Ordovician ocean plate stratigraphy and thrust duplexes of the Ballantrae Complex, SW Scotland: Implications for the pelagic deposition rate and forearc accretion in the closing Iapetus Ocean

Wataru Fujisaki, Hisashi Asanuma, Kazue Suzuki, Yusuke Sawaki, Shuhei Sakata, Takafumi Hirata, Shigenori Maruyama, Brian F. Windley

    Research output: Contribution to journalArticle

    9 Citations (Scopus)

    Abstract

    The Ballantrae Complex (at Bennane Lea in SW Scotland) contains important ocean plate stratigraphy (basalt, chert, mudstone, sandstone) in an accretionary prism that is associated with a classic Ordovician ophiolite. We used the ocean plate stratigraphy to sub-divide the prism into 11 tectonic units. To determine the depositional age of bedded cherts, zircons were separated from 9 tuffbeds from 6 different units. All the tuffs have early to middle Ordovician ages, even though their present positions are mutually distant. These ages are consistent with microfossil records of radiolaria and graptolites. The stratigraphic-structural relationships demonstrate that the ocean plate stratigraphy has been repeated by bedding-parallel thrusts; this is typical of a modern accretionary duplex. We calculated the sedimentation rate of Early to Middle Ordovician bedded cherts at Bennane Lea on the basis of U-Pb zircon ages obtained from several tuffbeds; the data indicate that the depositional rate (0.6-3 m/myr) was as slow as that of Mesozoic-Cenozoic equivalents defined by radiolaria. The age spectra of detrital zircons from Ballantrae sandstones show prominent single peaks at ca. 467 and 478 Ma, and a lack of Precambrian zircons. Integration of our new zircon ages with published isotopic data and palaeo-geographic maps indicates that the sandstones were deposited near an intra-oceanic arc and far from any continent containing Precambrian rocks. The pelagic-to-clastic sediments at Bennane Lea were deposited in the closing Iapetus Ocean from ca. 477 Ma to ca. 464 Ma, when they were accreted with the intra-oceanic arc of Ballantrae.

    Original languageEnglish
    Pages (from-to)312-327
    Number of pages16
    JournalTectonophysics
    Volume662
    DOIs
    Publication statusPublished - Nov 20 2014

    Keywords

    • Ballantrae Complex
    • Deep-sea sediments
    • LA-ICP-MS
    • Ocean plate stratigraphy
    • Zircon U-Pb age

    ASJC Scopus subject areas

    • Geophysics
    • Earth-Surface Processes

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