Reconstruction of ocean plate stratigraphy in the Gwna Group, NW Wales

Implications for the subduction-accretion process of a latest Proterozoic trench-forearc

Hisashi Asanuma, Yoshihiro Okada, Wataru Fujisaki, Kazue Suzuki, Tomohiko Sato, Yusuke Sawaki, Shuhei Sakata, Shinji Yamamoto, Takafumi Hirata, Shigenori Maruyama, Brian F. Windley

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

The Gwna Group in Anglesey island and Lleyn peninsula, Wales consists of a latest Proterozoic volcano-sedimentary trench mélange, which has a complicated accretionary structure, and is poorly constrained by isotopic ages. The mélange contains oceanic-trench rocks including pillow basalts, cherts, mudstones and sandstones, which have not previously been interpreted as ocean plate stratigraphy (OPS). We reconstructed imbricated OPS at 5 localities in the coastal Lleyn peninsula. In order to constrain the depositional U-Pb age of the upper clastic sediments, detrital zircons, separated from 9 clastic sediments, were analyzed with a Nu AttoM single-collector inductively-coupled plasma-mass spectrometer. The ages indicate that there are two Gwna Groups (maximum depositional ages of: 1 at 608-601. Ma, and 2 at 564-539. Ma) that were deposited between the late Neoproterozoic and the Middle Cambrian contemporaneously with dated calc-alkaline arc magmatism and regional metamorphism in the Anglesey-Lleyn complex. The age spectra of the detrital zircons show a prominent peak at ca. 650-600. Ma, and several Proterozoic and Archean ages. To account for the older ages, we integrated our new isotopic data with published radiometric and fossil ages, and conclude that the clastic sediments at the top of the OPS were deposited in a trench on the western active margin of Avalonia when it was close to the Amazonian craton, and that the Gwna Group OPS began to be incorporated into an accretionary wedge in an active subduction zone in the latest Proterozoic.

Original languageEnglish
JournalTectonophysics
DOIs
Publication statusAccepted/In press - Dec 2 2014
Externally publishedYes

Fingerprint

Wales
stratigraphy
trench
Proterozoic
oceans
subduction
accretion
sediments
peninsulas
ocean
clastic sediment
cratons
fossils
sandstones
basalt
volcanoes
accumulators
wedges
mass spectrometers
margins

Keywords

  • Gwna Group
  • LA-ICP-MS
  • Lleyn peninsula
  • Ocean plate stratigraphy
  • Zircon U-Pb age

ASJC Scopus subject areas

  • Earth-Surface Processes
  • Geophysics

Cite this

Reconstruction of ocean plate stratigraphy in the Gwna Group, NW Wales : Implications for the subduction-accretion process of a latest Proterozoic trench-forearc. / Asanuma, Hisashi; Okada, Yoshihiro; Fujisaki, Wataru; Suzuki, Kazue; Sato, Tomohiko; Sawaki, Yusuke; Sakata, Shuhei; Yamamoto, Shinji; Hirata, Takafumi; Maruyama, Shigenori; Windley, Brian F.

In: Tectonophysics, 02.12.2014.

Research output: Contribution to journalArticle

Asanuma, Hisashi ; Okada, Yoshihiro ; Fujisaki, Wataru ; Suzuki, Kazue ; Sato, Tomohiko ; Sawaki, Yusuke ; Sakata, Shuhei ; Yamamoto, Shinji ; Hirata, Takafumi ; Maruyama, Shigenori ; Windley, Brian F. / Reconstruction of ocean plate stratigraphy in the Gwna Group, NW Wales : Implications for the subduction-accretion process of a latest Proterozoic trench-forearc. In: Tectonophysics. 2014.
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abstract = "The Gwna Group in Anglesey island and Lleyn peninsula, Wales consists of a latest Proterozoic volcano-sedimentary trench m{\'e}lange, which has a complicated accretionary structure, and is poorly constrained by isotopic ages. The m{\'e}lange contains oceanic-trench rocks including pillow basalts, cherts, mudstones and sandstones, which have not previously been interpreted as ocean plate stratigraphy (OPS). We reconstructed imbricated OPS at 5 localities in the coastal Lleyn peninsula. In order to constrain the depositional U-Pb age of the upper clastic sediments, detrital zircons, separated from 9 clastic sediments, were analyzed with a Nu AttoM single-collector inductively-coupled plasma-mass spectrometer. The ages indicate that there are two Gwna Groups (maximum depositional ages of: 1 at 608-601. Ma, and 2 at 564-539. Ma) that were deposited between the late Neoproterozoic and the Middle Cambrian contemporaneously with dated calc-alkaline arc magmatism and regional metamorphism in the Anglesey-Lleyn complex. The age spectra of the detrital zircons show a prominent peak at ca. 650-600. Ma, and several Proterozoic and Archean ages. To account for the older ages, we integrated our new isotopic data with published radiometric and fossil ages, and conclude that the clastic sediments at the top of the OPS were deposited in a trench on the western active margin of Avalonia when it was close to the Amazonian craton, and that the Gwna Group OPS began to be incorporated into an accretionary wedge in an active subduction zone in the latest Proterozoic.",
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AU - Okada, Yoshihiro

AU - Fujisaki, Wataru

AU - Suzuki, Kazue

AU - Sato, Tomohiko

AU - Sawaki, Yusuke

AU - Sakata, Shuhei

AU - Yamamoto, Shinji

AU - Hirata, Takafumi

AU - Maruyama, Shigenori

AU - Windley, Brian F.

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KW - Zircon U-Pb age

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