Geochemistry of accreted metavolcanic rocks from the Neoproterozoic Gwna Group of Anglesey-Lleyn, NW Wales, U.K. MORB and OIB in the Iapetus Ocean

Takuya Saito, Masaoki Uno, Tomohiko Sato, Wataru Fujisaki, Satoru Haraguchi, Yi bing Li, Yusuke Sawaki, Shinji Yamamoto, Shigenori Maruyama

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

The Gwna Group in Anglesey-Lleyn, NW Wales, UK, is a Neoproterozoic accretionary complex that consists of basalt, bedded chert, red claystone, and trench turbidite that have been intercalated in coherent and incoherent mélanges that are considered typical Ocean plate stratigraphy (OPS). The sediments in the OPS can be useful for constraining the geological environment in the Iapetus Ocean. Most basalts in this area have undergone hydrothermal alteration, greenschist facies regional metamorphism, and surface oxidation. This indicates that immobile elements such as Al2O3 and TiO2, Rare Earth Elements (REE) and High Field Strength Elements (HSFE) are appropriate for discriminating the origin of the basalts in the Gwna Group.Most basalts showing light REE-enriched pattern in CI chondrite-normalized spider diagrams in within-plate basalt (WPB) fields, and some have flat patterns in spider diagrams in mid-oceanic ridge basalt (MORB) fields. In view of these relations, we conclude that the former erupted in an oceanic island. Oceanic island basalts (OIB) are common in Phanerozoic accretionary complexes, and this study presents the first evidence of OIB in a Neoproterozoic accretionary complex of the Gwna Group in Anglesey-Llyen and Llyen area. The OIB-like basalts are locally capped by red hematite-rich claystones. This indicates that a fully oxic pelagic condition was present around the oceanic island in the Iapetus Ocean in the Neoproterozoic, which is consistent with the redox condition estimated from contemporaneous shallow marine sediments. On the other hand, the presence of black mudstones on top of MORB-like meta-basalts suggests that deep-sea anoxia conditions were prevalent during the end-Proterozoic.

Original languageEnglish
JournalTectonophysics
DOIs
Publication statusAccepted/In press - Dec 25 2014
Externally publishedYes

Fingerprint

Iapetus
Iapetus Ocean
Wales
metavolcanic rock
mid-ocean ridges
geochemistry
basalt
oceans
rocks
spiders
claystone
stratigraphy
spider
sediments
rare earth element
rare earth elements
flat patterns
diagram
diagrams
anoxia

Keywords

  • Anglesey-Lleyn region
  • Gwna Group
  • LA-ICP-MS
  • Meta-basalt
  • Neoproterozoic

ASJC Scopus subject areas

  • Earth-Surface Processes
  • Geophysics

Cite this

Geochemistry of accreted metavolcanic rocks from the Neoproterozoic Gwna Group of Anglesey-Lleyn, NW Wales, U.K. MORB and OIB in the Iapetus Ocean. / Saito, Takuya; Uno, Masaoki; Sato, Tomohiko; Fujisaki, Wataru; Haraguchi, Satoru; Li, Yi bing; Sawaki, Yusuke; Yamamoto, Shinji; Maruyama, Shigenori.

In: Tectonophysics, 25.12.2014.

Research output: Contribution to journalArticle

Saito, Takuya ; Uno, Masaoki ; Sato, Tomohiko ; Fujisaki, Wataru ; Haraguchi, Satoru ; Li, Yi bing ; Sawaki, Yusuke ; Yamamoto, Shinji ; Maruyama, Shigenori. / Geochemistry of accreted metavolcanic rocks from the Neoproterozoic Gwna Group of Anglesey-Lleyn, NW Wales, U.K. MORB and OIB in the Iapetus Ocean. In: Tectonophysics. 2014.
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abstract = "The Gwna Group in Anglesey-Lleyn, NW Wales, UK, is a Neoproterozoic accretionary complex that consists of basalt, bedded chert, red claystone, and trench turbidite that have been intercalated in coherent and incoherent m{\'e}langes that are considered typical Ocean plate stratigraphy (OPS). The sediments in the OPS can be useful for constraining the geological environment in the Iapetus Ocean. Most basalts in this area have undergone hydrothermal alteration, greenschist facies regional metamorphism, and surface oxidation. This indicates that immobile elements such as Al2O3 and TiO2, Rare Earth Elements (REE) and High Field Strength Elements (HSFE) are appropriate for discriminating the origin of the basalts in the Gwna Group.Most basalts showing light REE-enriched pattern in CI chondrite-normalized spider diagrams in within-plate basalt (WPB) fields, and some have flat patterns in spider diagrams in mid-oceanic ridge basalt (MORB) fields. In view of these relations, we conclude that the former erupted in an oceanic island. Oceanic island basalts (OIB) are common in Phanerozoic accretionary complexes, and this study presents the first evidence of OIB in a Neoproterozoic accretionary complex of the Gwna Group in Anglesey-Llyen and Llyen area. The OIB-like basalts are locally capped by red hematite-rich claystones. This indicates that a fully oxic pelagic condition was present around the oceanic island in the Iapetus Ocean in the Neoproterozoic, which is consistent with the redox condition estimated from contemporaneous shallow marine sediments. On the other hand, the presence of black mudstones on top of MORB-like meta-basalts suggests that deep-sea anoxia conditions were prevalent during the end-Proterozoic.",
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AU - Uno, Masaoki

AU - Sato, Tomohiko

AU - Fujisaki, Wataru

AU - Haraguchi, Satoru

AU - Li, Yi bing

AU - Sawaki, Yusuke

AU - Yamamoto, Shinji

AU - Maruyama, Shigenori

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