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  • 1
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    Torellian (c. 640 Ma) metamorphic overprint of Tonian (c. 950 Ma) basement in the Caledonides of southwestern Svalbard (2014)
    Cambridge University Press
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    Publication Date: 2014-07-23
    Description: Ion microprobe dating in Wedel Jarlsberg Land, southwestern Spitsbergen, provides new evidence of early Neoproterozoic ( c . 950 Ma) meta-igneous rocks, the Berzeliuseggene Igneous Suite, and late Neoproterozoic ( c . 640 Ma) amphibolite-facies metamorphism. The older ages are similar to those obtained previously in northwestern Spitsbergen and Nordaustlandet where they are related to the Tonian age Nordaustlandet Orogeny. The younger ages complement those obtained recently from elsewhere in Wedel Jarlsberg Land of Torellian deformation and metamorphism at 640 Ma. The Berzeliuseggene Igneous Suite occurs in gently N-dipping, top-to-the-S-directed thrust sheets on the eastern and western sides of Antoniabreen where it is tectonically intercalated with younger Neoproterozoic sedimentary formations, suggesting that it provided a lower Tonian basement on which upper Tonian to Cryogenian sediments (Deilegga Group) were deposited. They were deformed together during the Torellian Orogeny, prior to deposition of Ediacaran successions (Sofiebogen Group) and overlying Cambro-Ordovician shelf carbonates, and subsequent Caledonian and Cenozoic deformation. The regional importance of the late Neoproterozoic Torellian Orogeny in Svalbard's Southwestern Province and its correlation in time with the Timanian Orogeny in the northern Urals as well as tectonostratigraphic similarities between the Timanides and Pearya (northwestern Ellesmere Island) favour connection of these terranes prior to the opening of the Iapetus Ocean and Caledonian Orogeny.
    Print ISSN: 0016-7568
    Electronic ISSN: 1469-5081
    Topics: Geosciences
    Published by Cambridge University Press
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  • 2
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    Direct measurements of skin friction in a turbulent boundary layer with a strong adverse pressure gradient (1980)
    Cambridge University Press
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    Publication Date: 1980-11-13
    Description: This paper describes a new balance, suitable for direct measurement of skin friction in turbulent boundary layers with severe pressure gradients. The gaps between the floating element and the surrounding wall are filled with a liquid in order to eliminate disturbing pressure forces on the element. The resulting friction forces are measured with piezo-electric transducers with high sensitivity and extremely small element displacement. Skin friction measurements were taken in the turbulent boundary layer of a wind tunnel with circular cross-section at M ≤ 0·25. Severe adverse pressure gradients were generated by means of a step on the wall or, alternatively, by a conical centre body. The new apparatus was mainly used to investigate the error of Preston tubes in adverse pressure gradients. It was necessary to develop a new measuring technique to improve the repeatability of the Preston tube readings. The Preston tube error was found to depend on both the local pressure gradient P = (dp/dx) ν/ρ3τ and on the Preston tube diameter uτd/ν and to be independent of the upstream pressure distribution for the range of parameters covered by the experiments. © 1980, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Cambridge University Press
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  • 3
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    Crustal geodynamics from the Archaean Bundelkhand Craton, India: constraints from zircon U–Pb–Hf isotope studies (2015)
    Cambridge University Press
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    Publication Date: 2015-10-21
    Description: A comprehensive study based on U–Pb and Hf isotope analyses of zircons from gneisses has been conducted along the western part (Babina area) of the E–W-trending Bundelkhand Tectonic Zone in the central part of the Archaean Bundelkhand Craton. 207Pb–206Pb zircon ages and Hf isotopic data indicate the existence of a felsic crust at ~ 3.59 Ga, followed by a second tectonothermal event at ~ 3.44 Ga, leading to calc-alkaline magmatism and subsequent crustal growth. The study hence suggests that crust formation in the Bundelkhand Craton occurred in a similar time-frame to that recorded from the Singhbhum and Bastar cratons of the North Indian Shield.
    Print ISSN: 0016-7568
    Electronic ISSN: 1469-5081
    Topics: Geosciences
    Published by Cambridge University Press
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  • 4
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    Sand supply to the Lake Albert Basin (Uganda) during the Miocene-Pliocene: A multiproxy provenance approach (2017)
    American Geophysical Union
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    Publication Date: 2017-06-01
    Description: A multiproxy provenance approach (heavy mineral analysis, U-Pb zircon geochronology, and Pb isotopic analysis of K-feldspar) has constrained sediment supply within the Upper Nile drainage system in the Miocene-Pliocene. Provenance data from sandstones were obtained from three exploration wells, two situated on the north-eastern margin and one on the eastern flank of the Lake Albert Basin, NW Uganda. Data suggest that high-grade to low-grade metamorphic rocks and granitoids have variably supplied the heavy mineral assemblages around the Lake Albert Basin during the Miocene-Pliocene, with contributions from the isotopically heterogeneous Archean Cratons (including the local Ugandan Craton, Tanzanian, and Congo Cratons) and the Pan-African rocks (the Mozambique Belt) with possible contributions from the Neoproterozoic and Paleoproterozoic rocks. These data also highlight clear differences between supply to the eastern basin margin, compared with the northeast, which is reconcilable with current models for Miocene-Pliocene drainage in the region. Supply to northeastern Lake Albert during the Miocene-Pliocene appears to have been through a proto-Albert Nile (draining from NE to SW) and from a proto-Victoria Nile or similarly oriented palaeo-river systems draining from the east. In contrast, the eastern flanks of the basin were likely supplied via the palaeo-Nkusi river, tapping local hinterland sources and more distal basement to the far-east (Mozambique Belt). This study highlights the importance of utilizing a multiproxy approach in provenance analysis as no one signal is capable of distinguishing the different source lands and constraining the evolving drainage patterns. © 2017. American Geophysical Union. All Rights Reserved.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by American Geophysical Union
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