shale up to a core depth of 110 m. Heavily silicified volcaniclastic sediments, with interbedded cherts and sandstones underlie the siltstone for 150 m. The remaining 500m of core consists of interbedded shale, conglomerate, sandstone, breccias and minor chert bands at the base. An impact spherule layer occurs at the uppermost part of this zone accompanied by localized brecciation. Pyrite is common throughout the section as both discreet layers and disseminated grains. Forthcoming geological, geochemical and isotopic investigations with this core are expected to reveal key information about the nature of Archean sedimentary, biological and hydrothermal processes.

Mason, Paul; Galic, Aleksandra; Montinaro, Alice; Strauss, Harald; Hofmann, Axel; Chunnett, Gordon; Wilson, Allan; Arndt, Nick

2013-04-01

94

Implications of Pb-isotopic compositions at the Geita gold deposit, Sukumaland Greenstone Belt, Tanzania  

NASA Astrophysics Data System (ADS)

Pb-isotopic determinations have been made of mineralised and unmineralised Banded Iron Formations (BIF) from the Geita gold deposit, Sukumaland Greenstrone Belt, north-western Tanzania and also of barrent BIf some 80 km south-east of Geita. Indistinguishable dates of 2721+198-230 Ma and 2696+127-140 Ma have been obtained for the mineralised and unmineralised BIF respectively. In contrast, Pb-data from barren BIF from the Geita gold deposit indicate a significantly younger date of 1788+400-548 Ma. The older dates are consistent with existing age date (in particular galena and sulphide model age data as well as recent U?Pb zircon age data) from the Nyanzian in Tanzania and sorrounding regions, and are interpreted as the age of sedimentation of the BIF. This implies that the gold mineralisation at Geita, for which a maximum age limit of 2644±3 Ma is imposed by a pre-mineralisation lamprophyre dyke, must be epigenetic in origin. The younger date obtained from the barren BIF approximates the ages found for numerous dykes and sills of Ubendian age which intrude the BIF in the Geita region but insufficient data is available to fully evaluate the significance of this date.

Walraven, F.; Pape, J.; Borg, G.

1994-02-01

95

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

96

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

NASA Astrophysics Data System (ADS)

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 units pillow basalts). The belt is surrounded by plutonic rocks including granite, TTG suite granitoids and granite gneiss. The sequences where subjected to two phases of deformation, and several phases of contact metamorphosed to hornblende-hornfels facies during emplacement of pyroxenite-gabbro-norite, granodiorite-tonalite and gabbro dykes and porphyritic sills. The OGGB is bounded and/or crosscut by several major NNE to NE-trending shear zones including the steeply east-dipping Markoye Shear Zone (western margin of the OGGB), Tin Takanet-Bellekcire Shear Zone, Dori Shear Zone, Kargouna Shear Zone, Takabougou Shear Zone, and Bom Kodjelé Shear Zone (transects the centre of the OGGB). The structures were readily identified using LANDSAT, Aster, aeromagnetic and RTP magnetic data, with follow-up strategic mapping, highlighting the value of interpreting geophysical and remotely sensed data in regional mapping in Burkina Faso and Niger. Structural studies completed in 2007 adjacent to the Essakane gold mine indicated that the NE-trending, first-order crustal-scale Markoye Shear Zone (MSZ) has undergone at least two phases of reactivation concomitant to two phases of regional deformation (Tshibubudze et al., 2009). The first phase of deformation, D1, resulted in the formation of NNW-NW trending folds and thrusts during dextral-reverse displacement on the MSZ. The deformation predates the Eburnean Orogeny is termed the Tangaean Event (meaning low hills in the Moré language of Burkina Faso) and is tentatively dated at ca. 2170-2130 Ma (Hein, 2009). D2 involved a period of SE-NW crustal shortening and sinistral-reverse displacement on the MSZ, and is correlated to the Eburnean Orogeny ~2.1 Ga of Feybesse et al. (2006). Deformation in D2 is characterised by NE-trending regional folds (F2) and a pervasive NE-trending foliation (S2-C to S2). Since 2007 an identical tectonic history has been established for a number of shear zones in the OGGB including the north-trending Kargouna Shear Zone, which is subtended by NW- and NE-trending shears. However the metamorphic grade and mineral assemblages vary from one shear zone to the next. Structural studies completed adjacent to the Dori batholith have indicated that the MSZ forms a shear complex that was active during pluton emplacement. However, the MSZ has two main branches that join at the location of a mylonite zone located north west of Essakane. Southwest of Essakane, a NW-trending mylonite zone crosscuts the Dori batholith and near the village of Kargouna, which is situated southeast of Essakane, the Kargouna shear crosscuts and deforms the Dori batholith. It is thus likely that the Dori batholith was emplacement prior to D1 in the OGGB. Gold mineralization in the OGGB is generally hosted in the hanging-wall of NE-trending faults and or NW-trending folds in metasiltstone-sandstone-shale sequences. Nkuna (2009) concluded that the deposits can be classified as orogenic gold deposits under the sub-class of "intrusion related" due to their proximity to plutonic masses, which concurs with geophysical studies for the OGGB. References: Feybesse, J.L., Billa, M., Guerrot, C., Duguey, E., Lescuyer, J.L., Milési, J.P., Bouchot, V., 2006. The Palaeoproterozoic Ghanaian province: Geodynamic model and ore controls, including regional stress modelling. Precambrian Research 149, 149-196. Hein, K.A.A., 2009 (In press). Structural chronologies in the Goren Greenstone belt (Burkina Faso); Implications for West African tectonics. Journal of African Earth Sciences. Tshibubudze, A., Hein, K.A.A., Marquis, P. 2009. The Markoye Shear Zone in NE Burkina Fas

Tshibubudze, Asinne; Hein, Kim A. A.

2010-05-01

97

The relationship between adakitic, calc-alkaline volcanic rocks and TTGs: implications for the tectonic setting of the Karelian greenstone belts, Baltic Shield  

NASA Astrophysics Data System (ADS)

Two types of coeval acid-intermediate rocks with different petrological, geochemical and isotopic features have been discovered among volcanic rocks and surrounding synkinematic tonalite-trondhjemite-granodiorite (TTG) plutons of Late Archaean greenstone belts in the Karelian granite-greenstone terrane. Type-1 rocks comprise trondhjemites and sub-volcanic, occasionally volcanic dacite-rhyolite rocks. They are characterized by high Sr, low Y and HREE contents, high Sr/Y ratios, and strongly fractionated REE patterns with no significant positive or negative Eu anomaly. Initial ?Nd is positive, indicating a generation from juvenile source with little or no contribution of ancient continental crust. Type 2 is represented by diorite-granodiorites and calc-alkaline basalt-andesite-dacite-rhyolite (BADR) series. As compared to type 1, these rocks differ by their lower Sr, higher Y and HREE contents, lower Sr/Y ratios and less fractionated HREE patterns with negative Eu anomalies. Initial ?Nd varies from negative to positive values, thus indicating a variable contribution of sialic crust. Geochemistry of the two magmatic series suggests their formation in a convergent plate margin setting. The type-1 rocks resemble Phanerozoic adakites, which represent slab-derived melts contaminated by overlying mantle wedge. The type-2 rocks resemble BADR series, which were derived from a mantle wedge metasomatized by slab-derived fluids and melts, with subsequent variable crustal contamination. The spatial distribution of these two types of magmatic series defines the asymmetry of the studied granite-greenstone structures, which presumably reflects the primary lateral zoning of island arc formed under specific thermal conditions in the Archaean mantle. Adakite melts upraised to the surface in the frontal part of the island arc, where mantle wedge was thin, showing no or little interaction with metasomatized mantle, and formed adakite-type plutonic and sub-volcanic rocks. At greater depths, adakitic melts and fluids interacted with the overlying mantle wedge and caused its partial melting with generation of calc-alkaline BADR volcanic rocks and diorite-granodiorite plutons in the rear part of the island arc. Our data suggest that greenstone belt volcano-plutonic arcs were initiated on different types of crust, which presumably determined the petrogenetic and isotope variations of the studied BADR- and adakite-type island-arc complexes.

Samsonov, A. V.; Bogina, M. M.; Bibikova, E. V.; Petrova, A. Yu.; Shchipansky, A. A.

2005-01-01

98

Record of mid-Archaean subduction from metamorphism in the Barberton terrain, South Africa.  

PubMed

Although plate tectonics is the central geological process of the modern Earth, its form and existence during the Archaean era (4.0-2.5 Gyr ago) are disputed. The existence of subduction during this time is particularly controversial because characteristic subduction-related mineral assemblages, typically documenting apparent geothermal gradients of 15 degrees C km(-1) or less, have not yet been recorded from in situ Archaean rocks (the lowest recorded apparent geothermal gradients are greater than 25 degrees C km(-1)). Despite this absence from the rock record, low Archaean geothermal gradients are suggested by eclogitic nodules in kimberlites and circumstantial evidence for subduction processes, including possible accretion-related structures, has been reported in Archaean terrains. The lack of spatially and temporally well-constrained high-pressure, low-temperature metamorphism continues, however, to cast doubt on the relevance of subduction-driven tectonics during the first 1.5 Gyr of the Earth's history. Here we report garnet-albite-bearing mineral assemblages that record pressures of 1.2-1.5 GPa at temperatures of 600-650 degrees C from supracrustal amphibolites from the mid-Archaean Barberton granitoid-greenstone terrain. These conditions point to apparent geothermal gradients of 12-15 degrees C-similar to those found in recent subduction zones-that coincided with the main phase of terrane accretion in the structurally overlying Barberton greenstone belt. These high-pressure, low-temperature conditions represent metamorphic evidence for cold and strong lithosphere, as well as subduction-driven tectonic processes, during the evolution of the early Earth. PMID:16885983

Moyen, Jean-François; Stevens, Gary; Kisters, Alexander

2006-08-01

99

A mid-Archaean ophiolite complex, Barberton Mountain land  

NASA Astrophysics Data System (ADS)

New field observations and structurally restored geologic sections through the southern part of 3.5-3.6 Ga Barberton greenstone belt show that its mafic to ultramafic rocks form a pseudostratigraphy comparable to that of Phanerozoic ophiolites; this ancient ophiolite is referred to as the Jamestown ophiolite complex. It consists of an intrusive-extrusive mafic-ultramafic section, underlain by a high-temperature tectono-metamorphic residual peridotitic base, and is capped by a chert-shale sequence which it locally intrudes. Geochemical data support an ophiolitic comparison. Fraction of high temperature melting PGE's 2500 C in the residual rocks suggest a lower mantle origin for the precursors of this crust. An oceanic rather than arc-related crustal section can be inferred from the absence of contemporaneous andesites. The entire simatic section has also been chemically altered during its formation by hyrothermal interaction with the Archean hydrosphere. The most primitive parent liquids, from which the extrusive sequence evolved, may have been picritic in character. Rocks with a komatiitic chemistry may have been derived during crystal accumulation from picrite-crystal mushes (predominantly olivine-clinopyroxene) and/or by metasomatism during one or more subsequent episodes of hydration-dehydration. The Jamestown ophiolite complex provides the oldest record with evidence for the formation of oceanic lithosphere at constructive tectonic boundaries.

Dewit, M. J.; Hart, R.; Hart, R.

100

Ion microprobe zircon U Pb dating of the late Archaean metavolcanics and associated granites of the Musoma-Mara Greenstone Belt, Northeast Tanzania: Implications for the geological evolution of the Tanzania Craton  

NASA Astrophysics Data System (ADS)

Ion microprobe zircon U-Pb ages from metavolcanic and associated granitic rocks of the late Archaean Musoma-Mara Greenstone Belt (MMGB) of northeast Tanzania reveal that the oldest mafic volcanism in the belt occurred at 2676-2669 Ma followed by felsic volcanism at ˜2668 Ma. The felsic volcanism was coeval with the emplacement of the oldest pulse of massive granitoids that is dated at 2668 Ma. The youngest volcanic episode, represented by a volcanic horizon in the largely sedimentary Kavirondian Supergroup that overlies the greenstone sequence with a marked unconformity, occurred at ˜2667 Ma. A younger phase of post-orogenic granites concluded the magmatic evolution of the MMGB at ˜2649 Ma. Our age data suggests that the entire volcano-sedimentary sequence in MMGB was emplaced in a relatively short time interval between ˜2676 and ˜2667 Ma. It also shows that contrary to arguments based on the degree of deformation, the foliated granites and some amphibolite rafts enclosed in them do not constitute the basement to the greenstone sequence. The data further shows that volcanism in the MMGB was younger than the ˜2820 Ma age of volcanism in the Sukumaland Greenstone Belt (SGB) to the far southwest and the ˜2720 Ma age of volcanism in the nearby Kilimafedha Greenstone Belt (KGB) to the south. The age of granitic magmatism (ca. 2.69-2.55 Ga) in the three belts was, however, largely coeval. Granitic magmatism of this age has also been reported in different parts of the Tanzania Craton suggesting that it was responsible for the late Archaean crustal growth and marks the beginning of a period of stability (or of cratonization).

Manya, Shukrani; Kobayashi, Katsura; Maboko, Makenya A. H.; Nakamura, Eizo

2006-07-01

101

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

NASA Technical Reports Server (NTRS)

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.

1992-01-01

102

Identification of hydrothermal paleofluid pathways, the pathfinders in the exploration of mineral deposits: A case study from the Sukumaland Greenstone Belt, Lake Victoria Gold Field, Tanzania  

NASA Astrophysics Data System (ADS)

Hydrothermal fluids play a key role in the process of metalliferous mineralization such as gold deposits. The modern exploration indicators for such deposits are tectonic structures and characteristic alteration minerals observed as detectable halos adjacent to mineral deposits. Tectonic fractures are the conduits to these hydrothermal fluids and thus control the spatial locations for the formation of mineral deposits. Along crustal structures, hydrothermal fluids commonly induce mineral alteration in the adjacent wall rocks depending on the physical-chemical conditions. These alteration patterns, which are the pathfinders for the proxies in the modern mineral exploration, can be detected by innovative application of combined remote sensing techniques. The study area has experienced intense tectonic deformations, which resulted to two major sets of structures, the NW-SE and NE-SW-trending structures. The knowledge-based analysis applied to SRTM data was useful in identifying crustal lineaments, which the above two set of structures, truncating lithological units of the Sukumaland Greenstone Belt were identified. The Feature Oriented Principal Component Selection (FPCS) together with the GIS functions applied to Landsat 7 ETM+ data, were useful to enhance signals from hydrothermal alteration minerals. Results have revealed that the Sukumaland Greenstone Belt is intensively fractured, in a systematic pattern, and has apparently been "injected" with large volumes of hydrothermal fluids. Both processes together have resulted in the systematic and structurally controlled hydrothermal alteration patterns. In this study linear alteration patches are interpreted to represent the hydrothermal paleofluid pathways. Alteration patches coincide spatially with regional and local tectonic structures and are consistent with major gold occurrences and gold mines. This study indicate that careful analysis of SRTM and Landsat ETM+ data can identify crustal lineaments, the likely hydrothermal paleofluid conduits, which may lead to the discovery of potential ore deposits.

Mshiu, Elisante Elisaimon; Gläßer, Cornelia; Borg, Gregor

2015-02-01

103

Reassessment of Archean crustal development in the Barberton Mountain Land, South Africa, based on U-Pb dating  

NASA Astrophysics Data System (ADS)

This paper presents U-Pb ages for 23 samples from the Barberton Mountain Land, an Archean granite-greenstone terrain in the Kaapvaal craton of South Africa. A reexamination of the geology of this area in the light of previous U-Pb dating and the new ages indicates that much of its deformation can probably be accounted for by a single short-lived compressional event within the time span 3230-3215 Ma which was synchronous with deposition of the Moodies Group and the upper part of the Fig Tree Group sediments. This event may have been responsible for thrusting of much older sequences in the Onverwacht Group, including slivers of 3.54 Ga old gneiss, circa 3.47 Ga old komatiitic and tholeiitic sequences, and circa 3.45 Ga old felsic sequences. Key constraints on the timing of deformation are previously determined 3227-3225 Ma ages for detrital zircons in thrusted units of the Fig Tree Group; a 3229 +4/-3 Ma age for a deformed porphyry which is pre- or synthrusting; a previously determined 3227 ± 3 Ma age for an undeformed porphyry in an inferred thrust fault; 3227 ± 1 Ma ages for both the Kaap Valley pluton and an ignimbrite in the Stolzburg syncline, both of which predate regional upright folding; and a 3216 ± 2 Ma age for the Dalmein pluton which appears to cut regional, upright NE-SW trending folds in the Kromberg syncline, part of the final phase of deformation associated with regional compression. Areally extensive granitoid sheets and syenogranitic plutons were subsequently emplaced into the Barberton region at about 3105 Ma. The linear configuration of the syenogranitic plutons, which are also aligned with the gabbroic Usushwana complex as well as the geometry of the granitoid sheets, suggests that the circa 3105 Ma magmatism was caused by incipient rifting around a NW-SE trending crustal fracture. This episode was probably coeval with a late regional transtensional phase of deformation recorded in the greenstone belt. Some of the above interpretations are in conflict with previous models for early development of the Barberton greenstone belt. A 3352 ± 6 Ma age from a metagabbro which is comagmatic with a proposed ultramafic sheeted dike complex is over 100 m.y. younger than the probable age of volcanic rocks which host the dikes. This conflicts with the suggestion that much of the Onverwacht Group comprises an ophiolitic section, obducted in an intraoceanic setting at circa 3.45 Ga, that partially melted to form trondhjemitic magmas which intruded along active thrust faults. Present data suggest that, despite its antiquity and the diversity of ages and lithologies found within it, the Barberton greenstone belt can generally be understood in terms of actualistic tectonic processes at convergent margins.

Kamo, S. L.; Davis, D. W.

1994-02-01

104

Crustal-scale shear zones recording 400 m.y. of tectonic activity in the North Caribou greenstone belt, western Superior Province of Canada  

NASA Astrophysics Data System (ADS)

A series of crustal-scale shear zones demarcates the northern and eastern margins of the North Caribou greenstone belt (NCGB), proximal to a Mesoarchean terrane boundary in the core of the western Superior Province of Canada. The dominant deformation produced a pervasive steeply dipping fabric that trends broadly parallel to the doubly arcuate shape of the belt and was responsible for tight folding the banded iron formation host to Goldcorp's prolific gold deposit at Musselwhite mine. The shear zones in the North Caribou greenstone belt are of particular interest because of their ability to channel hydrothermal fluids with the potential to bear ore and cause alteration of the middle to shallow crust. Shear zones are commonly reactivated during subsequent tectonism, but exhibit a consistent and dominant dextral shear sense across the belt; fabric-forming micas and chlorite are generally Mg-rich. Although garnets samples from within the shear zones are dominantly almandine, they possess variable geochemical trends (HREEs of >2 orders of magnitude) and can be syn-, intra-, or post-tectonic in origin. In situ geochronological analysis of zircon (U-Pb) and monazite (total-Pb) in high strain rocks in and around the NCGB, interpreted in light of in situ geochemical analysis of garnet and fabric-forming micas and chlorite, reveals four relatively discrete events that span 400 million years. Metamorphism of the mid-crust was coeval with magmatism during docking of the Island Lake domain at c. 2.86 Ga and subsequent terrane accretion at the north and south margins of the North Caribou Superterrane from c. 2.75 to 2.71 Ga. Transpressive shear at c. 2.60 to 2.56 Ga and late re-activation of shear zones at c. 2.44 Ga produced a steeply-dipping pervasive fabric, and channeled fluids for late crystallization of garnet and monazite recorded in the Markop Lake deformation zone. These observations implicate a horizontal tectonic model similar to the modern eastern Pacific plate margin. Further, this study highlights the caution that should be exercised when using traditional rock forming metamorphic minerals (mica, chlorite, garnet) when attempting to vector into zones of hydrothermal alteration within midcrustal rocks. Keywords: North Caribou, Superior Province, shear zone, metamorphism, garnet, monazite, zircon, geochronology

Kalbfleisch, Netasha

105

Vesicular komatiites, 3.5Ga Komati Formation, Barberton Greenstone Belt, South Africa: inflation of submarine lavas and origin of spinifex zones  

Microsoft Academic Search

Komatiites of the 3.5-Ga Komati Formation are ultramafic lavas (>23% MgO) erupted in a submarine, lava plain environment. Newly discovered vesicular komatiites have vesicular upper crusts disrupted by synvolcanic structures that are similar to inflation-related structures of modern lava flows. Detailed outcrop maps reveal flows with upper vesicular zones, 2-15 m thick, which were (1) rotated by differential inflation, (2)

Jesse C. Dann

2001-01-01

106

Trace element geochemistry and petrogenesis of the granitoids and high-K andesite hosting gold mineralisation in the Archean Musoma-Mara Greenstone Belt, Tanzania  

NASA Astrophysics Data System (ADS)

Modern and ancient active continental margins are well known for their potential for hosting important gold deposits. The Neoarchean Musoma-Mara Greenstone Belt of the Tanzania Craton is also known for hosting several important gold deposits. Previous geochemical studies of the belt demonstrated that the rocks formed along Neoarchean convergent margins. The host rocks of the three important deposits in this belt had not yet been geochemically investigated. Therefore, we studied the host rocks of the Gokona, Nyabigena and Nyabirama gold deposits in the Neoarchean Musoma-Mara Greenstone Belt of the Tanzania Craton to determine the tectonic setting of their formation and constrain their petrogenesis. The host rocks of the Gokona and Nyabigena deposits are classified as high-K andesite, whereas the host rocks of the Nyabirama deposit are classified primarily as trondhjemite and granite and minor granodiorite (TGG). The high-K andesite and TGG were formed in an active continental margin similar to that of other Neoarchean volcanic rocks found in the Musoma-Mara Greenstone Belt. The host rocks contain low Ni and Cr concentrations and are characterised by negative Eu anomalies (Eu/Eu* = 0.67-0.72 and 0.17-0.6). The chondrite-normalised rare earth element (REE) patterns of the rocks display strong enrichment in light REEs over heavy REEs (high-K andesite (La/Yb)N = 21.7-35.6, and TGG (La/Yb)N = 2.4-94.4). Moreover, the primitive normalised diagrams show enrichment in large-ion lithophile elements (Ba, Rb, Th and K), negative Nb and Ta anomalies and depletion in heavy rare earth elements and high field-strength elements (Y and Ti). The high-K andesite has a Nb/Ta value close to that of depleted mantle (mean = 15.0), lower Zr/Sm values (19.4-30.6) and higher concentrations of REEs, large ion lithophile elements, Sr (607 ppm) and Y than in the TGG. The TGG has a low mean Nb/Ta value (13.2) and Sr concentration (283 ppm) and a lower amount of HREEs and higher values of Zr/Sm (32.5-91.0) compared to the high-K andesite. However, all of the rock types contain high Ta/Yb and Th/Yb values (high-K andesite and granitoids; mean = 5.9 and 0.8, 17 and 21.3). These characteristics are interpreted as an indication of the formation of the Gokona, Nyabigena and Nyabirama host rocks from the hydrous partial melting of mantle peridotite, similar to the evolution of classical island arc rocks. The primary melts subsequently underwent fractional crystallisation to form high-K andesite, dacite and TGG prior to their extrusion or emplacement in the continental crust.

Kazimoto, Emmanuel Owden; Ikingura, Justinian R.

2014-03-01

107

Sm-Nd studies at Mina III gold deposit, Crixás greenstone belt, central Brazil: implications for the depositional age of the upper metasedimentary rocks and associated Au mineralization  

NASA Astrophysics Data System (ADS)

The Crixás greenstone belt, central Brazil, is a volcanosedimentary sequence comprised of ultramafic and mafic metavolcanic rocks at the base and detrital and chemical metasedimentary rocks at the top. The sequence is part of the Archean sialic block exposed in the central part of the Neoproterozoic Bras?´lia belt and therefore is strongly affected by the Brasiliano orogeny. Important gold deposits, such as Mina III, are mainly associated with carbonaceous and Fe- and Al-rich metasedimentary rocks of the upper unit. Sm-Nd isochron data for the basal metakomatiites and metabasalts indicate an age of 3.00±0.07 Ga. However, Nd isotopes for the upper metasedimentary rocks show TDM model ages of mostly 2.33-2.49 Ga, which indicates that neither they nor the associated Au mineralization are Archean. Also, garnet whole-rock dating for a Au-bearing chlorite-garnet schist yields an age of 505±7 Ma, suggesting that the mineralization is Neoproterozoic. The Nd model ages suggest that the metasedimentary sequence of Crixás represents a thrust sheet of Proterozoic rocks emplaced over the Archean terrains during the Neoproterozoic Brasiliano orogeny.

de Tarso Ferro de Oliveira Fortes, Paulo; Martins Pimentel, Márcio; Ventura Santos, Roberto; Luiz Junges, Sérgio

2003-12-01

108

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. PMID:23228450

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

109

Neoarchean crustal growth by accretionary processes: Evidence from combined zircon-titanite U-Pb isotope studies on granitoid rocks around the Hutti greenstone belt, eastern Dharwar Craton, India  

NASA Astrophysics Data System (ADS)

The Neoarchean Hutti greenstone belt hosts mesothermal gold deposits and is surrounded by granitoid rocks on all sides. Combined U-Pb dating of zircon and titanite from the granitoid rocks constrains their emplacement history and subsequent geologic evolution. The Golapalli and Yelagatti granodiorites occurring to the north of the Hutti greenstone belt were emplaced at 2569 ± 17 Ma. The Yelagatti granodiorite yielded a younger titanite age of 2530 ± 6 Ma which indicates that it was affected by a post-crystallization thermal event that exceeded the titanite closure temperature. The western granodiorites from Kardikal have identical titanite and zircon ages of 2557 ± 6 Ma and 2559 ± 19 Ma, respectively. The eastern Kavital granodiorites yielded titanite ages of 2547 ± 6 Ma and 2544 ± 24 Ma which are identical to the published U-Pb zircon SHRIMP ages. These ages imply that the granitoid rocks surrounding the Hutti greenstone belt were formed as discrete batholiths within a short span of ca. 40 Ma between 2570 Ma and 2530 Ma ago. They were juxtaposed by horizontal tectonic forces against the supracrustal rocks that had formed in oceanic settings at the end of the Archean. The first phase of gold mineralization coincided with the last phase of granodiorite intrusion in the Hutti area. A metamorphic overprint occurred at ca. 2300 Ma ago that reset the Rb-Sr isotope system in biotites and possibly caused hydrothermal activity and enrichment of Au in the ore lodes. The eastern Dharwar Craton consists of quartz monzodiorite-granodiorite-granite suites of rocks that are younger than the greenstone belts that are older than ˜2650 Ma reported from earlier studies. The granitoid magmatism took place between 2650 and 2510 Ma ago indicating accretionary growth of the eastern Dharwar Craton.

Anand, R.; Balakrishnan, S.; Kooijman, E.; Mezger, K.

2014-01-01

110

Subaerial exposure surfaces in a Palaeoproterozoic 13 C -rich dolostone sequence from the Pechenga Greenstone Belt: palaeoenvironmental and isotopic implications for the 2330–2060 Ma global isotope excursion of 13 C\\/ 12 C  

Microsoft Academic Search

This article reports the discovery of numerous subaerial exposure surfaces which occur in the ca. 2200Ma Kuetsjärvi Sedimentary Formation (KSF) from the Pechenga Greenstone Belt, NE Fennoscandian Shield, Russia. The formation was accumulated within an intraplate rift and is composed of fluviatile-deltaic siliciclastic deposits and lacustrine dolostones. The dolostones are enriched in 13C (?13C=+6.6 to +7.6‰ V-PDB, ?18O=16.7 to 21.5‰

V. A. Melezhik; A. E. Fallick; S. M. Grillo

2004-01-01

111

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

112

Emplacement of pillow lavas from the ~ 2.8 Ga Chitradurga Greenstone Belt, South India: A physical volcanological, morphometric and geochemical perspective  

NASA Astrophysics Data System (ADS)

The physical volcanology and morphometric analyses of pillowed lava flows from the Chitradurga basin of Chitradurga Greenstone Belt, South India have been undertaken. In the Chitradurga hills individual pillowed flows alternate with massive submarine sheet flows. The pillows from such flows are separated by chert and occur as spheroidal, elongated or reniform units that are devoid of vesicles, vesicle bands or pipe vesicles. The Mardihalli flow is exposed as a small elongated mound in the basin and consists of a massive core that is draped by pillows along the flow crest and flanks. The pillows from Mardihalli occur as spheroidal to elongate units with smooth, spalled or wrinkled surfaces with vesicular interiors. Repeated budding of larger pillows have produced a series of interconnected pillow units indicating fluid lava that was emplaced on steeply dipping flanks. Based on the morphological features the pillowed flows from the Chitradurga basin were emplaced at low effusion rates (? 5 m3/s). Pillows in these flows formed from low viscosity lavas that underwent negligible to moderate inflation due to rapid chilling. Sporadic occurrences of pillow breccias, hyaloclastite and chert breccias in the pillowed flow fields indicate disruption of pillows due to lava surges and slumping. It is envisaged that the Chitradurga basin witnessed distinct episodes of submarine tholeiite eruptions that produced pillowed lavas that variably interacted with sea water to produce geochemistries. The field and stratigraphic relationships of the volcanics and associated clastic sediments suggest that the pillow lavas were emplaced in a shallow marine marginal inter/back arc basin.

Duraiswami, Raymond A.; Inamdar, Mustaqueem M.; Shaikh, Tahira N.

2013-08-01

113

Geochemistry and petrogenesis of the late Archaean high-K granites in the southern Musoma-Mara Greenstone Belt: Their influence in evolution of Archaean Tanzania Craton  

NASA Astrophysics Data System (ADS)

Musoma-Mara Greenstone Belt (MMGB) is abundantly occupied by the post-orogenic high-K granites which also they mark the end of magmatism in the area. The granites are characterized by high SiO2 and Al2O3 contents that average 74.42% and 13.08% by weight respectively. They have low Na2O content (mean = 3.36 wt.%) and high K2O contents (mean = 4.95 wt.%) which resulted to relatively high K2O/Na2O ratios (mean = 1.50). They also characterized by low Mg# (mean = 33) as well as low contents of transition elements such as Cr and Ni which are below detection limit (<20 ppm). Negative anomalies in Eu (Eu/Eu*, mean = 0.56), Nd, Ta and Ti elements as shown in the chondrite and primitive mantle normalized diagrams indicate MMGB high-K granites originated from a subduction related environments. These high-K granites also characterized by relative enrichment of the LREE compared to HREE as revealed by their high (La/Yb)CN ratio ranging from 8.71 to 50.93 (mean = 26.32). They have relatively flat HREE pattern with (Tb/Yb)CN ratio varying between 0.81 and 2.12 (mean = 1.55). Their linear trend in the variation diagrams of both major and trace elements indicate magmatic differentiation was also an important process during their formation. Conclusively, the geochemical characteristics as well as experimental evidences suggests MMGB high-K granites were formed from partial melting of pre-existing TTG rocks, under low pressure at 15 km depth or less and temperature around 950 °C in which plagioclase minerals were the stable phases in the melt.

Mshiu, Elisante Elisaimon; Maboko, Makenya A. H.

2012-05-01

114

Source characteristics of the ?2.5 Ga Wangjiazhuang Banded Iron Formation from the Wutai greenstone belt in the North China Craton: Evidence from neodymium isotopes  

NASA Astrophysics Data System (ADS)

Here we first present samarium (Sm)-neodymium (Nd) isotopic data for the ?2.5 Ga Wangjiazhuang BIF and associated lithologies from the Wutai greenstone belt (WGB) in the North China Craton. Previous geochemical data of the BIF indicate that there are three decoupled end members controlling REE compositions: high-T hydrothermal fluids, ambient seawater and terrigenous contaminants. Clastic meta-sediment samples were collected for major and trace elements studies in an attempt to well constrain the nature of detrital components of the BIF. Fractionated light rare earth elements patterns and mild negative Eu anomalies in the majority of these meta-sedimentary samples point toward felsic source rocks. Moreover, the relatively low Th/Sc ratios and positive ?Nd(t) values are similar to those of the ?2.5 Ga granitoids, TTG gneisses and felsic volcanics in the WGB, further indicating that they are derived from less differentiated terranes. Low Chemical Index of Weathering (CIW) values and features in the A-CN-K diagrams for these meta-sediments imply a low degree of source weathering. Sm-Nd isotopes of the chemically pure BIF samples are characterized by negative ?Nd(t) values, whereas Al-rich BIF samples possess consistently positive ?Nd(t) features. Significantly, the associated supracrustal rocks in the study area have positive ?Nd(t) values. Taken together, these isotopic data also point to three REE sources controlling the back-arc basin depositional environment of the BIF, the first being seafloor-vented hydrothermal fluids (?Nd(t) < -2.5) derived from interaction with the underlying old continental crust, the second being ambient seawater which reached its composition by erosion of parts of the depleted landmass (likely the arc) (?Nd(t) > 0), the third being syndepositional detritus that received their features by weathering of a nearby depleted source (likely the arc) (?Nd(t) > 0).

Wang, Changle; Zhang, Lianchang; Dai, Yanpei; Li, Wenjun

2014-10-01

115

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

116

Septate-tubular textures in 2.0-Ga pillow lavas from the Pechenga Greenstone Belt: a nano-spectroscopic approach to investigate their biogenicity.  

PubMed

Pillow lava rims and interpillow hyaloclastites from the upper part of the Pechenga Greenstone Belt, Kola Peninsula, N-Russia contain rare tubular textures 15-20 ?m in diameter and up to several hundred ?m long in prehnite-pumpellyite to lower greenschist facies meta-volcanic glass. The textures are septate with regular compartments 5-20 ?m across and exhibit branching, stopping and no intersecting features. Synchrotron micro-energy dispersive X-ray was used to image elemental distributions; scanning transmission X-ray microscopy, Fe L-edge and C K-edge were used to identify iron and carbon speciation at interfaces between the tubular textures and the host rock. In situ U-Pb radiometric dating by LA-MC-ICP-MS (laser ablation multicollector inductively coupled plasma mass spectrometry) of titanite from pillow lavas yielded a metamorphic age of 1790 ± 89 Ma. Focused ion-beam milling combined with transmission electron microscopy was used to analyze the textures in three dimensions. Electron diffraction showed that the textures are mineralized by orientated pumpellyite. On the margins of the tubes, an interface between mica or chlorite and the pumpellyite shows evidence of dissolution reactions where the pumpellyite is replaced by mica/chlorite. A thin poorly crystalline Fe-phase, probably precipitated out of solution, occurs at the interface between pumpellyite and mica/chlorite. This sequence of phases leads to the hypothesis that the tubes were initially hollow, compartmentalized structures in volcanic glass that were mineralized by pumpellyite during low-grade metamorphism. Later, a Fe-bearing fluid mineralized the compartments between the pumpellyite and lastly the pumpellyite was partially dissolved and replaced by chlorite during greenschist metamorphism. The most plausible origin for a septate-tubular texture is a progressive etching of the host matrix by several generations of microbes and subsequently these tubes were filled by authigenic mineral precipitates. This preserves the textures in the rock record over geological time. The micro textures reported here thus represent a pumpellyite-mineralized trace fossil that records a Paleoproterozoic sub-seafloor biosphere. PMID:20698893

Fliegel, D; Wirth, R; Simonetti, A; Furnes, H; Staudigel, H; Hanski, E; Muehlenbachs, K

2010-12-01

117

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

118

Contrasting geochemical patterns in the 3.7-3.8 Ga pillow basalt cores and rims, Isua greenstone belt, Southwest Greenland: implications for postmagmatic alteration processes  

NASA Astrophysics Data System (ADS)

Pillow basalts from the early Archean (3.7 to 3.8 Ga) Isua greenstone belt, West Greenland, are characterized by well-preserved rims and concentric core structures. The pillow rims and cores have different mineral assemblages, and chemical and isotopic compositions. The rims have systematically higher contents of Fe 2O 3, MgO, MnO, K 2O, Rb, Ba, Ga, Y, and transition metals than the cores. In contrast, the cores possess higher concentrations of SiO 2, Na 2O, P 2O 5, Sr, Pb, U, Nb, and the light rare earth elements (REEs than the rims). These compositional variations in the rims and cores are likely to reflect the mobility of these elements during posteruption alteration. Variations of many major and trace element concentrations between the rims and cores of the Isua pillow basalts are comparable to those of modern pillow basalts undergoing seafloor hydrothermal alteration. Al 2O 3, TiO 2, Th, Zr, and the heavy REEs display similar values in both rims and cores, suggesting that these elements were relatively immobile during postemplacement alteration. In addition, the rims and cores have distinctive Sm-Nd and Rb-Sr isotopic compositions in that the rims are characterized by higher 143Nd/ 144Nd and 87Sr/ 86Sr ratios than the cores. The pillow basalts yield 2569 ± 170 Ma and 1604 ± 170 Ma errorchron ages on 143Nd/ 144Nd vs. 147Sm/ 144Nd and 87Sr/ 86Sr vs. 87Rb/ 86Sr diagrams, respectively. The Sm-Nd errorchron age may correspond, within errors, to a late Archean tectonothermal metamorphic event recorded in the region. The Sm-Nd errorchron may have resulted from a combination of isotopic homogenization and preferential loss of Nd, relative to Sm, during late Archean metamorphism. Although the Rb-Sr errorchron age overlaps with the timing of an early to mid-Proterozoic tectonothermal metamorphic event recorded in the region, because of a considerably large mean square of weighted deviates value and scatter in 86Sr/ 87Sr and 87Rb/ 86Sr ratios, this age may not have a precise geological significance. The 1.6 Ga Rb-Sr errorchron is likely to have resulted from the loss of radiogenic 87Sr. Collectively, the Sm-Nd and Rb-Sr data obtained from the 3.7-3.8 Ga Isua pillow basalt rims and cores are consistent with disturbances of the Sm-Nd and Rb-Sr systems by tectonothermal metamorphic events long after their eruption. In contrast to the Sm-Nd and Rb-Sr systems, the Lu-Hf system appears to be largely undisturbed by metamorphism. Five core samples and three rim samples yield a 3935 ± 350 Ma age, within error of the approximate age of eruption (3.7 to 3.8 Ga). Two rim samples that have gained Lu give an age of 1707 ± 140 Ma, within error of the Rb-Sr errorchron age. Initial 176Hf/ 177Hf ratios of the undisturbed samples at 3.75 Ga lie within ±1 ?-unit of the chondritic value, suggesting no long-term depletion in the mantle source of the basalts.

Polat, Ali; Hofmann, Albrecht W.; Münker, Carsten; Regelous, Marcel; Appel, Peter W. U.

2003-02-01

119

A billion years of crustal evolution recorded in the Nuvvuagittuq greenstone belt: Pb-Hf evidence for Eoarchean TTGs produced from melting of Hadean mafic crust  

NASA Astrophysics Data System (ADS)

Investigation of Earth's primitive crust is limited by the scarcity of Eoarchean/Hadean terrains. Most of these terrains are dominated by felsic Tonalite-Trondhjemite-Granodiorite (TTG) rocks. These felsic rocks however, cannot be directly produced from melting of the mantle but must instead have been derived from the melting of an older mafic precursor. Obtaining accurate ages on old terrestrial mafic rocks is challenging. The geochronology constraints on Archean mafic rocks commonly come from long-lived radiogenic isotopic systems that can be affected by younger metamorphic/metasomatic events. The short-lived 146Sm-142Nd isotopic system is less susceptible to partial resetting because 146Sm became extinct prior to ~4 Ga. The mafic rocks from the Nuvvuagittuq greenstone belt (NGB), called the Ujaraaluk unit, have 146Sm-142Nd systematics consistent with them being formed in the Hadean, between 4.3 and 4.4 Ga. This age has been challenged because the oldest U-Pb ages on zircons obtained in the NGB are ~3.8 Ga. The ~3.8 Ga zircons, however, are from trondhjemetic bands intruding the NGB and thus provide only a minimum age for the mafic rocks. The NGB is surrounded by 3.65 Ga tonalites having deficits in 142Nd suggesting derivation from an Hadean precursor such as the Ujaraaluk unit. We have now identified two additional tonalite generations dated at 3.75 Ga and 3.4-3.5 Ga suggesting a more complex thermal history for the NGB. In order to better constrain the geologic relationship between the mafic and the felsic rocks and the evolution of the NGB through time, we present whole-rock Lu-Hf data for the Nuvvuagittuq rocks as well as combined Pb-Hf analyses in zircons from a series of surrounding TTGs dated at 3.35 Ga, 3.4-3.5 Ga, 3.65 Ga and 3.75 Ga. The Lu-Hf isotopic compositions of the NGB mafic rocks have been partially reset by a Neoarchean metamorphic/metasomatic event, consistent with what is observed for the long-lived 147Sm-143Nd system. Zircons from the 3.35 to 3.65 TTGs have strongly subchondritic initial ?Hf values and display an ?Hf vs. age array consistent with their derivation from a 4.3-4.4 Ga mafic precursor. The 3.75 Ga TTGs have initial ?Hf values consistent either with derivation from the ~4.2 Ga NGB gabbros or with incorporation of more juvenile mantle-derived material. The Hf-zircon and 142Nd data for the Eoarchean NGB TTGs is consistent with their formation from the melting of the Hadean Ujaraaluk unit. The time integrated ?Hf-zircon data also is consistent with the Hf isotopic compositions of the Jack Hills zircons suggesting a similar primitive mafic precursor for the Eoarchean/Hadean TTGs forming Earth's early crust.

O'Neil, J.; Boyet, M. M.; Carlson, R. W.; Paquette, J.

2012-12-01

120

Progress and Observations of the Tjakastad Core- Barberton ICDP  

NASA Astrophysics Data System (ADS)

The Barberton International Continental Drilling Program (ICDP) has drilled and recovered cores from four sites in the Barberton greenstone belt in South Africa. The BARB 1 (417 m) and BARB 2 (431 m) cores are drilled through a section of the Komati formation. These cores are drilled at a 45° angle, 50 m apart, and have a 140 m stratigraphic overlap. The BARB 1 and BARB 2 cores contain discernible komatiite and komatiitic basalt flow units along with unique volcanic textures such as spinifex, hyaloclastite and harrisite. A tumulus feature is present within the top 100 m of the BARB 1 core. The tumulus unit is 90 m thick and consists of a coarse-grained, basal olivine cumulate layer, a harrisite layer, a pyroxene spinifex layer and a hyaloclastite upper layer. Using major and trace element analyses together with petrological observations these layers are compared with komatiite flows (1-3 m thick) found in other parts of the core. The olivine cumulates from the tumulus layer are macrocrystic, ellipse shaped (2 cm in length) and contain a higher MgO content (45%) then the corresponding euhedral (0.5 mm) olivine cumulates of the komatiite flows which contain 34% MgO. Harrisitic texture forms by skeletal olivine megacrysts crystallizing upward from cumulate layers. The harrisite layer in the tumulus forms in the traditional fashion (above a cumulate layer) and is 14 m thick. It is similar in chemistry and texture to a unique harrisite layer (1.5 m thick) that has formed in a single komatiite flow. The harrisite in the tumulus has higher MgO content and larger skeletal olivines than the komatiite flow. The spinifex in the tumulus is predominantly pyroxene, whilst some flows contain olivine spinifex. The spinifex in the tumulus is commonly centimetres long and is light green grey in colour. The spinifex from the flows reaches a maximum of 5 cm in length; are green-grey to dark grey in colour and are often randomly oriented. The tumulus spinifex has 14-31% MgO whilst the spinifex in the flows has 25-32% MgO. The hyaloclastite, a quench fragmentation texture, in the tumulus section is analogous to the chill zones of the komatiite flows. It consists of fractured blocky fragments (30 cm in length) of lava, surrounded by a matrix of spherical particles of glass (0.5 mm to 1 cm) which have chill margins and inward cooling textures. It is important to determine which of these features is comparable to the chill margin of the flows and to establish if this glassy matrix material has been derived from a different source. The hyaloclastite comprises 24% volume of the tumulus, while chill margins comprise 15% volume. Comparing the chemistry and petrography of the tumulus to komatiite flows gives insight into processes occurring during tumulus formation.

Coetzee, Grace; Wilson, Allan; Arndt, Nicholas; Yobregat, Elsa

2013-04-01

121

Petrology of greenstones in southern Wyoming Province  

NASA Astrophysics Data System (ADS)

Archean greenstones occur in South Pass area and southern Wind River Canyon area in central Wyoming State, U.S.A. These two areas are near about 100 km away from each other and belong to the same sub- province named Wyoming greenstone province (WGP, composed of meta-mafic rocks and meta- sedimentary rocks) (Mueller et al., 1998). The South Pass area is one of the greenstone belts in the southern Wyoming Province and is located in the northwestern part of the WGP. The greenstones (15 km long) occur along the later Archean granitic batholith (Louis Lake batholith, 2.63 Ga) and are composed of meta-pillow lavas, meta diabasic rocks, meta-gabbroic rocks, meta basaltic tuffs, and other meta sediments. The meta diabasic rocks occur as dykes. Banded iron formation lies along the contact between these greenstones and the batholith. Several previous studies suggested that these greenstones were metamorphosed under conditions of amphibolite, and locally greenschist (Harper et al., 1985; Wilks and Harper, 1997; Frost et al., 2000). However we found evidence indicating limited distribution of the amphibolite facies zone which is restricted along the batholith. Greenstones in this area were regionally metamorphosed under low-grade and the amphibolite facies greenstones were formed by the thermal effects by the batholith. Many characteristics of the protolith are well preserved. The following textures are preserved; pillow lava structure, relic igneous augite grains in meta basaltic rocks, relic igneous brown hornblende grains in meta diabasic rocks, gabbroic textures, and some sedimentary textures. The pillow lavas (5-10 cm x 15-30 cm) are composed of pale green core and thin dark gray rim (about 0.5 cm wide) and the core domain is rich in carbonate. The southern Wind River Canyon area is located in the northern part of the WGP. Archean greenstones in this area are composed of meta pillow lavas, meta gabbroic rocks, and meta pelites. From south toward north, mafic rocks generally grade into pelitic rocks. All the greenstones were metamorphosed under a condition of amphibolite and no relic of protolith minerals are preserved. Ring structures suggesting pillow lavas (core, 20- 30 cm x 30-50 cm; rim, 1.0-3.0 cm wide) occur in fine-grained mafic greenstones. Skarn (several cm to several tens cm in scale) occurs only near these ring structures and cuts the greenstones. This skarn is cut by granite intrusions. Both the South Pass area and the southern Wind River Canyon area are possibly regarded as upper part of Archean oceanic crust. The South Pass greenstones were regionally metamorphosed under low-grade (lower greenschist facies). Amphibolite facies greenstones were formed by thermal effects by the granitic batholith. The southern Wind River Canyon greenstones were subjected to amphibolite facies regional metamorphism and no thermal effect by the granites was observed. Archean skarn occurs only in the southern Wind River Canyon area. What did make these differences between Archean greenstones in the South Pass area and the southern Wind River Canyon area? Comparisons of greenstones between these two areas are significant for the formation of the Archean greenstones and the formation of Archean skarn in these areas.

Takeuchi, Y.; Yuasa, T.; Ogasawara, Y.

2006-12-01

122

Rb-Sr and Sm-Nd isotope systematics and geochemical studies on metavolcanic rocks from Peddavura greenstone belt: Evidence for presence of Mesoarchean continental crust in easternmost part of Dharwar Craton, India  

NASA Astrophysics Data System (ADS)

Linear, north-south trending Peddavura greenstone belt occurs in easternmost part of the Dharwar Craton. It consists of pillowed basalts, basaltic andesites, andesites (BBA) and rhyolites interlayered with ferruginous chert that were formed under submarine condition. Rhyolites were divided into type-I and II based on their REE abundances and HREE fractionation. Rb-Sr and Sm-Nd isotope studies were carried out on the rock types to understand the evolution of the Dharwar Craton. Due to source heterogeneity Sm-Nd isotope system has not yielded any precise age. Rb-Sr whole-rock isochron age of 2551 ± 19 (MSWD = 1.16) Ma for BBA group could represent time of seafloor metamorphism after the formation of basaltic rocks. Magmas representing BBA group of samples do not show evidence for crustal contamination while magmas representing type-II rhyolites had undergone variable extents of assimilation of Mesoarchean continental crust (>3.3 Ga) as evident from their initial ? Nd isotope values. Trace element and Nd isotope characteristics of type I rhyolites are consistent with model of generation of their magmas by partial melting of mixed sources consisting of basalt and oceanic sediments with continental crustal components. Thus this study shows evidence for presence of Mesoarchean continental crust in Peddavura area in eastern part of Dharwar Craton.

Rajamanickam, M.; Balakrishnan, S.; Bhutani, R.

2014-06-01

123

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

Glikson, Andrew; Vickers, John

2006-01-01

124

Greenstone Digital Library Software  

NSDL National Science Digital Library

Greenstone is a suite of software designed to build and distribute digital library collections. Produced by the New Zealand Digital Library Project at the University of Waikato, this innovative tool was created to "empower users, particularly in universities, libraries, and other public service institutions, to build their own digital libraries." The software consists of the Collector, which helps create new collections, modify or add to existing ones, or delete collections; and the Administration, which allows the addition of new users, summarizes the collections in the system, and gives technical information on the installation. Also included is a section comprising the Greenstone manuals, and a section that tells about the Greenstone software and where the New Zealand Digital Library Project originated. The software runs on Windows and Unix, and both source codes and binaries are available for downloading on the site.

1969-12-31

125

Insights into early Earth from Barberton komatiites: Evidence from lithophile isotope and trace element systematics  

NASA Astrophysics Data System (ADS)

Major, minor, and lithophile trace element abundances and Nd and Hf isotope systematics are reported for two sets of remarkably fresh, by Archean standards, samples of komatiitic lavas from the 3.48 Ga Komati and the 3.27 Ga Weltevreden Formations of the Barberton Greenstone Belt (BGB) in South Africa. These data are used to place new constraints on the thermal history of the early Archean mantle, on the timing of its differentiation, and on the origin and chemical nature of early mantle reservoirs and their evolution through time. Projected moderate to strong depletions of highly incompatible lithophile trace elements and water in the mantle sources of both komatiite systems, combined with the partitioning behavior of V during lava differentiation, are consistent with anhydrous conditions during generation of the komatiite magmas. Komati and Weltevreden lavas are inferred to have erupted with temperatures of ?1600 °C, and, thus, represent the hottest known lavas on Earth. The calculated mantle potential temperatures of ?1800 °C for both komatiite systems are 150-200 °C higher than those of contemporary ambient mantle. Combined, these observations are consistent with the origin of these BGB komatiite magmas in mantle plumes in the lower mantle. New Sm-Nd and Lu-Hf isotopic data allow precise determination of initial ?143Nd = +0.46 ± 0.10 and +0.50 ± 0.11 and initial ?176Hf = +1.9 ± 0.3 and +4.7 ± 0.8 for the Komati and the Weltevreden system komatiites, respectively. These positive initial values reflect prior fractionation of Sm/Nd and Lu/Hf in the mantle early in Earth history. Conversely, ?142Nd values are 0.0 ± 2.4 and +2.2 ± 4.1 for the Komati and the Weltevreden systems, respectively. These values overlap, within uncertainties, those of modern terrestrial rocks, thus, limiting the magnitudes of possible Sm/Nd fractionations generated by early Earth processes in the sources of these rocks. Combined 142,143Nd and Hf isotope and lithophile trace element systematics are consistent with formation and long-term isolation of deep-seated mantle domains with fractionated Sm/Nd and Lu/Hf at ca. 4400 Ma. These domains were likely generated as a result of crystallization of a primordial magma ocean, with Mg-perovskite and minor Ca-perovskite acting as fractionating phases. The inferred mantle domains were evidently mixed away by 2.7 Ga on the scale of mantle reservoirs sampled by late Archean komatiite lavas emplaced worldwide.

Puchtel, I. S.; Blichert-Toft, J.; Touboul, M.; Walker, R. J.; Byerly, G. R.; Nisbet, E. G.; Anhaeusser, C. R.

2013-05-01

126

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

127

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

128

Metallogenic geodynamic background of Mesozoic gold deposits in granite-greenstone terrains of North China Craton  

Microsoft Academic Search

The spatial distribution map of 65 mid-large gold-deposits hosted in the granite-greenstone terrains of the North China Craton\\u000a is first drawn. These gold deposits mainly concentrate in the Mesozoic remobilized Yinshan-Yan-shan-Liaoning-Jilin intracontinental\\u000a collisional orogenic belt, the northern Qinling and the Jiaodong Mesozoic collisional orogenic belts, and the Mesozoic intracontinental\\u000a fault-magmatic belts developed along the Taihangshan and the Tan-Lu faults; their

Yanjing Chen; Guangjun Guo; Xin Li

1998-01-01

129

Mars mission relevant investigations on a ~ 3.5 Ga Mars analogue rock from the Pilbara and Barberton  

NASA Astrophysics Data System (ADS)

Volcaniclastic sediments deposited in shallow water basins on the early Earth represent ideal analogues for Noachian volcanic sediments since the environmental conditions and settings for both were quite similar: important volcanic and hydrothermal activity (somewhat less on Mars), period of late heavy bombardment (~4.0 Ga), water bodies with a slightly acidic pH, higher salt content, atmosphere with minimal O2 (<0.2 % PAL), high UV flux to the surface. Life apparently thrived in these conditions on Earth, leaving structural and geochemical signatures in the Early Archaean sediments. Within the framework of the PAFS-net* programme, using space qualified instrumentation, we analysed previously well-characterised volcanic sedimentary rocks from a number of locations in the 3.5-3.3 Ga-old greenstone belts of the Pilbara (Australia) and Barberton (South Africa). They included mud flat sediments containing traces of probable chemolithotrophic and anoxygenic photosynthetic microorganisms, a small stromatolite (some microfossil traces) and a banded iron formation sample (also some microfossil traces). All the sediments were silicified by early diagenetic processes. The instruments used were the Beagle2 Development Model (DM) stereo camera for proximal (~100 cm) and macroscopic (~10 cm) imaging, the Beagle 2 microscope for microscopic (~1 cm) imaging, a Nuance multi-spectral imager, a TN Technologies Spectrace 9000 commercial energy dispersive XRF spectrometer, a Philips PW1710 diffractometer for XRD, and the Beagle2 spare Mössbauer spectrometer. The camera systems were well able to depict the fine-scale sedimentological structures of the rock samples that, in the case of the volcaniclastic sediment and the stromatolite, can be used to interpret a shallow water environment of deposition (the flaser-linsen bedding of the former and the convex, sinuous layering of the latter). The massively quartz-rich (chert) composition of the silicified sediments was picked up by the XRD and the Raman spectrometers. The silicified volcanics also contain feldspar, identified by the Raman, whereas the XRF analyses showed that they are K-feldspars. The traces of Ba and Cu in this sample are probably related to the mostly hydothermal origin of the silica that cemented the volcanic sediments. Raman spectroscopy also identified a greater abundance of carbon (matured kerogen) in the black layers of this sample (finer grained volcaniclastics). The stromatolite sample, on the other hand, consists largely of quartz although Raman showed some dolomite and carbon (mature kerogen) in the grey layers (silicified stromatolitic layers). The layering in the laminated volcaniclastic sediment was too fine for the Mössbauer spectrometer to pick up any details. The Mössbauer was able to detect a very thin layer of Fe oxide <<0.2 mm on the surface of the stromatolite. Compositional layering in the BIF was clearly visible using multispectral imaging with the Nuance camera and the Mössbauer could identify highly crystalline and chemically pure goethite in the Fe-rich layers with minor goethite and hematite occurring in the quartz-rich layers. The combination of the instrumentation used for imaging and chemical analysis was quite sufficient to identify the sedimentary origin of the finely laminated volcaniclastic and stromatolite rocks and to demonstrate their pervasive silicification. The presence of carbon in these rocks would, in a Mars scenario, make them ideal subjects for organo-geochemical analysis. The same suite of instruments was also able to demonstrate the origin of the BIF, again, a suitable candidate for further analysis. * Planetary Analogue Field Study network (main coordinator D. Pullan)

Westall, F.; Pullan, D.; Schröder, C.; Klingelhöfer, G.; Fernández-Sánchez, J.; Jorge, S.; Edwards, H.; Cressey, G.

2007-08-01

130

New insights into typical Archaean structures in greenstone terranes of western Ontario  

NASA Technical Reports Server (NTRS)

Ongoing detailed field work in selected granitoid complexes of the western Wabigoon and Wawa Subprovinces, southern Canadian Shield, has led to several new conclusions: (1) Prominent gneiss domes are composed of prestrained tonalite-granodiorite and represent dense hoods of magmatic granitoid diapirs; (2) the deformation history of the prestrained gneiss remains to be unraveled; (3) the gneiss lacked a thick cover of mafic metavolcanics or other dense rocks at the time of magmatic diaprisim; (4) the synclinoral structure of large greenstone belts is older than the late gneiss domes and may have been initiated by volcano-tectonic processes; (5) small greenstone masses within the gneiss are complexly deformed, together with the gneiss; and, (6) no compelling evidence has been found of ductile early thrusting in the gneiss terranes. Zones of greenstone enclaves occur in hornblende-rich contaminated tonalite and are apt to be deformed magmatic septa. Elsewhere, the tonalite gneiss is biotite-rich and hornblende-poor. These conclusions rest on several new pieces of structural evidence; (1) oval plutons of syenite-diorite have magmatic strain fabrics and sharp contacts that are parallel to an axial-plane foliation in the surrounding refolded gneiss; (2) gneiss domes are lithologically composite and contain large sheath-like structures which are deformed early plutons, distorted earlier gneiss domes, or early ductile nappes produced by folding of planar plutonic septa, and (3) the predomal attitudes of gneissosity varied from point to point.

Schwerdtner, W. M.

1986-01-01

131

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

132

Geology and Neoarchean tectonic setting of the Central Hearne supracrustal belt, Western Churchill Province, Nunavut, Canada  

Microsoft Academic Search

The Central Hearne supracrustal belt, one of the largest Neoarchean “greenstone” terranes in the Canadian Shield, occurs in the Hearne domain of the Western Churchill Province, one of the largest, poorly known fragments of Archean crust on Earth. The belt contains two isotopically juvenile volcano–plutonic assemblages (I: ?2710–2690Ma, and II: ?2685–2680Ma), separated in time by localised, ?2690Ma, greenschist-facies deformation (D1),

Simon Hanmer; Hamish A. Sandeman; William J. Davis; Lawrence B. Aspler; Robert H. Rainbird; James J. Ryan; Carolyn Relf; Tony D. Peterson

2004-01-01

133

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

134

Belt-driven conveyor belts  

SciTech Connect

An intermediate belt drive system offers a number of advantages over conventional systems, including lower power requirements and the ability to use lower quality, cheaper, conveyor belts. The advantages of a correctly designed belt conveyor with end pulley drives are included.

Not Available

1984-01-01

135

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

136

Age of the Mulcahy Lake intrusion, northwest Ontario, and implications for the evolution of greenstone-granite terrains  

NASA Technical Reports Server (NTRS)

An investigation of zircon data from the Mulcahy Lake gabbro, a 63 sq km layered mafic intrusion in the Wabigoon subprovince of Ontario, which show that the gabbro crystallized at 2733.2 +1.0, -0.9 Ma, is considered. It is shown that the gabbro intrudes tholeiites of the Crow Lake-Savant Lake greenstone belt. Whole rock samples and mineral separates from the Mulcahy Lake intrusion are dated by Rb-Sr, Sm-Nd, and Ar-30-Ar-40 techniques. Disturbances in the system are revealed by the Rb-Sr data and an initial Sr ratio of 0.7007 for an age of 2733 Ma is indicated by samples with low Rb/Sr ratios. The age determined for the Sm-Nd data is 2744 + or 55 Ma with an epsilon Nd value of +2.6 + or - 1.2 which indicates a source region depleted in a light rare earth element. Primary hornblende is analyzed for Ar-40/Ar-39 and an age of 2703 + or - 20 is obtained. Some implications for the development of greenstone-granite belts are discussed.

Morrison, D. A.; Bogard, D. D.; Phinney, W. C.; Davis, D. W.; Wooden, J. L.; Ashwal, L. D.; Maczuga, D. E.

1985-01-01

137

Radiation Belts  

NSDL National Science Digital Library

The inner radiation belt, discovered by Van Allen, consists of very energetic protons, a by-product of collisions of cosmic ray ions with atoms in the atmosphere. This site provides information on the behavior and relative energies of the particles in the belts. Historic information about the discoveries made in 1958 by a University of Iowa team, headed by James Van Allen, is cited as well.

Stern, David

138

Tropical Belt  

NSDL National Science Digital Library

This lesson familiarizes learners with the term "tropical belt." First, learners locate the equator, Tropic of Cancer and Tropic of Capricorn on a map and trace these lines with a crayon. Learners also color in the locations of tropical rainforests. Next, learners cut along the colored lines of the Tropic of Cancer and Tropic of Capricorn. Educators can punch a hole at each end of this map and tie the ends together with yarn. Learners can wear the belt in class to remind themselves that rainforests are found near the equator or midsection of the Earth. This lesson includes extension ideas and is standards-based.

Sciences, California A.

2008-01-01

139

Sediment-infill volcanic breccia from the Neoarchean Shimoga greenstone terrane, western Dharwar Craton: Implications on pyroclastic volcanism and sedimentation in an active continental margin  

NASA Astrophysics Data System (ADS)

We report sediment-infill volcanic breccia from the Neoarchean Shimoga greenstone belt of western Dharwar Craton which is associated with rhyolites, chlorite schists and pyroclastic rocks. The pyroclastic rocks of Yalavadahalli area of Shimoga greenstone belt host volcanogenic Pb-Cu-Zn mineralization. The sediment-infill volcanic breccia is clast-supported and comprises angular to sub-angular felsic volcanic clasts embedded in a dolomitic matrix that infilled the spaces in between the framework of volcanic clasts. The volcanic clasts are essentially composed of alkali feldspar and quartz with accessory biotite and opaques. These clasts have geochemical characteristics consistent with that of the associated potassic rhyolites from Daginkatte Formation. The rare earth elements (REE) and high field strength element (HFSE) compositions of the sediment-infill volcanic breccia and associated mafic and felsic volcanic rocks suggest an active continental margin setting for their generation. Origin, transport and deposition of these rhyolitic clasts and their aggregation with infiltrated carbonate sediments may be attributed to pyroclastic volcanism, short distance transportation of felsic volcanic clasts and their deposition in a shallow marine shelf in an active continental margin tectonic setting where the rhyolitic clasts were cemented by carbonate material. This unique rock type, marked by close association of pyroclastic volcanic rocks and shallow marine shelf sediments, suggest shorter distance between the ridge and shelf in the Neoarchean plate tectonic scenario.

Manikyamba, C.; Saha, Abhishek; Ganguly, Sohini; Santosh, M.; Lingadevaru, M.; Rajanikanta Singh, M.; Subba Rao, D. V.

2014-12-01

140

Metallogeny of precious and base metal mineralization in the Murchison Greenstone Belt, South Africa  

E-print Network

, located at the eastern end of the Antimony Line. Crystallization of a granodiorite in the Malati Pump mine and of the Baderoukwe granodiorite are dated at 2964 ± 7 Ma and 2970 ± 7 Ma, respectively (zircon U-Pb), while pyrite associated with gold mineralization yielded a Pb-Pb age of 2967 ± 48 Ma. Therefore, granodiorite emplacement

Boyer, Edmond

141

Seat Belt Fact Sheet  

MedlinePLUS

Travel & Motor Vehicle Safety Seat Belt Fact Sheet Safety belts are the most effective means of reducing deaths and serious injuries ... than 90 people die every day in motor vehicle crashes When lap and shoulder belts are used ...

142

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

143

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

144

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

Microsoft Academic Search

Hafnium isotopic compositions were measured in Al-depleted and Al-enriched komatiites from the 3450-Ma-old Barberton greenstone belt, southern Afric. All samples have initial epsilon (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

G. Gruau; C. Chauvel; N. T. Arndt; J. Cornichet

1990-01-01

145

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

146

Geochronology of an archaean tonalitic gneiss dome in Northern Finland and its relation with an unusual overlying volcanic conglomerate and komatiitic greenstone  

Microsoft Academic Search

Archaean gneiss-greenstone relationships are still unresolved in many ancient cratonic terrains although there is growing evidence that most of the late Archaean greenstone assemblages were deposited on older tonalitic crust.

A. Kröner; K. Puustinen; M. Hickman

1981-01-01

147

Greenstone-hosted lode-gold mineralization at Dungash mine, Eastern Desert, Egypt  

NASA Astrophysics Data System (ADS)

The auriferous quartz ± carbonate veins at Dungash mine, central Eastern Desert of Egypt, are confined to ?E-trending dilation zones within variably foliated/sheared metavolcanic/volcaniclastic rocks. The vein morphology and internal structures demonstrate formation concurrent with a dextral shear system. The latter is attributed to flexural displacement of folded, heterogeneous rock blocks through transpression increment, late in the Neoproterozoic deformation history of the area. Geochemistry of the host metavolcanic/metavolcaniclastic rocks from the mine area suggests derivation from a low-K, calc-alkaline magma in a subduction-related, volcanic arc setting. In addition, chemistry of disseminated Cr-spinels further constrain on the back-arc basin setting and low-grade metamorphism, typical of gold-hosting greenstone belts elsewhere. Mineralogy of the mineralized veins includes an early assemblage of arsenopyrite-As-pyrite-gersdorffite ± pyrrhotite, a transitional pyrite-Sb-arsenopyrite ± gersdorffite assemblage, and a late tetrahedrite-chalcopyrite-sphalerite-galena-gold assemblage. Based on arsenopyrite and chlorite geothermometers, formation of gold-sulfide mineralization occurred between ?365 and 280 °C. LA-ICP-MS measurements indicate the presence of refractory Au in arsenian pyrite (up to 53 ppm) and Sb-bearing arsenopyrite (up to 974 ppm). Abundant free-milling gold associated with the late sulfide assemblage may have been mobilized and re-distributed by circulating, lower temperature ore fluids in the waning stages of the hydrothermal system. Based on the isotopic values of vein quartz and carbonate, the calculated average ?18OH2O values of the ore fluids are 5.0 ± 1.4‰ SMOW for quartz, and 3.3 ± 1.4‰ for vein carbonate. The measured carbonate ?13C values correspond to ore fluids with ?13CCO2 = -6.7 ± 0.7‰ PDB. These results suggest a mainly metamorphic source for ore fluids, in good agreement with the vein morphology, textures and hydrothermal alteration. The calculated ?34SH2S values for early, transitional, and late sulfide assemblages define three distinct ranges (?1.5-3.6‰), (?0.4-1.0‰), and (-3.7‰ to -1.9‰), respectively. The systematic evolution towards lighter ?34S values may be attributed to recrystallization, or to ore fluid buffering under variable physicochemical conditions. The shear zone-related setting, mineralogy and isotopic characteristics of gold mineralization in Dungash mine are comparable with other orogenic gold deposits in the region (e.g., Barramiya deposit), which may suggest a regional setting controlling gold metallogeny of the region. This setting should guide future exploration programs in the central Eastern Desert province.

Zoheir, Basem; Weihed, Pär

2014-11-01

148

Enriched and depleted arc basalts, with Mg-andesites and adakites: A potential paired arc-back-arc of the 2.6 Ga Hutti greenstone terrane, India  

NASA Astrophysics Data System (ADS)

The ˜2.6 Ga Hutti greenstone belt is one of several Neoarchean greenstone terranes of the eastern Dharwar Craton. There are prevalent mafic volcanic flows with subordinate felsic volcanic units and siliciclastic sedimentary rocks. All lithologies show variable intensities of submarine hydrothermal alteration, polyphase deformation and greenschist to amphibolite grade metamorphism, yet pillow, cumulus, and other primary volcanic features are locally preserved. Well exposed interlayered metabasalts, Mg-andesites (MA), and felsic flows outcrop along an 11 km sector in the SE of the terrane. Based on combined petrographic and geochemical characteristics, two tholeiitic basalt populations have been identified within the metabasalts: (1) those with enriched LREE at 20-50 times chondrite, and (2) an depleted LREE population at 12-20 times chondrite. The former has fractionated LREE, where (La/Sm) N = 1.2-1.7, but flat HREE, and negative anomalies at Nb, P, and Ti relative to neighbouring REE. The latter has lower absolute abundances of compatible and incompatible elements, mildly fractionated LREE, smaller anomalies at Nb, P, and Ti, with (Gd/Yb) N = 1.1-1.6. Several samples have the "N-MORB" signature of LREE depletion coupled with positive Nb anomalies. On the Th/Yb vs. Nb/Yb discrimination diagram depleted basalts plot near the MORB field whereas enriched basalts overlap the backarc and arc fields, consistent with a paired arc-back-arc. Mg-andesites feature SiO 2 57-61 wt.%, multielement pattens similar to enriched basalts, coupled with Cr, Co, Ni contents greater than "normal" andesites. Felsic volcanic rocks are characterized by low Y, high (La/Yb) N, and Zr/Sm, but low Nb/Ta, with zero to positive Eu anomalies, thus conforming to most of the compositional criteria of Archean and Phanerozoic adakites. Similar associations of enriched and depleted arc basalts, with adakites, are known from Neoarchean greenstone terranes of the Superior Province. During intraoceanic subduction, slab dehydration-wedge melting generated arc basalts whereas slab melting-wedge hybridization, generated adakites and Mg-andesites.

Manikyamba, C.; Kerrich, R.; Khanna, Tarun C.; Satyanarayanan, M.; Krishna, A. Keshav

2009-03-01

149

Belt conveyor apparatus  

SciTech Connect

A belt conveyor apparatus is described comprising: means defining a conveyance path including a first pulley and at least a second pulley, an endless belt member adapted for continuous travel about the pulleys defining thereby an upper and lower reach, the endless belt member having a lower portion which engages the pulleys and an integral upper portion adapted to receive objects at a first location on the conveyance path and transport the objects to and then discharge the objects at a second location on the conveyance path; and motive means in communication with the means defining a conveyance path, for effecting the travel of the endless belt member about the conveyance path.

Oakley, D.J.; Bogart, R.L.

1987-05-05

150

[Seat belts and pregnancy].  

PubMed

The best safety for the mother and her unborn child while driving a car is the proper use of a seat belt. Only a correctly constructed and fitted lap-shoulder safety harness should be used. The instruction to wear a seat belt and to wear it correctly should be part of the pregnancy-care-program for each physician. PMID:971900

Schumann, K

1976-09-23

151

A User-Oriented Approach to Scheduling Collection Building in Greenstone  

E-print Network

for the automated and scheduled maintenance of Greenstone digital library collections. Existing systems require the user either to add new data manually to a collection, or to have programming knowledge in order to use to collection maintenance is preferred. An automated approach should not be time consuming for the user, leaving

Seldin, Jonathan P.

152

Belt conveyor apparatus  

SciTech Connect

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

153

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

154

Synchronous belt drives save energy  

SciTech Connect

The author says synchronous belt drives in power transmission systems can save energy. Laboratory tests support the conclusion that synchronous belts use less power than some other drive systems. The author explains how a drive with three V belts was tested next to an 8 mm synchronous belt drive under identical conditions. The tests measured the relationship of efficiency, torque, speed, pulley diameter, and single and multiple V belts. This article discusses the findings. Synchronous belts prove to work better. They also offer favorable financial benefits.

Wallin, A.W.

1988-04-28

155

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

156

Evaluation of early Archean volcaniclastic and volcanic flow rocks as possible sites for carbonaceous fossil microbes.  

PubMed

Sedimentary rocks have traditionally been the focus of the search for Archean microfossils; the Earth's oldest fossil bacteria are associated with carbonaceous matter in sedimentary cherts in greenstone belts in the eastern Pilbara block of Western Australia and Barberton greenstone belt of South Africa. Reports of possible fossils in a martian meteorite composed of igneous rock and the discovery of modern bacteria associated with basalts have stimulated a new look at Archean volcanic rocks as possible sites for fossil microbes. This study examines silicified volcaniclastic rocks, near-surface altered volcanic flow rocks, and associated stromatolite- like structures from the Archean Barberton greenstone belt to evaluate their potential for the preservation of carbonaceous fossils. Detrital carbonaceous particles are widely admixed with current-deposited debris. Carbonaceous matter is also present in altered volcanic flow rocks as sparse particles in silica veins that appear to be fed by overlying carbonaceous chert layers. Neither microfossils nor mat-like material was identified in the altered volcanic rocks or adjacent stromatolite-like structures. Ancient volcanic flow and volcaniclastic rocks are not promising sites for carbonaceous fossil preservation. PMID:15684724

Walsh, Maud M

2004-01-01

157

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

158

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

159

The Stroke Belt Consortium.  

PubMed

The "Stroke Belt" describes a region of the southeastern United States with a high incidence of stroke and mortality due to stroke. In an effort to address the problem of stroke in this region, we have formed the Stroke Belt Consortium (SBC). This report describes the formation and functions of the SBC. The SBC is a unique organization with representatives from many areas, including health care, government, nonprofit organizations, the pharmaceutical industry, minority groups, educational groups, and managed care. The goals of the consortium are to advance public and professional education about stroke in the Stroke Belt, with a special emphasis on the populations in that region. The first meeting of the consortium was held in November 1994. Many helpful and innovative ideas and initiatives were generated at the first SBC meeting. These included improved techniques for professional education, the development of a mass media campaign for public education, screening of college students for stroke risk factors, and using fast-food restaurants and sporting events as venues to promote stroke education. This type of organized effort may produce cost-effective programs and initiatives, particularly for largescale educational efforts, that will enhance the prevention and treatment of stroke patients. If successful in the Stroke Belt, similar organizations can be formed in other regions of the nation to address specific issues related to stroke prevention, education, and treatment. PMID:17894966

Alberts, M J

1996-01-01

160

Two Corn Belt Farms  

Microsoft Academic Search

Case studies of two farms in eastern Iowa illustrate changes in the Corn Belt since World War II. The Hoffman farm was a classic example of a traditional operation that used a three-year rotation of corn, oats and leguminous hay on 160 acres of land. These crops were used to fatten feeder cattle from western range areas and hogs that

John Fraser Hart

1984-01-01

161

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

162

Pre-3000 Ma thermal history of the Archean Kaap Valley puton, South Africa  

NASA Astrophysics Data System (ADS)

The Kaap Valley pluton is one of several early Archean (3200-3500 Ma) tonalite-trondhjemite plutons that surround the Barberton Greenstone belt, southern Africa. Precise dating using single-grain 207Pb/206Pb evaporation of zircon and 40Ar/39Ar laser step-heating of hornblende and biotite indicates that, in its interior, the Kaap Valley pluton preserves a memory of its initial intrusion and cooling, which spanned a time from 3225 to 3142 Ma. The pluton also records the effect of a low-temperature thermal event at its margin as seen by a 40Ar/39Ar biotite age of 3035 Ma, which is perhaps related to hydrothermal activity and gold mineralization in the adjacent Barberton Greenstone belt. These pre-3000 Ma ages are not in agreement with results of dating studies from sedimentary rocks in the Barberton Greenstone belt and plutons south of the belt which show evidence of having been overprinted by late Archean events (2650-2700 Ma), and the Bushveld Complex intrusion (2050 Ma). These events have been interpreted as affecting most of the Kaapvaal craton. That the Kaap Valley pluton has escaped these and all other events since 3035 Ma with temperatures never reaching 250 °C implies that these large-scale events did not affect the entire craton and the overprinting seen elsewhere is of a more local nature. Thus, it is possible to determine the intrusive and cooling history of the pluton; these data can be used in developing models of heat flow, paleomagnetic remanence acquisition, and deformation events.

Layer, Paul W.; Kröner, Alfred; York, Derek

1992-08-01

163

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

164

Belt.io  

NSDL National Science Digital Library

Belt.io is a great way to share materials with collaborators and colleagues from Indiana to Indonesia. Essentially, it is a central place for storing and sharing simple items such as text or links. It's a bit like a clipboard with more control and the ability to sync across a diverse set of devices. First-time visitors can click on Learn More to explore the various features before signing up. This version is compatible with all operation devices.

Alrawaf, Saad

2013-12-12

165

Magnetosphere of Earth: Radiation Belts  

NASA Astrophysics Data System (ADS)

The Van Allen radiation belts, first discovered by the EXPLORER I satellite in 1958, consist of charged particles in orbits determined by the Earth's magnetic field (see VAN ALLEN BELTS). The Earth's magnetic field is approximately a dipole, see figure 1. Both electrons and ions which make up the radiation belts have typical energies of one million electron volts (1 MeV), and execute three differ...

Hudson, M.; Murdin, P.

2000-11-01

166

SLH Timing Belt Powertrain  

SciTech Connect

The main goal of this proposal was to develop and test a novel powertrain solution for the SLH hydroEngine?, a low-cost, efficient low-head hydropower technology. Nearly two-thirds of U.S. renewable electricity is produced by hydropower (EIA 2010). According to the U.S. Department of Energy; this amount could be increased by 50% with small hydropower plants, often using already-existing dams (Hall 2004). There are more than 80,000 existing dams, and of these, less than 4% generate power (Blankinship 2009). In addition, there are over 800 irrigation districts in the U.S., many with multiple, non-power, low-head drops. These existing, non-power dams and irrigation drops could be retrofitted to produce distributed, baseload, renewable energy with appropriate technology. The problem is that most existing dams are low-head, or less than 30 feet in height (Ragon 2009). Only about 2% of the available low-head hydropower resource in the U.S. has been developed, leaving more than 70 GW of annual mean potential low-head capacity untapped (Hall 2004). Natel Energy, Inc. is developing a low-head hydropower turbine that operates efficiently at heads less than 6 meters and is cost-effective for deployment across multiple low-head structures. Because of the unique racetrack-like path taken by the prime-movers in the SLH, a flexible powertrain is required. Historically, the only viable technological solution was roller chain. Despite the having the ability to easily attach blades, roller chain is characterized by significant drawbacks, including high cost, wear, and vibration from chordal action. Advanced carbon-#12;fiber-reinforced timing belts have been recently developed which, coupled with a novel belt attachment system developed by Natel Energy, result in a large reduction in moving parts, reduced mass and cost, and elimination of chordal action for increased fatigue life. The work done in this project affirmatively addressed each of the following 3 major uncertainties concerning a timing-belt based hydroEngine ?powertrain: 1. Can a belt handle the high torques and power loads demanded by the SLH? (Yes.) 2. Can the SLH blades be mounted to belt with a connection that can withstand the loads encountered in operation? (Yes.) 3. Can the belt, with blade attachments, live through the required cyclic loading? (Yes.) The research adds to the general understanding of sustainable small hydropower systems by using innovative system testing to develop and demonstrate performance of a novel powertrain solution, enabling a new type of hydroelectric turbine to be commercially developed. The technical effectiveness of the methods investigated has been shown to be positive through an extensive design and testing process accommodating many constraints and goals, with a major emphasis on high cycle fatigue life. Economic feasibility of the innovations has been demonstrated through many iterations of design for manufacturability and cost reduction. The project is of benefit to the public because it has helped to develop a solution to a major problem -- despite the large available potential for new low-head hydropower, high capital costs and high levelized cost of electricity (LCOE) continue to be major barriers to project development. The hydroEngine? represents a significant innovation, leveraging novel fluid mechanics and mechanical configuration to allow lower-cost turbine manufacture and development of low head hydropower resources.

Schneider, Abe

2014-04-09

167

Moving belt metal detector  

NASA Astrophysics Data System (ADS)

The Johns Hopkins University Applied Physics Laboratory (APL) has developed a prototype metal detection survey system that will increase the search speed of conventional technology while maintaining high sensitivity. Higher search speeds will reduce the time to clear roads of landmines and improvised explosive devices (IED) and to locate unexploded ordnance (UXO) at Base Realignment and Closure (BRAC) sites, thus reducing remediation costs. The new survey sensor system is called the moving belt metal detector (MBMD) and operates by both increasing sensor speed over the ground while maintaining adequate sensor dwell time over the target for good signal-to-noise ratio (SNR) and reducing motion-induced sensor noise. The MBMD uses an array of metal detection sensors mounted on a flexible belt similar to a tank track. The belt motion is synchronized with the forward survey speed so individual sensor elements remain stationary relative to the ground. A single pulsed transmitter coil is configured to provide a uniform magnetic field along the length of the receivers in ground contact. Individual time-domain electromagnetic induction (EMI) receivers are designed to sense a single time-gate measurement of the total metal content. Each sensor module consists of a receiver coil, amplifier, digitizing electronics and a low power UHF wireless transmitter. This paper presents the survey system design concepts and metal detection data from various targets at several survey speeds. Although the laboratory prototype is designed to demonstrate metal detection survey speeds up to 10 m/s, higher speeds are achievable with a larger sensor array. In addition, the concept can be adapted to work with other sensor technologies not previously considered for moving platforms.

Nelson, Carl V.; Mendat, Deborah P.; Huynh, Toan B.

2006-05-01

168

Number Conveyor Belt  

NSDL National Science Digital Library

This activity for the interactive white board (free access with registration) allows a teacher to create an arithmetic sequence for students to watch being built as the sequence of numbers moves along a conveyor. Learners must determine the pattern being used so when the belt randomly stops, the missing number in the sequence can be dragged/ dropped into its place. The teacher sets the start number (0-19), the interval or common difference (1-10) and if the sequence will count up or down. This last option provides an opportunity to display patterns with integers.

2012-01-01

169

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

170

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

171

An archean impact layer from the Pilbara and Kaapvaal cratons.  

PubMed

The Barberton greenstone belt of South Africa and the eastern Pilbara block of Western Australia provide information about Earth's surface environments between 3.2 and 3.5 billion years ago, including evidence for four large bolide impacts that likely created large craters, deformed the target rocks, and altered the environment. We have obtained identical single-zircon uranium-lead ages of 3470 +/- 2 million years ago for the oldest impact events from each craton. These deposits represent a single global fallout layer that is associated with sedimentation by an impact-generated tsunami and in Western Australia is represented by a major erosional unconformity. PMID:12193781

Byerly, Gary R; Lowe, Donald R; Wooden, Joseph L; Xie, Xiaogang

2002-08-23

172

The Glória quartz-monzodiorite: isotopic and chemical evidence of arc-related magmatism in the central part of the Paleoproterozoic Mineiro belt, Minas Gerais State, Brazil.  

PubMed

The Glória quartz-monzodiorite, one of the mafic plutons of the Paleoproterozoic Mineiro belt, is intrusive into banded gneisses, amphibolites, schists and phyllites of the Rio das Mortes greenstone belt, in the southern portion of the São Francisco Craton, State of Minas Gerais, Brazil. The Glória quartz-monzodiorite yields a SHRIMP U-Pb zircon age of 2188 +/- 29 Ma, suggesting a tectonic relationship with the pre-collisional phase of the Mineiro belt. According to the Nd isotopic evidence (epsilonNd(T) = -3.4; T DM = 2.68 Ga) the original magmas was formed by a mixture among Archean crustal material and Paleoproterozoic juvenile magma. The Glória quartz-monzodiorite shows metaluminous and calc-alkaline tendency with intermediate K content, comparable to that of volcanic-arc rocks. The primary mineralogical assemblage was partly modified by metamorphism, dated between 2131-2121 Ma in nearby coeval plutons. Such metamorphism is significantly older than the reported metamorphic episodes of the Mineiro belt in the Quadrilátero Ferrífero region (2059-2041 Ma) in the eastern portion of the study area. This evidence, together with chemical and isotopic data from other mafic and felsic plutons coeval with the Glória quartz-monzodiorite, indicate a tectonic and magmatic migration within the Mineiro belt from west to east. PMID:16936942

Avila, Ciro A; Teixeira, Wilson; Cordani, Umberto G; Barrueto, Héctor R; Pereira, Ronaldo M; Martins, Veridiana T S; Dunyi, Liu

2006-09-01

173

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

174

Investigating Potential Main Belt Comets  

NASA Astrophysics Data System (ADS)

The discovery of a new class of objects, the Main Belt Comets, has confirmed that ice has been preserved within the Main Belt, despite the fact that the snowline long ago migrated outwards to ~5AU. Main Belt Comets are cometary in appearance, with comae and dust tails visible, but are dynamically unremarkable when compared to asteroids within the Main Belt. Three of the four known Main Belt Comets are dynamically linked to the Themis Family - a collisional family of ~550 asteroids that was created when a 380km progenitor catastrophically disrupted approximately 2Gyr ago. Other Themis Family members are likely to have retained ice deposits and are, thus, potential Main Belt Comets, yet, conversely, hydrated minerals have been detected on one member of the family, asteroid 24 (Themis). The presence of these minerals imply that liquid water was once present on the asteroid, and suggest post-formation heating took place. The preservation of ice within Main Belt Comets suggests that the Themis Family may have once been, and may still be, an important reservoir of ice, while the detection of hydrated minerals on asteroid 24 (Themis) argues for post-formation heating in that region. We will search for hydration features on Themis Family asteroids to constrain the possible thermal evolution of potential Main Belt Comets.

Stevenson, Rachel; Jewitt, David

2009-08-01

175

Geology, geochemistry and genesis of BIF of Kushtagi schist belt, Archaean Dharwar Craton, India  

NASA Astrophysics Data System (ADS)

The Banded Iron-Formation (BIF) of the Kushtagi schist belt, Dharwar Craton is interbedded with metavolcanics. The oxide fades cherty (Al2O3 < 2%) and shaley (Al2O3 > 2%) BIFs show large-scale variations in their major and trace elements abundance. Cherty Banded Iron-Formation (CBIF) is depleted in Al2O3, TiO2, Zr, Hf and other trace elements like Cr, Ni, Co, Rb, Sr, V, Y and REE in comparison to Shaley Banded Iron-Formation (SBIF). Depleted ?REE, positive Eu anomalies and the flat to HREE-enriched pattern of CBIF indicate that Fe and SiO2 for these BIFs were added to ambient ocean water by hydrothermal solutions at the AMOR vent sites. It is inferred that the higher amount of hydrothermal fluid flux with a higher exit temperature provided enormous quantities of iron and silica. Fine-grained sedimentation in the basin gave rise to the observed variability in the composition of BIF. During transgression a wave base was raised up, consequently deposition of CBIF became possible, whereas, during the regressive stage, these chemical sediments were buried by and/or mixed with the terrigenous sediments resulting in deposition of SBIF and interbedded shales. Volcaniclastic activity within the basin appears to have contributed significantly to the composition of some SBIF and shales. The hydrothermal exhalative hypothesis combined with the Archaean miniplate model explains most of the chemical features of the BIFs of greenstone belts.

Khan, R. M. K.; Naqvi, S. M.

1996-01-01

176

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

NASA Technical Reports Server (NTRS)

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 amphibole-bearing, 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.

Beard, James S.; Lofgren, Gary E.

1989-01-01

177

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

178

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

179

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

180

Foreland basins and fold belts  

SciTech Connect

The papers in this book describe six foreland basins and fold belts in terms of their regional setting, stratigraphy, tectonics, and structure, and their oil and gas systems. All of the basins show general similarities, but each differs significantly in detail from the others, posing something of a problem in terms of arriving at a 'typical' foreland basin and fold belt. Some are major hydrocarbon producers; others are not. The major characteristics of the six foreland basins and fold belts are summarized in Tables 1 through 5, which provide a convenient means of comparing and contrasting these basins and their hydrocarbon resources. The Western Canada foreland basin and fold belt serves as the type example for several reasons. These include: its setting and clear relationship to a major orogene of Mesozoic-Cenozoic age; the fact that it is uncomplicated by later overprinting, segmentation, or cover rocks unlike the Ouachita, Eastern Venezuela, and U.S. Rocky Mountain foreland basins and fold belts); the fact that there is a large volume of publicly available data on the basin and an active exploration and research community; and the fact that it has reasonable oil and gas reserves in a well-defined stratigraphic framework.

Macqueen, R.W.; Leckie, D.A. (Geological Survey of Canada, Inst. of Sedimentary and Petroleum Geology, Calgary, Alberta (Canada))

1992-01-01

181

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

182

14 CFR 27.1413 - Safety belts.  

Code of Federal Regulations, 2012 CFR

... 2012-01-01 false Safety belts. 27.1413 Section...DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS...CATEGORY ROTORCRAFT Equipment Safety Equipment § 27.1413 Safety belts. Each safety...

2012-01-01

183

14 CFR 27.1413 - Safety belts.  

Code of Federal Regulations, 2011 CFR

... 2011-01-01 false Safety belts. 27.1413 Section...DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS...CATEGORY ROTORCRAFT Equipment Safety Equipment § 27.1413 Safety belts. Each safety...

2011-01-01

184

14 CFR 27.1413 - Safety belts.  

Code of Federal Regulations, 2013 CFR

... 2013-01-01 false Safety belts. 27.1413 Section...DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS...CATEGORY ROTORCRAFT Equipment Safety Equipment § 27.1413 Safety belts. Each safety...

2013-01-01

185

14 CFR 27.1413 - Safety belts.  

Code of Federal Regulations, 2010 CFR

... 2010-01-01 false Safety belts. 27.1413 Section...DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS...CATEGORY ROTORCRAFT Equipment Safety Equipment § 27.1413 Safety belts. Each safety...

2010-01-01

186

14 CFR 27.1413 - Safety belts.  

... 2014-01-01 false Safety belts. 27.1413 Section...DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS...CATEGORY ROTORCRAFT Equipment Safety Equipment § 27.1413 Safety belts. Each safety...

2014-01-01

187

30 CFR 77.1107 - Belt conveyors.  

Code of Federal Regulations, 2011 CFR

...Protection § 77.1107 Belt conveyors. Belt conveyors in locations where fire would create a hazard to personnel shall be provided with switches to stop the drive pulley automatically in the event of excessive...

2011-07-01

188

30 CFR 77.1107 - Belt conveyors.  

Code of Federal Regulations, 2010 CFR

...Protection § 77.1107 Belt conveyors. Belt conveyors in locations where fire would create a hazard to personnel shall be provided with switches to stop the drive pulley automatically in the event of excessive...

2010-07-01

189

30 CFR 77.1107 - Belt conveyors.  

Code of Federal Regulations, 2012 CFR

...Protection § 77.1107 Belt conveyors. Belt conveyors in locations where fire would create a hazard to personnel shall be provided with switches to stop the drive pulley automatically in the event of excessive...

2012-07-01

190

30 CFR 77.1107 - Belt conveyors.  

...Protection § 77.1107 Belt conveyors. Belt conveyors in locations where fire would create a hazard to personnel shall be provided with switches to stop the drive pulley automatically in the event of excessive...

2014-07-01

191

30 CFR 77.1107 - Belt conveyors.  

Code of Federal Regulations, 2013 CFR

...Protection § 77.1107 Belt conveyors. Belt conveyors in locations where fire would create a hazard to personnel shall be provided with switches to stop the drive pulley automatically in the event of excessive...

2013-07-01

192

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

193

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

194

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. PMID:11209879

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

2001-01-01

195

Mesoarchean oceanic sedimentary sequences: Dixon Island-Cleaverville formations of Pilbara vs Komati section of Fig Tree Group in Barberton  

NASA Astrophysics Data System (ADS)

During the Neoarchean to Paleoproterozoic, atmospheric conditions varied from lower levels of oxygen contents to oxic conditions in atmosphere, with the Great Oxidation Event occurring at 2.5 Ga (e.g. Canfield, 2005, Farquhar et al., 2007). However, many iron formations and oxic iron rich sediments occur in the Mesoarchean. We evaluate the sedimentation history of some well-preserved Mesoarchean iron rich sequences by focusing on their stratigraphic pattern and geochemical characteristics. Our study focuses on three iron formation bearing deeper facies sedimentary sequences in Mesoarchean - 1) Dixon Island (Pilbara), 2) Cleaverville (Pilbara) and 3) Mapepe (Barberton) formations. The Dixon Island-Cleaverville formations include volcano-sedimentary sequences as indicated by drill core samples (DXCL) (Kiyokawa et al., 2006, Yamaguchi et al., 2009). It shows coarsening and thickening upward black shale-BIF sequences which indicate oceanic caldera environment. Estimated sedimentation rate from Dixon Island Formation (3195+15 Ma) to Cleaverville Formation (3108+13 Ma) is 2-4 cm/1000year. The Komati section of the Mappepe Formation in the Fig Tree Group consists of a more than 300m thick bedded black shale-chert-iron formation sequence. Based on mapping at 1/100 and 1/1000 scales, we reconstructed 150m thick stratigraphic section. This sequence conformably overlies volcanic rocks, which are in turn overlain by iron rich red bed sequences. Organic rich sequences of three different thickness were identified; 1) less than 1mm thick thin laminated black and white chert and pyrite lamination sequence, 2) 3-5 cm thick black shale-chert-iron rich sequence, and 3) 20 cm thick black chert with fine grained volcanic rocks to banded iron formation sequence. Each sequence contains cycles of organic matter rich shale at the bottom, with chert, pyrite or iron rich bed to the top. Total organic carbon of DXCL core reaches maximum values over 3.0 wt%. (ave 1.2 wt%). Total organic carbon of the Mappepe formation has a maximum value over 16 wt% (ave 2.7 wt%). Carbon isotope (d13C) compositions of organic matter in DXCL drill core is homogenous, ranging from -32 to -28%. This may be due to hydrothermal related biogenic activity. On the other hand, the Komati section values range from -38.8 to -20.5% (ave 26.6%) and varies within the formation. The three types of stratigraphic sections indicate deeper ocean to relative shallow ocean conditions. During Mesoarchean, ocean floor was stagnant and formed black shale. Homogeneous organic carbon isotope data of the organic matter of the Dixon Island and Cleaverville formations indicate biologic activity on ocean surface. It is consistent with an oceanic island arc setting. On the other hand, thicker lamina, and organic matter rich character of the Komati section indicate influence of continental material input. Biogenic activity in Mesoarchean, may have been more intense along the continent marginal ocean than pelagic ocean, similar to modern oceans.

Kiyokawa, S.; Ito, T.; Ikehara, M.; Yamaguchi, K. E.; Horie, K.; Sakamoto, R.; Takehara, M.; Teraji, S.

2011-12-01

196

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. PMID:24479100

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

2013-01-01

197

Mantle heterogeneity and crustal recycling in Archean granite-greenstone belts - Evidence from Nd isotopes and trace elements in the Rainy Lake area, Superior Province, Ontario, Canada  

NASA Technical Reports Server (NTRS)

Crustal evolution in the Rainy Lake area, Ontario is studied in terms of geochemical characteristics. The Nd isotope data are examined for heterogeneity of the Archean mantle, and the Sm/Nd depletion of the mantle is analyzed. The Nd isotope systematics of individual rock suites is investigated in order to understand the difference between crust and mantle sources; the precursors and petrogenetic processes are discussed. The correlation between SiO2 content and Nd values is considered. Rapid recycling of crustal components, which were previously derived from depleted mantle sources, is suggested based on the similarity of the initial Nd isotopic composition for both mantle-derived and crustally-derived rocks.

Shirey, Steven B.; Hanson, Gilbert N.

1986-01-01

198

Detritic zircons from the Archean quartzites of the Matlakhta greenstone belt of the Karelian Craton: Hydrothermal alterations, mineral inclusions, and isotope age  

Microsoft Academic Search

Zircon, which is one of the most universal minerals applicable to geochronometry, is an important source of information about the age of rocks and superim? posed processes. The special role of ancient detritic zircons in the reconstruction of the earliest Hadean processes of formation and transformation of the Earth’s continental crust was established. As it turned out, in detritic zircons

V. N. Kozhevnikov; S. G. Skublov

2010-01-01

199

Fluid evolution in the H 2O-CH 4-CO 2-NaCl system during emerald mineralization at Gravelotte, Murchison Greenstone Belt, Northeast Transvaal, South Africa  

NASA Astrophysics Data System (ADS)

Fluid evolution during emerald mineralization at the Gravelotte emerald mine has been studied by microthermometry and laser Raman microprobe spectrometry. The emeralds and associated phenakites occur on the flanks of a highly metasomatised albitite pegmatoid body and in the biotite schists at and near its contact. The fluids lie in the H 2O-CH 4-CO 2-NaCl system and four types of inclusions are characterised based on time of trapping and fluid contents. The earliest type 1 inclusions, found in phenakites and the emeralds which formed from them, are low salinity (<6 wt% NaCl) with up to 18 mol% CH 4. The carbonic phase contains over 93 mol% CH 4 and variable small amounts of CO 2, C 2H 6, N 2, and H 2S. The solvus crest for this system lies at ?400°C, closer to the H 2O end of the join. With time the fluids become less CH 4 rich and more saline. The type 2 fluids are highly variable in both CH 4-CO 2 contents and salinity, reflecting mixing of type 1 fluids with higher salinity brines. The late type 3 and 4 inclusions are CH 4-CO 2-free high salinity inclusions with up to 38 wt% NaCl. Trapping conditions for the type 1 fluids were around 450-500°C and 4 kb based on model isochores and geologic evidence. During the trapping of type 2 inclusions, fluid pressures probably fluctuated due to opening and resealing of fractures. Approximate P- T ranges of trapping for these and other later inclusions have been defined, minimum trapping temperatures for types 2, 3, and 4 being, respectively, 250, 150, and 240°C, and pressures in the range of 1-4 kb. Calculations of ƒ O 2 show an initial low ƒ O 2 between QFM and the synthetic graphite-CH 4 buffer for the type 1 fluids. This rises to above QFM in the later stages. Such low initial values are uncharacteristic of granitic pegmatite systems, and it is suggested that the phenakites formed in the post-magmatic stage of alkali metasomatism when the albitization took place. In the later stages, phenakite was converted to emerald as alumina activities in the system increased. Concomitantly higher salinity brines, at least some of which are probably related to regional metamorphism in the area, were trapped under higher ƒ O 2 conditions. Metasomatic exchange with the mafic host rocks also increased as evidenced by the incorporation of Cr in the late emeralds. The energy necessary for the continuous growth of the later emeralds was probably supplied by regional metamorphism.

Nwe, Yin Yin; Morteani, Giulio

1993-01-01

200

Plutonism, deformation, and metamorphism in the Proterozoic Flin Flon greenstone belt, Canada: Limits on timing provided by the single-zircon Pb-evaporation technique  

SciTech Connect

The authors have used the single-zircon Pb-evaporation technique to determine the age of granitoids in the western Flin Flon domain of the Trans-Hudson orogen in Canada and to constrain the timing of molasse sedimentation, deformation, metamorphism, and mesothermal gold mineralization. The plutons were intruded between 1,860 and 1,834 Ma, about 30 m.y. after volcanism, and provide further evidence of a major period of intrusive activity throughout the Trans-Hudson orogen at that time. The older plutons (1,860 to 1,848 Ma) are synchronous with P2 deformation and the early stages of peak metamorphism, whereas the younger plutons are synchronous with or postdate the P3 deformation event. Molasse sedimentary units are deformed and metamorphosed; thus, deposition must have begun at about 1,860 Ma. Mesothermal gold mineralization postdates all plutons and may be related to high-grade peak metamorphism in adjacent terranes at about 1,815 Ma. This study also provides further support for the use of the Pb-evaporation technique as a suitable method for dating single zircons and indicates that the {sup 208}Pb/{sup 206}Pb ratio of zircons may be a useful tool in detecting the presence and source of xenocrystic zircons.

Ansdell, K.M.; Kyser, T.K. (Univ. of Saskatchewan, Saskatoon (Canada))

1991-05-01

201

Composition and origin of fluids associated with lode gold deposits in a Mesoarchean greenstone belt (Warrawoona Syncline, Pilbara Craton, Western Australia) using synchrotron radiation X-ray fluorescence  

Microsoft Academic Search

Microthermometry and Raman spectroscopy techniques are routinely use to constrain ore-fluids ?18O and molar proportions of anhydrous gas species (CO2, CH4, N2). However, these methods remain imprecise concerning the ore-fluids composition and source. Synchrotron radiation X-ray fluorescence allows access to major and trace element concentrations (Cl, Br and K, Ca, Fe, Cu, Zn, As, Rb, Sr) of single fluid inclusion.

Nicolas Thébaud; Pascal Philippot; Patrice Rey; Jean Cauzid

2006-01-01

202

HREE-enriched low-Ti tholeiites, western Abitibi greenstone belt: A heterogeneous mantle plume-convergent margin environment. Geochim. Cosmochim. Acta 61, 47234744 (1997).  

E-print Network

. Carlson, R. W. et al. in The J.B. Dawson Volume--Proc. 7th Int. Kimberlite Conf (eds Gurney, J. J., Gurney study of peridotite xenoliths from Lesotho kimberlites. Geophys. Res. Lett. 28, 2505­2508 (2001). 25

Benoit-Bird, Kelly J.

203

The Scattered Kuiper Belt Objects  

NASA Astrophysics Data System (ADS)

We describe a continuing survey of the Kuiper Belt conducted at the 3.6-m Canada France Hawaii Telescope on Mauna Kea, Hawaii. The survey employs a 12288 x 8192 pixel CCD mosaic to image the sky to red magnitude 24. All detected objects are targeted for systematic follow-up observations, allowing us to determine their orbital characteristics. Three new members of the rare Scattered Kuiper Belt Object class have been identified, bringing the known population of such objects to four. The SKBOs are thought to have been scattered outward by Neptune, and are a potential source of the short-period comets. Using a Maximum Likelihood method, we place observational constraints on the total number and mass of the SKBOs.

Trujillo, C. A.; Jewitt, D. C.; Luu, J. X.

1999-09-01

204

The Virtual Radiation Belt Observatory  

NASA Astrophysics Data System (ADS)

ViRBO (Virtual Radiation Belt Observatory) is one of the domain-specific virtual observatories funded under the NASA Heliophysics Data Environment (HPDE) program that began development in 2006. In this work, we report on the search, display, and data access functionality of ViRBO along with plans for interaction with upcoming missions, including Radiation Belt Storms Probes (RBSP). We also describe the relationship between the services and data provided by ViRBO and the general architecture of the HPDE and the plan articulated in the 2010 Senior Review of Data Centers. The lessons learned in the development of ViRBO include issues related to (1) creating a user base given the limits of the types of activities a virtual observatory are charged with supporting and (2) dealing with limitations on existing software and standards when developing data services.

Weigel, R. S.; O'Brien, T. P.; Friedel, R. H.; Green, J. C.; Zhizhin, M.; Mishin, D. Y.

2010-12-01

205

Liquid belt radiator design study  

NASA Technical Reports Server (NTRS)

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 rejection systems. The technical efforts associated with this study concentrate on refining the concept of the LBR as well as examining the issues of belt dynamics and potential application of the LBR to intermediate and high temperature heat rejection applications. A low temperature point design developed in previous work is updated assuming the use of diffusion pump oil, Santovac-6, as the heat transfer media. Additional analytical and design effort is directed toward determining the impact of interface heat exchanger, fluid bath sealing, and belt drive mechanism designs on system performance and mass. The updated design supports the earlier result by indicating a significant reduction in system specific system mass as compared to heat pipe or pumped fluid radiator concepts currently under consideration (1.3 kg/sq m versus 5 kg/sq m).

Teagan, W. P.; Fitzgerald, K. F.

1986-01-01

206

Tectonic evolution of Boromo and Houndé belts (western Burkina Faso) : contemporaneous crustal scale folding of volcano-sedimentary sequences and granitoid plutons emplacement (~2.2 - 2.0 Ga)  

NASA Astrophysics Data System (ADS)

Interpretation of regional scale airborne geophysical data of western Burkina Faso integrated with structural, geochemical and petrological data suggest that the Boromo and Houndé belts were parts of the same volcano-sedimentary basin characterised by basalts and gabbros of tholeiitic composition at the base, evolving to calc-alkaline mafic and intermediate volcanics followed by flysh sediments, typical for the volcanic island arcs. A specific lithology, consisting of basalts with plagioclase megacrysts was observed at the eastern margin of the Houndé belt as well as at the western part of the Boromo belt, representing an important stratigraphic marker allowing us to make the link between the two belts. The equivalent structural evolution of stratigraphic sequences in the two belts is consistent with NNE-SSW trending regional scale synforms with an antiform localized in between the Boromo and Houndé belts and also at their eastern and western limits, respectively. The antiform structures are obliterated by numerous tonalite-trondjemite-granodiorite-granite plutons, characterized by the same structural grain as the adjacent greenstone belts. Magnetic and radiometric data show a previously unrecorded NNW-SSE oriented regional scale shear zone affecting the the granitoids between the Houndé and Banfora belts. In the south, this shear zone joins by a fan-like relationship another large scale (200km) N-S trending shear zone bordering the Houndé belt in the west and running down to the Côte d'Ivoire border. In the eastern part of the Houndé belt, continuous N-S unit of detrital "Tarkwaian" type metasediments occurs, reaching up to 400km in length. They are affected at the eastern and western limits by a crustal scale belt-parallel shear zone. Based on regional scale structural correlations, we suppose that a D1 deformation event affected the volcanic sequence of Houndé and Boromo belts. However, it was almost entirely overprinted by the major deformation phase D2, responsible for the structural grain present in all western Burkina Faso. Most of the NNE-SSW steeply dipping penetrative metamorphic fabrics and isoclinals folds in greenstone belts developed contemporaneously with the subvertical magmatic banding in the TTG's during the D2a. Deformation partitioning between dominant flattening and sinistral NNE-SSW shearing is typical for this phase. Metavolcanic rocks are afftected by regional metamorphism of greenschist facies and only narrow zones adjacent to granitoid plutons reach amphibolites facies conditions. Continuous transition into transcurrent ENE-WSW and NNW-SSE trending conjugate shear zones is assigned to D2b. Late D3 deformation characterized by spaced crenulation cleavage and kink folds with subvertical E-W oriented shear zones occurs mainly in highly anisotropic fine grained metasediments and it is either late Eburnean or perhaps Pan-African.

Baratoux, Lenka; Metelka, Václav; Naba, Séta; Jessell, Mark; Grégoire, Michel; Ganne, Jérôme

2010-05-01

207

Greenstone and diabase utilization in the stone age of western Norway: Technological and socio?cultural aspects of axe and adze production and distribution  

Microsoft Academic Search

The subject of this article is the production and distribution of stone axes and adzes originating from two large Stone Age quarries in western Norway: the greenstone quarry on the small island of Hespriholmen, Bømlo kommune, Hordaland fylke, and the diabase quarry at Stakaneset, Flora kommune, Sogn og Fjordane Fylke. The identification of production sites and distributed products associated with

Asle Bruen Olsen; Sigmund Alsaker

1984-01-01

208

Synchronous and Cogged Fan Belt Performance Assessment  

SciTech Connect

The GSA Regional GPG Team commissioned the National Renewable Energy Laboratory (NREL) to perform monitoring of cogged V-belts and synchronous belts on both a constant volume and a variable air volume fan at the Byron G. Rodgers Federal Building and U.S. Courthouse in Denver, Colorado. These motor/fan combinations were tested with their original, standard V-belts (appropriately tensioned by an operation and maintenance professional) to obtain a baseline for standard operation. They were then switched to the cogged V-belts, and finally to synchronous belts. The power consumption by the motor was normalized for both fan speed and air density changes. This was necessary to ensure that the power readings were not influenced by a change in rotational fan speed or by the power required to push denser air. Finally, energy savings and operation and maintenance savings were compiled into an economic life-cycle cost analysis of the different belt options.

Cutler, D.; Dean, J.; Acosta, J.

2014-02-01

209

Belt type continuously variable transmission system  

SciTech Connect

This patent describes a belt type continuously variable transmission system comprising: a belt type continuously variable transmission device wherein a transmission belt is racked across an input pulley and an output pulley and rotation is continuously variably transmitted from the input pulley to the output pulley; and an auxiliary transmission device disposed on the output side of the belt type continuously variable transmission device and having at least a forward-reverse shift mechanism, wherein the belt type continuously variable transmission device and the auxiliary transmission device are respectively housed in a belt type continuously variable transmission device housing and an auxiliary transmission device housing, both of which are formed by case members and separated by a radial partition member of the case members into independent sealed housings, respectively, and wherein the auxiliary transmission device is detacheble from the continuously variable transmission device housing as an independent unit.

Okada, M.; Morisawa, K.; Kakamu, M.; Kato, N.

1988-11-15

210

30 CFR 75.1731 - Maintenance of belt conveyors and belt conveyor entries.  

Code of Federal Regulations, 2010 CFR

...ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Miscellaneous § 75.1731...belt must maintain flame-resistant properties of the belt. [73 FR 80616,...

2010-07-01

211

Microslip friction in flat belt drives  

Microsoft Academic Search

The microslip shear model of belt mechanics is extended to fully incorporate belt inertia effects and used to analyse the steady state of a two-pulley drive. The belt is modelled as an axially moving string consisting of a tension-bearing member and a pliable elastomer envelope. Relative displacement between the tension-bearing member and the pulley surfaces shears the elastomer envelope, transferring

L Kong; R G Parker

2005-01-01

212

Cooling system for a belt type transmission  

SciTech Connect

This patent describes a cooler for a belt type transmission in a power unit for vehicles having an engine body, a transmission casing provided on one side of the engine body, and a belt type transmission composed of a drive pulley connected with the crankshaft of the engine body, a driven pulley connected with an output shaft and an endless transmitting belt engaged between the pulleys contained in a transmitting chamber in the transmission casing.

Tanaka, K.; Ochiai, H.; Ikenoya, Y.

1987-06-09

213

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

214

Investigation of moving belt radiator technology issues  

NASA Astrophysics Data System (ADS)

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.

1994-06-01

215

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. PMID:20882150

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

2010-01-01

216

China belting up or down? Seat belt wearing trends in Nanjing and Zhoushan  

Microsoft Academic Search

National seat belt wearing legislation became effective in China May 2004 and associated provincial and city regulations followed. Despite rapid motorisation seat belt studies in China have been scarce. Patterns and trends in urban seat belt wearing were observed for all driver, front and rear seating positions over the years 2005–2007 in two eastern cities Nanjing (Jiangsu Province) and Zhoushan

Virginia Routley; Joan Ozanne-Smith; Dan Li; Min Yu; Jianyue Wang; Junhe Zhang; Zhendong Tong; Ming Wu; Peihua Wang; Yu Qin

2008-01-01

217

Tertiary magmatic belts in Java  

NASA Astrophysics Data System (ADS)

Evidence of the earliest magmatic event (Late Eocene-Early Miocene) has recently been discovered in East Java (Pacitan area) as exposures of pillow lava flows. Stratigraphically they represent the lowermost part of Besole Formation (Oligocene-Early Miocene) which is made up mainly of volcanic turbidites. Major element chemistry of the lava flows indicates typical island arc tholieites with a significant Nb anomaly and relatively flat REE patterns. In Central Java the same magmatic event resulted in the emplacement of tholeitic intrusion at Karangsambung, Luk Ulo. The corresponding volcanic products of this event in West Java are represented by the Jampang Formation (Oligocene-Early Miocene) which is limited to the southern part of West Java. The chemistry of Neogene volcanic rocks which have been collected from the Jatiluhur-Sanggabuana area in West Java show that they are calc-alkali basalts and andesites. Some of them are marked by higher K 2O contents leading to the potassic calc-alkali and shoshonitic rock series; similar phenomena are found in the Neogene volcanics of Karangkobar in Central Java. In East Java (Pacitan-Trenggalek area) outcrops of calc-alkali basalt flows underlie the limestones of the Punung Formation (Middle-late Miocene); the latter is also cut by dykes and volcanic necks of more differentiated rocks. From the pattern of distribution of the Tertiary volcanics, two parallel east-west trending magmatic belts may be recognized; the belt along the southern part of Java is related to Paleogene subduction, whereas the other to the north is related to Neogene subduction. The Quaternary volcanic cones in general are distributed within the Neogene magmatic belt.

Soeria-Atmadja, R.; Maury, R. C.; Bellon, H.; Pringgoprawiro, H.; Polve, M.; Priadi, B.

218

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

219

Simulation Worksheet: Kuiper Belt Interactions Instructor Guidelines  

E-print Network

Simulation Worksheet: Kuiper Belt Interactions Instructor Guidelines The goal of this activity interaction with the asteroid belt and the Kirkwood Gaps. This worksheet makes use of simulations contained that each student in the class will have their own photocopy of the worksheet that they will annotate

Farritor, Shane

220

The thrust belts of Western North America  

Microsoft Academic Search

Most of the Basin and Range physiographic province of western North America is now believed to be part of the overthrust. The more obvious overthrust belt along the eastern edge of the Basin and Range Province is named the Sevier orogenic belt, where older rocks are observed thrust onto younger rocks. More detailed surface geological mapping, plus deep multiple-fold geophysical

1993-01-01

221

High-energy proton radiation belt  

Microsoft Academic Search

The experiments and theories to explain the high-energy protons trapped ; in the Earth's radiation belt are reviewed. The theory of cosmic-ray albedo ; neutron decay injection of protons into the radiation belt is discussed. Radial ; diffusion and change in the Earth's dipole moment are included along with losses ; of protons by ionization and nuclear collision. It is

R. Stephen White

1973-01-01

222

Apparatus for heat treating plastic belts  

NASA Technical Reports Server (NTRS)

Apparatus performs programed rotating, stretching/shrinking and heat treatment necessary to fabrication of high-performance plastic belts. Belts can be treated in lengths varying from 7 to 48 in., in widths up to 1 in., and in thicknesses up to approximately 0.003 in.

Topits, A., Jr.

1975-01-01

223

The Administrator's "Handy Dandy" Tool Belt  

ERIC Educational Resources Information Center

Every good leader needs a tool belt. Throughout the author's years of building early childhood programs, she has acquired a number of tools for her personal belt. These tools have helped her sharpen her skills in supporting teachers and staff, connecting with families, and educating children. This article focuses on those leadership skills that…

Anderson, Terry

2012-01-01

224

Pitch difference and belt tooth configuration effect on load distribution of timing belt using FEM analysis  

SciTech Connect

A timing belt used for an automotive engine`s camshaft consists of a facing fabric, elastoeric body and glass fiber cords. These materials show significant non-linear characteristics. Therefore, a model of the timing belt was analyzed using ABAQUS (a general non-linear finite element program). As a result, the mechanism that generates the belt load distribution was successfully confirmed by calculation. It was found that the pitch difference existing between the timing belt and pulley, and belt tooth configuration both have a large affect on load distribution of toothed belts. This paper reports the development of an analytical model which shows the effects of pitch difference and pulley tooth configuration on belt contact pressure.

Uchida, Takanao; Furukawa, Yoshihisa; Tomono, Kiyohisa; Takahashi, Hideaki

1996-09-01

225

Use of seatbelts in cars with automatic belts.  

PubMed Central

Use of seatbelts in late model cars with automatic or manual belt systems was observed in suburban Washington, DC, Chicago, Los Angeles, and Philadelphia. In cars with automatic two-point belt systems, the use of shoulder belts by drivers was substantially higher than in the same model cars with manual three-point belts. This finding was true in varying degrees whatever the type of automatic belt, including cars with detachable nonmotorized belts, cars with detachable motorized belts, and especially cars with nondetachable motorized belts. Most of these automatic shoulder belts systems include manual lap belts. Use of lap belts was lower in cars with automatic two-point belt systems than in the same model cars with manual three-point belts; precisely how much lower could not be reliably estimated in this survey. Use of shoulder and lap belts was slightly higher in General Motors cars with detachable automatic three-point belts compared with the same model cars with manual three-point belts; in Hondas there was no difference in the rates of use of manual three-point belts and the rates of use of automatic three-point belts. PMID:1561301

Williams, A F; Wells, J K; Lund, A K; Teed, N J

1992-01-01

226

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

227

Electric filter with movable belt electrode  

SciTech Connect

A method and apparatus are disclosed for removing airborne contaminants entrained in a gas or airstream. The apparatus 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, W.

1982-02-23

228

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

229

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

230

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

231

INCREASED POWER DENSITY OF PUSH-BELT CVTs USING A NEW MARAGING STEEL FOR BELT MANUFACTURE  

Microsoft Academic Search

Since the commercial introduction of push-belt type continuously variable transmission (CVT) systems, customer specifications concerning power density (transmittable power, torque, transmission size, ratio coverage, and durability) have become increasingly demanding. Consequently, the increase of push-belt power density is a permanent goal for Van Doorne's Transmissie, Bosch Group. Maximum power density is mainly determined by the ability of the push-belt rings

Bert Pennings; Minh-Duc Tran; Michel Derks; Arjen Brandsma

232

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

233

Effectiveness of behavioral safety belt interventions.  

PubMed

A wide variety of approaches have been developed to promote safety belt use. This paper evaluates the relationship of types of behavioral safety belt programs to short- and long-term safety belt use rates. Five types of programs were examined: Law, Incentive, Education, Monitoring, and Prompt. Programs were generally effective in increasing use rates, with a median increase of 17.0% (95% CI = 13.4%, 20.1%). Program type differentially affected use rates, with Law and Incentive producing the highest increase in rates. Length of intervention and number of interventions within one program were not significantly related to use rates. Immediately after intervention ended, safety belt use declined but soon stabilized, with rates remaining significantly higher than baseline. PMID:8011044

Johnston, J J; Hendricks, S A; Fike, J M

1994-06-01

234

14 CFR 31.63 - Safety belts.  

Code of Federal Regulations, 2013 CFR

...TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: MANNED FREE BALLOONS Design Construction § 31.63 Safety belts...subpart C of this part. (b) This section does not apply to balloons that incorporate a basket or gondola. [Amdt....

2013-01-01

235

14 CFR 31.63 - Safety belts.  

...TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: MANNED FREE BALLOONS Design Construction § 31.63 Safety belts...subpart C of this part. (b) This section does not apply to balloons that incorporate a basket or gondola. [Amdt....

2014-01-01

236

14 CFR 31.63 - Safety belts.  

Code of Federal Regulations, 2010 CFR

...TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: MANNED FREE BALLOONS Design Construction § 31.63 Safety belts...Subpart C of this part. (b) This section does not apply to balloons that incorporate a basket or gondola. [Amdt....

2010-01-01

237

14 CFR 31.63 - Safety belts.  

Code of Federal Regulations, 2011 CFR

...TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: MANNED FREE BALLOONS Design Construction § 31.63 Safety belts...Subpart C of this part. (b) This section does not apply to balloons that incorporate a basket or gondola. [Amdt....

2011-01-01

238

14 CFR 31.63 - Safety belts.  

Code of Federal Regulations, 2012 CFR

...TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: MANNED FREE BALLOONS Design Construction § 31.63 Safety belts...subpart C of this part. (b) This section does not apply to balloons that incorporate a basket or gondola. [Amdt....

2012-01-01

239

A study of binary Kuiper Belt objects  

E-print Network

About 105 bodies larger than 100km in diameter (Jewitt 1998) reside in the Kuiper Belt, beyond the orbit of Neptune. Since 1992 observational surveys have discovered over one thousand of these objects, believed to be fossil ...

Kern, Susan Diane

2006-01-01

240

Heat engine with corrugated-shape memory drive belt  

SciTech Connect

An endless drive belt made of shape memory material is entrained about spaced pulleys, one of which projects into a thermal heating region within which the drive belt undergoes contraction to form corrugations therein through which variable spaced contact is established with said one of the pulleys to induce rotation thereof and movement of the belt. The belt expands as it moves out of the thermal heating region causing the corrugations to flatten out as the belt approaches the outer pulley.

Goldstein, D.

1990-07-19

241

Gaps in the Earths Radiation Belts  

NSDL National Science Digital Library

The Earth's radiation belts (violet & white) change considerably due to a number of influences, ranging from a changing solar wind to the lightning on the Earth. Here we see a range of variation in the electron flux in early December 2003. White indicates higher electron flux than violet. The gray curves represent the lines of the Earth's magnetic field. These radiation belts are constructed on a per-orbit basis with data from SAMPEX.

Bridgman, Tom; Green, James

2005-03-08

242

Oil generation in overthrust belts  

SciTech Connect

The burial of immature sediments beneath a thrust sheet may result in sufficient heating to generate hydrocarbons. The authors present a model for the thermally activated generation of oil from kerogen and the subsequent destruction of the oil through cracking. Using this oil generation model in conjunction with a model applicable to the thermal evolution of overthrust belts, the evolution is studied of oil in sediments beneath a thrust sheet composed of sedimentary rocks. Oil generation may begin soon after emplacement of the thrust sheet. Beneath thick thrust sheets (>8 km), all oil in the sedimentary section may be destroyed less than 5 m.y. after thrusting. The authors results to the timing of oil generation in the sedimentary section beneath the Absaroka thrust plate in the Fossil syncline of western Wyoming. Calculations indicate that the Paleozoic and a part of the Mesozoic section were thermally mature prior to emplacement of the Absaroka plate. The remaining part of Mesozoic sediments matured only after thrusting. The results are in agreement with Warner's 1980 observations that oil being produced from reservoirs in the Absaroka plate was generated in the underthrust Mesozoic section.

Angevine, C.L.; Turcotte, D.L.

1983-02-01

243

1. THE RADIATION BELTS The outer zone radiation belts consist of energetic elec-  

E-print Network

1. THE RADIATION BELTS The outer zone radiation belts consist of energetic elec- trons trapped and external processes. This paper reviews what is currently understood of the interactions between energetic and Space Physics, University of Colorado, Boulder, Colorado, USA Energetic particle fluxes in the outer

Elkington, Scot R.

244

Satellites of the largest Kuiper belt objects  

E-print Network

We have searched the four brightest objects in the Kuiper belt for the presence of satellites using the newly commissioned Keck Observatory Laser Guide Star Adaptive Optics system. Satellites are seen around three of the four objects: Pluto (whose satellite Charon is well-known), 2003 EL61, and 2003 UB313. The object 2005 FY9, the brightest Kuiper belt object after Pluto, does not have a satellite detectable within 0.4 arcseconds with a brightness of more than 0.5% of the primary. The presence of satellites to 3 of the 4 brightest Kuiper belt objects is inconsistent with the fraction of satellites in the Kuiper belt at large at the 99.1% confidence level, suggesting a different formation mechanism for these largest KBO satellites. The satellites of 2003 EL61 and 2003 UB313, with fractional brightnesses of 5% and 2% of their primaries, respectively, are significantly fainter relative to their primaries than other known Kuiper belt object satellites, again pointing to possible differences in their origin.

M. E. Brown; M. A. van Dam; A. H. Bouchez; D. Le Mignant; R. D. Campbell; J. C. Y. Chin; A. Conrad; S. K. Hartman; E. M. Johansson; R. E. Lafon; D. L. Rabinowitz; P. J. Stomski, Jr.; D. M. Summers; C. A. Trujillo; P. L. Wizinowich

2005-10-03

245

Flat belt continuously variable high speed drive  

SciTech Connect

A study was undertaken at Kumm Industries funded by DOE in the NBS/DOE Energy-Related Inventions Program starting in August 1990 to design, construct and test a novel very high speed flat belt drive. The test arrangement as shown in Figure 1 consists of a multiple belt-pulley configuration that transmits power from a low speed (2000--4000 RPM) input to a small pulley turbine'' (27,000 to 55,000 RPM) and then to the low speed output variable radius pulley (2000--5000 RPM) via a special self-active tensioner. Transmitting 25 HP to and from the turbine'' corresponds to obtaining 50 HP in one direction only in a possible turbo compounded engine application. The high speed of the turbine'' belts, i.e. 100 meters/sec. at 55,000 RPM, while transferring substantial power is a new much higher operating regime for belts. The study showed that the available belts gave overall test rig efficiencies somewhat above 80% for the higher speeds (50,000 RPM) and higher powers (corresponding to above 90% in the turbocompound application) and a significantly better efficiencies at slightly lower speeds. The tests revealed a number of improved approaches in the design of such high speed drives. It appears that there is considerable possibility for further improvement and application of such equipment.

Kumm, E.L.

1992-02-01

246

Magmatism and Tectonics in the Meso-Archean Pongola Supergroup, South Africa  

NASA Astrophysics Data System (ADS)

The Pongola Supergroup is one of the most extensive and well preserved volcano-sedimentary successions emplaced in a continental setting in the Meso-Archean (c. 2.95 Ga). It contrasts with both the older (Barberton type c.3.5 Ga) and younger (Belingwe type c.2.7 Ga) greenstone belts in southern Africa in that the sequence has not undergone the strong horizontal compressional tectonics typically related to greenstone belt-TTG environments. However, it is appropriate to compare this sequence with rocks of the Barberton greenstone belt by which the final phase of deposition preceded that of the juxtaposed Pongola basin with a relatively small time interval. The Pongola succession, which commenced with the first major magmatic event after the Barberton greenstone belt, overlies granitoids and remnants of greenstone belts in SE South Africa and in SW Swaziland. Formation was not in a continental rift environment but most likely in a marginal epicontinental basin with syn-depositional subsidence in a half-graben fault system in the type area. The Pongola rocks occur in two domains related to a NW-trending central basement high in the Kaapvaal Craton and achieving a maximum thickness of 8 km in the northern areas. The lower section (Nsuze group 3.7 km thick) is made up mainly of lavas and pyroclastic rocks and the upper section (Mozaan Group 4.3 km thick) is aranaceous sediments and argillites with a thick volcanic unit observed in the south-eastern facies. Chemical affinities of the lavas include tholeiite and calc-alkaline over the compositional range of basalt to rhyolite. There is a preponderance of andesites in the compositional array. The preservation of these rocks gives insight into the range of volcanic processes that took place at this stage of Earth history and in some areas it is possible to identify eruptions from a single source over several kilometres, as well as feeder-dyke systems to the lava flows. Simultaneous eruption of contrasting magmas from several vents is a feature of this uniquely preserved magmatic record. New precise zircon U-Pb ages give an indication that the entire basin formed in a remarkably short period of geological time between 2980 ±10 Ma and 2954 ±9 Ma, although complications arising from inherited zircons cannot be ruled out. While komatiites are not present in the Pongola a sequence of volcaniclastic rocks with well-preserved bombs of picrite composition and contained within a sandy matrix gives rise to a geochemical signature high in Cr and Ni which is the first evidence of an ultramafic component to this succession. Evidence of rapid deposition, a preponderance of intermediate lavas, discordance of bounding (earlier) crustal blocks and consistent structural trends in the area, are similar to features found in continental arc basins currently observed in the south-western USA, and may present an alternative model to those currently accepted for Archean terranes in early-formed cratons.

Wilson, Allan

2013-04-01

247

Belt-MRF for large aperture mirrors.  

PubMed

With high-determinacy and no subsurface damage, Magnetorheological Finishing (MRF) has become an important tool in fabricating high-precision optics. But for large mirrors, the application of MRF is restricted by its small removal function and low material removal rate. In order to improve the material removal rate, shorten the processing cycle, we proposed a new MRF concept, named Belt-MRF to expand the application of MRF to large mirrors and made a prototype with a large remove function, using a belt instead of a very large polishing wheel to expand the polishing length. A series of experimental results on Silicon carbide (SiC) and BK 7 specimens and fabrication simulation verified that the Belt-MRF has high material removal rates, stable removal function and high convergence efficiency which makes it a promising technology for processing large aperture optical elements. PMID:25321011

Ren, Kai; Luo, Xiao; Zheng, Ligong; Bai, Yang; Li, Longxiang; Hu, Haixiang; Zhang, Xuejun

2014-08-11

248

The Gould Belt, the de Vaucouleurs-Dolidze belt, and the Orion arm  

NASA Astrophysics Data System (ADS)

Based on masers with measured trigonometric parallaxes, we have redetermined the spatial orientation parameters of the Local (Orion) arm. Using 23 sources (the Gould Belt objects were excluded), we have found that their spatial distribution can be approximated by a very narrow ellipsoid elongated in the direction L 1 = 77.1° ± 2.9° whose symmetry plane is inclined to the Galactic plane at an angle of 5.6° ± 0.2°. The longitude of the ascending node of the symmetry plane is . A newestimate for the pitch angle of the Local spiral arm has been obtained by an independent method: i = 12.9° ± 2.9°. Previously, a belt of young B stars, the de Vaucouleurs-Dolidze belt, was pointed out on the celestial sphere with parameters close to such an orientation. We have refined the spatial orientation parameters of this belt based on a homogeneous sample of protostars. The de Vaucouleurs-Dolidze belt can be identified with the Local arm, with the belt proper as a continuous band on the celestial sphere like the Gould Belt being absent due to the peculiarities of the spatial orientation of the Local arm. Using the entire sample of 119 Galactic masers, we have shown that the third axis of their position ellipsoid has no deviation from the direction to the Galactic pole: B 3 = 89.7° ± 0.1°.

Bobylev, V. V.; Bajkova, A. T.

2014-12-01

249

Illinois PER Interactive Examples: Conveyor Belt  

NSDL National Science Digital Library

This is an interactive homework problem for introductory physics students relating to Newton's Second Law and kinetic friction. A box of known mass is dropped vertically onto a conveyor belt moving at a constant speed. The student must determine how much time it takes for the box to attain the same speed as the conveyor belt. A user-activated "help" sequence is provided for each step of the problem-solving, from conceptual analysis through quantitative calculation. To promote critical thinking, immediate feedback is received for both correct and incorrect responses. This item is part of a larger collection of interactive homework problems for introductory physics.

Gladding, Gary

2008-09-10

250

14 CFR 29.1413 - Safety belts: passenger warning device.  

Code of Federal Regulations, 2010 CFR

... 2010-01-01 false Safety belts: passenger warning device...DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS...CATEGORY ROTORCRAFT Equipment Safety Equipment § 29.1413 Safety belts: passenger warning...

2010-01-01

251

14 CFR 29.1413 - Safety belts: passenger warning device.  

Code of Federal Regulations, 2011 CFR

... 2011-01-01 false Safety belts: passenger warning device...DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS...CATEGORY ROTORCRAFT Equipment Safety Equipment § 29.1413 Safety belts: passenger warning...

2011-01-01

252

14 CFR 29.1413 - Safety belts: passenger warning device.  

Code of Federal Regulations, 2013 CFR

... 2013-01-01 false Safety belts: passenger warning device...DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS...CATEGORY ROTORCRAFT Equipment Safety Equipment § 29.1413 Safety belts: passenger warning...

2013-01-01

253

14 CFR 29.1413 - Safety belts: passenger warning device.  

... 2014-01-01 false Safety belts: passenger warning device...DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS...CATEGORY ROTORCRAFT Equipment Safety Equipment § 29.1413 Safety belts: passenger warning...

2014-01-01

254

14 CFR 29.1413 - Safety belts: passenger warning device.  

Code of Federal Regulations, 2012 CFR

... 2012-01-01 false Safety belts: passenger warning device...DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS...CATEGORY ROTORCRAFT Equipment Safety Equipment § 29.1413 Safety belts: passenger warning...

2012-01-01

255

Assessment of a Worksite Safety Belt Promotion Program.  

ERIC Educational Resources Information Center

A study examined the feasibility and replicability of informational and reinforcement strategies designed to increase safety belt use in a university setting. The findings revealed moderate increases in safety belt use over repeated observations. (CB)

Nelson, Gary D.; Bruess, Clint E.

1986-01-01

256

CDC Vital Signs: Adult Seat Belt Use in the US  

MedlinePLUS

... enforcement seat belt laws achieved 88% use.* Motor vehicle crashes are the leading cause of death for ... to the driver just because someone in the vehicle is not wearing a seat belt. A secondary ...

257

The Radiation Belt Storm Probes - Duration: 3:26.  

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 ...

258

30 CFR 56.14212 - Chains, ropes, and drive belts.  

Code of Federal Regulations, 2011 CFR

...56.14212 Chains, ropes, and drive belts. Chains, ropes, and drive belts shall be guided mechanically onto moving pulleys, sprockets, or drums except where equipment is designed specifically for hand...

2011-07-01

259

30 CFR 56.4503 - Conveyor belt slippage.  

Code of Federal Regulations, 2011 CFR

...belt-slippage shall be equipped with a detection system capable of automatically stopping the drive pulley. A person shall attend the belt at the drive pulley when it is necessary to operate the conveyor while temporarily bypassing the automatic...

2011-07-01

260

30 CFR 57.4263 - Underground belt conveyors.  

Code of Federal Regulations, 2011 CFR

... § 57.4263 Underground belt conveyors. Fire protection shall be provided at the head, tail, drive, and take-up pulleys of underground belt conveyors. Provisions shall be made for extinguishing fires along the beltline. Fire protection...

2011-07-01

261

30 CFR 57.14212 - Chains, ropes, and drive belts.  

Code of Federal Regulations, 2012 CFR

...57.14212 Chains, ropes, and drive belts. Chains, ropes, and drive belts shall be guided mechanically onto moving pulleys, sprockets, or drums except where equipment is designed specifically for hand...

2012-07-01

262

30 CFR 56.14212 - Chains, ropes, and drive belts.  

Code of Federal Regulations, 2010 CFR

...56.14212 Chains, ropes, and drive belts. Chains, ropes, and drive belts shall be guided mechanically onto moving pulleys, sprockets, or drums except where equipment is designed specifically for hand...

2010-07-01

263

30 CFR 57.4263 - Underground belt conveyors.  

... § 57.4263 Underground belt conveyors. Fire protection shall be provided at the head, tail, drive, and take-up pulleys of underground belt conveyors. Provisions shall be made for extinguishing fires along the beltline. Fire protection...

2014-07-01

264

30 CFR 56.14212 - Chains, ropes, and drive belts.  

Code of Federal Regulations, 2012 CFR

...56.14212 Chains, ropes, and drive belts. Chains, ropes, and drive belts shall be guided mechanically onto moving pulleys, sprockets, or drums except where equipment is designed specifically for hand...

2012-07-01

265

30 CFR 57.14212 - Chains, ropes, and drive belts.  

Code of Federal Regulations, 2013 CFR

...57.14212 Chains, ropes, and drive belts. Chains, ropes, and drive belts shall be guided mechanically onto moving pulleys, sprockets, or drums except where equipment is designed specifically for hand...

2013-07-01

266

30 CFR 57.4263 - Underground belt conveyors.  

Code of Federal Regulations, 2012 CFR

... § 57.4263 Underground belt conveyors. Fire protection shall be provided at the head, tail, drive, and take-up pulleys of underground belt conveyors. Provisions shall be made for extinguishing fires along the beltline. Fire protection...

2012-07-01

267

30 CFR 56.4503 - Conveyor belt slippage.  

...belt-slippage shall be equipped with a detection system capable of automatically stopping the drive pulley. A person shall attend the belt at the drive pulley when it is necessary to operate the conveyor while temporarily bypassing the automatic...

2014-07-01

268

30 CFR 57.14212 - Chains, ropes, and drive belts.  

Code of Federal Regulations, 2011 CFR

...57.14212 Chains, ropes, and drive belts. Chains, ropes, and drive belts shall be guided mechanically onto moving pulleys, sprockets, or drums except where equipment is designed specifically for hand...

2011-07-01

269

30 CFR 57.14212 - Chains, ropes, and drive belts.  

Code of Federal Regulations, 2010 CFR

...57.14212 Chains, ropes, and drive belts. Chains, ropes, and drive belts shall be guided mechanically onto moving pulleys, sprockets, or drums except where equipment is designed specifically for hand...

2010-07-01

270

30 CFR 56.4503 - Conveyor belt slippage.  

Code of Federal Regulations, 2013 CFR

...belt-slippage shall be equipped with a detection system capable of automatically stopping the drive pulley. A person shall attend the belt at the drive pulley when it is necessary to operate the conveyor while temporarily bypassing the automatic...

2013-07-01

271

30 CFR 56.4503 - Conveyor belt slippage.  

Code of Federal Regulations, 2012 CFR

...belt-slippage shall be equipped with a detection system capable of automatically stopping the drive pulley. A person shall attend the belt at the drive pulley when it is necessary to operate the conveyor while temporarily bypassing the automatic...

2012-07-01

272

30 CFR 57.4263 - Underground belt conveyors.  

Code of Federal Regulations, 2013 CFR

... § 57.4263 Underground belt conveyors. Fire protection shall be provided at the head, tail, drive, and take-up pulleys of underground belt conveyors. Provisions shall be made for extinguishing fires along the beltline. Fire protection...

2013-07-01

273

30 CFR 56.14212 - Chains, ropes, and drive belts.  

Code of Federal Regulations, 2013 CFR

...56.14212 Chains, ropes, and drive belts. Chains, ropes, and drive belts shall be guided mechanically onto moving pulleys, sprockets, or drums except where equipment is designed specifically for hand...

2013-07-01

274

30 CFR 57.14212 - Chains, ropes, and drive belts.  

...57.14212 Chains, ropes, and drive belts. Chains, ropes, and drive belts shall be guided mechanically onto moving pulleys, sprockets, or drums except where equipment is designed specifically for hand...

2014-07-01

275

30 CFR 56.4503 - Conveyor belt slippage.  

Code of Federal Regulations, 2010 CFR

...belt-slippage shall be equipped with a detection system capable of automatically stopping the drive pulley. A person shall attend the belt at the drive pulley when it is necessary to operate the conveyor while temporarily bypassing the automatic...

2010-07-01

276

30 CFR 57.4263 - Underground belt conveyors.  

Code of Federal Regulations, 2010 CFR

... § 57.4263 Underground belt conveyors. Fire protection shall be provided at the head, tail, drive, and take-up pulleys of underground belt conveyors. Provisions shall be made for extinguishing fires along the beltline. Fire protection...

2010-07-01

277

30 CFR 56.14212 - Chains, ropes, and drive belts.  

...56.14212 Chains, ropes, and drive belts. Chains, ropes, and drive belts shall be guided mechanically onto moving pulleys, sprockets, or drums except where equipment is designed specifically for hand...

2014-07-01

278

Petrology and structure of greenstone blocks encased in mud-matrix melange of the Franciscan complex near San Simeon, California  

SciTech Connect

Greenstones comprise about 20% of all mappable (>1 m) blocks encased in blueschist-block-bearing mud-matrix melange exposed in a 10 km-length of sea cliffs near San Simeon. Field and petrographic analysis of 25 blocks show they vary from finely crystalline (<1 mm) locally porphyritic or amygdaloidal, volcanics to coarsely crystalline (1 to 5 mm) diabase. Some are in contact with bedded chert and two have relict pillows. However, most blocks are intensely deformed. Pinch-and-swell and boundinage are recognized on scales from cm to about 10 m. Distortion was accommodated by cataclasis to an aggregate of pieces from mm to m across. Generally, m-sized blocks are pervasively cataclastic whereas larger blocks are crosscut by cataclastic zones that emanate from pervasively cataclastic margins or necked regions of boudins. Discontinuous, cm-thick veins and cavities that are lined by quartz and clacite and rarely, laumontite, prehnite and aragonite locally crosscut all other structures. Relict igneous textures show the primary minerals are plagioclase and clinopyroxene. Abundant secondary minerals, particularly in cataclastic zones, are albite, chlorite, pumpellyite (some have high Al), and calcite. The metamorphic parageneses indicate relatively minor greenschist-facies, sea-floor-type alterations under static conditions followed by lower-temperature alterations synchronous with cataclasis and the development of boudinage. If the blocks are fragments of disrupted ophiolites, only the uppermost section of the suite are present within the mud-matrix melange near San Simeon. The simplest explanation for their crystallization, metamorphism and incorporation into the melange is that they are fragments of seamounts dismembered during subduction.

Davidsen, R.K.; Cloos, M.

1985-01-01

279

The geological record of life 3500 Ma ago: Coping with the rigors of a young earth during late accretion  

NASA Technical Reports Server (NTRS)

Thin cherty sedimentary layers within the volcanic portions of the 3,500 to 3,300 Ma-old Onverwacht and Fig Tree Groups, Barberton Greenstone belt, South Africa, and Warrawoona Group, eastern Pilbara Block, Western Australia, contain an abundant record of early Archean life. Five principal types of organic and probably biogenic remains and or structures can be identifed: stromatolites, stromatolite detritus, carbonaceous laminite or flat stromalite, carbonaceous detrital particles, and microfossils. Early Archean stromatolites were reported from both the Barberton and eastern Pilbara greenstone belts. Systematic studies are lacking, but two main morphological types of stromatolites appear to be represented by these occurrences. Morphology of the stromalites is described. Preserved early Archean stromatolites and carbonaceous matter appear to reflect communities of photosynthetic cyanobacteria inhabiting shallow, probably marine environments developed over the surfaces of low-relief, rapidly subsiding, simatic volcanic platforms. The overall environmental and tectonic conditions were those that probably prevailed at Earth's surface since the simatic crust and oceans formed sometime before 3,800 Ma. Recent studies also suggest that these early Archean sequences contain layers of debris formed by large-body impacts on early Earth. If so, then these early bacterial communities had developed strategies for coping with the disruptive effects of possibly globe-encircling high-temperature impact vapor clouds, dust blankets, and impact-generated tsunamis. It is probable that these early Archean biogenic materials represent organic communities that evolved long before the beginning of the preserved geological record and were well adapted to the rigors of life on a young, volcanically active Earth during late bombardment. These conditions may have had parallels on Mars during its early evolution.

Lowe, Donald R.

1989-01-01

280

The geological record of life 3500 MA ago: Coping with the rigors of a young earth during late accretion  

NASA Astrophysics Data System (ADS)

Thin cherty sedimentary layers within the volcanic portions of the 3,500 to 3,300 Ma-old Onverwacht and Fig Tree Groups, Barberton Greenstone belt, South Africa, and Warrawoona Group, eastern Pilbara Block, Western Australia, contain an abundant record of early Archean life. Five principal types of organic and probably biogenic remains and or structures can be identifed: stromatolites, stromatolite detritus, carbonaceous laminite or flat stromalite, carbonaceous detrital particles, and microfossils. Early Archean stromatolites were reported from both the Barberton and eastern Pilbara greenstone belts. Systematic studies are lacking, but two main morphological types of stromatolites appear to be represented by these occurrences. Morphology of the stromalites is described. Preserved early Archean stromatolites and carbonaceous matter appear to reflect communities of photosynthetic cyanobacteria inhabiting shallow, probably marine environments developed over the surfaces of low-relief, rapidly subsiding, simatic volcanic platforms. The overall environmental and tectonic conditions were those that probably prevailed at Earth's surface since the simatic crust and oceans formed sometime before 3,800 Ma. Recent studies also suggest that these early Archean sequences contain layers of debris formed by large-body impacts on early Earth. If so, then these early bacterial communities had developed strategies for coping with the disruptive effects of possibly globe-encircling high-temperature impact vapor clouds, dust blankets, and impact-generated tsunamis. It is probable that these early Archean biogenic materials represent organic communities that evolved long before the beginning of the preserved geological record and were well adapted to the rigors of life on a young, volcanically active Earth during late bombardment. These conditions may have had parallels on Mars during its early evolution.

Lowe, Donald R.

1989-03-01

281

Microscale mapping of alteration conditions and potential biosignatures in basaltic-ultramafic rocks on early Earth and beyond.  

PubMed

Subseafloor environments preserved in Archean greenstone belts provide an analogue for investigating potential subsurface habitats on Mars. The c. 3.5-3.4 Ga pillow lava metabasalts of the mid-Archean Barberton greenstone belt, South Africa, have been argued to contain the earliest evidence for microbial subseafloor life. This includes candidate trace fossils in the form of titanite microtextures, and sulfur isotopic signatures of pyrite preserved in metabasaltic glass of the c. 3.472 Ga Hooggenoeg Formation. It has been contended that similar microtextures in altered martian basalts may represent potential extraterrestrial biosignatures of microbe-fluid-rock interaction. But despite numerous studies describing these putative early traces of life, a detailed metamorphic characterization of the microtextures and their host alteration conditions in the ancient pillow lava metabasites is lacking. Here, we present a new nondestructive technique with which to study the in situ metamorphic alteration conditions associated with potential biosignatures in mafic-ultramafic rocks of the Hooggenoeg Formation. Our approach combines quantitative microscale compositional mapping by electron microprobe with inverse thermodynamic modeling to derive low-temperature chlorite crystallization conditions. We found that the titanite microtextures formed under subgreenschist to greenschist facies conditions. Two chlorite temperature groups were identified in the maps surrounding the titanite microtextures and record peak metamorphic conditions at 315 ± 40°C (XFe3+(chlorite) = 25-34%) and lower-temperature chlorite veins/microdomains at T = 210 ± 40°C (lower XFe3+(chlorite) = 40-45%). These results provide the first metamorphic constraints in textural context on the Barberton titanite microtextures and thereby improve our understanding of the local preservation conditions of these potential biosignatures. We suggest that this approach may prove to be an important tool in future studies to assess the biogenicity of these earliest candidate traces of life on Earth. Furthermore, we propose that this mapping approach could also be used to investigate altered mafic-ultramafic extraterrestrial samples containing candidate biosignatures. PMID:24588497

Grosch, Eugene G; McLoughlin, Nicola; Lanari, Pierre; Erambert, Muriel; Vidal, Olivier

2014-03-01

282

The state of knowledge concerning the Kuiper belt  

NASA Technical Reports Server (NTRS)

The arguments for and against the idea that most short-period comets originate in the Kuiper belt are discussed. Observational constraints on the distribution of mass in the Kuiper belt are reviewed as well as a model of the physical conditions that now exist. Finally, predictions from this model about the detectability of the Kuiper belt are compared to optical surveys.

Levison, Harold F.

1992-01-01

283

Modeling of the outer electron belt during magnetic storms  

Microsoft Academic Search

The flux dropout of relativistic electrons in the earth’s outer radiation belt, during the main phase of the 26 March 1995 magnetic storm is examined. Outer belt measurements by the Radiation Environment Monitor, REM aboard the STRV-1b satellite are presented to characterize this dropout. In order to simulate the dynamics of the electron belt during the storm main phase a

L. Desorgher; P. Bühler; A. Zehnder; E. Daly; L. Adams

1999-01-01

284

Design of Multi-Loading Control System for Belt Conveyor  

Microsoft Academic Search

In this paper, according to the problem of multi-load on centerlized belt conveyor during mine production process, an autocontrol system based on armoured belt feeder and PLC, is studied to ensure conterlized belt conveyor running steadily and safely. This system realizes a clock loop control via the feedback signal of driving motor current which reflect the change of coal quantity,

Wei Li; Zhengduo Pang; Haitao Zhang; Guoying Meng

2010-01-01

285

The Magnetic Field of the Quiet-Time Proton Belt  

Microsoft Academic Search

The distortion of the earth's magnetic field produced by the proton belt is dis- cussed. The magnetic field is calculated numerically, to a first approximation, for an analogous model belt in a steady state. It is estimated that in the equatorial plane, at the earth's surface, the magnetic field produced by this belt is of the order of 38 ?.

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

1962-01-01

286

46 CFR 111.105-27 - Belt drives.  

Code of Federal Regulations, 2010 CFR

...111.105-27 Belt drives. Each belt drive in a hazardous location must have: (a) A conductive belt; and (b) Pulleys, shafts, and driving equipment grounded to meet NFPA 77 (incorporated by reference, see 46 CFR 110.10-1)....

2010-10-01

287

46 CFR 111.105-27 - Belt drives.  

Code of Federal Regulations, 2011 CFR

...111.105-27 Belt drives. Each belt drive in a hazardous location must have: (a) A conductive belt; and (b) Pulleys, shafts, and driving equipment grounded to meet NFPA 77 (incorporated by reference, see 46 CFR 110.10-1)....

2011-10-01

288

46 CFR 111.105-27 - Belt drives.  

Code of Federal Regulations, 2012 CFR

...111.105-27 Belt drives. Each belt drive in a hazardous location must have: (a) A conductive belt; and (b) Pulleys, shafts, and driving equipment grounded to meet NFPA 77 (incorporated by reference, see 46 CFR 110.10-1)....

2012-10-01

289

46 CFR 111.105-27 - Belt drives.  

Code of Federal Regulations, 2013 CFR

...111.105-27 Belt drives. Each belt drive in a hazardous location must have: (a) A conductive belt; and (b) Pulleys, shafts, and driving equipment grounded to meet NFPA 77 (incorporated by reference, see 46 CFR 110.10-1)....

2013-10-01

290

46 CFR 111.105-27 - Belt drives.  

...111.105-27 Belt drives. Each belt drive in a hazardous location must have: (a) A conductive belt; and (b) Pulleys, shafts, and driving equipment grounded to meet NFPA 77 (incorporated by reference, see 46 CFR 110.10-1)....

2014-10-01

291

The Overthrust Belt of Western North America  

Microsoft Academic Search

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

1993-01-01

292

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

293

Radiation Belt Storm Probes Ion Composition Experiment  

E-print Network

-of-flight Radiation belt Space weather #12;3 Table of Contents 1. Introduction 2. RBSPICE Hot Plasma Objectives.4.1 Deployable Cover 4.4.2 Thermal Design 4.5 Foils and Detectors 4.5.1 Microchannel Plates 4.5.2 Solid State theory of the initiation and life of geomagnetic storms, Chapman and Ferraro (1931, 1932, 1933

294

Outer radiation belt variations during 1995  

Microsoft Academic Search

The dynamics of the relativistic electron flux in the earth's outer radiation belt measured by the Radiation Environment Monitor aborad the STRV-1B satellite is presented from August 1994 to end of April 1996. During this period the earth's magnetosphere was driven by recurrent fast solar wind streams which had periodically compressed the magnetosphere and caused large variations of the trapped

L. Desorgher; P. Bühler; A. Zehnder; E. Daly; L. Adams

1998-01-01

295

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.

296

5, 1072310745, 2005 Antarctic NAT belt  

E-print Network

Sounding (MIPAS) reveal the formation of a belt of polar strato- spheric clouds (PSCs) of nitric acid nitric acid containing particles (likely nitric acid trihydrate, NAT) that, via sedimentation, are now generally believed to be the major cause of denitrification. However, the nucleation processes of nitric

Paris-Sud XI, Université de

297

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

298

Resolving the Asteroid Belt of HR 8799  

Microsoft Academic Search

In 2008, three orbiting planets were discovered and confirmed around HR8799 marking it as the first imaged extra solar planetary system with multiple planets. There are many similarities between HR8799 and our Solar System. IRAS and ISO detected a Kuiper belt around this star based on far infrared dust excess and Spitzer IRS spectroscopy revealed a separate population of warmer

Inseok Song; Christian Marois; Jennier Patience; Ben Zuckerman; Bruce Macintosh; Travis Barman; David Lafrenier; Rene Doyon

2009-01-01

299

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

300

Imaging Jupiter Radiation Belts At Low Frequencies  

NASA Astrophysics Data System (ADS)

The ultra-relativistic electrons, trapped in the inner radiation belts of Jupiter, generates a strong synchrotron radio emission (historically known as the jovian decimeter radiation (DIM)) which is beamed, polarized (~20% linear, ~1% circular) and broadband. It has been extensively observed by radio telescopes/ probes and imaged by radio interferometers over a wide frequency spectrum (from >300 MHz up to 22 GHz). This extended emission presents two main emission peaks constantly located on both sides of the planet close to the magnetic plane. High latitude emissions were also regularly observed at particular frequencies, times and in particular observational configurations. This region of the magnetosphere is "frozen" due to the strong magnetic field (~4.2 G as the equator) and therefore is forced to rotate at the planetary period (T?9h55m). Due to the tilt (~ 10o) between the spin axis of the planet and the magnetic axis (which can be seen as dipolar in first approximation), the belts and the associated radio emission wobble around the planet center. The analysis of the flux at different frequencies highlighted spatial, temporal and spectral variabilities which origins are now partly understood. The emission varies at different time scales (short-time variations of hours to long-term variation over decades) due to the combination of visibility effect (wobbling, beaming, position of the observer in the magnetic rotating reference frame) [1], [2] and intrinsic local variations (interaction between relativistic electrons and satellites/dust, delayed effect of the solar wind ram pressure, impacts events) [3], [4], [5]. A complete framework is necessary to fully understand the source, loss and transport processes of the electrons originating from outside the belt, migrating by inward diffusion and populating the inner region of the magnetosphere. Only a few and unresolved measurements were made below 300 MHz and the nonsystematic observation of this radio emission, at different epochs only provided, each time, glimpses of the spectral content in different observational configurations. As the synchrotron emission frequency peaks at Vmax / E2B (with max in MHz, E, the electron energy in MeV and B, the magnetic field in Gauss), the low frequency content of this emission is associated with low energy electron populations inside the inner belt and the energetic electrons located in regions of weaker magnetic field (at few jovian radii). Therefore, there is much interest in extending and completing the current knowledge of the synchrotron emission from the belts, with low frequency resolved observations. LOFAR, the LOw Frequency ARray (LOFAR) [6], is a giant flexible and digital ground-based radio interferometer operating in the 30-250 MHz band. It brings very high time (~ ?s), frequency (~ kHz) and angular resolutions (~1") and huge sensitivity (mJy). In November 2011, a single 10-hour track enabled to cover an entire planetary rotation and led to the first resolved image of the radiation belts between 127- 172 MHz [7,8]. In Feb 2013, an 2×5h30 joint LOFAR/ WSRT observing campaign seized the state of the radiation belts from 45 MHz up to 5 GHz. We will present the current state of the study (imaging, reconstruction method and modeling) of the radiation belts dynamic with this current set of observations. LOFAR can contribute to the understanding of the physics taking place in the inner belt as well as possibly providing a fast and a systematic "diagnostic" of the state of the belts. The latter represents an opportunity to give context and ground-based support for the arrival of JUNO (NASA) scheduled in July 2016 and also for future missions, such as JUICE (ESA), at the vicinity of Jupiter by the exploration of its icy satellites.

Girard, J. N.; de Pater, I.; Zarka, P.; Santos-Costa, D.; Sault, R.; Hess, S.; Cecconi, B.; Fender, R.; Pewg, Lofar

2014-04-01

301

VERO cells harbor a poly-ADP-ribose belt partnering their epithelial adhesion belt  

PubMed Central

Poly-ADP-ribose (PAR) is a polymer of up to 400 ADP-ribose units synthesized by poly-ADP-ribose-polymerases (PARPs) and degraded by poly-ADP-ribose-glycohydrolase (PARG). Nuclear PAR modulates chromatin compaction, affecting nuclear functions (gene expression, DNA repair). Diverse defined PARP cytoplasmic allocation patterns contrast with the yet still imprecise PAR distribution and still unclear functions. Based on previous evidence from other models, we hypothesized that PAR could be present in epithelial cells where cadherin-based adherens junctions are linked with the actin cytoskeleton (constituting the adhesion belt). In the present work, we have examined through immunofluorescence and confocal microscopy, the subcellular localization of PAR in an epithelial monkey kidney cell line (VERO). PAR was distinguished colocalizing with actin and vinculin in the epithelial belt, a location that has not been previously reported. Actin filaments disruption with cytochalasin D was paralleled by PAR belt disruption. Conversely, PARP inhibitors 3-aminobenzamide, PJ34 or XAV 939, affected PAR belt synthesis, actin distribution, cell shape and adhesion. Extracellular calcium chelation displayed similar effects. Our results demonstrate the existence of PAR in a novel subcellular localization. An initial interpretation of all the available evidence points towards TNKS-1 as the most probable PAR belt architect, although TNKS-2 involvement cannot be discarded. Forthcoming research will test this hypothesis as well as explore the existence of the PAR belt in other epithelial cells and deepen into its functional implications. PMID:25332845

Vilchez Larrea, Salomé C.; Kun, Alejandra

2014-01-01

302

The Gould Belt, the de Vaucouleurs-Dolidze Belt, and the Orion Arm  

E-print Network

Based on masers with measured trigonometric parallaxes, we have redetermined the spatial orientation parameters of the Local (Orion) arm. Using 23 sources (the Gould Belt objects were excluded), we have found that their spatial distribution can be approximated by a very narrow ellipsoid elongated in the direction L_1=77.1+/-2.9^o whose symmetry plane is inclined to the Galactic plane at an angle of 5.6+/-0.2^o. The longitude of the ascending node of the symmetry plane is l_\\Omega=70+/-3^o. A new estimate for the pitch angle of the Local spiral arm has been obtained by an independent method: i=12.9+/-2.9^o. Previously, a belt of young B stars, the de Vaucouleurs.Dolidze belt, was pointed out on the celestial sphere with parameters close to such an orientation. We have refined the spatial orientation parameters of this belt based on a homogeneous sample of protostars. The de Vaucouleurs.Dolidze belt can be identified with the Local arm, with the belt proper as a continuous band on the celestial sphere like the ...

Bobylev, V V

2014-01-01

303

Coupled silicon-oxygen isotope fractionation traces Archaean silicification  

NASA Astrophysics Data System (ADS)

Silica alteration zones and cherts are a conspicuous feature of Archaean greenstone belts worldwide and provide evidence of extensive mobilisation of silica in the marine environment of the early Earth. In order to understand the process(es) of silicification we measured the silicon and oxygen isotope composition of sections of variably silicified basalts and overlying bedded cherts from the Theespruit, Hooggenoeg and Kromberg Formations of the Barberton Greenstone Belt, South Africa. The ?30Si and ?18O values of bulk rock increase with increasing amount of silicification from unsilicified basalts (-0.64‰ < ?30Si < -0.01‰ and + 8.6‰ < ?18O < + 11.9‰) to silicified basalts (?30Si and ?18O values as high as + 0.81‰ and + 15.6‰, respectively). Cherts generally have positive isotope ratios (+ 0.21‰ < ?30Si < + 1.05‰ and + 10.9 < ?18O < + 17.1), except two cherts, which have negative ?30Si values, but high ?18O (up to + 19.5‰). The pronounced positive correlations between ?30Si, ?18O and SiO2 imply that the isotope variation is driven by the silicification process which coevally introduced both 18O and 30Si into the basalts. The oxygen isotope variation in the basalts from about 8.6‰ to 15.6‰ is likely to represent temperature-dependent isotope fractionation during alteration. Our proposed model for the observed silicon isotope variation relies on a temperature-controlled basalt dissolution vs. silica deposition process.

Abraham, K.; Hofmann, A.; Foley, S. F.; Cardinal, D.; Harris, C.; Barth, M. G.; André, L.

2011-01-01

304

Dynamic load sharing for conveyor belts with multiple drive stations  

SciTech Connect

The characteristics and limitations of multiple drive station belt conveyors are explored and a computational method is presented as a means of providing drive coordination which can skirt some of the limitations. This paper will describe some of the design parameters of concern for belt conveyors, including belt tension and how it varies with load, how the unpredictably non-uniform loading of the belt affects performance, and will explore the relationship of friction between the belt and a drive pulley and how this limits the amount of horsepower which can be transmitted to the belt. The way in which these parameters change in configurations with multiple drives and multiple drive stations is outlined. The two main means of employing booster drives are presented; tripper booster and linear booster. The tripper booster technology is amenable to tension control, in which the torque provided by each drive station is controlled by the tension in the belt measured immediately downstream of the drive station. This approach has proved successful in belt systems with as many as four booster drive stations, operating at belt loads in excess of 3200 tons per hour over 12,000 ft of belt. The linear booster arrangement does not allow a convenient method of measuring belt tension, thus a computational algorithm was devised to take advantage of the geometry of the belt system to control tension of the belt within certain limits without the use of tension feedback. This approach has proven useful in 10,000 foot belt system which has a single booster drive station, operating at loads up to 4000 tons per hour.

Churchill, F.T. [Reliance Electric, Seattle, WA (United States)

1995-05-01

305

A late Archean tectonic mélange belt in the Central Orogenic Belt, North China Craton  

NASA Astrophysics Data System (ADS)

We present the first documentation of a late Archean mélange belt in the Zanhuang massif, southern Taihang Mountains, of the North China Craton (NCC). The mélange belt separates a passive margin sequence developed on the western edge of the Eastern Block of the NCC, from an arc terrane consisting of trondhjemitic, tonalitic and granodioritic (TTG) gneisses in the Central Orogenic Belt (COB) of the NCC. The mélange belt is 2-10 km wide, and contains a structurally complex tectonic mixture of metapelites, metapsammites, marble, metalimestone, and tectonic blocks of ultramafites and metagabbroic rocks, metabasites that locally include relict pillow lavas, and TTG gneisses. All units in the mélange have been intruded by mafic dikes that were subsequently deformed, and are now preserved as garnet-amphibolite boudins. We interpret the mélange belt to mark the suture zone between the Eastern Block and the arc terrane in the COB. The field relationships suggest that the ultramafites-metagabbro-metabasaltic blocks are possible slivers of oceanic crust incorporated into the suture zone during the arc/continent collisional process. A circa 2.5 Ga granitic pluton intrudes the mélange belt and undeformed circa 2.5 Ga pegmatites cut the mélange belt. Tectonic models for the evolution of the COB of the NCC are varied, but include models that favor collision at 2.5 Ga, 2.1 Ga, and 1.8 Ga. This work shows clearly, from field, structural relationships and geochronology data, that the collision must have occurred prior to 2.5 Ga, favoring late Archean suturing of the western margin of the Eastern Block with an arc terrane during an arc/continent collision.

Wang, J.; Kusky, T. M.; Polat, A.; Wang, L.; Deng, H.; Wang, S.

2012-12-01

306

Geochemistry and zircon geochronology of the Archean granite suites of the Rio Maria granite-greenstone terrane, Carajás Province, Brazil  

NASA Astrophysics Data System (ADS)

The Archean granites exposed in the Mesorchean Rio Maria granite-greenstone terrane (RMGGT), southeastern Amazonian craton can be divided into three groups on the basis of petrographic and geochemical data. (1) Potassic leucogranites (Xinguara and Mata Surrão granites), composed dominantly of biotite monzogranites that have high SiO2, K2O, and Rb contents and show fractionated REE patterns with moderate to pronounced negative Eu anomalies. These granites share many features with the low-Ca granite group of the Yilgarn craton and CA2-type of Archean calc-alkaline granites. These granites result from the partial melting of rocks similar to the older TTG of the RMGGT. (2) Leucogranodiorite-granite group (Guarantã suite, Grotão granodiorite, and similar rocks), which is composed of Ba- and Sr-rich rocks which display fractionated REE patterns without significant Eu anomalies and show geochemical affinity with the high-Ca granite group or Transitional TTG of the Yilgarn craton and the CA1-type of Archean calc-alkaline granites. These rocks appear to have been originated from mixing between a Ba- and Sr-enriched granite magma and trondhjemitic liquids or alternatively product of interaction between fluids enriched in K, Sr, and Ba, derived from a metasomatized mantle with older TTG rocks. (3) Amphibole-biotite monzogranites (Rancho de Deus granite) associated with sanukitoid suites. These granites were probably generated by fractional crystallization and differentiation of sanukitoid magmas enriched in Ba and Sr. The emplacement of the granites of the RMGGT occurred during the Mesoarchean (2.87-2.86 Ga). They are approximately coeval with the sanukitoid suites (˜2.87 Ga) and post-dated the main timing of TTG suites formation (2.98-2.92 Ga). The crust of Rio Maria was probably still quite warm at the time when the granite magmas were produced. In these conditions, the underplating in the lower crust of large volumes of sanukitoid magmas may have also contributed with heat inducing the partial melting of crustal protoliths and opening the possibility of complex interactions between different kinds of magmas.

Almeida, José de Arimatéia Costa de; Dall'Agnol, Roberto; Leite, Albano Antonio da Silva

2013-03-01

307

Persistence of Salmonella on egg conveyor belts is dependent on the belt type but not on the rdar morphotype.  

PubMed

Commercial caged layer flocks in Alberta, Canada, are commonly monitored for Salmonella enterica serovar Enteritidis (SE) and S. enterica serovar Typhimurium (ST) by environmental sampling. In one recent case, a SE strain isolated from the egg conveyor belt was a source of persistent infection for the flock. This study was undertaken to examine Salmonella colonization on egg conveyor belts and to determine whether the rdar morphotype, a conserved physiology associated with aggregation and long-term survival, contributed to persistence. Four woven belts constructed of natural or nonnatural fibers and a 1-piece belt made of vinyl were tested with rdar-positive ST and SE strains and a rdar-negative ST DeltaagfD reference strain. The type of egg belt was the most important factor influencing Salmonella colonization and persistence. The vinyl belt, with the least surface area available for colonization, had the fewest Salmonella remaining after washing and disinfection, whereas the hemp-plastic belt, with the greatest surface area, had the most Salmonella remaining. Real-time gene expression indicated that the rdar morphotype was involved in colonizing the egg belt pieces; however, it was not essential for persistence. In addition, rdar-positive and rdar-negative strains were equally similarly to disinfection on the egg belt pieces. The results indicate that Salmonella can persist on a variety of egg belts by mechanisms other than the rdar morphotype, and that using egg conveyer belts with reduced surface area for bacterial colonization can lessen contamination problems. PMID:17954588

Stocki, S L; Annett, C B; Sibley, C D; McLaws, M; Checkley, S L; Singh, N; Surette, M G; White, A P

2007-11-01

308

Dynamics of a belt-drive system using a linear complementarity problem for the belt pulley contact description  

NASA Astrophysics Data System (ADS)

The aim of this study was to develop an efficient and realistic numerical model in order to predict the dynamic response of belt drives. The belt was modeled as a planar beam element based on an absolute nodal coordinate formulation. A viscoelastic material was adopted for the belt and the corresponding damping and stiffness matrices were determined. The belt-pulley contact was formulated as a linear complementarity problem together with a penalty method. This made it possible for us to accurately predict the contact forces, including the stick and slip zones between the belt and the pulley. The belt-drive model was verified by comparing it with the available analytical solutions. A good agreement was found. Finally, the applicability of the method was demonstrated by considering non-steady belt-drive operating conditions.

?epon, Gregor; Boltežar, Miha

2009-01-01

309

Outer radiation belt variations during 1995  

NASA Astrophysics Data System (ADS)

The dynamics of the relativistic electron flux in the earth's outer radiation belt measured by the Radiation Environment Monitor aboard the STRV-1B satellite is presented from August 1994 to end of April 1996. During this period the earth's magnetosphere was driven by recurrent fast solar wind streams which had periodically compressed the magnetosphere and caused large variations of the trapped particle fluxes in the outer radiation belt. The periodic variations are characterized by a rapid depletion, strong and rapid increase and a more steady phase. The flux level reached depends on the velocity of the interacting solar wind stream. The effectiveness of the solar wind - magnetosphere interaction shows a semiannual modulation with a maximum during the equinoxes.

Desorgher, L.; Bühler, P.; Zehnder, A.; Daly, E.; Adams, L.

310

The Kuiper Belt and Other Debris Disks  

E-print Network

We discuss the current knowledge of the Solar system, focusing on bodies in the outer regions, on the information they provide concerning Solar system formation, and on the possible relationships that may exist between our system and the debris disks of other stars. Beyond the domains of the Terrestrial and giant planets, the comets in the Kuiper belt and the Oort cloud preserve some of our most pristine materials. The Kuiper belt, in particular, is a collisional dust source and a scientific bridge to the dusty "debris disks" observed around many nearby main-sequence stars. Study of the Solar system provides a level of detail that we cannot discern in the distant disks while observations of the disks may help to set the Solar system in proper context.

David Jewitt; Amaya Moro-Martín; Pedro Lacerda

2008-08-24

311

High-energy proton radiation belt.  

NASA Technical Reports Server (NTRS)

The experiments and theories to explain the high-energy protons trapped in the earth's radiation belt are reviewed. The theory of cosmic ray albedo neutron decay injection of protons into the radiation belt is discussed. Radial diffusion and change in the earth's dipole moment are considered along with losses of protons by ionization and nuclear collision. It is found that the measured albedo neutron escape current is sufficient to supply trapped protons above 30 MeV. The theoretical calculations of the trapped protons are in agreement with the measurements for L less than or equal to 1.7 both on and off the equator. For L greater than or equal to 1.7, additional trapped proton differential energy measurements should be made before the theory can be adequately tested. It appears that an additional loss mechanism such as pitch angle scattering may be required.

White, R. S.

1973-01-01

312

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

313

Monitoring 2005 Corn Belt Yields From Space  

Microsoft Academic Search

The U.S. corn belt, centered on Illinois, suffered extreme drought conditions during the 2005 growing season (Figure 1). The April-September rainfall ranked 10th lowest of the past 113 years (see http:\\/\\/www.ncdc.noaa.gov\\/oa\\/climate\\/research\\/monitoring.html#state). Throughout Illinois, counties were declared agricultural disaster areas and corn yields were predicted to be 30 percent less than the record year of 2004, which had the highest corn

Ping Zhang; Bruce T. Anderson; Ranga Myneni

2006-01-01

314

Biomechanics of 4-point seat belt systems in frontal impacts.  

PubMed

The biomechanical behavior of 4-point seat belt systems was investigated through MADYMO modeling, dummy tests and post mortem human subject tests. This study was conducted to assess the effect of 4-point seat belts on the risk of thoracic injury in frontal impacts, to evaluate the ability to prevent submarining under the lap belt using 4-point seat belts, and to examine whether 4-point belts may induce injuries not typically observed with 3-point seat belts. The performance of two types of 4-point seat belts was compared with that of a pretensioned, load-limited, 3-point seat belt. A 3-point belt with an extra shoulder belt that "crisscrossed" the chest (X4) appeared to add constraint to the torso and increased chest deflection and injury risk. Harness style shoulder belts (V4) loaded the body in a different biomechanical manner than 3-point and X4 belts. The V4 belt appeared to shift load to the clavicles and pelvis and to reduce traction of the shoulder belt across the chest, resulting in a reduction in chest deflection by a factor of two. This is associated with a 5 to 500-fold reduction in thoracic injury risk, depending on whether one assumes 4-point belts apply concentrated or distributed load. In four of six post mortem human subjects restrained by V4 belts during 40 km/h sled tests, chest compression was zero or negative and rib fractures were nearly eliminated. Submarining was not observed in any test with post mortem human subjects. Though lumbar, sacral and pelvic injuries were noted, they are believed to be due to the artificial restraint environment (no knee bolsters, instrument panels, steering systems or airbags). While they show significant potential to reduce thoracic injury risk, there are still many issues to be resolved before 4-point belts can be considered for production vehicles. These issues include, among others, potential effects on hard and soft neck tissues, of interaction with inboard shoulder belts in farside impacts and potential effects on the fetus of latch/buckle junctions at the centerline of pregnant occupants. Work continues at Ford Motor Company to resolve these issues. PMID:17096257

Rouhana, Stephen W; Bedewi, Paul G; Kankanala, Sundeep V; Prasad, Priya; Zwolinski, Joseph J; Meduvsky, Alex G; Rupp, Jonathan D; Jeffreys, Thomas A; Schneider, Lawrence W

2003-01-01

315

Radiation Belt Electron Loss mechanisms: New results  

NASA Astrophysics Data System (ADS)

The radiation belt electron precipitation (RBEP) into the topside ionosphere is a phenomenon which is known for several decades. However, the radiation belt source and loss mechanisms have not still well understood, including PBEP. Here we present the results of a systematic study of RBEP observations, as obtained from the satellite DEMETER and the series of POES satellites, in comparison with variation of seismic activity. We found that this type of RBEP bursts present special characteristics in the inner region of the inner radiation belt before large (M>7, or even M>5) earthquakes (EQs), as for instance characteristic (a) flux-time profiles, (b) energy spectrum, (c) electron flux temporal evolution, (d) spatial distributions and (e) they are associated with broad band VLF activity, some days before an EQ. The RBEP before EQs appears, not only as a burst, but as an increase of the normal electron background flux in large range of latitudes during magnetospheric storms. Recent results, in the presence of a magnetospheric storm and of strong seismic activity, seem to suggest an increase of the normal flux in the slot region as well. We found significant evidence that, among EQs-lightings-Earth based transmitters, seismic activity is that agent which probably make the main contribution to the RBEP at middle latitudes. Further research is in progress in order to further test the present results.

Anagnostopoulos, G.; Barlas, G.; Sidiropoulos, N.; Vassiliadis, V.

2013-09-01

316

A model for Jupiter's proton radiation belt  

NASA Technical Reports Server (NTRS)

A model for electron and proton energy and density in Jupiter's radiation belt is proposed. It is assumed that electrons diffuse inward from the solar wind. The Davis and Chang diffusion model, in which there is a very steep L-shell dependence in density and energy, is scaled outwards from the peak of the belts at about 1.5 to 2 Jupiter radii to the magnetopause as defined by the magnetic moment. The energetic electron density is calculated to be one billionth of the density in the solar wind, and that is assumed to be the trapping ratio of Jupiter's synchrotron belts. It is further assumed that the same figures apply to protons. The flux density at 80 MHz was measured by the Culgoora ring to be identical to that at 3000 MHz, implying a constant flux density of the synchrotron source of over 20 or 30 to 1 in frequency. It is suggested that the synchrotron spectrum is flat over more than an order of magnitude of frequency. Jupiter is an enormous synchrotron source and has a strong magnetic field, causing long diffusion times for electrons in the magnetosphere.

Warwick, J.

1972-01-01

317

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

318

The gravitational sculpting of the Kuiper belt  

NASA Astrophysics Data System (ADS)

Results are presented of numerical integrations over billion year time scales of the orbital evolution of more than one thousand test particles on initially low-inclination, low-eccentricity orbits within the proposed Kuiper belt beyond Neptune. Particles which eventually crossed Neptune's orbit often showed long periods (up to several billion years) of relatively low-eccentricity oscillations punctuated by a very rapid jump to Neptune-crossing eccentricity. This flux may be the ultimate source of present-day short-period comets. It is found here that there exists a correlation between Liapunov and crossing times in the Kuiper belt. None of the particles in the study with Liapunov time scales greater than about 1 Myr actually became a Neptune-crosser in 4 Gyr. An intricate structure to the region between 35 and 45 AU is found at the end of the billion year simulation. Implications for the origins of short-period comets and the detectability of objects currently in the Kuiper belt are discussed.

Levison, H. F.; Duncan, M. J.

1993-03-01

319

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

320

From transmission error measurement to Pulley-Belt slip determination in serpentine belt drives: influence of tensioner and belt character istics  

Microsoft Academic Search

Serpentine belt drives are often used in front end accessory drive of automotive engine. The accessories resistant torques are getting higher within new technologi - cal innovations as stater-alternator, and belt transmissi ons are always asked for higher capacity. Two kind of tension- ers are used to maintain minimum tension that insure power transmission and minimize slip: dry friction or

L. Manin; G. Michon; D. Remond; R. Dufour

2007-01-01

321

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

322

Seat belt usage: A potential target for applied behavior analysis  

PubMed Central

Results of 1,579 observations of cars entering or exiting campus parking lots showed direct relationships between seat belt wearing and the intrusiveness of the engineering device designed to induce belt usage, and between device intrusiveness and system defeat. For example, all drivers with working interlocks or unlimited buzzer reminders were wearing a seat belt; but 62% of the systems with interlocks or unlimited buzzers had been defeated, and only 15.9% of the drivers in these cars were wearing a seat belt. The normative data indicated marked ineffectiveness of the negative reinforcement contingencies implied by current seat belt inducement systems; but suggested that unlimited buzzer systems would be the optimal system currently available if contingencies were developed to discourage the disconnection and circumvention of such systems. Positive reinforcement strategies are discussed that would be quite feasible for large-scale promotion of seat belt usage. PMID:16795638

Geller, E. Scott; Casali, John G.; Johnson, Richard P.

1980-01-01

323

Observed seat belt use in Kumasi Metropolis, Ghana.  

PubMed

We conducted an observational survey of seat belt use to determine the use rate of drivers and front-right passengers of vehicles in Kumasi, Ghana. Unobtrusive observations of seat belt use were made at 41 locations composed of signalized intersections and roundabouts where vehicles come to a halt or slow down considerably. The overall driver seat belt use rate was 17.6% compared to 4.9% for front-right passengers. Driver belt use was 33.2% for private cars, 9.0% for taxis, 8.3% for minibus (trotro), 13.1% for large buses and 9.7% for trucks. Overall seat belt use was higher for female drivers than for male drivers (44.8% versus 16.4%, p < .001), was lowest within the Central Business District (CBD) compared to the outskirts of the city (16.3% versus 21.0%, p < .001) and seat belt use rate increased with age. Passengers belted more often if drivers were belted, but about three-quarters of male passengers and 70-80% of female passengers were unbelted even when drivers were belted. In conclusion, the seat belt use rate was generally low in Kumasi, Ghana, and it is a function of occupant seating position, gender, vehicle type and usage, age group, and location setting. The results provide important preliminary data about seat belt use, particularly among male drivers and commercial vehicle occupant population. The study also suggests the need to develop effective strategies and programs that address low seat belt use in Ghana. PMID:20945246

Afukaar, Francis K; Damsere-Derry, James; Ackaah, Williams

2010-10-01

324

Fluid chemistry of Archean seafloor hydrothermal vents: Implications for the composition of circa 3.2 Ga seawater  

NASA Astrophysics Data System (ADS)

Seafloor hydrothermal vents of mid-Archean age (ca. 3230 Ma) have been identified and mapped in the Barberton greenstone belt, South Africa and are known as the Ironstone Pods. Fluid inclusion homogenization temperature data, when combined with gas chromatographic data, provide a minimum calculated water depth for the pods of 982 m. Ironstone Pod hydrothermal fluid endmember concentrations (Mg = 0) of various dissolved components derived from bulk fluid inclusion crush-leach experiments, include: Cl(730 mmol/L), Br (2.59), I (0.058), Na (822), NH 4 (11.4), K (21.5), Ca (42.6), and Sr (0.15). This hydrothermal fluid also contains up to 1.07 mol% CO 2, 0.03 mol% N 2, 0.02 mol% CH 4, 262 ppm COS, and minor amounts of C2-C4 hydrocarbons. Hydrothermal endmember Ca, Sr, and NH 4, in particular, and to a lesser degree K, I, and CO 2, commonly plot on, or very close to, modern vent fluid trends. By contrast, endmember Na and Br concentrations are distinct (higher) from modern vent fluids. High I and NH 4 concentrations are consistent with contributions from sediments and/or organic matter. Calculated ?18O H 2O values for the pod hydrothermal endmember fluid define a narrow range from 0.9 to 1.6‰ very similar to that of modern vent fluid values (0.4-2.1‰). A best estimate for the Ironstone Pod seawater endmember composition is Cl (920 mmol/L), Br (2.25), SO 4 (2.3), I (0.037), Na (789), NH 4 (5.1), K (18.9), Mg (50.9), Ca (232), and Sr (4.52). Barberton seawater components are commonly within an order of magnitude of modern seawater values, with the exception of significantly higher 1, NH 4, Ca, and Sr in the inclusions. Sulfate concentrations are minimum estimates for Barberton seawater. Fluid inclusion samples containing the greatest amount of seawater component have higher N 2 (up to 0.1 mol%) and low CO 2, when compared to samples dominated by the hydrothermal endmember fluid. Barberton ambient seawater is considered to have been an evaporative brine of NaCl?CaCl 2 composition during the time of pod deposition. Ironstone Pod fluid inclusion seawater endmember Br/Cl and I/Cl values of 2.45 × 10 -3 and 40.2 × 10 -6, respectively, are within error of bulk Earth (2.38 × 10 -3 and 190 × 10 -6) and are consistent with the chemistry of 3.23 Ga Barberton seawater being buffered by the mantle.

De Ronde, Cornel E. J.; Channer, Dominic M. deR.; Faure, Kevin; Bray, Colin J.; Spooner, Edward T. C.

1997-10-01

325

Evaluation of an intervention to increase seat belt use.  

PubMed

People continue to travel without wearing seat belts despite their proven safety value. Numerous interventions in primary care physicians' offices to enhance the use of seat belts have met with limited success. In a rural neighborhood health center, an intervention using the language of self-responsibility was evaluated. Of 105 patients receiving the intervention, seat belt use increased from 20% before to 35.2% after the intervention (P less than .001). No change in seat belt use occurred in a control group of patients who did not receive the intervention. PMID:2612803

Gordon, P

1989-01-01

326

Colors of Inner Disk Classical Kuiper Belt Objects  

NASA Astrophysics Data System (ADS)

We present new optical broadband colors, obtained with the Keck 1 and Vatican Advanced Technology telescopes, for six objects in the inner classical Kuiper Belt. Objects in the inner classical Kuiper Belt are of interest as they may represent the surviving members of the primordial Kuiper Belt that formed interior to the current position of the 3:2 resonance with Neptune, the current position of the plutinos, or, alternatively, they may be objects formed at a different heliocentric distance that were then moved to their present locations. The six new colors, combined with four previously published, show that the ten inner belt objects with known colors form a neutral clump and a reddish clump in B-R color. Nonparametric statistical tests show no significant difference between the B-R color distribution of the inner disk objects compared to the color distributions of Centaurs, plutinos, or scattered disk objects. However, the B-R color distribution of the inner classical Kuiper Belt Objects does differ significantly from the distribution of colors in the cold (low inclination) main classical Kuiper Belt. The cold main classical objects are predominately red, while the inner classical belt objects are a mixture of neutral and red. The color difference may reveal the existence of a gradient in the composition and/or surface processing history in the primordial Kuiper Belt, or indicate that the inner disk objects are not dynamically analogous to the cold main classical belt objects.

Romanishin, W.; Tegler, S. C.; Consolmagno, G. J.

2010-07-01

327

COLORS OF INNER DISK CLASSICAL KUIPER BELT OBJECTS  

SciTech Connect

We present new optical broadband colors, obtained with the Keck 1 and Vatican Advanced Technology telescopes, for six objects in the inner classical Kuiper Belt. Objects in the inner classical Kuiper Belt are of interest as they may represent the surviving members of the primordial Kuiper Belt that formed interior to the current position of the 3:2 resonance with Neptune, the current position of the plutinos, or, alternatively, they may be objects formed at a different heliocentric distance that were then moved to their present locations. The six new colors, combined with four previously published, show that the ten inner belt objects with known colors form a neutral clump and a reddish clump in B-R color. Nonparametric statistical tests show no significant difference between the B-R color distribution of the inner disk objects compared to the color distributions of Centaurs, plutinos, or scattered disk objects. However, the B-R color distribution of the inner classical Kuiper Belt Objects does differ significantly from the distribution of colors in the cold (low inclination) main classical Kuiper Belt. The cold main classical objects are predominately red, while the inner classical belt objects are a mixture of neutral and red. The color difference may reveal the existence of a gradient in the composition and/or surface processing history in the primordial Kuiper Belt, or indicate that the inner disk objects are not dynamically analogous to the cold main classical belt objects.

Romanishin, W. [Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019 (United States); Tegler, S. C. [Department of Physics and Astronomy, Northern Arizona University, Flagstaff, AZ 86011 (United States); Consolmagno, G. J., E-mail: wromanishin@ou.ed, E-mail: Stephen.Tegler@nau.ed, E-mail: gjc@specola.v [Vatican Observatory, Specola Vaticana, V-00120 (Vatican City State, Holy See)

2010-07-15

328

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.

329

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

330

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

331

Great Ocean Conveyor Belt: Part I  

NSDL National Science Digital Library

The oceans are in constant flux. The movement of ocean water is readily observable in the rise and fall of the tides and the continual lapping of waves along the coastlines of continents and islands. Less obvious is the network of currents that constantly circulates ocean water from one side of the globe to another. This map illustrates the network of currents known as the great ocean conveyor belt, or the thermohaline conveyor, and shows which portions are travelled by warm and shallow, or cold and salty, currents. A background essay and discussion questions are included.

2010-12-27

332

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

333

Stratospheric Polar Freezing Belt Causes Denitrification  

NASA Technical Reports Server (NTRS)

Trajectory cloud model calculations are presented to show that homogeneous freezing of nitric acid hydrates can produce a polar freezing belt in both hemispheres that can cause denitrification. While hydrate cloud microphysical properties are similar over both poles, the shorter persistence of clouds in the Arctic prevents the depth of the denitrified layers from growing beyond a few kilometers. The 1999-2000 Arctic winter is unique in showing a distinct denitrification profile with a depth of approx. 4.5 km that is nearly half as deep as that computed for a typical Antarctic winter.

Tabazadeh, A.; Jensen, E. J.; Toon, O. B.; Drdla, K.; Schoeberl, M. R.; Gore, Warren J. (Technical Monitor)

2001-01-01

334

Great Ocean Conveyor Belt: Part I  

NSDL National Science Digital Library

The oceans are in constant flux. The movement of ocean water is readily observable in the rise and fall of the tides and the continual lapping of waves along the coastlines of continents and islands. Less obvious is the network of currents that constantly circulates ocean water from one side of the globe to another. This map illustrates the network of currents known as the great ocean conveyor belt, or the thermohaline conveyor, and shows which portions are travelled by warm and shallow, or cold and salty, currents. A background essay and discussion questions are included.

335

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. PMID:18056315

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

2007-01-01

336

23 CFR Appendix D to Part 1240 - Determination of National Average Seat Belt Use Rate  

... Determination of National Average Seat Belt Use Rate D Appendix D to Part 1240 Highways NATIONAL HIGHWAY TRAFFIC SAFETY...BELTS-ALLOCATIONS BASED ON SEAT BELT USE RATES Pt. 1240, App. D Appendix D to Part 1240—Determination of National...

2014-04-01

337

The Dynamical Evolution of the Asteroid Belt  

E-print Network

The asteroid belt is the leftover of the original planetesimal population in the inner solar system. However, currently the asteroids have orbits with all possible values of eccentricities and inclinations compatible with long-term dynamical stability, whereas the initial planetesimal orbits should have been quasi-circular and almost co-planar. The total mass in the asteroid population is a small fraction of that existing primordially. Also, asteroids with different chemical/mineralogical properties are not ranked in an orderly manner with mean heliocentric distance as one could expect from the existence of a radial gradient of the temperature in the proto-planetary disk, but they are partially mixed. These properties show that the asteroid belt has been severely sculpted by one or a series of processes during its lifetime. This paper reviews the processes that have been proposed so far, discussing the properties that they explain and the problems that they are confronted with. Emphasis is paid to the interpl...

Morbidelli, Alessandro; O'Brien, David P; Minton, David A; Bottke, William F

2015-01-01

338

WATER ICE IN THE KUIPER BELT  

SciTech Connect

We examine a large collection of low-resolution near-infrared spectra of Kuiper Belt objects (KBOs) and centaurs in an attempt to understand the presence of water ice in the Kuiper Belt. We find that water ice on the surface of these objects occurs in three separate manners: (1) Haumea family members uniquely show surfaces of nearly pure water ice, presumably a consequence of the fragmentation of the icy mantle of a larger differentiated proto-Haumea; (2) large objects with absolute magnitudes of H < 3 (and a limited number to H = 4.5) have surface coverings of water ice-perhaps mixed with ammonia-that appears to be related to possibly ancient cryovolcanism on these large objects; and (3) smaller KBOs and centaurs which are neither Haumea family members nor cold-classical KBOs appear to divide into two families (which we refer to as 'neutral' and 'red'), each of which is a mixture of a common nearly neutral component and either a slightly red or very red component that also includes water ice. A model suggesting that the difference between neutral and red objects due to formation in an early compact solar system either inside or outside, respectively, of the {approx}20 AU methanol evaporation line is supported by the observation that methanol is only detected on the reddest objects, which are those which would be expected to have the most of the methanol containing mixture.

Brown, M. E.; Fraser, W. C. [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States); Schaller, E. L., E-mail: mbrown@caltech.edu [NASA Dryden Aircraft Operations Facility, Palmdale, CA 93550 (United States)

2012-06-15

339

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

340

Rotation Rates of 8 Main Belt Asteroids  

NASA Astrophysics Data System (ADS)

We report the rotation rates of the 8 main-belt asteroids 205 Martha, 252 Clementina, 506 Marion, 567 Eleutheria, 613 Ginevra, 869 Mellena, 996 Hilaritas, and 1490 Limpopo and discuss future work. These bodies include one P and seven C-class asteroids located at heliocentric distances of 2.3 to 3.6 AU. Seven of the light curves produced useful results; three of the periods are reported here for the first time, one expands on a previous publication, and the remaining three periods support previously published results. The study of main belt asteroids is an important topic because they can give us insight into planet formation and evolution. The focus of this paper is to use photometry to learn rotation periods. Future work will focus on using this information to obtain shape and pole orientation. Knowing the rotation rate, shape and orientation and their dynamics can place constraints on the early solar system. This project was funded by the National Science Foundation Research Experiences for Undergraduates (REU) program through grant NSF AST-1004872.

Saylor, Dicy Ann E.; leake, M. A.

2011-01-01

341

Water Ice in the Kuiper Belt  

NASA Astrophysics Data System (ADS)

We examine a large collection of low-resolution near-infrared spectra of Kuiper Belt objects (KBOs) and centaurs in an attempt to understand the presence of water ice in the Kuiper Belt. We find that water ice on the surface of these objects occurs in three separate manners: (1) Haumea family members uniquely show surfaces of nearly pure water ice, presumably a consequence of the fragmentation of the icy mantle of a larger differentiated proto-Haumea; (2) large objects with absolute magnitudes of H < 3 (and a limited number to H = 4.5) have surface coverings of water ice—perhaps mixed with ammonia—that appears to be related to possibly ancient cryovolcanism on these large objects; and (3) smaller KBOs and centaurs which are neither Haumea family members nor cold-classical KBOs appear to divide into two families (which we refer to as "neutral" and "red"), each of which is a mixture of a common nearly neutral component and either a slightly red or very red component that also includes water ice. A model suggesting that the difference between neutral and red objects due to formation in an early compact solar system either inside or outside, respectively, of the ~20 AU methanol evaporation line is supported by the observation that methanol is only detected on the reddest objects, which are those which would be expected to have the most of the methanol containing mixture.

Brown, M. E.; Schaller, E. L.; Fraser, W. C.

2012-06-01

342

CO depletion in the Gould Belt clouds  

NASA Astrophysics Data System (ADS)

We present a statistical comparison of CO depletion in a set of local molecular clouds within the Gould Belt using Sub-millimetre Common User Bolometer Array (SCUBA) and Heterodyne Array Receiver Programme (HARP) data. This is the most wide-ranging study of depletion thus far within the Gould Belt. We estimate CO column densities assuming local thermodynamic equilibrium and, for a selection of sources, using the radiative transfer code RADEX in order to compare the two column density estimation methods. High levels of depletion are seen in the centres of several dust cores in all the clouds. We find that in the gas surrounding protostars, levels of depletion are somewhat lower than for starless cores with the exception of a few highly depleted protostellar cores in Serpens and NGC 2024. There is a tentative correlation between core mass and core depletion, particularly in Taurus and Serpens. Taurus has, on average, the highest levels of depletion. Ophiuchus has low average levels of depletion which could perhaps be related to the anomalous dust grain size distribution observed in this cloud. High levels of depletion are often seen around the edges of regions of optical emission (Orion) or in more evolved or less dynamic regions such as the bowl of L1495 in Taurus and the north-western region of Serpens.

Christie, H.; Viti, S.; Yates, J.; Hatchell, J.; Fuller, G. A.; Duarte-Cabral, A.; Sadavoy, S.; Buckle, J. V.; Graves, S.; Roberts, J.; Nutter, D.; Davis, C.; White, G. J.; Hogerheijde, M.; Ward-Thompson, D.; Butner, H.; Richer, J.; Di Francesco, J.

2012-05-01

343

LANL*: Radiation belt drift shell modeling  

NASA Astrophysics Data System (ADS)

LANL* calculates the magnetic drift invariant L*, used for modeling radiation belt dynamics and other space weather applications, six orders of magnitude (~ one million times) faster than convectional approaches that require global numerical field lines tracing and integration. It is based on a modern machine learning technique (feed-forward artificial neural network) by supervising a large data pool obtained from the IRBEM library, which is the traditional source for numerically calculating the L* values. The pool consists of about 100,000 samples randomly distributed within the magnetosphere (r: [1.03, 11.5] Re) and within a whole solar cycle from 1/1/1994 to 1/1/2005. There are seven LANL* models, each corresponding to its underlying magnetic field configuration that is used to create the data sample pool. This model has applications to real-time radiation belt forecasting, analysis of data sets involving tens of satellite-years of observations, and other problems in space weather.

Yu, Yiqun; Koller, Josef

2014-09-01

344

Respiratory Belt Transducer Constructed Using a Singing Greeting Card Beeper  

ERIC Educational Resources Information Center

An article by Belusic and Zupancic described the construction of a finger pulse sensor using a singing greeting card beeper. These authors felt that this beeper made of piezoelectric material could be easily modified to function as a respiratory belt transducer to monitor respiratory movements. Commercially available respiratory belt transducers,…

Bhaskar, Anand; Subramani, Selvam; Ojha, Rajdeep

2013-01-01

345

CORN BELT PLAIN RIVER AND STREAMS PROJECT - 3 BIOCRITERIA PRODUCTS  

EPA Science Inventory

This effort resulted in eight products, as follows: 1) Development of Index of Biotic Integrity Expectations for the Ecoregions of Indiana I. Central Corn Belt Plain; 2) Ibid. II. Huron-Erie Lake Plain; 3) Ibid III. Northern Indiana Till Plain; 4) Ibid .IV.Eastern Corn Belt Plain...

346

Physical drawbacks of linear high-speed tooth belt drives  

Microsoft Academic Search

Production rate plays an important role in industrial applications, which means higher demands for accelerations and speeds of the systems. The requirements for accuracy and repeatability are also increasing. A solution for these demands is a high-speed tooth belt linear drive; however, the drawbacks of system of this kind are non-linear friction and flexibility of the belt, which make the

M. Jokinen; S. Saarakkala; M. Niemela; R. Pollanen; J. Pyrhonen

2008-01-01

347

Does a pelvic belt influence sacroiliac joint laxity?  

Microsoft Academic Search

Objective. To evaluate the influence of different positions and tensions of a pelvic belt on sacroiliac joint laxity in healthy young women.Background. Clinical experience has shown that positive effects can be obtained with different positions and tensions of a pelvic belt. A functional approach to the treatment of the unstable pelvic girdle requires an understanding of the effect of a

Léonie Damen; Cornelis W Spoor; Chris J Snijders; Henk J Stam

2002-01-01

348

The effects of standard enforcement on Michigan safety belt use  

Microsoft Academic Search

The purpose of this study was to assess the effects of standard enforcement legislation on safety belt use in Michigan through a series of seven statewide direct observation surveys. A secondary purpose of the study was to compare the results in Michigan to the results in other states that have changed the provision of their mandatory safety belt use law

David W Eby; Jonathon M Vivoda; Tiffani A Fordyce

2002-01-01

349

ORIGINAL PAPER Analysis of conveyor belts in winter Mediterranean cyclones  

E-print Network

ORIGINAL PAPER Analysis of conveyor belts in winter Mediterranean cyclones B. Ziv & H. Saaroni & M to Mediterranean cyclones (MCs) is examined using data from two winters. Eight MCs, which exhibit typical midlatitude cyclone structure, were scrutinized and their conveyor belts were examined. The analysis was based

Harnik, Nili

350

Teenage Years in the "Stroke Belt" Drive up Risk  

MedlinePLUS

Teenage Years in the “Stroke Belt” Drive up Risk Follow NINDSnews For release: Thursday, May 16, 2013 Adolescence is inarguably a vulnerable time of life, ... the southeastern United States region known as the “Stroke Belt” adds an extra hazard: It raises one’s ...

351

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

352

Promoting Automobile Safety Belt Use by Young Children.  

ERIC Educational Resources Information Center

A program of behavioral practice, assertiveness training, and social and contrived reinforcers was successful in establishing and maintaining automobile safety belt use by 16 children (ages 4-7) who never used them during a five-day preobservation period. Safety belt use occurred during 76%-90% of follow-up observations after two-three months.…

Sowers-Hoag, Karen M.; And Others

1987-01-01

353

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

354

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.

355

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

356

Anorthosite Belts, Continental Drift, and the Anorthosite Event  

Microsoft Academic Search

Most anorthosites lie in two principal belts when plotted on a predrift continental reconstruction. Anorthosite ages in the belts cluster around 1300 ± 200 million years and range from 1100 to 1700 million years. This suggests that anorthosites are the product of a unique cataclysmic event or a thermal event that was normal only during the earth's early history.

Norman Herz

1969-01-01

357

Anorthosite belts, continental drift, and the anorthosite event.  

PubMed

Most anorthosites lie in two principal belts when plotted on a predrift continental reconstruction. Anorthosite ages in the belts cluster around 1300 +/- 200 million years and range from 1100 to 1700 million years. This suggests that anorthosites are the product of a unique cataclysmic event or a thermal event that was normal only during the earth's early history. PMID:17775597

Herz, N

1969-05-23

358

Anorthosite belts, continental drift, and the anorthosite event  

USGS Publications Warehouse

Most anorthosites lie in two principal belts when plotted on a predrift continental reconstruction. Anorthosite ages in the belts cluster around 1300 ?? 200 million years and range from 1100 to 1700 million years. This suggests that anorthosites are the product of a unique cataclysmic event or a thermal event that was normal only during the earth's early history.

Herz, N.

1969-01-01

359

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

360

Structural deformation of the Daqingshan granulite belt, North China craton  

NASA Astrophysics Data System (ADS)

The Daqingshan granulite belt of Inner Mongolia, which is the western section of the North China granulite belt, consists of granulite facies rocks of the late Archean Wulashan group. These rocks had been subjected to 750-850°C and 0.7-0.9 GPa metamorphic conditions at the end of the Archean as a result of continental collision. Regional foliations, S 1 and S 2, are well developed in the granulite belt and have two preferred orientations 174°/83° and 352°/88°. The S 1 fabric generally coincides with the original sedimentary bedding S 0. Folding in the Daqingshan granulite belt can be divided into three phases. F 1 folds result from S 1 shearing. F 2 folds, the major structure of the granulite belt, are a series of major anticlines and synclines which complicate the stratigraphic sequence of the Wulashan group. F 3 folds are small-scale synforms and antiforms produced by superposition. Two sets of mineral lineations, L 1 and L 2, can be identified in the Daqingshan granulite belt. Strain analysis demonstrates that in the Daqingshan granulite belt, the minimum extension along foliation is 67-86% and the minimum shortening normal to foliation is 48-68%. Four phases of deformation are responsible for the structures in the Daqingshan granulite belt.

Gan, Sheng-fei

361

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

362

Tectonic evolution of the Triassic fold belts of Tibet  

Microsoft Academic Search

The Triassic fold belt of North Tibet is mainly composed, from west to east, of the Bayan Har, Songpan–Garzê, and Yidun (or Litang–Batang) terranes. The Indosinian orogeny results from interactions between the South China, North China and Qiangtang (North Tibet) blocks during the closure of the Palaeotethys. A synthesis of the tectonic and geochronological data available on this belt is

Françoise Roger; Marc Jolivet; Jacques Malavieille

2008-01-01

363

30 CFR 57.4503 - Conveyor belt slippage.  

Code of Federal Regulations, 2011 CFR

...capable of automatically stopping the drive pulley. (b) Underground belt conveyors...capable of automatically stopping the drive pulley if slippage could cause ignition of the...person shall attend the belt at the drive pulley when it is necessary to operate the...

2011-07-01

364

30 CFR 57.4503 - Conveyor belt slippage.  

Code of Federal Regulations, 2013 CFR

...capable of automatically stopping the drive pulley. (b) Underground belt conveyors...capable of automatically stopping the drive pulley if slippage could cause ignition of the...person shall attend the belt at the drive pulley when it is necessary to operate the...

2013-07-01

365

30 CFR 57.4503 - Conveyor belt slippage.  

Code of Federal Regulations, 2010 CFR

...capable of automatically stopping the drive pulley. (b) Underground belt conveyors...capable of automatically stopping the drive pulley if slippage could cause ignition of the...person shall attend the belt at the drive pulley when it is necessary to operate the...

2010-07-01

366

30 CFR 57.4503 - Conveyor belt slippage.  

...capable of automatically stopping the drive pulley. (b) Underground belt conveyors...capable of automatically stopping the drive pulley if slippage could cause ignition of the...person shall attend the belt at the drive pulley when it is necessary to operate the...

2014-07-01

367

30 CFR 57.4503 - Conveyor belt slippage.  

Code of Federal Regulations, 2012 CFR

...capable of automatically stopping the drive pulley. (b) Underground belt conveyors...capable of automatically stopping the drive pulley if slippage could cause ignition of the...person shall attend the belt at the drive pulley when it is necessary to operate the...

2012-07-01

368

Increased safety-belt use--United States, 1991.  

PubMed

From 1980 to 1990, safety-belt use among passenger-vehicle drivers in the United States increased from 11% to 49%; in 1990, use of safety belts prevented approximately 4800 deaths and 120,000 serious injuries among front-seat occupants (1). The increased use of safety belts from 1984 through 1990 was associated primarily with the enactment of state laws (Figure 1). In recent years, however, the rate of increase in use has declined. To increase safety-belt and child passenger restraint use in the United States, in February 1991, the National Highway Traffic Safety Administration (NHTSA) initiated the "70% by '92" program to increase safety-belt use to 70% by the end of 1992 through emphasis on enforcement efforts combined with public awareness campaigns. This report summarizes an assessment of the impact of the program through 1991. PMID:1598094

1992-06-19

369

Promoting safety belt use with traffic signs and prompters.  

PubMed Central

Two studies were conducted examining the stimulus-control effects of conventional traffic signs as prompts for motor vehicle driver safety belt use. Following pilot research which suggested that a traffic sign reading "Fasten Safety Belt" posted at a parking lot exit was effective in producing small increases in safety belt use, Study I demonstrated the superiority of having human prompters display such signs compared to simply posting the signs. Study II replicated the findings of Study I and found that posted signs became more effective in prompting safety belt use if simple posting was preceded by a period involving human prompters who displayed the signs. The results bear upon the development of more effective use of traffic signs in promoting safety belt use and in viewing such use as an instance of rule-governed behavior. PMID:2708173

Williams, M; Thyer, B A; Bailey, J S; Harrison, D F

1989-01-01

370

Correlating Color and Composition in the Kuiper Belt  

NASA Astrophysics Data System (ADS)

We propose to obtain colors and variability studies for 30 Kuiper Belt binaries to identify relationships between color and bulk physical properties: mass, albedo and density. We will also identify any binaries that have large amplitude variation indicative of non-spherical shapes or rapid rotation. In the Kuiper Belt, there is growing evidence that the very broad range of colors may reflect primordial bulk properties of Kuiper Belt objects rather than simply a veneer of altered materials. Kuiper Belt binaries are the only subset of Kuiper Belt objects for which masses are available. The correlation of color with physical properties opens a path to understanding the radial stratification of the protoplanetary disk and provides a link to disks around other stars.

Benecchi, Susan; Noll, Keith; Grundy, Will

2009-08-01

371

Secular Resonance Sweeping in a Self-Gravitating Kuiper Belt  

NASA Astrophysics Data System (ADS)

One of the more puzzling aspects of the Kuiper Belt is the high inclinations exhibited by Kuiper Belt Objects (KBOs). One possible explanation is that these high inclinations are due to sweeping secular resonances (Nagasawa and Ida 2000). In this scenario the depletion of the solar nebula's gas causes several secular resonances to sweep across the Kuiper Belt and excite substantial eccentricities and inclinations among massless bodies in a Kuiper Belt. We have reexamined this scenario but for a Kuiper Belt having some modest mass. The secular evolution of our system is computed using a so-called N-ring integrator that treats all the giant planets and small bodies as gravitating rings whose mutual perturbations cause the rings to flex and tilt over time. The secular perturbations from an exponentially decaying nebula gas disk is also included. When this code is applied to a massless Kuiper Belt it reproduces the Nagasawa and Ida result, namely, that large KBO eccentricities and inclinations are excited under certain circumstances and for sufficiently slow dispersal of the solar nebula. But when the primordial Kuiper Belt has sufficient mass, roughly one-tenth the minimum mass, then the giant planets instead launch very long wavelength spiral density and spiral bending waves among the inner KBO rings, and these disturbances propagate further into the outer Kuiper Belt. We find that wave propagation dramatically reduces the level of dynamical excitation that occurs in the inner a < 45 AU part of the Kuiper Belt after nebular dispersal, with very low-level excitation instead occurring throughout the Belt. The research is supported by J.M. Hahn's NASA Origins grant NAG5-10946.

Hahn, J. M.; Ward, W. R.

2002-09-01

372

Early Archaean collapse basins, a habitat for early bacterial life.  

NASA Astrophysics Data System (ADS)

For a better definition of the sedimentary environment in which early life may have flourished during the early Archaean, understanding of the basin geometry in terms of shape, depth, and fill is a prerequisite. The basin fill is the easiest to approach, namely from the well exposed, low-grade metamorphic 3.4 - 3.5 Ga rock successions in the greenstone belts of the east Pilbara (Coppin Gap Greenstone Belt and North Pole Dome) in West Australia and of the Barberton Greenstone Belt (Buck Ridge volcano-sedimentary complex) in South Africa. They consist of mafic to ultramafic volcanic rocks, largely pillow basalts, with distinct intercalations of intermediate to felsic intrusive and volcanic rocks and of silicious sediments. The, partly volcaniclastic, silicious sediments of the Buck Ridge and North Pole volcano-sedimentary complexes form a regressive-transgressive sequence. They were deposited close to base level, and experienced occasional emersion. Both North Pole Chert and the chert of the Kittys Gap volcano-sedimentary complex in the Coppin Gap Greenstone Belt preserve the flat-and-channel architecture of a shallow tidal environment. Thickness and facies distribution appear to be genetically linked to systems, i.e. arrays, of syn-depositionally active, extensional faults. Structures at the rear, front and bottoms of these fault arrays, and the fault vergence from the basin margin towards the centre characterize the basins as due to surficial crustal collapse. Observations in the Pilbara craton point to a non-linear plan view and persistence for the basin-defining fault patterns over up to 50 Ma, during which several of these fault arrays became superposed. The faults linked high-crustal level felsic intrusions within the overall mafic rock suite via porphyry pipes, black chert veins and inferred hydrothermal circulations with the overlying felsic lavas, and more importantly, with the cherty sediments. Where such veins surfaced, high-energy breccias, and in the case of the North Pole Chert huge barite growths, are juxtaposed with the otherwise generally low-energy sediments. Such localities are interpreted as sites of hydrothermal vents. Within this large-scale geological context, many environments on the micro-scale were habitable for life, such as hydrothermal vents and their vicinities, volcanic rock surfaces, subsurface sediments and sediment surfaces. These early collapse basins, hosting this bacterial life, are only partially comparable to Earthly analogues. A resemblance with Venus' coronae and the chaos terranes on Mars is suggested. This study forms part of an international project on Earth's Earliest Sedimentary Basins, supported by the Dutch Foundation Dr. Schürmannfonds. 2

Nijman, W.

373

Prompting safety-belt use in the context of a belt-use law: The flash-for life revisited  

Microsoft Academic Search

ProblemSafety-belt use reduces motor vehicle crash-related morbidity and mortality, yet an estimated 18% of drivers do not consistently buckle up (NHTSA, 2005). In 1985, Geller and colleagues developed an interpersonal Flash-for-Life prompt that increased belt use among 22% of 1,087 unbuckled drivers (Geller, Bruff, & Nimmer, 1985).

Leah V. Farrell; Matthew G. Cox; E. Scott Geller

2007-01-01

374

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

375

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

376

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

377

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

378

Very energetic protons in Saturn's radiation belt  

NASA Technical Reports Server (NTRS)

Very energetic protons are trapped in the inner Saturnian radiation belt. The University of California at San Diego instrument on Pioneer 11 has definitely identified protons of energy greater than 80 MeV on channel M3 and has tentatively detected protons of energy greater than 600 MeV on channel C3. The spatial distribution of the protons is distinct from that of the trapped electrons, the main difference being that the protons are strongly absorbed by the innermost moons and that the electrons are not. The source strength for injecting protons by the decay of cosmic ray albedo neutrons generated in the rings of Saturn has been estimated. The required proton lifetime is approximately 20 years.

Fillius, W.; Mcilwain, C.

1980-01-01

379

Flat belt continuously variable high speed drive  

SciTech Connect

The contracted work calls for the design, construction and test of flat belt pulley equipment that would demonstrate the practicality of transferring substantial power (up to 37.5 KW) from a high speed turbine shaft (50,000 RPM) to much lower speed output shaft with the availability of varying the speed of the output shaft over a two to one speed range relative to the high speed shaft. Such operation would permit the power available from an exhaust gas turbine to be more efficiently utilized in a turbo-charged diesel engine. The overall work progress corresponds quite well with expenditures made to data. At the end of March, 1991, the preliminary and detailed design is complete -- including analyses together with drawings (about 30 to date) of the test components. Initial tests are scheduled to start in April. 9 figs.

Not Available

1991-01-01

380

INCLINATION MIXING IN THE CLASSICAL KUIPER BELT  

SciTech Connect

We investigate the long-term evolution of the inclinations of the known classical and resonant Kuiper Belt objects (KBOs). This is partially motivated by the observed bimodal inclination distribution and by the putative physical differences between the low- and high-inclination populations. We find that some classical KBOs undergo large changes in inclination over gigayear timescales, which means that a current member of the low-inclination population may have been in the high-inclination population in the past, and vice versa. The dynamical mechanisms responsible for the time variability of inclinations are predominantly distant encounters with Neptune and chaotic diffusion near the boundaries of mean motion resonances. We reassess the correlations between inclination and physical properties including inclination time variability. We find that the size-inclination and color-inclination correlations are less statistically significant than previously reported (mostly due to the increased size of the data set since previous works with some contribution from inclination variability). The time variability of inclinations does not change the previous finding that binary classical KBOs have lower inclinations than non-binary objects. Our study of resonant objects in the classical Kuiper Belt region includes objects in the 3:2, 7:4, 2:1, and eight higher-order mean motion resonances. We find that these objects (some of which were previously classified as non-resonant) undergo larger changes in inclination compared to the non-resonant population, indicating that their current inclinations are not generally representative of their original inclinations. They are also less stable on gigayear timescales.

Volk, Kathryn; Malhotra, Renu, E-mail: kvolk@lpl.arizona.edu [Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 (United States)

2011-07-20

381

Radiation Belt Storm Probes: Resolving Fundamental Physics with Practical Consequences  

NASA Technical Reports Server (NTRS)

The fundamental processes that energize, transport, and cause the loss of charged particles operate throughout the universe at locations as diverse as magnetized planets, the solar wind, our Sun, and other stars. The same processes operate within our immediate environment, the Earth's radiation belts. The Radiation Belt Storm Probes (RBSP) mission will provide coordinated two-spacecraft observations to obtain understanding of these fundamental processes controlling the dynamic variability of the near-Earth radiation environment. In this paper we discuss some of the profound mysteries of the radiation belt physics that will be addressed by RBSP and briefly describe the mission and its goals.

Ukhorskiy, Aleksandr Y.; Mauk, Barry H.; Fox, Nicola J.; Sibeck, David G.; Grebowsky, Joseph M.

2011-01-01

382

The variable extension of Saturn's electron radiation belts  

NASA Astrophysics Data System (ADS)

Contrary to the permanent MeV ion belts which are relatively stable in intensity over both short and long time scales and are modulated by a single Galactic Cosmic Ray driven source, the electron belts of Saturn appear to be much more complex in both structure and temporal evolution. In order to understand the responses of this system to the different factors that may control it (internal or external/solar sources) we study its long-term, temporal evolution. We achieve that by tracking the equatorial distance of the belts' outer boundary, using MIMI/LEMMS energetic charged particle observations over a period of more than 7 years. This boundary is defined at the distance that a selected count rate level is measured in a LEMMS channel that has the properties of an omnidirectional, integral energy detector. Simulated solar wind moments, energetic neutral atom (ENA) observations and solar irradiance data are used to support the analysis. In many cases, correlations of the different datasets are weak, suggesting that the electron belts are modulated in time scales that are much shorter than the sampling of the electron belt boundary (typically every 10-30 days). Still, we find several cases of persistent, long term and strong perturbations in the system that appear to have corresponding disturbances in the extension of the electron belts, even on such long time scales. From the analysis of those intervals we believe that we have established a solid link with the planetary ring current as the primary source of the electron belts of Saturn. This is concluded mostly on the basis of an extended ring current decay in 2011 (inferred through ENA observations), coinciding with a similar, unusual drop in the electron belt extension (and intensity). This means that the electron belts should reflect also the modulation of the ring current. We suggest that possible sources of long term modulation are both the solar UV irradiance of the Saturnian thermosphere and the solar wind. The former appears to acquire large values and exhibit significant changes during the period of the electron belt/ring current decay, while an approximate 2-week periodicity (characteristic for the case of two solar wind streams per solar rotation) appears in the electron belts in the form of recurrent expansions or intensifications. The latter finding indicates that external forcing by the solar wind can have a considerable impact on the planet's electron belts, contrary to the expectations that Saturn's magnetospheric dynamics are rotationally dominated and internally driven.

Roussos, E.; Krupp, N.; Paranicas, C.; Carbary, J. F.; Kollmann, P.; Krimigis, S. M.; Mitchell, D. G.

2014-12-01

383

The Consecutive Dynamic Modeling of Vertically Bending Belt Conveyor under Irregularly Distributed Load  

Microsoft Academic Search

This paper probes into the vertically bending belt conveyor and sets up the consecutive dynamic modeling of this kind of belt conveyor. The formulas of static tension, static displacement, dynamic tension and dynamic displacement of the belt conveyor under operation condition have been deduced. Besides, simulation and analysis of a belt conveyor of Sihe Coal Mine in Shanxi Province by

Xiaohan Cheng; Guoying Meng; Xiao He; Jie Yang

2010-01-01

384

Participative Education for Children: An Effective Approach to Increase Safety Belt Use.  

ERIC Educational Resources Information Center

Practicing safety belt use and presenting a skit about it were found to nearly double the rate of belt use among six kindergarten participants who had been inconsistent belt users. Eleven older children and parents of the kindergartners, who watched the play, also increased and subsequently maintained safety belt use. (Author/JDD)

Lehman, Galen R.; Geller, E. Scott

1990-01-01

385

Effect of one-way clutch on the nonlinear vibration of belt-drive systems with a continuous belt model  

NASA Astrophysics Data System (ADS)

This study focuses on the nonlinear steady-state response of a belt-drive system with a one-way clutch. A dynamic model is established to describe the rotations of the driving pulley, the driven pulley, and the accessory shaft. Moreover, the model considers the transverse vibration of the translating belt spans for the first time in belt-drive systems coupled with a one-way clutch. The excitation of the belt-drive system is derived from periodic fluctuation of the driving pulley. In automotive systems, this kind of fluctuation is induced by the engine firing harmonic pulsations. The derived coupled discrete-continuous nonlinear equations consist of integro-partial-differential equations and piece-wise ordinary differential equations. Using the Galerkin truncation, a set of nonlinear ordinary differential equations is obtained from the integro-partial-differential equations. Applying the Runge-Kutta time discretization, the time histories of the dynamic response are numerically solved for the driven pulley and the accessory shaft and the translating belt spans. The resonance areas of the coupled belt-drive system are determined using the frequency sweep. The effects of the one-way clutch on the belt-drive system are studied by comparing the frequency-response curves of the translating belt with and without one-way clutch device. Furthermore, the results of 2-term and 4-term Galerkin truncation are compared to determine the numerical convergence. Moreover, parametric studies are conducted to understand the effects of the system parameters on the nonlinear steady-state response. It is concluded that one-way clutch not only decreases the resonance amplitude of the driven pulley and shaft's rotational vibration, but also reduces the resonance region of the belt's transverse vibration.

Ding, Hu; Zu, Jean W.

2013-11-01

386

Meningococcal carriage in the African meningitis belt  

PubMed Central

A meningococcal serogroup A polysaccharide/tetanus toxoid conjugate vaccine (PsA-TT) (MenAfriVac#x2122;) 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. Un vaccin conjugué contenant un polysaccharide du sérogroupe A méningococcique et une anatoxine du tétanos (PsA-TT) (MenAfriVac™) est en cours de déploiement dans les pays de la ceinture africaine de la méningite. L’ expérience avec d’ autres vaccins conjugués polysaccharide/protéine a montré qu’ une partie importante de leur succès a été leur capacité à empêcher l’ acquisition du portage pharyngé et donc à arrêter la transmission et à induire une immunité de group. Si PsA-TT doit d’ atteindre l’ objectif de prévenir les épidémies, il devrait être en mesure d’ empêcher l’ acquisition du portage pharyngé ainsi que la méningococcie invasive et le fait que PsA-TT puisse empêcher le portage pharyngé devrait être déterminé. Pour résoudre ce problème, le consortium MenAfriCar (Consortium Africain du Portage Méningococcique) a été établi en 2009 pour étudier le mode de portage du méningocoque dans les pays de la ceinture africaine de la méningite avant et après l’ introduction de PsA-TT. Cet article décrit comment le consortium a été établi, ses objectifs et les méthodes de laboratoire et de terrain standardisées qui ont été utilisées pour atteindre ces objectifs. L’ expérience du consortium MenAfriCar aidera à planifier les futures études sur l’ épidémiologie du portage du méningocoque dans les pays de la ceinture africaine de la méningite et d’ ailleurs. Se está utilizando una vacuna meningocócica conjugada (MenAfriVac™) de polisacárido del serogrupo A / tétano toxoide (PsA-TT) en países del cinturón Africano de meningitis. Las experiencias obtenidas con otras vacunas conjugadas polisacárido/proteína han demostrado que una parte importante de su éxito se debe a su habilidad para prevenir la colonización faríngea de los portadores, acabando por lo tanto con la transmisión, y a la de inducir la protección de rebaño. Si PsA-TT ha de cumplir el objetivo de prevenir epidemias, debe ser capaz de prevenir el estado de portador faríngeo, al igual que la enfermedad invasiva por meningococo, y para ello es necesario determinar si la PsA-TT puede prevenir la colonización faríngea. Con el fin de abordar esta cuestión se estableció un consorcio africano en el 2009 - el MenAfriCar (African Meningococcal Carriage Consortium) – para investigar los patrones del estado de portador de meningococo en paí

2013-01-01

387

Electron Flux of Radiation Belts Animation - Duration: 0:31.  

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...

388

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

389

5. Detail, date stone in belt course above keystone, east ...  

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

5. Detail, date stone in belt course above keystone, east portal of Tunnel 22, view to southeast, 380mm lens with electronic flash fill. - Southern Pacific Railroad Natron Cutoff, Tunnel 22, Milepost 581.85, Oakridge, Lane County, OR

390

MAIN-BELT COMET P/2012 T1 (PANSTARRS)  

E-print Network

We present initial results from observations and numerical analyses aimed at characterizing the main-belt comet P/2012 T1 (PANSTARRS). Optical monitoring observations were made between 2012 October and 2013 February using ...

Hsieh, Henry H.

391

Previously Undetected Radiation Belt Revealed - Duration: 1:03.  

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...

392

2. Left to right: coke ovens, wharf with belt conveyor, ...  

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

2. Left to right: coke ovens, wharf with belt conveyor, coal bunker, coke stack, brick quencher, gas holder, view framed by bracing for overhead conveyor. Looking south/southeast - Rouge Steel Company, 3001 Miller Road, Dearborn, Wayne County, MI

393

Bifurcation for Dynamical Systems of Planet-Belt Interaction  

E-print Network

The dynamical systems of planet-belt interaction are studied by the fixed-point analysis and the bifurcation of solutions on the parameter space is discussed. For most cases, our analytical and numerical results show that the locations of fixed points are determined by the parameters and these fixed points are either structurally stable or unstable. In addition to that, there are two special fixed points: the one on the inner edge of the belt is asymptotically stable and the one on the outer edge of the belt is unstable. This is consistent with the observational picture of Asteroid Belt between the Mars and Jupiter: the Mars is moving stablely close to the inner edge but the Jupiter is quite far from the outer edge.

Ing-Guey Jiang; Li-Chin Yeh

2002-01-03

394

VIEW SOUTH, NORTH ELEVATION OF (FROM LEFT) ENGINE HOUSE, BELT ...  

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

VIEW SOUTH, NORTH ELEVATION OF (FROM LEFT) ENGINE HOUSE, BELT SHED, ECCENTRIC HOUSE, NOTE ROD LINES EXITING ECCENTRIC HOUSE. - Golden Oil Company, Lot 410 Lease, Sheffield Field, Donaldson, Warren County, PA

395

VIEW NORTH, SOUTH ELEVATION OF (FROM LEFT) ECCENTRIC HOUSE, BELT ...  

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

VIEW NORTH, SOUTH ELEVATION OF (FROM LEFT) ECCENTRIC HOUSE, BELT SHED, AND ENGINE HOUSE, NOTE EXHAUST LOWER RIGHT OF ENGINE HOUSE. - Golden Oil Company, Lot 410 Lease, Sheffield Field, Donaldson, Warren County, PA

396

30 CFR 75.1108 - Approved conveyor belts.  

Code of Federal Regulations, 2010 CFR

...HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Fire Protection Fire Suppression Devices and Fire-Resistant Hydraulic Fluids on Underground Equipment § 75.1108 Approved conveyor belts. (a) Until December 31, 2009 conveyor...

2010-07-01

397

9. GATEHOUSE, INTERIOR, COUNTERSHAFT WHICH HELD BELT ATTACHED TO ENGINE ...  

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

9. GATEHOUSE, INTERIOR, COUNTERSHAFT WHICH HELD BELT ATTACHED TO ENGINE FOR HYPOCHLORITE MIXER, VIEW EAST - Lake Roland Dam, Gatehouse, Spanning outlet of Lake Roland near Woodbridge Road, Towson, Baltimore County, MD

398

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

399

30 CFR 57.15005 - Safety belts and lines.  

Code of Federal Regulations, 2010 CFR

...2010-07-01 2010-07-01 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...

2010-07-01

400

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

401

Seat belt use among rear passengers: validity of self-reported versus observational measures  

Microsoft Academic Search

BACKGROUND: The effects of seat belt laws and public education campaigns on seat belt use are assessed on the basis of observational or self-reported data on seat belt use. Previous studies focusing on front seat occupants have shown that self-reports indicate a greater seat belt usage than observational findings. Whether this over-reporting in self reports applies to rear seat belt

Francesco Zambon; Ugo Fedeli; Maria Marchesan; Elena Schievano; Antonio Ferro; Paolo Spolaore

2008-01-01

402

“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

403

Seat belt use in Argentina--a 10-year struggle.  

PubMed

Can a nongovernmental organization influence or determine seat belt use in a nation? The problems that implementing such a simple, yet effective, measure for traffic safety may trigger in a developing country are impossible to imagine. Just having the right laws is not enough: A great effort is necessary to create awareness and inform the population, but the governmental authorities in Argentina are not doing this, nor do they show any interest in it. In most of the developing countries, the situation is similar. Starting from a diagnosis of seat belt use by means of systematic observations, a program of awareness and massive education was developed for national radio and TV about the advantages of seat belt use. The first stage of this program was launched at the end of 1991, and it continues to this day. Articles in newspapers and communications and requests on the same subject sent to public officials also have helped mobilize public opinion on seat belt use. After 10 years of systematic and continued work by a nongovernmental organization, seat belt use is now part of the government's agenda and there is a high rate of "almost voluntary" seat belt use. The voluntary seat belt use in the city of Buenos Aires has reached 26.9%, and in national highways 58.9%. The roads that have been traveled in Argentina (documented with follow-up statistics) may be useful as guidelines for other countries that are starting this process, and may help to shorten times, avoid pitfalls, and save lives since it is estimated that 1,100 more lives could be saved every year in Argentina when seat belts become the norm. PMID:16210203

Silveira, Alberto J

2003-06-01

404

High energy proton model for the inner radiation belt.  

NASA Technical Reports Server (NTRS)

Reconsideration of inner radiation belt processes and proton theories. The ability of trapped particles to diffuse across magnetic shells is shown radically to alter the view of magnetospheric processes and to call for such a reconsideration. Inner belt calculations incorporating radial diffusion processes are performed in a manner parametrizing the radial diffusion coefficient. The latter is then varied so as to obtain agreement with experiment. The diffusion coefficient thus obtained is compared with coefficients derived by other means.

Walt, M.; Farley, T. A.

1972-01-01

405

The 2010-2011 revival of Jupiter's South Equatorial Belt  

NASA Astrophysics Data System (ADS)

In 2009-2010, Jupiter's South Equatorial Belt (SEB) faded to a very pale colour before the 2010-2011 revival restored the belt to its ordinary dark appearance. Mid-infrared images of the revival were taken using VISIR (VLT) across a range of wavelengths from 7 to 25 ?m. These were used to retrieve changes in temperature and aerosol optical depth as the revival proceeded between November 2010 and September 2011.

Giles, R. S.; Fletcher, L. N.; Irwin, P. G. J.; Orton, G. S.; Rogers, J. H.

2013-09-01

406

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

407

Promoting automobile safety belt use by young children.  

PubMed

A program using behavioral practice, assertiveness training, and social and contrived reinforcers was developed to establish and maintain automobile safety belt use by young children. Sixteen children (ages 4.8 to 7 years) who never used their safety belts during a 5-day preexperimental observation period were randomly assigned to two groups of eight each. A multiple baseline design across groups was used to evaluate the effectiveness of the training program. During the 8-day baseline period for Group 1, no children used their safety belts when unobtrusively observed while being driven from school. During the 26-day intervention period, the children were buckled up on 96% of the observations. Follow-up probes conducted 2-3 months after program discontinuance found safety belt use to range from 86% to 100%. For Group 2, the 14-day baseline safety belt use averaged 6% and increased to a mean of 81% during the 20-day training and maintenance program. Follow-up probes 2-3 months later found safety belt use to occur during 75% to 96% of the observations. Parent questionnaires indicated the generalizability and social validity of the program. PMID:3610893

Sowers-Hoag, K M; Thyer, B A; Bailey, J S

1987-01-01

408

Condoms and seat belts: the parallels and the lessons.  

PubMed

This paper investigates the relation between behavior adaptation and safety benefits of seat belts and whether condom promotion can be undermined by unintended changes in sexual risk perception and behavior. The comparison between 13 countries that passed seat belt laws and 4 countries without such laws shows a significant number of deaths among countries with seat belt laws. It has been suggested that drivers who wear seat belts feel safer and drive faster and more carelessly compared to those without seat belts. A model of individual risk management, postulating that every individual is comfortable with a certain level of risk and aims to balance the rewards of risk-taking against perceived hazards was developed to describe the behavior. This increase in seat belt use was then paralleled with condom use since the rise of HIV, with 3 ways in which a large increase in condom use could fail to affect transmission: 1) it appeals to risk-averse individuals who contribute little to epidemic transmission; 2) increased use of condom increases the number of transmission caused by condom failure; and 3) the increased use of condoms reflect the change in the decision of individuals from one partner to maintaining higher rates of partners and reliance on condoms. This paper, in conclusion, emphasizes the need for program development and implementation in response to this sexual behavior, particularly among developing countries. PMID:10665571

Richens, J; Imrie, J; Copas, A

2000-01-29

409

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

410

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

411

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

412

Radiation Belt Electron Dynamics: Modeling Atmospheric Losses  

NASA Technical Reports Server (NTRS)

The first year of work on this project has been completed. This report provides a summary of the progress made and the plan for the coming year. Also included with this report is a preprint of an article that was accepted for publication in Journal of Geophysical Research and describes in detail most of the results from the first year of effort. The goal for the first year was to develop a radiation belt electron model for fitting to data from the SAMPEX and Polar satellites that would provide an empirical description of the electron losses into the upper atmosphere. This was largely accomplished according to the original plan (with one exception being that, for reasons described below, the inclusion of the loss cone electrons in the model was deferred). The main concerns at the start were to accurately represent the balance between pitch angle diffusion and eastward drift that determines the dominant features of the low altitude data, and then to accurately convert the model into simulated data based on the characteristics of the particular electron detectors. Considerable effort was devoted to achieving these ends. Once the model was providing accurate results it was applied to data sets selected from appropriate periods in 1997, 1998, and 1999. For each interval of -30 to 60 days, the model parameters were calculated daily, thus providing good short and long term temporal resolution, and for a range of radial locations from L = 2.7 to 3.9. .

Selesnick, R. S.

2003-01-01

413

Energetic protons in Jupiter's radiation belts  

NASA Technical Reports Server (NTRS)

Estimates of the location, density, and energy of energetic protons in the Jupiter radiation belts are presented. A model of the Jupiter magnetosphere is developed by scaling from the Earth magnetosphere. Solar wind parameters, and magnetic and electric field characteristics in the magnetosphere are given for the Earth and projected for Jupiter. The upper limit of the number density of energetic protons is calculated to be 310,000/cu m, and the energy density would be about 310,000 MeV/cu m, or 51 nJ/cu m. A magnetic moment of 100 MeV/gauss for solar wind particles, a magnetic field on Jupiter's surface of 10 gauss, and a McIlwain parameter L of 7 are used. Sources of energetic particles are cosmic rays, satellite-magnetosphere interaction, and the solar wind, and their contributions are discussed. The two components of trapped energetic particle drift, one due to corotational and convective fields and the other due to gradients in the magnetic field, are described, and their periods are given.

Brice, N.

1972-01-01

414

Monitoring 2005 Corn Belt Yields From Space  

NASA Astrophysics Data System (ADS)

The U.S. corn belt, centered on Illinois, suffered extreme drought conditions during the 2005 growing season (Figure 1). The April-September rainfall ranked 10th lowest of the past 113 years (see http://www.ncdc.noaa.gov/oa/climate/research/monitoring.html#state). Throughout Illinois, counties were declared agricultural disaster areas and corn yields were predicted to be 30 percent less than the record year of 2004, which had the highest corn yields in the last 50 years [Christian Science Monitor, 2005]. However, the Illinois Agricultural Statistics Service estimated the overall corn yield was 145 bushels per acre, or just seven percent below the previous five-year average, with `many farmers. . .surprised by the better than expected yields after the drought conditions' (see http://www.agstats.state.il.us/releases/crop.pdf and http://usda.mannlib.cornell.edu/reports/nassr/field/pcp-bb/2005/crop1005.pdf). This better-than-expected yield has been attributed to advancements in seed genetics, equipment, and water-management practices [Barrionuevo and Bradsher, 2005].

Zhang, Ping; Anderson, Bruce T.; Myneni, Ranga

2006-04-01

415

Late Archean greenstone tectonics: Evidence for thermal and thrust-loading lithospheric subsidence from stratigraphic sections in the Slave Province, Canada  

NASA Technical Reports Server (NTRS)

How late Archean tectonics could be seen to have operated in the Slave Province is illustrated. Lithospheric thinning and stretching, with the formation of rifted margins (to continental or island arc fragments), and lithospheric flexural loading of the kind familiar in arcs and mountain belts could be discerned.

Kidd, W. S. F.; Kusky, T. M.; Bradley, D. C.

1988-01-01

416

Seat Belts Pay Off. The Use of Economic Incentives and Public Education to Increase Seat Belt Use in a Community. Final Report.  

ERIC Educational Resources Information Center

A six-month campaign to increase seat belt use in Chapel Hill and Carrboro, North Carolina centered around the idea of giving out economic incentives for seat belt wearing. The approach was to stop vehicles at random and give all belted vehicle occupants a small prize and a chance for a large cash prize. Precampaign activities involve collecting…

Campbell, B. J.; And Others

417

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

418

Rotationally driven `zebra stripes' in Earth's inner radiation belt  

NASA Astrophysics Data System (ADS)

Structured features on top of nominally smooth distributions of radiation-belt particles at Earth have been previously associated with particle acceleration and transport mechanisms powered exclusively by enhanced solar-wind activity. Although planetary rotation is considered to be important for particle acceleration at Jupiter and Saturn, the electric field produced in the inner magnetosphere by Earth's rotation can change the velocity of trapped particles by only about 1-2 kilometres per second, so rotation has been thought inconsequential for radiation-belt electrons with velocities of about 100,000 kilometres per second. Here we report that the distributions of energetic electrons across the entire spatial extent of Earth's inner radiation belt are organized in regular, highly structured and unexpected `zebra stripes', even when the solar-wind activity is low. Modelling reveals that the patterns are produced by Earth's rotation. Radiation-belt electrons are trapped in Earth's dipole-like magnetic field, where they undergo slow longitudinal drift motion around the planet because of the gradient and curvature of the magnetic field. Earth's rotation induces global diurnal variations of magnetic and electric fields that resonantly interact with electrons whose drift period is close to 24 hours, modifying electron fluxes over a broad energy range into regular patterns composed of multiple stripes extending over the entire span of the inner radiation belt.

Ukhorskiy, A. Y.; Sitnov, M. I.; Mitchell, D. G.; Takahashi, K.; Lanzerotti, L. J.; Mauk, B. H.

2014-03-01

419

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

420

Rotationally driven 'zebra stripes' in Earth's inner radiation belt.  

PubMed

Structured features on top of nominally smooth distributions of radiation-belt particles at Earth have been previously associated with particle acceleration and transport mechanisms powered exclusively by enhanced solar-wind activity. Although planetary rotation is considered to be important for particle acceleration at Jupiter and Saturn, the electric field produced in the inner magnetosphere by Earth's rotation can change the velocity of trapped particles by only about 1-2 kilometres per second, so rotation has been thought inconsequential for radiation-