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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

Emplacement features of Archaean TTG plutons along the southern margin of the Barberton greenstone belt, South Africa  

Microsoft Academic Search

The Barberton greenstone belt in South Africa and its surrounding granitoid terrane represents one of the type localities for Archaean granite-greenstone tectonics. Contact relationships between early Archaean granitoids and greenstone sequences along the southern margin of the greenstone belt illustrate multiple, simultaneously operating emplacement mechanisms for the plutons. These emplacement mechanism, which can be identified in individual plutons comprise ductile

A. F. M. Kisters; C. R. Anhaeusser

1995-01-01

3

Carbonate dykes associated with Arch?an lode-Au mineralisation, Barberton greenstone belt, South Africa  

NASA Astrophysics Data System (ADS)

Carbonate dykes, exposed within the Barberton greenstone belt, display geochemical signatures similar to altered carbonatite. The trace element signature normalised to primordial mantle, and the chondrite-normalised REE trends of the Ulundi Dyke display geochemical similarities to carbonatites. In addition, stable isotope results from the Ulundi Dyke (?13Cwhole rock and ?18Owhole rock range from -3.7 to -4.9‰ and 12.8 to 13.2‰, respectively) are similar to values found for samples of wall rock and vein carbonate from Arch?an Au-quartz-carbonate-sulphide vein systems studied in the Barberton greenstone belt. Although the data do not plot in the field of primary igneous carbonatite, they are similar to data of deuterically-altered carbonatite. These associations strengthen the deduction that Iode-Au mineralised fractures and shear zones in the Barberton greenstone belt were open to mantle-tapping fundamental faults.

Schürmann, L. W.; Ward, J. H. W.; Horstmann, U. E.; Jordaan, L. J.; Eaton, B.

2000-02-01

4

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

5

Metamorphism and exhumation of the basal parts of the Barberton greenstone belt, South Africa: Constraining the rates of Mesoarchaean tectonism  

Microsoft Academic Search

The Paleo- to Mesoarchaean Barberton granitoid-greenstone terrain of South Africa consists of two main components: the low-grade metamorphic supracrustal greenstone sequence of the Barberton greenstone belt in the north and a high-grade metamorphic granitoid-gneiss terrain to the south. The boundary between the two different domains corresponds to the highly tectonized, amphibolite-facies rocks of the Theespruit Formation that occur along the

Johann F. A. Diener; Gary Stevens; Alexander F. M. Kisters; Marc Poujol

2005-01-01

6

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

PubMed

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. PMID:11540244

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

1994-03-01

7

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

NASA Astrophysics Data System (ADS)

The Moodies Group of the Barberton Greenstone Belt is one of the oldest and best-preserved quartz-rich sedimentary sequences on Earth. Its strata, approx. 3 km thick, record an initial extensional setting, followed by a strong shortening pulse which resulted in the dominant large-scale final deformation of the greenstone belt. We investigated the apparently rapid transition from Moodies extensional to compressive setting through detailed mapping, correlation of measured sections and the analysis of a prominent basaltic lava which extends for approx. 60 km along strike, in order to constrain the tectonic and depositional setting of some of the earliest stable life-providing habitats on Earth. In the middle Moodies Group, large-scale cross-bedded coarse-grained sandstones, interpreted as an offshore dune field, are abruptly overlain by a discontinuous cobble and boulder conglomerate of up to 4 m thickness, possibly representing local small alluvial fans above a cryptic disconformity. A basaltic lava, reaching approx. 50 m thick, regionally exists above this unit and forms the most prominent marker unit in the Moodies Group. In most places, the lava is metasomatically altered to a fine-grained mesh of illite, sericite, chlorite and very fine-grained quartz. In its upper third, it contains abundant amygdules approx. 0.5 - 1 cm in diameter. We did not record significant thickness changes hinting at eruption centers, feeder channels, flow markers nor pillows. Two thin but regionally continuous dacitic tuffs overlying the lava yielded concordant single-zircon ages of 3229+-6 Ma (Heubeck et al., in prep.) which are statistically indistinguishable from underlying Fig Tree Group volcanics and suggest high depositional and subsidence rates (mm/yr or higher) of intervening Moodies Group strata. Overlying clastic sediments up to 1 km thick show a very high lateral and vertical variability in grain size and petrography. Their facies ranges from alluvial conglomeratic wedges, fluvial gravelly sandstones, nearshore cross-bedded sandstones, tuffaceous shales to thin BIFs; sandstones show isolated occurrences of laminated curly biomats. The rapid facies changes attest to the termination of a uniform sedimentation regime and suggest the incipient breakup of the basin in numerous subbasins. The boulder conglomerate below the base of the basaltic lava likely represents the tectonic turning point in the evolution of the Moodies Basin by marking a pronounced increase in local depositional slope, the subsequent initiation of horizontal shortening, basin margin uplift and erosion, and final tight greenstone belt shortening. The eruption of the basaltic lava may be related to brittle segmentation of the basement, causing small-scale faulting, alluvial fan development on a former shelf, and allowing magma ascent.

Kirstein, Jens; Heubeck, Christoph; Lippold, Wigbert

2010-05-01

8

Quantifying rates of dome-and-keel formation in the Barberton granitoid-greenstone belt, South Africa  

Microsoft Academic Search

The Barberton granitoid-greenstone belt is a classic dome-and-keel province, characterized by kilometer-scale gneiss domes and elongate keels of largely folded supracrustal rocks. Combined U–Pb SHRIMP data and structural mapping demonstrate that the geometry of the Barberton belt reflects events that occurred over ?30 million year interval, from ca. 3230 and 3203Ma. Early deformation with NW–SE shortening in the upper crust

Cristiano Lana; Eric Tohver; Peter Cawood

2010-01-01

9

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

PubMed

The 3.55-3.22 Ga Barberton Greenstone Belt, South Africa and Swaziland, and surrounding coeval plutons can be divided into four tectono-stratigraphic blocks that become younger toward the northwest. Each block formed through early mafic to ultramafic volcanism (Onverwacht Group), probably in oceanic extensional, island, or plateau settings. Volcanism was followed by magmatic quiescence and deposition of fine-grained sediments, possibly in an intraplate setting. Late evolution involved underplating of the mafic crust by tonalitic intrusions along a subduction-related magmatic arc, yielding a thickened, buoyant protocontinental block. The growth of larger continental domains occurred both through magmatic accretion, as new protocontinental blocks developed along the margins of older blocks, and when previously separate blocks were amalgamated through tectonic accretion. Evolution of the Barberton Belt may reflect an Early Archean plate tectonic cycle that characterized a world with few or no large, stabilized blocks of sialic crust. PMID:11539408

Lowe, D R

1994-12-01

10

Stable isotope and Rare Earth Element evidence for recent ironstone pods within the Archean Barberton greenstone belt, South Africa  

Microsoft Academic Search

There is considerable debate about the mode and age of formation of large (up to ˜200 m long) hematite and goethite ironstone bodies within the 3.2 to 3.5 Ga Barberton greenstone belt. We examined oxygen and hydrogen isotopes and Rare Earth Element (REE) concentrations of goethite and hematite components of the ironstones to determine whether these deposits reflect formation from

Michael T. Hren; Donald R. Lowe; Michael M. Tice; Gary Byerly; C. Page Chamberlain

2006-01-01

11

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

12

Stable isotope and Rare Earth Element evidence for recent ironstone pods within the Archean Barberton greenstone belt, South Africa  

Microsoft Academic Search

There is considerable debate about the mode and age of formation of large (up to ?200m long) hematite and goethite ironstone bodies within the 3.2 to 3.5 Ga Barberton greenstone belt. We examined oxygen and hydrogen isotopes and Rare Earth Element (REE) concentrations of goethite and hematite components of the ironstones to determine whether these deposits reflect formation from sea-floor

Michael T. Hren; Donald R. Lowe; Michael M. Tice; Gary Byerly; C. Page Chamberlain

2006-01-01

13

300 million years of komatiite evolution of the Barberton Greenstone Belt  

NASA Astrophysics Data System (ADS)

The 3.5-3.2 Ga Barberton greenstone belt in South Africa is the type locality of komatiite and ultramafic lavas erupted throughout most of its 300 m.y. history. Despite 30 years of investigation, there are very few complete geochemical analyses of these rocks and we are undertaking a detailed analytical study, including major and trace elements, Nd, Hf, Os, O isotopes and melt inclusion studies, of samples from four stratigraphic formations that span the complete history of the belt. The oldest well preserved komatiites are the in 3.5 Ga Komati Formation near the base of the sequence. These have sub-chondritic Al/Ti and depleted HREE and are thought to have formed during deep (>300km) partial melting in a hot mantle plume. The majority are non-vesicular and show no evidence of having erupted as hydrous lavas, but some uncommon examples contain large amygdales and are coarse-grained, and they may have contained some water. The 3.3 Ga Weltevreden komatiites have slightly super-chondritic Al/Ti and a positively sloping REE profiles, characteristics consistent with shallower melting of a source that either was enriched in garnet or had previously undergone extensive partial melting. Some Weltevreden komatiites contain olivine with the composition Fo96. The liquid composition inferred using this composition and whole-rock compositions contains 33% MgO. If anhydrous, as supported by analysis of melt inclusions, this magma erupted at about 1660° C making it the hottest magma on earth. Two types of komatiites occur in the 3.3 Ga Mendon Formation. The first has Al/Ti and HREE similar to Komati formation; the second has highly super-chondritic Al/Ti which may indicate a garnet enriched source.

Robin, C.; Arndt, N. T.; Gary, B.; Kareem, K.

2008-12-01

14

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

15

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

16

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

17

200 million years of komatiite evolution in the Barberton Greenstone Belt, South Africa  

NASA Astrophysics Data System (ADS)

Komatiites with complex and contrasting chemical compositions erupted throughout the 200 m.y. history of the Barberton greenstone belt in South Africa. The oldest well-preserved examples, from the ca. 3.5 Ga Komati Formation, display a range of volcanic structures, from thin differentiated spinifex-textured flows to much thicker flows or sills composed mainly of massive olivine cumulate. Pyroxene spinifex layers that cap the latter units indicate crystallization from komatiitic basaltic liquids. Although some rare, unusually coarse, vesicular, completely serpentinized units may have contained a small fraction of water, most of the flows are essentially anhydrous. Two geochemical types are present in the Komati Fm; Al-depleted komatiites with moderately enriched LREE and depleted HREE, and Al-undepleted komatiites with near-chondritic REE ratios. Komatiites from the 3.2 Ga Mendon and Weltevreden Fm display two patterns -Al-undepleted with near-chondritic REE ratios and Al-enriched with extremely low REE concentrations and marked depletion of LREE. In many units, both geochemical types are present. The Al- and HREE-depletion of Komati Fm magmas indicates that residual garnet was retained in the mantle source and their high MgO contents require that melting was at great depth. Up to 30% batch melting at 300 km depth is indicated; the high percentage of batch melting is possible because melt is neutrally buoyant at these depths. The Al-undepleted to enrichedmagmas formed by up to 50% cumulative fractional melting that terminated at shallower depth. The. presence of both types inseveral units points to complex dynamics in the mantle plumes that yielded these magmas. Epsilon Nd in all Barbertonkomatiites ranges from 0 to +2; epsilon Hf from +2 to +7; gamma Os from 0 to +3.7. The combination of fractionated REE, positive epsilon Nd and Hf, and near-chondritic Os in certain komatiites is attributed to differentiation of the komatiite sourcevery early in Earth history followed by fractionation during komatiite formation.

Christoph, Robin; Arndt, Nick; Byerly, Gary; Puchtel, Igor; Blichert-Toft, Janne; Wilson, Allan

2010-05-01

18

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

Microsoft Academic Search

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

Alfred Kröner; Wolfgang Todt

1988-01-01

19

Abundant pyroclastic komatiitic volcanism in the 3.5-3.2 Ga Barberton greenstone belt, South Africa  

NASA Astrophysics Data System (ADS)

The paucity of komatiitic pyroclastic rocks in Archean greenstonesequences is commonly interpreted to reflect the low volatilecontents of komatiitic liquids and the mechanical difficultiesin explosively erupting highly fluid ultramaficmagmas. Herewe report the presence of multiple layers of ultramafic pyroclasticdebris in 3481-3243 Ma rocks of the Onverwacht Group inthe Barberton greenstone belt, South Africa. In the northernpart of the belt, layers of serpentinized tuff are interbeddedwith komatiites and komatiitic basalts and constitute 30%-40%of the stratigraphic column, including sections of tuff as thickas 60 m. They retain elevated MgO contents and incompatibleelement abundances consistent with derivation from komatiiticliquids. In the southern part of the belt, more than 80 individualbeds of silicified and carbonated tuffs, most <1 m thick,are associated with komatiite, komatiitic basalt, and tholeiiticflow rocks. These tuffs contain abundant accretionary lapilli,attesting to their pyroclastic origins, and ratios of immobileelements, such as Al, Ti, Th, Nb, Zr, and the heavy rare earthelements, that are most compatible with those of associatedBarberton komatiites. These deposits appear to reflect the explosiveinteraction of high-Mg melts with dominantly external water.

Thompson Stiegler, M.; Lowe, Donald R.; Byerly, Gary R.

2008-10-01

20

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

21

Early Archaean hydrothermal fluids; a study of inclusions from the ? 3.4 Ga Buck Ridge Chert, Barberton Greenstone Belt, South Africa  

Microsoft Academic Search

Fluid inclusions have been studied from cavities and breccias in one of the oldest well-preserved, relatively low-grade metamorphosed sedimentary sequences on Earth. The fluid inclusion-bearing samples are from the uppermost part of the early Archaean (?3.4 Ga) Buck Ridge volcano-sedimentary complex in the Barberton Greenstone Belt (South Africa), which was affected by hydrothermal alteration during and immediately after its deposition. In

Sjoukje T. de Vries; Jacques L. R. Touret

2007-01-01

22

New U–Pb and 40Ar\\/ 39Ar ages from the northern margin of the Barberton greenstone belt, South Africa: Implications for the formation of Mesoarchaean gold deposits  

Microsoft Academic Search

Gold mineralization in the Mesoarchaean New Consort gold mine in the Barberton greenstone belt, South Africa, is situated in the immediate hanging wall of an exhumed, composite granitoid gneiss dome known as the Stentor Pluton. The granitoid-greenstone contact is characterized by a contact-parallel high-strain zone that separates the mid-crustal gneisses from the greenschist facies greenstone belt. In contrast to the

Annika Dziggel; Marc Poujol; Alexander Otto; Alexander F. M. Kisters; Mario Trieloff; Winfried H. Schwarz; F. Michael Meyer

2010-01-01

23

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

24

Ferromagnetic resonance and magnetic carriers in Archean Buck Reef Chert from the Barberton Greenstone Belt, South Africa  

NASA Astrophysics Data System (ADS)

The nature of the magnetic carriers in the ˜3.4 billion year old Buck Reef Chert of the Barberton Greenstone Belt, South Africa, has been studied as it has been suggested that the chert may contain potential biogenic microstructures. Depositional environments of the Buck Reef Chert may have included shallow water environments and, as such, biogenic magnetite might be associated with them. Scanning Electron Microscope observations of magnetic separates and thin sections show cubo-octahedral to quasi-rectangular and hexagonally shaped grains that fall within a stable single domain range typical of biogenic magnetite. Preliminary transmission electron microscope and Energy Dispersive Spectrometer data have also been collected. Magnetic hysteresis properties of bulk samples show a variety of hysteresis behaviors (including multi-domain, pseudo-single domain and wasp-waisted curves). Analyses of bulk magnetic susceptibility versus temperature suggest alteration on heating (100-400 degrees C). Ferromagnetic resonance (FMR) has been used to investigate the possibility of magnetite produced by magnetotactic bacteria. Preliminary FMR spectra of some bulk Buck Reef Chert samples appear asymmetrical and skew towards low fields, suggesting a magnetic anisotropy that is similar to the spectra seen with some strains of magnetotactic bacteria. However, results to date should be interpreted in terms of the original depositional environment, and the subsequent geologic history. While some of the magnetic minerals within the separates observed in SEM may be primary, it is important to recognize low grade metamorphism has occurred to peak temperatures of 250 to 320 degrees C in the region. Depositional sulfides (e.g. greigite) in the originally sulfur rich environment may have been converted to other iron oxides during subsequent metamorphic events. We will discuss attempts to better distinguish primary from secondary magnetic minerals in the Barberton rocks.

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

2009-05-01

25

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

26

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

27

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

28

Stable isotope and Rare Earth Element evidence for recent ironstone pods within the Archean Barberton greenstone belt, South Africa  

NASA Astrophysics Data System (ADS)

There is considerable debate about the mode and age of formation of large (up to ˜200 m long) hematite and goethite ironstone bodies within the 3.2 to 3.5 Ga Barberton greenstone belt. We examined oxygen and hydrogen isotopes and Rare Earth Element (REE) concentrations of goethite and hematite components of the ironstones to determine whether these deposits reflect formation from sea-floor vents in the Archean ocean or from recent surface and shallow subsurface spring systems. Goethite ?18O values range from -0.7 to +1.0‰ and ?D from -125 to -146‰, which is consistent with formation from modern meteoric waters at 20 to 25 °C. Hematite ?18O values range from -0.7 to -2.0‰, which is consistent with formation at low to moderate temperatures (40 55 °C) from modern meteoric water. REE in the goethite and hematite are derived from the weathering of local sideritic ironstones, silicified ultramafic rocks, sideritic black cherts, and local felsic volcanic rocks, falling along a mixing line between the Eu/Eu* and shale-normalized HREEAvg/LREEAvg values for the associated silicified ultramafic rocks and felsic volcanic rocks. Contrasting positive Ce/Ce* of 1.3 to 3.5 in hematite and negative Ce/Ce* of 0.2 to 0.9 in goethite provides evidence of oxidative scavenging of Ce on hematite surfaces during mineral precipitation. These isotopic and REE data, taken together, suggest that hematite and goethite ironstone pods formed from relatively recent meteoric waters in shallow springs and/or subsurface warm springs.

Hren, Michael T.; Lowe, Donald R.; Tice, Michael M.; Byerly, Gary; Chamberlain, C. Page

2006-03-01

29

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

NASA Astrophysics Data System (ADS)

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, evaporites, and shallow-water sedimentary structures and the virtual absence of tourmaline in correlative deep-water facies rocks in the greenstone bels 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 analysis 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 ?11B values (+2.2 to-1.9‰); lower ?11B values of late quartz veins (-3.7 to-5.7‰) reflect intermediate temperature, hydrothermal remobilization of evaporitic boron. The ?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.

Byerly, Gary R.; Palmer, Martin R.

1991-05-01

30

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

NASA Astrophysics Data System (ADS)

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

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

2004-05-01

31

Vestiges of a 3.2 Ga Subduction Zone, as Evidenced by High-Pressure, Low-Temperature Metamorphism in the Barberton Greenstone Belt  

NASA Astrophysics Data System (ADS)

The lack of high-pressure, low-temperature metamorphism in the Archaean rock record, one of the most diagnostic fingerprints of subduction-driven tectonics, is commonly considered to indicate that plate tectonics was absent during the Archean, or at least very different in form and function from what it is now. Here we report evidence for high-pressure, low-temperature metamorphism in supracrustal amphibolites from the mid-Archaean Barberton granitoid-greenstone terrain in South Africa that challenges this paradigm. In the Inyoni shear zone, located between the 3.45 Ga Stolzburg homogeneous tronhjemite pluton and the ca. 3.2 Ga Badplaas granodioritic to trondhjemitic gneissic complex, garnet-bearing amphibolites are preserved within the 3.22 Ga greenschist to amphibolite facies high-strain structure. Peak temperature conditions for these amphibolites are recorded by epidote-amphibole-plagioclase (An30) ± clinopyroxene assemblages, which yield PT conditions via conventional thermobarometry of 750 to 850 °C and 0.7 to1.0 GPa. However, the cores of garnet crystals, that are of more calcic and less magnesian composition than the rims, contain inclusions of quartz, clinopyroxene, amphibole, epidote and plagioclase (An10), which also differ in composition from the matrix generations of the same minerals. This earlier assemblage constrains peak pressure conditions to between 1.2 and 1.5 GPa at temperatures below 650-700 °C. This points to very low apparent geothermal gradients of 12-15 °C. These values are similar to those found in recent subduction zone settings. These highest-pressure metamorphic rocks occur on the eastern margin of a coherent granitoid terrain, at least some 500 km2 in extent, which has experienced peak metamorphic pressures of 0.8 to 1.1 GPa. This clearly demonstrates that the ca 3.23 crust in this area was cold enough and stiff enough to allow for tectonic doubling of crustal thickness. The timing of high-pressure metamorphism coincides with the proposed main phase of terrane accretion in the structurally overlying Barberton greenstone belt. We suggest that these high-pressure, low-temperature conditions represent the first metamorphic evidence for subduction-driven burial of continental crust in the mid-Archaean and are the deep crustal manifestation of the terrane accretion proposed on the grounds of structural, geochronological and sedimentological evidence from the fold and thrust belt.

Stevens, G.; Moyen, J.; Kisters, A.

2005-12-01

32

Timing of mid- to lower-crustal metamorphism in the granitoid-gneiss terrain south of the Barberton greenstone belt, South Africa  

NASA Astrophysics Data System (ADS)

SHRIMP U-Pb zircon and sphene dating has been carried out in order to constrain the timing of mid- to lower-crustal metamorphism (ca. 650--700^oC and 8--11 kbars) and syn-kinematic melting in the granitoid gneiss-dominated terrain to the south of the Barberton greenstone belt, South Africa. Existing U-Pb zircon data indicate that the majority of granitoid rocks were emplaced between ca. 3460--3430 Ma, contemporaneously with an early phase of compressional tectonics in the southern part of the belt. The U-Pb ages were obtained from a clastic metasedimentary unit exposed in one of several greenstone xenoliths, as well as a late-kinematic trondhjemite intrusive into spatially closely associated mixed gneisses. The clastic metasediments are characterized by peak metamorphic mineral assemblages of garnet + andesine + quartz + diopside ± hornblende ± K-feldspar. The replacement of peak metamorphic minerals by epidote and sphene during retrogression is linked to a variety of net transfer reactions. The sphenes yield an upper intercept date of 3229 ± 9 Ma, and provide a minimum age for the peak of metamorphism. The consistency of the data, as well as the lack of a clear age-grain size relationship in the grains suggests that this date approximates the age of sphene growth rather than cooling, thus implying that the metamorphic peak was followed by rapid exhumation. In contrast, zircons separated from the same unit record a range of concordant and near-concordant 207Pb/206Pb dates between 3560--3230 Ma, with a youngest weighted mean date of 3227 ± 7 Ma. This range is here interpreted to be due to a combination of metamorphic recrystallisation and high-temperature Pb-loss in originally detrital zircons during regional metamorphism. A minimum age for the timing of deformation is given by the emplacement age of 3229 ± 5 Ma for the late-kinematic trondhjemite. Thus, geochronological data support a major metamorphic event that postdates the intrusion of the trondhjemites by more than 200 million years. The established ages coincide with the timing of a major terrain accretion event, thus providing further evidence that these gneiss bodies represent exhumed basement complexes rather than granitoid diapirs.

Dziggel, A.; Armstrong, R. A.; Stevens, G.; Anhaeusser, C. R.

2003-04-01

33

Evidence for a low-O 2 Archean atmosphere from nickel-rich chrome spinels in 3.24 Ga impact spherules, Barberton greenstone belt, South Africa  

NASA Astrophysics Data System (ADS)

The composition of spinels in 3.24-billion-year-old Archean impact spherules in the S3 spherule bed in the Barberton greenstone belt, South Africa, provides important clues about the environments within which they formed, including the redox conditions of the impact plume and the oxygen levels in the early atmosphere. Despite pervasive diagenetic alteration of the impact spherules and nearly complete alteration of primary mineralogy, primary Ni-rich chrome spinel is preserved. The impact spinels are significantly more oxidized than detrital spinels of komatiitic origin that are also present in the spherule bed. The average Fe + 3 /Fe T (atoms) value in the Ni-rich impact spinels is 0.43 whereas the average Fe + 3 /Fe T of detrital spinels is 0.17. Fe 3+/Fe T ratios of the impact spinels range from 0.26 to 0.69 (atoms) and suggest formation at oxygen fugacities below 10 -4 bar based on comparisons with experimental results. Comparison of the S3 impact spinels with similar spinels from the K/T boundary layer, Eocene impact layer, and Late Pliocene impact layer also suggests much lower O 2 levels in the 3.24 Ga atmosphere. Oxidation of spinels present in condensed melt droplets was affected by the oxygen fugacity of the atmospheric component mixed with the ejected plume, and the broad range in values may reflect fO 2 heterogeneity both temporally and spatially within the impact-produced rock-vapor plume. Compositional and morphological variability of spinels in the spherules suggests temperature and cooling rate were heterogeneous through the plume.

Krull-Davatzes, Alexandra E.; Byerly, Gary R.; Lowe, Donald R.

2010-08-01

34

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

35

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.

Nelson, Pamela

36

Siderophile element patterns, PGE nuggets and vapour condensation effects in Ni-rich quench chromite-bearing microkrystite spherules, ˜ 3.24 Ga S3 impact unit, Barberton greenstone belt, Kaapvaal Craton, South Africa  

NASA Astrophysics Data System (ADS)

Energy dispersive spectrometry (EDS), laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) track analyses of chlorite-dominated quench-textured microkrystite spherules and LA-ICPMS spot analyses of intra-spherule Ni-rich skeletal quench chromites from the 3243 ± 4 Ma Barberton S3 impact fallout unit (lower part of the Mapepe Formation, Fig Tree Group, Barberton greenstone belt, Kaapvaal Craton, South Africa) reveal fractionated siderophile and PGE trace element patterns corresponding to chondrite-contaminated komatiite/basalt compositions. The chlorites, interpreted as altered glass, contain sharp siderophile elements and PGE spikes inherited from decomposed metal and Ni-rich chromite particles. LA-ICPMS spot analysis identifies PGE-rich micronuggets in Ni-chromites (Ir ˜ 12-100 ppm, Os ˜ 9-86 ppm, Ru ˜ 5-43 ppm) and lower levels of the volatile PGEs (Rh ˜ 1-11 ppm, Pd ˜ 0.68-0.96 ppm). Previously reported PGE anomalies in the order of hundreds of ppb in some Barberton microkrystite spherules are accounted for in terms of disintegration of PGE-rich micronuggets. Replacement of the Ni-chromites by sulphide masks primary chondritic patterns and condensation element distribution effects. High refractory/volatile PGE ratios pertain to both the chlorites and the Ni-rich chromites, consistent with similar compositional relations in microkrystite spherules from other impact fallout units in the Barberton greenstone belt and the Pilbara Craton, Western Australia. The near-consistent low Pt/Re and high V/Cr and V/Sc ratios in chlorite of the spherules, relative to komatiites, are suggestive of selective atmospheric condensation of the spherules which favored the relatively more refractory Re and V. Selective condensation may also be supported by depletion in the volatile Yb relative to Sm. Ni-Cr relationships allow estimates of the proportion of precursor crustal and meteoritic components of the spherules. Mass balance calculations based on the iridium flux allow estimates of the order of magnitude of the diameter of the chondritic projectile.

Glikson, Andrew

2007-01-01

37

The Tectonometamorphic Evolution of a 3.2 Ga Tectonic Mélange at the Base of the Barberton Greenstone Belt, South Africa: P-T-t Constraints From the Theespruit Formation  

NASA Astrophysics Data System (ADS)

The Paleo- to Mesoarchaean Barberton granite-greenstone terrain in South Africa consists of two main components: a southern high-grade metamorphic granite-gneiss terrain and the low-grade metamorphic supracrustal sequence of the Barberton greenstone belt in the north. The gneiss terrain records peak metamorphic conditions of 8 - 11 kbar and 650 - 700 °C, attained at 3229 ± 9 Ma (Dziggel et al., 2002), coinciding with the main phase of collisional tectonics in the greenstone belt (De Ronde and De Wit, 1994). Conversely, estimates of 2.6 ± 0.6 kbar and 360 ± 50 °C reflect metamorphic conditions in the low-grade supracrustal at this time (Cloete, 1999). The boundary of the two different domains corresponds to the Theespruit Formation, a highly tectonized mélange of metabasites, felsic volcanics and rare, aluminous clastic sediments. The metamorphic and structural evolution of the Theespruit Formation was investigated in the Tjakastad Schist Belt in order to constrain the tectonometamorphic history and the significance of this basal mélange for the juxtaposition of these two crustal domains. The pretectonic peak metamorphic assemblage Ky-St-Bt-Ms-Pl-Q quartz occurs in aluminous horizons within the metasediments. These horizons are intercalated with more Fe-Mg-rich sediments that record the peak metamorphic assemblage Grt-St-Bt-Chl-Pl-Q. THERMOCALC estimates from the garnet-bearing metasediments constrain peak P-T conditions at 7.7 ± 0.9 kbar and 560 ± 15 °C. Associated metabasites display peak assemblages consisting of garnet + hornblende + epidote + plagioclase + quartz, which yields a P-T estimate of 7.0 ± 1.6 kbar and 560 ± 60 °C. Retrograde estimates of 3.8 ± 1.3 kbar and 543 ± 20 °C, as well as sillimanite overgrowths on kyanite, indicate that retrogression involved close to isothermal decompression of ca. 4 kbar prior to cooling into the greenschist facies. The age of amphibolite facies metamorphism has been determined by in situ LA-ICP-MS analysis of sphene in metabasite and is constrained at 3229 ± 25 Ma. The timing of peak metamorphic conditions in the Theespruit Formation and granite-gneiss terrain are identical and both localities exhibit a similar style of high-P low-T metamorphism with remarkably low apparent geothermal gradients of 18 - 20 °C/km. Thus, rocks of both the Theespruit Formation and the gneiss terrain record burial metamorphism to mid- and lower crustal levels during the main collisional event at 3230 Ma. P-T estimates from the Onverwacht Group some 4 km north of the study area indicate that a metamorphic break of at least 5 kbar, corresponding to a crustal column of ~18 km, exists between these two localities. This investigation has revealed that the metamorphic history of the Theespruit Formation is very similar to that experienced by the granite-gneiss terrain and differs radically from that experienced by the greenstone sequence. This high-grade terrain is allochtonous to the greenstone belt and represents a tectonically exhumed and underplated terrain. The depths of burial and extremely low geothermal gradients recorded in this terrain are only possible in cool and rigid crustal environments, indicating that a modern continental crustal thermal regime must have been established in the Barberton terrain as early as 3230 Ma. Cloete, M. (1999), Mem. Geol. Survey S. Africa, 84, 232pp De Ronde, C.E.J., De Wit, M.J. (1994), Tectonics, 13, 983 - 1005 Dziggel, A., Stevens, G., Poujol, M., Anhaeusser, C.R., Armstrong, R.A. (2002), Precambrian Res., 114, 221 - 247

Diener, J.; Stevens, G.; Kisters, A.; Poujol, M.

2004-05-01

38

Extensional detachment faulting and core-complex formation in the southern Barberton granite–greenstone terrain, South Africa: evidence for a 3.2 Ga orogenic collapse  

Microsoft Academic Search

The Barberton greenstone belt in South Africa is an Early- to Mid-Archaean, very low-grade metamorphic supracrustal belt that is bordered in the south by a mid- to lower crustal gneiss terrain. Detailed mapping of the contacts between the supracrustal and gneiss domains along the southern margin of the greenstone belt shows that the supracrustal rocks are separated from the high-grade

Alexander F. M Kisters; Gary Stevens; Annika Dziggel; Richard A Armstrong

2003-01-01

39

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.  

PubMed

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 approximately 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. PMID:12804363

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

2003-01-01

40

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

NASA Astrophysics Data System (ADS)

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 40Ar /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. In most cases the apparent age plateaux can be identified by corresponding Ca/K and Cl/K ratio plots as belonging to separate mineral phases. Most of the samples exhibit simple Ar diffusion loss during the low temperature part of the experiments while occasionally showing excess Ar, or possible 39Ar recoil, effects. The various sediments analyzed show evidence for distinct overprinting between 2025 and 2090 Ma. One barite sample gave T0 (original blocking age) = 2673 ± 3 Ma (1?) which is close to a calculated model Ar diffusion-loss age for the same sample of 2688 ± 3 Ma (1?). This age is interpreted as representing final granitoid activity adjacent to the BGB, and/or craton-scale tectonism associated with the Limpopo Orogeny. Two samples gave T0 ages of ˜2350-2400 Ma which may reflect increased thermal gradients associated with the formation of the thick Transvaal sedimentary basin that may once have covered the BGB. The dominant apparent age plateaux together with modelled diffusive Ar loss ages of 2025-2090 Ma, are thought to represent regional thermal anomalies related to large-scale tectono-thermal activity in the Kaapvaal craton, of which the Bushveld Complex (which covers a surface area of ~ 60,000 km 2) and formation of the Vredefort Structure are obvious manifestations. The strong thermal overprinting recorded by the sediments has effectively removed any ancient atmosphere (i.e., 40Ar /36Ar ratios < 295.5) signatures.

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

1991-07-01

41

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

42

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

PubMed Central

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

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

2006-01-01

43

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

PubMed

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

Krüner, A; Byerly, G R; Lowe, D R

1991-04-01

44

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

NASA Astrophysics Data System (ADS)

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.

1989-12-01

45

Early Archean Spherule Beds of Possible Impact Origin from Barberton, South Africa: A Detailed Mineralogical and Geochemical Study.  

National Technical Information Service (NTIS)

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., th...

C. Koeberl W. U. Reimold R. H. Boer

1992-01-01

46

Geology of Volcanic Rocks in the South Half of the Ishpeming Greenstone Belt, Michigan (Chapter P).  

National Technical Information Service (NTIS)

The south half of the Ishpeming greenstone belt is dominated by a thick succession of subaqueously erupted volcanic rocks. A regional structural interpretation of the belt provides a framework for placing this succession in a stratigraphic order. The sout...

T. J. Bornhorst R. C. Johnson

1993-01-01

47

Geochemistry of volcanic rocks from the Wawa greenstone belt  

NASA Astrophysics Data System (ADS)

The Wawa greenstone belt is located in the District of Algoma and extends east-northeast from Lake Superior to the western part of the Sudbury District in Ontario, Canada. Recent mapping by Attoh has shown that an unconformity at the base of the Dore' Formation and equivalent sedimentary rocks marks a significant stratigraphic break which can be traced throughout the volcanic belt. This break has been used to subdivide the volcanic-sedimentary into pre- and post-Dore' sequences. The pre-Dore' sequence includes at least two cycles of mafic-to-felsic volcanism, each capped by an iron-formation unit. The post-Dore' sequence includes an older mafic-to-felsic unit, which directly overlies sedimentary rocks correlated with the Dore' Formation, and a younger felsic breccia unit interpreted to have formed as debris flows from a felsic volcanic center. In the present study, samples of both the pre-and post-Dore' volcanic sequences were analyzed for major and trace elements, incuding rare earths (REE). This preliminary study is part of an ongoing program to assess the petrogenesis of the volcanic rocks of the Wawa greenstone belt.

Schulz, K. J.; Sylvester, P. J.; Attoh, K.

48

Distribuicao da scheelita ao longo da faixa anfibolitica do greenstone belt, Barbacena, MG. (Scheelite distribution a long of amphibolitic belt from greenstone belt Barbacena, Minas Gerais, Brazil).  

National Technical Information Service (NTIS)

In the middle southern portion of the Minas Gerais state a 60 Km long and 12 Km wide tungsten belt was discovered, and related to the amphibolitic rocks of the Barbacena Greenstone. Tungsten, present as scheelite, is associated with amphibolites, amphibol...

R. M. Pereira C. A. Alexandre

1990-01-01

49

Gold Deposits Related to Greenstone Belts in Brazil. Deposit Modeling Workshop. Part A. Excursions.  

National Technical Information Service (NTIS)

Contents: Introduction to a workshop on gold deposits related to greenstone belts in Brazil, Belo Horizonte, Brazil, 1986; Geological field excursion from Belo Horizonte to Ouro Preto, Minas Gerais, Brazil; Field excursion from Belo Horizonte to Ouro Pret...

C. H. Thorman E. A. Ladeira D. C. Schnabel

1991-01-01

50

Structure of Southwestern Michipicoten Greenstone Belt, Ontario: Evidence for Archean Accretion.  

National Technical Information Service (NTIS)

The results of detailed mapping of a well exposed (by a large fume kill) Archean Michipicoten greenstone belt of Ontario is discussed. Numerous structural features are described including soft sediment deformation, thrust faults, isoclinal folds, and sill...

G. E. McGill C. H. Shrady

1988-01-01

51

Archean Geology of the Northern Block of the Ishpeming Greenstone Belt, Marquette County, Michigan. Chapter F.  

National Technical Information Service (NTIS)

The investigation is a continuation of mapping of the Ishpeming greenstone belt by Michigan Technological University personnel begun during the summer of 1984 under the direction of Bornhorst and continued during successive summers represents approximatel...

R. C. Johnson T. J. Bornhorst

1991-01-01

52

Yandal greenstone belt, Western Australia: 12 million ounces of gold in the 1990s  

Microsoft Academic Search

After a century of virtual neglect, exploration in the Yandal greenstone belt of the Yilgarn Craton of Western Australia\\u000a has yielded resources of 12 Moz Au during the 1990s. Success has come from a combination of conceptual geological models,\\u000a surface prospecting, understanding the weathering environment, and systematic drilling. The Archaean Yandal greenstone belt\\u000a comprises a lowermost banded iron formation, extensive

G. Neil Phillips; J. R. Vearncombe; E. Eshuys

1998-01-01

53

THE POTENTIAL FOR GOLD MINERALISATION IN THE GREENSTONE BELT OF BUSIA DISTRICT, SOUTH EASTERN UGANDA  

Microsoft Academic Search

Busia district in south eastern Uganda is one of the areas in the country with a history of potential for gold mineralisation and exploitation. Gold was first discovered in the Archaean greenstone belt of Busia by Davies in 1932. Only small mining operations, mostly artisan in character, have taken place in the district since then except the newly opened mines

A. B. Mbonimpa; E. Barifaijo; J. V. Tiberindwa

54

A Possible Impact Structure in the Belinga Greenstone Belt of Northeast Gabon  

NASA Astrophysics Data System (ADS)

An ~7-km-diameter, near-circular structure with indications of raised rim and disturbed central terrane has been identified on radar imagery in the Belinga Greenstone Belt of northeast Gabon. This structure should be further investigated as a possible impact structure.

Reimold, W. U.; Ayres, N.; Hatton, C.; Thomas, R. J.; Chevallier, L.; Master, S.; Antoine, L. A. G.

2001-03-01

55

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

56

Early Proterozoic Evolution of the Alto Jauru Greenstone Belt, Southern Amazonian Craton, Brazil  

Microsoft Academic Search

The Alto Jauru Greenstone Belt in west-central Brazil comprises three belts of Early Proterozoic volcano-sedimentary sucessions that were invaded by Early to Middle Proterozoic intrusions, including tonalites, gabbros, and granites. Volcanic rocks represent a bimodal suite with ultrabasic-basic rocks of komatiitic-tholeiitic affinities at the base and intermediate-felsic calc-alkaline lavas and pyroclastic units on the top. Chemical differences exist between basic

Francisco E. C. Pinho; William S. Fyfe; Marcia A. S. B. Pinho

1997-01-01

57

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

58

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

NASA Astrophysics Data System (ADS)

Boninites are rare in Archaean arcs all over the world whilst there are some reports from the Phanerozoic convergent margins. In this paper, boninites are reported for the first time from an Archaean greenstone belt of India, which have not been reported from any other Indian greenstone belt as yet. The greenstone belts of western Dharwar Craton are characterized by high-Mg basalts and komatiites whereas in the greenstone belts of eastern Dharwar Craton boninites represent the high-Mg lavas. These boninites are characterized by (1) high MgO (12-24 wt.%), (2) enriched in transition elements such as Ni (423-1184 ppm), Cr (943-2765 ppm), (3) low TiO2 (0.22-0.36 wt.%), (4) high Al2O3/TiO2 ratio (29-50), (5) Gd/Ybn less than one, (6) slight enrichment in LREE, depletion in MREE compared to LREE and HREE resulting in U-shaped REE patterns, (7) negative Nb, Ta, Zr, Hf, Ti and V anomalies despite the depletion in MREE. These characteristics differentiate them from deep mantle plume-related magmas. These boninites are compositionally similar to those found in modern and fossil island arcs from intraoceanic subduction settings and provide evidence to propose that two-stage melting of the Archaean mantle wedge generated this type of high-Mg magma. The other high-Mg type magma (komatiitic suite) found in the greenstone belts of western Dharwar Craton has an enriched deep mantle plume source and its dry melting whereas boninites are generated by wet melting of the refractory depleted mantle wedge under high temperature and fluid pressure generated by dehydration of the slab. The geological setting, HFSE and REE data show that possibly the 2.7-Ga peak of geological activity had transitional characteristics between those of Paleoarchaean and Phanerozoic. High thermal and fluid flux is inferred to generate these Mg-enriched and MREE-, HFSE-, LFSE-depleted suite. This discovery of boninites from Gadwal greenstone belt indicate that even in Archaean, subduction of small, young and hot oceanic plates produced magmatic assemblage resembling to those of some of the Cenozoic subduction complexes.

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

2005-01-01

59

Subaqueous calderas in the Archean Abitibi greenstone belt: An overview and new ideas  

Microsoft Academic Search

The 300×700 km Abitibi greenstone belt in Canada contains numerous world class Archean volcanogenic massive sulfide (VMS) deposits, yet documentation of Archean subaqueous calderas hosting such deposits is lacking. The modern Sunrise deposit in the Myojin Knoll caldera of the Izu–Bonin arc shows that submarine calderas are first order sites for VMS. The Hunter Mine and Normetal calderas, as well as

W. U. Mueller; J. Stix; P. L. Corcoran; R. Daigneault

2009-01-01

60

Fluid inclusion characteristics of the Uti gold deposit, Hutti-Maski greenstone belt, southern India  

Microsoft Academic Search

The Uti gold deposit occurs within amphibolites of the late Archaean Hutti-Maski greenstone belt of southern India. Gold mineralization is associated with intense silicification, biotite-actinolite- and sulfide-rich alteration zones in between small anastomozing shear zones. Characteristic biotite-K-feldspar alteration and arsenopyrite thermometry constrain the mineralizing event to above 400 °C, which is concordant with evidence of dynamic recrystallization in mineralized quartz

Biswajit Mishra; Nabarun Pal; Amit Basu Sarbadhikari

2005-01-01

61

Geochemistry of an ultramafic-rodingite rock association in the Paleoproterozoic Dixcove greenstone belt, southwestern Ghana  

NASA Astrophysics Data System (ADS)

Rodingite occurs in ultramafic rocks within the Paleoproterozoic (Birimian) Dixcove greenstone belt in southwestern Ghana. U Pb analyses of zircons from granitoids intrusive into the greenstone belt constrain the age of the rodingite-ultramafic association to be older than 2159 Ma. The ultramafic complex consists of variably serpentinized dunite and harzburgite overlain by gabbroic rocks, which together show petrographic and geochemical characteristics consistent with their formation by fractional crystallization involving olivine and plagioclase cumulates. Major and trace element concentrations and patterns in the ultramafic mafic cumulate rocks and associated plagiogranite are similar to rocks in ophiolitic suites. The rodingites, which occur as irregular pods and lenses, and as veins and blocks in the serpentinized zones, are characterized by high Al2O3 and CaO contents, which together with petrographic evidence indicate their formation from plagioclase-rich protoliths. The peridotites are highly depleted in REE and display flat, chondrite-normalized REE patterns with variable, but mostly small, positive Eu anomalies whereas the rodingites, which are also highly depleted, with overall REE contents from 0.04 to 1.2 times chondrite values, display distinct large positive Eu anomalies. It is proposed that the rodingite-bearing Birimian ultramafic complex and associated pillowed greenstone belt basalts may represent fragments of a Paleoproterozoic oceanic lithosphere.

Attoh, Kodjopa; Evans, Matthew J.; Bickford, M. E.

2006-07-01

62

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

PubMed

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

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

1989-01-01

63

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

NASA Astrophysics Data System (ADS)

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

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

2009-02-01

64

Horizontal tectonic deformation geometries in a late Archaean sedimentary sequence, Belingwe greenstone belt, Zimbabwe  

NASA Astrophysics Data System (ADS)

In the Belingwe greenstone belt of Zimbabwe, structural evidence from the circa 2.65 Ga old sedimentary Cheshire Formation which overlies and is imbricated with a mafic volcanic unit is consistent with thrusting of the greenstone sequence. The Cheshire Formation consists of a karstified carbonate ramp sequence overlain by siliciclastic turbidite deposits that formed in a southeast deepening basin. The earliest deformational structures formed during a syndepositional to postdepositional, thin-skinned thrusting event (D1) that affected poorly consolidated sediments and is recorded in bedding-parallel ductile shear zones, boudins, folds, and block-in-matrix structures. D1 shear zones separate the volcanic sequence and the overlying sediments and occur between the carbonate and siliciclastic units. Syntectonic sulphide mineralization and silicification of mainly fine-grained sediments along the main thrust faults gave rise to the formation of rocks similar in appearance to banded iron formations. Stratigraphic units were locally duplicated along the D1 thrust faults, including a tectonic slice of mafic volcanics that was emplaced onto carbonates along a chaotic unit similar to a tectonic melange. The elongation of inclusions in the melange zone and lineations in ironstones together with kinematic indicators suggest that stratigraphic duplication resulted from northwestward directed tectonic transport. Deposition of the Cheshire Formation took place in an asymmetric, foreland-type basin contemporaneously with thrusting. Soon after deposition the formation was incorporated into the thrust stack. Subsequent deformation events include tight upright folding, gentle cross-folding, and dextral strike-slip faulting of the greenstone succession. Evidence for early thrusting suggests that horizontal tectonic processes played an important role in the evolution of the Belingwe greenstone belt.

Hofmann, Axel; Dirks, Paul H. G. M.; Jelsma, Heilke A.

2001-12-01

65

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

NASA Astrophysics Data System (ADS)

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

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

2004-12-01

66

Middle Archaean gold deposits in the North Shaw–Coongan Greenstone Belt, Australia: the relative timing of events responsible for gold mineralisation  

Microsoft Academic Search

Gold deposits of the Mid-Archaean East Pilbara Granitoid–Greenstone Terrane, Australia, are unique because they characterise metallogenic evolution of the Early Earth. In the North Shaw–Coongan Greenstone Belt, quartz–sulphide lodes within shear and fault zones are host to gold mineralisation. Detailed field mapping of crosscutting structures at the Sharks Well Mining Centre and Blue Bar Mine in the Coongan Greenstone Belt,

A. F. Scherrenberg; K. A. A. Hein; S. White

2004-01-01

67

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

PubMed

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

Cousens

2000-03-01

68

Overview and Preliminary results of a magnetotelluric experiment across the southern Barberton greenstone belt  

Microsoft Academic Search

The Kaapvaal Craton of South Africa is the oldest well-preserved continental fragment on the planet and thus is a key area for studies of geodynamic processes of the early Earth. One major controversy concerns the importance of plate tectonic processes in Archean times and the time when this may have been first initiated. Several potential ancient suture zones have been

U Weckmann; A Nube; X Chen; O Ritter

69

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

Microsoft Academic Search

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

Napoleon Q. Hammond; John M. Moore

2006-01-01

70

Micro-PIXE elemental imaging of pyrites from the Bulawayan-Bubi Greenstone Belt, Zimbabwe  

NASA Astrophysics Data System (ADS)

Micro-PIXE at the NAC nuclear microprobe was used for studies of a sequence of unusual pyrite-bearing carbonate sediments from the east of Turk Mine, Bubi Greenstone Belt, Zimbabwe. This pyrite mineralization shows a variety of textures, and its petrographic interpretation needed more solid geochemical evidence. Elemental maps were obtained using Dynamic Analysis (DA) (a rapid matrix transform method) which forms part of the GeoPIXE software package, and were complemented by point analyses in selected areas. The implemented on-demand beam deflection system allowed for count rates of the order of 3000 counts/s with negligible dead time. The distribution of As and other elements confirmed the petrographic interpretation of three different pyrite generations. In addition, point analyses showed that Sb and Pb were significantly elevated in the zones of As enrichment.

Xenophontos, L.; Stevens, G.; Przybylowicz, W. J.

1999-04-01

71

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

Microsoft Academic Search

Komatiites in the western part of the Norseman-Wiluna greenstone belt in the Yilgarn Block of Western Australia display a wide variety of volcanic facies, ranging from very thin differentiated Munro Township-type flow units through to very thick olivine-rich cumulate flow units containing high proportions of adcumulate dunite.Cumulate flow units have been mapped in detail in the Agnew-Wiluna segment of the

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

1995-01-01

72

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

Microsoft Academic Search

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

Napoleon Q. Hammond; John M. Moore

2006-01-01

73

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

Microsoft Academic Search

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

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

2006-01-01

74

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

Microsoft Academic Search

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

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

2006-01-01

75

Constraints on the timing of lode?gold mineralisation in the Wiluna greenstone belt, Yilgarn Craton, Western Australia  

Microsoft Academic Search

Ar?Ar ages of hydrothermal muscovites constrain the age of gold mineralisation in the Wiluna greenstone belt, Western Australia. A single muscovite sample from the Matilda M1 deposit, hosted in the greenschist?amphibolite facies Matilda domain, has a Ar?Ar plateau?like segment corresponding to an age of 2623 ± 12 Ma (2 ?). This is interpreted as the probable age of mineralisation and

A. J. R. Kent; S. G. Hagemann

1996-01-01

76

Fluid evolution and chemical controls in the Fazenda Maria Preta (FMP) gold deposit, Rio Itapicuru Greenstone Belt, Bahia, Brazil  

Microsoft Academic Search

The Fazenda Maria Preta (FMP) gold deposit is confined to two regional-scale, sinistral-oblique brittle–ductile shear zones which are located in a greenschist facies metamorphosed volcano-sedimentary sequence in the northern sector of the lower Proterozic Rio Itapicuru greenstone belt, NE Brazil. Alteration is pervasive throughout the shear zones and characterized by carbonatization and sericitization of intermediate volcanic, volcaniclastic, and sub-volcanic rocks.

Roberto P. Xavier; Robert P. Foster

1999-01-01

77

Major and trace element geochemistry and genesis of supracrustal rocks of the North Spirit Lake Greenstone belt, NW Ontario, Canada  

Microsoft Academic Search

Supracrustal rocks of the North Spirit Lake (NSL) greenstone belt comprise three stratigraphic units. The basal unit (Unit 1) consists of pillowed, massive and tuffaceous, tholeiitic basalts and komatiitic basalts (approximately 3.1Ga) with minor interbeds of greywacke and black pelite displaying characteristics of turbidites and mass flow deposits. REE patterns indicate basalt genesis at comparatively shallow depths (spinel-lherzolite field). Although

H. W. Nesbitt; G. M. Young; S. A. Bosman

2009-01-01

78

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

79

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

80

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

81

Physical volcanology of the mafic segment of the subaqueous New Senator caldera, Abitibi greenstone belt, Quebec, Canada  

NASA Astrophysics Data System (ADS)

Archean calderas provide valuable insight into internal geometries of subaqueous calderas. The New Senator caldera, Abitibi greenstone belt, Canada, is an Archean example of a subaqueous nested caldera with a basal stratigraphy dominated by gabbro-diorite dykes and sills, ponded magmas and basalt and andesite lava flows. The aim of our study is to focus on the use of physical volcanology to differentiate between the various mafic units found at the base of the New Senator caldera. Differentiation between these various mafic units is important from an exploration point of view because in modern subaqueous summit calders (e.g. Axial Seamount) margins of ponded magmas are often sites of VMS formation.

Moore, Lyndsay N.; Mueller, Wulf U.

2008-10-01

82

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

83

3.4-Billion-Year-Old Biogenic Pyrites from Barberton, South Africa: Sulfur Isotope Evidence  

NASA Astrophysics Data System (ADS)

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, Hiroshi; Kakegawa, Takeshi; Lowe, Donald R.

1993-10-01

84

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

85

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

Microsoft Academic Search

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

N. C. Williams

2009-01-01

86

Light rare earth element depleted to enriched basaltic flows from 2.8 to 2.7 Ga greenstone belts of the Uchi Subprovince, Ontario, Canada  

Microsoft Academic Search

A compositionally diverse group of basaltic flows are present in the 2.7 Ga St. Joseph assemblage of the St. Joseph greenstone belt, Uchi Subprovince. A spectrum of light rare earth element (LREE) depleted to enriched patterns corresponds to low-, medium- and high-K series (LKS, MKS, HKS) basalts, shoshonites and leucitites of some modern arcs. More primitive, tholeiitic LKS and MKS

Pete Hollings; Robert Kerrich

2006-01-01

87

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

88

Field and geochemical characteristics of Mesoarchean to Neoarchean volcanic rocks in the Storø greenstone belt, SW Greenland: Evidence for accretion of intra-oceanic volcanic arcs  

Microsoft Academic Search

The Storø greenstone belt, southern West Greenland, consists of thrust-imbricated slices of Mesoarchean (>3060Ma) and Neoarchean (ca. 2800Ma) mafic to ultramafic volcanic rocks, volcaniclastic sediments, and gabbro–anorthosite associations. The belt underwent polyphase metamorphism at upper amphibolite facies conditions between 2650 and 2600Ma. The contacts between the Mesoarchean and Neoarchean volcanic rocks, and surrounding Eoarchean to Neoarchean tonalite–trondhjemite–granodiorite (TTG) gneisses are

J. C. Ordóñez-Calderón; A. Polat; B. J. Fryer; J. E. Gagnon

2011-01-01

89

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

NASA Astrophysics Data System (ADS)

The greenstone sequence at Golden Pride gold deposit in Nzega greenstone belt of northern Tanzania is cross-cut by several intrusions whose geochemistry and petrogenesis is unknown. We present major and trace elements geochemistry of the Golden Pride igneous intrusions with the aim of constraining their petrogenesis and their ancient tectonic setting. The Golden Pride intrusions are geochemically categorized into two main rock suites: the granodiorites (which include the porphyries) and the lamprophyres (formerly intermediate intrusions). The granodiorites are characterized by SiO2 contents of 54.5-69.9 wt%, elevated MgO (1.22-3.59 wt%) Cr (up to 54 ppm), Mg# (35-55) pointing to a mantle component in the source. Compared to the TTG and adakites, the granodiorites are characterized by higher K2O (1.52-4.30 wt%), medium HREE (Gd/ErCN = 2.13-3.77) and marked enrichment in Ba and Sr (Ba + Sr = 819-2922 ppm) and are in these respects similar to Archean high Ba-Sr sanukitoids. The rocks in this suite are interpreted to have formed by partial melting of an enriched mantle wedge through two metasomatic events: subduction-related fluids/melts and by metasomatism related to asthenospheric mantle upwelling caused by slab break-off.

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

2013-10-01

90

An Archean oceanic felsic dyke swarm in a nascent arc: the Hunter Mine Group, Abitibi Greenstone Belt, Canada  

NASA Astrophysics Data System (ADS)

The 2730-Ma-old Hunter Mine Group (HMG), a dominantly felsic subaqueous volcanic sequence, was formed during early arc construction in the Abitibi greenstone belt (Quebec, Canada). The western part of the HMG contains a felsic dyke swarm up to 1.5 km wide and traceable up-section for 2.5 km. Five distinct generations were identified: (1) aphanitic to feldspar-phyric dykes; (2) quartz-feldspar-phyric dykes with < 5% quartz phenocrysts; (3) quartz-feldspar-phyric dykes with 10-25% quartz phenocrysts; (4) dacitic feldspar-phyric dykes; and (5) mafic dykes. The felsic dykes collectively constitute more than 90% of the dyke swarm. Geochemically, they resemble modern calc-alkaline dacites and rhyolites. Their mantle-normalized incompatible trace-element patterns display a moderate enrichment of Th and light REE relative to HFSE and heavy REE as well as negative Nb, Ta, Eu and Ti anomalies. Most of the major- and trace-element abundance variations in these rocks can be explained by crystallization of feldspars. Geochemical data including depleted mantle-like ? Nd values suggest that an older sialic substrate was not involved in their genesis. We infer that the felsic rocks were generated by melting of mafic oceanic crust. The swarm was emplaced during nascent oceanic island-arc development and was related to rifting of the arc. The conformably overlying MORB-like basalts and basaltic komatiites of the Stoughton-Roquemaure Group used the same conduits and further indicate splitting of the arc. HMG and associated parts of the Abitibi greenstone belts bear a strong resemblance to modern rifted intraoceanic arcs of the western Pacific.

Dostal, J.; Mueller, W.

1996-07-01

91

A 3.2 Ga Magmatic arc Preserving 50 Ma of Crustal Convergence in the Barberton Terrain, South Africa  

NASA Astrophysics Data System (ADS)

The tectonic setting, sources and conditions of melting of Archean tonalite-trondhjemite-granodiorite (TTG) rocks, the main building blocks of all Archean continental kernels, are a matter of ongoing debate. In the 3.5- 3.1 Ga Barberton granitoid-greenstone terrain in South Africa, the main phase of terrane accretion in the greenstone belt (D2), associated shortlived, but voluminous TTG plutonism, and high-P low-T metamorphism in the southern TTG gneiss terrain of the Stolzburg domain are all recorded at 3.23 Ga. While terrane accretion and the deep-crustal burial of parts of the granitoid-greenstone terrane are interpreted to have occurred during subduction-driven processes in an arc-trench setting, the existence of a longlived magmatic arc, a tell-tale sign of crustal convergence preceding the final collisional events has, to date, not been identified. We document field and geochronological results from the hitherto poorly documented Badplaas domain, located to the immediate west of the high-grade Stolzburg domain south of the Barberton greenstone belt. The Badplaas domain is made up of a variety of compositionally and texturally distinct, variably gneissose trondhjemites. Multiple intrusive relationships between different phases are common and large parts of the Badplaas domain are developed as heterogeneous, intrusive breccias. The distinction of regional-scale lithotypes in this magmatic terrain has enabled us to constrain the relative timing of emplacement of the main TTGs. Geochronological work on the five main TTG phases reveals that the Badplaas domain was assembled over a period of ca. 50 Ma between ca. 3290 and 3240 Ma. We interpret the Badplaas domain to record 50Ma of convergence-related TTG plutonism, located above the NW-dipping subduction zone. The ages of this plutonism overlap with the sedimentation of 3260-3225 Ma fore- or back-arc deposits preserved in sediments of the Fig Tree Group in the greenstone belt. The results indicate that the different tectonostratigraphic domains of the Barberton granitoid-greenstone terrain may well preserve an almost complete inventory of a Mesoarchaean arc-trench system.

Kisters, A.; Belcher, R.; Poujol, M.; Stevens, G.; Moyen, J.

2006-12-01

92

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

Microsoft Academic Search

Hydrogen and carbon isotope ratios of secondary phases formed during seafloor hydrothermal alteration provide constraints on important reservoirs affected by oxygen build-up in the atmosphere. We determined hydrogen and carbon isotope ratios from the well-preserved, ~3.5 Gyr Pilbara greenstone belt to constrain:1) whether hydrogen loss is a viable mechanism for changing the oxidation state of the Archean atmosphere and the

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

2005-01-01

93

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

94

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

95

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

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

96

Sulfur- and oxygen-isotope constraints on the sedimentary history of apparent conglomerates from the Nuvvuagittuq Greenstone Belt (Nunavik, Québec)  

NASA Astrophysics Data System (ADS)

Mafic igneous rocks of the Nuvvuagittuq Greenstone Belt (NGB) crystallized before 3.8 Ga and possibly as early as 4.3 Ga, potentially making the belt the oldest known supracrustal sequence on Earth. However, detrital zircons from a rare quartz-biotite schist in the NGB yield significantly younger ages of ?3.77 Ga or less. These appear to be inconsistent with the ages of the mafic igneous rocks, as the quartz-biotite schist has been interpreted as a metaconglomerate, formed by the dismantling of preexisting lithologies. In order to assess this genetic interpretation, we performed a sulfur and oxygen isotope study of the quartz-biotite schist. Sulfide grains found in quartz clasts and the matrix show significant mass-independent fractionation of sulfur isotopes (+0.2‰??33S‰?+1.0‰; mean ?33S=+0.5±0.1‰). Secondary sulfides from crosscutting veins do not show mass-independent fractionation of sulfur isotopes (-0.1‰??33S?+0.3‰; mean ?33S=+0.1±0.1‰). Oxygen isotope compositions of quartz from clasts, matrix and a fine-grained lens are highly enriched in 18O (16.9‰??18O?26.7‰). Non-zero ?33S values indicate a surficial origin for sulfur, probably the Eoarchean atmosphere, while high ?18O values suggest a low-temperature (65±18 °C) origin for the quartz, likely as chemical precipitation of a chert precursor from Si-saturated seawater. Therefore, the coupled S- and O-isotope measurements show that primary isotopic signatures characteristic of surficial environments survived the protracted metamorphic history of the NGB, and suggest that the quartz-biotite schist contains material that originated as chemical metasediments. The near mono-mineralic compositions of the clasts (quartz) and their shared 18O-enrichment suggest that they had a common protolith, which was deposited prior to the formation of the schist, and subsequently reworked. Whether the quartz-biotite schist represents a metaconglomerate or a structural melange, it preserves remnants of some of the oldest chemical sediments on Earth.

Kitayama, Y.; Thomassot, E.; O'Neil, J.; Wing, B. A.

2012-11-01

97

Origins of apparent conglomerates of the Nuvvuagittuq Greenstone Belt (Nunavik, Québec): Sulfur and oxygen isotope evidence and chronological implications  

NASA Astrophysics Data System (ADS)

Recent work on the Nuvvuagittuq Greenstone Belt (NGB, Nunavik, Québec) raises the possibility that the Hadean may be studied underfoot at least back to the Canadian Period (4.2 to 4.3Ga) [1]. Many mafic volcanic and intrusive lithologies from the NGB yield a range of stratigraphically controlled 142Nd and 143Nd isochron ages from ~4.1 to 4.3Ga [2]. These ages would make the belt the oldest known supracrustal sequence on Earth. However, chronological inconsistencies are present in the NGB, with zircons from rare intrusive felsic horizons and from apparent metaconglomerates yielding ages of ~3.8Ga [3;4]. While the conglomeratic units host a remarkable pebble-like structure, this horizon also reflects a complex metamorphic history that makes a straightforward assessment of its protolith difficult. To evaluate the possible sedimentary origin of the conglomeratic units, we have undertaken a detailed S- and O-isotope study of sulfides and quartz from both the quartz-rich clasts and the surrounding biotite-rich matrix. Quartz grains in clasts in the conglomeratic units have substantially 18O-enriched compositions (16.9% ? ?18O ? 26.7%). These values fall in the upper end of the range previously measured from Archean cherts, potentially linking the ultimate origin of the silica in the clasts to direct precipitation from silica-saturated seawater. The prospect of an ultimate surficial origin is consistent with our measurements of significant mass-independent S isotope fractionation in trace sulfides in the clasts, which is an isotopic characteristic of atmospheric sulfur on early Earth. Despite the clear bulk compositional differences between the biotite-rich matrix and the quartz-rich clasts, quartz and sulfide grains in the matrix share the O- and S-isotopic characteristics of their counterparts in the clasts. Quartz grains in the matrix have ?18O values of 19.9 to 22.3% and sulfide grains in the matrix record significant mass-independent S isotope fractionation. In fact, the entire population of S isotope analyses exhibits an impressive degree of homogeneity characterized by a mean ?33S value of 0.49±0.15%. It is unlikely that this homogeneity represents overprinting by an externally derived sulfur-bearing fluid as rare cross-cutting sulfide veins in the conglomeratic units possess a mean ?33S value of 0.07±0.08%. To a first-order then, our O- and S-isotope analyses suggest an ultimate sedimentary origin for the quartz and sulfide grains in the conglomeratic units. In this presentation, we will explore how these observations constrain the sedimentary origin of the conglomeratic units in light of: (1) the isotopic homogeneity of the rock; (2) the isotopic characteristics of other lithologies in the NGB, and (3) the geochronological implications of potential depositional models for the conglomeratic units. [1] Goldblatt et al. (2010). Solid Earth, 1, 1-3 [2] O'Neil et al. (2008). Science 321, 1828-1831 [3] David et al. (2009). GSA Bulletin 121, 150-163. [4] Cates and Mojzsis (2007), EPSL 255, 9-21

Kitayama, Y.; Thomassot, E.; O'Neil, J.; Francis, D.; Wing, B. A.

2011-12-01

98

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

NASA Astrophysics Data System (ADS)

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

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

2006-07-01

99

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

100

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

101

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

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

102

Physical volcanology, stratigraphy, and lithogeochemistry of an Archean volcanic arc: evolution from plume-related volcanism to arc rifting of SE Abitibi Greenstone Belt, Val d'Or, Canada  

Microsoft Academic Search

The eastern segment of the Southern Volcanic Zone (SVZ) of the Abitibi greenstone belt is a complex sequence of volcano-sedimentary rocks interleaved with syn- to post-volcanic plutonic suites. The eastern segment can be broken into two stratigraphic groups based on regional tectonics and volcano-sedimentary stratigraphy, the basal Malartic Group (MG), composed of the La Motte-Vassan, Dubuisson and Jacola Formations (JFs),

Craig R. Scott; Wulf U. Mueller; Pierre Pilote

2002-01-01

103

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

Microsoft Academic Search

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

Robert Frei; Ali Polat

2007-01-01

104

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

Microsoft Academic Search

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

Jesse C. Dann

2001-01-01

105

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

Microsoft Academic Search

Timing the appearance of photosynthetic microorganisms is crucial to understanding the evolution of life on Earth. The ability of the biosphere to use sunlight as a source of energy (photoautotrophy) would have been essential for increasing biomass and for increasing the biogeochemical capacity of all prokaryotes across the range of redox reactions that support life. Typical proxies for photosynthesis in

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; Gordon Southam; Lachlan Maclean; Susan Wirick; Axel Hofmann; Anders Meibom; François Robert; Christian Défarge

2011-01-01

106

Synchrotron Radiation X-Ray Fluorescence nanoanalyses of the metallome of a ~3.3 Ga-old microbial biofilm from the Barberton greenstone belt, South Africa.  

NASA Astrophysics Data System (ADS)

Combining in situ nanometer-scale techniques on the fossilized Josefsdal Chert Microbial Biofilm (JCMB) reveals a distinct vertical structural and compositional organisation: the lower part is calcified as aragonite, while the upper non-calcified kerogenous layer is characterised by up to 1% sulphur [1]. The in situ analysis of all the metals as a group represents a useful microbial fingerprint [2] and we will continue to explore it. Synchrotron Radiation X-Ray Fluorescence maps of high spatial resolution (< 0.3 µm) were recorded on a unique FIB section (15 x 10 x 3 µm3) of the JCMB. A 300 nm resolution was reached at 2500 eV on the ID21 scanning X-ray microscope (SXM) and a 120x165 (horizontal x vertical) nm at 17450 eV on ID22NI at the European Synchrotron Radiation Facility (ESRF). All maps reveal chemical heterogeneities not previously discernible by scanning the same FIB cut using micron resolution. The feasibility of high-resolution analyses with high flux on rock samples was first shown for samples that had in this respect an ideal hotspot geometry in a uniform silica matrix [3, 4]. Our FIB sample preparation ensures negligible thickness variations so quantitation of all the metals in the JCMB is presently only limited by the important intrinsic heterogeneity of the sample. Methods to deal with micrometer bulk heterogeneity have just been developed by performing redundant volumetric scans in fluorescence tomography to counterbalance the complex sample geometry [5]. An alternative methodology more adapted to the thin slice geometry is tested here. A relationship between the ratio of the Compton to Rayleigh (C-R) scatterings and the average atomic number (Zave), only established with unpolarized X-rays [6], was measured using fully polarized synchrotron beams [7]. C-R peaks measured on thick Astimex standards (1 mm) and those calculated from Monte-Carlo simulations of thick and thin (100 µm and 1 µm) samples having the same compositions were analyzed using a version of the PyMCA software [8] specially optimised for this purpose. The empirical relations of the type Zave = a•(C/R)b obtained for the three analyses sets provide a comprehensive set of calibrations suitable for any sample of any thickness. On the basis of these calibrations, we inferred positions and concentrations of undetected low-Z phases in the JCMB and further corrected the concentrations of the detected metals in the organic phases. 1. Westall F., et al., 2011. Earth & Planet. Sci. Lett., 310, 468-479. 2. Zerkle A L., et al., 2005. Am. J. Science, 305, 467-502. 3. Westphal A. J., et al., 2010. AIP Conference Proceedings, 1221, 131-138. 4. Bleuet P., et al., 2008. App. Phys. Lett., 92, 213111-1-3. 5. Golosio B., et al., 2003. Appl. Phys., 94, 145-157. 6. M. Haschke, 2003. PhD dissertation, T.U. Berlin. 7. Simionovici A. S., et al., 2010. Proceedings of the Meteoritical Society Conference, N.Y., USA. 8. Solé V.A., et al., 2006, Elsevier, 62, 63-68.

Hubert, A.; Lemelle, L.; Salome, M.; Cloetens, P.; Westall, F.; Simionovici, A.

2012-04-01

107

Geochemistry and petrogenesis of the granitoids of the Barberton Mountain Land, South Africa  

NASA Astrophysics Data System (ADS)

The Barberton Mountain Land, situated in the Kaapvaal craton of southern Africa, is a well preserved pre-3.0 Ga granite-greenstone terrane. The greenstone belt consists of a sequence of mafic to ultramafic lavas and metasedimentary rocks emplaced/deposited between 3.5 and 3.2 Ga. The granitoid rocks were emplaced over a 500 Myr time-span and can be divided into two suites. The TTG suite (emplaced ca 3.5 - 3.2 Ga) contains tonalites, trondhjemites and granodiorites; and the GMS suite (emplaced ca 3.2 - 3.1 Ga) includes granites, monzogranites and a small syenite-granite complex. Geochemically, the TTGs are typically low- to medium-K, metaluminous I-type granites, Their chondrite-normalised rare-earth-element (REE) patterns show two trends. The majority of plutons are LREE-enriched, HREE-depleted and with small or no Eu anomalies, whilst the Steynsdorp and Doornhoek plutons are relatively HREE-undepleted with significant Eu anomalies. Nd isotope analyses show that the 3.4 Ga TTGs have positive ?Nd values (0 to +3.7), indicative of depleted-mantle sources, similar to the oldest greenstone belt formations (the Onverwacht). In contrast, the 3.2 Ga TTGs have negative ?Nd, suggesting crustal or enriched-mantle input into the magmas. The GMS rocks, on the other hand, are medium- and high-K metaluminous I-type rocks. They display two dominant REE patterns. Medium-K GMS rocks (the Dalmein and portions of Heerenveen) are LREE-enriched, HREE-depleted and have no Eu-anomalies, whereas, the high-K GMSs (Heerenveen, Mpuluzi and Boesmanskop) are relatively HREE-enriched with negative Eu anomalies. Positive and negative ?Nd values (-4.4 to +4.8) for the Boesmanskop Syenite suggests depleted-mantle and crustal signatures. The ?Nd and REE patterns, in particular, provide insights into the compositions of potential source rocks and restites for the TTG and GMS suites. Since HREEs and Eu are readily accommodated in garnet and plagioclase, respectively, their depletion suggests the presence of these minerals in the restite. For the TTG suite, we therefore suggest a garnet-rich amphibolitic or eclogitic depleted-mantle source at a depth > 40 km. This has been confirmed by experimental work constraining the stability of garnet in the trondhjemite compositions, and at magmatic temperatures, to a pressure of 15.24 ± 0.5 kbar corresponding to a depth of 54.9 ± 1.8 km. In contrast, the GMS suite most probably had a plagioclase-rich, garnet-poor source that may be a mixture of depleted-mantle and crustal materials. Tectonically, the Barberton area is dominated by two episodes of terrane accretion at ˜3.5 and 3.2 Ga, the ages of TTG magmatism. This compressional tectonic regime, coupled with the results of experimental work on the partial melting of greenstone type material leads us to suggest basaltic amphibolites of the greenstone sequences as likely source materials for the TTGs. The likely source rocks for the GMS suite, however, are not so easily constrained. The chemistry and ?Nd values of the Boesmanskop syenite suggest a hybrid mantle-crustal source. This type of hybrid source might also explain the features of the monzogranitic batholiths. Close associations between syenite and monzogranites are common, particularly in post-orogenic extensional/transtensional settings. Although extensional activity has not been documented in Barberton, ˜3.1 Ga strike-slip activity has. A post orogenic thinning of the crust might explain the production of large voluminous monzogranite batholiths and the passive nature of their intrusion dynamics.

Yearron, L.; Clemens, J.; Stevens, G.; Anhaeusser, C.

2003-04-01

108

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

NASA Astrophysics Data System (ADS)

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

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

2007-11-01

109

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

NASA Astrophysics Data System (ADS)

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

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

1992-12-01

110

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

111

UPb zircon geochronology of the Yellowknife volcanic belt, NWT, Canada: New Constraints on the timing and duration of greenstone belt magmatism  

Microsoft Academic Search

Volcanic and sedimentary rocks in the Slave Province, collectively termed the Yellowknife Supergroup, have long been considered to represent laterally continuous and correlative, stratigraphically coherent homoclinal sequences. Correlation based on the lithologic analysis of certain distinctive units has been most intensely applied to the Yellowknife volcanic belt in the southern Slave Province. U-Pb zircon data for seven samples collected from

S. E. Isachsen; S. A. Bowring; W. A. Padgham

1991-01-01

112

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

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

113

U-Pb zircon geochronology of the Yellowknife volcanic belt, NWT, Canada: New Constraints on the timing and duration of greenstone belt magmatism  

SciTech Connect

Volcanic and sedimentary rocks in the Slave Province, collectively termed the Yellowknife Supergroup, have long been considered to represent laterally continuous and correlative, stratigraphically coherent homoclinal sequences. Correlation based on the lithologic analysis of certain distinctive units has been most intensely applied to the Yellowknife volcanic belt in the southern Slave Province. U-Pb zircon data for seven samples collected from within the belt are reported here. The distinctiveness of the Townsite Formation, a term applied to three lenticles of rhyodacitic to dacitic tuffs, breccias, and pillowed flows, in comparison to the overlying and underlying tholeiitic basalts (Kam Group), has led to its use as a key marker unit for stratigraphic correlations and palinspastic restorations of offsets on Proterozoic faults in the area. A sample from each of the three segments was collected for U-Pb zircon geochronology. In addition, numerous thinner tuffaceous beds from the Kam Group were also dated. Upper intercept ages of 2,683 {plus minus} 5 Ma, and 2,703 {plus minus} 2 Ma, and 2,705 {plus minus} 3 Ma for the three Townsite segments show that they are not all correlative. Ages of other felsic units from the Kam Group are 2,716 {plus minus} 9 Ma, 2,712 {plus minus} 2 Ma, 2,707 {plus minus} 2 Ma, and 2,688 {plus minus} 3 Ma. These ages are amongst the oldest yet reported for supracrustal rocks in the Slave Province and reveal a protracted magmatic history for the Yellowknife volcanic belt.

Isachsen, S.E.; Bowring, S.A. (Washington Univ., St. Louis, MO (USA)); Padgham, W.A. (Dept. of Indian Affairs and Northern Development, Yellowknife, Northwest Territory (Canada))

1991-01-01

114

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

115

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

116

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

NASA Astrophysics Data System (ADS)

Major and trace element, samarium (Sm)-neodymium (Nd) and lead (Pb) isotopic analyses of individual mesobands of five Banded Iron Formations (BIFs) and associated metavolcanic and metasedimentary rocks from the Neoarchean Tati Greenstone Belt (TGB, Northeastern Botswana) were conducted in order to characterize and determine the source(s) and depositional environment(s) of these chemical sediments and to compare their features with other Archean BIFs. Rare earth element (REE)-yttrium (Y) patterns of individual BIF mesobands from the TGB show features characteristic of other Archean BIFs; these are (relative to Post Archean Australian Shale (PAAS) normalization), LREE depletions relative to MREE and HREE, positive lanthanum La/La*PAAS, europium Eu/Eu*PAAS, and Y/holmium (Ho) ratios. The TGB BIFs also lack defined cerium Ce/Ce*PAAS anomalies. Generally, the REY patterns are similar to modern seawater and together with low concentrations of high-field strength elements these features are indicative of an essentially detritus-free precipitation. Uranogenic Pb isotope data for the BIFs define individual correlation lines with slopes corresponding to apparent ages of ~2.7 Ga, interpreted as closely reflecting the depositional time frames. An exception to this are the BIFs at Mupane mine in the central part of the TGB which exhibit disturbed U-Pb isotope systematics. They indicate a pronounced resetting around 2.0 Ga. This is also reflected by Pb isotope data of gold-bearing sulfides and Pb-stepwise leaching (PbSL) data of garnets from associated metasedimentary rocks at this location. The garnet PbSL data define a correlation line in uranogenic Pb isotope space with a slope corresponding to an apparent age of 1976±88 Ma. This age is interpreted as a metamorphic age that can be correlated with ~2.0 Ga tectono- metamorphic events within the adjacent Limpopo orogenic belt, and which apparently have, also affected parts of the adjacent Zimbabwe craton to the north. Elevated, but variable 207Pb/204Pb relative to 206Pb/204Pb ratios of BIFs are indicative of a high-? (238U/204Pb) prehistory of their source materials which, in accordance with Nd model ages defined by the BIFs, can best be modeled by a 3.0 - 3.2 Ga extraction of these sources from a depleted mantle reservoir. Sm-Nd isotopic relationships between silica (SiO2)- and iron (Fe2O3)-rich mesobands of one of the studied BIFs point to essentially two REY sources controlling the depositional environment. The first is characterized by elevated Sm-Nd ratios and a negative inferred ?Nd(2.7 Ga) value of -2.5 and is associated with high Fe fluxes. The second source, associated with high Si fluxes, is instead characterized by lower Sm-Nd ratios and a slightly positive inferred ?Nd(2.7 Ga) value of +0.4. While the association of high Fe concentrations and elevated Sm-Nd in BIF mesobands is characteristic of a hydrothermal seawater input, the Sm-Nd isotopic characterization of this source, unlike other Archean BIFs, points to a significantly LREE enriched (rather than depleted) mantle source. This finding is compatible with the potential existence of a subcontinental lithospheric mantle reservoir beneath the Zimbabwe and Kaapvaal craton.

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

2008-12-01

117

The geology of the Morro Velho gold deposit in the Archean Rio das Velhas greenstone belt, Quadrila??tero Ferri??fero, Brazil  

USGS Publications Warehouse

The Morro Velho gold deposit, Quadrila??tero Ferri??fero region, Minas Gerais, Brazil, is hosted by rocks at the base of the Archean Rio das Velhas greenstone belt. The deposit occurs within a thick carbonaceous phyllite package, containing intercalations of felsic and intermediate volcaniclastic rocks and dolomites. Considering the temporal and spatial association of the deposit with the Rio das Velhas orogeny, and location in close proximity to a major NNW-trending fault zone, it can be classified as an orogenic gold deposit. Hydrothermal activity was characterized by intense enrichment in alteration zones of carbonates, sulfides, chlorite, white mica??biotite, albite and quartz, as described in other Archean lode-type gold ores. Two types of ore occur in the deposit: dark gray quartz veins and sulfide-rich gold orebodies. The sulfide-rich orebodies range from disseminated concentrations of sulfide minerals to massive sulfide bodies. The sulfide assemblage comprises (by volume), on average, 74% pyrrhotite, 17% arsenopyrite, 8% pyrite and 1% chalcopyrite. The orebodies have a long axis parallel to the local stretching lineation, with continuity down the plunge of fold axis for at least 4.8??km. The group of rocks hosting the Morro Velho gold mineralization is locally referred to as lapa seca. These were isoclinally folded and metamorphosed prior to gold mineralization. The lapa seca and the orebodies it hosts are distributed in five main tight folds related to F1 (the best examples are the X, Main and South orebodies, in level 25), which are disrupted by NE- to E-striking shear zones. Textural features indicate that the sulfide mineralization postdated regional peak metamorphism, and that the massive sulfide ore has subsequently been neither metamorphosed nor deformed. Lead isotope ratios indicate a model age of 2.82 ?? 0.05??Ga for both sulfide and gold mineralization. The lapa seca are interpreted as the results of a pre-gold alteration process and may be divided into carbonatic, micaceous and quartzose types. The carbonatic lapa seca is subdivided into gray and brown subtypes. Non-mineralized, gray carbonatic lapa seca forms the hanging wall to the orebodies, and is interpreted as the product of extreme CO2 metasomatism during hydrothermal alteration. This dolomitic lapa seca ranges in composition from relatively pure limestone and dolomite to silty limestone and dolomite. The brown carbonatic and micaceous lapa secas are the host rocks to gold. These units are interpreted to correspond to the sheared and hydrothermal products of metamorphosed volcaniclastic and/or volcanic rocks of varying composition from dacitic to andesitic, forming various types of schists and phyllites. The high-grade, massive sulfide orebodies occur at the base of the gray carbonatic lapa seca. Both disseminated mineralization and quartz veins are hosted by micaceous lapa seca. The data are consistent with a model of epigenetic mineralization for the lapa seca, from a hydrothermal fluid derived in part from the Archean basement or older crust material. ?? 2007 Elsevier B.V. All rights reserved.

Vial, D. S.; DeWitt, E.; Lobato, L. M.; Thorman, C. H.

2007-01-01

118

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

119

Progress and Observations of the Tjakastad Core- Barberton ICDP  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

120

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

NASA Astrophysics Data System (ADS)

Volcanic rocks of the Kushtagi Hungund greenstone belt from the Eastern Dharwar Craton (EDC) show extreme diversity due to the presence of high-Mg, high Fe-, high Mg Fe basalts, high Mg-dacites and andesites (boninitic affinities), and sodic plagioclase quartz rich felsic rocks (adakites with Na2O (˜4 6 wt.%). The adakites (Drummond and Defant, 1990; Martin, 1999) and high-Mg-dacites andesites are being reported for the first time from greenstone belts of the Dharwar craton. Trace elements in these different types of volcanic rocks have distinct characteristics. For example, the basalts have (1) Al2O3/TiO2 ˜16 (PM value of 17), (2) (La/Yb)N˜1 3, (3) low order negative anomalies of Nb/Nb*, Zr/Zr*, Hf/Hf* and Ti/Ti*, (4) Zr/Nb ˜4 10 and (5) Ce/Nb ˜3 4. Two samples of andesites having Mg-enrichment and Al2O3/TiO2 ratios of 31 35 are interpreted to have boninitic affinities. Other dacites and andesites are characterized by (1) high-Mg (8 10 wt.%), (2) high Al2O3/TiO2=22 27, (3) Zr/Nb=8 14, (4) (La/Yb)N ˜2 7, (5) negative Nb/Nb*, Zr/Zr*, Hf/Hf* and Ti/Ti* anomalies and (6) Sc/Lu=67 172. The adakites are characterized by (1) a narrow range of SiO2 (67 70 wt.%), (2) enriched Na2O (4 6 wt.%) with very high Na2O/K2O (2.5 7.7), (3) Low Mg# (0.38 0.48), (4) high (La/Yb)N (13 31) with fractionated patterns, no Eu anomaly and (Gd/Yb)N=2 4, (5) very high Al2O3/TiO2 (50 80) and (6) enriched Ni, Cr and Co (total 50 ppm). These adakites resemble 3.0 Ga tonalite trondhjemite gneisses of the Dharwar craton, which are interpreted as products of partial melting of the basaltic slab. The available data suggests that partial melting of the different mantle and slab sources generated this collage of compositionally different rocks within an island arc setting.

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

2006-06-01

121

Strain in Archean Granite-Greenstone terrains  

NASA Astrophysics Data System (ADS)

A long-standing problem in Archean tectonics is the mode of origin of granite-greenstone belts. Based on structural and morphological similarities to salt domes and Rayleigh-Taylor structures, diapirism has long been an obvious but controversial candidate, as it implies the operation of vertical tectonics in the Archean. Current strain patterns are one of the few field observables available to test hypotheses about the kinematic history of granite-greenstone belts. Previous laboratory (Dixon & Summers, 1983) and numerical (Mareschal & West, 1980) experiments which have been used to predict strain in diapiric structures may not be realistic because of the lack of large thermally activated viscosity contrasts in these models. We have numerically modeled temperature-dependent, non-Newtonian visco-elastic solid-state diapirism under conditions appropriate to Archean crust (Robin & Bailey, 2009). Here we present analyses of strain derived from these models. Our results show important differences from those of previous modelers. These include the formation of narrow high strain zones in the greenstone at the batholith contact and in the axis of the keel, with a low-strain zone between the two, as well as only very small strains in the batholith itself. This suggests that strain recorded in the granitic domes of granite-greenstone terrains must be unrelated to the diapiric overturn mechanism. Our strain analyses should be useful for comparison with published and future field observations, and provide a basis for the interpretation of strain in these ubiquitous Archean structures. Principle strain directions for an evolved diapir resulting from an altered basaltic crust deposited over a granitic basement. Viscosities are temperature- and stress-dependent and viscoelastic.

Robin, C. M.; Bailey, R. C.

2009-12-01

122

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

NASA Astrophysics Data System (ADS)

We report trace element, samarium (Sm) neodymium (Nd) and lead (Pb) isotopic data for individual micro-and mesobands of the Earth's oldest Banded Iron Formation (BIF) from the ˜ 3.7 3.8 Ga Isua Greenstone Belt (IGB, West Greenland) in an attempt to contribute to the characterization of the depositional environment and to the understanding of depositional mechanisms of these earliest chemical sediments. Rare earth element (REE)-yttrium (Y) patterns of the individual mesobands show features of modern seawater with diagnostic cerium (Ce/Ce*), presodymium (Pr/Pr*) and Y/holmium (Ho) anomalies. Very low high field strength elements (HFSE) concentrations indicate essentially detritus-free precipitation. Uranogenic Pb isotope data define a correlation line with a slope of 3691 ± 41 Ma, indicating that the uranium (U) lead (Pb) system remained closed after the formation of this BIF. High 207Pb/204Pb relative to 206Pb/204Pb ratios compared to average mantle growth evolution models are a feature shared by BIF, penecontemporaneous basalts and clastic volcanogenic metasediments and are indicative of the ultimate high-? (238U/204Pb) character of the source region, an essentially mafic Hadean protocrust. Sm Nd isotopic relations on a layer-by-layer basis point to two REE sources controlling the back-arc basin depositional environment of the BIF, one being seafloor-vented hydrothermal fluids (?Nd (3.7 Ga) ˜ + 3.1), the other being ambient surface seawater which reached its composition by erosion of parts of the protocrustal landmass (?Nd(3.7 Ga) ˜ + 1.6). The validity of two different and periodically interacting water masses (an essentially two-component mixing system) in the deposition of alternating iron- and silica-rich layers is also reflected by systematic trends in germanium (Ge)/silicon (Si) ratios. These suggest that significant amounts of silica were derived from unexposed and/or destroyed mafic Hadean landmass, unlike iron which probably originated from oceanic crust following hydrothermal alteration by deep percolating seawater. Ge/Si distributional patterns in the early Archean Isua BIF are similar to those reported from the Paleoproterozoic Hamersley (Western Australia) BIF, but overall Ge concentrations are about one order of magnitude higher in the Archean BIF. This seems consistent with other lines of evidence that the ambient Archean seawater was enriched with iron relative to Proterozoic and recent seawater.

Frei, Robert; Polat, Ali

2007-01-01

123

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

124

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

NASA Astrophysics Data System (ADS)

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

Glikson, Andrew; Vickers, John

2006-01-01

125

Metamorphic fluid flow in the northeastern part of the 3.8 3.7 Ga Isua Greenstone Belt (SW Greenland): A re-evalution of fluid inclusion evidence for early Archean seafloor-hydrothermal systems  

NASA Astrophysics Data System (ADS)

Fluid inclusions in quartz globules and quartz veins of a 3.8-3.7 Ga old, well-preserved pillow lava breccia in the northeastern Isua Greenstone Belt (IGB) were studied using microthermometry, Raman spectrometry and SEM Cathodoluminescence Imaging. Petrographic study of the different quartz segregations showed that they were affected by variable recrystallization which controlled their fluid inclusion content. The oldest unaltered fluid inclusions found are present in vein crystals that survived dynamic and static recrystallization. These crystals contain a cogenetic, immiscible assemblage of CO 2-rich (+H 2O, +graphite) and brine-rich (+CO 2, +halite, +carbonate) inclusions. The gas-rich inclusions have molar volumes between 44.8 and 47.5 cm 3/mol, while the brine inclusions have a salinity of ˜33 eq. wt% NaCl. Modeling equilibrium immiscibility using volumetric and compositional properties of the endmember fluids indicates that fluid unmixing occurred at or near peak-metamorphic conditions of ˜460 °C and ˜4 kbar. Carbonate and graphite were precipitated cogenetically from the physically separated endmember fluids and were trapped in fluid inclusions. In most quartz crystals, however, recrystallization obliterated such early fluid inclusion assemblages and left graphite and carbonate as solid inclusions in recrystallized grains. Intragranular fluid inclusion trails in the recrystallized grains of breccia cementing and crosscutting quartz veins have CO 2-rich assemblages, with distinctly different molar volumes (either between 43.7 and 47.5 cm 3/mol or between 53.5 and 74.1 cm 3/mol), and immiscible, halite-saturated H 2O-CO 2-NaCl(-other salt) inclusions. Later intergranular trails have CH 4-H 2 ( X up to ˜0.3) inclusions of variable density (ranging from 48.0 to >105.3 cm 3/mol) and metastable H 2O-NaCl(-other salt?) brines (˜28 eq. wt% NaCl). Finally, the youngest fluid inclusion assemblages are found in non-luminescent secondary quartz and contain low-density CH 4 (molar volume > 105.33 cm 3/mol) and low-salinity H 2O-NaCl (0.2-3.7 eq. wt% NaCl). These successive fluid inclusion assemblages record a retrograde P-T evolution close to a geothermal gradient of ˜30 °C/km, but also indicate fluid pressure variations and the introduction of highly reducing fluids at ˜200-300 °C and 0.5-2 kbar. The quartz globules in the pillow fragments only contain sporadic CH 4(+H 2) and brine inclusions, corresponding with the late generations present in the cementing and crosscutting veins. We argue that due to the large extent of static recrystallization in quartz globules in the pillow breccia fragments, only these relatively late fluid inclusions have been preserved, and that they do not represent remnants of an early, seafloor-hydrothermal system as was previously proposed. Modeling the oxidation state of the fluids indicates a rock buffered system at peak-metamorphic conditions, but suggests a change towards fluid-graphite disequilibrium and a logf/fO above the Quartz-Fayalite-Magnetite buffer during retrograde evolution. Most likely, this indicates a control on redox conditions and on fluid speciation by ultramafic rocks in the IGB. Finally, this study shows that microscopic solid graphite in recrystallized metamorphic rocks from Isua can be deposited inorganically from a fluid phase, adding to the complexity of processes that formed reduced carbon in the oldest, well-preserved supracrustal rocks on Earth.

Heijlen, Wouter; Appel, Peter W. U.; Frezzotti, Maria-Luce; Horsewell, Andy; Touret, Jacques L. R.

2006-06-01

126

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

Microsoft Academic Search

The ?2.6Ga Hutti greenstone belt is one of several Neoarchean greenstone terranes of the eastern Dharwar Craton. There are prevalent mafic volcanic flows with subordinate felsic volcanic units and siliciclastic sedimentary rocks. All lithologies show variable intensities of submarine hydrothermal alteration, polyphase deformation and greenschist to amphibolite grade metamorphism, yet pillow, cumulus, and other primary volcanic features are locally preserved.

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

2009-01-01

127

Nd and Hf isotopic analysis of Barberton komatiites  

NASA Astrophysics Data System (ADS)

In order to constrain the origin of komatiites from the Barberton Belt, particularly the nature of their mantle source and the conditions of partial melting, we analyzed the Nd and Hf isotopic compositions of 33 komatiite samples. Of these 15 were from the ca. 3.5 Ga Komati Formation, 3 were from the 3.47 Ga Hooggenoeg Fm and 15 from the 3.3 Ga Weltevreden Fm. The samples were collected from outcrop and represent the three main types of komatiite found in the Barberton Belt: i.e. Al-depleted, Al-undepleted and Al-enriched. The analyses were carried out at ENS Lyon using the procedure described by Blichert-Toft et al. For each sample suite we obtained a relatively large range of calculated initial isotopic values. In each suite, one or more samples gave an unreasonably high or low value, particularly for the Hf isotopic system. Excluding these outliers, the values are as follows: Komati Fm, epsilon Nd = -0.8 to +2.5, epsilon Hf = +1 to +8; Hooggenoeg Fm, epsilon Nd = -0.1 to +0.2, epsilon Hf = +1 to +2; Weltevreden Fm, epsilon Nd = 0.3 to +2.0, epsilon Hf = +4 to +13. There were no systematic differences between the isotopic compositions of the three different types of komatiite. Within the relatively large variability of the data, the epsilon Hf values tend to become more positive with age while the epsilon Nd values remain essentially constant. These results are broadly in line with those obtained in most of the previous studies of Barberton komatiites. Notably: 1) there is a wide range in initial isotopic compositions that is not compatible with normal magmatic processes. At least part of the range can be attributed to disturbance, particularly of the Lu-Hf system, after eruption of the lavas; 2) notwithstanding this uncertainty, both the Nd and Hf isotopic compositions are slightly radiogenic, indicating formation from a moderately depleted mantle source. To obtain more reliable data, we intend a) to analyse carefully chosen and prepared samples from core recovered during the ICDP drilling project; 2) analyse magmatic pyroxene separated from selected samples.

Robin, Christophe; Blichert-Toft, Janne; Arndt, Nicholas; Wilson, Allan; Byerly, Gary

2013-04-01

128

Archean Sedimentation and Tectonics in Southern Africa.  

National Technical Information Service (NTIS)

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 ass...

W. S. F. Kidd

1984-01-01

129

Stromatolites at ~3,500 Myr and a greenstone-granite unconformity in the Zimbabwean Archaean  

NASA Astrophysics Data System (ADS)

Two controversial areas of geological endeavour are the establishment of the antiquity of life and the tectonic setting of greenstone sequences. We record here the recent discoveries in the Fort Victoria greenstone belt of stromatolites in limestones assigned to ~3,500 Myr (minimum age) Sebakwian Group rocks of the Rhodesian Archaean Craton within Zimbabwe, and a nearby outcrop of a thin sedimentary formation, basal to a thick ~2,700 Myr volcanic pile, resting with definite unconformity on ~3,500 Myr Mushandike Granite.

Orpen, J. L.; Wilson, J. F.

1981-05-01

130

Archean granite-greenstone tectonics at Kolar (South India): Interplay of diapirism and bulk inhomogeneous contraction during juvenile magmatic accretion  

NASA Astrophysics Data System (ADS)

The structural study of the Kolar greenstone belt and surrounding granite-gneiss terrains combined with U-Pb dating reveals that the middle and lower crustal tectonoplutonic pattern of the eastern Dharwar craton developed during a major magmatic accretion event between 2550 and 2530 Ma. The granite-greenstone pattern resulted from the interference of gravity-driven sagging of the greenstones (i.e., diapirism), E-W bulk inhomogeneous shortening combined with horizontal N-S stretching, and syntectonic juvenile pluton emplacement. Bulk inhomogeneous contraction is accommodated by the synchronous development of a pervasive, N-S trending vertical foliation, shallow stretching lineation, and conjugate strike-slip shear zone pattern within and outside the greenstone belt, resulting in regional horizontal pure shear deformation. The plutons around the greenstone belt record regional contraction by developing one set of strike-slip C-S fabrics of the shear zone pattern. The development of the granite-greenstone pattern was coeval and compatible with deformation during juvenile magmatic accretion, melting, and granulite metamorphism in the lower crust. The Kolar example points to a specific crustal rheology that allowed sagduction of the greenstones and regional distributed bulk inhomogeneous strain, due to mechanical homogeneity and low viscosity provided by large-scale melting during the accretion event. This example further suggests specific boundary conditions to the craton that allowed E-W inhomogeneous shortening to be accommodated by N-S stretching and spreading of the crust without significant tectonic thickening. Such tectonoplutonic pattern is specific to the Archean and may develop as a consequence of mantle plume activity in intracontinental settings.

Chardon, Dominique; Peucat, Jean-Jacques; Jayananda, Mudlappa; Choukroune, Pierre; Fanning, C. Mark

2002-06-01

131

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

Microsoft Academic Search

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

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

1993-01-01

132

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

133

Gold mineralisation and alteration of Penakacherla schist belt, India, constraints on Archaean subduction and fluid processes  

Microsoft Academic Search

In the Dharwar Craton, southern India, gold deposits are found mostly along the six arcuate shear zones passing through late Archaean greenstone belts (2.7 Ga). One such shear zone complex extends for about 400 km within and along the Ramagiri–Hungund schist belt. The Penakacherla sector of this shear zone is excellently exposed, enabling a detailed investigation of synorogenic gold mineralisation

C. Manikyamba; S. M. Naqvi; M. Ram Mohan; T. Gnaneshwar Rao

2004-01-01

134

A Bridge between Greenstone and DSpace  

Microsoft Academic Search

Greenstone and DSpace are widely used software systems for digital libraries, and prospective users sometimes wonder which one to adopt. In fact, the aims of the two are very different, although their domains of application do overlap. This article describes the two systems and identifies their similarities and differences. We also present StoneD (note 1) a bridge between the production

Ian H. Witten; David Bainbridge; Robert Tansley; Chi-Yu Huang; Katherine J. Don

135

Greenstone: a comprehensive open-source digital library software system  

Microsoft Academic Search

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

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

2000-01-01

136

Greenstone: A Comprehensive Open-Source Digital Library Software System  

Microsoft Academic Search

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

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

1999-01-01

137

Structural analysis of the southern Ashanti Belt, Ghana, using airborne geophysical data  

Microsoft Academic Search

The southern Ashanti Greenstone Belt, in Ghana, is an area of major economic importance for West Africa, where many companies are actively exploring for gold. As a consequence, a significant geological data set has been collected over the years, but it has not always been subjected to an integrated interpretation, especially away from the main Ashanti fault system and the

Stéphane Perrouty; Mark Jessell; Lenka Baratoux; Laurent Aillères; Yan Bourassa

2010-01-01

138

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

Abstract—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; T H. M EISEL; F. N ÄGLER

2005-01-01

139

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

140

Preliminary Survey Report: Control Technology for the Ceramics Industry at Ohio Brass Company, Barberton, Ohio.  

National Technical Information Service (NTIS)

Health hazard control methods, work processes, and existing control technologies were evaluated at Ohio Brass Company (SIC-3264), Barberton, Ohio, in September, 1982. The company employed 550 workers involved in the production of ceramic electrical insula...

F. W. Godbey

1983-01-01

141

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

142

Tropical Belt  

NSDL National Science Digital Library

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

Sciences, California A.

2008-01-01

143

Radiation Belts  

NSDL National Science Digital Library

This article provides an outline of the motion of charged particles in the Earth's magnetic fields, and the Van Allen and outer radiation belts. It summarizes their discovery, their properties and their physics, as well as providing links to background materials and additional information. This is part of a large web site on the Exploration of the Earth's Magnetosphere. A Spanish translation is available.

Stern, David

2005-09-19

144

The oldest impact deposits on earth --- First confirmation of an extraterrestrial component  

Microsoft Academic Search

The chromium isotopic compositions of samples from an early Archean (3.22 Ga) spherule bed (S4) from the Barberton Greenstone Belt, South Africa, are distinct from that in background rocks and other terrestrial samples. This positively confirms the presence of an extraterrestrial component in this bed and supports hypotheses of an impact origin. The source of the extraterrestrial Cr is most

Alexander Shukolyukov; Frank T. Kyte; Günter W. Lugmair; Donald R. Lowe; Gary R. Byerly

2000-01-01

145

Preliminary survey report: control technology for the ceramics industry at Ohio Brass Company, Barberton, Ohio  

Microsoft Academic Search

Health-hazard control methods, work processes, and existing control technologies were evaluated at Ohio Brass Company, Barberton, Ohio, in September, 1982. The company employed 550 workers involved in the production of ceramic electrical insulations from feldspar, kaolin, alumina, locally mined flint, and ball clays. Production-sized raw materials were formed into a batch mixture, combined with water, mixed, and filtered through a

Godbey

1983-01-01

146

Stability and Tightness of the Columbus Limestone and Surrounding Rocks in the Vicinity of Barberton, Ohio.  

National Technical Information Service (NTIS)

A study was conducted which was prompted by the fact that the deep limestone mine operated by the Columbia Chemical Division of the Pittsburgh Plate Glass Company in Barberton, Ohio is somewhat unique in being a dry mine. The mine is also unique from the ...

D. W. Byerly

1975-01-01

147

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

148

Tectono-stratigraphy of late Archaean greenstone terranes in the southern Eastern Goldfields, Western Australia  

Microsoft Academic Search

Late Archaean greenstone terranes in the southern part of the Eastern Goldfields are regionally extensive, faultbounded entities defined on the basis of small but distinct differences in stratigraphy and structure. The greenstones comprise volcano-sedimentary successions that were all deposited at the same time (c. 2720-2675 Ma) on sialic crust. Hence, the terranes are interpreted to represent contemporaneous, probably adjacent, basins.

C. P. Swager

1997-01-01

149

Conveyor belt plow for ideal belt cleaning  

SciTech Connect

The accumulation of excess material around the return drum of a conveyor arises from an inefficient belt plow. The frequency with which this problem occurs would indicate a design problem rather than faulty installation or negligent maintenance. The reasons for the poor operation of the plow become obvious after applying basic physical principles. Simple and cheap improvements can be implemented to improve plow performance. To be effective, a plow should be installed either near the tail end, to protect the return drum, or ahead of the automatic belt tensioning device, to prevent spillage from falling onto the take-up pulley. In order to perform well, the scraping blade of the plow must be in continuous contact with the belt across its full width, having contact pressure as uniform as possible. It has been proven, though, that uniform contact pressure cannot be achieved under operating conditions with the standard arrangement shown in Figure 1. There are two solutions to this problem which can be carried out in most mine workshops and help reduce belt downtime. All too often an ineffective plow allows material to be needlessly trapped against the belt, causing excessive wear and, ultimately, tearing the belt. Even with highly experienced belt crews, a short stoppage in the main belt can have serious effects throughout the mine. An efficient plow means a cleaner running belt.

Michaelsen, W.J.

1982-05-01

150

Main Belt Comets  

Microsoft Academic Search

We have identified objects which are physically comets but which occupy orbits within the main belt of asteroids No dynamical routes from the Kuiper belt or Oort Cloud cometary reservoirs have been identified Therefore we conclude that these are true comets formed in-place and constituting a new type of comet from a previously unobserved reservoir The main belt comets MBCs

D. Jewitt; H. Hsieh

2006-01-01

151

Exploring Main Belt Asteroids  

Microsoft Academic Search

Terrestrial planet formation in the main asteroid belt was interrupted when growing protoplanets became sufficiently massive to gravitationally perturb the local population, causing bodies to collide with increased energy, thus ending accretion and commencing fragmentation and disruption. Few of these protoplanets are thought to have survived unshattered (e.g., Ceres, Vesta, Pallas), leaving a main belt population dominated by fragments of

M. V. Sykes; S. M. Larson; R. Whiteley; U. Fink; R. Jedicke; J. Emery; R. Fevig; M. Kelley; A. W. Harris; S. Ostro; K. Reed; R. P. Binzel; A. Rivkin; C. Magri; W. Bottke; D. Durda; R. Walker; D. Davis; W. K. Hartmann; D. Sears; H. Yano; J. Granahan; A. Storrs; S. J. Bus; J. F. Bell; D. Tholen; A. Cellino

2001-01-01

152

Seat belt aorta  

Microsoft Academic Search

This review of 11 cases of seat-belt associated blunt abdominal aortic trauma, includes nine cases reported in the literature and two new cases. Lap-type seat belts were the cause of this injury in eight of the 11 patients (73%). Clinical presentation was acute in 73% of the cases, with symptoms of acute arterial insufficiency, or an acute abdomen or neurologic

P. S. Mohinder; Randhawa; James O. Menzoian

1990-01-01

153

To Belt or Not To Belt?  

ERIC Educational Resources Information Center

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

Vail, Kathleen

1999-01-01

154

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

155

In-situ dating of the Earth's oldest trace fossil at 3.34 Ga  

Microsoft Academic Search

Microbial activity in volcanic glass within the oceanic crust can produce micron sized pits and tunnels. Such biogenic textures have been described from the recent oceanic crust and mineralized equivalents in pillow lavas as old as 3.47–3.45Ga from the Barberton Greenstone Belt (BGB) of South Africa. In meta-volcanic glasses these microbial traces are preserved by titanite mineralization (CaTiSiO5) and on

D. Fliegel; J. Kosler; N. McLoughlin; A. Simonetti; M. J. de Wit; R. Wirth; H. Furnes

2010-01-01

156

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

Microsoft Academic Search

Hafnium isotopic compositions were measured in Al-depleted and Al-enriched komatiites from the 3450-Ma-old Barberton greenstone belt, southern Afric. All samples have initial epsilon (Hf) values close to zero. Such values are at variance with the strongly negative or positive values that should be observed if these rocks came from old garnet-depleted or garnet-enriched layers, such as may have formed during

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

1990-01-01

157

Belt conveyor apparatus  

DOEpatents

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

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

1987-01-01

158

Preliminary report on the geology and gold mineralization of the South Pass granite-greenstone terrain, Wind River Mountains, western Wyoming (US)  

NASA Astrophysics Data System (ADS)

The South Pass granite-greenstone terrain lies near the southern tip of the Wind River Mountains of western Wyoming. This Archean supracrustal pile has been Wyoming's most prolific source of gold and iron ore. From 1962 to 1983, more than 90 million tons of iron ore were recovered from oxide-facies banded iron formation, and an estimated 325,000 ounces of gold were mined from metagreywacke-hosted shears and associated placers. Precambrian rocks at South Pass are unconformably overlain by Paleozoic sediments along the northeast flank, and a Tertiary pediment buries Archean supracrustals on the west and south. To the northwest, the supracrustals terminate against granodiorite of the Louis Lake batholith; to the east, the supracrustals terminate against granite of the Granite Mountains batholith. The Louis Lake granodiorite is approximately 2,630 + or - 20 m.y. old, and the Granite Mountains granite averages 2,600 m.y. old. The geometry of the greenstone belt is best expressed as a synform that has been modified by complex faulting and folding. Metamorphism is amphibolite grade surrounding a small island of greenschist facies rocks. The younger of the Archean supracrustal successions is the Miners Delight Formation. This unit yielded a Rb-Sr isochron of 2,800 m.y. A sample of galena from the Snowbird Mine within the Miners Delight Formation yielded a model age averaging 2,750 m.y. The Snowbird mineralization appears to be syngenetic and is hosted by metavolcanics of calc-alkaline affinity. Discussion follows.

Hausel, W. D.

159

A three-component Sr-Nd isotopic mixing model for granitoid genesis, Lachlan fold belt, eastern Australia  

NASA Astrophysics Data System (ADS)

Previous Sr-Nd isotopic models of two-component crust-mantle mixing (based on an apparently simple hyperbolic ?Nd-Sri array) have failed to account for all the geochemical and isotopic features of granitoids from the Lachlan fold belt, eastern Australia. Here we show that a three-component mixture of mantle-derived magma and two contrasting crustal components successfully explains the isotopic compositions of the granitoids. New isotopic data from the Moruya granitoids of the fold belt reveal that a separate isotopic trend exists at the most primitive end of the ?Nd-Sri array, defined by a depleted mantle component (?Nd = +8.0; Sri = 0.7032) and a mafic crustal component (?Nd = +2.7; Sri = 0.7049). This crustal component has isotopic characteristics similar to Cambrian greenstones within the fold belt, and appears to be widespread in the lower crust. After also considering data from the ubiquitous Ordovician turbidites which host the granitoids (?Nd = -9.61 to -10.64; Sri = 0.7204 to 0.7273), three-component isotopic mixing curves are constructed that enclose all the granitoids of the fold belt, indicating that contributions from the Ordovician turbidites, Cambrian greenstones, and a depleted mantle component could produce the isotopic characteristics of the granitoids. Important implications of the model are that (1) S- and I-type granites appear to be mixtures of, rather than unique products from, contrasting sources and so Lachlan granitoids do not directly “image” their source-rock compositions; (2) the chemical variation lines defining granitoid suites are neither mixing lines nor lines reflecting restite separation; (3) previously inferred Precambrian continental basement beneath the fold belt is unnecessary; and (4) Lachlan granitoids may have formed in an environment related to subduction, where arc magmatism promoted crustal fusion and crust-mantle mixing.

Keay, Sue; Collins, W. J.; McCulloch, M. T.

1997-04-01

160

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.

161

Moving belt radiator development status  

SciTech Connect

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.A.

1988-07-01

162

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

NASA Astrophysics Data System (ADS)

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 from 2.95 to 2.2 Ga. Moderately oxidizing conditions are required to mobilize Re and Mo in the environment, Mo fractionation only occurs in solution, and these parameters thus have potential use as paleoredox proxies for the early Earth. PGE + Re abundance patterns of Barberton Greenstone Belt sediments are uniform and very similar in shape to those of komatiites. This indicates (1) that the PGE came from a source of predominantly ultramafic composition and, (2) that PGE were transported and deposited essentially in particulate form. Sediments from the younger Belingwe Greenstone Belt show more fractionated PGE + Re patterns and have Re/Os ratios 10 to 100× higher than those of Barberton sediments. Their PGE abundance patterns and Re/Os ratios are intermediate between those of the mid-Archean shales and Neoproterozoic to Recent black shales. They reflect scavenging of Re from solution in the sedimentary environment. ?98/95Mo values of black shales of all ages correlate with their concentrations. The Barberton Greenstone Belt samples have ˜1 3 ppm Mo, similar to a granitoid-basaltic source. This Mo has ?98/95Mo between -1.9 and -2.4‰ relative to present day mean ocean water molybdenum, MOMO and is thus not isotopically fractionated relative to such a source. Similar to the PGE this indicates transport in solid form. Sediments from the Belingwe Greenstone Belt show in part enhanced Mo concentrations (up to 6 ppm) and Mo isotope fractionation (?98/95Mo up to -1.4‰ relative to MOMO). The combined PGE + Re and Mo data show mainly reducing conditions in the mid-Archean and suggest that by 2.7 Ga, the atmosphere and oceans had become more oxidizing. Substantially younger samples from the Transvaal Supergroup (to ca. 2.2 Ga) surprisingly have mainly low Mo concentrations (around 1 ppm) and show no significant Mo isotope fractionation relative to the continental source. Among possible explanations for this are a return to reducing atmospheric conditions after 2.7 Ga, reservoir effects, or Mo removal by sulfide precipitation following sulfate reduction in early Proterozoic oceans.

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

2005-04-01

163

3-D visualization of structural field data: examples from the Archean Caopatina Formation, Abitibi greenstone belt, Québec, Canada  

Microsoft Academic Search

A series of 3-D visualization approaches is presented with the aim of developing better interpretation tools for field-based geologists. Structural data from outcrop, mine and regional scales are used to create speculative 3-D surfaces that can be useful in addressing geological problems. These tools could help in resolving cryptic early fold geometries, extending stratiform mineralizations and the sub-surface interpretation of

Eric A de Kemp

2000-01-01

164

The geochemistry of repetitive cyclical volcanism from basalt through rhyolite in the uchi-confederation greenstone belt, canada  

NASA Astrophysics Data System (ADS)

Archean volcanic rocks in the Confederation Lake area, northwestern Ontario, Canada, are in three mafic to felsic cycles collectively 8,500 to 11,240 m thick. Each cycle begins with pillowed basalt and andesite flows and is capped with andesitic to rhyolitic pyroclastic rocks and minor flows. Seventy five samples from this succession were analyzed for major and trace elements including the rare earth elements. In two cycles, tholeiitic basalts are overlain by calcalkaline andesite to rhyolite. In the third, cycle, the tholeiitic basalts are overlain by tholeiitic rhyolites. Fe enrichment in basalts is accompanied by depletion of Ca, Al, Cr, Ni, and Sr, and enrichment in Ti, P, the rare earth elements, Nb, Zr, and Y. This is interpreted as open system fractionation of olivine, plagioclase, and clinopyroxene. Si enrichment in dacites and rhyolites is attributed to fractional crystallization of plagioclase, K-feldspar, and biotite. Tholeiitic basalt liquids are believed to be mantle-derived. Intercalated andesites with fractionated rare earth patterns appear to be products of mixing of tholeiitic basalt and rhyolite liquids and, andesites with flat rare earth patterns are probably produced by melting of previously depleted mantle. Felsic magmas are partial melts of tholeiitic basalt or products of liquid immiscibility in a tholeiitic system perhaps involving extreme fractionation in a high level magma chamber, and assimilation of sialic crust. It is concluded that Archean cyclical volcanism in this area involves the interplay of several magmatic liquids in processes of fractional crystallization, magma mixing, liquid immiscibility, and the probable existence of compositionally zoned magma chambers in the late stages of each cycle. The compositionally zoned chambers existed over the time period represented by the upper felsic portion of each cycle.

Thurston, P. C.; Fryer, B. J.

1983-09-01

165

Kuiper Belt & Oort Cloud  

NSDL National Science Digital Library

This NASA website provides information about the group of short-period comets in the Kuiper Belt. The article compares the sizes and composition of these objects to Earth and Pluto. Telescopic images and artists' conceptions illustrate the site. There is a link to a kid's page that has information over the same subject but more appropriate for children.

2007-07-03

166

Evolution of the Archaean granite-greenstone terranes of the Eastern Goldfields, Western Australia: SHRIMP U?Pb zircon constraints  

Microsoft Academic Search

Thirty-five high-precision SHRIMP U?Pb zircon dates (with an average 95% confidence error of ±6 Ma) have been obtained from the granite-greenstone terranes in the southern part of the Eastern Goldfields of Western Australia. These dates establish the timing of major deformation, metamorphism and granite intrusion events, and test inferred stratigraphic relationships within the greenstones. These new data reveal that felsic

D. R. Nelson

1997-01-01

167

Preliminary survey report: control technology for the ceramics industry at Ohio Brass Company, Barberton, Ohio  

SciTech Connect

Health-hazard control methods, work processes, and existing control technologies were evaluated at Ohio Brass Company, Barberton, Ohio, in September, 1982. The company employed 550 workers involved in the production of ceramic electrical insulations from feldspar, kaolin, alumina, locally mined flint, and ball clays. Production-sized raw materials were formed into a batch mixture, combined with water, mixed, and filtered through a 120 mesh screen to form slip. The slip was dehydrated into clay press cakes which were charged into a pug mill. The material was extruded and cut into appropriate lengths, then shredded and blended, and automatically cut into blanks. The blanks were formed and trimmed into a fully formed insulator body. After drying, the body was glazed, formed with portland cement, fired, inspected, and cured. The insulators were automatically cleaned and tested, then packed and shipped to the consumer. Monthly inspections of the work areas were conducted along with periodic environmental sampling. Workers were provided with safety glasses, hearing protectors, respirators, and safety shoes. Local exhaust ventilation was used throughout the facility. The author does not recommend an in-depth study of the company since there is no raw material.

Godbey, F.W.

1983-01-01

168

Orogenic belts on Venus  

NASA Astrophysics Data System (ADS)

Recent radar observations of Venus show evidence for three types of deformational features in the linear mountain belts of Ishtar Terra: linear ridges and troughs oriented parallel to the strike of the mountains and interpreted to be anticlines and synclines; broad low arches similar to mare-ridge-type features seen on the Moon and interpreted to represent low-angle thrusting and buckling; and linear discontinuities that cut across the strike of the ridges and troughs and are interpreted to represent strike-slip movement. On the basis of the localized concentration of these features, their orientations and patterns of distribution, and their association with linear mountainous topography, we conclude that they mark the location of concentrated horizontal compressional deformation and that Akna and Freyja Montes represent erogenic belts on Venus.

Crumpler, L. S.; Head, James W.; Campbell, Donald B.

1986-12-01

169

Infrared Kuiper Belt Constraints  

SciTech Connect

We compute the temperature and IR signal of particles of radius {ital a} and albedo {alpha} at heliocentric distance {ital R}, taking into account the emissivity effect, and give an interpolating formula for the result. We compare with analyses of {ital COBE} DIRBE data by others (including recent detection of the cosmic IR background) for various values of heliocentric distance {ital R}, particle radius {ital a}, and particle albedo {alpha}. 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 (40{lt}R{lt}50{endash}90 AU) and a more distant sector with a higher density. We consider the case in which passage through a molecular cloud essentially cleans the solar system of dust. We apply a simple model of dust production by comet collisions and removal by the Poynting-Robertson effect to find limits on total and dust masses in the near and far sectors as a function of time since such a passage. Finally, we compare Kuiper belt IR spectra for various parameter values. Results of this work include: (1) numerical limits on Kuiper belt dust as a function of ({ital R}, {ital a}, {alpha}) 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. {copyright} {ital {copyright} 1999.} {ital The American Astronomical Society}

Teplitz, V.L. [Physics Department, Southern Methodist University, Dallas, TX 75275 (United States); Stern, S.A. [Southwest Research Institute, Boulder, CO 80302 (United States); Anderson, J.D. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Rosenbaum, D.; Scalise, R.J.; Wentzler, P. [Physics Department, Southern Methodist University, Dallas, TX 75275 (United States)

1999-05-01

170

49 CFR 393.93 - Seats, seat belt assemblies, and seat belt assembly anchorages.  

Code of Federal Regulations, 2011 CFR

...2011-10-01 2011-10-01 false Seats, seat belt assemblies, and seat belt assembly anchorages. 393.93 Section 393...Miscellaneous Parts and Accessories § 393.93 Seats, seat belt assemblies, and seat belt assembly...

2011-10-01

171

49 CFR 393.93 - Seats, seat belt assemblies, and seat belt assembly anchorages.  

Code of Federal Regulations, 2012 CFR

...2012-10-01 2012-10-01 false Seats, seat belt assemblies, and seat belt assembly anchorages. 393.93 Section 393...Miscellaneous Parts and Accessories § 393.93 Seats, seat belt assemblies, and seat belt assembly...

2012-10-01

172

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

173

Physics and Automobile Safety Belts.  

ERIC Educational Resources Information Center

|This collection of problems and experiments related to automobile safety belt usage is intended to serve as a supplement to a standard physics course. Its purpose is to convince the students that the use of safety belts to prevent injury or death is firmly supported by the considerations of physical quantities and laws which apply in a collision…

Kortman, Peter; Witt, C. Edwin

174

Previously Undetected Radiation Belt Revealed  

NASA Video Gallery

Since their discovery over 50 years ago, the Earth’s Van Allen radiation belts have been considered to consist of two distinct zones of trapped, highly energetic charged particles. Observations from NASA’s Van Allen Probes reveal an isolated third ring in the outer radiation belt.

gsfcvideo

2013-02-27

175

The Radiation Belt Storm Probes  

NASA Video Gallery

The Radiation Belt Storm Probe mission (RBSP) will explore the Van Allen Radiation Belts in the Earth's magnetosphere. The charge particles in these regions can be hazardous to both spacecraft and astronauts. The mission will explore space weather -- changes in Earth's space environment caused by the sun -- which can affect our technology.

gsfcvideo

2012-08-09

176

Teaching Science: Seat Belt Science.  

ERIC Educational Resources Information Center

Describes activities that will help students understand how car seat belts work, the limited reaction time available to passengers in an automobile accident, and the force of impact in a car collision. These activities will provide students with hands-on experiences that demonstrate the importance of always wearing seat belts while in an…

Leyden, Michael B.

1994-01-01

177

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

178

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

179

Seat Belt Use and Stress in Adolescents.  

ERIC Educational Resources Information Center

Explored adolescent seat belt use and psychosocial risk factors in urban minority population (n=541). Found seat belt use reported by 49 percent of respondents. Those reporting no or intermittent seat belt use were significantly more likely than seat belt users to feel down, have decreased home support, have problems with school and the law, and…

Schichor, Aric; And Others

1990-01-01

180

Calculating Belt Velocity and Horsepower  

NSDL National Science Digital Library

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

Bourassa, James; Rosz, John

2008-10-23

181

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

NASA Astrophysics Data System (ADS)

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

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

1992-08-01

182

The distant Kuiper Belt  

NASA Astrophysics Data System (ADS)

We present results from a series of deep imaging surveys designed to look for very faint objects in the outer solar system. We find roughly 10-20 percent of our detections outside a heliocentric distance of 48 AU, a much larger fraction than all previously published surveys. The implications of this result for the radial structure of the Kuiper Belt will be discussed, as well as how it interacts with various theories regarding the sculpting of the orbital distribution of the trans-Neptunian region. We find a luminosity function with a continuing steep slope down to the limit of our detections at about 26th magnitude, implying that observations are just on the threshold of reaching the level where the TNO size distribution is exptected to `roll over' to a shallower collisional slope. The size distribution in the observed region is expected to hold information about the time scale and physics of planetesimal building in the early outer Solar System. This work has been supported by a Henri Chretien international research grant (AAS), by NASA Origins grants NAG5-8198 and NAG5-9678, by an ACI Jeune award from the French Research Ministry, and an Observatoire de la Côte d'Azur BQR grant.

Gladman, B.; Kavelaars, J. J.; Petit, J. M.; Morbidelli, A.; Holman, M.; Loredo, T.

2000-10-01

183

1,700-Myr greenstone volcanic successions in southwestern North America and isotopic evolution of Proterozoic mantle  

Microsoft Academic Search

Nd and Sr isotopic data were collected from Rocky Mountain metavolcanic greenstone rock about 1700 Myr old traverse in order to determine the Nd and Sr isotopic composition of the mantle 1700 Myr ago and to assess the meaning of the isotopic data for the evolution of the upper mantle and for the petrogenesis of these and other rocks of

B. K. Nelson; D. J. Depaolo

1984-01-01

184

A mantle conveyor belt beneath the Tethyan collisional belt  

NASA Astrophysics Data System (ADS)

Collisional belts are generated by the arrival of continental lithosphere into a subduction zone, leading to stacking of crustal slices during indentation. The Tethyan suture from the Bitlis to the Himalayas is a prime example where the Arabian and Indian plates collided with Eurasia during the Cenozoic, generating the highest mountain belts on Earth (Argand, 1924). While the kinematics of this process are well established, its dynamics are more uncertain. India and Arabia intriguingly keep advancing in spite of large collisional resisting forces. We perform global mantle circulation computations to test the role of deep mantle flow as a driving force for the kinematics of the Tethyan collisional belt, evaluating different boundary conditions and mantle density distributions as inferred from seismic tomography or slab models. Our results show that mantle drag exerted on the base of the lithosphere by a large-scale upwelling is likely the main cause for the ongoing indentation of the Indian and Arabian plates into Eurasia.

Becker, T. W.; Faccenna, C.

2011-12-01

185

Proton Spectrometer Belt Research (PSBR)  

NASA Astrophysics Data System (ADS)

The National Reconnaissance Office (NRO), NASA, the Air Force Research Laboratory (AFRL), the Aerospace Corporation, the Los Alamos National Laboratory (LANL) and the Naval Research Laboratory (NRL) have jointly formed the Proton Spectrometer Belt Research (PSBR) program to meet two primary objectives: to measure the high-energy proton spectrum by placing the Relativistic Proton Spectrometer (RPS) instrument on board the Radiation Belt Storm Probes (RBSP) spacecraft to measure the inner Van Allen belt protons with energies from 50 MeV to 2 GeV, and to produce the next generation radiation belt models. Presently, the intensity of trapped protons with energies beyond about 150 MeV is not well known and thought to be underestimated in existing specification models. Such protons are known to pose a number of hazards to astronauts and spacecraft; including total ionizing dose, displacement damage, single event effects, and nuclear activation. The RPS addresses a priority highly ranked by the scientific and technical community and will extend the measurement capability of the RBSP mission to a range beyond that originally planned. The PSBR program will use the RPS data, coupled with other data sets, to upgrade existing radiation belt models, significantly improving the radiation hazards specified by increasing the spectral and spatial coverage, and the time-correlated probability of occurrence statistics, quantifying the model accuracy and uncertainty.

Byers, David

186

Proton Spectrometer Belt Research (PSBR)  

NASA Astrophysics Data System (ADS)

The National Reconnaissance Office (NRO), NASA, the Air Force Research Laboratory (AFRL), the Aerospace Corporation, the Los Alamos National Laboratory (LANL) and the Naval Research Laboratory (NRL) have jointly formed the Proton Spectrometer Belt Research (PSBR) program to meet two primary objectives: to measure the high-energy proton spectrum by placing the Relativistic Proton Spectrometer (RPS) instrument on board the Radiation Belt Storm Probes (RBSP) spacecraft to measure the inner Van Allen belt protons with energies from 50 MeV to 2 GeV, and to produce the next generation radiation belt models. Presently, the intensity of trapped protons with energies beyond about 150 MeV is not well known and thought to be underestimated in existing specification models. Such protons are known to pose a number of hazards to astronauts and spacecraft; including total ionizing dose, displacement damage, single event effects, and nuclear activation. The RPS addresses a priority highly ranked by the scientific and technical community and will extend the measurement capability of the RBSP mission to a range beyond that originally planned. The PSBR program will use the RPS data, coupled with other data sets, to upgrade existing radiation belt models, significantly improving the radiation hazards specified by increasing the spectral and spatial coverage, and the time-correlated probability of occurrence statistics, quantifying the model accuracy and uncertainty.

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

2008-12-01

187

Trends in PVC conveyor belting  

SciTech Connect

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

Hopwood, J.E.

1984-03-01

188

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

189

High speed abrasive belt grinding  

NASA Astrophysics Data System (ADS)

A project was established to reduce current stock removal costs and eliminate finish turning operations of tubes by combining rough stock removal and finish grinding. The first phase was designated for engineering and investigation into the feasibility and application of abrasive belt grinding technology. This information was then used to generate a specification establishing some criteria for design and manufacture of a machine to remove heavy stock and finish tubes using abrasive belt technology. The specification was subsequently used for the acquisition of a machine to perform the tasks. The second phase was designated for testing of the equipment and establishing production parameters.

Bak, Joseph

1989-01-01

190

Seat Belt Use in 2012 - Overall Results  

MedlinePLUS

... Belt Use by Major Characteristics Occupant Group1 2011 2012 2011 – 2012 Change Belt Use2 Confidence That Use Is High ... Sites, Vehicles, and Occupants* Observed Numbers of 2011 2012 Percentage Change Sites Observed 1,700 1,700 ...

191

36 CFR 1004.15 - Safety belts.  

Code of Federal Regulations, 2011 CFR

...seat that was not originally equipped by the manufacturer with a safety belt nor does it apply to a person who can demonstrate that a medical condition prevents restraint by a safety belt or other occupant restraining...

2011-07-01

192

Effectiveness of Seat Belts in Reducing Injuries.  

National Technical Information Service (NTIS)

This study estimated the effectiveness of seat belts in reducing injuries and estimated the associated economic benefits using state of Kansas data. The estimation process included three stages. In the first stage, seat belt effectiveness in reducing inju...

S. Dissanayake I. Ratnayake

2007-01-01

193

46 CFR 169.723 - Safety belts.  

Code of Federal Regulations, 2010 CFR

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

2010-10-01

194

46 CFR 169.723 - Safety belts.  

Code of Federal Regulations, 2010 CFR

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

2009-10-01

195

Extensional emplacement of a high-grade granite gneiss complex into low-grade greenstones, Eastern Goldfields, Yilgarn Craton, Western Australia  

Microsoft Academic Search

A high-grade granite gneiss complex was emplaced into low-grade greenstones after an early episode of Late Archaean deformation (D1) in the Eastern Goldfields of Western Australia. The components of the granitic gneiss complex range from migmatitic granitic gneiss to foliated and massive granite. The complex is surrounded by a marginal zone of high-grade (amphibolite facies) greenstones. The oldest phases of

C. P. Swager; D. R. Nelson

1997-01-01

196

Radiation Belt's Reaction to Geomagnetic Storms  

NASA Video Gallery

From October to December 2003, the radiation belts swelled and shrank in response to geomagnetic storms as particles entered and escaped the belts. At one point, 3 radiation belts are detected. Under the wave of energetic particles from the Halloween 2003 solar storm events, the Earth's radiation belts underwent significant changes in structure. This visualization is constructed using daily-averaged particle flux data from the SAMPEX satellite installed in a simple dipole model for the Earth's magnetic field.

Holly Zell

2012-01-18

197

Promoting Safety Belt Use in Shopping Carts\\  

Microsoft Academic Search

A multiple baseline design across two supermarkets examined the effectiveness of prompts on the use of safety belts in shopping carts. At baseline, safety belt use was low at Store 1 (9 days; M = 14.7%) and at Store 2 (13 days; M = 9.9%). However, belt use increased when fliers, posters, a taped message, and buttons were incorporated as

Joseph R. Ferrari; Charles H. Baldwin

1989-01-01

198

36 CFR 4.15 - Safety belts.  

Code of Federal Regulations, 2013 CFR

...park area will have the safety belt or child restraint system properly...vehicle is in motion. The safety belt and child restraint system will...not apply to an occupant in a seat that was not originally equipped by the manufacturer with a safety belt nor does it apply to a...

2013-07-01

199

36 CFR 1004.15 - Safety belts.  

Code of Federal Regulations, 2012 CFR

...Presidio Trust will have the safety belt or child restraint system properly...vehicle is in motion. The safety belt and child restraint system will...not apply to an occupant in a seat that was not originally equipped by the manufacturer with a safety belt nor does it apply to a...

2012-07-01

200

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

201

Effects of Obesity on Seat Belt Fit.  

National Technical Information Service (NTIS)

Obesity has been shown to increase the risk of some types of injury in crashes. One hypothesis is that obesity adversely effects belt fit by changing the routing of the belt relative to the underlying skeletal structures. To evaluate this hypothesis, belt...

J. D. Rupp M. P. Reed S. M. Ebert-Hamilton

2011-01-01

202

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 ...

203

Early life recorded in archean pillow lavas.  

PubMed

Pillow lava rims from the Mesoarchean Barberton Greenstone Belt in South Africa contain micrometer-scale mineralized tubes that provide evidence of submarine microbial activity during the early history of Earth. The tubes formed during microbial etching of glass along fractures, as seen in pillow lavas from recent oceanic crust. The margins of the tubes contain organic carbon, and many of the pillow rims exhibit isotopically light bulk-rock carbonate delta13C values, supporting their biogenic origin. Overlapping metamorphic and magmatic dates from the pillow lavas suggest that microbial life colonized these subaqueous volcanic rocks soon after their eruption almost 3.5 billion years ago. PMID:15105498

Furnes, Harald; Banerjee, Neil R; Muehlenbachs, Karlis; Staudigel, Hubert; de Wit, Maarten

2004-04-23

204

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

PubMed

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

Layer; Kroner; McWilliams

1996-08-16

205

An archean impact layer from the Pilbara and Kaapvaal cratons.  

PubMed

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

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

2002-08-23

206

Metasedimentary influence on metavolcanic-rock hosted greenstone gold deposits: Geochemistry of the Giant mine, Yellowknife, Northwest Territories, Canada  

Microsoft Academic Search

The Giant mine is a mesothermal, greenstone-hosted gold deposit that has produced ˜250 metric tons of gold, principally from sulfide ores in altered metavolcanic rocks. Previous studies concluded that mineralizing fluids acquired metals and other ore-forming components from within the ore-hosting metavolcanic rocks and ascended a steep-dipping shear zone to the site of ore deposition. Our studies indicate that although

Edmond H. P. van Hees; Kevin L. Shelton; Todd A. McMenamy; Louis M. Ross Jr.; Brian L. Cousens; Hendrik Falck; Malcolm E. Robb; Tim W. Canam

1999-01-01

207

Crustal structure of granite-greenstone terranes in the Eastern Goldfields, Yilgarn Craton, as revealed by seismic reflection profiling  

Microsoft Academic Search

A deep crustal seismic reflection profile across granite-greenstones of the Eastern Goldfields in the Archaean Yilgarn Craton has revealed new constraints on upper crustal geometries. The Ida Fault, which forms the western boundary of the Eastern Goldfields, is a 30° east-dipping normal fault that can be traced to a depth of about 25 km. A mid-crustal boundary is displaced with

C. P. Swager; B. R. Goleby; B. J. Drummond; M. S. Rattenbury; P. R. Williams

1997-01-01

208

Drivers' assessment of Ford's belt reminder system.  

PubMed

In recent model years, Ford vehicles have been equipped with a supplementary seat belt reminder system that flashes and chimes intermittently for up to 5 min if the driver is unbelted. Sound- and light-based belt reminder systems of various types are beginning to appear in the market place, and it is important to learn about their acceptance and ability to increase belt use. The present study was designed to ascertain consumer reaction and reported belt use regarding the Ford system. Personal interviews were conducted with 405 drivers of vehicles with the reminder system. Among the drivers, 67% said they had activated the belt reminder one or more times, 73% said that the last time this happened they fastened their belts, 46% said their belt use had increased since driving this vehicle, 78% said they liked the reminder system, and 79% said they wanted a reminder system like this in their next vehicle. Five percent had disabled the system. Part-time users were responsive to the reminder, for example, of those who said they currently used belts usually but not on some occasions, 70% said they fastened their seat belts the last time the reminder was activated and 76% said their belt use had increased. Five percent spontaneously mentioned the belt reminder as an especially disliked feature of their new vehicles, and 2% said their belt use had decreased since having it. The 7% of respondents who reported they used belts never or very occasionally were least responsive to the system. Overall, the Ford belt reminder system is being favorably received. PMID:14630585

Williams, Allan F; Wells, Joann K

2003-12-01

209

The Southeast Asian Tin Belt  

NASA Astrophysics Data System (ADS)

The Southeast Asian Tin Belt is a north-south elongate zone 2800 km long and 400 km wide, extending from Burma (Myanmar) and Thailand to Peninsular Malaysia and the Indonesian Tin Islands. Altogether 9.6 million tonnes of tin, equivalent to 54% of the world's tin production is derived from this region. Most of the granitoids in the region can be grouped geographically into elongate provinces or belts, based on petrographic and geochronological features. - The Main Range Granitoid Province in western Peninsular Malaysia, southern Peninsular Thailand and central Thailand is almost entirely made up of biotite granite (184-230 Ma). Tin deposits associated with these granites contributed 55% of the historic tin production of Southeast Asia. - The Northern Granitoid Province in northern Thailand (0.1% of tin production) also has dominant biotite granite (200-269 Ma) but it is distinguished by abundant post-intrusion deformation. - The Eastern Granitoid Province extends from eastern Peninsular Malaysia to eastern Thailand. The Malaysian part is subdivided into the East Coast Belt (220-263 Ma), Boundary Range Belt (197-257 Ma) and Central Belt (79-219 Ma). The granitoids cover a wide compositional range from biotite granite to hornblende-biotite granite/granodiorite and diorite-gabbro. Tin deposits are associated with biotite granite in the East Coast Belt (3% of tin production). The granitoids in the other areas of the Eastern Granitoid Province are barren. - The Western Granitoid Province (22-149 Ma) in northern Peninsular Thailand, western Thailand and Burma has biotite granite and hornblende-biotite granite/granodiorite. Tin deposits are associated with biotite granite, which probably is the dominant phase (14% of tin production). The granitoids of the Indonesian Tin Islands (193-251 Ma) do not permit grouping into geographically distinct units. Main Range-type and Eastern Province-type plutons occur next to each other. Most of the tin deposits are associated with Main Range-type plutons (28% of tin production). Tin-mineralized plutons are characterized by high concentrations of SiO 2, K 2O, Rb, Sn, Th and U, whereas the concentrations of Fe 2O 3, MgO, CaO, Na 2O, Ba and Sr as well as the Fe2O3/FeO ratios are low. Tin-mineralized plutons are also distinguished by high initial 87Sr/86Sr ratios low magnetic susceptibilities.

Schwartz, M. O.; Rajah, S. S.; Askury, A. K.; Putthapiban, P.; Djaswadi, S.

1995-07-01

210

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

PubMed

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

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

2001-01-22

211

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

PubMed Central

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

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

2001-01-01

212

Plains tectonism on Venus - The deformation belts of Lavinia Planitia  

Microsoft Academic Search

The belts of the Lavinia Planitia region of Venus are discussed in detail with reference to high-resolution radar images from the Magellan spacecraft. Two types of deformation belts are identified: ridge belts and fracture belts. Ridge belts are composed of parallel ridges, each a few hundred meters in elevation, that are interpreted as folds. Typical fold spacings are 5-10 km.

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

1992-01-01

213

How States Achieve High Seat Belt Use Rates.  

National Technical Information Service (NTIS)

This study compared States with high seat belt use rates and States with low seat belt use rates using statistical analyses and conducted case studies of 10 high seat belt use States. Primary enforcement seat belt use laws clearly help increase seat belt ...

D. Preusser J. Hedlund K. Ledingham S. H. Gilbert

2008-01-01

214

[The "seat belt" syndrome in pregnancy].  

PubMed

The submitted article deals with the seat belt syndrome and its possible effects for pregnancy. The term "seat belt" syndrome is used for the injuries caused by contact forces between human body and safety belt which result from their relative acceleration. They were published many studies which confirmed the existence of this syndrome. The authors resume the results of published date and present the possibilities of reducing the danger of this syndrome. PMID:9446249

Turková, Z; Kovanda, J

1997-07-01

215

Drive Alive: Teen Seat Belt Survey Program  

PubMed Central

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

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

2010-01-01

216

Safety belt promotion: theory and practice.  

PubMed

The purpose of this paper is to provide practitioners a rationale and description of selected theoretically based approaches to safety belt promotion. Theory failure is a threat to the integrity and effectiveness of safety belt promotion. The absence of theory driven programs designed to promote safety belt use is a concern of this paper. Six theoretical models from the social and behavioral sciences are reviewed with suggestions for application to promoting safety belt use and include Theory of Reasoned Action, the Health Belief Model, Fear Arousal, Operant Learning, Social Learning Theory, and Diffusion of Innovations. Guidelines for the selection and utilization of theory are discussed. PMID:3276342

Nelson, G D; Moffit, P B

1988-02-01

217

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

218

Predicting seat belt use in fatal motor vehicle crashes from observation surveys of belt use  

Microsoft Academic Search

There is a large difference between the rates of observed seat belt use by the general public and belt use by motor vehicle occupants who are fatally injured in crashes. Seat belt use rates of fatally injured occupants, as reported in the Fatality Analysis Reporting System (FARS), are much lower than the use rates found in observation surveys conducted by

Philip Salzberg; Anna Yamada; Charlie Saibel; John Moffat

2002-01-01

219

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

220

The geology, mineralogy and geochemistry of the broomstock gold deposit, Kwekwe Greenstone Belt, Zimbabwe; Some implications for gold mineralization in jaspilite iron formations  

Microsoft Academic Search

Summary At Broomstock Mine, three types of gold mineralization have been identified: (i) jaspilite-hosted ore, (ii) ore confined to shear zones within meta-basalts, and (iii) supergene ore. The present study, which is focused on the jaspilite-hosted ore, revealed that areas carrying economic gold grades are characterized by fracturing, brecciation and abundant arsenopyrite-pyrite mineralization. The mineralization was introduced by hydrothermal fluids

T. H. C. Nutte; T. Oberthfir; R. Saager; H.-P. Tomschi

1988-01-01

221

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

222

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 Astrophysics Data System (ADS)

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.

1986-12-01

223

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

224

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

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

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

225

14 CFR 29.1413 - Safety belts: passenger warning device.  

Code of Federal Regulations, 2013 CFR

...Equipment § 29.1413 Safety belts: passenger warning device...indicate to the passengers when safety belts should be fastened, they must...to be operated from either pilot seat. (b) Each safety belt must be equipped with a...

2013-01-01

226

Exploring the Earth's Radiation Belts  

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

227

Physical Properties of Kuiper Belt Objects  

Microsoft Academic Search

The discovery of the first object in the Kuiper belt -- a formerly hypothetical ancient reservoir of icy objects located beyond Neptune's orbit -- started a revolution in our understanding of the outer Solar System; there was no longer a sharp edge to our planetary system at Pluto's orbit. About 1000 Kuiper belt objects (KBOs), intermediate in size between comets

Stephen Tegler

2007-01-01

228

Orbit dynamics of the Kuiper Belt Objects  

Microsoft Academic Search

A new subject of the solar system dynamics, the orbit dynamics of the Kuiper Belt Objects, is reviewed in this paper. Early studies were connected with the origin of short-period comets. After the first Kuiper Belt Object (KBO) was found, attentions are turned on the phase space structure of the resonant KBOs. Morbidelli and Malhotra adopted different models to study

Xiaosheng Wan; Tianyi Huang

2002-01-01

229

Safety Belt Use in 2003: Demographic Characteristics.  

National Technical Information Service (NTIS)

This report presents results on the demographics of safety belt use from the 2003 National Occupant Protection Use Survey (NOPUS), with particular emphasis on results that evaluate aspects of the 2003 Click It or Ticket campaign to raise safety belt use n...

D. Glassbrenner

2004-01-01

230

Effects of Obesity on Seat Belt Fit  

Microsoft Academic Search

Introduction Obesity has been shown to increase the risks of some types of injury in crashes. One way in which obesity may increase injury risk is by changing the routing of the belt relative to the underlying skeletal structures.Methods Belt fit was measured in a laboratory study of 54 men and women, 48 percent of whom were obese, defined by

Matthew P. Reed; Sheila M. Ebert-Hamilton; Jonathan D. Rupp

2012-01-01

231

Safety Belt Usage Survey in Kentucky, 2011.  

National Technical Information Service (NTIS)

The objective of this study was to establish 2011 safety belt and child safety seat usage rates in Kentucky. The 2011 survey continues to document the results after enactment of the original 'secondary enforcement' statewide mandatory Safety belt law in 1...

E. R. Green K. R. Agent

2011-01-01

232

Conveyor belts for transporting tar sands  

Microsoft Academic Search

A method for transporting tar sands in an open pit mine utilizing flexible belt conveyors between a receiving area and a discharge area consists of providing a conveyor belt having an upper surface layer of an elastomeric material which is flexible at low temperatures. It is substantially resistant to excess swelling when exposed to petroleum liquids containing up to 30

1976-01-01

233

Radiation Belt Storm Probe Mission Trailer  

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 space age. Even though we have know about their existence for half a century, they are still a mystery today. Credit: JHU/APL

Holly Zell

2010-12-09

234

Seat Belts on School Buses: Some Considerations.  

ERIC Educational Resources Information Center

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

Soule, David

1982-01-01

235

Increasing seat belt use in North Carolina  

Microsoft Academic Search

North Carolina has embarked on an ambitious multiyear program designed to increase seat belt and child restraint use and to reduce other traffic law violations, including alcohol-impaired driving. Increasing seat belt use, based on the Canadian model of a combination of intensive enforcement and publicity about the enforcement, was emphasized during the first phase. The program called “Click It or

Allan F. Williams; Donald Reinfurt; JoAnn K. Wells

1996-01-01

236

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

237

Coal mine combustion products: conveyor belts  

Microsoft Academic Search

The Federal Bureau of Mines, under a contract with Ultrasystems, Inc., investigated the thermal oxidative degradation characteristics of conveyor belts used in underground mines. This included the determination of smoke evolution, glow characteristics, char yields, and the identification and quantification of all volatile decomposition products in the form of gram of specific product formed per gram of belt sample tested.

A. M. Hartstein; D. R. Forshey

1976-01-01

238

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.

Williams, A; Wells, J; Farmer, C

2002-01-01

239

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.

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

1992-01-01

240

The Value of Safety Belts: A Review  

PubMed Central

The literature is reviewed to ascertain the values and dangers of safety belts. They are said to reduce the risk of major or fatal injury in impacts by nearly 60%. An incidence of abdominal trauma of the order of 0.5% is ascribed to the safety belt, and in addition there is a low incidence of a specific type of spinal fracture. The safety belt has not been shown to make injuries worse, and in causing injuries of its own has prevented more serious ones. The design of the safety belt is discussed; the three-point (lap-and-diagonal) belt is probably the best type for automobiles currently available. Recent research suggests that more sophisticated restraint systems may make survival possible in very severe impacts.

Hodson-Walker, N. J.

1970-01-01

241

Astrobiological and Planetary Exploration Implications of Microbial Ichnofossils in Terrestrial Basaltic Glasses  

NASA Astrophysics Data System (ADS)

Over the past decade, studies have demonstrated that terrestrial basaltic glass in pillow rims and hyaloclastites are suitable microbial habitats. Microbes rapidly begin colonizing the glassy surfaces along fractures and cracks that have been exposed to water. Microbial colonization of basaltic glass leads to the alteration and modification of the rocks to produce characteristic granular and/or tubular bioalteration textures. The early precipitation of sub-micron titanite grains within the biologically etched alteration structures serves as an agent for preservation that may persist for geologically extended periods of time in the absence of later penetrative deformation. These microbial alteration structures have been observed in several Archean greenstone belts including the Abitibi greenstone belt (2.7 Ga), Pilbara craton (3.35 Ga), and the Barberton greenstone belt (3.5 Ga). Archean subaqueous volcanic rocks provide an excellent analogue for a potential habitat for possible early Martian life, given that basaltic rocks are a major component of the Martian crust. A wide variety of recent evidence strongly suggests the long-term existence of abundant liquid water on ancient Mars. Recent orbiter, lander, and rover missions have found evidence for the presence of transient liquid water on Mars, perhaps persisting to the present day. Beyond Mars, other solar system bodies, notably Europa, Enceladus, and other icy satellites, may well host subaqueous basaltic glasses. We will explore the implications of the newly discovered geological record of basaltic glass bioalteration and basaltic glass as a microbial habitat for planetary exploration and astrobiology.

Bridge, N. J.; Izawa, M. M.; Banerjee, N. R.; Flemming, R. L.; Schultz, C.

2009-05-01

242

Archean sedimentary styles and early crustal evolution  

NASA Astrophysics Data System (ADS)

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

Lowe, D. R.

243

Observed use of automatic seat belts in 1987 cars.  

PubMed

Usage of the automatic belt systems supplied by six large-volume automobile manufacturers to meet the federal requirements for automatic restraints were observed in suburban Washington, D.C., Chicago, Los Angeles, and Philadelphia. The different belt systems studied were: Ford and Toyota (motorized, nondetachable automatic shoulder belt), Nissan (motorized, detachable shoulder belt), VW and Chrysler (nonmotorized, detachable shoulder belt), and GM (nonmotorized detachable lap and shoulder belt). Use of automatic belts was significantly greater than manual belt use in otherwise comparable late-model cars for all manufacturers except Chrysler; in Chrysler cars, automatic belt use was significantly lower than manual belt use. The automatic shoulder belts provided by Ford, Nissan, Toyota, and VW increased use rates to about 90%. Because use rates were lower in Ford cars with manual belts, their increase was greater. GM cars had the smallest increase in use rates; however, lap belt use was highest in GM cars. The other manufacturers supply knee bolsters to supplement shoulder belt protection; all--except VW--also provide manual lap belts, which were used by about half of those who used the automatic shoulder belt. The results indicate that some manufacturers have been more successful than others in providing automatic belt systems that result in high use that, in turn, will mean fewer deaths and injuries in those cars. PMID:2619852

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

1989-10-01

244

Belt Conveyor Modeling and Performance Simulation Based on AMESim  

Microsoft Academic Search

This paper introduces new modeling software - AMESim - to a belt conveyor. Based on AMESim, the performance simulation on belt velocity, acceleration, tension and movement of gravity take-up of one belt conveyor in starting process is carried out. The simulation illustrates the belt does not slide on the drive pulley and its safety factor is enough at any cases.

Li Guangbu; Li Ruqiong

2009-01-01

245

More evidence on the effectiveness of seat belt laws  

Microsoft Academic Search

A state cross-sectional model of traffic fatalities estimates the effectiveness of seat belt laws. Seat belt laws have no statistically significant effect on total or occupant fatalities. However, the results suggest that seat belt laws lead to increased non-occupant deaths possibly as a result of more dangerous driving. In an indirect fashion, the zero effect of seat belt laws on

Christopher Garbacz

1992-01-01

246

Seat belt use among African Americans, Hispanics, and Whites  

Microsoft Academic Search

Objectives: This study investigated seat belt use among White, Black, and Hispanic drivers, in cities in which standard enforcement of the belt use law is permitted (primary enforcement) and in cities in which a motorist has to be first cited for another offense (secondary enforcement). Socioeconomic and gender differences in belt use were also studied. Methods: Belt use observations were

JoAnn K. Wells; Allan F. Williams; Charles M. Farmer

2002-01-01

247

Increasing Automobile Seat Belt Use: An Intervention Emphasizing Risk Susceptibility  

Microsoft Academic Search

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

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

1986-01-01

248

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

249

Controls on thrust belt curvature, Wyoming-Idaho thrust belt  

SciTech Connect

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

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

1993-04-01

250

Alcohol and Safety Belt Education Program.  

National Technical Information Service (NTIS)

The purpose of the grant was to support NHTSA's two major programs: Alcohol and Driving and increasing Safety Belt/Child Passenger Safety Seat Usage through educational programs, workshops, media campaigns, and numerous other organized activities to gain ...

1986-01-01

251

[Rare lesions caused by seat belts].  

PubMed

The authors report a number of rare traumatic lesions which can be described under the heading of "safety belt syndrome". The superficial haematoma which is invariably present ("seat belt sign") would seem to be a reliable indication of improper wearing of the seat belt which has been attached too loosely. The lesions seen were a vertebral arteriovenous fistula after cervical contusion, a closed rupture of a rectus abdominis muscle, associated with rupture of the homolateral renal artery and finally pelvi-ureteric disinsertion with laceration of the renal pelvis. It is important to be aware of such lesions which must be suspected in case of accident with a seat belt since the diagnosis is often difficult. The superficial haematoma is a valuable sign which should suggest the possibility of underlying deep lesions. PMID:6841478

Vinard, J L; Brichon, P Y; Ohanessian, J H; Maudrux, G; Latreille, R

1983-01-01

252

Automatic Safety Belt Usage in 1981 Toyotas.  

National Technical Information Service (NTIS)

The objectives of the study were to evaluate the effectiveness of automatic restraint systems provided in Toyota Cressidas in increasing use of seat belts, and to evaluate attitude of owners toward those systems. Data were collected through telephone inte...

S. B. Wagner M. Bagley

1982-01-01

253

Seat Belt Usage on School Buses.  

ERIC Educational Resources Information Center

Studies on seat belt usage conducted under contract with governmental organizations or prepared by professional societies, state and local organizations, and transportation specialists have made significant contributions, but none has successfully resolved the issue. (MLF)

Farmer, Ernest

1985-01-01

254

Emission products from combustion of conveyor belts  

SciTech Connect

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

Egan, M.R.

1988-01-01

255

46 CFR 169.723 - Safety belts.  

Code of Federal Regulations, 2011 CFR

...CONTINUED) NAUTICAL SCHOOLS SAILING SCHOOL VESSELS Vessel Control, Miscellaneous Systems, and Equipment § 169.723 Safety belts...standards for each person on watch or required to work the vessel in heavy...

2011-10-01

256

46 CFR 169.723 - Safety belts.  

Code of Federal Regulations, 2012 CFR

...CONTINUED) NAUTICAL SCHOOLS SAILING SCHOOL VESSELS Vessel Control, Miscellaneous Systems, and Equipment § 169.723 Safety belts...standards for each person on watch or required to work the vessel in heavy...

2012-10-01

257

Initiatives to Address Safety Belt Use.  

National Technical Information Service (NTIS)

The following report presents an in-depth look at one of the most significant safety issues impacting highway safety and the success of the National Highway Transportation Safety Administration's (NHTSA) mission -safety belt use. This document describes t...

2003-01-01

258

The Use of Seat Belts in Cars with Smart Seat Belt Reminders—Results of an Observational Study  

Microsoft Academic Search

Recently, smart seat belt reminders (SBR) have been introduced in cars. By increasingly reminding drivers and passengers if they are not using the seat belt, the intention is to increase the belt use to almost 100%.Objective. The objective was to study if there were differences in driver's seat belt use between cars with and without SBR.Methods. Drivers of cars with

Maria Krafft; Anders Kullgren; Anders Lie; Claes Tingvall

2006-01-01

259

Earth's radiation belts. Environmental research papers  

SciTech Connect

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

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

1983-09-20

260

Electron radiation belts of the solar system  

Microsoft Academic Search

To address factors dictating similarities and differences between solar system radiation belts, we present comparisons between relativistic electron radiation belt spectra of all five strongly magnetized planets: Earth, Jupiter, Saturn, Uranus, and Neptune. We choose observed electron spectra with the highest intensities near ?1 MeV and compare them against expectations based on the so-called Kennel-Petschek limit (KP). For evaluating the

Barry Mauk; Nicola Fox

2010-01-01

261

Decay rate of the second radiation belt.  

PubMed

Variations in the Earth's trapped (Van Allen) belts produced by solar flare particle events are not well understood. Few observations of increases in particle populations have been reported. This is particularly true for effects in low Earth orbit, where manned spaceflights are conducted. This paper reports the existence of a second proton belt and it's subsequent decay as measured by a tissue-equivalent proportional counter and a particle spectrometer on five Space Shuttle flights covering an eighteen-month period. The creation of this second belt is attributed to the injection of particles from a solar particle event which occurred at 2246 UT, March 22, 1991. Comparisons with observations onboard the Russian Mir space station and other unmanned satellites are made. Shuttle measurements and data from other spacecraft are used to determine that the e-folding time of the peak of the second proton belt. It was ten months. Proton populations in the second belt returned to values of quiescent times within eighteen months. The increase in absorbed dose attributed to protons in the second belt was approximately 20%. Passive dosimeter measurements were in good agreement with this value. PMID:11540362

Badhwar, G D; Robbins, D E

1996-01-01

262

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

National Technical Information Service (NTIS)

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

1970-01-01

263

Primary enforcement seat belt laws are effective even in the face of rising belt use rates  

Microsoft Academic Search

A recent systematic literature review found that primary enforcement laws are more effective at increasing seat belt use than secondary laws in the United States. This report reexamines the studies included in the systematic review to explore whether the benefits of a primary law differ based on: (1) the baseline seat belt use rate; or (2) whether or not the

Ruth A Shults; Randy W Elder; David A Sleet; Robert S Thompson; James L Nichols

2004-01-01

264

Characteristics of drivers not using seat belts in a high belt use state  

Microsoft Academic Search

A study was undertaken in North Carolina to determine the characteristics of the minority of drivers who were not using seat belts following an extensive publicity\\/enforcement campaign, which had increased statewide use to 80%. Vehicles and drivers whose seat belt use was observed at sites across North Carolina were matched against Division of Motor Vehicles registration and driver history files

Donald Reinfurt; Allan Williams; JoAnn Wells; Eric Rodgman

1996-01-01

265

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

Microsoft Academic Search

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

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

1996-01-01

266

Fatality risk reduction from safety belt use.  

PubMed

This paper presents an overview of recent estimations of safety belt effectiveness obtained using a new technique--the double-pair comparison method. By effectiveness is meant the reduction, expressed as per cent, in fatalities to a presently unbelted population that would result if all of its members were to use belts, but not otherwise change their driving behavior. The double-pair comparison method is presented more simply, with less mathematical detail and rigor, than in earlier descriptions of it. The method is applied to determine the effectiveness of three-point lap/shoulder belts in preventing fatalities to drivers and right front passengers in passenger cars of model year 1974 or later, averaged over the distribution of crashes which occur in U.S. traffic. The method is then applied to investigate the dependence of effectiveness on a variety of vehicular, accident, roadway, and environmental factors. It is reported that if all presently unbelted drivers and right front passengers were to use the provided lap/shoulder belts, but not otherwise change their behavior, fatalities to this group would decline by (43 +/- 3)%. Safety belt effectiveness for drivers is higher in single-car crashes than in multiple-vehicle crashes, but does not depend much on a variety of other vehicle factors (for example, car size), accident factors (travel speed), roadway factors (posted speed limit), and environmental factors (light versus dark). PMID:3612846

Evans, L

1987-07-01

267

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

268

Ionospheric heating for radiation-belt control  

SciTech Connect

Pitch-angle scattering interactions of electromagnetic waves in the ELF/VLF bands with trapped electrons, as formulated by Kennel and Petschek 1, describe the dynamics of the freshly filled radiation belts flux tubes. The natural existence of a slot region with electron fluxes below the Kennel-Petschek limit requires non-local wave sources. We describe a set of planned, active experiments in which VLF radiation will be injected from ground and space based transmitters in conjunction with the CRRES satellite in the radiation belts. These experiments will measure the intensity of waves driving pitch-angle diffusion and the electron energies in gyroresonance with the waves. An ability to reduce the flux of energetic particles trapped in the radiation belts by artificial means could improve the reliability of microelectronic components on earth-observing satellites in middle-altitude orbits.

Burke, W.J.; Villalon, E.

1990-10-01

269

Mars: Dissipating Behavior of the Cloud Belt  

NASA Astrophysics Data System (ADS)

This is a brief report on the Martian climate, based on our observations in 2001 as well as those in 1997 and 1999. The focus is the dissipating behavior of the low-latitude cloud belt appearing around the aphelion, the behavior of which has never been explicitly examined. We derive the optical thickness of water ice clouds (WICs) as ?WIC ? 0.1 (? ~= 4400 Å) at the solar longitude Ls = 174° in 2001. The latitudinal coverage of the cloud belt is approximately Ls-independent just until its end. The cloud belt divides into a ``semi-encircling'' cloud band and discrete WICs before its dissipation (over Ls ~ 100°-110°) in many cases. We suggest that this cloud division should embody localization of the cross-equatorial Hadley circulation.

Nakakushi, Takashi; Akabane, Tokuhide; Iwasaki, Kyosuke; Larson, Stephen M.

2002-06-01

270

Venus orogenic belt environments - Architecture and origin  

NASA Astrophysics Data System (ADS)

Orogenic belt environments (Danu, Akna, Freyja, and Maxwell Montes) in Western Ishtar Terra, Venus, display a range of architectural elements, including (from the center of Western Ishtar outward) an inboard plateau (Lakshmi Planum), the linear orogenic belts themselves, outboard plateaus, steep scarps bounding Ishtar, adjacent linear foredeeps and outboard rises, and outboard low-lying volcanic plains. The main elements of the architecture are interpreted to be due to the convergence, underthrusting, and possible subduction of lowland plains at the margins of a preexisting tessera plateau of thicker crust.

Head, James W.; Vorder Bruegge, Richard W.; Crumpler, L. S.

1990-08-01

271

Illinois PER Interactive Examples: Conveyor Belt  

NSDL National Science Digital Library

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

Gladding, Gary

2008-09-10

272

A shell model for tyre belt vibrations  

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

273

30 CFR 57.4263 - Underground belt conveyors.  

Code of Federal Regulations, 2013 CFR

...METAL AND NONMETAL MINES Fire Prevention and Control Firefighting Equipment § 57.4263 Underground belt conveyors. Fire protection shall be provided at the head, tail, drive, and take-up pulleys of underground belt...

2013-07-01

274

29. Elevator no. 3: top floor, conveyor belt rollers for ...  

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

29. Elevator no. 3: top floor, conveyor belt rollers for belt to gangway (in background) connecting with elevator no. 2, facing northwest - Washburn Crosby Company Elevators No. 2 & 3, 900 & 1000 Second Avenue, South, Minneapolis, Hennepin County, MN

275

30 CFR 75.1403-5 - Criteria-Belt conveyors.  

Code of Federal Regulations, 2013 CFR

...Criteria-Belt conveyors. 75.1403-5 Section 75.1403-5 Mineral Resources MINE SAFETY AND...AND HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Hoisting and Mantrips § 75.1403-5 CriteriaâBelt...

2013-07-01

276

46 CFR 169.825 - Wearing of safety belts.  

Code of Federal Regulations, 2011 CFR

...safety belts. 169.825 Section 169.825 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) NAUTICAL SCHOOLS SAILING SCHOOL VESSELS Operations § 169.825 Wearing of safety belts. The master of each...

2011-10-01

277

Seat belts and trauma: Clinical clues for the surgeon  

Microsoft Academic Search

Since their introduction over 30 years ago, seat belts have reduced the overall mortality associated with motor vehicle accidents by as much as 50%. The position and adjustment of the seat belt appear to play an important role in preventing injury. The lap portion of the belt should be kept low on the abdomen at the level of the anterior

Jeanette M. Dolezal; Paul R. G. Cunningham

1999-01-01

278

The role of enforcement programs in increasing seat belt use  

Microsoft Academic Search

Seat belt laws by themselves led to increased belt use in the United States and Canada, but initial effects were limited. Canadian provincial officials launched highly publicized enforcement campaigns in the early 1980s that resulted in substantially increased belt use. Canadian-style enforcement programs subsequently were adopted in the United States, and the use of such programs has grown in recent

Allan F. Williams; JoAnn K. Wells

2004-01-01

279

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

National Technical Information Service (NTIS)

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

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

1994-01-01

280

30 CFR 56.14131 - Seat belts for haulage trucks.  

Code of Federal Regulations, 2013 CFR

... 2013-07-01 2013-07-01 false Seat belts for haulage trucks. 56.14131 Section...and Maintenance Requirements § 56.14131 Seat belts for haulage trucks. (a) Seat belts shall be provided and worn in haulage...

2013-07-01

281

14 CFR 125.211 - Seat and safety belts.  

Code of Federal Regulations, 2013 CFR

...2013-01-01 false Seat and safety belts. 125.211 Section...Requirements § 125.211 Seat and safety belts. (a) No person may...multiple lounge or divan seat may share one approved safety belt during en route flight...

2013-01-01

282

The Medical Case for Seat Belts on School Buses.  

ERIC Educational Resources Information Center

A group is actively supporting legislation to require seat belts on only newly manufactured school buses. However, misinformation is being circulated to oppose the installation of seat belts in school buses. If the industry continues to block the installation of seat belts, punitive legislation may be passed. (MLF)

Yeager, Arthur

1985-01-01

283

Seat belt use during pregnancy in Iran: attitudes and practices  

Microsoft Academic Search

ObjectiveSeat belt use during pregnancy reduces injury to the mother and her fetus. During recent years, the use of seat belts has been mandated by law in Iran. The purpose of this study was to determine the attitudes and practices of pregnant women regarding seat belt use.

Mojgan Karbakhsh; Zahra Ershadi; Ali Khaji; Fatemeh Rahimi-Sharbaf

2010-01-01

284

Radiation Belt Storm Probes (RBSP) mission overview  

Microsoft Academic Search

The Radiation Belt Storm Probes (RBSP) mission is part of NASA's Living With a Star Program, and is scheduled to launch in September, 2012. The fundamental goal of the mission is to provide an understanding, ideally to the point of predictability, of how populations of relativistic electrons and penetrating ions in space form or change in response to variable inputs

James Stratton; Nicola J. Fox

2012-01-01

285

Studies with belt integrated vehicular seats  

Microsoft Academic Search

Static and dynamic studies were conducted with conventional and belt integrated vehicular seats. Most conventional seat backs failed with a static rearward torque of approximately 700 to 800 Newton meters (Nm) while integrated seats sustain a torque up to approximately 3,500 to 4,000 Nm. Correspondingly greater rearward changes in speed can be sustained by integrated seats

K. J. Saczalski

1999-01-01

286

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

287

Depletion of the Outer Asteroid Belt  

NASA Astrophysics Data System (ADS)

The depletion of the outer asteroid belt has been a puzzle for planetary scientists for a long time. Theories based on gravitational perturbations from planets at their current orbits fail to explain the observed structure of the outer belt, particularly between 3.5 and 3.9 astronomical units. However, the orbital configuration of planets today may not represent what it was when asteroids were formed. In the early history of the Solar system, orbital migration of the giant planets has been shown to be quite possible (Fernandez and Ip, 1984, Icarus 58:109-120; Fernandez and Ip, 1996, Planet. Sp. Sci. 44:431-439). This early dynamical history of the outer planets is also supported by a recent theory for the origin of Pluto and the structure of the Kuiper belt (Malhotra 1993, Nature 365:819-821; Malhotra 1995, AJ 110:420-429). We have studied the evolution of asteroids subject to perturbations of the giant planets, and we show that outer belt asteroids are depleted efficiently due to the mean motion resonance sweeping that accompanied the migration of giant planets.

Liou, J. C.; Malhotra, R.

1996-09-01

288

The seat belt law and after.  

PubMed Central

We report a retrospective study of 378 perforating eye injuries presenting between August 1981 and July 1984 to four major teaching hospitals. The aetiological groups have been analysed together and by region, and preventive measures for some groups are discussed. We have confirmed the effectiveness of seat belt legislation in reducing serious eye injury.

Cole, M D; Clearkin, L; Dabbs, T; Smerdon, D

1987-01-01

289

The thrust belts of Western North America  

SciTech Connect

Most of the Basin and Range physiographic province of western North America is now believed to be part of the overthrust. The more obvious overthrust belt along the eastern edge of the Basin and Range Province is named the Sevier orogenic belt, where older rocks are observed thrust onto younger rocks. More detailed surface geological mapping, plus deep multiple-fold geophysical work and many oil and gas wildcat wells, have confirmed an east-vergent shortened and stacked sequence is present in many places in the Basin and Range. This western compressive deformed area in east central Nevada is now named the Elko orogenic belt by the U.S. Geological Survey. This older compressed Elko orogenic belt started forming approximately 250 m.y. ago when the North American plate started to move west as the Pangaea supercontinent started to fragment. The North American plate moved west under the sediments of the Miogeocline that were also moving west. Surface-formed highlands and oceanic island arcs on the west edge of the North American plate restricted the westward movement of the sediments in the Miogeocline, causing east-vergent ramp thrusts to form above the westward-moving North American plate. The flat, eastward-up-cutting thrust assemblages moved on the detachment surfaces.

Moulton, F.C.

1993-08-01

290

Electron Radiation Belts of the Solar System  

NASA Astrophysics Data System (ADS)

To address the question of what factors dictate similarities and differences between radiation belts, we present comparisons between the electron radiation belt spectra of all five strongly magnetized planets within the solar system: Earth, Jupiter, Saturn, Uranus, and Neptune. We choose the highest intensity observed electron spectrum within each system (highest specifically near 1 MeV) and compare them against expectations based on the so-called Kennel-Petschek limit (KP; 1966) for each system. For evaluating the KP limit, we begin with the new relativis-tically correct formulation of Summers et al. (2009) but then add several refinements of our own. Specifically, we: 1) utilized a much more flexible analytic spectral shape that allows us to accurately fit observed radiation belt spectra; 2) adopt the point of view that the anisotropy parameter is not a free parameter but must take on a minimal value, as originally proposed by Kennel and Petschek (1966); and 3) examine the differential characteristics of the KP limit along the lines of what Schulz and Davidson (1988) performed for the non-relativistic formula-tion. We find that three factors limit the highest electron radiation belt intensities within solar system planetary magnetospheres: a) whistler mode interactions that limit spectral intensities to a differential Kennel-Petschek limit (3 planets); b) the absence of robust acceleration pro-cesses associated with injection dynamics (1 planet); and c) material interactions between the radiation particles and clouds of gas and dust (1 planet).

Mauk, Barry; Fox, Nicola

291

The Bomb-Produced Radiation Belt  

Microsoft Academic Search

The distributions of electrons trapped in the earth's magnetic field, ; produced by a 1.4-Mt nuclear explosion at altitude of 400 km in the Central ; Pacific Ocean, are measured by several satellites. The decay of this bomb-; produced radiation belt is described, in terms of the time since the explosion ; (July 9, 1962) and the distance from the

W. N. Hess

1963-01-01

292

Dynamic model of Earth's radiation belts  

NASA Astrophysics Data System (ADS)

The radiation belts are the region that energetic charged particles are trapped by Earth's magnetic field. It is well known that the energetic particle flux vary during geomagnetic distur-bances, and, the relativistic electrons in the outer radiation belt change with solar wind speed. Many researches have been studied about the flux variation of radiation belt, but the mecha-nism of the variation has not been understood in detail. We have developed a new dynamic model of energetic particles trapped in the based on the data from the MDS-1 spacecraft. This model reproduces the dynamic of radiation belt by running average using magnetic activity index(AP) and running average solar wind speed. This model covers the energy ranges of 0.4-2MeV for electrons, 0.9-210 MeV for protons, and 6-140 MeV for helium ions, and it is valid from low altitudes (approximately 500km) to geosynchronous orbit altitude. We discuss the advantage of the new model, and comparisons between MDS-1 data and our new model.

Matsumoto, Haruhisa; Koshiishi, Hideki; Goka, Tateo; Obara, Takahiro

293

The seat belt law and after  

Microsoft Academic Search

We report a retrospective study of 378 perforating eye injuries presenting between August 1981 and July 1984 to four major teaching hospitals. The aetiological groups have been analysed together and by region, and preventive measures for some groups are discussed. We have confirmed the effectiveness of seat belt legislation in reducing serious eye injury.

M D Cole; L Clearkin; T Dabbs; D Smerdon

1987-01-01

294

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

295

School Buses & Seat Belts: A Discussion.  

ERIC Educational Resources Information Center

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

Alaska State Dept. of Education, Juneau.

296

The Case for School Bus Seat Belts.  

ERIC Educational Resources Information Center

Argues for seat belt installation on school buses and forced retirement of vehicles manufactured prior to 1977, when federal safety standards were upgraded to include compartmentalization features. Discredits a Transport Canada study for improper design and methodology used. Advises communities to examine research, consult experts, and visit…

Corda, Salvatore J.

1987-01-01

297

Reference Governors for Controlled Belt Restraint Systems  

Microsoft Academic Search

This paper presents a novel control strategy for real-time controlled restraint systems. Today's restraint systems typically include a number of airbags, and a three-point seat belt with load limiter and pretensioner. In the class of real- time controlled restraint systems, the restraint actuator settings are continuously manipulated during the crash. The control strategy developed here is based on reference management,

E. P. van der Laan; H. J. C. Luijten; W. P. M. H. Heemels; F. E. Veldpaus; M. Steinbuch

2009-01-01

298

Reference governors for controlled belt restraint systems  

Microsoft Academic Search

This paper presents a novel control strategy for real-time controlled restraint systems. Todaypsilas restraint systems typically include a number of airbags, and a three-point seat belt with load limiter and pretensioner. In the class of realtime controlled restraint systems, the restraint actuator settings are continuously manipulated during the crash. The control strategy developed here is based on reference management, in

E. P. van der Laan; H. J. C. Luijten; W. P. M. Heemels; F. E. Veldpaus; M. Steinbuch

2008-01-01

299

Reference governors for controlled belt restraint systems  

Microsoft Academic Search

Today's restraint systems typically include a number of airbags, and a three-point seat belt with load limiter and pretensioner. For the class of real-time controlled restraint systems, the restraint actuator settings are continuously manipulated during the crash. This paper presents a novel control strategy for these systems. The control strategy developed here is based on a combination of model predictive

E. P. van der Laan; W. P. M. H. Heemels; HJC Luijten; F. E. Veldpaus; M. Steinbuch

2010-01-01

300

The Case for School Bus Seat Belts.  

ERIC Educational Resources Information Center

|Argues for seat belt installation on school buses and forced retirement of vehicles manufactured prior to 1977, when federal safety standards were upgraded to include compartmentalization features. Discredits a Transport Canada study for improper design and methodology used. Advises communities to examine research, consult experts, and visit…

Corda, Salvatore J.

1987-01-01

301

Analysis of teenage seat belt use: From the 2007 Missouri high school seat belt survey  

Microsoft Academic Search

IntroductionThis study analyzed high school teenagers' seat belt use based on the observational surveys of more than 15,000 teenagers at 150 schools and was conducted in the state of Missouri, U.S., in 2007. Since fatal car accidents involving high school teenagers are disproportionately high, and increased seat belt use saves lives in what would otherwise be fatal accidents, it is

Sungyop Kim; Leanna Depue; LaGena Spence; Judi Reine

2009-01-01

302

Geochemical Evidence for Subduction in the Early Archaean from Quartz-Carbonate-Fuchsite Mineralization, Isua Supracrustal Belt, West Greenland  

NASA Astrophysics Data System (ADS)

Quartz, carbonate and fuchsite (chromian muscovite) is a common metasomatic assemblage observed in orogenic gold systems, both in Phanerozoic convergent margin settings, and within supracrustal and greenstone belts of Precambrian rocks. Geologic and geochemical observations in younger orogenic systems suggest that ore-forming metasomatic fluids are derived from subduction-related devolitilization reactions, implying that orogenic Au-deposits in Archaean and Proterozoic supracrustal rock suites are related to subduction-style plate tectonics beginning early in Earth history. Justification of this metasomatic-tectonic relationship requires that 1) Phanerozoic orogenic Au-deposits form in subduction-zone environments, and 2) the geochemical similarity of Precambrian orogenic deposits to their younger counterparts is the result of having the same petro-genetic origin. Hydrogen and oxygen isotope compositions of fuchsite and quartz from auriferous mineralization in the ca. 3.8 Ga Isua Supracrustal Belt (ISB) in West Greenland, in conjunction with elevated concentrations of CO2, Cr, Al, K and silica relative to protolith assemblages, suggest that this mineralization shares a common petro-tectonic origin with Phanerozoic orogenic deposits and that this type of metasomatism is a unique result of subduction-related processes. Fuchsite from the ISB has a ?18O and ?D of +7.7 to +17.9% and -115 to -61%, respectively. ?18O of quartz from the same rocks is between +10.3 and +18.6%. Muscovite-quartz oxygen isotope thermometry indicates that the mineralization occurred at 560 ± 90oC, from fluids with a ?D of -73 to -49% and ?18O of +8.8 to +17.2%. Calculation of isotopic fractionation during fluid-rock reactions along hypothetical fluid pathways demonstrates that these values, as well as those in younger orogenic deposits, are the result of seawater-derived fluids liberated from subducting lithosphere interacting with ultramafic rocks in the mantle wedge and lower crust, before migrating up crustal-scale vertical fracture zones. Thus, the presence of quartz-carbonate-fuchsite mineralization in the Isua supracrustal belt and other Archaean-age deposits provides strong evidence for the existence of modern-style subduction as early as 3.8 Ga.

Pope, E. C.; Rosing, M. T.; Bird, D. K.

2011-12-01

303

Resonance dynamics in the Kuiper Belt  

NASA Astrophysics Data System (ADS)

Orbital resonances --- both, mean motion resonances as well as secular resonances --- are essential to understanding the present-day dynamical behavior of objects in the Kuiper Belt. Furthermore, during the formation and subsequent dynamical evolution of the outer planets, the region beyond the orbit of Neptune and up to approximately 50 AU would have been swept by strong resonant perturbations from the giant planets, particularly Neptune. Previous work [Malhotra 1995, AJ 110:420] has indicated that the mass in the Kuiper Belt would have been gravitationally sculpted into a highly non-uniform distribution, with most of the Kuiper Belt objects being swept into narrow zones of long-term stable orbits at mean motion resonances with Neptune. The resonance sweeping process would have excited the orbital eccentricities in the Kuiper Belt to moderately high values, e ~ 0.1-0.3. I have determined the locations, widths, and capture cross sections of these resonance zones and have studied the dynamical properties of resonant orbits. The short term ( ~ 10(5) yr) dynamics of resonance-trapped objects is determined primarily by Neptune's perturbations alone, but the long term dynamics is sensitive to the secular perturbations of all the giant planets as well as weak higher-order mean motion resonances. If the majority of Kuiper Belt objects do indeed reside in the narrow stable libration zones at Neptune resonances, then an important observational consequence is that detection probability for KB objects is highly non-uniform in ecliptic longitude. A comparison of theory with current observations will be presented.

Malhotra, Renu

1995-12-01

304

Making the Most of the Worst-Case Scenario: Should Belt-Positioning Booster Seats Be Used in Lap-Belt-Only Seating Positions?  

Microsoft Academic Search

Objective: Examine real-world crash injury data to determine whether children seated with lap belts only are better protected with or without belt-positioning booster seats.Methods: Crash injury rates among booster-age children were examined for three restraint categories: lap belt only, belt-positioning booster seat with lap belt, and booster seat with lap\\/shoulder belt. Data were drawn from the National Automotive Sampling System–Crashworthiness

Bevan B. Kirley; Eric R. Teoh; Adrian K. Lund; Kristy B. Arbogast; Michael J. Kallan; Dennis R. Durbin

2009-01-01

305

Physical Properties of Kuiper Belt Objects  

NASA Astrophysics Data System (ADS)

The discovery of the first object in the Kuiper belt -- a formerly hypothetical ancient reservoir of icy objects located beyond Neptune's orbit -- started a revolution in our understanding of the outer Solar System; there was no longer a sharp edge to our planetary system at Pluto's orbit. About 1000 Kuiper belt objects (KBOs), intermediate in size between comets and planets, are now known to exist on orbits about the Sun. Since KBOs are the preserved building blocks of an outer Solar System planet, studying their physical and chemical properties provides an opportunity for a better understanding of the formation and evolution of the Solar System. Here we describe the progress made by ground-based and orbiting telescopes in studying the physical and chemical properties of KBOs over the last 15 years.

Tegler, Stephen

2007-10-01

306

QUAOAR: A ROCK IN THE KUIPER BELT  

SciTech Connect

Here we report Wide-Field Planetary Camera 2 observations of the Quaoar-Weywot Kuiper Belt binary. From these observations, we find that Weywot is on an elliptical orbit with an eccentricity of 0.14 {+-} 0.04, a period of 12.438 {+-} 0.005 days, and a semimajor axis of 1.45 {+-} 0.08 x 10{sup 4} km. The orbit reveals a surprisingly high-Quaoar-Weywot system mass of (1.6 {+-} 0.3) x 10{sup 21} kg. Using the surface properties of the Uranian and Neptunian satellites as a proxy for Quaoar's surface, we reanalyze the size estimate from Brown and Trujillo. We find, from a mean of available published size estimates, a diameter for Quaoar of 890 {+-} 70 km. We find Quaoar's density to be {rho} = 4.2 {+-} 1.3gcm{sup -3}, possibly the highest density in the Kuiper Belt.

Fraser, Wesley C.; Brown, Michael E. [Division of Geological and Planetary Sciences, California Institute of Technology, MC 150-21. 1200 E. California Blvd. Pasadena, CA 91125 (United States)

2010-05-10

307

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

308

Recent Breakups in the Asteroid Belt  

NASA Astrophysics Data System (ADS)

Much of what we see in the asteroid belt today is a consequence of past collisions, which shaped the size-frequency distribution of asteroids and led to their heavily-cratered surfaces. Perhaps the most remarkable features of the belt are the asteroid families [1]. An asteroid family is a group of asteroid fragments with similar orbits and spectra produced by a collisional breakup of a large parent body. More than fifty families have been identified to date in the main belt [2]. These structures, when properly analyzed, hold important clues to the interior structure of asteroids, the physics of large scale collisions, and the overall evolution of the main belt since its formation [3]. Most of the known families are very old and thus have experienced significant dynamical and collisional erosion since their formation. This makes it difficult to clearly distinguish between features produced by the original breakup and those produced by on-going processes. Recent dynamical studies, however, have identified several asteroid families that are extremely young: the Iannini, Karin and Veritas families apparently formed at <5, 5.8 and 8.3 Ma, respectively [4,5]. These families represent nearly pristine examples of ejected fragments produced by disruptive asteroid collisions, because the observed remnants of recent breakups have apparently suffered limited dynamical and collisional erosion. Here we will discuss how studies of young asteroid families help us glean insights into the physics of large scale collisions, dynamical processes that affect small bodies in the Solar System, and the surface and interior properties of asteroids. [1] Hirayama, 1918, AJ 31, 185--188. [2] Zappala et al., 2002, In Asteroids III, pp. 619-629. [3] Bottke et al., 2005, Icarus, 175, 111-140. [4] Nesvorny et al., 2002, Nature 417, 720--722. [5] Nesvorny et al., 2003, ApJ 591, 486--497.

Nesvorny, D.

2005-08-01

309

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

310

Substyles of belting: phonatory and resonatory characteristics.  

PubMed

Belting has been described as speechlike, yell-like, or shouting voice production commonly used in contemporary commercial music genres and substantially differing from the esthetic of the Western classical voice tradition. This investigation attempts to describe phonation and resonance characteristics of different substyles of belting (heavy, brassy, ringy, nasal, and speechlike) and the classical style. A professional singer and voice teacher, skilled in these genres, served as the single subject. The recorded material was found representative according to a classification test performed by an expert panel. Subglottal pressure was measured as the oral pressure during the occlusion for the consonant /p/. The voice source and formant frequencies were analyzed by inverse filtering the audio signal. The subglottal pressure and measured flow glottogram parameters differed clearly between the styles heavy and classical assuming opposite extremes in most parameters. The formant frequencies, by contrast, showed fewer less systematic differences between the substyles but were clearly separated from the classical style with regard to the first formant. Thus, the differences between the belting substyles mainly concerned the voice source. PMID:21439776

Sundberg, Johan; Thalén, Margareta; Popeil, Lisa

2011-03-25

311

Mantle conveyor beneath the Tethyan collisional belt  

NASA Astrophysics Data System (ADS)

Collisional belts are generated by the arrival of continental lithosphere into a subduction zone. The Tethyan suture from the Bitlis to the Himalayas is a prime example where the Arabian and Indian plates collided with Eurasia during the Cenozoic. While the kinematics of this process are well established, its dynamics are more uncertain. India and Arabia intriguingly keep advancing, in spite of large collisional resisting forces, and in the absence of a substantial, upper mantle slab driving force at present-day. We perform global mantle circulation computations to test the role of deep mantle flow as a driving force for the kinematics of the Tethyan collisional belt, evaluating different boundary conditions and mantle density distributions as inferred from seismic tomography or slab models. Our results show that mantle drag exerted on the base of the lithosphere by a large-scale, convective "conveyor belt" with an active upwelling component is likely the main cause for the ongoing indentation of the Indian and Arabian plates into Eurasia

Faccenna, C.; Becker, T. W.

2012-04-01

312

Chaotic Diffusion of Resonant Kuiper Belt Objects  

NASA Astrophysics Data System (ADS)

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

Tiscareno, Matthew S.; Malhotra, Renu

2009-09-01

313

Rapid rebuilding of the outer radiation belt  

NASA Astrophysics Data System (ADS)

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

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

2011-09-01

314

Aortic ruptures in seat belt wearers.  

PubMed

Several investigations have indicated that rupture of the thoracic aorta is one of the leading causes of immediate death in victims of road traffic accidents. In Finland in 1983, 92% of front-seat passengers were seat belt wearers on highways and 82% in build-up areas. The mechanisms of rupture of the aorta have been intensively investigated, but the relationship between seat belt wearing and injury mechanisms leading to aortic rupture is still largely unknown. This study comprises 4169 fatally injured victims investigated by the Boards of Traffic Accident Investigation of Insurance Companies during the period 1972 to 1985. Chest injuries were recorded as the main cause of death in 1121 (26.9%) victims, 207 (5.0%) of those victims having worn a seat belt. Aortic ruptures were found at autopsy in 98 victims and the exact information of the location of the aortic tears was available in 68. For a control group, we analyzed 72 randomly chosen unbelted victims who had a fatal aortic rupture in similar accidents. The location of the aortic rupture in unbelted victims was more often in the ascending aorta, especially in drivers, whereas in seat belt wearers the distal descending aorta was statistically more often ruptured, especially in right-front passengers (p less than 0.05). The steering wheel predominated statistically as the part of the car estimated to have caused the injury in unbelted victims (37/72), and some interior part of the car was the most common cause of fatal thoracic impacts in seat belt wearers (48/68) (p less than 0.001). The mechanism of rupture of the aorta in the classic site just distal to the subclavian artery seems to be rapid deceleration, although complex body movements are also responsible in side impact collisions. The main mechanism leading to rupture of the ascending aorta seems to be severe blow to the bony thorax. This also often causes associated thoracic injuries, such as heart rupture and sternal fracture. Injuries in the ascending aorta were mostly found in unbelted victims and were sustained in frontal impact collisions, the injury-causing part of the car being the steering wheel. Ruptures of the distal descending part of the aorta were frequently associated with fractures of the thoracic vertebra. PMID:2770317

Arajärvi, E; Santavirta, S; Tolonen, J

1989-09-01

315

Seat belt usage: A potential target for applied behavior analysis  

PubMed Central

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

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

1980-01-01

316

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

2006-03-23

317

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

PubMed

Absorption features having depths up to 5% are identified in high-quality, high-resolution reflectance spectra of 16 dark asteroids in the main belt and in the Cybele and Hilda groups. Analogs among the CM2 carbonaceous chondrite meteorites exist for some of these asteroids, suggesting that these absorptions are due to iron oxides in phyllosilicates formed on the asteroidal surfaces by aqueous alteration processes. Spectra of ten additional asteroids, located beyond the outer edge of the main belt, show no discernible absorption features, suggesting that aqueous alteration did not always operate at these heliocentric distances. PMID:17748705

Vilas, F; Gaffey, M J

1989-11-10

318

The relationship between perceived risk of being ticketed and self-reported seat belt use  

Microsoft Academic Search

Problem: Twenty-nine percent of Americans failed to use their seat belts in 2000. Efforts to improve safety belt usage can be enhanced by identifying specific factors that motivate belt use. Method: Motorist survey data were used to examine the effect of Perceived Risk of being Ticketed (PRT) for a seat belt infraction on self-reported seat belt use. Results: Analyses indicated

Neil K. Chaudhary; Mark G. Solomon; Linda A. Cosgrove

2004-01-01

319

Finite element analysis of seat belt bunching phenomena  

Microsoft Academic Search

Some safety belt D-rings lead to a non-systematic instability; the webbing, which should scroll without hindrance through the D-ring, laterally shifts, bunches and produces the overturning of the ring. To expertise this so-called seat belt bunching phenomenon, finite element numerical simulations are undertaken at a mesoscopic scale. A new shell element is developed to simulate seat belt fabric behaviour. To

D. Dubois; P. Gross; A. Tramecon; E. Markiewicz

2006-01-01

320

New compounds will help coal operators comply with BELT standards  

SciTech Connect

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

NONE

2009-04-15

321

Analysis of conveyor belts in winter Mediterranean cyclones  

Microsoft Academic Search

The relevance of the midlatitude conveyor belt model to Mediterranean cyclones (MCs) is examined using data from two winters.\\u000a Eight MCs, which exhibit typical midlatitude cyclone structure, were scrutinized and their conveyor belts were examined. The\\u000a analysis was based on satellite imagery, isentropic wind maps, vertical cross-sections of potential and equivalent potential\\u000a temperatures, and air back-trajectories. The conveyor belts found

B. Ziv; H. Saaroni; M. Romem; E. Heifetz; N. Harnik; A. Baharad

2010-01-01

322

Magnetic refrigeration apparatus with belt of ferro or paramagnetic material  

DOEpatents

A magnetic refrigerator operating in the 12 to 77K 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, John A. (Madison, WI); Stewart, Walter F. (Marshall, WI); Henke, Michael D. (Los Alamos, NM); Kalash, Kenneth E. (Los Alamos, NM)

1987-01-01

323

Decomposition of noise sources of synchronous belt drives  

NASA Astrophysics Data System (ADS)

In this paper, the noise sources of synchronous belt are decomposed and formulated based on the analysis of the impact dynamics of belt-sprocket tooth interface. The impact/contact of belt-sprocket tooth and the vibration of belt span are modeled. The friction-vibrations interaction of belt tooth and the airflow-induced acoustic wave during belt-sprocket tooth engagement are comprehensively formulated. The structure-borne noise consists of structural impact noise and friction-induced noise. The airborne noise is due to airflow-induced acoustic wave during belt-sprocket tooth engaging. The spectral signatures of the varied noise are quantified, and the case studies are given to illustrate the influences of the tooth parameters and operation conditions on noise. The noise due to belt span vibration under impact ranges from hundreds to several thousand Hz. The impact noise, friction-induced noise and airflow-induced noise of belt tooth ranges from 3 kHz to 10 kHz.

Chen, Gang (Sheng); Zheng, Hui; Qatu, Mohamad

2013-04-01

324

OXYGEN AND HYDROGEN ISOTOPE GEOCHEMISTRY OF THE IRON ORE GROUP (IOG), INDIA: THE STABLE ISOTOPIC COMPOSITION OF THE ARCHEAN OCEAN  

NASA Astrophysics Data System (ADS)

The Iron Ore Group (IOG) of the Singbhum-Orissa craton in eastern India is an Archean greenstone belt that crops out within a NNE plunging asymmetric synclinorium, sandwiched between the Singbhum Granite Complex to the east and the Bonai Granite to the west. The IOG sequence consists of submarine rocks with lower basaltic-andesite at the base of the section followed successively upwards by lower shale, tuffs, banded iron ore, upper shale and upper lava. The metamorphic conditions for the lower lava of the western limb are higher (lower amphibolites facies) than the lower lava of the eastern limb and the upper lava, where conditions range from zeolite to greenschist facies. Oxygen isotope analysis of 23 metaigneous rocks exhibit a range of 0 ? ?18O ? 10 ‰, (mean 6.8‰). The lower lava (3.7 ? ?18O ? 6.4‰; 7 lavas) and a single gabbro (-0.2‰) of the western limb are depleted relative to the mean of +6.8‰ whereas the lower (6.7 ? ?18O ? 8.3‰; 8 samples) and upper lavas (6.9 ? ?18O ? 10.1‰; 7 samples) of the eastern limb are both enriched in 18O compared to the mean of 6.8‰ and the average mantle ?18 value (5.7‰). The depletion in 18O of the western limb may be due to regional thermal metamorphism from the Bonai granite, and may not represent a complementary 18O-depleted oceanic crust as seen in the Phanerozoic. The ?18O of amphibole (1.6 ? ?18O ? 7.3‰) and feldspar (3.8 ? ?18O ? 11.8‰) show a wide range of values with both enrichments and depletions relative to primary igneous ?18O values. Hydrogen isotopes of 22 samples (-80 ? ?D ? -59‰, except for two values of -94.3 and -114.6‰) lie within the Phanerozoic ?D ranges of similar rocks. Hydrogen and oxygen isotopic data indicate that the alteration of the IOG greenstones was due to interaction with 18O-shifted Archean ocean water (0-10‰) whose most depleted calculated oxygen isotope ratio is similar to modern seawater (~0‰). This study compliments the results of other Archean greenstone belts, such as, the Barberton greenstone belt of western South Africa, the Pilbara block of western Australia, the Abitibi belt of Canada and the Isua greenstone belt of Greenland.

Banerjee, S.; Richards, I.; Ferguson, K.; Basu, A. R.; Gregory, R. T.

2009-12-01

325

The Overthrust Belt of Western North America  

SciTech Connect

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

Verrall, P.

1993-02-01

326

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

SciTech Connect

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

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

1991-03-01

327

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

ERIC Educational Resources Information Center

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

Genc, Humeyra

2012-01-01

328

Kinematical structure of the asteroid belt  

NASA Astrophysics Data System (ADS)

The velocity dispersion of asteroids in the main belt is calculated by using their orbital elements. One component of the velocity dispersion perpendicular to the invariable plane shows a definite positive correlation to the asteroid diameter. It is consistent with the fact that the smaller asteroids form the thinner space distribution perpendicular to the invariable plane. The trend is strong for the C-type asteroids and weak for the S-type asteroids. The difference in the space distribution between the C-type steroids and the S-type ones is attributed to the difference in the braking effect on the asteroids with different diameters and specific densities.

Mikami, Takao; Ishida, Keiichi

329

Nonlinear Phase Bunching of Radiation Belt Electrons  

NASA Astrophysics Data System (ADS)

Electrons interacting with strong, coherent waves experience phase bunching and phase trapping, which tend to have strong but oppositely directed effects on the first adiabatic invariant. For VLF waves propagating away from the equator, phase bunching typically causes both energy and pitch angle to systematically decrease, which may help explain storm time radiation belt dropouts. A simple analytical estimate of the changes has long been available, but direct numerical simulations show a distribution of particle behavior. Here refined expressions are given, and compared to direct test particle simulations. The new results still show preferentially directed adiabatic invariant changes but also capture their spread, suggesting a combined diffusion-advection model in velocity space.

Albert, J. M.; Bortnik, J.; Thorne, R. M.

2011-12-01

330

Solar Neutrons and the Earth's Radiation Belts.  

PubMed

The intensity and spectrum of solar neutrons in the vicinity of the earth are calculated on the assumption that the low-energy protons recently detected in balloon and satellite flights are products of solar neutron decay. The solar-neutron flux thus obtained exceeds the global average cosmic-ray neutron leakage above 10 Mev, indicating that it may be an important source of both the inner and outer radiation belts. Neutron measurements in the atmosphere are reviewed and several features of the data are found to be consistent with the estimated solar neutron spectrum. PMID:17752571

Lingenfelter, R E; Flamm, E J

1964-04-17

331

Numerical modeling of fold-and-thrust belts: Applications to Kuqa foreland fold belt, China  

NASA Astrophysics Data System (ADS)

We constructed discrete element models to simulate the evolution of fold-and-thrust belts. The impact of rock competence and decollement strength on the geometric pattern and deformation mechanics of fold-and-thrust belts has been investigated. The models reproduced some characteristic features of fold-and-thrust belts, such as faulted detachment folds, pop-ups, far-traveled thrust sheets, passive-roof duplexes, and back thrusts. In general, deformation propagates farther above a weak decollement than above a strong decollement. Our model results confirm that fold-and-thrust belts with strong frictional decollements develop relatively steep and narrow wedges formed by closely spaced imbricate thrust slices, whereas fold belts with weak decollements form wide low-taper wedges composed of faulted detachment folds, pop-ups, and back thrusts. Far-traveled thrust sheets and passive-roof duplexes are observed in the model with a strong lower decollement and a weak upper detachment. Model results also indicate that the thickness of the weak layer is critical. If it is thick enough, it acts as a ductile layer that is able to flow under differential stress, which helps to partition deformation above and below it. The discrete element modeling results were used to interpret the evolution of Kuqa Cenozoic fold-and-thrust belt along northern Tarim basin, China. Seismic and well data show that the widely distributed Paleogene rock salt has a significant impact on the deformation in this area. Structures beneath salt are closely spaced imbricate thrust and passive-roof duplex systems. Deformation above salt propagates much farther than below the salt. Faults above salt are relatively wide spaced. A huge controversy over the Kuqa fold-and-thrust belt is whether it is thin-skinned or thick-skinned. With the insights from DEM results, we suggest that Kuqa structures are mostly thin-skinned with Paleogene salt as decollement, except for the rear part near the backstop, where the faults below the salt are thick-skinned and involve the Paleozoic basement. We think that most basement-involved sub-salt faults, if not all, formed later than the above salt-detached thin-skinned structures.

Yin, H.; Morgan, J. K.; Zhang, J.; Wang, Z.

2009-12-01

332

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

Code of Federal Regulations, 2010 CFR

... 2010-07-01 false Test for flame resistance of conveyor belts. 14...PRODUCTS REQUIREMENTS FOR THE APPROVAL OF FLAME-RESISTANT CONVEYOR BELTS Technical Requirements § 14.22 Test for flame resistance of conveyor belts....

2010-07-01

333

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

Code of Federal Regulations, 2010 CFR

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

2009-07-01

334

49 CFR 571.210 - Standard No. 210; Seat belt assembly anchorages.  

Code of Federal Regulations, 2011 CFR

...Definitions. School bus torso belt adjusted height means the vertical height above the seating reference point (SgRP) of...located 25 mm to 75 mm forward of the torso belt height adjuster device, when the torso belt...

2011-10-01

335

49 CFR 571.210 - Standard No. 210; Seat belt assembly anchorages.  

Code of Federal Regulations, 2010 CFR

...false Standard No. 210; Seat belt assembly anchorages. 571.210 Section 571...210 Standard No. 210; Seat belt assembly anchorages. S1. Purpose and scope...establishes requirements for seat belt assembly anchorages to insure their proper...

2010-10-01

336

49 CFR 571.210 - Standard No. 210; Seat belt assembly anchorages.  

Code of Federal Regulations, 2010 CFR

...false Standard No. 210; Seat belt assembly anchorages. 571.210 Section 571...210 Standard No. 210; Seat belt assembly anchorages. S1. Purpose and scope...establishes requirements for seat belt assembly anchorages to insure their proper...

2009-10-01

337

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

Code of Federal Regulations, 2013 CFR

...2013-01-01 false Seats, berths, litters, safety belts, and shoulder harnesses...Accommodations § 23.785 Seats, berths, litters, safety belts, and shoulder harnesses...airplanes must consist of a seat, a safety belt, and a shoulder...

2013-01-01

338

77 FR 20550 - Uniform Criteria for State Observational Surveys of Seat Belt Use  

Federal Register 2010, 2011, 2012, 2013

...for State Observational Surveys of Seat Belt Use AGENCY: National Highway Traffic...for State Observational Surveys of Seat Belt Use. With this change, States may...for State Observational Surveys of Seat Belt Use.'' 76 FR 18042. That...

2012-04-05

339

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

Code of Federal Regulations, 2013 CFR

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

2013-04-01

340

49 CFR 571.210 - Standard No. 210; Seat belt assembly anchorages.  

Code of Federal Regulations, 2012 CFR

...2012-10-01 false Standard No. 210; Seat belt assembly anchorages. 571.210...571.210 Standard No. 210; Seat belt assembly anchorages. S1. Purpose...standard establishes requirements for seat belt assembly anchorages to insure...

2012-10-01

341

30 CFR 56.14130 - Roll-over protective structures (ROPS) and seat belts.  

Code of Federal Regulations, 2013 CFR

...protective structures (ROPS) and seat belts. 56.14130 Section 56.14130...protective structures (ROPS) and seat belts. (a) Equipment included. ...protective structures (ROPS) and seat belts shall be installed onâ...

2013-07-01

342

14 CFR 25.785 - Seats, berths, safety belts, and harnesses.  

Code of Federal Regulations, 2013 CFR

... 2013-01-01 false Seats, berths, safety belts, and harnesses. 25...Accommodations § 25.785 Seats, berths, safety belts, and harnesses. (a...reactions among the occupant, seat, safety belt, and harness for each...

2013-01-01

343

14 CFR 121.311 - Seats, safety belts, and shoulder harnesses.  

Code of Federal Regulations, 2013 CFR

... 2013-01-01 false Seats, safety belts, and shoulder harnesses...Requirements § 121.311 Seats, safety belts, and shoulder harnesses... (i) At each unoccupied seat, the safety belt and shoulder harness,...

2013-01-01

344

23 CFR 1340.10 - Submission and approval of seat belt survey design.  

Code of Federal Regulations, 2013 CFR

...false Submission and approval of seat belt survey design. 1340.10 Section...FOR STATE OBSERVATIONAL SURVEYS OF SEAT BELT USE Administrative Requirements...10 Submission and approval of seat belt survey design. (a)...

2013-04-01

345

Noble metal abundances in an Early Archean impact deposit.  

PubMed

We report detailed analyses on the concentrations of the noble metals Pd, Os, Ir, Pt, and Au in an early Archean spherule bed (S4) of probable impact origin from the lower Fig Tree Group, Barberton Greenstone Belt, South Africa. Compared to other sedimentary deposits of known or suspected impact origin, some noble metals are present in exceptionally high concentrations. Noble metal abundances are fractionated relative to abundances in chondrites with ratios of Os/Ir, Pt/Ir, Pd/Ir, and Au/Ir at only 80, 80, 41, and 2% of these values in CI chondrites. Although an extraterrestrial source is favored for the noble metal enrichment, the most plausible cause of the fractionation is by regional hydrothermal/metasomatic alteration. PMID:11537203

Kyte, F T; Zhou, L; Lowe, D R

1992-01-01

346

Geological and geochemical record of 3400-million-year-old terrestrial meteorite impacts  

SciTech Connect

Beds of sand-sized spherules in the 3400-million-year-old Fig Tree Group, Barberton Greenstone belt, South Africa, were formed by the fall of quenched liquid silicate droplets into a range of shallow- to deep-water depositional environments. The regional extent of the layers, their compositional complexity, and lack of included volcanic debris suggest that they are not products of volcanic activity. The layers are greatly enriched in iridium and other platinum group elements in roughly chondritic proportions. Geochemical modeling based on immobile element abundances suggests that the original average spherule composition can be approximated by a mixture of fractionated tholeiitic basalt, komatiite, and CI carbonaceous chondrite. The spherules are thought to be the products of large meteorite impacts on the Archean earth. 21 refs., 4 figs., 1 tab.

Lowe, D.R. (Stanford Univ., CA (USA)); Byerly, G.R. (Louisiana State Univ., Baton Rouge (USA)); Asaro, F. (Lawrence Berkeley Lab., CA (USA)); Kyte, F.T. (Univ. of California, Los Angeles (USA))

1989-09-01

347

Geological and geochemical record of 3400-million-year-old terrestrial meteorite impacts.  

PubMed

Beds of sand-sized spherules in the 3400-million-year-old Fig Tree Group, Barberton Greenstone belt, South Africa, formed by the fall of quenched liquid silicate droplets into a range of shallow-to deep-water depositional environments. The regional extent of the layers, their compositional complexity, and lack of included volcanic debris suggest that they are not products of volcanic activity. The layers are greatly enriched in iridium and other platinum group elements in roughly chondritic proportions. Geochemical modeling based on immobile element abundances suggests that the original average spherule composition can be approximated by a mixture of fractionated tholeiitic basalt, komatiite, and CI carbonaceous chondrite. The spherules are thought to be the products of large meteorite impacts on the Archean earth. PMID:17780536

Lowe, D R; Byerly, G R; Asaro, F; Kyte, F J

1989-09-01

348

Orbit dynamics of the Kuiper Belt Objects  

NASA Astrophysics Data System (ADS)

A new subject of the solar system dynamics, the orbit dynamics of the Kuiper Belt Objects, is reviewed in this paper. Early studies were connected with the origin of short-period comets. After the first Kuiper Belt Object (KBO) was found, attentions are turned on the phase space structure of the resonant KBOs. Morbidelli and Malhotra adopted different models to study the sizes of the resonance regions, espically the 3:2 mean motion resonance which Pluto is in. For its orbital characters, Pluto should be called a large KBO. There are other two resonances in its motion, the Kozai resonance and 1:1 super resonance. It is because of these resonances that Pluto keeps its orbital stability. Observations show that lots of KBOs are in mean motion resonances with Neptune. In some early theories, these resonances were thought to be caused by catastrophic events such as collision, which can not explain the resonances well for their small probability. Malhotra proposed that Pluto was swept into the 3:2 resonance by planets migration, which happened very easily in the early stage of the solar system. This theory can also explain the resonance formation of KBO successfully.

Wan, Xiaosheng; Huang, Tianyi

2002-12-01

349

Seat belt utilisation and awareness in UAE.  

PubMed

Seat belts (SBs) are effective devices for reducing injury risk due to traffic accidents. Seat belt wearing was made compulsory in the United Arab Emirates (UAE) in January 1999 for drivers and front seat passengers (FSPs). No comprehensive study has ever assessed SB wearing rates across the country. Also, little is known on drivers' awareness of the importance of wearing seatbelts and how human factors affect wearing habits. This study aims to determine SB wearing rates for drivers and FSPs in UAE through an observational field study. It also aims to investigate perceptions and behaviour of drivers on this issue as well as human factors that affect wearing rate through a randomly distributed questionnaire. The results of the field study show that the overall SB wearing rate across the country was 61% for drivers and 43.4% for FSPs and that there were significant differences between the seven emirates that constitute the country. The questionnaire results show that age, education level, gender, marital status and nationality of drivers affect wearing habits and perceptions. Future implications in terms of improving traffic safety awareness are discussed. PMID:23163241

Bendak, S; Al-Saleh, K

2012-11-19

350

Cretaceous biostratigraphy in the Wyoming thrust belt  

SciTech Connect

Biostratigraphy is essential to exploration for oil and gas in the Wyoming thrust belt because fossils provide a temporal framework for interpretation of events of faulting, erosion, sedimentation, and the development of hydrocarbon traps and migration pathways. In the Cretaceous section, fossils are especially useful for dating and correlating repetitive facies of different ages in structurally complex terrain. The biostratigraphic zonation for the region is based on megafossils (chiefly ammonites), which permit accurate dating and correlation of outcrop sections, and which have been calibrated with the radiometric time scale for the Western Interior. Molluscan and vertebrate zone fossils are difficult to obtain from the subsurface, however, and ammonities are restricted to rocks of margin origin. Palynomorphs (plant microfossils) have proven to be the most valuable fossils in investigations of stratigraphy and structures in the subsurface of the thrust belt because palynomorphs can be recovered from drill cuttings. Palynomorphs also are found in both marine and nonmarine rocks and can be used for correlation between facies. In this paper, stratigraphic ranges of selected Cretaceous marine and nonmarine palynomorphs in previously designated reference sections in Fossil Basin, Wyoming, are correlated with the occurrence of ammonities and other zone fossils in the same sections. These correlations can be related to known isotopic ages, and they contribute to the calibration of palynomorph ranges in the Cretaceous of the Western Interior.

Nichols, D.J. (U.S. Geological Survey, Denver, CO); Jacobson, S.R.

1982-07-01

351

Exploration for uranium deposits, Grants mineral belt  

SciTech Connect

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

Fitch, D.C.

1980-01-01

352

Kuiper Belt Objects Along the Pluto-Express Path.  

National Technical Information Service (NTIS)

The science objective of this work is to identify objects in the Kuiper Belt which will, in the 5 years following Pluto encounter, be close to the flight path of NASA's Pluto Express. Our hope is that we will find a Kuiper Belt object or objects close eno...

D. Jewitt

1997-01-01

353

Does a pelvic belt influence sacroiliac joint laxity?  

Microsoft Academic Search

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

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

2002-01-01

354

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

355

Dewatering of Coal Fines with Vacuum Belt Filter Installations.  

National Technical Information Service (NTIS)

It is reported about operation results of the primary use of a vacuum belt filter in coal mining to dewater flotation concentrate. A high availability, accessibility and good servicing were achieved. The belt filter can be adapted to varying conditions of...

1982-01-01

356

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

Bhaskar, Anand; Subramani, Selvam; Ojha, Rajdeep

2013-01-01

357

Failure of plastic press release buttons in automobile seat belts  

Microsoft Academic Search

In the late 1980s and early 1990s Honda, Nissan, Mitsubishi, Mazda, Suzuki, Subaru, Isuzu and Daihatsu and other automobile manufacturers modified their restraint system seat belt buckle assemblies in several models of vehicles. These automobile manufacturers incorporated plastic seat belt buckle assemblies manufactured by Takata Corporation as the 52 and A7 model series [National Highway Transportation Safety Administration (NHTSA), 1997,

Russell F. Dunn; Richard H. McSwain; Terry Mills; Brian Malone

2005-01-01

358

An Adaptive Modeling Method for a Robot Belt Grinding Process  

Microsoft Academic Search

A robot belt grinding system has a good prospect for releasing hand grinders from their dirty and noisy work environment. However, as a kind of manufacturing system with a flexible grinder, it is a challenge to model its processes and control grinding removal precisely for free-formed surfaces. In the belt grinding process, material removal is related to a variety of

Song Yixu; Lv Hongbo; Yang Zehong

2012-01-01

359

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

360

Ingress Clearance Requirements and Seat Positioning for Automatic Belt Systems.  

National Technical Information Service (NTIS)

The purposes of this study were (1) to determine how much clearance between a seat belt and seat cushion is needed for a driver to enter the front seat of an automobile equipped with automatic seat belts---without his/her having to lift the webbing, and (...

W. E. Woodson P. H. Selby

1981-01-01

361

DYNAMIC SIMULATION AND CONTROL OF CONVEYOR-BELT DRYERS  

Microsoft Academic Search

The dynamic behavior of conveyor-belt dryers involving externally controlled heat and mass transfer phenomena has been studied via digital simulation. The investigation concerned an industrial dryer used for the moisture removal from wet raisins. The dryer consisted of three drying chambers and a cooling section, all involving the same conveyor belt. For each chamber, perfect temperature control was assumed for

C. T. Kiranoudis; Z. B. Maroulis; D. Marinos-Kouris

1994-01-01

362

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...

363

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 ...

364

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

365

Response of the North American Corn Belt to Climatic Warming.  

National Technical Information Service (NTIS)

The climate of the North American corn belt was characterized as part of an effort to estimate the effects of climatic change on that agricultural region. Heat and moisture characteristics of the current corn belt were first identified. Locations of those...

T. J. Blasing A. M. Solomon

1983-01-01

366

Effectiveness of Automatic Shoulder Belt Systems in Motor Vehicle Crashes  

Microsoft Academic Search

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

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

2000-01-01

367

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

368

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

369

Research Says "No" to School Bus Seat Belts.  

ERIC Educational Resources Information Center

Presents factual data on research in school bus safety that shows that seat belts in school buses may actually be detrimental to students. Includes data from surveys and research tests and sources for additional information on seat belts in school buses. (MD)

Wineland, Charles L.

1986-01-01

370

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

371

Seat Belt Injuries of the Breast: Findingson Mammographyand Sonography  

Microsoft Academic Search

OBJECTIVE. The purpose of this study was to determine the mammographic and sonographic findings of injuries of the breast caused by seat belts in automobile acci- dents. The imaging findings of such injuries must be differentiated from those of car- cinoma, so that inappropriate treatment is avoided. MATERIALS AND METHODS. Five patients who had breast injuries caused by seat belts

Pamela J. DiPiro; Jack E. Meyer; Thomas H. Fnenna; Christine M. Denison

372

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…

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

2006-01-01

373

Discovery of a transient radiation belt at Saturn  

Microsoft Academic Search

Radiation belts have been detected in situ at five planets. Only at Earth however has any variability in their intensity been heretofore observed, in indirect response to solar eruptions and high altitude nuclear explosions. The Cassini spacecraft's MIMI\\/LEMMS instrument has now detected systematic radiation belt variability elsewhere. We report three sudden increases in energetic ion intensity around Saturn, in the

E. Roussos; N. Krupp; T. P. Armstrong; C. Paranicas; D. G. Mitchell; S. M. Krimigis; G. H. Jones; K. Dialynas; N. Sergis; D. C. Hamilton

2008-01-01

374

A Novel Approach to Vibration Reduction in Flexible Belt Drives  

Microsoft Academic Search

. This paper presents a novel method to compensate the effects of flexibilityin belt-driven drive trains. Such drives are found in robot manipulators, forexample, where drive flexibility is undesirable. Unfortunately, the effects of flexibilitycan be difficult to compensate using the primary actuator, due to bandwidth limitations.By introducing a second actuator, which applies a force to the belt at a pointbetween

Robert B. Gorbet; Scott A. Bortoff

375

Biomechanical considerations for abdominal loading by seat belt pretensioners.  

PubMed

While seat belts are the most effective safety technology in vehicles today, there are continual efforts in the industry to improve their ability to reduce the risk of injury. In this paper, seat belt pretensioners and current trends towards more powerful systems were reviewed and analyzed. These more powerful systems may be, among other things, systems that develop higher belt forces, systems that remove slack from belt webbing at higher retraction speeds, or both. The analysis started with validation of the Ford Human Body Finite Element Model for use in evaluation of abdominal belt loading by pretensioners. The model was then used to show that those studies, done with lap-only belts, can be used to establish injury metrics for tests done with lap-shoulder belts. Then, previously-performed PMHS studies were used to develop AIS 2+ and AIS 3+ injury risk curves for abdominal interaction with seat belts via logistic regression and reliability analysis with interval censoring. Finally, some considerations were developed for a possible laboratory test to evaluate higher-powered pretensioners. PMID:21512915

Rouhana, Stephen W; El-Jawahri, Raed E; Laituri, Tony R

2010-11-01

376

The effects of standard enforcement on Michigan safety belt use  

Microsoft Academic Search

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

David W Eby; Jonathon M Vivoda; Tiffani A Fordyce

2002-01-01

377

Belt Use in Serious Impacts Estimated from Fatality Data.  

National Technical Information Service (NTIS)

Drivers in fatal crashes were less frequently reported (by the police) to have been using their safety belts if the driver was reported to have been exceeding the speed limit, to have been drinking, or to have had previous crashes. Reported belt use was a...

S. C. Partyka

1989-01-01

378

Compositional variations in the Mesoarchean chromites of the Nuggihalli schist belt, Western Dharwar Craton (India): potential parental melts and implications for tectonic setting  

NASA Astrophysics Data System (ADS)

The chromite deposits in the Archean Nuggihalli schist belt are part of a layered ultramafic-mafic sequence within the Western Dharwar Craton of the Indian shield. The 3.1-Ga ultramafic-mafic units occur as sill-like intrusions within the volcano-sedimentary sequences of the Nuggihalli greenstone belt that are surrounded by the tonalite-trondhjemite-granodiorite (TTG) suite of rocks. The entire succession is exposed in the Tagdur mining district. The succession has been divided into the lower and the upper ultramafic units, separated by a middle gabbro unit. The ultramafic units comprise of deformed massive chromitite bodies that are hosted within chromite-bearing serpentinites. The chromitite bodies occur in the form of pods and elongated lenses (~60-500 m by ~15 m). Detailed electron microprobe studies reveal intense compositional variability of the chromite grains in silicate-rich chromitite (~50% modal chromite) and serpentinite (~2% modal chromite) throughout the entire ultramafic sequence. However, the primary composition of chromite is preserved in the massive chromitites (~60-75% modal chromite) from the Byrapur and the Bhaktarhalli mining district of the Nuggihalli schist belt. These are characterized by high Cr-ratios (Cr/(Cr + Al) = 0.78-0.86) and moderate Mg-ratios (Mg/(Mg + Fe2+) = 0.38-0.58). The compositional variability occurs due to sub-solidus re-equilibration in the accessory chromite in the serpentinite (Mg-ratio = 0.01-0.38; Cr-ratio = 0.02-0.99) and in silicate-rich chromitite (Mg-ratio = 0.06-0.48; Cr-ratio = 0.60-0.99). In the massive chromitites, the sub-solidus re-equilibration for chromite is less or absent. However, the re-equilibration is prominent in the co-existing interstitial and included olivine (Fo96-98) and pyroxene grains (Mg-numbers = 97-99). Compositional variability on the scale of a single chromite grain occurs in the form of zoning, and it is common in the accessory chromite grains in serpentinite and in the altered grains in chromitite. In the zoned grains, the composition of the core is modified and the rim is ferritchromit. In general, ferritchromit occurs as irregular patches along the grain boundaries and fractures of the zoned grains. In this case, ferritchromit formation is not very extensive. This indicates a secondary low temperature hydrothermal origin of ferritchromit during serpentinization. In some occurrences, the ferritchromit rim is very well developed, and only a small relict core appears to remain in the chromite grain. However, complete alteration of the chromite grains to ferritchromit without any remnant core is also present. The regular, well-developed and continuous occurrence of ferritchromit rims around the chromite grain boundaries, the complete alteration of the chromite grains and the modification of the core composition indicate the alteration in the Nuggihalli schist belt to be intense, pervasive and affected by later low-grade metamorphism. The primary composition of chromite has been used to compute the nature of the parental melt. The parental melt calculations indicate derivation from a high-Mg komatiitic basalt that is similar to the composition of the komatiitic rocks reported from the greenstone sequences of the Western Dharwar Craton. Tectonic discrimination diagrams using the primary composition of chromites indicate a supra-subduction zone setting (SSZ) for the Archean chromitites of Nuggihalli and derivation from a boninitic magma. The composition of the komatiitic basalts resembles those of boninites that occur in subduction zones and back-arc rift settings. Formation of the massive chromitites in Nuggihalli may be due to magma mixing process involving hydrous high-Mg magmas or may be related to intrusions of chromite crystal laden magma; however, there is little scope to test these models because the host rocks are highly altered, serpentinized and deformed. The present configurations of the chromitite bodies are related to the multistage deformation processes that are common in Archean greenstone belts.

Mukherjee, Ria; Mondal, Sisir K.; Rosing, Minik T.; Frei, Robert

2010-12-01

379

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

380

Late orogenic extension in mountain belts: Insights from the basin and range and the late paleozoic Variscan belt  

Microsoft Academic Search

From two examples of orogenic domains, some general mechanisms significant of late orogenic tectonic processes in mountain belts are characterized. The Basin and Range province and the Variscan belt in the French Massif Central have both suffered important compressional orogenic crustal thickening, and the results of late orogenic processes can be observed in the field. Both areas are covered by

Jacques Malavieille

1993-01-01

381

Late Orogenic extension in mountain belts: Insights from the basin and range and the Late Paleozoic Variscan Belt  

Microsoft Academic Search

From two examples of orogenic domains, some general mechanisms significant of late orogenic tectonic processes in mountain belts are characterized. The Basin and Range province and the Variscan belt in the French Massif Central have both suffered important compressional orogenic crustal thickening, and the results of late orogenic processes can be observed in the field. Both areas are covered by

Jacques Malavieille

1993-01-01

382

Safety knowledge of users and non-users of the lap belt on two-point motorized belt systems  

Microsoft Academic Search

A field study of 1146 drivers and passengers of vehicles equipped with motorized passive belts was conducted in shopping malls and other locations in the states of Arizona and Indiana. The Indiana data was collected the summer of 1994 and the Arizona data the summer of 1995. Shoulder belt use by drivers and passengers was 93.4% in Indiana and 87.8%

Mark R. Lehto; Dwayne S. James

1997-01-01

383

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

ERIC Educational Resources Information Center

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

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

1988-01-01

384

Simulation of radiation belt electron diffusion  

NASA Astrophysics Data System (ADS)

This thesis presents theoretical and numerical studies of the radial diffusion of relativistic radiation belt electrons. The research has been focused particularly on the radiation belt phase space density profile, and radial diffusion due to particle drift resonance with ULF waves. Observations have shown a strong connection between magnetospheric ULF oscillations and electron flux enhancements. I investigate radial diffusion coefficients based on theoretical analysis of particle diffusion in ULF perturbation electric and magnetic fields. The analytical diffusion coefficients consist of two terms: a symmetric term and an asymmetric term. The symmetric term agrees with earlier works, and the asymmetric terms are new. Both terms show good agreement with numerical test particle simulations. The asymmetric terms have higher L dependence, which indicates they might be more important at higher L -shells or at times when the magnetospheric field is highly asymmetric. A numerical radial diffusion model has been developed which can take into account: dynamic boundary locations and values, plus effects of losses and sources. Several test cases are considered to study the effects of different diffusion coefficients, internal sources, external sources, and loss. A method of converting observational particle flux to phase space density is also presented. Identifying the source and loss processes using observational data is currently one of the key issues for understanding and modeling radiation belt dynamics. We present a new measurement technique which utilizes two GOES satellites located at different local times to calculate the radial gradient of phase space density at geostationary locations. The result shows positive gradient at geomagnetic quiet periods. To further study the high energy electron transport, especially the ULF related acceleration during storm times, I use the numerical radial diffusion model for the September 24-26, 1998 storm and compare the results with an MHD test particle simulation. The diffusion result using ULF-wave diffusion coefficients and a time-dependent outer-boundary condition can reproduce the main features of the MHD-particle results quite well. Using wave driven diffusion coefficients gives better results than using power law or Kp -dependent diffusion coefficients.

Fei, Yue

2007-02-01

385

[Seat belt syndrome. Acute spinal cord injury due to incorrect use of two-point seat belts].  

PubMed

Traumatic spinal cord injury (SCI) is a rare entity in the pediatric age group. These injuries are mainly caused by road traffic accidents (RTA), especially in children not wearing a seat belt. The use of child safety devices such as seat belt restraints has decreased morbidity and mortality in RTA but their incorrect use can also produce serious injuries that are grouped under the term "seat-belt syndrome". This syndrome associates vertebral and spinal cord injuries, intra-abdominal, cutaneous, and muscle-skeletal lesions. We present three patients with complete spinal cord and intra-abdominal injuries, requiring urgent surgery in two of them. On examination, all three patients had seat belt marks on the lower abdominal region. The three patients can be included in this syndrome and its main cause was the use of a two-point seat belt. PMID:17266855

Gargallo Burriel, E; Palomeque Rico, A; Claret Teruel, G; Pons Odena, M; Cambra Lasaosa, F J

2007-01-01

386

Preservation of modern and ancient microbial ichnofossils in basaltic glass by titanite mineralization  

NASA Astrophysics Data System (ADS)

Subaqueous volcanic rocks are a relatively new setting in the search for early life on Earth but recent studies have demonstrated that submarine basaltic glass in pillow rims and hyaloclastites are suitable microbial habitats. Microbes rapidly colonize the glassy surfaces along fractures and cracks that have been exposed to water producing characteristic granular and/or tubular bioalteration structures. The minerals within these structures have been investigated using micro X-ray diffraction that confirms early formation of titanite and other mineral phases associated with microbial alteration structures in modern basaltic glass. Incipient titanite formation in modern samples implies that mineralization of these trace fossils is penecontemporaneous with bioalteration. The early precipitation of sub-micron titanite grains within the biologically etched alteration structures serves as an agent for preservation that may persist for geologically extended periods of time in the absence of later penetrative deformation. Titanite-mineralized microbial alteration structures have been observed in several Archean greenstone belts including the Abitibi greenstone belt (2.7 Ga), Pilbara craton (3.35 Ga), and the Barberton greenstone belt (3.5 Ga). The ubiquity of these bioalteration structures and their relative durability compared with many other purported trace fossils makes them attractive as a biomarker for Archean Earth and, potentially, Mars. Basaltic rocks are commonplace on Mars and could have easily come into contact with water in the past. Archean subaqueous volcanic rocks thus provide an excellent analogue for studies addressing the presence of early life on Mars and the potential for the preservation of traces of microbial life in the Martian crust.

Izawa, M. R.; Bridge, N. J.; Banerjee, N. R.; Flemming, R. L.; Mueller, W.; Muehlenbachs, K.; Chacko, T.

2008-12-01

387

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 SiO 2 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

388

The Foundations of Radiation Belt Research  

NASA Astrophysics Data System (ADS)

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

Ludwig, G. H.

2008-12-01

389

The Compositional Classes of the Kuiper Belt  

NASA Astrophysics Data System (ADS)

Here we present the observations of the centaurs and low-perihelion Kuiper belt objects targeted by the H/WTSOSS survey. With the multi-colour spectrophotometry, we show how the surfaces of Centaurs clearly divide into two unique compositional classes, each of which exhibits correlated optical and NIR colours. We show how this bifurcation continues into low-perihelia scattered disk and resonant objects. We discuss possible causes of the observed colours and show how the colours are best explained by an intimate mixture of a neutral and red component, the neutral component of which is common between both classes. Using the presented observations along with available albedos measurements, we constrain possible candidate materials for the neutral component. Likely candidates include silicate materials observed on the irregular satellites of the gas-giants and the Jupiter Trojans.

Fraser, W. C.; Brown, M. E.; Batygin, K.

2011-10-01

390

Locating Planetesimal Belts in Planetary Systems  

NASA Astrophysics Data System (ADS)

Debris disks are disks of dust that surround a significant fraction of stars of a wide range of masses and ages. From dust lifetime arguments it is inferred that these dust particles originate from the collision/sublimation of planetesimals, similar to the asteroids, comets and KBOs in our Solar system. Therefore, the presence of debris disk around planet-bearing stars indicate that these stars also harbor planetary systems composed of planets and planetesimals belts. We use Spitzer and new Herschel data to set constraints on the location of these dust-producing planetesimals; we use a radiative transfer model to analyze the spectral energy distributions and images of the dust disks, and a dynamical model to assess the long-term stability of the planetesimals’ orbits. With the new Herschel data, we revisit the question on whether or not debris disks and planets are correlated. These studies can help us learn about the diversity of planetary systems.

Moro-Martin, Amaya

2011-09-01

391

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

392

A physical model for electron radiation belts of Saturn  

NASA Astrophysics Data System (ADS)

Radiation belts cause irreversible damages to on-board instrument materials. Studies about radiation belts can provide precious information for future interplanetary missions. Pioneer 11, Voyager 2 and nowadays Cassini missions give the characteristics of Saturn's inner magnetosphere: Saturn's famous rings, various moons, neutral particles ejected from Enceladus and waves. Thanks to its experience with the Earth's and Jupiter's radiation belt studies, ONERA is now able to develop an electron radiation belt model for Saturn's environment, i.e., a new version of Salammbô. The study of Saturn's inner magnetosphere emphasizes the most important physical processes governing radiation belt dynamics: electrons losses due to dense rings are the dominant physical process near the planet (L < 2.3). For high energies (E > ˜50 keV), radial diffusion and local losses due to the moons are predominant from L = 2.3 to the boundary condition (L = 6). The analysis of spacecraft in situ data (Pioneer 11, Voyager 2, and Cassini) allows a boundary condition to be built for the model and the Salammbô results to be validated. The Salammbô Kronian model has also been compared to the empirical radiation belt model SATRAD (for SATurn RADiation model) based on Pioneer 11 and Voyager 2 data. Comparisons of Salammbô results with in situ data and SATRAD confirm that Salammbô is a good mean model for Saturn electron radiation belts, for energies from about a hundred keV to a few MeV.

Lorenzato, Lise; Sicard, AngéLica; Bourdarie, SéBastien

2012-08-01

393

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

394

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

395

The Effects of Mandatory Seat Belt Laws on Driving Behavior and Traffic Fatalities  

Microsoft Academic Search

This paper investigates the effects of mandatory seat belt laws on driver behavior and trafé c fatalities. Using a unique panel data set on seat belt usage in all U.S. jurisdictions, we analyze how such laws, by inè uencing seat belt use, affect the incidence of trafé c fatalities.Allowing for the endogeneity of seat belt usage, we é nd that

Alma Cohen; Liran Einav

2001-01-01

396

The Effects of Mandatory Seat Belt Laws on Driving Behavior and Traffic Fatalities  

Microsoft Academic Search

This paper investigates the effects of mandatory seat belt laws on driver behavior and traffic fatalities. Using a unique panel data set on seat belt usage in all U.S. jurisdictions, we analyze how such laws, by influencing seat belt use, affect the incidence of traffic fatalities. Allowing for the endogeneity of seat belt usage, we find that such usage decreases

Alma Cohen; Liran Einav

2003-01-01

397

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

398

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.

399

Design Study of Flat Belt CVT for Electric Vehicles.  

National Technical Information Service (NTIS)

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

E. L. Kumm

1980-01-01

400

"Abomination"--life as a Bible belt gay.  

PubMed

Drawing on observation, autoethnography, and audio-taped interviews, this article explores the religious backgrounds and experiences of Bible Belt gays. In the Bible Belt, Christianity is not confined to Sunday worship. Christian crosses, messages, paraphernalia, music, news, and attitudes permeate everyday settings. Consequently, Christian fundamentalist dogma about homosexuality-that homosexuals are bad, diseased, perverse, sinful, other, and inferior-is cumulatively bolstered within a variety of other social institutions and environments in the Bible Belt. Of the 46 lesbians and gay men interviewed for this study (age 18-74 years), most describe living through spirit-crushing experiences of isolation, abuse, and self-loathing. This article argues that the geographic region of the Bible Belt intersects with religious-based homophobia. Informants explained that negative social attitudes about homosexuality caused a range of harmful consequences in their lives including the fear of going to hell, depression, low self-esteem, and feelings of worthlessness. PMID:20391006

Barton, Bernadette

2010-01-01

401

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

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

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

402

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

403

Promoting the use of seat belts. Wessex Positive Health Team.  

PubMed

A six-month study into the effect of a substantial programme of integrated health education promoting the use of seat belts showed no major change in the rates for occupants of front seats, which remained around 35%. Though there were increases of up to 5% in the rates for wearing seat belts immediately after the multimedia campaigns which achieved high penetration, only those among women drivers were sustained. Of the methods used to disseminate information, television had the greatest impact on the community, followed by press reports and radio broadcasts. It is concluded that health education alone is insufficient to increase significantly the use of car seat belts. Britain should follow its European partners and pass legislation requiring front seat occupants to wear belts. As the recent experience in Australia shows, the benefits will be considerable in terms of reducing mortality, morbidity, and consequential expenditure. PMID:7437832

1980-11-29

404

46 CFR 111.105-27 - Belt drives.  

Code of Federal Regulations, 2012 CFR

...105-27 Section 111.105-27 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) ELECTRICAL ENGINEERING ELECTRIC SYSTEMS-GENERAL REQUIREMENTS Hazardous Locations § 111.105-27 Belt drives. Each...

2012-10-01

405

30 CFR 75.350 - Belt air course ventilation.  

Code of Federal Regulations, 2010 CFR

...specific mine conditions. Air velocities must be compatible with all fire detection systems and fire suppression systems used... (b) The use of air from a belt air course...be met: (1) The air current that will pass...

2009-07-01

406

30 CFR 75.350 - Belt air course ventilation.  

Code of Federal Regulations, 2013 CFR

...specific mine conditions. Air velocities must be compatible with all fire detection systems and fire suppression systems used... (b) The use of air from a belt air course...be met: (1) The air current that will pass...

2013-07-01

407

30 CFR 75.350 - Belt air course ventilation.  

Code of Federal Regulations, 2010 CFR

...specific mine conditions. Air velocities must be compatible with all fire detection systems and fire suppression systems used... (b) The use of air from a belt air course...be met: (1) The air current that will pass...

2010-07-01

408

29 CFR 1926.104 - Safety belts, lifelines, and lanyards.  

Code of Federal Regulations, 2013 CFR

...2013-07-01 2013-07-01 false Safety belts, lifelines, and lanyards...Relating to Labor (Continued) OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR (CONTINUED) SAFETY AND HEALTH REGULATIONS FOR...

2013-07-01

409

30 CFR 57.15005 - Safety belts and lines.  

Code of Federal Regulations, 2013 CFR

...HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Personal Protection Surface and Underground § 57.15005 Safety belts and lines...shall tend the lifeline when bins, tanks, or other dangerous areas are...

2013-07-01

410

Should Seat Belts Be Required on All School Buses?  

ERIC Educational Resources Information Center

Examines the limited case law involving seat belts for school buses and explores emerging legal issues surrounding use of common law causes of action to challenge school bus safety. (51 footnotes) (MLF)

Mawdsley, Ralph D.

1996-01-01

411

Effects of North Carolina's mandatory safety belt law on children.  

PubMed Central

OBJECTIVES: To assess the effect of the North Carolina law mandating that all front seat passengers use a safety belt on children 4 through 15 years of age. METHODS: North Carolina collision reports, completed by local police or the state highway patrol for crashes with greater than $500 worth of damage, were analyzed using time series analysis on the monthly percentage of deaths and serious injuries between January of 1980 and February of 1994. RESULTS: Following the 1985 implementation of the law, children 4 to 15 years of age experienced a 42% decline in deaths and serious injuries. CONCLUSIONS: The mandatory safety belt law in North Carolina has been associated with a decline in deaths and serious injuries. Additional research in needed to assess the seat belt behaviors of this age group as well as the specific effects of seat belt use using outcome measures more precise than those available in police crash reports.

Margolis, L. H.; Bracken, J.; Stewart, J. R.

1996-01-01

412

The Radiation Belt Storm Probes (RBSP) and Space Weather  

NASA Astrophysics Data System (ADS)

Following the launch and commissioning of NASA's Radiation Belt Storm Probes (RBSP) in 2012, space weather data will be generated and broadcast from the spacecraft in near real-time. The RBSP mission targets one part of the space weather chain: the very high energy electrons and ions magnetically trapped within Earth's radiation belts. The understanding gained by RBSP will enable us to better predict the response of the radiation belts to solar storms in the future, and thereby protect space assets in the near-Earth environment. This chapter details the presently planned RBSP capabilities for generating and broadcasting near real-time space weather data, discusses the data products, the ground stations collecting the data, and the users/models that will incorporate the data into test-beds for radiation belt nowcasting and forecasting.

Kessel, R. L.; Fox, N. J.; Weiss, M.

2012-12-01

413

The Kuiper Belt after 20 years: Past, Present & Future  

NASA Astrophysics Data System (ADS)

I will present an overview of what we have learned about the Kuiper Belt, starting with its discovery 20 years ago to its current state and will speculate about what new discoveries the future may hold.

Schlichting, Hilke

2013-10-01

414

Discovery of a transient radiation belt at Saturn  

NASA Astrophysics Data System (ADS)

Radiation belts have been detected in situ at five planets. Only at Earth however has any variability in their intensity been heretofore observed, in indirect response to solar eruptions and high altitude nuclear explosions. The Cassini spacecraft's MIMI/LEMMS instrument has now detected systematic radiation belt variability elsewhere. We report three sudden increases in energetic ion intensity around Saturn, in the vicinity of the moons Dione and Tethys, each lasting for several weeks, in response to interplanetary events caused by solar eruptions. However, the intensifications, which could create temporary satellite atmospheres at the aforementioned moons, were sharply restricted outside the orbit of Tethys. Unlike Earth, Saturn has almost unchanging inner ion radiation belts: due to Saturn's near-symmetrical magnetic field, Tethys and Dione inhibit inward radial transport of energetic ions, shielding the planet's main, inner radiation belt from solar wind influences.

Roussos, E.; Krupp, N.; Armstrong, T. P.; Paranicas, C.; Mitchell, D. G.; Krimigis, S. M.; Jones, G. H.; Dialynas, K.; Sergis, N.; Hamilton, D. C.

2008-11-01

415

A Physical Model of Electron Radiation Belts of Saturn  

NASA Astrophysics Data System (ADS)

Enrolling on the Cassini age, a physical Salammbô model for the radiation belts of Saturn have been developed including several physical processes governing the kronian magnetosphere. Results have been compared with Cassini MIMI LEMMS data.

Lorenzato, L.; Sicard-Piet, A.; Bourdarie, S.

2012-09-01

416

Discovery of a transient radiation belt at Saturn  

NASA Astrophysics Data System (ADS)

Radiation belts have been detected in situ at five planets. Only at Earth however has any variability in their intensity been heretofore observed, in indirect response to solar eruptions and high altitude nuclear explosions. The Cassini spacecraft's MIMI/LEMMS instrument has now detected systematic radiation belt variability elsewhere. We report three sudden increases in energetic ion intensity around Saturn, in the vicinity of the moons Dione and Tethys, each lasting for several weeks, in response to interplanetary events caused by solar eruptions in the year 2005. However, the intensifications, which could create temporary satellite atmospheres at the aforementioned moons, were sharply restricted outside the orbit of Tethys. Unlike Earth, Saturn has almost unchanging inner ion radiation belts: due to Saturn's near-symmetrical magnetic field, Tethys and Dione inhibit inward radial transport of energetic ions, shielding the planet's main, inner radiation belt from solar wind influences.

Krupp, N.; Roussos, E.; Armstrong, T.; Paranicas, C.; Mitchell, D.; Krimigis, S.; Jones, G. H.; Dialynas, K.; Sergis, N.; Hamilton, D.

2008-12-01

417

30 CFR 75.1108 - Approved conveyor belts.  

Code of Federal Regulations, 2013 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...

2013-07-01

418

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

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

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

419

Lightcurve Analysis of Ten Main-belt Asteroids  

NASA Astrophysics Data System (ADS)

We report lightcurve periods for ten main-belt asteroids observed at the Evelyn L. Egan Observatory: 26 Proserpina, 78 Diana, 242 Kriemhild, 287 Nephthys, 348 May, 368 Haidea, 446 Aeternitas, 872 Holda, 905 Universitas, and 1013 Tombecka.

Fauerbach, Michael; Marks, Scott A.; Lucas, Michael P.

2008-06-01

420

65. Modular bed storage unit, safety belt at left center, ...  

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

65. Modular bed storage unit, safety belt at left center, north side - Ellsworth Air Force Base, Delta Flight, Launch Control Facility, County Road CS23A, North of Exit 127, Interior, Jackson County, SD

421

Destrucción of Binary Systems in the Transneptunain Belt  

NASA Astrophysics Data System (ADS)

We are presenting a statistical study to estimate the efficiency of a mechanism of binary destruction in case of gravitational perturbation from an encounter with a third body. We apply this to equal mass binary systems in the transneptunian belt.

Benavidez, P. G.; Gil-Hutton, R.; Campo Bagatin, A.; López Sisterna, C.; Cañada-Assandri, M.

2012-05-01

422

7. Band Wheel, Showing Cloth Web Belt and Wooden Bearing ...  

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

7. Band Wheel, Showing Cloth Web Belt and Wooden Bearing Blocks, Looking West - David Renfrew Oil Rig, East side of Connoquenessing Creek, 0.4 mile North of confluence with Thorn Creek, Renfrew, Butler County, PA

423

Periumbilical allergic contact dermatitis: blue jeans or belt buckles?  

PubMed

Nickel is the most ubiquitous contact allergen among children and adolescents. Metal blue jeans buttons and belts have been noted to cause nickel dermatitis around the umbilicus. For these children, traditional teaching is strict avoidance of all pants with metal snaps/buttons, particularly blue jeans. In this study we tested 90 pairs of blue jeans and 47 belts for nickel using the dimethylglyoxime spot test. Only 10% of blue jeans tested positive, while 53% of belts tested positive. Furthermore, 10 pairs of nickel-negative blue jeans remained negative after 10 washings. Overall we found no resistance to testing in clothing stores. From these results, we recommend that patients with allergic contact dermatitis secondary to nickel need not strictly avoid blue jeans and metal belt buckles. Rather, families should be encouraged to use the dimethylglyoxime spot test to test these items for nickel prior to purchase. PMID:15165199

Byer, Tara T; Morrell, Dean S

424

3. VIEW TO SOUTH; MAINTENANCE DEPARTMENT BUILDING, BELT DRIVEN MACHINE ...  

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

3. VIEW TO SOUTH; MAINTENANCE DEPARTMENT BUILDING, BELT DRIVEN MACHINE SHOP - Los Angeles Union Passenger Terminal, Maintenance Deptartment Building, 800 North Alameda Street, Los Angeles, Los Angeles County, CA

425

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

426

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

427

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

428

Stochastic modeling of multidimensional diffusion in the radiation belts  

Microsoft Academic Search

A new code for solving radiation belt diffusion equations has been developed and applied to the 2-D bounce-averaged energy pitch angle quasi-linear diffusion equation. The code uses Monte Carlo methods to solve Itô stochastic differential equations (SDEs) which are mathematically equivalent to radiation belt diffusion equations. We show that our SDE code solves the diffusion equation with off-diagonal diffusion coefficients

Xin Tao; Anthony A. Chan; Jay M. Albert; James A. Miller

2008-01-01

429

Seat belts: Relations between beliefs, attitude, and use  

Microsoft Academic Search

A sample of 368 car owners answered a mailed questionnaire constructed on the basis of a model of attitudes toward seat-belt use. A factor analysis yielded a belief pattern interpreted in terms of 5 factors-Discomfort, Worry, Risk, Effect, and Inconvenience. The model appeared useful since an independent measure of attitude to seat-belt use could be predicted (r = .84) from

Gunilla Fhaner; Monica Hane

1974-01-0