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Sample records for gneiss belt northern

  1. P- T- t constraints on the development of the Doi Inthanon metamorphic core complex domain and implications for the evolution of the western gneiss belt, northern Thailand

    NASA Astrophysics Data System (ADS)

    Macdonald, A. S.; Barr, S. M.; Miller, B. V.; Reynolds, P. H.; Rhodes, B. P.; Yokart, B.

    2010-01-01

    The western gneiss belt in northern Thailand is exposed within two overlapping Cenozoic structural domains: the extensional Doi Inthanon metamorphic core complex domain located west of the Chiang Mai basin, and the Mae Ping strike-slip fault domain located west of the Tak batholith. New P- T estimates and U-Pb and 40Ar/ 39Ar age determinations from the Doi Inthanon domain show that the gneiss there records a complex multi-stage history that can be represented by a clockwise P- T- t path. U-Pb zircon and titanite dating of mylonitic calc-silicate gneiss from the Mae Wang area of the complex indicates that the paragneissic sequence experienced high-grade, medium-pressure metamorphism (M1) in the Late Triassic - Early Jurassic (ca. 210 Ma), in good agreement with previously determined zircon ages from the underlying core orthogneiss exposed on Doi Inthanon. Late Cretaceous monazite ages of 84 and 72 Ma reported previously from the core orthogneiss are attributed to a thermal overprint (M2) to upper-amphibolite facies in the sillimanite field. U-Pb zircon and monazite dating of granitic mylonite from the Doi Suthep area of the complex provides an upper age limit of 40 Ma (Late Eocene) for the early stage(s) of development of the actual core complex, by initially ductile, low-angle extensional shearing under lower amphibolite-facies conditions (M3), accompanied by near-isothermal diapiric rise and decompression melting. 40Ar/ 39Ar laserprobe dating of muscovite from both Doi Suthep and Doi Inthanon provided Miocene ages of ca. 26-15 Ma, representing cooling through the ca. 350 °C isotherm and marking late-stage development of the core complex by detachment faulting of the cover rocks and isostatic uplift of the sheared core zone and mantling gneisses in the footwall. Similarities in the thermochronology of high-grade gneisses exposed in the core complex and shear zone domains in the western gneiss belt of northern Thailand (and also in northern Vietnam, Laos, Yunnan

  2. The structural setting and deformation associated with pseudotachylite occurrences in the Palala Shear Belt and Sand River Gneiss, Northern Transvaal

    NASA Astrophysics Data System (ADS)

    Brandl, G.; Reimold, W. U.

    1990-01-01

    Two occurrences of shear-related pseudotachylite from the Limpopo Metamorphic Province are described. In particular, the structural setting as well as deformation textures in pseudotachylite inclusions and host rocks are presented for these occurrences in gabbroic anorthosite from the Palala Shear Belt and dioritic to granodioritic rocks from the Sand River Gneiss locality. The Palala Shear Belt is a 13 km wide zone of intensely mylonitized rocks of the Beit Bridge and Bushveld Complexes, situated at the southern boundary of the Central Zone of the Limpopo Metamorphic Province. The Sand River Gneiss comprises a bimodal suite of high-grade dioritic and granodioritic rocks which were subjected to at least three periods of deformation. In the context of comparisons between pseudotachylites from different geological settings (i.e. cryptoexplosion structures, meteorite craters and tectonic settings) the major results are as follows: (1) The deformation phenomena associated with pseudotachylite formation as recorded in quartz and feldspar, occurring as inclusions or at the host rock contact, are undulatory extinction in quartz, brecciation, mechanical twinning and kinking of plagioclase, and characteristic formation of irregular and planar (Vredefort-type) fractures, the latter occurring in quartz. (2) Frequency distributions of crystallographic orientations of planar fractures and their annealed manifestation (planar fluid inclusion trails) are very similar for the Vredefort structure, the Sudbury structure, the Johannesburg dome, the Witwatersrand basin and the Limpopo pseudotachylites. It is therefore concluded that planar fractures in quartz are the typical microdeformation associated with pseudotachylite, irrespective of the geological setting of the latter. Planar fractures alone do not provide unambiguous information on the genesis of the structure in which they are found.

  3. Structure, age, and regional significance of syntectonic augen gneisses in the Pan-African Zambezi belt, south-central Zambia

    SciTech Connect

    Hanson, R.E.; Wilson, T.J.; Wardlaw, M.S.

    1985-01-01

    The Pan-African Zambezi belt in Zambia contains two major augen gneiss units that are elongated parallel to regional strike. These were previously regarded as slices of sialic basement structurally interleaved with Katangan metasedimentary rocks. New field and geochronologic evidence suggests that the gneisses are syntectonic granites intruded as large concordant sheets during main-phase (D/sub 1/) Pan-African deformation. A pervasive, horizontal or shallowly plunging mineral lineation on S/sub 1/ in the gneisses indicates that the parent granites were injected along major zones of transcurrent shear. The northern gneiss unit shows local discordant contacts against, and contains xenoliths of, adjacent Katangan rocks. Large, partly polygonized K-spar augen in the gneiss are wrapped around by S/sub 1/ and offset by microfractures antithetic to S/sub 1/. Finer grained granites intruding the gneiss are penetratively foliated to nondeformed, indicating that they were injected at various times relative to D/sub 1/. In the more intensely deformed southern gneiss unit, local pods of protomylonitic flaser gneiss grade into mylonites containing asymmetric K-spar augen set in a dynamically recrystallized matrix. U-Pb analyses of four fractions plus an air-abraded split of one fraction form a normal linear discordance pattern with an upper intercept of 820 +/- 7 Ma, taken as the age of igneous crystallization. Comparison with other available geochronologic data indicates that this age dates main-phase deformation in the Zambezi belt, and that deformation in the supposedly continuous Damaran belt to the SW was significantly younger.

  4. Geochemical Signatures of Neoproterozoic Granites and Granitoid-gneisses from Angavo Belt, Central Madagascar

    NASA Astrophysics Data System (ADS)

    Raharimahefa, T.

    2015-12-01

    The basement rocks of Madagascar record high-grade metamorphism, magmatism, and contractional and extensional structures that accompanied the collision of the eastern and western Gondwana segments of the supercontinent followed by its collapse. In the eastern central Madagascar, granitoids dominate the landscape and occur in a large area near and within the N-S trending highly strained zone known as the Angavo Shear Zone or Angavo belt. The area is a key in understanding the evolution of basement of Madagascar and the reconstruction of the Gondwana supercontinent. These granitoids range from layered to massive and previously published U-Pb zircon dating yielded three distinctive Neoproterozoic magmatisms at 770 Ma to 820 Ma, ca. 660Ma, and ca 550Ma. However, it was unknown whether these ages represent distinct magmatic pulses or reflect a continuous granitoid emplacement. This work contributes to the knowledge of the Malagasy basement rocks and to explore and discuss the origin and petrotectonic evolution of the granites and granitoid-gneisses from this part of the Madagascar. The rock samples are placed into three groups: group A and B for granitoid-gneisses and a third group for the granite layers. Group A and B are metaluminous and slightly peraluminous, respectively. All rocks have typical subduction zone calc-alkaline signatures. Group A is characterized by enrichment in large ion lithophile elements (LILE) but low U, LREE enrichment, depletion in the high field strength elements (HFSE). In contrast, Group B has REE patterns closely similar to Archean sediments. The granite layers show fractionated REE patterns in which HREE patterns show strong correlation with Zr abundances. Trends in major element variation diagrams and the enrichment of incompatible elements could be explained by simple fractional crystallization, while the overall geochemical signatures reflect either (1) melting of ancient crust or (2) crustal contamination of a more evolved magmas that

  5. U-Pb ages and Sr, Pb and Nd isotope data for gneisses near the Kolar Schist Belt: Evidence for the juxtaposition of discrete Archean terranes

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

    Uranium-lead ages and Sr, Pb, and Nd isotopic data for gneisses near the Kolar Schist Belt and their interpretation as evidence for the juxtaposition of discrete Archean terranes were presented. The granodioritic Kambha gneiss east of the schist belt has a zircon age of 2532 + or - 3 Ma and mantle-like initial Sr, Pb, and Nd isotopic ratios. Therefore these gneisses are thought to represent new crust added to the craton in the latest Archean. By contrast, more mafic Dod gneisses and leucocratic Dosa gneisses west of the schist belt (2632 + or - 7 and 2610 + or - 10 Ma) show evidence for contamination of their magmatic precursors (LREE-enriched mantle-derived for the Dod gneisses) by older (greater than 3.2 Ga) continental crust. Fragments of this older crust may be present as granitic and tonalitic inclusions in the 2.6-Ga gneisses and in shear zones. The antiquity of these fragments is supported by their Nd, Sr, and Pb isotopic compositions and by 2.8 to greater than 3.2 Ga zircon cores.

  6. U-Pb ages and Sr, Pb and Nd isotope data for gneisses near the Kolar Schist Belt: Evidence for the juxtaposition of discrete Archean terranes

    NASA Astrophysics Data System (ADS)

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

    Uranium-lead ages and Sr, Pb, and Nd isotopic data for gneisses near the Kolar Schist Belt and their interpretation as evidence for the juxtaposition of discrete Archean terranes were presented. The granodioritic Kambha gneiss east of the schist belt has a zircon age of 2532 + or - 3 Ma and mantle-like initial Sr, Pb, and Nd isotopic ratios. Therefore these gneisses are thought to represent new crust added to the craton in the latest Archean. By contrast, more mafic Dod gneisses and leucocratic Dosa gneisses west of the schist belt (2632 + or - 7 and 2610 + or - 10 Ma) show evidence for contamination of their magmatic precursors (LREE-enriched mantle-derived for the Dod gneisses) by older (greater than 3.2 Ga) continental crust. Fragments of this older crust may be present as granitic and tonalitic inclusions in the 2.6-Ga gneisses and in shear zones. The antiquity of these fragments is supported by their Nd, Sr, and Pb isotopic compositions and by 2.8 to greater than 3.2 Ga zircon cores.

  7. New models for Paleoproterozoic orogenesis in the Cheyenne belt region: Evidence from the geology and U-Pb geochronology of the Big Creek Gneiss, southeastern Wyoming

    USGS Publications Warehouse

    Jones, D.S.; Snoke, A.W.; Premo, W.R.; Chamberlain, K.R.

    2010-01-01

    The disputed age of the deep crust of the Colorado Province is central to hypotheses for Paleoproterozoic crustal growth in the region. We studied the high-grade Big Creek Gneiss, southeastern Wyoming, as a potential exposure of pre-1780 Ma basement rocks. New geologic mapping and U-Pb geochronological data indicate that the Big Creek Gneiss exposes a deeper, but coeval, level of the Green Mountain arc relative to the predominantly supracrustal section to the west. The Big Creek Gneiss is composed of: supracrustal rocks; a ca. 1780 Ma Green Mountain arc-correlative, bimodal intrusive suite; a ca. 1763 Ma extensional(?) bimodal intrusive suite; and widespread ca. 1630 Ma pegmatitic leucogranite. The mafic member of the younger bimodal suite is documented here for the first time. U-Pb zircon ages from migmatite leucosomes indicate penetrative deformation of the Big Creek Gneiss at ca. 1750 Ma. We find that the postarc intrusive suite is mantle-involved, implying a second period of crustal growth. Shortening postdates arc magmatism by ~20 m.y., implying that termination of arc magmatism and accretion were separate events. Finally, criteria previously used to constrain the polarity of subduction for the Green Mountain arc are not reliable. We propose two competing models: (1) southward-dipping Green Mountain arc subduction (present coordinates), with slab breakoff-related magmatism following arc accretion; or (2) northward-dipping subduction, with extensional postarc magmatism. In both models, high-temperature deformation coincides with accretion along the Cheyenne belt, and extensional magmatism is an important component of crustal growth. We prefer the northward-dipping subduction model because it can be better integrated with regional tectonic events and published isotopic compositions of the igneous rocks. ?? 2010 Geological Society of America.

  8. Geochronology and geochemistry of zircon from the northern Western Gneiss Region: Insights into the Caledonian tectonic history of western Norway

    NASA Astrophysics Data System (ADS)

    Gordon, Stacia M.; Whitney, Donna L.; Teyssier, Christian; Fossen, Haakon; Kylander-Clark, Andrew

    2016-03-01

    The Western Gneiss Region (WGR) of Norway is divided by the Møre-Trøndelag shear zone (MTSZ) into a southern region that contains domains of Caledonian ultrahigh-pressure (UHP) metamorphic rocks (> 2.5 GPa) and a northern area of similar Caledonian-aged rocks that record a maximum pressure reported thus far of ~1.5 GPa. Although both regions contain similar lithologies (primarily migmatitic quartzofeldspathic gneiss containing mafic lenses) and structural relationship of basement rocks to infolded nappes, this difference in maximum pressure implies a difference in tectonic history (continental subduction south of the shear zone, none to the north) and raises questions about the role of the MTSZ in the metamorphic history (including exhumation) of the WGR. Previous geochronology results indicated a difference in timing of peak metamorphism (older in north, younger in south). In order to better understand the tectonic history of the northern WGR and the MTSZ, and in particular the late- to post-Caledonian tectonic history, U-Pb zircon geochronology and trace-element abundances were obtained using the split-stream, laser-ablation ICPMS technique from metabasaltic lenses and migmatitic quartzofeldspathic host rocks from the structurally lowest exposed region of the northern WGR (Roan Peninsula basement), as well as leucosomes from an intercalated portion of the Seve Nappe Complex and a pegmatite in the MTSZ. Zircon from Roan gneiss and metabasite yield metamorphic ages of ca. 410-406 Ma, and zircon from a variety of migmatite samples (foliation-parallel leucosome to dikes) indicate melt crystallization at ca. 410 to 405 Ma. The Seve Nappe leucosomes yield only early Caledonian dates that cluster at ca. 437 Ma and ca. 465 Ma, suggesting that the allochthons in this region did not experience (or record) the same Scandian tectonic history as the basement rocks. Zircon from a weakly deformed pegmatite dike within the MTSZ crystallized at ca. 404 Ma, indicating that this

  9. U-Pb geochronology of zircon and monazite from Mesoproterozoic granitic gneisses of the northern Blue Ridge, Virginia and Maryland, USA

    USGS Publications Warehouse

    Aleinikoff, J.N.; Burton, W.C.; Lyttle, P.T.; Nelson, A.E.; Southworth, C.S.

    2000-01-01

    Mesoproterozoic granitic gneisses comprise most of the basement of the northern Blue Ridge geologic province in Virginia and Maryland. Lithology, structure, and U-Pb geochronology have been used to subdivide the gneisses into three groups. The oldest rocks, Group 1, are layered granitic gneiss (1153 ?? 6 Ma), hornblende monzonite gneiss (1149 ?? 19 Ma), porphyroblastic granite gneiss (1144 ?? 2 Ma), coarse-grained metagranite (about 1140 Ma), and charnockite (>1145 Ma?). These gneisses contain three Proterozoic deformational fabrics. Because of complex U-Pb systematics due to extensive overgrowths on magmatic cores, zircons from hornblende monzonite gneiss were dated using the sensitive high-resolution ion microprobe (SHRIMP), whereas all other ages are based on conventional U-Pb geochronology. Group 2 rocks are leucocratic and biotic varieties of Marshall Metagranite, dated at 1112??3 Ma and 1111 ?? 2 Ma respectively. Group 3 rocks are subdivided into two age groups: (1) garnetiferous metagranite (1077 ?? 4 Ma) and quartz-plagioclase gneiss (1077 ?? 4 Ma); (2) white leucocratic metagranite (1060 ?? 2 Ma), pink leucocratic metagranite (1059 ?? 2), biotite granite gneiss (1055 ?? 4 Ma), and megacrystic metagranite (1055 ?? 2 Ma). Groups 2 and 3 gneisses contain only the two younger Proterozoic deformational fabrics. Ages of monazite, seprated from seven samples, indicate growth during both igneous and metamorphic (thermal) events. However, ages obtained from individual grains may be mixtures of different age components, as suggested by backscatter electron (BSE) imaging of complexly zoned grains. Analyses of unzoned monazite (imaged by BSE and thought to contain only one age component) from porphyroblastic granite gneiss yield ages of 1070, 1060, and 1050 Ma. The range of ages of monazite (not reset to a uniform date) indicates that the Grenville granulite event at about 1035 Ma did not exceed about 750??C. Lack of evidence for 1110 Ma growth of monazite in

  10. Soil responses to stover management in the Northern Corn Belt

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Minnesota, at the northern edge of the United States Corn Belt, is among the top corn producing states in the country. National and local interest in using corn stover for energy sparked concerns that over-harvesting biomass would degrade the highly productive soils in the region. Therefore, a study...

  11. Crustal influx, indentation, ductile thinning and gravity redistribution in a continental wedge: Building a Moldanubian mantled gneiss dome with underthrust Saxothuringian material (European Variscan belt)

    NASA Astrophysics Data System (ADS)

    Chopin, F.; Schulmann, K.; Skrzypek, E.; Lehmann, J.; Dujardin, J. R.; Martelat, J. E.; Lexa, O.; Corsini, M.; Edel, J. B.; Å TíPská, P.; Pitra, P.

    2012-02-01

    The contribution of lateral forces, vertical load, gravity redistribution and erosion to the origin of mantled gneiss domes in internal zones of orogens remains debated. In the Orlica-Śnieżnik dome (Moldanubian zone, European Variscan belt), the polyphase tectono-metamorphic history is initially characterized by the development of subhorizontal fabrics associated with medium- to high-grade metamorphic conditions in different levels of the crust. It reflects the eastward influx of a Saxothuringian-type passive margin sequence below a Teplá-Barrandian upper plate. The ongoing influx of continental crust creates a thick felsic orogenic root with HP rocks and migmatitic orthogneiss. The orogenic wedge is subsequently indented by the eastern Brunia microcontinent producing a multiscale folding of the orogenic infrastructure. The resulting kilometre-scale folding is associated with the variable burial of the middle crust in synforms and the exhumation of the lower crust in antiforms. These localized vertical exchanges of material and heat are coeval with a larger crustal-scale folding of the whole infrastructure generating a general uplift of the dome. It is exemplified by increasing metamorphic conditions and younging of 40Ar/39Ar cooling ages toward the extruded migmatitic subdomes cored by HP rocks. The vertical growth of the dome induces exhumation by pure shear-dominated ductile thinning laterally evolving to non-coaxial detachment faulting, while erosion feeds the surrounding sedimentary basins. Modeling of the Bouguer anomaly grid is compatible with crustal-scale mass transfers between a dense superstructure and a lighter infrastructure. The model implies that the Moldanubian Orlica-Śnieżnik mantled gneiss dome derives from polyphase recycling of Saxothuringian material.

  12. How does the deep orogenic crust deform? The example of the Central Gneiss Belt (CGB), Grenville Province, Ontario.

    NASA Astrophysics Data System (ADS)

    Culshaw, Nicholas; Gerbi, Christopher; Marsh, Jeffrey; Slagstad, Trond

    2013-04-01

    The CGB may be understood as the product of deep crustal nappe flow requiring high strains during thickening- (P1) and flow- (P2) related phases. We attempt to describe, in terms of structural geometry and rheology, how these deformations are accommodated. The CGB consists of domains (thrust sheets) primarily composed of Proterozoic allochthonous and parautochthonous granitoid continental arc protoliths. These were either deformed at high grade (polycyclic) or never deformed (monocyclic) prior to granulite and amphibolite facies deformation in the Grenville orogeny. Grenville-age structure: polycyclic rocks do not melt and in P1-2 form narrow gneissic shear zones transposing pre-Grenville fabric or uniform domain-wide transposition gneissosity. Monocyclic rocks interlayed with polycylic form thick uniform migmatite sheets. Monocyclic domains not associated with polycyclic units form nappe complexes of highly strained granulite gneiss (P1) or migmatite sheets (P2). At later stages of progressive deformation accompanying nappe flow (P2), gneissosity of monocyclic rocks may be deformed coplanar with P1 gneissosity or form spectacular shear zone systems (amphibolite facies-on-granulite facies, or amphibolite-on-amphibolite). Overall, tracts of uniform deformation (gneiss domains/thrust sheets) are dominant over discrete shear zones. Grenville-age rheology: the largest scale rheological gradient, that between the Archean foreland, showing minor Grenville deformation, and highly deformed Proterozoic arc rocks, depends on the latters' protolith age and history as upper plate in a convergent margin. On the oceanward orogen margin, contrasting arc and back-arc properties resulted in P1 granulite- to amphibolite grade juxtaposition of upper- and deep crustal lithologies. At smaller scale, melting of fertile monocyclic granitoids is a major process, controlling formation of the large uniformly deformed thrust sheets (few internal strain gradients) and low competency layers

  13. Paleoproterozoic migmatitic gneisses from the Tandilia belt (Argentina), Río de la Plata craton, record cooling at deep crustal levels

    NASA Astrophysics Data System (ADS)

    Martínez, Juan Cruz; Massonne, Hans-Joachim; Dristas, Jorge Anastasio; Theye, Thomas; Graff, Ailín Ayelén

    2016-04-01

    We studied high-grade metamorphic rocks of the El Cristo hill area of the Tandilia belt. Mineral analyses and thermodynamic calculations were carried out for two adjacent rock samples: an amphibole-biotite gneiss and a garnet-biotite-bearing migmatite. Peritectic garnets in the migmatite show core compositions of pyr4.5(gro + andr)10spes6alm79.5 changing to pyr3.5(gro + andr)17spes6alm73.5 at their thin rims. Garnet compositions in the gneiss are pyr6.5(gro + andr)26spes12alm55.5 and pyr4.5(gro + andr)34spes12alm49.5 for core and rim, respectively. A P-T path was constructed by calculating pseudosections in the 11-component system Si-Ti-Al-Fe-Mn-Mg-Ca-Na-K-O-H and contouring them by isopleths for garnet components using the PERPLE_X software package. Supra-solidus crystallization of garnet cores in the migmatite began at 5.8 kbar and 660 °C. Garnet rims equilibrated at 7.0 kbar and 640 °C compatible with garnet cores in the amphibole-biotite gneiss (7.6 kbar and 660 °C). The further chemical development of garnet in this rock points to P-T conditions of 11.6 kbar and 620 °C and 12.2 kbar and 595 °C (outermost garnet rim). At this high-pressure stage Ca-amphibole was not stable. Most biotite formed during exhumation whereas the high-pressure accessory minerals, titanite and epidote, persisted. According to the obtained anti-clockwise P-T path the originally partly melted material was tectonically transported from ∼22 km (middle crust) to ∼40 km (lower crust) depths reaching a geothermal gradient as low as 15 °C km-1. This transport probably occurred along a major suture zone, which was active during the Paleoproterozoic (2.25-2.10 Ga), before a terminating collision of terranes near the SW boundary of the Rio de la Plata craton.

  14. Future aerosol reductions and widening of the northern tropical belt

    NASA Astrophysics Data System (ADS)

    Allen, Robert J.; Ajoku, Osinachi

    2016-06-01

    Observations show that the tropical belt has widened over the past few decades, a phenomenon associated with poleward migration of subtropical dry zones and large-scale atmospheric circulation. Although part of this signal is related to natural climate variability, studies have identified an externally forced contribution primarily associated with greenhouse gases (GHGs) and stratospheric ozone loss. Here we show that the increase in aerosols over the twentieth century has led to contraction of the northern tropical belt, thereby offsetting part of the widening associated with the increase in GHGs. Over the 21st century, however, when aerosol emissions are projected to decrease, the effects of aerosols and GHGs reinforce one another, both contributing to widening of the northern tropical belt. Models that have larger aerosol forcing, by including aerosol indirect effects on cloud albedo and lifetime, yield significantly larger Northern Hemisphere (NH) tropical widening than models with direct aerosol effects only. More targeted simulations show that future reductions in aerosols can drive NH tropical widening as large as greenhouse gases, and idealized simulations show the importance of NH midlatitude aerosol forcing. Mechanistically, the 21st century reduction in aerosols peaks near 40°N, which results in a corresponding maximum increase in surface solar radiation, NH midlatitude tropospheric warming amplification, and a poleward shift in the latitude of maximum baroclinicity, implying a corresponding shift in atmospheric circulation. If models with aerosol indirect effects better represent the real world, then future aerosol changes are likely to be an important -- if not dominant -- driver of NH tropical belt widening.

  15. Geological evolution of the Neoproterozoic Bemarivo Belt, northern Madagascar

    USGS Publications Warehouse

    Thomas, Ronald J.; De Waele, B.; Schofield, D.I.; Goodenough, K.M.; Horstwood, M.; Tucker, R.; Bauer, W.; Annells, R.; Howard, K. J.; Walsh, G.; Rabarimanana, M.; Rafahatelo, J.-M.; Ralison, A.V.; Randriamananjara, T.

    2009-01-01

    The broadly east-west trending, Late Neoproterozoic Bemarivo Belt in northern Madagascar has been re-surveyed at 1:100 000 scale as part of a large multi-disciplinary World Bank-sponsored project. The work included acquisition of 14 U-Pb zircon dates and whole-rock major and trace element geochemical data of representative rocks. The belt has previously been modelled as a juvenile Neoproterozoic arc and our findings broadly support that model. The integrated datasets indicate that the Bemarivo Belt is separated by a major ductile shear zone into northern and southern "terranes", each with different lithostratigraphy and ages. However, both formed as Neoproterozoic arc/marginal basin assemblages that were translated southwards over the north-south trending domains of "cratonic" Madagascar, during the main collisional phase of the East African Orogeny at ca. 540 Ma. The older, southern terrane consists of a sequence of high-grade paragneisses (Sahantaha Group), which were derived from a Palaeoproterozoic source and formed a marginal sequence to the Archaean cratons to the south. These rocks are intruded by an extensive suite of arc-generated metamorphosed plutonic rocks, known as the Antsirabe Nord Suite. Four samples from this suite yielded U-Pb SHRIMP ages at ca. 750 Ma. The northern terrane consists of three groups of metamorphosed supracrustal rocks, including a possible Archaean sequence (Betsiaka Group: maximum depositional age approximately 2477 Ma) and two volcano-sedimentary sequences (high-grade Milanoa Group: maximum depositional age approximately 750 Ma; low grade Daraina Group: extrusive age = 720-740 Ma). These supracrustal rocks are intruded by another suite of arc-generated metamorphosed plutonic rocks, known as the Manambato Suite, 4 samples of which gave U-Pb SHRIMP ages between 705 and 718 Ma. Whole-rock geochemical data confirm the calc-alkaline, arc-related nature of the plutonic rocks. The volcanic rocks of the Daraina and Milanoa groups also

  16. Brother is high Sr/Y two-mica granite and sister is leucogranite: twin granites in the Northern Himalayan Gneiss Domes, southern Tibet

    NASA Astrophysics Data System (ADS)

    Zeng, L.; Gao, L.; Xie, K.

    2011-12-01

    Leucogranites in the Himalayan orogen is widely considered as the type example of crustal melts, which provides a probe to investigate the interplay among high-grade metamorphism, crustal anatexis, and tectonic transition in large-scale collisional belts. Whether the leucogranite was a daughter product from a more primitive granitic melt is an interesting question that deserves careful examination to address the above issue. We report a new suite of two-mica granite (TMG) and leucogranite (LG) in the Yardoi gneiss dome (YGD) in the easternmost of the Northern Himalayan Gneiss Domes (NHGD), south of the Yarlung-Tsangpo suture. SHRIMP and LA-ICP-MS zircon U/Pb dating show that TMG and LG formed at ~17.7 Ma to ~20.0 Ma and at ~17.1 Ma, respectively. Both suites of granite have high Na/K (>1.30) ratios. The TMGs are characterized by (1) high Sr (>450 ppm), low Rb (<95 ppm) and Y (<6 ppm), and high Sr/Y (>86) ratios; (2) no Eu anomalies; and (3) low initial 87Sr/86Sr ratios (<0.7098) and higher ɛNd (>-8.5) values. In contrast, the LGs have (1) lower Sr (<130 ppm) and higher Rb (92-130 ppm); (2) pronounced negative Eu anomalies with Eu/Eu*<0.55; and (3) relatively higher Sr (87Sr/86Sr(t) =0.7136-0.7148) and unradiogenic Nd (ɛNd(t)=-7.7~-11.1). These data demonstrate that these Mid-Miocene granites have major and trace element and radiogenic isotope compositions similar to those of >35 Ma granites, but significantly different from those granites of similar ages in the High Himalaya as well as in the NHGD. High Sr/Y and relatively unradiogenic Sr isotope compositions in the TMGs could be derived from partial melting of mafic materials formed during previous compressional thickening event which was triggered by the input of juvenile heat and material associated with the Miocene E-W extension. An AFC process (plagioclase fractional crystallization and contamination by crustal materials) could be a primary factor leading to the formation of these LGs. Concurrence of high Sr

  17. Deformation of the Eastern Franciscan Belt, northern California

    USGS Publications Warehouse

    Jayko, A.S.; Blake, M.C., Jr.

    1989-01-01

    The late Jurassic and Cretaceous Eastern Franciscan belt of the northern California Coast Range consists of two multiply deformed, blueschist-facies terranes; the Pickett Peak and Yolla Bolly terranes. Four deformations have been recognized in the Pickett Peak terrane, and three in the Yolla Bolly terrane. The earliest recognized penetrative fabric, D1, occurs only in the Pickett Peak terrane. The later penetrative fabrics, D2 and D3, occur in both the Yolla Bolly and Pickett Peak terranes. D1 and D2 apparently represent fabrics that formed during subduction and accretion of the terranes. Fabrics from both D1 and D2 are consistent with SW-NE movement directions with respect to their present geographic positions. D3 postdates blueschist-facies metamorphism of the terranes and may be related to emplacement of the terranes to higher structural levels. A broad regional warping, D4, is evident from the map pattern and folding of large metamorphosed thrust sheets. D4 folds may be related to deformation associated with oblique convergence along the continental margin in late Cretaceous and (or) early Tertiary time. ?? 1989.

  18. Pre-35 Ma Na-rich peraluminous leucogranites in the Yardoi gneiss dome, southern Tibet

    NASA Astrophysics Data System (ADS)

    Gao, L.; Zeng, L.; Liu, J.; Xie, K.

    2008-12-01

    The Northern Himalayan Gneiss Dome (NHGD) consists of a series of semi-continuous east-west trending gneiss domes within the Tethyan Himalayan Belt. The Yardoi gneiss dome, the easternmost among these domes, consists of garnet two-mica gneiss, garnet amphibolite,Cenozoic two-mica granite and leucogranite. New SHRIMP zircon U/Pb dating show that the Yardoi leucogranite formed at 35.5±1.1Ma, which is older than those similar leucogranites to the west (commonly with ages < 25 Ma). We have performed bulk chemical and Sr and Nd isotope analyses on a suite of leucogranites and the wall-rocks to characterize their geochemistry and evaluate their formation mechanism. These data show that: (1) a majority of the Yardoi leucogranites are of Na-rich peraluminous granite; (2) similar to the wall-rock gneisses, the Yardoi leucogranites are enriched in LILE (K, Sr, Rb, Ba, and Th), but highly depleted in Ti, Y, Yb, Sc, and Cr; (3) as compared to those either in the gneisses or in the amphibolites, the Yardoi leucogranites are depleted both in LREE and in HREE. However, they are enriched in LREE relative to HREE;(4) the Yardoi leucogranites have initial Sr isotope compositions (0.71195~0.71934), similar to those of the amphibolites, whereas their "ÕNd(i) values (-8.9~-15.0) are between those in the amphibolites and the gneisses. Simple mixing calculations indicate that partial melting of a source mixed of garnet amphibolite with subordinate pelitic gneiss could account for the formation of the Yardoi Na-rich peraluminous melts. Though both H2O-fluxed melting of metapelite at high pressures (~10 kbar) and amphibolite parting melting can produce Na-rich peraluminous granitic melts, the ~35 Ma anatectic event in the Yardoi gneiss dome was dominated by amphibolite partial melting. This event might be a major factor led to transition from compressional to extensional deformation in the overthickened Himalayan belt.

  19. Gneisses (Serizzi and Beole) of the Verbano-Cusio-Ossola district (Piedmont, Northern Italy): possible candidates for the designation of "Global Heritage Stone province"

    NASA Astrophysics Data System (ADS)

    Antonella Dino, Giovanna; Borghi, Alessandro; Cavallo, Alessandro; Primavori, Piero

    2016-04-01

    The Verbano-Cusio-Ossola quarrying district (Piedmont, northern Italy) produces many different ornamental stones (granites, gneisses, marbles): two really important categories are represented by Serizzo and Beola gneisses. Several varieties of Serizzo and Beola crop out in the upper and middle Ossola Valley: Serizzo derives from the Antigorio, Monte Leone and Monte Rosa Penninic Units, whereas Beola from the Monte Leone, Orselina-Moncucco-Isorno and Monte Rosa Penninic Units, as well from the Fobello-Rimella schists (Austroalpine). The Serizzo, represented by a group of foliated granitoid orthogneisses (Serizzo Antigorio, Serizzo Formazza, Serizzo Sempione and Serizzo Monte Rosa varieties), is probably the most important and extensively exploited ornamental stones from the VCO province (about 70% of the VCO stone production). The quarries are mostly concentrated in the Antigorio and Formazza valleys, where the Antigorio nappe has a sub-horizontal attitude and reaches its greatest thickness (up to 1000 m). This stone was largely used to produce columns since the end of XV century (e.g. the old Ospedale Maggiore in Milano, now University of Milano) and later on it was replaced with granites. It was also used in the building structure of the Duomo di Milano, for the plinth and the piers. Nowadays, thanks to its good wear resistance and low cost, it is mainly used in polished slabs for paving: a recent application is the Frankfurt airport floor. Beola is the name of a group of heterogeneous orthogneisses with mylonitic foliation and strong mineralogical lineation (Beola Grigia, Bianca, Ghiandonata, Striata varieties), easy to split into thin slabs with hammer and chisel, occurring in the middle Ossola Valley, between Vogogna and Montecrestese. The quarries of Beola are probably the oldest of the Ossola Valley, although the precise period in which the stone started to be exported is unknown. The Beola trade probably started at the end of the XIII century, with the

  20. The dehydration, rehydration and tectonic setting of greenstone belts in a portion of the northern Kaapvaal Craton, South Africa

    NASA Technical Reports Server (NTRS)

    Vanreenen, D. D.; Barton, J. M., Jr.; Roering, C.; Vanschalkwyk, J. C.; Smit, C. A.; Debeer, J. D.; Stettler, E. H.

    1986-01-01

    High-grade gneiss terranes and low-grade granite-greenstone terranes are well known in several Archaean domains. The geological relationship between these different crustal regions, however, is still controversial. One school of thought favors fundamental genetic differences between high-grade and low-grade terranes while others argue for a depth-controlled crustal evolution. The detailed examination of well-exposed Archaean terranes at different metamorphic grades, therefore, is not only an important source of information about the crustal levels exposed, but also is critical to the understanding of the possible tectonic and metamorphic evolution of greenstone belts with time. Three South African greenstone belts are compared.

  1. Relation of the Wissahickon mica gneiss to the Shenandoah limestone and Octoraro schist of the Doe Run and Avondale region, Chester County, Pennsylvania

    USGS Publications Warehouse

    Bliss, Eleanora F.; Jonas, Anna I.

    1917-01-01

    The region discussed in this paper lies in Chester County, Pa., and is included in the eastern half of the Coatesville quadrangle. (See fig. 3.) It is within the belt of crystal-line schists and gneisses of the Piedmont Plateau. The northern half of the area, which will be called the Doe Run region, from the village of that name (see Fig. 4, p. 15), has been surveyed by Eleanora F. Bliss in connection with the problem of the relation of the Wissahickon mica gneiss to the Octoraro schist.

  2. Combined analysis of land cover change and NDVI trends in the Northern Eurasian grain belt

    NASA Astrophysics Data System (ADS)

    Wright, Christopher K.; de Beurs, Kirsten M.; Henebry, Geoffrey M.

    2012-06-01

    We present an approach to regional environmental monitoring in the Northern Eurasian grain belt combining time series analysis of MODIS normalized difference vegetation index (NDVI) data over the period 2001-2008 and land cover change (LCC) analysis of the 2001 and 2008 MODIS Global Land Cover product (MCD12Q1). NDVI trends were overwhelmingly negative across the grain belt with statistically significant ( p⩽0.05) positive trends covering only 1% of the land surface. LCC was dominated by transitions between three classes; cropland, grassland, and a mixed cropland/natural vegetation mosaic. Combining our analyses of NDVI trends and LCC, we found a pattern of agricultural abandonment (cropland to grassland) in the southern range of the grain belt coinciding with statistically significant ( p⩽0.05) negative NDVI trends and likely driven by regional drought. In the northern range of the grain belt we found an opposite tendency toward agricultural intensification; in this case, represented by LCC from cropland mosaic to pure cropland, and also associated with statistically significant ( p⩽0.05) negative NDVI trends. Relatively small clusters of statistically significant ( p⩽0.05) positive NDVI trends corresponding with both localized land abandonment and localized agricultural intensification show that land use decision making is not uniform across the region. Land surface change in the Northern Eurasian grain belt is part of a larger pattern of land cover land use change (LCLUC) in Eastern Europe, Russia, and former territories of the Soviet Union following realignment of socialist land tenure and agricultural markets. Here, we show that a combined analysis of LCC and NDVI trends provides a more complete picture of the complexities of LCLUC in the Northern Eurasian grain belt, involving both broader climatic forcing, and narrower anthropogenic impacts, than might be obtained from either analysis alone.

  3. Aeromagnetic and aeromagnetic-based geologic maps of the Coastal Belt, Franciscan Complex, northern California

    USGS Publications Warehouse

    Langenheim, V.E.; Jachens, R.C.; McLaughlin, R.J.

    2011-01-01

    The Coastal belt of the Franciscan Complex represents a Late Cretaceous to Miocene accretionary prism and overlying slope deposits. Its equivalents may extend from the offshore outer borderland of southern California to north of the Mendocino Triple Junction under the Eel River Basin and in the offshore of Cascadia. The Coastal belt is exposed on land in northern California, yet its structure and stratigraphy are incompletely known because of discontinuous exposure, structural disruption, and lithologically non-distinctive clastic rocks. The intent of this report is to make available, in map form, aeromagnetic data covering the Coastal belt that provide a new dataset to aid in mapping, understanding, and interpreting the incompletely understood geology and structure in northern California. The newly merged aeromagnetic data over the Coastal belt of the Franciscan Complex reveal long, linear anomalies that indicate remarkably coherent structure within a terrane where mapping at the surface indicates complex deformation and that has been described as "broken formation" and, even locally as "melange". The anomalies in the Coastal belt are primarily sourced by volcanic-rich graywackes and exotic blocks of basalt. Some anomalies along the contact of the Coastal belt with the Central belt are likely caused by local interleaving of components of the Coast Ranges ophiolite. These data can be used to map additional exotic blocks within the Coastal belt and to distinguish lithologically indistinct graywackes within the Coastal terrane. Using anomaly asymmetry allows projection of these "layers" into the subsurface. This analysis indicates predominant northeast dips consistent with tectonic interleaving of blocks within a subduction zone.

  4. Tectonics of the Himalayan thrust belt in northern Pakistan

    NASA Technical Reports Server (NTRS)

    Yeats, R. S.; Lawrence, R. D.

    1982-01-01

    It is pointed out that the Himalayan ranges of southern Asia represent a dilemma in modern plate tectonic theory. Alvarez (1982) has tried to resolve some of the problems, but inconsistencies remain. The present investigation considers some of the problems which are now encountered in light of present knowledge. The investigation is concerned mainly with the evolution of the Himalaya south of the Main Mantle Thrust (MMT) and the Indus-Tsangpo suture zone, taking into account the neotectonic setting of northern Pakistan. Attention is given to subdivisions of the central Indian Himalaya, the transition from central Himalaya to northern Pakistan, subdivisions of the Himalaya of northern Pakistan, and aspects of neotectonics. Problems for future work are also discussed.

  5. Possible extension of mineral belts, northern part of Coeur d'Alene district, Idaho

    USGS Publications Warehouse

    Gott, Garland B.; Botbol, Joseph M.

    1975-01-01

    The ore deposits in the northern part of the Coeur d'Alene district are located within rocks of the Belt Supergroup that have been intruded by Cretaceous quartz monzonites. Lead-zinc-silver replacement veins constitute most of the deposits. The geometry of the district has been modified by post-ore faulting along the Osburn, Dobson Pass, and other faults. The original position of the Gem stocks, before their separation from the Diego Peak stocks by the Dobson Pass fault, can be approximately reconstructed by moving the truncated stocks and associated geochemical dispersion patterns back into matching positions. The known mineral belts are defined by dispersion patterns of both lead and the Pb:Zn ratio. Similar dispersion patterns of lead and the Pb:Zn ration northwest of the original position of the Gem stocks suggest that the mineral belts extend into that area.

  6. Southward shift of the northern tropical belt from 1945 to 1980

    NASA Astrophysics Data System (ADS)

    Brönnimann, Stefan; Fischer, Andreas M.; Rozanov, Eugene; Poli, Paul; Compo, Gilbert P.; Sardeshmukh, Prashant D.

    2015-12-01

    Changes in the position and width of the tropical belt are societally and ecologically relevant, because they are associated with shifts of the subtropical dry zones. The tropical belt has widened since about 1980, but little is known about its earlier variability. Here we analyse historical surface and upper-level observations, three global reanalysis data sets, and a reconstruction of total column ozone, to show that the northern tropical edge retracted from 1945 to 1980, while the northern Hadley cell shifted southwards in both summer and winter. We present chemistry-climate model simulations that reproduce the retraction and southward shift. We find that retraction of the tropical belt was largely due to cooling sea-surface temperatures north of the Equator and warming south of the Equator, most prominently over the Atlantic. Substantial hydroclimatic anomalies such as European droughts of the 1940s and 1950s and the Sahel drought of the 1970s were associated with this shift of the Hadley cell. Our results suggest that multidecadal changes in the position of the northern Hadley cell are an important component of climate variability.

  7. Early Eocene tectonics and sedimentation in Northern Fossil basin, Wyoming Overthrust Belt

    SciTech Connect

    Hurst, D.J.; Steidtmann, J.R.

    1984-07-01

    The Tunp Member of the early Eocene Wasatch Formation in southwestern Wyoming was shed from rising thrust sheets as debris flows containing abundant, very poorly sorted to unsorted, coarse clastic material in a mudstone matrix. Deposition occurred on the margins of the northern Fossil basin as coalesced alluvial fans and fan deltas. Small braided streams traversed the surface of these fans and reworked debris flow material, but the resultant fluvial deposits are volumetrically minor. Tunp Member deposits are preserved in three north-south-trending belts around the periphery of the northern Fossil basin. Each belt had a separate source in discrete highlands created by early Eocene motion on the Absaroka, Tunp, and Crawford thrust faults. These thrusts possessed unique characteristics of uplift style, provenance, and duration of in-situ weathering that are reflected by differences in clast lithology, size and rounding, as well as thickness and areal extent of the deposits resulting from each thrust. The results of this study have several important implications about thrust belt development: (1) passive rotation of older thrusts by younger ones can provide an uplifted source for syntectonic sediments, (2) the tenet that major thrusts young in the direction of tectonic transport may be violated by the Tunp and Crawford thrusts in the Fossil basin area, and (3) those heretical faults (i.e., Tunp and Crawford) possess a similar geometry that is distinct from other thrust faults in the area.

  8. Structural and geochronological constraints on the Pan-African tectonic evolution of the northern Damara Belt, Namibia

    NASA Astrophysics Data System (ADS)

    Lehmann, Jérémie; Saalmann, Kerstin; Naydenov, Kalin V.; Milani, Lorenzo; Belyanin, George A.; Zwingmann, Horst; Charlesworth, Guy; Kinnaird, Judith A.

    2016-01-01

    The Pan-African Orogen formed by convergence of numerous continental blocks during the Neoproterozoic to early Cambrian. This convergence eventually led to amalgamation of Gondwana, a supercontinent crosscut by a network of highly oblique linear orogenic belts that locally intersect each other, as in NW Namibia, where the NNW trending Kaoko Belt joins the NE trending Damara Belt. The northern Damara Belt has preserved well three regional Pan-African tectonic events due to the dominance of weak Neoproterozoic marine sediments (Damara Supergroup) that have been affected by low-grade metamorphism. A newly discovered early N-S horizontal contraction, dated by 40Ar/39Ar at ~590 Ma, is tentatively linked to convergence between the Congo and Kalahari cratons. This was superseded by collision between the Congo and Rio de la Plata cratons between 580 and 530 Ma that thickened and exhumed the orogenic crust of the Kaoko Belt and produce upper crustal N-S oriented folds of earlier fold trains and associated axial planar schistosities in the northern Damara Belt. A switch from E-W to NW-SE horizontal shortening occurred at ~530 Ma as a result of collision with the Kalahari Craton, triggering extensive syn-orogenic magmatism in the entire Damara Belt. During this last event, southward indentation and underthrusting of the Congo Craton promontory below the Neoproterozoic cover sequences produced a deformation front in the northern Damara Belt. Our results show that highly oblique convergent processes competed over a period of ~120 Ma to build Gondwana in Namibia during the late Neoproterozoic to early Cambrian.

  9. Arsenic in groundwaters in the Northern Appalachian Mountain belt: a review of patterns and processes.

    PubMed

    Peters, Stephen C

    2008-07-29

    Naturally occurring arsenic in the bedrock of the Northern Appalachian Mountain belt was first recognized in the late 19th century. The knowledge of the behavior of arsenic in groundwater in this region has lagged behind nearly a century, with the popular press reporting on local studies in the early 1980s, and most peer-reviewed research articles on regional patterns conducted and written in the late 1990s and early 2000s. Research reports have shown that within this high arsenic region, between 6% and 22% of households using private drinking water wells contain arsenic in excess of 10 microg/L, the United States Environmental Protection Agency's maximum contaminant level. In nearly all reports, arsenic in drinking water was derived from naturally occurring geologic sources, typically arsenopyrite, substituted sulfides such as arsenian pyrite, and nanoscale minerals such as westerveldite. In most studies, arsenic concentrations in groundwater were controlled by pH dependent adsorption to mineral surfaces, most commonly iron oxide minerals. In some cases, reductive dissolution of iron minerals has been shown to increase arsenic concentrations in groundwater, more commonly associated with anthropogenic activities such as landfills. Evidence of nitrate reduction promoting the presence of arsenic(V) and iron(III) minerals in anoxic environments has been shown to occur in surface waters, and in this manuscript we show this process perhaps applies to groundwater. The geologic explanation for the high arsenic region in the Northern Appalachian Mountain belt is most likely the crustal recycling of arsenic as an incompatible element during tectonic activity. Accretion of multiple terranes, in particular Avalonia and the Central Maine Terrane of New England appear to be connected to the presence of high concentrations of arsenic. Continued tectonic activity and recycling of these older terranes may also be responsible for the high arsenic observed in the Triassic rift

  10. Arsenic in groundwaters in the Northern Appalachian Mountain belt: A review of patterns and processes

    NASA Astrophysics Data System (ADS)

    Peters, Stephen C.

    2008-07-01

    Naturally occurring arsenic in the bedrock of the Northern Appalachian Mountain belt was first recognized in the late 19th century. The knowledge of the behavior of arsenic in groundwater in this region has lagged behind nearly a century, with the popular press reporting on local studies in the early 1980s, and most peer-reviewed research articles on regional patterns conducted and written in the late 1990s and early 2000s. Research reports have shown that within this high arsenic region, between 6% and 22% of households using private drinking water wells contain arsenic in excess of 10 µg/L, the United States Environmental Protection Agency's maximum contaminant level. In nearly all reports, arsenic in drinking water was derived from naturally occurring geologic sources, typically arsenopyrite, substituted sulfides such as arsenian pyrite, and nanoscale minerals such as westerveldite. In most studies, arsenic concentrations in groundwater were controlled by pH dependent adsorption to mineral surfaces, most commonly iron oxide minerals. In some cases, reductive dissolution of iron minerals has been shown to increase arsenic concentrations in groundwater, more commonly associated with anthropogenic activities such as landfills. Evidence of nitrate reduction promoting the presence of arsenic(V) and iron(III) minerals in anoxic environments has been shown to occur in surface waters, and in this manuscript we show this process perhaps applies to groundwater. The geologic explanation for the high arsenic region in the Northern Appalachian Mountain belt is most likely the crustal recycling of arsenic as an incompatible element during tectonic activity. Accretion of multiple terranes, in particular Avalonia and the Central Maine Terrane of New England appear to be connected to the presence of high concentrations of arsenic. Continued tectonic activity and recycling of these older terranes may also be responsible for the high arsenic observed in the Triassic rift basins

  11. Regional magnetic anomalies, crustal strength, and the location of the northern Cordilleran fold-and-thrust belt

    USGS Publications Warehouse

    Saltus, R.W.; Hudson, T.L.

    2007-01-01

    The northern Cordilleran fold-and-thrust belt in Canada and Alaska is at the boundary between the broad continental margin mobile belt and the stable North American craton. The fold-and-thrust belt is marked by several significant changes in geometry: cratonward extensions in the central Yukon Territory and northeastern Alaska are separated by marginward re-entrants. These geometric features of the Cordilleran mobile belt are controlled by relations between lithospheric strength and compressional tectonic forces developed along the continental margin. Regional magnetic anomalies indicate deep thermal and compositional characteristics that contribute to variations in crustal strength. Our detailed analysis of one such anomaly, the North Slope deep magnetic high, helps to explain the geometry of the fold-and-thrust front in northern Alaska. This large magnetic anomaly is inferred to reflect voluminous mafic magmatism in an old (Devonian?) extensional domain. The presence of massive amounts of malic material in the lower crust implies geochemical depletion of the underlying upper mantle, which serves to strengthen the lithosphere against thermal erosion by upper mantle convection. We infer that deep-source magnetic highs are an important indicator of strong lower crust and upper mantle. This stronger lithosphere forms buttresses that play an important role in the structural development of the northern Cordilleran fold-and-thrust belt. ?? 2007 The Geological Society of America.

  12. Polyphase Neoproterozoic orogenesis within the east Africa- Antarctica orogenic belt in central and northern Madagascar

    USGS Publications Warehouse

    Key, R.M.; Pitfield, P.E.J.; Thomas, Ronald J.; Goodenough, K.M.; Waele, D.; Schofield, D.I.; Bauer, W.; Horstwood, M.S.A.; Styles, M.T.; Conrad, J.; Encarnacion, J.; Lidke, D.J.; O'connor, E. A.; Potter, C.; Smith, R.A.; Walsh, G.J.; Ralison, A.V.; Randriamananjara, T.; Rafahatelo, J.-M.; Rabarimanana, M.

    2011-01-01

    Our recent geological survey of the basement of central and northern Madagascar allowed us to re-evaluate the evolution of this part of the East Africa-Antarctica Orogen (EAAO). Five crustal domains are recognized, characterized by distinctive lithologies and histories of sedimentation, magmatism, deformation and metamorphism, and separated by tectonic and/or unconformable contacts. Four consist largely of Archaean metamorphic rocks (Antongil, Masora and Antananarivo Cratons, Tsaratanana Complex). The fifth (Bemarivo Belt) comprises Proterozoic meta-igneous rocks. The older rocks were intruded by plutonic suites at c. 1000 Ma, 820-760 Ma, 630-595 Ma and 560-520 Ma. The evolution of the four Archaean domains and their boundaries remains contentious, with two end-member interpretations evaluated: (1) all five crustal domains are separate tectonic elements, juxtaposed along Neoproterozoic sutures and (2) the four Archaean domains are segments of an older Archaean craton, which was sutured against the Bemarivo Belt in the Neoproterozoic. Rodinia fragmented during the early Neoproterozoic with intracratonic rifts that sometimes developed into oceanic basins. Subsequent Mid- Neoproterozoic collision of smaller cratonic blocks was followed by renewed extension and magmatism. The global 'Terminal Pan-African' event (560-490 Ma) finally stitched together the Mid-Neoproterozoic cratons to form Gondwana. ?? The Geological Society of London 2011.

  13. U-Pb geochronology of two augen gneiss terranes, Idaho - new data and tectonic implications.

    USGS Publications Warehouse

    Evans, K.V.; Fischer, L.B.

    1986-01-01

    The augen-gneiss of Red River (Idaho) is interpreted as being approx 1370 m.y. old. U-Pb systematics of cogenetic zircons indicate at least one component of inherited radiogenic lead. Field relationships indicate some intense deformation of the host rocks prior to or synchronous with intrusion of the augen-gneiss of Red River. The augen-gneiss of Priest River is 1576 + or - 13 m.y. old, there being no indication of inherited radiogenic lead. The Priest River augen-gneiss probably forms a pre-belt basement that is either tectonically interleaved with belt strata, unconformably underlies belt strata, or both. In any case, the age of 1576 m.y. is probably a maximum for deposition of the Prichard formation.-J.M.H.

  14. Evolution of the northern Sierra Nevada metamorphic belt: Petrological, structural, and Ar/Ar constraints

    SciTech Connect

    Hacker, B.R.

    1993-05-01

    The Sierra Nevada metamorphic belt constitutes an important record of the growth of continental crust from essentially oceanic materials. In the northern Sierra, the central part of the belt is made up of volcanoplutonic arcs and sediment-dominated units inferred to be accretionary wedges or closed ocean basins. The latter are broken formation and melange composed of radiolarian chert, lava, and volcanogenic and continental turbidites. Sedimentary detritus in the largest of these units can be plausibly linked to sources farther east in the Sierra, suggesting that deposition occurred near the eastern Sierran arc. Isoclinal folds, steeply dipping foliations, and steeply plunging down-dip lineations are characteristics structures. The westernmost unit is only feebly recrystallized, and deformation was accomplished principally by stress solution and local redeposition in veins. More easterly, inboard units are compositionally similar, but they recrystallized at pumpellyite-actinolite-and blueschist-facies conditions and deformed via solution-transfer and dislocation creep. Phengite silica contents, the degree of quartz veining, and the locations of pseudo-isograds support an eastward increase in metamorphic pressure and temperature. Metamorphic conditions during the growth of pumpellyite and actinolite ranged from {approximately}150-350 {degrees}C and 200-400 MPa, compatible with recrystallization and deformation in subduction zones or the deeper levels of magmatic arcs. Ar/Ar ages of volcanisclastic rocks and crosscutting plutons constrain the age of deformation and metamorphism in the western part of the region to 174-165 Ma. Deformation and recrystallization in more easterly units may have been coeval or begun as early as Triassic time. 58 refs., 14 figs., 4 tabs.

  15. Early Archean tonalite gneiss in the upper peninsula of Michigan

    NASA Technical Reports Server (NTRS)

    Peterman, Z. E.; Zartman, R. E.; Sims, P. K.

    1986-01-01

    Geochronological results on tonalite gneiss of northern Michigan that is 3.56 Ga or slightly older is presented. Tonalitic augen gneiss and structurally overlying biotite gneiss and schist are exposed in a dome near Watersmeet. They are part of an extensive gneiss terrane of southern Minnesota, Wisconsin and Michigan that includes rocks of early to late Archean ages and lies south of the Wawa volcanic subprovince. Two samples of the augen gneiss and one of the biotite gneiss show zircon grains of similar shape, zoning, color, and development of crystal faces. These zircons give Pb/U isotopic ratios that plot on a chord of 3,560 + or - 40 m.y. upper intersect and of 1,250 + or m.y. lower intersect. The 3,560 m.y. number is believed to be a minimum age because analysis of one of the least discordant zircon fractions by ion microprobe that gave a nearly concordant age of 3,650 m.y. The 1,250 m.y. lower intersect is without geological significance: it is interpreted to be a result of multiple lead loss at 2.7, 1.8, and 0.5 Ga by U/Pb in zircon. Archean rocks 10 to 25 km northwest of the Watersmeet dome give a 2.75 Ga age on zircons. Quartz monzonite here is dated at 2.65 Ga.

  16. The Variscan belt of Northern France Southern Belgium: geodynamic implications of new palaeomagnetic data

    NASA Astrophysics Data System (ADS)

    Márton, Emő; Mansy, Jean-Louis; Averbuch, Olivier; Csontos, László

    2000-09-01

    Palaeomagnetic investigations were carried out in Devonian-early Carboniferous rocks of the Variscan foreland chain of Northern France-Southern Belgium in order to reveal the origin of its arcuate shape. The Brabant Parautochthon was sampled in the Boulonnais (near Calais) and near Tournai, while the Ardenne Allochthon was sampled near Maubeuge and in the Givet area. All the sampled localities yielded characteristic remanent magnetization as a result of stepwise demagnetization and component analysis. Fold or tilt tests were possible for three localities, with negative results indicating pervasive remagnetization. The tectonic position was sub-horizontal at two localities, while the tilt was monoclinal for the rest. Therefore, the acquisition time of the magnetic signals was estimated by comparing the palaeolatitude computed from each magnetic component to the palaeolatitudes of Variscan Europe calculated after Van der Voo (1993). Three components showing: A, a southern B, a near-Equatorial, and C, a northern palaeolatitude are recognized from our data. Since a pre-Variscan age of component A (observed only in Boulonnais, at 10 sites) is not supported by data, it is assigned to an early phase of deformation. Component B (16 sites) was acquired during the peak of the Variscan tectonics (late Westphalian), while component C (five sites) originated during Permian times. Regardless of the palaeolatitudes, declinations fall between 190 and 210°, thus being conformable with the declinations expected for Variscan Europe. The declinations show no correlation with the arcuate shape of the belt, neither are they different in the Paraauthochthon and in the Allochthon, nor in the different components. Arc formation by moulding of the Allochthon on the Brabant Parautochthon is, therefore, not supported by these data, since this mechanism requires substantial (opposed) rotations on both wings of the arc. The available palaeomagnetic data are conformable with a pre-formed arc

  17. Filamentous microbial fossil from low-grade metamorphosed basalt in northern Chichibu belt, central Shikoku, Japan

    NASA Astrophysics Data System (ADS)

    Sakakibara, M.; Sugawara, H.; Tsuji, T.; Ikehara, M.

    2014-05-01

    The past two decades have seen the reporting of microbial fossils within ancient oceanic basalts that could be identical to microbes within modern basalts. Here, we present new petrographic, mineralogical, and stable isotopic data for metabasalts containing filamentous structures in a Jurassic accretionary complex within the northern Chichibu Belt of the Yanadani area of central Shikoku, Japan. Mineralized filaments within these rocks are present in interstitial domains filled with calcite, pumpellyite, or quartz, and consist of iron oxide, phengite, and pumpellyite. δ13CPDB values for filament-bearing calcite within these metabasalts vary from -2.49‰ to 0.67‰. A biogenic origin for these filamentous structures is indicated by (1) the geological context of the Yanadani metabasalt, (2) the morphology of the filaments, (3) the carbon isotope composition of carbonates that host the filaments, and (4) the timing of formation of these filaments relative to the timing of low-grade metamorphism in a subduction zone. The putative microorganisms that formed these filaments thrived between eruption (Late Paleozoic) and accretion (Early Jurassic) of the basalt. The data presented here indicate that cryptoendolithic life was present within water-filled vesicles in pre-Jurassic intraplate basalts. The mineralogy of the filaments reflects the low-grade metamorphic recrystallization of authigenic microbial clays similar to those formed by the encrustation of prokaryotes in modern iron-rich environments. These findings suggest that a previously unusual niche for life is present within intraplate volcanic rocks in accretionary complexes.

  18. Previously unrecognized regional structure of the Coastal Belt of the Franciscan Complex, northern California, revealed by magnetic data

    USGS Publications Warehouse

    Langenheim, V.E.; Jachens, R.C.; Wentworth, C.M.; McLaughlin, R.J.

    2013-01-01

    Magnetic anomalies provide surprising structural detail within the previously undivided Coastal Belt, the westernmost, youngest, and least-metamorphosed part of the Franciscan Complex of northern California. Although the Coastal Belt consists almost entirely of arkosic graywacke and shale of mainly Eocene age, new detailed aeromagnetic data show that it is pervasively marked by long, narrow, and regularly spaced anomalies. These anomalies arise from relatively simple tabular bodies composed principally of magnetic basalt or graywacke confined mainly to the top couple of kilometers, even though metamorphic grade indicates that these rocks have been more deeply buried, at depths of 5–8 km. If true, this implies surprisingly uniform uplift of these rocks. The basalt (and associated Cretaceous limestone) occurs largely in the northern part of the Coastal Belt; the graywacke is recognized only in the southern Coastal Belt and is magnetic because it contains andesitic grains. The magnetic grains were not derived from the basalt, and thus require a separate source. The anomalies define simple patterns that can be related to folding and faulting within the Coastal Belt. This apparent simplicity belies complex structure mapped at outcrop scale, which can be explained if the relatively simple tabular bodies are internally deformed, fault-bounded slabs. One mechanism that can explain the widespread lateral extent of the thin layers of basalt is peeling up of the uppermost part of the oceanic crust into the accretionary prism, controlled by porosity and permeability contrasts caused by alteration in the upper part of the subducting slab. It is not clear, however, how this mechanism might generate fault-bounded layers containing magnetic graywacke. We propose that structural domains defined by anomaly trend, wavelength, and source reflect imbrication and folding during the accretion process and local plate interactions as the Mendocino triple junction migrated north, a

  19. Previously unrecognized regional structure of the Coastal Belt of the Franciscan Complex, northern California, revealed by magnetic data

    USGS Publications Warehouse

    Langenheim, Victoria; Jachens, Robert C.; Wentworth, Carl M.; McLaughlin, Robert J.

    2013-01-01

    Magnetic anomalies provide surprising structural detail within the previously undivided Coastal Belt, the westernmost, youngest, and least-metamorphosed part of the Franciscan Complex of northern California. Although the Coastal Belt consists almost entirely of arkosic graywacke and shale of mainly Eocene age, new detailed aeromagnetic data show that it is pervasively marked by long, narrow, and regularly spaced anomalies. These anomalies arise from relatively simple tabular bodies composed principally of magnetic basalt or graywacke confi ned mainly to the top couple of kilometers, even though metamorphic grade indicates that these rocks have been more deeply buried, at depths of 5–8 km. If true, this implies surprisingly uniform uplift of these rocks. The basalt (and associated Cretaceous limestone) occurs largely in the northern part of the Coastal Belt; the graywacke is recognized only in the southern Coastal Belt and is magnetic because it contains andesitic grains. The magnetic grains were not derived from the basalt, and thus require a separate source. The anomalies defi ne simple patterns that can be related to folding and faulting within the Coastal Belt. This apparent simplicity belies complex structure mapped at outcrop scale, which can be explained if the relatively simple tabular bodies are internally deformed, fault-bounded slabs. One mechanism that can explain the widespread lateral extent of the thin layers of basalt is peeling up of the uppermost part of the oceanic crust into the accretionary prism, controlled by porosity and permeability contrasts caused by alteration in the upper part of the subducting slab. It is not clear, however, how this mechanism might generate fault-bounded layers containing magnetic graywacke. We propose that structural domains defined by anomaly trend, wavelength, and source reflect imbrication and folding during the accretion process and local plate interactions as the Mendocino triple junction migrated north, a

  20. Preliminary bedrock geologic map of part of the northern disturbed belt, Lewis and Clark, Teton, Pondera, Glacier, Flathead, and Powell Counties, Montana

    USGS Publications Warehouse

    Mudge, Melville R.; Earhart, Robert L.; Rice, Dudley D.; Heisey, E.L.

    1977-01-01

    The geologic map covers the Sawtooth and Lewis and Clark Ranges and part of the Flathead Range. It includes most of the disturbed belt in northwestern Moutana except the area east of the northern Rocky Mountains and the norhtern and southern parts of the belt. Most data are from an unpublished map of the Bob Marshall Wilderness and of the many proposed additions to the Wilderness. Strike and dip symbols are omitted from the map, and all contacts are shown in solid lines, alhough locally they are inferred beneath a Quaternary cover. Future studies will complete mapping of the northern disturbed belt in Montana.

  1. Do mitigation strategies reduce global warming potential in the northern U.S. corn belt?

    PubMed

    Johnson, Jane M-F; Archer, David W; Weyers, Sharon L; Barbour, Nancy W

    2011-01-01

    Agricultural management practices that enhance C sequestration, reduce greenhouse gas emission (nitrous oxide [N₂O], methane [CH₄], and carbon dioxide [CO₂]), and promote productivity are needed to mitigate global warming without sacrificing food production. The objectives of the study were to compare productivity, greenhouse gas emission, and change in soil C over time and to assess whether global warming potential and global warming potential per unit biomass produced were reduced through combined mitigation strategies when implemented in the northern U.S. Corn Belt. The systems compared were (i) business as usual (BAU); (ii) maximum C sequestration (MAXC); and (iii) optimum greenhouse gas benefit (OGGB). Biomass production, greenhouse gas flux change in total and organic soil C, and global warming potential were compared among the three systems. Soil organic C accumulated only in the surface 0 to 5 cm. Three-year average emission of N₂O and CH was similar among all management systems. When integrated from planting to planting, N₂O emission was similar for MAXC and OGGB systems, although only MAXC was fertilized. Overall, the three systems had similar global warming potential based on 4-yr changes in soil organic C, but average rotation biomass was less in the OGGB systems. Global warming potential per dry crop yield was the least for the MAXC system and the most for OGGB system. This suggests management practices designed to reduce global warming potential can be achieved without a loss of productivity. For example, MAXC systems over time may provide sufficient soil C sequestration to offset associated greenhouse gas emission.

  2. The Circum-Rhodope Belt, northern Greece: Age, provenance, and tectonic setting

    NASA Astrophysics Data System (ADS)

    Meinhold, Guido; Kostopoulos, Dimitrios K.

    2013-06-01

    The Circum-Rhodope Belt (CRB) sensu stricto comprises low-grade metamorphosed Triassic and Jurassic sedimentary rocks fringing the high-grade metamorphic rocks of the Serbo-Macedonian and Rhodope massifs in northern Greece. Main outcrops occur in the easternmost part of the Vardar suture zone in the Chalkidiki peninsula (Melissochori Formation; formerly Svoula flysch) and in Thrace (Makri unit and Melia Formation). The tectonostratigraphic relationship between the CRB and the high-grade metamorphics has been the subject of long discussions. Older interpretations maintain that the CRB represents the original Mesozoic stratigraphic cover of the Serbo-Macedonian crystalline basement, whereas later revisions propose the existence of two distinct greenschist-facies Mesozoic metasedimentary units: an eastern unit related to the development of a Jurassic black shale basin north of the Rhodope, and a western unit related to the development of an olistostromic flysch in the Cretaceous. Here we present a critical re-evaluation of the CRB with regard to its age, provenance, and tectonic setting based on novel geochemical and isotopic data. The Makri unit and the Melissochori Formation belong to the CRB proper and were deposited in proximity to Carboniferous-Early Permian igneous basement rocks (Pelagonia / Strandja / Thracia Terrane) in latest Triassic and Jurassic times, as shown by a prominent detrital zircon age population of 350-290 Ma. By contrast, the Melia Formation is unrelated to the CRB and was deposited in a foreland basin in front of a metamorphic nappe pile with Rhodopean affinities in the early Cretaceous, as shown by a prominent detrital zircon age population of 315-285 Ma and xenocrysts of ~ 550 Ma and ~ 450 Ma. Thus, the commonly accepted CRB concepts have to be revisited. All units have been tectonically juxtaposed to their present location during Balkan and Alpine orogenic processes.

  3. U-Th-Pb isotope chronology of sulfide ores and rocks in the early Proterozoic metavolcanic belt of northern Wisconsin.

    USGS Publications Warehouse

    Afifi, A.; Doe, B.R.; Sims, P.K.; Delevaux, M.H.

    1984-01-01

    Lead from galena of massive sulphide deposits in the metavolcanic belt of northern Wisconsin was probably derived from 3700 m.y. old source material 1800-1900 m.y. ago. Approximately 3500 m.y. old rocks occur within 100-300 km to the north and west. The U-Th-Pb systems of the metavolcanic and granitic rocks in the belt were reset about 1600 m.y. ago during retrogressive metamorphism. The ages from lead isotope data are in accord with Rb/Sr whole-rock, Rb/Sr and K/Ar mineral, and U-Th-Pb zircon dating. A concordia plot of whole-rock lead data shows that many of the rocks lost lead 200-400 m.y. ago during uplift and erosion. Meta-volcanic rocks near Crandon, Wisconsin, had lead isotope compositions 20 m.y. ago that match those in the Pb-Zn ores in Palaeozoic rocks of the upper Mississippi valley. Possibly the volcanic rocks were a source of lead for the Pb-Zn ores. Similar ores might therefore occur between the northern Wisconsin metavolcanic belt and the upper Mississippi valley.-G.J.N.

  4. Spatial and temporal relations between coronae and extensional belts, northern Lada Terra, Venus

    NASA Technical Reports Server (NTRS)

    Baer, Gidon; Schubert, Gerald; Bindschadler, Duane L.; Stofan, Ellen R.

    1994-01-01

    Preliminary studies of the distribution of coronae and volcanic rises on Venus show that many of these features tend to cluster along zones of rifting and extension. The plains north of Lada Terra are crossed by two such extensional belts. Each belt is composed of grabens, ridges, faults, volcanic flows, coronae and coronalike features. The longer and more prominent belt is the NW trending Alpha-Lada extensional belt, which is over 6000 km long and 50-200 km wide, and includes the coronae Eve, Tamfana, Carpo, Selu, Derceto, Otygen, and an unnamed corona south of Otygen. The second belt is the NNE trending Derceto-Quetzalpetlatl extensional belt, which is about 2000 km long and in places over 300 km wide, and includes the coronae Sarpanitum, Eithinoha, and Quetzalpetlatl. The two belts intersect at the 1600 x 600 km wide Derceto volcanic plateau. It is apparent that deformation along the two belts overlapped in time, though deformation along the Alpha-Lada extensional belt probably continued after the deformation along the Derceto-Quetzalpetlatl extensional belt terminated. In certain areas, volcanism originated in grabens within the extensional belts, whereas in other areas, such as in Eve, Selu, Derceto, and Quetzalpetlatl, volcanism originated in the coronae and flowed into the lower parts of the extensional belts. Regional extension has affected the evolution of all the coronae at some stage of their development. Regional deformation occurred before the initiation of Derceto and Eithinoha of their development. Regional deformation occurred before the initiation of Derceto and Eithinoha and after the initiation of Carpo, Tamfana, Otygen, and Sarpanitum. It is thus unlikely that coronae formation along the belts is solely a consequence of the regional extension, and it is also unlikely that regional extension has been caused solely by the coronae. No corona along the belts was formed subsequent to the cessation of the regional extension. We therefore suggest that

  5. Spatial and temporal relations between coronae and extensional belts, northern Lada Terra, Venus

    NASA Astrophysics Data System (ADS)

    Baer, G.; Schubert, G.; Bindschadler, D. L.; Stofan, E. R.

    1994-04-01

    Preliminary studies of the distribution of coronae and volcanic rises on Venus show that many of these features tend to cluster along zones of rifting and extension. The plains north of Lada Terra are crossed by two such extensional belts. Each belt is composed of grabens, ridges, faults, volcanic flows, coronae and coronalike features. The longer and more prominent belt is the NW trending Alpha-Lada extensional belt, which is over 6000 km long and 50-200 km wide, and includes the coronae Eve, Tamfana, Carpo, Selu, Derceto, Otygen, and an unnamed corona south of Otygen. The second belt is the NNE trending Derceto-Quetzalpetlatl extensional belt, which is about 2000 km long and in places over 300 km wide, and includes the coronae Sarpanitum, Eithinoha, and Quetzalpetlatl. The two belts intersect at the 1600 x 600 km wide Derceto volcanic plateau. It is apparent that deformation along the two belts overlapped in time, though deformation along the Alpha-Lada extensional belt probably continued after the deformation along the Derceto-Quetzalpetlatl extensional belt terminated. In certain areas, volcanism originated in grabens within the extensional belts, whereas in other areas, such as in Eve, Selu, Derceto, and Quetzalpetlatl, volcanism originated in the coronae and flowed into the lower parts of the extensional belts. Regional extension has affected the evolution of all the coronae at some stage of their development. Regional deformation occurred before the initiation of Derceto and Eithinoha of their development. Regional deformation occurred before the initiation of Derceto and Eithinoha and after the initiation of Carpo, Tamfana, Otygen, and Sarpanitum. It is thus unlikely that coronae formation along the belts is solely a consequence of the regional extension, and it is also unlikely that regional extension has been caused solely by the coronae. No corona along the belts was formed subsequent to the cessation of the regional extension. We therefore suggest that

  6. Tectonic evolution of greenstone-Gneiss association in Dharwar Craton, South India: Problems and perspectives for future research

    NASA Technical Reports Server (NTRS)

    Rao, Y. J. B.

    1986-01-01

    The two fold stratigraphic subdivision of the Archean-Proterozoic greenstone-gneiss association of Dharwar craton into an older Sargur group (older than 2.9 Ga.) and a younger Dharwar Supergroup serves as an a priori stratigraphic model. The concordant greenstone (schist)-gneiss (Peninsular gneiss) relationships, ambiguities in stratigraphic correlations of the schist belts assigned to Sargur group and difficulties in deciphering the older gneiss units can be best appreciated if the Sargur group be regarded as a trimodal association of: (1) ultrabasic-mafic metavolcanics (including komatiites), (2) clastic and nonclastic metasediments and paragneisses and (3) mainly tonalite/trondhemite gneisses and migmatites of diverse ages which could be as old as c. 3.4 ga. or even older. The extensive occurrence of this greenstone-gneiss complex is evident from recent mapping in many areas of central and southern Karnataka State.

  7. Ultra-high temperature granulite-facies metamorphic rocks from the Mozambique belt of SW Tanzania

    NASA Astrophysics Data System (ADS)

    Sommer, H.; Kröner, A.

    2013-06-01

    The metamorphic rocks in the Neoproterozoic (Pan-African) Mozambique belt of southwestern Tanzania, around the town of Songea, can be subdivided into one- and two pyroxene bearing charnockitic gneisses, migmatitic granitoid gneisses and amphibolite-facies metapelites. Lower-grade amphibolite-facies rocks are rare and can be classified as sillimanite- and/or garnet-bearing metapelites. Most of the studied charnockitic gneisses show excellent corona textures with large orthopyroxene grains rimmed by clinopyroxene, followed by quartz and well developed garnet rims due to the reaction Opx + Pl = Grt + Cpx + Qtz that formed during isobaric cooling. These and other charnockitic gneisses show symplectites of orthopyroxene and An-rich plagioclase that resulted from the breakdown of garnet during isothermal decompression due to the reaction Grt + Cpx + Qtz = Opx + Pl. Geothermobarometric calculations yield up to ~ 1050 °C and up to ~ 12 kbar for peak metamorphic conditions. These are higher temperature and slightly lower pressure conditions than reported for other granulite-facies terrains in the Mozambique belt of Tanzania. Single zircon Pb-Pb evaporation and U-Pb SHRIMP ages for magmatic zircons extracted from two charnockitic and two granitic gneisses cluster in two groups, one at ~ 750 Ma and one at ~ 1150 Ma with the older reflecting the time of emplacement of the igneous precursors, and the younger approximating the time of charnockitization. These protolith ages are similar to those farther east in the Masasi area of southern Tanzania, as well as in northern Mozambique and in southern Malawi, and suggest that the Mozambique belt consists of chronologically heterogeneous assemblages whose pre-metamorphic tectonic setting remains obscure.

  8. Zooming in the kinematic of a curved belt from large- to small-scale: Examples from the Northern Apennines (Italy)

    NASA Astrophysics Data System (ADS)

    Satolli, S.; Turtù, A.

    2013-12-01

    The Apennine-Maghrebide belt is characterized by a first-order curved shape showing the Calabrian units in the apical zone and the Tyrrhenian extensional basin in the inner area. It is further divided into two second-order arcs: the Northern Apennines arc and the Southern Apennines-Calabrian arc, with NE and SE convexity, respectively. These two arcs are characterized by differences in paleogeographic domains, stratigraphic successions, structural settings and geodynamics. The Apennines experienced widespread vertical axes rotations during the orogenesis: paleomagnetic data from back-arc extensional basins along the Tyrrhenian margin show no rotation; conversely, data collected in Mesozoic and Miocene-Lower Pliocene sediments show rotations of varying magnitude and sign. After almost 40 years of paleomagnetic studies, the kinematic of the regional-scale curved belts has been unraveled. Notwithstanding, the Apennines are also characterized by several minor structures, whose kinematic can be understood only throught detailed paleomagnetic study. Here, we report some examples from: 1. the Northern Apennines fold-and-thrust belt; 2. a minor salient in the Central Apennines (i.e., the Gran Sasso range); 3. a crustal strike-slip faults which separate the northern and the central Apennines (as, the Olevano-Antrodoco line); 4. along-strike variations of the thrust architecture at small scale (in the Northern Apennines). 1. The outer Northern Apennines fold-and-thrust belt has been interpreted in the literature either as an orocline, a primary or a progressive arc, with a thin- or thick-skinned tectonic style. Paleomagnetic and structural data indicate that the Northern Apennines are a progressive arc whose development was influenced by inversion tectonics, involving the reactivation of pre-thrusting normal faults. 2. The detailed paleomagnetic study of the Gran Sasso arc documents how rotations change along the limbs of a kilometric-scale indenter-controlled range salient

  9. The Blaník Gneiss in the southern Bohemian Massif (Czech Republic): a rare rock composition among the early palaeozoic granites of Variscan Central Europe

    NASA Astrophysics Data System (ADS)

    René, Miloš; Finger, Fritz

    2016-08-01

    Metamorphosed and deformed tourmaline-bearing leucogranites with a Cambro-Ordovician formation age are widespread in the Monotonous Group of the Variscan southern Bohemian Massif, Czech Republic. The rocks, known locally as Blaník gneiss, are strongly peraluminous and classify as phosphorus-rich low-T, S-type granite. The magma formed from a metapelitic source, most likely through muscovite dehydration melting. With respect to its low-T origin and the abundance of tourmaline, the Blaník gneiss is exotic within the spectrum of Early Palaeozoic granites of the Variscan fold belt of Central Europe. Coeval granitic gneisses in the neighbouring Gföhl unit of the Bohemian Massif can be classified as higher T S-type granites and were probably generated through biotite dehydration melting. The geochemical differences between the Early Palaeozoic granitic magmatism in the Gföhl unit and the Monotonous Group support models claiming that these two geological units belonged to independent peri-Gondwana terranes before the Variscan collision. It is suggested here, that the Gföhl unit and the Monotonous Group represent zones of higher and lower heat flow within the Early Palaeozoic northern Gondwana margin, respectively. The geochemical data presented in this study could be helpful for terrane correlations and palaeogeographic reconstructions.

  10. Porphyry molybdenum deposits in the Tianshan-Xingmeng orogenic belt, northern China

    NASA Astrophysics Data System (ADS)

    Zeng, Qingdong; Qin, Kezhang; Liu, Jianming; Li, Guangming; Zhai, Mingguo; Chu, Shaoxiong; Guo, Yunpeng

    2015-06-01

    Molybdenum (Mo) exploration activity in China has increased tremendously over the past decade, and China is now known to have the largest Mo reserves in the world. The Tianshan-Xingmeng orogenic belt, the second largest Mo metallogenic belt, possesses over 8.2 Mt of Mo reserves. Porphyry Mo deposits contain 99 % of the Mo reserves in the Tianshan-Xingmeng orogenic belt; other Mo deposits contain 1 % of the Mo reserves. Five subtypes of the porphyry Mo deposits can be distinguished by deposit associations, such as Mo, Mo-Cu, Mo-W, Mo-Pb-Zn-Ag, and Cu-Mo deposits. These porphyry Mo deposits are formed at different stages: during the Ordovician, Devonian, Carboniferous, Late Permian, Triassic, Jurassic, and Cretaceous Periods. The polystage porphyry Mo mineralizations indicate that polystage tectonic-magmatic activity occurred in the orogenic belt. The Ordovician-Carboniferous porphyry Cu-Mo deposits are formed in an island-arc setting; the Late Permian porphyry Mo deposits are formed in a syn-collisional tectonic setting; and the Triassic porphyry Mo deposits are formed in a syn-collisional to post-collisional tectonic setting. The Ordovician-Triassic porphyry deposits are related to the Paleo-Asian Ocean tectonic system. The Jurassic porphyry Mo deposits are formed at the eastern margin of the Asian continent and are associated with a Paleo-Pacific plate-subduction tectonic setting. Cretaceous porphyry Mo deposits are formed in a lithospheric thinning setting and are related to the rollback of the Paleo-Pacific subduction plate.

  11. Growth of the Zagros Fold-Thrust Belt and Foreland Basin, Northern Iraq, Kurdistan

    NASA Astrophysics Data System (ADS)

    Koshnaw, Renas; Horton, Brian; Stockli, Daniel; Barber, Douglas; Ghalib, Hafidh; Dara, Rebwar

    2016-04-01

    The Zagros orogenic belt in the Middle Eastern segment of the Alpine-Himalayan system is among the youngest seismically active continental collision zones on Earth. However, due to diachronous and incremental collision, the precise ages and kinematics of shortening and deposition remain poorly understood. The Kurdistan region of the Zagros fold-thrust belt and foreland basin contains well-preserved Neogene wedge-top and foredeep deposits that include clastic nonmarine fill of the Upper Fars, Lower Bakhtiari, and Upper Bakhtiari Formations. These deposits record significant information about orogenic growth, fold-thrust dynamics, and advance of the deformation front. Thermochronologic and geochronologic data from thrust sheets and stratigraphic archives combined with local earthquake data provide a unique opportunity to address the linkages between surface and subsurface geologic relationships. This research seeks to constrain the timing and geometry of exhumation and deformation by addressing two key questions: (1) Did the northwestern Zagros fold-thrust belt evolve from initial thin-skinned shortening to later thick-skinned deformation or vice-versa? (2) Did the fold-thrust belt advance steadily under critical/supercritical wedge conditions involving in-sequence thrusting or propagate intermittently under subcritical conditions with out-of-sequence deformation? From north to south, apatite (U-Th)/He ages from the Main Zagros Thrust, the Mountain Front Flexure (MFF), and additional frontal thrusts suggest rapid exhumation by ~10 Ma, ~5 Ma, and ~8 Ma respectively. Field observations and seismic sections indicate progressive tilting and development of growth strata within the Lower Bakhtiari Formation adjacent to the frontal thrusts and within the Upper Bakhtiari Formation near the MFF. In the Kurdistan region of Iraq, a regional balanced cross section constrained by new thermochronometric results, proprietary seismic reflection profiles, and earthquake hypocenters

  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.

    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.

  13. Bouguer gravity trends and crustal structure of the Palmyride Mountain belt and surrounding northern Arabian platform in Syria

    SciTech Connect

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

    1990-12-01

    This study examines the crustal structure of the Palmyrides and the northern Arabian platform in Syria by two- and three-dimensional modeling of the Bouguer gravity anomalies. Results of the gravity modeling indicate that (1) western Syria is composed of at least two different crustal blocks, (2) the southern crustal block is penetrated by a series of crustal-scale, high-density intrusive complexes, and (3) short-wavelength gravity anomalies in the southwest part of the mountain belt are clearly related to basement structure. The crustal thickness in Syria, as modeled on the gravity profiles, is approximately 40{plus minus}4 km, which is similar to crustal thicknesses interpreted from refraction data in Jordan and Saudi Arabia. The different crustal blocks and large-scale mafic intrusions are best explained, though not uniquely, by Proterozoic convergence and suturing and early Paleozoic rifting, as interpreted in the exposed rocks of the Arabian shield. These two processes, combined with documented Mesozoic rifting and Cenozoic transpression, compose the crustal evolution of the northern Arabian platform beneath Syria.

  14. Northward extension of Carolina slate belt stratigraphy and structure, South-Central Virginia: Results from geologic mapping

    USGS Publications Warehouse

    Hackley, P.C.; Peper, J.D.; Burton, W.C.; Horton, J.W.

    2007-01-01

    Geologic mapping in south-central Virginia demonstrates that the stratigraphy and structure of the Carolina slate belt extend northward across a steep thermal gradient into upper amphibolite-facies correlative gneiss and schist. The Neoproterozoic greenschist-facies Hyco, Aaron, and Virgilina Formations were traced northward from their type localities near Virgilina, Virginia, along a simple, upright, northeast-trending isoclinal syncline. This syncline is called the Dryburg syncline and is a northern extension of the more complex Virgilina synclinorium. Progressively higher-grade equivalents of the Hyco and Aaron Formations were mapped northward along the axial trace of the refolded and westwardly-overturned Dryburg syncline through the Keysville and Green Bay 7.5-minute quadrangles, and across the northern end of the Carolina slate belt as interpreted on previous geologic maps. Hyco rocks, including felsic metatuff, metawacke, and amphibolite, become gneisses upgrade with areas of local anatexis and the segregation of granitic melt into leucosomes with biotite selvages. Phyllite of the Aaron Formation becomes garnet-bearing mica schist. Aaron Formation rocks disconformably overlie the primarily felsic volcanic and volcaniclastic rocks of the Hyco Formation as evidenced by repeated truncation of internal contacts within the Hyco on both limbs of the Dryburg syncline at the Aaron-Hyco contact. East-northeast-trending isograds, defined successively by the first appearance of garnet, then kyanite ?? staurolite in sufficiently aluminous rocks, are superposed on the stratigraphic units and synclinal structure at moderate to high angles to strike. The textural distinction between gneisses and identifiable sedimentary structures occurs near the kyanite ?? staurolite-in isograd. Development of the steep thermal gradient and regional penetrative fabric is interpreted to result from emplacement of the Goochland terrane adjacent to the northern end of the slate belt during

  15. Comparison of the tectonics and geophysics of the major structural belts between the northern and southern continental margins of the South China Sea

    NASA Astrophysics Data System (ADS)

    Xia, Kan-yuan; Huang, Ci-liu; Jiang, Shao-ren; Zhang, Yi-xiang; Su, Da-quan; Xia, Si-gao; Chen, Zhong-rong

    1994-07-01

    A comparison of the tectonics and geophysics of the major structural belts of the northern and the southern continental margins of South China Sea has been made, on the basis of measured geophysical data obtained by ourselves over a period of 8 years (1984-1991). This confirmed that the northern margin is a divergent one and the southern margin is characterized by clearly convergent features. The main extensional structures of the northern margin are, from north to south: (1) The Littoral Fault Belt, a tectonic boundary between the continental crust and a transitional zone, along the coast of the provinces of Guangdong and Fujian in South China. It is characterised by earthquake activities, high magnetic anomalies and a rapid change in crustal thickness. (2) The Northern and Southern Depression zones (i.e., the Pearl River Mouth Basin), this strikes NE-ENE and is a very large Cenozoic depression which extends from offshore Shantou westwards to Hainan Island. (3) The Central Uplift Zone. This includes the Dongsha Uplift, Shenhu Uplift and may be linked with the Penghu uplift and Taiwan shoals to the east, forming a large NE-striking uplift zone along the northern continental slope. It is characterized by high magnetic anomalies. (4) Southern Boundary Fault Belt of the transitional crust. This has positive gravity anomalies on the land side and negative ones on the sea side. (5) The Magnetic Quiet Zone. This is located south of the southern Boundary Fault Belt and between the continental margin and the Central Basin of the South China Sea. Magnetic anomalies in this belt are of small amplitude and low gradient. We consider the Magnetic Quiet Zone to be a very important tectonic zone. The major structures of southern continental margin southwards are: (1) The Northern Fault Belt of the Nansha Block. This extends along the continental slope north of the Liyue shoal (Reed Bank) and Zhongye reef, and is a tectonic boundary between oceanic crust and the Nansha Block

  16. The geochemical nature of the Archean Ancient Gneiss Complex and Granodiorite Suite, Swaziland: a preliminary study

    USGS Publications Warehouse

    Hunter, D.R.; Barker, F.; Millard, H.T., Jr.

    1978-01-01

    The Ancient Gneiss Complex (AGC) of Swaziland, an Archean gray gneiss complex, lies southeast and south of the Barberton greenstone belt and includes the most structurally complex and highly metamorphosed portions of the eastern Kaapvaal craton. The AGC is not precisely dated but apparently is older than 3.4 Ga. The AGC consists of three major units: (a) a bimodal suite of closely interlayered siliceous, low-K gneisses and metabasalt; (b) homogeneous tonalite gneiss; and (c) interlayered siliceous microcline gneiss, metabasalt, and minor metasedimentary rocks - termed the metamorphite suite. A geologically younger gabbro-diorite-tonalite-trondhjemite suite, the Granodiorite Suite, is spatially associated with the AGC and intrusive into it. The bimodal suite consists largely of two types of low-K siliceous gneiss: one has SiO2 14%, low Rb/Sr ratios, and depleted heavy rare earth elements (REE's); the other has SiO2 > 75%, Al2O3 < 13%, high Rb/Sr ratios, and relatively abundant REE's except for negative Eu anomalies. The interlayered metabasalt ranges from komatiitic to tholeiitic compositions. Lenses of quartz monzonitic gneiss of K2O/Na2O close to 1 form a minor part of the bimodal suite. Tonalitic to trondhjemitic migmatite locally is abundant and has major-element abundances similar to those of non-migmatitic varieties. The siliceous gneisses of the metamorphic suite show low Al2O, K2O/Na2O ratios of about 1, high Rb/Sr ratios, moderate REE abundances and negative Eu anomalies. K/Rb ratios of siliceous gneisses of the bimodal suite are very low (???130); of the tonalitic gneiss, low (???225); of the siliceous gneiss of the metamorphite suite, moderate (???300); and of the Granodiorite Suite, high (???400). Rocks of the AGC differ geochemically in several ways from the siliceous volcanic and hypabyssal rocks of the Upper Onverwacht Group and from the diapirs of tonalite and trondhjemite that intrude the Swaziland Group. ?? 1978.

  17. Anorogenic nature of magmatism in the Northern Baikal volcanic belt: Evidence from geochemical, geochronological (U-Pb), and isotopic (Pb, Nd) data

    USGS Publications Warehouse

    Neymark, L.A.; Larin, A.M.; Nemchin, A.A.; Ovchinnikova, G.V.; Rytsk, E. Yu

    1998-01-01

    The Northern Baikal volcanic belt has an age of 1.82-1.87 Ga and extends along the boundary between the Siberian Platform and the Baikal foldbelt. The volcanic belt is composed of volcanics of the Akitkan Group and granitic rocks of the Irel and Primorsk complexes. The geochemistry of the rocks points to the intraplate anorogenic nature of the belt. U-Pb zircon dating of the Chuya granitoids revealed that they are older (2020-2060 Ma) than the Northern Baikal volcanic belt and, thus, cannot be regarded as its component. Data on the Pb isotopic system of feldspars from the granitoids confirm the contemporaneity of all volcanic rocks of the belt except the volcanics of the upper portion of the Akitkan Group (Chaya Formation). Our data suggest its possibly younger (???1.3 Ga) age. The isotopic Nd and Pb compositions of the acid volcanic rocks provide evidence of the heterogeneity of their crustal protoliths. The volcanics of the Malaya Kosa Formation have ??Nd(T) = -6.1, ??2 = 9.36, and were most probably produced with the participation of the U-depleted lower continental crust of Archean age. Other rocks of the complex show ??Nd(T) from -0.1 to -2.4, ??2 = 9.78, and could have been formed by the recycling of the juvenile crust. The depletion of the Malaya Kosa volcanics in most LILEs and HFSEs compared with other acid igneous rocks of the belt possibly reflects compositional differences between the Late Archean and Early Proterozoic crustal sources. The basaltic rocks of the Malaya Kosa Formation (??Nd varies from -4.6 to -5.4) were produced by either the melting of the enriched lithospheric mantle or the contamination of derivatives of the depleted mantle by Early Archean lower crustal rocks, which are not exposed within the area. Copyright ?? 1998 by MAEe Cyrillic signK Hay??a/Interperiodica Publishing.

  18. Chloritites of the Tocantins Group, Araguaia fold belt, central-northern Brazil: Vestiges of basaltic magmatism and metallogenetic implications

    NASA Astrophysics Data System (ADS)

    Kotschoubey, Basile; Villas, Raimundo Netuno; Aires, Benevides

    2016-08-01

    Chloritites from different localities (Arapoema, Couto Magalhães Velho, Juarina, Morro Grande, Morro do Jabuti, Morro do Pau Ferrado, Morro do Salto, Serra do Jacu, Serra do Quatipuru, Serra do Tapa, Serrinha) of the Araguaia fold belt, Tocantins geotectonic province, central-northern Brazil, have been investigated. Based on field work and petrographic, diffractometric, geochemical and mineral chemistry data, these rocks, commonly associated with metacherts and banded iron formations, have been interpreted as products of ocean-floor exhalative-hydrothermal activity on MORB basalts. Distribution patterns of rare earth elements and diagrams of relatively immobile components in the hydrothermal environment highlight not only the genetic link between the chloritites and the basaltic rocks that occur in the region (Serra do Tapa and Morro do Agostinho), but also some peculiar characteristics of the submarine environment. The rock association and anomalous contents of Cu, Zn, Ni, As, and Au are suggestive that the region was favorable to the formation of volcanogenic massive sulfide deposits, what makes it a potential target for mineral exploration programs.

  19. Enhanced detection of gossans using hyperspectral data: Example from the Cape Smith Belt of northern Quebec, Canada

    NASA Astrophysics Data System (ADS)

    Laakso, K.; Rivard, B.; Rogge, D.

    2016-04-01

    Owing to the links between gossans and mineral deposits, detecting gossans by remote sensing means is essential for mineral exploration. In northern regions, gossans can develop as thin oxidized surfaces, named thin gossans, that can be covered with lichens. This study investigates the effects of spectral mixing between such gossans with lichens and their rock substrates using laboratory spectroscopic data obtained from samples collected in the Cape Smith Belt of Canada. These observations are then scaled up to the airborne hyperspectral data obtained from the same area. Our laboratory results indicate that the presence of lichens on gossans induces a general spectral shift towards shorter wavelengths of the iron absorption typical of gossan spectra. The opposite shift is observed due to the influence of the rock substrates. These effects can thus impede classification of gossans based on the interpretation of iron oxide mineralogy from spectra. Our airborne spectral results suggest that thin gossans can be detected and discriminated from thick gossans, and further broken down into several classes according to their host rock substrates. The ability to define distinct classes of thin gossans is significant since the association of these gossans with specific rock substrates can be exploited for exploration. The ability to distinguish thin and thick gossans alone can contribute to mineral exploration since it can be either the former or the latter group of gossans that acts as an ore deposit vector.

  20. Overview of radiometric ages in three allochthonous belts of Northern Venezuela: Old ones, new ones, and their impact on regional geology

    USGS Publications Warehouse

    Sisson, V.B.; Ave Lallemant, H.G.; Ostos, M.; Blythe, A.E.; Snee, L.W.; Copeland, Peter; Wright, J.E.; Donelick, R.A.; Guth, L.R.

    2005-01-01

    The margin of northern Venezuela is a complex zone representing the orogenic events from basement formation to subsequent subduction and exhumation during transpressional collision. This boundary zone has six east-west-trending belts that each record a different segment of its development. This geologic complexity requires radiometric ages to unravel, and we herein provide 48 new ages including U-Pb (4), Rb-Sr (2), 40Ar/39Ar (24), zircon and apatite fission-track (17), and 14C (1) ages to constrain the evolution of three of these belts. These three belts are the Cordillera de la Costa, Caucagua-El Tinaco, and Serran??a del Interior belts. In the Cordillera de la Costa belt, U-Pb geochronologic data indicate portions of the basement igneous and metaigneous rocks formed in the Cambro-Ordovician (513-471 Ma). New 40Ar/39Ar data from Margarita Island indicate that some of the subduction complex was rapidly cooled and exhumed, whereas other portions indicate slower cooling. This contrasts with new 40Ar/39Ar data from the Puerto Cabello. ?? 2005 Geological Society of America.

  1. Micas in experimentally shocked gneiss

    NASA Technical Reports Server (NTRS)

    Lambert, P.; Mackinnon, I. D. R.

    1984-01-01

    Powder-propellant guns are used to shock biotites and muscovites from a gneiss at pressures between 18 and 70 GPa. It is shown that shock in biotite and muscovite can produce homogeneous and devolatilized glasses within microseconds. Shock-deformed micas are found to exhibit fracturing, kinking, and complex extinction patterns over the entire pressure range investigated. Localized melting of micas commences at 33 GPa and reaches completion at 70 GPa. Even though melted biotite and muscovite are opaque optically, they exhibit extensive microvesiculation and flow when observed with the SEM. It is confirmed through electron diffraction that biotite and muscovite have transformed to a glass. The distribution of vesicles in shock-vitrified mica reveals escape of volatiles within the short duration of the shock experiment. It is noted that experimentally shocked biotite and muscovite undergo congruent melting. It is noted that the compositions of the glasses are similar to the unshocked micas except for volatiles (H2O loss and and K loss). These unusual glasses produced from mica can be quenched by rapid cooling conditions during the shock experiment. On the basis of the results, it is pointed out that the extremely low H2O content of tektites can be reconciled with a terrestrial origin by impact.

  2. Clustering of velocities in a GPS network spanning the Sierra Nevada Block, the northern Walker Lane Belt, and the Central Nevada Seismic Belt, California-Nevada

    USGS Publications Warehouse

    Savage, James C.; Simpson, Robert W.

    2013-01-01

    The deformation across the Sierra Nevada Block, the Walker Lane Belt, and the Central Nevada Seismic Belt (CNSB) between 38.5°N and 40.5°N has been analyzed by clustering GPS velocities to identify coherent blocks. Cluster analysis determines the number of clusters required and assigns the GPS stations to the proper clusters. The clusters are shown on a fault map by symbols located at the positions of the GPS stations, each symbol representing the cluster to which the velocity of that GPS station belongs. Fault systems that separate the clusters are readily identified on such a map. Four significant clusters are identified. Those clusters are strips separated by (from west to east) the Mohawk Valley-Genoa fault system, the Pyramid Lake-Wassuk fault system, and the Central Nevada Seismic Belt. The strain rates within the westernmost three clusters approximate simple right-lateral shear (~13 nstrain/a) across vertical planes roughly parallel to the cluster boundaries. Clustering does not recognize the longitudinal segmentation of the Walker Lane Belt into domains dominated by either northwesterly trending, right-lateral faults or northeasterly trending, left-lateral faults.

  3. The Mesoproterozoic Irumide belt of Zambia

    NASA Astrophysics Data System (ADS)

    De Waele, B.; Kampunzu, A. B.; Mapani, B. S. E.; Tembo, F.

    2006-09-01

    The Mesoproterozoic Irumide belt is a northeast-trending structural province stretching from central Zambia to the Zambia-Tanzania border and northern Malawi. Mesoproterozoic and Neoproterozoic transcurrent shear zones within reactivated parts of the Palaeoproterozoic Ubendian belt define its northeastern limit. The northwestern margin is defined by the largely undeformed basement lithologies of the Bangweulu block. An intensely folded and sheared zone at the southeastern margin of the Mporokoso Group sedimentary depocentre on the Bangweulu block, interpreted to have developed above a thrust at the basement-cover interface, indicates that far-field effects of the Irumide Orogen also affected the southeastern part of the Bangweulu block sedimentary cover. To the west and southwest, Irumide and basement lithologies were reworked by the Damara-Lufilian-Zambezi Orogen within the Neoproterozoic Zambezi and Lufilian belts. The Choma-Kalomo block, previously regarded as the southwesterly continuation of the Irumide belt, is a distinct Mesoproterozoic province, while a succession of structurally juxtaposed tectonic terranes in eastern Zambia record a deformation event related to the Irumide Orogen. The lithological units identified in the Irumide belt include: (1) limited Neoarchaean rocks emplaced between 2.73 and 2.61 Ga and representing the oldest rocks in the Bangweulu block; (2) ca. 2.05-1.85 Ga volcano-plutonic complexes and gneisses representing the most important components in the Bangweulu block; (3) an extensive quartzite-metapelite succession with minor carbonate forming the Muva Supergroup, and deposited at ca. 1.85 Ga; (4) granitoids emplaced between 1.65 and 1.55 Ga; (5) a minor suite of anorogenic plutons (nepheline syenite and biotite granite) restricted to the far northeastern Irumide belt and emplaced between 1.36 and 1.33 Ga; (6) voluminous syn- to post-kinematic Irumide granitoids emplaced between 1.05 and 0.95 Ga. Crustal shortening and thickening in

  4. Study of Magnetic Fabrics and Paleomagnetism Across Northern Transect of Taiwan Mountain Belt and Thier Implications

    NASA Astrophysics Data System (ADS)

    Yeh, E. C.; Peng, X. J.; Tseng, Y. C.; Chou, Y. M.; Lee, T. Q.; Aubourg, C.; Chen, C. C.; Lin, S. T.; Chen, C. T.

    2015-12-01

    Anisotropy of magnetic susceptibility (AMS) can be regarded as a useful tool for understanding the variation of finite strain pattern for regional deformation. In order to evaluate the interrelationship between maximum metamorphic temperature and deformation during mountain building, oriented samples of low-grade metamorphic rocks across the northern Taiwan were collected. In addition to the study of magnetic susceptibility anisotropy, experiments of natural remanent magnetization, hysteresis loop, and temperature-function magnetic susceptibility were also conducted. Results show that K1 orientation of magnetic ellipsoids suggested NW-SE compression, which is consistent with plate convergence direction. Both deformation intensity and anisotropy increase from the west to east with abnormally strong intensity and oblate strain near major faults. Magnetic fabrics have grouped six-stage from Type I to VI upon increasing strain. Study area can be divided into four domain A to D by geological characteristics and distribution of magnetic fabric. Rocks in Domain A begin to be influenced by horizontal tectonic strain. Ellipsoid is oblate and K1 is in northeast-southwest orientation, indicating NW-SW compression. Magnetic fabric belongs to Type II. K3 orientation in Domain B started to be affected by cleavage. The shape of ellipsoid is mainly oblate. Magnetic fabric is classified as Type II-III. The shape of ellipsoid in Domain C gradually converts to prolate. Distribution of K3, influenced by cleavage development, becomes a girdle in NW-SE orientation. It is treated as Type III-IV. In Domain D, though both anisotropy and deformation intensity are increased, the direction of K3 is still concentrated in vertical, not in horizontal. Results might be the reflective of discontinuous strain response to different kinematic mechanisms between the Backbone Range and the Hsueshan Range. Thermopaleogeomagnetic records of pyrrhotite remanence on both limbs of the Chungling Anticline

  5. Cover cropping to reduce nitrate loss through subsurface drainage in the northern U.S. corn belt.

    PubMed

    Strock, J S; Porter, P M; Russelle, M P

    2004-01-01

    Despite the use of best management practices for nitrogen (N) application rate and timing, significant losses of nitrate nitrogen (NO3(-)-N) in drainage discharge continue to occur from row crop cropping systems. Our objective was to determine whether a autumn-seeded winter rye (Secale cereale L.) cover crop following corn (Zea mays L.) would reduce NO3(-)-N losses through subsurface tile drainage in a corn-soybean [Glycine mar (L.) Merr.] cropping system in the northern Corn Belt (USA) in a moderately well-drained soil. Both phases of the corn-soybean rotation, with and without the winter rye cover crop following corn, were established in 1998 in a Normania clay loam (fine-loamy, mixed, mesic Aquic Haplustoll) soil at Lamberton, MN. Cover cropping did not affect subsequent soybean yield, but reduced drainage discharge, flow-weighted mean nitrate concentration (FWMNC), and NO3(-)-N loss relative to winter fallow, although the magnitude of the effect varied considerably with annual precipitation. Three-year average drainage discharge was lower with a winter rye cover crop than without (p = 0.06). Over three years, subsurface tile-drainage discharge was reduced 11% and NO3(-)-N loss was reduced 13% for a corn-soybean cropping system with a rye cover crop following corn than with no rye cover crop. We estimate that establishment of a winter rye cover crop after corn will be successful in one of four years in southwestern Minnesota. Cover cropping with rye has the potential to be an effective management tool for reducing NO3(-)-N loss from subsurface drainage discharge despite challenges to establishment and spring growth in the north-central USA.

  6. Geochemistry of the mafic volcanic rocks of the Buzwagi gold mine in the Neoarchaean Nzega greenstone belt, northern Tanzania

    NASA Astrophysics Data System (ADS)

    Manya, Shukrani

    2016-11-01

    The Buzwagi gold mine, found in the Neoarchaean Nzega greenstone belt of northern Tanzania; is underlain by mafic volcanic rocks which are associated with a massive body of ultramafic rocks that are considered to be cumulates. The mafic-ultramafic rocks association are cross-cut by ~ 2.71 Ga grey TTG and ~ 2.67 Ga pink microcline K-rich granites. The Buzwagi mine mafic volcanic rocks are Fe-rich tholeiites (MgO = 3.59-7.67 wt.%, Fe2O3 = 12.5-17.7 wt.% and Mg# = 30-56) that are characterized by flat REE (La/SmCN = 0.78-1.12) and N-MORB like patterns except for moderate negative anomalies of Nb (Nb/Lapm = 0.46-1.13) and Ta, Zr and Hf. The rocks exhibit sub-chondritic Zr/Hf ratios of 28.5-40.5 (average = 32.6) and Ti/Zr ratios of 102-136 (average = 124) and suggest that they are mantle-derived. Their La/Nb ratios of 0.85-2.10 encompass the range of oceanic ridge/plateau (La/Nb < 1.4) and arc-like (La/Nb > 1.4) basalts. The Buzwagi mine mafic volcanic rocks have been interpreted as products of 4-10% (average = 5%) non-modal partial melting of the DMM source leaving a residual mineralogy comprised of olivine (57%), orthopyroxene (28%), clinopyroxene (13%) and spinel (2%). The DMM source was metasomatized by the slab-derived hydrous fluids in a back arc setting. This study corroborates previous evidence that crustal growth in the late Archaean Tanzania Craton occurred at convergent margins.

  7. Microfacies Analysis and Paleoenvironmental Interpretation of the Eocene Kohat Formation, Gumbat Section, Himalayan Fold and Thrust Belt, Northern Pakistan.

    NASA Astrophysics Data System (ADS)

    Mirza, Kamran

    2015-04-01

    A section of the Middle Eocene Kohat Formation has been measured and sampled systematically for the microfacies analysis and paleoenvironmental interpretation from the Gumbat Section, Kohat Basin, Himalayan Fold and Thrust Belt, Northern Pakistan. The section of Kohat Formation is 84 m thick in this area. A total number of 45 samples were collected from bottom to top in such a way that minor lithological variations were noticed and sampled. Out of these samples, 67 thin sections were made that were later on studied under the microscope for microfacies analysis and paleoenvironmental interpretation. Four microfacies and eight subfacies have been identified in the section. These microfacies and their subfacies are: Lime Mudstone Facies Benthic Foraminiferal Wackstone Facies This microfacies is further divided into five subfacies: Nummulites-Milliolid Wackestone Facies, Nummulites-Alveolina-Milliolid Wackestone Facies, Nummulites-Alveolina Wackestone Facies, Alveolinid Wackestone Facies, Nummulites-Coskinolina Wackestone Facies, Benthic Foraminiferal Packstone Facies This microfacies is again divided into three subfacies namely: Nummulites-Alveolina Packstone Facies, Milliolid-Peloid Packstone Facies and Nummulites-Assilina Packstone Facies. And Milliolid-Peloid Grainstone Facies. These microfacies indicate some interesting results about the paleoenvironments at the time of deposition of the Kohat Formation in this area. The larger benthic foraminifera of different groups have been used for the interpretation of paleoenvironments. These micro organisms show a great susceptibility to the minor changes in climate, depth zone and the nature of substrate. These can safely be used for the paleoenvironmental interpretation of any carbonate system deposited in the marine realm. On the basis of above mentioned microfacies, it can be concluded that the Kohat Formation in Gumbat area was deposited in low to moderate energy conditions, open marine, shallow shelf environments.

  8. Anatomy of a volcanic district in a carbonate fold-and-thrust belt: the northern Volsci Range (Italy)

    NASA Astrophysics Data System (ADS)

    Cardello, Giovanni Luca; Consorti, Lorenzo; Di Filippo, Michele

    2015-04-01

    The Volsci Range is a carbonate fold-and-thrust belt crossed by important normal faults in places associated with explosive volcanic deposits and hydrothermal ongoing activity within a moderately active seismic area (e.g., Latina earthquake 2012, Mw=3.8). Though distribution of volcanites is known, origin, volume and field characterization of a previously unstudied volcanic district is far to be addressed and it is the topic of this work. Several monogenic phreatomagmatic vents occur at the edges of the chain and within its backbone. The most relevant ones are characterized at the base by well welded to zeolitized tuffs, followed either by incoherent tuffs or by surges (e.g., Patrica, Valvisciolo) and locally by lavas (i.e., Giuliano di Roma, Pofi, Terracina) and finally by late Quaternary slope deposits. Most explosive units are largely composed by local Mesozoic platform carbonate litic clasts, showing different degrees of rounding and decarbonation. Micropalaeontology and facies analysis confirm that clasts are not older than late Jurassic and not younger than Cenomanian (Upper part of the Ostracoda and Miliolidae biozone). Therefore considering the stratigraphy beneath the vent points, litics could come from depths of about 400-600 meters. Juvenile litics of different composition, accretionary lapilli and the above mention carbonate litic clasts testify for a complex conduct composition and for the rupture of the carbonatic aquifer during eruption. Right at the southern slope of the Lepini Mounts (northern Volsci Range), as detected from the analysis of the n-2 residual gravity anomalies, monogenic circular vents (tuff rings) occur buried under Quaternary deposits or are just barely cropping out as necks (Doganella di Ninfa). Further south, despite the occurrence of pyroclastic deposits in boreholes, thickness and shape of volcanic deposits below the Pontina Plain is still unconstrained, providing a challenge for further geophysical studies. However, the

  9. Permian alkaline granites in the Erenhot-Hegenshan belt, northern Inner Mongolia, China: Model of generation, time of emplacement and regional tectonic significance

    NASA Astrophysics Data System (ADS)

    Tong, Ying; Jahn, Bor-ming; Wang, Tao; Hong, Da-wei; Smith, Eugene I.; Sun, Min; Gao, Jian-feng; Yang, Qi-di; Huang, Wei

    2015-01-01

    The Central Asian Orogenic Belt (CAOB) is known to be the Earth's largest Phanerozoic accretionary orogenic belt. Its southern margin, particularly in the southern Mongolia and Inner Mongolia (SMIM), shows an extensive distribution of alkaline granites. Study of these granites could shed light on long-debated hypotheses on the late Paleozoic tectonic evolution of this region. In this work, we performed a detailed zircon age determination and whole rock geochemical analysis on alkaline granites from four granitic plutons in northern Inner Mongolia (Hongol, Saiyinwusu, Baolag, and Baiyinwula). U-Pb zircon dating yielded early Permian ages (ca. 280 Ma) for the four plutons. Whole-rock geochemical analyses show chemical characteristics typical of alkaline granites. Coeval alkaline granites from southern Mongolia to northern Inner Mongolia constitute a gigantic (∼900 km) Permian (292-275 Ma) alkaline granite belt in the southern CAOB. Furthermore, these alkaline granites have whole-rock εNd(t) varying between +3.6 and +6.4 and zircon εHf(t) from +4.9 to +20.3. The geochemical and Nd-Hf isotopic signatures suggest derivation by partial melting of a protolith assemblage dominated by metasomatised mantle, and followed by fractional crystallization in a post-collisional extensional environment.

  10. Sr-Pb isotopic studies of primitive and near-primitive basaltic magmas, Garibaldi volcanic belt, northern Cascadia subduction system

    NASA Astrophysics Data System (ADS)

    Green, N. L.; Sinha, A. K.

    2003-12-01

    The northern Cascadia subduction system is intimately associated with aseismic subduction of extremely young and presumably `hot' oceanic lithosphere beneath northwestern Washington and southwestern British Columbia. Sr and Pb isotopic analyses are presented for primitive and near-primitive (>6.0 wt. % MgO) basalts from a southeast-northwest transect along the Garibaldi volcanic belt (GVB), which overlies subducted oceanic lithosphere that decreases in age from ca. 22 m.y. below Glacier Peak at its southern end to about 13 m.y. beneath the northernmost eruptive centers in the Mosaic (Meager Mountain) and Salal Glacier-Bridge River areas. The basaltic rocks have initial 87Sr/86Sr ratios of 0.70317-0.70426, with minimum observed values in individual lava suites decreasing northward. Values of Pb isotopic ratios for GVB basaltic suites range from 18.22 to 18.97 for 206Pb/204Pb, from 15.51 to 15.59 for 207Pb/204Pb, and from 37.73 to 38.49 for 208Pb/204Pb. Sr isotopic compositions, unsupported by lava Rb contents, show positive correlations with Cs/Rb, La/Nb, Ba/La, Ba/Nb, Ba/Ta, B/La, B/Zr, Sr/Nd, and primitive mantle normalized Sr/P; and negative correlations with high field strength elements (HFSE: Nb, and Ta), FeO and other transition metals (Co and Zn), Ce/Pb,Cr/Ni, Sm/Yb, Ta/Yb, Hf/Yb, K/Ba, K/Sr, and La/Yb. Moderate to strong correlations between 87Sr/86Sr and ratios involving fluid-mobile and less-fluid-mobile elements are compatible with decreased slab input northward along the volcanic front as the subducted plate becomes hotter. The Pb isotopic compositions exhibit only limited variations when examined against position along the volcanic arc, but show uniform to extremely weak positive correlations of 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb with 87Sr/86Sr, Ba/La, Sr/Nd, Ba/Nb, Zr/Nb, Mg-Number and SiO2; and similarly weak negative correlation of Ce/Pb with 206Pb/204Pb and 207Pb/204Pb. The isotopic data suggest that GVB basaltic magmas have experienced with

  11. The Gogebic Iron Range - A Sample of the Northern Margin of the Penokean Fold and Thrust Belt

    USGS Publications Warehouse

    Cannon, William F.; LaBerge, Gene L.; Klasner, John S.; Schulz, Klaus J.

    2008-01-01

    The Gogebic iron range is an elongate belt of Paleoproterozoic strata extending from the west shore of Lake Gogebic in the upper peninsula of Michigan for about 125 km westward into northern Wisconsin. It is one of six major informally named iron ranges in the Lake Superior region and produced about 325 million tons of direct-shipping ore between 1887 and 1967. A significant resource of concentrating-grade ore remains in the western and eastern parts of the range. The iron range forms a broad, gently southward-opening arc where the central part of the range exposes rocks that were deposited somewhat north of the eastern and western parts. A fundamental boundary marking both the tectonic setting of deposition and the later deformation within the Penokean orogen lies fortuitously in an east-west direction along the range so that the central part of the range preserves sediments deposited north of that boundary, whereas the eastern and western parts of the range were deposited south of the boundary. Thus, the central part of the range provides a record of sedimentation and very mild deformation in a part of the Penokean orogen farthest from the interior of the orogen to the south. The eastern and western parts of the range, in contrast, exhibit a depositional and deformational style typical of parts closer to the interior of the orogen. A second fortuitous feature of the iron range is that the entire area was tilted from 40 degrees to 90 degrees northward by Mesoproterozoic deformation so that the map view offers an oblique cross section of the Paleoproterozoic sedimentary sequence and structures. Together, these features make the Gogebic iron range a unique area in which to observe (1) the lateral transition from deposition on a stable platform to deposition in a tectonically and volcanically active region, and (2) the transition from essentially undeformed Paleoproterozoic strata to their folded and faulted equivalents. Paleoproterozoic strata in the Gogebic iron

  12. Thermobarometric studies on the Levack Gneisses: Footwall rocks to the Sudbury Igneous Complex

    NASA Technical Reports Server (NTRS)

    James, R. S.; Peredery, W.; Sweeny, J. M.

    1992-01-01

    Granulite and amphibolite facies gneisses and migmatites of the Levack Gneiss Complex occupy a zone up to 8 km wide around the northern part of the Sudbury Igneous Complex (SIC). Orthopyroxene- and garnet-bearing tonalitic and semipelitic assemblages of granulite facies grade occur within 3 km of the SIC together with lenses of mafic and pyroxenitic rock compositions normally represented by an amphibole +/- cpx-rich assemblage; amphibolite facies assemblages dominate elsewhere in this terrain. These 2.711-Ga gneisses were introduced by (1) the Cartier Granite Batholith during late Archaean to early Proterozoic time and (2) the SIC, at 1.85 Ga, which produced a contact aureole 1-1.5 km wide in which pyroxene hornfelses are common within 200-300 m of the contact. A suite of 12 samples including both the opx-gt and amphibole-rich rock compositions have been studied. Garnets in the semipelitic gneisses are variably replaced by a plg-bio assemblage. Thermobarometric calculations using a variety of barometers and thermometers reported in the literature suggest that the granulite facies assemblages formed at depths in the 21-28 km range (6-8 kbar). Textures and mineral chemistry in the garnet-bearing semipelitic rocks indicate that this terrain underwent a second metamorphic event during uplift to depth in the 5-11 km range (2-3 kbar) and at temperatures as low as 500-550 C. This latter event is distinct from thermal recrystallization caused by the emplacement of the SIC; it probably represents metamorphism attributable to intrusion of the Cartier Granite Batholith. These data allow two interpretations for the crustal uplift of the Levack Gneisses: (1) The gneisses were tectonically uplifted prior to the Sudbury Event (due to intrusion of the Cartier Batholith); or (2) the gneisses were raised to epizonal levels as a result of meteorite impact at 1.85 Ga.

  13. Thermal structure and melting conditions associated with `hot' subduction: Implications from thermobarometry of Garibaldi belt basalts, northern Cascadia Subduction System

    NASA Astrophysics Data System (ADS)

    Green, N. L.

    2005-12-01

    The northern Cascadia margin of North America is the classic example of a "hot" subduction system. The downgoing Juan de Fuca plate decreases in age from ca. 10 m.y. off the central Washington coast to less than 5 m.y. off central Vancouver Island; beneath the Garibaldi volcanic belt (GVB) 250 km east of the convergent margin, inferred age of the oceanic lithosphere decreases northward from ca. 22 m.y to 13 m.y. Primitive and near-primitive mafic lavas, which primarily occur trenchward of the GVB volcanic front, range northward from high-Al olivine tholeiites, Mg-andesites and LILE- and LREE-enriched calc-alkaline basalts at Glacier Peak, through transitional basalts in the Cheakamus Valley to alkali olivine basalts and trachybasalts at Meager Mountain, Salal Glacier and Bridge River. The more northerly GVB basaltic magmas show the least evidence of slab-derived components in their source regions. Application of various olivine-melt and pyroxene-melt thermobarometers to GVB basalts indicates a general increase in magmatic temperatures from 1150-1200 C in Mount Baker and Glacier Peak basalts to 1225-1300 C in Bridge River and Salal Glacier lavas. Fe-Ti oxide thermobarometry suggests that northernmost basalts equilibrated under oxygen fugacities conditions between QFM and NNO, whereas Glacier Peak lavas equilibrated at higher oxygen fugacities (ca. 1 log unit above NNO). Estimated P and T conditions of mantle segregation suggest that GVB basalts ascended from increasingly greater depths northward along the volcanic arc. Similar variation is indicated by calculated P-T of basalt equilibrations with both Mg- and Fe-rich peridotite mineral assemblages, based on diopside and albite activity-composition relations. Estimated mantle equilibration temperatures correlate positively with some HFSE abundances (e.g., Hf), but negatively with those of fluid mobile elements (e.g., Cs and B). These relationships are considered in terms of the influence of slab thermal structure on

  14. Structural analysis of the Itapucumí Group in the Vallemí region, northern Paraguay: Evidence of a new Brasiliano/Pan-African mobile belt

    NASA Astrophysics Data System (ADS)

    Campanha, Ginaldo Ademar da Cruz; Warren, Lucas; Boggiani, Paulo César; Grohmann, Carlos Henrique; Cáceres, Alberto Arias

    The Neoproterozoic (Ediacaran) Itapucumí Group in northern Paraguay is composed of carbonate and siliciclastic rocks, including ooid grainstones, marls, shales and sandstones, containing Cloudina fossils in the eastern region. It is almost undeformed over the Rio Apa Cratonic Block but shows a strong deformational pattern at its western edge. A detailed structural analysis of the Itapucumí Group was conducted in the Vallemí Mine, along with a regional survey in other outcrops downstream in the Paraguay River and in the San Alfredo, Cerro Paiva and Sargento José E. López regions. In the main Vallemí quarry, the structural style is characterized by an axial-plane slaty cleavage in open to isoclinal folds, sometimes overturned, associated with N-S trending thrust faults and shear zones of E-vergence and with a low-grade chlorite zone metamorphism. The structural data presented here are compatible with the hypothesis of a newly recognized mobile belt on the western side of the Rio Apa Cratonic Block, with opposite vergence to that of the Paraguay Mobile Belt in Brazil. Both belts are related to the Late Brasiliano/Pan-African tectonic cycle with a Lower Cambrian deformation and metamorphism age. The deformation could be due to the late collision of the Amazonian Craton with the remainder of Western Gondwana or to the western active plate boundary related to the Pampean Belt. The structural and lithologic differences between the western Itapucumí Group in the Vallemí and Paraguay River region and the eastern region, near San Alfredo and Cerro Paiva, suggest that this group could be divided into two lithostratigraphic units, but more stratigraphic and geochronological analyses are required to confirm this possibility.

  15. Geology of the Eoarchean, > 3.95 Ga, Nulliak supracrustal rocks in the Saglek Block, northern Labrador, Canada: The oldest geological evidence for plate tectonics

    NASA Astrophysics Data System (ADS)

    Komiya, Tsuyoshi; Yamamoto, Shinji; Aoki, Shogo; Sawaki, Yusuke; Ishikawa, Akira; Tashiro, Takayuki; Koshida, Keiko; Shimojo, Masanori; Aoki, Kazumasa; Collerson, Kenneth D.

    2015-11-01

    The Earth is a unique planet, which has been highly evolved, diversified and complicated through geologic time, and underwent many key events, including giant impact, magma ocean, core formation, large-scale mantle differentiation and late heavy bombardment, especially in its dawn. But, our knowledge of early Earth is limited due to the lack of the Hadean supracrustal rocks. The supracrustal rocks with the Eoarchean ages provide key evidence for the Earth's early evolution, but few supracrustal rocks have been comprehensively investigated. Therefore, we mapped in seven areas of the Saglek Block, northern Labrador, where ancient supracrustal sequences are interleaved with a diverse assemblage of orthogneisses. Early studies suggested that some of them have the Mesoarchean ages because of the lack of the Mesoarchean Saglek dyke, but we found the Saglek dykes in the areas to recognize the Eoarchean Nulliak supracrustal rocks and Uivak Gneiss in all the areas. Recent reassessment of U-Pb dating and cathodoluminescence observation of zircons from the oldest suites of the Uivak Gneiss showed that the Uivak Gneiss has the Eoarchean age, > 3.95 Ga, and forms the Iqaluk-Uivak Gneiss series. Because our geological survey clearly showed that the Iqaluk-Uivak Gneisses were intruded into the Nulliak supracrustal belts, the Nulliak supracrustal rocks are the oldest supracrustal rock in the world. The supracrustal belts consist of piles of fault-bounded blocks, which are composed of the ultramafic rocks, mafic rocks and sedimentary rocks in ascending order, similar to modern ocean plate stratigraphy (OPS). In addition, small-scale duplex structures are found over the areas. The presence of duplex structure and OPS indicates that the > 3.95 Ga Nulliak supracrustal belts originate from an accretionary complex. The presence of the accretionary complex, ophiolite and granitic continental crust provides the oldest evidence for the plate tectonics on the early Earth.

  16. The Cordilleran foreland thrust belt in northwestern Montana and northern Idaho from COCORP and industry seismic reflection data

    SciTech Connect

    Yoos, T.R.; Potter, C.J.; Thigpen, J.L.; Brown, L.D. )

    1991-06-01

    COCORP and petroleum industry seismic reflection profiles in northwestern Montana reveal the structure of the Cordilleran foreland thrust belt. The Front Ranges consist of thick thrust sheets containing Precambrian Belt Supergroup and Paleozoic miogeoclinal shelf rocks above a thin remnant of Paleozoic rocks and gently westward-dipping North American basement. Interpretation of the seismic data and results from a recent petroleum exploration well suggest that 15-22 km of Precambrian Belt Supergroup sedimentary rocks are present in several thrust plates beneath the eastern Purcell anticlinorium. Previous hypotheses of a large mass of Paleozoic miogeoclinal sedimentary rocks or slices of crystalline basement located beneath the eastern Purcell anticlinorium do not appear to be supported by the data. The easternmost occurrence of allochthonous basement is interpreted to be in the western part of the anticlinorium near the Montana-Idaho border. Comparison of the Cordilleran foreland thrust belt in northwestern Montana and southern Canada suggest that a change in the deep structure of the Purcell anticlinorium occurs along strike. The anticlinorium in southern Canada has been interpreted as a hanging-wall anticline that was thrust over the western edge of thick Proterozoic North American basement, whereas in northwestern Montana the anticlinorium appears to consist of a complex series of thrust sheets above highly attenuated North American basement.

  17. Zircon geochronology of the Webb Canyon Gneiss and the Mount Owen Quartz Monzonite, Teton Range, Wyoming: Significance to dating late Archean metamorphism in the Wyoming craton

    USGS Publications Warehouse

    Zartman, R.E.; Reed, J.C.

    1998-01-01

    The Webb Canyon Gneiss is a strongly foliated and lineated orthogneiss intercalated with layered Archean gneisses in the northern part of the Teton Range in northwestern Wyoming. The Mount Owen Quartz Monzonite is a non-foliated or weakly flow foliated rock which forms a discordant pluton exposed in the central part of the range and that cuts the Webb Canyon Gneiss and the associated layered gneisses. U-Pb zircon geochronology reported here indicates that euhedral pink zircon grew in the Webb Canyon Gneiss at about 2680 Ma, probably during the peak of regional metamorphism and that the Mount Owen was emplaced at 2547??3 Ma. These dates provide the best constraints so far reported on the age of Late Archean regional metamorphism in the western part of the Wyoming craton.

  18. Fluxed melting of metapelite and the formation of Miocene high-CaO two-mica granites in the Malashan gneiss dome, southern Tibet

    NASA Astrophysics Data System (ADS)

    Gao, Li-E.; Zeng, Lingsen

    2014-04-01

    Identifying the timing of formation and geochemical nature of the Cenozoic granites along the Himalayan orogen is essential to test or formulate models that link crustal anatexis with tectonic transition during the evolution of large-scale collisional orogenic belts. The Malashan gneiss dome, one of the prominent domes within the Tethyan Himalaya, experienced Barrovian-type metamorphism and partial melting of pelitic rocks at relatively deep levels during the collision between India and Eurasia. New LA-MC-ICP-MS zircon U-Pb analyses yielded that the Malashan two-mica granites formed at a time span of 17.6 ± 0.1 to 16.9 ± 0.1 Ma. The Malashan two-mica granites are characterized by: (1) high SiO2 (>71.3 wt.%), Al2O3 (>14.8 wt.%), and relatively high CaO (>1.3 wt.%); (2) relatively high Sr (>146 ppm), but low Rb/Sr ratios (<1.3) which are nearly constant relative to large variations in Ba concentrations; (3) enrichment in LREE, depletion in HREE, and no or weak negative Eu anomalies (Eu/Eu∗ = 0.7-0.9); (4) as compared to granites in the other Northern Himalayan Gneiss Domes and High Himalayan Belt, relatively lower initial 87Sr/86Sr ratios (0.7391-0.7484) and similar unradiogenic Nd isotope compositions (εNd(t) = -13.7 to -14.4). These characteristics imply that the two-mica granites were derived from fluid-fluxing melting of metapelite, possibly triggered by the E-W extension. Our new data in combination with literature data indicate that there are three types of granites with diverse geochemical characteristics and distinct formation mechanisms along the Himalayan orogen since the Cenozoic India-Eurasia continental collision. Conceivably, our new results will provide new insights on how the partial melting behavior of relatively deeper crustal rocks evolved as the tectonic evolution of large orogenic belts.

  19. Ion microprobe zircon geochronology of the Uivak Gneisses: Implications for the evolution of early terrestrial crust in the North Atlantic Craton

    NASA Technical Reports Server (NTRS)

    Collerson, K. D.

    1983-01-01

    Ion microprobe U-Pb results for zircons from three Uivak I gneisses and one specimen of Uivak II gneiss, from the Saglek-Hebron area of Northern Labrador are reported. These results are compared with interpretations based on published conventional U-Pb zircon results and with conclusions about crustal evolution in the NAC derived from Rb-Sr, Sm-Nd and Pb-Pb isotopic studies.

  20. Age and nature of the basement in northeastern Washington and northern Idaho: isotopic evidence from Mesozoic and Cenozoic granitoids

    USGS Publications Warehouse

    Whitehouse, M.J.; Stacey, J.S.; Miller, F.K.

    1992-01-01

    K-feldspar Pb and whole rock Nd isotopic analyses from 25 Mesozoic and Cenozoic plutonic rocks and two gneisses from NE Washington and northern Idaho are used to elucidate the age and nature of the concealed cratonic basement. The plutons form two highly distinct isotopic groups: Group I have isotopic compositions suggesting derivation from rocks of the Belt Supergroup or their metamorphosed equivalents, Group II have highly retarded Pb isotopic compositions relative to the present day crustal average and require a source region with long-term U depletion, characteristic of cratonic lower crust. A U-Pb zircon upper intercept age of c2600 Ma obtained from one of the Group II samples, together with Sm-Nd data from the gneisses, indicates possible late-Archean crust at depth, which acted as a source region for Eocene extension-related plutonism. -from Authors

  1. Is the Cameron River greenstone belt allochthonous?

    NASA Technical Reports Server (NTRS)

    Kusky, T. M.

    1986-01-01

    Many tectonic models for the Slave Province, N.W.T., Canada, and for Archean granite - greenstone terranes in general, are implicitly dependent on the assumption that greenstone belt lithologies rest unconformably upon older gneissic basement. Other models require originally large separations between gneissic terranes and greenstone belts. A key question relating to the tectonics of greenstone belts is therefore the original spatial relationship between the volcanic assemblages and presumed-basement gneisses, and how this relationship has been modified by subsequent deformation. What remains unclear in these examples is the significance of the so-called later faulting of the greenstone - gneiss contacts. Where unconformities between gneisses and overlying sediments are indisputable, such as at Point Lake, the significance of faults which occur below the base of the volcanic succession also needs to be evaluated. As part of an on-going investigation aimed at answering these and other questions, the extremely well-exposed Cameron River Greenstone Belt and the Sleepy Dragon Metamorphic Complex in the vicinity of Webb Lake and Sleepy Dragon Lake was mapped.

  2. Alkali metasomatism in the major gneiss, northwest Adirondacks, New York: open system or closed?

    NASA Astrophysics Data System (ADS)

    Carl, James D.

    1981-09-01

    The thickest clastic unit in the northwest Adirondacks. New York, undergoes gradual transition from amphibolite to granulite facies over a distance of 55 km from Emeryville to Colton. This Precambrian quartz-biotite-oligoclase-K-feldspar gneiss with migmatite characteristics has long been cited as having undergone progressive loss of K, Si, Fe2+, Ba and H2O toward Colton and granulite facies conditions (ENGEL and ENGEL, 1958, 1960a. b). Chemical data obtained from new samples, however, cast doubt upon the interpretation of open system alkali metasomatism. Outcrop to outcrop chemical variation is shown to be of similar magnitude to the chemical variation recorded across the entire gneiss belt. Chemical differences between Emeryville and Colton are not those expected from progressive degranitization by loss of alkali-bearing fluid. Ratios of {K}/{Rb} and Ca-Na K suggest that metamorphism was isochemical on the scale of outcrop. These new data were obtained from mixtures of leucosome and fine-grained paragneiss at each of 7 outcrops. The sampling technique contrasts with that of A.E.J. and C. Engel who analyzed leucosome separately from fine grained (‘least altered’) gneiss.

  3. Influence of syn-sedimentary faults on orogenic structures in a collisional belt: Insights from the inner zone of the Northern Apennines (Italy)

    NASA Astrophysics Data System (ADS)

    Brogi, Andrea

    2016-05-01

    This paper discusses the possible influence of syn-sedimentary structures on the development of orogenic structures during positive tectonic inversion in the inner Northern Apennines (Italy). Examples from key areas located in southern Tuscany provided original cartographic, structural and kinematics data for Late Oligocene-Early Miocene thrusts, organized in duplex systems, verging in the opposite direction of the foreland propagation (back-thrusts), which affected the Late Triassic-Oligocene sedimentary succession of the Tuscan Domain, previously affected by pre-orogenic structures. These latter consist of mesoscopic-to cartographic-scale Jurassic syn-sedimentary normal faults and extensional structures, which gave rise to effective stratigraphic lateral variation and mechanical heterogeneities. Structural analysis of both syn-sedimentary faults and back-thrusts were therefore compared in order to discuss the possible role of the pre-existing anisotropies in influencing the evolution of the back-thrusts. As a result, it can be reasonably proposed that back-thrusts trajectories and stacking pattern were controlled by relevant syn-sedimentary normal faults; these latter were reactivated, in some cases, if properly oriented. Such an issue adds new inputs for discussing the potential role of structural inheritance during tectonic inversions, and helps to better understand the processes suitable for the development of back-thrusts in the inner zones of orogenic belts, as it is the case of the inner Northern Apennines.

  4. Meso-Cenozoic building of the northern Central Asian Orogenic Belt: thermotectonic history of the Tuva region

    NASA Astrophysics Data System (ADS)

    De Grave, Johan; De Pelsmaeker, Elien; Zhimulev, Fedor; Glorie, Stijn; Buslov, Mikhail; Van den haute, Peter

    2014-05-01

    The Tuvinian and West-Sayan mountain ranges (West Sayan, Shapshal, Tannu Ola and Sengilen Range) form part of the Central Asian Orogenic Belt (CAOB), and more specifically they align along the Altai-Sayan-Hangai zone of the CAOB in South Siberia and Mongolia. Its Precambrian-Palaeozoic basement has been subjected to Meso-Cenozoic tectonic reactivation. Two North-South transects across the mountain belts and intervening Meso-Cenozoic basins of Tuva were sampled for apatite fission-track (AFT) thermochronology in order to elucidate the thermal history of the Tuvinian basement in relation to Meso-Cenozoic reactivation of the CAOB. Mainly Palaeozoic granitoid basement was targeted for sampling. Most AFT ages of these granitoids are Late Cretaceous and range between 55 and 115 Ma. Mean lengths of confined fission tracks are relatively long with most values between 13 and 14 µm. Thermal history modeling shows a rapid Late Jurassic - Cretaceous cooling for the sampled Tuvinian crystalline rocks, related to exhumation of the Palaeozoic basement. This exhumation is most likely related to the building and subsequent orogenic collapse of the Mongol-Okhotsk orogen that formed between the Siberian and North China - Mongolian (Sino-Korean or Amurian) continental blocks during the Late Mesozoic. Far-field effects of this orogeny and its collapse, affected the Baikal, Altai and Sayan units of the Central Asian Orogenic Belt, including the Tuvinian basement. After a Palaeogene period of stability, thermal history models for some samples hint at a renewed period of basement cooling during the Neogene. In support of this Neogene event, a single sample from the main West Sayan fault zone contains an apatite population with ~2 Ma reset AFT ages. This is interpreted in the framework of ongoing building of the modern Central Asian orogens and associated fault movements and exhumation of the basement, presumably related with the ongoing India-Eurasia convergence. Sediments derived from

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

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

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

  6. Evolution of the Chilka Lake granulite complex, northern Eastern Ghats Belt, India: First evidence of ~ 780 Ma decompression of the deep crust and its implication on the India-Antarctica correlation

    NASA Astrophysics Data System (ADS)

    Bose, S.; Das, K.; Torimoto, J.; Arima, M.; Dunkley, D. J.

    2016-10-01

    High-grade para- and orthogneissic rocks near the Chilka Lake granulite complex, northern part of the Eastern Ghats Belt show complex structural and petrological history. Based on field and petrographic characters, five (M1-M5) metamorphic events could be identified. The earliest metamorphic event (M1) produced amphibolite grade mineral assemblage which produced the peak granulite (M2) assemblages at 900-950 °C, 8.5-9.0 kbar. The third metamorphic event caused decompression of the deeper crust up to 700-800 °C, 6.0-6.5 kbar. This was followed by cooling (M4) and subsequent thermal overprinting (M5). Fluid-composition during M3 was dominated by high-density CO2 and changed to low-density mixed CO2-H2O during the M3. Zircon U-Pb SHRIMP data suggest 781 ± 9 Ma age for M3 event. Texturally constrained monazite U-Th-Pb EPMA data, on the other hand, yield a group age of 988 ± 23 Ma from grain interior, which can signifies the age of M2 event. Few spots with younger dates in the range of 550-500 Ma are also noted. This interpretation changes the existing tectonothermal history of northern Eastern Ghats Belt. Our data show that the two adjacent crustal domains of the Eastern Ghats Belt show distinctly contrasting Neoproterozoic histories. While the central Domain 2 evolved through early anticlockwise P-T path culminating in ultrahigh temperature, the northern Domain 3 evolved through a clockwise P-T path. It appears that the Domain 3 was contiguous to East Antarctica and became part of the Eastern Ghats Belt during the assembly of Gondwana. The ca. 780 Ma decompression event in the northern Eastern Ghats Belt opens up new possibilities for interpreting the breakup of Rodinia.

  7. The geology and tectonic significance of the Big Creek Gneiss, Sierra Madre, southeastern Wyoming

    NASA Astrophysics Data System (ADS)

    Jones, Daniel S.

    The Big Creek Gneiss, southern Sierra Madre, southeastern Wyoming, is a heterogeneous suite of upper-amphibolite-facies metamorphic rocks intruded by post-metamorphic pegmatitic granite. The metamorphic rocks consist of three individual protolith suites: (1) pre- to syn-1780-Ma supracrustal rocks including clastic metasedimentary rocks, calc-silicate paragneiss, and metavolcanic rocks; (2) a bimodal intrusive suite composed of metagabbro and granodiorite-tonalite gneiss; and (3) a younger bimodal suite composed of garnet-bearing metagabbronorite and coarse-grained granitic gneiss. Zircons U-Pb ages from the Big Creek Gneiss demonstrate that: (1) the average age of detrital zircons in the supracrustal rocks is ~1805 Ma, requiring a significant source of 1805-Ma (or older) detritus during deposition, possibly representing an older phase of arc magmatism; (2) the older bimodal igneous suite crystallized at ~1780 Ma, correlative with arc-derived rocks of the Green Mountain Formation; (3) the younger bimodal igneous suite crystallized at ~1763 Ma, coeval with the extensional(?) Horse Creek anorthosite complex in the Laramie Mountains and Sierra Madre Granite batholith in the southwestern Sierra Madre; (4) Big Creek Gneiss rocks were tectonically buried, metamorphosed, and partially melted at ~1750 Ma, coeval with the accretion of the Green Mountain arc to the Wyoming province along the Cheyenne belt; (5) the posttectonic granite and pegmatite bodies throughout the Big Creek Gneiss crystallized at ~1630 Ma and are correlative with the 'white quartz monzonite' of the south-central Sierra Madre. Geochemical analysis of the ~1780-Ma bimodal plutonic suite demonstrates a clear arc-affinity for the mafic rocks, consistent with a subduction environment origin. The granodioritic rocks of this suite were not derived by fractional crystallization from coeval mafic magmas, but are instead interpreted as melts of lower-crustal mafic material. This combination of mantle

  8. Formation of the giant Shakhdara migmatitic gneiss dome, Pamir, India-Asia collision zone

    NASA Astrophysics Data System (ADS)

    Stübner, Konstanze; Ratschbacher, Lothar; Hacker, Bradley; Dunkl, István; Gloaguen, Richard

    2013-04-01

    Cenozoic gneiss domes comprise one third of the surface exposure of the Pamir Mountains and provide a window into deep crustal processes of the India-Asia collision. The largest of these is the 350 × 90 km Shakhdara-Alichur composite dome of the southern Pamir, Tajikistan and Afghanistan. The Shakhdara and Alichur domes formed by footwall exhumation of two low-angle detachments: In the larger Shakhdara dome the top-to-S South Pamir shear zone (SPSZ) exhumed crust from 30-40 km depth; in the Alichur dome the top-to-N Alichur shear zone exhumed upper crustal rocks. The subdomes are separated by a low-strain horst. Non-coaxial shear in the Shakhdara dome is pervasive over the ~4 km thick SPSZ. The top of the shear zone is preserved at mountain peaks, the base is incised by the Panj gorge, which exposes the 'core' of the dome; total erosion is less than 4 km throughout most of the dome. We use a comprehensive geo-thermochronologic dataset of titanite, monazite, and zircon U/Th-Pb, mica Rb-Sr and 40Ar/39Ar, zircon and apatite fission track, and zircon (U-Th)/He ages to constrain the exhumation history of the southern Pamir domes. Doming started at ~21 Ma by crustal buckling and activation of a top-to-N normal shear zone (Gunt shear zone) along the northern rim of the Shakhdara dome, resulting in exhumation and cooling. The bulk of the exhumation was accomplished by northward extrusion of the SPSZ footwall, which was active from ~18-15 Ma to ~2 Ma; exhumation rates were 1-3 mm/yr. Erosion rates during and after the end of doming were 0.3-0.5 mm/yr within the domes and 0.1-0.3 mm/yr in the horst and in the SE Pamir plateau; incision rates of the major drainages were up to 1.0 mm/yr. Doming by footwall exhumation of the SPSZ resulted in up to 90 km N-S extension, coeval with ongoing N-S convergence between India and Asia. Extension opposes shortening along and above the reactivated Rushan-Pshart suture zone, a wide fold-thrust belt north of the Shakhdara-Alichur domes

  9. Researching the Link Between Biomass Burning and Drought Across the Northern Sub-Saharan African Savanna/Sahel Belt

    NASA Technical Reports Server (NTRS)

    Ichoku, Charles; Ellison, Luke

    2012-01-01

    The northern sub-Saharan African (NSSA) region, bounded by the Sahara, Equator, and the West and East African coastlines, is subjected to intense biomass burning every year during the dry season. This is believed to be one of the drivers of the regional carbon and energy cycles, with serious implications for the water cycle anomalies that probably contribute to drought and desertification. In this presentation, we will discuss a new multi-disciplinary research in the NSSA region, review progress, evaluate preliminary results, and interact with the research and user communities to examine how best to coordinate with other research activities in order to address related environmental issues most effectively.

  10. Neoproterozoic diamictite-bearing sedimentary rocks in the northern Yili Block and their constraints on the Precambrian evolution of microcontinents in the Western Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    He, Jingwen; Zhu, Wenbin; Zheng, Bihai; Wu, Hailin; Cui, Xiang; Lu, Yuanzhi

    2015-12-01

    The origin and tectonic setting of Precambrian sequences in the Central Asian Orogenic Belt (CAOB) have been debated due to a lack of high resolution geochronological data. Answering this question is essential for the understanding of the tectonic framework and Precambrian evolution of the blocks within the CAOB. Here we reported LA-ICP-MS detrital zircon U-Pb ages and in-situ Hf isotopic data for Neoproterozoic sedimentary cover in the northern Yili Block, an important component of the CAOB, in order to provide information on possible provenance and regional tectonic evolution. A total of 271 concordant U-Pb zircon ages from Neoproterozoic sedimentary cover in the northern Yili Block define three major age populations of 1900-1400 Ma, 1300-1150 Ma and 700-580 Ma, which are quite different from cratons and microcontinents involved in the CAOB. Although it is not completely consistent with the local basement ages, an autochthonous provenance interpretation is more suitable. Some zircon grains show significant old Hf model ages (TDMC; 3.9-2.4 Ga) and reveal continental crust as old as Paleoarchean probably existed. Continuous Mesoproterozoic zircon age populations exhibit large variations in the εHf(t) ratios, suggesting the long-time involvement of both reworked ancient crust and juvenile material. Similar Mesoproterozoic evolution pattern is identified in many continental terranes involved in the CAOB that surround the Tarim Craton. Based on our analysis and published research, we postulate that the northern Yili Block, together with Chinese Central Tianshan, Kyrgyz North Tianshan and some other microcontinents surrounding the Tarim Craton, once constituted the continental margin of the Tarim Craton in the Mesoproterozoic, formed by long-lived accretionary processes. Most of the late Neoproterozoic zircons exhibit significant positive εHf(t) ratios, suggesting the addition of juvenile crust. It is consistent with the tectonic event related to the East Africa

  11. Association of deformation and fluid events in the central Brooks Range fold-and-thrust belt, Northern Alaska

    USGS Publications Warehouse

    Moore, Thomas E.; Potter, Christopher J.; O'Sullivan, Paul B.; Shelton, Kevin L.; Underwood, Michael B.

    2003-01-01

    Ocentral Brooks Range consists of two superposed north-directed contractional orogens, one formed between 140-120 Ma and the other at ~60-45 Ma. The older orogen was an arc-continent collisional zone characterized by far-traveled allochthons and relatively low structural relief. The younger orogen is a retroarc thrust belt with relatively low amounts of shortening and high structural relief. Folding and thrusting of the younger episode is superimposed on the thin-skinned deformational wedge of the earlier orogen and also produced a frontal triangle zone in a thick sequence of mid-Cretaceous foreland basin sediments to the north. Stable isotope compositions of calcite and quartz veins indicate two fluid events including: (1) an earlier, higher-temperature (~250-300° C) event that produced veins in deformed Devonian clastic rocks, and (2) a younger, lower-temperature (~150° C) event that deposited veins in deformed Mississippian through Albian strata. The fluids in the first event had variable d18O values, but nearly constant d13C values buffered by limestone lithologies. The vein-forming fluids in the second event had similarly variable d18O values, but with distinctly lower d13C values as a result of oxidation of organic matter and/or methane. Zircon fission track ages demonstrate cooling to temperatures below 200° C between 140-120 Ma for the Devonian rocks, whereas zircon and apatite fission track ages show that Mississippian to Albian rocks were never heated above 200° C and cooled below 110-90° C at ~60-45 Ma. These data are interpreted as indicating that the older, high-temperature fluid event was active during thrusting at 120-140 Ma, and the younger fluid event during deformation at ~60-45 Ma. The data and results presented in this poster will be published in early 2004 in Moore and others (in press).

  12. The Northern Extent of the Southern Hemisphere Westerly Wind Belt since the Last Glacial Maximum Tracked via Sediment Provenance

    NASA Astrophysics Data System (ADS)

    Franzese, A. M.; Goldstein, S. L.; Hemming, S. R.

    2015-12-01

    The Southern Hemisphere Westerlies are known to be important for climate due to their effects on the global carbon cycle and on the global thermohaline circulation. Many proxy records suggest that the strength and position of the Southern Hemisphere westerly winds have changed significantly since the Last Glacial Maximum (LGM) at ~21,000 years BP. However, a recent compilation of all available evidence for Southern Hemisphere westerly wind changes during the Last Glacial Maximum (LGM) led to the conclusion that "their strength and position in colder and warmer climates relative to today remain a wide open question" (Kohfeld et al. (2013) Quaternary Science Reviews, 68). This paper finds that an equatorward displacement of the glacial winds is consistent with observations, but cannot rule out other, competing hypotheses. Using the geochemical characteristics of deep-sea sediments deposited along the Mid-Atlantic Ridge, I test the hypothesis that the LGM Southern Hemisphere Westerlies were displaced northward. In the central South Atlantic, dust can be delivered from South America via the Westerlies, or from Africa via the Trade Winds. The continental sources of South America and Africa have very different geochemical signatures, making it possible to distinguish between eolian transport via the Westerlies vs. the Trade Winds. Any northward shift in the Southern Hemisphere Westerlies would increase the northward extent of a South American provenance in sediments dominated by eolian sources. I will present geochemical provenance data (radiogenic isotope ratios; major and trace element concentrations) in a latitudinal transect of cores along the Mid-Atlantic Ridge that document whether, in fact, such a shift occurred, and put an important constraint on how far north the wind belts shifted during the LGM.

  13. Multiscale tectonic analysis of the basement-involved Malargüe fold-and-thrust-belt, Northern Neuquén Basin, (Argentina).

    NASA Astrophysics Data System (ADS)

    Branellec, Matthieu; Callot, Jean-Paul; Nivière, Bertrand; Aubourg, Charles; Ringenbach, Jean-Claude

    2015-04-01

    The Malargüe fold-and-thrust-belt (MFTB), which is located in the northern part of the Neuquén basin (Argentina), is known as a basement-involved orogenic wedge. The results presented here aim to make the link between the macroscopic structure and the strain record at both mesoscopic and microscopic scales (i.e damage). The cross-sections we produced show that basement contraction is strongly controlled by the extensive structural inheritance localizing deep seated thrusts. The second part of this work is dedicated to mesoscopic strain pattern analysis recorded by fracture networks. Throughout the MFTB, we are able to describe the occurrence of four main fractures sets emplaced in several stress regime that are linked (1) to the inheritance and (2) to the well-known compression phases from pre-folding to syn-folding settings. Finally the third part of this work describes the microscopic damage measured by the anisotropy of magnetic susceptibility. We evidence that there is no clear gradient of magnetic fabric intensity from foreland to hinterland, and that deformation is compartmentalized by structural inheritance and particularly by the localization of basement thrusts. This atypical pattern of magnetic fabrics succession reveals that the matrix damage is governed by the same strain distribution as those observed at macroscopic scale, thus providing a supplementary argument to consider the dynamics of the Andean system, at these latitudes, as singularly different from a classical Coulomb wedge propagation.

  14. Rare earth geochemistry of Lewisian granulite-facies gneisses, northwest Scotland: Implications for the petrogenesis of the Archaean lower continental crust

    NASA Astrophysics Data System (ADS)

    Weaver, Barry L.; Tarney, John

    1980-12-01

    Rare earth element (REE) data, together with data for major elements and 14 other trace elements, are presented for ultramafic, mafic, intermediate, tonalitic, trondhjemitic, anorthositic and microline gneisses, representative of the range of rock types making up the 2.9-b.y. Lewisian granulite complex of northwest Scotland. The data are used to constrain petrogenetic models for the Archaean lower crust. Ultramafic gneisses have flat REE patterns with 3-5 times chondrite abundance. The more Fe-rich mafic gneisses show slight light-REE enrichment, range up to 40 times chondritic and some have negative Eu anomalies. Intermediate gneisses have more fractionated REE distributions (Ce N/Yb N= 4-25) but with rather constant heavy REE. Tonalitic gneiss REE patterns are also strongly fractionated, show variable heavy-REE depletion and have positive Eu anomalies. REE patterns of trondhjemitic gneisses are very strongly fractionated (Ce N/Yb N up to ˜ 300), show strong heavy-REE depletion and most have marked positive anomalies. Anorthosites and microcline gneisses have similar REE distributions to the trondhjemites in spite of different major element compositions. Modelling of the REE and other trace element patterns of processes such as fractional crystallisation and partial melting suggests that whereas the mafic gneisses can be related by low-pressure fractional crystallisation, the more silicic gneisses can only be related by high-pressure partial melting of a mafic source. Most of the gneisses represent liquid compositions; few can be regarded as cumulates or the residues of partial melting. The computed average Lewisian granulite does have a positive Eu anomaly, but this is imparted by the more fractionated tonalites and trondhjemites and not by the more mafic components of the gneiss complex. Elements such as K, Rb, Cs, Th and U are removed from the lower crust by a fluid (CO 2-rich) not a melt phase during granulite-facies metamorphism. The Archean lower crust is

  15. The eastern Central Pamir Gneiss Domes: temporal and spatial geometry of burial and exhumation

    NASA Astrophysics Data System (ADS)

    Rutte, Daniel; Stearns, Michael; Ratschbacher, Lothar

    2013-04-01

    of the domes are Paleozoic. Detrital zircon data from the low-grade cover and surrounding units of the Muskol dome suggest that low-grade cover and high-grade dome formed from the same Paleozoic, possibly early Mesozoic strata. This indicates that the upper crust of the Central Pamir thickened to at least 30 km in phase (1). Based on our data and those of Robinson et al. (2012) underthrusted Karakul-Mazar (Songpan-Ganze) material (as discussed by Schwab et al. 2004), in analogy to the Tibetan Qiangtang domes (Kapp et al. 2000), can be ruled out as protolith for the Muskol and Shatput domes. (3) Neogene shortening is bi-vergent: top-to-S back-thrusting north of the Central Pamir Gneiss Domes opposes top-to-N thrusting in the south. Neogene deformation affected ~18 Ma (Ar-Ar) coarse fluvial and alluvial fan strata with basaltic dikes and flows south of the dome; restoration of these strata yielded up to 40% shortening. Total shortening by thrusting of the Central Pamir is at least 40% in the Shatput-Muskol area with a minimal total shortening of 70 km; internal deformation with recumbent north-verging folds within the domes and its cover indicate much higher values. Literature: Kapp, P., Yin, A., Manning, C. E., Murphy, M., Harrison, T. M., Spurlin, M., Lin, D., Yi-Guang, D., Cun-Ming, W. (2000) Blueshist-bearing metamorphic core complexes in the Qiangtang block reveal deep crustal structure of northern Tibet, Geology, v. 28; no. 1; p.19-22 Robinson, A. C., M. Ducea, and T. J. Lapen (2012), Detrital zircon and isotopic constraints on the crustal architecture and tectonic evolution of the northeastern Pamir, Tectonics, 31, TC2016, doi:10.1029/2011TC003013. Schwab, M., Ratschbacher, L., Siebel, W., McWilliams, M., Minaev, V., Lutkov., V., Chen, F., Stanek, K., Nelson, B. and Wooden, J. L. (2004) Assembly of the Pamir: Age and origin of magmatic belts from the southern Tien Shan to the southern Pamir and their relation to Tibet, Tectonics, 23, No. 4, TC4002

  16. Belt-driven conveyor belts

    SciTech Connect

    Not Available

    1984-01-01

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

  17. The Ross Orogen and Lachlan Fold Belt in Marie Byrd Land, Northern Victoria Land and New Zealand: implication for the tectonic setting of the Lachlan Fold Belt in Antarctica

    USGS Publications Warehouse

    Bradshaw, J.D.

    2007-01-01

    Correlation of the Cambrian Delamerian Orogen of Australia and Ross Orogen of the Transantarctic Mountains widely accepted but the extension of the adjacent Lachlan Orogen into Antarctica is controversial. Outside the main Ross-Delamerian belt, evidence of this orogeny is preserved at Mt Murphy in Marie Byrd Land and the in Takaka Terrane of New Zealand. In all pre-break- configurations of the SW Pacific, these two areas are far removed from the Ross-Delamerian belt. Evidence from conglomerates in the Takaka Terrane, however, shows that in Late Cambrian times it was adjacent to the Ross Orogen. This indicates major tectonic displacements within Gondwana after the Cambrian and before break-up. The Lachlan Orogen formed in an extensional belt in a supra-subduction zone setting and the Cambrian rocks of Marie Byrd Land and New Zealand are interpreted as parts of a rifted continental ribbon on the outboard side of the Lachlan belt.

  18. Experimental Cratering into Layered Targets: MEMIN Experiments with Maggia Gneiss

    NASA Astrophysics Data System (ADS)

    Poelchau, M. H.; Winkler, R.; Schäfer, F.; Kenkmann, T.

    2016-08-01

    We performed impact experiments into gneiss targets. Craters are larger and ejecta cones wider when layering is perpendicular to the impact direction than when it is parallel. We'll try to look into subsurface deformation before the conference.

  19. Small scale heterogeneity of Phanerozoic lower crust: evidence from isotopic and geochemical systematics of mid-Cretaceous granulite gneisses, San Gabriel Mountains, southern California

    USGS Publications Warehouse

    Barth, A.P.; Wooden, J.L.; May, D.J.

    1992-01-01

    An elongate belt of mid-Cretaceous, compositionally banded gneisses and granulites is exposed in Cucamonga terrane, in the southeastern foothills of the San Gabriel Mountains of southern California. Banded gneisses include mafic granulites of two geochemical types: type 1 rocks are similar to high Al arc basalts and andesites but have higher HFSE (high-field-strength-element) abundances and extremely variable LILE (largeion-lithophile-element) abundances, while type 2 rocks are relatively low in Al and similar to alkali rich MOR (midocean-ridge) or intraplate basalts. Intercalated with mafic granulites are paragneisses which include felsic granulites, aluminous gneisses, marble, and calc-silicate gneisses. Type 1 mafic granulites and calcic trondhjemitic pegmatites also oceur as cross-cutting, synmetamorphic dikes or small plutons. Small-scale heterogeneity of deep continental crust is indicated by the lithologic and isotopic diversity of intercalated ortho-and paragneisses exposed in Cucamonga terrane. Geochemical and isotopic data indicate that K, Rb, and U depletion and Sm/Nd fractionation were associated with biotite +/- muscovite dehydration reactions in type 1 mafic granulites and aluminous gneisses during high-grade metamorphism. Field relations and model initial isotopic ratios imply a wide range of protolith ages, ranging from Early Proterozoic to Phanerozoic. ?? 1992 Springer-Verlag.

  20. Activity in Jupiter's Northern Hemisphere Before and During the Juno Mission: Waves Associated with the North Equatorial Belt and Relation to Expansion Phase

    NASA Astrophysics Data System (ADS)

    Orton, Glenn S.; Momary, Thomas W.; Sinclair, James; Fletcher, Leigh N.; Rogers, John H.; Fernandes, Joshua; Kasaba, Yasumasa; Sato, Takao M.; Fujiyoshi, Takuya; Yanamandra-Fisher, Padma A.; Baines, Kevin

    2016-10-01

    Visible and infrared observations of Jupiter in 2015-2016 reveal phenomena that may be active during the Juno mission. For the North Equatorial Belt (NEB), near-infrared observations of Jupiter's upper-tropospheric particulate field at wavelengths of strong gaseous absorption reveal a zonal wave structure that encompasses the longitudes of a northward expansion of dark-colored regions of the NEB. The longitudinal structure of the waves appears to be highly correlated with the structure of zonal waves in the upper-tropospheric temperature field. This wave pattern was also observed by Cassini and ground-based observers in late 2000 / early 2001 during its flyby of Jupiter, which Li et al. (2006, Icarus 185, 416) argued was a planetary (Rossby) wave. The 2000-2001 wave was also observed during a period of NEB expansion. Using our historical infrared observations, as well as CCD images at 889 nm, the NEB expansion sequences in 2004 and 2009 also appear to be accompanied by zonal waves in the upper-tropospheric particulate field as well as by zonal waves in the upper-tropospheric temperature field. This correlation implies that the wave is a commonplace consequence of the dynamical reconfiguration at the northern edge of the NEB during its apparent expansion, created by a downwelling that causes sublimation of white aerosols at some longitudes. Properties of the 2015-2016 wave do not appear to be correlated with those of a nearby prominent stratospheric zonal temperature wave, although both began within months of each other. At cloud-top level, the NEB expansions lead to the generation of cyclonic circulations ('barges'), which are expected to be visible in 2016-2017. The current NEB-related phenomena, together with other types of waves and instabilities, mark a very interesting period for Juno observations and its coordinated campaign of Earth-based support.

  1. Petrological and geochemical features of the Jingtieshan banded iron formation (BIF): A unique type of BIF from the Northern Qilian Orogenic Belt, NW China

    NASA Astrophysics Data System (ADS)

    Yang, Xiu-Qing; Zhang, Zuo-Heng; Duan, Shi-Gang; Zhao, Xin-Min

    2015-12-01

    The Jingtieshan banded iron formation (BIF) is located in the Northern Qilian Orogenic Belt (NQOB) in NW China. The BIFs are hosted in Mesoproterozoic Jingtieshan Group, a dominantly clastic-carbonate sedimentary formation, and was metamorphosed to lower greenschist facies. The Jingtieshan BIFs include oxide-, carbonate- and mixed carbonate-oxide facies, and consist of alternating iron-rich and silica-rich bands. The BIFs are composed essentially of specularite and jasper, with minor carbonate minerals and barite. The SiO2 + Fe2O3 content is markedly high in the oxide facies BIF, followed by FeO, CO2 and Ba, with the other elements usually lower than 1%, suggesting that the original chemical sediments were composed of Fe, Si, CO32- and Ba. The positive correlation between Al2O3, TiO2 and Zr in the BIFs indicates that these chemical sediments incorporate minor detrital components. Oxide facies BIF shows low HFSE, low ∑REE and low Y/Ho. The Post Archean Australian Shale-normalized REE patterns for Jingtieshan BIFs are characterized slight LREE depletion, strong positive Eu anomalies and lack of significant negative Ce anomalies. Siderite in the carbonate- and mixed carbonate-oxide facies BIF shows negative δ13C values varying from -8.4‰ to -3.0‰, and δ18O values show a range of -16.6‰ to -11.7‰. The geochemical signatures and carbon-oxygen isotopes suggest origin from high-temperature hydrothermal fluids with weak seawater signature for the sediments of Jingtieshan BIFs. The absence of negative Ce anomalies and the high Fe3+/∑Fe ratios of the oxide facies BIF do not support ocean anoxia. In contrast to the three main types (Algoma-, Superior- and Rapitan-type) of global BIFs, the Jingtieshan BIFs represent a unique type with features similar to those of sedimentary-exhalative mineralization.

  2. Types and Evolutionary Processes of Formation of the Ordovician Taconic Mélanges in the Central and Northern Appalachian Orogenic Belt, Eastern USA

    NASA Astrophysics Data System (ADS)

    Codegone, Giulia; Festa, Andrea; Dilek, Yildirim; Pini, Gian Andrea

    2010-05-01

    We examined in eastern Pennsylvania, New York and Vermont (USA) various types of unmetamorphosed mélanges, which formed at an accretionary wedge-front of the Ordovician Taconic allochthon in the central and northern Appalachian orogenic belt. These mélange occurrences display structural evidence for progressive deformation of a middle-late Ordovician trench-fill succession during the subduction-accretion to collision tectonic episodes of the Taconic Orogeny. Mélanges and broken formations (mélanges s.l.) commonly represent the products of tectonic, sedimentary and diapiric processes during the evolution of accretionary wedges. Geologic mapping and stratigraphic-structural observations in the central and northern Appalachians indicate that different types of mélanges s.l. appear to have developed in different structural positions with respect to the wedge front, and that they show different types of chaotic arrangements and deformation intensities depending on their origin, evolution, and tectonic position. Mass-wasting deposits and/or olistostromes were emplaced at the wedge front as precursory olistostromes of the advancing allochthons, providing exotic material into a flysch succession. These sedimentary mélanges were then overridden by the advancing thrust sheet and were incorporated into the shear zone forming an olistostromal carpet. Shearing led to the juxtaposition and mixing of rocks (in some cases including exotic blocks) of various ages, and subsequently to the formation of boudinage, enucleation of isoclinals folds, and phacoidal microshear cleavages. Broken formations, mainly formed at the base of the wedge front and Taconic thrust fault systems, occur in a continuum ranging from originally coherent stratigraphic successions to variously disrupted strata, and finally to an entirely chaotic block-in-matrix fabric, which lacks a stratigraphic continuity. In-situ accretion-related deformation caused by tectonic loading and related increase of fluid

  3. Magnetofabrics of ultrahigh-pressure gneisses from the Chinese Continental Scientific Drilling (CCSD) project: Retrogression of ferromagnetic gneisses

    NASA Astrophysics Data System (ADS)

    Grimmer, J.-C.; Qi, X. X.; Xu, Z. Q.

    2009-04-01

    In order to better understand retrograde processes during exhumation of ultrahigh pressure (UHP) rocks the anisotropy of magnetic susceptibility (AMS) was measured on UHP-gneisses from the 5138 m deep CCSD-mainhole. The Sulu UHP-gneisses are composed of variable proportions of quartz, K-feldspar, plagioclase, biotite, and white mica with variable contents of garnet, chlorite, epidote, amphibole, and accessory phases such as zircon, apatite, and Fe-Ti-oxides. 111 samples from 21 oriented core pieces from the uppermost 1800 m of the CCSD-mainhole were measured for their AMS. The mean susceptibilities (Kmean) of the gneisses vary from 0.1x10-3 to 37.2x10-3 SI. Some core pieces outline a large intra-sample variation of Kmean. The anisotropies (Ṕ) of the gneisses vary from 1.05 to 1.62. 83% of the samples display positive shape factors (T) and thus oblate AMS-ellipsoids. Magnetic foliations coincide with metamorphic foliations dipping to the ENE with variable dip angles. The orientations of the principal susceptibility axes show no systematic variation with Kmean at the intra- and inter-sample scale. The average gneiss density is 2.67±0.12 g/cm3. The main carrier of susceptibility is biotite for the paramagnetic gneisses (Kmean < 0.5x10-3 SI) and magnetite for the ferromagnetic gneisses (Kmean > 5x10-3 SI). Variation diagram of Kmean versus density outlines a well-constrained positive correlation for paramagnetic gneisses since higher contents of biotite augment both density and Kmean. For the ferromagnetic gneisses the correlation is also well constrained and positive since higher contents of magnetite augment both density and Kmean. Cogenetic gneisses with a large intra-sample variation of Kmean are in particular suitable to better understand possible genetic links between the para- and ferromagnetic gneisses. These particular samples outline diffuse, but nevertheless negative correlations between Kmean and the density corroborating decomposition of magnetite and

  4. Influence of slab thermal structure on basalt source regions and melting conditions: REE and HFSE constraints from the Garibaldi volcanic belt, northern Cascadia subduction system

    NASA Astrophysics Data System (ADS)

    Green, Nathan L.

    2006-03-01

    Garibaldi volcanic belt (GVB) basalts were erupted above the relatively young (≤ 24 Ma) Juan de Fuca plate, which comprises the subducted oceanic lithosphere that becomes progressively younger (22-13 Ma), and presumably hotter, northward along the northern Cascadia convergent margin. Primitive and near-primitive mafic lavas of the 15-km-wide volcanic belt change from high-alumina olivine tholeiites and magnesian andesites near Glacier Peak, northwestern Washington, through transitional basalts to alkali-olivine basalts and basanites in the Bridge River-Salal Glacier areas, southwestern British Columbia. The distribution of different basalt types is consistent with varied source conditions imposed by differences in the thermal structure of the underlying subducted plate. Significant arc-parallel variations characterize REE and HFSE contents in GVB basalts and suggest that source enrichment processes and melting conditions vary within the mantle wedge as the age and thermal state of the underlying subducted plate changes. More northerly GVB basaltic suites tend to have higher TiO 2, Nb, Ta, total REE, La, Sm / Yb, Nb / Yb, Ti / V, Y / Sc and Zr / Yb and lower Th / U, Zr / Ti and Zr / Nb than their southern counterparts. The basalts have sub-chondritic to chondritic Nb / Ta (6-21) and super-chondritic Zr / Hf (up to 55.90) ratios that exhibit positive correlation. Only Mount Baker and Glacier Peak basalts exhibit the distinctive negative Nb-Ta anomalies associated with arc lavas. Inter-HFSE and REE fractionations (including La / Yb, La / Nb and Ce / Pb) show significant correlations with the inferred age of the underlying subducted plate. Proportions of slab-derived HFSE-REE components (SC) transferred to basalt sources in the Cascadia mantle wedge appear to vary from negligible (Ti, Nb, Ta, Zr, Hf, Y, Sm, Eu and Tb: less than 15% SC) to perceptible (Nd: up to 35% SC) through moderate (La: up to 75% SC) to substantial (U, Th and Pb: up to 95% SC). Arc-parallel HFSE

  5. 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 Tav

  6. Fluid inclusion and stable isotope (O, H, C, and S) constraints on the genesis of the Serrinha gold deposit, Gurupi Belt, northern Brazil

    NASA Astrophysics Data System (ADS)

    Klein, Evandro L.; Harris, Chris; Renac, Christophe; Giret, André; Moura, Candido A. V.; Fuzikawa, Kazuo

    2006-05-01

    The Serrinha gold deposit of the Gurupi Belt, northern Brazil, belongs to the class of orogenic gold deposits. The deposit is hosted in highly strained graphitic schist belonging to a Paleoproterozoic (˜2,160 Ma) metavolcano-sedimentary sequence. The ore-zones are up to 11 m thick, parallel to the regional NW-SE schistosity, and characterized by quartz-carbonate-sulfide veinlets and minor disseminations. Textural and structural data indicate that mineralization was syn- to late-tectonic and postmetamorphic. Fluid inclusion studies identified early CO2 (CH4-N2) and CO2 (CH4-N2)-H2O-NaCl inclusions that show highly variable phase ratios, CO2 homogenization, and total homogenization temperatures both to liquid and vapor, interpreted as the product of fluid immiscibility under fluctuating pressure conditions, more or less associated with postentrapment modifications. The ore-bearing fluid typically has 18-33mol% of CO2, up to 4mol% of N2, and less than 2mol% of CH4 and displays moderate to high densities with salinity around 4.5wt% NaCl equiv. Mineralization occurred around 310 to 335°C and 1.3 to 3.0 kbar, based on fluid inclusion homogenization temperatures and oxygen isotope thermometry with estimated oxygen fugacity indicating relatively reduced conditions. Stable isotope data on quartz, carbonate, and fluid inclusions suggest that veins formed from fluids with δ18OH2O and δDH2O (310-335°C) values of +6.2 to +8.4‰ and -19 to -80‰, respectively, which might be metamorphic and/or magmatic and/or mantle-derived. The carbon isotope composition (δ13C) varies from -14.2 to -15.7‰ in carbonates; it is -17.6‰ in fluid inclusion CO2 and -23.6‰ in graphite from the host rock. The δ34S values of pyrite are -2.6 to -7.9‰. The strongly to moderately negative carbon isotope composition of the carbonates and inclusion fluid CO2 reflects variable contribution of organic carbon to an originally heavier fluid (magmatic, metamorphic, or mantle-derived) at the site

  7. Timing and nature of the Xinlin-Xiguitu Ocean: constraints from ophiolitic gabbros in the northern Great Xing'an Range, eastern Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Feng, Zhiqiang; Liu, Yongjiang; Liu, Binqiang; Wen, Quanbo; Li, Weimin; Liu, Qing

    2016-03-01

    Jifeng ophiolitic mélange (ultramafic rocks, meta-basalts and gabbros) crops out in the northern segment of the Great Xing'an Range, the eastern segment of the Central Asian Orogenic Belt, which marks the closure of the Xinlin-Xiguitu Ocean associated with the collision between the Erguna block and Xing'an block. In order to investigate the formation age and magma source of the Jifeng ophiolitic mélange, the gabbros from newly discovered the Jifeng ophiolitic mélange are studied with zircon U-Pb ages, whole-rock geochemistry and zircon Hf isotopes. Zircon U-Pb dating from the ophiolitic gabbros yields U-Pb age of 647 ± 5.3 Ma, which may represent the formation age of the ophiolitic mélange. The gabbros display low SiO2, TiO2, K2O contents, high Na2O, LREE contents and indistinctive REE fractionation [(La/Yb)N = 1.97-2.98]. It shows an E-MORB-like affinity, while the element concentrations of the Jifeng samples are lower than that of E-MORB. More importantly, Nb displays negative anomaly in comparison with Th, which shows a transitional SSZ-type ophiolite signature. Moreover, the ɛ Hf ( t) values of ~647 Ma zircons in the gabbros range from +8.4 to +13.4, and the corresponding Hf single-stage ages ( T DM1) are between 687 and 902 Ma, which is obviously older than the crystallization age of 647 Ma. These geochemical features can be explained as melts from the partial melting of a depleted mantle source meta-somatized by fluids derived from a subducted slab. Accordingly, we conclude that the Jifeng ophiolitic mélange is probably related to transitional SSZ-type ophiolite and developed in an intra-oceanic subduction, which indicates that an ocean (the Xinlin-Xiguitu Ocean) existed between the Erguna block and Xing'an block. The Ocean's formation might be no later than the Neoproterozoic (647 Ma), and it was closed in the Late Cambrian because of the collision between the Erguna block and Xing'an block.

  8. Source and evolution of ore-forming hydrothermal fluids in the northern Iberian Pyrite Belt massive sulphide deposits (SW Spain): evidence from fluid inclusions and stable isotopes

    NASA Astrophysics Data System (ADS)

    Sánchez-España, Javier; Velasco, Francisco; Boyce, Adrian J.; Fallick, Anthony E.

    2003-08-01

    A fluid inclusion and stable isotopic study has been undertaken on some massive sulphide deposits (Aguas Teñidas Este, Concepción, San Miguel, San Telmo and Cueva de la Mora) located in the northern Iberian Pyrite Belt. The isotopic analyses were mainly performed on quartz, chlorite, carbonate and whole rock samples from the stockworks and altered footwall zones of the deposits, and also on some fluid inclusion waters. Homogenization temperatures of fluid inclusions in quartz mostly range from 120 to 280 °C. Salinity of most fluid inclusions ranges from 2 to 14 wt% NaCl equiv. A few cases with Th=80-110 °C and salinity of 16-24 wt% NaCl equiv., have been also recognized. In addition, fluid inclusions from the Soloviejo Mn-Fe-jaspers (160-190 °C and ≈6 wt% NaCl equiv.) and some Late to Post-Hercynian quartz veins (130-270 °C and ≈4 wt% NaCl equiv.) were also studied. Isotopic results indicate that fluids in equilibrium with measured quartz (δ18Ofluid ≈-2 to 4‰), chlorites (δ18Ofluid ≈8-14‰, δDfluid ≈-45 to -27‰), whole rocks (δ18Ofluid ≈4-7‰, δDfluid ≈-15 to -10‰), and carbonates (δ18Oankerite ≈14.5-16‰, δ13Cfluid =-11 to -5‰) evolved isotopically during the lifetime of the hydrothermal systems, following a waxing/waning cycle at different temperatures and water/rock ratios. The results (fluid inclusions, δ18O, δD and δ13C values) point to a highly evolved seawater, along with a variable (but significant) contribution of other fluid reservoirs such as magmatic and/or deep metamorphic waters, as the most probable sources for the ore-forming fluids. These fluids interacted with the underlying volcanic and sedimentary rocks during convective circulation through the upper crust.

  9. Constraints on slab inputs and mantle source compositions in the northern Cascade arc (Garibaldi belt) from Sr-Nd-Pb-Hf isotopes and trace elements in primitive basalts

    NASA Astrophysics Data System (ADS)

    Mullen, E. K.; Carpentier, M.; Weis, D.

    2011-12-01

    The northernmost segment of the Cascade arc, known as the Garibaldi volcanic belt (GVB), extends from Glacier Peak in Washington to the Bridge River cones in British Columbia. GVB primitive basalts display strong arc-parallel geochemical gradients, most prominently a northerly progression from calc-alkaline to highly alkalic compositions, which present an ideal opportunity to address key questions regarding the origin of primary arc basalts including the compositions and relative inputs of sub-arc mantle sources and slab-derived fluids/melts. The gradient in GVB basalt alkalinity was proposed to result from a northerly reduction in slab-derived contributions to the sub-arc mantle wedge, a consequence of the ~4 myr decrease in slab age at the trench [1-3]. As a test of this hypothesis, we have obtained new whole-rock high-precision isotopic (Sr, Nd, Pb, Hf) and trace element data for the GVB basalt suites previously investigated by Green and others. La/Nb decreases from south (4.25 at Glacier Peak) to north (0.78 at Bridge River), confirming a progressive reduction in the "arc signature" (elevated LILE and LREE abundances relative to HFSE and HREE). 87Sr/86Sr ranges from 0.70310 to 0.70396, 206Pb/204Pb from 18.65 to 18.92, ɛNd from 8.5 to 3.8, and ɛHf from 13.3 to 8.7. Our data overlap the Sr-Nd-Pb isotopic compositions of primitive samples at Mt. Baker and Chilliwack batholith [4], but extend to more depleted compositions. GVB basalts are isotopically distinct from other Cascade arc primitive basalts, with systematically lower 208Pb/206Pb at a given 206Pb/204Pb and higher ɛNd at a given 87Sr/86Sr. In Pb-Pb space, GVB basalts define a linear trend extending from Explorer MORB to local subducting sediments drilled at ODP Sites 888 and 1027 in the northern Cascadia basin. We interpret this array as a mixing line reflecting variable sediment input to the mantle. However, Sr, Pb and Nd isotope ratios are only weakly correlated with La/Nb and latitude, whereas 208Pb

  10. Paleoproterozoic igneous and metamorphic events in the Hongcheon area, southern margin of the Northern Gyeonggi Massif in the Korean Peninsula, and their links to the Paleoproterozoic collision in the North China Craton

    NASA Astrophysics Data System (ADS)

    Oh, Chang W.; Lee, Byung C.; Yengkhom, Kesorjit S.; Yi, Sang B.

    2014-05-01

    The Hongcheon area is located at the northern part of Gyeonggi Massif (GM) in the Korean Peninsula. The Hongcheon area is composed of the Paleoproterozoic Yongduri Gneiss Complex (YGC), Euiam Group (EG) and Euiam Gneiss Complex (EGC). Quartz-feldspathic gneisses in the northeastern part of the YGC record M2 peak metamorphic conditions of 790-840°C and 7.2-8.9 kbar, whereas granitic and garnet gneisses in the western part of the YGC record peak metamorphic conditions of 690-720°C and 6.1-6.9 kbar, and 640-660°C and 5.0-5.4 kbar, respectively. The M2 metamorphic conditions represent a regional low-P/T metamorphic event in which metamorphic grade increased towards east. SHRIMP zircon U-Pb age dating indicates that the M2 metamorphism occurred at ca. 1867-1883 Ma. The presence of relict kyanite in the gneisses within the YGC suggests that the M1 intermediate-P/T metamorphism (ca. 1925 Ma) occurred prior to the low-P/T metamorphic event. The YGC also records M3 metamorphic event related to Permo-Triassic continental collision between the North and South China Craton. Whole-rock geochemistry indicates that augen gneisses in the EGC were originally post-collision granitoids, and that amphibolites within these gneisses were originally within-plate mafic intrusions. These augen gneisses and amphibolites were emplaced between ca. 1864 and 1885 Ma, and metamorphosed during the Permo-Triassic event (ca. 246 and 265 Ma). The similarity in age between the Paleoproterozoic intrusion and the M2 low-P/T metamorphism indicates that the M2 metamorphism also occurred in a post-collision tectonic setting. The M1 intermediate-P/T metamorphism and post-collision events in the study area can be correlated to the 1.91-1.93 Ga collision related metamorphism and 1.84-1.88 Ga post-collision events in the North Korea and the Jiao-Liao-Ji collision belt in the North China Craton.

  11. Glastonbury Gneiss and mantling rocks (a modified Oliverian dome) in south-central Massachusetts and north-central Connecticut; geochemistry, petrogenesis, and isotopic age

    USGS Publications Warehouse

    Leo, G.W.; Zartman, R.E.; Brookins, D.G.

    1984-01-01

    The Glastonbury dome is a long, narrow structure trending approximately 70 km north-northeast through Connecticut and Massachusetts along the west side of the Bronson Hill anticlinorium. Structurally and stratigraphically the dome is analogous to the Oliverian domes of New Hampshire. It is cored by Glastonbury Gneiss and is mantled by Ammonoosuc Volcanics and Partridge Formation (or their equivalents) of Ordovician age. The Glastonbury Gneiss intrudes the Ammonoosuc and, thereby, establishes the relative age of the two units. Monson Gneiss, which unconformably underlies the Ammonoosuc Volcanics in the Monson anticline to the east, is not in contact with Glastonbury Gneiss except near Stafford Springs, Conn., where the contact may be gradational. In some places, Monson Gneiss shows evidence of plastic flow and potential anatexis. The northern part of the Glastonbury Gneiss typically is leucocratic, granoblastic, relatively potassium-poor gneiss that appears homogeneous in outcrop, but proves to be chemically and modally inhomogeneous over short distances, as shown by variation diagrams and REE plots. The gneiss straddles the compositional fields of trondhjemite, tonalite, and granodiorite, and partly overlaps that of Monson Gneiss. The southern part of the Glastonbury Gneiss is consistently more potassic than the northern, having compositions ranging from granite to granodiorite. All of the Glastonbury Gneiss show pervasive, strong foliation, deformation, and local shearing related to the Acadian orogeny. Field relations, textures, and chemistry of the northern part of the Glastonbury suggest an origin by anatexis of the premetamorphic Monson sequence at temperatures of about 690 DC to 750 DC and pressures of <3kbars. The southern part of the Glastonbury appears to have been generated contemporaneously but not comagmatically from calcalkaline crust. U-Pb zircon ages for both the northern and southern bodies are slightly discordant with 207PbfosPb ages of 445 to 467

  12. Early Miocene granitoids from the Leo Pargil gneiss dome, northwest Himalaya

    NASA Astrophysics Data System (ADS)

    Hassett, W.; Leech, M. L.

    2007-12-01

    The Leo Pargil gneiss dome is comprised of upper amphibolite-facies metasedimentary rocks of the lower Tethyan Himalayan sequence (known as the Haimantas Group), that are intruded by numerous small granitoid bodies and leucogranite dikes. The dome is located in northern India/southwestern Tibet at the junction of the Sutlej and Spiti rivers, west of the Zada basin. U-Pb SHRIMP dating of zircon yield concordant ages ranging from Late Archean to Late Proterozoic for paragneisses (2.6 Ga to 970 Ma) corresponding to the Haimantas group, and Early Oligocene to Middle Miocene ages for granitoid intrusions (33 Ma to 15 Ma). Concordant analyses and lower intercept ages from Tera-Wasserburg concordia plots range from 28.1-17.2 Ma. Late Oligocene to Early Miocene ages are from zircon domains with consistently high U contents (1500 to over 25000 ppm). Linear regression of age vs. U content scatter plots show a trend toward younger ages (22-20 Ma) corresponding to ages from zircon with lower U contents (1000-3000 ppm) and that is consistent with lower intercept ages. These Early Miocene ages for Leo Pargil granitoids correspond to the ages for the widespread leucogranite bodies exposed throughout the Himalaya and granites from the North Himalayan gneiss domes further east.

  13. The Last Glacial Maximum in the Northern European loess belt: Correlations between loess-paleosol sequences and the Dehner Maar core (Eifel Mountains)

    NASA Astrophysics Data System (ADS)

    Zens, Joerg; Krauß, Lydia; Römer, Wolfgang; Klasen, Nicole; Pirson, Stéphane; Schulte, Philipp; Zeeden, Christian; Sirocko, Frank; Lehmkuhl, Frank

    2016-04-01

    The D1 project of the CRC 806 "Our way to Europe" focusses on Central Europe as a destination of modern human dispersal out of Africa. The paleo-environmental conditions along the migration areas are reconstructed by loess-paleosol sequences and lacustrine sediments. Stratigraphy and luminescence dating provide the chronological framework for the correlation of grain size and geochemical data to large-scale climate proxies like isotope ratios and dust content of Greenland ice cores. The reliability of correlations is improved by the development of precise age models of specific marker beds. In this study, we focus on the (terrestrial) Last Glacial Maximum of the Weichselian Upper Pleniglacial which is supposed to be dominated by high wind speeds and an increasing aridity. Especially in the Lower Rhine Embayment (LRE), this period is linked to an extensive erosion event. The disconformity is followed by an intensive cryosol formation. In order to support the stratigraphical observations from the field, luminescence dating and grain size analysis were applied on three loess-paleosol sequences along the northern European loess belt to develop a more reliable chronology and to reconstruct paleo-environmental dynamics. The loess sections were compared to newest results from heavy mineral and grain size analysis from the Dehner Maar core (Eifel Mountains) and correlated to NGRIP records. Volcanic minerals can be found in the Dehner Maar core from a visible tephra layer at 27.8 ka up to ~25 ka. They can be correlated to the Eltville Tephra found in loess section. New quartz luminescence ages from Romont (Belgium) surrounding the tephra dated the deposition between 25.0 + 2.3 ka and 25.8 + 2.4 ka. In the following, heavy minerals show an increasing importance of strong easterly winds during the second Greenland dust peak (~24 ka b2k) correlating with an extensive erosion event in the LRE. Luminescence dating on quartz bracketing the following soil formation yielded ages of

  14. Ancient Granite Gneiss in the Black Hills, South Dakota.

    PubMed

    Zartman, R E; Norton, J J; Stern, T W

    1964-07-31

    Granite gneiss, with an age of approximately 2.5 billion years, in the Black Hills, South Dakota, provides a link between ancient rocks in western Wyoming and Montana and in eastern North and South Dakota and Minnesota. The discovery suggests that early Precambrian rocks covered an extensive area in northcentral United States and were not restricted to several small nuclei.

  15. Ancient granite gneiss in the Black Hills, South Dakota

    USGS Publications Warehouse

    Zartman, R.E.; Norton, J.J.; Stern, T.W.

    1964-01-01

    Granite gneiss, with an age of approximately 2.5 billion years, in the Black Hills, South Dakota , provides a link betweeen ancient rocks in western Wyoming and Montana and in eastern North and South Dakota and Minnesota. The discovery suggests that early Precambrian rocks covered an extensive area in northcentral United States and were not restricted to several small nuclei.

  16. Age and origin of gneisses south of Ameralik, between Kangimut-Sangmissoq and Qasigianguit

    NASA Technical Reports Server (NTRS)

    Jones, N. W.; Moorbath, S.; Taylor, P. N.

    1986-01-01

    Gneisses which crop out along the southern coast of Ameralik between Kangimut-sangmissoq and Qasigianguit (K-s-Q) are the subject of long-standing controversy concerning their relationship to the early Archean Amitsoq gneisses of the Godthaab district. On the basis of field observations, it was argued that gneisses at Kangimut-sangmissoq and Qasigianguit are correlatives of the early Archean Amitsoq gneisses. The data were reexamined and it is concluded that the K-s-Q gneisses represent an addition of substantially juvenile mantle-derived material to the Archean craton of West Greenland during the late Archean times. Some of the parent magmas have undergone interaction with older crust, as indicated by Pb isotope evidence for contamination with Amitsoq-derived Pb. However, the positive epsilon Nd(I) value for the K-s-Q gneisses firmly rules out any significant material contribution from the Amitsoq gneisses to the K-s-Q gneisses.

  17. Andean evolution of the Aluminé fold and thrust belt, Northern Patagonian Andes (38°30‧-40°30‧S)

    NASA Astrophysics Data System (ADS)

    García Morabito, Ezequiel; Ramos, Víctor A.

    2012-10-01

    The Aluminé fold and thrust belt between 38°30' and 40°30'S is the result of two periods of progression of deformation toward the foreland. The chronology of deformation and its relationship with magmatism through time show spatially and temporally separated magmatic events closely linked to distinct deformational stages. Data presented here confirms a Late Cretaceous mountain-building phase that coexisted in space and time with an eastward arc-migration. During this stage, a belt of deformation expanded through the foreland where it produced the Southern Neuquen Precordillera. This eastern independent mountain grew separately from the main Andean axis through a combination of inversion of the old rift systems and interaction with a pre-Andean belt which acted as a foreland obstacle. On the basis of tectonostratigraphic controls we define the last Andean contractional phase between the Late Miocene and the Pliocene. This event induced the reactivation of both sectors of the fold and thrust belt with minor propagation toward the foreland, leading to the uplift of the Patagonian Andes and reshaping the Southern Neuquén Precordillera. Both intervals of shortening are separated by a period of localized extension that resulted in the development of the Collón Cura basin within this Andean segment. Here, large thicknesses of volcanosedimentary sequences accumulated contemporaneously with the extensional activity between the earliest Oligocene and the Early Miocene.

  18. Petrogenesis of the Neoproterozoic West Highland Granitic Gneiss, Scottish Caledonides: Cryptic mantle input to S-type granites?

    NASA Astrophysics Data System (ADS)

    Fowler, M.; Millar, I. L.; Strachan, R. A.; Fallick, A. E.

    2013-05-01

    The Neoproterozoic (c. 870 Ma) West Highland Granitic Gneiss, exposed in the Northern Highlands Terrane of Scotland, has elemental characteristics that are strikingly similar to those of the host Moine metasediments, which are thus consistent with an origin involving major Moine melting. Most of the constituent bodies have compositions significantly removed from minimum melts of pelites, and trace element constraints suggest variable but significant restite entrainment leading to less silicic bulk compositions with enhanced REE, Zr and Y. However, initial Nd and Hf isotope ratios are not coincident with contemporary Moine and imply a significant juvenile contribution. Close association with a regional suite of metabasites prompts consideration of mafic magma input, for which binary mixing models offer qualitative support. Quantitative difficulties with typical Moine metasediments are eased with radiogenic pelites or by partial melting of the mafic component. A possible alternative is currently unexposed Grenvillian felsic crust. Subsequent interaction of the granitic gneisses with meteoric water has significantly perturbed the oxygen and Sr isotope systems, the timing of which is equivocal but probably occurred during Caledonian events. The elemental characteristics of the West Highland Granitic Gneiss show many similarities with Scandinavian (rift-related?) granites of the same age, but since their geochemistry is largely inherited from the protolith it would be unwise to pursue palaeotectonic attribution on this basis. However, the probable incorporation of significant mantle-derived mafic magma of MORB-like affinity is consistent with an extensional setting.

  19. Kibaran magmatism and Pan-African granulite metamorphism in northern Mozambique: single zircon ages and regional implications

    NASA Astrophysics Data System (ADS)

    Kroner, A.; Sacchi, R.; Jaeckel, P.; Costa, M.

    1997-10-01

    Single zircons from granitoid orthogneisses in the foreland of the Lurio Belt of northern' Mozambique were dated by the evaporation method and yielded 207Pb/ 206Pb magmatic emplacement ages between 1040.1 ±0.4 and 1148.2±0.4 Ma. These data confirm previous RbSr whole rock and SHRIMP zircon analyses and record a period of magmatic activity corresponding to the Kibaran event of east central Africa. A1300 Ma old zircon xenocryst in one sample suggests the presence of still older crust in the region. Metamorphic zircons from a granulite-facies psammopelitic gneiss of the Mugeba klippe, which is derived tectonically from the Lurio Belt, were dated by evaporation, conventional techniques and SHRIMP at ˜615 Ma. This us interpreted as reflecting the peak of high-grade metamorphism in this rock and, by implication, in the Lurio Belt. It is concluded from this that the main metamorphism in the basement of northern Mozambique occured in Pan-African times, as is the case in adjacent regions of Tanzania and Malawi, and that this may be the result of collision between East and West Gondwana

  20. Zircon U-Pb ages and Hf isotopes of the Askot klippe, Kumaun, northwest India: Implications for Paleoproterozoic tectonics, basin evolution and associated metallogeny of the northern Indian cratonic margin

    NASA Astrophysics Data System (ADS)

    Mandal, Subhadip; Robinson, Delores M.; Kohn, Matthew J.; Khanal, Subodha; Das, Oindrila; Bose, Sukhanjan

    2016-04-01

    Throughout the Himalayan thrust belt, klippen of questionable tectonostratigraphic affinity occur atop Lesser Himalayan rocks. Integrated U-Pb ages, Hf isotopic, and whole rock trace element data establish that the Askot klippe, in northwest India, is composed of Paleoproterozoic lower Lesser Himalayan rocks, not Greater Himalayan rocks, as previously interpreted. The Askot klippe consists of 1857 ± 19 Ma granite-granodiorite gneiss, coeval 1878 ± 19 Ma felsic volcanic rock, and circa 1800 Ma Berinag quartzite, representing a small vestige of a Paleoproterozoic (circa 1850 Ma) continental arc, formed on northern margin of the north Indian cratonic block. Detrital zircon from Berinag quartzite shows ɛHf1850 Ma values between -9.6 and -1.1 (an average of -4.5) and overlaps with ɛHf1850 Ma values of the Askot klippe granite-granodiorite gneiss (-5.5 to -1.2, with an average of -2.7) and other Paleoproterozoic arc-related Lesser Himalayan granite gneisses ( -4.8 to -2.2, with an average of -4.0). These overlapping data suggest a proximal arc source for the metasedimentary rocks. Subchondritic ɛHf1850 Ma values (-5.5 to -1.2) of granite-granodiorite gneiss indicate existence of a preexisting older crust that underwent crustal reworking at circa 1850 Ma. A wide range of ɛHf1850 Ma values in detrital zircon (-15.0 to -1.1) suggests that a heterogeneous crustal source supplied detritus to the northern margin of India. These data, as well as the presence of a volcanogenic massive sulphide deposit within the Askot klippe, are consistent with a circa 1800 Ma intra-arc extensional environment.

  1. Granitoid generation and laxfordian tectonic evolution in the northern part of the lewisian complex

    NASA Astrophysics Data System (ADS)

    Castro, A.; Lopez, S.; Fernandez, C.

    2003-04-01

    Several terranes have been distinguished in the Lewisian complex of Scotland. The contact between the Rhiconich and Assynt terranes, in the northern part of the mainland Lewisian complex, is outlined by a major shear zone, the Laxford front. The tectonic activity in this shear zone took place mainly during the Early Proterozoic (1900 to 1600 Ma), defining a Laxfordian period of deformation and metamorphism. Generalized migmatization of the tonalite-trondhjemite (TT) gneisses developed coeval with the intrusion of abundant Fe-diorite tabular bodies in the Rhiconich terrane. Field structures indicate that both TT gneisses and Fe-diorites coexisted as melts or partially molten systems. The composition of the TT gneisses changes to granodioritic in the vicinity of the diorite intrusions. It is suggested that percolation of alkali-rich fluids released from the crystallising diorite magma through the TT migmatites could explain this compositional change. The presence of granite and pegmatite dikes is characteristic of the Rhiconich terrane. The observed structural relationships indicate that the migmatization of the TT gneisses and the intrusion of basic and granitic rocks are simultaneous processes, and that they developed in association with the Laxfordian deformation. In contrast, the Assynt terrane is almost devoid of basic and granitic intrusions during the Laxfordian period. The main structures developed within the Laxford front are a WNW-ESE oriented foliation, dipping to the north, and a lineation slightly plunging to the ESE. Kinematic criteria include composite planar fabrics, asymmetric porphyroclast systems and sheath folds, and allow us to deducing a dextral-reverse sense of movement. Similarly, the Laxfordian deformation in the Rhiconich terrane gave place to a pervasive foliation and lineation, north-verging folds and dextral-reverse minor shear zones. Accordingly, the Laxfordian period in the northern Lewisian can be wholly described as a dextral

  2. Component geochronology in the polyphase ca. 3920 Ma Acasta Gneiss

    USGS Publications Warehouse

    Mojzsis, Stephen J.; Cates, Nicole L.; Caro, Guillaume; Trail, Dustin; Abramov, Oleg; Guitreau, Martin; Blichert-Toft, Janne; Hopkins, Michelle D.; Bleeker, Wouter

    2014-01-01

    The oldest compiled U–Pb zircon ages for the Acasta Gneiss Complex in the Northwest Territories of Canada span about 4050–3850 Ma; yet older ca. 4200 Ma xenocrystic U–Pb zircon ages have also been reported for this terrane. The AGC expresses at least 25 km2 of outcrop exposure, but only a small subset of this has been documented in the detail required to investigate a complex history and resolve disputes over emplacement ages. To better understand this history, we combined new ion microprobe235,238U–207,206Pb zircon geochronology with whole-rock and zircon rare earth element compositions ([REE]zirc), Ti-in-zircon thermometry (Tixln) and 147Sm–143Nd geochronology for an individual subdivided ∼60 cm2 slab of Acasta banded gneiss comprising five separate lithologic components. Results were compared to other variably deformed granitoid-gneisses and plagioclase-hornblende rocks from elsewhere in the AGC. We show that different gneissic components carry distinct [Th/U]zirc vs. Tixln and [REE]zirc signatures correlative with different zircon U–Pb age populations and WR compositions, but not with 147Sm–143Nd isotope systematics. Modeled  [REE] from lattice-strain theory reconciles only the ca. 3920 Ma zircons with the oldest component that also preserves strong positive Eu∗ anomalies. Magmas which gave rise to the somewhat older (inherited) ca. 4020 Ma AGC zircon age population formed at ∼IW (iron–wüstite) to gneisses.

  3. Revisiting the high temperature metamorphic field gradient of the Ryoke Belt (SW Japan): New constraints from the Iwakuni-Yanai area

    NASA Astrophysics Data System (ADS)

    Skrzypek, Etienne; Kawakami, Tetsuo; Hirajima, Takao; Sakata, Shuhei; Hirata, Takafumi; Ikeda, Takeshi

    2016-09-01

    We revisit the origin of the metamorphic field gradient exposed in the Ryoke Belt (SW Japan) - the type locality for low pressure/high temperature (LP/HT) conditions - based on combined structural, petrological and geochronological data from the Iwakuni-Yanai area (W Ryoke). In this area metasedimentary rocks pass from schist in the north to partly migmatitic paragneiss in the south, and are surrounded by numerous granitoid bodies. Three deformation phases are emphasized; an accretionary-stage or burial deformation of weak intensity (D0), a vertical shortening (D1) which generated a subhorizontal, locally extensional foliation in the southern gneiss zone, and E-W upright folding (D2) which reworked both the northern schist and southern gneiss zones. Crystallization-deformation relationships indicate that, in the schist zone, most andalusite, cordierite and mica porphyroblasts formed after D0 and before D1. Syn-D1 mineral assemblages define E-W trending metamorphic zones with increasing grade from north to south, and rare syn-D2 parageneses reveal a similar pattern. Continuous magmatic activity lasted from ca. 105 to 94 Ma. The oldest granitoids (Shimokuhara, Soo, Namera), found in the western part of the belt, were emplaced below schistose rocks at 105-100 Ma. Subsequently, syn- to post-D1 granodiorite (Gamano) intruded concordantly with the foliation of southern, high-grade gneissic rocks from 100 to 94 Ma. A large, syn-D1 pluton (Kibe) intruded the center of the belt at 98 Ma, whereas a younger granite (Iwakuni) and its satellite dykes were emplaced to the northeast at 96-94 Ma. Constraints on the timing of D1 (103-99 Ma) and the likely diachronous D2 phase (100-94 Ma) suggest a deformation continuum during magma intrusion and metamorphism. We conclude that the exposed metamorphic field gradient is an apparent, but fortuitous, alignment of P-T data resulting from spatially and temporally distinct thermal events. Peak temperature conditions in the relatively

  4. Geochemistry, geochronology and zircon Hf isotopic study of peralkaline-alkaline intrusions along the northern margin of the North China Craton and its tectonic implication for the southeastern Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Zhao, Pan; Jahn, Bor-ming; Xu, Bei; Liao, Wen; Wang, Yanyang

    2016-09-01

    A giant Permian alkaline magmatic belt has recently been identified in southern Inner Mongolia, along the northern margin of the North China Craton (NCC). This belt is mainly composed of syenite, quartz syenite, alkaline granite and mafic microgranular enclaves (MME)-bearing granodiorite. In order to study the petrogenesis and tectonic implications of these rocks, we undertook zircon U-Pb dating and geochemical analysis of two Permian alkaline plutons. The first Guangxingyuan Pluton occurs in the Hexigten area and is composed of MME-bearing tonalite, K-feldspar granite and syenite. The second Durenwuliji Pluton, located in the Xianghuangqi area, comprises syenite, quartz syenite and K-feldspar granite. Zircon U-Pb dating on tonalite, K-feldspar granite, syenite and quartz syenite from the two plutons yielded a tight range of ages from 259 to 267 Ma. The peralkaline-alkaline rocks show high abundance of total alkalis (K2O + Na2O = 7.9-12.9%) and K2O contents (3.9-8.0%), enrichment in large ion lithophile elements (LILE) and light rare earth element (LREE), and depletion of high field strength elements (HFSE). The associated tonalite and MMEs display I-type granitic geochemical affinity, with less total abundance of trace elements than the peralkaline-alkaline rocks. Zircon Hf isotopic analysis of the Guangxingyuan pluton yielded a large range of εHf(t) values from - 15.5 to + 6.7 and model ages (TDMC) from 781 to 2012 Ma. By contrast, the Hf isotopic data of the Durenwuliji pluton shows a small range of εHf(t) from + 6.2 to + 8.9 and TDMC from 667 to 816 Ma. The geochemical and Hf isotopic characteristics indicate that the parental magma was derived from a mixing of metasomatic mantle-derived mafic magma with different amount of crust-derived felsic magma, and followed by fractional crystallization. Considering previous tectonic studies in Inner Mongolia, a Permian post-orogenic extension was proposed to account for these peralkaline-alkaline intrusions following

  5. Caribbean affinities of mafic crust from northern Colombia: preliminary geochemical results from basaltic rocks of the Sinu-San Jacinto belt

    NASA Astrophysics Data System (ADS)

    Bustamante, C.; Cardona, A.; Valencia, V.; Weber, M.; Guzman, G.; Montes, C.; Ibañez, M.; Lara, M.; Toro, M.

    2009-12-01

    The petrotectonic characterization of accreted mafic remnants within the northern Andes and the Caribbean yield major insights on the growth and evolution of oceanic plates, as well as in the identification of the role of terrane accretion within the northern Andes orogeny. Within the northern termination of the Andes, in northern Colombia, several exposures of mafic and ultramafic rocks have been identified. However, extensive sedimentary cover and difficulties in field access have left the petogenetic analysis and tectonic implications of this rocks scarcely studied. Preliminary geochemical constrains from volcanic rocks obtained in outcrops and as clasts from a Paleocene-Eocene conglomerate indicate that the mafic rocks are mainly andesitic in composition, with well defined enrichment in Th and Ce and depletion in Nb and flat to weakly enriched LREE. These features suggest a relatively immature intra-oceanic volcanic arc setting for the formation of these rocks. Hornblende-dioritic dikes in peridotites also attest to the role of water in the magmatic evolution, and the affinity to a subduction related setting. The tectonic implications of this arc remnants and the relation between these rocks and other oceanic domains in the northern Andes suggest that the compositional and tectonic setting on the different accreted margins of the Caribbean plate are heterogeneous.

  6. The Late Cretaceous Aarya flora of the northern Okhotsk region and phytostratigraphy of the lower part of the Okhotsk-Chukotka volcanogenic belt section

    NASA Astrophysics Data System (ADS)

    Shczepetov, S. V.; Golovneva, L. B.

    2014-07-01

    The Zarya flora comes from volcanogenic sedimentary rocks of the Zarya and Parnyi formations that correspond to the basal part of the section of the Okhotsk-Chukotka volcanogenic belt in the Omsukchan district (Magadan oblast, Russia). The revision of its taxonomic composition resulted in identifying approximately 25 species of horsetails, ferns, cycads, ginkgoalens, czekanowskians, conifers, and angiosperms. The Zarya flora is characterized by a combination of the Early Cretaceous relicts ( Hausmannia, Birisia, Sphenobaiera, Phoenicopsis, Nilssonia, Podozamites) and typical Late Cretaceous taxa ( Taxodium, Sequoia, Menispermites, Dalembia, Trochodendroides, Cissites, Terechovia, Platanaceae). Among all the paleofloral assemblages of the Okhotsk-Chukotka volcanogenic belt, the Zarya flora is the most similar to the Turonian-Coniacian Arman flora of the Magadan region, which indicates their synchronism and floral unity. The Chingandzha flora of the Omsukchan area, which comes from the same stratigraphic level as Zarya flora, differs substantially from the latter in its taxonomic composition. It is conceivable that the Chingandzha flora was confined to a large river valley which was connected to coastal lowlands. The plant remains of the Arman flora with many mountain relicts could be buried in sediments of intermountain troughs isolated from coastal lowlands. Araucarites ochotensis sp. nov. is described.

  7. Multiple deformation at the western edge of the Carolina slate belt, north-central North Carolina

    SciTech Connect

    Hibbard, J.P.; Shell, G.S.; Wilkins, J.K. ); Samson, S.; Wortman, G. . Dept. of Geology)

    1994-03-01

    In north-central North Carolina, volcanic-plutonic rocks of the Carolina slate belt are separated from gneisses of the Milton belt to the west by a wide, ENE-trending, polygenetic structural zone. Within a portion of this zone, the Country Line Creek complex (CLCC) forms the western edge of the slate belt. Rocks of the CLCC span a wide age range and include mafic and granitoid gneisses with subordinate pelitic schist, granitoid pegmatite, and a concordant sheet-like intrusion, the Yanceyville metagranite. The complex is heterogeneously deformed and metamorphosed. Along the SE margin of the structural zone, steeply-dipping, strongly foliated biotite granitoid and mafic gneisses of the complex appear to be intruded by the Roxboro metagranite of the Carolina slate belt. To the NW, in more interior portions of the zone, the CLCC is affected by multiphase foliations and folds that record a dextral oblique normal shear event. Here, the Yanceyville metagranite is affected by a strong foliation that is folded. A preliminary new date on the Roxboro pluton of ca. 545 Ma, indicates a Late Precambrian or older timing of deformation along the SE margin of the zone. In contrast, a preliminary, ca. 340 Ma, age on the Yanceyville metagranite indicates multiple stage Late Paleozoic deformation for interior portions of the zone. Regional structural and isotopic data hint that the Precambrian deformation may record initial interactions between the Milton and Carolina slate belts. Subsequently, this contact was reactivated during Alleghanian orogenesis.

  8. New Sr, Nd, and Pb isotopic data from plutons in the northern Great Basin: Implications for crustal structure and granite petrogenesis in the hinterland of the Sevier thrust belt

    SciTech Connect

    Wright, J.E. ); Wooden, J.L. )

    1991-05-01

    The influence of tectonic setting and age on the variation of isotopic signatures of granitic plutons in the northern Great Basin has, in general, not been apparent from previous investigations. None of these studies revealed the remarkable correlation shown by this expanded Sr, Nd, and Pb isotopic data base. Jurassic-Early Cretaceous plutons in the northern Great Basin have a limited range of Sr and Nd isotopic values that cluster near bulk earth. Construction of Sr 0.706 and {epsilon}{sub Nd} = {minus}7 isotopic boundaries is virtually impossible for plutons of this age range. In contrast, Upper Cretaceous peraluminous granites east of the {epsilon}{sub Nd} = {minus}7 line have very negative {epsilon}{sub Nd} values and high initial Sr ratios, and they appear to represent essentially pure crustal melts. The data favor a model that equates generation of these plutons via crustal thickening associated with the Sevier thrust belt. Cenozoic plutons appear to be mixtures of mantle and crustal reservoirs, and their isotopic systematics, along with those of the Late Cretaceous age plutonic suite, define a previously unrecognized, approximately east-west-trending crustal boundary between predominantly Archean crust to the north and predominantly Proterozoic crust to the south. The isotopic data from the Jurassic-Early Cretaceous plutonic suite do not reflect the presence of this boundary, suggesting that the isotopic systematics of this plutonic suite may not have been controlled by the same variations in crustal and/or mantle lithospheric structure at depth.

  9. The pre-Mesozoic tectonic unit division of the Xing-Meng orogenic belt (XMOB)

    NASA Astrophysics Data System (ADS)

    Xu, Bei; Zhao, Pan

    2014-05-01

    According to the viewpoint that the paleo-Asian ocean closed by the end of early Paleozoic and extended during the late Paleozoic, a pre-Mesozoic tectonic unit division has been suggested. Five blocks and four sutures have been recognized in the pre-Devonia stage, the five blocks are called Erguna (EB), Xing'an (XB), Airgin Sum-Xilinhot (AXB), Songliao-Hunshandak (SHB) and Jiamusi (JB) blocks and four sutures, Xinlin-Xiguitu (XXS), Airgin Sum-Xilinhot-Heihe (AXHS), Ondor Sum-Jizhong-Yanji (OJYS) and Mudanjiang (MS) sutures. The EB contains the Precambrian base with the ages of 720-850Ma and ɛHf(T)=+2.5to +8.1. The XB is characterized by the Paleoproterozoic granitic gneiss with ɛHf(T)=-3.9 to -8.9. Several ages from 1150 to 1500 Ma bave been acquired in the AXB, proving presence of old block that links with Hutag Uul block in Mongolia to the west. The Paleoproterozoic (1.8-1.9Ga) and Neoproterozoic (750-850Ma) ages have been reported from southern and eastern parts of the SHB, respectively. As a small block in east margin of the XMOB, the JB outcrops magmatite and granitic gneiss bases with ages of 800-1000Ma. The XXS is marked by blueschists with zircon ages of 490-500Ma in Toudaoqiao village, ophiolites in Xiguitu County and granite with ages of about 500Ma along the northern segment of XXS. The AXHS is characterized by the early Paleozoic arc magmatic rocks with ages from 430Ma to 490Ma, mélange and the late Devonia molass basins, which indicates a northward subduction of the SHB beneath the AXB during the early-middle Paleozoic. The OJYS is composed of the early Paleozoic volcanic rocks, diorites and granites with ages of 425-475Ma, blueschists, ophiolitic mélange, the late Silurian flysch and Early-Middle Devonian molasses in western segment, granites (420-450Ma) in middle segment, and plagiogranites (443Ma) and the late Silurian molasses in eastern segment. This suture was caused by a southward subduction of the SHB beneath the North China block. The MS

  10. New U-Pb SHRIMP dating for the Leo Pargil gneiss dome, western Himalaya

    NASA Astrophysics Data System (ADS)

    Leech, M. L.; Sas, R.

    2006-12-01

    The Leo Pargil gneiss dome is comprised of upper amphibolite-facies metasedimentary rocks of the lower Tethyan Himalayan sequence (the Haimantas unit) that are intruded by numerous small granitoid bodies and leucogranite dikes. The dome is exposed in northern India/southwestern Tibet at the confluence of the Sutlej and Spiti rivers west of the Zada basin. The dome is bound by generally N-S trending normal faults; the western boundary is termed the Kaurik-Chango normal fault and has a history of recent seismicity. The Leo Pargil dome differs from other North Himalayan domes in that it exhibits orogen-parallel stretching lineations and a uniform top-to-the-northwest sense-of-shear on its western flank (in contrast to approximately arc-normal stretching lineations and variable sense-of-shear in other North Himalayan domes; the youngest phase of Leo Pargil dome development is related to an orogen-parallel extensional structure similar to that which bounds the Gurla Mandhata dome to the southeast. New U-Pb SHRIMP dating of zircon yields Late Archean to Late Proterozoic ages for Leo Pargil paragneisses (c. 800-900 Ma and rarer 2-3 Ga zircons) and Late Oligocene to Early Miocene ages for granitoid intrusions (c. 27-16 Ma). These Oligocene to Miocene ages for Leo Pargil granitoids may correspond to magmatism associated with the widespread leucogranite bodies exposed througout the Himalaya. The Leo Pargil dome, like other similar Himalayan gneiss domes, may be exposures of a ductile mid-crustal channel.

  11. Systematic conveyor belt cleaning

    SciTech Connect

    Rappen, A.

    1984-01-01

    The currently available conveyor belt cleaning devices are enumerated. Recent investigations have confirmed the belt scraping devices based on intermittent linear contact by means of individually adjustable and spring-loaded scraper blades, usually of metallic construction as the most advanced type of belt cleaner. The system also allows application on reversing belts. Criteria are presented for assessing the performance of a belt cleaner.

  12. Origin and dynamics of the northern South American coastal savanna belt during the Holocene - the role of climate, sea-level, fire and humans

    NASA Astrophysics Data System (ADS)

    Alizadeh, Kamaleddin; Cohen, Marcelo; Behling, Hermann

    2015-08-01

    Presence of a coastal savanna belt expanding from British Guiana to northeastern Brazil cannot be explained by present-day climate. Using pollen and charcoal analyses on an 11.6 k old sediment core from a coastal depression in the savanna belt near the mouth of the Amazon River we investigated the paleoenvironmental history to shed light on this question. Results indicate that small areas of savanna accompanied by a forest type composed primarily by the genus Micropholis (Sapotaceae) that has no modern analog existed at the beginning of the Holocene. After 11,200 cal yr BP, savanna accompanied by few trees replaced the forest. In depressions swamp forest developed and by ca 10,000 cal yr BP replaced by Mauritia swamps. Between 8500 and 5600 cal yr BP gallery forest (composed mainly of Euphorbiaceae) and swamp forest succeeded the treeless savanna. The modern vegetation with alternating gallery forest and savanna developed after 5600 cal yr BP. We suggest that the early Holocene no-analog forest is a relict of previously more extensive forest under cooler and moister Lateglacial conditions. The early Holocene savanna expansion indicates a drier phase probably related to the shift of the Intertropical Convergence Zone (ITCZ) towards its northernmost position. The mid-Holocene forest expansion is probably a result of the combined influence of equatorwards shift of ITCZ joining the South Atlantic Convergence Zone (SACZ). The ecosystem variability during the last 5600 cal yr BP, formed perhaps under influence of intensified ENSO condition. High charcoal concentrations, especially during the early Holocene, indicate that natural and/or anthropogenic fires may have maintained the savanna. However, our results propose that climate change is the main driving factor for the formation of the coastal savanna in this region. Our results also show that the early Holocene sea level rise established mangroves near the study site until 7500 cal yr BP and promoted swamp formation in

  13. Structural record of mechanisms of granite intrusion in the Achaean gneisses

    NASA Astrophysics Data System (ADS)

    Perchuk, L. L.; van Reenen, D. D.

    2009-04-01

    A model of diapiric formation of granite domes within green-stone areas is based on gravitational re-distribution mechanisms of rocks in the Precambrian continental crust (e.g. McGregor, 1951; Ramberg, 1951; Perchuk, 1989, 1993; Perchuk et al., 1992). In addition, the gravitational re-distribution is the leading mechanism to form Precambrian granulite facies terrains among green-stone belts. It has been proven by data on general geology, tectonics, petrology, geochemistry, isotopic geology, geophysics, and numerical modeling (Perchuk et al., 2001; Gerya et al., 2000, 2002). However the behavior of granite melt within gneisses of similar bulk composition is questionable. If the above mechanisms works well in the case of "granitic gneiss - granite melt", the ascending rocks must have structural features that indicate upward movement, while the adjacent wall rocks must demonstrate structural features of the opposite movement. In metamorphic rocks these features are represented by lineation, drag folds, orientation of fold hinges etc. Apart from "straight gneisses" (Davidson, 1984; Smit & van Reenen, 1997) no direct evidence for the internal dynamics of the formation of high-grade terrains has ever been considered. In this paper we formulate a rule allowing discrimination between cylindrical metamorphogenic and magmatogenic structures and demonstrate a model of their formation. Two types of ring structures are considered as indicators of ascending granulites toward the surface, i.e. cylindrical folds (sheath fold) and granite stocks. Systematic studies of such structures at diverse erosion sections allowing the conclusion on their formation. During exhumation (decompression) of granulite facies terrains the formation of sheath folds are resulted from generation of the granite magma within the same granitogneissic material and subsequent uprising due to difference in densities of contacting materials because all sheath folds con. This is recorded in the contrasting

  14. Distinct magnetic fabric in weakly deformed sediments from extensional basins and fold-and-thrust structures in the Northern Apennine orogenic belt (Italy)

    NASA Astrophysics Data System (ADS)

    Caricchi, Chiara; Cifelli, Francesca; Kissel, Catherine; Sagnotti, Leonardo; Mattei, Massimo

    2016-02-01

    We report on results from anisotropy of magnetic susceptibility (AMS) analyses carried out on weakly deformed fine-grained sediments from the Northern Apennine orogenic system (Italy). We sampled 63 sites from preorogenic, synorogenic, and postorogenic sequences, which differ in age, composition, depositional environment, degrees of deformation, and tectonic regimes. The magnetic fabric is typical of weakly deformed sediments, with a magnetic foliation subparallel to the bedding plane and a magnetic lineation well defined in this plane. Northern Apennine chain deposits are characterized by strongly oblate magnetic susceptibility ellipsoids, indicating that the magnetic fabric is the result of both compaction process and tectonic load experienced by the sediments during diagenesis and orogenic events. The orientation of magnetic lineation is significantly different depending whether the studied sites underwent extensional or compressional tectonic regimes. In the Northern Apennine chain, the magnetic lineation is mostly oriented NNW-SSE, parallel to the main compressional structures. It suggests a tectonic origin of the magnetic lineation with an acquisition related to the Apennines compressional phases. In the extensional Tuscan Tyrrhenian margin, magnetic lineation is oriented ENE-WSW, almost perpendicular to the main extensional faults, which represent the main deformation elements of the area. Our results demonstrate a close relationship between the shape and orientation of magnetic fabric and the tectonic history of rocks, confirming that AMS represents a valuable tool to investigate the tectonic history of weakly deformed sedimentary rocks.

  15. Deep Structure of the Fold-and-Thrust Belt in the Tenpoku Area, Northern Hokkaido Island, Japan, Revealed by Reprocessing of Seismic Reflection Data From the 1990 MITI Geophysical Explorations.

    NASA Astrophysics Data System (ADS)

    Yokokura, T.; Miyazaki, T.; Kano, N.

    2005-12-01

    The Tenpoku area, the northern part of Hokkaido island, Japan, is believed to have hydrocarbon potential in the thick Cretaceous-Tertiary sediments. Ministry of International Trade and Industry (MITI, present Ministry of Economy, Trade and Industry) and some private companies have conducted many geological and geophysical explorations and test drillings in this area. These surveys have revealed that some anticlines (e.g. Horonobe and Toyotomi anticlines) and faults (e.g. Ohmagari and Horonobe faults) exist in the mountainous area and that a large sedimentary basin extends from the west of the mountainous area to the Japan Sea. The area shows a fold-and-thrust belt structure of west vergence. There is an active Sarobetsu flexural zone in the eastern end of the sedimentary basin. The flexural zone is believed to have become active since the middle Pliocene. In this way, overall geological structure down to around 5km in depth is well known, while there is few information about the deeper part. Japan National Oil Corporation (present Japan Oil, Gas and Metals National Corporation (JOGMEC)) conducted seismic reflection surveys in this area in 1990 on consignment from MITI. Part of the seismic reflection data was acquired by using dynamite and has long two-way traveltime of 18sec. As the seismic data may provide us deeper information on this fold-and-thrust belt, we tried to reprocess the data with permission by JOGMEC. As a result, we found that two low-angle east-dipping thrusts extend to around 10km in depth, which are related to the Ohmagari fault and Sarobetsu flexural zone. Beneath these thrusts, some other east-dipping thrusts also exist which may be related to micro-earthquake activity of this area.

  16. A ground electromagnetic survey used to map sulfides and acid sulfate ground waters at the abandoned Cabin Branch Mine, Prince William Forest Park, northern Virginia gold-pyrite belt

    USGS Publications Warehouse

    Wynn, Jeffrey C.

    2000-01-01

    INTRODUCTION AND BACKGROUND: Prince William Forest Park is situated at the northeastern end of the Virginia Gold-Pyrite belt northwest of the town of Dumfries, VA. The U. S. Marine Corps Reservation at Quantico borders the park on the west and south, and occupies part of the same watershed. Two abandoned mines are found within the park: the Cabin Branch pyrite mine, a historic source of acid mine drainage, and the Greenwood gold mine, a source of mercury contamination. Both are within the watershed of Quantico Creek (Fig.1). The Cabin Branch mine (also known as the Dumfries mine) lies about 2.4 km northwest of the town of Dumfries. It exploited a 300 meter-long, lens-shaped body of massive sulfide ore hosted by metamorphosed volcanic rocks; during its history over 200,000 tons of ore were extracted and processed locally. The site became part of the National Capitol Region of the National Park Service in 1940 and is currently managed by the National Park Service. In 1995 the National Park Service, in cooperation with the Virginia Department of Mines, Minerals, and Energy reclaimed the Cabin Branch site. The Virginia Gold-Pyrite belt, also known as the central Virginia volcanic-plutonic belt, is host to numerous abandoned metal mines (Pavlides and others, 1982), including the Cabin Branch deposit. The belt itself extends from its northern terminus near Cabin Branch, about 50 km south of Washington, D.C., approximately 175 km to the southwest into central Virginia. It is underlain by metamorphosed volcanic and clastic (non-carbonate) sedimentary rocks, originally deposited approximately 460 million years ago during the Ordovician Period (Horton and others, 1998). Three kinds of deposits are found in the belt: volcanic-associated massive sulfide deposits, low-sulfide quartz-gold vein deposits, and gold placer deposits. The massive sulfide deposits such as Cabin Branch were historically mined for their sulfur, copper, zinc, and lead contents, but also yielded byproduct

  17. Geochronology of the Franciscan Eastern Belt in the Yolla Bolly Area, Northern California, and the Nature of the South Fork Mountain Schist

    NASA Astrophysics Data System (ADS)

    Dumitru, T. A.; Wright, J. E.; Wakabayashi, J.; Wooden, J. L.

    2006-12-01

    Using the SHRIMP-RG, we have determined U-Pb ages of 285 detrital zircon grains from 7 metagraywacke samples of the Franciscan Eastern Belt in the Yolla Bolly area. The youngest clusters of zircon ages place upper brackets on the depositional ages of the protoliths of the various Eastern Belt units at the specific sampled locations as follows: South Fork Mtn Schist (SFMS), <=135 Ma; Valentine Springs Fm (VSF), <=120 Ma; Yolla Bolly terrane (YBT), <=111 Ma. An Ar/Ar age of small sills farther SW indicates the YBT also contains protolith >= 119 Ma (Mertz et al., 2001). Ages of subsequent accretion and metamorphism must be younger. Three new step-heat Ar/Ar analyses on metamorphic white mica separates from the SFMS at Yolla Bolly clustered tightly at 121 Ma. Therefore the depositional age of at least part of the SFMS protolith is bracketed between 135 and c. 123 Ma. Small amounts of excess argon are apparent in two of these samples, but excellent isochron fits permit correction for this complication. About 38 Ar/Ar total gas (not step heat) and K-Ar total gas ages have previously been reported on whole rock samples from the SFMS proper and generally cluster around 120 Ma. However, some ages deviate markedly. These deviations show little correlation with location, structural position, etc. Reconsideration of these data in light of our new data strongly suggests that the entire 330-km-long outcrop belt of the SFMS is characterized by a single, strikingly consistent argon cooling age of approximately 121 Ma. Older SFMS argon ages appear to be unreliable, possibly due to excess argon in some cases. The total volume of exposed Franciscan rocks that are demonstrably older than the SFMS is exceedingly small (e.g., high-grade blocks, Ward Creek, Skaggs Spring schist), whereas the volume that is slightly younger is large (e.g., VSF, YBT, Diablo Range). This suggests that the accretion of the SFMS marks a transition from predominately nonaccretionary to accretionary conditions

  18. Evolution of the siliciclastic-carbonate shelf system of the northern Kenyan coastal belt in response to Late Pleistocene-Holocene relative sea level changes

    NASA Astrophysics Data System (ADS)

    Accordi, Giovanni; Carbone, Federico

    2016-11-01

    A classification of depositional environments of the Lamu Archipelago is proposed based on a sedimentary facies analysis of unconsolidated and hard bottoms of the study area. The genesis of the siliciclastic-carbonate depositional pattern, typical of this East African region, is closely related both to the presence of a quartz-dominate Pleistocene riverine net-flooded during the Holocene sea level rise-and to the coeval development on the shallow shelf of a coral ecosystem producing vast skeletal sediments. The present facies pattern originates from the variable contribution in time and space of three sediment types: skeletal carbonate, quartz and palimpsest debris. The facies analysis allowed to distinguish 10 depositional facies and to differentiate them into three main types of substratum: soft bottom, reefal hard bottom and non-reefal hard bottom. These three types define both the loose facies typical of the channelized coastal belt and several facies of the shallow shelf. In the first, the amounts and textures of the stored sediment are strictly related to three major geomorphic types of substratum: sheltered mangal flat, shallow channel and deep channel. In the second and the third, a wide range of textures is related to coastal flats, benches, islets and emerging rocks. This modern facies pattern is implemented through a series of evolutionary phases: i-during the Last Interglacial Period, since isotope substage 5b, the shallow shelf-above -20 m-is permanently exposed for about 80 ka, with erosion, karstification and cuts of river channels through the shelf; ii-after the Last Glacial Maximum, when the sea level fell to about 110-115 m b.p.s.l. (below present sea level) at 18-17 ka BP, the sea level rose at -20 m for about 9 ka, flooding the shallow shelf area and gradually drowning the riverine net; iii-the maximum flooding of the coastal belt was reached at about 4.5 ka BP, when a gradual moisture reduction caused a decrease of siliciclastic sediment supply

  19. Rare Earth and HFSE Constraints on Basalt Source Regions and Melting Conditions in the Garibaldi Volcanic Belt, Northern Cascadia Subduction System

    NASA Astrophysics Data System (ADS)

    Green, N. L.

    2002-12-01

    Garibaldi belt (GVB) basalts were erupted above the relatively young (<24 Ma) Juan de Fuca plate, subducted oceanic lithosphere that becomes progressively younger (22-13 Ma), and presumably hotter, northward along the Cascadia convergent margin. Mafic lavas of the 15-km-wide volcanic belt range from high-alumina olivine tholeiites and magnesian andesites near Glacier Peak, northwestern Washington, through transitional basalts to alkali-olivine basalts and basanites in the Bridge River-Salal Glacier areas, southwestern British Columbia. Significant strike-parallel variations characterize REE and HFSE contents of these (GVB) basalts and provide insight into the nature of mantle source heterogeneities that may characterize subduction regimes. Lavas of more northerly volcanic suites tend to have (1) somewhat higher Ti, Nb, Ta, Zr, Hf, La, total REE, La/Yb, Sm/Yb, Nb/Y, Zr/Y, Y/Sc and Zr/Yb and (2) lower Th/U, La/Nb, and Th/Yb. The basalts have sub-chondritic to chondritic Na/Tb (6-21) and chondritic to super-chondritic Zr/Hf (up to 55.90) ratios. Only Mount Baker and Glacier Peak basalts exhibit the distinctive negative Na-Ta anomalies associated with arc lavas. REE systematics suggest that the more northerly basaltic suites formed as lower degree melts of mantle sources typically containing 1) garnet + spinel peridotite rather than spinel peridotite and 2) slightly more garnet (4% versus 2%) than in garnet-bearing source regions beneath more southerly eruptive centers. Inverse REE modeling suggests that the Bridge River-Salal Glacier lavas may have been derived from at least two distinct source regions (garnet-bearing and garnet-free). Nb/Ta exhibits slight positive correlations with Nb, Ta, La/Yb, and Th/Yb in some GVB basaltic suites, implying the role of a residual mineral, most likely rutile, in controlling extremely low HFSE partitioning into suduction-related fluids that equilibrated with basalt source regions in the mantle wedge.

  20. Origin and dynamics of the northern South American coastal savanna belt during the Holocene - the role of climate, sea-level, fire and humans

    NASA Astrophysics Data System (ADS)

    Alizadeh, Kamaleddin; Cohen, Marcelo; Behling, Hermann

    2015-08-01

    Presence of a coastal savanna belt expanding from British Guiana to northeastern Brazil cannot be explained by present-day climate. Using pollen and charcoal analyses on an 11.6 k old sediment core from a coastal depression in the savanna belt near the mouth of the Amazon River we investigated the paleoenvironmental history to shed light on this question. Results indicate that small areas of savanna accompanied by a forest type composed primarily by the genus Micropholis (Sapotaceae) that has no modern analog existed at the beginning of the Holocene. After 11,200 cal yr BP, savanna accompanied by few trees replaced the forest. In depressions swamp forest developed and by ca 10,000 cal yr BP replaced by Mauritia swamps. Between 8500 and 5600 cal yr BP gallery forest (composed mainly of Euphorbiaceae) and swamp forest succeeded the treeless savanna. The modern vegetation with alternating gallery forest and savanna developed after 5600 cal yr BP. We suggest that the early Holocene no-analog forest is a relict of previously more extensive forest under cooler and moister Lateglacial conditions. The early Holocene savanna expansion indicates a drier phase probably related to the shift of the Intertropical Convergence Zone (ITCZ) towards its northernmost position. The mid-Holocene forest expansion is probably a result of the combined influence of equatorwards shift of ITCZ joining the South Atlantic Convergence Zone (SACZ). The ecosystem variability during the last 5600 cal yr BP, formed perhaps under influence of intensified ENSO condition. High charcoal concentrations, especially during the early Holocene, indicate that natural and/or anthropogenic fires may have maintained the savanna. However, our results propose that climate change is the main driving factor for the formation of the coastal savanna in this region. Our results also show that the early Holocene sea level rise established mangroves near the study site until 7500 cal yr BP and promoted

  1. Low-temperature thermochronologic constraints on cooling and exhumation trends along conjugate margins, within core complexes and eclogite-bearing gneiss domes of the Woodlark rift system of eastern Papua New Guinea

    NASA Astrophysics Data System (ADS)

    Fitzgerald, P. G.; Baldwin, S.; Bermudez, M. A.; Miller, S. R.; Webb, L. E.; Little, T.

    2012-12-01

    In eastern Papua New Guinea, active sea-floor spreading within the Woodlark Basin has been propagating westward since at least 6 Ma into heterogeneous crust of the Woodlark Rift. The seafloor spreading system divides the northern conjugate margin (Woodlark Rise) from the southern margin (Pocklington Rise). West of the seafloor spreading rift-tip are high-standing extensional gneiss domes and core complexes of the D'Entrecasteaux Islands (DEI). Domes comprise amphibolite and eclogite-facies gneisses, and Pleistocene granitoid intrusions. Flanked by mylonitic shear zone carapaces and normal faults, the domes are juxtaposed against an upper plate that includes ultramafic rocks and gabbro, correlated with the Papuan ultramafic belt. Petrologic and structural evidence from the DEI has been interpreted as evidence for diapiric ascent of the largely felsic domes, with thermo-mechanical modeling proposing (U)HP exhumation in terms of diapiric flow aided by propagating extension, with feedback between the two. Core complexes lacking evidence for diapiric-aided exhumation include the Prevost Range (eastern Normanby Island), Dayman Dome (Papuan Peninsula), and Misima Island (southern conjugate margin). Thermochronology is being applied to understand the thermal and exhumation history, and hence help constrain mechanisms of (U)HP exhumation. AFT and AHe ages from samples near sea-level along conjugate margins and DEI range from ca. 12 Ma to <1 Ma, generally decreasing from east to west, although with some localized variation. Confined track length distributions (CTLD), obtained using 252Cf implantation, generally indicate rapid cooling (means ≥~14 μm), except on Goodenough Island, the western-most and highest-standing dome. On Goodenough Island, samples from the core zone have AFT ages from ~3 - <1 Ma with age decreasing with decreasing elevation. Core zone samples have mean track lengths (7-13 μm) and are positively skewed, whereas samples from shear zones are younger (<1

  2. Permeability Evolution of Granite Gneiss During Triaxial Creep Tests

    NASA Astrophysics Data System (ADS)

    Liu, L.; Xu, W. Y.; Wang, H. L.; Wang, W.; Wang, R. B.

    2016-09-01

    Permeability is an important factor for seepage analysis of rock material, and a key factor in ensuring the safety of underground works. In this study, the permeability evolution of granite gneiss during triaxial creep tests was investigated. In the context of an underground oil storage cavern in China, a series of hydro-mechanical coupling creep tests were conducted on rock cores of granite gneiss at three different pore pressures to reveal the effect of pore pressure on the permeability evolution and to investigate the correlation between the permeability and volumetric strain during the creep process. During the creep tests, the permeability decreases in the initial loading phase. At all deviatoric stress levels, the permeability remains stable in the steady creep stage and increases rapidly in the accelerated creep stage. Based on the test data, the initial permeability, steady permeability and peak permeability at various stress levels are defined. The effect of pore pressure on the permeability is captured by a linear model. In addition, the relationship between permeability and volumetric strain can be described as a process divided into three phases, with different functions in each phase.

  3. Behavior of Fluid Mobile Elements Across hot Subduction Zone: Insights from Along-Strike B, As, Sb and Cs Systematics in Mafic Lavas from the Garibaldi Volcanic Belt, Northern Cascadia Subduction System.

    NASA Astrophysics Data System (ADS)

    Savov, I. P.; Green, N. L.; Price, R.

    2005-12-01

    We explore the consequences of "hot" subduction zone thermal structure for the recycling of fluid mobile elements across convergent margins. We selected the Late Cenozoic Garibaldi Volcanic Belt (GVB) of the Northern Cascadia Subduction System because it is associated with the subduction of extremely young (< 23 Ma) and "hot" oceanic lithosphere. The volcanic belt is ~ 15 km wide and consists of near primitive high-Al tholeiites and Mg-andesites (near Glacier Peak in NW Washington) through transitional basalts to alkali olivine basalts and basanites (near Bridge River- Salal Glacier area in SW British Columbia). The age of the subducted lithosphere decreases northward (latitude range 48 to 51 North) by almost 10 Ma, and thus the thermal structure of the convergent margin must be hotter in the northern part of GVB. The average B (3.3 ppm), As (0.2 ppm), Sb (0.1 ppm) and Cs (0.2 ppm) contents of the GVB mafic lavas are much lower compared to those reported from other convergent margins (Noll et al., 1996, Geochimica et Cosmochimica Acta, v. 60, No. 4, pp. 587-611). As expected the B/La (range = 0.003- 0.63; ave. ~ 0.2), Cs/La (range = 0-0.032; ave. ~ 0.01) and Sb/Ce (range = 0.001-0.013; ave. ~ 0.003) ratios show progressively lower values with transition from volcanic centers sampling old (19-23 Ma) (colder) slabs (Glacier Peak and Mount Baker areas) toward volcanic centers sampling young (15-17) (hot) slabs (Meager-Elaho, Helm Creek, Cheakamus, Bridge River and Salal Glacier areas). Surprisingly, the As/Ce (range = 0.001-0.015; ave. ~ 0.005) increases with decreasing slab age. Fluid mobile elements are extremely enriched in all members of the subducted slab inventory (to extremes in the serpentinized mantle wedge) and are depleted in slab melts (adakites), OIBs and MORBs. Their enrichment-depletion patterns could potentially be used to trace the extent of slab devolatilization and to test models about the mantle structure beneath volcanic arc fronts.

  4. The Acasta Gneisses revisited: Evidence for an early depleted mantle

    NASA Astrophysics Data System (ADS)

    Scherer, E. E.; Sprung, P.; Bleeker, W.; Mezger, K.

    2010-12-01

    The oldest known mineral samples crystallized on the Earth are the up to 4.4 Ga zircon grains from the Jack Hills, Australia [e.g., 1,2]. Zircon, which is datable by U-Pb, contains ca. 1 wt% Hf, and has very low Lu/Hf, is well suited to recording the initial 176Hf/177Hf of its parent magma. It has therefore been widely used to track Earth’s crust-mantle differentiation over time and to estimate the relative amounts of juvenile and recycled components that contributed to Archean and Hadean crust. [e.g., 3,4,5,6]. Zircon studies may be subject to sampling bias, however: Juvenile mafic magmas are likely to stem from depleted sources, but are less likely to crystallize zircon. Processes such as host-rock metamorphism, remelting, weathering of the host rock, and sedimentary transport of grains may have further biased the zircon population. Metamict grains or those with high aspect ratios are likely to be destroyed by these processes, potentially biasing the zircon Hf record toward enriched compositions such that the degree of mantle depletion remains poorly defined before 4 Ga. In addition, incorrect age assignments to Hf analyses result in spurious initial ɛHf values. Here, we attempt to overcome these issues by investigating the bulk rock Lu-Hf and Sm-Nd systematics of some of the oldest rocks on Earth, the Acasta Gneisses (Northwest Territories, Canada). Earlier studies showed that zircon grains in these gneisses tend to come from enriched sources [e.g, 3,7,8] and are thus of little use for directly tracking the degree of mantle depletion. Furthermore, the gneisses themselves have been multiply metamorphosed and are often affected by mixing: The banded gneisses in particular comprise several magmatic precursor rocks of different age that have been repeatedly folded into each other. This promted questions of whether zircon ages should be used in the calculation of bulk rock initial epsilon Nd, and whether linear trends on Sm-Nd isochron represented meaningful

  5. Laterally bendable belt conveyor

    SciTech Connect

    Peterson, W.J.

    1982-09-24

    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.

  6. Laterally bendable belt conveyor

    SciTech Connect

    Peterson, W.J.

    1985-07-02

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

  7. 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.

  8. Tectonic setting and evolution of late Archaean greenstone belts of Superior Province, Canada

    NASA Technical Reports Server (NTRS)

    Card, K. D.

    1986-01-01

    Late Archean (3.0-2.5 Ga) greenstone belts are a major component of the Superior Province of the Canadian Shield where alternating, metavolcanic - rich and metasedimentary - rich subprovinces form a prominent central striped region bordered in part by high-grade gneiss subprovinces, the Pikiwitonei and Minto in the north, and the Minnesota River Valley in the south. The high-grade gneiss subprovinces are characterized by granulite facies gneiss of plutonic and supracrustal origin, and by abundant plutonic rocks. Minnesota River Valley has rocks older than 3.5 Ga; absolute ages of Pikiwitonei and Minto rocks are unknown but Minto does have north-south structural trends distinctive from the dominant east-west structures of Superior Province. A discussion follows.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    Archean greenstone belts are key to understanding the evolution and tectonic framework of the oldest preserved continental fragments in the Earth's stable cratons. Detailed structural studies of Archean greenstone belts are needed in the literature. We present a detailed structural study of the 2.931 - 3.003 Ga Finlayson Lake greenstone belt, which is located in the south-central Wabigoon Subprovince of the Superior Province in Canada. The Finlayson belt is situated between three TTG gneiss domes of similar ages: the 3.002 Ga Marmion gneiss; the 2.982 Ma Eye-Dashwa gneiss; and the 2.936 Ga Hardtack gneiss. Although greenstone belts globally show unique features and we do not assume that the Finlayson belt is a general class for all other greenstone belts, we aim to produce a structural framework and deformational history that is wholly supported by field data. Previous work documented tectonic foliation and way-up indicators with variable lithological and chronological boundary interpretations (Stone and Kamineni 1992, Stone 2008). The dominant fabric that we see throughout the Finlayson belt is a strong flattening foliation trending between 044o and 080o with approximately vertical dip. No clear gradation in the intensity of foliation has been observed across the belt and zones of lesser and stronger foliation intensity are intercalated. All lithological boundaries and structural features in the Finlayson belt (except those on the far western margin) lie approximately parallel to the eastern boundary with the Marmion gneiss. Transects across the belt reveal no discrete sutures, meso-scale folds or faults. Way-up indicators from pillow basalts remain generally consistent, although the western and central portion of the belt are oppositely facing and are also distinguished by their petrography. The prevalent metamorphic grade in the Finlayson belt is lower amphibolite facies with peak epidote-hornblende mineralogy preserved. Peak metamorphism is coeval with the

  10. Magnetization of the Austell Gneiss, northwest Georgia Piedmont

    NASA Astrophysics Data System (ADS)

    Ellwood, Brooks B.; Abrams, Charlotte

    1982-04-01

    The Austell gneiss is located in the Piedmont 16 km west of Atlanta, Georgia, and 8 km northwest of the Brevard fault zone. This metamorphosed granite gneiss lies refolded in the nose of the Austell-Frolona antiform, a doubly plunging structure of regional extent. Subsequent to intrusion, the unit has undergone four episodes of deformation. The first and second generation folds (F1 and F2) are coaxial but not coplanar. The two later fold events were less intense and have little effect on local outcrop patterns in the study area. The age of the unit has been estimated to be greater than 325 m.y. but less than 365 m.y. The induced and remanent magnetic properties for at least six cores drilled at each of 10 sites within the Austell gneiss have been determined. The magnetic foliation for the unit is approximately parallel with field estimates for S1 foliation planes exhibited by mineral orientations within the body, indicating post-emplacement magnetic grain mobility. The stable remanent magnetization exhibited by the body was therefore probably acquired during or slightly after the F1 or F2 deformational events as a result of cooling from metamorphic temperatures (˜600°C), or, alternatively, from secondary magnetite grain nucleation and growth. A paleopole position calculated for these data without structural correction, ϕ = 126.2, θ = 34.4, dp = 6.6, dm = 13.2, can be explained by magnetic acquisition in at least three possible geologic settings. From simple to complex, these are the following: First, since a large oval of confidence is observed for the unit and minor tilting can not be resolved, the data may be explained by magnetization of the Austell at its present site during cooling from metamorphic temperatures. Second, a northwestward thrust event may have resulted in bringing the Austell to its present location. Third, the data can be explained by two major translational events. The Austell may have initially been magnetized and then moved to the

  11. Climatic and morphological controls on post-glacial lake and river valley evolution in the Weichselian belt - an example from the Wda valley, Northern Poland

    NASA Astrophysics Data System (ADS)

    Kramkowski, M. A.; Błaszkiewicz, M.; Piotrowski, J. A.; Brauer, A.; Gierszewski, P.; Kordowski, J.; Lamparski, P.; Lorenz, S.; Noryśkiewicz, A. M.; Ott, F.; Slowinski, M. M.; Tyszkowski, S.

    2014-12-01

    The River Wda valley is a classical example of a polygenetic valley, consisting of former lake basins joined by erosive gap sections. In its middle section, which was the subject of our research, a fragment of an abandoned Lateglacial river valley is preserved, which is unique for the Weichselian moraine belt in the Central European Lowlands. The analysis of the relationship between the lacustrine and fluvial sediments and landforms enabled the authors to report many evolutionary connections between the initial period of the river system formation and the emergence of lakes during the Weichselian Lateglacial. The surface drainage essentially determined the progress of melting of dead ice blocks buried in the glacial depressions, which finally led to lake formation there. Most of the lake basins in the study area were formed during the Bølling-Allerød period. However, one section of the subglacial channel was not exposed to the thermokarst conditions and was therefore preserved with dead ice blocks throughout the entire Lateglacial. The dead ice decay at the beginning of the Holocene, as well as the emergence of another lake, created a lower base level of erosion in the close vicinity of the abandoned valley and induced a change of the river's course. Both fluvial and lacustrine deposits and landforms distributed in the central section of the River Wda valley indicate two processes, which proceeded simultaneously: (1) emergence of fluvially joined lake basins within a glacial channel, (2) degradation of the river bed in the gap sections interfering between the lakes. The processes described for the central section of the River Wda channel indicate a very dynamic river valley development during the Weichselian Lateglacial and the early Holocene. The valley formation was tightly interwoven with the morphogenesis of the primary basins within the valley, mainly with the melting of the buried blocks of dead ice and the development of lakes. This study is a contribution

  12. 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.

  13. 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

  14. CORN BELT PLAIN RIVER AND STREAMS PROJECT - 3 BIOCRITERIA PRODUCTS

    EPA Science Inventory

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

  15. 14. INTERIOR VIEW OF REFINING MILL, SHOWING CONVEYOR BELT IN ...

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

    14. INTERIOR VIEW OF REFINING MILL, SHOWING CONVEYOR BELT IN PULVERIZING AND PACKING PLANT, LOOKING NORTH - Clay Spur Bentonite Plant & Camp, Refining Mill, Clay Spur Siding on Burlington Northern Railroad, Osage, Weston County, WY

  16. The Hurd Peak gneiss of the Long Lake shear zone, eastern Sierra Nevada, California

    SciTech Connect

    Holland, K.S.; Reed, W.E. . Dept. of Earth and Space Sciences)

    1993-04-01

    The Hurd Peak gneiss is located within the Long Lake valley of the east-central Sierra Nevada, California. This unit is the principle orthogneiss in Hathaway's (1993) Long Lake shear zone. The rock shows porphyroclasts of plagioclase and quartz, abundant mafic enclaves, and cross-cutting field associations which suggest that the gneiss had a plutonic protolith. The gneiss varies from biotite-poor nearest the contact with the Lamarck to biotite-rich nearest Long Lake. The contact zone between the gneiss and the Lamarck pluton ranges from sharp to gradational and from migmatitic to mixed, i.e., the mixed zone being greater than 50% intermingled dikes of 10 cm or greater thickness. In places this contact is marked by a quartz-free biotite hornfels approximately 5 m thick. Based on their relative deformation, at least 3 suites of aplite dikes cross-cut the gneiss, and 5 other lithologies, including basaltic, mixed, composite, andesitic, and quartz dioritic compositions, also cross-cut the gneiss. The Rb-Sr whole rock isochron age of the Hurd Peak gneiss has been determined to be 90.2 Ma. The authors interpret this isochron to be the result of mobilization of the Rb-Sr isotopic system during intrusion of the Lamarck Granodiorite (90 Ma); this may represent a regional cooling age. The initial [sup 87]/Sr[sup 86]Sr ratio of the gneiss is 0.7098, i.e., much more evolved than the surrounding plutons which have [sup 87]Sr/[sup 86]Sr ratios near 0.706. Sr model ages indicate that the protolith of the gneiss is considerably older than 90 Ma, one such calculation suggests an age of approximately 250 Ma. Single crystals of zircon have been isolated from the gneiss for U-Pb dating, and analytical work on the zircons is presently on-going.

  17. Provenance and accommodation pathways of late Quaternary sediments in the deep-water northern Ionian Basin, southern Italy

    NASA Astrophysics Data System (ADS)

    Perri, Francesco; Critelli, Salvatore; Dominici, Rocco; Muto, Francesco; Tripodi, Vincenzo; Ceramicola, Silvia

    2012-12-01

    The northern Calabria along the southeastern coast of Italy provides a favorable setting in which to study complete transects from continental to deep-marine environments. The present northern Ionian Calabrian Basin is a wedge-top basin within the modern foreland-basin system of southern Italy. The Ionian margin of northern Calabria consists of a moderately developed fluvial systems, the Crati and Neto rivers, and diverse smaller coastal drainages draining both the Calabria continental block (i.e., Sila Massif) and the southern Apennines thrust belt (i.e., Pollino Massif). The main-channel sand of the Crati and Neto rivers is quartzofeldspathic with abundant metamorphic and plutonic lithic fragments (granodiorite, granite, gneiss, phyllite and sedimentary lithic fragments). Sedimentary lithic fragments were derived from Jurassic sedimentary successions of the Longobucco Group. The mud samples contain mostly phyllosilicates, quartz, calcite, feldspars and dolomite. Traces of gypsum are present in some samples. The I-S mixed layers, 10 Å-minerals (illite and micas), chlorite and kaolinite are the most abundant phyllosilicates, whereas smectite and chlorite/smectite mixed layers are in small amounts. The geochemical signatures of the muds reflect a provenance characterized by both felsic and mafic rocks with a significant input from carbonate rocks. Furthermore, the degree of source-area weathering was most probably of low intensity rather than moderately intense because CIA values for the studied mud samples are low. Extrapolation of the mean erosion budget from 1 to 25 Ma suggests that at least 5 to 8 km of crust have been removed from the Calabrian orogenic belt and deposited in the marine basins. The Calabrian microplate played an important role in the dynamic evolution of southern Italian fossil and modern basins, representing the key tectonic element of the entire orogenic belt.

  18. Association of gold with uraninite and pyrobitumen in the metavolcanic rock hosted hydrothermal Au-U mineralisation at Rompas, Peräpohja Schist Belt, northern Finland

    NASA Astrophysics Data System (ADS)

    Molnár, Ferenc; Oduro, Harry; Cook, Nick D. J.; Pohjolainen, Esa; Takács, Ágnes; O'Brien, Hugh; Pakkanen, Lassi; Johanson, Bo; Wirth, Richard

    2016-06-01

    The Peräpohja Schist Belt comprises a supracrustal sequence of quartzites, mafic volcanics and volcaniclastics, carbonate rocks, black shales, mica schists and greywackes which were deposited from ca. 2.44 to ~1.91 Ga, during the rifting of the Archaean basement in the eastern part of the Fennoscandian shield. Metamorphism and multiple folding of the basin fill took place during the Svecofennian orogeny (1.9-1.8 Ga) followed by intrusions of late-orogenic (1.84-1.80 Ga) and post-orogenic granitoids (1.79-1.76 Ga). The Rompas Au-U mineralisation is hosted by deformed calcsilicate veins in mafic volcanic rocks and locally contains very high grade (>10,000 g/t Au) gold pockets with strict spatial association of gold minerals to uraninite and pyrobitumen. Chemical ages from the unaltered domains in the structure of uraninite indicate a 1.95-1.90 Ga age for the deposition of the primary, high temperature (e.g. U/Th < 100 in uraninite) hydrothermal uranium mineralisation. These data are in agreement with the results of previous U-Pb dating of uraninite by SIMS. Textural evidence suggests that metamorphic recrystallisation of the uraninite-bearing quartz-dolomite veins into calcsilicate mineral assemblages during the Svecofennian orogeny (1.9-1.8 Ga) was followed by a hydrocarbon-bearing fluid flow event and radiolytic polymerisation of hydrocarbons around grains of uraninite. Gold precipitated during a subsequent hydrothermal process in the fractures of uraninite, as well as in the cracks and on the botryoidal surfaces of uraninite-pyrobitumen nodules. Remobilisation and redeposition of uranium by these hydrothermal events produced secondary uraninite grains with chemical ages between 1.85 and 1.65 Ga. Native gold is associated with galena, altaite, hunchunite, nickeline and rare cobaltite, Pb-bearing maldonite, pyrite, pyrrhotite, chalcopyrite, molybdenite and titanite. Raman spectra show disordered structure of undeformed pyrobitumen nodules in contrast with the well

  19. U-Pb, Re-Os, and 40Ar/39Ar geochronology of the Nambija Au-skarn and Pangui porphyry Cu deposits, Ecuador: implications for the Jurassic metallogenic belt of the Northern Andes

    NASA Astrophysics Data System (ADS)

    Chiaradia, Massimo; Vallance, Jean; Fontboté, Lluis; Stein, Holly; Schaltegger, Urs; Coder, Joshua; Richards, Jeremy; Villeneuve, Mike; Gendall, Ian

    2009-05-01

    New U-Pb, Re-Os, and 40Ar/39Ar dates are presented for magmatic and hydrothermal mineral phases in skarn- and porphyry-related ores from the Nambija and Pangui districts of the Subandean zone, southeastern Ecuador. Nambija has been one of the main gold-producing centers of Ecuador since the 1980s due to exceptionally high-grade ores (average 15 g/t, but frequently up to 300 g/t Au). Pangui is a recently discovered porphyry Cu-Mo district. The geology of the Subandean zone in southeastern Ecuador is dominated by the I-type, subduction-related, Jurassic Zamora batholith, which intrudes Triassic volcanosedimentary rocks. The Zamora batholith is in turn cut by porphyritic stocks, which are commonly associated with skarn formation and/or porphyry-style mineralization. High precision U-Pb and Re-Os ages for porphyritic stocks (U-Pb, zircon), associated prograde skarn (U-Pb, hydrothermal titanite), and retrograde stage skarn (Re-Os, molybdenite from veins postdating gold deposition) of the Nambija district are all indistinguishable from each other within error (145 Ma) and indicate a Late Jurassic age for the gold mineralization. Previously, gold mineralization at Nambija was considered to be Early Tertiary based on K-Ar ages obtained on various hydrothermal minerals. The new Jurassic age for the Nambija district is slightly younger than the 40Ar/39Ar and Re-Os ages for magmatic-hydrothermal minerals from the Pangui district, which range between 157 and 152 Ma. Mineralization at Nambija and Pangui is associated with porphyritic stocks that represent the last known episodes of a long-lived Jurassic arc magmatism (˜190 to 145 Ma). A Jurassic age for mineralization at Nambija and Pangui suggests that the Northern Andean Jurassic metallogenic belt, which starts in Colombia at 3° N, extends down to 5° S in Ecuador. It also adds a new mineralization style (Au-skarn) to the metal endowment of this belt.

  20. The Santa Terezinha-Campos Verdes emerald district, central Brazil: structural and Sm-Nd data to constrain the tectonic evolution of the Neoproterozoic Brası´lia belt

    NASA Astrophysics Data System (ADS)

    D'el-Rey Silva, Luiz José Homem; Barros Neto, Leonel de Souza

    2002-12-01

    Structural analysis coupled with Sm-Nd isotope data and a detailed description of the geology of the Santa Terezinha-Campos Verdes emerald district (Goiás State, Central Brazil) constrain the evolution of the Neoproterozoic Brası´lia belt. The area is composed of tectonic slices of Archean-Paleoproterozoic gneiss, a Meso-Neoproterozoic metavolcanic sedimentary sequence called the Santa Terezinha sequence, and crustal-derived intrusive rocks such as mylonitic (ortho)gneiss and a syntectonic porphyry granite. It underwent a Neoproterozoic greenschist facies polyphase ductile deformation (D 1-D 3). Structures indicate an event of rotational deformation along a typical frontal ramp dipping gently to the west (i.e. an event of simple shear with top to ESE relative regional movement due to a subhorizontal WNW-ESE compression). A Sm-Nd whole-rock isochron age of 577±77 Ma for the intrusive rocks constrains the timing of at least part of the deformation/metamorphism in the area. Primary and metamorphic planar structures (mainly D 1-D 2) strike SW-NE and dip at low to moderate angles to the NW in the northern part of the area. However, they gradually rotate to SSE in the central SE part, where the Peixe River synclinorium is developed. This synclinorium is also the nest of the D 2 sheath folds that control emerald ore shoots. The Santa Cruz dome is a basement-cored, major elliptic structure in the SW of the area. The Santa Terezinha sequence represents a back-arc basin that received input from the Neoproterozoic Goiás magmatic arc to the west and the São Francisco ancient continental margin to the east. The basal and upper sections of this sequence correlate, respectively, with other passive margin and back-arc sequences of the Brası´lia belt.

  1. Conveyor belt plow for ideal belt cleaning

    SciTech Connect

    Michaelsen, W.J.

    1982-05-01

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

  2. Trondhjemitic, 1.35-1.31 Ga gneisses of the Mount Holly Complex of Vermont: evidence for an Elzevirian event in the Grenville Basement of the United States Appalachians

    USGS Publications Warehouse

    Ratcliffe, N.M.; Aleinikoff, J.N.; Burton, W.C.; Karabinos, P.

    1991-01-01

    A newly recognized suite of trondhjemite-tonalite and dacitic gneiss forms a 10 km wide belt of rocks within the Mount Holly Complex in the central part of the Green Mountain massif. Field relationships and chemistry indicate that these gneisses are calc-alkaline, volcanic, and hypabyssal plutonic rocks older than the Middle Proterozoic regional deformation that affected the Mount Holly Complex. U-Pb zircon dates indicate ages as great as 1.35 Ga for crystallization of the volcanic protoliths and for intrusion of crossing trondhjemite. Tonalitic plutonism continued until 1.31 Ga. The Mount Holly intrusives and volcanics may have formed during 1.35-1.31 Ga ensialic volcanic-arc activity, contemporaneous with ensimatic arc activity during the early part of the Elzevirian phase of the Grenville orogeny. -from Authors

  3. Geochemistry and origin of albite gneisses, northeastern Adirondack Mountains, New York

    USGS Publications Warehouse

    Whitney, P.R.; Olmsted, J.F.

    1988-01-01

    Albite gneisses containing up to 8.7 percent Na2O and as little as 0.1% K2O comprise a significant part of the Proterozoic Lyon Mountain Gneiss in the Ausable Forks Quadrangle of the northeastern Adirondacks, New York State. Two distinct types of albite gneisses are present. One is a trondhjemitic leucogneiss (LAG) consisting principally of albite (Ab95-Ab98) and quartz with minor magnetite and, locally, minor amounts of amphibole or acmiterich pyroxene. LAG probably originated by metamorphism of a rhyolitie or rhyodacitic ash-flow tuff with A-type geochemical affinities, following post-depositional analcitization in a saline or saline-alkaline environment. The other type is a mafic albite gneiss (MAG) containing albite and pyroxene along with 0-45 percent quartz, minor amphibole, and titanite. MAG locally displays pinstripe banding and contains albite (Ab98) megacrysts up to 5 cm across. Its precursor may have been a sediment composed of diagenetic analcite or albite, dolomite, and quartz. Both types of albite gneiss are interlayered with granitic gneisses (LMG) of variable composition derived from less altered tuffs. A potassium-rich (up to 9.7% K2O) microcline gneiss facies may have had a protolith rich in diagenetic K feldspar. We propose that the albite gneisses and associated granitic gneisses are the granulite-facies metamorphic equivalent of a bimodal, dominantly felsic, volcanic suite with minor intercalated sediments, probably including evaporites. The volcanics were erupted in an anorogenic setting, such as an incipient or failed intracontinental rift. Deposition took place in a closed-basin, playa lake environment, where diagenetic alteration resulted in redistribution of the alkalis and strong oxidation. ?? 1988 Springer-Verlag.

  4. 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)

  5. Geochronological, geochemical and mineralogical constraints of emplacement depth of TTG suite from the Sinassi Batholith in the Central African Fold Belt (CAFB) of northern Cameroon: Implications for tectonomagmatic evolution

    NASA Astrophysics Data System (ADS)

    Houketchang Bouyo, M.; Penaye, J.; Njel, U. O.; Moussango, A. P. I.; Sep, J. P. N.; Nyama, B. A.; Wassouo, W. J.; Abaté, J. M. E.; Yaya, F.; Mahamat, A.; Ye, Hao; Wu, Fei

    2016-04-01

    The Sinassi Batholith in the Central African Fold Belt (CAFB) of northern Cameroon represents the largest volume of plutonic rocks or granitoids massif of the Western Cameroonian Domain. It is made up dominantly of tonalite-trondhjemite-granodiorite (TTG) suite and lesser granite which are locally more or less deformed, and composed of varying proportions of quartz, plagioclase, K-feldspar, biotite, hornblende, sphene, magnetite, apatite and zircon. Major and trace element compositions of fifteen rock samples of granitoids (Djourdé granodiorite, Sinassi quartz diorite and orthogneisses groups) indicate that investigated rocks from the Sinassi Batholith are characterized by medium- to high-K calc-alkaline affinity and metaluminous I-type signature. In addition, their chondrite- and primitive mantle-normalized trace element patterns are strongly fractionated ((La/Yb)N = 2.96-61.40) and show respectively enrichment in LREE relative to HREE and enrichment in LILE compared to HFSE with moderate to slight negative Nb-Ta, Ti and Eu anomalies consistent with a continental magmatic arc setting related to a subduction zone. Geothermobarometric calculations using hornblende-plagioclase thermometry and aluminum-in-hornblende barometry on eleven rock samples indicate that plutons from Sinassi Batholith were emplaced at average temperatures and pressures ranging between 698 and 720 °C and 4.06-5.82 kbar (Djourdé granitoids), 698-728 °C and 4.04-5.34 kbar (Sinassi granitoids) and 667-670 and 4.23-4.76 kbar (orthogneisses group) respectively. The average emplacement depths estimates for the investigated granitoids is constrained at ca 16-18 km, indicating that at least 16 km of crustal rocks of the Sinassi Batholith must have been eroded or uplifted at approximately exhumation rates of 0.08-0.10 mm/year. Regardless of their Th/U ratios, geochronological results highlight three main events characterizing the Neoproterozoic tectonomagmatic evolution within the Sinassi Batholith

  6. Geochemical study of the Cambrian-Ordovician meta-sedimentary rocks from the northern Altai-Mongolian terrane, northwestern Central Asian Orogenic Belt: Implications on the provenance and tectonic setting

    NASA Astrophysics Data System (ADS)

    Chen, Ming; Sun, Min; Cai, Keda; Buslov, Mikhail M.; Zhao, Guochun; Rubanova, Elena S.

    2014-12-01

    The Altai-Mongolian terrane (AM) is a key component of the Central Asian Orogenic Belt (CAOB), but its tectonic nature has been poorly constrained. This paper reports geochemical compositions of Cambrian-Ordovician meta-sedimentary rocks from the northern AM to trace their source nature and depositional setting, which in turn place constraints on the geodynamic evolution of the AM. The Cambrian-Ordovician meta-sedimentary rocks from the northern AM show variable major-element compositions, with negative correlation between SiO2 and TiO2, Al2O3, Fe2O3T, MgO and K2O. Their high ICV values (1.18-2.53) and relatively low CIA values (37.9-76.3) indicate that the sediments were immature and probably underwent mild to moderate chemical weathering. The low-SiO2 samples are characterized by relatively restricted SiO2/Al2O3 (mostly 2.60-6.07) and low Rb/Sr ratios (0.02-1.89), implying their proximal deposition without obvious sedimentary sorting and recycling. In contrast, the high-SiO2 samples show much higher SiO2/Al2O3 ratios (15.4-19.9) possibly due to sedimentary sorting and/or silicification. All these samples yield relatively high Al2O3/TiO2 ratios (15.6-22.8), strong LREEs/HREEs differentiation ((La/Yb)N = 4.86-10.7) and obvious negative Eu anomalies (δEu = 0.61-0.83). Combined with their Th/Sc, Zr/Sc, La/Th and Co/Th ratios comparable with intermediate-acidic magmatic rocks, we infer that these kinds of magmatic rocks served as a major source for the investigated meta-sedimentary rocks. The TiO2, Al2O3 and Fe2O3T + MgO concentrations are mostly higher than typical sediments from passive margin, and the Th/U, La/Sc, Th/Sc, Eu/Eu∗, Zr/Hf, Zr/Th and La/Th ratios are quite similar to sediments from continental arcs. These data suggest that the Cambrian-Ordovician meta-sedimentary rocks from the northern AM were most likely deposited in an environment related to a continental arc setting rather than a passive regime. These rocks show strong similarities to their

  7. Timing, petrogenesis and tectonic setting of the Late Paleozoic gabbro-granodiorite-granite intrusions in the Shalazhashan of northern Alxa: Constraints on the southernmost boundary of the Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Shi, Xingjun; Wang, Tao; Zhang, Lei; Castro, Antonio; Xiao, XuChang; Tong, Ying; Zhang, Jianjun; Guo, Lei; Yang, Qidi

    2014-11-01

    The Late Paleozoic tectonic setting and location of the southernmost boundary of the Central Asian Orogenic Belt (CAOB) with respect to the Alxa Block or Alxa-North China Craton (ANCC) are debated. This paper presents new geochronological, petrological, geochemical and zircon Hf isotopic data of the Late Paleozoic intrusions from the Shalazhashan in northern Alxa and discusses the tectonic setting and boundary between the CAOB and ANCC. Using zircon U-Pb dating, intrusions can be broadly grouped as Late Carboniferous granodiorites (~ 301 Ma), Middle Permian gabbros (~ 264 Ma) and granites (~ 266 Ma) and Late Permian granodiorites, monzogranites and quartz monzodiorites (254-250 Ma). The Late Carboniferous granodiorites are slightly peraluminous and calcic. The remarkably high zircon Hf isotopes (εHf(t) = + 6-+ 10) and characteristics of high silica adakites suggest that these granodiorites were mainly derived from "hot" basaltic slab-melts of the subducted oceanic crust. The Middle Permian gabbros exhibited typical cumulate textures and were derived from the partial melting of depleted mantle. The Middle Permian granites are slightly peraluminous with high-K calc-alkaline and low εHf(t) values from - 0.9 to + 2.9. These granites were most likely derived from juvenile materials mixed with old crustal materials. The Late Permian granodiorites, monzogranites and quartz monzodiorites are characterized as metaluminous to slightly peraluminous, with variable Peacock alkali-lime index values from calc-alkalic to alkali-calcic. These rocks were mainly derived from juvenile crustal materials, as evidenced by their high εHf(t) values (+ 3.3 to + 8.9). The juvenile sources of the above intrusions in the Shalazhashan are similar to those of the granitoids from the CAOB but distinct from the granitoids within the Alxa Block. These findings suggest that the Shalazhashan Zone belongs to the CAOB rather than the Alxa Block and that its boundary with the Alxa block can be

  8. Nature, geochemistry and petrogenesis of the syn-tectonic Amspoort suite (Pan-African Boundary Igneous Complex, Kaoko Belt, NW Namibia)

    NASA Astrophysics Data System (ADS)

    Janousek, Vojtech; Konopasek, Jiri; Ulrich, Stanislav

    2010-05-01

    Crucial information on the Neoproterozoic-Cambrian amalgamation of Western Gondwana is provided by studies of the large Pan-African collisional belt in central-northern Namibia. This so-called Damara Orogen (Miller, 1983) can be subdivided into two branches, the SW-NE trending Damara Belt and a roughly perpendicular, NNW-SSE trending Kaoko Belt further north. The Kaoko Belt consists of two principal crustal units. The easterly part has a Congo Craton affinity (a basement built mostly by ≥ 1.5 Ga granitic gneisses with Neoproterozoic metasedimentary cover), whereas the westerly Coastal Terrane consists of Neoproterozoic (c.850-650 Ma) metapsammites and minor metabasic bodies; no exposures of the basement were found. The at least 180 km long, NNW-SSE trending suture between both units was intruded by numerous syn-tectonic magmatic bodies with ages spanning the interval 580-550 Ma (Seth et al., 1998; Kröner et al., 2004) designated as the Boundary Igneous Complex by Konopásek et al. (2008). The most typical representatives of this syn-collision igneous association are c.550 Ma old K-feldspar-phyric, Bt ± Cam granites-granodiorites of the Amspoort suite, with minor Cpx gabbro and rare two-pyroxene dolerite bodies. The petrological character, whole-rock geochemistry and Sr-Nd isotopic signatures of the scarce Opx-Cpx-Bt dolerites indicate an origin from a CHUR-like mantle-derived melts (87Sr/86Sr550 ~ 0.7045, ɛNd550 ~ 0) modified by extensive (?Ol-) Cpx fractionation. The rest of the suite is interpreted as a product of a high-temperature anatexis of a heterogeneous lower crust, built mainly by immature metapsammites - rich in arc-derived detritus - with minor metabasite and intermediate metaigneous bodies. The most likely source appears to be the anatectic Coastal Terrane gneisses. Yet, partial melting of the so far little constrained Congo Craton cover, if formed by immature and youthful detritus unrelated to the basement, cannot be discounted. In any case, the

  9. Belt conveyor apparatus

    SciTech Connect

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

    1987-05-05

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

  10. New radiometric ages on gneisses of the Oliverian domes in New Hampshire and Massachusetts

    SciTech Connect

    Zartman, R.E.; Leo, G.W.

    1985-03-01

    Gneissic plutons of the Oliverian domes, mantled by Ammonoosuc Volcanics, are located along the axis of the Bronson Hill anticlinorium from New Hampshire to Connecticut. The contacts between the plutonic and volcanic rocks appear to be concordant on a regional scale, but gneiss intrudes the volcanics in several domes. Available radiometric and fossil evidence suggests that the Ammonoosuc Volcanics have a Middle Ordovician age but are somewhat older than the Oliverian gneisses. New U-Pb zircon data from Oliverian gneisses of six domes plot on a concordia diagram as an almost colinear array that yields an upper intercept age of about 444 m.y. The plotted data vary from nearly concordant to moderately discordant, the degree of discordance, correlating with /sup 207/Pb//sup 206/Pb ages that range from 459 to 415 m.y. The pattern of discordance does not relate to the uranium contents of the zircons nor to the geographic distribution of the domes. If /sup 207/Pb//sup 206/Pb ages are considered individually without an assumed consanguinity of the units, however, they do not find particular support in geologic relationships. Thus, they prefer the concordia intercept age of 444 +/- 8 m.y. for the suite as the best estimate for the time of crystallization of the Oliverian gneisses. Possibly, the Whitefield, Gneiss in the Jefferson dome represents a 10 to 15 m.y. older unit, although they are cautious about claiming such resolution with the present data.

  11. Strain analysis and strain path modelling in the Loch Tollie gneisses, Gairloch, NW Scotland

    NASA Astrophysics Data System (ADS)

    Odling, N. E.

    A quantitative structural analysis is presented for the Loch Tullie gneisses of the Lewisian complex outcropping at Gairloch. The gneisses and the dykes they contain are folded into a large antiformal structure known as the Tollic Antiform. Quartz aggregates in quartzo-feldspathic gneisses have been used as finite strain markers in eleven specimens across the antiform. Two models, using rotational strain (simple shear) and irrotational strain (pure shear), are used to reconstruct the strain path. Results show that only the rotational strain model satisfies the strain data and the field evidence, and indicates a steeply northeast (75°) dipping shear plane and moderately northwest (55°) plunging shear direction, with a southwest-side-down sense of shear. A strain profile is constructed for the Tollie gneisses using the model and the attitude of gneissose layering. This shows increasing shear strain to the southwest to a maximum gamma value of approximately 8. The strain profile indicates a horizontal dextral displacement of 4.7 km and a vertical displacement of 6.8 km for the Tollie gneisses. The Tollie Antiform thus lies on the northeast margin of a large-scale shear zone, the main zone of deformation of which can be traced southwestwards some 4 km. Such a shear zone presents a major tectonic boundary within the Lewisian of northwest Scotland.

  12. Regional variation in the Amitsoq gneisses related to crustal levels during late Archean granulite facies metamorphism: Southern west Greenland

    NASA Technical Reports Server (NTRS)

    Nutman, A. P.; Bridgwater, D.; Mcgregor, V. R.

    1986-01-01

    The dominant lithology at Kangimut sangmissoq is described as nebulitic tonalitic gneiss containing highly distended plagioclase phyric amphibolites. The gneiss amphibolite complex was intruded by Nuk gneiss between 3.05 and 2.90 Ga and later (2.6 to 2.7 Ga) by post granulite facies granitoid sheets. The amphibolites are though to be Ameralik dikes and the older gray gneiss are then Amitsoq by definition. The problem arises when the isotopic data are considered, none of which indicate rocks older that about 3.0 Ga.

  13. 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.

  14. 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

  15. 18O/16O and V/Cr ratios in gem tsavorites from the Neoproterozoic Mozambique metamorphic belt: a clue towards their origins?

    NASA Astrophysics Data System (ADS)

    Giuliani, Gaston; Fallick, Anthony E.; Feneyrol, Julien; Ohnenstetter, Daniel; Pardieu, Vincent; Saul, Mark

    2011-10-01

    The combination of oxygen isotope composition with V-Cr-Mn trace element concentrations of V-bearing garnets (tsavorites) originating from the main deposits of the Neoproterozoic Mozambique Metamorphic Belt is reported for the first time. The database enables the identification of the geological and geographical sources of the main productive areas from northern and southern Tanzania, Kenya, and Madagascar. Three consistent sets of δ18O values between 9.5‰ and 11.0‰, 11.6‰ and 14.5‰, and 15.5‰ and 21.1‰ have been recognized for primary deposits hosted in graphitic gneisses related to the Neoproterozic metasedimentary series. The δ18O value of tsavorite is a good tracer of the environment of its formation; the δ18O of the fluid in equilibrium with tsavorite was buffered by the host rock during metamorphism and fluid-rock interaction. This study is a first step in characterizing the geochemistry of gem tsavorite from most of the deposits and occurrences worldwide.

  16. Zircon U-Pb age and Sr-Nd-Hf isotope geochemistry of the Ganluogou dioritic complex in the northern Triassic Yidun arc belt, Eastern Tibetan Plateau: Implications for the closure of the Garzê-Litang Ocean

    NASA Astrophysics Data System (ADS)

    Wu, Tao; Xiao, Long; Wilde, Simon A.; Ma, Chang-Qian; Li, Zi-Long; Sun, Yi; Zhan, Qiong-Yao

    2016-04-01

    The Triassic Yidun arc belt (YAB) lies between the Jinshajiang suture zone to the west and the Garzê-Litang suture zone to the east, Eastern Tibetan Plateau. To study the YAB can not only help us to better understand the evolutionary history of the Garzê-Litang Ocean but can also provide some important information to constrain the evolution of the eastern Paleo-Tethys. In this paper, the geochronological and geochemical data of the Ganluogou dioritic complex were systematically investigated in order to decipher the geodynamic setting of the complex and to further determine the final closure time of the Garzê-Litang Ocean. The Ganluogou dioritic complex is located in the northern part of the YAB. It consists of ferrodiorite, diorite and a mixing zone between them and is the largest intermediate-mafic pluton in the YAB. The ferrodiorites were emplaced at 213 ± 2 Ma have low SiO2 and high Fe2O3* contents, whereas the diorites formed at 209 ± 2 Ma and have relatively higher SiO2, Na2O + K2O, Th, U, Zr, and Hf contents, but lower Al2O3, MgO, CaO, Co, and Sr contents than the ferrodiorites. Relative to the primitive mantle both the ferrodiorites and diorites are depleted in Nb and Ta. However, the ferrodiorites exhibit strong depletion in Zr and Hf, whereas the diorites contain relatively higher Th and U contents without negative Zr and Hf anomalies. Both rock-types have similar chondrite-normalized rare earth element patterns with (La/Yb)N ratios = 4.4 to 18.2, and show weak Eu anomalies, with Eu/Eu* of 0.47 to 1. They both show narrow ranges in Sr-Nd-Hf isotopic compositions. However, the ferrodiorites contain lower initial 87Sr/86Sr ratios (0.7052-0.7057) and relatively higher εNd(t) values (- 3.8 to - 2.4) than the diorites, which record values of 0.7062-0.7066 and - 5.5 to - 5.7, respectively. For the zircon Hf isotopic composition, the ferrodiorites also exhibit higher 176Hf/177Hf ratios (0.282738-0.282804) and more depleted εHf(t) values (3.4-5.6) than

  17. 3,800-Myr granitic gneiss in South-Western Minnesota

    USGS Publications Warehouse

    Goldich, S.S.; Hedge, C.E.

    1974-01-01

    WE have previously arrived at an age of 3,550 Myr for granitic1 gneiss in the vicinities of Morton and Montevideo in the Minnesota River valley, south-western Minnesota. We now report new Rb-Sr analyses (Table 1) and an age of 3,800 Myr for the fine grained foliated phase of the Montevideo Gneiss of Lund2. The rocks have undergone a complex history of metamorphism which remains to be deciphered, but the age determinations reveal that the geological mapping and previous interpretations did not provide a proper basis for sampling. ?? 1974 Nature Publishing Group.

  18. Rutile and topaz in Precambrian gneiss, Jefferson and Clear Creek Counties, Colorado

    USGS Publications Warehouse

    Sheridan, Douglas M.; Taylor, Richard B.; Marsh, Sherman P.

    1968-01-01

    Disseminated rutile and major amounts of topaz have been identified in Precambrian topaz-quartz gneiss northwest of Evergreen, Colo. The rutile occurs in quartz-topaz-sillimanite gneiss that forms a stratigraphic unit which is 11 to 100 feet thick and is identified along strike for more than 7,000 feet. Three composite chip samples taken across this unit contain 2.2 to 4.2 percent of rutile, by weight, in grains averaging from 0.1 to 0.3 millimeter in size. The topaz content, by weight, in the same samples ranges from 23 to 67 percent.

  19. 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…

  20. Generation of early Archean felsic volcanics and TTG gneisses through crustal melting, eastern Kaapvaal craton, southern Africa

    NASA Astrophysics Data System (ADS)

    Kröener, A.; Hoffmann, J.; Xie, H.; Wu, F.; Münker, C.; Hegner, E.; Wong, J.; Wan, Y.; Liu, D.

    2012-12-01

    An unresolved question in early Archean granite-gneiss-greenstone terranes is whether they evolved in oceanic environments or whether older continental crust was involved. We investigated felsic volcanic rocks of the 3.55-3.2 Ga Barberton Greenstone Belt (BGB) and adjacent 3.66-3.45 TTGs in the Ancient Gneiss Complex (AGC) of Swaziland, southern Africa, using SHRIMP zircon dating as well as whole-rock Nd-Hf and Hf-in-zircon isotopes. Xenocrystic zircons in BGB felsic rocks and negative whole-rock ɛNd(t)-values with model ages of 3.6-3.7 Ga question models whereby these rocks resulted from differentiation of mafic precursors. Involvement of older crust was also likely in the formation of several TTGs and is supported by rare zircon xenocrysts and Hf-in-zircon isotopic data suggesting at least partial cannibalistic recycling of older continental crust. The felsic volcanics, interlayered with basalts and komatiites, exhibit REE patterns with distinct negative Eu-anomalies. 3 samples from the oldest felsic unit (Theespruit Fm.) have zircon ages of 3529-3552 Ma, whole-rock Nd isotopic values of -1.1 to +1.1, and model ages of 3.55-3.73 Ga. Hf isotopic data were acquired on concordant or near-concordant zircon domains analyzed on SHRIMP, and most analyses show negative ɛHf(t)-values, suggesting zircon derivation from older crustal protoliths, whereas a few analyses suggest input from a juvenile source. Hf crustal model ages are 3.60-3.95 Ga and imply a heterogeneous crustal source. The younger felsic rocks (Hoogenoeg Fm.) display well-preserved volcanic and/or sedimentary textures, and some are high in K2O and contain primary magmatic K-feldspar. 4 samples have zircon ages of 3447-3462 Ma, and 3 samples contain 3499-3541 Ma xenocrysts. Whole-rock Nd isotopic values are around -1.5 with a model age of ca. 3.69 Ga. Hf-in-zircon isotopic data are similar to those of the Theespruit rocks, and most analyses show negative ɛHf(t)-values, suggesting zircon derivation from a

  1. Imbricate stacking on a highly oblique ramp, but no antiformal culmination - the Dundonnell sector of the Caledonian Moine Thrust Belt, Northwest Highlands of Scotland.

    NASA Astrophysics Data System (ADS)

    Leslie, Graham; Krabbendam, Maarten; Goodenough, Kathryn

    2010-05-01

    the north side undeformed, massive sandstone dominates, within which there is little or no evidence for ductile deformation. We instead interpret the Dundonnell structure as a steeply-inclined imbricate stack, lacking antiformal upright folding. The imbricate stack bulges up and displaces both the ductile and brittle Moine Thrust. The northern limit of the Dundonnell imbricate stack is defined by a brittle or brittle-ductile fault breaching the Moine Thrust; the Loch an Daimh Fault. The Loch an Daimh Fault clearly displaces the Moine Thrust but does not displace the structurally lowest thrust plane at Dundonnell, instead it flattens and roots southwards into the brittle base of the thrust pile. This fault continues WNW and also defines the northern limit of a 200 m wide linear belt of transpressional mylonitic deformation belt in the structurally higher Moine rocks. We argue that the Dundonnell stack and the transpressional deformation in the Moine rocks are located on a (highly) oblique lateral ramp. North of Dundonnel, the Ullapool Thrust Sheet comprises Archaean gneisses and Neoproterozoic sedimentary rocks; this thrust sheet terminates southwards at Dundonnell. We propose that the Dundonnell Stack, and the transpressional flower structure in the Moine rocks, are constrained by the oblique lateral ramp corresponding to the southern limit of this thrust sheet. The degree of obliquity with respect to the thrust transport direction may control the architecture of tranverse zones with higher angles of obliquity favouring imbrication and breaching rather than antiformal folding.

  2. Regional and local controls on mineralization and pluton emplacement in the Bondy gneiss complex, Grenville Province, Canada interpreted from aeromagnetic and gravity data

    NASA Astrophysics Data System (ADS)

    Dufréchou, G.; Harris, L. B.; Corriveau, L.; Antonoff, V.

    2015-05-01

    The Bondy gneiss complex in the Grenville Province of Southwest Quebec hosts a mineralized iron oxide- and copper-rich hydrothermal system. The northern part of the complex overlies the lithospheric-scale Mont-Laurier lineament and is cut by the regional Mont-Laurier South shear zone interpreted from Bouguer gravity. A sinistral 6 km wide strike-slip corridor defined by several second-order shears (the Mont-Laurier South shear zone) in the complex was identified from geophysical data, including a new high-resolution airborne magnetic survey, and field observations. The spatial association of a metamorphosed alteration system, several pre- to post-metamorphic mineralized zones and mafic intrusions within the Mont-Laurier South shear zone suggests that (i) underlying basement structures controlled hydrothermal fluid migration during the formation of epithermal-IOCG mineralization and associated alteration system before ca. 1.2 Ga high-grade metamorphism and penetrative ductile deformation in the complex; (ii) post-metamorphic reactivation allowed magma ascent and pluton emplacement in the complex and adjacent supracrustal rocks within dilatational sites; and (iii) brittle-ductile shears that postdate high-grade metamorphism provided channel ways for fluid migration associated with magnetite-related mineralization. Although the complex does not host an economic mineral deposit, the role between structures at different levels and the combination of gravity and aeromagnetics at different scales provides an example of an approach for mineral exploration in similar high grade gneiss terrains.

  3. Characterization of fluids involved in the Gneiss-Charnockite transformation in Southern Kerala (India)

    NASA Technical Reports Server (NTRS)

    Klatt, E.; Hoernes, S.; Raith, M.

    1988-01-01

    The characterization of fluids involved in the gneiss-charnockite transformation in southern Kerala are discussed. Using a variety of techniques, including microthermometry, Raman laser probe analysis, and mass spectrometry, it was concluded that the CO2-rich, N2-bearing metamorphic fluids in these rocks were internally-derived rather than having been introduced by CO2-streaming.

  4. Geometry, evolution, and tectonic framework of the Skeena Fold Belt, north central British Columbia

    NASA Astrophysics Data System (ADS)

    Evenchick, Carol A.

    1991-06-01

    The Intermontane Belt of the Canadian Cordillera has long been viewed as a passive, relatively rigid block between two metamorphic-plutonic belts, the Coast Plutonic Complex and the Omineca Belt. However, the Skeena Fold Belt, which spans most of the width of the northern Intermontane Belt, exhibits shortening comparable with that in the Rocky Mountain Fold and Thrust Belt. The Skeena Fold Belt has many features of thin-skinned fold and thrust belts, such as thrust faults which sole into a detachment, a wide variety of structural styles which depend on rock type, a foreland basin which was cannibalized by continued deformation, a frontal triangle zone, and a hinterland of metamorphic and plutonic rocks (Coast Plutonic Complex). The Skeena Fold Belt thus is comparable with the Rocky Mountain Fold and Thrust Belt, but rather than deforming a continental terrace wedge, it developed in a terrane (Stikinia) which had accreted to North America in the early Mesozoic, and in Jurassic and Cretaceous clastic successions (Bowser Lake and Sustut groups) which overlie Stikinia. Structural and stratigraphic relationships show that the earliest deformation occurred between Oxfordian and Albian time and that the last folds developed in latest Cretaceous or early Tertiary time. As much as 160 km of northeastward shortening in the Skeena Fold Belt was broadly contemporaneous with crustal thickening in the Coast Plutonic Complex and Omineca Belt, with dextral strike-slip faulting east of the Skeena Fold Belt, and with shortening in the Rocky Mountain Fold and Thrust Belt. Therefore, between latest Jurassic and early Tertiary times, horizontal shortening occured across most of the width of the northern Canadian Cordillera. Concurrent shortening across the Cordillera suggests that a common detachment (or detachments) fed all of these zones as far east as the Rocky Mountain Fold and Thrust Belt.

  5. Lap seat belt injuries.

    PubMed

    Hingston, G R

    1996-08-01

    Over a 4 month period, three patients presented acutely to Whangarei Area Hospital after receiving severe abdominal injuries caused directly by lap seat belts. They were involved in road traffic crashes and were all seated in the middle rear seat of the car. The aim of this paper is to alert people to the injuries that can occur from two point lap belts. To this end, the patients and injuries sustained are described and a review of the literature is presented.

  6. 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.

  7. 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.

  8. The provenance of Archean clastic metasediments in the Narryer Gneiss Complex, western Australia: Trace element geochemistry, Nd isotopes, and U-Pb ages for detrital zircons

    SciTech Connect

    Maas, R. Curtin Univ., Perth ); McCulloch, M.T. )

    1991-07-01

    Clastic metasedimentary rocks of mid-Archean age from the Mt. Narryer and Jack Hills metasedimentary belts have REE patterns resembling those of mid- to late-Archean pelitic-quartzitic cratonic sequences elsewhere, and post-Archean continental rocks in general. Detrital zircons in the metasediments range in age from ca. 3,000 to 3,700 Ma. This indicates a provenance from mature cratonic sources controlled by K-rich granitic rocks. Additional minor sediment sources were identified as older, mainly chemical sedimentary sequences, ultramafic rocks, and felsic rocks characterized by low HREE contents, perhaps of tonalitic affinity. Differences between sedimentary REE patterns and those in the surrounding 3.73-3.0 Ga orthogneiss terrain, and between detrital zircon ages and the age distribution in the gneisses, suggest that the present association of the metasedimentary belts with the orthogneiss terrain is of tectonic origin. The occurrence of detrital zircons with U-Pb ages > 4 Ga in certain quartzites and conglomerates of the Jack Hills and Mt. Narryer metasedimentary sequences indicates a further, most likely granitic, source. {epsilon}{sub Nd}(T{sub Dep}) values in Jack Hills metasediments vary widely (+5 to {minus}12) but have a smaller range in the Mt. Narryer belt ({minus}5 to {minus}9). The lowest {epsilon}{sub Nd} values of both sequences are interpreted to reflect the presence of detritus derived from 4.1-4.2 Ga old LREE-enriched continental crust in proportions considerably larger ({ge} 10%) than estimated previously from the abundance of pre-4 Ga detrital zircons ({approx}3%). This would imply the former existence of significant volumes of pre-4 Ga continental crust in the provenance of the Mt. Narryer and Jack Hills metasediments.

  9. Geology of the Northern Part of the Harcuvar Complex, West-Central Arizona

    USGS Publications Warehouse

    Bryant, Bruce; Wooden, J.L.

    2008-01-01

    In west-central Arizona near the northeast margin of the Basin and Range Province, the Rawhide detachment fault separates Tertiary and older rocks lacking significant effects of Tertiary metamorphism from Precambrian, Paleozoic, and Mesozoic rocks in the Harcuvar metamorphic core complex below. Much of the northern part of the Harcuvar complex in the Buckskin and eastern Harcuvar Mountains is layered granitic gneiss, biotite gneiss, amphibolite, and minor pelitic schist that was probably deformed and metamorphosed in Early Proterozoic time. In the eastern Buckskin Mountains, Early and Middle Proterozoic plutons having U-Pb zircon ages of 1,683?6.4 mega-annum (Ma) and 1,388?2.3 Ma, respectively, intruded the layered gneiss. Small plutons of alkaline gabbro and diorite intruded in Late Jurassic time. A sample of mylonitized diorite from this unit has a U-Pb zircon age of 149?2.8 Ma. In the Early Cretaceous, amphibolite facies regional metamorphism was accompanied by partial melting and formation of migmatite. Zircon from a granitic layer in migmatitic gneiss in the eastern Harcuvar Mountains has a U-Pb age of 110?3.7 Ma. In the Late Cretaceous, sills and plutons of the granite of Tank Pass were emplaced in both the Buckskin and eastern Harcuvar Mountains. In the Buckskin Mountains those intrusions are locally numerous enough to form an injection migmatite. A pluton of this granite crops out over almost half the area of the eastern Harcuvar Mountains. Paleozoic and Mesozoic sedimentary rocks were caught as slices along south-vergent Cretaceous thrusts related to the Maria fold and thrust belt and were metamorphosed beneath a thick sheet of Proterozoic crustal rocks. Inception of volcanism and basin formation in upper-plate rocks indicates that regional extension started at about 26 Ma, in late Oligocene. The Swansea Plutonic Suite, composed of rocks ranging from gabbro to granite, intruded the lower-plate rocks in the Miocene and Oligocene(?). Granite and a gabbro

  10. Preliminary results, Central Gneiss Complex of the Coast Range batholith, southeastern Alaska: the roots of a high-K, calc-alkaline arc?

    USGS Publications Warehouse

    Barker, F.; Arth, Joseph G.

    1984-01-01

    The Central Gneiss Complex (CGC) of the Coast Range batholith is the oldest unit of the batholith east of Ketchikan, Alaska, being dated by the zircon UPb method (by T.W. Stern) at 128-140 Ma. Heterogeneous, layered, commonly migmatitic, orthogneiss of hornblende-biotite quartz diorite, tonalite, quartz monzodiorite and granodiorite compositions (IUGS terminology) form the major part of the CGC. These gneisses show a range of 50-65% SiO2 and are high in Al2O3 (c. 15-19%), K2O (1.5-4%) and Sr (800-900 ppm). Most major elements show coherent, typically magmatic trends with SiO2. La and Rb show maxima at ??? 58% SiO2. Initial 87Sr/86Sr ratios are relatively high and range from 0.7052 to 0.7066. Wallrocks of the CGC are mostly metagraywacke, pelite and metavolcanic rocks at amphibolite facies; they are geochemically dissimilar to the CGC. Major and minor elements of the CGC are very similar to those of high-K orogenic, calc-alkaline andesitic suites. The CGC may have formed largely by fractionation of mantle-derived, high AlKSr basaltic liquid in an ascending diapir, having hornblende, plagioclase, and biotite as major precipitating phases. The CGC probably represents the plutonic equivalent of a continental-margin or Andean arc that formed when the Taku terrane of the Insular belt on the west collided with the previously emplaced (but also allochthonous) Stikine terrane on the east in Late Jurassic or Early Cretaceous time. ?? 1984.

  11. 1.99 Ga mafic dykes of the Lewisian Gneiss Complex of Scotland: An upper age limit for the Palaeoproterozoic Loch Maree Group

    NASA Astrophysics Data System (ADS)

    Baker, Thomas; Prave, Tony; Spencer, Christopher

    2015-04-01

    Mafic dyke swarms are often used as geochronological markers, as they are widespread and emplaced over short timespans. The ca. 2.4 Ga Scourie dyke swarm is one such example that has played a key role in understanding the complex tectonic and metamorphic history of the Lewisian Gneiss Complex of Scotland (LGC), part of the North Atlantic Craton (NAC). The LGC consists of Archean and Palaeoproterozoic terranes that experienced polyphase deformation prior to their assembly at ca. 1.8 Ga. Zircons separated from a doleritic dyke from the Gairloch terrane have yielded a concordant U-Th-Pb age (1,989 +4.3 / -0.99 Ma) using the ID-TIMS method. The doleritic dyke is emplaced in Lewisian gneiss that experienced both granulite and amphibolite-facies metamorphism. Partial recrystallisation and amphibolitisation of the dyke demonstrate that it pre-dates the most recent (Laxfordian) amphibolite-facies metamorphic event. The age obtained from the dyke overlaps the U-Pb age of a previously dated olivine gabbro dyke from the Assynt terrane (1,992 Ma). These combined ages provide strong corroborating evidence for a ca. 2.0 Ga mafic dyke swarm event, distinct from the older ca. 2.4 Ga Scourie dyke event known from elsewhere in the LGC. The existence of a ca. 2.0 Ga mafic dyke swarm provides an upper age limit for the Loch Maree Group (LMG), a Palaeoproterozoic succession of metasediment and metavolcanic rocks that overlie the LGC and which are not cross-cut by the Scourie dykes. This study proposes that a period of crustal extension took place in the region at ca. 2.0 Ga. Later, subduction may have resulted in the accretion of the LMG and the adjacent Ard Gneiss, which has previously been regarded as a magmatic arc. The ca. 1.9 Ga age of the earliest stage of the Laxfordian metamorphic event, which affected the LMG, could therefore mark the onset of collision. This sequence of events can be correlated with other coeval areas of the NAC, including the Nagssugtoqidian mobile belt of

  12. The Beaufort Sea fold-and-thrust belt, northwestern Canada: Implications for thrust-belt evolution

    SciTech Connect

    Root, K.G. )

    1991-06-01

    The northeasternmost segment of the Cordilleran thrust belt of western North American underlies the Beaufort Sea continental margin. Folds and associated northesat-directed thrusts in this region formed synchronously with Tertiary sedimentation. As a result, the times of fold development can be determined from reflection seismic data by analyzing lateral thickness changes in stratigraphic sequences of known ages, and onlap and truncation relationships at unconformities. Thrust faulting occurred throughout the late Paleocene-Pliocene. The abundant temporal data indicate the deformational seuqence was significantly differet from the simple, steplike, foreland-propagating model formulated in other less well-dated thrust belts. Many thrusts were active simultaneously, especially during the late Eocnee, when the region of active thrusting had an across-strike width of greater than 200 km. This observation calls into question the popular concept that only one thrust moves at a time as a thrust belt develops. The thrust belt propagated along, as well as across, strike. During the late Paleocene-middle Eocene, the area of active thrusting was bounded on the southeast by poorly imaged zones of right-lateral strike-slip faults that apparently are the northern offshore continuation of the Rapid fault array. The change in the age of thrusting along strike results in no obvious geometrical anomalies and could not be deduced without timing information. This has an important implication: temporal data cannot necessarily be projected along strike in a thrust belt.

  13. Evaluation of Silurian-Niagaran reef belt in Northeastern Michigan

    SciTech Connect

    Aminian, K.; Ameri, S.; Bomar, R.M.

    1987-12-01

    Silurian pinnacle reefs have remained the main exploration targets in the Michigan basin over the last decade. Recent discoveries have extended the reef belt into new areas in the western and northeastern parts of Michigan's lower peninsula. Meanwhile, the exploration for these reefs has continued in more developed areas of the belt in northern Michigan, southwestern Ontario, and southern Michigan. The results of exploration activities in northeastern Michigan in Cheboygan, Montmorency, and Presque Isle counties is different from the rest of the northern portion of the belt. A detailed study used the data available from the exploration activities in this area to determine the reef belt characteristics and reserves potential in northeastern Michigan and its extension into Lake Huron. The results indicated some interesting features, including the narrowing of the belt as it approaches Lake Huron. It was concluded that the different depositional environment during the Silurian Age had affected the development of the belt and the hydrocarbon accumulation in the pinnacle reefs in this part of the basin.

  14. Quantitative estimates of metamorphic equilibria: Tallassee synform, Dadeville belt, Alabama's Inner Piedmont

    SciTech Connect

    Drummond, M.S.; Neilson, M.J. . Dept. of Geology)

    1993-03-01

    The Tallassee synform is the major structural feature in the western part of the Dadeville belt. This megascopic F2 structure folds amphibolite (Ropes Creek Amphibolite) and metasedimentary units (Agricola Schist, AS), as well as tonalitic (Camp Hill Gneiss, CHG), granitic (Chattasofka Creek Gneiss, CCG), and mafic-ultramafic plutons (Doss Mt. and Slaughters suites). Acadian-age prograde regional metamorphism preceded the F2 folding event, producing the pervasive S1 foliation and metamorphic recrystallization. Prograde mineralogy in the metapelites and metagraywackes of the AS includes garnet, biotite, muscovite, plagioclase, kyanite, sillimanite, and epidote. The intrusive rocks, both felsic and mafic-ultramafic, are occasionally garnetiferous and provide suitable mineral assemblages for P-T evaluation. The AS yields a range of T-P from 512--635C and 5.1--5.5 kb. Muscovite from the AS exhibits an increase in Ti content from 0.07 to 0.15 Ti/22 O formula unit with progressively increasing T's from 512 to 635C. This observation is consistent with other studies that show increasing Ti content with increasing grade. A CHG sample records an average metamorphic T-P of 604C and 5.79 kb. Hornblende-garnet pairs from a Doss Mt. amphibolite sample provides an average metamorphic T of 607C. These data are consistent with regional Barrovian-type middle to upper amphibolite facies metamorphism for the Tallassee synform. Peak metamorphism is represented by kyanite-sillimanite zone conditions and localized migmatization of the AS. The lithotectonic belts bounding the Dadeville belt to the NW and SE are the eastern Blue Ridge and Opelika belts. Studies have shown that these belts have also experienced Acadian-age amphibolite facies metamorphism with comparable P-T estimates to those presented here. These data suggest that the eastern Blue Ridge and Inner Piedmont of AL experienced the same pervasive dynamothermal Barrovian-type metamorphic episode during Acadian orogenesis.

  15. Geochronology of the Baltica crust in the Western Gneiss Region, Norway: Palaeoproterozoic augen gneisses, Sveconorwegian zircon neocrystallization and Caledonian zircon deformation

    NASA Astrophysics Data System (ADS)

    Røhr, Torkil S.; Bingen, Bernard; Robinson, Peter; Reddy, Steven M.

    2013-04-01

    The Western Gneiss Region, Western Norway, is dominated by Palaeoproterozoic to Mesoproterozoic felsic crust of Baltica ancestry (Baltican Basement), partly subducted to high- and ultrahigh-pressure (HP-UHP) conditions during the Caledonian (Scandian) orogeny between 415 and 395 Ma. The dominant felsic gneisses, in contrast with mafic rocks, carry little evidence for the HP-UHP history, but were affected by amphibolite-facies reworking during exhumation. LA-ICPMS and SIMS zircon U-Pb data were collected in augen orthogneiss samples to constrain the magmatic and metamorphic geochronology in this crust. Five samples from the eclogite-bearing HP-UHP basement near Molde yield intrusion ages ranging from 1644 +/-6 to 1594 +/-10 Ma. Two samples of the structurally underlying eclogite-free basement yield ages of 1685 ±18 and 1644 +/-13 Ma, and a sample from the infolded Middle Allochthon Risberget Nappe yields an equivalent age of 1676 +/-18 Ma. Two samples of the eclogite-bearing basement contain low Th/U neocrystallized zircon with an age of 950 +/-26 Ma. This zircon provides the northernmost direct evidence for at least amphibolite-facies Sveconorwegian metamorphism in unquestionable Baltican crust, close to the known "Sveconorwegian boundary" in the Western Gneiss Region. The Western Gneiss Region characterized by 1686-1594 Ma magmatism, the Eastern Segment of the Sveconorwegian Orogen characterized by 1795-1640 Ma magmatism, and the Idefjorden terrane hosting the type Gothian active margin magmatism dated between 1659 and 1520 Ma, probably represent three distinct Proterozoic growth zones of Baltica into which Sveconorwegian reworking propagated. Samples of the eclogite-bearing basement lack Scandian neocrystallization of zircon, but show partial recrystallization of zircon. Paired CL and EBSD images indicate that zircon crystals underwent crystal-plastic deformation during the Scandian subduction-exhumation cycle. They illustrate a relationship between crystal

  16. Strontium and neodymium isotopic variations in early Archean gneisses affected by middle to late Archean high-grade metamorphic processes: West Greenland and Labrador

    NASA Technical Reports Server (NTRS)

    Collerson, K. D.; Mcculloch, M. T.; Bridgwater, D.; Mcgregor, V. R.; Nutman, A. P.

    1986-01-01

    Relicts of continental crust formed more than 3400 Ma ago are preserved fortuitously in most cratons. The cratons provide the most direct information about crust and mantle evolutionary processes during the first billion years of Earth history. In view of their polymetamorphic character, these terrains are commonly affected by subsequent tectonothermal events. Hence, their isotope systematics may be severely disturbed as a result of bulk chemical change or local isotopic homogenization. This leads to equivocal age and source information for different components within these terrains. The Sr and Nd isotopic data are presented for early Archean gneisses from the North Atlantic Craton in west Greenland and northern Labrador which were affected by younger metamorphic events.

  17. The Rwenzori Mountains, a Palaeoproterozoic crustal shear belt crossing the Albertine rift system

    NASA Astrophysics Data System (ADS)

    Koehn, D.; Link, K.; Sachau, T.; Passchier, C. W.; Aanyu, K.; Spikings, A.; Harbinson, R.

    2016-09-01

    This contribution discusses the development of the Palaeoproterozoic Buganda-Toro belt in the Rwenzori Mountains and its influence on the western part of the East African Rift System in Uganda. The Buganda-Toro belt is composed of several thick-skinned nappes consisting of Archaean Gneisses and Palaeoproterozoic cover units that are thrusted northwards. The high Rwenzori Mountains are located in the frontal unit of this belt with retrograde greenschist facies gneisses towards the north, which are unconformably overlain by metasediments and amphibolites. Towards the south, the metasediments are overthrust by the next migmatitic gneiss unit that belongs to a crustal-scale nappe. The southwards dipping metasedimentary and volcanic sequence in the high Rwenzori Mountains shows an inverse metamorphic grade with greenschist facies conditions in the north and amphibolite facies conditions in the south. Early D1 deformation structures are overgrown by cordierite, which in turn grows into D2 deformation, representing the major northwards directed thrusting event. We argue that the inverse metamorphic gradient develops because higher grade rocks are exhumed in the footwall of a crustal-scale nappe, whereas the exhumation decreases towards the north away from the nappe leading to a decrease in metamorphic grade. The D2 deformation event is followed by a D3 E-W compression, a D4 with the development of steep shear zones with a NNE-SSW and SSE-NNW trend including the large Nyamwamba shear followed by a local D5 retrograde event and D6 brittle reverse faulting. The Palaeoproterozoic Buganda-Toro belt is relatively stiff and crosses the NNE-SSW running rift system exactly at the node where the highest peaks of the Rwenzori Mountains are situated and where the Lake George rift terminates towards the north. Orientation of brittle and ductile fabrics show some similarities indicating that the cross-cutting Buganda-Toro belt influenced rift propagation and brittle fault development

  18. The Rwenzori Mountains, a Palaeoproterozoic crustal shear belt crossing the Albertine rift system

    NASA Astrophysics Data System (ADS)

    Koehn, D.; Link, K.; Sachau, T.; Passchier, C. W.; Aanyu, K.; Spikings, A.; Harbinson, R.

    2015-04-01

    This contribution discusses the development of the Palaeoproterozoic Buganda-Toro belt in the Rwenzori Mountains and its influence on the western part of the East African Rift System in Uganda. The Buganda-Toro belt is composed of several thick-skinned nappes consisting of Archaean Gneisses and Palaeoproterozoic cover units that are thrusted northwards. The high Rwenzori Mountains are located in the frontal unit of this belt with retrograde greenschist facies gneisses towards the north, which are unconformably overlain by metasediments and amphibolites. Towards the south, the metasediments are overthrust by the next migmatitic gneiss unit that belongs to a crustal-scale nappe. The southwards dipping metasedimentary and volcanic sequence in the high Rwenzori Mountains shows an inverse metamorphic grade with greenschist facies conditions in the north and amphibolite facies conditions in the south. Early D1 deformation structures are overgrown by cordierite, which in turn grows into D2 deformation, representing the major northwards directed thrusting event. We argue that the inverse metamorphic gradient develops because higher grade rocks are exhumed in the footwall of a crustal-scale nappe, whereas the exhumation decreases towards the north away from the nappe leading to a decrease in metamorphic grade. The D2 deformation event is followed by a D3 E-W compression, a D4 with the development of steep shear zones with a NNE-SSW and SSE-NNW trend including the large Nyamwamba shear followed by a local D5 retrograde event and D6 brittle reverse faulting. The Palaeoproterozoic Buganda-Toro belt is relatively stiff and crosses the NNE-SSW running rift system exactly at the node where the highest peaks of the Rwenzori Mountains are situated and where the Lake George rift terminates towards the north. Orientation of brittle and ductile fabrics show some similarities indicating that the cross-cutting Buganda-Toro belt influenced rift propagation and brittle fault development

  19. Distant Kuiper Belt Objects

    NASA Astrophysics Data System (ADS)

    Allen, R. Lynne; Bernstein, Gary; Malhotra, Renu

    2001-02-01

    Kuiper Belt Object surveys indicate a lack of objects with semi- major axis a⪆50 AU in low eccentricity, low inclination orbits. This presents a problem for the simplest theories of Kuiper Belt evolution, which predict a dense, primordial outer Kuiper Belt. A possible solution is that the outer Belt is very dynamically cold, appearing as a razor-thin plane on the sky. If this disk was inclined only 0.5° from the ecliptic, present surveys could fail to detect it since the deep surveys (limiting magnitude R~26) lack sufficient sky coverage and the shallow surveys (limiting mag R~24.4) lack sufficient depth to see small (radius ⪉130 km) objects beyond 50 AU. If this cold, dense disk were to cross a Mosaic field with a limiting magnitude R=25.8, we would expect to see at least 15 distant KBOs. By observing strategically placed large fields we could detect any cold, dense distant disk inclined at up to 0.7° from the invariable plane. This would place a strong constraint on the location of a cold, dense outer Kuiper Belt.

  20. Precambrian coal or anthraxolite: A source for graphite in high-grade schists and gneisses-a reply

    SciTech Connect

    Mancuso, J.J.; Seavoy, R.E.

    1982-08-01

    Argues that without considering data for igneous carbon (carbonatites) or for ultrahigh metamorphic calcareous gneisses such as are found in the Grenville province of North America, the conclusion that the source of carbon for vein graphite is magmatic or carbonate carbon is not justified. Points out that marbles and calc-silicate gneisses occur with the graphite-bearing granulite facies rocks in Sri Lanka. Calcite may also be seen in the veins with the graphite. Concludes that whether the graphite in epigenetic veins in high grade schists and gneisses has variable carbon isotope ratios depends on whether it was derived from organic material in carbonate or noncarbonate metasediments.

  1. Fluid-deposited graphite and its geobiological implications in early Archean gneiss from Akilia, Greenland.

    PubMed

    Lepland, A; van Zuilen, M A; Philippot, P

    2011-01-01

    Graphite, interpreted as altered bioorganic matter in an early Archean, ca. 3.83-Ga-old quartz-amphibole-pyroxene gneiss on Akilia Island, Greenland, has previously been claimed to be the earliest trace of life on Earth. Our petrographic and Raman spectroscopy data from this gneiss reveal the occurrence of graphitic material with the structure of nano-crystalline to crystalline graphite in trails and clusters of CO₂, CH₄ and H₂O bearing fluid inclusions. Irregular particles of graphitic material without a fluid phase, representing decrepitated fluid inclusions are common in such trails too, but occur also as dispersed individual or clustered particles. The occurrence of graphitic material associated with carbonic fluid inclusions is consistent with an abiologic, fluid deposited origin during a poly-metamorphic history. The evidence for fluid-deposited graphitic material greatly complicates any claim about remnants of early life in the Akilia rock. PMID:21070588

  2. Fluid-deposited graphite and its geobiological implications in early Archean gneiss from Akilia, Greenland.

    PubMed

    Lepland, A; van Zuilen, M A; Philippot, P

    2011-01-01

    Graphite, interpreted as altered bioorganic matter in an early Archean, ca. 3.83-Ga-old quartz-amphibole-pyroxene gneiss on Akilia Island, Greenland, has previously been claimed to be the earliest trace of life on Earth. Our petrographic and Raman spectroscopy data from this gneiss reveal the occurrence of graphitic material with the structure of nano-crystalline to crystalline graphite in trails and clusters of CO₂, CH₄ and H₂O bearing fluid inclusions. Irregular particles of graphitic material without a fluid phase, representing decrepitated fluid inclusions are common in such trails too, but occur also as dispersed individual or clustered particles. The occurrence of graphitic material associated with carbonic fluid inclusions is consistent with an abiologic, fluid deposited origin during a poly-metamorphic history. The evidence for fluid-deposited graphitic material greatly complicates any claim about remnants of early life in the Akilia rock.

  3. Gaspé Belt subsurface geometry in the northern Québec Appalachians as revealed by an integrated geophysical and geological study: 2 — Seismic interpretation and potential field modelling results

    NASA Astrophysics Data System (ADS)

    Pinet, Nicolas

    2013-03-01

    Geological information, seismic reflection profiles and potential field data are used to study the geometry of the Middle Paleozoic Gaspé Belt (eastern Canada) that has been interpreted in various ways in the past. On the western edge of the Gaspé Belt, in the Matapédia area, growth strata are imaged on seismic profiles and testify of normal (or transtensional) motion during the period spanning the Silurian (and possibly Late Ordovician) to earliest Devonian along several faults, including the Shickshock-Sud Fault. In this area, Acadian deformation during the Middle to Late Devonian is associated with relatively modest shortening (less than 20%) accommodated by broad open folds, steeply-dipping neo-formed faults and inversion of previously formed faults. Neo-formed faults cut the entire Middle Paleozoic succession and offset the Ordovician Taconian unconformity suggesting that no sedimentary interval acted as an efficient décollement level. Toward the SE, the Sainte-Florence Fault divides rock assemblages with different paleogeographic settings and structural styles. Increase in tectonic complexity and amount of shortening to the south of the fault is interpreted as resulting of a vise effect between two basement blocks.

  4. Regional tectonic context, timing, and intrusion mechanism of gneiss domes, eastern Papua New Guinea, from offshore seismic reflection and well data

    NASA Astrophysics Data System (ADS)

    Fitz, G. G.; Mann, P.; Lavier, L. L.

    2011-12-01

    The D'Entrecasteaux Island (DEI) gneiss domes are fault-bounded topographic domes with ~2.5 km of relief exposing ultrahigh-pressure (UHP) and high-pressure (HP) metamorphic gneisses and migmatites that began to exhume ~8 Ma in a zone of continental extension 120 km west of the tip of the westward propagating Woodlark seafloor spreading. Two previous models for the origin and emplacement of the gneiss domes include: 1) the domes are metamorphic core complexes formed as footwall blocks on north-dipping, low-angle (<30 deg.) normal faults of Plio-Pleistocene age; and 2) the domes are diapirs of buoyant lower crustal material extruding vertically through narrow zones of extension (~30 km wide) in an overlying dense layer of ultramafic rock. To study the style of continental extension accompanying exhumation of the DEI gneiss domes, we interpreted a loose grid of 1,518 km of 2-D multi-channel seismic (MCS) reflection data and well data from the offshore areas surrounding the DEI, including the Trobriand basin and the Goodenough basin. MCS and well data show the Trobriand basin initially formed as an asymmetrical Miocene forearc basin overlying the south-dipping Trobriand subduction zone that underwent a late Miocene (~11-9 Ma) inversion event that deformed and uplifted the basin's southern and northern margins. Since extension began 8 Ma, the Trobriand basin has evolved as a symmetrical sag basin with 1-3 km of subsidence and few normal faults deforming the upper crust. The Goodenough basin to the south of the Trobriand basin formed as an asymmetrical and southward-tilted half-graben whose master normal fault is the Owen-Stanley fault zone (OSFZ) along the southern edge of the basin. Reconstruction on this structure based on the geometry of faults in the hanging wall indicates a minimum slip on the order of 10 km along a listric fault plane shallowly dipping to the north. The western extension of the OSFZ dips 18 deg. to 24 deg. north along the northern edge of the

  5. Effects of weathering on the UPb ages of zircon from the Morton Gneiss, Minnesota

    USGS Publications Warehouse

    Stern, T.W.; Goldich, S.S.; Newell, M.F.

    1966-01-01

    Weathering has caused large losses of lead from the zircon in the residual clay derived from the Morton Gneiss of southwestern Minnesota, drastically reducing the 206Pb/238U and the 207Pb/235U ages. The 207Pb/206Pb age probably has not been significantly affected. Loss of lead by leaching during weathering has not been adequately considered in explanation of discordant ages of zircon. ?? 1966.

  6. Gneiss-charnockite-granite connection in the archaean crust of Karnataka Craton, India

    NASA Technical Reports Server (NTRS)

    Ananthaiyer, G. V.

    1988-01-01

    It is explained that the big picture of the Indian crust contains essentially three components: (1) the upper crust, which is composed of platformal sedimentary sequences (including banded iron formations), (2) the middle crust, which is represented by the Peninsular gneiss, and (3) the deep crust, which is composed predominantly of charnockites. The charnockitization controversy was addressed by stating that CO2 is absolutely not essential for charnockite formation, and it is suggested rather that molecular hydrogen movements play an important role.

  7. The Radiation Belt Storm Probes

    NASA Video Gallery

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

  8. Fluid-rock interaction at a carbonatite-gneiss contact, Alnö, Sweden

    NASA Astrophysics Data System (ADS)

    Skelton, A.; Hode Vuorinen, J.; Arghe, F.; Fallick, A.

    2007-07-01

    We evaluate balanced metasomatic reactions and model coupled reactive and isotopic transport at a carbonatite-gneiss contact at Alnö, Sweden. We interpret structurally channelled fluid flow along the carbonatite-gneiss contact at ˜640°C. This caused (1) metasomatism of the gneiss, by the reaction: {biotite + quartz + oligoclase + K2 O + Na2O ± CaO ± MgO ± FeO = albite + K-feldspar + arfvedsonite + aegirene-augite + H2 O + SiO2}, (2) metasomatism of carbonatite by the reaction: calcite + SiO2 = wollastonite + CO2, and (3) isotopic homogenization of the metasomatised region. We suggest that reactive weakening caused the metasomatised region to widen and that the metasomatic reactions are chemically (and possibly mechanically) coupled. Spatial separation of reaction and isotope fronts in the carbonatite conforms to a chromatographic model which assumes local calcite-fluid equilibrium, yields a timescale of 102-104 years for fluid-rock interaction and confirms that chemical transport towards the carbonatite interior was mainly by diffusion. We conclude that most silicate phases present in the studied carbonatite were acquired by corrosion and assimilation of ijolite, as a reactive by-product of this process and by metasomatism. The carbonatite was thus a relatively pure calcite-H2O-CO2-salt melt or fluid.

  9. Lu-Hf total-rock age for the Amîtsoq gneisses, West Greenland

    USGS Publications Warehouse

    Pettingill, H.S.; Patchett, P.J.

    1981-01-01

    Lu-Hf total-rock data for the Amîtsoq gneisses of West Greenland yield an age of 3.55±0.22Gy(2σ), based on the decay constant λ176Lu=1.96×10−11y−1, and an initial176Hf/177Hf ratio of 0.280482±33. The result is in good agreement with Rb-Sr total-rock and U-Pb zircon ages. In spite of severe metamorphism of the area at 2.9 Gy, zircons from two of the samples have remained on the total-rock line, and define points close to the initial Hf ratio. The initial176Hf/177Hf lies close to a chondritic Hf isotopic evolution curve from 4.55 Gy to present. This is consistent with the igneous precursors to the Amîtsoq gneisses having been derived from the mantle at or shortly before 3.6 Gy. Anomalous relationships between Hf concentration and the176Lu/177Hf ratio may suggest that trace element abundances in the Amîtsoq gneisses are partly controlled by processes related to metamorphism.

  10. Lu-Hf total-rock age for the Amitsoq gneisses, West Greenland

    NASA Technical Reports Server (NTRS)

    Pettingill, H. S.; Patchett, P. J.

    1981-01-01

    Lu-Hf total-rock data for the Amitsoq gneisses of West Greenland yield an age of 3.55 + or - 0.22 billion years, based on the decay constant for Lu-176 of 1.96 x 10 to the -11th/year, and an initial Hf-176/Hf-177 ratio of 0.280482 + or - 33. The result is in good agreement with Rb-Sr total-rock and U-Pb zircon ages. In spite of severe metamorphism of the area at 2.9 billion years, zircons from two of the samples have remained on the total-rock line, and define points close to the initial Hf ratio. The initial Hf-176/Hf-177 lies close to a chondritic Hf isotopic evolution curve from 4.55 billion years to present. This is consistent with the igneous precursors to the Amitsoq gneisses having been derived from the mantle at or shortly before 3.6 billion years. Anomalous relationships between Hf concentration and the Lu-176/Hf-177 ratio may suggest that trace element abundances in the Amitsoq gneisses are partly controlled by processes related to metamorphism.

  11. Oxygen isotopes of some trondhjemites, siliceous gneisses, and associated mafic rocks

    USGS Publications Warehouse

    Barker, F.; Friedman, I.; Hunter, D.R.; Gleason, J.D.

    1976-01-01

    Analyses of oxygen isotopes in whole-rock samples of 58 Precambrian and Phanerozoic trondhjemites and siliceous gneisses and of 28 cogenetic mafic to intermediate rocks from North America, Fennoscandia, and southern Africa give the following results: 1. (1) 47 trondhjemites, tonalites, and mostly Archean acidic gneisses that apparently are not isotopically disturbed show an overage ?? 15O of +7.3??? and a range of 5.2-8.9???; 11 other samples are slightly to moderately disturbed and show higher values; and 2. (2) the mafic rocks show a wide range of ??-values, from about 0-9??? but the undisturbed ones give an average ?? 18O of 5.2???. The ?? 18O values of the trondhjemitic intrusives and siliceous gneisses of similar composition are lower than those of most granitic rocks and support models for derivation of these rocks from basaltic parents. This approach, however, cannot be used to determine if individual bodies formed by differentiation or by partial melting. ?? 1976.

  12. Geochemical and isotopic constraints on the tectonic setting of Serra dos Carajas belt, eastern Para, Brazil

    NASA Technical Reports Server (NTRS)

    Olszewski, W. J., Jr.; Gibbs, A. K.; Wirth, K. R.

    1986-01-01

    The lower part of the Serra dos Carajas belt is the metavolcanic and metasedimentary Grao para Group (GPG). The GPG is thought to unconformably overlie the older (but undated) Xingu Complex, composed of medium and high-grade gneisses and amphibolite and greenstone belts. The geochemical data indicate that the GPG has many features in common with ancient and modern volcanic suites erupted through continental crust. The mafic rocks clearly differ from those of most Archean greenstone belts, and modern MORB, IAB, and hot-spot basalts. The geological, geochemical, and isotopic data are all consistent with deposition on continental crust, presumably in a marine basin formed by crustal extension. The isotopic data also suggest the existence of depleted mantle as a source for the parent magmas of the GPG. The overall results suggest a tectonic environment, igneous sources, and petrogenesis similar to many modern continental extensional basins, in contrast to most Archean greenstone belts. The Hammersley basin in Australia and the circum-Superior belts in Canada may be suitable Archean and Proterozoic analogues, respectively.

  13. Effects of weathering on the RbSr and KAr ages of biotite from the Morton Gneiss, Minnesota

    USGS Publications Warehouse

    Goldich, S.S.; Gast, P.W.

    1966-01-01

    Weathering has drastically reduced the RbSr and, to a lesser extent, the KAr age of biotite from the Morton Gneiss of southwestern Minnesota. The ages are approximately 75% and 25% lower than the corresponding ages for biotite from the fresh gneiss. The effects of even incipient weathering cannot be neglected in RbSr dating of biotite and, by analogy, of feldspar and whole-rock samples. ?? 1966.

  14. From oceanic subduction to continental collision: An overview of HP-UHP metamorphic rocks in the North Qaidam UHP belt, NW China

    NASA Astrophysics Data System (ADS)

    Zhang, Guibin; Zhang, Lifei; Christy, Andrew G.

    2013-02-01

    The North Qaidam UHPM belt is unique among "continental type" subduction zones in showing well-preserved subducted oceanic relics that predate continental subduction and collision. We review petrologic, thermobarometric, geochemical and geochronological studies for the Yuka, Luliang Shan, Xitieshan and Dulan terranes in this belt. UHP conditions are demonstrated by coesite inclusions in eclogite and country gneiss, and diamond inclusions from garnet peridotite. The relict subducted oceanic lithology crops out in the Shaliuhe cross-section in Dulan terrane; it originated as the floor of a Paleo-Qilian Ocean that existed between Qaidam and Qilian blocks before the early Ordovician. Whereas most eclogites of this belt are derived from mafic rocks of either a Neoproterozoic continental rift or incipient oceanic basin setting, which were subducted along with continental rocks in the early Paleozoic. The data, especially the two protolith sources for eclogites, demonstrate tectonic evolution of the North Qaidam UHPM belt from oceanic subduction to continental collision.

  15. Cenozoic intracontinental deformation of the Kopeh Dagh Belt, Northeastern Iran

    NASA Astrophysics Data System (ADS)

    Chu, Yang; Wan, Bo; Chen, Ling; Talebian, Morteza

    2016-04-01

    Compressional intracontinental orogens represent large tectonic zones far from plate boundaries. Since intracontinental mountain belts cannot be framed in the conventional plate tectonics theory, several hypotheses have been proposed to account for the formations of these mountain belts. The far-field effect of collision/subduction at plate margins is now well accepted for the origin and evolution of the intracontinental crust thickening, as exemplified by the Miocene tectonics of central Asia. In northern Iran, the Binalud-Alborz mountain belt witnessed the Triassic tectonothermal events (Cimmerian orogeny), which are interpreted as the result of the Paleotethys Ocean closure between the Eurasia and Central Iran blocks. The Kopeh Dagh Belt, located to the north of the Binalud-Alborz Belt, has experienced two significant tectonic phases: (1) Jurassic to Eocene rifting with more than 7 km of sediments; and (2) Late Eocene-Early Oligocene to Quaternary continuous compression. Due to the high seismicity, deformation associated with earthquakes has received more and more attention; however, the deformation pattern and architecture of this range remain poorly understood. Detailed field observations on the Cenozoic deformation indicate that the Kopeh Dagh Belt can be divided into a western zone and an eastern zone, separated by a series of dextral strike-slip faults, i.e. the Bakharden-Quchan Fault System. The eastern zone characterized by km-scale box-fold structures, associated with southwest-dipping reverse faults and top-to-the NE kinematics. In contrast, the western zone shows top-to-the SW kinematics, and the deformation intensifies from NE to SW. In the northern part of this zone, large-scale asymmetrical anticlines exhibit SW-directed vergence with subordinate thrusts and folds, whereas symmetrical anticlines are observed in the southern part. In regard to its tectonic feature, the Kopeh Dagh Belt is a typical Cenozoic intracontinental belt without ophiolites or

  16. Geochronologic Constraints on the Location of the Sino-Korean/Yangtze Suture and Evolution of the Northern Dabie Shan

    NASA Astrophysics Data System (ADS)

    Bryant, D. L.; Ayers, J. C.; Gao, S.; Miller, C. F.; Zhang, H.

    2002-05-01

    The Northern Dabie Complex (NDC) has been proposed to be either a Paleozoic magmatic arc, an exhumed piece of subducted continental crust, or young crust produced almost entirely by Cretaceous extensional magmatism. Ion microprobe zircon 238U-206Pb ages of separates from NDC gneisses center around 689Ma (+/- 31(95%CL)), consistent with the characteristic zircon dates of the Yangtze Craton [1]. Field observations also show that these gneisses, ranging from granitic to dioritic composition, make up a sizeable area ( ~30%) of the NDC. Zircon separates from the Baimajian granitoid, the largest of the widespread Cretaceous intrusions in the NDC, have yielded ages clustered around 677Ma (+/- 79), and 120Ma (+/- 3.4), the latter of which agrees with ion probe Th-Pb monazite ages. The ~700Ma age indicates that this intrusion may be linked with partial melting of underlying Yangtze crust, while the 120Ma age is the age of its crystallization. Granitic intrusions from Sanzushi and Yerenshai in the Dabie ultrahigh-pressure (UHP) region also show clusters of ages at 714Ma (+/- 55) from zircon cores, as well as rims around 250Ma (+/- 38), which is interpreted as the time of collision of the two continental blocks. These age data support the hypothesis set forth by Zhang et al. [2] using Sm-Nd and Pb isotopic data, that the Yangtze block lies beneath the exhumed UHP belt and outcrops as the NDC, which lies between the UHP belt and the Sino-Korean/Yangtze suture. The Baimajian granitoid, however, also shows a range of older zircon core ages from 1.4-2.0Ga, which may represent the early stages of formation of the Yangtze craton. Zhang et al. [2] suggested craton formation at 1.6-2.4Ga but few such ages have been reported for rocks of the Yangtze or Sino-Korean cratons. 1. Hacker, et al. (2000) Journal of Geophysical Research. Vol. 105. p. 13,339. 2. Zhang, et al. (In press) Chemical Geology.

  17. Metamorphic and geochemical signatures within calc-silicate gneisses of the Sawtooth Metamorphic Complex, ID: Implications for western North America crustal evolution

    NASA Astrophysics Data System (ADS)

    Fukai, I.; Dutrow, B. L.; Henry, D.; Mueller, P. A.; Foster, D. A.

    2012-12-01

    -plagioclase thermometer to SMC calc-silicates results in upper-amphibolite facies temperatures of 651°C at an assumed pressure of 7 kbar. Whole-rock phase diagram calculations (pseudosections: Perple_X) yield a similar temperature result of 660-625°C at 7 kbar (assumed), and a fluid composition of X(CO2) >0.2. These estimates are lower than peak granulite facies conditions recorded by SMC aluminous gneisses, and slightly higher than greenschist-amphibolite facies metasediments of the nearby Mesoproterozoic Belt Supergroup and Neoproterozoic Windermere Supergroup. Amphibolite facies temperatures recorded by calc-silicates may represent a retrograde event, or peak metamorphism in a lower-grade area of the SMC relative to the granulite facies aluminous gneisses further west. Upper-amphibolite-lower-granulite metamorphic conditions and a geochemical signature characteristic of recycled sediments of continental affinity reported in this study, and supported by previous work, suggest that the SMC represents a distinct, significant portion of middle-to-lower crust with uncertain affinity to nearby crustal provinces.

  18. Impact of textural anisotropy on syn-kinematic partial melting of natural gneisses: an experimental approach.

    NASA Astrophysics Data System (ADS)

    Ganzhorn, Anne-Céline; Trap, Pierre; Arbaret, Laurent; Champallier, Rémi; Fauconnier, Julien; Labrousse, Loic; Prouteau, Gaëlle

    2015-04-01

    Partial melting of continental crust is a strong weakening process controlling its rheological behavior and ductile flow of orogens. This strength weakening due to partial melting is commonly constrained experimentally on synthetic starting material with derived rheological law. Such analog starting materials are preferentially used because of their well-constrained composition to test the impact of melt fraction, melt viscosity and melt distribution upon rheology. In nature, incipient melting appears in particular locations where mineral and water contents are favorable, leading to stromatic migmatites with foliation-parallel leucosomes. In addition, leucosomes are commonly located in dilatants structural sites like boudin-necks, in pressure shadows, or in fractures within more competent layers of migmatites. The compositional layering is an important parameter controlling melt flow and rheological behavior of migmatite but has not been tackled experimentally for natural starting material. In this contribution we performed in-situ deformation experiments on natural rock samples in order to test the effect of initial gneissic layering on melt distribution, melt flow and rheological response. In-situ deformation experiments using a Paterson apparatus were performed on two partially melted natural gneissic rocks, named NOP1 & PX28. NOP1, sampled in the Western Gneiss Region (Norway), is biotite-muscovite bearing gneiss with a week foliation and no gneissic layering. PX28, sampled from the Sioule Valley series (French Massif Central), is a paragneiss with a very well pronounced layering with quartz-feldspar-rich and biotite-muscovite-rich layers. Experiments were conducted under pure shear condition at axial strain rate varying from 5*10-6 to 10-3 s-1. The main stress component was maintained perpendicular to the main plane of anisotropy. Confining pressure was 3 kbar and temperature ranges were 750°C and 850-900°C for NOP1 and PX28, respectively. For the 750

  19. In-situ Hf isotope analysis of early Archean zircons in the Acasta Gneisses from the Slave province, Northwestern Canada

    NASA Astrophysics Data System (ADS)

    Iizuka, T.; Komiya, T.; Maruyama, S.; Hirata, T.

    2003-12-01

    Lu-Hf and Sm-Nd isotopic systems of early Archean rocks provide insights into the early crustal evolution and early mantle differentiation of the Earth. The Acasta Gneisses have been established as the oldest known intact terrestrial rocks (Bowring et al., 1999). The Acasta Gneiss Complex comprises mainly of Gray Gneiss (granodioritic gneiss), White Gneiss (tonalitic to granitic gneiss), and Foliated Granite, with many aplite and basaltic intrusions, and the relation between these rocks is very complex. Bowring et al. (1989) carried out the whole-rock Sm-Nd isotopic system measurement of the Acasta gneisses, and demonstrated that the gneisses exhibit a wide range of initial ɛ (Nd) (+3.5 to -4 at 4.0 Ga and +4 to -7 at 3.6 Ga). However, because most of the Acasta gneisses have experienced amphibolite facies metamorphism, it is difficult that the whole-rock isotopic system remains closed. Zircon, which is extremely resistant against erosion and/or metamorphic events, and it can be also dated precisely by U-Pb chronometer. Because of high Hf content (ca. 1 wt%) and low Lu/Hf ratio, zircon has been widely used for the isotopic study using Lu-Hf system, too. Recent Lu-Hf isotopic studies were carried out using a multiplecollector inductively coupled plasma mass spectrometer (MC-ICPMS). Amelin et al. (2000) carried out the Hf isotope analyses of some zircon grains from the Acasta Gneisses using MC-ICPMS. The zircon grains exhibit enriched initial ɛ (Hf) (+0.16 to -4.1 at ca. 3.6 Ga), while other early Archean zircon grains from the Amitsoq gneisses and the Barberton gneisses indicate depleted signature (Amelin et al., 2000). One possible reason is that the zircon grains from the Acasta Gneisses are grown at partial melting of the gneisses and/or underwent isotopic disturbance caused by intrusion of younger granites. Therefore, it is very important to reveal the growth features of zircon, such as oscillatory zoning, in order to derive inherent information of the early

  20. 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.

  1. 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.

  2. Kuiper Belt Objects (Invited)

    NASA Astrophysics Data System (ADS)

    Tegler, S. C.; Romanishin, W.

    1999-09-01

    The Kuiper belt represents an exciting, new frontier in solar system research. About 200 Kuiper belt objects (KBOs) with diameters larger than 100 km are known to exist between 30 and 50 AU from the Sun. Surveys indicate that there may be as many as 100,000 KBOs larger than 100 km and perhaps billions of KBOs larger than 1 km between 30 and 50 AU. Although the total mass in these bodies is perhaps a few tenths of an Earth mass, accretion calculations indicate that the primordial Kuiper belt must have contained 10 to 30 Earth masses of material between 30 and 50 AU in order to explain the growth of large KBOs and the Pluto and Charon system in the 100 million years before the onset of the disruptive influence of Neptune. Once Neptune reached a fraction of its current mass, dynamical studies indicate that a combination of erosional collisions and mean motion and secular resonances sculpted the belt into its present day mass and structure. The influence of the resonances can be seen in the belt today as about one-third of the known KBOs are in a stable 2:3 mean motion resonance with Neptune, i.e. eccentric and inclined orbits, that approach or cross the orbit of Neptune, and semi-major axes, a, about 39.4 AU. Many KBOs with a > 42 AU are sufficiently far from Neptune that they are on stable, low inclination, low eccentricity, non-resonant orbits. A combination of resonances and disruptive collisions continue to deplete the Kuiper belt today as they inject KBOs or collision fragments inward into the solar system as Centaur objects and Jupiter family comets. Physical studies of KBOs are in their infancy. Perhaps one of the most surprising results is the observation that KBO colors and hence their surface compositions divide neatly into a grey and an extraordinarily red population. The red population suggests some surfaces are rich in complex carbon-bearing molecules. The colors exhibit no trend with resonant or non-resonant orbits or object size and suggest that

  3. 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.

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

    NASA Technical Reports Server (NTRS)

    Naqvi, S. M.

    1986-01-01

    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.

  5. «Granulite» zircons of the Lapland granulite belt

    NASA Astrophysics Data System (ADS)

    Kaulina, T.

    2003-04-01

    An age of the main stage of granulite metamorphism, which followed the overthrusting of the Lapland granulite belt (LGB) is estimated at about 1.91-1.95 Ga (Tugarinov, Bibikova, 1980; Bernard-Griffiths et al., 1984; Bibikova et al., 1993; Mitrofanov et al., 1993). This high-grade metamorphism is dated by U-Pb method on short prismatic gem-quality zircons that are typical for granulites and are interpreted as formed under stress and space-shortage conditions of the high pressure. And the common belief is that these zircon ages are dating the peak conditions of a metamorphic P-T path, since zircon has a high closure temperature of its U-Pb system. We studied rocks with different degree of metamorphism from Yavr and Pados rivers district (Kola Peninsula, Russia) located in the connection zone of the Tanaelv belt and LGB. Samples from the Tanaelv belt were taken from: 1) leucocratic garnet-clinopyroxene-amphibole plagiogneiss, chemically corresponds to andesite and formed under amphibolite facies 2) leucocratic biotite-pyroxene plagiogneiss with mineral association of granulite facies. Lapland granulites are represented by sillimanite-garnet-biotite gneiss from khondalite complex and leuco-mesocratic amphibole-pyroxene-plagioschist, belonging to the charnockite complex. Metamorphic zircons in all studied samples are represented practically by crystals of the same image. These are round or isometric (rarely subidiomorphic-prismatic in mafic granulites) large crystals with bright luster and high transparency. They are colorless or weakly colored into yellowish-pinkish tones. Crystals are zoneless but may contain cores, especially zircons from khondalite, 60% of which contain zoned cores. Thus typically “granulitic” zircon, described in many works, is the dominant type both in granulites of the Lapland belt and in amphiboles gneisses of the Tanaelv belt. Zircons are distinguished by low U contents (up to 100 ppm) and high Th/U and Zr/Hf ratios (0.6-0.7 and 42

  6. Geochemistry and geochronology of late Mesozoic volcanic rocks in the northern part of the Eastern Pontide Orogenic Belt (NE Turkey): Implications for the closure of the Neo-Tethys Ocean

    NASA Astrophysics Data System (ADS)

    Özdamar, Şenel

    2016-04-01

    This paper presents 40Ar/39Ar and U-Pb age data, Sr-Nd isotopes, whole-rock and mineral compositions of Upper Cretaceous volcanic rocks from the Ordu area of the Eastern Pontide Orogenic Belt (EPOB) in northeastern Turkey. The volcanic rocks exhibit a wide compositional range: basalt, basaltic-andesites, andesites and a rhyodacite suite; they are characterized by subparallel light rare earth element (LREE)-enrichment, relatively flat heavy rare earth element (HREE) patterns with Eu anomalies and moderate fractionation [average (La/Yb)N = 8.55]. The geochemical results show that the volcanic rocks have calc-alkaline affinity consistent with arc volcanic rocks erupted in an active continental margin. Initial 87Sr/86Sr values vary between 0.70569 and 0.70606, while initial 143Nd/144Nd values lie between 0.51244 and 0.51249. Crustal contamination affected the mantle-originated primary magma, as indicated by increased 87Sr/86Sr and decreased 143Nd/144Nd ratios with increasing SiO2. New precise laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) 206Pb-238U age analyses of zircon and 40Ar/39Ar age data of plagioclase from the volcanics enable a more precise reconstruction of the EBOP. The ages provide insight into the timing of arc formation in this region, constrain the volcanic activity between 86 My (Coniacian) and 75 My (Campanian) and constrain the timing of closure of the Neo-Tethys.

  7. Geochemistry and origin of ferruginous nodules in weathered granodioritic gneisses, Mysore Plateau, Southern India

    NASA Astrophysics Data System (ADS)

    Tripathi, Jayant K.; Rajamani, V.

    2007-04-01

    Fe-nodules occur within saprolites formed from weathering of granodioritic gneisses in the rain-shadow region of the Mysore Plateau adjacent to the Sahyadri Mountains in Southern India. These nodules and their host saprolites were studied for their geochemistry, including chemical speciation, to understand nodule formation and chemical redistribution processes during rock weathering. From their mode of occurrence, and mineralogical and geochemical data, we infer that the nodules originated by a two-stage process in which the initial extensive weathering of gneisses likely facilitated subsequent ferrolysis weathering and nodule formation. Nodules originated by precipitation of goethite, hematite and gibbsite along with several amorphous phases within the matrix of weathered gneisses. This is possible only under hydromorphic conditions, suggesting that parts of the plateau must have gone through a humid phase prior to the present aridity. In the saprolites, Al, Fe, and Ti become enriched because of the removal of Si, Ca, Na, and K. However within the nodule, Fe, Ti, Cr, and Ni are deposited after their chemical transport from the saprolite. Titanium, known for its immobile nature, was also mobilized and concentrated under the conditions of nodule formation. The most important elements in the nodule constitution are Fe, Al, Ti, and Mn, each having both crystalline and amorphous phases. Fe-Ti and Mn oxyhydroxides grain coatings in the saprolites and discrete amorphous Mn and Ti phases in the nodules seem to have scavenged trace elements from the weathering profile. REE were mobilized during weathering and nodule genesis in which Ce and Ti show a strong geochemical coherence. The enrichment of only HREE in saprolite, and both HREE and LREE with significant Ce in the nodule, indicate the control of evolving secondary minerals in the REE redistribution during rock weathering. Strong enrichment of Ce in the weathering profile and in nodules has important implications to

  8. Partial melting of UHP calc-gneiss from the Dabie Mountains

    NASA Astrophysics Data System (ADS)

    Liu, Penglei; Wu, Yao; Liu, Qiang; Zhang, Junfeng; Zhang, Li; Jin, Zhenmin

    2014-04-01

    Exhumation melting has been proposed for the ultra-high pressure (UHP) metamorphic rocks in the Dabie Mountains based on melting experiments. We document here the first petrological and mineralogical evidence demonstrating that the UHP calc-gneisses from the Ganjialing area in the Dabie Mountains experienced partial melting during early exhumation. The assemblage of garnet, phengite (Si = 3.65 pfu), coesite, rutile and carbonate preserved in the calc-gneisses indicates a peak metamorphic condition of 692-757 °C and 4.0-4.8 GPa. Partial melting is indicated by several lines of evidence: the melting textures of phengite, the feldspar-dominated films, bands, branches, blebs and veins, the euhedral K-feldspars, the intergrowth film of plagioclase and K-feldspar, the plagioclase + biotite intergrowth after garnet and the epidote poikiloblasts. Polyphase inclusions in garnet are characterized with wedge-like offshoots and serrate outlines whereas those in epidote display negative crystal shapes, which can be best interpreted by entrapment of former melts. We propose a wet melting reaction of Phn + Q ± Na-Cpx + H2O = Bt + Pl + Grt + felsic melts, which likely took place at ca.650-800 °C and ca.1.0-2.0 GPa, to interpret the melting event in the calc-gneisses. Chemical exchanges between garnet and melts produced new garnet domains with higher almandine, spessartine, MREE, HREE and Y but lower grossular, pyrope, P, Sc, Ti, V and Zr contents. Zr-in-rutile thermometer reveals a low temperature of 620-643 °C at 5 GPa, indicating a later reset for Zr in rutile. Healed fractures are suggested to be responsible for the formation of some polyphase inclusions in garnet.

  9. Evolution of high-pressure mafic granulites and pelitic gneisses from NE Madagascar: Tectonic implications

    NASA Astrophysics Data System (ADS)

    Ishwar-Kumar, C.; Sajeev, K.; Windley, B. F.; Kusky, T. M.; Feng, P.; Ratheesh-Kumar, R. T.; Huang, Y.; Zhang, Y.; Jiang, X.; Razakamanana, T.; Yagi, K.; Itaya, T.

    2015-11-01

    The occurrence of high-pressure mafic-ultramafic bodies within major shear zones is one of the indicators of paleo-subduction. In mafic granulites of the Andriamena complex (north-eastern Madagascar) we document unusual textures including garnet-clinopyroxene-quartz coronas that formed after the breakdown of orthopyroxene-plagioclase-ilmenite. Textural evidence and isochemical phase diagram calculations in the Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2 system indicate a pressure-temperature (P-T) evolution from an isothermal (780 °C) pressure up to c. 24 kbar to decompression and cooling. Such a P-T trajectory is typically attained in a subduction zone setting where a gabbroic/ultramafic complex is subducted and later exhumed to the present crustal level during oceanic closure and final continental collision. The present results suggest that the presence of such deeply subducted rocks of the Andriamena complex is related to formation of the Betsimisaraka suture. LA-ICPMS U-Pb zircon dating of pelitic gneisses from the Betsimisaraka suture yields low Th/U ratios and protolith ages ranging from 2535 to 2625 Ma. A granitic gneiss from the Alaotra complex yields a zircon crystallization age of ca. 818 Ma and Th/U ratios vary from 1.08 to 2.09. K-Ar dating of muscovite and biotite from biotite-kyanite-sillimanite gneiss and garnet-biotite gneiss yields age of 486 ± 9 Ma and 459 ± 9 Ma respectively. We have estimated regional crustal thicknesses in NE Madagascar using a flexural inversion technique, which indicates the presence of an anomalously thick crust (c. 43 km) beneath the Antananarivo block. This result is consistent with the present concept that subduction beneath the Antananarivo block resulted in a more competent and thicker crust. The textural data, thermodynamic model, and geophysical evidence together provide a new insight to the subduction history, crustal thickening and evolution of the high-pressure Andriamena complex and its link to the terminal

  10. Ancient Protolith Ages and Scandian Metamorphism Across the Western Gneiss Region, Norway

    NASA Astrophysics Data System (ADS)

    Walsh, E. O.; Hacker, B. R.; Gans, P. B.; Grove, M.; Gehrels, G.

    2004-12-01

    Recent work shows the ultrahigh-pressure (UHP) eclogite-facies event in the Western Gneiss Region (WGR) occurred ˜415-400 Ma. However, other (U)HP eclogite-facies events in the Scandinavian Caledonides make it necessary to determine eclogite ages across the WGR before constructing tectonic models. Also, insufficient data exist to constrain the ages of two amphibolite-facies events (at 650-750° C, ˜11 kbar and at 6-7 kbar) characteristic to the WGR, which provide important pins on the exhumation process. To these ends, we dated zircon from eclogites, monazite and muscovite from pelites in a 220 x 100 km E-W band across the WGR. Zircon and monazite were dated by secondary ion mass spectrometry and laser-ablation inductively coupled plasma mass spectrometry to extract igneous core and metamorphic rim ages. Most eclogites record Gothian ( ˜1.7-1.5 Ga) or Sveconorwegian ( ˜1.2-0.9 Ga) igneous protolith ages similar to those of the Baltica orthogneiss. The easternmost eclogite records a Svecofennian ( ˜1.8-2.0 Ga) upper intercept age; zircon and monazite from the Trollstigen area record upper intercept and concordia ages > 2 Ga, not previously known in the WGR. While Upper Allochthon eclogites and pelitic gneisses retain the Early to Middle Ordovician and Early Silurian ages of their Iapetan protoliths, the age of the last metamorphism in all the eclogites is Scandian. Basement eclogites were least affected by this Scandian (re)crystallization, and the westernmost eclogites were most affected. Precambrian monazite ages occur only within basement gneisses; Upper Allochthon gneisses yield peak monazite ages of ˜424 Ma and ˜374 Ma. The most robust geochronological signature of the Scandian metamorphism is a steady westward decrease in muscovite 40Ar/39Ar ages from \\sim394 Ma to \\sim384 Ma. The entire WGR was involved in the Scandian phase of the Caledonian Orogeny, including the allochthons, which were emplaced onto the Baltica basement before subduction to UHP

  11. Lap belt injuries in children.

    PubMed

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

    2010-01-01

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

  12. 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- 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

  13. Simulation of a true-triaxial deformation test on anisotropic gneiss using FLAC3D

    NASA Astrophysics Data System (ADS)

    Ye, Shenghua; Sehizadeh, Mehdi; Nasseri, Mohammad; Young, Paul

    2016-04-01

    A series of true-triaxial experiments have been carried out at the University of Toronto's Rock Fracture Dynamics Laboratory. Isotropic pegmatite and gneiss have been used to systematically study the effect of anisotropy on the strength, behaviour and seismic response. Samples were loaded under true-triaxial stress conditions and subjected to complex loading and unloading histories associated with rock deformation around underground openings. The results show expected patterns of weakness from preferentially oriented samples and highlight the importance of unloading history under true-triaxial conditions on the deformation and seismic response of the samples. These tests have been used to validate a synthetic simulation using the Itasca FLAC3D numerical code. The paper describes the FLAC3D simulations of the complex true-triaxial loading and unloading history of the different anisotropic samples. Various parameters were created to describe the physico-mechanical properties of the synthetic rock samples. Foliation planes of preferential orientations with respect to the primary loading direction were added to the synthetic rock samples to reflect the anisotropy of the gneiss. These synthetic rock samples were subjected to the same loading and unloading paths as the real rock samples, and failed in the same mechanism as what was observed from the experiments, and thus it proved the validity of this numerical simulation with FLAC3D.

  14. Strain-collapsed metamorphic isograds in a sillimanite gneiss dome, Seward Peninsula, Alaska

    SciTech Connect

    Miller, E.L.; Calvert, A.T.; Little, T.A. )

    1992-06-01

    Unusually closely spaced Barrovian series isograds have been described along the flanks of the Kigluaik Mountains, Seward Peninsula, Alaska, where they separate a high-grade gneiss complex intruded by granites of Cretaceous age from surrounding, regionally developed, blueschist to greenschist facies rocks. Structural mapping of the transition zone between the two metamorphic types indicates that their juxtaposition was aided by significant syn- to late-metamorphic solid-state flow that served to attenuate the overlying rock column and thus collapse the field metamorphic gradient. On the basis of field relations, structural data, petrography, and geochronologic data, strain appears to have accompanied the rapid (adiabatic) rise of high-temperature rocks from several tens of kilometers to less than 10 km depth during the Cretaceous, in an event younger than the unrelated to high-P metamorphism. Granite-cored gneiss domes on the Seward Peninsula may have formed during extension of previously thickened continental crust, resulting in the {approximately}35-km-thick crust and near-sea-level elevations of the region today.

  15. A Rubidium-Strontium study of the Twilight Gneiss, West Needle Mountains, Colorado

    USGS Publications Warehouse

    Barker, F.; Peterman, Z.E.; Hildreth, R.A.

    1969-01-01

    The Precambrian trondhjemitic Twilight Gneiss (Twilight Granite of Cross and Howe, 1905b) of the West Needle Mountains, southwestern Colorado, and its interlayered amphibolite and metarhyodacite yield a Rb-Sr isochron of 1,805??35 m.y. A low initial Sr87/Sr86 ratio of 0.7015 implies that metamorphism of these rocks to amphibolite facies took place soon after their emplacement. The mild metamorphism of Uncompahgran age, prior to 1,460 m.y. ago, and Laramide volcanism did not affect the Rb-Sr system in the Twilight. Rb contents of 26.5 to 108 ppm, Sr contents of 114 to 251 ppm, and K2O percentages of 1.23 to 3.64 in the Twilight Gneiss, in conjunction with high K/Rb ratios and the low initial ratio of Sr87/Sr86, lend support to geologic data that suggest the Twilight originated as volcanic or hypabyssal igneous rocks in a basaltic volcanic pile. ?? 1969 Springer-Verlag.

  16. A different duration of the formation of leucosome of migmatites in the K- and Na-zones of the northern Ladoga region of the southeastern Svecofennian belt, Fennoscandian shield

    NASA Astrophysics Data System (ADS)

    Baltybaev, Sh. K.; Glebovistkii, V. A.; Rizvanova, N. G.; Fedoseenko, A. M.; Lobikov, A. F.

    2014-11-01

    The duration of migmatite formation in the K and Na geochemical zones was first estimated for the Svecofennides of the northern Ladoga region. The U-Pb (TIMS) age of monazite was determined for the most complete sequence of leucosomes with geological control of their relations and relative age observed in the outcrops. The duration of formation of the leucosomes in two zones is different and is not overlapped by the error of the age analysis: about 5 and no less than 10-15 Ma in the K and Na zones, respectively. The different duration of migmatite formation may reflect different temperature evolution of the rocks of the two zones and also the influence of the composition and rheological properties of migmatizing sequences, which govern the conditions of liquation, transportation, and crystallization of the anatectic melt.

  17. The UHP metamorphic Seve Nappe Complex of the Swedish Caledonides - a new occurrence of the microdiamond-bearing gneisses and their exhumation

    NASA Astrophysics Data System (ADS)

    Klonowska, Iwona; Janák, Marian; Majka, Jarosław; ‎ Froitzheim, Nikolaus; Gee, David G.

    2015-04-01

    The ultra-high pressure metamorphism (UHPM) in the Seve Nappe Complex of the Swedish Caledonides has been recently recognized within several lithologies including gneisses, eclogites and garnet pyroxenites (e.g. Janák et al. 2013, Klonowska et al. 2014a, Majka et al. 2014). Thermodynamic modelling and thermobarometric calculations indicate peak pressure conditions of >3GPa at c. 800-900°C (reaching the diamond stability field) for eclogites and garnet pyroxenites from northern Jämtland (e.g. Klonowska et al. 2014b). In addition to this, the first microdiamonds were found in paragneisses from the Snasahögarna Mt. in central Jämtland (Majka et al. 2014). Here we report a new discovery of microdiamond together with moissanite (SiC) from one of the world's most famous localities for thrusting, Mount Åreskutan, where long transport distances were recognized already in the 19th century (Törnebohm 1888). Garnet porphyroblasts in gneisses from the Åreskutan Mt. contain abundant mineral inclusions, mainly graphite, carbonates and quartz, together with fluid inclusions of CO2 concentrated in swarms. Among these inclusions three microdiamonds were found in two gneiss samples. In one of the samples moissanite was also discovered. Both minerals were identified by micro-Raman spectroscopy. In addition to these 'swarm' inclusions, biotite, kyanite, rutile, feldspars, zircon, monazite, ±phengite, ±muscovite, ±spinel, ±ilmenite, ±apatite occur in garnets. Phase equilibrium modelling for the phengite-bearing gneiss confirms its UHP history at temperatures of c. 800°C. Recent discoveries of UHP metamorphism within the Seve Nappe Complex derived from the Baltican outer margin (part of the Middle Allochthon) challenged us to present a new tectonic model incorporating exhumation of the deeply subducted continental rocks together with mantle lithosphere peridotites. Majka et al. (2014) introduced a new "under-pressure"-driven exhumation mechanism of rocks buried in

  18. An exposed slab window margin: the eastern part of the Neoproterozoic Baikal-Muya belt, Russia

    NASA Astrophysics Data System (ADS)

    Fedotova, A.; Khain, E.; Razumovskiy, A.; Anosova, M.; Orlova, A.

    2012-04-01

    A series of dykes and small laccolith-type magmatic bodies of tonalite, trondhjemite, granodiorite and granites marks the final stage in the geological history of the Baikal-Muya belt in an adjacent area of the Siberian craton. These bodies intrude granulite-enderbite-charnokite complex, as well as troctolite Tonkiy Mys massif. These high-silica (SiO2N56%), high alumina (Al2O3>15%), pyroxene or and amphibole bearing granitoids, with Na2O>4%, high Sr (>400 ppm), low Y (<7 ppm), high Sr/Y(>35), low Yb (<1), and are geochemically similar to adakites. The same structural position was defined for granites showing K2O=4.5% and K2O/Na2O=1,4. The tonalites of this complex collected f yielded the U-Pb zircon age of 591±3 Ma (LA ICP-MS data). Previously obtained age estimate for the enderbites is 617±5 Ma [Amelin et al., 2000]. Three samples of enderbites and gneisse provided U-Pb zircon ages fallen into the time span between 603-620 Ma. The Slyudinskii massif of high-Ti gabbronorites spatially related to the enderbite-granulite complex was crystallized 618±61 Ma ago [Makrygina et al., 1993]. The published data obtained for the massif (585±22 Ma [Makrygina et al., 1993]) show that troctolite-gabbro massifs crystallized simultaneously or insignificantly later than granulite-enderbite complex at upper levels of the lithosphere. Rocks of these massifs and the gabbro-granulite-enderbite series formed at lower levels have been joined during a stage of tectonic activity and intruded by adakites 591±3 Ma ago. High tectonic activity also reflected in deposition of the coarse clastics occurred in a lower part of Kholodnenskaya suite and contemporary formations. The following events can be reconstructed for the eastern part of the Baikal-Muya belt. Formation of the heterogeneous accretional orogenic structure (tectonic collage), with ophiolites and remnants of earlier formed Neoproterozoic island arcs and related complexes [Izokh, 1998; Rytsk, 2001; Shatskii et al., 1996], was

  19. Gould Belt Origin

    NASA Astrophysics Data System (ADS)

    Rivera, Leticia; Loinard, Laurent; Dzib, Sergio

    2013-07-01

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

  20. Zircon growth in (U)HP quartzo-feldspathic host gneisses exhumed in the Woodlark Rift of Papua New Guinea

    NASA Astrophysics Data System (ADS)

    Zirakparvar, N. A.; Baldwin, S. L.; Schmitt, A. K.

    2014-04-01

    To understand zircon behavior as a function of bulk composition and metamorphic grade in the world's youngest (U)HP terrane, we report U-Pb SIMS spot-mode and depth-profiling analyses for quartzo-feldspathic gneisses. Zircons from two gneisses contain Cretaceous inherited cores, with μm sized metamorphic rims requiring depth profiling for reliable dating. Linear regression of the common-Pb uncorrected data for rims yield 206Pb/238U ages of 2.89 ± 0.29 Ma and 2.77 ± 0.99 Ma (concordia intercept ages at 95% confidence). The older age is within two-sigma error of previously reported 206Pb/238U ages on zircons from mafic eclogite within the gneiss, indicating that rims formed on inherited cores within host gneisses during eclogite facies metamorphism. At the (U)HP locality zircons from host gneiss lack inheritance and yield a 206Pb/238U age of 3.66 ± 0.13 Ma. These results are younger than previously reported 206Pb/238U ages on zircons from coesite eclogite within the gneiss, but are within error of the youngest reported LA-ICP-MS 206Pb/238U zircon ages on retrogressed mafic eclogite. We also report intragrain geochemical heterogeneity, indicated by zircon Hf, Y, and Ti variations in depth profiles which suggest chemical disequilibrium over the interval of zircon growth. Collectively, these results indicate that zircon recrystallization and new growth of zircon rims on relict grains occurred during eclogite facies metamorphism and during subsequent retrogression, but not at (U)HP conditions. Comparison between results from PNG and other (U)HP terranes bolsters previous suggestions that the PNG (U)HP terrane evolved rapidly.

  1. The migmatite-gneiss complex of the Chuya-Kendyktas sialic massif (Southern Kazakhstan): Structure and age

    NASA Astrophysics Data System (ADS)

    Tretyakov, A. A.; Degtyarev, K. E.; Kovach, V. P.; Kotov, A. B.; Salnikova, E. B.; Pilitsyna, A. V.; Yakovleva, S. Z.

    2016-03-01

    A migmatite-gneiss complex made up of paraand orthogneisses and crystalline schists with bodies of ultrametagenic tonalites is distinguished in the basement of the northwestern part of the Chuya-Kendyktas Massif. ID-TIMS dating of accessory zircon from orthogneisses and ultrametagenic tonalites in combination with LA-ICP-MS analyses of detrital zircons from garnet-biotite paragneisses showed that the migmatite-gneiss complex was formed after protoliths with an age within 800-770 Ma and completed its evolution in the first half of the Neoproterozoic.

  2. 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.

  3. 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…

  4. 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…

  5. Depositional setting and paleogeographic implications of earth's oldest supracrustal rocks, the >3.7 Ga Isua Greenstone belt, West Greenland

    NASA Astrophysics Data System (ADS)

    Fedo, Christopher M.; Myers, John S.; Appel, Peter W. U.

    2001-06-01

    New structural and stratigraphic mapping in the Isua greenstone belt, West Greenland has revealed that the exposed lithologic succession is quite different to that depicted in earlier studies. The key to a better understanding of the stratigraphy has been the recognition of intense strain and metasomatic effects combined with ductile fault structures that segment the belt into a number of tectonic slices. In some of these slices, deformation and metasomatism are somewhat lower than in surrounding slices (though still significant), which permit the recognition of primary depositional features that may be used to compare with lithologies from elsewhere in the belt. The belt is dominated by amphibolite that in a number of places show well-defined pillows. Pillow breccias and basaltic debris flows also occur within this package. Strongly recrystallized ultramafic bodies that occur in the belt are interpreted as intrusions or komatiitic flows. The most common sedimentary rock type is chert/banded iron-formation. These lithologies have been strongly affected by brittle and ductile deformation in combination with coarse recrystallization. Siliciclastic detrital rocks such as conglomerate and sandstone are much less common in the belt, and where present, have intrabasinally derived sources. Highly deformed quartzo-feldspathic schist crops out in a number of places in the belt and most likely has multiple origins. Previously these schists have been considered to be felsic volcaniclastic rocks, though recent mapping, and geochemical, and isotopic studies support the hypothesis that at least some of these schists are highy deformed and carbonated tonalitic gneiss sheets or replaced pillow-lava successions. Carbonate rocks in the belt are now considered to be mostly, or entirely, replacement in origin, where metasomatizing fluids have particularly utilized amphibolite-chert contacts; additionally, some carbonate may represent the products of early sea-floor alteration. We

  6. Geochemical and zircon U-Pb dating analysis of metamagmatic rocks from the Yuli belt in Taiwan

    NASA Astrophysics Data System (ADS)

    Hung, Chia-Chia

    2016-04-01

    The Tananao Schist Complex of the oldest rocks in Taiwan is exposed at the eastern limb of Backbone Range. Based on the lithologic and metamorphic characteristics, the complex can be divided into the Tailuko and Yuli belts. The Tailuko belt consists of marble, gneiss, and subordinate scattered metabasite; the Yuli belt is composed of greenschist, serpentinite, meta-tuff, meta-gabbro, metabasite, and glaucophane-schist blocks which enclosed by spotted schist of the host rocks. The metamorphic belts were inferred as a Mesozoic mélange. It's still controversial due to the difficulty of analyzing metamorphic rocks. In this study, we focus on the zircon U-Pb dating, geochemistry, and petrographic analysis of spotted schist, metabasite, meta-gabbro, and meta-tuff in order to constrain the formation and crystallization ages and interpret its tectonic setting. Based on zircon U-Pb dating, the host rocks of spotted schist and the exotic blocks of meta-tuff, meta-gabbro (the peak age of 14.4, 15.8, and 16.7 Ma), and metabasite occurred at Miocene. Geochemical characteristics for metabasite and meta-gabbro blocks show Ta-Nd-Ti depletion and LREE depletion in spidergram occurring volcanic arc and N-MORB type affinities, respectively. Results as above mentioned, we suggest that the metamagmatic rocks in the Yuli belt occur within a mélange during the Eurasia continental margin subduction at the Middle-Late Miocene.

  7. Re-Os, Rb-Sr, and O isotopic systematics of the Archean Kolar schist belt, Karnataka, India

    NASA Technical Reports Server (NTRS)

    Walker, Richard J.; Shirey, Steven B.; Hanson, Gilbert N.; Rajamani, V.; Horan, Mary F.

    1989-01-01

    The Re-Os, Rb-Sr, and O isotopic compositions of mafic and ultramafic amphibolites, gold ores, and granitic gneisses of the circa 2700 Ma Kolar schist belt are reported which reveal at least two episodes of postmagmatic alteration that affected these systems. The Re-Os isotopic systematics of many of the belt rocks indicate that Os was introduced to the area via fluids that carried very radiogenic Os, probably from ancient crust. The Rb-Sr systematics of most of these rocks indicate that the alteration event probably occurred no later than the early Proterozoic. Samples of several komatiitic amphibolites have very Os-187-depleted compositions, indicating that open-system behavior also occurred at a much later time than the late Archean or early Proterozoic. The results suggest that the Re-Os system may have only limited utility for geochronologic applications in regions for which postcrystallization noble metal mineralization is evident.

  8. Exhumation of high-pressure rocks beneath the Solund Basin, Western Gneiss Region of Norway

    USGS Publications Warehouse

    Hacker, B.R.; Andersen, T.B.; Root, D.B.; Mehl, L.; Mattinson, J.M.; Wooden, J.L.

    2003-01-01

    The Solund-Hyllestad-Lavik area affords an excellent opportunity to understand the ultrahigh-pressure Scandian orogeny because it contains a near-complete record of ophiolite emplacement, high-pressure metamorphism and large-scale extension. In this area, the Upper Allochthon was intruded by the c. 434 Ma Sogneskollen granodiorite and thrust eastward over the Middle/Lower Allochthon, probably in the Wenlockian. The Middle/Lower Allochthon was subducted to c. 50 km depth and the structurally lower Western Gneiss Complex was subducted to eclogite facies conditions at c. 80 km depth by c. 410-400 Ma. Within 100. Exhumation to upper crustal levels was complete by c. 403 Ma. The Solund fault produced the last few km of tectonic exhumation, bringing the near-ultrahigh-pressure rocks to within c. 3 km vertical distance from the low-grade Solund Conglomerate.

  9. Fabric controls on the brittle failure of folded gneiss and schist

    NASA Astrophysics Data System (ADS)

    Agliardi, Federico; Zanchetta, Stefano; Crosta, Giovanni B.

    2014-12-01

    We experimentally studied the brittle failure behaviour of folded gneiss and schist. Rock fabric and petrography were characterised by meso-structural analyses, optical microscopy, X-ray diffraction, and SEM imaging. Uniaxial compression, triaxial compression and indirect tension laboratory tests were performed to characterise their strength and stress-strain behaviour. Fracture patterns generated in compression were resolved in 3D through X-ray computed tomography at different resolutions (30 to 625 μm). Uniaxial compression tests revealed relatively low and scattered values of unconfined compressive strength (UCS) and Young's modulus, with no obvious relationships with the orientation of foliation. Samples systematically failed in four brittle modes, involving different combinations of shear fractures along foliation or parallel to fold axial planes, or the development of cm-scale shear zones. Fracture quantification and microstructural analysis show that different failure modes occur depending on the mutual geometrical arrangement and degree of involvement of two distinct physical anisotropies, i.e. the foliation and the fold axial planes. The Axial Plane Anisotropy (APA) is related to micro-scale grain size reduction and shape preferred orientation within quartz-rich domains, and to mechanical rotation or initial crenulation cleavage within phyllosilicate-rich domains at fold hinge zones. In quartz-rich rocks (gneiss), fracture propagation through quartz aggregates forming the APA corresponds to higher fracture energy and strength than found for fracture through phyllosilicate-rich domains. This results in a strong dependence of strength on the failure mode. Conversely, in phyllosilicate-rich rocks (schist), all the failure modes are dominated by the strength of phyllosilicates, resulting in a sharp reduction of strength anisotropy.

  10. Particle Swarm Optimization for inverse modeling of solute transport in fractured gneiss aquifer.

    PubMed

    Abdelaziz, Ramadan; Zambrano-Bigiarini, Mauricio

    2014-08-01

    Particle Swarm Optimization (PSO) has received considerable attention as a global optimization technique from scientists of different disciplines around the world. In this article, we illustrate how to use PSO for inverse modeling of a coupled flow and transport groundwater model (MODFLOW2005-MT3DMS) in a fractured gneiss aquifer. In particular, the hydroPSO R package is used as optimization engine, because it has been specifically designed to calibrate environmental, hydrological and hydrogeological models. In addition, hydroPSO implements the latest Standard Particle Swarm Optimization algorithm (SPSO-2011), with an adaptive random topology and rotational invariance constituting the main advancements over previous PSO versions. A tracer test conducted in the experimental field at TU Bergakademie Freiberg (Germany) is used as case study. A double-porosity approach is used to simulate the solute transport in the fractured Gneiss aquifer. Tracer concentrations obtained with hydroPSO were in good agreement with its corresponding observations, as measured by a high value of the coefficient of determination and a low sum of squared residuals. Several graphical outputs automatically generated by hydroPSO provided useful insights to assess the quality of the calibration results. It was found that hydroPSO required a small number of model runs to reach the region of the global optimum, and it proved to be both an effective and efficient optimization technique to calibrate the movement of solute transport over time in a fractured aquifer. In addition, the parallel feature of hydroPSO allowed to reduce the total computation time used in the inverse modeling process up to an eighth of the total time required without using that feature. This work provides a first attempt to demonstrate the capability and versatility of hydroPSO to work as an optimizer of a coupled flow and transport model for contaminant migration.

  11. Slow exhumation of UHP terranes: Titanite and rutile ages of the Western Gneiss Region, Norway

    NASA Astrophysics Data System (ADS)

    Kylander-Clark, A. R. C.; Hacker, B. R.; Mattinson, J. M.

    2008-08-01

    U-Pb ages of titanite and rutile were obtained from the central Western Gneiss Region, Norway, to assess the style and timing of exhumation and cooling of the Western Gneiss UHP terrane. Approximately half of the titanite ages are concordant, the majority of which yield a limited age range from 393 to 390 Ma. The other titanite data are discordant, and define discordia arrays with upper intercept ages of either ˜ 938 Ma or ˜ 1.6 Ga, and a lower intercept of ˜ 389 Ma. Concordant rutile analyses range from 385 to 392 Ma. Both titanite and rutile ages young WNW toward the core of the orogen and are ˜ 4 Ma older than 40Ar/ 39Ar muscovite ages, corresponding to a cooling rate of ˜ 90 °C/Ma. A well-defined boundary between concordant and discordant titanite ages, in combination with the WNW-increasing P- T gradient and the similarity between muscovite cooling ages in the east and eclogite ages in the west, suggests that the WGR remained coherent throughout its exhumation history, and was progressively unroofed from east to west. A 390.2 ± 0.8 Ma titanite in the Sørøyane UHP domain indicates that exhumation occurred at a vertical rate of ˜ 7 mm/yr for ˜ 12 Ma. These rates are slower than estimates from smaller UHP terranes, but similar to other large UHP terranes, suggesting that there may be fundamental differences in the mechanisms controlling the evolution of large UHP terranes that undergo protracted subduction and exhumation, and smaller UHP terranes that undergo rapid subduction and exhumation.

  12. Particle Swarm Optimization for inverse modeling of solute transport in fractured gneiss aquifer

    NASA Astrophysics Data System (ADS)

    Abdelaziz, Ramadan; Zambrano-Bigiarini, Mauricio

    2014-08-01

    Particle Swarm Optimization (PSO) has received considerable attention as a global optimization technique from scientists of different disciplines around the world. In this article, we illustrate how to use PSO for inverse modeling of a coupled flow and transport groundwater model (MODFLOW2005-MT3DMS) in a fractured gneiss aquifer. In particular, the hydroPSO R package is used as optimization engine, because it has been specifically designed to calibrate environmental, hydrological and hydrogeological models. In addition, hydroPSO implements the latest Standard Particle Swarm Optimization algorithm (SPSO-2011), with an adaptive random topology and rotational invariance constituting the main advancements over previous PSO versions. A tracer test conducted in the experimental field at TU Bergakademie Freiberg (Germany) is used as case study. A double-porosity approach is used to simulate the solute transport in the fractured Gneiss aquifer. Tracer concentrations obtained with hydroPSO were in good agreement with its corresponding observations, as measured by a high value of the coefficient of determination and a low sum of squared residuals. Several graphical outputs automatically generated by hydroPSO provided useful insights to assess the quality of the calibration results. It was found that hydroPSO required a small number of model runs to reach the region of the global optimum, and it proved to be both an effective and efficient optimization technique to calibrate the movement of solute transport over time in a fractured aquifer. In addition, the parallel feature of hydroPSO allowed to reduce the total computation time used in the inverse modeling process up to an eighth of the total time required without using that feature. This work provides a first attempt to demonstrate the capability and versatility of hydroPSO to work as an optimizer of a coupled flow and transport model for contaminant migration.

  13. Geochemical investigation of Archaean Bimodal and Dwalile metamorphic suites, Ancient Gneiss Complex, Swaziland

    USGS Publications Warehouse

    Hunter, D.R.; Barker, F.; Millard, H.T.

    1984-01-01

    The bimodal suite (BMS) comprises leucotonalitic and trondhjemitic gneisses interlayered with amphibolites. Based on geochemical parameters three main groups of siliceous gneiss are recognized: (i) SiO2 14%, and fractionated light rare-earth element (REE) and flat heavy REE patterns; (ii) SiO2 and Al2O3 contents similar to (i) but with strongly fractionated REE patterns with steep heavy REE slopes; (iii) SiO2 > 73%, Al2O3 < 14%, Zr ??? 500 ppm and high contents of total REE having fractionated light REE and flat heavy REE patterns with large negative Eu anomalies. The interlayered amphibolites have major element abundances similar to those of basaltic komatiites, Mg-tholeiites and Fe-rich tholeiites. The former have gently sloping REE patterns, whereas the Mg-tholeiites have non-uniform REE patterns ranging from flat (??? 10 times chondrite) to strongly light REE-enriched. The Fe-rich amphibolites have flat REE patterns at 20-30 times chondrite. The Dwalile metamorphic suite, which is preserved in the keels of synforms within the BMS, includes peridotitic komatiites that have depleted light REE patterns similar to those of compositionally similar volcanics in the Onverwacht Group, Barberton, basaltic komatiites and tholeiites. The basaltic komatiites have REE patterns parallel to those of the BMS basaltic komatiites but with lower total REE contents. The Dwalile tholeiites have flat REE patterns. The basic and ultrabasic liquids were derived by partial melting of a mantle source which may have been heterogeneous or the heterogeneity may have resulted from sequential melting of the mantle source. The Fe-rich amphibolites were derived either from liquids generated at shallow levels or from liquids generated at depth which subsequently underwent extensive fractionation. ?? 1984.

  14. The separation of the Hartland Formation and Ravenswood Granodiorite from the Fordham Gneiss at Cameron's Line in the New York City area

    USGS Publications Warehouse

    Baskerville, C.A.; Mose, D.G.

    1989-01-01

    Recent study of the rocks in City Water Tunnel Number 3 between Roosevelt Island and beneath 34th Street and the 63rd Street subway-rail tunnels at 41st Avenue in Long Island City, as well as study of drill core from other sites in western Queens, establishes that this area of New York City is underlain by the Ravenswood Granodiorite and the Hartland Formation. The Fordham Gneiss does not appear east of the East River at these sites. Cameron's Line can be traced down the east side of the East River, as learned from observations in the tunnels, separating the Middle Proterozoic Fordham Gneiss to the west from the Cambrian and Ordovician Hartland Formation and related Ravenswood Granodiorite to the east. The older, adequately defined, Ravenswood Granodiorite, Hartland Formation, and the Fordham Gneiss, are the rock units that make up the poorly defined Brooklyn gneiss or Brooklyn Injection Gneiss and thus appropriately should supercede these later classifications. -from Authors

  15. Implications of Sm-Nd model ages and single grain U-Pb zircon geochronology for the age and heritage of the Swakane gneiss, Yellow Aster Complex, and Skagit gneiss, North Cascades, Wash

    SciTech Connect

    Rasbury, E.T.; Walker, N.W. . Dept. of Geological Sciences)

    1992-01-01

    Uncertainties regarding the protolith, age, and tectonic affinity of the Swakane gneiss (Swg), Skagit gneiss (Skg), and Yellow Aster complex (YAc) have long been obstacles to deciphering the tectonic history of the North Cascades. Single-grain zircon U-Pb data and Sm-Nd model ages now demonstrate these units are genetically unrelated metasediments derived from Early Proterozoic and younger sources. Zircon populations from Swg samples include rounded, subrounded, and euhedral grains. Three of four analyzed grains define a well-correlated discordia array that intercepts concordia at 1.4 Ga whereas the fourth grain has a 1.6 Ga 207Pb/206Pb age. the Sm-Nd depleted mantle model ages of two samples of Swg are 1.18 Ga and 1.27 Ga. The authors suggest that the Swg gneiss is a metaclastic rock derived chiefly from rocks of Middle Proterozoic age. A single analyzed zircon crystal extracted from garnet-biotite yields a nearly concordant age of 0.14 Ga. The YAc consists of fragments of metaplutonic rocks and quartz-pyroxene gneisses of uncertain protolith that are imbricated with Paleozoic and Mesozoic rocks of the Cretaceous Northwest Cascades thrust system. U-Pb data from 6 single zircons extracted from mylonitic quartz-pyroxene gneiss are interpreted to indicate the presence of Grenville orogen-derived grains of ca 0.9--1.3 Ga age whereas one analyzed zircon has an ca 0.6 Ga age. Analyses of abraded zircons from a post-mylonitic pegmatite dike indicate pegmatite crystallization at ca0.22 Ga and imply the presence of ca1.85 Ga xenocrystic zircons.

  16. Late Cenozoic deep weathering patterns on the Fennoscandian shield in northern Finland: A window on ice sheet bed conditions at the onset of Northern Hemisphere glaciation

    NASA Astrophysics Data System (ADS)

    Hall, Adrian M.; Sarala, Pertti; Ebert, Karin

    2015-10-01

    The nature of the regolith that existed on the shields of the Northern Hemisphere at the onset of ice sheet glaciation is poorly constrained. In this paper, we provide the first detailed account of an exceptionally preserved, deeply weathered late Neogene landscape in the ice sheet divide zone in northern Finland. We mine data sets of drilling and pitting records gathered by the Geological Survey of Finland to reconstruct regional preglacial deep weathering patterns within a GIS framework. Using a large geochemical data set, we give standardised descriptions of saprolite geochemistry using a variant of the Weathering Index of Parker (WIP) as a proxy to assess the intensity of weathering. We also focus on mineral prospects and mines with dense pit and borehole data coverage in order to identify links between geology, topography, and weathering. Geology is closely linked to topography on the preglacial shield landscape of northern Finland and both factors influence weathering patterns. Upstanding, resistant granulite, granite, gabbro, metabasalt, and quartzite rocks were associated with fresh rock outcrops, including tors, or with thin (< 5 m) grusses. Plains developed across less resistant biotite gneisses, greenstones, and belts of alternating rock types were mainly weathered to thick (10-20 m) grusses with WIPfines values above 3000 and 4000. Beneath valley floors developed along mineralised shear and fracture zones, weathering penetrated locally to depths of > 50 m and included intensely weathered kaolinitic clays with WIPfines values below 1000. Late Neogene weathering profiles were varied in character. Tripartite clay-gruss-saprock profiles occur only in limited areas. Bipartite gruss-saprock profiles were widespread, with saprock thicknesses of > 10 m. Weathering profiles included two discontinuities in texture, materials and resistance to erosion, between saprolite and saprock and between saprock and rock. Limited core recovery when drilling below the soil

  17. 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.

  18. 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

  19. Evidence for the importance of ductile shear in regional fabric development in Grenville-age gneisses of the Beaver Creek region, Northwest Lowlands, New York State

    SciTech Connect

    Tewksbury, B.; Culbertson, H.; Marcoline, J.; Walvoord, M. . Dept. of Geology)

    1993-03-01

    In the Beaver Creek region of the Northwest Lowlands, Brown (1989) has described Grenville-age metasedimentary and metaigneous rocks as showing a prominent regional foliation, early southeastward emplacement of a nappe complex (the North Gouverneur Nappe), 2 subsequent generations of folds, and late regional faulting along the Beaver Creek, Pleasant Lake, and Hickory-Mud Lakes faults. The authors examined a variety of units across the Beaver Creek region, including a granitic augen gneiss immediately west of the Beaver Creek Fault Zone, an alaskitic gneiss immediately below Brown's (1989) North Gouverneur Nappe Sole Fault, a biotitic granitic gneiss within the body of Brown's North Gouverneur Nappe, and hornblende augen gneisses and metasediments adjacent to the granitic gneisses. Each of the granitic units has moderately well-developed to extremely well-developed quartz ribbon lineations, and all show at least 2 ductile shear fabrics. Shear fabrics are present as well in the hornblende augen gneisses but are essentially absent in most of the metasedimentary lithologies, even those immediately adjacent to well-lineated, sheared granitic gneiss. The earliest shear fabrics exhibit spectacular quartz ribbon lineations, sigma grains, and, in the hornblende augen gneiss, shear bands. Granitic gneisses in the Beaver Creek Region show shear fabrics in addition to the main fabric in the rock. A second, variably-recovered shear fabric with quartz ribbons and well-developed sigma grains with core and mantle structure overprints the main shear fabric and shows largely the same sense of shear. The authors suggest further that a regional kinematic model for the Beaver Creek region must take into account significant, protracted regional shear, perhaps including formation of sheath folds, as in the Hyde School Gneiss at Payne Lake and Dobbs Creek.

  20. Geological and structural conditions of eclogitization of Paleoproterozoic basic dikes in the eastern Belomorian Mobile Belt

    NASA Astrophysics Data System (ADS)

    Kozlovsky, V. M.; Aranovich, L. Ya.

    2008-07-01

    A new, Krasnaya Guba dike field that comprises more than 30 minor gabbronorite intrusions and dikes of “garnet” Fe-gabbro was revealed at the northeastern flank of the Belomorian Mobile Belt. Gabbronorite intrusions were emplaced along the faults that formed as a result of brittle failure under conditions of general extension. As follows from the structural relationships, dikes of Fe-gabbro are younger than gabbronorite. They were formed under compression and shearing. The mobile melt was pumped into gneisses that underwent ductile deformation. Eclogitization in the Krasnaya Guba dike field was selective and affected only dikes of Fe-gabbro and minor gabbronorite intrusions and did not develop in country rocks. The bodies of Fe-gabbro are eclogitized almost completely, whereas gabbronorite is transformed into eclogite only along shear zones. Eclogites were formed after the complete solidification of intrusive bodies, and their localization is controlled by the concentration of deformations owing to the different elastoplastic properties of gabbroic rocks and country gneisses and migmatites. The different degree of fracturing in basic dikes and country gneisses resulted in the concentration of fluid flows in fracture systems within competent rocks. Late Svecofennian pegmatites (1.86 Ga) distinctly crosscut eclogites that experienced retrograde metamorphism. The eclogitic rocks from the Krasnaya Guba are the youngest known in the Belomorye. The age of eclogitization is 2.12 1.86 Ga. A new finding of eclogitic rocks in the Belomorye, as well as previously known similar rocks near Gridino Village, emphasize tectonic activity of the northwestern Umba Collision Zone. The eclogitization of basic rocks in Krasnaya Guba is related to their desilification in shearing zones in the course of interaction of plagioclase with ortho-and clinopyroxene with the formation of garnet-omphacite aggregate and removal of silica. The currently observed texture, structure, and chemical

  1. Investigation of a new type charging belt

    SciTech Connect

    Jones, N.L.

    1994-12-31

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

  2. Neoproterozoic collision tectonics in the Mozambique Belt of East Africa: evidence from the Uluguru mountains, Tanzania

    NASA Astrophysics Data System (ADS)

    Muhongo, Sospeter

    1994-10-01

    The fault-bounded Proterozoic metamorphic terranes lying to the E of the Tanzanian craton make up the Usagara tectonic domain and are a part of the transcontinental Mozambique Orogenic Belt (MB). The lithotectonic units in the MB of the East Africa consist of comparable rock assembles which underwent the same complex deformational history and are thought to represent large thrust sheets or nappes. Their shelf- and fore-deep terranes border the Tanzanian craton and make up the foreland terranes of the Pan-African Mozambique Belt. Granulite-gneiss nappes are ubiquitous in the orogen. Granulite-facies metamorphism, associated with recumbent folds, was due to crustal thickening, which took place during the collision between Gondwana fragments. Isotope data suggest a collision (and concomitant granulite-facies metamorphism) age of between 700 and 550 Ma. The orientations of planar and linear fabrics in the granulite-facies rocks of the Uluguru mountains are used to infer the relative crustal block motions during this collisional event. This Pan-African collisional event was characterized by NW-directed movements, oblique to the N-S trend of the orogen, and involved SE-directed backthrusting. The Ubendian Belt of Tanzania and the Aswa Shear Zone in Uganda and Kenya, which both bifurcate around the Tanzania craton, accommodated the tectonically thickened crust, created by the collisional event, through NW-SE sinistral strike-slip movements.

  3. 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

  4. Previously Undetected Radiation Belt Revealed

    NASA Video Gallery

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

  5. 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...

  6. 30 CFR 75.1731 - Maintenance of belt conveyors and belt conveyor entries.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 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...

  7. 30 CFR 75.1731 - Maintenance of belt conveyors and belt conveyor entries.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 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...

  8. Petrology and tectonic development of supracrustal sequence of Kerala Khondalite Belt, Southern India

    NASA Technical Reports Server (NTRS)

    Kumar, G. R. Ravindra; Chacko, Thomas

    1988-01-01

    The granulite terrain of southern India, of which the Kerala Khondalite belt (KKB) is a part, is unique in exposing crustal sections with arrested charnockite growth in different stages of transformation and in varied lithological association. The KKB with rocks of surficial origin and incipient charnockite development, poses several problems relating to the tectonics of burial of vast area and mechanisms involved in expelling initial H2O (causes of dryness) for granulite facies metamorphism. It is possible to infer the following sequence of events based on the field and laboratory studies: (1) derivation of protoliths of KKB from granitic uplands and deposition in fault bounded basin (cratonic rift); (2) subhorizontal deep burial of sediments; (3) intense deformation of infra and supracrustal rocks; (4) early granulite facies metamorphism predating F sub 2 - loss of primary structure in sediments and formation of charnockites from amphibole bearing gneisses and khondalites from pelites; (5) migmatisation and deformation of metasediments and gneisses; (6) second event of charnockite formation probably aided by internal CO2 build-up; and (7) isothermal uplift, entrapment of late CO2 and mixed CO2-H2O fluids, formation of second generation cordierites and cordierite symplectites.

  9. Geology and geochemistry of the Middle Proterozoic Eastern Ghat mobile belt and its comparison with the lower crust of the Southern Peninsular shield

    NASA Technical Reports Server (NTRS)

    Rao, M. V. Subba

    1988-01-01

    Two prominent rock suites constitute the lithology of the Eastern Ghat mobile belt: (1) the khondalite suite - the metapelites, and (2) the charnockite suite. Later intrusives include ultramafic sequences, anorthosites and granitic gneisses. The chief structural element in the rocks of the Eastern Ghats is a planar fabric (gneissosity), defined by the alignment of platy minerals like flattened quartz, garnet, sillimanite, graphite, etc. The parallelism between the foliation and the lithological layering is related to isoclinal folding. The major structural trend (axial plane foliation trend) observed in the belt is NE-SW. Five major tectonic events have been delineated in the belt. A boundary fault along the western margin of the Eastern Ghats, bordering the low grade terrain has been substantiated by recent gravity and the deep seismic sounding studies. Field evidence shows that the pyroxene granulites (basic granulites) post-date the khondalite suite, but are older than the charnockites as well as the granitic gneisses. Polyphase metamorphism, probably correlatable with different periods of deformation is recorded. The field relations in the Eastern Ghats point to the intense deformation of the terrain, apparently both before, during and after metamorphism.

  10. Long-range laser scanning and 3D imaging for the Gneiss quarries survey

    NASA Astrophysics Data System (ADS)

    Schenker, Filippo Luca; Spataro, Alessio; Pozzoni, Maurizio; Ambrosi, Christian; Cannata, Massimiliano; Günther, Felix; Corboud, Federico

    2016-04-01

    In Canton Ticino (Southern Switzerland), the exploitation of natural stone, mostly gneisses, is an important activity of valley's economies. Nowadays, these economic activities are menaced by (i) the exploitation costs related to geological phenomena such as fractures, faults and heterogeneous rocks that hinder the processing of the stone product, (ii) continuously changing demand because of the evolving natural stone fashion and (iii) increasing administrative limits and rules acting to protect the environment. Therefore, the sustainable development of the sector for the next decades needs new and effective strategies to regulate and plan the quarries. A fundamental step in this process is the building of a 3D geological model of the quarries to constrain the volume of commercial natural stone and the volume of waste. In this context, we conducted Terrestrial Laser Scanning surveys of the quarries in the Maggia Valley to obtain a detailed 3D topography onto which the geological units were mapped. The topographic 3D model was obtained with a long-range laser scanning Riegl VZ4000 that can measure from up to 4 km of distance with a speed of 147,000 points per second. It operates with the new V-line technology, which defines the surface relief by sensing differentiated signals (echoes), even in the presence of obstacles such as vegetation. Depending on the esthetics of the gneisses, we defined seven types of natural stones that, together with faults and joints, were mapped onto the 3D models of the exploitation sites. According to the orientation of the geological limits and structures, we projected the different rock units and fractures into the excavation front. This way, we obtained a 3D geological model from which we can quantitatively estimate the volume of the seven different natural stones (with different commercial value) and waste (with low commercial value). To verify the 3D geological models and to quantify exploited rock and waste volumes the same

  11. First field identification of the Cuonadong dome in southern Tibet: implications for EW extension of the North Himalayan gneiss dome

    NASA Astrophysics Data System (ADS)

    Fu, Jiangang; Li, Guangming; Wang, Genhou; Huang, Yong; Zhang, Linkui; Dong, Suiliang; Liang, Wei

    2016-07-01

    The Cuonadong dome exposes in east-southern margin of the North Himalayan gneiss domes (NHGD), which is reported first time in this study. The Cuonadong dome is located at the southern part of the Zhaxikang ore concentration area, which is divided into three tectono-lithostratigraphic units by two curved faults around the dome geometry from upper to lower (or from outer to inner): the upper unit, middle unit and lower unit, and the outer fault is Nading fault, while the inner fault is Jisong fault. The Cuonadong dome is a magmatic orthogneiss and leucogranite mantled by orthogneiss and metasedimentary rocks, which in turn are overlain by Jurassic metasedimentary and sedimentary rocks. The grades of metamorphism and structural deformation increase towards the core, which is correspondence with the Ridang Formation low-metamorphic schist, tourmaline granitic-biotite gneiss, garnet-mica gneiss and mylonitic quartz-mica gneiss. The Cuonadong dome preserves evidences for four major deformational events: firstly top-to-S thrust (D1), early approximately N-S extensional deformation (D2), main approximately E-W extensional deformation (D3), and late collapse structural deformation (D4) around the core of the Cuonadong dome, which are consistent to three groups lineation: approximately N-S-trending lineation including L1 and L2, E-W trending L3, and L4 with plunging towards outside of the dome, respectively. The formation of the Cuonadong dome was probably resulted from the main E-W extensional deformation which is a result of eastward flow of middle or lower crust from beneath Tibet accommodated by northward oblique underthrusting of Indian crust beneath Tibet. The establishment of the Cuonadong dome enhanced the E-W extension of the NHGD, which is further divided into two structural dome zones according to the different extensional directions: approximately N-S extensional North Himalayan gneiss domes (NS-NHGD) and E-W extensional North Himalayan gneiss domes (EW

  12. 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.

  13. Middle Precambrian detrital monazite and zircon from the hida gneiss on Oki-Dogo Island, Japan: their origin and implications for the correlation of basement gneiss of Southwest Japan and Korea

    NASA Astrophysics Data System (ADS)

    Suzuki, Kazuhiro; Adachi, Mamoru

    1994-08-01

    Monazite and zircon from seven paragneiss samples of the upper amphibolite facies grade from Oki-Dogo Island in the Hida terrane, western Japan, were analyzed for Th, U and Pb on an electron microprobe. Most monazite grains are chronologically unzoned and give unequivocal CHIME (chemical Th-U-total Pb isochron) ages of 250 Ma, but some grains show a distinct core-overgrowth relationship. The cores retain evidence of pre-250 Ma ages and are interpreted to be of detrital origin, suggesting that monazite can be more immune to diagenetic and low-grade metamorphic decompositions than had been thought previously. Zircon grains, rounded to nearly euhedral, give CHIME ages ranging from 3000 to 350 Ma. Of particular interest are several rounded 3000 Ma recycled zircons which perhaps originated from an Archean terrain in the Sino-Korean craton. The youngest age of detrital zircons constrains that the gneiss protolith deposited after the 350 Ma event. The CHIME monazite and zircon ages for the paragneisses from Oki-Dogo Island, and from the main part of the Hida terrane, reveal that the gneisses formed from Permo-Carboniferous clastic sediments during a single metamorphism at ca. 250 Ma. The results are in marked contrast to the current view that (1) the Hida gneiss is a polymetamorphosed Precambrian complex; (2) the central part ('Hida gneiss' region) and the eastern marginal part (Unazuki schist' region) of the Hida terrane are correlative with the Precambrian Kyonggi massif and the Paleozoic Okchon zone in the Korean Peninsula, respectively. Instead, we consider that the Okchon zone alone can be correlatable with the Paleozoic Hida terrane.

  14. Geochronology of the Palaeoproterozoic Kautokeino Greenstone Belt, Finnmark, Norway, in its Fennoscandian context

    NASA Astrophysics Data System (ADS)

    Bingen, Bernard; Solli, Arne; Viola, Giulio; Sverre Sandstad, Jan; Torgersen, Espen; Whitehouse, Martin J.; Skår, Øyvind; Nasuti, Aziz

    2016-04-01

    The northeastern part of the Fennoscandian Shield consists of Archaean cratonic blocks alternating with Palaeoproterozoic greenstone belts ranging in age from c. 2500 to 1950 Ma. Traditionally, the greenstones are interpeted as evidence for rifting of the Archaean continent(s) although it remains unclear whether modern-style oceanic lithosphere developed, followed by a Wilson-cycle-type closure during the Svecokarelian orogeny. Existing geological, isotopic and geochronological data show that the exposed basins hosting the greenstones have distinct lithostratigraphies and geological evolutions and are pericontinental rather than oceanic. A diversity of Palaeoproterozoic mafic mantle derived magmatic rocks show a secular increase of Nd value with time, from EpsilonNd =-2 at 2500 Ma (Shalskiy dikes, Onega, Russia) to EpsilonNd =+4.4 at 2090 Ma (Jouttiaapa basalts, Peräpohja, Finland), suggesting that the regional asthenospheric mantle was less depleted than the model MORB-producing depleted mantle before 2090 Ma. In this work, we report new zircon U-Pb geochronological data in 19 samples from Finnmarkvidda, Norway, to constrain the evolution of the Palaeoproterozoic high-strain Kautokeino Greenstone Belt and its relations with the neighbouring felsic Jergul and Ráiseatnu gneiss complexes. The Jergul complex is an Archaean, low heat flow, TTG cratonic bloc of Karelian affinity formed between 2975 ±10 and 2776 ±6 Ma. The Masi formation, at the base of the Kautokeino Greenstone Belt, is a typical Jatulian quartzite unconformably overlying the Archean basement. An albite-magnetite-rich mafic sill, similar to the Haaskalehto intrusion in Finland, provides a minimum age of 2220 ±7 Ma for the deposition of the quartzite. The Likčá and Čáskejas formations represent the main basaltic volcanism. Direct evidence of an oceanic setting or oceanic suture is lacking. A probably synvolcanic gabbro sill gives an age of 2137 ±5 Ma. Published Sm-Nd whole-rock data on

  15. Metamorphism of cordierite gneisses from Eastern Ghat Granulite Terrain, Andhra Pradesh, South India

    NASA Technical Reports Server (NTRS)

    Murthy, D. S. N.; Charan, S. Nirmal

    1988-01-01

    Cordierite-bearing metapelites of the Eastern Ghat granulite terrain occur in close association of Khondalites, quartzites, calc-silicate rocks and charnockites. Rocks occurring between Bobbili in the north and Guntur in the south of Andhra Pradesh are studied. The association of the mineral and textural relationships suggest the following metamorphic reactions: Garnet + sillimanite + quartz = cordierite, hypersthene + sillimanite + quartz = cordierite, sillimanite + spinel = cordierite + corundum, and biotite + quartz + sillimanite = cordierite + K=feldspar. Generally the minerals are not chemically zoned except garnet-biotite showing zoning when they come in close contact with one another. The potential thermometers are provided by the Fe-Mg distribution of coexisting biotite-garnet and cordierite-garnet. Conflicting interpretation of the P/T dependence of these reactions involving cordierite are due to H2O in the cordierite. The presence of alkali feldspar-quartz assemblage which is common in these gneisses will be constrained from melting only if H2O activity is less than 0.5. The piezometric array inferred is convex towards the temperature array, indicating a rapid and isothermal crustal uplift probably aided by thrust tectonics.

  16. Hydrogeological impacts of a railway tunnel in fractured Precambrian gneiss rocks (south-eastern Norway)

    NASA Astrophysics Data System (ADS)

    Kværner, Jens; Snilsberg, Petter

    2013-11-01

    Groundwater monitoring along the Romeriksporten tunnel, south-eastern Norway, provided an opportunity for studying the impacts of tunnelling on groundwater in fractured Precambrian gneiss rocks, and examining relations between bedrock hydrology, tectonic weakness zones and catchments. Tunnel leakage resulted in groundwater drawdown up to 35 m in weakness zones, converted groundwater discharge zones into recharge zones, and affected groundwater chemistry. The magnitude of drawdown and fluctuations in groundwater level differed between weakness zones, and varied with distance from the tunnel route, tunnel leakage, and recharge from catchments. Clear differences in groundwater level and fluctuation patterns indicated restricted groundwater flow between weakness zones. The groundwater drawdowns demonstrated coherent water-bearing networks to 180-m depth in faults and fracture zones. Similar groundwater levels with highly correlated fluctuations demonstrated hydraulic connectivity within fracture zones. Different groundwater drawdown and leakage in weakness zones with different appearance and influence of tectonic events demonstrated the importance of the geological history for bedrock hydrogeology. Water injection into the bedrock counteracted groundwater drawdowns. Even moderate leakage to underground constructions may lead to large groundwater drawdown in areas with small groundwater recharge. Hydrogeological interpretation of tectonic weakness zones should occur in the context of geological history and local catchment hydrology.

  17. Age and significance of felsic dikes from the UHP western gneiss region

    NASA Astrophysics Data System (ADS)

    Kylander-Clark, Andrew R. C.; Hacker, Bradley R.

    2014-12-01

    Twenty-one plagioclase-bearing dikes were analyzed to place firmer limits on the end of (ultra)high-pressure (UHP) metamorphism across the Western Gneiss Region (WGR). Nineteen dikes were analyzed with laser ablation split-stream petrochronology to tie the U-Pb dates to zircon rare earth element (REE) chemistry, and a few key samples were analyzed by chemical abrasion thermal ionization mass spectrometry to provide high-precision constraints. All analyzed dikes yielded zircons with REE chemistry consistent with low-pressure crystallization. Approximately half of the dikes yield Precambrian dates; nondeformed dikes of this age support previous interpretations that much of the WGR underwent limited deformation during Caledonian subduction and exhumation. The oldest Caledonian dikes have dates that overlap with the circa 420-400 Ma eclogite dates from the region; this discrepancy indicates that either (1) cryptic structures separate early exhumed material from later exhumed material, (2) some of the dike dates are not low-pressure crystallization ages, or (3) post-406 Ma dates from eclogites are posteclogite-facies retrogression ages.

  18. Trends in PVC conveyor belting

    SciTech Connect

    Hopwood, J.E.

    1984-03-01

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

  19. 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.

  20. 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.

  1. Late Cretaceous and early Tertiary plutonism and deformation in the Skagit Gneiss Complex, north Cascade Range, Washington and British Columbia

    USGS Publications Warehouse

    Haugerud, R.A.; Van Der Heyden, P.; Tabor, R.W.; Stacey, J.S.; Zartman, R.E.

    1991-01-01

    The Skagit Gneiss Complex forms a more-or-less continuous terrane within the North Cascade Range. The complex comprises abundant plutons intruded at mid-crustal depths into a variety of metamorphosed supracrustal rocks of both oceanic and volcanic-arc origin. U-Pb zircon ages from gneissis plutons within and near the Skagit Gneiss Complex indicate magmatic crystallziations between 75 and 60 Ma. Deformation, recrystallization, and migmatization in part postdate intrusion of the 75-60 Ma plutons. This latest Cretaceous and earliest Tertiary plutonism and migmatization may reflect thermal relaxation following early Late Cretaceous orogeny. The complex was ductilely extended northwest-southeast shortly after intrusion of granite dikes at ~45 Ma, but before emplacement of the earliest (~34 Ma) plutons of the Cascade arc. -from Authors

  2. 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

  3. 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

  4. A faunistic survey of bees (Hymenoptera: Apoidea) in the Black Belt Prairie of Mississippi

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A survey of bees (Apoidea) in the Black Belt Prairie of northern Mississippi was conducted from 1991 to 2001. Collecting methods included netting specimens from floral hosts and use of malaise traps. The survey resulted in collection of 6138 specimens, of which 3627 were identified to 118 species. O...

  5. Correlates of seat-belt use by adolescents: implications for health promotion.

    PubMed

    Maron, D J; Telch, M J; Killen, J D; Vranizan, K M; Saylor, K E; Robinson, T N

    1986-11-01

    This study examined the psychosocial and behavioral correlates of seat-belt use among 1,728 10th-graders in four Northern California high schools. Parent and friend seat-belt use patterns were most highly correlated with student seat-belt use (r = 0.66 and r = 0.61, respectively) and together accounted for 46% of the variation in use. These relationships held across differences in sex, ethnicity, and socioeconomic status. Failure to wear seat belts was associated with a higher use of alcohol, cigarettes, marijuana, and cocaine; more tolerance toward speeding and drinking while driving; less exercise; and more preference for fat in the diet. Our findings attest to the power of parent and peer influences in shaping seat-belt use by adolescents and suggest that not wearing seat belts can be conceptualized as one facet of a pattern of general risk-taking behavior. These findings suggest several possible educational interventions to increase seat-belt use by adolescents.

  6. 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.

  7. The Hardwood Gneiss: Evidence for high P-T Archean metamorphism in the southern province of the Lake Superior region

    SciTech Connect

    Peterson, J.W. ); Geiger, C.A. )

    1990-03-01

    The Hardwood Gneiss is an areally small unit of Precambrian granulite-grade rocks exposed in the Archean gneiss terrane of the southern Lake Superior region. The rocks are located in the southwestern portion of the Upper Peninsula of Michigan and consist of a structurally conformable package of quartzitic, metapelitic, amphibolitic, and metabasic units. Three texturally distinct garnet types are present in the metabasites and are interpreted to represent two metamorphic events. Geothermobarometry indicates conditions of {approximately}8.2-11.6 kbar and {approximately}770C for M1, and conditions of {approximately}6.0-10.1 kbar and {approximately}610-740C for M2. It is proposed that M1 was Archean and contemporaneous with a high-grade metamorphic event recorded in the Minnesota River Valley. The M2 event was probably Early Proterozoic and pre-Penokean, with metamorphic conditions more intense than those generally ascribed to the Penokean Orogeny in Michigan, but similar to the conditions reported for the Kapuskasing zone of Ontario. The high paleopressures and temperatures of the M1 event make the Hardwood Gneiss distinct from any rocks previously described in the southern Lake Superior region, and suggest intense tectonic activity during the Archean.

  8. A comparison of the chemistry of pseudotachylyte breccias in the Archean Levack Gneisses of the Sudbury structure, Ontario

    NASA Technical Reports Server (NTRS)

    Thompson, Lucy M.; Spray, John G.

    1992-01-01

    The Archean Levack Gneisses of the North Range host millimeter-thick veins and centimeter-thick lenses of pseudotachylyte, as well as substantially larger meter-wide, dykelike bodies of pseudotachylytic 'breccia'. The 'breccia' occurs up to several tens of kilometers away from the Sudbury Igneous Complex and is commonly sited within or near joints and other natural weaknesses such as bedding, dyke contacts, and lithological boundaries. The larger 'breccia' dykes comprise a generally dark matrix containing rounded to subrounded and occasionally angular rock fragments derived predominantly from Levack Gneiss. Selected samples of bulk Sudbury Breccia and Sudbury Breccia matrices were chemically analyzed and compared to existing data on the Levack Gneisses and Sudbury Breccia. The matrices are apparently enriched in Fe and, to a lesser extent, Mg, Ti, and Ca compared to the wallrocks and the majority of clasts. This enrichment can be partly explained by the preferential cataclasis and/or frictional melting of hydrous ferromagnesian wallrock minerals, but also appear to require contamination by more basic exotic lithologies. This suggests that certain components of pseudotachylitic Sudbury Breccia have undergone significant transport during their formation.

  9. Zircon from charnockite gneiss, charnockite, and leucosome of migmatite in the Nimnyr Block of the Aldan Shield

    NASA Astrophysics Data System (ADS)

    Glebovitsky, V. A.; Sedova, I. S.; Berezhnaya, N. G.; Skublov, S. G.; Samorukova, L. M.

    2015-12-01

    The microgeochemistry of zircon was studied in three samples: charnockite gneiss (1594), charnockite (1594a), and migmatite leucosome Lc4 (1594c). Prismatic (Zrn I) and oval (Zrn II) zircon morphotypes are distinguished in the first two samples. Most zircon grains consist of two-phase cores and overgrowth rims variable in thickness. The average weighted concordant U-Pb age of Zrn II cores from charnockite gneiss is 2436 ± 10 Ma. The concordant ages of Zrn I and Zrn II cores from charnockite are 2402 ± 16 Ma and 2453 ± 14 Ma, respectively. Some overgrowth rims are 1.9-2.1 Ga in age. In leucosome Lc4, all measured prismatic zircon crystals yielded a discordant age of 1942 ± 11 Ma (the upper intersection of discordia with concordia). These zircons are strongly altered and anomalously enriched in U and Th. Zrn I grains are enriched relative to Zrn II in REE, Li, Ca, Sr, Ba, Hf, Th, and U. Zrn I is considered to be a product of melt crystallization or subsolidus recrystallization in the presence of melt. Zrn II is relict or crystallizing from melt and then partly fused again. Zrn I from charnockite gneiss and especially from charnockite are markedly altered and have a more discordant age than Zrn II. This is probably related to concentration of fluid in the residual melt left after zircon crystallization.

  10. Crustal structure of central Syria: The intracontinental Palmyride mountain belt

    NASA Astrophysics Data System (ADS)

    Al-Saad, Damen; Sawaf, Tarif; Gebran, Ali; Barazangi, Muawia; Best, John A.; Chaimov, Thomas A.

    1992-07-01

    Along a 450-km transect across central Syria seismic reflection data, borehole information, potential field data and surface geologic mapping have been combined to examine the crustal structure of the northern Arabian platform beneath Syria. The transect is surrounded by the major plate boundaries of the Middle East, including the Dead Sea transform fault system along the Levantine margin to the west, the Bitlis suture and East Anatolian fault to the north, and the Zagros collisional belt to the northeast and east. Three main tectonic provinces of the northern Arabian platform in Syria are crossed by this transect from south to north: the Rutbah uplift, the Palmyra fold-thrust belt, and the Aleppo plateau. The Rutbah uplift in southern Syria is a broad, domal basement-cored structure with a thick Phanerozoic (mostly Paleozoic) cover of 6-7 km. Isopachs based on well and seismic reflection data indicate that this region was an early Paleozoic depocenter. The Palmyra fold-thrust belt, the northeastern arm of the Syrian Arc, is a northeast-southwest-trending intracontinental mountain belt that acts as a mobile tectonic zone between the relatively stable Rutbah uplift to the south and the less stable Aleppo plateau to the north. Short-wavelength en-echelon folds characterized by relatively steep, faulted southeast flanks dominate in the southwest, most strongly deformed segment of the belt, while a complex system of deeply rooted faults and broad folds characterize the northeastern region, described in this study. The Aleppo plateau lies immediately north of the Palmyride belt, with a combined Paleozoic and Mesozoic sedimentary section that averages 4-5 km in thickness. Although this region appears relatively undeformed on seismic reflection data when compared to Palmyride deformation, a system of near-vertical, probable strike-slip faults crosscut the region in a dominantly northeasterly direction. Gravity and magnetic modeling constrains the deep crustal structure

  11. Insights on high-grade deformation in quartzo-feldspathic gneisses during the early Variscan exhumation of the Cabo Ortegal nappe, NW Iberia

    NASA Astrophysics Data System (ADS)

    José Fernández, Francisco; Llana-Fúnez, Sergio; Valverde-Vaquero, Pablo; Marcos, Alberto; Castiñeiras, Pedro

    2016-04-01

    High-grade, highly deformed gneisses crop out continuously along the Masanteo peninsula and constitute the upper part of the lower crustal section in the Cabo Ortegal nappe (NW Spain). The rock sequence formed by migmatitic quartzo-feldspathic (qz-fsp) gneisses and mafic rocks records the early Ordovician (ca. 480-488 Ma) injection of felsic dioritic/granodioritic dykes at the base of the qz-fsp gneisses, and Devonian eclogitization (ca. 390.4 ± 1.2 Ma), prior to its exhumation. A SE-vergent ductile thrust constitutes the base of quartzo-feldspathic gneissic unit, incorporating mafic eclogite blocks within migmatitic gneisses. A NW-vergent detachment displaced metasedimentary qz-fsp gneisses over the migmatites. A difference in metamorphic pressure of ca. 0.5 GPa is estimated between both gneissic units. The tectono-metamorphic relationships of the basal ductile thrust and the normal detachment bounding the top of the migmatites indicate that both discrete mechanical contacts were active before the recumbent folding affecting the sequence of gneisses during their final emplacement. The progressive tectonic exhumation from eclogite to greenschist facies conditions occurred over ca. 10 Ma and involved bulk thinning of the high-grade rock sequence in the high pressure and high temperature (HP-HT) Cabo Ortegal nappe. The necessary strain was accommodated by the development of a widespread main foliation, dominated by flattening, that subsequently localized to a network of anastomosing shear bands that evolved to planar shear zones. Qz-fsp gneisses and neighbouring mafic granulites were exhumed at > 3 mm yr-1, and the exhumation path involved a cooling of ˜ 20 °C/100 MPa, These figures are comparable to currently active subduction zones, although exhumation P-T trajectory and ascent rates are at the hotter and slower end in comparison with currently active similar settings, suggesting an extremely ductile deformation environment during the exhumation of qz

  12. Radiation Belt Storm Probe Mission Trailer

    NASA Video Gallery

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

  13. The origin of jarosite associated with a gossan on Archean gneiss in Southwest Greenland

    NASA Astrophysics Data System (ADS)

    Peng, Y.; Pratt, L. M.; Young, S. A.; Cadieux, S. B.; White, J. R.

    2013-12-01

    The mineral Jarosite [KFe3(SO4)2(OH)6] since its discovery, by Opportunity rover at Meridiani Planum on Mars, has been the subject of intense geochemical and environmental study over the last 5-10 years. Jarosite requires highly acidic, K-enriched, and oxidizing aqueous conditions for formation. Stable isotopes of O, H, and S of jarosite have the ability to record the temperatures of formation, environments of deposition, fluids, and fluid/atmospheric interactions. Therefore, the origin of jarosite is important for understanding present and past environmental conditions on Mars. Unfortunately, the origin of jarosite on Mars remains unclear. Jarosite is commonly found on Earth in the weathering zones of pyrite-bearing ore deposits, near-surface playa sediments in acid-saline lakes, or epithermal environments and hot springs. Here, we report the occurrence of jarosite in association with a gossan overlying weathered Archean gneiss and Paleoproterozoic mafic dikes at the ice-free margin of southwestern Greenland. In our 2012 field campaign, we excavated soil pits to a depth of 40 cm with a high vertical sampling resolution. No visible pyrite was found in the nearby outcroppings of gneiss in the field. XRD data show that all samples were composed of anorthite, quartz, albite, jarosite, muscovite, and microcline. Jarosite was the only sulfur-bearing mineral identified by XRD, with abundance of jarosite increasing with depth (up to 8.4 wt. %) in the soil pits. Water soluble and acid soluble sulfate were sequentially extracted using 10% NaCl and 2N HCl solutions, respectively. Pyrite was then subsequently extracted from insoluble residues by a chromium reduction method. The average abundance of water soluble sulfate, acid soluble sulfate, and pyrite were 100 ppm, 7 wt. %, and 10 ppm, respectively. The δ34S values of water soluble sulfate, acid soluble sulfate, and pyrite range from -0.7‰ to 3.1‰ (average= 1.5‰), -1.2 to 1.5‰ (average= 0.7‰), and 0.3‰ to 6.7

  14. Microfabric reconstruction via quantitative digital petrographic image analysis for weakly foliated gneisses

    NASA Astrophysics Data System (ADS)

    Yeh, Meng-Wan; Lin, Yu-Ling; Lee, Tung-Yi; Ji, Jian-Qing

    2013-03-01

    Detection and documentation of petro-structural features such as alignment features of minerals/grains, and extraction of such spatial property data are two fundamental steps for structural geology. Such tasks were mostly carried out manually. However, manual analysis is laborious and potentially biased. These drawbacks are less obvious when the foliation is well developed and the amount of platy mineral is higher. For samples with weakly developed foliation and low platy mineral content, automatic method is required for subjective interpretation. A semi-automatic computerized method of 3D foliation orientation reconstruction via two-dimensional petrographic-shape fabric analysis from serial oriented digital microphotograph has been developed and demonstrated in this study. The foliation is reconstructed by fitting a best fitting plane to the maximum modal peaks of micro textural parameters (SPO) for different mineral groups of platy and granular minerals from each thin section on a stereonet for four coarse grained biotite gneiss samples collected along the Jialie fault, SE Tibet, China. Regardless of platy or granular mineral aggregates, the reconstructed foliations showed similar orientation within 10° angular variation to the field measurement. The 10° angular variation can be maintained if the foliations are reconstructed by consecutive thin section groupings ≦ 50° angular intervals and a horizontal thin section. The angular spread increased to 30° for thin section groupings with > 50° to 100° angular intervals with a horizontal thin section. Major advantages of the computerized photometric methods demonstrated by this study are: the reduction of human prejudice and obtaining quantified and repeatable data sets.

  15. Metamorphic signature of the Gneiss Canyon Shear Zone, Lower Granite Gorge, Grand Canyon, Arizona

    SciTech Connect

    Robinson, K.; Williams, M.L. . Dept. of Geology and Geography)

    1992-01-01

    The Proterozoic orogen in Arizona consists of structural blocks separated by NE trending shear zones. The Gneiss Canyon Shear Zone (GCSZ) is important because it appears to define in part the boundary between the amphibolite facies Yavapai Province and the granulite facies Mojave Province. An early NW striking foliation is clearly visible in many samples from the Lower Granite Gorge (LGG). In Travertine Canyon, east of the GCSZ, pelitic schists contain And-Sil-Crd-Bi and Gar-Sil-Sta-Bi. Mafic rocks exhibit complex phase relations between cummingtonite, anthophyllite, gedrite, garnet, and cordierite. The coexistence of cordierite-cummingtonite is indicative of low pressure metamorphism. Microprobe analyses of garnets reveal prograde growth zoning profiles. Temperature and pressure estimates of peak metamorphism are 550--600 C and 3 kb. Just east of the GCSZ, pelitic assemblages contain Gar-Bi [+-] Sil [+-] Mus, and garnet zoning profiles are flat in the cores. In Spencer Canyon, west of the GCSZ, samples commonly contain Gar-Bi-Sil-Crd, and in many samples cordierite is being replaced by sillimanite. Thermobarometric calculations yield temperature and pressure estimates of 650 C and 3.5 kb. Mineral assemblages and quantitative thermobarometry suggest higher peak metamorphic temperature west of the GCSZ but relatively constant pressures across the LGG. On the east side of the GCSZ, temperatures increase toward the Shear Zone, probably due to the presence of extensive dikes, pods, and veins of variably deformed granite. Peak mineral assemblages are syntectonic with respect to the NE-striking GCSZ fabric. If a suture exists in the LGG, the GCSZ fabrics apparently reflect post-accretionary tectonism, with accretion occurring prior to the peak of metamorphism.

  16. Convergent radial tracing of viral and solute transport in gneiss saprolite.

    PubMed

    Taylor, Richard; Tindimugaya, Callist; Barker, John; Macdonald, David; Kulabako, Robinah

    2010-01-01

    Deeply weathered crystalline rock aquifer systems comprising unconsolidated saprolite and underlying fractured bedrock (saprock) underlie 40% of sub-Saharan Africa. The vulnerability of this aquifer system to contamination, particularly in rapidly urbanizing areas, remains poorly understood. In order to assess solute and viral transport in saprolite derived from Precambrian gneiss, forced-gradient tracer experiments using chloride and Escherichia coli phage PhiX174 were conducted in southeastern Uganda. The bacteriophage tracer was largely unrecovered; adsorption to the weathered crystalline rock matrix is inferred and enabled by the low pH (5.7) of site ground water and the bacteriophage's relatively high isoelectric point (pI = 6.6). Detection of the applied PhiX174 phage in the pumping well discharge at early times during the experiment traces showed, however, that average ground water flow velocities exceed that of the inert solute tracer, chloride. This latter finding is consistent with observations in other hydrogeological environments where statistically extreme sets of microscopic flow velocities are considered to transport low numbers of fecal pathogens and their proxies along a selected range of linked ground water pathways. Application of a radial advection-dispersion model with an exponentially decaying source term to the recovered chloride tracer estimates a dispersivity (alpha) of 0.8 +/- 0.1 m over a distance of 4.15 m. Specific yield (S(y)) is estimated to be 0.02 from volume balance calculations based on tracer experiments. As single-site observations, our estimates of saprolite S(y) and alpha are tentative but provide a starting point for assessing the vulnerability of saprolite aquifers in sub-Saharan Africa to contamination and estimating quantitatively the impact of climate and abstraction on ground water storage. PMID:19245374

  17. Keeping conveyor belts clean reduces operating costs

    SciTech Connect

    Leroy, T.C.

    1982-07-01

    Surveys devices for cleaning conveyor belts. Inefficient belt cleaning will result in material sticking to the return belt. This material then accumulates and forms piles underneath the conveyor, as shown in an illustration. Unevenly worn idlers bring about off-centering of the belt, causing spillage, and often, considerable damage. Continued accumulation of the material brings about stoppages and unscheduled shut downs of the plant. Devices examined include brushes, metallic cable and depression rollers.

  18. Three-dimensional data assimilation and reanalysis of radiation belt electrons: Observations of a four-zone structure using five spacecraft and the VERB code

    NASA Astrophysics Data System (ADS)

    Kellerman, A. C.; Shprits, Y. Y.; Kondrashov, D.; Subbotin, D.; Makarevich, R. A.; Donovan, E.; Nagai, T.

    2014-11-01

    Obtaining the global state of radiation belt electrons through reanalysis is an important step toward validating our current understanding of radiation belt dynamics and for identification of new physical processes. In the current study, reanalysis of radiation belt electrons is achieved through data assimilation of five spacecraft with the 3-D Versatile Electron Radiation Belt (VERB) code using a split-operator Kalman filter technique. The spacecraft data are cleaned for noise, saturation effects, and then intercalibrated on an individual energy channel basis, by considering phase space density conjunctions in the T96 field model. Reanalysis during the CRRES era reveals a never-before-reported four-zone structure in the Earth's radiation belts during the 24 March 1991 shock-induced injection superstorm: (1) an inner belt, (2) the high-energy shock-injection belt, (3) a remnant outer radiation belt, and (4) a second outer radiation belt. The third belt formed near the same time as the second belt and was later enhanced across keV to MeV energies by a second particle injection observed by CRRES and the Northern Solar Terrestrial Array riometer network. During the recovery phase of the storm, the fourth belt was created near L*=4RE, lasting for several days. Evidence is provided that the fourth belt was likely created by a dominant local heating process. This study outlines the necessity to consider all diffusive processes acting simultaneously and the advantage of supporting ground-based data in quantifying the observed radiation belt dynamics. It is demonstrated that 3-D data assimilation can resolve various nondiffusive processes and provides a comprehensive picture of the electron radiation belts.

  19. 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.

  20. 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...

  1. 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...

  2. 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...

  3. 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...

  4. 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...

  5. 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...

  6. 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...

  7. 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...

  8. 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...

  9. 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...

  10. 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.

  11. Appendiceal transection associated with seat belt restraint

    PubMed Central

    Go, Seung Je; Ye, Jin Bong; Kim, Joong Suck

    2016-01-01

    The seat belt is designed for safety in a motor vehicle and should be worn to prevent severe injuries. But, the seat belt itself can be an injury factor in combination with deceleration forces applied to fixation points of mobile viscera. Here, we present a 23-year-man with traumatic transection of the appendix, highly mobile viscera, following seat belt injury. PMID:27478816

  12. 30 CFR 77.406 - Drive belts.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Drive belts. 77.406 Section 77.406 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY... Mechanical Equipment § 77.406 Drive belts. (a) Drive belts shall not be shifted while in motion unless...

  13. 30 CFR 75.1727 - Drive belts.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Drive belts. 75.1727 Section 75.1727 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Miscellaneous § 75.1727 Drive belts. (a) Drive belts shall not...

  14. 30 CFR 75.1727 - Drive belts.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Drive belts. 75.1727 Section 75.1727 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Miscellaneous § 75.1727 Drive belts. (a) Drive belts shall not...

  15. 30 CFR 77.406 - Drive belts.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Drive belts. 77.406 Section 77.406 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY... Mechanical Equipment § 77.406 Drive belts. (a) Drive belts shall not be shifted while in motion unless...

  16. 30 CFR 77.406 - Drive belts.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Drive belts. 77.406 Section 77.406 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY... Mechanical Equipment § 77.406 Drive belts. (a) Drive belts shall not be shifted while in motion unless...

  17. 30 CFR 75.1727 - Drive belts.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Drive belts. 75.1727 Section 75.1727 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Miscellaneous § 75.1727 Drive belts. (a) Drive belts shall not...

  18. 30 CFR 75.1727 - Drive belts.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Drive belts. 75.1727 Section 75.1727 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Miscellaneous § 75.1727 Drive belts. (a) Drive belts shall not...

  19. 30 CFR 77.406 - Drive belts.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Drive belts. 77.406 Section 77.406 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY... Mechanical Equipment § 77.406 Drive belts. (a) Drive belts shall not be shifted while in motion unless...

  20. 30 CFR 75.1727 - Drive belts.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Drive belts. 75.1727 Section 75.1727 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Miscellaneous § 75.1727 Drive belts. (a) Drive belts shall not...

  1. 30 CFR 77.406 - Drive belts.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Drive belts. 77.406 Section 77.406 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY... Mechanical Equipment § 77.406 Drive belts. (a) Drive belts shall not be shifted while in motion unless...

  2. Limited Flow of Continental Crust at UHP Depths: Coupled Age and Trace-Element Analyses of Titanite in the Western Gneiss Region, Norway

    NASA Astrophysics Data System (ADS)

    Garber, J. M.; Hacker, B. R.; Kylander-Clark, A. R.

    2015-12-01

    Coupled age and trace-element data from titanites in the Western Gneiss Region (WGR) of Norway suggest that continental crust underwent limited recrystallization and ductile flow through ~40 My of deep subduction and subsequent exhumation. Precambrian igneous titanites in granitic to tonalitic orthogneisses from the WGR were metastably preserved though Caledonian ultrahigh-pressure (UHP) metamorphism and variably recrystallized through subsequent amphibolite-facies metamorphism from ~420-385 Ma. The inherited Precambrian titanites are not present everywhere but rather cluster primarily in a cooler "southern domain" (peak T ~650oC) and a hotter "northern domain" (peak T ~750-800oC).Titanite data were collected using LASS (laser-ablation split stream inductively-coupled plasma mass spectrometry) at UCSB, and a principal component analysis (PCA) was used to define age and trace-element populations. These data indicate that inherited titanites are LREE-enriched, HFSE-enriched, and have higher Th/U, consistent with Precambrian neocrystallization from a granitic melt. In contrast, the recrystallized titanites have generally lower Th/U and flat, LREE-depleted, or hump-shaped trace-element patterns. These data suggest that (1) Caledonian titanite recrystallization occurred in the presence of LREE-depleted melts or fluids, or that (2) recrystallization was accompanied by a "typical" granitic melt, but that titanite/bulk-rock distribution coefficients are different for neo- and recrystallization; on-going whole-rock analyses will clarify these hypotheses. Critically, the geochemical signature of recrystallized titanite in felsic orthogneisses is comparable across the entire WGR - emphasizing that the petrologic process of titanite recrystallization was similar orogen-wide, but was less extensive in the domains where inherited titanite was preserved. In this case, large volumes of crust outside of the "old domains" may also have retained metastable titanite during subduction

  3. Evidence of 1.7- to 1.8-Ga Collisional Arc in the Kaoko Belt, NW Namibia

    NASA Astrophysics Data System (ADS)

    Luft, João Luiz; Chemale, Farid; Armstrong, Richard

    2011-04-01

    Detailed structural and isotopic analyses in the Hoanib and Ugab River Valleys indicate the existence of an exotic 1.7- to 1.8-Ga terrane in the Pan-African Kaoko Belt. This crustal block, called as Mudorib Complex, is imbricated between autochthonous and para-autochthonous rocks of Congo Craton, Kaoko Basin, and Western Kaoko Batholith units during the main tectono-thermal phase of Kaoko Belt collision around 580 Ma, involving the Rio de La Plata, Congo and Kahalari paleoplates. This terrain is positioned between the 1.9-Ga Pruwes Complex units of SW edge of the Congo Craton and the 0.58- to 0.55-Ga Amspoort Suite granitoids of the Western Kaoko Batholith. It is coincident with a regional positive aeromagnetic anomaly trending from NNW in the Ugab region to the Namibia-Angola border. Internally, Mudorib Complex consists in 1.73- to 1.81-Ga tonalitic-trondhjemitic-dioritic-granodioritic sequence of gneisses associated with cogenetic gabbroic and anothositic-gneisses in the core zone of this Pan-African structure. Field relationship and U-Pb zircon and Sm-Nd whole-rock isotope data combined with geochemical information suggest the existence of two rock associations in the Mudorib Complex, namely late Paleoproterozoic tonalitic-trondhjemitic-dioritic-gneisses with island-arc affinity and tholeiitic metabasites of juvenile origin, showing Nd model age of 1.73-2.17 Ga and ɛNd( t) of -2.05-+4.3. This 1.8- to 1.7-Ga complex is also intruded by granitic dykes formed at 1.49-1.50 Ga with Nd model age of 1.75-2.34 Ga during stable tectonic conditions. In addition to widespread Pan-African tectono-metamorphic events, a secondary metamorphic event of ~1.3 Ga is also recognized in the Mudorib rocks, which may be associated with accretion process of the complex to the Paleoproterozoic to Archean nucleus of the Kaoko Belt in the Hoanib River Valley.

  4. Main Stages of Geodynamic Evolution of the Caucasian Segment of the Alpine-Mediterranean Belt

    NASA Astrophysics Data System (ADS)

    Gamkrelidze, Irakli; Shengelia, David; Maisadze, Ferando; Tsutsunava, Tamara; Chichinadze, Giorgi

    2013-04-01

    Within the oceanic area of Tethys, with a typical oceanic crust, in geological past relatively small continental or subcontinental plates (terranes) were situated. The Greater Caucasian, Black Sea - Central Transcaucasian, Baiburt - Sevanian and Iran - Afghanian accretionary terranes, which in geological past represented island arcs or microcontinents, are identified in the Caucasian segment of the Alpine-Mediterranean belt. They are separated by ophiolite sutures (relics of small or large oceanic basins) of different age. During the Late Precambrian, Paleozoic and Early Mesozoic these terranes underwent horizontal displacement in different directions and ultimately they joined the Eurasian continent. New LA-ICP-MS U-Pb zircon dating along with available geologic, petrologic and geochemical investigations, allow to trace with confidence the main stages of regional metamorphism, granite formation and, consequently, pre-Alpine continental crust making within the Caucasus. At the pre-Grenville stage (1200 Ma and more) between the Baltica and Gondvana ancient continents, on the oceanic crust of Prototethys accumulation mainly of terrigenous sediments and of basic volcanites took place. At the Grenville stage (1000-800 Ma) subcontinental or primitive continental crust (gneiss-migmatite complex and synmetamorphic grenitoids of sodium series) were formed in suprasubduction conditions by both sides of Proto-Paleotethys and along the northern peripheries of comparatively small oceanic basins of the Arkhiz and Southern Slope of the Greater Caucasus. At the Baikalian stage (650-550 Ma) plagiogneissic complex has been cut by Precambrian gabbroids and intruded by large bodies of quartz-diorites. The next, Late Baikalian stage (540-500 Ma) is determined by the intrusion of Cambrian basites and Late Baikalian granitoids and by manifestation of intensive suprasubduction regional metamorphism. Late Baikalian tectogenesis is accompanied by contraction of the small oceanic basin of

  5. Timing and origin of migmatitic gneisses in south Karakoram: Insights from U-Pb, Hf and O isotopic record of zircons

    NASA Astrophysics Data System (ADS)

    Mahar, Munazzam Ali; Mahéo, Gweltaz; Goodell, Philip C.; Pavlis, Terry L.

    2016-04-01

    The timing and origin of partial melting in collision belts is crucial to understand the thermotectonic evolution and the relationship between HT metamorphism and magmatism in over-thickened crust. In the present study, we used the in-situ isotopic (Hf, O and U-Pb) record of zircons to investigate the timing and origin of migmatitic gneisses exposed in the core of the Dassu dome in south Karakoram. The new U-Pb zircon dating identified the Proterozoic inherited cores (1.8-1.9 Ga and 2.3-2.5 Ga) surrounded by a Neogene overgrowth with ages ranging from ∼6 to ∼20 Ma. These ages imply that the partial melting in the Karakoram Metamorphic Complex lasted from >20 Ma to ∼6 Ma and can be correlated with the Miocene magmatism in the adjacent Baltoro region. Oxygen isotopic data from Proterozoic inherited cores (1.8-1.9 Ga) and Neogene overgrowths are indistinguishable and generally vary from 8‰ to 9.5‰. These values are slightly higher than the most igneous zircons (6.5-8‰, Valley et al., 2005) indicating an igneous precursor with heavy initial O composition that later might have equilibrated with low temperature environment or some involvement of supracrustal material is likely. However, a few low U/Th, relatively old inherited cores (2.3-2.5 Ga) showed mantle-like (δ18O = 5.3 ± 0.6‰, Valley et al., 2005) values of δ18O = 5.5 ± 2.7‰. The present-day weighted mean εHf (0) of the Proterozoic inherited cores ranges from -50 ± 1.0 to -44.3 ± 1.2. In contrast, the Neogene rims are 15-20 ε-units higher than the inherited core with present-day εHf (0) = -30.6 ± 0.9. This implies that the Hf composition of the Neogene overgrowth is not controlled exclusively by the dissolution of the inherited cores and that contamination by external melts is likely. We suggest a contribution from the Neogene, less-evolved magmatism in the Baltoro region (εHf (0) = ∼-4 to -10). The elevated oxygen composition is not consistent with the contribution from pristine

  6. AMT survey in the Outokumpu ore Belt, Eastern Finland

    NASA Astrophysics Data System (ADS)

    Lahti, Ilkka; Kontinen, Asko; Aatos, Soile; Smirnov, Maxim

    2015-04-01

    The Outokumpu ore belt comprises Paleoroterozoic turbiditic deep-water sediments enclosing fault-bound ophiolitic slices composed dominantly of serpentinites derived from oceanic upper mantle peridotites. These together form the allochthonous Outokumpu suite that was emplaced onto the Karelian Craton margin during the early stages of the Svecofennian Orogeny. The area which has been over 100 years among the most important mining regions in Finland is still supporting active mining and exploration. The main prospectivity is for polymetallic (Cu-Co-Zn-Ni-Ag-Au) sulfide ores that are hosted by carbonate, calc-silicate and quartz rocks fringing serpentinite bodies embedded in extensive formations of electrically conductive iron sulfide and graphite-bearing black schists that are showing no geochemical vectors to the ores (e.g. Peltonen et al., 2008). The presence of conductive schists makes also electromagnetic exploration of the sulfide ores challenging. However, the detection of the black schists at depth would be useful in locating new environments with potential for the serpentinites and prospective Outokumpu rock assemblage. Audiomagnetotelluric (AMT) data has been recently collected to image subsurface conductivity structure of the belt. These data were acquired along five profiles transecting several key-features, including the Miihkali serpentinite, Archean Sotkuma gneiss window and the area SE from the Outokumpu mine. Altogether 91 sites were measured with the site spacing of 300 m - 2 km. AMT data (f = 1 - 10 000 Hz) were acquired during daytime whereas night-recordings enabled to obtain data at the frequency range of 0.01 - 10 000 Hz. Measurements were done using two Metronix 24bit ADU-07e broadband electromagnetic acquisition systems. Robust remote reference processing yielded mostly good data quality, particularly for data recorded during night-time. The survey area is favorable for 2-D modeling as it is characterized by thin, laterally extensive

  7. Geochemistry and origin of gold mineralization in the Kolar Schist Belt

    NASA Technical Reports Server (NTRS)

    Siddaiah, N. Siva; Rajamani, V.

    1988-01-01

    Geological, mineralogical, mineral-textural and geochemical data of the sulfide lodes in the belt indicate that the gold mineralization could be related to low temperature, low Eh and high pH rock-dominated geothermal systems set up in the submarine volcanic pile prior to amphibolite metamorphism. A relatively long-lived geothermal system produced an economic deposit, whereas short-lived ones, because of rapid burial by younger basalts throttled the geothermal system and diffused the discharge yielding low grade ore bodies. The source for gold and iron could be iron enriched tholeiites derived from source regions enriched in komatiitic melt components and komatiitic rocks derived by very low extents of melting of metasomatised mantle sources. On the other hand, the geographical restriction of the quartz-calcite lodes, their mineralogical and geochemical data and their estimated temperature of formation all seem to suggest that a major part of the hydrothermal fluids, and a significant portion of gold could have been derived from mantle derived intrusive, sanukitoid type magma sources, similar to the Champion Gneiss occurring on the eastern part of the belt. However, the possibility of some input by remobilization of a premetamorphic sulfide protore to quartz lodes cannot be ruled out completely.

  8. Geometric and kinematic analysis, and geochemical study of the Corbin Gneiss Complex and its associated sheared rocks in the Blue Ridge of NW Georgia

    SciTech Connect

    Gargi, S.P.

    1985-01-01

    The Corbin Gneiss Complex forms the core of the Salem Church anticlinorium in the Blue Ridge of NW Georgia, and is composed of quartz monzodiorite (Corbin gneiss) and pyroxene-biotite diorite. The observed foliation and the presence of thin zones of ultramylonites and phyllonites in the rocks of the gneiss complex are the result of the ductile shearing. Subsequent to the development of the mylonitic foliation these rocks were subjected for four episodes of flexural slip folding. The first generation folds were associated with the formation of the Salem Church anticlinorium. The northeasterly striking axial planes and the southeasterly plunging fold axes of the last three systems of folds suggest that these folds were formed on the southeasterly dipping foliation planes of the Salem Church anticlinorium. The trace element study of the pyroxene-biotite diorite, the Corbin gneiss (quartz monzodiorite) including its variably sheared equivalents shows that these rocks originated from independent sources by primary petrogenetic processes, and do not show any mixing relationship. The whole rock Rb-Sr isochron of the ultramylonitic Corbin gneiss yields an age of 296 +/- 4 Ma and an initial /sup 87/Sr//sup 86/Sr ratio of 0.7208 +/- 7. The much younger age of the ultramylonite in comparison to that of the unsheared Corbin gneiss (age approx. 1 Ga) is the result of resetting of the Rb-Sr systematics of the latter due to shearing, and denotes the minimum age limit of the shearing. A two point whole rock isochron of the diorite gives an apparent age of 1.22 Ga and an initial /sup 87/Sr//sup 86/Sr ratio of 0.7036. The total crustal age of the diorite is slightly greater than the Corbin gneiss.

  9. Pressure-Temperature-Time Relationships of Allochthons to Basement, Western Gneiss Region, Norway

    NASA Astrophysics Data System (ADS)

    Walsh, E. O.; Hacker, B. R.

    2002-12-01

    The Western Gneiss region of Norway contains one of the largest expanses of ultrahigh-pressure (UHP) rocks in the world. Our new findings of coesite pseudomorphs increase the known width of the UHP terrane to 100 km. In this same area, continental and oceanic allochthons are folded into the Baltica basement in complex patterns. To determine the role that the allochthons played in the UHP metamorphism, it is essential to understand the relationship of the allochthons to the Baltica basement. To this purpose, we have studied the temperature-pressure-time histories of the rocks along a 160 x 100 km E-W transect from orogen core to foreland. Allochthon pelites (garnet + biotite +/- kyanite +/- staurolite) and garnet amphibolites record consistent pressures of ~1.1 GPa across the entire transect; this contends earlier studies that implied a westward increasing P-T gradient. Temperatures are high, ranging from 650-800 °C. Basement rocks record similar temperatures but lower pressures (0.6-0.7 GPa). In situ eclogites in both allochthons and basement yield minimum pressures of ~1.5 GPa, and a basement orthopyroxene eclogite yields about 3 GPa and 825 °C. While basement garnets are homogeneous, allochthon garnets display prograde zoning. All garnets show retrograde resorption, the effects of which were removed by recalculation using the Mn peak at garnet rims. The Gibbs method of Spear was used to model P-T paths for the rocks. Although the presence of in situ eclogites requires at least 0.4 GPa decompression of the allochthons, modeling of garnets across the area reveals only uniform heating and mild compression. We tentatively attribute the lack of decompression recorded in garnet zoning to resorption of garnets during decompression. In summary, our observations suggest that: i) the eclogites formed in a relatively warm subduction zone; ii) the allochthon recrystallized as a subhorizontal sheet that stalled at lower crustal conditions (1.1 GPa) after exhumation from the

  10. [Influence of surface roughness on degree of polarization of biotite plagioclase gneiss varying with viewing angle].

    PubMed

    Xiang, Yun; Yan, Lei; Zhao, Yun-sheng; Gou, Zhi-yang; Chen, Wei

    2011-12-01

    Polarized reflectance is influenced by such factors as its physical and chemical properties, the viewing geometry composed of light incident zenith, viewing zenith and viewing azimuth relative to light incidence, surface roughness and texture, surface density, detection wavelengths, polarization phase angle and so on. In the present paper, the influence of surface roughness on the degree of polarization (DOP) of biotite plagioclase gneiss varying with viewing angle was inquired and analyzed quantitatively. The polarized spectra were measured by ASD FS3 spectrometer on the goniometer located in Northeast Normal University. When the incident zenith angle was fixed at 50 degrees, it was showed that on the rock surfaces with different roughness, in the specular reflection direction, the DOP spectrum within 350-2500 nm increased to the highest value first, and then began to decline varying with viewing zenith angle from 0 degree to 80 degrees. The characterized band (520 +/- 10) nm was picked out for further analysis. The correlation analysis between the peak DOP value of zenith and surface roughness showed that they are in a power function relationship, with the regression equation: y = 0.604x(-0.297), R2 = 0.985 4. The correlation model of the angle where the peak is in and the surface roughness is y = 3.4194x + 51.584, y < 90 degrees , R2 = 0.8177. With the detecting azimuth farther away from 180 degrees azimuth where the maximum DOP exists, the DOP lowers gradually and tends to 0. In the detection azimuth 180 dgrees , the correlation analysis between the peak values of DOP on the (520 =/- 10) nm band for five rocks and their surface roughness indicates a power function, with the regression equation being y = 0.5822x(-0.333), R2 = 0.9843. F tests of the above regression models indicate that the peak value and its corresponding viewing angle correlate much with surface roughness. The study provides a theoretical base for polarization remote sensing, and impels the

  11. Tectonic evolution of the Black Sea orogene belt and the history of opening of the Black Sea basin

    SciTech Connect

    Uesuemezsoy, S. )

    1988-08-01

    The Black Sea basin is surrounded by successive orogenic belts of Hercynian, Cimmerian, and Alpine ages. The Rhodope, Thracian, western Pontian, and Transcaucasian (RTPT) blocks of Precambrian age were involved by the circum-Black Sea orogene belts. The Hercynian orogene was documented in the Balkanide, Great Caucasian, Kriastide, southern Pontian, and Transcaucasian belts. The Cimmerian orogene extended north and south of the Black Sea. The southern Cimmerian orogene was represented by the circum-Rhodope and East Thracian-Strandja-Kuere belts. The northern Cimmerian orogene belt extended along the Dobruca-Crimean and southern slope belts. Following the demise of the Black Sea Cimmerian basin, the northernmost oceanic branch extending from Nish-Trajan through the present Black Sea to the intra-Transcaucasian basin, was opened within the Hercynian and Cimmerian consolidated terrain in the Late Jurassic. The other oceanic branch, extending from Izmir-Ankara through circum Kirsehir to various basins, was opened within the Paleotethyan collision belt, considered to be eastern extension of the Pindus basin. The Nish-Trajan sector of the northernmost basin was closed in the middle Cretaceous, and the Moesian platform re-fused to the Getic-Serbo-Macedonian-Rhodope belt. The easternmost extension of the intra-Transcaucasian basin disappeared in the Late Cretaceous. Consequently, the northernmost oceanic branch was reduced to the present Black Sea basin.

  12. The tropical Atlantic surface wind divergence belt and its effect on clouds

    NASA Astrophysics Data System (ADS)

    Tubul, Y.; Koren, I.; Altaratz, O.

    2015-12-01

    A well-defined surface wind divergence (SWD) belt with distinct cloud properties forms over the equatorial Atlantic during the boreal summer months. This belt separates the deep convective clouds of the Intertropical Convergence Zone (ITCZ) from the shallow marine stratocumulus cloud decks forming over the cold-water subtropical region of the southern branch of the Hadley cell in the Atlantic. Using the QuikSCAT-SeaWinds and Aqua-MODIS instruments, we examined the large-scale spatiotemporal variability in the SWD belt during a 6-year period (2003-2008) and the related links to cloud properties over the Atlantic Ocean. The Atlantic SWD belt was found to be most pronounced from May to August, between the Equator and 2° N latitude. A positive correlation and a strong link were observed between formation of the SWD belt and a sharp sea-surface temperature gradient on the northern border of the cold tongue, supporting Wallace's vertical-mixing mechanism. The dominant cloud type over this region was shallow cumulus. Cloud properties were shown to be strongly linked to the formation and strength of the SWD zone. The findings will help to understand the link between ocean-atmosphere dynamics and cloud properties over this region, and suggest that the SWD zone be considered a unique cloud belt of the southern branch of the Atlantic Hadley cell.

  13. The tropical Atlantic surface wind divergence belt and its effect on clouds

    NASA Astrophysics Data System (ADS)

    Tubul, Y.; Koren, I.; Altaratz, O.

    2015-08-01

    A well-defined surface wind divergence (SWD) belt with distinct cloud properties forms over the equatorial Atlantic during the boreal summer months. This belt separates the deep convective clouds of the intertropical convergence zone (ITCZ) from the shallow marine stratocumulus cloud decks forming over the cold-water subtropical region of the southern Hadley cell. Using the QuikSCAT-SeaWinds and Aqua-MODIS instruments, we examined the large-scale spatiotemporal variability of the SWD belt during a 6 year period (2003-2008) and the related links to cloud properties over the Atlantic Ocean. The Atlantic SWD belt was found to be most pronounced from May to August, between the equator and 2° N latitude. A positive correlation and a strong link were observed between formation of the SWD belt and a sharp sea-surface temperature gradient on the northern border of the cold tongue, supporting Wallace's vertical-mixing mechanism. The dominant cloud type over this region was shallow cumulus. Cloud properties were shown to be strongly linked to the formation and strength of the SWD zone. Our findings help understand the link between ocean-atmosphere dynamics and cloud properties over this region, and suggest that the SWD zone be considered a unique cloud belt of the southern branch of the Atlantic Hadley cell.

  14. Seat-belt syndrome revisited.

    PubMed

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

    2001-10-01

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

  15. Nature and time of emplacement of a pegmatoidal granite within the Delhi Fold Belt near Bayalan, Rajasthan, India

    NASA Astrophysics Data System (ADS)

    Dasgupta, N.; Sen, J.; Pal, T.; Ghosh, T.

    2009-04-01

    The study area is situated about 70 km south east of Ajmer, in Rajasthan, India around the village Bayala (26o 02' 19 N''; 74o 21' 01'') within the Ajmer district of Central Rajasthan. The area is along the eastern flank of the central portion of the Precambrian South Delhi Fold Belt (SDFB) and it stratigraphically belongs to the Bhim Group of rocks. Basement rocks of Archaean age, commonly known as the Banded gneissic Complex (BGC), is exposed to the east, where the rocks of the Bhim Group rests unconformably over BGC. To the west gneissic basement rocks of mid-Proterozoic times underlie the Bhim Group and have been referred to as the Beawar gneiss (BG). The Bhim Group of rocks comprises of metamorphosed marls and calc-silicate gneisses with minor amounts of quartzites and pelitic schists, indicative of its shallow marine origin. Within the Bhim Group, a pegmatoidal granite has intruded the calc silicate gneisses of the area. The pegmatoidal granite body is elliptical in outline with the long dimension(20 km) trending N-S and covers an area of 300 sq. km. approximately. This granite have so far been mapped as basement rocks (BG) surrounding the Beawar town (26o 06' 05'' N; 74o 19' 03'' E), 50 km south east of Ajmer. Rafts of calc-silicate gneisses, belonging to the Bhim Group, are seen to be entrapped within granite. Fragments of BG and its equivalents have also been found as caught up blocks within this pegmatoidal granite body near Andheri Devari, a small hamlet east of Beawar. The objective of the study was to map this pegmatoidal body, and decipher the mechanism and time of emplacement of this granite. A detailed structural mapping of the area in a 1:20000 scale spread over a 30 sq. km area in the vicinity of Bayala was carried out to analyse the geometry and the time of emplacement of the pegmatitic granite. The ridges of calc silicates and marbles adjoining the area were studied for the structural analyses of the Delhi fold belt rocks of the area. The calc

  16. Geology of the Trenton Prong, west-central New Jersey

    SciTech Connect

    Volkert, R.A. ); Drake, A.A.Jr. )

    1993-03-01

    The Trenton Prong in New Jersey is underlain by a heterogeneous sequence of rocks that is divisible into northern and southern belts separated by the steeply southeast-dipping Huntingdon Valley fault (HVF). The northern belt contains metagabbro, charnockite, and dacite/tonalite, upon which biotite-bearing quartzofeldspathic gneiss, calc-silicate gneiss, and minor marble may rest unconformably. The mineralogy and geochemistry of these rocks are remarkably similar to those of Middle Proterozoic rocks in the New Jersey Highlands, and the authors interpret them to be correlative. Northern belt rocks are unconformably overlain by the Cambrian Chickies Quartzite, which is cut off to the northeast by the HVF. The southern belt contains felsic to intermediate quartzofeldspathic gneiss and schist and minor amounts of metavolcanic rocks, all of which may be at slightly lower metamorphic grade than those in the northern belt. High TiO[sub 2] metabasalt is chemically identical to diabase dikes that intrude Middle Proterozoic rocks in the New Jersey Highlands; it is interpreted to be Late Proterozoic in age. Rocks in the southern belt have been thrust northwestward over the Chickies and Middle Proterozoic rocks along the HVF. South of the southern belt, biotite schist and gneiss of the Wissahickon Formation are thrust onto both belts of basement rocks on the HVF and a splay from the HVF, the Morrisville thrust fault. Both faults are marked by augen gneiss that shows evidence of dextral shear.

  17. Petrofabrics and Water Contents of Peridotites from the Western Gneiss Region (Norway): Implications for Fabric Transition of Olivine in Continental Subduction Zones

    NASA Astrophysics Data System (ADS)

    Wang, Q.; Xia, Q.; O'Reilly, S.; Griffin, W. L.; Beyer, E.

    2010-12-01

    The Western Gneiss Region (WGR) of Norway lies within the Caledonian collision zone, which was subjected to the eclogites-facies metamorphism during the Silurian-Devonian continental collision of Baltica and Laurentia. Exhumed from depths of 80-200 km, the peridotites enclosed in Proterozoic gneisses in the WGR can be divided into two groups: garnet-free Archean dunites with extremely depleted compositions, and garnet-bearing peridotites that resulted from refertilization of the dunites during the Proterozoic time (Beyer et al., 2006). Therefore peridotites from the WGR provide a unique window to investigate petrofabrics of the upper mantle with different compositions and deformation history. Using the electron backscatter diffraction (EBSD) technique, we measured lattice-preferred orientations of 10 peridotite samples from the WGR. The water contents of olivine were determined by Fourier transform infrared spectroscopy in Paterson’s calibration (1982). For dunites from Almklovdalen in the southern WGR, one sample with water content of 0.5 ppm H2O displays the [100](010) (the A-type) olivine fabric, while the other two samples with water contents of 5-7 ppm H2O developed [001](010) (the B-type) fabric. In contrast, garnet lherzolites and wehrlites with various water content of 0.2-7 ppm H2O from Almklovdalen and Gurskøy yield the B-type fabric. The [001](100) (the C-type) fabric of olivine was observed in garnet harzburgite with very low water content (1.4 ppm H2O) from Otrøy in the northern WGR, where coesite, majoritic garnet and microdiamond were found by previous studies. Compared with the fabric diagram of olivine proposed by Jung and Karato (2001), all 10 peridotite samples came from dry conditions, under which the A-type or the D-type fabric is expected at low or high stress, respectively. Clearly, our results indicate that water is not the key to producing the different fabrics in the WGR peridotites, and the Proterozoic refertilization did not

  18. Magmatic and metamorphic belts and plutonic-metamorphic complexes of southeastern Alaska

    SciTech Connect

    Brew, D.A.; Himmelberg, G.R.; Ford, A.B.; Loney, R.A. . Branch of Alaskan Geology Univ. of Missouri, Columbia, MO . Dept. of Geology)

    1993-04-01

    The Cordilleran orogen in southeastern Alaska includes 24 distinct magmatic belts, ranging in age from Cambrian to Holocene, that are defined by map relations, lithology, age, and chemical composition. The youngest magmatic features are Quaternary-age pre- and post-glacial volcanic rocks that occur in three major fields in the region, as well as in isolated locations. Cenozoic magmatic features consist of four major and three minor belts. The major Tkope-Portland Peninsula belt of Oligocene age includes both volcanic and plutonic rocks. The major calcalkalic Coast Mountains belt of early and middle Eocene age is the single largest magmatic feature of the region. Early Tertiary and latest Cretaceous magmatism is represented by the major calcalkalic great tonalite sill belt, a remarkable long and narrow feature along the west side of the Coast Mountains. Cretaceous and Jurassic intrusive rocks occur in five major belts and two minor belts in the region and Paleozoic intrusive rocks occur in four major and two minor belts. The three major plutonic-metamorphic complexes (PMC), from east to west, are: the Coast PMC in the Coast Mountains; the Glacier Bay-Chichag of plutonic complex (Chugach MC) in the northern outer islands. The Coast PMC records dynamothermal and regional contact metamorphic events related to regional plutonism within several juxtaposed terranes; its lengthy and complicated history is related to the Late Cretaceous collision of the Alexander and Wrangellia terranes and the Gravina overlap assemblage to the west against the Yukon prong and Stikine terrane to the east. The relatively simple Glacier Bay PC history is recorded as the roots of a Late Jurassic through late Early Cretaceous island arc that probably developed during the early stages of the above tectonic event. The complicated Chugach MC history developed during and after the Late Cretaceous collision of the Chugach terrane with the Wrangellia and Alexander terranes.

  19. Isotopic ages for alkaline igneous rocks, including a 26 Ma ignimbrite, from the Peshawar plain of northern Pakistan and their tectonic implications

    NASA Astrophysics Data System (ADS)

    Ahmad, Irshad; Khan, Shuhab; Lapen, Thomas; Burke, Kevin; Jehan, Noor

    2013-01-01

    New isotopic ages on zircons from rocks of the Peshawar Plain Alkaline Igneous Province (PPAIP) reveal for the first time the occurrence of ignimbritic Cenozoic (Oligocene) volcanism in the Himalaya at 26.7 ± 0.8 Ma. Other new ages confirm that PPAIP rift-related igneous activity was Permian and lasted from ˜290 Ma to ˜250 Ma. Although PPAIP rocks are petrologically and geochemically typical of rifts and have been suggested to be linked to rifting on the Pangea continental margin at the initiation of the Neotethys Ocean, there are no documented rift-related structures mapped in Permian rocks of the Peshawar Plain. We suggest that Permian rift-related structures have been dismembered and/or reactivated during shortening associated with India-Asia collision. Shortening in the area between the Main Mantle Thrust (MMT) and the Main Boundary Thrust (MBT) may be indicative of the subsurface northern extension of the Salt Range evaporites. Late Cenozoic sedimentary rocks of the Peshawar Plain deposited during and after Himalayan thrusting occupy a piggy-back basin on top of the thrust belt. Those sedimentary rocks have buried surviving evidence of Permian rift-related structures. Igneous rocks of the PPAIP have been both metamorphosed and deformed during the Himalayan collision and Cenozoic igneous activity, apart from the newly recognized Gohati volcanism, has involved only the intrusion of small cross-cutting granitic bodies concentrated in areas such as Malakand that are close to the MMT. Measurements on Chingalai Gneiss zircons have confirmed the occurrence of 816 ± 70 Ma aged rocks in the Precambrian basement of the Peshawar Plain that are comparable in age to rocks in the Malani igneous province of the Rajasthan platform ˜1000 km to the south.

  20. Down to the southeast kinematic indicators associated with the Goat Rock fault and gneisses to the south

    SciTech Connect

    Hanley, T.B. . Dept. of Chemistry and Geology); Steltenpohl, M.G. . Dept. of Geology)

    1993-03-01

    Right slip movement has long been recognized as the dominant movement sense along the Goat Rock fault zone (GRfz). However, down to the southeast displacements have been reported based on megascopic south-verging folds of GRfz blastomylonite and a listric normal fault and its associated secondary structures (e.g., SE directed folds and top to the E directed shears) that deform gneiss in the hanging wall block. Microscopic observations of GRfz blastomylonites that document top to the southeast normal movement include mica fish, folded mica porphyroclasts and deformation bands that extend the dominant mylonitic foliation. In hanging wall gneisses, biotite schist patches with a dip-slip lineation contain mica fish and slip-cleavage of feldspar also indicating top to the southeast normal displacement. Deformational conditions for the GRfz span a broad range from high T shear zones to very late stage retrogressive zones, the latter of which deform the right-slip mylonitic fabric reported to have formed between approximately 292 and 276 m.y. ago. They may represent minor antithetic adjustments in a thrust sheet during emplacement, extensional features related to gravitational collapse on the flanks of a growing basement-cored arch (the Pine Mountain arch to the northwest) or they be an early effect of Mesozoic rifting.

  1. Age, field, and petrological relationships of the Hyde School Gneiss, Adirondack lowlands, New York: Criteria for an intrusive igneous origin

    SciTech Connect

    McLelland, J. ); Perham, A. ); Chiarenzelli, J.

    1992-01-01

    Alaskitic and tonalitic rocks constituting Hyde School Gneiss (HSG) occur in 14 domical bodies in the Adirondack lowlands. Recent models have interpreted these bodies as metamorphosed rhyolitic and dacitic ash-flow deposits forming the basal member of a regional stratigraphic package. In contrast, this paper presents criteria and evidence for an intrusive origin for HSG. Field evidence includes intrusion breccias and complex crosscutting relationships involving mafic layers resembling synplutonic dikes. Petrologic constraints supporting an intrusive origin include: (1) the common occurrence of quartz-mesoperthite hypersolvus assemblages; (2) magmatic features in tonalitic, trondhjemitic, and alaskitic facies, (3) local occurrences of orthopyroxene in all facies of HSG; and (4) the development of marginal garnet-sillimanite gneiss with corundum-spinel-garnet-sillimanite assemblages yielding paleotemperatures of 780-810C and interpreted as restite remaining after anatexis of country rock metapelite by intrusions of hypersolvus granitoids. U-Pb zircon ages reported here suggest that the majority of the HSG was intruded at ca. 1230 Ma, contemporaneous with high-grade metamorphic activity in the Adirondacks and elsewhere in the SW sector of the Grenville Province. Geochronological evidence from a leucogranitic rock crosscutting metasediments on Wellesley Island suggest that these metasediments are older than 1416 {plus minus} 5 Ma.

  2. Archean granulite gneisses from eastern Hebei Province, China: rare earth geochemistry and tectonic implications

    NASA Astrophysics Data System (ADS)

    Jahn, Bor-Ming; Zhang, Zong-Qing

    1984-03-01

    The granulite gneisses and their retrograded products of the Qianxi Group from eastern Hebei Province, China, have been investigated for their isotope and trace element geochemistry. A consistent age of about 2.5 AE has been obtained by the Rb-Sr and Sm-Nd whole-rock isochron methods, in agreement with the zircon U-Pb data (Pidgeon 1980; D.Y. Liu, unpubl.). Geochemical arguments from initial isotopic ratios (ISr and INd) and elemental distribution patterns have led us to conclude that this age of about 2.5 AE represents the time of granulite facies metamorphism, which must have followed closely the primary emplacement of their protoliths. Previous claims for early Archean ages (>3.5 AE) of these granulites are not substantiated. The mineral isotope systematics register an important thermal event at about 1.7 AE, roughly corresponding to the time of the widespread Luliang Orogeny (Ma and Wu 1981) or Chungtiao Movement (Huang 1978). The granulites of the Qianxi Group have diverse compositions ranging from ultrabasic through basic-intermediate to acid. Discriminant function calculations suggest that most analyzed samples have igneous parentage. Only a few show characteristics of metasedimentary rocks. The igneous protoliths apparently belong to two series — tholeiitic and calc-alkaline, with the latter dominating in abundance. The majority of the acid granulites have compositions corresponding to tonalite-granodiorite. Except for ultrabasic and metasedimentary rocks, all REE patterns are significantly fractionated with LREE enrichment. The degree of fractionation, as measured by the (La/Yb)N ratios, is most important in the acid granulites. These rocks often show positive Eu anomalies and HREE depletions that are typical of Archean TTG rocks (tonalitetrondhjemite-granodiorite). The existence of komatiites has been previously reported in this region. Although a few rocks have a major element chemistry similar to that for peridotitic komatiites, the lack of associated

  3. Northern Ireland.

    PubMed

    1998-01-01

    The anti-choice lobby has expressed concern that the government may consider reviewing or reforming abortion law in Northern Ireland. The legal status of abortion is similar to that in Britain before the introduction of the 1967 Abortion Act. However, the commemoration of the 30th anniversary of abortion law reform in Britain presents an opportunity to discuss the benefits of such change in Northern Ireland. Such discussion may cause ministers to reconsider the status of abortion. Anticipating possible discussion, some anti-choice Northern Ireland Members of Parliament tabled Early Day Motion (EDM) 352 "Northern Ireland and the Abortion Act," opposing the introduction of abortion services into Northern Ireland. Member of Parliament Harry Barnes tabled an amendment to the motion noting that current abortion law in Northern Ireland violates the standards of international human rights law and that about 2000 women travel from Northern Ireland annually for abortions. EDM 352 has been signed by 17 Members of Parliament; the amendment, by 13. PMID:12321442

  4. 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.

  5. 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.

  6. Pediatric lap belt injuries: care and prevention.

    PubMed

    Shoemaker, B L; Ose, M

    1997-01-01

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

  7. 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.

  8. Hyperextension along the pre-Caledonian margin of the Iapetus? Age and origin of discontinuous gneiss sheets associated with deep-marine sediments, Alpine metaperidotites and detrital serpentinites

    NASA Astrophysics Data System (ADS)

    Jakob, Johannes; Alsaif, Manar; Corfu, Fernando; Andersen, Torgeir B.

    2016-04-01

    A mélange zone is positioned structurally below some large Proterozoic crystalline nappe complexes (NC), including the Upper Bergsdalen, Jotun and Lindås NCs in the South Norwegian Caledonides. The mélange is characterized by a lithological association of originally deep marine sediments intercalated with some coarser grained siliciclastic metasediments including meta-sandstone and conglomerates, thin slivers of gneisses, as well as detrital serpentinites and 'Alpine-type' metaperidotites. The formation of the mélange and particularly the origin of the detrital serpentinites are disputed. Several models have been suggested including formation as a) an ophiolitic mélange during ophiolite obduction, b) an unconformable post-obduction transgressive sequence or c) a mélange formed during hyperextension along the pre-Caledonian margin of Baltica. Here we present new ID-TIMS U-Pb geochronology of zircon and titanite separated from some of the laterally discontinuous gneiss slivers of variably granitic to gabbroic composition. These gneisses are intercalated with the metasediments as sheets with a maximum strike length of up to 40 km, in the case of the Haukenes gneiss in the Bergen area. Two main groups of gneisses can be distinguished; a) rocks formed at ca. 1495 Ma, 1212 Ma, and 1094 Ma, respectively and b) felsic to mafic meta-intrusives formed in the Early Ordovician between 486 and 474 Ma. In the Samnanger Complex the mélange was truncated by little deformed minor granitoid intrusives at 420 Ma. We propose a Baltican origin for the Mesoproterozoic gneisses. This also implies that the mélange has an affinity with Baltica as is also suggested by its tectonostratigraphic position below the Jotun, Lindås and Upper Bergsdalen Nappe complexes.

  9. 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.

  10. 30 CFR 75.1731 - Maintenance of belt conveyors and belt conveyor entries.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Maintenance of belt conveyors and belt conveyor entries. 75.1731 Section 75.1731 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Miscellaneous § 75.1731 Maintenance of belt conveyors...

  11. 30 CFR 75.1731 - Maintenance of belt conveyors and belt conveyor entries.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Maintenance of belt conveyors and belt conveyor entries. 75.1731 Section 75.1731 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Miscellaneous § 75.1731 Maintenance of belt conveyors...

  12. Timing of Deformation in the Central Metasedimentary Belt Boundary Thrust Zone (CMBbtz), southern Ontario, Canada, from Electron Microprobe Dating of Monazite

    NASA Astrophysics Data System (ADS)

    Markley, M. J.; Dunn, S. R.; Peck, W. H.; Jercinovic, M. J.; Williams, M. L.

    2015-12-01

    In the Grenville Province of Southern Ontario, the Central Metasedimentary Belt boundary thrust zone (CMBbtz) is a crustal-scale tectonic boundary between the older, granulite-facies Central Gneiss Belt to the NW and the younger, amphibolite-facies Central Metasedimentary Belt to the SE. Although there are a range of tectonic models for the CMBbtz, most workers agree it is a major tectonic boundary that accommodated ductile thrusting and crustal shortening during the Ottawan phase of the Grenville Orogeny (~1080-1020 Ma). Some studies suggest that ductile thrusting in the CMBbtz was roughly synchronous with synorogenic extensional collapse below an orogenic lid. Previous geochronological studies also provide evidence of earlier deformation and/or metamorphic events in the CMBbtz, although the relation between deformation in the CMBbtz to the Elzeviran (~1230 Ma) and Shawinigan (~1180 Ma) orogenies is unclear. Our study is the first to report in situ electron microprobe monazite (mnz) dates from amphibolite-grade ortho- and para-gneisses of the CMBbtz. Our results are broadly consistent with other chronometers. We present dates from 132 age-domains within 83 mnz grains in 14 samples. Although our data provide strong evidence for deformation and metamorphism along the length of the CMBbtz during the Ottawan (1080-1020 Ma), we also report two other clusters of ages: 1140-1110 Ma and 1230-1170 Ma. The latter cluster falls between the widely accepted ranges for the Elzeviran and Shawinigan orogenies. In addition, some individual outcrops, particularly those in Killaloe and Minden, show mnz ages spanning over 200 m.y., and the setting and compositions of individual monazite domains allow us to link mnz growth to episodes of garnet growth during multiple events. Together these data indicate an unexpectedly continuous and long-lived period of deformation and metamorphism in the CMBbtz.

  13. Numerical experiments on the role of buoyancy and rheology during the formation of extension-driven gneiss domes

    NASA Astrophysics Data System (ADS)

    Korchinski, Megan; Rey, Patrice; Teyssier, Christian; Whitney, Donna; Mondy, Luke

    2016-04-01

    Domal structures that are cored with crystallized partially melted crustal rocks are ubiquitous features in active and exhumed orogens. The exposure of these gneiss/migmatite domes at the Earth's surface represents an opportunity to study the mechanisms of flow within the deep crust, and the mode of emplacement of high-pressure rocks into the shallow crust. End-member gneiss dome types include (1) extension-driven domes that core metamorphic core complexes, and (2) buoyancy-driven domes that are exhumed by diapiric flow. Numerical models are ideally suited to test the relative roles of buoyancy and extension-driven mechanisms in dome dynamics, and therefore to explore the interaction of physical parameters involved in doming. To that end, this research utilizes a 2D visco-plastic thermomechanical modeling framework to undertake a parametric numerical experiment where the density (range of 2700-3100 kg.m3) and viscosity (range of 1E19-1E21 Pa.s) of the lower crust are systematically varied. The style and timing of "intrusion" of partially molten lower crust into non-molten lower crust is similar for densities of 2700-3100 kg.m3 across two lower crustal viscosities tested here (1E19 Pa.s, 1E21 Pa.s). However, dome development and upwards flow of lower crust material for a relatively high-density, middle-viscosity lower crust (2900-3100 kg.m^3; 1E20 Pa.s) involves a significant upward translation of the Moho, relative to the low-density, middle-viscosity model results. In addition, the high-density, middle-viscosity model shows a decrease in the volume of partial melt in the lower crust, and distributed brittle faulting in the upper crust. Thus, this experiment suite illustrates that variations in density and viscosity of the lower crust influence (1) faults distribution in the upper crust, (2) flow patterns within the lower crust, (3) upward translation of the solidus into the lower crust, and (4) upward displacement of the Moho. The style of extension within the

  14. High-velocity Frictional Behavior of Dunite, Biotite Gneiss, Phyllite and Coal Show Evidence for Melting and Thermal Degasing

    NASA Astrophysics Data System (ADS)

    O'Hara, K. D.; Mizoguchi, K.; Shimamoto, T.

    2004-12-01

    We conducted high-velocity frictional experiments on dunite, biotite gneiss, phyllite gouge and coal gouge at Kyoto University using a rotary high-velocity frictional testing machine. The purpose was to examine the effect of frictional melting in various rock types and to explore the effect of thermal degassing using coal as an analogue for a volatile fault zone. Experiments were conducted dry at equivalent slip rates of 1 m/s (1200 rpm) at normal stresses of 0.6-16 MPa for distances up to 90 m. Solid cylinders (25 mm diameter) of dunite and biotite gneiss were sheared with aluminum-alloy jackets at high stress, whereas phyllite and coal gouges were sheared with Teflon sleeves at low stress. The metal jackets allow high stress experiments to be performed and are inferred to melt before rock melting occurs. Dunite sheared at 10-16 MPa shows a weakening-strengthening followed by second weakening on melting, similar to previous experiments on gabbro without a metal jacket. Dunite melting is confirmed by, as yet unidentified, dendritic microlites, and a rapid reduction of steady-state frictional strength to 0.15. Under similar conditions, biotite gneiss shows apparent melting, but undergoes continuous strengthening without reaching steady state. Bituminous coal gouge sheared at 0.6 MPa undergoes a highly reproducible rapid weakening from 0.75 to 0.2, with odorous white gas emissions, sometimes accompanied by liquid hydrocarbons. Shear stress decreases prior to gasification and rapidly oscillating sample shortening/elongation occurs during gas emission. A slowly sheared sample (15 rpm) did not show weakening or gas emission. This is the first experimental demonstration of weakening associated with devolatilization during rapid slip. Vitrinite reflectance measurements on sheared coal samples may provide constraints on the temperature during gasification. Phyllite gouge sheared under the same conditions shows a gradual weakening to a steady-state strength of about 0

  15. The Kuiper Belt Recovery Program

    NASA Astrophysics Data System (ADS)

    Parker, Joel; Allen, Lynne; Gladman, Brett; Hergenrother, Carl; Kavelaars, J. J.

    2002-08-01

    The number of known Kuiper belt objects continues to increase each year, and the rate will soon accelerate significantly due to new and continuing wide-field projects dedicated to the discovery of these outer solar system bodies. A focused program dedicated to the recovery of these objects is necessary if the considerable effort and observing time spent on the discoveries are to have any long-term scientific significance. Our project explicitly addresses that need by providing reliable recovery observations (integrated with a CFHT survey we are conducting) at sufficient frequency to keep pace with the discoveries that need follow-up, as well as to provide photometric data for use in analysis of Kuiper belt physical properties such as size distribution, dynamics, formation, and structure. This NOAO proposal requests two KPNO observing runs at the end of semester 2002B to continue our successful recovery project. Our measurements will assure that the calculated orbits are determined well enough for future photometric and spectroscopic observations for physical studies. We have an efficient and proven pipeline to: find objects, provide sub- arcsecond absolute astrometry and calibrated photometry, determine orbits, and report results to the Minor Planet Center to refine the orbital elements.

  16. The Kuiper Belt Recovery Program

    NASA Astrophysics Data System (ADS)

    Parker, Joel; Allen, Lynne; Gladman, Brett; Grav, Tommy; Hergenrother, Carl; Holman, Matthew; Kavelaars, J. J.

    2002-02-01

    The number of known Kuiper belt related objects is increasing at an accelerated rate due to many wide-field projects dedicated to the discovery of these outer solar system bodies. A focused and dedicated recovery program is necessary and urgent if the considerable effort and observing time spent on the discoveries are to have any long-term scientific significance. This project (integrated with a CFHT survey we are conducting) will address that need by providing reliable recovery observations at sufficient frequency to keep pace with the discoveries that need follow-up, as well as to provide photometric data for use in analysis of Kuiper belt physical properties such as size distribution, dynamics, formation, and structure. Our measurements will assure that the calculated orbits are determined well enough for future photometric and spectroscopic observations for physical studies. We have an efficient and proven pipeline to: find objects, provide sub-arcsecond absolute astrometry and calibrated photometry, determine orbits, and report results to the Minor Planet Center to refine the orbital elements.

  17. Radiation Belt Analysis and Modeling

    NASA Astrophysics Data System (ADS)

    Bass, J. N.; Dasgupta, U.; Hein, C. A.; Griffin, J. M.; Reynolds, D. S.

    1995-04-01

    Efforts have been conducted in modeling of radiation belts, and cosmic radiation, principally in connection with the CRRES mission. Statistical studies of solar particle events have been conducted in a search for predictors of the occurrence of geomagnetic storms. Certain spectral and temporal properties of protons and electrons were found to correlate with the occurrence of storms. Comparative studies of solar proton fluxes observed at locations inside (using CRRES and GOES-7) and outside (using INP-8) the inner magnetosphere were performed in an attempt to measure penetration of solar protons to various L shells as functions of time during a proton event and the subsequent magnetic storm. The failure to observe large increases in proton fluxes at the sudden commencement of the great magnetic storm of March, 1991, indicates a magnetospheric process was involved. An attempt was made to model the acceleration of radiation belt protons by magnetospheric compression during this event. The access of Helium into the inner magnetosphere was studied during this event. Modeling of instrument contamination and dosage were performed to enhance interpretation of measurements by the Proton Telescope and the Space Radiation Dosimeter. Support software packages developed include a science summary data base, a data processing system for the microelectronics package, and software to analyze measurements by the Low Energy Plasma Analyzer to produce a three dimensional plasma distribution function.

  18. 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.

  19. Weak Turbulence in Radiation Belts

    NASA Astrophysics Data System (ADS)

    Ganguli, G.; Crabtree, C. E.; Rudakov, L.

    2015-12-01

    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.

  20. Neoproterozoic ophiolite and related high-grade rocks of the Baikal-Muya belt, Siberia: Geochronology and geodynamic implications

    NASA Astrophysics Data System (ADS)

    Kröner, A.; Fedotova, A. A.; Khain, E. V.; Razumovskiy, A. A.; Orlova, A. V.; Anosova, M. O.; Perelyaev, V. I.; Nekrasov, G. E.; Liu, D. Y.

    2015-11-01

    We report zircon for from ophiolitic and high-grade rocks of the Neoproterozoic Baikal-Muya belt of Siberia that occupies an arc-shaped area on the southeastern margin of the Siberian craton. It consists of arc-related plutonic, metavolcanic and metasedimentary rocks as well as fragmented ophiolites and high-grade metamorphic assemblages. Magmatic zircons from two plagiogranite dyke samples of the Mamakan ophiolite complex in the Sredne-Mamakan massif of the eastern Baikal-Muya belt yielded similar and concordant SHRIMP mean 206Pb/238U ages of 640.0 ± 4.1 and 650 ± 6 Ma, respectively, that reflect the time of dyke emplacement and from which we suggest an age of ca. 645 Ma as the most likely time of ophiolite formation. Enderbitic gneisses of the North Baikal area, in the western part of the Baikal-Muya belt, contain complex zircon populations that reflect variable recrystallization, Pb-loss and metamorphic overgrowth during granulite-facies metamorphism. LA-ICP-MS dating of these zircons yielded inconclusive results that led us to undertake a detailed study of cathodoluminescence images combined with U-Pb SHRIMP dating. Well-preserved magmatic domains in zircons from enderbite sample 2821 yielded concordant results with a mean 206Pb/238U age of 640 ± 5 Ma, slightly higher but broadly comparable with the data obtained by LA-ICP-MS. The zircon populations of two more enderbitic gneiss samples are more complex, and their LA-ICP-MS data constitute broad swaths along concordia between ca. 840 and 600 Ma, reflecting two end-member isotopic components, namely an igneous crystallization event at ca. 800 Ma and a Pb-loss and recrystallization event at ca. 600 Ma. SHRIMP analyses of magmatic zircon domains of these samples yielded concordant data with identical mean 206Pb/238U ages of 826 ± 7.5 Ma and 826 ± 8 Ma, respectively, whereas low-U metamorphic rims crystallized at 640 ± 7 Ma. Newly crystallized ball-round metamorphic zircons in one sample produced a mean 206Pb

  1. 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

  2. Structural ensembles of the north belt of Venus deformations and possible mechanisms of their formation

    NASA Technical Reports Server (NTRS)

    Markov, M. S.

    1986-01-01

    The author discusses structural formations in the northern deformation belt of Venus, studied according to the data of the radar pictures obtained with the Venera 15 and 16 probes. He shows that it consists of regions of compression with submeridional orientation, regions of displacement, extending in the sublatitudinal direction and individual slightly deformed blocks. He puts forward the hypothesis that the formation of these structures is related with horizontal movements in the mantle in the sublatitudinal direction.

  3. 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...

  4. 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...

  5. 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...

  6. 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...

  7. 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...

  8. 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...

  9. 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...

  10. 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...

  11. 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...

  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. 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...

  14. 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...

  15. 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...

  16. 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...

  17. 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)

  18. Seat belt use and stress in adolescents.

    PubMed

    Schichor, A; Beck, A; Bernstein, B; Crabtree, B

    1990-01-01

    This study explored the association of adolescent seat belt use with psychosocial risk factors in an urban minority population after the enactment of a mandatory seat belt law. Data on seat belt use, family support, feelings of being down, suicidal ideation, substance abuse, sexual activity, school troubles, and problems with the law were obtained from 541 self-report intake forms administered to an adolescent medicine clinic population from 1986 to 1987. Respondents were almost exclusively black and Hispanic; 315 (59%) were females and 222 (41%) males, with a mean age of 15.4. Seat belt use was reported by 249 (46%) and no or intermittent use by 292 (54%). Chi-square and Wilcoxon rank sums tests were used to examine associations between seat belt use and risk factors. Results showed that the group comprised of those reporting no and intermittent seat belt use was significantly more likely to feel down, have decreased home support, have problems with school and the law, have been on probation, and feel that life in general was not going very well. No association was found between seat belt use and cigarette, drug, or alcohol use or sexual activity without contraceptives. Taking into account the lack of observed behavioral information to validate such self-report questionnaires, these data nevertheless point to the nonuse or intermittent use of seat belts as a possible manifestation of a lack of self-care due to feeling down and/or preoccupation with family, school, or societal problems. PMID:2275431

  19. 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…

  20. 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...

  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. Tensioning of a belt around a drum using membrane element

    NASA Technical Reports Server (NTRS)

    Chen, C. H. S.

    1980-01-01

    An application of the membrane element to the problem of the tensioning of a conveyer belt which wraps around a drum is presented. Two cases were investigated: (1) belt tension increase due to drum edge wear; and (2) material trapped between the drum and the belt. In both cases it was found that the increase in belt tension was due to the additional stretching of the belt resulting from the drum radius change rather than from the transverse deflection of the belt.

  3. Precambrian coal or anthraxolite: A source for graphite in high-grade schists and gneisses-a discussion

    SciTech Connect

    Douthitt, C.B.

    1982-08-01

    Presents histograms of carbon-isotope analyses of anthraxolite and organic carbon in Precambrian sedimentary rocks, graphite in noncalcareous Precambrian schists and gneisses, and vein graphites from Ceylon, Montana, and New Hampshire. Shows that vein graphites constitute a fairly homogeneous population and are substantially heavier than Precambrian organic carbon, especially anthraxolites. Concludes that carbon in vein graphite is not derived from organic matter unless an ad hoc step of equilibrium with an isotopically heavy carbon reservoir is invoked. Rules out the lateral migration hypothesis proposed for the origin of graphite veins in Ceylon. Suggests that the carbon source for vein graphites is either magmatic carbon or carbonate carbon; the absence of carbonates in the exposed sections in both Ceylon and New Hampshire suggests that magmatic, rather than carbonate, carbon is the source.

  4. New U/Pb ages from granite and granite gneiss in the Ruby geanticline and southern Brooks Range, Alaska ( USA).

    USGS Publications Warehouse

    Patton, W.W.; Stern, T.W.; Arth, Joseph G.; Carlson, C.

    1987-01-01

    New U/Pb zircon ages from the Ray Mountains of central Alaska clarify the plutonic history of the Ruby geanticline and support earlier suggestions that the Ruby geanticline and S Brooks Range were once parts of the same tectonostratigraphic terrane. U/Pb zircon ages of 109 to 112 Ma from the Ray Mountains pluton confirm previously reported mid-Cretaceous K/Ar ages and rule out the possibility that the earliest intrusive phase of the pluton is older than mid-Cretaceous K/Ar ages and rule out the possibility that the earliest intrusive phase of the pluton is older than mid- Cretaceous. New U/Pb zircon ages from 4 granite gneiss samples in the Ray Mountains indicate a Devonian protolith age of 390+ or -12 Ma and suggest that the Ruby geanticline, like the S Brooks Range, underwent a major plutonic event in mid-Paleozoic time.-Authors

  5. Geochemical characteristics of charnockite and high grade gneisses from Southern Peninsular Shield and their significance in crustal evolution

    NASA Astrophysics Data System (ADS)

    Sugavanam, E. B.; Vidyadharan, K. T.

    Presented here are the results of detailed investigations encompassing externsive structural mapping in the charnockite-high grade gneiss terrain of North Arcot district and the type area in Pallavaram in Tamil Nadu supported by petrography, mineral chemistry, major, minor and REE distribution patterns in various lithounits. This has helped in understanding the evolutionary history of the southern peninsular shield. A possible tectonic model is also suggested. The results of these studies are compared with similar rock types from parts of Andhra Pradesh, Kerala, Sri Lanka, Lapland and Nigeria which has brought about a well defined correlation in geochemical characteristics. The area investigated has an interbanded sequence of thick pile of charnockite and a supracrustal succession of shelf type sediments, layered igneous complex, basic and ultrabasic rocks involved in a complex structural, tectonic, igneous and metamorphic events.

  6. U-Pb ID-TIMS zircon ages of TTG gneisses of the Aravalli Craton of India

    NASA Astrophysics Data System (ADS)

    Chauhan, Hiredya; Saikia, Ashima; Kaulina, Tatiana; Bayanova, Tamara; Ahmad, Talat

    2015-04-01

    The crystalline basement of the Aravalli Craton is a heterogeneous assemblage dominated by granitic gneisses and granites with sporadic occurrences of amphibolites and dismembered sedimentary enclaves (Upadhyaya et al., 1992). This assemblage is known to have experienced multiple deformation and metamorphic events followed by emplacement of voluminous granites and basaltic dykes. Based on Sm-Nd whole rock data on the basement Mewar orthogneisses of Jhamarkotra region (Gopalan et al., 1990) and Pb/Pb ages of zircon from Gingla Granites which intrudes the basement (Wiedenbeck et al., 1996), it has been inferred that the whole magmatic episode leading to the formation of the basement spanned from 3300 to 2400 Ma and that the Aravalli cratonic block had broadly stabilized by 2500 Ma on which the younger Aravalli and Delhi Supergroup unconformably deposited. However, no comprehensive age data on the basement gneisses from the study area spanning the entire magmatic episode is available. This work attempts to provide a time frame work for evolution of the basement gneisses of the Aravalli Craton. We present here U-Pb zircon ages from the Precambrian basement TTG gneisses of the Aravalli Craton of north western India. Pb and U were measured on multicollector Finnigan-MAT 262 mass spectrometer. The temperatures of measurements were 1300°C for Pb and 1500°C for U. Pb isotope ratios were corrected for mass fractionation with a factor of 0.10% per amu, based on repeat analyses of the standard NBS SRM 982. The U analyses were corrected for mass fractionation with a factor of 0.003% per amu, based on repeat analyses of the NBS U 500 standard. Reproducibility of the U-Pb ratios was determined from the repeated analysis of standard zircon IGFM-87 (Ukraine) and taken as 0.5% for 207Pb/235U and 206Pb/238U ratios, respectively, at 95% confidence level. All calculations were done using the programs PBDAT and ISOPLOT (Ludwig 1991, 2008). Four zircon fractions corresponding to four

  7. Geochemical characteristics of charnockite and high grade gneisses from Southern Peninsular Shield and their significance in crustal evolution

    NASA Technical Reports Server (NTRS)

    Sugavanam, E. B.; Vidyadharan, K. T.

    1988-01-01

    Presented here are the results of detailed investigations encompassing externsive structural mapping in the charnockite-high grade gneiss terrain of North Arcot district and the type area in Pallavaram in Tamil Nadu supported by petrography, mineral chemistry, major, minor and REE distribution patterns in various lithounits. This has helped in understanding the evolutionary history of the southern peninsular shield. A possible tectonic model is also suggested. The results of these studies are compared with similar rock types from parts of Andhra Pradesh, Kerala, Sri Lanka, Lapland and Nigeria which has brought about a well defined correlation in geochemical characteristics. The area investigated has an interbanded sequence of thick pile of charnockite and a supracrustal succession of shelf type sediments, layered igneous complex, basic and ultrabasic rocks involved in a complex structural, tectonic, igneous and metamorphic events.

  8. Cable Belt Conveyors in mine haulage

    SciTech Connect

    Brown, D.E.

    1983-06-01

    The Cable Belt is not a conveyor in the conventional sense, but rather a continuous bulk handling system. It is custom built for the application. It may come as a surprise to some people to learn that the Cable Belt system is not new, having been invented in the requirements at that time for long-haul, high-lift, single-flight, heavy duty applications, primarily in the coal mining industry. In those days, belt conveyors of 200 HP were regarded as heavy duty units; it was therefore inevitable that, as mining progressed into the next decade and the demand for minerals increased, technology also had to keep pace to fulfill the industries' needs. With the simplicity of the Cable Belt design, this was achieved, a position which today is maintained by Cable Belt as leaders in long-distance, single-flight, single-drive conveyor applications.

  9. 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.

  10. The behaviour of monazite from greenschist facies phyllites to anatectic gneisses: An example from the Chugach Metamorphic Complex, southern Alaska

    PubMed Central

    Gasser, Deta; Bruand, Emilie; Rubatto, Daniela; Stüwe, Kurt

    2012-01-01

    Monazite is a common accessory mineral in various metamorphic and magmatic rocks, and is widely used for U–Pb geochronology. However, linking monazite U–Pb ages with the PT evolution of the rock is not always straightforward. We investigated the behaviour of monazite in a metasedimentary sequence ranging from greenschist facies phyllites into upper amphibolites facies anatectic gneisses, which is exposed in the Eocene Chugach Metamorphic Complex of southern Alaska. We investigated textures, chemical compositions and U–Pb dates of monazite grains in samples of differing bulk rock composition and metamorphic grade, with particular focus on the relationship between monazite and other REE-bearing minerals such as allanite and xenotime. In the greenschist facies phyllites, detrital and metamorphic allanite is present, whereas monazite is absent. In lower amphibolites facies schists (~ 550–650 °C and ≥ 3.4 kbar), small, medium-Y monazite is wide-spread (Mnz1), indicating monazite growth prior and/or simultaneous with growth of garnet and andalusite. In anatectic gneisses, new low-Y, high-Th monazite (Mnz2) crystallised from partial melts, and a third, high-Y, low-Th monazite generation (Mnz3) formed during initial cooling and garnet resorption. U–Pb SHRIMP analysis of the second and third monazite generations yields ages of ~ 55–50 Ma. Monazite became unstable and was overgrown by allanite and/or allanite/epidote/apatite coronas within retrograde muscovite- and/or chlorite-bearing shear zones. This study documents polyphase, complex monazite growth and dissolution during a single, relatively short-lived metamorphic cycle. PMID:26525358

  11. 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.

  12. Collisions in the Kuiper belt

    NASA Astrophysics Data System (ADS)

    Brown, Michael

    2007-07-01

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

  13. SHRIMP U-Pb age and high temperature conditions of the collisional metamorphism in the Várzea do Capivarita Complex: Implications for the origin of Pelotas Batholith, Dom Feliciano Belt, southern Brazil

    NASA Astrophysics Data System (ADS)

    Philipp, Ruy Paulo; Bom, Francisco Molina; Pimentel, Márcio Martins; Junges, Sérgio Luiz; Zvirtes, Gustavo

    2016-03-01

    The Várzea do Capivarita Complex is composed of pelitic gneisses with subordinate calc-silicate rock, marble and rare quartzite. It is part of the neoproterozoic Dom Feliciano Belt, in southern Brazil. The gneisses are associated to veins and tabular leucogranite bodies, which are the product of anatexis of the pelitic gneiss. The paragneisses of the Várzea do Capivarita Complex are tectonically juxtaposed to orthogneisses of the Arroio dos Ratos Complex. This complex is exposed as megaxenoliths in granites of the Encruzilhada do Sul Suite and as smaller fragments in the Quitéria and Cordilheira Granites, all part of the Pelotas Batholith. The metamorphic foliation is oriented to N30°W, with dips between 35 and 55° to the SW and mineral lineation is suborizontal with rake ranging from 15° to 30° and down dip to NW and SE, suggesting deformation associated with a transpressive system. Based on the paragenesis garnet-cordierite-sillimanite-biotite, metamorphism occurred at 720-820° C and pressure of 8-9 kbar, characterizing it as of intermediate pressure and high temperature series. Zircon grains of one sample of garnet-cordierite-sillimanite-biotite gneiss and one of peraluminous leucogranite was dated by the U-Pb SHRIMP method. The paragneiss metamorphic zircon yielded an age of 619 ± 4.3 Ma interpreted as an age of the main metamorphic event, whereas igneous zircon grains from the leucogranite indicates that magma crystallization took place at 620 ± 6.3 Ma. The main metamorphic foliation (S2) of the paragneiss and the leucogranite magmatic foliation (S0) are parallel to each other, indicating that they were formed during the same event. This suggests that anatexis of the paragneisses of the Várzea do Capivarite Complex generated the peraluminous leucogranites right after the climax of the collisional metamorphism.

  14. Northern Nutrition.

    ERIC Educational Resources Information Center

    Northwest Territories Dept. of Education, Yellowknife.

    This guide contains nutrition information and nutrition education strategies aimed at residents of the Canadian Arctic. Section I: (1) defines nutrition terms; (2) describes the sources and functions of essential nutrients; (3) explains Canada's food guide and special considerations for the traditional northern Native diet and for lactose…

  15. Lead-isotope study of the sulphide ore and alteration zone, Bleikvassli zinc-lead deposit, northern Norway

    NASA Astrophysics Data System (ADS)

    Skauli, H.; Bjørlykke, A.; Thorpe, R. I.

    1992-09-01

    The Bleikvassli Zn-Pb deposit is located in the Uppermost Allochthon of the northern Norwegian Caledonides and is enclosed in amphibolite facies, multiply deformed supracrustal rocks. The stratiform orebody occurs stratigraphically above a sequence of gneiss and amphibolite and below a thick carbonate unit. The orebody, spatially associated with a footwall microcline gneiss that contains as much as 12wt‰ K2O, occurs in the lower part of the Mine Sequence which also comprises (kyanite-) mica schist and quartzo-feldspathic to siliceous rocks. The host rock lithology and the metal content of the Bleikvassli orebody are consistent with a SEDEX origin of the deposit. Field relationships and chemistry suggest that the microcline gneiss represents a potassic alteration of pelitic sediments related to the ore-forming process. A 464 ± 22 Ma Rb-Sr isochron for the microcline gneiss is interpreted to be a metamorphic age resulting from resetting of the Rb-Sr isotopic system during the Caledonian orogeny. The U-Pb in the whole rock shows evidence of recent mobilization of uranium and a partial or total resetting of the system during peak metamorphism. As with most SEDEX deposits, the lead isotope composition of the Bleikvassli ore plots close to the orogen growth curve. The geological setting of the ore and the lead — isotope compositions of the galenas indicate a Cambrian age of mineralization. However, the slope of the lead isotope data indicate an age of about 1000 Ma, which is also a maximum age of ore deposition. The lead isotope data for the galena, in conjunction with the compositions of the microcline gneiss during peak metamorphism, support a model whereby the microcline rock was formed as an alteration product by the ore forming fluid and the initial lead isotope composition of the microcline rock was similar to that of the galenas during ore deposition.

  16. Hydrocarbon potential of Altiplano and northern Subandean, Bolivia

    SciTech Connect

    Edman, J.D.; Kirkpatrick, J.R.; Lindsey, D.D.; Lowell, J.D.; Cirbian, M.; Lopez, M.

    1989-03-01

    Seismic, stratigraphic, structural, and geochemical data from the Altiplano, northern Subandean, and northern plains of Bolivia were interpreted in order to evaluate the exploration potential of each province. Identification of three possible source rock intervals, primarily the Devonian and secondarily the Permian and Cretaceous, was used as the basis for recognizing active hydrocarbon systems. For those areas containing source intervals, their analysis revealed that possible reservoir and seal units range in age from Paleozoic to Tertiary; the majority of structures, however, are Eocene or younger. With these general concepts in mind, traps were identified in all three sedimentary provinces. In the northern Altiplano, the most prospective area is along the eastern margin near a southwest and west-vergent thrust belt where hanging-wall anticlines and a warped Eocene-Oligocene(.) unconformity surface form the most likely potential traps. In the central and southern Altiplano, both thrust-related and wrench-related structures present possible exploration targets. In the northern Subandean and Beni plains north of the Isiboro-Chapare area, traps can be classified into two broad groups. First, there are a wide variety of structural traps within the northern Subandean thrust belt, the most attractive of which are footwall structures that have been shielded from surface flushing by hanging-wall strata. Second, in the plains just northeast of the thrust belt, hydrocarbons sourced from the remnant Paleozoic basin may have migrated onto the Isarsama and Madidi highs.

  17. Thermobarometry in the Hadean: The Nuvvuagittuq Greenstone Belt

    NASA Astrophysics Data System (ADS)

    Scher, S.; Minarik, W.

    2009-05-01

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

  18. 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.

  19. 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.

  20. The inaccessibility of seat belts in taxicabs.

    PubMed Central

    Davis, R M

    1989-01-01

    The accessibility of seat belts was determined in a total sample of 200 taxicabs waiting to pick up passengers at eight city airports. A rear seat belt was "accessible" (able to be fastened within 10 seconds) in 111 (55.5 per cent) taxicabs. The proportion varied by city from 16.0 per cent (New York City) to 96.0 per cent (Minneapolis-St. Paul) and was higher for taxicabs in cities covered by mandatory state seat belt legislation. PMID:2916721

  1. 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.

  2. Timing of middle Paleozoic (Acadian) metamorphism in the southern Appalachians: K-Ar studies in the Talladega belt, Alabama

    SciTech Connect

    Kish, S.A. )

    1990-07-01

    The Talladega belt of Alabama and Georgia is located at the southernmost exposed part of the southern Appalachian orogen and is one of the westernmost metamorphic terranes in this part of the orogen. The presence of the Lower Devonian Jemison Chert of the Talladega Group provides a maximum age for the timing of greenschist facies metamorphism and penetrative slaty cleavage formation in this terrane. Six slate collected form upper Precambrian( )-Lower Cambrian, and Silurian( )-Devonian rocks of the Talladega belt have an average K-Ar age of 399 {plus minus} 17 Ma. This age is interpreted to be the approximate time of regional greenschist facies metamorphism. The timing of metamorphism in the Talladega belt is similar to the age of the Acadian orogeny in the Maritime and northern Appalachians. Unlike the accreted nature of the Acadian terranes in the northern Appalachians, the Talladega belt appears to have been part of the early to middle Paleozoic cratonic margin of North America. The results of this study indicate that Acadian dynamothermal events extended into parts of the Laurentian margin in the southern Appalachians. Paleozoic igneous activity in the southern Appalachians was less extensive compared with the voluminous Acadian plutonism of the northern Appalachians; however, synkinematic to postkinematic Devonian plutons are present in the central and western parts of the orogen.

  3. 30 CFR 56.4503 - Conveyor belt slippage.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 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...

  4. 30 CFR 56.4503 - Conveyor belt slippage.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 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...

  5. 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...

  6. Testing steel-cord belt splices with a magnetic conveyor belt monitor

    SciTech Connect

    Harrison, A.

    1985-03-01

    Steel-cord belt splices fail for a variety of reasons, including corrosion, poor vulcanising, and incorrect construction. The latter often leads to early failure. A conveyor belt monitor (CBM) has been used to evaluate the splice lay-up. The mass of the overlapping cords and their magnetic signature are used to rapidly locate suspect splices in the belt. The general shape of the magnetic signature for ideal splices will be discussed.

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

    NASA Astrophysics Data System (ADS)

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

    2011-08-01

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

  8. Extrusional Tectonics over Plate Corner: an Example in Northern Taiwan

    NASA Astrophysics Data System (ADS)

    Lu, Chia-Yu; Lee, Jian-Cheng; Li, Zhinuo; Lee, Ching-An; Yeh, Chia-Hung

    2016-04-01

    In northern Taiwan, contraction, transcurrent shearing, block rotation and extension are four essential tectonic deformation mechanisms involved in the progressive deformation of this arcuate collision mountain belt. The neotectonic evolution of the Taiwan mountain belt is mainly controlled not only by the oblique convergence between the Eurasian plate and the Philippine Sea plate but also the corner shape of the plate boundary. Based on field observations and analyses, and taking geophysical data (mostly GPS) and experimental modelling into account, we interpret the curved belt of northern Taiwan as a result of of contractional deformation (with compression, thrust-sheet stacking & folding, back thrust duplex & back folding) that induced vertical extrusion, combined with increasing transcurrent & rotational deformation (with transcurrent faulting, bookshelf-type strike-slip faulting and block rotation) that induced transcurrent/rotational extrusion and extension deformation which in turn induced extensional extrusion. As a consequence, a special type of extrusional folds was formed in association with contractional, transcurrent & rotational and extensional extrusions subsequently. The extrusional tectonics in northern Taiwan reflect a single, albeit complicated, regional pattern of deformation. The crescent-shaped mountain belt of Northeastern Taiwan develops in response to oblique indentation by an asymmetric wedge indenter, retreat of Ryukyu trench and opening of the Okinawa trough.

  9. Extrusional Tectonics at Plate Corner: an Example in Northern Taiwan

    NASA Astrophysics Data System (ADS)

    Lu, C. Y.; Lee, J. C.; Li, Z.; Yeh, C. H.; Lee, C. A.

    2015-12-01

    In northern Taiwan, contraction, transcurrent shearing, block rotation and extension are four essential tectonic deformation mechanisms involved in the progressive deformation of this arcuate collision mountain belt. The neotectonic evolution of the Taiwan mountain belt is mainly controlled not only by the oblique convergence between the Eurasian plate and the Philippine Sea plate but also the corner shape of the plate boundary. Based on field observations and analyses, and taking geophysical data (mostly GPS) and experimental modelling into account, we interpret the curved belt of northern Taiwan as a result of of contractional deformation (with compression, thrust-sheet stacking & folding, back thrust duplex & back folding) that induced vertical extrusion, combined with increasing transcurrent & rotational deformation (with transcurrent faulting, bookshelf-type strike-slip faulting and block rotation) that induced transcurrent/rotational extrusion and extension deformation which in turn induced extensional extrusion. As a consequence, a special type of extrusional folds was formed in association with contractional, transcurrent & rotational and extensional extrusions subsequently. The extrusional tectonics in northern Taiwan reflect a single, albeit complicated, regional pattern of deformation. The crescent-shaped mountain belt of Northeastern Taiwan develops in response to oblique indentation by an asymmetric wedge indenter and opening of the Okinawa trough at plate corner.

  10. The basement of the Mount Athos peninsula, northern Greece: insights from geochemistry and zircon ages

    NASA Astrophysics Data System (ADS)

    Himmerkus, F.; Zachariadis, P.; Reischmann, T.; Kostopoulos, D.

    2012-09-01

    The Mount Athos Peninsula is situated in the south-easternmost part of the Chalkidiki Peninsula in northern Greece. It belongs to the Serbo-Macedonian Massif (SMM), a large basement massif within the Internal Hellenides. The south-eastern part of the Mount Athos peninsula is built by fine-grained banded biotite gneisses and migmatites forming a domal structure. The southern tip of the peninsula, which also comprises Mount Athos itself, is built by limestone, marble and low-grade metamorphic rocks of the Chortiatis Unit. The northern part and the majority of the western shore of the Mount Athos peninsula are composed of highly deformed rocks belonging to a tectonic mélange termed the Athos-Volvi-Suture Zone (AVZ), which separates two major basement units: the Vertiskos Terrane in the west and the Kerdillion Unit in the east. The rock-types in this mélange range from metasediments, marbles and gneisses to amphibolites, eclogites and peridotites. The gneisses are tectonic slivers of the adjacent basement complexes. The mélange zone and the gneisses were intruded by granites (Ierissos, Ouranoupolis and Gregoriou). The Ouranoupolis intrusion obscures the contact between the mélange and the gneisses. The granites are only slightly deformed and therefore postdate the accretionary event that assembled the units and created the mélange. Pb-Pb- and U-Pb-SHRIMP-dating of igneous zircons of the gneisses and granites of the eastern Athos peninsula in conjunction with geochemical and isotopic analyses are used to put Athos into the context of a regional tectonic model. The ages form three clusters: The basement age is indicated by two samples that yielded Permo-Carboniferous U-Pb-ages of 292.6 ± 2.9 Ma and 299.4 ± 3.5 Ma. The main magmatic event of the granitoids now forming the gneiss dome is dated by Pb-Pb-ages between 140.0 ± 2.6 Ma and 155.7 ± 5.1 Ma with a mean of 144.7 ± 2.4 Ma. A within-error identical age of 146.6 ± 2.3 Ma was obtained by the U

  11. Congressional panel makes recommendations on belt safety

    SciTech Connect

    Fiscor, S.

    2007-12-15

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

  12. Equipment guide - stage loaders, conveyor belting, takeups

    SciTech Connect

    Not Available

    1982-12-01

    Tables provide mine operators with a general guide to stageloaders, conveyor belting, and takeups. This is not a complete list of the models available, nor of the US manufacturers that produce this equipment.

  13. Emission products from combustion of conveyor belts

    SciTech Connect

    Egan, M.R.

    1988-01-01

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

  14. Visualization of Radiation Belts from REPT Data

    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...

  15. Electron Flux of Radiation Belts Animation

    NASA Video Gallery

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

  16. New Mexico structural zone - An analogue of the Colorado mineral belt

    USGS Publications Warehouse

    Sims, P.K.; Stein, H.J.; Finn, C.A.

    2002-01-01

    Updated aeromagnetic maps of New Mexico together with current knowledge of the basement geology in the northern part of the state (Sangre de Cristo and Sandia-Manzano Mountains)-where basement rocks were exposed in Precambrian-cored uplifts-indicate that the northeast-trending Proterozoic shear zones that controlled localization of ore deposits in the Colorado mineral belt extend laterally into New Mexico. The shear zones in New Mexico coincide spatially with known epigenetic precious- and base-metal ore deposits; thus, the mineralized belts in the two states share a common inherited basement tectonic setting. Reactivation of the basement structures in Late Cretaceous-Eocene and Mid-Tertiary times provided zones of weakness for emplacement of magmas and conduits for ore-forming solutions. Ore deposits in the Colorado mineral belt are of both Late Cretaceous-Eocene and Mid-Tertiary age; those in New Mexico are predominantly Mid-Tertiary in age, but include Late Cretaceous porphyry-copper deposits in southwestern New Mexico. The mineralized belt in New Mexico, named the New Mexico structural zone, is 250-km wide. The northwest boundary is the Jemez subzone (or the approximately equivalent Globe belt), and the southeastern boundary was approximately marked by the Santa Rita belt. Three groups (subzones) of mineral deposits characterize the structural zone: (1) Mid-Tertiary porphyry molybdenite and alkaline-precious-metal deposits, in the northeast segment of the Jemez zone; (2) Mid-Tertiary epithermal precious-metal deposits in the Tijeras (intermediate) zone; and (3) Late Cretaceous porphyry-copper deposits in the Santa Rita zone. The structural zone was inferred to extend from New Mexico into adjacent Arizona. The structural zone provides favorable sites for exploration, particularly those parts of the Jemez subzone covered by Neogene volcanic and sedimentary rocks. ?? 2002 Published by Elsevier Science B.V.

  17. [Effects of human engineering activities on permafrost active layer and its environment in northern Qinghai-Tibetan plateau].

    PubMed

    Guo, Zhenggang; Wu, Qingbo; Niu, Fujun

    2006-11-01

    With disturbed and undisturbed belts during the construction of Qinghai-Tibet highway as test objectives, this paper studied the effects of human engineering activities on the permafrost ecosystem in northern Qinghai-Tibetan plateau. The results showed that the thickness of permafrost active layer was smaller in disturbed than in undisturbed belt, and decreased with increasing altitude in undisturbed belt while no definite pattern was observed in disturbed belt. Different vegetation types had different effects on the thickness of permafrost active layer, being decreased in the order of steppe > shrub > meadow. In the two belts, altitude was the main factor affecting the vertical distribution of soil moisture, but vegetation type was also an important affecting factor if the altitude was similar. Due to the human engineering activities, soil temperature in summer was lower in disturbed than in undisturbed belt.

  18. Structural analysis and implicit 3D modelling of high-grade host rocks to the Venetia kimberlite diatremes, Central Zone, Limpopo Belt, South Africa

    NASA Astrophysics Data System (ADS)

    Basson, I. J.; Creus, P. K.; Anthonissen, C. J.; Stoch, B.; Ekkerd, J.

    2016-05-01

    The Beit Bridge Complex of the Central Zone (CZ) of the Limpopo Belt hosts the 519 ± 6 Ma Venetia kimberlite diatremes. Deformed shelf- or platform-type supracrustal sequences include the Mount Dowe, Malala Drift and Gumbu Groups, comprising quartzofeldspathic units, biotite-bearing gneiss, quartzite, metapelite, metacalcsilicate and ortho- and para-amphibolite. Previous studies define tectonometamorphic events at 3.3-3.1 Ga, 2.7-2.5 Ga and 2.04 Ga. Detailed structural mapping over 10 years highlights four deformation events at Venetia. Rules-based implicit 3D modelling in Leapfrog Geo™ provides an unprecedented insight into CZ ductile deformation and sheath folding. D1 juxtaposed gneisses against metasediments. D2 produced a pervasive axial planar foliation (S2) to isoclinal F2 folds. Sheared lithological contacts and S2 were refolded into regional, open, predominantly southward-verging, E-W trending F3 folds. Intrusion of a hornblendite protolith occurred at high angles to incipient S2. Constrictional-prolate D4 shows moderately NE-plunging azimuths defined by elongated hornblendite lenses, andalusite crystals in metapelite, crenulations in fuchsitic quartzite and sheath folding. D4 overlaps with a: 1) 2.03-2.01 Ga regional M3 metamorphic overprint; b) transpressional deformation at 2.2-1.9 Ga and c) 2.03 Ga transpressional, dextral shearing and thrusting around the CZ and d) formation of the Avoca, Bellavue and Baklykraal sheath folds and parallel lineations.

  19. Gravity evidence for a mafic intrusion beneath a mineralized zone in the Bondy gneiss complex, Grenville Province, Quebec - Exploration implications

    NASA Astrophysics Data System (ADS)

    Dufréchou, Grégory; Harris, Lyal B.; Corriveau, Louise; Antonoff, Vladimir

    2011-09-01

    A ground gravity survey over the Bondy gneiss complex and its mineralized iron oxide- and copper-rich hydrothermal system(s) in the Grenville Province of SW Quebec was undertaken to aid mineral exploration in mapping subsurface intrusions. Several kilometric-scale positive Bouguer anomalies were identified that coincide with outcropping mafic and intermediate intrusive rocks of the post peak-metamorphic, 1.17-1.16 Ga mafic to intermediate Chevreuil suite intrusions and a 1.09-1.07 Ga Rolleau ultramafic stock. An additional 4 × 3 kilometre positive gravity anomaly indicates a mafic body underlies part of the metamorphosed hydrothermal system in the area of magnetite, pyrite, pyrrhotite, and chalcopyrite mineralization. Advanced argilic alteration associated with sulphide enrichment here is however indicative of an epithermal system with a felsic intrusion fluid source. As a felsic intrusion cannot explain the positive Bouguer gravity anomaly both felsic and mafic bodies must be present beneath the mineralized zone. Our preferred interpretation based on integrating gravity data and 2D forward gravity modelling with the results of field and geochemical studies is that this anomaly corresponds to a ca. 500 m deep mafic 1.17-1.16 Ga Chevreuil suite pluton that may have provided the source for hydrothermal fluids associated with late ductile shear- and fault-related mineralization or remobilization of early mineralization associated with a felsic pluton into late structures. This interpretation is compatible with gabbro xenoliths in the 1.07 Ga Rivard lamprophyre dyke on the NW margin of the gravity anomaly that bear significant similarities with those of the Chevreuil intrusive suite. The presence of both early felsic and late mafic intrusions beneath a group of three mineral occurrences in the Bondy gneiss complex strengthens their prospectivity in comparison to other mineral occurrences in the area. That early, pre-metamorphic mineralization was upgraded late in the

  20. Deformation and Brittle Failure of Folded Gneiss in Triaxial Compression: Failure Modes, Acoustic Signatures and Microfabric Controls

    NASA Astrophysics Data System (ADS)

    Agliardi, F.; Vinciguerra, S.; Dobbs, M. R.; Zanchetta, S.

    2014-12-01

    Fabric anisotropy is a key control of rock behavior in different geological settings and over different timescales. However, the effect of tectonically folded fabrics on the brittle strength and failure mode of metamorphic rocks is poorly understood. Recent data, obtained from uniaxial compression experiments on folded gneiss (Agliardi et al., 2014), demonstrated that their brittle failure modes depend upon the arrangement of two anisotropies (i.e. foliation and fold axial planes) and that rock strength correlates with failure mode. Since lithostatic pressure may significantly affect this rock behavior, we investigated its effect in triaxial compression experiments. We tested the Monte Canale Gneiss (Italian Alps), characterized by low phyllosilicate content and compositional layering folded at the cm-scale. We used a servo-controlled hydraulic loading system to test 19 air-dry cylindrical specimens (ø = 54 mm) that were characterized both in terms of fold geometry and orientation of foliation and fold axial planes to the axial load direction. The specimens were instrumented with direct contact axial and circumferential strain gauges. Acoustic emissions and P- and S-wave velocities were measured by piezoelectric transducers mounted in the compression platens. The tests were performed at confining pressures of 40 MPa and axial strain rates of 5*10-6 s-1. Post-failure study of fracture mechanisms and related microfabric controls was undertaken using X-ray CT, optical microscopy and SEM. Samples failed in three distinct brittle modes produced by different combinations of fractures parallel to foliation, fractures parallel to fold axial planes, or mm-scale shear bands. The failure modes, consistent with those described in uniaxial compression experiments, were found to be associated with distinct stress-strain and acoustic emission signatures. Failure modes involving quartz-dominated axial plane anisotropy correspond to higher peak strength and axial strain, less

  1. The Role of Accessory Phases in the Sm-Nd Isotope Systematics of the Acasta Gneiss Complex

    NASA Astrophysics Data System (ADS)

    Bauer, A.; Fisher, C. M.; Vervoort, J. D.; Bowring, S. A.

    2015-12-01

    The Acasta Gneiss Complex (AGC) of the Slave Craton in the Northwest Territories, Canada, contains some of Earth's oldest continental crust. It is characterized by a range of compositionally diverse gneisses with crystallization ages of 3.3 to > 4.0 Ga1-5. The AGC has undergone a multistage history of metamorphism and deformation. Given these post-crystallization processes, the extent of Nd isotope heterogeneity suggested by published4-7 whole rock Sm-Nd analyses of these rocks has been called into question. Criticisms include the likelihood of mixed lithologies at the hand-sample scale and the potential for open-system behavior of the Sm-Nd isotopic system in these rocks. We obtained whole rock compositional, Sm-Nd and Lu-Hf isotope data paired with Hf in zircon and Nd in titanite and apatite data to further evaluate the isotope record, and use U-Pb and Lu-Hf of zircon as a basis for identifying mixed or complex samples. Preferential preservation of Lu-Hf over Sm-Nd isotope systematics in multiply deformed, complex rocks may be controlled by the minerals that dominate the Hf and Nd budgets, with the majority of the Hf effectively sheltered in zircon and the Nd largely hosted in accessory phases such as apatite and titanite. This composite dataset enables us to evaluate the possibility that Hf and Nd isotopic systematics have been decoupled in these samples that have such critical bearing on our understanding of early crust-forming processes. [1]Bowring and Williams (1999). CoMP, 134(1), 3-16. [2]Iizuka, T. et al. (2006) Geology, 34(4), 245-248. [3]Iizuka et al (2007). Precambrian Res, 153(3), 179-208. [4]Bowring et al. 1989. Nature, 340: 222-225. [5]Mojzsis et al. (2014). GCA, 133, 68-96. [6]Bowring and Housh (1995) Science 269, 1535-1540. [7]Moorbath et al (1997) Chem. Geol. 135, 213-231.

  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. 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.

  4. Archean crustal evolution of the northern North China Craton

    NASA Technical Reports Server (NTRS)

    Qian, Xianglin; Chen, Yaping; Liu, Jinzhong

    1988-01-01

    The Archean granultie facies rocks of the North China (Sino-Korean) Craton mostly occur inside the northern boundary forming a unique and spectacular granulite belt trending roughly E-W from eastern Hebei, North China in the east to Mt. Daqinchan, western Inner Mongolia in the west, ranging about 1,000 km long. Over the years in the middle portion of this Archean high-grade metamorphic belt a stratigraphic unconformity between the khondalite rock assemblage and the medium in composition granulite assemblage in Datong-Xinghe area is determined. The geological structural properties of the North China Craton are discussed.

  5. The Compositional Structure of the Asteroid Belt

    NASA Astrophysics Data System (ADS)

    DeMeo, F. E.; Alexander, C. M. O'D.; Walsh, K. J.; Chapman, C. R.; Binzel, R. P.

    The past decade has brought major improvements in large-scale asteroid discovery and characterization, with over half a million known asteroids, more than 100,000 of which have some measurement of physical characterization. This explosion of data has allowed us to create a new global picture of the main asteroid belt. Put in context with meteorite measurements and dynamical models, a new and more complete picture of solar system evolution has emerged. The question has changed from "What was the original compositional gradient of the asteroid belt?" to "What was the original compositional gradient of small bodies across the entire solar system?" No longer is the leading theory that two belts of planetesimals are primordial, but instead those belts were formed and sculpted through evolutionary processes after solar system formation. This chapter reviews the advancements on the fronts of asteroid compositional characterization, meteorite measurements, and dynamical theories in the context of the heliocentric distribution of asteroid compositions seen in the main belt today. This chapter also reviews the major outstanding questions relating to asteroid compositions and distributions and summarizes the progress and current state of understanding of these questions to form the big picture of the formation and evolution of asteroids in the main belt. Finally, we briefly review the relevance of asteroids and their compositions in their greater context within our solar system and beyond.

  6. 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.

  7. Ophiolites in the Xing'an-Inner Mongolia accretionary belt of the CAOB: Implications for two cycles of seafloor spreading and accretionary orogenic events

    NASA Astrophysics Data System (ADS)

    Song, Shuguang; Wang, Ming-Ming; Xu, Xin; Wang, Chao; Niu, Yaoling; Allen, Mark B.; Su, Li

    2015-10-01

    The Xing'an-Inner Mongolia accretionary belt in the southeastern segment of the Central Asian Orogenic Belt (CAOB) was produced by the long-lived subduction and eventual closure of the Paleo-Asian Ocean and by the convergence between the North China Craton and the Mongolian microcontinent. Two ophiolite belts have been recognized: the northern Erenhot-Hegenshan-Xi-Ujimqin ophiolite belt and the southern Solonker-Linxi ophiolite belt. Most basalts in the northern ophiolite belt exhibit characteristics of normal-type to enriched-type mid-ocean ridge basalt affinities with depleted Nd isotopic composition (ɛNd(t) > +5), comparable to modern Eastern Pacific mid-ocean ridge basalts. Most basaltic rocks in the southern belt show clear geochemical features of suprasubduction zone-type oceanic crust, probably formed in an arc/back-arc environment. The inferred back-arc extension along the Solonker-Linxi belt started at circa 280 Ma. Statistics of all the available age data for the ophiolites indicates two cycles of seafloor spreading/subduction, which gave rise to two main epochs of magmatic activity at 500-410 Ma and 360-220 Ma, respectively, with a gap of ~50 million years (Myr). The spatial and temporal distribution of the ophiolites and concurrent igneous rocks favor bilateral subduction toward the two continental margins in the convergence history, with final collision at ~230-220 Ma. In the whole belt, signals of continental collision and Himalayan-style mountain building are lacking. We thus conclude that the Xing'an-Inner Mongolia segment of the CAOB experienced two cycles of seafloor subduction, back-arc extension, and final "Appalachian-type" soft collision.

  8. Application of graphite as a geothermometer in hydrothermally altered metamorphic rocks of the Merelani-Lelatema area, Mozambique Belt, northeastern Tanzania

    NASA Astrophysics Data System (ADS)

    Malisa, Elias Pausen

    1998-02-01

    Upper Precambrian pelitic and psammitic gneisses in the Mozambique Belt are usually graphite rich. The determination of crystallisation temperatures around and in the hydrothermally altered rocks of the Merelani-Lelatema mining areas, northeastern Tanzania, were made by studying the lattice parameter C of graphite. In this way, the migration of the chromophore elements giving colour to the gemstones, e.g. tanzanite, green garnet and green tourmaline in the area, can be studied. Within the hydrothermally altered zone graphite gives temperatures that range from 523°C to 880°C. These temperatures are much higher than the 390-440°C obtained through fluid inclusion studies of tanzanite, which indicates that the graphite was not hydrothermally introduced. Furthermore the hydrothermal solutions are post-metamorphic.

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

    NASA Technical Reports Server (NTRS)

    Dewit, M. J.

    1986-01-01

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

  10. Using High Resolution Aeromagnetic Data to Map Pervasive Folding in the Lithologically Indistinct Franciscan Coastal Belt

    NASA Astrophysics Data System (ADS)

    Phelps, G. A.; McLaughlin, R. J.; Jachens, R. C.; Wentworth, C. M.

    2008-12-01

    We use high-resolution aeromagnetic data to map magnetic bodies of graywacke of limited exposure that are either interbedded or structurally emplaced within broader areas of non-magnetic graywacke within the Franciscan Complex Coastal belt in northern California, which is bounded by the San Andreas Fault on the west and the Franciscan Complex Central belt on the south and east. Previous work has not extensively subdivided the Coastal belt because of the poor exposure and the fact that the exposed lithology is primarily graywacke indistinguishable in outcrop and hand sample and is thus difficult to map in the field. A hand-held magnetic susceptibility meter, however, in combination with thin-section analysis, reveals that some Coastal belt graywackes are magnetic. The thin-section analysis shows that the magnetic samples have a significant component of andesitic grains, whereas the non-magnetic samples do not. Further, the locations of these magnetic rocks correspond to elongate regions of high magnetic intensity (magnetic anomalies) kilometers to tens of kilometers in length. Previous 2D modeling showed that the bodies of magnetic graywacke can be modeled as a folded sheet, with antiformal limbs near or exposed at the surface and synformal limbs reaching a depth of about 1 km. Locations of edges of magnetic source bodies can be extracted from their magnetic anomalies. Near surface, steeply dipping edges lie beneath local maxima in the horizontal gradient of the magnetic potential surface. The edges are demarcated by locating discrete points along the local maxima. We connected these points, using an algorithm with a specific set of parameters, to delineate the edges of the magnetic graywacke bodies. Together with the previous 2D modeling, the anomalies and their edges show that the Coastal belt contains antiformal structures 5 to 20 km in length and 1.5 km in width, with a wavelength approximately 1.5 km. The modal direction of elongation is oriented approximately

  11. GPS measurements of crustal deformation across the northern Apennines, northern Italy

    NASA Astrophysics Data System (ADS)

    Bennett, R. A.; Elosegui, P.; Normandeau, J. E.; Serpelloni, E.

    2003-12-01

    Continuous GPS stations within and around the northern Apennines, northern Italy, provide sparse but very precise constraints on crustal deformation associated with Africa, Eurasia, and Adriatic plate interactions. We analyzed data acquired by these stations during the time period of 1996 to 2003.5, finding distributed northwest range-parallel crustal shortening, totaling some 2 mm/yr, and northeast directed crustal extension across the Apennines hinterland, totaling 2.5--3.0 mm/yr or more. Extensional strain rates vary as a function of latitude within the northern Apennines, with higher strain rates across a narrow belt in the central part of the northern Apennines (latitude ˜43N) and lower strain rates across a broader zone further north (latitude ˜44N). Northeast directed crustal extension is prominent in the geology and seismicity of the Apennines hinterland, and forms an important observational basis for contemporary geodynamical models describing present-day deformation processes in northern Italy. Range-parallel crustal shortening is less well understood, however, because there are very few geological or seismological indicators of northwest directed crustal shortening for the northern Apennines. On the other hand, combined paleomagnetic and tomographic inferences suggest that the northern Apennines is an orocline, achieving its arcuate shape as a result of progressive bending of an originally straight orogen. The rates and patterns of range-parallel deformation may thus provide important new constraints on geodynamical models for this complex region.

  12. Assessment of Blasting Performance Using Electronic Vis-à-Vis Shock Tube Detonators in Strong Garnet Biotite Sillimanite Gneiss Formations

    NASA Astrophysics Data System (ADS)

    Sharma, Suresh Kumar; Rai, Piyush

    2016-04-01

    This paper presents a comparative investigation of the shock tube and electronic detonating systems practised in bench blasting. The blast trials were conducted on overburden rocks of Garnet Biotite Sillimanite Gneiss formations in one of the largest metalliferous mine of India. The study revealed that the choice of detonating system was crucial in deciding the fragment size and its distribution within the blasted muck-piles. The fragment size and its distribution affected the digging rate of excavators. Also, the shape of the blasted muck-pile was found to be related to the degree of fragmentation. From the present work, it may be inferred that in electronic detonation system, timely release of explosive energy resulted in better overall blasting performance. Hence, the precision in delay time must be considered in designing blast rounds in such overburden rock formations. State-of-art image analysis, GPS based muck-pile profile plotting techniques were rigorously used in the investigation. The study revealed that a mean fragment size (K50) value for shock tube detonated blasts (0.55-0.59 m) was higher than that of electronically detonated blasts (0.43-0.45 m). The digging rate of designated shovels (34 m3) with electronically detonated blasts was consistently more than 5000 t/h, which was almost 13 % higher in comparison to shock tube detonated blasts. Furthermore, favourable muck-pile shapes were witnessed in electronically detonated blasts from the observations made on the dozer performance.

  13. First-report on Mesozoic eclogite-facies metamorphism preceding Barrovian overprint from the western Rhodope (Chalkidiki, northern Greece)

    NASA Astrophysics Data System (ADS)

    Kydonakis, Konstantinos; Moulas, Evangelos; Chatzitheodoridis, Elias; Brun, Jean-Pierre; Kostopoulos, Dimitrios

    2015-04-01

    The Chalkidiki block in Northern Greece represents the southwesternmost piece of the ultrahigh-pressure Rhodope and has played an important role in the evolution of the North Aegean. The eastern part of the Chalkidiki block is a basement complex (Vertiskos Unit) that is made largely of Palaeozoic granitoids and clastic sediments that metamorphosed during the Mesozoic. This basement is traditionally considered as part of the Rhodopean hanging-wall, an assignment mainly supported by the absence of high-pressure mineral indicators and the presence of a regional medium-pressure/medium-temperature amphibolite-facies Barrovian metamorphic imprint. Toward the west, the basement is juxtaposed with meta-sedimentary (Circum-Rhodope belt) and arc units (Chortiatis Magmatic Suite) that carry evidence of a Mesozoic high-pressure/low-temperature event. In this study, garnet-staurolite-mica schists from the eastern part of the basement were examined by means of micro-textures, mineral chemistry and isochemical phase-diagram sections in the system NCKFMASHMn(Ti) [Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-MnO-(TiO2)]. The schists represent former Mesozoic sedimentary sequences deposited on the Palaeozoic basement. We document the presence of a relict eclogite-facies mineral assemblage (garnet + chloritoid + phengite + rutile) in an amphibolite-facies matrix composed of garnet + staurolite + phengite ± kyanite. Model results suggest the existence of a high-pressure/medium-temperature metamorphic event (1.9 GPa/520 °C) that preceded regional re-equilibration at medium-pressure/medium-temperature conditions (1.2 GPa/620 °C). Clearly, the eastern part of the Chalkidiki block (basement complex) retains memory of an as yet unidentified Mesozoic eclogitic metamorphic event that was largely erased by the later Barrovian overprint. In light of our findings, the basement complex of the Chalkidiki block shares a common tectono-metamorphic evolution with both the high-pressure units to the west

  14. Crustal Development in the Northeast Asian Orogenic Belt and its comparison with the Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Jahn, Bor-ming

    2016-04-01

    The Northeast Asian Orogenic Belt is a Mesozoic-Cenozoic accretionary orogenic collage, and it constitutes the northern and principal part of the "Nipponides" (Sengor and Natal'in, 1996). The tectonic framework was formed in Mesozoic and Cenozoic, and it continues to evolve along the modern Pacific arc-trench systems. Generally, a oceanward younging of tectonic units may be discerned, but such a simple pattern is disrupted in many places by extensive strike-slip faulting, most of which is left-lateral. In this talk, the issue of crustal development in the sector of Sikhote-Alin and Japanese Islands will be discussed based on the geochemical and isotopic analyses of granitoids that intruded in various tectonostratigraphic terrains. The majority of granitoids in the NE Asian Orogenic Belt formed from Jurassic to late Cenozoic, with Cretaceous as the dominant period of granitic magmatism and tectonothermal events. A few Early Paleozoic granitic rocks (500 to 450 Ma) have been identified in SW Japan (Kurosegawa Belt) as well as in NE Japan (Kitakami Belt), among them the ca. 500 Ma diorites and tonalites of southern Kitakami are the oldest rocks in Japan and interpreted as the first TTG crust of proto-Japan (Isozaki et al., 2015). Cretaceous granitoids are widespread in Sikhote-Alin and in NE and SW Japan. However, granitoids were emplaced only in the Cenozoic in Sakhalin (ca. 44 - 42 Ma) and Hokkaido (45, 37 and 18 Ma). Most granitoids from Sikhote-Alin are of I-type and have ISr = 0.7040 to 0.7083, and ɛNd(T) = +3.0 to -6.0 (mostly 0 to -5). The Sr-Nd isotopic data fall within the range of granitoids from SW Japan (0.704 to 0.712; +5.0 to -13.0), and the data of Cretaceous granitoids from Sikhote-Alin and SW Japan overlap almost completely. The Cenozoic granitoids of Hokkaido are characterized by ISr = 0.7044 - 0.7061, ɛNd(T) = +1.0 to +4.7, and Sm-Nd model-1 ages = 400-1000 Ma. This is remarkably similar to the Sakhalin granitoids with ISr = 0.7047 - 0.7050,

  15. 49 CFR 393.93 - Seats, seat belt assemblies, and seat belt assembly anchorages.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... § 393.93 Seats, seat belt assemblies, and seat belt assembly anchorages. (a) Buses—(1) Buses manufactured on or after January 1, 1965, and before July 1, 1971. After June 30, 1972, every bus manufactured... Safety Administration. 1200 New Jersey Ave., SE., Washington, DC 20590-0001. (2) Buses manufactured on...

  16. 49 CFR 393.93 - Seats, seat belt assemblies, and seat belt assembly anchorages.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... § 393.93 Seats, seat belt assemblies, and seat belt assembly anchorages. (a) Buses—(1) Buses manufactured on or after January 1, 1965, and before July 1, 1971. After June 30, 1972, every bus manufactured... Safety Administration. 1200 New Jersey Ave., SE., Washington, DC 20590-0001. (2) Buses manufactured on...

  17. Tectonic uplift mechanism of the Goodenough and Fergusson Island gneiss domes, eastern Papua New Guinea: Constraints from seismic reflection and well data

    NASA Astrophysics Data System (ADS)

    Fitz, Guy; Mann, Paul

    2013-10-01

    The D'Entrecasteaux Island (DEI) gneiss domes are fault-bounded domes with ˜2.5 km of relief exposing ultrahigh-pressure (UHP) and high-pressure (HP) metamorphic gneisses and migmatites exhumed in an Oligocene-Miocene arc-continent collision and subduction zone subject to Late Miocene to Recent continental extension. To study the style of continental extension accompanying exhumation of the DEI gneiss domes, a grid of 1518 km of 2-D multichannel seismic (MCS) reflection data and well data is interpreted from the offshore areas surrounding the DEI, including the Trobriand basin and the Goodenough basin. The offshore study is combined with onshore geologic information to constrain the Oligocene to Recent tectonic evolution of the basins. MCS and well data are consistent with the Trobriand basin forming as a forearc basin caused by southward Miocene subduction at the Trobriand trench. At ˜8 Ma, the margin transitioned to an extensional tectonic environment. Since then, the Trobriand basin has subsided 1-2.5 km with few normal faults deforming the basin fill. South of the DEI, the Goodenough rift basin developed after extension began (˜8 Ma) with the hanging wall of the north-dipping Owen-Stanley normal fault bounding the southern margin of the basin. The lack of evidence of upper crustal extension accompanying subsidence in the Trobriand and Goodenough basins suggests depth-dependent lithospheric extension from 8 to 0 Ma has accompanied uplift of the DEI gneiss domes and supports schematic model of uplift of the DEI domes involving vertical exhumation of buoyant, postorogenic lower crust, far-field extension from slab rollback, and an inverted two-layer crustal density structure.

  18. Microstructures and quartz lattice-preferred orientations in the eclogite-bearing migmatitic gneisses of the D'Entrecasteaux Islands, Papua New Guinea

    NASA Astrophysics Data System (ADS)

    Little, T. A.; Hacker, B. R.; Brownlee, S. J.; Seward, G.

    2013-06-01

    Lattice preferred orientations (LPO) of quartz in gneiss domes of the D'Entrecasteaux Islands, Woodlark Rift shed insight into exhumation of the world's youngest (~5-7 Ma) eclogite-bearing terrane at cm/yr rates. We focus on deformation that affected the terrane as it transited between lower crustal depths and the surface, including: (1) grain-scale deformation mechanisms; and (2) style of flow and mode of emplacement of the domes. Electron-backscatter diffraction was used to analyze microstructure and LPOs of 37 quartzofeldspathic gneiss samples that enclose meter-scale mafic blocks preserving original eclogite-facies assemblages. During exhumation of the ultrahigh-pressure (UHP) terrane, gneisses were retrogressed in the amphibolite facies at lower crustal depths. The LPOs change from dome cores to carapaces, consistent with decreasing deformational temperatures. In the relatively chilled outer carapaces of the domes, the quartz LPOs consist of mostly crossed-girdle [c]-axis patterns, with some cleft-girdle and small-circle LPOs, and record dislocation creep accommodated by mixed- < a > slip. In the cores of the migmatitic domes, a chessboard pattern of subgrains is common, and quartz LPOs primarily record prism-[c] slip, probably at >630 °C. Other microstructures indicate recovery by high-temperature grain-boundary migration. Grain-boundary mobility was anisotropic, leading to strong grain-shape fabrics oblique to foliation, but not obviously relatable to shear sense. Evidence for melt-present deformation is abundant, and microstructures (including partially dissolved feldspar grains) indicate some deformation by fluid-assisted grain-boundary diffusion creep. LPOs in carapace rocks are symmetrical, recording flow that was dominantly coaxial. We interpret the gneiss domes to have been emplaced into the rift as partially molten diapirs.

  19. Metasedimentary rocks of the Angara-Kan granulite-gneiss block (Yenisey Ridge, south-western margin of the Siberian Craton): Provenance characteristics, deposition and age

    NASA Astrophysics Data System (ADS)

    Urmantseva, L. N.; Turkina, O. M.; Larionov, A. N.

    2012-04-01

    The Angara-Kan granulite-gneiss block (Yenisey Ridge) is one of the main basements uplift within the south-western margin of the Siberian Craton. The major part of the Angara-Kan block is composed of Early Precambrian high-grade metamorphic rocks. Metasedimentary association of the Kan granulitic complex is composed of garnet-bearing, garnet-orthopyroxene and orthopyroxene-bearing gneisses, garnet- and orthopyroxene-bearing gneisses with cordierite and sillimanite. Studied paragneisses were formed at the expense of granulite metamorphism of terrigenous rocks, ranging from graywacke to pelitic rock or mudstone. To estimate the time of sedimentation and metamorphism of the terrigenous deposits, the U-Pb zircon dating has been performed using the SHRIMP II ion microprobe. Detrital zircon cores from the biotite-orthopyroxene and high-alumina gneisses yield ages of 2.6-1.94 and 2.4-1.94 Ga, respectively. Together with the age of the magmatic zircons formed during high-grade metamorphism and partial melting (˜1.89 Ga) and metamorphic rims (˜1.87 Ga) it defines the time of sedimentation between 2.0-1.94 and 1.89-1.87 Ga. Detrital zircon ages indicate both Archean and Paleoproterozioc rocks in provenance source, that agrees with the Nd model ages of metasediments ranging in interval 2.4-2.8 Ga. Potential source of the Archean detrital zircons was the exposed basement of the southwestern Siberian Craton, whereas the Paleoproterozoic juvenile crustal source seems to be buried basement of the Tungus province of the Siberian Craton. Deposition of the Kan terrigeneous rocks was coeval with sedimentation in the southeastern part of the Sharyzhalgay uplift, where ages of detrital zircon cores and metamorphic rims from paragneisses bracket sediment deposition between 1.95 and 1.85 Ga.

  20. Provenance and tectonic-paleogeographic evolution: Constraints from detrital zircon U-Pb ages of Late Triassic-Early Jurassic deposits in the northern Sichuan basin, central China

    NASA Astrophysics Data System (ADS)

    Shao, Tongbin; Cheng, Nanfei; Song, Maoshuang

    2016-09-01

    U-Pb ages of 290 new detrital zircons from five Late Triassic-Early Jurassic sandstone samples in the northern Sichuan basin, along with other geological data, are used to constrain the sediment provenance and evaluate tectonic-paleogeographic evolution for the adjacent orogens through/from which these sediments were potentially derived. The Upper Triassic depocenter was located at the front of the Longmen Shan belt, and sediments in the western, southern and eastern Sichuan basin shared the southern North China block (NCB) and Qinling belt with the eastern Songpan-Ganzi terrane of Middle-Upper Triassic via the Longmen Shan belt, whereas the northern part of the basin was fed by dominant South Qinling belt (SQB) and northern Yangtze block and possibly subordinate southern NCB. Also, the youngest population in the northern Sichuan basin has a slightly younger age peak (∼235 Ma) than those (∼270 Ma) in other parts of the basin. During the Early Jurassic, the depocenter was still at the front of the Longmen Shan belt but only northern regions (e.g., SQB and northern Yangtze block) fed the basin. The northern Sichuan basin received less sediments from the southern NCB and more from the SQB and northern Yangtze block during the Early Jurassic than during the Late Triassic. The middle Mesoproterozoic detrital zircons, which likely originated from the North Qinling belt and northern Yangtze block where rocks with these zircons may be unexposed, occur more widely in the Lower Jurassic than in the Upper Triassic. These facts suggest that from the Late Triassic to Early Jurassic, it was increasingly difficult for sediments to transport from the NCB into the northern Sichuan basin and the provenance transferred progressively from the southern NCB to both the SQB and northern Yangtze block, implying the continuous South China block-NCB collision during that time.

  1. Stacked pneumatic cylinders automate conveyor belt operations

    SciTech Connect

    Thornton, G.

    1982-11-01

    Shows how clusters of remotely controlled pneumatic cylinders swing a hinged conveyor belt to 4 preselected vertical positions. Using a manual method to move the conveyor meant that the operator had to use a hand winch, sheaves, drums, and winch cable. There was a need to develop a simple, effective, and remotely controlled system which would perform 2 functions: eliminate the need for stopping the conveyor to reset the hinged belt, and not require the operator to leave the master control console. Using the developed system, the operator need only turn on the appropriate switching valves from the master console. Each pneumatic cylinder is actuated in sequence, on the retraction stroke only, through the elevating positions. To lower the conveyor belt, the head end of each cylinder is exhausted; the weight of the belt extends the cylinders, lowering the belt by gravity. Cylinder exhaust ports in the power valves are fitted with adjustable flow control valves to regulate cylinder speed; common exhaust ports in the interconnected manifolds are fitted with air silencers.

  2. 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.

  3. Post-Taconic blueschist suture in the northern Appalachians of northern New Brunswick, Canada

    SciTech Connect

    van Staal, C.R.; Ravenhurst, C.E.; Roddick, J.C. ); Winchester, J.A. ); Langton, J.P. )

    1990-11-01

    A narrow belt of Late Ordovician-Early Silurian blueschist, at least 70 km long, separates an allochthonous fragment of back-arc oceanic crust of the Middle Ordovician Fournier Group from underlying, rift-related volcanic rocks of the Middle Ordovician Tetagouche Group in northern New Brunswick, Canada. The basalts on both sides of the blueschist belt are predominantly metamorphosed to greenschist facies conditions. The blueschist belt is interpreted to be an out-of-sequence thrust zone that accommodated tectonic transport of higher pressure rocks on top of lower pressure rocks during post-peak blueschist facies metamorphism. The blueschists have higher Fe{sub 2}O{sub 3}/FeO ratios and total iron contents in comparison to otherwise chemically equivalent basalts of the Fournier and Tetagouche Groups that have been metamorphosed into greenschists. The blueschist belt was probably the site of channelized flow of oxidizing fluids during active deformation ina subduction complex formed during the closure of a wide Taconic back-arac basin in Late Ordovician-Silurian time.

  4. Post-Taconic blueschist suture in the northern Appalachians of northern New Brunswick, Canada

    NASA Astrophysics Data System (ADS)

    van Staal, Cees R.; Ravenhurst, Casey E.; Winchester, John A.; Roddick, J. Chris; Langton, John P.

    1990-11-01

    A narrow belt of Late Ordovician-Early Silurian blueschist, at least 70 km long, separates an afochthonous fragment of back-arc oceanic crust of the Middle Ordovician Fournier Group from underlying, rift-related volcanic rocks of the Middle Ordovician Tetagouche Group in northern New Brunswick, Canada. The basalts on both sides of the blueschist belt are predominantly metamorphosed to greenschist facies conditions. The blueschist belt is interpreted to be an out-of-sequence thrust zone that accommodated tectonic transport of higher pressure rocks on top of lower pressure rocks during post-peak blueschist facies metamorphism. The blueschists have higher FeO/FeO ratios and total iron contents in comparison to otherwise chemically equivalent basalts of the Fournier and Tetagouche Groups that have been metamorphosed into greenschists. The blueschist belt was probably the site of channelized flow of oxidizing fluids during active deformation in a subduction complex formed during the closure of a wide Taconic back-arc basin in Late Ordovician-Silurian time.

  5. Inferring protoliths of high-grade metamorphic gneisses of the Erzgebirge using zirconology, geochemistry and comparison with lower-grade rocks from Lusatia (Saxothuringia, Germany)

    NASA Astrophysics Data System (ADS)

    Tichomirowa, Marion; Sergeev, Sergey; Berger, Hans-Jürgen; Leonhardt, Dietmar

    2012-09-01

    Protoliths of highly metamorphosed gneisses from the Erzgebirge are deduced from the morphology, age and chemistry of zircons as well as from whole rock geochemistry and are compared with lower-grade rocks of Lusatia. Gneisses with similar structural appearance and/or geochemical pattern may have quite different protoliths. The oldest rocks in the Erzgebirge are paragneisses representing meta-greywackes and meta-conglomerates. The youngest group of zircon of meta-greywackes that did not undergo Pb loss represents the youngest igneous component for source rocks (about 575 Ma). Similar ages and zircon morphology reflect the subordinate formation of new zircon grains or only zircon rims in the augengneiss from Bärenstein and Wolkenstein, which probably represent metamorphic equivalents to Lower Cambrian two-mica granodiorites from Lusatia. Bulk rock chemistry, intense fracturing and high U and Th concentrations of zircons suggest deformation-induced and fluid-enhanced recrystallisation of zircon grains. Temperatures during tectonic overprinting—too low to reset zircon ages—indicate mid- or upper crustal levels for shearing recorded in these augengneisses. Lower Cambrian (~540 Ma) granodiorites are widespread in Lusatia but are exclusively represented by the Freiberg gneiss dome in the Eastern Erzgebirge. Ordovician protolith ages were recorded by zircons from the augengneisses of the Reitzenhain-Catherine dome and the Schwarzenberg dome (Western Erzgebirge) documenting significant regional differences between the eastern and the western Erzgebirge (~540 vs. ~490 Ma). In the Western Erzgebirge, most meta-volcanic rocks (muscovite gneisses) and meta-granites (mainly red augengneisses) yield Ordovician zircon ages, whereas in the Eastern part, similar rocks mainly recorded Lower Cambrian protolith ages. Zircon overprinting was highest within discrete tectonic zones where the combination of fluid infiltration and deformation induced variable degrees of

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

    NASA Astrophysics Data System (ADS)

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

    2004-05-01

    The Paleo- to Mesoarchaean Barberton granite-greenstone terrain in South Africa consists of two main components: a southern high-grade metamorphic granite-gneiss terrain and the low-grade metamorphic supracrustal sequence of the Barberton greenstone belt in the north. The gneiss terrain records peak metamorphic conditions of 8 - 11 kbar and 650 - 700 °C, attained at 3229 ± 9 Ma (Dziggel et al., 2002), coinciding with the main phase of collisional tectonics in the greenstone belt (De Ronde and De Wit, 1994). Conversely, estimates of 2.6 ± 0.6 kbar and 360 ± 50 °C reflect metamorphic conditions in the low-grade supracrustal at this time (Cloete, 1999). The boundary of the two different domains corresponds to the Theespruit Formation, a highly tectonized mélange of metabasites, felsic volcanics and rare, aluminous clastic sediments. The metamorphic and structural evolution of the Theespruit Formation was investigated in the Tjakastad Schist Belt in order to constrain the tectonometamorphic history and the significance of this basal mélange for the juxtaposition of these two crustal domains. The pretectonic peak metamorphic assemblage Ky-St-Bt-Ms-Pl-Q quartz occurs in aluminous horizons within the metasediments. These horizons are intercalated with more Fe-Mg-rich sediments that record the peak metamorphic assemblage Grt-St-Bt-Chl-Pl-Q. THERMOCALC estimates from the garnet-bearing metasediments constrain peak P-T conditions at 7.7 ± 0.9 kbar and 560 ± 15 °C. Associated metabasites display peak assemblages consisting of garnet + hornblende + epidote + plagioclase + quartz, which yields a P-T estimate of 7.0 ± 1.6 kbar and 560 ± 60 °C. Retrograde estimates of 3.8 ± 1.3 kbar and 543 ± 20 °C, as well as sillimanite overgrowths on kyanite, indicate that retrogression involved close to isothermal decompression of ca. 4 kbar prior to cooling into the greenschist facies. The age of amphibolite facies metamorphism has been determined by in situ LA

  7. Role of folded anisotropic fabric in the failure mode of gneiss: new insights from mechanical, microseismic and microstructural laboratory data

    NASA Astrophysics Data System (ADS)

    Agliardi, Federico; Vinciguerra, Sergio; Dobbs, Marcus R.; Zanchetta, Stefano

    2015-04-01

    Fabric anisotropy is a key control of the mechanical behaviour of rocks in a variety of geological settings and on different timescales. However, the effects of inherited, tectonically folded anisotropic fabrics on the brittle strength and failure mode of foliated metamorphic rocks is yet to be fully understood. Data from laboratory uniaxial compression tests on folded gneiss (Agliardi et al., 2014, Tectonophysics) recently showed that the brittle failure mode of this rock type depends on the arrangement of two distinct anisotropies (i.e. foliation and fold axial plane anisotropy), and that rock strength correlates with failure mode. Here we investigate the effects of confining pressure on this behaviour by performing triaxial compression experiments with acoustic emission (AE) monitoring, and analyse resulting fracture mechanisms and their microfabric controls using high resolution microanalysis techniques. We tested the Monte Canale Gneiss (Austroalpine Bernina nappe, Central Italian Alps), characterized by low phyllosilicate content, compositional layering folded at the cm-scale, and absence of a well-developed axial plane foliation. We used a servo-controlled hydraulic loading system to test 19 air-dry cylindrical specimens (diameter: 54 mm) that were characterized both in terms of fold geometry and orientation of foliation and fold axial planes to the axial load direction. We instrumented the specimens with direct contact axial and circumferential strain gauges. We performed tests at confining pressures of 40 MPa and constant axial strain rates of 5*10-6 s-1, measuring acoustic emissions and P- and S-wave velocities by three wideband (350-1000 kHz) piezoelectric transceivers with 40 dB preamps, mounted in the compression platens. We carried out post-failure microscale observation of fracture mechanisms, microcrack patterns and related fabric controls on resin-impregnated samples, using X-ray MicroCT (resolution: 9 μm), optical microscopy and SEM. Samples

  8. Simulation of sludge dewatering on belt filters.

    PubMed

    Christensen, Morten Lykkegaard; Petersen, Rasmus Rosenlund; Jørgensen, Lars Bjerg

    2010-01-01

    A mathematical model for belt filters was developed to determine optimum load rate and belt speed during drainage of flocculated biological sludge. Numerical simulations were performed for belt filters with and without plows, and the model fit experimental data well. Experiments showed that highly compressible cakes were formed during drainage, which was important. Due to cake compression, the final sludge dry matter content increased with load rates as long as the drainage time was sufficiently long. The dry matter content could be increased by stacking the cake at the end of the process. An optimum load rate was found. At high load rates, the drainage time was too short and the dry matter content decreased with load due to high cake resistance. The resistance could be lowered by mixing cake and suspension during the process.

  9. Perceptual findings on the broadway belt voice.

    PubMed

    DeLeo LeBorgne, Wendy; Lee, Linda; Stemple, Joseph C; Bush, Heather

    2010-11-01

    The present study required raters (casting directors) to evaluate the belt voice quality of 20 musical theater majors who were proficient in the singing style referred to as belting. Two specified vocalizes and six short excerpts from the belting repertoire were used for rating purposes. The raters were asked to judge the belters on a set of seven perceptual parameters (loudness, vibrato, ring, timbre, focus, nasality, and registration breaks), and then report an overall score for these student belters. The four highest and lowest average scores were used to establish the elite and average student belters. A correlation analysis and linear regression analysis provided insight regarding which perceptual judgments correlated most highly with the elite and average scores. The present study found the perceptual ratings of vibrato and ring to be most highly correlated to the elite student belter. In addition, vibrato and ring were found to highly correlate with perceived loudness. PMID:19900789

  10. Geochronology of Zircon in Eclogite Reveals Imbrication of the Ultrahigh-Pressure Western Gneiss Region of Norway.

    NASA Astrophysics Data System (ADS)

    Young, D. J.; Kylander-Clark, A. R.; Root, D. B.

    2014-12-01

    Eclogite provides the only record of kinematic events at the deepest levels of orogens. Integrating the U-Pb geochronology and trace element chemistry of zircon in eclogite reveals the most complete view of the PTt history, yet low concentrations of uranium and zirconium and drier compositions that hinder zircon growth at peak conditions render it a challenging rocktype for this approach. The iconic Western Gneiss Region (WGR) in Norway is one of the largest terranes of deeply subducted continental rocks in the world, and contains many indicators of ultrahigh-pressure metamorphic conditions (P>2.8 GPa) that developed during the Siluro-Devonian Caledonian Orogeny. A metamorphic transition from amphibolite-facies to ultrahigh-pressure eclogite facies broadly coincides with a km-scale shear zone that underlies the majority of the WGR. A critical unknown is the timing of movement on this feature, which emplaced allochthonous units above the Baltica basement, but might also have accommodated late-orogenic exhumation of the WGR from mantle depths. We carried out laser ablation split-stream ICPMS (LASS) and selected multigrain TIMS analyses of zircons from eleven eclogites across the southern WGR, of which eight are located within or above the shear zone. LASS spots on polished grains mostly yield weakly discordant Proterozoic intrusive ages, and often minimal indication of a Caledonian (U)HP metamorphic overprint. Direct ablation into unpolished zircon reveals thin rims of Caledonian age in some cases. Overall, the dataset shows that all samples began zircon growth at approximately the same time (ca. 430-420 Ma). Eclogite from lower levels of the shear zone does not contain any dates younger than ca. 410 Ma, however, while eclogite from higher levels continued growth until ca. 400 Ma. We interpret this to result from thrusting of the WGR above cooler basement after 410 Ma, terminating new zircon crystallization within the shear zone but allowing limited further growth in

  11. Were the world's youngest eclogites (NW D'Entrecasteaux Islands, Papua New Guinea) exhumed in rising gneiss domes or by shear on a deep-seated fault?

    NASA Astrophysics Data System (ADS)

    Little, T. A.; Hacker, B.; Seward, G.

    2008-12-01

    The up to ~2.5 km-high gneiss domes of the NW D'Entrecasteaux Islands of Papua New Guinea host the world's youngest terrane of HP (eclogite-facies, ~2-4 Ma) to UHP (coesite-bearing) gneissic rocks (~8 Ma). Previous models for their exhumation at >2 cm/yr have called upon: 1) buoyant rise of crustal diapers, or 2) normal-slip on deeply penetrating faults. A recent variant of the latter suggests that a paleo- subduction zone near the southern edge of the Solomon Sea has been inverted as a result of microplate tectonics. We present structural, microstructural, and electron back-scatter diffraction data of lattice preferred orientations (LPO's) from gneisses of Goodenough and Fergusson Islands to further explore mechanisms of exhumation. Relict eclogite-facies assemblages occur in mafic dikes and boudins, but most HP deformational fabrics are overprinted. The enclosing felsic gneisses are pervaded by amphibolite-facies ductile fabrics formed during their exhumation from the lower crust. These migmatitic rocks (metatexites) were partially molten during their deformation at temperatures of 570-730°C and pressures of 7-11 kb, but today are dominated by solid-state fabrics. The gneisses are capped by remnants of an ultramafic sheet that did not experience HP metamorphism. Below the ultramafics is a ~1 km-thick carapace zone. These high-strain gneisses generally have domal fabrics parallel to, and gradational to, those in the underlying core zone, which they locally rework. Active NE-dipping normal faults on the NE flank of the domes cut across the ultramafic contact and are underlain by a m-thick zone of pseudotachylite-bearing S/C fabrics. A sweeping pattern of stretching lineations reveals a 3-D pattern of ductile flow. In both the carapace and upper core zone, lineations are mostly EW: subparallel to the long dimension of the domes and perpendicular to plate motion in the Woodlark Rift. At greater structural depth, within the core zone, they deflect to become more

  12. Distribution of Dust from Kuiper Belt Objects

    NASA Technical Reports Server (NTRS)

    Gorkavyi, Nick N.; Ozernoy, Leonid; Taidakova, Tanya; Mather, John C.; Fisher, Richard (Technical Monitor)

    2000-01-01

    Using an efficient computational approach, we have reconstructed the structure of the dust cloud in the Solar system between 0.5 and 100 AU produced by the Kuiper belt objects. Our simulations offer a 3-D physical model of the 'kuiperoidal' dust cloud based on the distribution of 280 dust particle trajectories produced by 100 known Kuiper belt objects; the resulting 3-D grid consists of 1.9 x 10' cells containing 1.2 x 10" particle positions. The following processes that influence the dust particle dynamics are taken into account: 1) gravitational scattering on the eight planets (neglecting Pluto); 2) planetary resonances; 3) radiation pressure; and 4) the Poynting-Robertson (P-R) and solar wind drags. We find the dust distribution highly non-uniform: there is a minimum in the kuiperoidal dust between Mars and Jupiter, after which both the column and number densities of kuiperoidal dust sharply increase with heliocentric distance between 5 and 10 AU, and then form a plateau between 10 and 50 AU. Between 25 and 45 AU, there is an appreciable concentration of kuiperoidal dust in the form of a broad belt of mostly resonant particles associated with Neptune. In fact, each giant planet possesses its own circumsolar dust belt consisting of both resonant and gravitationally scattered particles. As with the cometary belts simulated in our related papers, we reveal a rich and sophisticated resonant structure of the dust belts containing families of resonant peaks and gaps. An important result is that both the column and number dust density are more or less flat between 10 and 50 AU, which might explain the surprising data obtained by Pioneers 10 & 11 and Voyager that the dust number density remains approximately distance-independent in this region. The simulated kuiperoidal dust, in addition to asteroidal and cometary dust, might represent a third possible source of the zodiacal light in the Solar system.

  13. Safety belt use, ejection and entrapment.

    PubMed

    O'Day, J; Scott, R E

    1984-01-01

    One in every five occupants thrown from a car receives fatal injuries. A motorist who uses a safety belt, in all probability, will not be thrown from the car during a crash. The rate of fatal injury for ejected occupants was found to be 40 times the rate for occupants not thrown from their cars, as determined from national accident sampling data. These data refute the popular notion that "being thrown clear" has survival benefit. In addition, there was no evidence that wearing a safety belt increased fatality risk from vehicle fire or submersion. PMID:6519997

  14. Circumferential truncal contouring: the belt lipectomy.

    PubMed

    Aly, Al; Mueller, Melissa

    2014-10-01

    The primary goal of belt lipectomy surgery is to improve the contour of the inferior truncal circumferential unit and to place the resultant scar in natural junctions. Excessive intra-abdominal content is a contraindication for belt lipectomy. The higher the presenting patient's body mass index (BMI), the higher the risk of postoperative complications and the less impressive the results. The converse is also true: the lower the BMI, the lower the risk of complications and the better the results. The most common complications are small wound separations and seromas.

  15. Satellite-Based Analysis of a Warm Conveyor Belt in a Marine Extratropical Cyclone

    NASA Astrophysics Data System (ADS)

    Crespo, J.; Posselt, D. J.

    2015-12-01

    Extratropical cyclones play a paramount role in Earth's climate through meridional energy transport from the equator to the poles, as well as through cloud and precipitation formation by providing a majority of observed precipitation in the midlatitudes. The warm conveyor belt is a poleward airstream of ascending moisture that rises from the boundary layer to the upper troposphere. It is responsible for transporting a preponderant amount of water vapor present in an extratropical cyclone, with nearly 100% efficiency at precipitating all transported moisture. The community's understanding of marine extratropical cyclones and their synoptic dynamics originates from the Shapiro and Keyser Model, but there is less understanding of the mesoscale evolution of the cloud and precipitation structures within an extratropical cyclone and its warm conveyor belt. This research aims to better understand extratropical cyclone and warm conveyor belt evolution on the mesoscale using a specific case study. In late November 2006, a marine extratropical cyclone formed east of Florida in the Atlantic Ocean, travelling parallel to the eastern seaboard for nearly a week. Model analysis showed the presence of a strong warm conveyor belt associated with the cyclone. Given that the system remained in nearly the same longitudinal position, it was observed multiple times by NASA's Afternoon-Train (A-Train) satellite constellation. CloudSat radar reflectivity profiles and ECMWF-AUX thermodynamic fields show a transition from stratiform to convective precipitation along the northern edge of the conveyer belt, with larger vertical instability and isolated higher rain rates. Examination of the storm scale context indicates this convection may develop in place rather than via interaction with the cold front. These results give us a better understanding of structural evolution of clouds and precipitation as it interacts with the cyclone-scale dynamics and surrounding thermodynamic environment.

  16. Gravity and tectonic model across the Sulaiman fold belt and the Chaman fault zone in western Pakistan and eastern Afghanistan

    NASA Astrophysics Data System (ADS)

    Jadoon, Ishtiaq A. K.; Khurshid, Akbar

    1996-03-01

    Gravity data from the western boundary of the Indian subcontinent have been analysed to infer the gross crustal structure across the Indian/Afghan collision zone. Seismic reflection profiles reveal the gross structural (duplex) geometry of the Sulaiman fold belt. These data show that the wedge, which is 10 km thick at the deformation front, thickens northwestward to attain a tectonic thickness (thickness due to deformation) of about 20 km in the hinterland. Gravity modeling depicts the depth of the Moho between 33 and 35 km at the deformation front of the Sulaiman fold belt. The Moho depth shows an upward convexity along an E-W profile. It decreases northward with a gentle gradient of 1.1° (20 m/km) below the Sulaiman fold belt, and then deepens abruptly with a gradient of about 7.8° (136 m/km) across the Chaman fault zone, attaining a depth of about 57 km in eastern Afghanistan. The model suggests that the Sulaiman fold belt is underlain by transitional crust (15-27 km thick), in contrast to the continental crust (38 km thick) underneath the fold belt of the Himalayan collision zone in northern Pakistan. The about 57-km-thick crystalline crust in eastern Afghanistan may be due to: (1) underplating by crust of the Indian subcontinent; and (2) structural thickening within the Afghan block.

  17. The Central Metasedimentary Belt (Grenville Province) as a failed back-arc rift zone: Nd isotope evidence

    NASA Astrophysics Data System (ADS)

    Dickin, A. P.; McNutt, R. H.

    2007-07-01

    Nd isotope data are presented for granitoid orthogneisses from the Central Metasedimentary Belt (CMB) of the Grenville Province in order to map the extent of juvenile Grenvillian-age crust within this orogenic belt that is composed mostly of older crustal terranes. The data reveal a 150 km-wide belt of juvenile crust in Ontario, but this belt contains a block of pre-Grenvillian crust (containing the Elzevir pluton) which yields an estimated crustal formation age of 1.5 Ga. The recognition of an older block within the CMB has profound implications for its structure and tectonic evolution, because it implies that juvenile Grenvillian crust, apparently forming a wide NE-SW belt, is in fact distributed in two narrower segments with approximately N-S strike. We suggest that the CMB comprises an en echelon series of ensimatic rift segments, created by back-arc spreading behind a continental margin arc. These rift segments extend southwards (in the subsurface) into the northeastern Unites States. The rift segments contain abundant marble outcrops, consistent with marine incursion into the rift zone, and these deposits also continue northwards into a 'Marble domain' of the CMB in Quebec. However, crustal formation ages in the latter domain are largely pre-Grenvillian, implying that the Quebec rift segment was ensialic. Hence, we interpret the CMB in Ontario and Quebec as the northern termination of a failed back-arc rift zone.

  18. Structural characteristic and origin of intra-continental fold belt in the eastern Sichuan basin, South China Block

    NASA Astrophysics Data System (ADS)

    Li, Chuanxin; He, Dengfa; Sun, Yanpeng; He, Jinyou; Jiang, Zaixing

    2015-11-01

    The fold-and-thrust belt in the eastern Sichuan basin is represented by a series of subparallel chevron anticlines. Under the orogenic tectonic setting within the South China Block in Meso-Cenozoic period and the influence of the multi-layer detachment fault, the deformation of the thrust belt exhibits remarkably layered and large-scale intracontinental thrusting structural characteristics. In this paper, we focus on the structural geometry and deformational mechanisms using the latest two-dimensional (2D) and three-dimensional (3D) seismic reflection data in combination with well and outcrop data. The multi-layer detachment faults, especially the upper gypsum-bearing detachment in the Middle Triassic Jialingjiang Formation and lower detachment with gypsum or shale in the Lower-Middle Cambrian system, directly control the deformational styles of the study area. Interpretation of seismic sections indicates that the fold-and-thrust belt has various deformational styles during folding, including fault-propagation fold, fault-bend fold, and detachment fold with box-fold or pop-up structural geometry. Regional location and structural boundaries play significant roles in controlling the deformational styles, and distinct differences exist among the different anticlines. The Huayingshan anticline located at the front of the thrust belt shows intense structural deformation with northwestward thrusting direction and a relatively weak opposite southeastward thrusting. In addition, the anticlines exhibit structural differences along strike and the fold-and-thrust belt in the northern segment is influenced by the North China Block.

  19. Ultra-fast Electrons Explain Third Radiation Belt

    NASA Video Gallery

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

  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. 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... estimated State seat belt use rate for the unknown calendar year. The estimated State seat belt use...

  2. Slope failures in Northern Vermont, USA

    USGS Publications Warehouse

    Lee, F.T.; Odum, J.K.; Lee, J.D.

    1997-01-01

    Rockfalls and debris avalanches from steep hillslopes in northern Vermont are a continuing hazard for motorists, mountain climbers, and hikers. Huge blocks of massive schist and gneiss can reach the valley floor intact, whereas others may trigger debris avalanches on their downward travel. Block movement is facilitated by major joints both parallel and perpendicular to the glacially over-steepened valley walls. The slope failures occur most frequently in early spring, accompanying freeze/thaw cycles, and in the summer, following heavy rains. The study reported here began in August 1986 and ended in June 1989. Manual and automated measurements of temperature and displacement were made at two locations on opposing valley walls. Both cyclic-reversible and permanent displacements occurred during the 13-month monitoring period. The measurements indicate that freeze/thaw mechanisms produce small irreversible incremental movements, averaging 0.53 mm/yr, that displace massive blocks and produce rockfalls. The initial freeze/thaw weakening of the rock mass also makes slopes more susceptible to attrition by water, and heavy rains have triggered rockfalls and consequent debris flows and avalanches. Temperature changes on the rock surface produced time-dependent cyclic displacements of the rock blocks that were not instantaneous but lagged behind the temperature changes. Statistical analyses of the data were used to produce models of cyclic time-dependent rock block behavior. Predictions based solely on temperature changes gave poor results. A model using time and temperature and incorporating the lag effect predicts block displacement more accurately.

  3. Transfer structures in the Northern Tarim Basin, Northwest China

    SciTech Connect

    Guang-Ya Zhang; Shi-Xia Gao

    1996-03-01

    The fold-thrust tectonics of the Northern Tarim Basin, oriented roughly parallel to the South Tianshan orogenic belt, consists of two large-scale tectonic regimes: (1) the foreland-basin, thin-skinned deformation belt; and (2) the foreland-craton, thick-skinned-dominated (i.e., basement-involved) deformation belt. Variations in the degree of deformation in these tectonic belts and style along the regional tectonic strike can be accounted for by longitudinal (progressive transfer or transverse (abrupt) transfer). Longitudinal transfer maintains the overall displacement or shortening within the fold-thrust belts as uniform or with gradual change along the tectonic strike. This includes the tectonic transfer between en echelon master thrusts and from the individual master thrust to terminal fold(s) or distributive thrusts. Transverse transfer resulted from an abrupt change in overall displacement or shortening along the tectonic strike. Within the transverse transfer zone, various tectonics-such as strike-slip faults, strike-slip thrusts, transverse anticlines, and en echelon folds-are developed. The development of longitudinal transfer zones can be attributed to the gradual variation of intrinsic and extrinsic and extrinsic deformational conditions along the tectonic strike. The initiation of transverse transfer may be related to variations in the thickness of sedimentary layers, detachment-layer distribution limits, and variation along strike of the degree and mode of the South Tianshan orogenic belt`s effect on the basin, as well as the variation of the boundary conditions of the deformation, such as in the geometry of plate margins. 15 refs., 8 figs.

  4. Achaean Continental Crust Under the Pan-African Orogenic Belt, East Antarctica

    NASA Astrophysics Data System (ADS)

    Ishikawa, M.

    2001-12-01

    Lützow-Holm Complex, located in East Antarctica, is a Cambrian collision zone between Achaean craton (Napier Complex) and Dronning Moud Land, where occurs the upper amphibolite- to granulite-facies rocks, and it is regarded as a part of the Pan-African orogenic belt during Gondwana continent amalgamation. The exhumation of the granulite-facies rocks with clockwise P-T path has been attributed to extensive surface erosion (up to 30 km thick) of double-thickened crust, but the common belief that higher-pressure garnet bearing rocks e.g. high-pressure granulites and/or eclogites exist at deeper level of crust is not supported by geophysical data. In this paper we reconstruct crustal structure beneath Lützow-Holm Complex by combining ultrasonic velocity of rocks with seismic velocity structure. Consequently our results suggest that Achaean continental crust (lower pressure) exists under the Pan-African Orogenic Belt (higher pressure), and propose a new tectonic model for exhumation of the granulite-facies metamorphic belt instead of the double-thickened crust model. P-wave velocity (Vp) in ultra-high temperature granulites (UHT) was measured up to 1.0 GPa from 25°C to 400°C with a piston-cylinder-type high-pressure apparatus. Rocks measured are meta-igneous UHT rocks collected from Mount Riiser-Larsen, Enderby Land, East Antarctica where the Achaean Napier Complex occurs. Core rock samples with 14mm diameter and 12mm long were subjected to high-pressure experiments. All rocks show a rapid increase of Vp at low pressure up to 0.4 GPa and nearly constant Vp at higher pressures. The Vp values measured at 1.0 GPa and 400°C are 7.17 km/s for a meta-pyroxenite, 6.93 km/s, 6.88 km/s for mafic granulites and 6.17 km/s for an orthopyroxene felsic gneiss. The Vp values measured for the Napier mafic granulites are comparable to the lower crustal layer (6.95 km/s of Vp at depth from 33 to 40 km) under the Lützow-Holm Complex. The present results suggest that the lower crust

  5. The Flux and Energy Spectra of the Protons in the Inner Van Allen Belt

    NASA Technical Reports Server (NTRS)

    Naugle, John E.; Kniffen, Donald A.

    1961-01-01

    A cylindrical stack of G-5 nuclear emulsions housed in the payload section of a four-stage research rocket was flown into the northern edge of the inner Van Allen belt on September 19, 1960. The experimental design permitted, for the first time, measurements of the particle fluxes and energy spectra as functions of position along the rocket trajectory. Eight points along the trajectory have been selected for analysis. Results are presented herein for three of these points, and they are discussed in the light of various theories on the trapped radiation.

  6. Glauconite from the Precambrian Belt Series, Montana.

    PubMed

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

    1963-04-26

    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.

  7. 30 CFR 77.1107 - Belt conveyors.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Belt conveyors. 77.1107 Section 77.1107 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY SAFETY STANDARDS, SURFACE COAL MINES AND SURFACE WORK AREAS OF UNDERGROUND COAL MINES Fire...

  8. 30 CFR 77.1107 - Belt conveyors.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Belt conveyors. 77.1107 Section 77.1107 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY SAFETY STANDARDS, SURFACE COAL MINES AND SURFACE WORK AREAS OF UNDERGROUND COAL MINES Fire...

  9. 30 CFR 77.1107 - Belt conveyors.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Belt conveyors. 77.1107 Section 77.1107 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY SAFETY STANDARDS, SURFACE COAL MINES AND SURFACE WORK AREAS OF UNDERGROUND COAL MINES Fire...

  10. 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 SAFETY STANDARDS, SURFACE COAL MINES AND SURFACE WORK AREAS OF UNDERGROUND COAL MINES Fire...

  11. 30 CFR 77.1107 - Belt conveyors.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Belt conveyors. 77.1107 Section 77.1107 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE SAFETY AND HEALTH MANDATORY SAFETY STANDARDS, SURFACE COAL MINES AND SURFACE WORK AREAS OF UNDERGROUND COAL MINES Fire...

  12. How to install main belts efficiently

    SciTech Connect

    Ketz, J.

    1985-03-01

    Belt conveyors and mine cars form an integral part of the connecting link between an underground working area and the preparation plant. Problems in the link are sometimes neglected while attention is centered on the face. Eventually the neglect may cause the mine to shut down because its operating costs are too high. Mine operators can reduce the chances of such a calamity by correctly installing one of those key links, the main haulage belt conveyors. The following recommendations are based on the author's engineering experience in deep mines. The drive is the heart of the belt conveyor. Five components must be installed properly so that the mechanics can fine tune the belt conveyor drive. A concrete base is essential for a main haulage conveyor projected to be in service for more than 10 years. Beams with 6-in.-wide flanges should be welded to rails embedded in the concrete base. The drive is welded to the 6-in. beams for a permanent installation, and the beams allow dust to be cleaned from under the drive.

  13. 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…

  14. 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.

  15. The thrust belts of Western North America

    SciTech Connect

    Moulton, F.C.

    1993-08-01

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

  16. Dynamic model of Earth's radiation belts

    NASA Astrophysics Data System (ADS)

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

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

  17. 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…

  18. NASA's Radiation Belt Storm Probes (RBSP) Mission

    NASA Astrophysics Data System (ADS)

    Fox, Nicola; Mauk, Barry; Ukhorskiy, Aleksandr; Takahashi, Kazue; Sibeck, David; Grebowsky, Joseph; Kessel, Ramona

    Understanding of radiation belt physics has matured to the extent that we have identified a set of processes which interplay to cause the creation and variation of radiation populations. These universal processes operate coherently across the planetary radiation belts of the solar system, and have far reaching impacts even beyond. Improvements in our understanding of these processes will substantially enhance our ability to predict radiation dynamics and mitigate the impacts on space assets. An important link in developing fully predictive understanding of such processes is the Radiation Belt Storm Probes mission to be launched into Earth's radiation belts in 2012 as a part of NASA's Living with a Star program. RBSP comprises two spacecraft making in situ measurements for at least 2 years in nearly the same highly elliptical, low inclination orbits (1.1 x 5.8 RE, 10 degrees). The orbits are slightly different so that 1 spacecraft laps the other spacecraft about every 2.5 months, allowing separation of spatial from temporal affects over spatial scales ranging from 0.1 to 5 RE. The unusually comprehensive suite of instruments, identical on the two spacecraft, measures the particle spectra (electrons, ions, ion compositions), fields (E and B), and wave distributions (dE and dB) that are needed to resolve the most critical science questions. Here we describe the RBSP mission characteristics, review the most pressing science issues that need to be resolved to develop predictive understanding, and describe how RBSP will be used to resolve those issues.

  19. 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.

  20. 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.

  1. 30 CFR 56.15020 - Life jackets and belts.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 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...

  2. 30 CFR 57.15020 - Life jackets and belts.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 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...

  3. 30 CFR 57.15020 - Life jackets and belts.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 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 57.15020 - Life jackets and belts.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 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...

  5. 30 CFR 56.15020 - Life jackets and belts.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 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...

  6. 30 CFR 56.15020 - Life jackets and belts.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 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...

  7. 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...

  8. A comparison of soft start mechanisms for mining belt conveyors

    SciTech Connect

    Nave, M.L.

    1996-12-31

    Belt Conveyors are an important method for transportation of bulk material in the mining industry. The control of the application of the starting torque from the belt drive system to the belt fabric effects the performance, life cost, and reliability of the conveyor. This paper examines application of each starting method within the coal mining industry.

  9. 30 CFR 57.4263 - Underground belt conveyors.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 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...

  10. 30 CFR 57.4503 - 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. 57.4503 Section 57.4503... Control Installation/construction/maintenance § 57.4503 Conveyor belt slippage. (a) Surface belt conveyors within confined areas where evacuation would be restricted in the event of a fire resulting from...

  11. 30 CFR 75.1403-5 - Criteria-Belt conveyors.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 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...

  12. Conveyor belt scale certification: weighing the various systems

    SciTech Connect

    Carpentier, P.T.

    1983-11-01

    The mechanics of belt weighing are explained. The author stresses the need for better and more consistent guidelines for the testing and certification of belt weighing systems, particularly in the US where more than one body issues these guidelines. Several recognised tests for conveyor belt scale systems are described.

  13. 30 CFR 57.4503 - Conveyor belt slippage.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Conveyor belt slippage. 57.4503 Section 57.4503... Control Installation/construction/maintenance § 57.4503 Conveyor belt slippage. (a) Surface belt conveyors within confined areas where evacuation would be restricted in the event of a fire resulting from...

  14. 30 CFR 57.4263 - Underground belt conveyors.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 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...

  15. 30 CFR 57.4503 - Conveyor belt slippage.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Conveyor belt slippage. 57.4503 Section 57.4503... Control Installation/construction/maintenance § 57.4503 Conveyor belt slippage. (a) Surface belt conveyors within confined areas where evacuation would be restricted in the event of a fire resulting from...

  16. 30 CFR 57.15005 - Safety belts and lines.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Safety belts and lines. 57.15005 Section 57.15005 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL... Protection Surface and Underground § 57.15005 Safety belts and lines. Safety belts and lines shall be...

  17. 30 CFR 56.15005 - Safety belts and lines.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Safety belts and lines. 56.15005 Section 56.15005 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL... § 56.15005 Safety belts and lines. Safety belts and lines shall be worn when persons work where...

  18. 30 CFR 57.15005 - Safety belts and lines.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Safety belts and lines. 57.15005 Section 57.15005 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL... Protection Surface and Underground § 57.15005 Safety belts and lines. Safety belts and lines shall be...

  19. 30 CFR 56.15005 - Safety belts and lines.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Safety belts and lines. 56.15005 Section 56.15005 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL... § 56.15005 Safety belts and lines. Safety belts and lines shall be worn when persons work where...

  20. Motorized two-point safety belt effectiveness in preventing fatalities.

    PubMed

    Evans, L

    1991-01-01

    The effectiveness of two-point motorized restraint systems in preventing fatalities to outboard front-seat car occupants is estimated using published fatality data for one model car equipped with a motorized two-point-belt system, together with a number of assumptions. Effectiveness estimates are obtained for the motorized belt system as used in the field, which reflects the mix of occupants who do and do not fasten the manual lap belt, and for effectiveness when the lap belt is not used. This latter estimate is, therefore, an estimate of the effectiveness of shoulder belts in preventing fatalities. In the data for the one car model, 18% of the fatally injured occupants were ejected. By assuming that three-point belt systems prevent ejection, these data are used to compute the difference in effectiveness between two-point and three-point systems. The result applies to the two-point belt system used in conjunction with whatever manual belt-use rates occurred in traffic. From published observations of lap-belt-use rates for this same vehicle, the effectiveness of the shoulder belt only is estimated. It is found that effectiveness of the two-point restraint system in conjunction with the lap-belt use that occurred in traffic is (32 +/- 5)%. The effectiveness of the shoulder belt only is estimated as (29 +/- 8)%. PMID:2029317