2012 Volume 121 Issue 1 Pages 168-180
Since Greenly (1919) first described a ‘mélange’ in Anglesey, as mixed, blocks-in-matrix rock, this has become the world's type locality for mélange. Most of Anglesey and western Lleyn consists of Late Precambrian-Cambrian Mona Complex, which is one of the best, low-grade accretionary orogenic belts in Europe. The prevailing view is that it formed by the fore-arc accretion of tectonic units above a subduction zone of West Pacific type, and thus is characterised by Ocean Plate Stratigraphy. This paper describes the change in thinking about the tectonic development of the Mona Complex and its mélanges over the last 200 years. The various types of mélange are described and their relevance to early life discussed.