These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Barberton greenstone belt volcanism: Succession, style and petrogenesis  

NASA Astrophysics Data System (ADS)

The Barberton Mountain Land is an early Archean greenstone belt along the eastern margin of the Kaapvaal Craton of southern Africa. Detailed mapping in the southern portion of the belt leads to the conclusion that a substantial thickness is due to original deposition of volcanics and sediments. In the area mapped, a minimum thickness of 12km of predominantly mafic and ultramafic volcanics comprise the Komati, Hooggenoeg, and Kromberg Formations of the Onverwacht Group, and at least one km of predominantly pyroclastic and epiclastic sediments derived from dacitic volcanics comprise the Fig Tree Group. The Barberton greenstone belt formed primarily by ultramafic to mafic volcanism on a shallow marine platform which underwent little or no concurrent extension. Vents for this igneous activity were probably of the non-constructional fissure type. Dacitic volcanism occurred throughout the sequence in minor amounts. Large, constructional vent complexes were formed, and explosive eruptions widely dispersed pyroclastic debris. Only in the final stages of evolution of the belt did significant thrust-faulting occur, generally after, though perhaps overlapping with, the final stage of dacitic igneous activity. A discussion follows.

Byerly, G. R.; Lowe, D. R.

2

Scientific Drilling in the Barberton Greenstone Belt, South Africa  

NASA Astrophysics Data System (ADS)

The Barberton Greenstone Belt in South Africa, one of the best-preserved successions of mid-Archean (3.5-3.2 Ga) supracrustal rocks in the world, is a remarkable natural laboratory 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 hope to obtain the continuous sections and relatively unaltered samples through the volcano-sedimentary successions. (1) Sedimentary sequences will 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) will provide information about the nature and magnitude of meteorite impact on the early Earth. (2) Successions of ultramafic to mafic volcanic rocks will provide new insights into volcanic processes, dynamics of the crust and mantle, interaction between oceanic volcanic crust and the hydrosphere and biosphere. The sources of hydrothermal fluids on the ocean floor, driven by circulation of seawater through the volcanic pile, constitute a second habitat of early life. A project supported by the International Continental Drilling Program and by scientists from 13 countries in five continents started on 15th July 2011. As of 31st July, two holes have been drilled in komatiites from the Tjakastad locality and another hole has been started in the Buck Reef Chert. Regular updates are available on the ICDP web site < www.icdp-online.org>. The distribution of samples and post-drilling research will be coordinated by a steering committee comprising representatives from all major participating countries. A workshop to decide who does what will be held in South Africa in early 2012 and core will then be distributed to interested scientists.

Arndt, N.; ICDP Barberton Scientific Drilling Team

2011-12-01

3

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

4

Archean Surface Environments and Komatiitic Volcanism: Evidence From the Barberton Greenstone Belt, South Africa  

Microsoft Academic Search

The Barberton Greenstone Belt (BGB) includes a stratigraphic succession 10-15 km thick with at least three major intervals dominated by komatiitic rocks totaling about five kilometers in aggregrate thickness that formed over an interval of approximately 200 million years (3.48 to 3.28 Ga). Significant aspects of the mid- Archean surface environment must have been controlled by the localized build-up of

G. R. Byerly; D. R. Lowe

2008-01-01

5

The New Consort Gold Mine, Barberton greenstone belt, South Africa: orogenic gold mineralization in a condensed metamorphic profile  

Microsoft Academic Search

The New Consort Gold Mine in the Palaeo- to Mesoarchaean Barberton greenstone belt, South Africa is one of the oldest recognized orogenic gold deposits on Earth. The gold mineralization is hosted by discrete mylonitic units that occur at, or close to, the contact between the mafic and ultramafic volcanic rocks of the c. 3,280 Ma Onverwacht Group and the mainly

A. Otto; A. Dziggel; A. F. M. Kisters; F. M. Meyer

2007-01-01

6

The New Consort Gold Mine, Barberton greenstone belt, South Africa: orogenic gold mineralization in a condensed metamorphic profile  

Microsoft Academic Search

The New Consort Gold Mine in the Palaeo- to Mesoarchaean Barberton greenstone belt, South Africa is one of the oldest recognized\\u000a orogenic gold deposits on Earth. The gold mineralization is hosted by discrete mylonitic units that occur at, or close to,\\u000a the contact between the mafic and ultramafic volcanic rocks of the c. 3,280 Ma Onverwacht Group and the mainly metasedimentary

A. Otto; A. Dziggel; A. F. M. Kisters; F. M. Meyer

2007-01-01

7

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

Microsoft Academic Search

Tourmaline-rich rocks are common in the lowgrade, 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 tourmalinite pebbles, and tourmaline-coated grains indicates that boron mineralization was a low-temperature, surficial process. The association of these lithologies with stromatolites,

Gary R. Byerly; Martin R. Palmer

1991-01-01

8

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

9

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

10

Fluid inclusion analysis of chert veins from the Mendon Formation, Barberton Greenstone Belt, South Africa  

NASA Astrophysics Data System (ADS)

Strongly silicified volcanic rocks and overlying sediments are a common feature in the Mesoarchean Barberton Greenstone Belt, South Africa. The silification predominantly occurs at the top of mafic to ultramafic lava flows at the contact to sedimentary chert horizons, and has been interpreted as a result of fluid circulation in shallow subseafloor convection cells (Hofmann & Harris, 2008). Six samples of silicified rocks of the Mendon Formation were used for a fluid inclusion study to better constrain the conditions of formation and the source and physico-chemical evolution of the fluid that might have been responsible for the alteration. The studied samples consist of silicified ultramafic rock and chemical precipitates with abundant chert and/or quartz veins. The silicified ultramafic rocks are mainly made up of quartz, Cr-muscovite and Cr-Spinell. Tourmaline and chlorite are locally present. Sedimentary cherts are nearly pure quartz with minor accessory minerals such as rutile and Fe-(hydr)oxides. Fluid inclusions are present in coarse-grained quartz in mainly bedding parallel syntaxial veins. Primary fluid inclusions occur as clusters in the crystal's core with an average size of 5-10 µm. They occur as two phase aqueous (liquid-vapour) inclusions at room temperature with a relatively constant vapour fraction (c.15-20 vol.%). Most fluid inclusions from veins crosscutting the silicified ultramafic rocks have a salinity between 0.5 and 11.0. wt.% NaCl equiv., one sample additionally contains inclusions with distinctly higher salinities (18 - 30 wt.% NaCl equiv.). Homogenization into the liquid phase occurs from 110°C to 210°C; with most values ranging between 150 and 180°C. The sample showing two distinct groups in salinity shows the lowest Th ranging from 110°C to 150°C. The sedimentary cherts show substantial differences i.e. the presence of a phase that prohibits freezing with a N-cooled freezing stage; probably CH4 or N2. Independent temperature estimates were derived from chlorite thermometry and illite cristallinity. Chlorite thermometry yielded temperatures of 250-350°C, whereas a Kübler index of < 0.25 ?°2? means the samples belong to the Epi-zone. Excluding the high salinity and sedimentary samples, the pressure during fluid inclusion entrapment is calculated at 1.6 - 2.4 kbar, corresponding to a depth of 5 - 8 km. These values argue against a shallow water deposition, yet could mean that the crystalline parts of the veins formed after burial during a later deformation or a late stage fluid infiltration event. However, if the veins formed at ca. 150 - 180°C during early seafloor alteration, the primary fluid inclusions may have also survived any subsequent thermal event.

Farber, Katja; Dziggel, Annika; Meyer, Franz M.

2013-04-01

11

Archean Surface Environments and Komatiitic Volcanism: Evidence From the Barberton Greenstone Belt, South Africa  

NASA Astrophysics Data System (ADS)

The Barberton Greenstone Belt (BGB) includes a stratigraphic succession 10-15 km thick with at least three major intervals dominated by komatiitic rocks totaling about five kilometers in aggregrate thickness that formed over an interval of approximately 200 million years (3.48 to 3.28 Ga). Significant aspects of the mid- Archean surface environment must have been controlled by the localized build-up of komatiitic landforms, perhaps unique tectonic styles associated with komatiitic volcanism, as well as the chemically highly reactive Mg-rich mineral and glass phases as they were deposited in contact with the Archean atmosphere and hydrosphere. The 3.48 Ga Komati Formation is composed of komatiitic and minor basaltic flow rocks, 3.5 km thick, without any sedimentary interbeds or stratiform zones of alteration that might suggest pauses in volcanism. We suggest this may represent a time interval as short as 105 years. These lavas were likely deposited in submarine lava fields of large dimensions and perhaps well away from the high heat flows associated with vent areas. There is no compelling evidence to support either a mid-oceanic rift or subduction zone tectonic setting. However, it is clear that this was a geologic environment removed from the input of continent-derived sediment. The 3.29 Ga Weltevreden Formation, over 3 km in stratigraphic thickness in places, also appears to have formed over a very short time span, with little or no deposition of sediment. Unlike the Komati Formation, abundant komatiitic tuffs are interbedded with the lavas and these may document environments somewhat more proximal to volcanic vents for the Weltevreden Formation. By contrast, the 0.6-1.0 km thick Mendon Formation is composed of six or more distinctive members that each include komatiitic lava flows capped by carbonate and silica-enriched alteration zones and sedimentary cherts. The base of the formation is 3.33 Ga, several units in the interior are 3.30 Ga, and conformable cherts of the immediately overlying Fig Tree are 3.27 Ga. Both geology and geochronology are consistent with 107 or more years for this formation - requiring up to 3-4 orders of magnitude lower rates of local volcanic deposition compared to other komatiitic units of the BGB. Immobile incompatible element ratios suggest that each member is from a discrete and separate mantle-derived magma batch, and like the Komati Formation, probably erupted from distant vents. However, significant changes in stratigraphy from south to north, and across a series of regional faults, do support an opening rift-basin model for the Mendon Formation. The geology of these komatiitic formations does not support models for vast, dynamic, and focused hydrothermal systems. Major cross-cutting zones of alteration do not exist; silica and carbonate alteration is stratiform and contemporary with sedimentation at each pause in volcanism. Komatiitic rocks only meters below the alteration zones typically contain fresh igneous minerals, commonly pyroxenes and rarely even olivine, and the rocks are generally only modified by hydration and minor losses of sodium and calcium. Our preferred model for the development of the Mendon units, as well as similar komatiitic units in the Hooggenoeg and Kromberg Formations, includes deposition of flows, shallow-marine to subaerial exposure and surface-driven hydration, silicification and carbonation contemporaneous with accumulation of organic sediments and volcanic ash from distal sources.

Byerly, G. R.; Lowe, D. R.

2008-12-01

12

Potential magnetofossils in ~3.4 billion-year-old cherts from the Barberton Greenstone Belt of South Africa  

NASA Astrophysics Data System (ADS)

Previous reported paleointensity data from ~3.45 Ga dacites of the Barberton Greenstone Belt indicate the presence of a relatively strong geomagnetic field requiring the presence of a dynamo (Tarduno et al., Science, 2010). The ~3.40 Ga Buck Reef Chert from the same belt includes shallow water environments that may have been conducive for magnetotactic bacteria, if such forms were present in the Paleoarchean, as might be expected given the presence of the field. Here we use rock magnetism, electron microscopy, and ferromagnetic resonance to test for the presence of bacterial magnetite particles. Magnetic hysteresis properties of bulk samples show a variety of rock magnetic behaviors, including multi-domain, pseudo-single domain, single domain, and wasp-waisted curves; the latter indicate grain and/or compositional mixtures. Electron microscopy of magnetic separates and in-situ particles from the Buck Reef Chert show cubo-octahedral to quasi-rectangular and hexagonally shaped grains that fall within a stable single domain range typical of biogenic magnetite. Ferromagnetic resonance (FMR) spectra from bulk samples appear asymmetrical and skew towards low fields, suggesting a magnetic anisotropy that is similar to the spectra seen from some strains of modern magnetotactic bacteria. Thus, while there is clearly a mixture of magnetic particles within the Buck Reef Chert, these data suggest one component could be ancient bacterial magnetite.

Voronov, Julia; Tarduno, John; Watkeys, Michael; Hofmann, Axel

2013-04-01

13

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

14

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

NASA Astrophysics Data System (ADS)

In the Barberton Greenstone Belt, South Africa, a 100-250 m thick complex of carbonaceous chert dikes marks the transition from the Mendon Formation to the Mapepe Formation (3260 Ma). The sub-vertical- to vertical position of the fractures, the abundance of highly shattered zones with poorly rotated angular fragments and common jigsaw fit, radial structures, and multiple injection features point to repetitive hydraulic fracturing that released overpressured fluids trapped within the shallow crust. The chemical and isotopic compositions of the chert favour a model whereby seawater-derived fluids circulated at low temperature (< 100-150 °C) within the shallow crust. From the microscopic structure of the chert, the injected material was a slurry of abundant clay-sized, rounded particles of silica, carbonaceous matter and minor clay minerals, all suspended in a siliceous colloidal solution. The dike geometry and characteristics of the slurry concur on that the chert was viscoelastic, and most probably thixotropic at the time of injection: the penetration of black chert into extremely fine fractures is evidence for low viscosity at the time of injection and the suspension of large country rock fragments in the chert matrix provides evidence of high viscosity soon thereafter. We explain the rheology by the particulate and colloidal structure of the slurry, and by the characteristic of silica suspensions to form cohesive 3-D networks through gelation. Our results provide valuable information about the compositions, physical characteristics and rheological properties of the fluids that circulated through Archean volcano-sedimentary sequences, which is an additional step to understand conditions on the floor of Archean oceans, the habitat of early life.

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

2015-02-01

15

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

NASA Astrophysics Data System (ADS)

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 varieties of lava are basaltic. Compositional differences between bands and variations in the lavas in general have been modified by alteration, but indicate mingling of two different basalts, one richer in TiO2, Al2O3, MgO, FeOt and probably Ni and Cr than the other, as the cause of the banding. The occurrence in certain pillows of blebs of dark metabasalt enclosed in pale green metabasalt, as well as cores of faintly banded or massive dark metabasalt, suggest that breakup into drops and slugs in the feeder channel to the lava flow initiated mingling. The inhomogeneous mixture was subsequently stretched and folded together during laminar shear flow through tubular pillows, while diffusion between bands led to partial homogenisation. The most common internal pattern defined by the flow banding in pillows is concentric. In some pillows the banding defines curious mushroom-like structures, commonly cored by dark, variolitic metabasalt, which we interpret as the result of secondary lateral flow due to counter-rotating, transverse (Dean) vortices induced by the axial flow of lava towards the flow front through bends, generally downward, in the tubular pillows. Other pillows exhibit weakly-banded or massive, dark, variolitic cores that are continuous with wedge-shaped apophyses and veins that intrude the flow banded carapace. These cores represent the flow of hotter and less viscous slugs of the dark lava type into cooled and stiffened pillows.

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

2010-07-01

16

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

NASA Astrophysics Data System (ADS)

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

Ledevin, Morgane; Arndt, Nicholas; Simionovici, Alexandre

2014-05-01

17

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

18

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

19

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

NASA Astrophysics Data System (ADS)

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

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

2007-02-01

20

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

21

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

22

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

23

LASER step-heating 40 Ar \\/ 39 Ar age spectra from early Archean (~3.5 Ga) Barberton greenstone belt sediments: A technique for detecting cryptic tectono-thermal events  

Microsoft Academic Search

Samples from sediments of the Fig Tree Group located in the central part of the circa 3.2 to 3.5 Ga Barberton greenstone belt (BGB) have been analyzed by the 40 Ar \\/ 39 Ar laser step-heating technique. This technique has enabled previously cryptic thermal overprints to be detected in various sedimentary units which include: reworked chemical sediments (barite), clastic sediments

C. E. J. de Ronde; C. M. Hall; D. York; C. Spooner E. T

1991-01-01

24

Laser step-heating sup 40 Ar\\/ sup 39 Ar age spectra from early Archean (@3. 5 Ga) Barberton greenstone belt sediments: A technique for detecting cryptic tectono-thermal events  

Microsoft Academic Search

Samples from sediments of the Fig Tree Group located in the central part of the circa 3.2 to 3.5 Ga Barberton greenstone belt (BGB) have been analyzed by the ⁴°Ar\\/³⁹Ar laser step-heating technique. This technique has enabled previously cryptic thermal overprints to be detected in various sedimentary units which include: reworked chemical sediments (barite), clastic sediments (sandstone\\/shale), and one stromatolite.

C. E. J. De Ronde; C. M. Hall; D. York; E. T. C. Spooner

1991-01-01

25

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

26

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

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

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

Microsoft Academic Search

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

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

2001-01-01

29

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

NASA Astrophysics Data System (ADS)

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

Sleep, Norman H.; Lowe, Donald R.

2014-04-01

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

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

32

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

33

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

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

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

PubMed

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

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

2006-10-29

41

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

42

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

NASA Technical Reports Server (NTRS)

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.

1987-01-01

43

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.

44

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

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

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

47

Archaean greenstone belts and associated granitic rocks - A review  

NASA Astrophysics Data System (ADS)

Archaean greenstone belts and associated granitic rocks comprise some of the most diverse rock types on the Earth's surface and were formed during the early stages of the development of the planet from Eoarchaean to Neoarchaean times - a period extending back from about 4000 to 2500 million years ago. Because of their great age, these rocks have received unprecedented attention from a wide spectrum of Earth scientists striving to learn more about the evolution of the Earth, including its crust, hydrosphere, atmosphere, the commencement of life, and the nature and distribution of mineral deposits. The knowledge gained thus far has accumulated incrementally, beginning with solid field-based studies, the latter being supplemented with increasingly advanced technological developments that have enabled scientists to probe fundamental questions of Earth history. Archaean granite-greenstone terranes display considerable variability of lithologies and geotectonic events, yet there are unifying characteristics that distinguish them from other geological environments. Most greenstone belts consist of a wide variety of volcanic and sedimentary rocks that reflect different evolutionary conditions of formation and all have invariably been influenced by subsequent geotectonic factors, including the intrusion of ultramafic, mafic and granitic complexes, resulting in widespread deformation, metamorphism, metasomatism, as well as mineralization. Geochemical and isotopic age determinations have shown how complex these ancient rocks are and efforts at understanding the nature and evolution of the hydrosphere, atmosphere and primitive life have made Archaean terranes exciting environments in which to study. Conflicting views as to the nature, history and origin of many of the rock types and events in Archaean terranes has been ongoing and stimulating. This review attempts to describe the main lithotypes and other characteristics of granite-greenstone belt geology and points to some areas where contrasting views have been expressed.

Anhaeusser, Carl R.

2014-12-01

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

Petrology and geochemistry of metamorphosed komatiites and basalts from the Sula Mountains greenstone belt, Sierra Leone  

Microsoft Academic Search

The Sula Mountains greenstone belt is the largest of the late-Archaean greenstone belts in the West African Craton. It comprises\\u000a a thick (5?km) lower volcanic formation and a thinner (2?km) upper metasedimentary formation. Komatiites and basalts dominate\\u000a the volcanic formation and komatiites form almost half of the succession. All the volcanic rocks are metamorphosed to amphibolite\\u000a grade and have been

Hugh Rollinson

1999-01-01

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

Thermobarometry in the Hadean: The Nuvvuagittuq Greenstone Belt  

NASA Astrophysics Data System (ADS)

The 4.28 Ga 142Nd model age of the faux-amphibolite formation makes it the oldest assemblage of the Nuvvuagittuq Greenstone Belt (Northeastern Superior Province, Quebec, Canada) and the oldest rocks yet found on Earth. The protolith of the faux-amphibolite, however, is uncertain. The bulk chemistry suggests that it is most likely mafic and basaltic to basaltic-andesite in composition (samples have 36-63 wt% SiO2 and 3.5- 14 wt% MgO), although it has very low Ca-content compared to typical basalt. This low-Ca content is reflected in the crystallization of the amphibole cummingtonite, as opposed to hornblende, that is characteristic of the faux-amphibolite's adjacent gabbro sill. This suggests that Ca and other elements were mobile, perhaps during metamorphism. On the other hand, we do not see low-Ca in the adjacent gabbro sill suggesting either a more complex history for the faux-amphibolite, i.e. a metamorphic event before the emplacement of the gabbro sill, or Ca-depletion as the result of weathering processes. The faux-amphibolite is a heterogeneous gneiss with the mineral assemblage: cummingtonite + quartz + biotite + plagioclase ± anthophyllite ± garnet ± alkali-feldspar with the majority of the biotite replaced by retrograde chlorite. The garnets are heavily fractured, poikioblastic and, apart from the rims, are not zoned with respect to Fe and Mg. The garnets, as well as the groundmass, contain inclusions of zircon, rutile, ilmenite, monazite and other REE phosphates, and iron sulfides. Preliminary garnet-biotite geothermometry has been done that supports upper amphibolite to granulite facies metamorphism. Unzoned garnets from different parts of the faux-amphibolite record distinct Fe-Mg exchange temperatures that range from 730 to 940 °C (assuming a constant pressure of 5 kbar) suggesting the preservation of a metamorphic field gradient. Further geothermobarometry with trace element and accessory phases will be used to further describe the PT path as the resulting trace element zoning profiles may record reactions and loss of phases during the prograde PT path; phases that otherwise are not preserved. Thus, future work using the LA-ICPMS will aim to better constrain the metamorphic compositional changes to the faux-amphibolite's protolith.

Scher, S.; Minarik, W.

2009-05-01

52

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

53

Basic lavas of the Archean La Grande Greenstone belt: Products of polybaric fractionation and crustal contamination  

Microsoft Academic Search

Despite the fact that some greenstone belts preserve the record of contemporaneous komatiitic and tholeiitic volcanism, a genetic link between the two is not widely accepted. The significance of a compositional gap seperating these magma types and differences in their respective degree of light rare earth element (LREE) enrichment, cited as evidence against a derivative relationship, are complicated by the

Thomas Skulski; Andrew Hynes; Don Francis

1988-01-01

54

Geochemistry of precambrian carbonates. II. Archean greenstone belts and Archean sea water  

SciTech Connect

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 {plus minus} 0.2 and {approximately}3.5 {plus minus} 0.1 Ga ago. The samples for the younger group are from the Abitibi, Yellowknife, Wabigoon, 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 {plus minus} 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 ({sup 87}Sr/{sup 86}Sr){sub o} of 0.7025 {plus minus} 0.0015 and 0.7031 {plus minus} 0.0008 for younger and older greenstones, respectively. The mineralogical and chemical attributes of Archean carbonates 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.

Veizer, J. (Univ. of Ottawa, Ontario (Canada)); Hoefs, J. (Geochemisches Institut der Universitat, Gottingen (West Germany)); Lowe, D.R. (Stanford Univ., CA (USA)); Thurston, P.C. (Ontario Geological Survey, Toronto (Canada))

1989-04-01

55

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

56

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

57

Stratigraphic framework of the ? 3.0 Ga Buhwa Greenstone Belt: a unique stable-shelf succession in the Zimbabwe Archean Craton  

Microsoft Academic Search

The ? 3.0 Ga Buhwa Greenstone Belt is the least understood major greenstone belt in the Archean Zimbabwe Craton, despite occupying a critical position adjacent to the Limpopo Belt. The cover succession at Buhwa consists of greenschist-facies sedimentary and subordinate volcanic rocks and is divisible into western shelf and eastern deeper-water basinal associations connected by a belt of transitional deposits.

Christopher M. Fedo; Kenneth A. Eriksson

1996-01-01

58

Petrology and geochemistry of metamorphosed komatiites and basalts from the Sula Mountains greenstone belt, Sierra Leone  

NASA Astrophysics Data System (ADS)

The Sula Mountains greenstone belt is the largest of the late-Archaean greenstone belts in the West African Craton. It comprises a thick (5km) lower volcanic formation and a thinner (2km) upper metasedimentary formation. Komatiites and basalts dominate the volcanic formation and komatiites form almost half of the succession. All the volcanic rocks are metamorphosed to amphibolite grade and have been significantly chemically altered. Two stages of alteration are recognised and are tentatively ascribed to hydrothermal alteration and later regional amphibolite facies metamorphism. Ratios of immobile trace elements and REE patterns preserve, for the most part, original igneous signatures and these are used to identify five magma types. These are: low-Ti komatiites - depleted in light REE; low-Ti komatiites - with flat REE patterns; high-Ti komatiitic basalts - with flat REE; low-Ti basalts - depleted in light REE; high-Ti basalts - with flat REE patterns. Much of the variation between the magma types can be explained in terms of different melt fractions of the mantle source, although there were two separate mantle sources one light REE depleted, the other not. The interleaving of the basalts and komatiites produced by this melting indicates that the two mantle sources were melted simultaneously. The simplest model with which to explain these complex melting processes is during melting within a rising mantle plume in which there were two different mantle compositions. The very high proportion of komatiites in the Sula Mountains relative to other greenstone belts suggests either extensive deep melting and/or the absence of a thick pre-existing crust which would have acted as a ``filter'' to komatiite eruption.

Rollinson, Hugh

59

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

60

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

61

Archaean greenstone belts of Sierra Leone with comments on the stratigraphy and metallogeny  

NASA Astrophysics Data System (ADS)

Four belts of weakly metamorphosed volcano-sedimentary material, of about 2700 Ma, are enclosed by older granulites, gneisses and migmatites in the eastern part, and (i) a basal ultramafic unit followed by (ii) mafic to feldspathic differentiate and then (iii) a terminal sedimentary formation has been recognized in all the four belts and their average ratio is ultramafic: mafic (greenstone): sedimentary unit (2:5:3). The belts are linear and tightly folded along N-S to NE-SW axis which is also the regional grain of the structures in the older basement complex that engulfs them. Structural and geochronological evidences suggest that the deformation of these volcano-sedimentary supracrustals began during the Liberian tectonism ( c. 2700 Ma) and culminated at the beginning of the Eburnean (2200 Ma). Diapiric rise of K-rich younger Aechaean granites which sharphy trangressed all the earlier rocks and their structural trends, marked the last geotectonic event in the Archaean of this part of West Africa. Chromite cumulate and asbestiform deposits characterize the layered ultramafic unit. whilst gold and associated base metal sulphides which were derived from the volcanic units became hydrothermally concentrated close to the contact between the volcanic units and the overlying sediments, and also in the fault zones. Iron ore deposits are restricted to the sedimentary units where they occur as banded iron formation. It is only in the huge metasedimetary piles of the Sula-Kangari belt that deposits of iron ore occur in commercially viable quantities. The patterns of distribution, deformation and mineralization in these greenstone belts appear to fit closely into island arc model of plate tectonic theory.

Umeji, A. C.

62

Albitization in the Antimony Line, Murchison Greenstone Belt (Kaapvaal Craton): A geochemical and geochronological investigation  

NASA Astrophysics Data System (ADS)

The 3.09-2.97 Ga Murchison Greenstone Belt is one of several Archean volcano-sedimentary belts within the Kaapvaal Craton in southern Africa. Among the diverse ore deposits found within the belt, a set of Sb-(± Au) deposits are located in a major quartz-carbonate altered brittle-ductile structure known as the Antimony Line. The Antimony Line is thus clearly related to hydrothermal fluid circulation. In this study, we focus on albitites that run along the Antimony Line. Petrological and geochemical investigations indicate that albitization developed at the expense of a granodioritic protoliths under high fluid/rock ratios and also that Sb enrichment was concomitant with albitization. Oxygen isotopes on albitites point to a crustal origin for the hydrothermal fluid responsible for the albitization process. Geochronology on zircon and hydrothermal monazite identifies a 2.97-2.92 Ga magmatic crystallization event, disconnected from a ca 2.8 Ga hydrothermal alteration, and a potentially younger event around 2.0 Ga. These data highlight a likely magmatic-related primary enrichment at 2.97-2.92 Ga, followed by a secondary metamorphic-related mobilization event around 2.8 Ga leading to a Sb-enrichment in the albitites and a last episode of alteration around 2.0 Ga.

Jaguin, Justine; Boulvais, Philippe; Poujol, Marc; Bosse, Valérie; Paquette, Jean-Louis; Vilbert, David

2013-05-01

63

Komatiites and island arc volcanics in Archean greenstone belts: biased preservation of a rare magmatic association  

NASA Astrophysics Data System (ADS)

The dominant volcanic rock in most Archean greenstone belts is submarine flood basalt that erupted in deep water, together with komatiite, to form oceanic plateaux. In many other parts of the same belts, komatiite lava flows are intercalated with volcanic rocks whose petrological and geochemical characteristics indicate that they erupted in island arcs. Although in some cases the komatiites and arc rocks are tectonically interleaved, in many other cases, firm geological and geochronological arguments establish that the two contrasting types of magma erupted simultaneously. The morphologies and textures of the komatiites and their geochemical characteristics eliminate the possibility that these magmas formed by hydrous melting in the mantle wedge above the subduction zone; rather they are the result of high-degree melting at great depth in an unusually hot, essentially anhydrous source, probably a mantle plume. The question then arises how komatiite magma from a deep, sub-subduction source reached the surface to form part of an island arc sequence. Neither the plume nor plume-derived magmas are likely to penetrate an actively subducting slab, and passage through slab windows is too haphazard to explain the frequency with which the rocks are associated. The probable explanation is that komatiite erupts far from the subduction zone, perhaps in volcanic plateaux on the adjacent oceanic plate. The diameter of Cretaceous plateaus such as Ontong Java reach 1400 km and the areas covered by high-volume magmas from hotter Archean plumes may be far larger. In this model, lavas from the oceanic plateaux apparently flowed across the hinge and trench, or across transforms, to alternate with subduction-derived lavas in the arc itself. The volume of komatiite within arc successions at the fringes of a plateau must be small compared with that in the oceanic plateaus themselves, and the association of komatiite with arc lavas can represent only a small fraction of the volcanic rocks that erupted in Archean oceanic basins. However, because the island arcs are composed of less dense rocks that normal oceanic crust or oceanic plateaux and because of their location at the margins of ocean basins they, and the intercalated komatiites, are preferentially preserved during the accretion of the volcanic sequences that now form Archean greenstone belts. Alternating komatiite and arc lavas represents a biased preservation of a rare magmatic association.

Arndt, N.

2003-04-01

64

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

65

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

66

Terrane amalgamation in the Eastern Goldfields Superterrane, Yilgarn Craton: Evidence from tectonostratigraphic studies of the Laverton Greenstone Belt  

Microsoft Academic Search

Tectonostratigraphic evolution of the Laverton Greenstone Belt involves amalgamation of structural relics of sedimentary basins and continental fragments in the Burtville Terrane to the east prior to their accretion to the Kurnalpi Terrane to the west. The Burtville Terrane records sedimentation and volcanism in a continental setting between ?2758Ma and ?2715Ma. The Kurnalpi Terrane is dominated by 2715–2700Ma andesitic volcaniclastic

Jonathan G. Standing

2008-01-01

67

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

68

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

69

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

70

Paleoarchean sulfur cycle and biogeochemical surface conditions on the early Earth, Barberton, South Africa  

NASA Astrophysics Data System (ADS)

This study presents the first multiple sulfur isotope dataset on sulfides from the ca. 3.5-3.2 Ga Onverwacht Group in the Paleoarchean Barberton Greenstone Belt (BGB) of South Africa. In situ ?34SCDT and ?33S values of pyrite (n=568) are reported from a wide range of hydrothermal, volcanic and sedimentary environments and are used to explore Mid-Archean biogeochemical sulfur cycling. Samples are from fresh drill core collected by the Barberton Scientific Drilling Project that intercepted cherts, metabasalts and sheared ultramafics of the ˜3.3-3.35 Ga Kromberg Formation; the sedimentary units of the ˜3.432 Ga Noisy formation; and the unconformably underlying metabasaltic pillow lavas of the ˜3.472 Ga Hooggenoeg Formation.

Grosch, Eugene G.; McLoughlin, Nicola

2013-09-01

71

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

72

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

73

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

74

Some Speculations Concerning The Abitibi Greenstone Belt As A Possible Analog To The Early Martian Crust  

NASA Astrophysics Data System (ADS)

The Noachian crust of Mars comprises basaltic and, potentially, komatiitic lavas derived from a hot mantle slightly more reducing and sulfur-rich than that of the Earth. Ultramafic volcanic sequences of the ~2.7Ga Tisdale Group of the Abitibi Greenstone Belt, Ontario, provide a potential analog to these early martian lavas. The Abitibi rocks are a possible source of quartz veins carrying, in places, pyrite, carbonate and gold. These were hydrothermally introduced into volcanic and sedimentary rocks during greenschist metamorphism. Kilometer-scale talc-magnesite zones, resulting from the carbonation of serpentinized ultramafics, may have been the source and seawater, with some magmatic addition, was probably responsible for the pervasive alteration, although the chemical nature of hydrothermal fluids circulating in such piles depends upon the temperature of wall-rock interactions and is largely independent of fluid origin. Any sulfides and gold in unaltered ultramafic putative source rocks may have been lost to the invasive convective fluids. Given high heat flow and the presence of a hydrosphere, hydrothermal convection cells were probably the main mechanism of heat transfer through the crust on both planets. Exploration of the Abitibi belt provides a template for possible martian exploration strategies. Orbital remote sensing indicates that some ultramafic rocks on Mars have also been serpentinized and isolated areas of magnesite have been recently discovered, overlying altered mafic crust, with characteristic ridges at scales of a few hundred meters. While cogent arguments have been made favoring sedimentary exhalative accumulations of hydrothermal silica of the kind that are known to harbor bacteria on our own planet, no in situ siliceous sinters or even quartz veins have been identified with certainty on Mars. Here, we report on the mineralogic and visible to infrared spectral characteristics of mafic and ultramafic lithologies at Abitibi for comparison to locations on Mars where hydrothermal activity has been proposed.

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

2011-12-01

75

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

76

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

77

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

78

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

79

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

80

Sedimentary Depositional Environment in the Nuvvuagittuq Greenstone Belt, Northeastern Superior Province, Canada  

NASA Astrophysics Data System (ADS)

Our knowledge of Earth's primitive surface environment is limited by the very few outcrops of demonstrably sedimentary rocks we have available. The Nuvvuagittuq Greenstone Belt (NGB) is an Eoarchean/Hadean volcano-sedimentary assemblage emplaced prior to 3.75 Ga (Cates and Mojzsis 2007) and likely as early as 4.28 Ga (O'Neil et al. 2008). Its recent discovery extends the inventory of available outcrops and pushes back the limit of time that we previously had access to. The rocks included within the NGB may represent Earth's oldest sedimentary rocks in the world and, in this respect, may provide crucial information about Earth's primitive surface environment. Our recent sampling of the NGB reveals three distinct sedimentary assemblages comprised of a sulfide-rich quartzite and two different types of banded iron formations (BIF). Here our aim is to constrain protoliths of these sedimentary rocks, with the aim of deducing the original depositional environments. Accordingly, we have mapped the relationships between the different lithologies in detail. The two BIF horizons are a few meters thick and run sub parallel to each other, separated by a horizon of cummingtonite-bearing amphibolite (previously referred to as Faux-amphibolite). Both contain cm-scale quartz-, magnetite-, and amphibole-rich laminations, but differ distinctly from each other. BIF 1 is very magnetite rich with quartz and is relatively poor in sulfides, while BIF 2 has large amounts of sulfides and green amphibolite, but is very poor in magnetite. The quartzite horizon is considerably larger (reaching thicknesses of ˜ 50 m) and is mainly formed of coarse quartz grains with minor disseminated sulfide grains. In order to supplement this field observation, we started a detailed petrological description and performed chemical analyses on our sample set. At the conference we will propose possible environmental deposition conditions for these rocks and reconstruct possible sedimentary protoliths. In addition we will present preliminary sulfur and iron isotope analyses that will allow further comparisons between the three sedimentary units.

Binnion, L.; Thomassot, E.; O'Neil, J.; Francis, D.; Busigny, V.; Wing, B.

2009-05-01

81

Lithofacies associations and structural evolution of the Archean Rio das Velhas greenstone belt, Quadrilátero Ferrífero, Brazil: A review of the setting of gold deposits  

Microsoft Academic Search

The Rio das Velhas greenstone belt is located in the Quadrilátero Ferrífero region, in the southern extremity of the São Francisco Craton, central-southern part of the State of Minas Gerais, SE Brazil. The metavolcano–sedimentary rocks of the Rio das Velhas Supergroup in this region are subdivided into the Nova Lima and Maquiné Groups. The former occurs at the base of

O. F. Baltazar; M. Zucchetti

2007-01-01

82

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

NASA Astrophysics Data System (ADS)

The occurrence of the Holenarasipur greenstone belt is explained by accretionary process at a trench. A sequence of amphibolite (MORB), chert, and banded iron formation associated with komatiitic amphibolite (oceanic island material) is an Archaean analogue to the modern oceanic crust grown through the migration from an active ridge to a trench. At a trench, slices of such a sequence mixed with or became covered by turbidite from land mass (quartzite and conglomerate) to form an accretionary complex. Available SHRIMP data suggest the synchronous formation of nearby tonalite-trondhjemite-granodiorite (TTG) with the greenstone belt by melting of subducting oceanic plate. The Dharwar craton has been built up stepwise: (1) Sargur stage—ocean-ocean collision to form oceanic island arc with TTG and an accretionary complex (older greenstone belt), followed by the collision of such arcs to form mini-continents at the early to middle Archaean (unit 3.0 Ga); (2) Dharwar stage—the amalgamation of mini-continents with newer accretionary complexes (younger greenstone belt) under the same subduction polarity caused by the change from two layered to whole mantle convection with the progressive cooling of the earth (3.0-2.5 Ga). The cessation of TTG activity was also due to the cooling of the earth. Tectospheric peridotite keel formed with TTG has acted as a thermal insulator to stabilize the Dharwar craton after the Archaean.

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

83

The Geology of Nuvvuagittuq Greenstone Belt and its Implications for the Early Earth's Evolution  

E-print Network

of the degree of Doctor of Philosophy Copyright © 2009, Jonathan O'Neil #12;Abstract The Nuvvuagittuq greenstone a basaltic to andesitic composition. It is composed of variable proportions of cummingtonite + biotite-amphibolite is basaltic in composition and has "tholeitic" affinities. The low-Ti faux-amphibolite above the BIF exhibits

84

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

85

The Fazenda Gavião granodiorite and associated potassic plutons as evidence for Palaeoproterozoic arc-continent collision in the Rio Itapicuru greenstone belt, Brazil  

NASA Astrophysics Data System (ADS)

Several granitic plutons have intruded the Palaeoproterozoic Rio Itapicuru greenstone belt, São Francisco craton, Brazil, in the time interval 2163-2080 Ma, but their tectonic significance is poorly understood. The Fazenda Gavião granodiorite (FGG) is one of a set of plutons emplaced along the western boundary of the greenstone belt with Archaean migmatite-gneiss basement. The pluton is mostly composed of hornblende granodiorite, occasionally crosscut by syn-plutonic mafic dykes. The FGG is metaluminous, medium- to high-K calc-alkaline with relatively constant silica abundances (SiO2 ? 63-66 wt%), high Sr (900-800 ppm) and high Ba (1000-1500 ppm). The associated mafic dykes are ultrapotassic, with high abundances of Ba, Sr, MgO, Ni, Cr, and light rare earth elements, suggesting derivation from partial melts of an enriched mantle source. The FGG originated probably by fractional crystallization from a primitive K-rich mafic magma that interacted with crustal melts. Its zircon U-Pb SHRIMP age of 2106 ± 6 Ma indicates that the FGG is younger than the early (2163-2127 Ma) tonalite-trondhjemite-granodiorite (TTG) and calc-alkaline arc plutons of the greenstone belt, and is closely related in time and space with potassic to ultrapotassic plutons (ca. 2110-2105 Ma). The negative ?Nd(t) of FGG and coeval K-rich plutons of the Rio Itapicuru greenstone belt contrasts markedly with the positive ?Nd(t) of the older arc plutons, indicating a major change of isotope signatures in granites of the Rio Itapicuru greenstone belt with time. This isotope shift may be related to magma contamination with older continental material and/or derivation of the parental potassic magma from enriched lithospheric mantle sources. We suggest that the K-rich plutons were emplaced during or shortly after Palaeoproterozoic arc-continent collision.

Costa, Felipe G.; Oliveira, Elson P.; McNaughton, Neal J.

2011-08-01

86

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

87

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

Microsoft Academic Search

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

Andrew Glikson; John Vickers

2006-01-01

88

Geochronology of the North Caribou greenstone belt, Superior Province Canada: Implications for tectonic history and gold mineralization at the Musselwhite Mine  

Microsoft Academic Search

The ?3 Ga North Caribou greenstone belt comprises a package of volcanic and sedimentary rocks metamorphosed from greenschist to upper amphibolite grade, surrounded by ?2.7 to 3.0 Ga granitoids and gneisses and is host to the Musselwhite gold mine, a large orogenic gold deposit. New U-Pb (zircon, monazite), Ar-Ar (biotite) and Sm-Nd (garnet) ages for volcanic, sedimentary and intrusive rocks

John Biczok; Pete Hollings; Paul Klipfel; Larry Heaman; Roland Maas; Mike Hamilton; Sandra Kamo; Richard Friedman

89

Geochemistry of shales from the Archean (~3.0 Ga) Buhwa Greenstone Belt, Zimbabwe: Implications for provenance and source-area weathering  

Microsoft Academic Search

Phyllites from the Archean (~3.0 Ga) Buhwa Greenstone Belt, Zimbabwe, were deposited on a stable cratonic platform. Analyses of the phyllites generally define a single geochemical group based on major-and trace-element abundances. The phyllites are strongly depleted in CaO, Na2O, and Sr with respect to average Archean upper crust. By contrast, K2O, Ba, and Rb are enriched several times relative

Christopher M. Fedo; Kenneth A. Eriksson; Eirik J. Krogstad

1996-01-01

90

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

91

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

NASA Astrophysics Data System (ADS)

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 Teofilândia tonalite. The emplacement age of the syntectonic Ambrósio 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 Ambrósio 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.

Mello, Edson F.; Xavier, Roberto P.; McNaughton, Neal J.; Hagemann, Steffen G.; Fletcher, Ian; Snee, Larry

2006-03-01

92

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

93

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

94

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

95

Chromitites of komatiitic affinity from the Archaean Nuggihalli greenstone belt in South India  

NASA Astrophysics Data System (ADS)

Mineral chemistry and petrological data of chromites from chromitite bands in the N S trending schist belt of Nuggihalli (southern Karnataka, India), belonging to the Dharwar craton of South India, are presented in this paper. Crystal chemical data indicate a komatiitic affinity of the chromitite. P T calculations of the chromite-hosting peridotites yielded a pressure range of 13 to 28 kbar and temperatures ranging from 775 to 1080 °C; the oxygen fugacity (log fO2) varies from +0.5 to +1.6 above the QFM buffer. The P, T and fO2 data indicate that Nuggihalli chromitites crystallized in an environment akin to the upper mantle. The studied samples also show partial resetting; the lower temperatures ranging from 515 to 680 °C are ascribed to subsequent metamorphism of the area.

Bidyananda, M.; Mitra, S.

2005-07-01

96

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

97

Metallogeny of precious and base metal mineralization in the Murchison Greenstone Belt, South Africa: indications from U-Pb and Pb-Pb geochronology  

NASA Astrophysics Data System (ADS)

The 3.09 to 2.97 Ga Murchison Greenstone Belt is an important metallotect in the northern Kaapvaal Craton (South Africa), hosting several precious and base metal deposits. Central to the metallotect is the Antimony Line, striking ENE for over 35 km, which hosts a series of structurally controlled Sb-Au deposits. To the north of the Antimony Line, hosted within felsic volcanic rocks, is the Copper-Zinc Line where a series of small, ca. 2.97 Ga Cu-Zn volcanogenic massive sulfide (VMS)-type deposits occur. New data are provided for the Malati Pump gold mine, located at the eastern end of the Antimony Line. Crystallizations of a granodiorite in the Malati Pump Mine and of the Baderoukwe granodiorite are dated at 2,964 ± 7 and 2,970 ± 7 Ma, respectively (zircon U-Pb), while pyrite associated with gold mineralization yielded a Pb-Pb age of 2,967 ± 48 Ma. Therefore, granodiorite emplacement, sulfide mineral deposition and gold mineralization all happened at ca. 2.97 Ga. It is, thus, suggested that the major styles of orogenic Au-Sb and the Cu-Zn VMS mineralization in the Murchison Greenstone Belt are contemporaneous and that the formation of meso- to epithermal Au-Sb mineralization at fairly shallow levels was accompanied by submarine extrusion of felsic volcanic rocks to form associated Cu-Zn VMS mineralization.

Jaguin, J.; Poujol, M.; Boulvais, P.; Robb, L. J.; Paquette, J. L.

2012-10-01

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

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

100

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

NASA Astrophysics Data System (ADS)

The Kalahari Goldridge Mine is located within the Archaean Kraaipan Greenstone Belt, about 60 km southwest of Mafikeng in the North West Province, South Africa. The ore body thickness varies from 15 to 45 m along a strike length of about 1.5 km within approximately N-S striking banded iron formation (BIF). The stratabound ore body is hosted primarily by BIF, which consists of alternating chert and magnetite-chlorite-stilpnomelane-sulphide-carbonate bands of millimetre- to centimetre scale. A footwall of sericite-carbonate-chlorite schist underlain by mafic amphibolite occurs to the west and carbonaceous metapelites in the hanging wall to the east. Overlying the hanging wall, carbonaceous metapelites, units of coarse-grained metagreywackes fining upwards, become increasingly conglomeratic up the stratigraphy. Small-scale isoclinal folds, brecciation, extension fractures and boudinage of cherty BIF units reflect brittle-ductile deformation. Fold axial planes have foliation, with subvertical plunges parallel to prominent rodding and mineral lineation in the footwall rocks. Gold mineralisation is associated with two generations of quartz-carbonate veins, dipping approximately 20° to 40° W. The first generation consists of ladder-vein sets (group IIA) preferentially developed in centimetre-scale Fe-rich mesobands, whereas the second generation consists of large quartz-carbonate veins (group IIB), which locally crosscut the entire ore body and extend into the footwall and hanging wall. The ore body is controlled by mesoscale isoclinal folds approximately 67° E, orthogonal to the plane of mineralised, gently dipping veins, defining the principal stretching direction and development of fluid-focussing conduits. The intersections of the mineralised veins and foliation planes of the host rock plunges approximately 08° to the north. Pervasive hydrothermal alteration is characterised by chloritisation, carbonatisation, sulphidation and K-metasomatism. Gold is closely associated with sulphides, mainly pyrite and pyrrhotite, and to a lesser extent, with bismuth tellurides and carbonate minerals. Mass balance transfer calculations indicate that hydrothermal alteration of BIF involved enrichment of Au, Ag, Bi, Te, S and CO2 (LOI), MgO, Ba, K and Rb, but significant depletion of SiO2 and, to a lesser extent, Fe2O3. Extensive replacement of magnetite and chlorite in BIF and other pelitic sedimentary rocks by sulphide and carbonate minerals, both on mesoscopic and microscopic scales, is evidence of interaction of CO2- and H2S-bearing fluids with the Fe-rich host rocks. The fineness of gold grains ranges from 823 to 921, similar to that of other epigenetic Archaean BIF-hosted gold deposits, worldwide.

Hammond, Napoleon Q.; Moore, John M.

2006-08-01

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

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

103

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

104

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

E-print Network

published positive conglomerate test (Y. Usui, J.A. Tarduno, M. Watkeys, A. Hofmann and R.D. Cottrell, 2009) and our new U­Pb date constrains the conglomerate to older than 3455±8 Ma. The new palaeomagnetic data. On the basis of this enhanced consistency in stratigraphic coordinates, the positive conglomerate test

Utrecht, Universiteit

105

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

106

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

107

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

108

Brazil's premier gold province. Part II: geology and genesis of gold deposits in the Archean Rio das Velhas greenstone belt, Quadrilátero Ferrífero  

NASA Astrophysics Data System (ADS)

Orogenic, gold deposits are hosted by rocks of the Archean Rio das Velhas greenstone belt in the Quadrilátero Ferrífero region, Minas Gerais state, Brazil, one of the major gold provinces in the world. The gold deposits occur at the base of the mafic-ultramafic succession, with the most important orebodies controlled by E-W-striking, strike-slip faults. The main mineralization styles are (1) structurally controlled, sulfide replacement zones in banded iron formation (BIF); (2) disseminated sulfide minerals and gold in hydrothermally altered rocks along shear zones; and (3) auriferous quartz-carbonate-sulfide veins and veinlets in mafic, ultramafic, and felsic volcanic rocks, and also in clastic sedimentary rocks. The most common host rocks for ore are metamorphosed oxide- and carbonate-facies banded iron (± iron-rich metachert) formations (e.g., the Cuiabá, São Bento and Raposos deposits) and the lapa seca unit, which is a local term for intensely carbonatized rock (e.g., the giant Morro Velho mine with >450 t of contained gold). Metabasalts host most of the remaining gold deposits. Mineralogical characteristics and fluid inclusion studies suggest variations in the H2O/CO2 ratio of a low-salinity, near-neutral, reducing, sulfur-bearing, ore fluid. The presence of abundant CH4-rich inclusions is related to reduction of the original H2O-CO2 fluid via interaction with carbonaceous matter in the wallrocks. Oxygen fugacity was close to that of graphite saturation, with variations likely to have been influenced by reaction with the carbonaceous matter. Carbon-rich phyllites and schists, which commonly bound ore-bearing horizons, seem to have played both a physical and chemical role in localizing hydrothermal mineral deposition. Microtextural studies indicate that gold deposition was mainly related to desulfidation reactions, and was paragenetically coeval with precipitation of arsenic-rich iron sulfide minerals. Carbon isotope data are compatible with dissolution of CO2 from pre-existing mantle-derived carbonation zones, and indicate fluids of metamorphic origin. A major episode of hydrothermal fluid introduction into different rock types caused epigenetic gold formation and wallrock alteration at about 300 to 400 °C during the late stages of regional deformation and metamorphism of the greenstone belt. The age of gold mineralization is constrained to be younger than 2,698 and perhaps closer to 2,670 Ma.

Lobato, Lydia; Ribeiro-Rodrigues, Luiz; Vieira, Frederico

2001-07-01

109

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

110

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

111

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

112

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

NASA Astrophysics Data System (ADS)

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 of conformable gabbroic and ultra mafic sills. Minor horizons in the belt include banded iron formations (BIF) with cm-scale quartz-rich and magnetite-rich laminations, and a pyrite-bearing quartzite in gradational contact with the BIF. These rocks and may represent the oldest remains of the sedimentary record on Earth. We performed multiple O-isotope measurements of individual minerals (quartz, garnet, amphibole and magnetite) from three NGB lithologies (BIF, faux amphibolites and quartzite). In BIF samples, ?18O values cover a narrow range (from 1.36 per mil magnetite to 4.98 per mil with one outlier at 9.99 per mil), whereas silicate minerals in the faux reveal a more scattered range that is more depleted in light isotopes (7.77 per mil ? ?18O ? 13.38 per mil). One quartzite sample has also been analyzed and reveals the most 16O-depleted composition yet measured from the belt (?18O = 15.44 per mil). The ?17O and ?18O values from these samples define a fractionation line for multiple oxygen isotopes with a slope of 0.528 ± 0.004 (MSWD = 0.47), statistically indistinguishable from the slope (0.524 +± 0.002) of the Archean Terrestrial Fractional Line (TFL) determined from other Archean rocks and minerals. These results show no evidence for the drastic O-isotope heterogeneity that would likely accompany the late heavy bombardment of the Earth-Moon system. We also performed multiple S-isotope ratio measurements (?34S, ?33S, ?36S) in samples covering the entire lithological suite of the NGB. Samples from the quartzite and BIF display a narrow range of ?34S values (0.8 per mil ? ?34S ? 3.3 per mil), in good agreement with ranges reported so far from early Archean sediments. The same samples exhibit non-zero ?33S and ?36S values (respectively ranging from 0.18 to 2.27 per mil and from -2.9 per mil to -0.6 per mil) that are negatively correlated (?36S ~ -0.9 ?33S) and conform to the linear array that characterizes most of the Archean Eon. Finally, the NGB BIF and silica formation reveal a tight correlation between ?33S and ?34S values (?33S ~ 0.9 ?34S) that matches previous observations from Neoarchean and Paleoarchean samples. In previous studies, the ?34S - ?33S - ?36S correlations observed here have been taken to reflect both a restricted chemistry of the atmosphere and a dynamic microbiologically-dominated sulfur cycle. Taken together, and considering the age of the NGB, the S- and O-isotope results suggest that conditions conducive to life on Earth were established very early in Earth's history. Either there was apparently no significant perturbation of the early Earth system by the late heavy bombardment, or the rocks of the NGC record a time interval that was not affected by this dramatic event. This talk will explore the implications of these two possibilities for the early establishment of a stable environment suitable for the emergence of life.

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

2009-05-01

113

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

114

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

115

Multiple sulfur and carbon isotope composition of sediments from the Belingwe Greenstone Belt (Zimbabwe): A biogenic methane regulation on mass independent fractionation of sulfur during the Neoarchean?  

NASA Astrophysics Data System (ADS)

To explore the linkage between mass-independent sulfur isotope fractionation (MIF-S) and ?13Corg excursions during the Neoarchean, as well as the contemporary redox state and biogeochemical cycling of carbon and sulfur, we report the results of a detailed carbon and multiple sulfur (?34S, ?33S, ?36S) isotopic study of the ?2.7 Ga Manjeri and ?2.65 Ga Cheshire formations of the Ngezi Group (Belingwe Greenstone Belt, Zimbabwe). Multiple sulfur isotope data show non-zero ?33S and ?36S values for sediments older than 2.4 Ga (i.e. prior to the Great Oxidation Event, GOE), indicating MIF-S thought to be associated with low atmospheric oxygen concentration. However, in several 2.7-2.5 Ga Neoarchean localities, small-scale variations in MIF-S signal (magnitude) seem to correlate with negative excursion in ?13Corg, possibly reflecting a global connection between the relative reaction rate of different MIF-S source reaction and sulfur exit channels and the biogenic flux of methane into the atmosphere during periods of localized, microbiologically mediated, shallow surface-water oxygenation. The Manjeri Formation black shales studied here display a wide range of ?13Corg between -35.4‰ and -16.2‰ (average of -30.3 ± 6.0‰, 1?), while the Cheshire Formation shales have ?13Corg between -47.7‰ and -35.1‰ (average -41.3 ± 3‰, 1?). The ?34S values of sedimentary sulfides from Manjeri Formation vary between -15.15‰ and +2.37‰ (average -1.71 ± 4.76‰, 1?), showing very small and mostly negative ?33S values varying from -0.58‰ to 0.87‰ (average 0.02 ± 0.43‰, 1?). Cheshire Formation black shale sulfide samples measured in this study have ?34S values ranging from -2.11‰ to 2.39‰ (average 0.25 ± 1.08‰, 1?) and near zero and solely positive ?33S anomalies between 0.14‰ and 1.17‰ (average 0.56 ± 0.29‰, 1?). Moreover, ?36S/?33S in the two formations are comparable with a slope of -1.38 (Manjeri Formation) and -1.67 (Cheshire Formation), respectively. This differs from the Archean reference line (i.e. -0.9). The sulfur and carbon isotopic signatures recorded here likely reflect different environmental conditions and/or ecosystems within the sampled Cheshire and Manjeri formations paleofacies. The differences in carbon isotopes in different sedimentological facies are interpreted as recording different metabolic pathways, including photosynthesis, methanogenesis and methanotrophy. Low ?13Corg values in the Cheshire Formation black shales suggest a strong influence of methanotrophy (likely preceded by bacterial methanogenesis), while the large range of Manjeri Formation ?34S may record bacterial sulfate reduction. The C and multiple S isotopic variations recorded here may imply different patterns of C and S fractionation, perhaps dependent on variations in the biogenic egress of methane to the atmosphere.

Thomazo, Christophe; Nisbet, Euan G.; Grassineau, Nathalie V.; Peters, Marc; Strauss, Harald

2013-11-01

116

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

117

Sulfur-and oxygen-isotope constraints on the sedimentary history of apparent conglomerates from the Nuvvuagittuq Greenstone  

E-print Network

igneous rocks of the Nuvvuagittuq Greenstone Belt (NGB) crystallized before 3.8 Ga and possibly as early or less. These appear to be inconsistent with the ages of the mafic igneous rocks, as the quartz Earth as some mafic volcanic rocks from the Nuvvuagittuq Greenstone Belt (NGB, Ungava peninsula, Nunavik

Long, Bernard

118

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

119

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

120

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

121

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

122

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

123

Cosmos greenstone terrane: Insights into an Archaean volcanic arc, associated with komatiite-hosted nickel sulphide mineralisation, from U-Pb dating, volcanic stratigraphy and geochemistry   

E-print Network

The Neoarchaean Agnew-Wiluna greenstone belt (AWB) of the Kalgoorlie Terrane, within the Eastern Goldfields Superterrane (EGS) of the Yilgarn Craton, Western Australia, contains several world-class, komatiite-hosted, ...

De Joux, Alexandra; Joux, Alexandra de

2014-06-30

124

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

125

Insights into early Earth from the Pt-Re-Os isotope and highly siderophile element abundance systematics of Barberton komatiites  

NASA Astrophysics Data System (ADS)

Highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, and Re) abundance and Pt-Re-Os isotopic data are reported for well-preserved komatiites from the Komati and Weltevreden Formations of the Barberton Greenstone Belt in South Africa. The Re-Os data for whole-rock samples and olivine and chromite separates define isochrons with ages of 3484 ± 38 and 3263 ± 12 Ma for the Komati and Weltevreden systems, respectively. The respective initial 187Os/188Os = 0.10335 ± 15 (?187Os = +0.34 ± 0.15) and 0.10442 ± 4 (?187Os = -0.14 ± 0.04) are well within the range defined by chondritic meteorites. When considered together with the Re-Os data for late Archean komatiite systems, these data indicate that the mantle sources of most Archean komatiites evolved with essentially uniform long-term Re/Os that is well within the chondritic range. By contrast, the initial 186Os/188Os = 0.1198283 ± 9 (?186Os = -0.12 ± 0.08) and 0.1198330 ± 8 (?186Os = +0.22 ± 0.07) for the Komati and Weltevreden systems, respectively, are outside of known chondritic evolution paths, indicating that the mantle sources of these two komatiite systems evolved with fractionated time-integrated Pt/Os. The new 186,187Os isotopic data for these early Archean komatiite systems, combined with published 142,143Nd and 176Hf isotopic data for these systems, are consistent with formation and long-term isolation of deep-seated mantle domains with fractionated time-integrated Sm/Nd, Lu/Hf, and Pt/Os ratios, at ca. 4400 Ma. These domains may have been generated as a result of late-stage crystallization of a primordial magma ocean involving Mg-perovskite, Ca-perovskite and Pt-alloys acting as the fractionating phases. The inferred fractionated mantle domains were sampled by the early Archean komatiites, but were largely mixed away by 2.7 Ga, as evidenced by uniform time-integrated Sm/Nd, Lu/Hf, and Pt/Os ratios inferred for the sources of most late Archean komatiite systems. The calculated total Pt + Pd abundances present in the sources of the early Archean komatiite systems fall only 7-14% short of those present in estimates for the modern primitive mantle. These are also within the range of the total Pt + Pd abundances present in the sources of late Archean komatiite systems, indicating little change in the HSE abundances in the Archean mantle between 3.5 and 2.7 Ga. The new HSE data for the early Archean komatiite systems may implicate late accretion of HSE to the mantle prior to completion of crystallization of a final terrestrial magma ocean, followed by sluggish mixing of diverse, post-magma ocean domains characterized by variably fractionated lithophile element and HSE abundances.

Puchtel, Igor S.; Walker, Richard J.; Touboul, Mathieu; Nisbet, Euan G.; Byerly, Gary R.

2014-01-01

126

On shearing, magmatism and regional deformation in Neoarchean granite-greenstone systems: Insights from the Yilgarn Craton  

NASA Astrophysics Data System (ADS)

The structure of the Neoarchean Yilgarn Craton is dominated by craton-scale high-strain zones, mostly associated with highly-deformed elongate granitic bodies and transposed greenstone belts. These shear zones developed during widespread and prolonged magmatic activity that led to a nearly complete reworking of the felsic continental crust. The spatial, temporal and genetic relationships between such a voluminous and protracted event of crustal reworking and the development of the craton-scale shear zone network are unclear. Here, we combine new structural, geophysical and geochemical data to investigate the relationship between crustal-scale shear zones and large syntectonic plutons in the Yilgarn Craton of Western Australia. We propose that Archean granite-greenstone systems may have commonly evolved through the interaction of three fundamental geological processes: (I) emplacement of large scale syntectonic plutons; (II) activity of crustal-scale shear zones; (III) pervasive, largely syn-metamorphic polyphase deformation in greenstone belts adjacent to syntectonic plutons. We propose that the concept of “Archean regional deformation event” need to be reassessed: a regional event is probably pluton- (or batholith-) size, and the structural/metamorphic evolution of adjacent greenstone belts might have proceeded quite independently and potentially in a time-transgressive way, if those belts were not spatially related to the same syntectonic pluton.

Zibra, I.; Gessner, K.; Smithies, H. R.; Peternell, M.

2014-10-01

127

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

128

PGE, Re-Os, and Mo isotope systematics in Archean and early Proterozoic sedimentary systems as proxies for redox conditions of the early Earth  

Microsoft Academic Search

Re-Os data and PGE concentrations as well as Mo concentrations and isotope data are reported for suites of fine clastic sediments and black shales from the Barberton Greenstone Belt, South Africa (Fig Tree and Moodies Groups, 3.25–3.15 Ga), the Belingwe Greenstone Belt, Zimbabwe (Manjeri Formation, ca. 2.7 Ga) and shales from the Witwatersrand, Ventersdorp and Transvaal Supergroups, South Africa ranging

C. Siebert; J. D. Kramers; Th. Meisel; Ph. Morel; Th. F. Nägler

2005-01-01

129

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

130

Episodic granitoid emplacement in the western Kaapvaal Craton: evidence from the Archæan Kraaipan granite-greenstone terrane, South Africa  

NASA Astrophysics Data System (ADS)

Field, petrological, geochemical, isotopic and geophysical data have been assembled to determine the nature and extent of Archæan Kraaipan granite-greenstone rocks on the western edge of the Kaapvaal Craton, southern Africa. The Kraaipan greenstone belts, consisting of metamorphosed mafic volcanic rocks and interlayered metasediments (mainly banded iron formations, jaspilites and ferruginous cherts), occur poorly exposed beneath cover sequences comprising mainly Neoarchæan Ventersdorp Supergroup volcanic rocks and a blanket of Tertiary-Recent Kalahari sediments. A variety of granitoid rocks intruded the Kraaipan greenstones, which, on the basis of whole rock Pb?Pb dating of banded iron formations, have yielded an age of 3410+61/-64 Ma. The earliest granitic rocks, which comprise tonalites and trondhjemitic gneisses, were dated using the single grain Pb evaporation technique on zircons, and yielded minimum ages ranging from 3162±8 to 3070±7 Ma in the study area. This, coupled with 3250-3030 Ma ages reported for gneisses in the Kimberley and other areas on the western edge of the Kaapvaal Craton, suggests a prolonged evolution for the basement gneisses which were also disturbed between 2940 and 2816 Ma ago, probably during episodes of migmatisation. Potassium-rich granitoids, also dated using the single grain Pb evaporation method, range in age from 2880±2 to 2846±22 Ma and extend from the Schweizer-Reneke area in the south to the Botswana border and beyond in the north. Geophysical evidence (aeromagnetic and Bouguer gravity data) suggest that the intrusions may be interconnected and might have been emplaced episodically across the study area. A close spatial relationship exists between these granodiorites and adamellites, and known Au mineralisation present in the Kraaipan-Madibe areas in the north and the Amalia area in the south. This suggests a possible genetic link which could be of significance in mineral exploration. Lastly, a late granitoid pluton, the Mosita Adamellite, yielded a Pb evaporation age of 2749±3 Ma and is the youngest intrusive body recorded in the Kraaipan granite-greenstone terrane. Its presence beneath Kalahari sand cover is defined by Bouguer gravity data. The Kraaipan granite-greenstone terrane, with a prominent north-south trend, appears to represent an Archæan crustal segment that may have accreted episodically on to the western edge of the Kaapvaal Craton. In a manner similar to the Murchison granite-greenstone terrane in the northeastern part of the craton, the region may also have constituted an important potential source of placer Au mineralisation found in the Witwatersrand Basin.

Anhaeusser, Carl R.; Walraven, Feo

1999-02-01

131

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

132

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

133

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

NASA Astrophysics Data System (ADS)

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.

1985-05-01

134

Barberton drilling project - Buck Reef Chert core BARB3  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

135

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

136

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.

2012-06-26

137

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

138

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

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

139

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 ...

140

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

141

The Cl ? Br ? I ? composition of ?3.23 Ga modified seawater: implications for the geological evolution of ocean halide chemistry  

Microsoft Academic Search

Fluid inclusion leachates obtained from vug and vein quartz samples from an Archean (?3.23 Ga) Fe-oxide hydrothermal deposit in the west-central part of the Barberton greenstone belt, South Africa, were analyzed by ion chromatography for chloride, bromide, and iodide. The deposit, known as the ironstone pods, formed by seafloor hydrothermal activity and fluid discharge. Quartz is dominated by type I

D. M. De R. Channer; C. E. J. de Ronde; E. T. C. Spooner

1997-01-01

142

The Cl - -Br - -I - composition of ~ 3.23 Ga modified seawater: implications for the geological evolution of ocean halide chemistry  

Microsoft Academic Search

Fluid inclusion leachates obtained from vug and vein quartz samples from an Archean (~ 3.23 Ga) Fe-oxide hydrothermal deposit in the west-central part of the Barberton greenstone belt, South Africa, were analyzed by ion chromatography for chloride, bromide, and iodide. The deposit, known as the ironstone pods, formed by seafloor hydrothermal activity and fluid discharge. Quartz is dominated by type

D. M. der. Channer; C. E. J. de Ronde; E. T. C. Spooner

1997-01-01

143

Platinum group elements in a 3. 5 Ga nickel-iron occurrence: Possible evidence of a deep mantle origin  

Microsoft Academic Search

The Bon Accord (BA) Ni-Fe deposit occurs in chemically depleted ultramafic rocks of the circa 3.5 Ga Jamestown opholite complex in the Barberton greenstone belt of the Kaapvaal craton, South Africa. BA is unusual both mineralogically and chemically. It consists of a rare Ni-rich assemblage: Ni-oxide (bunsenite), -spinels (trevorite, nichromite), and -silicates (e.g., liebenbergite, the Ni end-member olivine) and their

Marian Tredoux; R. J. Hart; N. M. Lindsay; J. P. F. Sellschop; M. J. de Wit; R. A. Armstrong

1989-01-01

144

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

145

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

146

Dynamic characteristics of conveyor belts  

Microsoft Academic Search

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

You-fu HOU; Qing-rui MENG

2008-01-01

147

The Gould Belt  

NASA Astrophysics Data System (ADS)

This review is devoted to studies of the Gould belt and the Local system. Since the Gould belt is the giant stellar-gas complex closest to the sun, its stellar component is characterized, along with the stellar associations and diffuse clusters, cold atomic and molecular gas, high-temperature coronal gas, and dust contained in it. Questions relating to the kinematic features of the Gould belt are discussed and the most interesting scenarios for its origin and evolution are examined.

Bobylev, V. V.

2014-12-01

148

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

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

149

Fluid inclusion studies of gold-bearing quartz veins from the Yirisen deposit, Sula Mountains greenstone belt, Masumbiri, Sierra Leone  

Microsoft Academic Search

The auriferous veins at Yirisen, Masumbiri, Sierra Leone, occurring mainly in the form of sericitic quartz-sulphide lodes and stringers, are hosted in metamorphosed volcano-sedimentary assemblages invaded by at least two generations of granitic intrusions. Detailed microthermometric studies of fluid inclusions from the veins coupled with laser Raman spectroscopic analysis show that the inclusions contain aqueous fluids of variable salinity (5

Ibrahim J. Barrie; Jacques L. R. Touret

1999-01-01

150

Platinum-group mineral occurrence associated with flow top amygdule sulfides in komatiitic basalt, Abitibi Greenstone Belt, Ontario  

Microsoft Academic Search

Summary Platinum-group mineral (PGM)-bearing amygdule Fe-Ni(±Cu) sulfide has been discovered in samples of amygdaloidal basalt and underlying olivine spinifex-textured basalt from the flow top of Fred's Flow, Munro Township, Ontario. The amygdules are rounded to slightly elongate in shape, up to 10 mm in diameter, filled by chlorite + quartz ± carbonate ± sulfide, and rimmed by relict igneous chromite

W. E. Stone; J. H. Crocket; M. E. Fleet

1996-01-01

151

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

152

Precambrian Cratons and Fold-Belts in Brazil: Overview  

NASA Astrophysics Data System (ADS)

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

Fuck, R.

2008-05-01

153

Geochemistry of two stratigraphically-related ultramafic (komatiite) layers from the Neoarchean Sigegudda greenstone terrane, Western Dharwar Craton, India: Evidence for compositional diversity in Archean mantle plumes  

NASA Astrophysics Data System (ADS)

Two compositionally different ultramafic units are present in the Neoarchean Sigegudda greenstone terrane, Western Dharwar Craton, India. These ultramafic units occur in the same volcano-sedimentary sequence and are separated by a fault-bounded volcanic arc association. Because of deformation and amphibolite facies metamorphism, the primary igneous textures have been extensively modified in both ultramafic units. Given their spatial and temporal association with sedimentary and volcanic rocks and high MgO contents (12-29 wt.%), these ultramafic rocks are interpreted as metamorphosed komatiites and komatiitic basalts. Field relationships and rock types indicate that the lower section of the Sigegudda volcano-sedimentary sequence was deposited in a peri-cratonic, continental rift setting. The lower ultramafic unit is characterized by 12.4-29.6 wt.% MgO, Mg# = 76-91, and 526-1150 ppm Ni. The upper ultramafic unit is overall more magnesian and compositionally restricted: MgO = 21.6-25.9 wt.%, Mg# = 86-89, and Ni = 610-1000 ppm. The lower unit features a combination of relatively elevated TiO2 (0.40-0.90 wt.%), Al2O3/TiO2 ? the chondritic ratio of 21, and (Gd/Yb)N ratios > 1; these are Ti-enriched komatiites reported for the first time from greenstone belts in the Dharwar Craton. The upper unit is compositionally comparable to Al-undepleted komatiites and characterized by Al2O3/TiO2 ? 21, LREE-depletion coupled with near-flat chondrite-normalized HREE patterns. Geochemical data indicate that the Sigegudda komatiites and komatiitic basalts were variably contaminated by either continental crust or sub-continental lithospheric mantle, or both. The geochemical differences between the two units are explained by variable depths and degrees of partial melting. The Ti-enriched lower unit appears to have been formed through lower degrees of partial melting at depths ? 90 km, whereas the Al-undepleted upper unit was generated by higher degrees of partial melting at depths ? 90 km. Field relationships and geochemical characteristics of the Sigegudda komatiites can be explained by a geodynamic model in which the stratigraphically lower Ti-enriched komatiites were erupted from a mantle plume onto a rifting continental margin, whereas the stratigraphically upper Al-undepleted komatiites originated from a younger mantle plume and erupted onto a volcanic arc sequence that accreted to the rifted continental margin.

Manikyamba, C.; Kerrich, Robert; Polat, A.; Saha, Abhishek

2013-09-01

154

Radiation Belts and Trapped Particles  

NSDL National Science Digital Library

This tutorial introduces students to Earth's radiation belts, also known as the Van Allen Belts after their discoverer. Topics include the structure of the radiation belts and the currents of particles trapped in Earth's magnetic fields, their properties, and where they come from. There is also a set of classroom activities for exploring radiation belts and solar storms and a set of illustrations and movies of the belts. Other materials include news items related to the radiation belts, recordings of 'space sounds' related to the influence of lightning on Earth's magnetic field, and a frequently-asked-questions feature.

155

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

156

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

157

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

158

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

159

Rust Belt Rebounds  

NSDL National Science Digital Library

This recent Census Brief (CENBR/98-7) looks at nonfarm business establishments, unemployment, crime, and new job generation in so-called "rust belt" metropolitan areas such as Detroit-Ann Arbor-Flint, MI and Cleveland-Akron, OH. The report notes an economic and demographic rebound, deemed a "statistical reversal of fortune," with some exceptions outside of the Midwest.

1998-01-01

160

Kuiper Belt Mapping Radar  

NASA Technical Reports Server (NTRS)

Since their initial discovery in 1992, to date only a relatively small number of Kuiper Belt Objects (KBO's) have been discovered. Current detection techniques rely on frame-to-frame comparisons of images collected by optical telescopes such as Hubble, to detect KBO's as they move against the background stellar field. Another technique involving studies of KBO's through occultation of known stars has been proposed. Such techniques are serendipitous, not systematic, and may lead to an inadequate understanding of the size, range, and distribution of KBO's. In this paper, a future Kuiper Belt Mapping Radar is proposed as a solution to the problem of mapping the size distribution, extent, and range of KBO's. This approach can also be used to recover radar albedo and object rotation rates. Additional information is contained in the original extended abstract.

Freeman, A.; Nilsen, E.

2001-01-01

161

Infrared Kuiper Belt Constraints  

NASA Astrophysics Data System (ADS)

We compute the temperature and IR signal of particles of radius a and albedo ? at heliocentric distance R, taking into account the emissivity effect, and give an interpolating formula for the result. We compare with analyses of COBE DIRBE data by others (including recent detection of the cosmic IR background) for various values of heliocentric distance R, particle radius a, and particle albedo ?. We then apply these results to a recently developed picture of the Kuiper belt as a two-sector disk with a nearby, low-density sector (40belt IR spectra for various parameter values. Results of this work include: (1) numerical limits on Kuiper belt dust as a function of (R, a, ?) on the basis of four alternative sets of constraints, including those following from recent discovery of the cosmic IR background by Hauser et al.; (2) application to the two-sector Kuiper belt model, finding mass limits and spectrum shape for different values of relevant parameters including dependence on time elapsed since last passage through a molecular cloud cleared the outer solar system of dust; and (3) potential use of spectral information to determine time since last passage of the Sun through a giant molecular cloud.

Teplitz, Vigdor L.; Stern, S. Alan; Anderson, John D.; Rosenbaum, Doris; Scalise, Randall J.; Wentzler, Paul

1999-05-01

162

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

163

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

164

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

165

Reexamining the Cold Conveyor Belt  

Microsoft Academic Search

Despite the popularity of the conveyor-belt model for portraying the airflow through midlatitude cyclones, questions arise as to the path of the cold conveyor belt, the lower-tropospheric airflow poleward of and underneath the warm front. Some studies, beginning with Carlson's analysis of the eastern U.S. cyclone of 5 December 1977, depict the cold conveyor belt moving westward, reaching the northwest

David M. Schultz

2001-01-01

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

Canada's Chinook Belt  

NASA Astrophysics Data System (ADS)

The chinook is the best example of the family of mountain winds that blows in regions where long mountain chains lie more or less at right angles to the prevailing wind. Apart from the unseasonable warmth it brings to Canada's interior in winter, it represents an efficient system through which latent heat drawn from the Pacific coast is converted into sensible heat and transported zonally across the continent. It also compromises both the physical and human environments. The severity of impacts depends on either the amount of anomalous warming experienced or on the number of chinook events occurring over a winter, and often on both.In Canada, the chinook belt lies almost exclusively in southern Alberta. In this paper, the belt is described and mapped with respect to the strength of the wind's temperature signal and numerical frequency. The temperature signal (the signal) is the difference between the highest temperature attained during a chinook event and the daily maximum. The frequency is the number of days in the winter with, at least, 1 h of chinook wind.Mean point values of the signal range from 13 to 25 K. Mean seasonal frequency varies from 43 days to 52 days per winter. The core of the belt for temperature and frequency do not coincide. The highest frequencies occur in the Crowsnest Pass area whereas the strongest signals are found further east of the mountains in an axis that includes Vauxhall and Brooks.Both signal strengths and frequency show strong decadal variations. The 1980s were chinook rich; the 1970s were chinook poor.

Nkemdirim, Lawrence C.

1996-04-01

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

Gould Belt Origin  

NASA Astrophysics Data System (ADS)

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

Rivera, Leticia; Loinard, Laurent; Dzib, Sergio

2013-07-01

170

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

171

Inner Radiation Belt Data Assimilation  

NASA Astrophysics Data System (ADS)

We present preliminary results of inner belt proton data assimilation using an augmented version of the Selesnick Inner Zone Model (SIZM). The physics-based model computes inner belt proton intensities as a function of time and of the three adiabatic invariants M, K, and L according to a comprehensive list of inner belt source and loss processes. We modify the model solution based on in-situ proton observations from SAMPEX/PET and HEO orbit and according to a data-assimilation method which exploits the non-Gaussian nature of inner belt proton intensities and Poisson or Gaussian counting statistics of the observations, as appropriate. We demonstrate the method by presenting data-assimilated inner belt proton intensities during a solar particle injection.

Guild, T. B.; O'Brien, T. P.

2011-12-01

172

Continuous Mass Measurement on Conveyor Belt  

Microsoft Academic Search

The continuous mass measurement of packages on a conveyor belt will become greatly important. In the mass measurement, the sequence of products is generally random. An interesting possibility of raising throughput of the conveyor line without increasing the conveyor belt speed is offered by the use of two or three conveyor belt scales (called a multi-stage conveyor belt scale). The

Yuki Tomobe; Ryosuke Tasaki; Takanori Yamazaki; Hideo Ohnishi; Masaaki Kobayashi; Shigeru Kurosu

2006-01-01

173

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

174

The Virtual Radiation Belt Observatory  

Microsoft Academic Search

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

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

2010-01-01

175

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

176

Northern Belt of Jupiter  

NASA Technical Reports Server (NTRS)

[figure removed for brevity, see original site]

A four-panel frame shows a section of Jupiter's north equatorial belt viewed by NASA's Cassini spacecraft at four different wavelengths, and a separate reference frame shows the location of the belt on the planet.

A fascinating aspect of the images in the four-panel frame is the small bright spot in the center of each. The images come from different layers of the atmosphere, so the spot appears to be a storm penetrating upward through several layers. This may in fact be a 'monster' thunderstorm, penetrating all the way into the stratosphere, as do some summer thunderstorms in the midwestern United States. These images were taken on Nov. 27, 2000, at a resolution of 192 kilometers (119 miles) per pixel. They have been contrast-enhanced to highlight features in the atmosphere.

The top panel of the four-panel frame is an image taken in a near-infrared wavelength at which the gases in Jupiter's atmosphere are relatively non-absorbing. Sunlight can penetrate deeply into the atmosphere at this wavelength and be reflected back out, providing a view of an underlying region of the atmosphere, the lower troposphere.

The second panel was taken in the blue portion of wavelengths detected by the human eye. At these wavelengths, gases in the atmosphere scatter a modest amount of sunlight, so the clouds we see tend to be at somewhat higher altitudes than in the top panel.

The third panel shows near-infrared reflected sunlight at a wavelength where the gas methane, an important constituent of Jupiter's atmosphere, absorbs strongly. Dark places are regions without high-level clouds and consequently large amounts of methane accessible to sunlight. Bright regions are locations with high clouds in the upper troposphere shielding the methane below.

The bottom panel was taken in the ultraviolet. At these very short wavelengths, the clear atmosphere scatters sunlight, and hazes in the stratosphere, above the troposphere, absorb sunlight. That makes it difficult to see into lower layers at all. The bright regions are generally free of high stratospheric hazes.

A small bright spot is visible near the center of each panel. Similar spots have been imaged in turbulent regions by the Galileo spacecraft, and they appear to be very energetic convective storms that move heat from the interior of Jupiter to higher altitudes. These storms are expected to penetrate to great heights, and so it is not surprising to see the storm in the first three images, which probe atmospheric altitudes from the lower to the upper troposphere. What is surprising is the appearance of the spot in the ultraviolet image. Higher resolution, time-lapse images to be captured by Cassini in coming weeks will shed more light on these spectacular features.

Cassini is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini mission for NASA's Office of Space Science, Washington, D.C.

2000-01-01

177

Satellite Feature Identification: Conveyor Belts  

NSDL National Science Digital Library

Conveyor belts highlight important atmospheric processes that can be advantageous for making forecasts. They can be used for identifying general temperature patterns, defining the extent of cloud cover, predicting moisture return, evaluating stability, forecasting wind gusts, pinpointing cyclogenesis, and understanding the three-dimensional structure of the atmosphere. For short-term forecasts, they can even augment NWP showing the three-dimensional structure and portraying the same information as equivalent or wet-bulb potential temperature and potential vorticity surfaces. Conveyor belts make representing the total wind easier than using isobaric surfaces which only cut through the processes giving limited, two-dimensional views of the total wind. In this lesson, learn to identify conveyor belts using water vapour imagery. You'll be able to understand the structure of the conveyor belt's isentropic surfaces from the water vapour imagery and use that knowledge to enhance your forecasting. Further analysis will allow you to break your conveyor belts into branches for even more forecasting ability. It is highly encouraged that students review the "Deformation Zone Analysis" and "Inferring Three Dimensions from Water Vapour imagery" lessons before attempting this lesson.

2014-09-14

178

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

179

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

180

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

181

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

182

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

183

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

184

14 CFR 27.1413 - Safety belts.  

Code of Federal Regulations, 2014 CFR

... 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

185

M.P. BELT DETERIORATION. ACCELERATOR STRUCTURE. BELT CAPABILITY  

E-print Network

of the drive motor and its grooves, to let the gas escape (Fig. 2). We know also that there are some reasons to have inhomogeneity in the belt FIG. 2. - Grooves on the drive motor. charge density [1]. The curve V

Paris-Sud XI, Université de

186

6Exploring the Donut-shaped Van Allen Belts The Van Allen belts were discovered in  

E-print Network

6Exploring the Donut-shaped Van Allen Belts The Van Allen belts were discovered in the late-1950s and resemble two donut-shaped clouds of protons (inner belt) and electrons (outer belt) with Earth at its center. A donut is an example of a simple mathematical shape called a torus that is created by rotating

187

1 The Main Asteroid Belt Carolyn Crow: NASA's Dawn Mission The Main Asteroid Belt  

E-print Network

1 The Main Asteroid Belt Carolyn Crow: NASA's Dawn Mission The Main Asteroid Belt Written to the main asteroid belt to visit two of the largest protoplanets, Vesta and Ceres. Using sunlight, a mere accomplished by a spacecraft before. What compelled astronomers to send Dawn to the asteroid belt and what does

Waliser, Duane E.

188

Insurance incentives and seat belt use.  

PubMed Central

In 1983, Nationwide Insurance Company increased compensation payments for its clients injured or killed in a motor vehicle crash while using a seat belt. A survey of belt use was undertaken in the month after all those so insured had been informed of the change. Belt use by drivers insured by Nationwide was not significantly different from that of drivers insured by other companies. The incentive appears to have had no apparent effect on belt use. PMID:6476174

Robertson, L S

1984-01-01

189

Chronology of the Mount Magnet granite-greenstone terrain, Yilgarn Craton, Western Australia: implications for field based predictions of the relative timing of granitoid emplacement  

Microsoft Academic Search

In this paper we report ion-probe U?Pb ages for zircons from thirteen granitoids and five supracrustal rocks from the Mount Magnet area of the Archaean Murchison Province of Western Australia. The oldest granitoids in the area are two porphyry dykes and three small, apparrently underformed bodies that intrude the greenstones. The porphyries have ages of 2715 and 2752 Ma and

Lasse Schiøtte; Ian H. Campbell

1996-01-01

190

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

191

Using the Abitibi Greenstone Belt to Understand Martian Hydrothermal Systems and the Potential for Biosignature Preservation in High Temperature Aqueous Environments  

NASA Technical Reports Server (NTRS)

Metabolic bone diseases like osteoporosis result from the disruption of normal bone mineral balance (BMB) resulting in bone loss. During spaceflight astronauts lose substantial bone. Bed rest provides an analog to simulate some of the effects of spaceflight; including bone and calcium loss and provides the opportunity to evaluate new methods to monitor BMB in healthy individuals undergoing environmentally induced-bone loss. Previous research showed that natural variations in the Ca isotope ratio occur because bone formation depletes soft tissue of light Ca isotopes while bone resorption releases that isotopically light Ca back into soft tissue (Skulan et al, 2007). Using a bed rest model, we demonstrate that the Ca isotope ratio of urine shifts in a direction consistent with bone loss after just 7 days of bed rest, long before detectable changes in bone mineral density (BMD) occur. The Ca isotope variations tracks changes observed in urinary N-teleopeptide, a bone resorption biomarker. Bone specific alkaline phosphatase, a bone formation biomarker, is unchanged. The established relationship between Ca isotopes and BMB can be used to quantitatively translate the changes in the Ca isotope ratio to changes in BMD using a simple mathematical model. This model predicts that subjects lost 0.25 +/- 0.07% (+/- SD) of their bone mass from day 7 to day 30 of bed rest. Given the rapid signal observed using Ca isotope measurements and the potential to quantitatively assess bone loss; this technique is well suited to study the short-term dynamics of bone metabolism.

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

2011-01-01

192

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

193

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

194

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.

195

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

196

Fluid chemistry and evolution of hydrothermal fluids in an Archaean transcrustal fault zone network: The case of the Cadillac Tectonic Zone, Abitibi greenstone belt, Canada  

USGS Publications Warehouse

Detailed fluid geochemistry studies on hydrothermal quartz veins from the Rouyn-Noranda and Val-d'Or areas along the transcrustal Cadillac Tectonic Zone (CTZ) indicate that unmineralized (with respect to gold) sections of the CTZ contained a distinct CO2-dominated, H2S-poor hydrothermal fluid. In contrast, both gold mineralized sections of the CTZ (e.g., at Orenada #2) and associated higher order shear zones have a H2O-CO2 ?? CH4-NaCl hydrothermal fluid. Their CO2/H2S ratios indicate H2S-rich compositions. The Br/Cl compositions in fluid inclusions trapped in these veins indicate that hydrothermal fluids have been equilibrated with the crust. Oxygen isotope ratios from hydrothermal quartz veins in the CTZ are consistently 2??? more enriched than those of associated higher order shear zones, which are interpreted to be a function of greater fluid/rock ratios in the CTZ and lower fluid/rock ratios, and more efficient equilibration of the hydrothermal fluid with the wall rock, in higher order shear zones. An implication from this study is that the lower metal endowment of the transcrustal CTZ, when compared with the higher metal endowment in higher order shear zones (ratio of about 1 : 1000), may be the result of the lack of significant amounts of H2O-H2S rich fluids in most of the CTZ. In contrast, gold mineralization in the higher order shear zones appear to be controlled by the high H2S activity of the aqueous fluids, because gold was likely transported in a bisulfide complex and was deposited during sulfidation reactions in the wall rock and phase separation in the quartz veins. ?? 2007 NRC Canada.

Neumayr, P.; Hagemann, S.G.; Banks, D.A.; Yardley, B.W.D.; Couture, J.-F.; Landis, G.P.; Rye, R.

2007-01-01

197

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

198

Model and Dynamic Simulation of Belt Conveyor  

Microsoft Academic Search

Belt conveyor is one of main electromechanical systems in the coal transport system, its safe operation plays an important role in the whole coal output systems. As the belt conveyors get longer, quicker and bulkier, the traditional static design method already can not satisfy the requirement of actual engineering. One of problems is that a huge peak belt tension induced

Chen Yan; Xue He

2010-01-01

199

30 CFR 77.406 - Drive belts.  

Code of Federal Regulations, 2010 CFR

...Resources 1 2010-07-01 2010-07-01 false Drive belts. 77.406 Section 77.406 Mineral Resources...Safeguards for Mechanical Equipment § 77.406 Drive belts. (a) Drive belts shall not be shifted while in motion...

2010-07-01

200

30 CFR 75.1727 - Drive belts.  

Code of Federal Regulations, 2010 CFR

...Resources 1 2010-07-01 2010-07-01 false Drive belts. 75.1727 Section 75.1727 Mineral...STANDARDS-UNDERGROUND COAL MINES Miscellaneous § 75.1727 Drive belts. (a) Drive belts shall not be shifted while in motion...

2010-07-01

201

Pregnancy: Should I Use a Seat Belt?  

MedlinePLUS

... injury or death in the event of a car crash. You should wear a seat belt no matter where you sit in the car. How should I wear my seat belt? The ... belts keep you from being thrown from the car during an accident. The shoulder strap also keeps ...

202

Six sigma black belt implementation  

Microsoft Academic Search

Examines different approaches that can be utilised to introduce a Six Sigma Black Belt programme. Compares and contrasts the implementation strategies used in both Motorola and General Electric. Provides information based on a literature review as well as interview evidence from employees in both firms. Concludes by defining the overall approach used by each company. The benefits as well as

Sarah Ingle; Willo Roe

2001-01-01

203

Seat-belt syndrome revisited.  

PubMed

This report describes a complex syndrome of injuries occurring in a young female who was a back seat passenger wearing a lap-belt restraint in a high-speed road traffic accident. As a consequence of the forced flexion distraction injury of her lumbar spine, she sustained a fracture-subluxation of the first lumbar vertebra in association with a jejunal perforation and extensive small intestinal mesenteric laceration. She also had a large traumatic hernia of the anterior abdominal wall, which was overlooked at primary laparotomy. This report highlights collectively the classical combination of injuries associated with the lap-belt syndrome and demonstrates the importance of carefully inspecting the anterior abdominal wall for deficiencies, because traumatic herniation may be easily overlooked. PMID:11695084

Thompson, N S; Date, R; Charlwood, A P; Adair, I V; Clements, W D

2001-10-01

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

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

206

The Kuiper Belt Legacy Project  

NASA Astrophysics Data System (ADS)

To advance our understanding of the Kuiper belt, the region of the solar system extending beyond 30 AU, we have identified three core issues: [i] Well-determined orbital elements of trans-Neptunian objects (TNOs) are essential for providing an accurate view of the Kuiper belt's physical properties such as dynamics, formation, and structure; [ii] A program of dedicated recovery observations of TNOs is absolutely necessary to obtain an unbiased collection of objects with well- determined orbital elements; and [iii] Such recoveries are most effective when they are coupled to a discovery program which is well understood and characterized. To address all those issues, this NOAO proposal is to make recovery observations of TNOs discovered by the Canada-France Ecliptic Plane Survey (CFEPS) over the past few years, and is a vital part of a coordinated international recovery effort. The resulting well- characterized database of TNOs will allow us and other researchers to determine the dynamical structure and distribution of the Kuiper belt, identify intriguing objects for further observations and analysis, and provide accurate orbital elements so that objects will not be lost for subsequent physical study. Our ultimate goal is to understand and map out the formation history of the outer solar system.

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

2006-08-01

207

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

208

Hafnium-neodymium isotope systematics of the 2.7 Ga Gadwal greenstone terrane, Eastern Dharwar craton, India: Implications for the evolution of the Archean depleted mantle  

NASA Astrophysics Data System (ADS)

The Neoarchean Gadwal greenstone belt in the eastern Dharwar craton, India, hosts a well preserved metavolcanic sequence that is dominated by tholeiitic and calc-alkaline basalt-andesite-dacite-rhyolite series, which includes boninitic geochemical varieties. Bulk-rock Lu-Hf and Sm-Nd isotope systematics of these apparently arc-related volcanic rocks yield indistinguishable ages of 2.701 ± 0.024 Ga and 2.702 ± 0.026 Ga, respectively. On the basis of the close spatial association and identical ages of the different rock types we suggest 2.70 ± 0.03 Ga as the age of crystallization of the different rock types within the Gadwal metavolcanic sequence. In contrast, bulk-rock Pb-Pb isotope systematics of the same samples yield a significantly younger and less precise age of 2.466 Ga (+0.068/-0.110 Ga). We tentatively interpret this younger age to represent a metallogenic and crustal reworking event in the Dharwar craton, which disturbed the U-Pb system but not the Lu-Hf or Sm-Nd systems. The Gadwal metavolcanic rocks have positive initial ?Hf(2.70Ga) = + 1.6 to + 8.7 and slightly negative to positive ?Nd(2.70Ga) = -0.1 to + 3.0 values, consistent with an origin from a long term depleted source relative to a chondritic reservoir at ˜2.7 Ga. Lack of correlation between initial isotopic compositions and major or trace element indices of fractionation and alteration suggest that the observed isotope variability probably reflects compositional variation in the Gadwal source, similar to that observed in modern day island arcs. Two boninitic samples of the Gadwal sequence have ?Hf ˜ 8.3 and 8.7, and are more radiogenic than average depleted mantle for the time period 3.2 to 2.5 Ga (?Hf = 4 to 6). Early (perhaps Hadean) differentiation events that led to a depleted and heterogeneous mantle are apparent in the Nd and Hf isotope systematics of 3.7-3.8 Ga Isua supracrustal rocks. The radiogenic Hf isotopes of the Gadwal boninites and the Hf, Nd isotope systematics of rocks from other locations in the 3.4 to 2.5 Ga time period are consistent with the survival of fragments of an early depleted mantle later in the Archean. From ˜2.0 Ga to present, the time-integrated 176Lu/177Hf and 147Sm/144Nd of the depleted mantle appears nearly constant and similar to the present day average MORB source. These data indicate that progressive elimination of early (>4.5 Ga) formed heterogeneities in the depleted mantle dominated the history of the Archean mantle, and that portions of early depleted reservoirs survived through the Mesoarchean. These results have implications for the mixing scales for the early terrestrial mantle and the timing of the initiation of present day plate tectonics.

Khanna, Tarun C.; Bizimis, Michael; Yogodzinski, Gene M.; Mallick, Soumen

2014-02-01

209

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

210

ACCURACY FOR CONTINUOUS MASS MEASUREMENTS IN MULTISTAGE BELT CONVEYORS  

Microsoft Academic Search

Large quantities of commodities in different sizes transported on belt conveyors should often be mea- sured automatically by two or three conveyor belt scales. Continuous measurement can be dynamically performed by multi-stage conveyor belt scales, so that the masses of discrete objects on belt conveyors can be determined in sequence according to the different lengths. Belt conveyor scales usually have

Takanori Yamazaki; Ryosuke Tasaki; Hideo Ohnishi; Masaaki Kobayashi; Shigeru Kurosu

2003-01-01

211

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

212

A simple tectonic model for crustal accretion in the Slave Province: A 2.7-2.5 Ga granite greenstone terrane  

Microsoft Academic Search

A prograding (direction unspecified) trench-arc system is favored as a simple yet comprehensive model for crustal generation in a 250,000 sq km granite-greenstone terrain. The model accounts for the evolutionary sequence of volcanism, sedimentation, deformation, metamorphism and plutonism, observed througout the Slave province. Both unconformable (trench inner slope) and subconformable (trench outer slope) relations between the volcanics and overlying turbidities;

P. F. Hoffman

1986-01-01

213

Puzzling Snowballs: Main Belt Comets  

NASA Astrophysics Data System (ADS)

Main belt comets (MBCs) are a class of newly discovered objects that exhibit comet-like appearances and yet are dynamically indistinguishable from ordinary main belt asteroids. The measured size and albedo of MBCs are similar to those of classical comets. At present, six MBCs have been discovered, namely 133P/Elst-Pizarro, 176P/LINEAR, 238P/Read, P/2008 R1, P/La Sagra and P/2006 VW139. The total number of active MBCs is estimated to be at the level of a few hundreds (Hsieh & Jewitt, 2006). Several explanations for the activity of MBCs have been suggested. These include impact ejection, sublimation and rotational instability. However, since renewed activity has been observed in 133P and 238P at successive perihelion passages, the most likely explanation may be a thermally-driven process - e.g sublimation of exposed surface ice. Although the proximity of MBCs to the Sun (r ~ 3 AU) makes the survival of surface ice improbable, thermal models have shown that water ice is thermally stable under a regolith layer a few meters thick. The study of MBCs has recently been complicated by the discoveries of two asteroid collisional events (P/2010 A2 (LINEAR) and (596) Scheila) in 2010, where comet-like dust coma/tail have been attributed to recent impacts. If MBCs are indeed icy, they represent the closest and the third established reservoir of comets (after the Oort cloud and the Kuiper belt). As such, they may have been an important source of water for the Earth's oceans. I will review the current state of MBC studies, present the latest observational results and discuss possible mechanisms that could produce the observed activity. I will also talk about current and future space missions that are dedicated or closely related to MBC studies.

Yang, Bin; Meech, Karen

2015-03-01

214

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

Code of Federal Regulations, 2010 CFR

... 2010-07-01 false Chains, ropes, and drive belts. 56.14212 Section 56.14212 Mineral...Procedures § 56.14212 Chains, ropes, and drive belts. Chains, ropes, and drive belts shall be guided mechanically onto...

2010-07-01

215

14 CFR 29.1413 - Safety belts: passenger warning device.  

Code of Federal Regulations, 2012 CFR

...2012-01-01 false Safety belts: passenger warning device. 29.1413... AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Equipment...29.1413 Safety belts: passenger warning device. (a...are means to indicate to the passengers when safety belts...

2012-01-01

216

14 CFR 29.1413 - Safety belts: passenger warning device.  

Code of Federal Regulations, 2010 CFR

...2010-01-01 false Safety belts: passenger warning device. 29.1413... AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Equipment...29.1413 Safety belts: passenger warning device. (a...are means to indicate to the passengers when safety belts...

2010-01-01

217

14 CFR 29.1413 - Safety belts: passenger warning device.  

Code of Federal Regulations, 2014 CFR

...2014-01-01 false Safety belts: passenger warning device. 29.1413... AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Equipment...29.1413 Safety belts: passenger warning device. (a...are means to indicate to the passengers when safety belts...

2014-01-01

218

14 CFR 29.1413 - Safety belts: passenger warning device.  

Code of Federal Regulations, 2013 CFR

...2013-01-01 false Safety belts: passenger warning device. 29.1413... AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Equipment...29.1413 Safety belts: passenger warning device. (a...are means to indicate to the passengers when safety belts...

2013-01-01

219

14 CFR 29.1413 - Safety belts: passenger warning device.  

Code of Federal Regulations, 2011 CFR

...2011-01-01 false Safety belts: passenger warning device. 29.1413... AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Equipment...29.1413 Safety belts: passenger warning device. (a...are means to indicate to the passengers when safety belts...

2011-01-01

220

30 CFR 57.14108 - Overhead drive belts.  

Code of Federal Regulations, 2010 CFR

... Safety Devices and Maintenance Requirements § 57.14108 Overhead drive belts. Overhead drive belts shall be guarded to contain the whipping action of a broken belt if that action could be hazardous to...

2010-07-01

221

30 CFR 56.14108 - Overhead drive belts.  

Code of Federal Regulations, 2011 CFR

... Safety Devices and Maintenance Requirements § 56.14108 Overhead drive belts. Overhead drive belts shall be guarded to contain the whipping action of a broken belt if that action could be hazardous to...

2011-07-01

222

30 CFR 57.14108 - Overhead drive belts.  

Code of Federal Regulations, 2011 CFR

... Safety Devices and Maintenance Requirements § 57.14108 Overhead drive belts. Overhead drive belts shall be guarded to contain the whipping action of a broken belt if that action could be hazardous to...

2011-07-01

223

30 CFR 56.14108 - Overhead drive belts.  

Code of Federal Regulations, 2010 CFR

... Safety Devices and Maintenance Requirements § 56.14108 Overhead drive belts. Overhead drive belts shall be guarded to contain the whipping action of a broken belt if that action could be hazardous to...

2010-07-01

224

Seat belt use in cars with air bags.  

PubMed Central

Seat belt use was observed in 1,628 cars with air bags and manual belts and 34,223 cars with manual seat belts only. Sixty-six percent of drivers in cars with air bags wore seat belts compared to 63 percent of drivers in cars with manual belts only. The study found no evidence for the speculation that drivers with air bags will reduce their seat belt use because they believe an air bag alone provides sufficient protection. PMID:2240346

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

1990-01-01

225

A BOOSTER SEAT positions the seat belt  

E-print Network

and chest to restrain the child safely in a crash. It should not rest on the stomach area or across the neck the lap belt must lie snugly across the upper thighs, not the stomach. The shoulder belt should lie snug

226

DESIGN AND OPERATION OF BELT FILTER PRESSES  

EPA Science Inventory

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

227

5, 1072310745, 2005 Antarctic NAT belt  

E-print Network

ACPD 5, 10723­10745, 2005 Antarctic NAT belt caused by mountain waves M. H¨opfner et al. Title Page Discussions MIPAS detects Antarctic stratospheric belt of NAT PSCs caused by mountain waves M. H¨opfner 1 , N(s). This work is licensed under a Creative Commons License. 10723 #12;ACPD 5, 10723­10745, 2005 Antarctic NAT

Paris-Sud XI, Université de

228

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

229

Understanding Quaternions and the Dirac Belt Trick  

ERIC Educational Resources Information Center

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

Staley, Mark

2010-01-01

230

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

231

Effectiveness of Ford's belt reminder system in increasing seat belt use  

PubMed Central

Objectives: The study investigated the effectiveness in increasing seat belt use of Ford's belt reminder system, a supplementary system that provides intermittent flashing lights and chimes for five minutes if drivers are not belted. Methods: Seat belt use of drivers in relatively new cars with and without the reminder system was unobtrusively observed as vehicles were brought to dealerships for service. Results: Overall use rates were estimated at 71% for drivers in vehicles without the reminder system and 76% for drivers in vehicles with belt reminders (p<0.01). Conclusions: Seat belt use is relatively low in the United States. The present study showed that vehicle based reminder systems can be at least modestly effective in increasing belt use, which may encourage further development of such systems. PMID:12460965

Williams, A; Wells, J; Farmer, C

2002-01-01

232

Belt separation system under slat in fattening pig housing: effect of belt type and extraction frequency.  

PubMed

The efficiency of manure separation by a conveyor belt under a partially slatted floor for fattening pigs was determined for two types of belts, a flat belt with an incline of up to 6 degrees transversely and a concave belt with an incline of up to 1 degrees longitudinally. A 31.20% and 23.75% dry matter content of the solid fraction was obtained for the flat and concave belt, respectively. The flat belt was more efficient at 6 degrees than other slope angles. The residence time of the manure on the two belt types influenced the separation efficiency from a live weight of 63.00 kg upwards. The quantity of residue produced with this system was reduced to 25-40% with respect to a pit system under slat. This could mean a remarkable reduction in costs of storage, transport and application of manure. PMID:20338748

Alonso, F; Vázquez, J; Ovejero, I; Garcimartín, M A; Mateos, A; Sánchez, E

2010-08-01

233

Inner Radiation Belt Dynamics and Climatology  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

234

Kuiper Belt Albedoes and Densities  

NASA Astrophysics Data System (ADS)

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

Rieke, George; Stansberry, John

2007-05-01

235

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

236

Possible eastward extension of Chinese collision belt in South Korea: The Imjingang belt  

Microsoft Academic Search

Structural, petrological, and geochronological data from the middle Korean peninsula indicate that the Qinling-Dabie-Sulu collisional belt of east-central China crosses the Yellow Sea and extends into the Imjingang belt. The Yeoncheon complex, first identified as the western Imjingang belt, comprises primarily north-dipping metamorphic sequences: (1) the northern Jingok unit, consisting of Barrovian-type metapelites, and (2) the southern Samgot unit, consisting

Jin-Han Ree; Moonsup Cho; Sung-Tack Kwon; Eizo Nakamura

1996-01-01

237

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

Microsoft Academic Search

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

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

2005-01-01

238

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

239

Occupant Protection (Seat Belt Use) - 2011 Data  

MedlinePLUS

... Use Laws The U.S. Department of Transportation’s July 1984 rulemaking on automatic occupant protection began a wave ... enacted in the State of New York in 1984. Adult belt use laws are now in effect ...

240

A repair of a charging belt  

SciTech Connect

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

Jones, N.L.

1989-01-01

241

Dynamical evolution of the asteroid belt  

NASA Astrophysics Data System (ADS)

We discusses the properties of the asteroid belt that dynamical evolution models should explain, i.e. mass deficit, orbital excitation, partial mixing of taxonomic types, the short cumulative collisional age of the asteroid belt (10 Gy; Bottke et al., 2005), and the rapid decay of the Ar-Ar shock ages for HEDs 4.5 Gy ago. We start by discussing the early dynamical sculpting of the asteroid belt, reviewing first the canonical model of Wetherill (1992), then the more recent Grand Tack Scenario (Walsh et al., 2011). In the second part of the talk, we describe the late evolution of the asteroid belt, affected by the dynamical instability that brought the giant planets to their current orbits about 4.1 Gy ago. The role of asteroids in the so-called Late Heavy Bombardment of the terrestrial planets will also be discussed.

Morbidelli, A.; Walsh, K.; O'Brien, D.; Minton, D.; Bottke, W.

2014-07-01

242

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.

Tom Bridgman

2005-03-08

243

Flat belt continuously variable high speed drive  

Microsoft Academic Search

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

Kumm

1992-01-01

244

The activity of Main Belt comets  

E-print Network

Main Belt comets represent a recently discovered class of objects. They are quite intriguing because, while having a Tisserand invariant value higher than 3, are showing cometary activity. We study the activity of the Main Belt comets making the assumption that they are icy-bodies and that the activity has been triggered by an impact. We determine the characteristics of this activity and if the nowadays impact rate in the Main Asteroid Belt is compatible with the hypothesis of an activity triggered by a recent impact. Due to the fact that the Main Belt comets can be considered as a kind of comets, we apply a thermal evolution model developed for icy bodies in order to simulate their activity. We also apply a model to derive the impact rate, with respect to the size of the impactor, in the Main Belt. We demonstrate that a stable activity can result from a recent impact, able to expose ice-rich layers, and that the impact rate in the Main Belt is compatible with this explanation.

Capria, Maria Teresa; De Sanctis, Maria Cristina; Coradini, Angioletta; Ammannito, Eleonora

2011-01-01

245

The activity of main belt comets  

NASA Astrophysics Data System (ADS)

Context. Main belt comets represent a recently discovered class of objects. They are quite intriguing because, while having a Tisserand invariant value higher than 3, are showing cometary activity. Aims: We study the activity of the main belt comets making the assumption that they are icy-bodies and that the activity has been triggered by an impact. We try to determine the characteristics of this activity. We also try to determine if the nowadays impact rate in the main asteroid belt is compatible with the hypothesis of an activity triggered by a recent impact. Methods: Due to the fact that the main belt comets can be considered as a kind of comets, we apply a thermal evolution model developed for icy bodies in order to simulate their activity. We also apply a model to derive the impact rate, with respect to the size of the impactor, in the main belt. Results: We demonstrate that a stable activity can result from a recent impact, able to expose ice-rich layers, and that the impact rate in the main belt is compatible with this explanation.

Capria, M. T.; Marchi, S.; de Sanctis, M. C.; Coradini, A.; Ammannito, E.

2012-01-01

246

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

247

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

248

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

249

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

Microsoft Academic Search

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

Norbert Opiyo-Akech; John Tarney; M. Hoshino

1999-01-01

250

The Double-belt Outer Radiation Belt During CME- and CIR-driven Geomagnetic Storms  

NASA Astrophysics Data System (ADS)

We have identified 8 events with double-belt structure in the outer radiation belt from 110 CME-driven magnetic storms and 223 CIR-driven storms during 1994 to 2003 based on the SAMPEX data sets. Among them, 3 cases are related to CME-driven magnetic storms and 5 cases are related CIR-driven storms. All double-belt structure events in the outer radiation belt are found during the recovery phase of a magnetic storm for both CME- and CIR-related events---they usually start to form within 3-4 days after the onset of the magnetic storm. The pre-conditions needed to form a double-belt structure, for all the CME-related events, are found to be high solar wind dynamic pressure (Pdy) and southward IMF Bz; Nevertheless, for the CIR-related events, they are found to be associated with high speed stream with southward interplanetary magnetic field caused by the Russell-McPherron effect. It is further found that the double-belt structure can be fitted well with a simple exponential decay function. Based on the RBC index, the proportion of the total number of 1.5-6.0MeV electrons inside the position of maximum fluxes to that outside the maximum fluxes keeps rising during the double-belt period, which implies that the acceleration mainly occurs at regions inside the location of maximum fluxes. We suggest that local acceleration mechanisms play an important role in the development of the higher belt during the period of the double-belt structure event in the outer radiation belt.

Yuan, C.; Zong, Q.

2013-12-01

251

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

NASA Astrophysics Data System (ADS)

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

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

2006-06-01

252

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

USGS Publications Warehouse

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

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

1983-01-01

253

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

254

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

255

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

256

IDENTIFYING COLLISIONAL FAMILIES IN THE KUIPER BELT  

SciTech Connect

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

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

2011-05-20

257

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

258

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

259

The Main Belt Distribution of Basaltic Asteroids  

NASA Astrophysics Data System (ADS)

The goal of this project is to constrain the Main Belt distribution of asteroids with basaltic material on their surface. Candidate basaltic asteroids are selected to have SDSS photometric colors (Ivezic, Z. et al., 2002, SPIE, 4836, 98) suggestive of a V-type taxonomy and are then prioritized based on a statistical determination of how closely their colors coincide with those of the Vestoid dynamical family. Dynamical constraints are applied to ensure that our targets are not part of this family. Preliminary results of this spectroscopic survey, suggest that 100% of our highest priority candidates are V-type. These criteria for the selection of basaltic candidates yield a distribution of objects across a range of semi-major axis. Correcting this distribution for the completeness of the SDSS as a function of semi-major axis and using the observed fraction of basaltic asteroids as determined by our survey, we calculate an unbiased distribution of basaltic asteroids throughout the Main Belt. This distribution can be compared with theory (Bottke, W.F. et al., 2006, Nature, 439, 821) to address whether partial melting and differentiation occurred within the Main Belt or whether these asteroids formed in the inner Solar System (where solid body accretion times were faster and thus greater internal temperatures were achieved) and later scatted outwards into stable Main Belt orbits. The determination of a distribution of basaltic asteroids will be an important tool for extrapolating the number of differentiated parent bodies that were once present in the Main Belt. This ultimate result will have implications for addressing the discrepancy between the large number of differentiated parent bodies represented by iron meteorites and the few known occurrences of Main Belt differentiation. This research is supported in part by NASA GSRP grant NNG04GL48G, P.I. E. Gaidos and NSF Planetary Astronomy grant AST04-07134, P.I. R. Jedicke.

Moskovitz, Nicholas; Willman, M.; Jedicke, R.; Gaidos, E.

2007-05-01

260

Radiation Belt Storm Probe Mission Trailer - Duration: 1:04.  

NASA Video Gallery

With launch scheduled for 2012, the Radiation Belt Storm Probe (RBSP) are two identical spacecraft that will investigate the doughnut shaped Van Allen radiation belts, the first discovery of the sp...

261

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 ...

262

The Palaeoproterozoic Ubendian shear belt in Tanzania: geochronology and structure  

Microsoft Academic Search

The Ubendian belt is a linear, NW-SE trending orogenic belt in western Tanzania. It is part of a larger Palaeoproterozoic orogen, developed around the west and south-western margin of the Archaean Tanzanian craton. The Ubendian Belt has experienced several periods of reactivation since the Palaeoproterozoic, acting as a zone of displacement during successive orogenic and rift-forming events. The Ubendian Belt

J. L. LENOIR; J-P Liégeois; K Theunissen; J Klerkx

1994-01-01

263

ENHANCED SEAT BELT REMINDER SYSTEMS FOR TEENAGE DRIVERS AND PASSENGERS  

Microsoft Academic Search

Summary: Failure to use a seat belt is a significant highway safety concern for teenagers. The current Federally-required seat belt reminder system is limited in its effectiveness, and many automobile manufacturers are now providing enhanced seat belt reminder (ESBR) systems. Current systems are designed for the general driving public and their design must represent a trade-off between effectiveness in promoting

Neil Lerner; Jeremiah Singer; Mark Freedman

264

46 CFR 111.105-27 - Belt drives.  

Code of Federal Regulations, 2010 CFR

... 2010-10-01 2010-10-01 false Belt drives. 111.105-27 Section 111.105-27 Shipping...REQUIREMENTS Hazardous Locations § 111.105-27 Belt drives. Each belt drive in a hazardous location must have: (a) A...

2010-10-01

265

Gears and belt drives for non-uniform transmission  

E-print Network

Gears and belt drives for non-uniform transmission Hellmuth Stachel stachel of gearing 2. Non-uniform belt drives 3. On the existence of strict non-uniform belt drives EUCOMES08. Finsterwalder's principle of gearing The driving wheel 1 rotates about O1 through 1, the out-put wheel 2 rotates

Stachel, Hellmuth

266

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

267

Colors of Kuiper Belt objects : the relationship between KBO colors and Kuiper Belt plane inclination  

E-print Network

A large population of small, icy bodies orbits the sun just beyond Neptune, known as the Kuiper Belt. These objects, thought to be the progenitors of short period comets, could provide a sample of primordial material in ...

Kane, Julia Frances

2006-01-01

268

Geochemical consequences of the metasomatic conversion of an Early Archean komatiite sequence into chert  

SciTech Connect

Duchac and Hanor (1985) have demonstrated from field and petrographic evidence that the stratiform, muscovite-bearing cherts of Skokhola Ridge, Barberton Mountain Land, South Africa, represent a pervasively silicified sequence of komatiites and komatiitic basalts of Early Archean age. Most alteration took place early, prior to any significant tectonic deformation. The isovolumetric nature of the alteration, as confirmed by excellent preservation of igneous textures, and the immobility of Al make it possible to quantify elemental gains and losses during metasomatism. The sequence was strongly depleted in Na, Mg, Ca, Sr, Fe, and Mn, and enriched in K, Rb, and Ba, Al, Y, Zr, Ti, and P were immobile. It is most likely that the sequence was altered by large volumes of ascending hydrothermal solutions, with the decrease in T upward favoring precipitation of silica and muscovite. The net effect was to convert an ultramafic igneous rock into a rock having a composition approaching that of the average sandstone. Such alteration, if regionally extensive, undoubtedly affected the geochemical evolution of both the Early Archean crust and hydrosphere in the Barberton greenstone belt.

Hanor, J.S.; Duchac, K.C.

1985-01-01

269

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

270

Six Sigma Black Belts Fight For Quality  

E-print Network

Six Sigma Black Belts Fight For Quality Ron Scott Ross Finnestad Rodney Kalsow IE 361 mini-paper 9/22/00 #12;Six Sigma is a breakthrough management strategy that is revolutionizing the world's top corporations. So what is Six Sigma? "It is a business process that allows companies to drastically improve

Vardeman, Stephen B.

271

Measurements of the Jovian radiation belts  

Microsoft Academic Search

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

R. W. Fillius; C. E. McIlwain

1974-01-01

272

Research on an Active Seat Belt System  

NASA Astrophysics Data System (ADS)

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

Kawashima, Takeshi

273

Stacked pneumatic cylinders automate conveyor belt operations  

Microsoft Academic Search

Shows how clusters of remotely controlled pneumatic cylinders swing a hinged conveyor belt to 4 preselected vertical positions. Using a manual method to move the conveyor meant that the operator had to use a hand winch, sheaves, drums, and winch cable. There was a need to develop a simple, effective, and remotely controlled system which would perform 2 functions: eliminate

Thornton

1982-01-01

274

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

275

MONECOM: Physical Characteristics Of Main Belt Comets  

NASA Astrophysics Data System (ADS)

The aim of the MONECOM project is to carry out photometric observations of several Main-Belt Comets (MBCs). Observations and data reduction were performed by high-school students from three countries (Croatia, Greece and Serbia), supervised by their teachers and local astronomers. Here we present some results obtained by the Serbian group.

Bogdanovic, N.; Smolic, I.; Bogosavljevic, M.; Milic, I.

2013-05-01

276

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

277

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

278

Rivet-fastener belt splices reduce conveyor downtime  

SciTech Connect

At Sahara Coal Co's No. 21 Mine in Illinois some 18 miles of conveyor belting are in underground use bringing coal from the faces to a main haulage conveyor which transports the coal to the surface. The belt material is nylon carcass with rubber cover. Because of relatively low roof clearance, thinner belt than is typically used underground is employed, since a 500 ft roll of thicker belting would be unable to negotiate low-clearance entries. This thinner belt material could not be spliced using conventional fasteners, but solid-plate rivetted splicing has been found to be satisfactory.

Not Available

1982-11-01

279

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.

280

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

281

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

282

Alien Asteroid Belt Compared to our Own  

NASA Technical Reports Server (NTRS)

[figure removed for brevity, see original site] Figure 1: Band of Light Comparison

This artist's concept illustrates what the night sky might look like from a hypothetical alien planet in a star system with an asteroid belt 25 times as massive as the one in our own solar system (alien system above, ours below; see Figure 1).

NASA's Spitzer Space Telescope found evidence for such a belt around the nearby star called HD 69830, when its infrared eyes spotted dust, presumably from asteroids banging together. The telescope did not find any evidence for a planet in the system, but astronomers speculate one or more may be present.

The movie begins at dusk on the imaginary world, when HD 69830, like our Sun, has begun to set over the horizon. Time is sped up to show the onset of night and the appearance of a brilliant band of light. This light comes from dust in a massive asteroid belt, which scatters sunlight.

In our solar system, anybody observing the skies on a moonless night far from city lights can see the sunlight that is scattered by dust in our asteroid belt. Called zodiacal light and sometimes the 'false dawn,' this light appears as a dim band stretching up from the horizon when the Sun is about to rise or set. The light is faint enough that the disk of our Milky Way galaxy remains the most prominent feature in the sky. (The Milky Way disk is shown perpendicular to the zodiacal light in both pictures.)

In contrast, the zodiacal light in the HD 69830 system would be 1,000 times brighter than our own, outshining even the Milky Way.

2005-01-01

283

Habitat Suitability Index Models: Belted Kingfisher  

USGS Publications Warehouse

A review and synthesis of existing information were used to develop a Habitat Suitability Index (HSI) model for the belted kingfisher (Ceryle alcyon). The model consolidates habitat use information into a framework appropriate for field application, and is scaled to produce an index between 0.0 (unsuitable habitat) to 1.0 (optimum habitat). HSI models are designed to be used with Habitat Evaluation Procedures previously developed by the U.S. Fish and Wildlife Service.

Prose, Bart L.

1985-01-01

284

Compositional structure of the asteroid belt  

Microsoft Academic Search

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

J. Gradie; E. Tedesco

1982-01-01

285

Attitudes of commercial motor vehicle drivers towards safety belts.  

PubMed

Despite the fact that Hawaii has one of the highest seat belt use rates for passenger vehicles in the United States, and has had a mandatory seat belt use law since the 1980s, studies have shown that commercial motor vehicles (CMV) seat belt use rates are low. To better understand this phenomenon, a comprehensive survey of commercial vehicle drivers was conducted in Hawaii to ascertain attitudes and self-reported behaviors regarding seat belt use. A total of 791 drivers responded to a written questionnaire implemented at weigh stations and distributed to various trucking firms and transport centers. Approximately 67% reported that they use seat belts "always" when driving a CMV (commercial motor vehicle), yet when asked how often do other CMV drivers use seat belts, only 31% responded "always." Interestingly, 86% of these same drivers reported that they use seat belts "always" when driving a personal vehicle. The major reason cited for non-use of belts was "frequent stops/inconvenience" (29%), and "not safety conscious" (23%). Notably, the self-reported use of safety belts is highest among operators of vans (88% said "always"), followed by buses (87% said "always") and lowest among truck drivers (only 60% said "always"). In this paper, some of the differences between self-reported users and non-users are explored and a multivariate logit model was developed to predict the odds of belt use as a function of various factors. PMID:17920831

Kim, Karl; Yamashita, Eric Y

2007-11-01

286

Rapid Rebuilding of the Outer Radiation Belt  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

287

Granulite belts of Central India with special reference to the Bhopalpatnam Granulite Belt: Significance in crustal evolution and implications for Columbia supercontinent  

NASA Astrophysics Data System (ADS)

The Central Indian collage incorporates the following major granulite belts: (1) the Balaghat-Bhandara Granulite Belt (BBG), (2) the Ramakona-Katangi Granulite Belt (RKG), (3) the Chhatuabhavna Granulite (CBG) of Bilaspur-Raigarh Belt, (4) the Makrohar Granulite Belt (MGB) of Mahakoshal supracrustals, (5) the Kondagaon Granulite Belt (KGGB), (6) the Bhopalpatnam Granulite Belt (BGB), (7) the Konta Granulite Belt (KTGB) and (8) the Karimnagar Granulite Belt (KNGB) of the East Dharwar Craton (EDC). We briefly synthesize the general geologic, petrologic and geochronologic features of these belts and explain the Precambrian crustal evolution in Central India. On the basis of the available data, a collisional relationship between Bastar craton and the EDC during the Paleo-Mesoproterozoic is reiterated as proposed by the earlier workers. The tectonic evolution of only few of the orogenic belts (BGB in particular) of Central India is related to Columbia.

Vansutre, Sandeep; Hari, K. R.

2010-11-01

288

A population of comets in the main asteroid belt.  

PubMed

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

Hsieh, Henry H; Jewitt, David

2006-04-28

289

On-Belt Analysis of Ash in Coal  

Microsoft Academic Search

A new neutron and gamma-ray analysis system has been developed for the direct on-conveyor belt analysis of ash in coal. This analysis system incorporates a method for ash measurements that is relatively independent of changes in segregation, belt loading, and ash composition. Consequently, the analysis system provides greater accuracy than on-belt dual energy gamma-ray transmission (DUET) gauges but at a

C. S. Lim; B. D. Sowerby; D. A. Abernethy

2002-01-01

290

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

291

Magnetic refrigeration apparatus with belt of ferro or paramagnetic material  

DOEpatents

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

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

1986-04-03

292

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

293

Period Determination of Six Main Belt Asteroids  

NASA Astrophysics Data System (ADS)

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

Ferrero, Andrea

2014-07-01

294

Euclid Asteroseismology and Kuiper Belt Objects  

E-print Network

Euclid, which is primarily a dark-energy/cosmology mission, may have a microlensing component, consisting of perhaps four dedicated one-month campaigns aimed at the Galactic bulge. We show that such a program would yield excellent auxilliary science, including asteroseimology detections for about 100,000 giant stars, and detection of about 1000 Kuiper Belt Objects (KBOs), down to 2--2.5 mag below the observed break in the KBO luminosity function at I ~26. For the 400 KBOs below the break, Euclid will measure accurate orbits, with fractional period errors <~ 2.5%.

Gould, A; Stello, D

2015-01-01

295

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

Code of Federal Regulations, 2014 CFR

... 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

296

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

Code of Federal Regulations, 2012 CFR

... 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...

2012-04-01

297

Geologic evolution of the neoproterozoic Zambezi orogenic belt in Zambia  

NASA Astrophysics Data System (ADS)

The Neoproterozoic Zambezi belt links with the Mozambique belt, Lufilian arc, and the inland branch of the Damara belt within the regional Pan-African tectonic framework of southern Africa. The belt contains a thick supracrustal sequence deposited on older sialic basement and penetratively deformed with it during Neoproterozoic (Pan-African) orogenesis. In Zambia, where the entire width of the orogen is exposed, local bimodal volcanic rocks at the base of the sequence are overlain by psammites and pelites, which in turn are succeeded by extensive carbonate and calc-silicate rocks. Abundant scapolite in metamorphic assemblages within the belt is taken as evidence for the original presence of evaporites. The nature of the rock types and the inferred stratigraphic sequence are consistent with deposition in an intracontinental rift basin invaded by marine waters. Available isotopic age brackets for the timing of supracrusta deposition show that the basin developed between 880 nad 820 Ma. Main-phase deformation in the belt involved both transcurrent shearing and south- to southwest-vergent thrusting and was associated with predominantly amphibolite-facies regional metamorphism. Mineral assemblages throughout much of the belt in Zambia, together with limited thermobarometric data, indicate typical Barrovian-type intermediate P/T conditions during metamorphism. Eclogites and other high-pressure metamorphic assemblages in parts of the belt, however, provide evidence that significant crustal thickening occurred, presumably in relation to thrusting. Reworked basement and syntectonic granite were subjected to extensive mylonitization related to strike-slip and oblique, reverse-slip shearing. The major orogenic event is dated at c. 820 Ma, based on an igneous age for a sheet-like, syntectonic batholith injected into a transcurrent shear zone within the central part of the belt. Pan-African orogenesis along the Zambezi-Lufilian-Damara trend was diachronous and records closure of intracratonic basins in the Zambezi belt and Lufilian arc, with evidence for the involvement of oceanic lithosphere present only in the Damara belt.

Hanson, Richard E.; Wilson, Terry J.; Munyanyiwa, Hubert

1994-02-01

298

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

299

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

300

Benefits of Seat Belt Reminder Systems  

PubMed Central

This study sought to determine whether fitting a more aggressive seat belt reminder system to new vehicles would be cost-beneficial for Australia. While seat belt wearing rates have been observed around 95% in the front seat, non-wearing rates in casualty crashes are as high as 33% among persons killed and 19% among seriously injured occupants. Benefits were computed for three device options (simple, simple-2 and complex) and three introduction scenarios (driver-only, front seat occupants and all occupants). Four levels of effectiveness were assumed, from 10% to 40%, depending on the type of device fitted. Unit benefits were computed assuming a 5% discount rate and a 15yr fleet life. Various industry experts provided the costs. The findings showed that Benefit-Cost-Ratios ranged from 4.0:1 at best (simple device for the driver only) to 0.9:1 for all seating positions. These figures are conservative, given the assumptions made and the discounted human capital methods used. PMID:12941229

Fildes, Brian; Fitzharris, Michael; Koppel, Sjaanie; Vulcan, Peter; Brooks, Chris

2003-01-01

301

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

302

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

303

Recovery Bias in the Kuiper Belt  

NASA Astrophysics Data System (ADS)

Are there observational biases in favor of recovering Kuiper belt objects (KBOs) in particular types of orbits? Depending on the quality, circumstances, and frequency of the discovery epoch astrometric measurements, an ephemeris used for a recovery observation may be highly uncertain, and based on an educated guess for an orbit (which in turn is based on the current understanding of Kuiper belt orbits). If enough time has passed since the previous measurements, only those objects for which the assumed orbits were nearly correct will be reliably recovered. The result of such a bias is that the KBOs that are preferentially lost are the very ones that are most interesting because they are not in ``typical'' assumed orbits. These biases are particularly sensitive to the measurements made within the first year of discovery. We use the objects from the well-characterized Canada-France Ecliptic Plane Survey (CFEPS) as the basis for our analysis of possible recovery biases, and compare results from different commonly-use methods of orbital fitting and ephemeris predictions. This work partially supported by grant NNG04GI29G through the NASA Planetary Astronomy Program.

Parker, Joel W.; CFEPS Team; Marsden, B. G.; Bieryla, A.

2007-10-01

304

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

305

Modulation of forelimb and hindlimb muscle activity during quadrupedal tied-belt and split-belt locomotion in intact cats.  

PubMed

The modulation of the neural output to forelimb and hindlimb muscles when the left and right sides step at different speeds from one another in quadrupeds was assessed by obtaining electromyography (EMG) in seven intact adult cats during split-belt locomotion. To determine if changes in EMG during split-belt locomotion were modulated according to the speed of the belt the limb was stepping on, values were compared to those obtained during tied-belt locomotion (equal left-right speeds) at matched speeds. Cats were chronically implanted for EMG, which was obtained from six muscles: biceps brachii, triceps brachii, flexor carpi ulnaris, sartorius, vastus lateralis and medial gastrocnemius. During tied-belt locomotion, cats stepped from 0.4 to 1.0m/s in 0.1m/s increments whereas during split-belt locomotion, cats stepped with left-right speed differences of 0.1 to 0.4m/s in 0.1m/s increments. During tied-belt locomotion, EMG burst durations and mean EMG amplitudes of all muscles respectively decreased and increased with increasing speed. During split-belt locomotion, there was a clear differential modulation of the EMG patterns between flexors and extensors and between the slow and fast sides. Changes in the EMG pattern of some muscles could be explained by the speed of the belt the limb was stepping on, while in other muscles there were clear dissociations from tied-belt values at matched speeds. Therefore, results show that EMG patterns during split-belt locomotion are modulated to meet task requirements partly via signals related to the stepping speed of the homonymous limb and from the other limbs. PMID:25644423

Frigon, A; Thibaudier, Y; Hurteau, M-F

2015-04-01

306

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

307

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

308

CONTINUOUS WEIGHING ON A CONVEYOR BELT WITH FIR FILTER  

Microsoft Academic Search

Today much higher speed of operation and highly accurate weighing of packages during crossing a conveyor belt has been getting more and more important in the food and distribution industries etc. Continuous weighing means that masses of discrete packages on a conveyor belt are automatically determined in sequence. Making the best use of new weighing scale called a multi-stage conveyor

Ryosuke Tasaki; Takanori Yamazaki; Hideo Ohnishi; Masaaki Kobayashi; Shigeru Kurosu

309

Adhesion degradation of rubber and steel insert for conveyor belts  

Microsoft Academic Search

The problem of degradation of rubber in conveyor belts is very important because they incorporate a lot of rubber and have a high value. In the paper we have analyzed the situation of rubber conveyor belts reinforced with metal insertions because it was found that they can sometimes be obsolete pretty fast due to the degradation of the connection between

Dan Dobrot?

2012-01-01

310

Crustal Deformation around Zhangjiakou-Bohai Seismically Active Belt  

NASA Astrophysics Data System (ADS)

Zhangjiakou-Bohai belt is a seismically active belt located in Northern China around Beijing, the capital of China. Near such a belt many great earthquakes occurred in the past centuries (e.g. the 1976 Tanshan Ms7.8 earthquake, the 1998 Zhangbei Ms6.2 earthquake, etc). Chinese Government established dense permanent and regional Global Positioning System (GPS) stations in and near the area. We collected and analyzed all the GPS observation data between 1999 and 2009 around Zhangjiakou-Bohai seismic belt, and obtained velocities at 143 stations. At the same time we investigated Zhangjiakou-Bohai belt slip rate for three profiles from northwest to southeast, and constructed a regional strain field on the Zhangjiakou-Bohai seismic belt region by least-square collocation. Based on the study we found that: 1) Nowadays the Zhangjiakou-Bohai seismic belt is creeping with left-lateral slip rate of 2.0mm~2.4mm/a, with coupling depth of 35~50km; 2) In total, the slip and coupling depth of the northwestern seismic belt is less than the one of southeast side; 3) The maximum shear strain is about 3×10-8 at Beijing-Tianjin-Tangshan area.

Jin, H.; Fu, G.; Kato, T.

2011-12-01

311

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

312

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

313

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

314

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

315

Gears and Belt Drives for Non-Uniform Transmission  

E-print Network

Gears and Belt Drives for Non-Uniform Transmission Hellmuth Stachel Abstract Ordinarily, gears and pulleys and their algorithmic computation. Concerning gears, we recall a method due to S. Finsterwalder without tightener. Keywords Nonuniform Transmission, Planar Gearing, Belt Drives, Geometric Kine- matics

Stachel, Hellmuth

316

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

317

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...

318

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 ...

319

THE PLANE OF THE KUIPER BELT Michael E. Brown  

E-print Network

THE PLANE OF THE KUIPER BELT Michael E. Brown Division of Geological and Planetary Sciences 30; accepted 2003 December 23 ABSTRACT We present a robust method for measuring the effective plane of the Kuiper belt. The derived plane has an inclination with respect to the ecliptic of 1 .86 and an ascending

Brown, Michael E.

320

ORIGINAL PAPER Analysis of conveyor belts in winter Mediterranean cyclones  

E-print Network

in half of the MCs. Third, the dry air intrusion originated north of the cyclone and extended southward conveyor belt (WCB), the cold conveyor belt (CCB), and the dry air intrusion (DAI). They are identified and the Human Environment, Tel Aviv University, Tel Aviv 69978, Israel E. Heifetz :N. Harnik :A. Baharad

Harnik, Nili

321

Prioritizing Safety with Seat Belts: The Unanswered Question.  

ERIC Educational Resources Information Center

Reviews conflicting federal and state developments (including liability lawsuits) involving seat belt installation on school buses. The National Highway Traffic Safety Administration and the National Transportation Safety Board differ on this issue, and several states are considering seat belt legislation or crashworthiness studies. Hints are…

Farrell, Elaine

1987-01-01

322

The fossilized size distribution of the main asteroid belt  

Microsoft Academic Search

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

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

2005-01-01

323

Visible and infrared photometry of Kuiper Belt objects: searching for evidence of trends  

E-print Network

Visible and infrared photometry of Kuiper Belt objects: searching for evidence of trends Neil Mc. © 2003 Elsevier Science (USA). All rights reserved. Keywords: Kuiper Belt objects; Photometry; Infrared

Sheppard, Scott S.

324

Neptune's eccentricity and the nature of the kuiper belt  

PubMed

The small eccentricity of Neptune may be a direct consequence of apsidal wave interaction with the trans-Neptune population of debris called the Kuiper belt. The Kuiper belt is subject to resonant perturbations from Neptune, so that the transport of angular momentum by density waves can result in orbital evolution of Neptune as well as changes in the structure of the Kuiper belt. In particular, for a belt eroded out to the vicinity of Neptune's 2:1 resonance at about 48 astronomical units, Neptune's eccentricity can damp to its current value over the age of the solar system if the belt contains slightly more than an earth mass of material out to about 75 astronomical units. PMID:9641913

Ward; Hahn

1998-06-26

325

Neptune's Eccentricity and the Nature of the Kuiper Belt  

NASA Technical Reports Server (NTRS)

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

Ward, William R.; Hahn, Joseph M.

1998-01-01

326

A search for active main-belt asteroids  

NASA Astrophysics Data System (ADS)

Active Main Belt asteroids are bodies within the Main Belt of asteroids which have shown comet-like activity during parts of their orbits. So far, just a handful of active Main Belt asteroids has been found. A representative example is the first known Main Belt comet 133P/(7968) Elst-Pizarro. Jewitt [1] proposed possible mechanisms for producing mass loss from asteroids, but the cause of the activity of all known active Main Belt asteroids remains still unknown. Statistically, there are indications that there exist many more currently active Main Belt asteroids, but hunting for them by searching for typical cometary features, like tail or coma, requires a lot of telescope time in the middle- and large-class telescopes, and does not guarantee success in detecting them all. If the mass-loss mechanisms causing the activities are too weak to develop visually evident comae or tails, the objects stay unnoticed. We are presenting a novel way to search [2] for active asteroids, based on looking for objects with deviations from their expected brightness in the MPCAT- OBS Observation Archive. From ~75 million observations in total, covering ~300'000 numbered objects, we have extracted five new candidate objects that possibly show a type of comet-like activity, and the already known Main Belt comet 133P/(7968) Elst-Pizarro. We discuss our search method, show deviation curves of the five new candidates compared to non-active Main Belt asteroids and give possible explanations for causes of their possible activities. The method could be implemented in the future sky survey programs like the Large Synoptic Sky Telescope (LSST) and the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) to detect outbursts on Main Belt objects almost simultaneously with their occurrence, which is potentially interesting when searching for impact events in the Main Belt.

Cikota, S.; Ortiz, J.; Cikota, A.; Morales, N.; Tancredi, G.

2014-07-01

327

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

328

Testing Collisional Grinding in the Kuiper Belt  

NASA Astrophysics Data System (ADS)

We propose a SNAP survey of 56 small Cold Classical TNOs to compare their colors and rate of binarity to larger members of this most-primitive Kuiper belt group. Collisional grinding models that can explain the observed turn-over in the magnitude-frequency distribution imply that small binaries should also be disrupted, but at a brighter, more readily observable threshold. Likewise, collisional erosion could expose differently-colored interior materials. If we do not see a decline in binary rates and a change in color statistics, these observations would pose a challenge to the collisional grinding scenario, suggesting instead that the magnitude-frequency distribution turnover is a more ancient signature of the planetesimal accretion process.

Grundy, William

2012-10-01

329

Kinematics of Gould's Belt: Model and Observations  

NASA Astrophysics Data System (ADS)

Using the available data for nearby stars we derive the velocity ellipsoid of dwarf O-B5.5 stars belonging to the Gould Belt (GB). The resulting vertex deviation for the whole sample is negative (l ~ -70^°) and this value is modified to l~ 20^° when the members of the Pleiades moving group are removed from the sample. This implies the existence of, at least, two different kinematic groups defining the GB system. We also model the evolution of a supershell in the solar neighborhood, and obtain a fit to the shape and kinematics of the gas in GB. Assuming that the expanding shell is also forming stars, we obtain the corresponding velocity fields for the shell and its newly formed stars. The average vertex deviation value resulting from these models for the new stars is l~ 20^°, and is consistent with the observed value when the Pleiades moving group members are excluded from the GB.

Alfaro, E. J.; Moreno, E.; Franco, J.

330

What Drives the Global Conveyer Belt?  

NSDL National Science Digital Library

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

331

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

332

A Comprehensive Simulation Method for Examining Radiation Belt Dynamics  

NASA Astrophysics Data System (ADS)

The particles comprising the Van Allen radiation belts are affected by a variety of electromagnetic and electrostatic waves present in the magnetosphere. For example, the Van Allen Probes mission has recently uncovered evidence for heating in the radiation belts as a result of local kHz wave-particle interactions, violating the cyclotron invariant. Similarly, global variations at mHz frequencies commensurate with the particle drift frequency can lead to effective transport, heating, and loss within the radiation belts as a result of changes to the third adiabatic invariant. The wide variety of waves occurring over this disparate frequency range presents a fundamental challenge in constructing dynamic models of the radiation belts. In this effort we present results from a new method for tracking the global dynamics of the radiation belts. Here we examine a well-observed flux dropout and subsequent acceleration event occurring on 20 September 2007. We use 3d magnetohydrodynamic (MHD) simulations of the solar wind/magnetospheric interaction to track particles in a bounce-averaged formalism, combined with stochastic differential equation (SDE) simulations of local wave-particle interactions, to provide a comprehensive model of the radiation belts encompassing both large-scale transport and local heating and loss within the radiation belts.

Elkington, S. R.; Chan, A. A.; Zheng, L.

2013-12-01

333

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

334

The Fossilized Size Distribution of the Main Asteroid Belt  

NASA Astrophysics Data System (ADS)

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

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

2004-05-01

335

Dynamic models for ridge belt formation on Venus  

NASA Technical Reports Server (NTRS)

The hypothesis is tested that the lithospheric shortening expressed by the ridge belts is the result of convective downwelling beneath the lowland planitia. Dynamical models are developed for the interaction of mantle convection with the crust and the models are compared to the characteristics of the ridge belts in Lavinia Planitia. The models support the hypothesis that convective stresses can produce the broad topographic depression of lowlands on Venus and can lead to the formation of ridge belts on either side of the topographic low.

Simons, Mark; Solomon, Sean C.; Hager, Bradford H.

1991-01-01

336

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

337

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

338

Mode-I fatigue crack growth analysis of V-ribbed belts  

Microsoft Academic Search

One factor which is critical to the life of automotive serpentine belts is their failure due to propagation of initially small flaws in the elastomer located in the belt rib. This paper aims to develop a predictive fatigue crack growth model for serpentine belts with initially small rib tip flaws. The study combines the fatigue crack growth tests for belt

S. Sundararaman; G. Liang; K. Chandrashekhara; L. R. Oliver; S. G. Holmes

2007-01-01

339

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

340

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

341

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...

342

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

343

Bifurcation for Dynamical Systems of Planet-Belt Interaction  

NASA Astrophysics Data System (ADS)

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.

Jiang, I.-G.; Yeh, L.-C.

2003-03-01

344

2. DETAIL OF CONVEYOR BELT PATH AND CATWALK, NORTHEAST VIEW. ...  

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

2. DETAIL OF CONVEYOR BELT PATH AND CATWALK, NORTHEAST VIEW. - Vanadium Corporation of America (VCA) Naturita Mill, Grinding Rod Mill, 3 miles Northwest of Naturita, between Highway 141 & San Miguel River, Naturita, Montrose County, CO

345

5. DETAIL OF ROD MILL BASE AND CONVEYOR BELT SUPPORT, ...  

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

5. DETAIL OF ROD MILL BASE AND CONVEYOR BELT SUPPORT, EAST VIEW. - Vanadium Corporation of America (VCA) Naturita Mill, Grinding Rod Mill, 3 miles Northwest of Naturita, between Highway 141 & San Miguel River, Naturita, Montrose County, CO

346

Nanomaterial modifications on conductivity of coal conveyer belt  

SciTech Connect

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

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

2008-08-15

347

Unbiased Inclination Distributions for Objects in the Kuiper Belt  

E-print Network

Using data from the Deep Ecliptic Survey (DES), we investigate the inclination distributions of objects in the Kuiper Belt. We present a derivation for observational bias removal and use this procedure to generate unbiased ...

Gulbis, Amanda A. S.

348

CDC Vital Signs: Adult Seat Belt Use in the US  

MedlinePLUS

... t wearing their seat belts on every trip. Motor vehicle crashes are the leading cause of death for people age 5 - 34. More than 2.3 million adult drivers and passengers were treated in emergency departments for ...

349

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

350

Previously Undetected Radiation Belt Revealed - Duration: 63 seconds.  

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...

351

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

352

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

353

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.

354

Collisional evolution of the asteroid belt  

NASA Astrophysics Data System (ADS)

A new synthesis of asteroid collisional evolution is motivated by the question of whether most asteroids larger than ˜1 km size are strengthless gravitational aggregates (rubble piles). NEAR found Eros not to be a rubble pile, but a shattered collisional fragment, with a through-going fracture system, and an average of about 20 m regolith cover. Of four asteroids visited by spacecraft, none appears likely to be a rubble pile, except perhaps Mathilde. Nevertheless, current understanding of asteroid collisions and size-dependent strength, and the observed distribution of rotation rates versus size, have led to a theoretical consensus that many or most asteroids larger than 1 km should be rubble piles. Is Eros, the best-observed asteroid, highly unusual because it is not a rubble pile? Is Mathilde, if it is a rubble pile, like most asteroids? What would be expected for the small asteroid Itokawa, the MUSES-C sample return target? An asteroid size distribution is synthesized from the Minor Planet Center listing and results of the Sloan Digital Sky Survey, an Infrared Space Observatory survey, the Small Main-belt Asteroid Spectroscopic Survey and the Infrared Astronomical Satellite survey. A new picture emerges of asteroid collisional evolution, in which the well-known Dohnanyi result, that the size distribution tends toward a self-similar form with a 2.5-index power law, is overturned because of scale-dependent collision physics. Survival of a basaltic crust on Vesta can be accommodated, together with formation of many exposed metal cores. The lifetimes against destruction are estimated as 3 Gyr at the size of Eros, 10 Gyr at ten times that size, and 40 Gyr at the size of Vesta. Eros as a shattered collisional fragment is not highly unusual. The new picture reveals the new possibility of a transition size in the collisional state, where asteroids below 5 km size would be primarily collisional breakup fragments whereas much larger asteroids are mostly eroded or shattered survivors of collisions. In this case, well-defined families would be found in asteroids larger than about 5 km size, but for smaller asteroids, families may no longer be readily separated from a background population. Moreover, the measured boulder size distribution on Eros is re-interpreted as a sample of impactor size distributions in the asteroid belt. The regolith on Eros may result largely from the last giant impact, and the same may be true of Itokawa, in which case about a meter of regolith would be expected there. Even a small asteroid like Itokawa may be a shattered object with regolith cover.

Cheng, Andrew F.

2004-06-01

355

Exploring fold and thrust belts in Google Earth  

NSDL National Science Digital Library

Google Earth enhances traditional geologic maps by allowing the viewer to explore three-dimensional map patterns and the interaction between structure and topography in dictating those map patterns. This activity overlays 4, 7.5' USGS quadrangles on Google Earth terrain and imagery data and encourages students to investigate common features of fold-and-thrust belts. Keywords: Google Earth, fold-and-thrust belt, visualization

Jack Loveless

356

Flat belt continuously variable high speed drive. Final report  

Microsoft Academic Search

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

Kumm

1992-01-01

357

The Gurupi Belt, northern Brazil: Lithostratigraphy, geochronology, and geodynamic evolution  

Microsoft Academic Search

The Gurupi Belt is located in northern Brazil on the southern margin of the São Luís Craton, which is dominated by juvenile calc-alkaline rocks formed in intra-oceanic island arcs between 2240 and 2150Ma. The Gurupi Belt consists of: (i) small lenses of an Archean metatonalite of 2594Ma; (ii) calc-alkaline\\/TTG tonalites and gneisses of 2147–2168Ma and juvenile Nd isotope signature, formed

Evandro L. Klein; Candido A. V. Moura; Robert S. Krymsky; William L. Griffin

2005-01-01

358

Sedimentology and facies of a Mississippi River meander belt  

SciTech Connect

The meander belt of the Mississippi River in Southeastern Missouri, consists of four facies: river channel, chute, levee, and abandoned channel fill. A depositional model and vertical sequences have been developed from drill cores, vibracores, fathometer surveys, and mapping of these facies. This model and the vertical sequences compare very well to ancient sequences. The vertical sequences observed in cores through the various facies systems have systematic variations and associations that serve as models for meander belt fluvial systems.

Pryor, W.A.; Jordan, D.W.

1988-01-01

359

External Prestressing Concrete Columns with Fibrous Composite Belts  

Microsoft Academic Search

Synopsis: Synopsis: Synopsis: Synopsis: Synopsis: Five square columns were constructed to model shear-deficient columns and tested under constant axial compression and reversed cyclic lateral load, simultaneously. The retrofitting scheme consisted of wrapping the column along its end parts, i.e. around the plastic hinge area, by use of FRP in the form of three-centimeter wide belts. Both carbon and aramid\\/epoxy belts

K. N. Nesheli; K. Meguro

360

Multifractal Fits to the Observed Main Belt Asteroid Distribution  

Microsoft Academic Search

Dohnanyi's (J. W. Dohnanyi, 1969, J. Geophys. Res.74, 2531–2554) theory predicts that a collisional system such as the asteroidal population of the main belt should rapidly relax to a power-law stationary size distribution of the kind N(m)?m??, with ? very close to 11\\/6, provided all the collisional response parameters are independent of size. The actual asteroid belt distribution at observable

Adriano Campo Bagatin; Vicent J. Mart??nez; Silvestre Paredes

2002-01-01

361

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

362

Energy exchange between subject and belt during treadmill walking.  

PubMed

Treadmill walking aims to simulate overground walking, but intra-stride belt speed variations of treadmills result in some interaction between treadmill and subject, possibly obstructing this aim. Especially in self-paced treadmill walking, in which the belt speed constantly adjusts to the subject, these interactions might affect the gait pattern significantly. The aim of this study was to quantify the energy exchange between subject and treadmill, during the fixed speed (FS) and self-paced (SP) modes of treadmill walking. Eighteen subjects walked on a dual-belt instrumented treadmill at both modes. The energy exchange was calculated as the integration of the product of the belt speed deviation and the fore-aft ground reaction force over the stride cycle. The total positive energy exchange was 0.44 J/stride and the negative exchange was 0.11 J/stride, which was both less than 1.6% of the performed work on the center of mass. Energy was mainly exchanged from subject to treadmill during both the braking and propulsive phase of gait. The two treadmill modes showed a similar pattern of energy exchange, with a slightly increased energy exchange during the braking phase of SP walking. It is concluded that treadmill walking is only mildly disturbed by subject-belt interactions when using instrumented treadmills with adequate belt control. PMID:24589022

Sloot, L H; van der Krogt, M M; Harlaar, J

2014-04-11

363

Radial transport in the Earth's radiation belts (Invited)  

NASA Astrophysics Data System (ADS)

For over forty years the standard approach to modeling the dynamics of the Earth's radiation belts has been based on a diffusion equation, which can be derived from the Vlasov equation using a quasilinear approximation. The radiation belt diffusion equation describes the evolution of a particle distribution function in a space of one or several of the three adiabatic invariants associated with the motions of a charged particle in a dipole magnetic field. Increasingly, observations and theoretical studies suggest that fully nonlinear transport, not modeled by quasilinear diffusion, plays an important role in radiation belt dynamics, e.g., the shock-drift mechanism modeled by Li et al. [1993]. This presentation will focus on radiation belt particle transport across magnetic L-shells (loosely called radial transport). Radial transport is thought to be one of the primary drivers of radiation belt dynamics. A comprehensive review of the known mechanisms of radial transport and some of their effects will be given, including those that can be modeled with a diffusion equation and those requiring a fully nonlinear treatment. Li, X., I. Roth, M. Temerin, J. R. Wygant, M. K. Hudson, and J. B. Blake, (1993), Simulations of the prompt energization and transport of radiation belt particles during the March 24, 1991 SSC, Geophys. Res. Lett., 20, 2423.

Kress, B. T.; Ukhorskiy, A. Y.; Hudson, M. K.

2010-12-01

364

Late Cretaceous deformation of the Pieniny Klippen Belt, West Carpathians  

NASA Astrophysics Data System (ADS)

The Late Cretaceous position and dynamics of the Pieniny Klippen Belt of the West Carpathians, which lies behind the Palaeogene flysch accretionary prism, are reconstructed. As shown by the reconstruction, based on structural, sedimentological and palaeomagnetic data, the Pieniny Klippen Belt occupied a WNW-ESE to NW-SE trending zone during the Late Cretaceous, which acted as an oblique convergent boundary between the ancestral West Carpathians and the oceanic lithosphere attached to the North European platform. Sediments of the Pieniny Klippen Belt were part of both the mountain belt and foredeep at that time. Known change from pelagic micritic limestone to a flysch sequence is progressively younger seawards in the thrust-slice stack forming the Pieniny Klippen Belt. The syn-sedimentary record includes flysch, olistostrome and wildflysch sediments. Both the NW-SE thrusting along the NE-SW striking faults and dextral strike-slip faulting along the WNW-ESE to NW-SE striking faults were active in the Late Cretaceous in the area of the current Pieniny Klippen Belt.

Nemcok, M.; Nemcok, J.

1994-12-01

365

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

366

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

367

The Walker Lane Belt in northeastern California  

SciTech Connect

The Walker Lane Belt (WLB) has been suspected to significantly project NW-ward into NE CA from the Pyramid Lake-Honey Lake area which has been generally regarded as its northwestern terminus. Within the WLB, most of the exposed rocks are Miocene to Late Quaternary (10--0.1 Ma) volcanics, mainly andesitic, but significantly rhyolitic and basaltic. The Hayden Hill Au mine within a Mid-Miocene NNW-SSE volcanotectonic depression and the Quaternary NE-SW Eagle lake volcanotectonic depression are confined within the WLB. Most of the faults are high-angle normal and right normal, W-dipping, NW- to N-trending, and locally left-stepping en echelon, and 2 to 18 km long. Dip slip varies from 10 to 200 m. Strike slip across the entire zone seems impossible to determine, but probably is less than 20 km since Mid-Miocene. Many faults localize volcanic vents, though most do not appear to. Tectonic tilt of beds within fault blocks is less than 10[degree]. Fault activity and volcanism both continued at a slow rate from Mid-Miocene to Late Quaternary. The WLB in NE CA is a transitional boundary between the Sierra Nevada-Cascade arc on the southwest and the Basin and Range-Modoc Plateau on the northeast.

Grose, T.L.T. (Colorado School of Mines, Golden, CO (United States). Dept. of Geology and Geological Engineering)

1993-04-01

368

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

Microsoft Academic Search

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

Brian Creaser; George Spence

2005-01-01

369

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

370

Processes on the Young Earth and the Habitats of Early Life  

NASA Astrophysics Data System (ADS)

Conditions at the surface of the young (Hadean and early Archean) Earth were suitable for the emergence and evolution of life. After an initial hot period, surface temperatures in the late Hadean may have been clement beneath an atmosphere containing greenhouse gases over an ocean-dominated planetary surface. The first crust was mafic and it internally melted repeatedly to produce the felsic rocks that crystallized the Jack Hills zircons. This crust was destabilized during late heavy bombardment. Plate tectonics probably started soon after and had produced voluminous continental crust by the mid Archean, but ocean volumes were sufficient to submerge much of this crust. In the Hadean and early Archean, hydrothermal systems around abundant komatiitic volcanism may have provided suitable sites to host the earliest living communities and for the evolution of key enzymes. Evidence from the Isua Belt, Greenland, suggests life was present by 3.8 Gya, and by the mid-Archean, the geological record both in the Pilbara in Western Australia and the Barberton Greenstone Belt in South Africa shows that microbial life was abundant, probably using anoxygenic photosynthesis. By the late Archean, oxygenic photosynthesis had evolved, transforming the atmosphere and permitting the evolution of eukaryotes.

Arndt, Nicholas T.; Nisbet, Euan G.

2012-05-01

371

Public Access to Digital Material; A Call to Researchers: Digital Libraries Need Collaboration across Disciplines; Greenstone: Open-Source Digital Library Software; Retrieval Issues for the Colorado Digitization Project's Heritage Database; Report on the 5th European Conference on Digital Libraries, ECDL 2001; Report on the First Joint Conference on Digital Libraries.  

ERIC Educational Resources Information Center

These six articles discuss various issues relating to digital libraries. Highlights include public access to digital materials; intellectual property concerns; the need for collaboration across disciplines; Greenstone software for construction and presentation of digital information collections; the Colorado Digitization Project; and conferences…

Kahle, Brewster; Prelinger, Rick; Jackson, Mary E.; Boyack, Kevin W.; Wylie, Brian N.; Davidson, George S.; Witten, Ian H.; Bainbridge, David; Boddie, Stefan J.; Garrison, William A.; Cunningham, Sally Jo; Borgman, Christine L.; Hessel, Heather

2001-01-01

372

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

PubMed

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

Grosch, Eugene G; McLoughlin, Nicola

2014-06-10

373

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

PubMed Central

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

Grosch, Eugene G.; McLoughlin, Nicola

2014-01-01

374

Use of rib belts in acute rib fractures.  

PubMed

The current treatment for uncomplicated rib fractures is the exclusion of associated injuries followed by symptomatic treatment with analgesics. Encouragement of deep breathing is also recommended to avoid secondary or delayed pulmonary complications. The use of circumferential rib belts in treating patients with acute rib fractures has been discouraged because of possible complications from restricted ventilation. A review of the literature revealed no previous clinical studies to support this view. We designed and conducted a controlled, prospective, randomized pilot study to determine if there was any increased morbidity associated with the use of rib belts in the treatment of patients with acute rib fractures. Twenty-five adult patients with radiographically proven acute rib fractures were randomized into two groups. The first group was treated with analgesics and a standard circumferential rib belt (Zimmer Universal Rib Belt). The second group was treated with oral analgesics alone. Patients were contacted by telephone three days after the initial injury and then reexamined 14 days postinjury. Rates of pain resolution, compliance, and delayed complications were determined. Rib belts were not found to significantly reduce the severity of pain. Four complications (one case of bloody pleural effusion requiring hospitalization, two cases of asymptomatic discoid atelectasis, and one case of allergic contact dermatitis) were identified, all occurring in the group of patients receiving rib belts. This pilot study indicates that while rib belts are widely accepted by patients for control of pain, they appear to be associated with an increased incidence of complications. Clinical studies with larger sample sizes will be needed to confirm these findings. PMID:2643965

Lazcano, A; Dougherty, J M; Kruger, M

1989-01-01

375

Super-Comet or Big Asteroid Belt?  

NASA Technical Reports Server (NTRS)

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

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

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

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

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

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

2005-01-01

376

The Fossilized Size Distribution of the Main Asteroid Belt  

NASA Astrophysics Data System (ADS)

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

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

2003-05-01

377

Basal Murphy belt and Chilhowee Group -- Sequence stratigraphic comparison  

SciTech Connect

The lower Murphy belt in the central western Blue Ridge is interpreted to be correlative to the Early Cambrian Chilhowee Group of the westernmost Blue Ridge and Appalachian fold and thrust belt. Basal Murphy belt depositional sequence stratigraphy represents a second-order, type-2 transgressive systems tract initiated with deposition of lowstand turbidites of the Dean Formation. These transgressive deposits of the Nantahala and Brasstown Formations are interpreted as middle to outer continental shelf deposits. Cyclic and stacked third-order regressive, coarsening upwards sequences of the Nantahala Formation display an overall increase in feldspar content stratigraphically upsection. These transgressive siliciclastic deposits are interpreted to be conformably overlain by a carbonate highstand systems tract of the Murphy Marble. Palinspastic reconstruction indicates that the Nantahala and Brasstown Formations possibly represent a basinward extension of up to 3 km thick siliciclastic wedge. The wedge tapers to the southwest along the strike of the Murphy belt at 10[degree] and thins northwestward to 2 km in the Tennessee depocenter where it is represented by the Chilhowee Group. The Murphy belt basin is believed to represent a transitional rift-to-drift facies deposited on the lower plate of the southern Blue Ridge rift zone.

Aylor, J.G. Jr. (Florida State Univ., Tallahassee, FL (United States). Dept. of Geology)

1994-03-01

378

Angle stations in or for endless conveyor belts  

DOEpatents

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

Steel, Alan (Glasgow, GB6)

1987-04-07

379

Fall Protection Characteristics of Safety Belts and Human Impact Tolerance  

PubMed Central

Abstract: Many fatal accidents due to falls from heights have occurred at construction sites not only in Japan but also in other countries. This study aims to determine the fall prevention performance of two types of safety belts: a body belt1), which has been used for more than 40?yr in the Japanese construction industry as a general type of safety equipment for fall accident prevention, and a full harness2, 3), which has been used in many other countries. To determine human tolerance for impact trauma, this study discusses features of safety belts with reference4,5,6,7,8,9) to relevant studies in the medical science, automobile crash safety, and aircrew safety. For this purpose, simple drop tests were carried out in a virtual workplace to measure impact load, head acceleration, and posture in the experiments, the Hybrid-III pedestrian model10) was used as a human dummy. Hybrid-III is typically employed in official automobile crash tests (New Car Assessment Program: NCAP) and is currently recognized as a model that faithfully reproduces dynamic responses. Experimental results shows that safety performance strongly depends on both the variety of safety belts used and the shock absorbers attached onto lanyards. These findings indicate that fall prevention equipment, such as safety belts, lanyards, and shock absorbers, must be improved to reduce impact injuries to the human head and body during falls. PMID:25345426

HINO, Yasumichi; OHDO, Katsutoshi; TAKAHASHI, Hiroki

2014-01-01

380

Jovian Early Bombardment: Planetesimal Erosion in the Inner Asteroid Belt  

NASA Astrophysics Data System (ADS)

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

Turrini, D.; Coradini, A.; Magni, G.

2012-05-01

381

JOVIAN EARLY BOMBARDMENT: PLANETESIMAL EROSION IN THE INNER ASTEROID BELT  

SciTech Connect

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

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

2012-05-01

382

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-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. PMID:24646996

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

2014-03-20

383

The binary Kuiper-belt object 1998 WW31.  

PubMed

The recent discovery of a binary asteroid during a spacecraft fly-by generated keen interest, because the orbital parameters of binaries can provide measures of the masses, and mutual eclipses could allow us to determine individual sizes and bulk densities. Several binary near-Earth, main-belt and Trojan asteroids have subsequently been discovered. The Kuiper belt-the region of space extending from Neptune (at 30 astronomical units) to well over 100 AU and believed to be the source of new short-period comets-has become a fascinating new window onto the formation of our Solar System since the first member object, not counting Pluto, was discovered in 1992 (ref. 13). Here we report that the Kuiper-belt object 1998 WW31 is binary with a highly eccentric orbit (eccentricity e approximately 0.8) and a long period (about 570 days), very different from the Pluto/Charon system, which was hitherto the only previously known binary in the Kuiper belt. Assuming a density in the range of 1 to 2 g cm-3, the albedo of the binary components is between 0.05 and 0.08, close to the value of 0.04 generally assumed for Kuiper-belt objects. PMID:11961547

Veillet, Christian; Parker, Joel Wm; Griffin, Ian; Marsden, Brian; Doressoundiram, Alain; Buie, Marc; Tholen, David J; Connelley, Michael; Holman, Matthew J

2002-04-18

384

Flat belt continuously variable high speed drive. Final report  

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

385

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

386

Seat belt use among overweight and obese adolescents.  

PubMed

Motor vehicle crashes are the leading cause of death for adolescents. Previous studies with adults found an association between weight status and decreased use of seat belts. Research has also found significantly higher morbidity and mortality rates in obese individuals who are involved in motor vehicle crashes. If these relationships hold true in obese adolescents they represent additional risk factors for complications from motor vehicle trauma. Given the prevalence of obesity in adolescents (17.4%) and the increased risk of harm associated with obese individuals involved in motor vehicle crashes, this study explored whether there was an association between obesity in adolescents and their use of seat belts. Initial investigation found that rarely/never wearing seat belts was significantly greater for African Americans (22.6%), 18 years of age or older (19.4%), lived with adults other than both parents (15.7%), and males (15.4%). Bivariate logistic regression analysis controlling for demographic variables found that there was no statistically significant difference between overweight and normal weight adolescents. However, obese students were 1.72 times as likely as normal weight students to never or rarely wear their seat belts when riding in a car as a passenger. In particular, obese females and obese students in the middle school age ranges were statistically significantly more likely than normal weight students to never or rarely wear their seat belts. PMID:21181247

Price, James H; Dake, Joseph A; Balls-Berry, Joyce E; Wielinski, Margaret

2011-08-01

387

Image processing system for monitoring of conveyor belt systems  

NASA Astrophysics Data System (ADS)

A prototype of an image processing system for the monitoring of conveyor belt systems in video real time is described. To avoid completely hazardous situations, special requirements on the robustness and the computational efficiency of the system under heavy climatic and illumination conditions have to be met. For the computation of the belt loading and the position of the conveyed masses the profile of the loaded belt is subtracted from a stored profile of the empty belt. Both empty and loaded belt profiles are estimated using the triangulation principle. A model based algorithm combined with a two-step classificator is applied to detect large stones or other bulky objects from a sequence of profiles. The gray level characteristics of the conveyed masses are computed, using features derived from the ID histogram. The structure of the masses is evaluated using a modified fractal operator. One class out of a predefined set of classes is selected. Image processing hardware based on the digital signal processor TMS320C30 is applied.

Ivanov, Eugenyi; Osten, Wolfgang; Jueptner, Werner P. O.

1994-03-01

388

Local Acceleration of Radiation Belt Electrons: Where? When? and How?  

NASA Astrophysics Data System (ADS)

Two broad classes of processes are capable of accelerating radiation belt electrons to ultra-relativistic energies: radial acceleration by inward diffusion from a high-altitude source population and local acceleration of an in situ source population by wave-particle interactions. Recently the Van Allen Probes mission provided unambiguous observations of local acceleration for one of the first radiation belt enhancement events of the mission on October 8-9, 2012 [Reeves et al., 2013]. Now, with over a year of Van Allen Probes observations, it is possible to conduct a larger survey of radiation belt enhancement events. Level 4 phase space densities recently been made available by the RBSP-ECT science operations center using data from the Magnetic Electron Ion Spectrometer (MagEIS) [Blake et al., 2013] and Van Allen Probes magnetic ephemeris files [Henderson et al., 2013]. In this presentation we survey the radial profiles of phase space density as a function of the magnetic invariants (mu, K, and L*) for characteristic signatures of local acceleration through wave particle interactions. We examine how many radiation belt enhancement events show signatures of local acceleration and determine where the peak acceleration occurred. We compare the observations with the expectations from theories of local acceleration in order to better understand the generation mechanisms and the relative roles of local acceleration and radial diffusion in controlling radiation belt dynamics.

Reeves, G. D.; Henderson, M. G.; Morley, S.; Larsen, B.; Friedel, R. H.; Claudepierre, S. G.; Fennell, J. F.; Blake, J. B.; Boyd, A. J.; Spence, H.; Kanekal, S. G.; Baker, D. N.; Skoug, R. M.; Funsten, H. O.

2013-12-01

389

Detection Biases for Resonant Kuiper Belt Objects  

NASA Astrophysics Data System (ADS)

Using the Canada-France Ecliptic Plane Survey (CFEPS) we have performed detailed modeling of Trans-Neptunian Objects (TNOs) in mean-motion resonances with Neptune, producing absolute population estimates for ten resonances. Because CFEPS is well-characterized, we are able to de-bias the survey to study the internal structure of the most populated resonances, especially the 3:2. To de-bias, we must account for the survey's pointings: TNOs will come to perihelion at specific ecliptic positions which depend on the resonant angle and the libration amplitude distribution. For the plutino Kozai subcomponent, the biases are more complicated, because pericenter will occur at high ecliptic latitudes. This results in ecliptic surveys being inherently biased against detecting Kozai resonators. We discuss constraints we can place on the inherent plutino Kozai fraction. For the 3:2 and 5:2 resonances, we are able to constrain the power-law H-magnitude distribution as well as the eccentricity, inclination, and libration amplitude distributions. The n:3, n:4, and 2:1 resonances have fewer detections, and we provide population estimates and constrain the inclination distributions. For poorly-sampled resonances (the 3:1 and 5:1), we give only rough population estimates. These are the first absolute population estimates for most of these resonances. In particular, we find the populations of H < 9 objects in the 3:2 and 5:2 resonances to be roughly equal. Although somewhat model-dependent, we find that the population of the 2:1 resonance is a factor of 4 smaller than that of the 3:2 resonance. If resonant TNOs were emplaced during migration late in the giant planet formation process, these population ratios may give clues about the state of the Kuiper Belt at the time of planet migration and about the migration rate. Our nominal 3:2/2:1/5:2 population ratios of 4/1/4 are not produced in published models of resonant TNO production.

Lawler, Samantha; Gladman, B.; Petit, J.; Kavelaars, J.; Jones, R.; Parker, J.

2010-10-01

390

The Size Frequency Distribution of Small Main-Belt Asteroids  

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

391

Jovian Early Bombardment: planetesimal erosion in the inner asteroid belt  

E-print Network

The asteroid belt is an open window on the history of the Solar System, as it preserves records of both its formation process and its secular evolution. The progenitors of the present-day asteroids formed in the Solar Nebula almost contemporary to the giant planets. The actual process producing the first generation of asteroids is uncertain, strongly depending on the physical characteristics of the Solar Nebula, and the different scenarios produce very diverse initial size-frequency distributions. In this work we investigate the implications of the formation of Jupiter, plausibly the first giant planet to form, on the evolution of the primordial asteroid belt. The formation of Jupiter triggered a short but intense period of primordial bombardment, previously unaccounted for, which caused an early phase of enhanced collisional evolution in the asteroid belt. Our results indicate that this Jovian Early Bombardment caused the erosion or the disruption of bodies smaller than a threshold size, which strongly depen...

Turrini, Diego; Magni, Gianfranco

2012-01-01

392

Two new basaltic asteroids in the Outer Main Belt  

E-print Network

The identification of other basaltic objects in the asteroid belt is mandatory to explain the diversity in the collection of basaltic meteorites. This diversity requires more than one differentiated parent body, a fact that is consistent with the diversity of differentiated parent bodies implied by the iron meteorites. Based on a list of previously identified candidate basaltic (V-type) asteroids, two asteroids in the outer main belt, (7472) Kumakiri and (10537) 1991 RY16, were spectroscopically observed during an observational run in Calar Alto Observatory, Spain. We confirm the V-type character of these two asteroids that, together with (1459) Magnya, become the only known traces of basaltic found in the outer main belt up to now. We also demonstrate that the searching for candidate V-type asteroids using a photometric survey, like the Sloan Digital Sky Survey, produces reliable results.

Duffard, R

2007-01-01

393

A Search for 23rd Magnitude Kuiper Belt Comets  

NASA Technical Reports Server (NTRS)

The goal of the project was to identify a statistically significant sample of large (200 km-sized) Kuiper Belt Objects (KBOs), by covering 10 sq. degrees of the sky to a red limiting magnitude m(sub R) = 23. This work differs from, but builds on, previous surveys of the outer solar system in that it will cover a large area to a limiting magnitude that is deep enough to guarantee positive results. The proposed work should provide us with a significant number of 200 km-size KBOs (approx. 20 are expected) for subsequent studies. Such a sample is crucial if we are to investigate the statistical properties of the Belt and its members. It was modified the original research strategy to accommodate unanticipated problems such as the urgent need for follow-up observations,the original goal was still reached: we have substantially increased the number of Kuiper Belt Objects brighter than 23rd mag.

Luu, Jane

1997-01-01

394

Recent Developments in the Radiation Belt Environment Model  

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

395

Radiation Belt Environment Model: Application to Space Weather and Beyond  

NASA Technical Reports Server (NTRS)

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

Fok, Mei-Ching H.

2011-01-01

396

A plan to clear energetic protons from the radiation belt  

NASA Astrophysics Data System (ADS)

The Earth's radiation belts have been a known hazard to satellites since at least 1962, when an American high-altitude nuclear weapons test named Starfish Prime produced an artificial belt that disabled the first commercial communications satellite, TelStar 1. In the years since the Cold War, thousands of satellites have been put into orbit, and surface charging, high-energy protons, high-energy electrons known as "killer electrons," and other hazards of the inner magnetosphere have continued to take their toll. Satellites can be hardened against these radiation hazards, but some researchers have recently floated a more radical idea: If specially designed transmitters are put into space and set to emit tightly tuned waves, known as electromagnetic ion cyclotron (EMIC) waves, they could potentially push the highly energetic protons out of the Earth's inner radiation belt, clearing the satellite's path.

Schultz, Colin

2013-11-01

397

Searching for Chips of Kuiper Belt Objects in Meteorites  

NASA Technical Reports Server (NTRS)

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

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

2009-01-01

398

Response of radiation belt simulations to different radial diffusion coefficients  

NASA Astrophysics Data System (ADS)

Resonant interactions between Ultra Low Frequency (ULF) waves and relativistic electrons may violate the third adiabatic invariant of motion, which produces radial diffusion in the electron radiation belts. This process plays an important role in the formation and structure of the outer electron radiation belt and is important for electron acceleration and losses in that region. Two parameterizations of the resonant wave-particle interaction of electrons with ULF waves in the magnetosphere by Brautigam and Albert [2000] and Ozeke et al. [2012] are evaluated using the Versatile Electron Radiation Belt (VERB) diffusion code to estimate their relative effect on the radiation belt simulation. The period of investigation includes quiet time and storm time geomagnetic activity and is compared to data based on satellite observations. Our calculations take into account wave-particle interactions represented by radial diffusion transport, local acceleration, losses due to pitch-angle diffusion, and mixed diffusion. We show that the results of the 3D diffusion simulations depend on the assumed parametrization of waves. The differences between the simulations and potential missing physical mechanisms are discussed. References Brautigam, D. H., and J. M. Albert (2000), Radial diffusion analysis of outer radiation belt electrons during the October 9, 1990, magnetic storm, J. Geophys. Res., 105(A1), 291-309, doi:10.1029/1999JA900344 Ozeke, L. G., I. R. Mann, K. R. Murphy, I. J. Rae, D. K. Milling, S. R. Elkington, A. A. Chan, and H. J. Singer (2012), ULF wave derived radiation belt radial diffusion coefficients, J. Geophys. Res., 117, A04222, doi:10.1029/2011JA017463.

Drozdov, A.; Shprits, Y.; Subbotin, D.; Kellerman, A. C.

2013-12-01

399

Aqueous alteration on main-belt asteroids  

NASA Astrophysics Data System (ADS)

The study of aqueous alteration is particularly important for unraveling the processes occurring during the earliest times in Solar System history, as it can give information both on the thermal processes and on the localization of water sources in the asteroid belt, and for the associated astrobiological implications. The aqueous alteration process produces the low temperature (< 320 K) chemical alteration of materials by liquid water which acts as a solvent and produces materials like phyllosilicates, sulphates, oxides, carbonates, and hydroxides. This means that liquid water was present in the primordial asteroids, produced by the melting of water ice by heating sources, very probably by ^{26}Al decay. Hydrated minerals have been found mainly on Mars surface, on primitive main-belt asteroids (C, G, B, F, and P-type, following the classification scheme by Tholen, 1984) and possibly also on few transneptunian objects. Reflectance spectroscopy of aqueous altered asteroids shows absorption features in the 0.6-0.9 and 2.5-3.5-micron regions, which are diagnostic of, or associated with, hydrated minerals. In this work, we investigate the aqueous alteration process on a large sample of 600 visible spectra of C-complex asteroids available in the literature. We analyzed all these spectra in a similar way to characterize the absorption-band parameters (band center, depth, and width) and spectral slope, and to look for possible correlations between the aqueous alteration process and the asteroids taxonomic classes, orbital elements, heliocentric distances, albedo, and sizes. We find that 4.6 % of P, 7.7 % of F, 9.8 % of B, 50.5 % of C, and 100 % of the G-type asteroids have absorption bands in the visible region due to hydrated silicates. Our analysis shows that the aqueous alteration sequence starts from the P-type objects, practically unaltered, and increases through the P ? F ? B ? C ? G asteroids, these last being widely aqueously altered, strengthening thus the results previously obtained by Vilas (1994). We confirm the strong correlation between the 0.7-?m band and the 3-? m band, the deepest feature associated with hydrated minerals, as 95 % of the asteroids showing the 0.7-? m band have also the 3-? m feature. 45 % of the asteroids belonging to the C-complex (the F, B, C, and G classes) have signatures of aqueously altered materials in the visible range. It must be noted that this percentage represents a lower limit in the number of hydrated asteroids, simply because the 3-? m band, the main absorption feature produced by hydrated silicates, may be present in the spectra of primitive asteroids when no bands are detected in the visible range. All this considered, we estimate that 70 % of the C-complex asteroids might have the 3-? m signature in the IR range and thus were affected by the aqueous alteration process in the past. We find that the aqueous alteration process dominates in primitive asteroids located between 2.3 and 3.1 au, that is, at smaller heliocentric distances than previously suggested by Vilas et al. (1993). The percentage of hydrated asteroids is strongly correlated with their size (Fornasier et al. 2014). The aqueous alteration process is less effective for bodies smaller than 50 km, while it dominates in the 50-240-km sized primitive asteroids. No correlation is found between the aqueous alteration process and the asteroid albedo or orbital elements. Aqueously altered asteroids are the plausible parent bodies of CM2 meteorites. Nevertheless, we see a systematic difference in the 0.7-? m band center position, the CM2 meteorites having a band centered at longer wavelengths (0.71-0.75 ? m) compared to that of hydrated asteroids. Moreover, the hydrated asteroids are more clustered in spectral slope and band depth than the CM meteorites. All these spectral differences may be attributed to different mineral abundances (CM2 meteorites being more serpentine rich than the asteroids), and/or to grain-size effects, or simply to the fact the CM2 collected on the Earth might not be representative

Fornasier, S.; Lantz, C.; Barucci, M.; Lazzarin, M.

2014-07-01

400

The Central Asian Orogenic Belt in northern China: Preface  

NASA Astrophysics Data System (ADS)

The Central Asian Orogenic Belt (CAOB) occupies a huge area, extending in the northern Eurasian continent from the Urals in the west via Mongolia, to the Chinese Far East, Inner Mongolia, and Xing'an in the east. It is characterized by various accretionary complexes, including island arcs, fore-arc or back-arc basins, ophiolitic belts, and microcontinents dating from the Neoproterozoic to the Mesozoic, and by its massive generation of juvenile crust in the Phanerozoic (Jahn et al., 2000; Jahn, 2004; Windley et al., 2007).

Xu, Bei; Song, Shuguang; Nie, Fengjun

2015-01-01

401

A Spectroscopically Unique Main Belt Asteroid: 10537 (1991 RY16)  

E-print Network

We present visible and near-infrared reflectance spectra and interpreted surface mineralogy for asteroid 10537 (1991 RY16). The spectrum of this object is without precedent amongst the Main Belt asteroids. A unique absorption band centered at 0.63 microns could be attributed to one of several mineralogies. Pronounced 1- and 2-micron absorption bands suggest that the composition of 10537 is a mixture of pyroxenes and olivine and that it originated from a parent body that was partially or fully differentiated. The closest available analog is the large Main Belt asteroid 349 Dembowska but 10537 may be an isolated fragment from a completely eroded parent body.

Nicholas A. Moskovitz; Samuel Lawrence; Robert Jedicke; Mark Willman; Nader Haghighipour; Schelte J. Bus; Eric Gaidos

2008-06-13

402

Hydraulic control system for continuously variable V-belt transmission  

SciTech Connect

A hydraulic control system is described for a continuously variable V-belt transmission which includes a continuously variable transmission mechanism having a drive pulley, a driven pulley and a V-belt interconnecting the drive and driven pulleys and a change-direction gearing disposed between an engine and the drive pulley to establish a forward drive path or a reverse drive path from the engine to the drive pulley, the change-direction gearing including a forward clutch and a reverse clutch.

Abo, K.; Kumura, H.; Tanaka, Y.; Hirano, H.; Yamamuro, S.

1986-04-29

403

14 CFR 23.785 - Seats, berths, litters, safety belts, and shoulder harnesses.  

Code of Federal Regulations, 2014 CFR

...2014-01-01 false Seats, berths, litters, safety belts, and shoulder harnesses...Accommodations § 23.785 Seats, berths, litters, safety belts, and shoulder harnesses...m) Each berth, or provisions for a litter, installed parallel to the...

2014-01-01

404

14 CFR 137.42 - Fastening of safety belts and shoulder harnesses.  

Code of Federal Regulations, 2013 CFR

...AND OPERATIONS AGRICULTURAL AIRCRAFT OPERATIONS Operating Rules § 137.42 Fastening of safety belts and shoulder harnesses. No person may operate an aircraft in operations required to...conducted under part 137 without a safety belt and shoulder...

2013-01-01

405

14 CFR 137.42 - Fastening of safety belts and shoulder harnesses.  

Code of Federal Regulations, 2010 CFR

...AND OPERATIONS AGRICULTURAL AIRCRAFT OPERATIONS Operating Rules § 137.42 Fastening of safety belts and shoulder harnesses. No person may operate an aircraft in operations required to...conducted under part 137 without a safety belt and shoulder...

2010-01-01

406

14 CFR 137.42 - Fastening of safety belts and shoulder harnesses.  

Code of Federal Regulations, 2012 CFR

...AND OPERATIONS AGRICULTURAL AIRCRAFT OPERATIONS Operating Rules § 137.42 Fastening of safety belts and shoulder harnesses. No person may operate an aircraft in operations required to...conducted under part 137 without a safety belt and shoulder...

2012-01-01

407

14 CFR 137.42 - Fastening of safety belts and shoulder harnesses.  

Code of Federal Regulations, 2014 CFR

...AND OPERATIONS AGRICULTURAL AIRCRAFT OPERATIONS Operating Rules § 137.42 Fastening of safety belts and shoulder harnesses. No person may operate an aircraft in operations required to...conducted under part 137 without a safety belt and shoulder...

2014-01-01

408

14 CFR 137.42 - Fastening of safety belts and shoulder harnesses.  

Code of Federal Regulations, 2011 CFR

...AND OPERATIONS AGRICULTURAL AIRCRAFT OPERATIONS Operating Rules § 137.42 Fastening of safety belts and shoulder harnesses. No person may operate an aircraft in operations required to...conducted under part 137 without a safety belt and shoulder...

2011-01-01

409

THE SURFACE COMPOSITION OF LARGE KUIPER BELT OBJECT 2007 OR10  

E-print Network

We present photometry and spectra of the large Kuiper belt object 2007 OR10. The data show significant near-infrared absorption features due to water ice. While most objects in the Kuiper belt with water ice absorption ...

Brown, M. E.

410

Ultra-fast Electrons Explain Third Radiation Belt - Duration: 44 seconds.  

NASA Video Gallery

In September 2012, NASA's Van Allen Probes observed the radiation belts around Earth had settled into a new configuration, separating into three belts instead of two. Scientists think the unusual p...

411

14 CFR 121.317 - Passenger information requirements, smoking prohibitions, and additional seat belt requirements.  

Code of Federal Regulations, 2010 CFR

... Passenger information requirements, smoking prohibitions, and additional seat belt... Passenger information requirements, smoking prohibitions, and additional seat belt...operate an airplane on a flight on which smoking is prohibited by part 252 of this...

2010-01-01

412

The development of an electronic system to continually monitor, indicate and control, 'belt slippage' in industrial friction 'V' belt drive transmission systems  

NASA Astrophysics Data System (ADS)

Belts have been used for centuries as a mechanism to transfer power from some form of drive system to a variety of load systems. Within industry today, many designs of belts but particularly friction, trapezoidal shaped 'V' belts are used and generally transfer power generated by electrical motors to numerous forms of driven load systems. It is suggested that belt systems, through their simplicity are sadly neglected by maintenance functions and generally are left unattended until high degrees of 'belt slippage' through loss of friction or 'belt breakage' provokes maintenance attention. These circumstances are most often identified through the reduced or loss of manufacturing production or the occurrence of catastrophic circumstances such as fire caused through excessive friction/ high