Peri-gondwanan terranes: age, provenance and tectonics of the Monian supergroup, Anglesey

Two projects are currently being undertaken which relate to some of the oldest rocks in Wales, exposed on Anglesey and the Llŷn Peninsula. They continue ongoing research into the early evolution of Wales undertaken at the National Museum of Wales in conjunction with a variety of co-workers from other institutes. Geochemical, isotopic and geophysical data show that during this early period (680-550 million years ago) Wales and Southern Britain formed part of Avalonia, a microcontinent or terrane, that lay initially on the edge of the Rodinian continent, and subsequently on the margin of the enormous Gondwana continent, in the southern hemisphere.

This early history was dominated by subduction processes, as oceanic crust was consumed below Avalonia, producing voluminous magmatism, associated volcanicity and sedimentation. It has been suggested that major fault activity, similar to that documented from the coast of California today, may have been responsible for shaving off slices of the crust and shuffling blocks of Avalonia together as subduction increased towards the end of the Neoproterozoic (around 540 million years ago). These projects, based on two separate suites of rocks, are concerned with establishing when this major faulting occurred and the source and nature of a thick succession of sediments.