[BCG08-P04] Geotectonic history of Mona Complex in Anglesey-Lleyn, Wales
Keywords:Avalonia, Anglesey-Lleyn, Pacific-type orogeny
The evidences of arc-related magmatism are widely distributed in Wales and Central England, and they date back to 760 Ma. Age data of calc-alkaline granites suggest that the Avalonian subduction and its arc-related magmatism had already started by 711–677 Ma. In the period of main arc magmatism (616–555 Ma), a subduction-related accretion of the Gwna Group sediments started (by 578 Ma) on an active margin of Avalonia. Its accretion likely continued to 530 Ma. Moreover, metamorphic rocks of the Blueschist unit and the Central Shear Zone were exhumed from different crustal depths in the interval 578–530 Ma. Afterwards, sedimentation of the New Harbour and South Stack Groups occurred at < 515 ± 13 Ma and < 501 ± 10 Ma. Sediments of the New Harbour and South Stack Groups were finally accreted underneath the base of the Gwna Group at the accretionary wedge. The greenschist facies metamorphism of the New Harbour Group at 474 Ma constrains its minimum depositional age. In a larger perspective, our new ages are broadly contemporaneous with the calc-alkaline continental arc magmatism in NW Wales and Central England that formed by successive eastward subduction from 711 to 474 Ma.