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Sample records for barberton greenstone belt

  1. Geology and metallogeny of the Barberton greenstone belt: a survey

    NASA Astrophysics Data System (ADS)

    Ward, J. H. W.

    1995-08-01

    The principal episodes of the geotectonic history of the Barberton greenstone belt span some 400 Ma from the initial submarine eruption of the Onverwacht laves (at about 3500 Ma) to the compression and inversion of the depository as a fold-and-thrust belt between 3230 and 3215 Ma, followed by late-tectonic hydrothermal Au mineralization at about 3100 Ma. The crust beneath the greenstone belt was fortified by sialic underplating due to episodic felsic plutonism at about 3445 Ma, 3227 Ma and 3105 Ma. The main stratigraphic units of the Barberton Supergroup comprise the Onverwacht Group, a thick assortment of ultramafic and mafic volcaulics including a number of sill-like layered ultramafic complexes, which is overlain by the Fig Tree Group of turbiditic greywacke sandstones and associated mudstones and banded ferruginous shales. These strata are, in turn, paraconformably overlain by continentally-derived shallow-water arenites of the Moodies Group. The broader aspects of the deformation of the Barberton depository can be considered in terms of one of two models: either the structures represent a single compressional episode of upright folding accompanied by high-angle thrusting between 3230 and 3215 Ma, or they resulted from an early episode of tectonic stacking, followed by a later event involving the rotation of early thrust slices into upright folds and accompanied by high-angle thrusting. Substantial deposits of chrysotile asbestos, magnesite and talc were developed in the ultramafic host rocks of the Onverwacht Group and important mesothermal deposits of Au were formed in the reactive host rocks belonging to all three Groups in splays adjacent to regionally-developed shear zones. There is still uncertainty as to the primary metallogenic setting of the belt during Onverwacht times and what part accretionary or collage tectonics may or may not have played in the evolution of the Barberton greenstone belt.

  2. Barberton greenstone belt volcanism: Succession, style and petrogenesis

    NASA Astrophysics Data System (ADS)

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

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

    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.

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

    PubMed

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

    1994-03-01

    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

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

    NASA Astrophysics Data System (ADS)

    Lamb, S. H.

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

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

    NASA Astrophysics Data System (ADS)

    Lowe, Donald R.

    1994-12-01

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

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

    NASA Technical Reports Server (NTRS)

    Lowe, D. R.

    1994-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2000-02-01

    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 (δ13Cwhole rock and δ18Owhole 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.

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

    NASA Astrophysics Data System (ADS)

    KröNer, Alfred; Todt, Wolfgang

    1988-12-01

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

  10. The stratigraphy of the 3.5-3.2 Ga Barberton Greenstone Belt revisited: A single zircon ion microprobe study

    NASA Astrophysics Data System (ADS)

    Armstrong, R. A.; Compston, W.; de Wit, M. J.; Williams, I. S.

    1990-11-01

    Recent field and geochemical studies indicate a need to test the stratigraphy of the ca. 3.5 Ga Barberton Greenstone Belt as it is presently adopted [1,2]. This work uses the ion microprobe SHRIMP, to attempt such a test. Results show that: (1) Volcaniclastic sediments of the Theespruit Formation (< 3453 ± 6Ma) could be younger than the (structurally) overlying mafic and ultramafic volcanics of the Komati Formation (3482 ± 5Ma). A major structural discontinuity may therefore exist between the two formations. (2) An age of 3538 ± 6Ma established for a tectonic wedge of tonalitic gneiss within the Theespruit Formation confirms the presence of a sialic basement and deformed unconformity below that unit. The tonalitic gneiss is the oldest unit yet recorded within the greenstone belt, equal in age to the older components of the adjacent Ancient Gneiss Complex. (3) The interpreted ages of felsic volcanic rocks from both the Hooggenoeg (3445 ± 8Ma) and Theespruit Formations and the nearby Theespruit Pluton (3437 ± 6Ma) are essentially the same, and corroborate field and geochemical evidence that the felsic units were probably cogenetic and emplaced simultaneously as high-level equivalents of trondjhemite-tonalite plutons that intrude the greenstone belt at its southwestern extremity. (4) Felsic-intermediate volcanic-volcaniclastic rocks locally separating the two major groups (the Fig Tree and Moodies Groups) which overlie the Onverwacht Group record a second major peak of tonalitic magmatism in the Barberton terrain at about 3250 Ma. This is close to the age of the Kaap Valley tonalite pluton which intrudes the Barberton Greenstone Belt at ca. 3226 Ma along its northwestern margin. The present results indicate the Barberton Greenstone Belt is part of an allochthonous sequence containing major tectonic and stratigraphic breaks, with a protracted history; of which the last 200 million years, at least, evolved within a tectonically active convergent environment.

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

    NASA Astrophysics Data System (ADS)

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

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

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

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

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

  13. Early terrestrial impact events: Archean spherule layers in the Barberton Greenstone Belt, South Africa

    NASA Astrophysics Data System (ADS)

    Ozdemir, Seda; Koeberl, Christian; Schulz, Toni; Reimold, W. Uwe; Hofmann, Axel

    2015-04-01

    In addition to the oldest known impact structure on Earth, the 2.02-billion-year-old Vredefort Structure in South Africa, the evidence of Early Earth impact events are Archean spherule beds in South Africa and Australia. These spherules have been interpreted as condensation products from impact plumes and molten impact ejecta or/and impact ejecta that were melted during atmospheric re-entry [e.g., 1,2]. The 3.2-3.5 Ga spherule layers in the Barberton Greenstone Belt in South Africa currently represent the oldest known remnants of impact deposits on Earth. Aiming at identification of extraterrestrial components and to determine the diagenetic and metamorphic history of spherule layer intersections recently recovered in the CT3 drill core from the northeastern part of the Barberton Greenstone Belt, we have studied samples from these layers in terms of petrography and geochemistry. All samples, including spherule layer intersections and intercalating country rocks, were studied for mineral identification by optical and electron microscopy, as well as electron microprobe analysis (EPMA) at Natural History Museum Vienna and Museum für Naturkunde Berlin (MfN). Major and trace element compositions were determined via X-ray fluorescence spectrometry at MfN and instrumental neutron activation analysis (INAA) at University of Vienna. Os isotopes were measured by thermal ionization mass spectrometry (N-TIMS) at University of Vienna. Eighteen spherule beds are distributed over 150 meter drill core in CT3. Spherules are variably, deformed or undeformed. The high number of these layers may have been caused by tectonic duplication. Spherule beds are intercalated with shale, chert, carbonate, and/or sulfide deposits (country rocks). The size range of spherules is 0.5 to 2 mm, and some layers exhibit gradation. Shapes of spherules differ from spherical to ovoid, as well as teardrops, and spherules commonly show off-center vesicles, which have been interpreted as a primary characteristic pointing toward an impact origin [3]. Mineralogical and petrographic studies indicate that most of the mineralogy of the spherule layers is secondary due to secondary overprint by alteration and metamorphism. The mineral assemblages comprise quartz, K-feldspar, various muscovite types, phyllosilicates, Mg-siderite, Ti/Fe-Ti oxides, sulfides such as pyrite, pyrrhotite, chalkopyrite, sphalerite, and galena. INAA data show that some spherule layer intersections have extremely high siderophile element contents, with up to 1.60 wt% Ni, 0.69 wt% Cr, 0.05 wt% Co, 2.06 ppm Ir and 0.02 ppm Au, which is considered extraterrestrial component. This is further supported by their chondritic to slightly supercondritic 187Os/188Os ratios (ranging from 0.11 to 0.19), contrasting more radiogenic values of the spherule layer intercalations in comparison to country rocks, and Os concentrations up to ~4312 ppb. References: [1] Artemieva, N.A., and Simonson, B.M., 2012, LPSC 43, abstract #1372. [2] Johnson, B.C., and Melosh, H.J., 2014, Icarus, 228, 347-363. [3] Glass, B.P. and Simonson, B.M., 2012, Elements 8, 15-60.

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    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.

  15. Continental growth on Early Earth: Crustal electrical conductivity models of the Barberton Greenstone Belt, South Africa

    NASA Astrophysics Data System (ADS)

    Weckmann, U.; Kutter, S.; De Wit, M.

    2014-12-01

    The Barberton Greenstone Belt (BGB, South Africa) is one of the few Archean remnants where the tectonic evolution of the Early Earth can be studied. The first formation of the crust is a controversially discussed topic among geoscientists. Tectonics on the Early Earth might have been similar to the plate movement and their driving forces that we observe today. However, regarding that some fundamental conditions like the thermal setting were considerably different at this time other processes like vertical mass transport might have played the governing role in tectonics. Therefore contrasting evolutionary models of the BGB exist, mainly based on a number of geological and petrological studies. However, there is only little information on its deeper architecture. For a better understanding of past processes and the character of the tectonic regime which led to the formation of the BGB, magnetotelluric (MT) surveys were carried out as a part of the German-South African Inkaba yeAfrica research initiative. At approximately 200 MT sites aligned along six profiles (approx. 80 to 110 km length) data was collected during two field experiments in 2009 and 2010. The MT method images the electrical conductivity of rocks and is particularly sensitive to imprints of tectonic processes resulting in persistent mineralization e.g. along shear planes. Against the surrounding of significantly conductive geological units like the Phanerozoic Transvaal cover, the rocks of the BGB are generally characterized by high electrical resistivities. Particularly plutons such as the Dalmein Pluton can be traced deeply into the crust. Contrary, faults of the BGB appear as zones of high conductivity down to a depth of 5 to 10 km. We will present 3D inversion results indicating an extension of the plutons of the western BGB beneath the Transvaal cover and a sharp conductivity contrast of the BGB compared to the eastern batholiths. We will discuss existing models of the evolution of the BGB in view of our 3D electrical conductivity images.

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

    PubMed

    Heubeck, C; Lowe, D R

    1994-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Heubeck, C.; Lowe, D. R.

    1994-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

    Archaean tectonophysical models distinguish between thick, rigid and thin, mobile crust; from these the major mechanisms and rates for continental growth are derived. Archaean sedimentary rocks, preserved in metamorphosed and highly deformed greenstone belts, can contribute to constrain these models by estimating subsidence rates, derived from the combination of facies changes and precise age dates. Largely siliciclastic strata of the Moodies Group form the topmost unit of the Barberton Supergroup of the Barberton Greenstone Belt (BGB), South Africa, represent one of the world's oldest unmetamorphosed quartz-rich sedimentary sequences, and reach ca. 3500m thick (Lowe and Byerly, 2007). Large parts of the Moodies Group were deposited in apparent sedimentary continuity in alluvial, fluvial, shoreline and shallow-marine environments (e.g., Eriksson, 1979; Heubeck and Lowe, 1994). Distinctive sources and variations in facies indicate that Moodies deposition occurred at times in several basins. In several now tectonically separated regions, a regional basaltic lava (unit MdL of Anhaeusser, 1968) separates a lower unit (ca. 2000m thick and possibly representing an extensional setting) from an upper unit (ca. 1500m thick and characterized by progressive unconformities, rapidly changing facies, thicknesses, and sandstone petrographic composition). Single zircons separated from a felsic air-fall tuff of the middle Moodies Group and immediately overlying the basaltic lava in the Saddleback Syncline were dated on the Stanford-USGS SHRIMP RG. Out of 24 dated grains, two near-concordant groups have mean ages of 3230,6+-6,1Ma (2σ; n=9) and 3519+-7 Ma (2σ; n=9), respectively. We interpret the former age as representing the depositional age of the tuff, the latter as representing inherited zircons from underlying Onverwacht-age basement. The interpreted depositional age of the Moodies tuff is indistinguishable from numerous similar ages from felsic and dacitic volcanics at the top of the underlying Fig Tree Group (Schoongezicht Fm.; Byerly et al., 1996), implying that ca. 2000m of Moodies sandstones and subordinate siltstones and conglomerates were deposited in not more than a few (0-6) Ma. Their comparatively low degree of facies variation and lithological change implies a balance between rates of sediment supply and of subsidence, creating thick stacked units. Ferruginous shales and thin BIFs of the upper Moodies Group suggest that background 'Fig-Tree-style' sedimentation continued during Moodies time but was mostly overwhelmed by the apparently brief but massive influx of medium- to coarse-grained quartzose sediment. Because two progressive unconformities, marking Moodies basin uplift and onset of renewed overall BGB shortening, occur only 50 m above this dated unit, they are likely of a similar age and imply that dominant NW-SE-directed shortening in the BGB began shortly after 3230+-6 Ma. The combination of these new data with published information thus suggest that the Moodies Basin formed after 3225+-6 Ma (i.e., at the earliest at 3231) but was already largely filled and began to be deformed by 3231+-6 (i.e., at the latest by 3225). Moodies deposition thus happened geologically nearly instantaneously following the end of Fig Tree volcanism, took very little time and deposited large volumes of sediments on a rapidly subsiding basement just prior to large-scale BGB deformation. REFERENCES Byerly, G.R., Kroner, A., Lowe, D.R., Todt W., Walsh, M.M., 1996, Prolonged magmatism and time constraints for sediment deposition in the early Archean Barberton greenstone belt: Evidence from the Upper Onverwacht and Fig Tree groups: Precambrian Research, 78, p. 125-138. Eriksson, K.A., 1979, Marginal marine depositional processes from the Archaean Moodies Group, Barberton Mountain Land, South Africa: Evidence and significance: Precambrian Res., 8, p. 153-182. Heubeck, C. and Lowe, D.R., 1994, Depositional and tectonic setting of the Archaean Moodies Group, Barberton Greenstone Belt, South Africa: Precambrian Res., 68, p. 257-290. Lowe, D.R., and Byerly, G.R., 2007, An overview of the geology of the Barberton Greenstone Belt and vicinity: Implications for early crustal development; in: M.J. von Kranendonk, R.H. Smithies and V.C. Bennett, eds., Earth's Oldest Rocks. - Elsevier (Developments in Precambrian Geology), vol. 15, p. 481-526.

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  2. Melting conditions and sources of 3.5 Ga komatiites from ICDP Drilling in the Barberton Greenstone Belt, South Africa

    NASA Astrophysics Data System (ADS)

    Coetz, Grace; Blichert-Toft, Janne; Wilson, Allan; Arndt, Nicholas

    2014-05-01

    We measured major and trace element concentrations and Sm-Nd and Lu-Hf isotope systematics in 18 samples of komatiites from the core recovered from the ICDP drilling project in the Barberton Greenstone Belt, South Africa. Two fractions of magmatic clinopyroxene from a surface sample were also analysed. All samples are of the Al-depleted Barberton-type komatiite and all show the geochemical signature of residual garnet in the source (low Al/Ti, depleted HREE). One sequence, however, is unusual in that it reveals petrographic and geochemical evidence that orthopyroxene as well as olivine was on the liquidus. For the Lu-Hf systems, the whole-rock data and the clinopyroxene separates define a linear array whose slope corresponds to an age of 3419±25 Ma which is within error of the accepted age of the rocks (3.48 Ga). The Sm-Nd scatterchron gives a younger age of 3371±20 Ma. Initial isotopic values for the clinopyroxene separates provide high-precision results, with epsilon Nd(T) = -1.1 and -1.5 and epsilon Hf(T) = +3.3 and +4.1. The positive epsilon Hf value is in line with other results from komatiites from the Barberton Belt but the negative epsilon Nd value is surprising in that it indicates an enriched source with low Sm/Nd. The peculiar characteristics of this source - low Sm/Nd and high Lu/Hf - is found in the trace element compositions of the komatiites, which have moderately enriched LREE and negative Hf anomalies. The enriched LREE are consistent with that of a liquid extracted after deep melting but the origin of the Hf deficit remains uncertain. The orthopyroxene-phyric komatiites are isotopically indistinguishable from the other komatiites indicating that its Si-rich character probably was acquired during melting rather than being derived from an older source. All these komatiites were produced by about 30% batch melting, at about 300 km depth, under conditions in which garnet remained in the residue during the melting process.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    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.

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

    PubMed

    Byerly, G R; Palmer, M R

    1991-05-01

    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

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

    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.

  6. The origin of large varioles in flow-banded pillow lava from the Hooggenoeg Complex, Barberton Greenstone Belt, South Africa

    NASA Astrophysics Data System (ADS)

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

    2011-08-01

    Exceptionally well-preserved pillowed and massive phenocryst-free metabasaltic lava flows in the uppermost part of the Palaeoarchaean Hooggenoeg Complex of the Barberton Greenstone Belt exhibit both flow banding and large leucocratic varioles. The flow banding is defined by blebs and bands of pale and dark green metabasalt and was the result of mingling of two types of basalt (Robins et al. in Bull Volcanol 72:579-592, 2010a). Varioles occur exclusively in the dark chlorite-, MgO- and FeO-rich metabasalt. Varioles are absent in the outermost rinds of pillows and increase in both abundance and size towards the centres of pillows. In the central parts of some pillows, they impinge to form homogeneous pale patches, bands or almost homogenous cores. Individual varioles consist essentially of radially orientated or outwardly branching dendritic crystals of albite. Many varioles exhibit concentric zones and finer-grained rims. Some varioles seem to have grown around tiny vesicles and vesicles appear to have been trapped in others between a core and a finer-grained rim. The matrix surrounding the ocelli contains acicular pseudomorphs of actinolite and chlorite after chain-like, skeletal Ca-rich pyroxenes that are partly overgrown by the margins of varioles. Varioles are enriched in the chemical constituents of feldspar but contain concentrations of immobile TiO2, Cr, Zr and REE that are similar to the host metabasalts. The shape, distribution, texture and composition of the varioles exclude liquid immiscibility and support an origin by spherulitic crystallisation of plagioclase from severely undercooled basalt melt and glass. Nucleation of plagioclase was strongly inhibited and took place on vesicles, on the bases of drainage cavities and along early fractures. Eruption in deep water and retention of relatively high concentrations of volatiles in the melt may be the principal cause of spherulitic crystallisation in the interiors of pillows rather than only in their margins as in younger submarine flows.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

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

    NASA Astrophysics Data System (ADS)

    Ledevin, Morgane; Arndt, Nicholas; Simionovici, Alexandre

    2014-05-01

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

  9. An Arch˦an arc-arc collisional event: a short-lived (ca 3 Myr) episode, Weltevreden area, Barberton greenstone belt, South Africa

    NASA Astrophysics Data System (ADS)

    De Ronde, Cornel E. J.; Kamo, Sandra L.

    2000-02-01

    Detailed mapping, structural analysis and high precision Usbnd Pb zircon ages from hypabyssal porphyries and tonalites has enabled the timing of the major collisional episode of the Barberton greenstone belt to be determined. This episode, known as the D2 deformation, can be divided into D2-early and D2-late. D2-early deformation, bracketed as having occurred between 3229 and 3227 Ma, was typified by isoclinal folding (F2 of shales and associated cherts (Fig Tree Group), but not of the overlying quartzose clastic rocks (Moodies Group). D2-late deformation was at 3226 Ma, or later, with large F3 open-tight folds dominating the map pattern in the Weltevreden study area. Late D2 faults, such as the Moodies Fault, that define the boundaries of the major structural domains converge near the Saddleback Fault, a major boundary within the Barberton greenstone belt. Strain calculations suggest that plane strain was dominant, with at least 60% shortening occurring during the D2 deformational events. Although an early and a late stage of D2 deformation can be distinguished in the field, precise Usbnd Pb zircon ages indicate that these events represent a continuum, ranging from the onset of an arc-arc assembly event (D2-early), through to major collisional and post-amalgamation events (D2-late), all of which spanned ˜3 million years.

  10. IIb trioctahedral chlorite from the Barberton greenstone belt: crystal structure and rock composition constraints with implications to geothermometry

    NASA Astrophysics Data System (ADS)

    Xie, Xiaogang; Byerly, Gary R.; Ferrell, Ray E., Jr.

    IIb trioctahedral chlorite in the Barberton greenstone belt (BGB) metavolcanic rocks was formed during pervasive greenschist metamorphism. The chem-ical composition of the chlorite is highly variable, with the Fe/(Fe+Mg) ratio ranging from 0.12 to 0.8 among 53 samples. The chemical variation of the chlorite results from the chemical diversity of the host rock, especially the MgO content of the rock, but major details of the variation pattern of the chlorite are due to the crystal structure of the chlorite. All major cation abundances in the chlorite are strongly correlated with each other. Sil-icon increases with Mg and decreases with Fe, while AlIV and AlVI decrease with Mg and increase with Fe2+. A complex exchange vector explains over 90% of the chlorite compositional variation: Mg4SiFe2+-3AlVI-1 AlIV-1, which has 3 parts Fe-Mg substitution coupled with one part tschermakite substitution. This ratio is required to maintain the charge and site balances and the dimensional fit between the tetrahedral and octahedral sheets. The subtle change in Al substitution in chlorite implies that AlVI is preferentially ordered in the M(4) site, and about 84% of the AlVI present is in the M(4) sites when they are nearly filled with AlVI. Based on 47 analyzed chlorite-bearing rock samples, chlorite (Chl) composition is strongly correlated with the MgO content of the host rock. Calculated correlation coefficients are +0.91 for SiO2Chl-MgORock, -0.87 for Al2O3Chl-MgORock, +0.89 for MgOChl-MgORock, and -0.85 for FeOChl-MgORock. Only weak correlations have been found between chlorite oxides and other oxides of rock (between same oxides in chlorite and rock: SiO2-0.67, Al2O3+0.59, FeO -0.41). However, MgOChl is saturated at about 36 wt% in rocks that have MgO above 22 wt%.The MgOChl is about 5 wt% when the host rock approaches 0 wt% of MgO. This implies that Mg substituting into the chlorite is approximately limited to 1.5-9.2 Mg atoms per formula unit and 1.0-3.2 AlIV. Chlorite geothermometers can not be applied to all BGB samples. However, the empirical chlorite geothermometer based on AlIV of chlorite may be applicable to chlorites formed under metamorphic conditions because it can predict the chemical composition of the chlorite from basaltic and dacitic samples in this study. An estimated temperature of about 320°C for the greenschist metamorphism of the greenstone belt through this geothermometer is consistent with that obtained by other geothermometers.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2007-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

    Sedimentary cherts are unusually abundant in early Archean (pre-3.0 Ga) sequences, suggesting a silica cycle that was profoundly different than the modern system. Previously applied for the purpose of paleothermometry, Si isotopes in ancient cherts can offer broader insight into mass fluxes and mechanisms associated with silica concentration, precipitation, diagenesis, and metamorphism. Early Archean cherts contain a rich suite of sedimentological and petrographic textures that document a history of silica deposition, cementation, silicification, and recrystallization. To add a new layer of insight into the chemistry of early cherts, we have used wavelength-dispersive spectroscopy and then secondary ion mass spectrometry (SIMS) to produce elemental and Si and O isotope ratio data from banded black-and-white cherts from the Onverwacht Group of the Barberton Greenstone Belt, South Africa. This geochemical data is then interpreted in the framework of depositional and diagenetic timing of silica precipitation provided by geological observations. SIMS allows the comparison of Si and O isotope ratios of distinct silica phases, including black carbonaceous chert beds and bands (many including well-defined sedimentary grains), white relatively pure chert bands including primary silica granules, early cavity-filling cements, and later quartz-filled veins. Including all chert types and textures analyzed, the δ30Si dataset spans a range from -4.78‰ to +3.74‰, with overall mean 0.20‰, median 0.51‰, and standard deviation 1.30‰ (n = 1087). Most samples have broadly similar δ30Si distributions, but systematic texture-specific δ30Si differences are observed between white chert bands (mean +0.60‰, n = 750), which contain textures that represent primary and earliest diagenetic silica phases, and later cavity-filling cements (mean -1.41‰, n = 198). We observed variations at a ∼100 μm scale indicating a lack of Si isotope homogenization at this scale during diagenesis and metamorphism, although fractionations during diagenetic phase transformations may have affected certain textures. We interpret these systematic variations to reflect fractionation during silica precipitation as well as isotopically distinct fluids from which later phases originated. SIMS δ18O values fall in a range from 16.39‰ to 23.39‰ (n = 381), similar to previously published data from bulk gas source mass spectrometry of Onverwacht cherts. We observed only limited examples of texture-related variation in δ18O and did not observe correlation of δ18O with δ30Si trends. This is consistent with hypotheses that Si isotope ratios are more resistant to alteration under conditions of rock-buffered diagenesis (Marin-Carbonne et al., 2011). Our results indicate that low temperature processes fractionated silicon isotopes in early Archean marine basins, a behavior that probably precludes the application of chert δ30Si as a robust paleothermometer. The values we observe for facies that sedimentological and petrographic observations indicate formed as primary and earliest diagenetic silica precipitates from seawater are more 30Si-rich than that expected for bulk silicate Earth. This is consistent with the hypothesis that the silicon isotope budget is balanced by the coeval deposition of 30Si-enriched cherts and 30Si-depleted iron formation lithologies. Precipitation of authigenic clay minerals in both terrestrial and marine settings may have also comprised a large 30Si-depleted sink, with the corollary of an important non-carbonate alkalinity sink consuming cations released by silicate weathering.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

  17. Petrography of sandstones from drill cores BARB4 and BARB5, Paleoarchean Mapepe Formation, Barberton greenstone belt, South Africa: Implications for provenance and tectonic reconstructions.

    NASA Astrophysics Data System (ADS)

    Drabon, N.; Lowe, D. R.; Heubeck, C. E.

    2014-12-01

    Paleogeographic and tectonic reconstructions in the Barberton greenstone belt (BGB) are challenged by syn- and post-depositional tectonics. The Barberton Drilling Project extracted two drill cores from the sedimentary rocks of the 3.26-3.22 Ga Mapepe Formation of the Fig Tree Group. The cores were taken from the Manzimnyama Syncline (BARB4) and the Barite Valley structural belt (BARB5), which are separated by belts of faulted older Onverwacht and younger Moodies strata. Stratigraphically, there is no clear correlation of Mapape strata in these two belts. Both BARB4 and BARB5 contain 25 to 300 m thick units of lithic sandstone that may represent correlative units. A comparative provenance analysis allows testing a possible correlation and evaluating the nature of tectonic uplifts that sourced the sediments. The sandstones have experienced pervasive metasomatic alteration and most primary silicate minerals except coarse quartz have been transformed into micromosaics of microquartz, phyllosilicates, and trace impurities. The majority of framework grains are chert, impure chert, and lithic grains while monocrystalline quartz and altered feldspar are minor components. The single thick sandstone in BARB4 displays a relatively uniform framework mode with average 38.7 % total quartz, 2.4% feldspars, and 58.9 % lithics and an increasing percentage of mafic to ultramafic grains upsection. In contrast, BARB5 includes three distinct sandstones with varying framework modes. The litharenite at 0 to 95m core depth was mainly sourced from an immediately underlying dacitic tuff. The chertarenite at 320 to 390m core depth is composed of 73% carbonaceous chert grains. All grain types appear to have been derived by erosion of sedimentary and volcanic rocks of the BGB as well as penecontemporaneous volcanism. Erosion did not reach deeper-seated plutonic rocks. The framework mode of the BARB4 sandstones represents a composite of common silicified BGB rocks and resembles those of other sediments in the southern domain of the BGB. In contrast, BARB5 sandstones derived locally by shallow erosion of underlying volcanic and sedimentary rocks. The distinct signatures suggest that these units are not correlative and were not derived from a common source. They may be a result of local uplifts of different parts of the greenstone sequence.

  18. High-resolution geology, petrology and age of a tectonically accreted section of Paleoarchean oceanic crust, Barberton greenstone belt, South Africa

    NASA Astrophysics Data System (ADS)

    Grosch, Eugene; Vidal, Olivier; McLoughlin, Nicola; Whitehouse, Martin

    2015-04-01

    The ca. 3.53 to 3.29 Ga Onverwacht Group of the Barberton greenstone belt (BGB), South Africa records a rare sequence of exceptionally well-preserved volcanic, intrusive and volcani-clastic Paleaoarchean rocks. Numerous conflicting models exist for the geologic evolution and stratigraphy of this early Archean greenstone belt, ranging from plume-type dynamics to modern-style plate tectonics. Although much work has focussed on the komatiites of the ca. 3.48 Ga Komati Formation since their discovery in 1969, far less petrological attention has been given to the younger oceanic rock sequences of the Kromberg type-section in the mid-Onverwacht Group. In this study, we present new field observations from a detailed re-mapping of the Kromberg type-section, and combine this with high-resolution lithological observations from continuous drill core of the Barberton Scientific Drilling Project [1]. The new mapping and field observations are compared to a recent preliminary study of the Kromberg type-section [2]. A U-Pb detrital provenance study was conducted on a reworked, volcani-clastic unit in the upper Kromberg type-section for the first time. This included U-Pb age determination of 110 detrital zircons by secondary ion microprobe analyses (SIMS), providing constraints on maximum depositional age, provenance of the ocean-floor detritus, and timing for the onset of Kromberg ocean basin formation. These new zircon age data are compared to a previous U-Pb detrital zircon study conducted on the structurally underlying sediments of the ca. 3.43 Ga Noisy formation [3]. A multi-pronged petrological approach has been applied to various rock units across the Kromberg, including thermodynamic modelling techniques applied to metabasalts and metapyroxenites for PT-estimates, bulk- and in-situ isotope geochemistry providing constraints on protolith geochemistry and metamorphic history. Consequently, it is shown that this previously poorly studied Kromberg oceanic rock sequence of the mid-Onverwacht, is a key area in resolving stratigraphy models and understanding the geologic evolution of the BGB. The combined field and petrological data provide new insight into mid-Paleoarchean ocean basin formation and subsequent tectonic destruction. [1]. Grosch et al., (2009b). EOS 90, 350-351. [2] Furnes et al., (2011) Precam. Research 186, 28-50. [3] Grosch et al. (2011) Precam. Research 191, 85-99.

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

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Grosch, Eugene

    2014-05-01

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

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

    NASA Astrophysics Data System (ADS)

    Sleep, Norman H.; Lowe, Donald R.

    2014-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  5. 3.2 Ga ocean sedimentary sequence in the Komati section of the Mapepe Formation in the Barberton Greenstone Belt, South Africa

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

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

    NASA Astrophysics Data System (ADS)

    McLoughlin, Nicola; Grosch, Eugene

    2014-05-01

    Silicified seafloor sediments of the Kromberg Formation from the Onverwacht Group of the Barberton greenstone belt (BGB), South Africa, have been argued to contain some of the world's oldest preserved carbonaceous microfossils. Previous studies of these cherts have reported filamentous, spheroidal and ellipsoidal microfossils in thin-section (Walsh 1992); and bacteriomorph like structures in HF-etched samples (Westall et al. 2001). These microtextural studies however, lack supporting in-situ geochemical data, and are hampered to some degree by re-mobilisation of the carbonaceous matter (Van Zuilen et al. 2007). In light of these concerns, and ongoing debates surrounding carbonaceous remains in other Archean cherts (e.g., W Australia), further in-situ data from the Kromberg is required to positively identify carbonaceous matter of biogenic origin. New data will also help to address outstanding questions regarding the relative contribution of benthic versus planktonic microorganisms, and the putative microbial metabolisms involved. This study focuses on surface samples and drill core from the Barberton Scientific Drilling Programme, (BSDP, Grosch et al. 2009) from the southeastern limb of the Onverwacht anticline of the BGB. We sampled the Footbridge chert and a second chert horizon in drill core KD1 of the BSDP in the upper Kromberg Fm; and surface outcrops of two black cherts from the lower Kromberg Fm. Sedimentological logging reveals horizons rich in volcaniclastics with interbedded finely laminated grey-black chert, also intrusive black cherts, and sulphide rich horizons. The TOC of the sampled cherts is 1.24 to 5.40 wt%. Preliminary bulk carbon isotope values range from δ13C -21.1 to -35.3o values that are consistent with organic matter produced by anoxygenic photosynthesis. Microfabrics preserved in the Kromberg cherts include, primary wispy-laminated carbonaceous films suggesting compaction of early carbonaceous laminae. Also large composite carbonaceous grains >30 μm across recording wave-motion on the seafloor. Secondary fabrics include hydrothermal veins containing remobilized carbon and sometimes sulphides, also void-filling silica spherulites coated in carbonaceous matter. A novel fabric discovered in the lower Kromberg chert is silicified carbonaceous fragments with plastic deformation that are morphologically comparable to microtextures reported from the 3.416 Ga Buck Reef Chert (Tice and Lowe 2004) interpreted to be deformed microbial mat fragments. These fabrics are currently being studied by raman spectroscopy to assess the effects of taphonomic processes and metamorphic alteration on this potential biosignature. In-situ sulphur isotope measurements by SIMS on sulphides associated with primary carbonaceous fabrics of the Footbridge chert found a narrow range in δ34SCDTvalues of -6.00 to + 1.50 o and positive Δ33S values up to +2.50 o suggesting the involvement of atmospheric sulphur aerosols, but do not strongly support either microbial sulphate reduction or disproportionation (Grosch and McLoughlin 2013). The geochemical evidence for microbial processes must therefore be further tested in the Kromberg cherts to build upon the bulk carbon isotope data that is consistent with, but alone not diagnostic of, microbial processes. In summary, this new survey of carbonaceous cherts from the Kromberg type section has identified well-preserved candidate microbial microfabrics that will be the target of ongoing high resolution in-situ geochemical and ultrastructure analysis.

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

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

  8. 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

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

    2003-01-01

    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

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

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

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

  10. 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

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

    2006-01-01

    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 μm 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

  11. 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

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

    2006-10-29

    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

  12. Workshop on Techtonic Evolution of Greenstone Belts

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

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

    SciTech Connect

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

    1991-07-01

    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 {sup 40}Ar/{sup 39}Ar laser step-heating technique. This technique has enabled previously cryptic thermal overprints to be detected in various sedimentary units which include: reworked chemical sediments (barite), clastic sediments (sandstone/shale), and one stromatolite. In most cases the apparent age plateau 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 {sup 39}Ar recoil, effects. The various sediments analyzed show evidence for distinct overprinting between 2,025 and 2,090 Ma. One barite sample gave T{sub 0} = 2,673 {plus minus} 3 Ma (1{sigma}) which is close to a calculated model Ar diffusion-loss age for the same sample of 2,688 {plus minus} 3 Ma (1{sigma}). 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 T{sub 0} ages of {approximately}2,350-2,400 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 plateau together with modeled diffusive Ar loss ages of 2,025-2,090 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 {approximately}60,000 km{sup 2}) and formation of the Vredefort Structure are obvious manifestations. The strong thermal overprinting recorded by the sediments has effectively removed any ancient atmosphere signatures.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    The striking abundance of chert in Early Archean sedimentary successions highlights a major difference between younger Archean and Proterozoic successions, engendering a number of questions regarding the behavior of the Earth's early silica cycle. Though previously applied largely for the purpose of paleothermometry, Si isotopes are emerging as a new tool for understanding mass flux and mechanisms of silica concentration, precipitation, diagenesis, and metamorphism. In addition, most previous studies lack a detailed petrographic context, laboring under the assumption that the cherts are isotopically homogeneous on a centimeter scale. We present a new suite of high resolution SIMS Si and O isotope ratio data from banded carbonaceous chert from the Onverwacht Group of the Barberton Greenstone Belt, South Africa - collected from the 3.42 Ga Buck Reef Chert and 3.33-3.26 Ga Mendon Formation. These materials contain several distinct silica phases, including carbonaceous bands (with or without well-defined grains), pure chert bands, early cavity filling cements, and later quartz-filled veins, which provide for isotopic comparisons between different textures. δ30Si values from all samples span a range of almost 7‰, from -3.38 to +3.42, with an overall mean of 0.36, median of 0.46, and standard deviation of 0.87. Within individual samples, isotope ratio data displays systematic texture-specific δ30Si variations both between phases and within phases. The observed variations occur on a ~100μm scale and likely reflect isotopically distinct fluids from which different silica phases originated, in addition to fractionation during precipitation. To constrain the causes of the silicon isotope trends, we made 18O/16O measurements on spots placed just adjacent to measured Si spots. SIMS δ18O values are generally 18O-depleted and fall in a range consistent with previously published data from bulk gas source mass spectrometry. Measurements from all samples span a range of ~6‰, from 16.39 to 22.22, but each individual sample has a smaller range of only 2-3‰. One sample shows clear δ18O differentiation between carbonaceous bands and pure chert bands, which is also consistent with previously published data from Onverwacht banded carbonaceous cherts. Importantly, δ18O values do not correlate with corresponding δ30Si points, suggesting that although diagenetic fluids have altered these rocks, the Si isotope ratios were largely rock-buffered and record fractionations incurred during primary and early diagenetic processes. Altogether these results suggest that there were conspicuous low temperature processes fractionating silicon isotopes in Early Archean marine basins—behavior that probably precludes the simple interpretation of Si isotope data from sedimentary cherts as a paleothermometer.

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

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

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

  16. Potential Greenstone Belt Continuity Undercover, Zimbabwe

    NASA Astrophysics Data System (ADS)

    González-Álvarez, I.; Aurore, J.; McCuaig, C. T.; Alok, P.

    2009-05-01

    The Zimbabwean craton is one of the most metal-endowed cratons on the Earth with abundant deposits of Au, Ni, Cr and PGE that are spatially and genetically associated with greenstone belts. This study aims at tracing the possible undercover continuity of these greenstone belts. A conjunctive interpretation of regional-scale geological, gravity and magnetic data was carried out, focusing on the Harare-Shamva region, NE Zimbabwe. The datasets used in the study included: (1) public geological maps and reports; (2) Zimbabwean Government aeromagnetic surveys (1983-1992) with line spacing and terrain clearance ranging 250-1000 m, and 120-305 m, respectively; and (3) the national gravity dataset of Zimbabwe (1996) with >12,000 gravity measurements. The Harare-Shamva gravity coverage corresponds to one station per ˜10 km2. A digital elevation model was generated from the NASA's Shuttle Radar Topography Mission data (90m resolution) to preprocess the gravity data. Standard gravity corrections, namely, the latitude, free-air, Bouguer- slab and terrain corrections, were applied to the observed gravity data. A distance of 167 km was used for the terrain correction, and an average density value of 2.67 g.cm3 (expected granite density) was used for the Bouguer-slab correction. In the Harare-Shamva area, long wavelength Bouguer anomalies were filtered out by applying a second-order polynomial and extracting the residual anomalies interpreted as representing the effect of density heterogeneities located below the surface down to a depth of ˜10 km. These residual gravity anomalies are used to characterize the geometry of the greenstone bodies in the area. Based on the composite Bouguer map, positive anomalies are associated with the geometry of the Harare, Shamva, Mutoko, Guruve, Filabusi, Masvingo, Fort Rixon, Shangani, Bulawayo and Gwanda greenstone belts. These greenstone belts comprise metamorphosed ultramafic-mafic suites that are intercalated with felsic volcanics, sedimentary units and banded iron formation (BIF). Based on the available geological information, magnetic positive anomalies are interpreted as BIF units and ultramafic-mafic suites, whereas the negative ones are interpreted as phyllitic and quartzitic units. On the residual Bouguer map, positive anomalies in the Harare-Shamva are associated with the Reliance F. within the previously mapped greenstone belt, which comprises up to 6-km thick succession of mafic- ultramafic rocks. On the contrary, the Zeederbergs F. (2-3 km thick sequence of sediments and tholeiitic basalts) and the Chinamora Complex (tonalites-granodiorites) are characterized by negative anomalies. Positive gravity anomalies in the Harare-Shamva area continue ˜20 km further to the N and probably ˜30 km to the E beyond the mapped greenstone belt, which suggests continuity of the mafic-ultramafic rocks under the cover sediments. Possible undercover continuity and thickening of the Harare-Shamva greenstone belts to the E is tested by applying petrophysical measurements, and direct 2D joint gravity and magnetic modeling using Geosoft-GM- SYS software by integrating the potential field data and available geological information. Several transverse cross-sections are developed through some key areas to verify the above interpretations. The 2.7 Ga greenstone belts with komatiite sequences in Zimbabwe are highly prospective for commodities such as Ni. This study contributes data for a potential re-evaluation of geological relationships in Zimbabwe, as well as delineation of new potential areas for targeting greenstone-hosted mineral deposits.

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

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

    PubMed

    Krüner, A; Byerly, G R; Lowe, D R

    1991-04-01

    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

  19. Workshop on the Tectonic Evolution of Greenstone Belts

    NASA Technical Reports Server (NTRS)

    1986-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

    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.

  1. Archaean greenstone belts and associated granitic rocks - A review

    NASA Astrophysics Data System (ADS)

    Anhaeusser, Carl R.

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Chaudhuri, Trisrota; Mazumder, Rajat; Arima, Makoto

    2015-01-01

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

  3. Recent Advancements in Full Tensor Gravity Gradiometry for Resource Exploration: A Case study from West Africa - Birmian Greenstone Belt

    NASA Astrophysics Data System (ADS)

    Brewster, J.; Mataragio, J.

    2014-12-01

    Over the years significant progress has been made in understanding the regional geologic models of the Greenstone Belts associated with gold mineralization in the fields of exploration geochemistry, geophysics and data integration. Improved knowledge of the geological models together with advancements in exploration techniques have resulted in the discovery of many near surface, and relatively large gold mines around the world such as the Abitibi, Isua, Barberton, Lake Victoria, Sadiola, and Yatela. However, the search for new deposits becomes more difficult due to the fact that most easily detectable, near surface deposits have been discovered. Many of the remaining deposits tend to be remotely located and deep underground. Effective exploration for new economically viable deposits requires approaches that integrate multiple techniques capable of resolving smaller, deeper and remotely located resources. Gravity surveys have been widely used to map and define geometry and structure of greenstones belts at a regional scale. Structure and hydrothermally altered zones can be mapped, either directly by gravity in weathered environments or inferred in terrains where geological units of different density are offset and/or altered Gravity gradiometry is increasingly becoming a standard method of commercial minerals exploration. Gradiometry presents a significant increase in spatial resolution when compared to previous airborne gravity methods. Airborne full tensor gravity gradiometry surveys have been flown in the past for prospect-level gold exploration in Quebec, Nunavut, Nevada, Brazil, Mali, Zambia and New Zealand and Nevada. The application of airborne gravity gradiometry for prospect-level gold exploration over greenstone belts is discussed in this paper. The high resolution system capability to detect small, high frequency targets is the key for successful results. In addition, this paper presents and discusses data enhancement and 3D inversion results. It is expected that the result of data enhancement and 3D inversion will help resolve subsurface structures associated with gold mineralization and updates the existing geological model over the property.

  4. The temporal variation of Mesoarchaean volcanism in the Suomussalmi greenstone belt, Karelia Province, Eastern Finland

    NASA Astrophysics Data System (ADS)

    Lehtonen, E.; Heilimo, E.; Halkoaho, T.; Hölttä, P.; Huhma, H.

    2016-04-01

    This study concentrates in the Kiannanniemi area, situated in the Archaean Suomussalmi greenstone belt, the Karelia Province, Fennoscandian Shield. A zircon U-Pb geochronological study from this area shows that ages of the volcanic rocks are between ca. 2.94 and 2.82 Ga. The results indicate multiphase felsic and intermediate volcanism in three episodes at ca. 2.94, 2.84 and 2.82 Ga, of which the 2.84 Ga event has not been reported earlier from the Suomussalmi greenstone belt. The youngest zircon population in a sedimentary rock sample suggests a depositional age of ≤2.82-2.81 Ga, and the sample contains also ≥2.96 Ga old zircon grains. Based on both new and previously published geochronological data from the volcanic rocks, we propose a chronostratigraphic model for the whole Suomussalmi greenstone belt, dividing it into four units based on their age: Luoma, Tormua, Ahvenlahti, and Mesa-aho. The youngest volcanic rocks in the Suomussalmi greenstone belt are contemporaneous with some of the volcanic rocks recorded from the Kuhmo and Tipasjärvi greenstone belts of the Karelia Province, Finland. The age group ca. 2.94 Ga, however, has not been so far recorded elsewhere. Conversely, in the Suomussalmi greenstone belt, volcanic rocks with an age of ca. 2.80 Ga and sedimentary rocks with depositional ages of <2.75 Ga, frequently found from the Kuhmo and Tipasjärvi greenstone belts, are unknown.

  5. Late Archaean foreland basin deposits, Belingwe greenstone belt, Zimbabwe

    NASA Astrophysics Data System (ADS)

    Hofmann, A.; Dirks, P. H. G. M.; Jelsma, H. A.

    2001-06-01

    The c. 2.65 Ga old sedimentary Cheshire Formation of the Belingwe greenstone belt (BDB), central Zimbabwe, has been studied in detail for the first time to shed some light on the much debated evolution of this classical belt. The Cheshire Formation rests sharply on a mafic volcanic unit (Zeederbergs Formation) and comprises a basal, eastward-sloping carbonate ramp sequence built of shallowing-upward, metre-scale sedimentary cycles. The cycles strongly resemble Proterozoic and Phanerozoic carbonate cycles and might have formed by small-scale eustatic sea level changes. The top of the carbonate ramp is represented by a karst surface. The carbonates are overlain by and grade laterally to the east into deeper water (sub-wave base) siliciclastic facies. Conglomerate, shale and minor sandstone were deposited by high- to low-density turbidity currents and were derived from the erosion of Zeederbergs-like volcanic rocks from the east. Shortly after deposition, the Cheshire Formation and underlying volcanics were affected by a northwest-directed thrusting event. Thrusting gave rise to the deformation of semi-consolidated sediments and resulted in the juxtaposition of a thrust slice of Zeederbergs basalts onto Cheshire sediments. The stratigraphy, asymmetric facies and sediment thickness distribution, palaeogeographic constraints and evidence for an early horizontal tectonic event suggest that the Cheshire Formation formed in a foreland-type sedimentary basin.

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

    NASA Technical Reports Server (NTRS)

    1986-01-01

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

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

    SciTech Connect

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

    1989-04-01

    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.

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

    NASA Technical Reports Server (NTRS)

    Mcgill, George E.; Shrady, Catherine H.

    1986-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Serov, Pavel

    2003-04-01

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

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

    PubMed

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

    1989-01-01

    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

  11. U-Pb isotopic evidence for episodic granitoid emplacement in the Murchison greenstone belt, South Africa

    NASA Astrophysics Data System (ADS)

    Poujol, M.

    2001-07-01

    This study presents new single-zircon U-Pb data that constrain the timing of granitoid emplacement within and to the south of the Murchison greenstone belt, South Africa. Four main magmatic events are identified at ca 3020, 2970, 2820 and 2680 Ma for the Baderoukwe, Discovery, Willie and Mashishimale intrusions, respectively. The age of 3020 Ma, found for the Baderoukwe Pluton, which is intrusive into the Letaba, Bawa and Sable schist belts, suggests that the schist belts are older than 3020 Ma. The age of the Discovery Granite is identical to that of the rhyodacitic Rubbervale Formation, suggesting that granite magmatism was associated with volcanism in the Murchison greenstone belt at around 2970 Ma. The emplacement of the Willie Granite is comtemporaneous with several other granites on the Kaapvaal Craton, suggesting that there was a major period of felsic magmatism on the craton between 2820 and 2880 Ma. The 2700 Ma Mashishimale Granite reflects, furthermore, the age of many of the late-stage potassic granite plutons on the Kaapvaal Craton, indicating that this period was also an important crust-forming event.

  12. The Paleoproterozoic komatiite-hosted PGE mineralization at Lomalampi, Central Lapland Greenstone Belt, northern Finland

    NASA Astrophysics Data System (ADS)

    Törmänen, T.; Konnunaho, J. P.; Hanski, E.; Moilanen, M.; Heikura, P.

    2015-10-01

    Several komatiite-hosted Ni-Cu-PGE deposits occur in Archean and Paleoproterozoic Greenstone Belts in Finland. Some of these deposits are enriched in platinum-group elements, especially in Pd and Pt. The Lomalampi PGE-(Cu-Ni) deposit is associated with a peridotitic cumulate body of the Sattasvaara Formation in the Paleoproterozoic Central Lapland Greenstone Belt. The sulfides in the deposit occur in disseminated form. Whole rock sulfur contents are 0.4-2 wt%, and Ni contents are <0.5 wt% and Cu <0.4 wt%, while PGE contents exceed 500 ppb. The sulfides consist of magmatic pentlandite, pyrrhotite, and chalcopyrite and have not been substantially modified by metamorphic processes. Palladium minerals are associated with sulfides and silicates, but the only Pt-bearing phase, sperrylite, occurs mainly within silicates. The host rock of the deposit is a chromite undersaturated Al-undepleted high-Mg basalt or low-Mg komatiite. In contrast to most other komatiite-hosted Ni-Cu-PGE deposits world-wide that have Pt/Pd around 0.5, the Lomalampi deposit is enriched in Pt over Pd (Pt/Pd = 2). Only a weak contamination signal in the host-cumulate is evident in REE data, but a strong signal is evident in S-isotope ratios (δ34S + 10 ‰ to +15 ‰), which differ substantially from the mantle value (0 ± 2 ‰). Geochemical characteristics (e.g., PGE enrichment) and R-factor modeling indicate certain similarities between Lomalampi and the Raglan Ni-Cu-PGE deposits of Canada. The combined data suggest that Lomalampi formed through contamination of a PGE-rich magnesian magma with S rich country rocks. This suggests that the extensive Central Lapland Greenstone Belt is favorable for komatiite-hosted Ni-Cu-PGE deposits, which are substantially enriched in platinum and palladium.

  13. The Paleoproterozoic komatiite-hosted PGE mineralization at Lomalampi, Central Lapland Greenstone Belt, northern Finland

    NASA Astrophysics Data System (ADS)

    Törmänen, T.; Konnunaho, J. P.; Hanski, E.; Moilanen, M.; Heikura, P.

    2016-03-01

    Several komatiite-hosted Ni-Cu-PGE deposits occur in Archean and Paleoproterozoic Greenstone Belts in Finland. Some of these deposits are enriched in platinum-group elements, especially in Pd and Pt. The Lomalampi PGE-(Cu-Ni) deposit is associated with a peridotitic cumulate body of the Sattasvaara Formation in the Paleoproterozoic Central Lapland Greenstone Belt. The sulfides in the deposit occur in disseminated form. Whole rock sulfur contents are 0.4-2 wt%, and Ni contents are <0.5 wt% and Cu <0.4 wt%, while PGE contents exceed 500 ppb. The sulfides consist of magmatic pentlandite, pyrrhotite, and chalcopyrite and have not been substantially modified by metamorphic processes. Palladium minerals are associated with sulfides and silicates, but the only Pt-bearing phase, sperrylite, occurs mainly within silicates. The host rock of the deposit is a chromite undersaturated Al-undepleted high-Mg basalt or low-Mg komatiite. In contrast to most other komatiite-hosted Ni-Cu-PGE deposits world-wide that have Pt/Pd around 0.5, the Lomalampi deposit is enriched in Pt over Pd (Pt/Pd = 2). Only a weak contamination signal in the host-cumulate is evident in REE data, but a strong signal is evident in S-isotope ratios (δ34S + 10 ‰ to +15 ‰), which differ substantially from the mantle value (0 ± 2 ‰). Geochemical characteristics (e.g., PGE enrichment) and R-factor modeling indicate certain similarities between Lomalampi and the Raglan Ni-Cu-PGE deposits of Canada. The combined data suggest that Lomalampi formed through contamination of a PGE-rich magnesian magma with S rich country rocks. This suggests that the extensive Central Lapland Greenstone Belt is favorable for komatiite-hosted Ni-Cu-PGE deposits, which are substantially enriched in platinum and palladium.

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

    NASA Astrophysics Data System (ADS)

    Rollinson, Hugh

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

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

    SciTech Connect

    Feiss, P.G.; Siyomana, S.

    1985-01-01

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

  16. Tectonic ironstones in the Zimbabwe craton and their significance for greenstone belt geology

    NASA Astrophysics Data System (ADS)

    Hofmann, A.; Dirks, P.; Jelsma, H.; Matura, N.

    2003-04-01

    The tectonic interpretation of Archaean greenstone belts hinges on the correct recognition, interpretation and correlation of unconformities, stratigraphic marker horizons and layer-parallel shear zones. Metre-thick horizons of ironstone lithologically similar to "sulfide-facies" banded iron formation are a common component of the greenstone stratigraphy of the late Archaean Zimbabwe craton. These rocks are commonly associated with proposed unconformities and have been used extensively as stratigraphic markers in the past. However, they show features which are not compatible with a sedimentary origin and are herein interpreted as silicified and sulfide-impregnated shear zones. Such tectonic ironstones separate different lithostratigraphic units commonly regarded as autochthonous rock sequences. On outcrop scale, shearing along ironstone horizons is indicated by anastomosing foliation domains, folding, boudinage and mylonitic fabrics, and, on a regional scale, by truncation of bedding and/or foliation, an anastomosing geometry of the horizons and duplication/juxtaposition of lithostratigraphic units. Tectonic ironstone formation is attributed to in situ silicification and iron (sulfide)-impregnation of rocks, commonly sediments, by mineralized fluids that penetrated the shear zones and their immediate wall rocks. Shear zones containing tectonic ironstone frequently represent detachment surfaces at the base of now juxtaposed lithotectonic units. These tectonic contacts can resemble angular unconformities where footwall cut-offs occur. The shear zones formed as a result of thin-skinned thrust tectonics that gave rise to horizontal accretion, imbrication and juxtaposition of volcanic and sedimentary rock units prior to deformation associated with granitoid diapirism. As a result, "layer-cake" stratigraphic models of greenstone sequences containing tectonic ironstone "layers" have to be treated with care. We also want to encourage caution when using cherts or ironstones as stratigraphic marker horizons in greenstone terrains. Caution is particularly necessary when angular rock relationships are involved.

  17. A small Archaean belt - diverse age ensemble: A U-Pb study of the Tipasjärvi greenstone belt, Karelia Province, central Fennoscandian Shield, Finland

    NASA Astrophysics Data System (ADS)

    Lehtonen, Elina; Käpyaho, Asko

    2016-03-01

    The Archaean Tipasjärvi greenstone belt is a small area (ca. 5 × 25 km) located within the Karelia Province in Central Fennoscandian Shield, Finland. The belt forms the southernmost part of the larger Archaean Suomussalmi-Kuhmo-Tipasjärvi greenstone complex. The present study results for this site are based on zircon grains of 12 metavolcanic and metasedimentary rock samples that were studied with the single-grain secondary ion mass spectrometry (SIMS) U-Pb method. Our data indicate that the volcanism in the belt took place over three separate episodes: ca. 2.84 Ga, 2.82 Ga and 2.80 Ga. The oldest volcanic rocks are older than the oldest dated tonalitic pluton adjacent to the belt. The main geochemical characteristics of the samples reveal that the felsic volcanic rocks of the different age groups resembled each other. However, contrasting trace element geochemical characteristics between the different age groups are also distinguishable. The detrital zircon record agrees with previous observations indicating that the sediments accumulated at least 50 Myr after the formation of the youngest volcanic rocks. During sediment deposition, older crustal material (> 3.0 Ga) was exposed within the source area. The geochronological results in this study enable us to update the chronostratigraphic interpretation of the Tipasjärvi greenstone belt and to compare these results to those from other parts of the Archaean Suomussalmi-Kuhmo-Tipasjärvi greenstone complex and adjacent tonalitic plutons.

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

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

    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 ɛ-values, whereas whole-rock ɛ- and ɛ-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.

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

    NASA Astrophysics Data System (ADS)

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

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

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

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

    SciTech Connect

    Ludden, J.N.

    1985-01-01

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

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

    SciTech Connect

    Feng, R.; Kerrich, R. )

    1991-11-01

    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.

  3. Geochemistry of contaminated komatiites from the Umburanas greenstone belt, Bahia State, Brazil

    NASA Astrophysics Data System (ADS)

    Menezes Leal, Angela Beatriz de; Santos, André Luis Dias; Bastos Leal, Luiz Rogério; Cunha, José Carlos

    2015-08-01

    The late Archaean Umburanas greenstone belt (UGB) is located in the São Francisco Craton, southwest of Bahia State, Brazil. The lower unit of UGB comprises basal komatiite lavas and tholeiitic basalts intercalated with felsic volcanic rocks. The regional crystalline basement rocks, the Gavião block, predominantly consist of granitic, granodioritic and migmatitic gneiss along with tonalite-trondhjemite-granodiorite (TTG) associations. Petrographic studies of UGB komatiites reveal characteristic spinifex igneous texture although primary mineralogy is rarely preserved. Based on textural relationships, komatiites are divided into cumulate, spinifex, and massive types. The MgO content varies in the range 31.5-40.4 wt%. The MgO-SiO2 negative correlation in komatiites suggests olivine fractionation trend. The UGB komatiites are of Al-undepleted type, characterized by Al2O3/TiO2 (21-48) ratio, enriched in highly incompatible LILE relative to moderately incompatible HFSE and distinct negative Nb, Sr and Eu anomalies. Also shows depletion of light rare earths, convex-downward rare earth patterns typically not observed in komatiites world-wide, and primitive mantle normalized Gd/Yb (1.03-1.23) and La/Sm (2.36-4.99) ratios. The negative Eu anomaly is attributed to the circulation of H2O-rich fluid, whereas the negative Nb and Sr anomalies are attributed to contamination from granitic basement rocks of the Gavião block. The UGB komatiites are most likely derived from adiabatic decompressional melting of a mantle plume. The melting took place at liquidus temperatures in the range 1572-1711 °C, which is consistent with mantle-plume origin invoked for several other komatiites in Archaean greenstone belts elsewhere. The melts were more likely generated at a depth shallower than 100 km (pressure < 2.5 GPa) where garnet was absent in the source mineralogy. Geochemical characteristics suggest contamination of primary melts with granitic basement rocks either during ascent of melt or during emplacement of magma in a continental basin setting. Greenschist to low-T amphibolite facies metamorphism at ˜2Ga may also have played a role in modifying the original komatiite petrography and composition.

  4. 3-D imaging of the Central Lapland Greenstone Belt using magnetotelluric and seismic data

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

    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.

  5. Single zircon ages for felsic to intermediate rocks from the Pietersburg and Giyani greenstone belts and bordering granitoid orthogneisses, northern Kaapvaal Craton, South Africa

    NASA Astrophysics Data System (ADS)

    Kröner, A.; Jaeckel, P.; Brandl, G.

    2000-05-01

    Previous models for the temporal evolution of greenstone belts and surrounding granitoid gneisses in the northern Kaapvaal Craton can be revised on the basis of new single zircon ages, obtained by conventional UPb dating and PbPb evaporation. In the Pietersburg greenstone belt, zircons from a metaquartz porphyry of the Ysterberg Formation yielded an age of 2949.7±0.2 Ma, while a granite intruding the greenstones, and deformed together with them, has an age of 2853 + 19/-18 Ma. These data show felsic volcanism in this belt to have been coeval with felsic volcanism in the Murchison belt farther east, and the date of ˜2853 Ma provides an older age limit for deformation in the region. In contrast, a meta-andesite of the Giyani greenstone belt has a zircon age of 3203.3±0.2 Ma, while a younger and cross-cutting feldspar porphyry has an emplacement age of 2874.1±0.2 Ma. The meta-andesite is intercalated with various mafic and ultramafic rocks and, therefore, the age of 3.2 Ga appears plausible for the bulk of the Giyani greenstones. Granitoid gneisses surrounding the Pietersburg and Giyani belts vary in composition from tonalite to granite and texturally from well-layered to homogeneous but strongly foliated. These rocks yielded zircon ages between 2811 and 3283 Ma. The pre-3.2 Ga gneisses are polydeformed and may have constituted a basement to the Giyani greenstone sequence, while the younger gneisses are intrusive into the older gneiss assemblage and/or into the greenstones. The Giyani and Pietersburg belts probably define two separate crustal entities that were originally close together but were later displaced by strike-slip movement.

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

    SciTech Connect

    Sylvester, P.J.

    1985-01-01

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

  7. Volcanic facies and preliminary geochemical observations of the Goren greenstone belt, Burkina Faso

    NASA Astrophysics Data System (ADS)

    Peters, Luke

    2013-04-01

    Volcanic facies and preliminary geochemical observations of the Goren greenstone belt, Burkina Faso L.F.H. Peters and K.A.A Hein School of Geosciences, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa. The Goren Greenstone Belt (GGB) is a Palaeoproterozoic volcano-sedimentary belt situated in the northeast of Burkina Faso in the West African craton (WAC). Basalt is the main volcanic constituent of the GGB, specifically mid-ocean ridge basalts (MORBS), which have undergone pervasive greenschist facies metamorphism during at least 2 deformation including the Tangaean Event (2170-2130 Ma) and Eburnean Orogeny (2130-1980 Ma). Remarkably, many of the primary textures and minerals remain intact in less deformed regions of the GBB. Textural characteristics and petrographic analyses include aphyric and aphanitic textures, amygdales, hyaloclastic brecciation, pillow structures and preserved (chloritised) volcanic glass. Despite the ubiquitous presence of chlorite and epidote, plagioclase and clinopyroxene microlites are fairly common albeit altered. Phenocrysts (< 1 mm) of plagioclase and CPX are present in some samples but aphyric texture is dominant. These textures indicate that the basalts represent coherent units of sub-aqueous extrusion from a proximal volcanic facies setting relative to the original magma conduit. A repetitious succession of Fe-rich meta-siltstones, fine-grained, carbonaceous, Fe-rich exhalatives and volcaniclastic units is intercalated with the basalts. The volcaniclastic units contrast with the MORBs, which raises questions about the source region of the volcaniclastics. In hand sample, the volcaniclastic rocks show an array of various sized fragments, compared to the fine-grained nature of the MORBs. They are dominated by euhedral, zoned, brown volcanic hornblende, large (2.5-5 mm) euhedral plagioclase crystals, and sub-angular to rounded quartz grains in a poorly sorted volcanogenic sedimentary sequence. Due to the alteration of the original mineralogy, whole rock geochemical analyses of the MORBs were approached with caution, focusing on immobile and trace elements. The REE chemistry displayed a flat trend with an average value of 10x chondrite. The sample suite shows both slight enrichments and depletions of light-REE relative to heavy-REE. This is typical of N-type MORBS. A multi-element diagram illustrates a distinct, negative phosphorus anomaly, which is consistent with previous studies throughout the WAC. However, the volcaniclastic unit has larger phosphorus and significantly lower Ti (ppm) values in comparison to the MORBs. The Mg # of the basalts range from 42-57 suggesting fractionation of the melt had already begun by the time eruption took place. We interpret the volcaniclastic units as an erosional product of a pre-existing volcanic arc, deposited in a back-arc basin which has undergone extension.

  8. Overview of the Barberton Drilling Project

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    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.

  9. 3.4-Billion-year-old biogenic pyrites from Barberton, South Africa: sulfur isotope evidence

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

    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.

  10. 3.4-Billion-year-old biogenic pyrites from Barberton, South Africa: sulfur isotope evidence.

    PubMed

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

    1993-10-22

    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

  11. Anomalous magnetizations in 3.4 b.y. old Barberton Mountain Land samples

    NASA Technical Reports Server (NTRS)

    Cisowski, S. M.

    1981-01-01

    The ratio of natural remanence (NRM) to saturation remanence is exceedingly high for a number of basaltic to ultramafic samples from the 3.4 billion year old Barberton Mountain Land greenstone belt, South Africa. Although conventional paleointensity methods indicate paleofields of several oersteds, demagnetization curves plotted on logarithmic scale clearly show the NRM in these samples to be unlike thermal remanence. It is probable that the observed NRM is a chemical remanence related to the greenschist metamorphic event, and that the intense magnetizations are the result of internally generated, rather than external fields.

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

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    The Archaean oceans differed from today in being anoxic, Fe-rich and S-poor. Despite the low abundance of marine sulfate, significant amounts of sedimentary pyrite are associated with shales and sandstones deposited in Palaeoarchean time. Combined Fe and S isotopes can be used in pyrite to trace element sources as well as pathways of mineral formation and environmental redox processes since they record the changes in redox state in abiotic and biological processes. In this study, Fe and S isotopes were measured in pyrite from sedimentary rocks sampled by diamond drilling in the Lower Mapepe Formation (3.26-3.23 Ga, Lowe, 1999)1 of the Archean Barberton Greenstone Belt, South Africa. We performed in situ Fe and multiple S isotopic analysis by secondary ionization mass spectrometry (SIMS) of single mineral grains. The grain size range from 10 to several hundreds of micrometers. The stratigraphy consists of barite-chert units and barite-free terrigeneous clastic sediments with pyrites occurring in both types of lithologies. The complete range of pyrite δ56Fe data vary from -2.61 to +2.74 ‰ . Most individual pyrite samples showed iron isotopic variability of between 1.0-1.5 ‰, consistent with the range induced by abiotic pyrite precipitation (Guilbaud et al. 2012)2, whilst one sample contained more extreme variability of close to 5 ‰. Clear correlations with multiple S isotopes were not seen in individual samples, but there was a clear shift in average Fe isotope values and mixing trends in multiple S isotopes on going from the barite-free to the barite-rich part of the drill core. Pyrites in barite-free lithologies show slightly more positive δ56Fe value than those in close association with the barite. This suggests different sources of iron in the lower and upper parts of the stratigraphy, with a possible hydrothermal source for the pyrite associated with the barite. The origin of the more negative δ56Fe values (up to -2.61 ‰) is unclear but might result from microbial activity or mixing with a light iron pool. Pyrites with a positive δ56Fe signature could suggest involvement of δ56Fe enriched oxyhydroxides. Our in situ Fe isotope data reveal fractionation, mixing and inherited variability on a scale that would be difficult to resolve using bulk rock analyses. This microscale approach is critical to better constrain iron biogeochemistry in the Mid-Archaean environment. 1 Lowe, D. R., 1999. Geologic evolution of the Barbeton Greenstone Belt and vicinity. Geol. Soc. Am. Spec. Pap. 329, 287-312 2Guilbaud, I.R., Butler, I.B., Ellam, R.M. 2011. Abiotic pyrite formation produces a large Fe isotope fractionation. Science 332, 1528-1551

  14. 3.5-Ga hydrothermal fields and diamictites in the Barberton Greenstone Belt-Paleoarchean crust in cold environments.

    PubMed

    de Wit, Maarten J; Furnes, Harald

    2016-02-01

    Estimates of ocean temperatures on Earth 3.5 billion years ago (Ga) range between 26° and 85°C. We present new data from 3.47- to 3.43-Ga volcanic rocks and cherts in South Africa suggesting that these temperatures reflect mixing of hot hydrothermal fluids with cold marine and terrestrial waters. We describe fossil hydrothermal pipes that formed at ~200°C on the sea floor >2 km below sea level. This ocean floor was uplifted tectonically to sea level where a subaerial hydrothermal system was active at 30° to 270°C. We also describe shallow-water glacial diamictites and diagenetic sulfate mineral growth in abyssal muds. These new observations reveal that both hydrothermal systems operated in relatively cold environments and that Earth's surface temperatures in the early Archean were similar to those in more recent times. PMID:26933677

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-10-01

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

  17. 3D structure and physical properties of the Kuhmo Greenstone Belt (eastern Finland): Constraints from gravity modelling and seismic data and implications for the tectonic setting

    NASA Astrophysics Data System (ADS)

    Silvennoinen, Hanna; Kozlovskaya, Elena

    2007-04-01

    In our paper we study 3D structure of the Kuhmo Greenstone Belt (2800-2760 Ma) located in the Finnish part of the Archean Karelian craton in the Fennoscandian Shield. Although the surface position of the belt is relatively well constrained by geological studies, its 3D structure is poorly known. Previously, two groups of competing geodynamic models have been proposed to explain formation and stabilization of the belt. The first group suggest that the belt may be formed in intracratonic, extensional rift environment with igneous rocks being derived from hot, upwelling mantle plume. In this case one would expect that the belt has a diapiric shape with deep root. The other suggests that the belt may be formed by collision and subduction processes, resulting in thin elongated shape and shallow root. Thus the knowledge of the 3D structure of the belt is essential to distinguish between two groups of models. The belt is marked by a regional-scale positive Bouguer anomaly, indicating strong density contrast between the belt and surrounding bedrock. In spite of that, previous seismic studies (SVEKA'81 wide-angle reflection and refraction profile and FIRE1 near-vertical reflection profile) revealed pronounced change in the crust-mantle boundary beneath the belt (from almost 60 to 40 km), but no any velocity or sharp reflectivity contrasts between the belt and its surrounding. In order to explain this apparent disagreement, we estimated seismic velocities and density of the main rock types of the belt from modal mineralogy. The result of the modelling suggests that the main rocks types of the belt have low seismic velocities and high densities due to high content of amphibole, biotite and muscovite. This explains why the belt is not seen in the seismic data, in spite of the gravity high. Thus we applied 3D gravity modelling and inversion in order to obtain the 3D density structure of the belt. Our result demonstrated that the Kuhmo Greenstone Belt is a surface structure that is 10-12 km wide with depth less than 7 km and average density of 2.84 × 10 3 kg/m 3. The belt has no deep "root" in the middle crust and lower crust. The difference in Bouguer anomaly west and east of the belt is explained by the regional trend produced by the Moho uplift. Our model implies that the belt was formed as a result of plate-tectonics like processes rather than mantle diapirism, although these processes not directly comparable to the Phanerozoic ones due to the higher heat flux in Late Archean.

  18. Estimation of uncertainties in a 3D geological model of the Sandstone Greenstone Belt, Yilgarn Craton, Western Australia

    NASA Astrophysics Data System (ADS)

    Wellmann, Florian; Murdie, Ruth; Gessner, Klaus

    2015-04-01

    Geological models representing the structure of the subsurface are becoming a regular product of geological surveys. 3-D models combine information from geological field mapping and interpretations of geophysical data, including gravity, aerial magnetic surveys, and seismic and magnetotelluric studies. It is widely accepted that the sparse data at depth and the ambiguity of structural interpretations of geophysical data lead to inherent model uncertainties. The analysis and visualisation of model uncertainties is therefore the scope of current research. We apply here a recently developed method to estimate uncertainties in 3D structural geological models to a model of the Sandstone Greenstone Belt in the Archean Yilgarn Craton in Western Australia. The geological modelling method is based on an implicit potential-field approach in order to handle complex structures in this region, including multiply deformed stratigraphic units and complex fault networks. We then identify uncertainties in relevant geological parameters and apply a random method to sample probable structural model realisations. The ensemble of generated models is then used as a basis for uncertainty investigations. We apply several methods for uncertainty quantification and visualisation, including unit probabilities, stratigraphic distances, and cell information entropies. The analysis shows that it is feasible to use these measures as indications of model uncertainties in 3D visualisations, as well as composite measures of uncertainties on maps. With the range of novel approaches analysing uncertainties in structural geological models, we are optimistic that uncertainty evaluations can form an integral part of future geological modelling products of geological surveys.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Tshibubudze, Asinne; Hein, Kim A. A.

    2010-05-01

    The Oudalan-Gorouol Greenstone Belt (OGGB) forms part of the Palaeoproterozoic as the Baoulé-Mossi domain of the West African Craton (WAC) and hosts gold deposits at Essakane, Gossey, Korizena, and Falagountou in NE Burkina Faso, and Kossa goldfield in Niger. The Birimian supracrustal sequences in the OGGB are dominated by meta-volcanoclastic greywacke intercalated meta-conglomerate, siltstone and shale, carbonate (dolomite) and volcanic units pillow basalts). The belt is surrounded by plutonic rocks including granite, TTG suite granitoids and granite gneiss. The sequences where subjected to two phases of deformation, and several phases of contact metamorphosed to hornblende-hornfels facies during emplacement of pyroxenite-gabbro-norite, granodiorite-tonalite and gabbro dykes and porphyritic sills. The OGGB is bounded and/or crosscut by several major NNE to NE-trending shear zones including the steeply east-dipping Markoye Shear Zone (western margin of the OGGB), Tin Takanet-Bellekcire Shear Zone, Dori Shear Zone, Kargouna Shear Zone, Takabougou Shear Zone, and Bom Kodjelé Shear Zone (transects the centre of the OGGB). The structures were readily identified using LANDSAT, Aster, aeromagnetic and RTP magnetic data, with follow-up strategic mapping, highlighting the value of interpreting geophysical and remotely sensed data in regional mapping in Burkina Faso and Niger. Structural studies completed in 2007 adjacent to the Essakane gold mine indicated that the NE-trending, first-order crustal-scale Markoye Shear Zone (MSZ) has undergone at least two phases of reactivation concomitant to two phases of regional deformation (Tshibubudze et al., 2009). The first phase of deformation, D1, resulted in the formation of NNW-NW trending folds and thrusts during dextral-reverse displacement on the MSZ. The deformation predates the Eburnean Orogeny is termed the Tangaean Event (meaning low hills in the Moré language of Burkina Faso) and is tentatively dated at ca. 2170-2130 Ma (Hein, 2009). D2 involved a period of SE-NW crustal shortening and sinistral-reverse displacement on the MSZ, and is correlated to the Eburnean Orogeny ~2.1 Ga of Feybesse et al. (2006). Deformation in D2 is characterised by NE-trending regional folds (F2) and a pervasive NE-trending foliation (S2-C to S2). Since 2007 an identical tectonic history has been established for a number of shear zones in the OGGB including the north-trending Kargouna Shear Zone, which is subtended by NW- and NE-trending shears. However the metamorphic grade and mineral assemblages vary from one shear zone to the next. Structural studies completed adjacent to the Dori batholith have indicated that the MSZ forms a shear complex that was active during pluton emplacement. However, the MSZ has two main branches that join at the location of a mylonite zone located north west of Essakane. Southwest of Essakane, a NW-trending mylonite zone crosscuts the Dori batholith and near the village of Kargouna, which is situated southeast of Essakane, the Kargouna shear crosscuts and deforms the Dori batholith. It is thus likely that the Dori batholith was emplacement prior to D1 in the OGGB. Gold mineralization in the OGGB is generally hosted in the hanging-wall of NE-trending faults and or NW-trending folds in metasiltstone-sandstone-shale sequences. Nkuna (2009) concluded that the deposits can be classified as orogenic gold deposits under the sub-class of "intrusion related" due to their proximity to plutonic masses, which concurs with geophysical studies for the OGGB. References: Feybesse, J.L., Billa, M., Guerrot, C., Duguey, E., Lescuyer, J.L., Milési, J.P., Bouchot, V., 2006. The Palaeoproterozoic Ghanaian province: Geodynamic model and ore controls, including regional stress modelling. Precambrian Research 149, 149-196. Hein, K.A.A., 2009 (In press). Structural chronologies in the Goren Greenstone belt (Burkina Faso); Implications for West African tectonics. Journal of African Earth Sciences. Tshibubudze, A., Hein, K.A.A., Marquis, P. 2009. The Markoye Shear Zone in NE Burkina Faso. Journal of African Earth Sciences 55, 245-256. Nkuna, B., 2009 Ore genesis of the Essakane, Falagountou and Sokadie Au deposits: Oudalan-Gorouol Greenstone Belt (OGGB), Burkina Faso, West African Craton (WAC). Unpublished Honours thesis, University of the Witwatersrand Johannesburg, 60p.

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

    NASA Astrophysics Data System (ADS)

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

    1984-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Genna, Dominique; Gaboury, Damien; Roy, Gilles

    2014-04-01

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

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

    PubMed Central

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

    2015-01-01

    Mass-independent fractionation of sulfur isotopes (S-MIF) results from photochemical reactions involving short-wavelength UV light. The presence of these anomalies in Archean sediments [(4–2.5 billion years ago, (Ga)] implies that the early atmosphere was free of the appropriate UV absorbers, of which ozone is the most important in the modern atmosphere. Consequently, S-MIF is considered some of the strongest evidence for the lack of free atmospheric oxygen before 2.4 Ga. Although temporal variations in the S-MIF record are thought to depend on changes in the abundances of gas and aerosol species, our limited understanding of photochemical mechanisms complicates interpretation of the S-MIF record in terms of atmospheric composition. Multiple sulfur isotope compositions (δ33S, δ34S, and δ36S) of the >3.8 billion-year-old Nuvvuagittuq Greenstone Belt (Ungava peninsula) have been investigated to track the early origins of S-MIF. Anomalous S-isotope compositions (Δ33S up to +2.2‰) confirm a sedimentary origin of sulfide-bearing banded iron and silica-rich formations. Sharp isotopic transitions across sedimentary/igneous lithological boundaries indicate that primary surficial S-isotope compositions have been preserved despite a complicated metamorphic history. Furthermore, Nuvvuagittuq metasediments recorded coupled variations in 33S/32S, 34S/32S, and 36S/32S that are statistically indistinguishable from those identified several times later in the Archean. The recurrence of the same S-isotope pattern at both ends of the Archean Eon is unexpected, given the complex atmospheric, geological, and biological pathways involved in producing and preserving this fractionation. It implies that, within 0.8 billion years of Earth’s formation, a common mechanism for S-MIF production was established in the atmosphere. PMID:25561552

  4. Geochemistry of fine-grained clastic sediments in the Archean Abitibi greenstone belt, Canada: Implications for provenance and tectonic setting

    NASA Astrophysics Data System (ADS)

    Feng, R.; Kerrich, R.

    1990-04-01

    Archean sandstone and shale samples from turbiditic (TF) and alluvial facies (AF) in the Southern Volcanic Zone of the Abitibi greenstone belt, Canada, have been analyzed for major and trace elements. The sandstones from TF are mainly greywackes, whereas those from AF are lithic arenite. SiO 2 ranges from 51 to 68%. Geochemically, the clastic sediments cluster into mafic element (MEP) and low mafic element (LMEP) populations. The MEP sediments, which include turbiditic facies sediment samples from the Larder Lake Group in the Kirkland Lake area, are characterized by elevated abundances of MgO (>5%), Ni (>200 ppm), Cr (>400 ppm), Sc (>22 ppm), and FeO (>7.5%) abundances; lower contents of incompatible elements, such as Th, U, Ta, Hf, Zr, and total REEs (<45 ppm); and lower contents of alkaline earth elements, Sr, Ba, and Cs, relative to the LMEP sediments. La/Yb N ratios are ≤4.5, with Eu/Eu* ≥ 1. The LMEP sediments (which include samples from the Beatty, Dome, and Three Nations Lake formations in Timmins, the Kewagama Group, Noranda area, and Timiskaming Group in the Kirkland Lake area), however, show reverse abundance distributions. The geochemical gaps shown by the major and trace elements define two populations of sediments, suggesting contrasting provenances for them: the MEP sediments require a dominantly mafic and ultramafic (90%) source with 10% felsic contribution, whereas the LMEP sediments require a mixture of felsic (75%) and mafic (25%) rocks. This compositional distribution of the sediments is closely related to their tectonic environments. The MEP was formed in basins proximal to or within an active oceanic rift, consequently having ultramafic and mafic rocks as the major source. For the LMEP, calc-alkaline volcanic sequences formed in an island arc-like setting were the major source. These two contrasting volcanic-plutonic terranes were tectonically juxtaposed during late Archean collisional tectonics.

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

    USGS Publications Warehouse

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

    2006-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-11-01

    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=+0.50.1). Secondary sulfides from crosscutting veins do not show mass-independent fractionation of sulfur isotopes (-0.1??33S?+0.3; mean ?33S=+0.10.1). 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 (6518 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.

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

    NASA Astrophysics Data System (ADS)

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

    1994-02-01

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

  8. Spinifex-textured komatiites in the south border of the Carajas ridge, Selva Greenstone belt, Carajás Province, Brazil

    NASA Astrophysics Data System (ADS)

    Siepierski, Lincoln; Ferreira Filho, Cesar Fonseca

    2016-03-01

    Spinifex-textured komatiites in the Selva greenstone belt are the first unequivocal examples of komatiites in the Transition Subdomain of the Carajás Mineral Province. Outcrops of spinifex-textured komatiites, located ∼1.5 km to the south of the Carajás ridge, were discovered during regional exploration for Ni-Cu-(PGE) sulfide deposits by VALE. They are associated with a 3.8 km long unit consisting of variable types of ultramafic rocks (talc schist, serpentinite and spinifex-textured komatiite). This ultramafic unit follows the steep dipping NW-SE trending Selva greenstone belt composed mainly by quartz-chlorite schists (interpreted as metasediments) and chlorite-actinolite schists (interpreted as metabasalts). Greenschist facies metamorphic parageneses characterize all rock types in the Selva greenstone belt. The komatiitic rocks in the Selva belt comprise a sequence of flows consisting of an upper spinifex-textured layer and a lower olivine cumulate layer. Although the spinifex and cumulus textures are well preserved in the field, the primary mineralogy of the komatiites has been completely replaced by greenschist facies metamorphic minerals. Platy olivine spinifex texture, consisting of an array of roughly parallel olivine plates, and random spinifex texture, consisting of randomly oriented olivine plates, are the most common primary volcanic textures in komatiites in the Selva greenstone belt. Platy and random spinifex texture is defined by former plates of olivine replaced by serpentine with minor actinolite, chlorite and magnetite, alternating with former matrix replaced by abundant actinolite and minor chlorite, talc, serpentine, and magnetite. The domains between olivine plates in both platy and random spinifex-textured rocks contain irregular arrays of fine-grained parallel crystals, representing primary fine-grained "quench" clinopyroxene crystals replaced by actinolite. Spinifex-textured komatiites have MgO contents bracket between 22.8 and 26.9 wt.%, and cumulate textured komatiites have MgO contents up to 40.6 wt.%. When plotted vs MgO contents, most major and minor elements fall on well-defined linear trends indicating control by olivine fractionation or accumulation. Komatiites from the Selva and Seringa (located in the Rio Maria Domain) belts are Al-undepleted with Al2O3/TiO2 ratios close to 20. Results for CaO, Na2O, and REE suggest that these elements were mobile and their abundances have been modified during metasomatic alteration. REE contents in some samples are very high (up to 40 times primitive mantle values) and REE patterns vary from flat (La/YbMN ∼ 1) to highly enriched in LREE (La/YbMN up to ∼ 10). The REE mobility may be related to hydrothermal alteration associated to Cu-Au mineralization in the region. The identification of spinifex-textured komatiites close to the Carajás Basin suggests the continuation of 3.0-2.9 Ga greenstone belts of the Rio Maria Domain within the Transition Subdomain, and enlarges the area with potential to host komatiite-associated Ni-Cu-PGE deposits.

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

    NASA Technical Reports Server (NTRS)

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

    2007-01-01

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

  10. The Asama igneous complex, central Japan: An ultramafic-mafic layered intrusion in the Mikabu greenstone belt, Sambagawa metamorphic terrain

    NASA Astrophysics Data System (ADS)

    Agata, T.

    1994-11-01

    The Asama igneous complex comprises layered mafic and ultramafic plutonic rocks exposed over about 500×6000 m in the Mikabu greenstone belt, Sambagawa metamorphic terrain of Mie Prefecture; its margins terminate by faults, and there is no trace of chilled rocks. The exposed layered sequence is about 460 m thick, and includes dunite, plagioclase wehrlite, olivine gabbro and two-pyroxene gabbro. The crystallization sequence of essential cumulus minerals is olivine, followed by plagioclase and clinopyroxene together, and finally the appearance of orthopyroxene. Olivine systematically varies in composition from Fo 89 to Fo 78 with stratigraphic height in the lower to middle portion of the layered sequence. The composition of clinopyroxene changes from Ca 49Mg 46Fe 5 to Ca 40Mg 47Fe 13 upward in the layered sequence; cumulus orthopyroxene, which occurs at the top of the exposed layered sequence, has a composition of Ca 2Mg 74Fe 24. Cumulus chromite occurs as disseminated grains in peridotitic rocks, and tends to increase its {Fe3+}/{(Cr+Al+Fe 3+) } ratio with stratigraphic height. The most aluminous chromite [ {Cr}/{(Cr+Al)} = 0.48 ] occurs in dunite that crystallized shortly before plagioclase began to separate as an essential phase. The {Cr}/{(Cr+Al)} ratio of the most aluminous chromite, coupled with the crystallization order of essential minerals, suggests that the Asama parental magma was moderately enriched in plagioclase and clinopyroxene components in the normative mineral diagram plagioclase-clinopyroxene-orthopyroxene. It was similar to a Hawaiian tholeiite and different from the Bushveld and Great "Dyke" parental magmas that were more enriched in orthopyroxene component; it also differed from mid-oceanic ridge basalts that are more depleted in the orthopyroxene component. The Asama clinopyroxene and chromite show characteristically high TiO 2 contents and are also similar to those in Hawaiian tholeiites. The Asama igneous complex probably resulted from the crystallization of a magma of a Hawaiian (oceanic-island) tholeiite composition and formed in an oceanic island regime.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    Recent work on the Nuvvuagittuq Greenstone Belt (NGB, Nunavik, Qubec) 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 0.490.15%. 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 0.070.08%. 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

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

    PubMed

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

    2006-08-01

    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

  13. Geochemistry of the metavolcanic rocks in the vicinity of the MacLellan Au-Ag deposit and an evaluation of the tectonic setting of the Lynn Lake greenstone belt, Canada: Evidence for a Paleoproterozoic-aged rifted continental margin

    NASA Astrophysics Data System (ADS)

    Glendenning, Michael W. P.; Gagnon, Joel E.; Polat, Ali

    2015-09-01

    The Paleoproterozoic (ca. 1900 Ma) Lynn Lake greenstone belt of northern Manitoba, Canada, has been previously characterized as comprising a series of tectonically juxtaposed intra-oceanic-derived metavolcanic rocks. The results of more recent local and regional studies, however, support a significant contribution of continental crust during formation of the metasedimentary, metavolcanic, and intrusive igneous rocks that comprise the majority of the Lynn Lake greenstone belt. The tectonic model previously proposed for the Lynn Lake greenstone belt, however, did not consider the geodynamics of the Lynn Lake greenstone belt in the context of all available data. In this study, we report the results of outcrop mapping and petrographic analysis, as well as major, minor, and trace element geochemical analyses for 54 samples from the Northern terrane, and integrate and compare the results with data from previously published studies. These data are used to recharacterize the metavolcanic rocks and to develop a new geodynamic model for the formation of the Lynn Lake greenstone belt. Ultramafic to intermediate rocks in the vicinity of the MacLellan Au-Ag deposit are characterized primarily by E-MORB-like trace element characteristics and Th-Nb-La systematics, which are interpreted to be the result of a primary, plume-derived melt interacting with continental lithosphere at a thinned (i.e., rifted) continental margin. Similarly, the majority of the mafic to intermediate rocks that comprise the Lynn Lake greenstone belt are characterized by flat to E-MORB-like trace element patterns and Th-Nb-La systematics, which are consistent with mantle plume-derived, contaminated, oceanic continental rift or rifted margin setting rocks. This study suggests that the metavolcanic rocks of the Lynn Lake greenstone belt were derived via rifting between the Superior and Hearne Cratons, which resulted in the formation and growth of the Manikewan Ocean. Alternatively, the metavolcanic rocks could have been derived from an upwelling plume generated from a back-arc-style subduction zone that formed between the Rae and Hearne Cratons during the closure of the Snowbird Ocean, which resulted in rifting of the passive Hearne margin.

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

    NASA Astrophysics Data System (ADS)

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

    2003-04-01

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

  15. 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)

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

    2012-04-01

    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.

  16. Trace-element fingerprints of chromite, magnetite and sulfides from the 3.1 Ga ultramafic-mafic rocks of the Nuggihalli greenstone belt, Western Dharwar craton (India)

    NASA Astrophysics Data System (ADS)

    Mukherjee, Ria; Mondal, Sisir K.; González-Jiménez, José M.; Griffin, William L.; Pearson, Norman J.; O'Reilly, Suzanne Y.

    2015-06-01

    The 3.1 Ga Nuggihalli greenstone belt in the Western Dharwar craton is comprised of chromitite-bearing sill-like ultramafic-mafic rocks that are surrounded by metavolcanic schists (compositionally komatiitic to komatiitic basalts) and a suite of tonalite-trondhjemite-granodiorite gneissic rocks. The sill-like plutonic unit consists of a succession of serpentinite (after dunite)-peridotite-pyroxenite and gabbro with bands of titaniferous magnetite ore. The chromitite ore-bodies (length ≈30-500 m; width ≈2-15 m) are hosted by the serpentinite-peridotite unit. Unaltered chromites from massive chromitites (>80 % modal chromite) of the Byrapur and Bhaktarhalli chromite mines in the greenstone belt are characterized by high Cr# (100Cr/(Cr + Al)) of 78-86 and moderate Mg# (100 Mg/(Mg + Fe2+)) of 45-55. In situ trace-element analysis (LA-ICPMS) of unaltered chromites indicates that the parental magma of the chromitite ore-bodies was a komatiite lacking nickel-sulfide mineralization. In the Ga/Fe3+# versus Ti/Fe3+# diagram, the Byrapur chromites plot in the field of suprasubduction zone (SSZ) chromites while those from Bhaktarhalli lie in the MOR field. The above results corroborate our previous results based on major-element characteristics of the chromites, where the calculated parental melt of the Byrapur chromites was komatiitic to komatiitic basalt, and the Bhaktarhalli chromite was derived from Archean high-Mg basalt. The major-element chromite data hinted at the possibility of a SSZ environment existing in the Archean. Altered and compositionally zoned chromite grains in our study show a decrease in Ga, V, Co, Zn, Mn and enrichments of Ni and Ti in the ferritchromit rims. Trace-element heterogeneity in the altered chromites is attributed to serpentinization. The trace-element patterns of magnetite from the massive magnetite bands in the greenstone belt are similar to those from magmatic Fe-Ti-V-rich magnetite bands in layered intrusions, and magnetites from andesitic melts, suggesting that magnetite crystallized from an evolved gabbroic melt. Enrichments of Ni, Co, Te, As and Bi in disseminated millerite and niccolite occurring within chromitites, and in disseminated bravoite within magnetites, reflect element mobility during serpentinization. Monosulfide solid solution inclusions within pyroxenes (altered to actinolite) in pyroxenite, and interstitial pyrites and chalcopyrites in magnetite, retain primary characteristics except for Fe-enrichment in chalcopyrite, probably due to sub-solidus re-equilibration with magnetite. Disseminated sulfides are depleted in platinum-group elements (PGE) due to late sulfide saturation and the PGE-depleted nature of the mantle source of the sill-like ultramafic-mafic plutonic rocks in the Nuggihalli greenstone belt.

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

    NASA Astrophysics Data System (ADS)

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

    1992-12-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

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

    NASA Astrophysics Data System (ADS)

    Kalbfleisch, Netasha

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

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

    PubMed

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

    2013-11-15

    This report summarizes recent findings of environmental arsenic (As) contamination and the consequent health effects in a community located near historic gold mining activities in the Mangalur greenstone belt of Karnataka, India. Arsenic contents in water, hair, nail, soil and food were measured by FI-HG-AAS. Elemental analyses of soils were determined by ICP-MS (inductively coupled plasma-mass spectrometry). Of 59 tube-well water samples, 79% had As above 10 μg L(-1) (maximum 303 μg L(-1)). Of 12 topsoil samples, six were found to contain As greater than 2000 mg kg(-1) possibly indicating the impact of mine tailings on the area. All hair and nail samples collected from 171 residents contained elevated As. Arsenical skin lesions were observed among 58.6% of a total 181 screened individuals. Histopathological analysis of puncture biopsies of suspected arsenical dermatological symptoms confirmed the diagnosis in three out of four patients. Based on the time-course of As-like symptoms reported by the community as well as the presence of overt arsenicosis, it is hypothesized that the primary route of exposure in the study area was via contaminated groundwater; however, the identified high As content in residential soil could also be a significant source of As exposure via ingestion. Additional studies are required to determine the extent as well as the relative contribution of geologic and anthropogenic factors in environmental As contamination in the region. This study report is to our knowledge one of the first to describe overt arsenicosis in this region of Karnataka, India as well as more broadly an area with underlying greenstone geology and historic mining activity. PMID:23228450

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

    PubMed Central

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

    2014-01-01

    This report summarizes recent findings of environmental arsenic (As) contamination and the consequent health effects in a community located near historic gold mining activities in the Mangalur greenstone belt of Karnataka, India. Arsenic contents in water, hair, nail, soil and food were measured by FI-HG-AAS. Elemental analyses of soils were determined by ICP-MS (inductively coupled plasma-mass spectrometry). Of 59 tube-well water samples, 79% had As above 10 μg L−1 (maximum 303 μg L−1). Of 12 topsoil samples, six were found to contain As greater than 2000 mg kg−1 possibly indicating the impact of mine tailings on the area. All hair and nail samples collected from 171 residents contained elevated As. Arsenical skin lesions were observed among 58.6% of a total 181 screened individuals. Histopathological analysis of puncture biopsies of suspected arsenical dermatological symptoms confirmed the diagnosis in 3 out of 4 patients. Based on the time-course of arsenic-like symptoms reported by the community as well as the presence of overt arsenicosis, it is hypothesized that the primary route of exposure in the study area was via contaminated groundwater; however, the identified high As content in residential soil could also be a significant source of As exposure via ingestion. Additional studies are required to determine the extent as well as the relative contribution of geologic and anthropogenic factors in environmental As contamination in the region. This study report is to our knowledge one of the first to describe overt arsenicosis in this region of Karnataka, India as well as more broadly an area with underlying greenstone geology and historic mining activity. PMID:23228450

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

  4. Crustal outgassing and LILE enrichment in major lithosphere structures, Archean Abitibi greenstone belt: evidence on the source reservoir from strontium and carbon isotope tracers

    NASA Astrophysics Data System (ADS)

    Kerrich, R.; Fryer, B. J.; King, R. W.; Willmore, L. M.; van Hees, E.

    1987-10-01

    Major structural discontinuities in the Abitibi greenstone belt acted as conduits for outgassing of the Archean crust, as reflected in fixation of a select group of lithophile elements including Si, C, K, Rb, Ba, Li, Cs, B and Pb, in metasomatized faults. For two of the largest structures, the Destor-Porcupine (DP) and Kirkland Lake — Cadillac (KC) fault zones ˜6×1015 g Si, 3×1015 g CO2 and 1015 g K were introduced into the faults during expulsion of an estimated 6×1018 g aqueous fluids. Strontium isotope ratios of tourmaline, piemontite, actinolite and scheelite mineral separates, characterized by Rb/Sr≤0.02, are concordant with respect to 87Sr/86Sr initial ratios over local sectors of the faults. The Sr isotope data record geographic variations which, from east to west on the KC fault is 0.7031 0.7041 (Val d'Or), 0.7008 0.7022 (Bourlemaque), 0.7017 0.7019 (Bousquet), 0.7029 0.7031 (Noranda), and 0.7013 to 0.7015 (Kirkland Lake). At Timmins, on the PD fault, 87Sr/86Sr initial ratios cluster at 0.7010 to 0.7020. Metasomatised fault zones are systematically more radiogenic than contiguous host lithologies, and imply a source reservoir (0.7010 to 0.7041) generally more radiogenic than the upper mantle at 2690 Ma (0.700±0.001), or contemporaneous volcanic rocks of mafic to ultramafic composition (0.700 to 0.7012). Whereas certain minerals are concordant and retentive, Rb-Sr isochrons based on suites of rocks at progressive intensities of metasomatism, have been systematically reset over an elpased time of ˜200 Ma after termination of outgassing, due to disturbance accompanying incremental displacements on structures. Carbon isotope compositions of ferroan dolomites in faults are tightly clustered along local fault sectors, but also display a marked provinciality: from east to west δ 13C=-6.0 to -8.5 (Malartic), -8.0 to -9.0 (Cadillac), -2.0 to -4.5 (Kirkland Lake), and -0.5 to -3.5 (Timmins). The observed provinciality of both δ 13C values and 87Sr/86Sr initial ratios is interpreted to reflect compositional heterogeneities in a radiogenic sialic crust and the green-stone belt supracrustal sequence, both of which supplied volatiles, magmas and lithophile elements to the fault structures during late stage transpressive tectonics.

  5. New palaeomagnetic results from outcrop and drill core samples of the 3.47 billion year old Komati Formation, Barberton Mountain Land, South Africa

    NASA Astrophysics Data System (ADS)

    Roberts, L.; Biggin, A.; Mac Niocaill, C.; De Wit, M.; Langereis, C. G.; Wilson, A.; Arndt, N.

    2013-12-01

    Palaeomagnetic results obtained in the 1980s and 1990s from the Komati Formation in the Palaeoarchaean Onverwacht Group in the Barberton Greenstone Belt constitute the world's oldest unrefuted palaeomagnetic pole. This pole has been crucial in arguing for the existence of a viable geomagnetic field early in the Earth's history but does not yet have the support of rigorous field tests in constraining its age and viability. Here we will present new palaeomagnetic data from a hitherto unexamined locality where these komatiites crop out along the Komati River and where two 400m drill cores have recently been extracted by an International Continental Drilling Programme (ICDP) project. Oriented samples have been taken from both of the deep drill cores and also from surface outcrops allowing detailed comparisons to take place between the new and old datasets. The implications of these new results for our understanding of the early Earth's geomagnetic field will be discussed.

  6. 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)

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

    2012-01-01

    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.

  7. 100 Ma timing paradox of Archean gold, Abitibi greenstone belt (Canada): New evidence from U-Pb and Pb-Pb evaporation ages of hydrothermal zircons

    NASA Astrophysics Data System (ADS)

    Kerrich, Robert; Kurtis Kyser, T.

    1994-12-01

    Abundant hydrothermal zircon occurs within quartz-tourma-line veins at four gold deposits in the Val d"Or district of the Archean Abitibi greenstone belt, Canada. Host rocks to the gold-bearing veins are characterized by pronounced metasomatic enrichment of Zr, Hf, Y, and rare earth elements. Hydrothermal zircons contain inclusions of quartz, tourmaline, scheelite, pyrite, and gold. In hydrothermal zircons and quartz, primary low-salinity H2-CO2, fluid inclusions coexist with CO2-rich inclusions, indicating CO2, unmixing and gold precipitation at 260 to 380 °C and ˜2 kbar. The zircons have 207Pb/206Pb evaporation ages of 2683 ±20 to 2703 ±4 Ma, close to a concordant U-Pb age of 2693 ±2 Ma, both commensurate with previous SHRIMP ages for the zircons. The same vein systems have U-Pb ages on rutile and titanite, Sm-Nd dates on scheelite, and 40Ar/39Ar ages on muscovite that scatter between 2630 to 2579 Ma; these ages gave rise to a "late gold" model. In the Archean Superior province, vein gold deposits are related in space and time to terrane boundary structures which mark the diachronous accretion of allochthonous tectonostratigraphic terranes from south to north from 2720 to 2680 Ma. Consequently, the vein zircon ages of ˜2690 to 2680 Ma at Val d"Or represent the primary mineralizing event, consistent with its late kinematic timing throughout the Superior Province and with Late Archean supercontinent assembly globally, whereas the young scattered ages record the time of secondary fluid events associated with reactivation of the structures, resetting some isotopic systems below their conventional blocking temperature.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2009-07-01

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

  10. Tracing sources of crustal contamination using multiple S and Fe isotopes in the Hart komatiite-associated Ni-Cu-PGE sulfide deposit, Abitibi greenstone belt, Ontario, Canada

    NASA Astrophysics Data System (ADS)

    Hiebert, R. S.; Bekker, A.; Houlé, M. G.; Wing, B. A.; Rouxel, O. J.

    2016-03-01

    Assimilation by mafic to ultramafic magmas of sulfur-bearing country rocks is considered an important contributing factor to reach sulfide saturation and form magmatic Ni-Cu-platinum group element (PGE) sulfide deposits. Sulfur-bearing sedimentary rocks in the Archean are generally characterized by mass-independent fractionation of sulfur isotopes that is a result of atmospheric photochemical reactions, which produces isotopically distinct pools of sulfur. Likewise, low-temperature processing of iron, through biological and abiotic redox cycling, produces a range of Fe isotope values in Archean sedimentary rocks that is distinct from the range of the mantle and magmatic Fe isotope values. Both of these signals can be used to identify potential country rock assimilants and their contribution to magmatic sulfide deposits. We use multiple S and Fe isotopes to characterize the composition of the potential iron and sulfur sources for the sulfide liquids that formed the Hart deposit in the Shaw Dome area within the Abitibi greenstone belt in Ontario (Canada). The Hart deposit is composed of two zones with komatiite-associated Ni-Cu-PGE mineralization; the main zone consists of a massive sulfide deposit at the base of the basal flow in the komatiite sequence, whereas the eastern extension consists of a semi-massive sulfide zone located 12 to 25 m above the base of the second flow in the komatiite sequence. Low δ56Fe values and non-zero δ34S and Δ33S values of the komatiitic rocks and associated mineralization at the Hart deposit is best explained by mixing and isotope exchange with crustal materials, such as exhalite and graphitic argillite, rather than intrinsic fractionation within the komatiite. This approach allows tracing the extent of crustal contamination away from the deposit and the degree of mixing between the sulfide and komatiite melts. The exhalite and graphitic argillite were the dominant contaminants for the main zone of mineralization and the eastern extension zone of the Hart deposit, respectively. Critically, the extent of contamination, as revealed by multiple S and Fe isotope systematics, is greatest within the deposit and decreases away from it within the komatiite flow. This pattern points to a local source of crustal contamination for the mantle-derived komatiitic melt and a low degree of homogenization between the mineralization and the surrounding lava flow. Coupled S and Fe isotope patterns like those identified at the Hart deposit may provide a useful tool for assessing the potential of a komatiitic sequence to host Ni-Cu-(PGE).

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

    PubMed

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

    2010-12-01

    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 μm in diameter and up to several hundred μm long in prehnite-pumpellyite to lower greenschist facies meta-volcanic glass. The textures are septate with regular compartments 5-20 μm 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

  12. 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)

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

    2008-12-01

    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-μ (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 ɛNd(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 ɛNd(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.

  13. Greenstone Belts: Synthesis and Density

    NASA Astrophysics Data System (ADS)

    In this section: A Tectonic Viewpoint by K. Burke A Geochronological Viewpoint by D. W. Davis A Structural Viewpoint by R. E. P. Fripp An Ore Deposits Viewpoint by B. Gorman and R. I. Valliant A Geophysical Viewpoint by L. Losier A Thermal Viewpoint by P. Morgan A Sedimentological Viewpoint by E. G. Nisbet A Petrologic Viewpoint by P. J. Wyllie

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  15. 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)

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

    2013-11-01

    To explore the linkage between mass-independent sulfur isotope fractionation (MIF-S) and δ13Corg 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 (δ34S, δ33S, δ36S) 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 Δ33S and Δ36S 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 δ13Corg, 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 δ13Corg between -35.4‰ and -16.2‰ (average of -30.3 ± 6.0‰, 1σ), while the Cheshire Formation shales have δ13Corg between -47.7‰ and -35.1‰ (average -41.3 ± 3‰, 1σ). The δ34S values of sedimentary sulfides from Manjeri Formation vary between -15.15‰ and +2.37‰ (average -1.71 ± 4.76‰, 1σ), showing very small and mostly negative Δ33S values varying from -0.58‰ to 0.87‰ (average 0.02 ± 0.43‰, 1σ). Cheshire Formation black shale sulfide samples measured in this study have δ34S values ranging from -2.11‰ to 2.39‰ (average 0.25 ± 1.08‰, 1σ) and near zero and solely positive Δ33S anomalies between 0.14‰ and 1.17‰ (average 0.56 ± 0.29‰, 1σ). Moreover, Δ36S/Δ33S 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 δ13Corg 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 δ34S 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.

  16. Early archean spherule beds in the Barberton mountain land, South Africa: Impact or terrestrial origin?

    NASA Astrophysics Data System (ADS)

    Reimold, Wolf Uwe; Koeberl, Christian; Johnson, Steven; McDonald, Iain

    The origin of multiple spherule-rich layers of millimeter to meter width, all occurring within the transition from the Fig Tree to the Onverwacht Group of the Barberton Greenstone Belt in South Africa, has been strongly debated during the last decade. One school subscribes to an origin by large meteorite impact, whereas others have preferred terrestrial processes. In particular, strong enrichments in siderophile elements, especially Ir, and chondrite-like PGE patterns for spherule layer samples have been cited as evidence favoring an impact origin. Recently, Cr isotopic signatures obtained for samples from two spherule layers have provided further support for this hypothesis. In contrast, our group has emphasized that secondary hydrothermal processes have pervasively overprinted the whole stratigraphy at this transition. Ir concentrations up to 5 times chondritic are suspect as primary impact-produced signatures. Here, we report new petrographic and geochemical data for samples from spherulitic horizons marking the S2 layer and from interlayered BIF, chert, and mudstone strata. In contrast to earlier work, the new samples were obtained from outside of the gold-sulfide mineralized ore zone on Agnes Mine. Both spherule and country rock samples are enriched in siderophile elements, with up to >1500 ppb Ir. Some of the highest values are related to clearly secondary fault and shear zone deposits. Chrome-spinel in spherule layers is often zoned. A proton microprobe study identified in one case the mineral gersdorffite, of likely secondary origin, as a carrier phase for Ir, whereas in other samples Ir must be contained in matrix silicates. New PGE analyses for more or less sulfidemineralized samples yielded uniformly flat, near-chondritic patterns.

  17. 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)

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

    2006-06-01

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

  18. Electron microscope methods in the search for the earliest life forms on Earth (in 3.5-3.3 GA cherts from the Barberton Greenstone Belt, South Africa): applications for extraterrestrial life studies

    NASA Astrophysics Data System (ADS)

    Westall, Frances; Gerneke, Dane

    1998-07-01

    A suite of previously unknown microfossils and related biogenic structures has been revealed in some of the oldest sediments on Earth using scanning electron microscopy. High resolution scanning electron microscopy of HF-etched, biolaminated charts has brought to light a variety of small fossil coccoid and rod-shaped bacteria and associated fossil biofilms containing bedding planes. These microfossils have ben completely replaced by minerals. This vastly improved early Archaean microfossil database sheds new light on the diversity of life on Earth relatively soon after the cessation of heavy bolide bombardment at about 3.8 Ga. This is the critical period when life may have been able to develop on Mars and these early Archaean terrestrial microfossils will serve as valuable analogues for possible extraterrestrial life.

  19. New palaeomagnetic results from outcrop and drill core samples of the 3.47 billion year old Komati Formation, Barberton Mountain Land, South Africa

    NASA Astrophysics Data System (ADS)

    Roberts Artal, Laura; Biggin, Andy; MacNiocaill, Conall; de Wit, Maarten; Langereis, Cor; Wilson, Allan; Arndt, Nicholas

    2014-05-01

    Palaeomagnetic results obtained in the 1980s and 1990s from the Komati Formation in the Palaeoarchaean Onverwacht Group in the Barberton Greenstone Belt constitute the world's oldest unrefuted palaeomagnetic pole. This pole has been crucial in arguing for the existence of a viable geomagnetic field early in the Earth's history but does not yet have the support of rigorous field tests in constraining its age and viability. Here we present new palaeomagnetic data from a hitherto unexamined locality where these komatiites crop out along the Komati River and where two 400m drill cores have recently been extracted by an International Continental Drilling Programme (ICDP) project. Oriented samples have been taken from both of the deep drill cores and also from surface outcrops allowing detailed comparisons to take place between the new and old datasets. Two ancient components have been identified. One of these is dual polarity and may be associated with widespread intrusive activity at 3.2 Gyr. The other is older and has a direction in agreement with previous results from the Komati Formation. The implications of these new results for our understanding of the early Earth's geomagnetic field will be discussed.

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

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

    Major, minor, and lithophile trace element abundances and Nd and Hf isotope systematics are reported for two sets of remarkably fresh, by Archean standards, samples of komatiitic lavas from the 3.48 Ga Komati and the 3.27 Ga Weltevreden Formations of the Barberton Greenstone Belt (BGB) in South Africa. These data are used to place new constraints on the thermal history of the early Archean mantle, on the timing of its differentiation, and on the origin and chemical nature of early mantle reservoirs and their evolution through time. Projected moderate to strong depletions of highly incompatible lithophile trace elements and water in the mantle sources of both komatiite systems, combined with the partitioning behavior of V during lava differentiation, are consistent with anhydrous conditions during generation of the komatiite magmas. Komati and Weltevreden lavas are inferred to have erupted with temperatures of ∼1600 °C, and, thus, represent the hottest known lavas on Earth. The calculated mantle potential temperatures of ∼1800 °C for both komatiite systems are 150-200 °C higher than those of contemporary ambient mantle. Combined, these observations are consistent with the origin of these BGB komatiite magmas in mantle plumes in the lower mantle. New Sm-Nd and Lu-Hf isotopic data allow precise determination of initial ε143Nd = +0.46 ± 0.10 and +0.50 ± 0.11 and initial ε176Hf = +1.9 ± 0.3 and +4.7 ± 0.8 for the Komati and the Weltevreden system komatiites, respectively. These positive initial values reflect prior fractionation of Sm/Nd and Lu/Hf in the mantle early in Earth history. Conversely, μ142Nd values are 0.0 ± 2.4 and +2.2 ± 4.1 for the Komati and the Weltevreden systems, respectively. These values overlap, within uncertainties, those of modern terrestrial rocks, thus, limiting the magnitudes of possible Sm/Nd fractionations generated by early Earth processes in the sources of these rocks. Combined 142,143Nd and Hf isotope and lithophile trace element systematics are consistent with formation and long-term isolation of deep-seated mantle domains with fractionated Sm/Nd and Lu/Hf at ca. 4400 Ma. These domains were likely generated as a result of crystallization of a primordial magma ocean, with Mg-perovskite and minor Ca-perovskite acting as fractionating phases. The inferred mantle domains were evidently mixed away by 2.7 Ga on the scale of mantle reservoirs sampled by late Archean komatiite lavas emplaced worldwide.

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

    NASA Astrophysics Data System (ADS)

    Rammensee, Philipp; Aulbach, Sonja

    2014-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2007-11-01

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

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

    NASA Astrophysics Data System (ADS)

    Hattori, Keiko

    1993-02-01

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

  4. Nd and Hf isotopic analysis of Barberton komatiites

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2007-08-01

    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)

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

    Highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, and Re) abundance and Pt-Re-Os isotopic data are reported for well-preserved komatiites from the Komati and Weltevreden Formations of the Barberton Greenstone Belt in South Africa. The Re-Os data for whole-rock samples and olivine and chromite separates define isochrons with ages of 3484 ± 38 and 3263 ± 12 Ma for the Komati and Weltevreden systems, respectively. The respective initial 187Os/188Os = 0.10335 ± 15 (γ187Os = +0.34 ± 0.15) and 0.10442 ± 4 (γ187Os = -0.14 ± 0.04) are well within the range defined by chondritic meteorites. When considered together with the Re-Os data for late Archean komatiite systems, these data indicate that the mantle sources of most Archean komatiites evolved with essentially uniform long-term Re/Os that is well within the chondritic range. By contrast, the initial 186Os/188Os = 0.1198283 ± 9 (ε186Os = -0.12 ± 0.08) and 0.1198330 ± 8 (ε186Os = +0.22 ± 0.07) for the Komati and Weltevreden systems, respectively, are outside of known chondritic evolution paths, indicating that the mantle sources of these two komatiite systems evolved with fractionated time-integrated Pt/Os. The new 186,187Os isotopic data for these early Archean komatiite systems, combined with published 142,143Nd and 176Hf isotopic data for these systems, are consistent with formation and long-term isolation of deep-seated mantle domains with fractionated time-integrated Sm/Nd, Lu/Hf, and Pt/Os ratios, at ca. 4400 Ma. These domains may have been generated as a result of late-stage crystallization of a primordial magma ocean involving Mg-perovskite, Ca-perovskite and Pt-alloys acting as the fractionating phases. The inferred fractionated mantle domains were sampled by the early Archean komatiites, but were largely mixed away by 2.7 Ga, as evidenced by uniform time-integrated Sm/Nd, Lu/Hf, and Pt/Os ratios inferred for the sources of most late Archean komatiite systems. The calculated total Pt + Pd abundances present in the sources of the early Archean komatiite systems fall only 7-14% short of those present in estimates for the modern primitive mantle. These are also within the range of the total Pt + Pd abundances present in the sources of late Archean komatiite systems, indicating little change in the HSE abundances in the Archean mantle between 3.5 and 2.7 Ga. The new HSE data for the early Archean komatiite systems may implicate late accretion of HSE to the mantle prior to completion of crystallization of a final terrestrial magma ocean, followed by sluggish mixing of diverse, post-magma ocean domains characterized by variably fractionated lithophile element and HSE abundances.

  7. 3.5-Ga hydrothermal fields and diamictites in the Barberton Greenstone Belt—Paleoarchean crust in cold environments

    PubMed Central

    de Wit, Maarten J.; Furnes, Harald

    2016-01-01

    Estimates of ocean temperatures on Earth 3.5 billion years ago (Ga) range between 26° and 85°C. We present new data from 3.47- to 3.43-Ga volcanic rocks and cherts in South Africa suggesting that these temperatures reflect mixing of hot hydrothermal fluids with cold marine and terrestrial waters. We describe fossil hydrothermal pipes that formed at ~200°C on the sea floor >2 km below sea level. This ocean floor was uplifted tectonically to sea level where a subaerial hydrothermal system was active at 30° to 270°C. We also describe shallow-water glacial diamictites and diagenetic sulfate mineral growth in abyssal muds. These new observations reveal that both hydrothermal systems operated in relatively cold environments and that Earth’s surface temperatures in the early Archean were similar to those in more recent times. PMID:26933677

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

    NASA Technical Reports Server (NTRS)

    Schwerdtner, W. M.

    1986-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Kröner, A.; Puustinen, K.; Hickman, M.

    1981-04-01

    Archaean gneiss-greenstone relationships are still unresolved in many ancient cratonic terrains although there is growing evidence that most of the late Archaean greenstone assemblages were deposited on older tonalitic crust. We report here well defined basement-cover relationships from a late Archaean greenstone belt in Lapland, north of the Polar Circle. The basal greenstone sequence contains quartzite, schist, komatiitic volcanics and an unusual volcanic conglomerate with well preserved granite pebbles of an older basement. These rocks surround a gneiss dome composed of foliated tonalite which shows a polyphase deformation pattern not seen in the neighbouring greenstones. Zircon fractions of the gneisses plot on two discordia lines and give upper intercept ages with concordia at 3,069±16 Ma and 3,110±17 Ma respectively. One fraction contains metamict zircons with components at least 3,135 Ma old. These are the oldest reliable ages yet reported from the Archaean of the Baltic Shield. Rb-Sr whole-rock dating of the tonalitic gneiss yielded an isochron age of 2,729±122 Ma and an ISr of 0.703±0.001. This is interpreted to reflect a resetting event during which the gneisses may have acquired their present tectonic fabric. Rb-Sr model age calculations yield mantle values for ISr at about 2,950±115 Ma and suggest that the tonalite was intruded into the crust as juvenile material at about 3.1 Ga ago as reflected by the zircon ages. It was subsequently deformed and isotopically reset at about 2.7 Ga ago, prior to greenstone deposition. Comparison with tonalitic gneisses of eastern Karelia displays significant differences and suggests that the Archaean of Finland may contain several generations of pre-greenstone granitoid rocks.

  10. Granite-greenstone terranes in the Pilbara Block, Australia, as coeval volcano-plutonic complexes; Evidence from U-Pb zircon dating of the Mount Edgar Batholith

    NASA Astrophysics Data System (ADS)

    Williams, I. S.; Collins, W. J.

    1990-02-01

    The Mount Edgar Batholith in the Pilbara Block, Western Australia, consists, in part, of a gneiss complex that resembles other Archean high-grade gneiss terranes. The complex is extensively intruded by variably foliated granitoids which also intrude the surrounding greenstone succession, the Warrawoona Group. The contact between the greenstone belt and the gneiss complex is tectonic. Field evidence indicates that the banded gneisses are the oldest part of the batholith; zircon U-Pb ages for three samples are 3429 ± 13Ma, ⩾ 3443 ± 10Ma and3448 ± 8Ma, all very similar to the age of zircons in the felsic volcanic rocks near the base of the greenstone succession ( Pidgeon, 1978) [1]. Two granitoids, representing pre- and post-tectonic phases respectively, give zircon ages of 3304 ± 10Ma and3314 ± 13Ma, thereby constraining the major structural events to be contemporary with granite magmatism, consistent with a diapiric model for the tectonic evolution of the batholith ( Collins, 1989) [2]. These ages are similar to the zircon age for terminal volcanism in the Warrawoona Group ( Pidgeon, 1984) [3], but are ˜ 100Ma older than the precisely-defined Rb-Sr whole-rock ages obtained throughout the batholith ( Collins and Gray, 1989) [4]. Batholith-wide resetting or late closure of Rb-Sr isotopic systems is implied, possibly associated with late fluid circulation. The temporal coincidence between plutonism and volcanism in the Mount Edgar region strongly suggests that the greenstone succession contains the extrusive equivalents of both the ˜ 3300Ma granites and the ˜ 3440Ma gneisses in the batholith. The isotopic evidence, combined with the structural data, indicates that the granites cannot be derived from the surrounding greenstone belt. Further, there is no compelling evidence for a sialic basement to the greenstone succession.

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

    NASA Astrophysics Data System (ADS)

    Tice, Michael M.; Lowe, Donald R.

    2006-06-01

    The geological record of carbonaceous matter from at least 3.5 Ga to the end of the Precambrian is fundamentally continuous in terms of carbonaceous matter structure, composition, environments of deposition/preservation, and abundance in host rocks. No abiotic processes are currently known to be capable of producing continuity in all four of these properties. Although this broad view of the geological record does not prove that life had arisen by 3.5 Ga, the end of the early Archean, it suggests a working hypothesis: most if not all carbonaceous matter present in rocks older than 3.0 Ga was produced by living organisms. This hypothesis must be tested by studies of specific early geological units designed to explore the form, distribution, and origin of enclosed carbonaceous matter. The carbonaceous, environmentally diverse 3416 Ma Buck Reef Chert (BRC) of the Barberton greenstone belt, South Africa, provides an opportunity for such a study. Upward facies progressions in the BRC reflect deposition in environments ranging from shallow marine evaporitic brine ponds to a storm- and wave-active shelf to a deep, low-energy basinal setting below storm wave base. Abundances and ratios of Al 2O 3, Zr, TiO 2, and Cr track inputs of various types of volcaniclastic and terrigenous clastic materials. In particular, Zr/Al 2O 3 and Zr serve as proxies for concentration of windblown dust and, indirectly, as proxies for sedimentation rate. Cu, Zn, Ni, and FeO were concentrated in the most slowly deposited transitional and basinal sediments, inconsistent with a hydrothermal setting but consistent with a normal marine setting. The distribution of microfacies defined by associations and layering of clastic, ferruginous, and carbonaceous grains correlates with facies transitions. Fine carbonaceous laminations, which occur only in shallow platform settings, represent photosynthetic microbial mats. These were ripped up and the debris widely redistributed in shallow and deep water by waves and storms. The isotopic composition of carbonaceous matter ranges from - 35‰ to - 30‰ in shallow-water settings and to - 20‰ in deep-water units. The heavier δ13C in deep-water carbonaceous matter is thought to reflect microbial processing, possibly by fermentation and methanogenesis, of organic matter originally produced in shallow water. Hydrothermal origins for BRC carbonaceous matter are clearly excluded by the inferred depositional setting of the rocks as a whole, an inference supported by field, petrographic, and geochemical analysis. We suggest that the biological model proposed here for BRC carbonaceous matter is the best currently available. The hypothesis that "at least some carbonaceous matter present in rocks older than 3.0 Ga was produced by living organisms" should be regarded as likely until extraordinary contradictory evidence is presented.

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

  13. Late Archean intermediate-felsic magmatism of the South Vygozersky and Kamennozersky greenstone structures of Central Karelia

    NASA Astrophysics Data System (ADS)

    Myskova, T. A.; Zhitnikova, I. A.; L'vov, P. A.

    2015-07-01

    The geochemistry and zircon geochronology (U-Pb, SHRIMP-II) of Late Archean intermediate-felsic dikes and plagiogranites of the Shilossky massif of the South Vygozersky and Kamennozersky greenstone belts of Central Karelia were studied. Subvolcanic rocks of the dike complex vary in composition from andesitobasalts to rhyolites, in structural-textural peculiarities, and in the formation age, from 2862 ± 8 to 2785 ± 15 Ma. Compositionally and geochronologically (2853 ± 11 Ma), plagiogranites of the Shilossky massif of the South Vygozersky greenstone belts are close to the most ancient dacite and granodiorite porphyry dikes. Dikes intruded synchronously with intrusion of plagiogranites over a period of at least 70 m.y. Geochronologically, subvolcanic rocks of the dike complex and plagiogranites of the Shilossky massif are similar to granitoids of the TTG assemblages of I- and M-type granites. The Sm-Nd model age of some dikes (2970-2880 Ma) is close to the age of rock crystallization, which is evidence in favor of juvenile origin of magma. Dikes with more ancient model age (3050 Ma) are presumed to contain crustal material. Variations in age and ɛNd (from -2.7 to +2.9) indicate the absence of a unified magmatic source.

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

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

    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.

  15. Barberton drilling project - Buck Reef Chert core BARB3

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  16. Magmatic-hydrothermal fluids in the Pahtohavare Cu-Au deposit in greenstone at Kiruna, Sweden

    NASA Astrophysics Data System (ADS)

    Lindblom, S.; Broman, C.; Martinsson, O.

    1996-05-01

    The Proterozoic Pahtohavare Cu-Au deposit is located in the greenstone belt near Kiruna, northern Sweden. The greenstone consists of mafic volcanic rocks with pillow lavas, mafic sills and albitized rocks, including tuffites, black schists and mafic sills, together with carbonates and mineralized zones. Mineralization occurs as impregnations, epigenetic quartz-rich breccias and fracture fillings with pyrite, chalcopyrite, pyrrhotite and gold in a complex tectonic environment. Fluid inclusions indicate an early formation of quartz and pyrite at temperatures initially near 500 °C and a pressure of 2 2.4 kbar from a supersaturated aqueous solution of magmatic origin. In addition to halite cubes, daughter minerals of sylvite, calcite, hematite, graphite and two unknown phases are found. The main stage of chalcopyrite and gold deposition is characterized by aqueous fluids of variable salinity (up to 30 eq. wt.% NaCl including CaCl2), at temperatures below 350 °C and pressures between 1 and 2 kbar. A minor CO2 phase with some N2 accompanies this stage. Gold was transported as a chloride complex which destabilized due to an increase in pH (as a consequence of the CO2 loss) as well as cooling and dilution of the solution. The ore deposition occurred as a result of mixing with a low salinity aqueous solution during tectonic fracturing with pressure fluctuations and CO2 unmixing. Late oxidation of ores was caused by low to moderately saline (3 to 13 eq. wt.% NaCl) low temperature aqueous solutions.

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

    NASA Astrophysics Data System (ADS)

    Anhaeusser, Carl R.; Walraven, Feo

    1999-02-01

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

  18. Mesoarchean sanukitoid rocks of the Rio Maria Granite-Greenstone Terrane, Amazonian craton, Brazil

    NASA Astrophysics Data System (ADS)

    de Oliveira, Marcelo Augusto; Dall'Agnol, Roberto; Althoff, Fernando Jacques; da Silva Leite, Albano Antonio

    2009-02-01

    The Archean sanukitoid Rio Maria Granodiorite yielded zircon ages of ˜2.87 Ga and is exposed in large domains of the Rio Maria Granite-Greenstone Terrane, southeastern Amazonian craton. It is intrusive in the greenstone belts of the Andorinhas Supergroup, in the Arco Verde Tonalite and Caracol Tonalitic Complex (older TTGs). Archean potassic leucogranites, younger TTGs and the Paleoproterozoic granites of Jamon Suite are intrusive in the Rio Maria Granodiorite. The more abundant rocks of the Rio Maria Granodiorite have granodioritic composition and display medium to coarse even-grained textures. These rocks show generally a gray color with greenish shades due to strongly saussuritized plagioclase, and weak WNW-ESE striking foliation. The significant geochemical contrasts between the occurrences of Rio Maria Granodiorite in different areas suggest that this unit corresponds in fact to a granodioritic suite of rocks derived from similar but distinct magmas. Mingling processes involving the Rio Maria Granodiorite and similar mafic to intermediate magmas are able to explain the constant occurrence of mafic enclaves in the granodiorite. The associated intermediate rocks occur mainly near Bannach, where mostly quartz diorite and quartz monzodiorite are exposed. The dominant rocks are mesocratic, dark-green rocks, with fine to coarse even-grained texture. The Rio Maria Granodiorite and associated intermediate rocks show similar textural and mineralogical aspects. They follow the calc-alkaline series trend in some diagrams. However, they have high-Mg#, Cr, and Ni conjugate with high contents of large ion lithophile elements (LILEs), typical of sanukitoids series. The patterns of rare earth elements of different rocks are similar, with pronounced enrichment in light rare earth elements (LREEs) and strong to moderate fractionation of heavy rare earth elements (HREEs). Field aspects and petrographic and geochemical characteristics denote that the granodiorites and intermediate rocks have sanukitoid affinity. However, geochemical data suggest that the intermediate rocks and the granodiorites are not related by a fractional crystallization process. It is concluded that the intermediate rocks derived from similar sources to the granodiorites, but probably result from a higher degree of melting, being both cogenetic, but not comagmatic rocks. Mineralogical aspects associated with experimental evidence suggest that the Rio Maria Granodiorite magma was relatively water-enriched (>4 wt.%), explaining the presence of hornblende at the liquidus and the absence of clinopyroxene and orthopyroxene in the studied rocks. The occurrence of well-preserved magmatic epidote crystals, admitting that the Rio Maria Granodiorite was emplaced at shallow crustal levels, points to a rapid ascent of the Rio Maria Granodiorite magma.

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

    NASA Technical Reports Server (NTRS)

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

    2007-01-01

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

  20. Economic geology of the Copper Mountain Supracrustal Belt, Owl Creek Mountains, Fremont County, Wyoming

    SciTech Connect

    Hausel, W.D.; Graff, P.J.; Albert, K.G.

    1985-01-01

    The Archean stratigraphy and associated mineral deposits at Copper Mountain were investigated to determine if this supracrustal belt has potential commercial mineral deposits. It was concluded Copper Mountain lacks the stratigraphic and structural character of a classical greenstone belt, exhibits higher metamorphic grade, and may be better classified as a high-grade terrain. However, potential is noted for stratiform Au associated with iron formation, stratiform W associated with gneiss, and Cu-Au mineralization in strike veins. 63 refs., 9 figs., 3 tabs. (ACR)

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  2. Laterally bendable belt conveyor

    DOEpatents

    Peterson, William J.

    1985-01-01

    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.

  3. [Greenstones mining is a risk for public health?].

    PubMed

    Manti, Antonio; Bancomina, Cristina; Capano, Giuseppe

    2013-01-01

    This article refers to the decision 3195/2012 issued by the State Administrative Council which maintains that operating in a greenstone quarry with consequent extraction and grinding of asbestos containing minerals can cause unacceptable risks to the public health. Therefore, the refusal to authorize the emissions into the atmosphere is highly justified, if properly motivated. The judgment states that the emission of the asbestos fibres into the atmosphere should be assessed from the health standpoint, and not just from the environmental one. Moreover, making reference only to the «release index» is not sufficient nor determining. The decision acknowledges the soundness of the criteria used by Local Health Unit of Chiavarese (Liguria, Northen Italy) in evaluating the danger caused to the human health and appreciates the reference made to the EU regulations on precaution and prevention, that state that well-grounded reasons are needed to postulate harmful consequences for the human health and the environment. This implies that the detailed data presented by the Local Health Unit can be considered «well-grounded reasons». PMID:23585437

  4. Belt attachment and system

    DOEpatents

    Schneider, Abraham D.; Davidson, Erick M.

    2016-02-02

    Disclosed herein is a belt assembly including a flexible belt with an improved belt attachment. The belt attachment includes two crossbars spaced along the length of the belt. The crossbars retain bearings that allow predetermined movement in six degrees of freedom. The crossbars are connected by a rigid body that attaches to the bearings. Implements that are attached to the rigid body are simply supported but restrained in pitching rotation.

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

    NASA Astrophysics Data System (ADS)

    Zoheir, Basem; Weihed, Pär

    2014-11-01

    The auriferous quartz ± carbonate veins at Dungash mine, central Eastern Desert of Egypt, are confined to ∼E-trending dilation zones within variably foliated/sheared metavolcanic/volcaniclastic rocks. The vein morphology and internal structures demonstrate formation concurrent with a dextral shear system. The latter is attributed to flexural displacement of folded, heterogeneous rock blocks through transpression increment, late in the Neoproterozoic deformation history of the area. Geochemistry of the host metavolcanic/metavolcaniclastic rocks from the mine area suggests derivation from a low-K, calc-alkaline magma in a subduction-related, volcanic arc setting. In addition, chemistry of disseminated Cr-spinels further constrain on the back-arc basin setting and low-grade metamorphism, typical of gold-hosting greenstone belts elsewhere. Mineralogy of the mineralized veins includes an early assemblage of arsenopyrite-As-pyrite-gersdorffite ± pyrrhotite, a transitional pyrite-Sb-arsenopyrite ± gersdorffite assemblage, and a late tetrahedrite-chalcopyrite-sphalerite-galena-gold assemblage. Based on arsenopyrite and chlorite geothermometers, formation of gold-sulfide mineralization occurred between ∼365 and 280 °C. LA-ICP-MS measurements indicate the presence of refractory Au in arsenian pyrite (up to 53 ppm) and Sb-bearing arsenopyrite (up to 974 ppm). Abundant free-milling gold associated with the late sulfide assemblage may have been mobilized and re-distributed by circulating, lower temperature ore fluids in the waning stages of the hydrothermal system. Based on the isotopic values of vein quartz and carbonate, the calculated average δ18OH2O values of the ore fluids are 5.0 ± 1.4‰ SMOW for quartz, and 3.3 ± 1.4‰ for vein carbonate. The measured carbonate δ13C values correspond to ore fluids with δ13CCO2 = -6.7 ± 0.7‰ PDB. These results suggest a mainly metamorphic source for ore fluids, in good agreement with the vein morphology, textures and hydrothermal alteration. The calculated δ34SH2S values for early, transitional, and late sulfide assemblages define three distinct ranges (∼1.5-3.6‰), (∼0.4-1.0‰), and (-3.7‰ to -1.9‰), respectively. The systematic evolution towards lighter δ34S values may be attributed to recrystallization, or to ore fluid buffering under variable physicochemical conditions. The shear zone-related setting, mineralogy and isotopic characteristics of gold mineralization in Dungash mine are comparable with other orogenic gold deposits in the region (e.g., Barramiya deposit), which may suggest a regional setting controlling gold metallogeny of the region. This setting should guide future exploration programs in the central Eastern Desert province.

  6. Seat belt restraint system

    NASA Technical Reports Server (NTRS)

    Garavaglia, A.; Matsuhiro, D.

    1972-01-01

    Shoulder-harness and lap-belt restraint system was designed to be worn by individuals of widely different sizes and to permit normal body motion except under sudden deceleration. System is divided into two basic assemblies, lap belt and torso or shoulder harness. Inertia-activated reels immediately lock when seat experiences sudden deceleration.

  7. To Belt or Not To Belt?

    ERIC Educational Resources Information Center

    Vail, Kathleen

    1999-01-01

    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…

  8. Geochemical characters and tectonic evolution of the Chitradurga schist belt: An Archaean suture (?) of the Dharwar Craton, India

    NASA Astrophysics Data System (ADS)

    Naqvi, S. M.

    The Chitradurga schist belt extending for about 450 km in a NS direction and 2-50 km across, is one of the most prominent Archean (2.6 b.y.) tectonic features of the Indian Precambrian terrain, comprising about 2 to 10 km thick sequence of volcano sedimentary rocks. The basal unit of this belt is composed of an orthoquartzite-carbonate facies, unlike many other contemporary greentone belts of the Gondwana land which begin with a basal mafic-ultramafic sequence. Eighty percent of the belt is made up of detrital and chemogenic sediments, their succession commencing with a poorly preserved quartz pebble basal conglomerate and current bedded quartzites which, in turn, rest on tonalitic gneisses, the latter having been further remobilized with along the schist belt. Deposition of current bedded matue arenites indicte the existence of platformal conditions near the shore line. Polymictic graywacke conglomerates, graywackes, shales, phyllites, carbonates, BIFs (oxide, carbonate and sulfide) BMF's (Banded Maganese Formations) and cherts thus constitute the main sedimentary rocks of the belt. The polymicitic conglomerates contain debris of rocks of older greenstone sequences, as well as an abundant measure of folded quartzites, BIF's and gneissic fragments which represent earlier orogenies.

  9. 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)

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

    2013-09-01

    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.

  10. Belt scales user's guide

    SciTech Connect

    Rosenberg, N.I. )

    1993-02-01

    A conveyor-belt scale provides a means of obtaining accurate weights of dry bulk materials without delaying other plant operations. In addition, for many applications a belt scale is the most cost-effective alternative among many choices for a weighing system. But a number of users are not comfortable with the accuracy of their belt scales. In cases of unsatisfactory scale performance, it is often possible to correct problems and achieve the accuracy that was expected. To have a belt scale system that is accurate, precise, and cost effective, practical experience has shown that certain basic requisites must be satisfied. These requisites include matching the scale capability to the needs of the application, selecting durable scale equipment and conveyor idlers, adopting improved conveyor support methods, employing superior scale installation and alignment techniques, and establishing and practicing an effective scale testing and performance monitoring program. The goal of the Belt Scale Users' Guide is to enable utilities to reap the benefits of consistently accurate output from their new or upgraded belt scale installations. Such benefits include eliminating incorrect payments for coal receipts, improving coal pile inventory data, providing better heat rate results to enhance plant efficiency and yield more economical power dispatch, and satisfying regulatory agencies. All these benefits can reduce the cost of power generation.

  11. Belt conveyor apparatus

    DOEpatents

    Oakley, David J.; Bogart, Rex L.

    1987-01-01

    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.

  12. Precambrian Cratons and Fold-Belts in Brazil: Overview

    NASA Astrophysics Data System (ADS)

    Fuck, R.

    2008-05-01

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

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

    PubMed

    Walsh, Maud M

    2004-01-01

    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

  14. Radiation belt probes launched

    NASA Astrophysics Data System (ADS)

    Showstack, Randy

    2012-09-01

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

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

    NASA Astrophysics Data System (ADS)

    Walsh, Maud M.; Lowe, Donald R.

    1985-04-01

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

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

    NASA Technical Reports Server (NTRS)

    Beard, James S.; Lofgren, Gary E.

    1989-01-01

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

  17. The levantine amber belt

    NASA Astrophysics Data System (ADS)

    Nissenbaum, A.; Horowitz, A.

    1992-02-01

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

  18. Kuiper Belt Mapping Radar

    NASA Technical Reports Server (NTRS)

    Freeman, A.; Nilsen, E.

    2001-01-01

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

  19. Metamorphic belts of Anatolia

    NASA Astrophysics Data System (ADS)

    Oberhänsli, Roland; Prouteau, Amaury; Candan, Osman; Bousquet, Romain

    2015-04-01

    Investigating metamorphic rocks from high-pressure/low-temperature (HP/LT) belts that formed during the closure of several oceanic branches, building up the present Anatolia continental micro-plate gives insight to the palaeogeography of the Neotethys Ocean in Anatolia. Two coherent HP/LT metamorphic belts, the Tavşanlı Zone (distal Gondwana margin) and the Ören-Afyon-Bolkardağ Zone (proximal Gondwana margin), parallel their non-metamorphosed equivalent (the Tauride Carbonate Platform) from the Aegean coast in NW Anatolia to southern Central Anatolia. P-T conditions and timing of metamorphism in the Ören-Afyon-Bolkardağ Zone (>70?-65 Ma; 0.8-1.2 GPa/330-420°C) contrast those published for the overlying Tavşanlı Zone (88-78 Ma; 2.4 GPa/500 °C). These belts trace the southern Neotethys suture connecting the Vardar suture in the Hellenides to the Inner Tauride suture along the southern border of the Kirşehir Complex in Central Anatolia. Eastwards, these belts are capped by the Oligo-Miocene Sivas Basin. Another HP/LT metamorphic belt, in the Alanya and Bitlis regions, outlines the southern flank of the Tauride Carbonate Platform. In the Alanya Nappes, south of the Taurides, eclogites and blueschists yielded metamorphic ages around 82-80 Ma (zircon U-Pb and phengite Ar-Ar data). The Alanya-Bitlis HP belt testifies an additional suture not comparable to the northerly Tavşanlı and Ören-Afyon belts, thus implying an additional oceanic branch of the Neotethys. The most likely eastern lateral continuation of this HP belt is the Bitlis Massif, in SE Turkey. There, eclogites (1.9-2.4 GPa/480-540°C) occur within calc-arenitic meta-sediments and in gneisses of the metamorphic (Barrovian-type) basement. Zircon U-Pb ages revealed 84.4-82.4 Ma for peak metamorphism. Carpholite-bearing HP/LT metasediments representing the stratigraphic cover of the Bitlis Massif underwent 0.8-1.2 GPa/340-400°C at 79-74 Ma (Ar-Ar on white mica). These conditions compares to the Tavşanlı-Afyon realm. However the differences in time and P-T conditions (eclogite- vs. blueschist-facies units) in the Bitlis Massif indicate that the different metamorphic peak conditions were reached at different times in a single subduction zone. Exhumation from approx. 65 to 35 km depth occurred within <10 myr. The special relations between eclogite-blueschist are due to the fact that collision with the Arabian plate was and still is on going in the Bitlis area. The Bitlis HP rocks represent a subduction realm that separated the Bitlis-Pütürge(-Bistun?) continental block from the South-Armenian (Tauride?) block, further north. Post-Eocene blueschists south of the Bitlis Massif witness the separation of the Bitlis-Pütüre block from the Arabian plate, and the southward migration of the subduction zone from the Late Cretaceous to the Oligocene. Continuous convergence of Africa and Eurasia engendered the simultaneous consumption of several, separated branches of the Neotethys Ocean and amalgamation of different terranes. The rise of the Eastern Anatolia Plateau is related to this complex geodynamic setting. Reduced seismic velocities inferred from geophysical observations, which are interpreted as complete replacement of lithospheric- by asthenospheric mantle, can be explained by thermodynamic modelling as partial hydration of the lithospheric mantle wedge during protracted subduction. Hydrated lithospheric mantle is interpreted as result of the complex geodynamic setting in Anatolia with multiple simultaneous subduction zones.

  20. Deconstructing the conveyor belt.

    PubMed

    Lozier, M Susan

    2010-06-18

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

  1. Exploring Main Belt Asteroids

    NASA Astrophysics Data System (ADS)

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

    2001-11-01

    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 fragments, and significantly depleted of mass as a consequence of dynamical scattering. Yet, these fragments retain a record of the early steps of planet formation and evolution, as well as a record of early solar system conditions and the primordial composition gradient in that region. By exploring main belt asteroids through groundbased observations and spacecraft, modeling and theoretical work, we seek ultimately to recover this information. A single mission to a single target is not sufficient to address, in isolation, these questions. They require a foundation of robust, broad, and continuing groundbased, theoretical, and modeling programs. Such work is funded at a small fraction of a typical mission cost through the NASA Research and Analysis Program. Therefore, within the context of planetary decadal study recommendations to NASA, highest priority needs to be given to maintaining and growing a healthy R&A program over the next ten years and beyond. Missions also have an important role to play. An Earth orbiting remote sensing mission needs to be considered as a means of collecting important data for a large fraction of all main belt asteroids above a sub-kilometer diameter (while also realizing synergistic benefits to astrophysics). Missions to specific main belt targets can provide important new insights and leverage new understanding of existing data, models, and theories, but target definition (and corresponding instrument complement) is critical and must be based on our existing knowledge of these very diverse objects. Technological innovations may increase the cost effectiveness of future missions, such as solar electric propulsion (which enables rendezvous with multiple targets) and microsatellite technology (which may allow a large number of flyby targets by using many microsatellites).

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

    PubMed

    Layer; Kroner; McWilliams

    1996-08-16

    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

  3. Early life recorded in archean pillow lavas.

    PubMed

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

    2004-04-23

    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

  4. An archean impact layer from the Pilbara and Kaapvaal cratons.

    PubMed

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

    2002-08-23

    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

  5. An Archean Impact Layer from the Pilbara and Kaapvaal Cratons

    NASA Astrophysics Data System (ADS)

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

    2002-08-01

    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.

  6. SLH Timing Belt Powertrain

    SciTech Connect

    Schneider, Abe

    2014-04-09

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

  7. Moving belt metal detector

    NASA Astrophysics Data System (ADS)

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

    2006-05-01

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

  8. Physics and Automobile Safety Belts.

    ERIC Educational Resources Information Center

    Kortman, Peter; Witt, C. Edwin

    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…

  9. Teaching Science: Seat Belt Science.

    ERIC Educational Resources Information Center

    Leyden, Michael B.

    1994-01-01

    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…

  10. Geography of the asteroid belt

    NASA Technical Reports Server (NTRS)

    Zellner, B. H.

    1978-01-01

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

  11. Inner Radiation Belt Data Assimilation

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1996-01-01

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

  13. A review of tectonic aspects of the Limpopo belt and other Archean high-grade gneissic terranes

    NASA Technical Reports Server (NTRS)

    Kidd, W. S. F.

    1985-01-01

    Published information on the Archean high grade terrains varies a great deal in the detail available. Such information as exists indicates marked differences in the lithic types and proportions present in the central Limpopo belt compared with the better studies of the other Archean high grade terrains. These differences may be important because they are expressed by the presence in the Limpopo belt of subordinate, but significant quantities (about 5% each) of two rock suites likely to have formed on a shallow marine platform of significant size (Eriksson and Kidd, in prep.). These suites consist of thick sections dominantly consisting of either carbonate and calc-silicate, or of pure metaquartzites, often fuchsite bearing, whose lithic characters are unlike those expected for metacherts but are very like those expected for platform arenites. Isotopic ages suggest these sediments are probably older than 3.3 Ga and younger than 3.5 Ga. Studies lead to the conclusions that (1) continental fragments large enough to provide a substrate for significant platform arenite and carbonate sedimentation existed by 3.3 to 3.5 Ga ago; (2) Wilson cycle tectonics seems to adequately explain most major features of the Archean gneissic terranes; and (3) Tibetan-Himalayan style collisional tectonics 2.6 Ga and older accounts for the large scale relationships between the Limpopo belt and the adjacent Archean greenstone granitoid terrane cratons. By inference, other more fragmentary Archean gneissic terranes may have once been part of such collisional zones.

  14. Evaluation of the static belt fit provided by belt-positioning booster seats.

    PubMed

    Reed, Matthew P; Ebert, Sheila M; Sherwood, Christopher P; Klinich, Kathleen D; Manary, Miriam A

    2009-05-01

    Belt-positioning booster seats are recommended for children who use vehicle seat belts as primary restraints but who are too small to obtain good belt fit. Previous research has shown that belt-positioning boosters reduce injury risk, but the belt fit produced by the wide range of boosters in the US market has not previously been assessed. The present study describes the development of a method for quantifying static belt fit with a Hybrid-III 6-year-old test dummy. The measurement method was applied in a laboratory seat mockup to 31 boosters (10 in both backless and highback modes) across a range of belt geometries obtained from in-vehicle measurements. Belt fit varied widely across boosters. Backless boosters generally produced better lap belt fit than highback boosters, largely because adding the back component moved the dummy forward with respect to the lap belt routing guides. However, highback boosters produced more consistent shoulder belt fit because of the presence of belt routing guides near the shoulder. Some boosters performed well on both lap belt and shoulder belt fit. Lap belt fit in dedicated boosters was generally better than in combination restraints that also can be used with an integrated harness. Results demonstrate that certain booster design features produce better belt fit across a wide range of belt geometries. Lap belt guides that hold the belt down, rather than up, and shoulder belt guides integrated into the booster backrest provided better belt fit. PMID:19393812

  15. Seat Belt Use and Stress in Adolescents.

    ERIC Educational Resources Information Center

    Schichor, Aric; And Others

    1990-01-01

    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…

  16. Paleoarchean trace fossils in altered volcanic glass

    PubMed Central

    Staudigel, Hubert; Furnes, Harald; DeWit, Maarten

    2015-01-01

    Microbial corrosion textures in volcanic glass from Cenozoic seafloor basalts and the corresponding titanite replacement microtextures in metamorphosed Paleoarchean pillow lavas have been interpreted as evidence for a deep biosphere dating back in time through the earliest periods of preserved life on earth. This interpretation has been recently challenged for Paleoarchean titanite replacement textures based on textural and geochronological data from pillow lavas in the Hooggenoeg Complex of the Barberton Greenstone Belt in South Africa. We use this controversy to explore the strengths and weaknesses of arguments made in support or rejection of the biogenicity interpretation of bioalteration trace fossils in Cenozoic basalt glasses and their putative equivalents in Paleoarchean greenstones. Our analysis suggests that biogenicity cannot be taken for granted for all titanite-based textures in metamorphosed basalt glass, but a cautious and critical evaluation of evidence suggests that biogenicity remains the most likely interpretation for previously described titanite microtextures in Paleoarchean pillow lavas. PMID:26038543

  17. Paleoarchean trace fossils in altered volcanic glass.

    PubMed

    Staudigel, Hubert; Furnes, Harald; DeWit, Maarten

    2015-06-01

    Microbial corrosion textures in volcanic glass from Cenozoic seafloor basalts and the corresponding titanite replacement microtextures in metamorphosed Paleoarchean pillow lavas have been interpreted as evidence for a deep biosphere dating back in time through the earliest periods of preserved life on earth. This interpretation has been recently challenged for Paleoarchean titanite replacement textures based on textural and geochronological data from pillow lavas in the Hooggenoeg Complex of the Barberton Greenstone Belt in South Africa. We use this controversy to explore the strengths and weaknesses of arguments made in support or rejection of the biogenicity interpretation of bioalteration trace fossils in Cenozoic basalt glasses and their putative equivalents in Paleoarchean greenstones. Our analysis suggests that biogenicity cannot be taken for granted for all titanite-based textures in metamorphosed basalt glass, but a cautious and critical evaluation of evidence suggests that biogenicity remains the most likely interpretation for previously described titanite microtextures in Paleoarchean pillow lavas. PMID:26038543

  18. 49 CFR 393.93 - Seats, seat belt assemblies, and seat belt assembly anchorages.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 5 2014-10-01 2014-10-01 false Seats, seat belt assemblies, and seat belt... § 393.93 Seats, seat belt assemblies, and seat belt assembly anchorages. (a) Buses—(1) Buses... the driver's seat and seat belt assembly anchorages that conform to the location and...

  19. 49 CFR 393.93 - Seats, seat belt assemblies, and seat belt assembly anchorages.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 5 2013-10-01 2013-10-01 false Seats, seat belt assemblies, and seat belt... § 393.93 Seats, seat belt assemblies, and seat belt assembly anchorages. (a) Buses—(1) Buses... the driver's seat and seat belt assembly anchorages that conform to the location and...

  20. 49 CFR 393.93 - Seats, seat belt assemblies, and seat belt assembly anchorages.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 5 2012-10-01 2012-10-01 false Seats, seat belt assemblies, and seat belt... § 393.93 Seats, seat belt assemblies, and seat belt assembly anchorages. (a) Buses—(1) Buses... the driver's seat and seat belt assembly anchorages that conform to the location and...

  1. 49 CFR 393.93 - Seats, seat belt assemblies, and seat belt assembly anchorages.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 5 2010-10-01 2010-10-01 false Seats, seat belt assemblies, and seat belt... § 393.93 Seats, seat belt assemblies, and seat belt assembly anchorages. (a) Buses—(1) Buses... the driver's seat and seat belt assembly anchorages that conform to the location and...

  2. 49 CFR 393.93 - Seats, seat belt assemblies, and seat belt assembly anchorages.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 5 2011-10-01 2011-10-01 false Seats, seat belt assemblies, and seat belt... § 393.93 Seats, seat belt assemblies, and seat belt assembly anchorages. (a) Buses—(1) Buses... the driver's seat and seat belt assembly anchorages that conform to the location and...

  3. 30 CFR 75.1731 - Maintenance of belt conveyors and belt conveyor entries.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Maintenance of belt conveyors and belt conveyor....1731 Maintenance of belt conveyors and belt conveyor entries. (a) Damaged rollers, or other damaged belt conveyor components, which pose a fire hazard must be immediately repaired or replaced. All...

  4. Chaos on the conveyor belt.

    PubMed

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

    2013-04-01

    The dynamics of a spring-block train placed on a moving conveyor belt is investigated both by simple experiments and computer simulations. The first block is connected by a spring to an external static point and, due to the dragging effect of the belt, the blocks undergo complex stick-slip dynamics. A qualitative agreement with the experimental results can be achieved only by taking into account the spatial inhomogeneity of the friction force on the belt's surface, modeled as noise. As a function of the velocity of the conveyor belt and the noise strength, the system exhibits complex, self-organized critical, sometimes chaotic, dynamics and phase transition-like behavior. Noise-induced chaos and intermittency is also observed. Simulations suggest that the maximum complexity of the dynamical states is achieved for a relatively small number of blocks (around five). PMID:23679502

  5. The earth's trapped radiation belts

    NASA Technical Reports Server (NTRS)

    Noll, R. B.; Mcelroy, M. B.

    1975-01-01

    The near-earth charged particle environment is discussed in terms of spacecraft design criteria. Models are presented of the trapped radiation belts and based on in-situ data obtained from spacecraft.

  6. The distant Kuiper Belt

    NASA Astrophysics Data System (ADS)

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

    2000-10-01

    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.

  7. Belt conveyors for bulk materials. 6th ed.

    SciTech Connect

    2007-07-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  9. Hydrothermal remobilisation around a deformed and remobilised komatiite-hosted Ni-Cu-(PGE) deposit, Sarah's Find, Agnew Wiluna greenstone belt, Yilgarn Craton, Western Australia

    NASA Astrophysics Data System (ADS)

    Le Vaillant, Margaux; Saleem, Ahmad; Barnes, Stephen J.; Fiorentini, Marco L.; Miller, John; Beresford, Steve; Perring, Caroline

    2015-09-01

    The Sarah's Find nickel deposit, located 4.5 km north of the Mount Keith nickel mine, Western Australia, was chosen as a case study to investigate the nature and three-dimensional geometry of a geochemical halo created by the hydrothermal remobilisation of base metals and platinum group elements into the country rock surrounding a small massive Ni sulphide orebody. Portable and laboratory-based XRF analyses were carried out on samples from a shear zone localised along the basal komatiite-dacite contact that hosts the orebody. A geochemical halo was identified that extends along the shear zone up to 1780 m away from the massive sulphides, parallel to a prominent stretching lineation. Elevated Ni and Pd are associated with high As, Co, Cu and S. Palladium and Pt concentrations increase with proximity to massive sulphides (from 6 to 1190 ppb Pd). These anomalous concentrations reflect the presence of sulfarsenides and sulphides, either physically remobilised and forming veinlets close to the massive sulphides, or hydrothermally transported and redeposited within the foliation. In situ laser ablation ICP-MS indicates that Pd and Pt are hosted within these nickel sulfarsenides. This Ni-Co-As-Pd geochemical halo, observed around the Sarah's Find ore body, is interpreted as forming syn deformation, by the circulation of As-rich hydrothermal fluids dissolving base metals, Pd and Pt from the orebody and redepositing them along the sheared footwall contact. Similar Ni-Co-Pd-Pt-As geochemical haloes could potentially exist around any magmatic nickel sulphide mineral system that has undergone a phase of arsenic metasomatism and may be a generally applicable proximity indicator for nickel sulphides in hydrothermally altered terranes.

  10. 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

    Ansdell, K.M.; Kyser, T.K. )

    1991-05-01

    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.

  11. Hydrothermal remobilisation around a deformed and remobilised komatiite-hosted Ni-Cu-(PGE) deposit, Sarah's Find, Agnew Wiluna greenstone belt, Yilgarn Craton, Western Australia

    NASA Astrophysics Data System (ADS)

    Le Vaillant, Margaux; Saleem, Ahmad; Barnes, Stephen J.; Fiorentini, Marco L.; Miller, John; Beresford, Steve; Perring, Caroline

    2016-03-01

    The Sarah's Find nickel deposit, located 4.5 km north of the Mount Keith nickel mine, Western Australia, was chosen as a case study to investigate the nature and three-dimensional geometry of a geochemical halo created by the hydrothermal remobilisation of base metals and platinum group elements into the country rock surrounding a small massive Ni sulphide orebody. Portable and laboratory-based XRF analyses were carried out on samples from a shear zone localised along the basal komatiite-dacite contact that hosts the orebody. A geochemical halo was identified that extends along the shear zone up to 1780 m away from the massive sulphides, parallel to a prominent stretching lineation. Elevated Ni and Pd are associated with high As, Co, Cu and S. Palladium and Pt concentrations increase with proximity to massive sulphides (from 6 to 1190 ppb Pd). These anomalous concentrations reflect the presence of sulfarsenides and sulphides, either physically remobilised and forming veinlets close to the massive sulphides, or hydrothermally transported and redeposited within the foliation. In situ laser ablation ICP-MS indicates that Pd and Pt are hosted within these nickel sulfarsenides. This Ni-Co-As-Pd geochemical halo, observed around the Sarah's Find ore body, is interpreted as forming syn deformation, by the circulation of As-rich hydrothermal fluids dissolving base metals, Pd and Pt from the orebody and redepositing them along the sheared footwall contact. Similar Ni-Co-Pd-Pt-As geochemical haloes could potentially exist around any magmatic nickel sulphide mineral system that has undergone a phase of arsenic metasomatism and may be a generally applicable proximity indicator for nickel sulphides in hydrothermally altered terranes.

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

    NASA Technical Reports Server (NTRS)

    Shirey, Steven B.; Hanson, Gilbert N.

    1986-01-01

    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.

  13. 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

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

    2007-01-01

    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.

  14. Spatial Distribution of Hydrogen Production Zone and Organic Carbon; Case Study from Jurassic Ocean Plateau, the Mikabu Greenstone Belt, Central Shikoku, Japan.

    NASA Astrophysics Data System (ADS)

    Ando, Y.; Okamoto, K.; Terabayashi, M.

    2014-12-01

    Hydrothermal activity in the Archean-Ridge system has been considered to play a major role to maintain the oldest biosphere in early Earth. In the present ridge-system, hydrogen production in the serpentinized peridotite layer, is considered as major energy source. However, low temperature hydrothermal zone in the lower crust layer in the ridge has been recognized as hydrogen producing zone. Then what is the hydrogen source in the oceanic lower crust? Accreted oceanic plateau is one of the best sample to describe hydration process due to deep-sea-hydrothermal alteration because it is easy to observe huge outcrops and collect samples systematically in whole section. We have collected rock samples from Mikabu high P/T rocks in Toba area and from Ootoyo area, Japan because there are large scale trench cliffs in the mine. Here, we report mineral composition surrounding organic carbon that was found in metabasaltic rocks from Otoyo area. The metabasalt underlies metachert, and exhibit extensive plagioclase veins. Carbonaceous material and FeS are concentrated near the veins. Serpentinization of olivine gabbro was recognized there. In the Toba area, wehrlite and hornblende gabbro are dominant as the oceanic lower crustal material, subsequently suffered high P/T metamorphism. Abundant serpentine with magnetite are along olivine grain boundaries. Cr-spinel and epidote are occasionally recognized. That is, hydrogen was produced due to hydration reaction in the intruded wherlite from the lower crust of the large plateau. In summary, the lower crust might be significant zone producing hydrogen, and provide bacteria cluster above.

  15. Applications of radiation belt research

    NASA Astrophysics Data System (ADS)

    Lanzerotti, Louis J.

    2011-10-01

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

  16. Foreland basins and fold belts

    SciTech Connect

    Macqueen, R.W.; Leckie, D.A. )

    1992-01-01

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

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

    PubMed

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

    2013-01-01

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

  18. 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

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

    2006-09-01

    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

  19. Magmatic origin of low-T mafic blueschist and greenstone blocks from the Franciscan mélange, San Simeon, California

    NASA Astrophysics Data System (ADS)

    Ukar, Estibalitz; Cloos, Mark

    2015-08-01

    The Franciscan mélange exposure near San Simeon contains abundant greenstone and minor blueschist blocks that were tectonically boudinaged while encased in the shale-matrix. Tectonic deformation of the blueschists is evident from variable amounts of cataclastic flow along their margins and in pinched tails. Major, trace, and rare earth elemental analyses indicate that blueschist and greenstone blocks in this area of the mélange were derived from sources with MORB-like composition along with some having trace element and REE patterns similar to OIB compositions. Most blocks are low LREE basalts that probably formed in an open ocean ridge setting, but some blocks have high LREE contents similar to off-axis seamounts. Linear trends of incompatible elements for both blueschist and greenstone blocks indicate that both lithologies were probably derived from a similar, variably fractionated, tholeiitic magma. Blueschist blocks with sodic amphibole + lawsonite ± epidote were pervasively recrystallized at 300-350 °C and foliated during ductile deformation that included folding. Their protolith can only be identified as mafic. A few blocks contain very small amounts of metasedimentary materials indicating some were probably seafloor basalts, but some may have been diabase or even gabbro. Where interlayered sediment was present, the mafic protolith was enriched in K, Rb, and Na. Greenstones, on the other hand, contain abundant pseudomorphic evidence of magmatic textures. Alteration to albite, chlorite and pumpellyite at temperatures of 100-200 °C is intense, especially in cataclastic margins and pinched tails. Some of the basaltic greenstones have attached radiolarian chert, and a few have relict diabasic textures. The mafic blueschists and greenstones in the mélange near San Simeon are probably fragments from the uppermost part of the Farallon plate. The blueschists may be mostly mafic slabs uprooted from the subducting crust, underplated to the base of the North American plate and later detached and carried back towards the surface in upwelling mélange. The greenstones are most likely fragments detached from seamounts subducted during times of mélange upwelling.

  20. Launching jets from accretion belts

    NASA Astrophysics Data System (ADS)

    Schreier, Ron; Soker, Noam

    2016-05-01

    We propose that sub-Keplerian accretion belts around stars might launch jets. The sub-Keplerian inflow does not form a rotationally supported accretion disk, but it rather reaches the accreting object from a wide solid angle. The basic ingredients of the flow are a turbulent region where the accretion belt interacts with the accreting object via a shear layer, and two avoidance regions on the poles where the accretion rate is very low. A dynamo that is developed in the shear layer amplifies magnetic fields to high values. It is likely that the amplified magnetic fields form polar outflows from the avoidance regions. Our speculative belt-launched jets model has implications on a rich variety of astrophysical objects, from the removal of common envelopes to the explosion of core collapse supernovae by jittering jets.

  1. Apparatus for forming drive belts

    NASA Technical Reports Server (NTRS)

    Topits, A., Jr. (Inventor)

    1974-01-01

    An apparatus for manufacturing belts, such as seamless belts, is provided, the apparatus has relatively movable rollers that are mounted in an oven. A belt blank, for example, of a thin polyester film, is rotated on the rollers as heat is applied. Four rollers, each mounted on a separate roller assembly, are movable along appropriate tracks while a fifth centrally located roller is stationary. A pair of dc motors are operatively connected to a speed reduction gear assembly to provide a pair of rotating drive shafts that extend into the oven. One rotating shaft drives all of the rollers through a rotational gear assembly while the other drive shaft is capable of positioning the movable rollers through respective rotating threaded shafts. Control devices are provided for controlling the motors while measuring devices are operatively connected to the positional drive shaft to indicate the position of the rollers.

  2. High speed abrasive belt grinding

    NASA Astrophysics Data System (ADS)

    Bak, Joseph

    1989-01-01

    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.

  3. Archean sedimentary styles and early crustal evolution

    NASA Astrophysics Data System (ADS)

    Lowe, D. R.

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2009-05-01

    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.

  5. Origin of Archean Chromitites in the Nuggihalli Schist Belt, Dharwar Craton (India)

    NASA Astrophysics Data System (ADS)

    Mukherjee, R.; Mondal, S. K.; Rosing, M. T.; Frei, R.

    2009-12-01

    Layered ultramafic-mafic rocks with chromitite bodies occur as sill-like intrusions within the Archean greenstone sequences of the Nuggihalli belt, Western Dharwar Craton. The 3.1Ga chromitite-bearing ultramafic-mafic rocks occur as dismembered en echelon, lenticular units that are conformable within the metasedimentary rocks, and surrounded by the tonalite-trondhjemite-granodiorite suite. The chromitite bodies are hosted within intensely deformed serpentinite, and associated with gabbro. The chromitite bodies have high length/width ratio (60-500 m/15 m) and occur in the form of pods and elongated lenses. Detailed electron microprobe study reveals high Cr/(Cr+Al)=0.85-0.86 and moderate Mg/(Mg+Fe2+)=0.38-0.58 of the primary chromite from the massive chromitite. Interstitial and included olivine and pyroxene grains within massive chromitite, exhibit very high Fo content (Fo96-98) and Mg-numbers (94-99) respectively. Chromite grains exhibit intense compositional variability due to subsolidus re-equilibration and low temperature hydrothermal alteration processes such as in the altered massive chromitite (70% chromite), serpentinite (2% chromite) and silicate-rich chromitite (45% chromite). In these associations, chromite grains are compositionally zoned and commonly altered to ferritchromit (rarely magnetite) along the rim and fractures. The primary chromite compositions are used to compute the parent melt that is characterised by low Al2O3 (8.38-10.63 wt%), moderate to high TiO2 (0.94-1.58 wt%) and FeO/MgO ratios of 0.46-0.92 wt%. The parent melt calculations indicate derivation from a high-Mg komatiitic basalt, and matches with the compositions of komatiitic rocks reported from the greenstone terrain. Parent melts are produced by high degrees of partial melting of a depleted source mantle evident from the refractory compositions of chromite, olivine and pyroxene. Tectonic discrimination diagrams indicate a supra-subduction zone setting (SSZ) for the Archean chromitites of Nuggihalli and derivation from a boninitic magma. Archean komatiitic basalts are thought to be similar to boninites that commonly occur in the SSZ settings. The high Ti of the calculated parental magma can be explained by recycled residual oceanic crust at the source that is confirmed from the positive HFSE anomalies of the ultramafic-mafic rocks (Mondal et al. 2008). The most acceptable model for chromitite formation is that of magma mixing postulated by Irvine (1977). The mixing model accounts for Mg/Fe variability of the units that overlie and underlie the chromitite body but, in the Nuggihalli belt, the host ultramafic rocks are intensely serpentinised and altered. Water can play an important role for chromitite formation in the SSZ-setting. Experiments show that water can suppress the crystallisation of silicate minerals, relative to chromite, thereby inducing crystallisation of massive chromitite bodies. Absorption of connate water by the high-Mg magma, as it intrudes into the wet-sediments of the greenstone sequence, may also play a role and cause the chromitite to form in these sill-like bodies. Mondal SK, Mukherjee R, Rosing MT, Frei R, Waight T, 2008 Eos Trans AGU 89(53) V33C-2237. Irvine TN 1977 Geology 5:273-277.

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

    PubMed

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

    2001-01-22

    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

  7. 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

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

    2001-01-01

    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

  8. Hazards of conveyor belt fires

    SciTech Connect

    Perzak, F.J.; Litton, C.D.; Mura, K.E.; Lazzara, C.P.

    1995-12-31

    This report describes a US Bureau of Mines study on the hazards of large-scale conveyor belt fires in underground coal mines, as a function of both air velocity and distance from belt surface to gallery roof. The fire hazards considered were smoke obscuration, toxic effects of carbon monoxide (CO), and elevated air temperatures downstream of the fire. All of these hazards scale with the ratio of fire intensity to ventilation airflow. These hazards were all found to be greater at the lower belt-to-roof distance, owing to the greater fire intensities that resulted. The hazards of smoke obscuration and elevated CO levels were greater at lower air velocities. Smoke obscuration was found to be the earliest hazard, reaching critical levels before the stages of flame spread. Fire growth rates during rapid flame spread were much greater than rates measured during the early stages of flame spread. Fire growth rates during rapid flame spread were much greater than rates measured during the early stages of belt burning. Data were analyzed to determine the early-warning capability of fire sensors. Smoke sensors provided the earliest warning, followed closely by CO sensors. Thermal sensors did not exhibit any early warning capability.

  9. 30 CFR 77.1107 - Belt conveyors.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Belt conveyors. 77.1107 Section 77.1107 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY... § 77.1107 Belt conveyors. Belt conveyors in locations where fire would create a hazard to...

  10. 36 CFR 4.15 - Safety belts.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 36 Parks, Forests, and Public Property 1 2010-07-01 2010-07-01 false Safety belts. 4.15 Section 4... TRAFFIC SAFETY § 4.15 Safety belts. (a) Each operator and passenger occupying any seating position of a motor vehicle in a park area will have the safety belt or child restraint system properly fastened...

  11. 46 CFR 169.723 - Safety belts.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 7 2013-10-01 2013-10-01 false Safety belts. 169.723 Section 169.723 Shipping COAST... Control, Miscellaneous Systems, 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...

  12. 46 CFR 169.723 - Safety belts.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 7 2014-10-01 2014-10-01 false Safety belts. 169.723 Section 169.723 Shipping COAST... Control, Miscellaneous Systems, 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...

  13. 36 CFR 4.15 - Safety belts.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 36 Parks, Forests, and Public Property 1 2011-07-01 2011-07-01 false Safety belts. 4.15 Section 4... TRAFFIC SAFETY § 4.15 Safety belts. (a) Each operator and passenger occupying any seating position of a motor vehicle in a park area will have the safety belt or child restraint system properly fastened...

  14. 46 CFR 169.723 - Safety belts.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 7 2011-10-01 2011-10-01 false Safety belts. 169.723 Section 169.723 Shipping COAST... Control, Miscellaneous Systems, 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...

  15. 36 CFR 4.15 - Safety belts.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 36 Parks, Forests, and Public Property 1 2013-07-01 2013-07-01 false Safety belts. 4.15 Section 4... TRAFFIC SAFETY § 4.15 Safety belts. (a) Each operator and passenger occupying any seating position of a motor vehicle in a park area will have the safety belt or child restraint system properly fastened...

  16. 46 CFR 169.723 - Safety belts.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 7 2012-10-01 2012-10-01 false Safety belts. 169.723 Section 169.723 Shipping COAST... Control, Miscellaneous Systems, 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...

  17. 36 CFR 4.15 - Safety belts.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 36 Parks, Forests, and Public Property 1 2014-07-01 2014-07-01 false Safety belts. 4.15 Section 4... TRAFFIC SAFETY § 4.15 Safety belts. (a) Each operator and passenger occupying any seating position of a motor vehicle in a park area will have the safety belt or child restraint system properly fastened...

  18. 36 CFR 4.15 - Safety belts.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 36 Parks, Forests, and Public Property 1 2012-07-01 2012-07-01 false Safety belts. 4.15 Section 4... TRAFFIC SAFETY § 4.15 Safety belts. (a) Each operator and passenger occupying any seating position of a motor vehicle in a park area will have the safety belt or child restraint system properly fastened...

  19. 46 CFR 169.723 - Safety belts.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 7 2010-10-01 2010-10-01 false Safety belts. 169.723 Section 169.723 Shipping COAST... Control, Miscellaneous Systems, 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...

  20. Grinding Glass Disks On A Belt Sander

    NASA Technical Reports Server (NTRS)

    Lyons, James J., III

    1995-01-01

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

  1. Characteristics of belted and unbelted drivers.

    PubMed

    Preusser, D F; Williams, A F; Lund, A K

    1991-12-01

    Drivers who had been observed wearing or not wearing shoulder belts were compared using vehicle registration data, driver records, and telephone interviews. The observations were made on the New York Thruway during a special seat belt publicity and enforcement program, which achieved a 75% overall belt use. The results showed that those drivers who still did not wear a shoulder belt despite New York law and the special Thruway program were more likely to be male, to be driving older vehicles, to have more prior traffic convictions, to have more prior injury crash involvements, and to say they are more likely to take risks than others. Although drivers reported that assessing points against the drivers license for belt law violations could increase belt use, citations for belt use law violations were very rare, and enforcement would probably have to increase before any new penalty could be effective. PMID:1772550

  2. The Southeast Asian Tin Belt

    NASA Astrophysics Data System (ADS)

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

    1995-07-01

    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.

  3. Timing of multiple hydrothermal events in the iron oxide-copper-gold deposits of the Southern Copper Belt, Carajás Province, Brazil

    NASA Astrophysics Data System (ADS)

    Moreto, Carolina P. N.; Monteiro, Lena V. S.; Xavier, Roberto P.; Creaser, Robert A.; DuFrane, S. Andrew; Melo, Gustavo H. C.; Delinardo da Silva, Marco A.; Tassinari, Colombo C. G.; Sato, Kei

    2015-06-01

    The Southern Copper Belt, Carajás Province, Brazil, hosts several iron oxide-copper-gold (IOCG) deposits, including Sossego, Cristalino, Alvo 118, Bacuri, Bacaba, Castanha, and Visconde. Mapping and U-Pb sensitive high-resolution ion microprobe (SHRIMP) IIe zircon geochronology allowed the characterization of the host rocks, situated within regional WNW-ESE shear zones. They encompass Mesoarchean (3.08-2.85 Ga) TTG orthogneiss, granites, and remains of greenstone belts, Neoarchean (ca. 2.74 Ga) granite, shallow-emplaced porphyries, and granophyric granite coeval with gabbro, and Paleoproterozoic (1.88 Ga) porphyry dykes. Extensive hydrothermal zones include albite-scapolite, biotite-scapolite-tourmaline-magnetite alteration, and proximal potassium feldspar, chlorite-epidote and chalcopyrite formation. U-Pb laser ablation multicollector inductively coupled mass spectrometry (LA-MC-ICP-MS) analysis of ore-related monazite and Re-Os NTIMS analysis of molybdenite suggest multiple Neoarchean (2.76 and 2.72-2.68 Ga) and Paleoproterozoic (2.06 Ga) hydrothermal events at the Bacaba and Bacuri deposits. These results, combined with available geochronological data from the literature, indicate recurrence of hydrothermal systems in the Southern Copper Belt, including 1.90-1.88-Ga ore formation in the Sossego-Curral ore bodies and the Alvo 118 deposit. Although early hydrothermal evolution at 2.76 Ga points to fluid migration coeval with the Carajás Basin formation, the main episode of IOCG genesis (2.72-2.68 Ga) is related to basin inversion coupled with Neoarchean (ca. 2.7 Ga) felsic magmatism. The data suggest that the IOCG deposits in the Southern Copper Belt and those in the Northern Copper Belt (2.57-Ga Salobo and Igarapé Bahia-Alemão deposits) do not share a common metallogenic evolution. Therefore, the association of all IOCG deposits of the Carajás Province with a single extensive hydrothermal system is precluded.

  4. The Scattered Kuiper Belt Objects

    NASA Astrophysics Data System (ADS)

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

    1999-09-01

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

  5. Overview of Radiation Belt Modelling

    NASA Astrophysics Data System (ADS)

    Heynderickx, D.

    The Earth's trapped radiation belts were discovered at the beginning of the space age and were immediately recognised as a considerable hazard to space missions. Consequently, considerable effort was invested in building models of the trapped proton and electron populations, culminating in the NASA AP-8 and AE-8 models which have been the de facto standards since the seventies. The CRRES mission has demonstatred that the trapped radiation environment is much more complex than the static environment described by the old models. Spatial and especially temporal variations were shown to be much more important than previously thought, and to require more complex models than those in use at that time. Such models are now becoming available, but they are limited in spatial or temporal coverage, and no global, dynamic, trapped radiation belt model is forthcoming. It is therefore vital to co-ordinate future modelling efforts in order to develop new standard models.

  6. Liquid belt radiator design study

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

  7. 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)

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

    2010-05-01

    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.

  8. Synchronous and Cogged Fan Belt Performance Assessment

    SciTech Connect

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

    2014-02-01

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

  9. Qingyuan high-grade granite-greenstone terrain in the Eastern North China Craton: Root of a Neoarchaean arc

    NASA Astrophysics Data System (ADS)

    Peng, Peng; Wang, Chong; Wang, Xinping; Yang, Shuyan

    2015-11-01

    The Qingyuan high-grade granite-greenstone terrain is one of the first recognized granite-greenstone terrains in the Eastern North China Craton. Similar to other Archaean terrains, its tectonic environment is debated: was it an intra-continental rift or a modern analogy of arc? Occurrence and petrogenesis of major igneous series, the ultramafic-mafic and felsic volcanic rocks (> 2510 Ma) and the plutons of the quartz diorite (2570-2510 Ma), TTG (2570-2510 Ma) and quartz monzodiorite (2510-2490 Ma) series in Xinbin area are investigated. The mafic intrusives and volcanic rocks have high MgO content (5.4-7.5 wt.%) and Mg-number (48-61). They show slightly depleted to flat trace element patterns. The ultramafic rocks (serpentinite) could be genetically related to the mafic rocks. The meta-dacite-rhyolite is adakitic with enriched light and middle REEs and LILEs, but significantly depleted HFSEs. The quartz diorite has high Mg-number (60-64), moderately enriched light and middle REEs and LILEs. The TTG shows distinct light but moderate middle REE-enrichment, prominent Nb-Ta-depletion but Zr-Hf-enrichment (Zr/Sm > 100). The quartz monzodiorite has moderate light and middle REE-enrichment, significant Nb-Ta-depletion, and negative Eu-/Sr-anomalies. The TTG has more depleted Sr-Nd isotopes (εNdt = + 2-+ 6; 87Sr/86Srt = ~ 0.700) than all the others (εNdt = 0-+ 2; 87Sr/86Srt = 0.701-703). Their petrogenesis can be explained by an Archaean-style subduction defined as a mantle wedge-absent flat-'hot'-subduction with significant vertical tectonism in the overriding slab: the ultramafic-mafic rocks were originated from primitive mantle; the meta-dacite-rhyolite was originated from the eclogite facies overriding crust; the quartz diorite was a mixture of melts from mantle and the overriding crust; the TTG was from the subducting slab under amphibolite to amphibole-bearing eclogite facies; and the quartz monzodiorite was from the subducting slab after the derivation of the TTG. The Qingyuan terrain represents remnants of the root of a Neoarchaean arc: its anticlockwise P-T-path recorded the initiation of the arc to its cession and exhumation/cratonization at ~ 2480 Ma.

  10. Safety belt promotion: theory and practice.

    PubMed

    Nelson, G D; Moffit, P B

    1988-02-01

    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

  11. Continuous Mass Measurement on Conveyor Belt

    NASA Astrophysics Data System (ADS)

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

    The continuous mass measurement of packages on a conveyor belt will become greatly important. In the mass measurement, the sequence of products is generally random. An interesting possibility of raising throughput of the conveyor line without increasing the conveyor belt speed is offered by the use of two or three conveyor belt scales (called a multi-stage conveyor belt scale). The multi-stage conveyor belt scale can be created which will adjust the conveyor belt length to the product length. The conveyor belt scale usually has maximum capacities of less than 80kg and 140cm, and achieves measuring rates of more than 150 packages per minute and more. The output signals from the conveyor belt scale are always contaminated with noises due to vibrations of the conveyor and the product to be measured in motion. In this paper an employed digital filter is of Finite Impulse Response (FIR) type designed under the consideration on the dynamics of the conveyor system. The experimental results on the conveyor belt scale suggest that the filtering algorithms are effective enough to practical applications to some extent.

  12. Investigation of Moving Belt Radiator Technology Issues

    NASA Technical Reports Server (NTRS)

    Teagan, W. Peter; Aguilar, Jerry L.

    1994-01-01

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

  13. Puzzling Snowballs: Main Belt Comets

    NASA Astrophysics Data System (ADS)

    Yang, Bin; Meech, Karen

    2015-03-01

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

  14. Weak Turbulence in Radiation Belts

    NASA Astrophysics Data System (ADS)

    Ganguli, Gurudas; Crabtree, Chris; Rudakov, Leonid

    2015-11-01

    Weak turbulence plays a significant role in space plasma dynamics. Induced nonlinear scattering dominates the evolution in the low-beta isothermal radiation belt plasmas and affects the propagation characteristics of waves. As whistler waves propagate away from the earth they are scattered in the magnetosphere such that their trajectories are turned earthward where they are reflected back towards the magnetosphere. Repeated scattering and reflection of the whistlers establishes a cavity in which the wave energy can be maintained for a long duration with, on average, a smaller wave-normal angle. Consequently, the cyclotron resonance time for the trapped energetic electrons increases, leading to an enhanced pitch-angle scattering rate. Enhanced pitch-angle scattering lowers the lifetime of the energetic electron population. Also, pitch-angle scattering of the trapped population in the cavity with a loss cone distribution amplifies the whistler waves, which in turn promotes a more rapid precipitation through a positive feedback mechanism. Typical storm-pumped radiation belt parameters and laboratory experiments will be used to elucidate this phenomenon Work supported by NRL Base Funds.

  15. Visible and infrared properties of unaltered to weathered rocks from Precambrian granite-greenstone terrains of the West African Craton

    NASA Astrophysics Data System (ADS)

    Metelka, Václav; Baratoux, Lenka; Jessell, Mark W.; Naba, Séta

    2015-12-01

    In situ and laboratory 0.35 μm-2.5 μm spectra of rocks from a Paleoproterozoic granite-greenstone terrain along with its Neoproterozoic sedimentary cover and derived regolith materials were examined in western Burkina Faso. The reflectance spectra show the influence of typical arid to semi-arid weathering with the formation of desert varnish, iron films, and dust coatings. Fe and Mg-OH absorption features related to chlorite, amphibole, pyroxene, epidote, and biotite are observable in the mafic and intermediate meta-volcanic rocks as well as in the granodiorites and tonalites. Al-OH absorption caused by kaolinite, smectite, illite/muscovite are typical for meta-volcano-sedimentary schists, Tarkwaian-type detrital meta-sediments, sandstones of the Taoudeni basin, all of the weathered surfaces and regolith materials. Ferric and ferrous iron absorptions related to both primary rock-forming minerals and secondary weathering minerals (goethite, hematite) were observed in most of the sampled materials. The results show that although weathering alters the spectral signature of the fresh rock, indicative absorption features located in the short wave infrared region remain detectable. In addition, spectra of soils partially reflect the mineral composition of the weathered rock surfaces. The analysis of the hyperspectral data shows the potential of differentiating between the sampled surfaces. The library presents a primary database for the geological and regolith analysis of remote sensing data in West Africa.

  16. 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

  17. Understanding Quaternions and the Dirac Belt Trick

    ERIC Educational Resources Information Center

    Staley, Mark

    2010-01-01

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

  18. Understanding Quaternions and the Dirac Belt Trick

    ERIC Educational Resources Information Center

    Staley, Mark

    2010-01-01

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

  19. The Administrator's "Handy Dandy" Tool Belt

    ERIC Educational Resources Information Center

    Anderson, Terry

    2012-01-01

    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…

  20. DESIGN AND OPERATION OF BELT FILTER PRESSES

    EPA Science Inventory

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

  1. 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 ... together keep you from being thrown from the car during an accident. The shoulder strap also keeps ...

  2. Seat Belts on School Buses: Some Considerations.

    ERIC Educational Resources Information Center

    Soule, David

    1982-01-01

    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)

  3. Apparatus for heat treating plastic belts

    NASA Technical Reports Server (NTRS)

    Topits, A., Jr.

    1975-01-01

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

  4. 14 CFR 27.1413 - Safety belts.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Safety belts. 27.1413 Section 27.1413 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL CATEGORY ROTORCRAFT Equipment Safety Equipment § 27.1413 Safety belts. Each safety...

  5. 14 CFR 27.1413 - Safety belts.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Safety belts. 27.1413 Section 27.1413 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL CATEGORY ROTORCRAFT Equipment Safety Equipment § 27.1413 Safety belts. Each safety...

  6. 14 CFR 31.63 - Safety belts.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Safety belts. 31.63 Section 31.63 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: MANNED FREE BALLOONS Design Construction § 31.63 Safety belts. (a) There must be a safety...

  7. 14 CFR 27.1413 - Safety belts.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Safety belts. 27.1413 Section 27.1413 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL CATEGORY ROTORCRAFT Equipment Safety Equipment § 27.1413 Safety belts. Each safety...

  8. 14 CFR 27.1413 - Safety belts.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Safety belts. 27.1413 Section 27.1413 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL CATEGORY ROTORCRAFT Equipment Safety Equipment § 27.1413 Safety belts. Each safety...

  9. 36 CFR 1004.15 - Safety belts.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 36 Parks, Forests, and Public Property 3 2013-07-01 2012-07-01 true Safety belts. 1004.15 Section 1004.15 Parks, Forests, and Public Property PRESIDIO TRUST VEHICLES AND TRAFFIC SAFETY § 1004.15 Safety... administered by the Presidio Trust will have the safety belt or child restraint system properly fastened at...

  10. 14 CFR 31.63 - Safety belts.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Safety belts. 31.63 Section 31.63 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: MANNED FREE BALLOONS Design Construction § 31.63 Safety belts. (a) There must be a safety...

  11. 36 CFR 1004.15 - Safety belts.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 36 Parks, Forests, and Public Property 3 2010-07-01 2010-07-01 false Safety belts. 1004.15 Section 1004.15 Parks, Forests, and Public Property PRESIDIO TRUST VEHICLES AND TRAFFIC SAFETY § 1004.15 Safety... administered by the Presidio Trust will have the safety belt or child restraint system properly fastened at...

  12. 14 CFR 31.63 - Safety belts.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Safety belts. 31.63 Section 31.63 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: MANNED FREE BALLOONS Design Construction § 31.63 Safety belts. (a) There must be a safety...

  13. 36 CFR 1004.15 - Safety belts.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 36 Parks, Forests, and Public Property 3 2012-07-01 2012-07-01 false Safety belts. 1004.15 Section 1004.15 Parks, Forests, and Public Property PRESIDIO TRUST VEHICLES AND TRAFFIC SAFETY § 1004.15 Safety... administered by the Presidio Trust will have the safety belt or child restraint system properly fastened at...

  14. 14 CFR 31.63 - Safety belts.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Safety belts. 31.63 Section 31.63 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: MANNED FREE BALLOONS Design Construction § 31.63 Safety belts. (a) There must be a safety...

  15. 36 CFR 1004.15 - Safety belts.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 36 Parks, Forests, and Public Property 3 2011-07-01 2011-07-01 false Safety belts. 1004.15 Section 1004.15 Parks, Forests, and Public Property PRESIDIO TRUST VEHICLES AND TRAFFIC SAFETY § 1004.15 Safety... administered by the Presidio Trust will have the safety belt or child restraint system properly fastened at...

  16. 14 CFR 27.1413 - Safety belts.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Safety belts. 27.1413 Section 27.1413 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL CATEGORY ROTORCRAFT Equipment Safety Equipment § 27.1413 Safety belts. Each safety...

  17. 36 CFR 1004.15 - Safety belts.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 36 Parks, Forests, and Public Property 3 2014-07-01 2014-07-01 false Safety belts. 1004.15 Section 1004.15 Parks, Forests, and Public Property PRESIDIO TRUST VEHICLES AND TRAFFIC SAFETY § 1004.15 Safety... administered by the Presidio Trust will have the safety belt or child restraint system properly fastened at...

  18. 14 CFR 31.63 - Safety belts.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Safety belts. 31.63 Section 31.63 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: MANNED FREE BALLOONS Design Construction § 31.63 Safety belts. (a) There must be a safety...

  19. Seat belt use in cars with air bags.

    PubMed Central

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

    1990-01-01

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

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

    PubMed

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

    2010-08-01

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

  1. Inner Radiation Belt Dynamics and Climatology

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  2. Use of seatbelts in cars with automatic belts.

    PubMed Central

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

    1992-01-01

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

  3. On the structure of coronal streamer belts

    NASA Astrophysics Data System (ADS)

    Eselevich, V. G.

    1998-02-01

    In an attempt to separate the temporal and spatial variations in polarization brightness (plasma density) along the coronal streamer belt, a study is made of the parts of the belt which are longitudinally aligned with the west or east limb of the sun. It is shown that the brightness distribution along streamer belts is inhomogeneous with relative brightness variations of about 1.1-2.0. Streamer belts consist of a sequence of coronal rays (streamers), each of which at distances of greater than 3 solar radii from the solar center has a cross section with a typical angular size of about 10-70 deg along the belt and about 10-30 deg across the belt with neighboring rays separated by L of about 10-70. Examples from CRs 1591 and 1592 show that in the absence of the influence of coronal mass ejection, the distribution of streamer rays along the streamer belt can be stable for nearly two complete Carrington rotations.

  4. Vision for a Virtual Radiation Belt Observatory

    NASA Astrophysics Data System (ADS)

    Green, J. C.; Baker, D. N.; Kroehl, H. W.; Kihn, E. A.; Fennell, J. F.; Blake, J. B.; Reeves, G. D.; Friedel, R. H.; McGuire, R. E.; Fung, S. F.; Kanekal, S. G.; Mason, G. M.; Rigler, E. J.; Weigel, R. S.; Elkington, , S. R.

    2004-05-01

    Satellite engineers, operators, and scientists now share a common desire to understand the structure and variability of the earth's radiation belts. Continuing upsets to space operations demonstrate a need for improved scientific understanding of the radiation belts, more accurate models, and better transfer of scientific understanding to space technology and operations. Currently, the resources necessary for such advancements are beyond the scope of an individual researcher. Thus, we discuss plans to advance our understanding of the radiation belts and mitigate the hazards they pose to society by creating a Virtual Radiation Belt Observatory (ViRBO). The observatory will be an open access near real time and long term archive of observed and simulated radiation belt model data. It will enable scientists to test theoretical mechanisms proposed to explain how particles are accelerated and removed from the radiation belts and it will provide improved tools for engineers designing satellites and operators assessing satellite malfunctions. The observatory will capitalize on radiation belt modeling efforts currently underway at institutions throughout the country and support the goals of the electronic Geophysical Year (eGY) endorsed by the world wide community.

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

    SciTech Connect

    Davidsen, R.K.; Cloos, M.

    1985-01-01

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

  6. Depletion of the Outer Asteroid Belt

    PubMed

    Liou; Malhotra

    1997-01-17

    During the early history of the solar system, it is likely that the outer planets changed their distance from the sun, and hence, their influence on the asteroid belt evolved with time. The gravitational influence of Jupiter and Saturn on the orbital evolution of asteroids in the outer asteroid belt was calculated. The results show that the sweeping of mean motion resonances associated with planetary migration efficiently destabilizes orbits in the outer asteroid belt on a time scale of 10 million years. This mechanism provides an explanation for the observed depletion of asteroids in that region. PMID:8994031

  7. Electric filter with movable belt electrode

    SciTech Connect

    Bergman, W.

    1982-02-23

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

  8. Electric filter with movable belt electrode

    DOEpatents

    Bergman, W.

    1983-09-20

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

  9. Electric filter with movable belt electrode

    DOEpatents

    Bergman, Werner

    1983-01-01

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

  10. Depletion of the Outer Asteroid Belt

    NASA Technical Reports Server (NTRS)

    Liou, Jer-Chyi; Malhotra, Renu

    1997-01-01

    During the early history of the solar system, it is likely that the outer planets changed their distance from the sun, and hence, their influence on the asteroid belt evolved with time. The gravitational influence of Jupiter and Saturn on the orbital evolution of asteroids in the outer asteroid belt was calculated. The results show that the sweeping of mean motion resonances associated with planetary migration efficiently destabilizes orbits in the outer asteroid belt on a time scale of 10 million years. This mechanism provides an explanation for the observed depletion of asteroids in that region.

  11. 30 CFR 57.14203 - Application of belt dressing.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Application of belt dressing. 57.14203 Section... and Equipment Safety Practices and Operational Procedures § 57.14203 Application of belt dressing. Belt dressings shall not be applied manually while belts are in motion unless a...

  12. 30 CFR 56.14203 - Application of belt dressing.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Application of belt dressing. 56.14203 Section... Equipment Safety Practices and Operational Procedures § 56.14203 Application of belt dressing. Belt dressings shall not be applied manually while belts are in motion unless a pressurized-type applicator...

  13. 30 CFR 56.14203 - Application of belt dressing.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Application of belt dressing. 56.14203 Section... Equipment Safety Practices and Operational Procedures § 56.14203 Application of belt dressing. Belt dressings shall not be applied manually while belts are in motion unless a pressurized-type applicator...

  14. 30 CFR 57.14203 - Application of belt dressing.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Application of belt dressing. 57.14203 Section... and Equipment Safety Practices and Operational Procedures § 57.14203 Application of belt dressing. Belt dressings shall not be applied manually while belts are in motion unless a...

  15. Web belt load measuring instrument has excellent stability

    NASA Technical Reports Server (NTRS)

    Walker, R. R.

    1967-01-01

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

  16. 30 CFR 56.4503 - Conveyor belt slippage.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Conveyor belt slippage. 56.4503 Section 56.4503... Control Installation/construction/maintenance § 56.4503 Conveyor belt slippage. Belt conveyors within... shall attend the belt at the drive pulley when it is necessary to operate the conveyor while...

  17. Albedos in the Kuiper belt

    NASA Astrophysics Data System (ADS)

    Brucker, Melissa J.

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

  18. Energy loss and efficiency of power transmission belts

    SciTech Connect

    Breig, W.F.; Oliver, L.R.

    1980-10-01

    A selection of belt type and construction from industrial, automotive, and agricultural applications was tested and compared for idling loss and power transmission efficiency. Data are documented for Vee, joined-V, V-ribbed, and synchronous belt types and for cogged, plain, and laminated V-belt constructions. The level of energy savings achieved by the replacement of plain-base wrapped V-belts with cogged V-belts is emphasized. Belt efficiency, slip, and temperature dependence on the basic drive parameters of torque, sheave diameter, belt tension, and contact angle is reported.

  19. A repair of a charging belt

    SciTech Connect

    Jones, N.L.

    1989-01-01

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

  20. Seat Belt Usage on School Buses.

    ERIC Educational Resources Information Center

    Farmer, Ernest

    1985-01-01

    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)

  1. A photometric survey of outer belt asteroids

    NASA Technical Reports Server (NTRS)

    Dimartino, M.; Gonano-Beurer, M.; Mottola, Stefano; Neukum, G.

    1992-01-01

    Since 1989, we have been conducting a research program devoted to the study of the Trojans and outer belt asteroids (Hilda and Cybele groups), in order to characterize their rotational properties and shapes. As an outcome of several observational campaigns, we determined rotational periods and lightcurve amplitudes for 23 distant asteroids, using both CCD and photoelectric photometry. In this paper, we compare the rotational properties of main belt asteroids and Trojans, based on the preliminary results of this survey.

  2. How to evaluate belt conveyor idlers

    SciTech Connect

    Tomsky, E.H.

    1985-11-01

    This article discusses how to evaluate the relative merits of tapered roller-bearing vs. ball-bearing idlers for use in belt conveyors. Considered are: bearing load capacity; bearing life; bearing life under misalignment conditions; relubricatable vs. factory sealed idlers; relubrication frequency, and rotational resistance. Each of these factors are discussed and some criteria are provided for selecting the best belt conveyor idler for a material handling application.

  3. Jupiter's radiation belts: Can Pioneer 10 survive?

    NASA Technical Reports Server (NTRS)

    Hess, W. N.; Birmingham, T. J.; Mead, G. D.

    1973-01-01

    Model calculations of Jupiter's electron and proton radiation belts indicate that the Galilean satellites can reduce particle fluxes in certain regions of the inner magnetosphere by as much as six orders of magnitude. Average fluxes should be reduced by a factor of 100 or more along the Pioneer 10 trajectory through the heart of Jupiter's radiation belts in early December. This may be enough to prevent serious radiation damage to the spacecraft.

  4. Oil generation in overthrust belts

    SciTech Connect

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

    1983-02-01

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

  5. Decay rate of the second radiation belt.

    PubMed

    Badhwar, G D; Robbins, D E

    1996-01-01

    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

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

    NASA Astrophysics Data System (ADS)

    Wilson, Allan

    2013-04-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

    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.

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

    PubMed

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

    1989-09-01

    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

  9. Early Archean Spherule Beds-Confirmation of Impact Origin

    NASA Technical Reports Server (NTRS)

    Shukolyukov, A.; Kyte, F. T.; Lugmair, G. W.; Lowe, D. R.; Byerly, G. R.

    2000-01-01

    The oldest record of major impact events on Earth may be a number of early Archean (3.5 to 3.2 Ga) spherule beds that have been identified in the Barberton Greenstone Belt, South Africa. Several field, petrographic, and geochemical criteria distinguish these beds from typical volcanic and clastic sediments. These criteria include the wide geographic distribution of two beds in a variety of depositional environments, the presence of relict quench textures, absence of juvenile volcaniclastic debris within the beds, and extreme enrichment of Ir and other platinum group elements (PGE) as compared to surrounding sediments. Some researchers, however, argued for a terrestrial origin for spherule bed formation, possibly related to volcanism and gold mineralization.

  10. Why Turks do not use seat belts? An interview study.

    PubMed

    Sim?eko?lu, Ozlem; Lajunen, Timo

    2008-03-01

    Despite the effectiveness of seat belt use and legislation, seat belt use rate is low in Turkey. The aim of this study was to investigate the motives to use and not to use a seat belt in different traveling conditions in a sample of car drivers and passengers. Interviews were made face to face with 221 interviewees from different age and occupation groups. Frequently reported reasons for using a seat belt were traveling conditions, safety, situational conditions, habit of using a seat belt, and avoiding punishment. Frequently reported reasons for not using a seat belt were situational conditions, not believing in the effectiveness, discomfort and having no habit. Safety was the strongest predictor of reported seat belt use in both low and high risk traveling conditions. Findings suggest that seat belt campaigns should mainly emphasize seat belt's safety impact and aim at habit formation. PMID:18329396

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

    NASA Astrophysics Data System (ADS)

    Yuan, C.; Zong, Q.

    2013-12-01

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

  12. IDENTIFYING COLLISIONAL FAMILIES IN THE KUIPER BELT

    SciTech Connect

    Marcus, Robert A.; Ragozzine, Darin; Murray-Clay, Ruth A.; Holman, Matthew J.

    2011-05-20

    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.

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

    NASA Technical Reports Server (NTRS)

    Lowe, Donald R.

    1989-01-01

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

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

    PubMed

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

    2014-03-01

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

  15. A Physical Model of the Radiation Belt

    NASA Astrophysics Data System (ADS)

    Fok, M.

    2006-12-01

    A data-driven physical model of the radiation belt has been activated, based on the kinetic model previously developed by Fok and coworkers. This model calculates radiation belt electron fluxes from 10 keV to 4 MeV in the inner magnetosphere. The model takes into account realistic, time-varying magnetic field and considers effects of wave-particle interactions. The only inputs to the model are upstream solar wind and concurrent Dst data. With the real-time solar wind data supplied by NOAA and Dst data from the Kyoto University, the model is running in real time to provide now-casting of the radiation belt environment. In this paper, the model logic and formulation are discussed. The model results for several storm simulations are presented. The paper concludes with discussion of further improvements of the model to better achieve additional LWS goals.

  16. Mars: Dissipating Behavior of the Cloud Belt

    NASA Astrophysics Data System (ADS)

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

    2002-06-01

    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 ) 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.

  17. How long solar proton radiation belts exists?

    NASA Astrophysics Data System (ADS)

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

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

  18. Ionospheric heating for radiation-belt control

    SciTech Connect

    Burke, W.J.; Villalon, E.

    1990-10-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Yuan, Chongjing; Zong, Qiugang

    2013-10-01

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

  20. 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

  1. Radiation Belt Storm Probe Mission Trailer - Duration: 64 seconds.

    NASA Video Gallery

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

  2. 14 CFR 29.1413 - Safety belts: passenger warning device.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... safety belts should be fastened, they must be installed to be operated from either pilot seat. (b) Each safety belt must be equipped with a metal to metal latching device. (Secs. 313, 314, and 601 through...

  3. 14 CFR 29.1413 - Safety belts: passenger warning device.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... safety belts should be fastened, they must be installed to be operated from either pilot seat. (b) Each safety belt must be equipped with a metal to metal latching device. (Secs. 313, 314, and 601 through...

  4. 14 CFR 29.1413 - Safety belts: passenger warning device.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... safety belts should be fastened, they must be installed to be operated from either pilot seat. (b) Each safety belt must be equipped with a metal to metal latching device. (Secs. 313, 314, and 601 through...

  5. 14 CFR 29.1413 - Safety belts: passenger warning device.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... safety belts should be fastened, they must be installed to be operated from either pilot seat. (b) Each safety belt must be equipped with a metal to metal latching device. (Secs. 313, 314, and 601 through...

  6. The Radiation Belt Storm Probes - Duration: 3 minutes, 26 seconds.

    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 ...

  7. 30 CFR 57.14212 - Chains, ropes, and drive belts.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... and Equipment Safety Practices and Operational Procedures § 57.14212 Chains, ropes, and drive belts. Chains, ropes, and drive belts shall be guided mechanically onto moving pulleys, sprockets, or...

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

    USGS Publications Warehouse

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

    1983-01-01

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

  9. 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)

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

    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 Ωm) towards the central region of the study area suggest a high groundwater potential, while high resistivities (>500 Ωm) 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.

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

    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.

  11. Glauconite from the precambrian belt series, Montana

    USGS Publications Warehouse

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

    1963-01-01

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

  12. Belts and Chains. FOS: Fundamentals of Service.

    ERIC Educational Resources Information Center

    John Deere Co., Moline, IL.

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

  13. Planetary Migration and Kuiper Belt Dynamics

    NASA Astrophysics Data System (ADS)

    Malhotra, Renu

    The Kuiper belt holds memory of the dynamical processes that shaped the architecture of the solar system, including the orbital migration history of the giant planets. We propose studies of the orbital dynamics of the Kuiper Belt in order to understand the origin of its complex dynamical structure and its link to the orbital migration history of the giant planets. By means of numerical simulations, statistical tests, as well as analytical calculations we will (1) investigate the origin of resonant Kuiper belt objects to test alternative scenarios of Neptune's migration history, (2) investigate the long term dynamical evolution of the Haumea family of Kuiper Belt objects in order to improve the age estimate of this family, and (3) investigate resonance-sticking behavior and the Kozai-Lidov mechanism and its role in the origin of the extended scattered disk. These studies directly support the goals of the NASA-OSS program by improving our understanding of the origin of the solar system's architecture. Our results will provide constraints on the nature and timing of the dynamical excitation event that is thought to have occurred in early solar system history and to have determined the architecture of the present-day solar system; our results will also provide deeper theoretical understanding of sticky mean motion resonances which contribute greatly to the longevity of many small bodies, improve our understanding of dynamical transport of planetesimals in planetary systems, and help interpret observations of other planetary systems.

  14. SAMPEX: A Remarkable Radiation Belt Sentinel

    NASA Astrophysics Data System (ADS)

    Baker, D. N.

    2012-12-01

    The NASA SAMPEX spacecraft launched in 1992 is expected to end its mission by December 2012 due to re-entry into the Earth's atmosphere. This space platform has revolutionized our views of the dynamic radiation belt environment. We show, using the SAMPEX data, that the near-Earth region of the magnetosphere responds powerfully to changes of driving forces from the Sun and the solar wind. The Earth's radiation belts and inner magnetosphere exhibit substantial differences in their characteristics as the Sun's magnetic field and solar wind plasma properties change over the approximately 11-year solar activity cycle. Solar coronal holes produce regular, recurrent fast solar wind streams in geospace, often enhancing highly relativistic electrons and causing recurrent geomagnetic storms. These phenomena are characteristic of the approach to sunspot minimum. On the other hand, major geomagnetic disturbances associated with aperiodic coronal mass ejections occur most frequently around sunspot maximum. Such disturbances also can often produce significant radiation belt enhancements. We describe the observational results that characterize the differences throughout the inner part of geospace during the course of the solar activity cycle. We conclude that SAMPEX has been a most successful and impactful mission for radiation belt studies.

  15. Radiation Belts Throughout the Solar System

    NASA Astrophysics Data System (ADS)

    Mauk, B. H.

    2008-12-01

    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.

  16. Lightcurve Analysis for Nine Main Belt Asteroids

    NASA Astrophysics Data System (ADS)

    Casalnuovo, Giovanni Battista

    2016-04-01

    Photometric observations of nine main-belt asteroids, 1361 Leuschneria, 1511 Dalera, 1536 Pielinen, 2136 Jugta, 2668 Tataria, 5186 Donalu, 10064 Hirosetamotsu, 11268 Spassky, and 14515 Koichisato, were made at the Eurac Observatory (MPC C62). Results of lightcurve analysis are presented.

  17. School Buses & Seat Belts: A Discussion.

    ERIC Educational Resources Information Center

    Alaska State Dept. of Education, Juneau.

    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…

  18. The Case for School Bus Seat Belts.

    ERIC Educational Resources Information Center

    Corda, Salvatore J.

    1987-01-01

    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…

  19. Research on an Active Seat Belt System

    NASA Astrophysics Data System (ADS)

    Kawashima, Takeshi

    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.

  20. Inner Belt Energy Structuring by VLF Emitters

    NASA Astrophysics Data System (ADS)

    Sauvaud, J.; Moreau, T.; Maggiolo, R.; Jacquey, C.; Parrot, M.; Berthelier, J.

    2005-12-01

    We present new results on the structure of the inner radiation belt obtained with the IDP spectrometer onboard the DEMETER low-altitude polar orbiting satellite. The data received during 2004-05 show for the first time that the electron component of the inner radiation belt (1.1< L <1.35) with energies lower than 1.5 MeV consists in the superposition of a large number of quasi mono-energetic peaks as expected from the interaction of electrons with a large number of high powered Earth-based VLF emitters (10-150 kHz) distributed along the particle longitudinal drift around the Earth. This energy-layered structure appears to depend on the longitude, being particularly evident in low magnetic field regions where particles from the inner belt can easily reach the satellite altitude. This is particularly clear West of America and inside the South Atlantic Anomaly itself. The wave instruments onboard Demeter indeed displays the strong emissions of human made monochromatic waves in the frequency range 10-150 kHz. We show that they are able to destabilize the low energy component of the inner radiation belt and use the energy variation of the electron energy peaks as a function of the McIlwain parameter to estimate the equatorial thermal electron content at altitudes corresponding to the transition between the upper ionosphere and the plasmasphere.

  1. 30 CFR 57.15020 - Life jackets and belts.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Life jackets and belts. 57.15020 Section 57.15020 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL... Protection Surface Only § 57.15020 Life jackets and belts. Life jackets or belts shall be worn where there...

  2. 30 CFR 56.15020 - Life jackets and belts.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Life jackets and belts. 56.15020 Section 56.15020 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL... § 56.15020 Life jackets and belts. Life jackets or belts shall be worn where there is danger...

  3. 30 CFR 57.15020 - Life jackets and belts.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Life jackets and belts. 57.15020 Section 57.15020 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL... Protection Surface Only § 57.15020 Life jackets and belts. Life jackets or belts shall be worn where there...

  4. 30 CFR 56.15020 - Life jackets and belts.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Life jackets and belts. 56.15020 Section 56.15020 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL... § 56.15020 Life jackets and belts. Life jackets or belts shall be worn where there is danger...

  5. 30 CFR 57.4503 - Conveyor belt slippage.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Fire Prevention and Control Installation/construction/maintenance § 57.4503 Conveyor belt slippage. (a) Surface belt conveyors...) Underground belt conveyors shall be equipped with a detection system capable of automatically stopping...

  6. 30 CFR 57.4503 - Conveyor belt slippage.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Fire Prevention and Control Installation/construction/maintenance § 57.4503 Conveyor belt slippage. (a) Surface belt conveyors...) Underground belt conveyors shall be equipped with a detection system capable of automatically stopping...

  7. 30 CFR 75.350 - Belt air course ventilation.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Belt air course ventilation. 75.350 Section 75.350 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Ventilation § 75.350 Belt air course ventilation. (a) The belt air course must not be...

  8. 30 CFR 75.350 - Belt air course ventilation.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Belt air course ventilation. 75.350 Section 75.350 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Ventilation § 75.350 Belt air course ventilation. (a) The belt air course must not be...

  9. 49 CFR 392.16 - Use of seat belts.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... has a seat belt assembly installed at the driver's seat shall not be driven unless the driver has properly restrained himself/herself with the seat belt assembly. ... 49 Transportation 5 2014-10-01 2014-10-01 false Use of seat belts. 392.16 Section...

  10. 49 CFR 392.16 - Use of seat belts.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... has a seat belt assembly installed at the driver's seat shall not be driven unless the driver has properly restrained himself/herself with the seat belt assembly. ... 49 Transportation 5 2011-10-01 2011-10-01 false Use of seat belts. 392.16 Section...

  11. The Medical Case for Seat Belts on School Buses.

    ERIC Educational Resources Information Center

    Yeager, Arthur

    1985-01-01

    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)

  12. 49 CFR 392.16 - Use of seat belts.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... has a seat belt assembly installed at the driver's seat shall not be driven unless the driver has properly restrained himself/herself with the seat belt assembly. ... 49 Transportation 5 2012-10-01 2012-10-01 false Use of seat belts. 392.16 Section...

  13. 49 CFR 392.16 - Use of seat belts.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... has a seat belt assembly installed at the driver's seat shall not be driven unless the driver has properly restrained himself/herself with the seat belt assembly. ... 49 Transportation 5 2013-10-01 2013-10-01 false Use of seat belts. 392.16 Section...

  14. 49 CFR 392.16 - Use of seat belts.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... has a seat belt assembly installed at the driver's seat shall not be driven unless the driver has properly restrained himself/herself with the seat belt assembly. ... 49 Transportation 5 2010-10-01 2010-10-01 false Use of seat belts. 392.16 Section...

  15. 30 CFR 57.4263 - Underground belt conveyors.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Underground belt conveyors. 57.4263 Section 57... 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 conveyors. Provisions shall...

  16. 30 CFR 75.1403-5 - Criteria-Belt conveyors.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... located as to be observable to all persons riding the belt conveyor. (f) After supplies have been... installed after March 30, 1970. Where roof supports are installed within 24 inches of a belt conveyor, a... conveyor. (h) On belt conveyors that do not transport men, stop and start controls should be installed...

  17. 30 CFR 75.1108 - Approved conveyor belts.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Approved conveyor belts. 75.1108 Section 75... Fire-Resistant Hydraulic Fluids on Underground Equipment § 75.1108 Approved conveyor belts. (a) Until December 31, 2009 conveyor belts placed in service in underground coal mines shall be: (1) Approved...

  18. 30 CFR 75.1403-5 - Criteria-Belt conveyors.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... used to transport men, and such controls should be readily accessible and maintained so that the belt... should be stopped while men are loading or unloading. (c) All belt conveyors used for the transportation... men board or leave such belt conveyors. (d) When men are being transported on regularly...

  19. Belt fires and mine escape problems

    SciTech Connect

    Kovac, J.G.; Lazzara, C.P.; Kravitz, J.H.

    1996-12-31

    A conveyor belt fire in an underground coal mine is a serious threat to life and property. About 30% of the reportable underground coal mine fires from 1988 through 1992 occurred in belt entries. In one instance, a fire started in the drive area of a belt line, spread rapidly, and resulted in seating of the entire mine. Large-scale studies conducted by the U.S. Bureau of Mines in an aboveground fire gallery at Lake Lynn Laboratory clearly show the hazards of conveyor belt fires. Mine conveyor belt formulations which passed the current Federal acceptance test for fire-resistant betting were completely consumed by propagating fires or propagated flame, with flame spread rates ranging from 0.3 to 9 m/min. High downstream temperatures and large quantities of smoke and toxic gases, such as carbon monoxide, were generated as the belting burned. The smoke and gases can be spread by the mine`s ventilation system and can create significant problems for miners in the process of evacuation, such as reduction in visibility and incapacitation. In the aftermath of a belt fire, the atmosphere inside of the mine can become smoke filled or unbreathable, forcing miners to evacuate while wearing Self-Contained Self-Rescuers (SCSR`s), Sometimes there is confusion about how to regard the rated duration of an MSHA/NIOSH-approved 60-min. SCSR, especially when an SCSR is used in a way which takes it outside of the test conditions under which it was approved. As examples, for a mine escape that takes a miner from the deepest point of penetration in the mine to the surface: How long will a 60-min. SCSR actually last? and How many SCSR`s will a miner need? To answer these kinds of questions, in-mine data being gathered on escape times, distance and heart rates using miners escaping on foot and under oxygen. A model will be developed and validated which predicts how much oxygen is actually needed for a mine escape, and compares oxygen consumption bare faced versus wearing an SCSR.

  20. Imaging Jupiter Radiation Belts At Low Frequencies

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

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

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

    PubMed

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

    2008-11-01

    National seat belt wearing legislation became effective in China May 2004 and associated provincial and city regulations followed. Despite rapid motorisation seat belt studies in China have been scarce. Patterns and trends in urban seat belt wearing were observed for all driver, front and rear seating positions over the years 2005-2007 in two eastern cities Nanjing (Jiangsu Province) and Zhoushan (Zhejiang Province). There were 35,256 vehicles observed in Nanjing, 20,939 in Zhoushan and 95,933 occupants overall. Males dominated all seating positions, especially drivers. Seat belt wearing overall was significantly higher for drivers (49.9% Nanjing, 47.4% Zhoushan) than for front seat passengers (9.1% Nanjing, 1.0% Zhoushan) and virtually nonexistent for rear passengers (0.5% Nanjing, 0.2% Zhoushan). Generally levels declined significantly from year to year (drivers Nanjing 66.7%, 47.7%, 38.6%; Zhoushan 57.4%, 57.9%, 30.6%; front passengers Nanjing 19.2%, 6.6%, 3.2%). Zhoushan wearing did not initially decline, 2006 observations coinciding with anticipation of provincial regulations (July 2006). Observations revealed an absence of child restraints. Pretend wearing/belt tampering was observed almost exclusively in taxi drivers (14.2% of Nanjing taxi drivers, 11.3% of Zhoushan's). Awareness of and attitudes to urban seat belt laws should be investigated, appropriate countermeasures developed and enforcement reassessed. PMID:19068286

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

    PubMed Central

    Vilchez Larrea, Salomé C.; Kun, Alejandra

    2014-01-01

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

  3. Weighing KBOs: Characterizing Kuiper Belt Binaries

    NASA Astrophysics Data System (ADS)

    Parker, Alex; Jones, Lynne; Gladman, Brett; Kavelaars, Jj; Lin, Edward; Margot, Jean-Luc; Mousis, Olivier; Parker, Joel; Petit, Jean-Marc; Rouselot, Phillipe

    2009-02-01

    Long period Kuiper Belt binaries - being difficult to create and very sensitive to perturbation - yield unique insight into the physical properties of these distant comets as well as probing the dynamical and collisional conditions over the history of the outer Solar System. The orbital, compositional and statistical properties of these binaries constrain the total mass and dynamical history of the various populations, with important implications for theories of Solar System formation. Here we propose an observational campaign to track and characterize the mutual orbits of all known wide-separation, equal-sized Kuiper Belt Binary systems that have poorly constrained orbits. Accurately measuring the orbits of binary systems with a series of high-SN optical (GMOS) observations allows determination of mass and system angular momentum, which provide constraints on formation mechanisms.

  4. Review on Modelling of the Radiation Belts

    NASA Astrophysics Data System (ADS)

    Heynderickx, D.

    2002-08-01

    The Earth's trapped radiation belts were discovered at the beginning of the space age and were immediately recognised as a considerable hazard to space missions. Consequently, considerable effort was invested in building models of the trapped proton and electron populations, culminating in the NASA AP-8 and AE-8 models which have been the de facto standards since the seventies. The CRRES mission has demonstrated that the trapped radiation environment is much more complex than the static environment described by the old models. Spatial and especially temporal variations were shown to be much more important than previously thought, and to require more complex models than those in use at that time. Such models are now becoming available, but they are limited in spatial or temporal coverage, and no global, dynamic, trapped radiation belt model is forthcoming. It is therefore vital to co-ordinate future modelling efforts in order to develop new standard models.

  5. Review on Modelling of the Radiation Belts

    NASA Astrophysics Data System (ADS)

    Heynderickx, D.

    The Earth's trapped radiation belts were discovered at the beginning of the space age and were immediately recognised as a considerable hazard to space missions. Consequently, considerable effort was invested in building models of the trapped proton and electron populatinos, culminating in the NASA AP-8 and AE-8 models which have been the de facto standards since the seventies. The CRRES mission has demonstrated that the trapped radiation environment is much more complex than the static environment described by the old models. Spatial and especially temporal variations were shown to be much more important that previously thought, and to require more complex models than those in use at that time. Such models are now becoming available, but they are limited in spatial or temporal coverage, and no global, dynamic, trapped radiation belt model is forthcoming. It is therefore vital to co-ordinate future modelling efforts in order to develop new standard models.

  6. A belted kingfisher flies above KSC

    NASA Technical Reports Server (NTRS)

    1999-01-01

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

  7. Ionic composition of the earth's radiation belts

    NASA Technical Reports Server (NTRS)

    Spjeldvik, W. N.

    1983-01-01

    Several different ion species have been positively identified in the earth's radiation belts. Besides protons, there are substantial fluxes of helium, carbon and oxygen ions, and there are measurable quantities of even heavier ions. European, American and Soviet space experimenters have reported ion composition measurements over wide ranges of energies: at tens of keV (ring-current energies) and below, and at hundreds of keV and above. There is still a gap in the energy coverage from several tens to several hundreds of keV where little observational data are available. In this review emphasis is placed on the radiation belt ionic structure above 100 keV. Both quiet time conditions and geomagnetic storm periods are considered, and comparison of the available space observations is made with theoretical analysis of geomagnetically trapped ion spatial, energy and charge state distributions.

  8. Alien Asteroid Belt Compared to our Own

    NASA Technical Reports Server (NTRS)

    2005-01-01

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

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

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

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

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

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

  9. EMIC Waves in the Radiation Belts

    NASA Astrophysics Data System (ADS)

    Usanova, M.; Mann, I. R.; Drozdov, A.; Orlova, K.; Shprits, Y.; Darrouzet, F.; Ergun, R.

    2014-12-01

    Electromagnetic ion cyclotron (EMIC) waves are believed to be important for influencing the dynamics of energetic particles in the inner magnetosphere - both ring current ions and radiation belt electrons - causing particle precipitation into the atmosphere. EMIC waves are generated from unstable ion distributions as a result of ion temperature anisotropy, with the ion dynamics being modified self-consistently by the growth of the EMIC instability. EMIC waves are also thought to influence higher energy electrons in the Van Allen belts through a Doppler shifted cyclotron resonance, including changes in electron pitch-angle distributions and electron scattering loss into the atmosphere. We will present some of the latest results addressing EMIC wave distribution, solar wind and magnetospheric conditions favorable for their generation and their role in energetic particle loss in the inner magnetosphere. We will focus on results from recent satellite missions including THEMIS and Cluster, as well as some of the latest results from the Van Allen Probes. We will also highlight the value of data from networks of modern ground-based magnetometers in providing continuous monitoring over global scales, especially in conjunction with in-situ measurements from satellites. Such coordinated ground-satellite conjunction studies represent a powerful tool for understanding the self-consistent and cross-energy coupling in the inner magnetosphere between ring current ions and radiation belt electrons via the intermediary of EMIC waves.

  10. A model for Jupiter's proton radiation belt

    NASA Technical Reports Server (NTRS)

    Warwick, J.

    1972-01-01

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

  11. Substyles of belting: phonatory and resonatory characteristics.

    PubMed

    Sundberg, Johan; Thalén, Margareta; Popeil, Lisa

    2012-01-01

    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

  12. Rapid Rebuilding of the Outer Radiation Belt

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  13. Rapid rebuilding of the outer radiation belt

    NASA Astrophysics Data System (ADS)

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

    2011-09-01

    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.

  14. CHAOTIC DIFFUSION OF RESONANT KUIPER BELT OBJECTS

    SciTech Connect

    Tiscareno, Matthew S.; Malhotra, Renu

    2009-09-15

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

  15. Recent estimates of safety belt use.

    PubMed

    Glassbrenner, Donna; Carra, Joseph S; Nichols, James

    2004-01-01

    The National Occupant Protection Use Survey (NOPUS) has shown that safety belt use in the United States has increased steadily over the past decade. Increases have been consistent since 2000, when the National Highway Traffic Safety Administration, in partnership with the Air Bag & Seat Belt Safety Campaign, increased its encouragement of states to implement highly visible enforcement programs. In 2003, significant increases were found in the South; in secondary law states; in all types of vehicles; during both weekdays and weekends; and during both rush-hours and non-rush-hours. In spite of these increases, use remains significantly lower in secondary law states; pickup trucks; the Northeast; and the Midwest. The differences between primary and secondary law states and between pickups and other passenger vehicles have been consistent from year to year. A controlled intersection study, which is part of the NOPUS, has shown that safety belt use has increased for both sexes, for nearly all age groups, and for all races for which data are available. Finally, the NOPUS suggests that children are 3-4 times as likely to be unrestrained when riding with an unbuckled driver as when driving with a buckled driver. PMID:15178244

  16. Binary Constraints on Kuiper Belt Collisions

    NASA Astrophysics Data System (ADS)

    Nesvorny, D.; Vokrouhlicky, D.; Bottke, W. F.; Noll, K.

    2011-10-01

    The size-frequency distribution (SFD) in the cold classical Kuiper belt (CKB) can be approximated by two idealized power laws: one with steep slope for radii R > R? and one with shallow slope for R < R?, where R? ˜ 25-50 km. Previous works suggested that the SFD roll-over at R? can be the result of extensive collisional grinding ([5]). Here we use a new code to test the effect of collisions in the Kuiper belt. We find that the observed roll-over could be explained by collisional grinding provided that the initial mass in large bodies was much larger than the one in the present Kuiper belt, and was dynamically depleted. In addition to the size distribution changes, our code also tracks the effects of collisions on binary systems. We find that the extensive collisional grinding required to produce the SFD roll-over at R? would imply a strong gradient of the binary fraction with R and separation, because it is generally easier to dissolve binaries with small components and/or those with wide orbits. The present observational data do not show such a gradient. This may indicate that the roll-over was not produced by disruptive collisions, but is instead a fossil remnant of the KBO formation process.

  17. Planet Imager Discovers Young Kuiper Belt

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-07-01

    A debris disk just discovered around a nearby star is the closest thing yet seen to a young version of the Kuiper belt. This disk could be a key to better understanding the interactions between debris disks and planets, as well as how our solar system evolved early on in its lifetime. Hunting for an analog The best way to understand how the Kuiper belt — home to Pluto and thousands of other remnants of early icy planet formation in our solar system — developed would be to witness a similar debris disk in an earlier stage of its life. But before now, none of the disks we've discovered have been similar to our own: the rings are typically too large, the central star too massive, or the stars exist in regions very unlike what we think our Sun's birthplace was like. A collaboration led by Thayne Currie (National Astronomical Observatory of Japan) has changed this using the Gemini Planet Imager (GPI), part of a new generation of extreme adaptive-optics systems. The team discovered a debris disk of roughly the same size as the Kuiper belt orbiting the star HD 115600, located in the nearest OB association. The star is only slightly more massive than our Sun, and it lives in a star-forming region similar to the early Sun's environment. HD 115600 is different in one key way, however: it is only 15 million years old. This means that observing it gives us the perfect opportunity to observe how our solar system might have behaved when it was much younger. A promising future GPI's spatially-resolved spectroscopy, combined with measurements of the reflectivity of the disk, have led the team to suspect that the disk might be composed partly of water ice, just as the Kuiper belt is. The disk also shows evidence of having been sculpted by the motions of giant planets orbiting the central star, in much the same way as the outer planets of our solar system may have shaped the Kuiper belt. The observations of HD 115600 are some of the very first to emerge from GPI and the new generation of planet-hunting instruments. The detection of this disk provides a promising outlook on what we can expect to discover in the future with these systems. Citation: Thayne Currie et al. 2015 ApJ 807 L7 doi:10.1088/2041-8205/807/1/L7

  18. Effects of a mandatory safety belt law on hospital admissions.

    PubMed

    Wagenaar, A C; Margolis, L H

    1990-06-01

    Although the effectiveness of automobile safety belts in reducing risk of serious injury in traffic crashes is well documented, safety belt use in many U.S. jurisdictions remains low. Michigan's mandatory safety belt law for front-seat occupants, implemented in July 1985, is one of 34 similar laws in the United States intended to increase belt use and reduce crash-related injuries. Using time-series intervention analyses of data from 14 hospitals throughout the state, we found a 19% reduction in the rate of admitted patients for all automobile occupant injuries and a 20% reduction in the rate of admitted patients with extremity injuries following implementation of the safety belt law. The utility of hospital data for the evaluation of interventions like the safety belt law reinforce the importance of consistently recording E-codes for all injury patients. PMID:2393473

  19. Radiation Belt Electron Acceleration and Role of Magnetotail

    NASA Astrophysics Data System (ADS)

    Reeves, Geoffrey D.

    2015-01-01

    This chapter considers the rapid evolution of radiation belt dynamics that has occurred over the past decade, a period that might be called "the radiation belt revolution," when new observations challenged long-held assumptions and new theoretical frameworks emerged. Studies of the radiation belts benefited from the growing network of satellites capable of measuring the belts. In the traditional radial diffusion model of radiation belt electron acceleration, the magnetotail provided a variable source of "seed" electrons that were further accelerated as they were transported inward to the heart of the radiation belts. Recent results from NASA's Van Allen Probes mission have shown that the growth of radial peaks in phase space density were fully consistent with local acceleration by wave-particle interactions and could not be explained by diffusive radial acceleration alone.

  20. Physiological effects of back belt wearing during asymmetric lifting.

    PubMed

    Bobick, T G; Belard, J L; Hsiao, H; Wassell, J T

    2001-12-01

    This study investigated the effect of wearing a back belt on subjects' heart rate, oxygen consumption, systolic and diastolic blood pressure, and respiratory frequency during asymmetric repetitive lifting. Thirty subjects with materials-handling experience utilized three different belts (ten subjects per belt). Subjects completed six 30-min lifting sessions--three while wearing a belt and three without. Data analyses were conducted on the second, third, and fourth lifting periods. A 9.4 kg box, without handles, was lifted 3 times/min, starting at 10 cm above the floor, ending at 79 cm, with a 60 degree twist to the right. Data analysis indicates that belt-wearing did not have a significant effect on the overall mean values for heart rate, systolic and diastolic blood pressure, and respiratory frequency. Belt-wearing had a significant effect on the overall mean oxygen consumption of the subjects. PMID:11703040

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

    NASA Astrophysics Data System (ADS)

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

    1989-04-01

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

  2. New compounds will help coal operators comply with BELT standards

    SciTech Connect

    2009-04-15

    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.

  3. Car safety belts: a study of two models adapted for people with arthritis.

    PubMed

    Arie, E

    1986-05-01

    People with arthritis find car seat belts difficult to use. Sixteen arthritic patients and 19 healthy volunteers completed a comparative study of one standard inertia-reel belt and two adapted inertia-reel belts with reduced retraction forces. Those with arthritis were strong enough to use the standard belt but both adapted belts had features making them easier to use. PMID:3708235

  4. Magnetic refrigeration apparatus with belt of ferro or paramagnetic material

    DOEpatents

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

    1986-04-03

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

  5. Magnetic refrigeration apparatus with belt of ferro or paramagnetic material

    DOEpatents

    Barclay, John A.; Stewart, Walter F.; Henke, Michael D.; Kalash, Kenneth E.

    1987-01-01

    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.

  6. Rogue Asteroids in the Inner Main Asteroid Belt

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

  7. State of the art in radiation belt research

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  8. Decomposition of noise sources of synchronous belt drives

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    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.

  9. COLORS OF INNER DISK CLASSICAL KUIPER BELT OBJECTS

    SciTech Connect

    Romanishin, W.; Tegler, S. C.; Consolmagno, G. J. E-mail: Stephen.Tegler@nau.ed

    2010-07-15

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

  10. Predicting Facies Patterns within Fluvial Channel Belts

    NASA Astrophysics Data System (ADS)

    Willis, B. J.; Sech, R.; Sun, T.; Pyrcz, M.

    2014-12-01

    Reservoirs (aquifers) in fluvial channel belt sandstones can have very different subsurface flow behavior depending on the degree and distribution of internal heterogeneities. Fluvial channel belts are composed of multiple "storeys" formed as individual channel segments increase in sinuosity and then are cut off and abandoned. Heterogeneities are defined by depositional variations across storeys and inter-story connectivity patterns along the channel belt. Although commonly inferred to reflect the formative river pattern (sinuosity & braiding), the spatial arrangement of facies depend most directly on the relative preservation of deposits formed within different areas of the migrating channels and the lateral stacking arrangement of storeys due to style of bend cutoff. Grains are poorly sorted across the inner bank along upstream parts of channel bends and become better sorted laterally in downstream areas adjacent to a deeper thalweg scour. If deposition occurs evenly along the entire inner bank (bar), this grain size pattern leads to an elliptical body in planview with weak vertical grain size trends upstream and more fining-upward trend downstream. As channel bend segments migrate to a greater extent downstream, preserved inner-bank-bar deposits are increasingly dominated by upward-fining deposits and more outer-bank-deposits are preserved ("concave bank" deposits). Although concave bank deposits have highly variable character in different systems, vertical-grainsize trends tend to be weaker in straighter systems dominated by downstream-accretion, and more strongly upward-fining in higher sinuosity systems where these deposits form by eddy accretion or low flow aggradation. River cutoffs of straighter channel segments abandon slowly, leading to more gradual vertical fining. Subsurface heterogeneity prediction requires documentation of shape and character of deposits preserved in different zones within the channel (upstream and downstream inner bank, concave bank, thalweg scour lags, and abandonment fill). Systems with similar paleochannel pattern can leave deposits with very different subsurface heterogeneity arrangement.

  11. The Origin of Jupiter's Outer Radiation Belt

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  12. The origin of Jupiter's outer radiation belt

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  13. The Overthrust Belt of Western North America

    SciTech Connect

    Verrall, P.

    1993-02-01

    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.

  14. LA-SF-ICP-MS zircon U-Pb geochronology of granitic rocks from the central Bundelkhand greenstone complex, Bundelkhand craton, India

    NASA Astrophysics Data System (ADS)

    Verma, Sanjeet K.; Verma, Surendra P.; Oliveira, Elson P.; Singh, Vinod K.; Moreno, Juan A.

    2016-03-01

    The central Bundelkhand greenstone complex in Bundelkhand craton, northern India is one of the well exposed Archaean supracrustal amphibolite, banded iron formation (BIF) and felsic volcanic rocks (FV) and associated with grey and pink porphyritic granite, tonalite-trondhjemite-granodiorite (TTG). Here we present high precision zircon U-Pb geochronological data for the pinkish porphyritic granites and TTG. The zircons from the grey-pinkish porphyritic granite show three different concordia ages of 2531 ± 21 Ma, 2516 ± 38 Ma, and 2514 ± 13 Ma, which are interpreted as the best estimate of the magmatic crystallization age for the studied granites. We also report the concordia age of 2669 ± 7.4 Ma for a trondhjemite gneiss sample, which is so far the youngest U-Pb geochronological data for a TTG rock suite in the Bundelkhand craton. This TTG formation at 2669 Ma is also more similar to Precambrian basement TTG gneisses of the Aravalli Craton of north western India and suggests that crust formation in the Bundelkhand Craton occurred in a similar time-frame to that recorded from the Aravalli craton of the North-western India.

  15. Validation of the Radiation Belt Environment Model

    NASA Astrophysics Data System (ADS)

    Perry, K. L.; Young, S. L.

    2011-12-01

    Extended periods of relativistic electron intensity at geosynchronous orbit (GEO) can create severe deep-charging hazards for satellites. Several empirical models have been developed over the last fifteen years to predict electron flux levels. In more recent years, physics-based models have been developed to not only calculate fluxes at GEO but everywhere inside the magnetosphere. We validate one of these models, the Radiation Belt Environment (RBE) model (Fok et al., 2005, Fok et al., 2008, Fok et al., 2010). Multiple versions are analyzed and compared to investigate the improvements made to the model and how well they compared to measured data.

  16. Kinematical structure of the asteroid belt

    NASA Astrophysics Data System (ADS)

    Mikami, Takao; Ishida, Keiichi

    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.

  17. Period Determination of Six Main Belt Asteroids

    NASA Astrophysics Data System (ADS)

    Ferrero, Andrea

    2014-07-01

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

  18. Euclid Asteroseismology and Kuiper Belt Objects

    NASA Astrophysics Data System (ADS)

    Gould, Andrew; Huber, Daniel; Stello, Dennis

    2016-02-01

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

  19. Water activities in the Kerala Khondalite Belt

    NASA Astrophysics Data System (ADS)

    Chacko, Thomas; Kumar, G. R. Ravindra; Peterson, J. W.

    The author and colleagues presented their determinations of water activities in various granulite-facies rocks of the Kerala Khondalite Belt. Using mineral equilibria, thermodynamic data, and assumed geopressure-geotemperature conditions of 5.5 kbar and 750 C, they calculated uniformly low a(H2O) values of about 0.27 over a large geographic region. They suggested that these conditions were produced by the presence of abundant CO2-rich fluids, derived either from deeper levels or from metamorphic reactions involving graphite.

  20. Water activities in the Kerala Khondalite Belt

    NASA Technical Reports Server (NTRS)

    Chacko, Thomas; Kumar, G. R. Ravindra; Peterson, J. W.

    1988-01-01

    The author and colleagues presented their determinations of water activities in various granulite-facies rocks of the Kerala Khondalite Belt. Using mineral equilibria, thermodynamic data, and assumed geopressure-geotemperature conditions of 5.5 kbar and 750 C, they calculated uniformly low a(H2O) values of about 0.27 over a large geographic region. They suggested that these conditions were produced by the presence of abundant CO2-rich fluids, derived either from deeper levels or from metamorphic reactions involving graphite.

  1. Aircraft radial-belted tire evaluation

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

  2. Stratospheric Polar Freezing Belt Causes Denitrification

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

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

    ERIC Educational Resources Information Center

    Genc, Humeyra

    2012-01-01

    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…

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

    SciTech Connect

    Chaimov, T.A.; Barazangi, M.; Best, J.A. ); Al-Saad, D.; Sawaf, T.; Gebran, A. )

    1991-03-01

    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.

  5. CO depletion in the Gould Belt clouds

    NASA Astrophysics Data System (ADS)

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

    2012-05-01

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

  6. Fading of Jupiter's South Equatorial Belt

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  7. The origin of Jupiter's outer radiation belt

    NASA Astrophysics Data System (ADS)

    Woodfield, Emma; Horne, Richard; Glauert, Sarah; Menietti, John; Shprits, Yuri

    2014-05-01

    The intense inner radiation belt at Jupiter (>50 MeV at 1.5 RJ) is the result of adiabatic transport of electrons from further away from the planet; however, a seed population of high energy electrons is still required at between 6 and 10 RJ with energies that exceed 1 MeV. Here we test the hypothesis that the seed population outside the orbit of the moon Io could be formed from a very soft energy spectrum due to particle injection processes, and acceleration via whistler mode chorus waves. Using particle data as an initial condition at an energy of 20 keV, we use the BAS radiation belt model to calculate the change in the electron energy spectrum between 6.5 and 15 RJ due to whistler mode chorus waves. Simulations show that the resulting energy spectrum lies very close to the empirical Galileo Interim Radiation Electron model (GIRE) spectrum at Jupiter after less than one day at 100 keV and less than 10 days at 1 MeV, suggesting that the seed population could indeed be formed by wave-particle interactions. The results are insensitive to the softness of the initial energy spectrum but do critically depend on the value of the flux at the minimum energy boundary. Simulations for wave acceleration and radial diffusion together show that the resulting spectrum remains close to the GIRE spectrum but the radial profile of phase space density is smoothed.

  8. Benefits of Seat Belt Reminder Systems

    PubMed Central

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

    2003-01-01

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

  9. Appropriate frontal barrier tests for belted occupants.

    PubMed

    Hill, J R; Frampton, R J; Mackay, M

    1995-12-01

    Vehicle damage from frontal impacts was classified and investigated together with injuries sustained by belted front seat occupants. The sample consisted of 1872 frontal crashes from the Midlands of England. Analysis focused on impacts with broad objects that might conceivably be simulated by a barrier test. Two asymmetrical front-end damage patterns were commonly identified, and these gave the greatest rates of non-minor (Abbreviated Injury Scale (AIS) > or = 2) injuries in a range of Estimated Test Speeds from 35 to 52km/h which is the regime of current legislative crash tests. The most injurious type involved oblique damage caused by a substantial overlap of the struck object. The other type was from a small overlap. Objects struck and passenger compartment intrusions were compared. Appropriate asymmetrical and deformable barrier concepts were discussed. Other findings were connected with the future role of full face barriers as used in current tests such as Federal Motor Vehicle Safety Standard 208. Fuller overlaps (> 50%) tended to give more torso injuries rated > or = AIS 2 caused by seat belt loads and, at high speeds (53-79km/h), caused the most fatalities. Full overlaps (100%) rarely resulted in symmetrical intrusion into the passenger compartment. PMID:8749284

  10. WATER ICE IN THE KUIPER BELT

    SciTech Connect

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

    2012-06-15

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

  11. 23 CFR Appendix D to Part 1240 - Determination of National Average Seat Belt Use Rate

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... of Seat Belt Use, 23 CFR Part 1340), NHTSA will calculate a State seat belt use rate, using the last..., along with information on seat belt use rates from the FARS, and an algorithm relating FARS seat...

  12. 23 CFR Appendix D to Part 1240 - Determination of National Average Seat Belt Use Rate

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... of Seat Belt Use, 23 CFR Part 1340), NHTSA will calculate a State seat belt use rate, using the last..., along with information on seat belt use rates from the FARS, and an algorithm relating FARS seat...

  13. 23 CFR Appendix D to Part 1240 - Determination of National Average Seat Belt Use Rate

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... of Seat Belt Use, 23 CFR Part 1340), NHTSA will calculate a State seat belt use rate, using the last..., along with information on seat belt use rates from the FARS, and an algorithm relating FARS seat...

  14. 23 CFR Appendix D to Part 1240 - Determination of National Average Seat Belt Use Rate

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... of Seat Belt Use, 23 CFR Part 1340), NHTSA will calculate a State seat belt use rate, using the last..., along with information on seat belt use rates from the FARS, and an algorithm relating FARS seat...

  15. 23 CFR Appendix D to Part 1240 - Determination of National Average Seat Belt Use Rate

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... of Seat Belt Use, 23 CFR Part 1340), NHTSA will calculate a State seat belt use rate, using the last..., along with information on seat belt use rates from the FARS, and an algorithm relating FARS seat...

  16. Anorthosite belts, continental drift, and the anorthosite event.

    PubMed

    Herz, N

    1969-05-23

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

  17. 30 CFR 56.15005 - Safety belts and lines.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ....15005 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-SURFACE METAL AND NONMETAL MINES Personal Protection § 56.15005 Safety belts and lines. Safety belts and lines shall be worn when persons work where...

  18. 30 CFR 56.15005 - Safety belts and lines.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ....15005 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-SURFACE METAL AND NONMETAL MINES Personal Protection § 56.15005 Safety belts and lines. Safety belts and lines shall be worn when persons work where...

  19. Promoting Automobile Safety Belt Use by Young Children.

    ERIC Educational Resources Information Center

    Sowers-Hoag, Karen M.; And Others

    1987-01-01

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

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

    ERIC Educational Resources Information Center

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

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

  1. Respiratory Belt Transducer Constructed Using a Singing Greeting Card Beeper

    ERIC Educational Resources Information Center

    Bhaskar, Anand; Subramani, Selvam; Ojha, Rajdeep

    2013-01-01

    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,…

  2. Return of the Sacred Wampum Belts of the Iroquois.

    ERIC Educational Resources Information Center

    Sullivan, Martin

    1992-01-01

    Relates history and process by which 12 historic wampum belts were turned over to representatives of Onondaga Nation (New York), one of six Indian tribal communities of Iroquois Confederacy. Describes history of belts from pre-Columbian times to modern times. Compliments both the New York State Board of Regent and leaders of the Onondaga Nation…

  3. 30 CFR 57.4503 - Conveyor belt slippage.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... within confined areas where evacuation would be restricted in the event of a fire resulting from belt-slippage shall be equipped with a detection system capable of automatically stopping the drive pulley. (b) Underground belt conveyors shall be equipped with a detection system capable of automatically stopping...

  4. 30 CFR 57.4503 - Conveyor belt slippage.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... within confined areas where evacuation would be restricted in the event of a fire resulting from belt-slippage shall be equipped with a detection system capable of automatically stopping the drive pulley. (b) Underground belt conveyors shall be equipped with a detection system capable of automatically stopping...

  5. 30 CFR 57.4503 - Conveyor belt slippage.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... within confined areas where evacuation would be restricted in the event of a fire resulting from belt-slippage shall be equipped with a detection system capable of automatically stopping the drive pulley. (b) Underground belt conveyors shall be equipped with a detection system capable of automatically stopping...

  6. 46 CFR 169.825 - Wearing of safety belts.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 7 2013-10-01 2013-10-01 false Wearing of 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 vessel shall ensure that each person...

  7. 46 CFR 169.825 - Wearing of safety belts.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 7 2014-10-01 2014-10-01 false Wearing of 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 vessel shall ensure that each person...

  8. 46 CFR 169.825 - Wearing of safety belts.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 7 2011-10-01 2011-10-01 false Wearing of 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 vessel shall ensure that each person...

  9. 46 CFR 169.825 - Wearing of safety belts.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 7 2010-10-01 2010-10-01 false Wearing of 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 vessel shall ensure that each person...

  10. Prioritizing Safety with Seat Belts: The Unanswered Question.

    ERIC Educational Resources Information Center

    Farrell, Elaine

    1987-01-01

    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…

  11. 30 CFR 56.14131 - Seat belts for haulage trucks.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... publications is approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Seat belts for haulage trucks. 56.14131 Section... Equipment Safety Devices and Maintenance Requirements § 56.14131 Seat belts for haulage trucks. (a)...

  12. Policy Implications from an Evaluation of Seat Belt Use Regulation.

    ERIC Educational Resources Information Center

    Desai, Anand; You, Min-Bong

    1992-01-01

    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)

  13. 14 CFR 29.1413 - Safety belts: passenger warning device.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Safety belts: passenger warning device. 29.1413 Section 29.1413 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Equipment Safety Equipment § 29.1413 Safety belts: passenger warning device....

  14. Research Says "No" to School Bus Seat Belts.

    ERIC Educational Resources Information Center

    Wineland, Charles L.

    1986-01-01

    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)

  15. 30 CFR 56.14131 - Seat belts for haulage trucks.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... publications is approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Seat belts for haulage trucks. 56.14131 Section... Equipment Safety Devices and Maintenance Requirements § 56.14131 Seat belts for haulage trucks. (a)...

  16. 14 CFR 125.211 - Seat and safety belts.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... share one approved safety belt and two persons occupying a multiple lounge or divan seat may share one..., takeoff, and landing. A safety belt provided for the occupant of a seat may not be used for more than one... Standard No. 213 (49 CFR 571.213)), vest- and harness-type child restraint systems, and lap held...

  17. An Evaluation of the Seat Belt Education Campaign.

    ERIC Educational Resources Information Center

    Rochon, James

    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…

  18. 30 CFR 56.14131 - Seat belts for haulage trucks.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... publications is approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Seat belts for haulage trucks. 56.14131 Section... Equipment Safety Devices and Maintenance Requirements § 56.14131 Seat belts for haulage trucks. (a)...

  19. 14 CFR 125.211 - Seat and safety belts.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... share one approved safety belt and two persons occupying a multiple lounge or divan seat may share one..., takeoff, and landing. A safety belt provided for the occupant of a seat may not be used for more than one... Standard No. 213 (49 CFR 571.213)), vest- and harness-type child restraint systems, and lap held...

  20. 14 CFR 125.211 - Seat and safety belts.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... share one approved safety belt and two persons occupying a multiple lounge or divan seat may share one..., takeoff, and landing. A safety belt provided for the occupant of a seat may not be used for more than one... Standard No. 213 (49 CFR 571.213)), vest- and harness-type child restraint systems, and lap held...

  1. 14 CFR 125.211 - Seat and safety belts.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... share one approved safety belt and two persons occupying a multiple lounge or divan seat may share one..., takeoff, and landing. A safety belt provided for the occupant of a seat may not be used for more than one... Standard No. 213 (49 CFR 571.213)), vest- and harness-type child restraint systems, and lap held...

  2. 30 CFR 56.14131 - Seat belts for haulage trucks.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... publications is approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Seat belts for haulage trucks. 56.14131 Section... Equipment Safety Devices and Maintenance Requirements § 56.14131 Seat belts for haulage trucks. (a)...

  3. 30 CFR 56.14108 - Overhead drive belts.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-SURFACE METAL AND NONMETAL MINES Machinery and Equipment Safety Devices and Maintenance Requirements 56.14108 Overhead drive belts. Overhead drive belts...

  4. Anorthosite belts, continental drift, and the anorthosite event

    USGS Publications Warehouse

    Herz, N.

    1969-01-01

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

  5. 33 CFR 142.42 - Safety belts and lifelines.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 33 Navigation and Navigable Waters 2 2011-07-01 2011-07-01 false Safety belts and lifelines. 142... (CONTINUED) OUTER CONTINENTAL SHELF ACTIVITIES WORKPLACE SAFETY AND HEALTH Personal Protective Equipment § 142.42 Safety belts and lifelines. (a) Except when moving from one location to another,...

  6. Crustal Deformation around Zhangjiakou-Bohai Seismically Active Belt

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  7. 14 CFR 125.211 - Seat and safety belts.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... Standard No. 213 (49 CFR 571.213)), vest- and harness-type child restraint systems, and lap held child... 14 Aeronautics and Space 3 2010-01-01 2010-01-01 false Seat and safety belts. 125.211 Section 125... Requirements § 125.211 Seat and safety belts. (a) No person may operate an airplane unless there are...

  8. 46 CFR 169.825 - Wearing of safety belts.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 7 2012-10-01 2012-10-01 false Wearing of safety belts. 169.825 Section 169.825... Operations § 169.825 Wearing of safety belts. The master of each vessel shall ensure that each person wears an approved safety harness when aloft or working topside in heavy weather. Tests, Drills,...

  9. Respiratory Belt Transducer Constructed Using a Singing Greeting Card Beeper

    ERIC Educational Resources Information Center

    Bhaskar, Anand; Subramani, Selvam; Ojha, Rajdeep

    2013-01-01

    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,

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

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

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

  11. Office education by pediatricians to increase seat belt use.

    PubMed

    Macknin, M L; Gustafson, C; Gassman, J; Barich, D

    1987-12-01

    We studied promoting seat belt use by school-aged children through discussions with their pediatricians. The study population consisted of 242 well children observed coming to and leaving from a private pediatric practice. Only four (5%) of 73 control patients who did not wear their seat belts coming in wore them going out. For intervention patients, this figure was 29 (38%) of 77. At one-year follow-up by questionnaire, there were no statistical differences between the percentage of seat belt use in control (67%) vs intervention (62%) patients. However, pediatricians' reported percentage of patients routinely counseled about seat belt use prior to the start of the study was highly correlated with patients' observed prestudy seat belt use. Pediatricians should include education about automobile safety as a part of all well-child visits. PMID:3687873

  12. Survey of current situation in radiation belt modeling.

    PubMed

    Fung, Shing F

    2004-01-01

    The study of Earth's radiation belts is one of the oldest subjects in space physics. Despite the tremendous progress made in the last four decades, we still lack a complete understanding of the radiation belts in terms of their configurations, dynamics, and detailed physical accounts of their sources and sinks. The static nature of early empirical trapped radiation models, for examples, the NASA AP-8 and AE-8 models, renders those models inappropriate for predicting short-term radiation belt behaviors associated with geomagnetic storms and substorms. Due to incomplete data coverage, these models are also inaccurate at low altitudes (e.g., <1000 km) where many robotic and human space flights occur. The availability of radiation data from modern space missions and advancement in physical modeling and data management techniques have now allowed the development of new empirical and physical radiation belt models. In this paper, we will review the status of modern radiation belt modeling. PMID:15881789

  13. Two-load weighed material testing of belt scales

    SciTech Connect

    Rosenberg, N.I.

    1993-12-31

    Because coal flow on conveyor belts is typically variable rather than constant, knowing the accuracy of belt scales over a broad range of flow rates is commercially important. But their present accuracy measurement technique is inadequate for judging a scale`s total performance. The method, which is to perform a weighed material test as described in National Institute of Science and Technology`s Handbook 44, yields data only at one load point rather than over the wide range of loads that they need. To determine the actual accuracy of installed belt scales, two-load weighed material testing should be performed. This paper is about belt scale tests, but will begin with some thoughts about static platform scales because understanding the testing of these scales lays the groundwork for understanding the testing of belt scales.

  14. Nonoperative management of pediatric aortic injury with seat belt syndrome.

    PubMed

    Parrish, Dan W; Barnhorst, Amanda; Trebska-McGowan, Katarzyna; Amendola, Michael; Haynes, Jeffrey H

    2015-08-01

    "Seat belt syndrome" was first described by Garret and Braunstein in 1962. The syndrome involves skin and abdominal wall ecchymosis (seat belt sign) intra-abdominal solid organ and visceral injuries, as well as Chance fractures (compression and/or wedging deformity of the anterior portion of the vertebral body with disruption or fracture of the posterior elements, generally at L1-L3). We present a case of a 12-year-old male involved in a high-speed motor vehicle collision wearing only a lap belt resulting in seat belt syndrome, with disruption of the abdominal wall, mesenteric avulsion with multiple intestinal perforations, abdominal aortic dissection, and an L2 Chance fracture with cord transection. Intraoperative decision making is outlined with this scenario of complex injuries, and the literature of seat belt syndrome associated with blunt aortic injuries and its management is reviewed. PMID:26028461

  15. Neptune's Eccentricity and the Nature of the Kuiper Belt

    NASA Technical Reports Server (NTRS)

    Ward, William R.; Hahn, Joseph M.

    1998-01-01

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

  16. Body mass as a determinant of seat belt use.

    PubMed

    Lichtenstein, M J; Bolton, A; Wade, G

    1989-04-01

    Prevention of death and injury from motor vehicle accidents depends in part on seat belt use. Understanding the determinants of seat belt use is important for developing strategies to increase seat belt use. The cross-sectional association between body mass index (BMI) and self-reported seat belt use was analyzed using data from 3,140 Health Risk Appraisals completed by Tennessee residents during 1986. Persons in the lowest quintile BMI (less than or equal to 21.8 kg/m2) stated they use seat belts 63% (SD = 38%) of the time compared to persons in the highest BMI quintile (greater than or equal to 29.0 kg/m2) who reported using seat belts 50% (SD = 38%) of the time. BMI remained associated with seat belt use after adjustment for age, sex, race, education, cigarette use, alcohol use, drug use, urban/rural residence, state area of residence, miles driven per year, self-reported physical activity, and satisfaction with life. For a 1 kg/m2 increase in BMI, seat belt use declined -0.73% (95% CI = -1.01, -0.46), and the relative odds of not being a frequent seat belt user increased 3% (odds ratio 1.03, 95% CI = 1.01, 1.05). BMI was the third variable selected in a step-wise multiple linear regression after education and race. The BMI/seat belt association, if causal, has implications for (1) targeting of education programs to likely nonusers by traffic safety agencies; (2) targeting health promotion messages to likely nonusers by primary care providers; and (3) design of automobile seats and restraint devices. PMID:2705462

  17. Unexpected D-type interlopers in the inner main belt

    NASA Astrophysics Data System (ADS)

    DeMeo, Francesca E.; Binzel, Richard P.; Carry, Benoît; Polishook, David; Moskovitz, Nicholas A.

    2014-02-01

    Very red featureless asteroids (spectroscopic D-types) are expected to have formed in the outer Solar System far from the Sun. They comprise the majority of asteroids in the Jupiter Trojan population, and are also commonly found in the outer main belt and among Hildas. The first evidence for D-types in the inner and middle parts of the main belt was seen in the Sloan Digital Sky Survey (SDSS). Here we report follow-up observations of SDSS D-type candidates in the near-infrared. Based on follow up observations of 13 SDSS D-type candidates, we find a ∼20% positive confirmation rate. Known inner belt D-types range in diameter from roughly 7 to 30 km. Based on these detections we estimate there are ∼100 inner belt D-types with diameters between 2.5 and 20 km. The lower and upper limits for total mass of inner belt D-types is 2 × 1016 kg to 2 × 1017 kg which represents 0.01-0.1% of the mass of the inner belt. The inner belt D-types have albedos at or above the upper end typical for D-types which raises the question as to whether these inner belt bodies represent only a subset of D-types, they have been altered by external factors such as weathering processes, or if they are compositionally distinct from other D-types. All D-types and candidates have diameters less than 30 km, yet there is no obvious parent body in the inner belt. Dynamical models have yet to show how D-types originating from the outer Solar System could penetrate into the inner reaches of the main belt under current scenarios of planet formation and subsequent Yarkovsky drift.

  18. Unexpected D-type interlopers in the inner main belt

    NASA Astrophysics Data System (ADS)

    DeMeo, F.; Binzel, R.; Carry, B.; Polishook, D.; Moskovitz, N.

    2014-07-01

    Very red featureless asteroids (spectroscopic D-types) are expected to have formed in the outer Solar System far from the Sun [1,2]. They comprise the majority of asteroids in the Jupiter Trojan population, and are also commonly found in the outer main belt and among Hildas. The first evidence for D-types in the inner and middle parts of the main belt was seen in the Sloan Digital Sky Survey (SDSS) [3]. Here we report follow-up observations of SDSS D-type candidates in the near-infrared. Based on follow up observations of 13 SDSS D-type candidates [4], we find a ˜20 % positive confirmation rate. Known inner belt D-types range in diameter from roughly 7 to 30 km. Based on these detections we estimate there are ˜ 100 inner belt D-types with diameters between 2.5 and 20 km. The lower and upper limits for total mass of inner belt D-types is 2×10^{16} kg to 2×10^{17} kg which represents 0.01-0.1 % of the mass of the inner belt [5]. The inner belt D-types have albedos at or above the upper end typical for D-types [6] which raises the question as to whether these inner belt bodies represent only a subset of D-types, they have been altered by external factors such as weathering processes, or if they are compositionally distinct from other D-types. All D-types and candidates have diameters less than 30 km, yet there is no obvious parent body in the inner belt. Dynamical models (e.g., [7]) have yet to show how D-types originating from the outer Solar System could arrive at the inner reaches of the main belt under current scenarios of planet formation and subsequent Yarkovsky drift.

  19. The Ocean-Atmosphere Hydrothermohaline Conveyor Belt

    NASA Astrophysics Data System (ADS)

    Döös, Kristofer; Kjellsson, Joakim; Zika, Jan; Laliberté, Frédéric; Brodeau, Laurent

    2015-04-01

    The ocean thermohaline circulation is linked to the hydrothermal circulation of the atmosphere. The ocean thermohaline circulation is expressed in potential temperature-salinity space and comprises a tropical upper-ocean circulation, a global conveyor belt cell and an Antarctic Bottom Water cell. The atmospheric hydrothermal circulation in a potential temperature-specific humidity space unifies the tropical Hadley and Walker cells as well as the midlatitude eddies into a single, global circulation. Superimposed, these thermohaline and hydrothermal stream functions reveal the possibility of a close connection between some parts of the water and air mass conversions. The exchange of heat and fresh water through the sea surface (precipiation-evaporation) and incoming solar radiation act to make near-surface air warm and moist while making surface water warmer and saltier as both air and water travel towards the Equator. In the tropics, air masses can undergo moist convection releasing latent heat by forming precipitation, thus acting to make warm surface water fresher. We propose that the Clausius-Clapeyron relationship for moist near-surface air acts like a lower bound for the atmospheric hydrothermal cell and an upper bound for the ocean thermohaline Conveyor-Belt cell. The analysis is made by combining and merging the overturning circulation of the ocean and atmosphere by relating the salinity of the ocean to the humidity of the atmosphere, where we set the heat and freshwater transports equal in the two stream functions By using simulations integrated with our Climate-Earth system model EC-Earth, we intend to produce the "hydrothermohaline" stream function of the coupled ocean-atmosphere overturning circulation in one single picture. We explore how the oceanic thermohaline Conveyor Belt can be linked to the global atmospheric hydrothermal circulation and if the water and air mass conversions in humidity-temperature-salinity space can be related and linked to each other along a "line" corresponding to the Clausius-Clapeyron relationship. A geographical description of how and where this occurs together with this new hydrothermohaline stream function will be searched for. The net heat and freshwater transport of the ocean and atmosphere can aslo be calculated from the thermohaline and hydrothermal stream functions. The heat transport across isohumes in the atmosphere and isohalines in the ocean as well as the freshwater transport across isotherms in both the atmosphere and ocean are computed. The maximum heat transport is about 16 PW in the atmosphere, while that of the ocean is just about 1 PW. The freshwater transport across isotherms in the atmosphere and ocean are shown to be tightly connected with a net maximum freshwater transport of 4 SV in the atmosphere and 2 Sv in the ocean.

  20. A study of binary Kuiper belt objects

    NASA Astrophysics Data System (ADS)

    Kern, Susan Diane

    2006-06-01

    About 10 5 bodies larger than 100km in diameter (Jewitt 1998) reside in the Kuiper Belt, beyond the orbit of Neptune. Since 1992 observational surveys have discovered over one thousand of these objects, believed to be fossil remnants of events that occurred nearly 4.5 billion years ago. Sixteen of these objects are currently known to be binaries, and many more are expected to be discovered. As part of the Deep Ecliptic Survey (DES) I have helped catalog nearly one third of the known Kuiper Belt object (KBO) population, and used that database for further physical studies. Recovery observations for dynamical studies of newly discovered objects with the Magellan telescopes and a high resolution imager, MagIC, revealed three binaries, 88611 (2001QT297), 2003QY90, and 2005EO304. One binary was found in the discovery observations, 2003UN284. Lightcurve measurements of these, and other non-binary KBOs, were obtained to look for unique rotational characteristics. Eleven of thirty-three objects, excluding the binaries, were found to have measurable variability. One of these objects, 2002GW32 has a particularly large amplitude (> 1 magnitude) of variability, and 2002GP32 has a relatively short (~3.3 hours, single-peaked) lightcurve. Among the binary population all the observed objects showed some level of variation. The secondary of 88611 was fit with a single-peaked period of 5.5±0.02 hours while the primary component appears to be non-variable above the measurement errors (0.05 magnitudes). Neither component appears to be color variable. The components of 2003QY90 are both highly variable yielding single- peaked rotation periods of 3.5±1.1 and 7.2±2.9 hours with amplitudes of 0.34±0.06 and 0.90±0.18 magnitudes, respectively. The rotation periods are comparable to those of other non-binary KBOs although distinct from that of an identified contact binary. Orbits and partial orbits for Kuiper belt binaries (KBBs) show a wide range of eccentricities, and an increasing number of binaries with decreasing binary semi-major axis. These characteristics exclude the formation models proposed by Funato et al. (2003) and Weidenschilling (2002), respectively. Conversely, the formation models of Astakhov et al. (2005) and Goldreich et al. (2002) appear to describe the observations, at least in part. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)

  1. Wampum Belts with Initials and/or Dates as Design Elements: A Preliminary Review of One Subcategory of Political Belts

    ERIC Educational Resources Information Center

    Becker, Marshall Joseph; Lainey, Jonathan

    2004-01-01

    Data on seventeen relatively well-documented examples as a preliminary review to an ongoing study of all that is known about belts that are a subcategory of the secular-political category is discussed. Evidence indicates that Wampum belts with initials and/or dates as design elements can clearly be demonstrated as but one subcategory of…

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

    ERIC Educational Resources Information Center

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

    1988-01-01

    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)

  3. Main-belt comets: sublimation-driven activity in the asteroid belt

    NASA Astrophysics Data System (ADS)

    Hsieh, Henry H.

    2016-01-01

    Our knowledge of main-belt comets (MBCs), which exhibit comet-like activity likely due to the sublimation of volatile ices, yet orbit in the main asteroid belt, has increased greatly since the discovery of the first known MBC, 133P/Elst-Pizarro, in 1996, and their recognition as a new class of solar system objects after the discovery of two more MBCs in 2005. I review work that has been done over the last 10 years to improve our understanding of these enigmatic objects, including the development of systematic discovery methods and diagnostics for distinguishing MBCs from disrupted asteroids (which exhibit comet-like activity due to physical disruptions such as impacts or rotational destabilization). I also discuss efforts to understand the dynamical and thermal properties of these objects.

  4. The JCMT Gould Belt Survey: Understanding the influence of outflows on Gould Belt clouds

    NASA Astrophysics Data System (ADS)

    Drabek-Maunder, E.; Hatchell, J.; Buckle, J. V.; Di Francesco, J.; Richer, J.

    2016-03-01

    Using James Clerk Maxwell Telescope (JCMT) Gould Belt Survey data from CO J = 3 → 2 isotopologues, we present a meta-analysis of the outflows and energetics of star-forming regions in several Gould Belt clouds. The majority of the regions are strongly gravitationally bound. There is evidence that molecular outflows transport large quantities of momentum and energy. Outflow energies are at least 20 per cent of the total turbulent kinetic energies in all of the regions studied and greater than the turbulent energy in half of the regions. However, we find no evidence that outflows increase levels of turbulence, and there is no correlation between the outflow and turbulent energies. Even though outflows in some regions contribute significantly to maintaining turbulence levels against dissipation, this relies on outflows efficiently coupling to bulk motions. Other mechanisms (e.g. supernovae) must be the main drivers of turbulence in most if not all of these regions.

  5. Ambient tremors in a collisional orogenic belt

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  6. Artificial perturbations of the radiation belts

    NASA Technical Reports Server (NTRS)

    Cladis, J. B.

    1972-01-01

    A review is given of the properties of the radiation belts which have been produced by high-altitude nuclear detonations. The low-yield, Argus devices, 1, 2, and 3, and the Soviet test of 1 November 1962 injected intense electron fluxes in narrow L-shell intervals, with peaks at L = 1.72, 2.11, 2.17, and 1.77, respectively. The energy spectra of the electrons were indistinguishable from the equilibrium fission beta spectrum, and the fluxes initially decayed at rates approximately proportional to (time) sup -1.1. The high-yield devices, Starfish and the Soviet tests of 22 October and 28 October 1962, injected electrons over wide ranges. At L values near the lower boundary, the electron spectra appeared to be softer at the higher L values.

  7. Testing Collisional Grinding in the Kuiper Belt

    NASA Astrophysics Data System (ADS)

    Grundy, William

    2012-10-01

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

  8. Herschel-Resolved Outer Belts of Two-Belt Debris Disks--Evidence of Icy Grains

    NASA Astrophysics Data System (ADS)

    Morales, Farisa Y.; Bryden, Geoffrey; Werner, Michael W.; Stapelfeldt, Karl

    2015-12-01

    We present dual-band Herschel/PACS imaging for 57 main sequence stars (42 A-type and 15 solar-type) with previously known warm dust (Twarm ~200K) detected and characterized by Spitzer. About half of the star-disk systems in our sample have spectral energy distributions (SEDs) that suggest two-ring disk architectures that mirror that of the asteroid-Kuiper belt geometry of our own solar system. The Herschel observations at 70 and/or 100 micron spatially resolve the cold/outer dust component for 18 two-belt debris systems (15 for the first time; 10 are also resolved at 160 micron), finding evidence of planetesimals at >100 AU, i.e. larger size than assumed from a simple blackbody fit to the SED. By breaking the degeneracy between the grain properties and the dust's radial location, the resolved images help constrain the grain size distribution and hint at the dust's composition for each system. Based on the combined Spitzer/IRS+MIPS (5 to 70 micron), the Herschel/PACS (70 and/or 100 and 160 micron) dataset, and under the assumption of idealized spherical grains, we find that the majority of resolved cold/outer belts of star+disk systems are well fit with a mixed ice/rock composition, rather than pure rocky grains. In the absence of spectral features for ice, we find that the behavior of the continuum can help constrain the composition of the grains well (of icy nature and not pure rocky material) given the Herschel-resolved locations of the cold/outer dust belts. We have also begin to identify the presence of candidate companions via Keck direct imaging, which may be interacting with the observed dust.

  9. INCLINATION MIXING IN THE CLASSICAL KUIPER BELT

    SciTech Connect

    Volk, Kathryn; Malhotra, Renu

    2011-07-20

    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.

  10. The Relative Sizes of Kuiper Belt Binaries

    NASA Astrophysics Data System (ADS)

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

    2006-09-01

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

  11. Plains tectonism on Venus: The deformation belts of Lavinia Planitia

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

  12. Plains tectonism on Venus: The deformation belts of Lavinia Planitia

    NASA Astrophysics Data System (ADS)

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

    1993-03-01

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

  13. The Use of Orbital Tethers to Remediate Geomagnetic Radiation Belts

    NASA Astrophysics Data System (ADS)

    Hudoba de Badyn, Mathias; Marchand, Richard; Sydora, Richard

    2014-10-01

    The Van Allen radiation belts pose a hazard to spacecraft and astronauts, and similar radiation belts around other planets pose a hazard to interplanetary probes. We discuss a method of remediating these radiation belts proposed by Hoyt, Minor and Cash where a long, charged tether is placed in orbit inside a radiation belt. The electric field of the tether adiabatically scatters the belt particles into a pitch angle loss cone due to absorption of the particles in the atmosphere. We present a test particle calculation which computes the scattered pitch angle of belt particles as a function of initial pitch angle and gyrophase for different particle energies. We then use the moments of the resulting histogram of scattered angle versus initial pitch angle to compute the number density of the belt as a function of time using a Fokker-Planck diffusion model. Finally, we use the characteristic timescales of scattering for particles of different energies to discuss the feasibility of using such a system of tethers as a long and short-term remediation solution.

  14. Using orbital tethers to remediate geomagnetic radiation belts

    NASA Astrophysics Data System (ADS)

    Hudoba de Badyn, Mathias; Marchand, Richard; Sydora, Richard D.

    2016-02-01

    The Van Allen radiation belts pose a hazard to spacecraft and astronauts, and similar radiation belts around other planets pose a hazard to interplanetary probes. We discuss a method of remediating these radiation belts first proposed by Danilov and Vasilyev, and recently improved by Hoyt, Minor, and Cash, where a long, charged tether is placed in orbit inside a radiation belt. In this approach, an electric field of the tether scatters the belt particles into a pitch angle loss cone leading to absorption of the particles in the atmosphere. A test particle calculation is presented which computes the scattered pitch angle of belt particles as a function of initial pitch angle and gyrophase for different particle energies. The moments of the resulting distribution of scattered angle versus initial pitch angle are used to compute the number density of the belt as a function of time using a Fokker-Planck diffusion approximation. Finally, we use the characteristic timescales of scattering for particles of different energies to discuss the feasibility of using such a system of tethers as a long and short-term remediation solution.

  15. Into the Kuiper Belt: New Horizons Post-Pluto

    NASA Astrophysics Data System (ADS)

    Harrison Parker, Alex; Spencer, John; Benecchi, Susan; Binzel, Richard; Borncamp, David; Buie, Marc; Fuentes, Cesar; Gwyn, Stephen; Kavelaars, JJ; Noll, Keith; Petit, Jean-Marc; Porter, Simon; Showalter, Mark; Stern, S. Alan; Sterner, Ray; Tholen, David; Verbiscer, Anne; Weaver, Hal; Zangari, Amanda

    2015-11-01

    New Horizons is now beyond Pluto and flying deeper into the Kuiper Belt. In the summer of 2014, a Hubble Space Telescope Large Program identified two candidate Cold Classical Kuiper Belt Objects (KBOs) that were within reach of New Horizons' remaining fuel budget. Here we present the selection of the Kuiper Belt flyby target for New Horizons' post-Pluto mission, our state of knowledge regarding this target and the potential 2019 flyby, the status of New Horizons' targeting maneuver, and prospects for near-future long-range observations of other KBOs.

  16. The small numbers of large Kuiper Belt objects

    SciTech Connect

    Schwamb, Megan E.; Brown, Michael E.; Fraser, Wesley C.

    2014-01-01

    We explore the brightness distribution of the largest and brightest (m(R) < 22) Kuiper Belt Objects (KBOs). We construct a luminosity function of the dynamically excited or hot Kuiper Belt (orbits with inclinations >5°) from the very brightest to m(R) = 23. We find for m(R) ≲ 23, a single slope appears to describe the luminosity function. We estimate that ∼12 KBOs brighter than m(R) ∼ 19.5 are present in the Kuiper Belt today. With nine bodies already discovered this suggests that the inventory of bright KBOs is nearly complete.

  17. Whole optic fiber weighing technique and device of belt conveyor

    NASA Astrophysics Data System (ADS)

    Li, Weilai; Liu, Jie; Pan, Jianjun

    2015-07-01

    Whole optic fiber weighing technique and its device of belt conveyor are developed and put into application. Four FBG stress cells support a frame in a belt conveying line. In each cell, two FBG strain gauges are respectively installed at the stretching and compressing places to get the effects of sensitivity enhancement and temperature compensation. The weighing signals are from both FBG wavelength shift of loading cells and fiber belt speed meter. By means of integral algorithm, the weighing result is obtained. Actual coal weighing test shows that the accuracy of this weighing device is under 0.5%.

  18. Dynamic models for ridge belt formation on Venus

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  19. Kuiper Belt Objects Along the Pluto-Express Path

    NASA Technical Reports Server (NTRS)

    Jewitt, David (Principal Investigator)

    1997-01-01

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

  20. The variable extension of Saturn's electron radiation belts

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  1. Dynamical studies of the Kuiper belt and the Centaurs

    NASA Astrophysics Data System (ADS)

    Volk, Kathryn Margaret

    The Kuiper belt is a population of small bodies located outside Neptune's orbit. The observed Kuiper belt objects (KBOs) can be divided into several subclasses based on their dynamical structure. I construct models for these subclasses and use numerical integrations to investigate their long-term evolution. I use these models to quantify the connection between the Kuiper belt and the Centaurs (objects whose orbits cross the orbits of the giant planets) and the short-period comets in the inner solar system. I discuss how these connections could be used to determine the physical properties of KBOs and what future observations could conclusively link the comets and Centaurs to specific Kuiper belt subclasses. The Kuiper belt's structure is determined by a combination of long-term evolution and its formation history. The large eccentricities and inclinations of some KBOs and the prevalence of KBOs in mean motion resonances with Neptune are evidence that much of the Kuiper belt's structure originated during the solar system's epoch of giant planet migration; planet migration can sculpt the Kuiper belt's scattered disk, capture objects into mean motion resonances, and dynamically excite KBOs. Different models for planet migration predict different formation locations for the subclasses of the Kuiper belt, which might result in different size distributions and compositions between the subclasses; the high-inclination portion of the classical Kuiper belt is hypothesized to have formed closer to the Sun than the low-inclination classical Kuiper belt. I use my model of the classical Kuiper belt to show that these two populations remain largely dynamically separate over long timescales, so primordial physical differences could be maintained until the present day. The current Kuiper belt is much less massive than the total mass required to form its largest members. It must have undergone a mass depletion event, which is likely related to planet migration. The Haumea collisional family dates from the end of this process. I apply long-term evolution to family formation models and determine how they can be observationally tested. Understanding the Haumea family's formation could shed light on the nature of the mass depletion event.

  2. Radiation Belt Storm Probes: Resolving Fundamental Physics with Practical Consequences

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  3. Trio of Neptunes and their Belt

    NASA Astrophysics Data System (ADS)

    2006-05-01

    Using the ultra-precise HARPS spectrograph on ESO's 3.6-m telescope at La Silla (Chile), a team of European astronomers have discovered that a nearby star is host to three Neptune-mass planets. The innermost planet is most probably rocky, while the outermost is the first known Neptune-mass planet to reside in the habitable zone. This unique system is likely further enriched by an asteroid belt. ESO PR Photo 18a/06 ESO PR Photo 18a/06 Planetary System Around HD 69830 (Artist's Impression) "For the first time, we have discovered a planetary system composed of several Neptune-mass planets", said Christophe Lovis, from the Geneva Observatory and lead-author of the paper presenting the results [1]. During more than two years, the astronomers carefully studied HD 69830, a rather inconspicuous nearby star slightly less massive than the Sun. Located 41 light-years away towards the constellation of Puppis (the Stern), it is, with a visual magnitude of 5.95, just visible with the unaided eye. The astronomers' precise radial-velocity measurements [2] allowed them to discover the presence of three tiny companions orbiting their parent star in 8.67, 31.6 and 197 days. "Only ESO's HARPS instrument installed at the La Silla Observatory, Chile, made it possible to uncover these planets", said Michel Mayor, also from Geneva Observatory, and HARPS Principal Investigator. "Without any doubt, it is presently the world's most precise planet-hunting machine" [3]. ESO PR Photo 18d/06 ESO PR Photo 18d/06 Phase Folded Measurements of HD 69830 The detected velocity variations are between 2 and 3 metres per second, corresponding to about 9 km/h! That's the speed of a person walking briskly. Such tiny signals could not have been distinguished from 'simple noise' by most of today's available spectrographs. The newly found planets have minimum masses between 10 and 18 times the mass of the Earth. Extensive theoretical simulations favour an essentially rocky composition for the inner planet, and a rocky/gas structure for the middle one. The outer planet has probably accreted some ice during its formation, and is likely to be made of a rocky/icy core surrounded by a quite massive envelope. Further calculations have also shown that the system is in a dynamically stable configuration. ESO PR Photo 18e/06 ESO PR Photo 18e/06 Formation Process of the Planetary System The outer planet also appears to be located near the inner edge of the habitable zone, where liquid water can exist at the surface of rocky/icy bodies. Although this planet is probably not Earth-like due to its heavy mass, its discovery opens the way to exciting perspectives. "This alone makes this system already exceptional", said Willy Benz, from Bern University, and co-author. "But the recent discovery by the Spitzer Space Telescope that the star most likely hosts an asteroid belt is adding the cherry to the cake." With three roughly equal-mass planets, one being in the habitable zone, and an asteroid belt, this planetary system shares many properties with our own solar system. "The planetary system around HD 69830 clearly represents a Rosetta stone in our understanding of how planets form", said Michel Mayor. "No doubt it will help us better understand the huge diversity we have observed since the first extra-solar planet was found 11 years ago." High resolution images and their captions are available on this page. Video footage and animations are also available on this page.

  4. 23 CFR 1240.13 - Determination of national average seat belt use rate.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 23 Highways 1 2013-04-01 2013-04-01 false Determination of national average seat belt use rate... BASED ON SEAT BELT USE RATES Determination of Allocations § 1240.13 Determination of national average seat belt use rate. The national average seat belt use rate for a calendar year shall be the sum of...

  5. 23 CFR 1240.13 - Determination of national average seat belt use rate.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 23 Highways 1 2014-04-01 2014-04-01 false Determination of national average seat belt use rate... BASED ON SEAT BELT USE RATES Determination of Allocations § 1240.13 Determination of national average seat belt use rate. The national average seat belt use rate for a calendar year shall be the sum of...

  6. 23 CFR 1240.13 - Determination of national average seat belt use rate.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 23 Highways 1 2011-04-01 2011-04-01 false Determination of national average seat belt use rate... BASED ON SEAT BELT USE RATES Determination of Allocations § 1240.13 Determination of national average seat belt use rate. The national average seat belt use rate for a calendar year shall be the sum of...

  7. 23 CFR 1240.13 - Determination of national average seat belt use rate.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 23 Highways 1 2010-04-01 2010-04-01 false Determination of national average seat belt use rate... BASED ON SEAT BELT USE RATES Determination of Allocations § 1240.13 Determination of national average seat belt use rate. The national average seat belt use rate for a calendar year shall be the sum of...

  8. 49 CFR 571.210 - Standard No. 210; Seat belt assembly anchorages.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... by Standard No. 208 (49 CFR 571.208). Seat belt anchorages for a Type 2 seat belt assembly shall be...) Type 2 and automatic seat belt assemblies that are installed to comply with Standard No. 208 (49 CFR... required to have a Type 1 or Type 2 seat belt assembly by Standard No. 208 (49 CFR 571.208)....

  9. 49 CFR 571.210 - Standard No. 210; Seat belt assembly anchorages.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... by Standard No. 208 (49 CFR 571.208). Seat belt anchorages for a Type 2 seat belt assembly shall be...) Type 2 and automatic seat belt assemblies that are installed to comply with Standard No. 208 (49 CFR... required to have a Type 1 or Type 2 seat belt assembly by Standard No. 208 (49 CFR 571.208)....

  10. 49 CFR 571.210 - Standard No. 210; Seat belt assembly anchorages.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... by Standard No. 208 (49 CFR 571.208). Seat belt anchorages for a Type 2 seat belt assembly shall be... with Standard No. 208 (49 CFR 571.208); and (b) Type 2 and automatic seat belt assemblies that are... 49 Transportation 6 2014-10-01 2014-10-01 false Standard No. 210; Seat belt assembly...

  11. 49 CFR 571.210 - Standard No. 210; Seat belt assembly anchorages.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... by Standard No. 208 (49 CFR 571.208). Seat belt anchorages for a Type 2 seat belt assembly shall be...) Type 2 and automatic seat belt assemblies that are installed to comply with Standard No. 208 (49 CFR... required to have a Type 1 or Type 2 seat belt assembly by Standard No. 208 (49 CFR 571.208)....

  12. Dynamics of the Earth's Radiation Belts and Inner Magnetosphere

    NASA Astrophysics Data System (ADS)

    Schultz, Colin

    2013-12-01

    Trapped by Earth's magnetic field far above the planet's surface, the energetic particles that fill the radiation belts are a sign of the Sun's influence and a threat to our technological future. In the AGU monograph Dynamics of the Earth's Radiation Belts and Inner Magnetosphere, editors Danny Summers, Ian R. Mann, Daniel N. Baker, and Michael Schulz explore the inner workings of the magnetosphere. The book reviews current knowledge of the magnetosphere and recent research results and sets the stage for the work currently being done by NASA's Van Allen Probes (formerly known as the Radiation Belt Storm Probes). In this interview, Eos talks to Summers about magnetospheric research, whistler mode waves, solar storms, and the effects of the radiation belts on Earth.

  13. Electron Flux of Radiation Belts Animation - Duration: 31 seconds.

    NASA Video Gallery

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

  14. Previously Undetected Radiation Belt Revealed - Duration: 63 seconds.

    NASA Video Gallery

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

  15. The Radiation Belt Storm Probes (RBSP) and Space Weather

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

    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.

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

    PubMed

    Barton, Bernadette

    2010-01-01

    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

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

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

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

  18. Visualization of Radiation Belts from REPT Data - Duration: 69 seconds.

    NASA Video Gallery

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

  19. Calculated limits for particle fluxes in Jupiter's Van Allen belts

    NASA Technical Reports Server (NTRS)

    Haffner, J.

    1972-01-01

    Electron and proton fluxes in Jupiter's radiation belts are calculated, along with the envelopes of dose rates. The following assumptions are made: the particles in the Jupiter belts are influenced only by the magnetic field of the planet; the particles act correspondingly to the particles in the Earth's belts and the Earth's belts can be used as a model; the magnetic field of Jupiter is essentially a dipole; the radiation of a decimetric nature received from Jupiter is synchrotron radiation due to the electrons, and to a first approximation it is emitted isotropically; and the strength of the emission in the decimetric wavelength range gives an upper bound considering how strong the field can be and how many electrons there are. The point dose rates for tissue and 0.1 gram/cm aluminum shielding at about 3 Jupiter radii are 10000 rads/hr for electrons and 1000 rads/hr for protons.

  20. 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