Research

GeoMon staff are available to assist with research projects whenever asked and sponsor research projects of their own and through research students.

We have been assisting Prof Brian Windley and a team of Japanese geoscientists carrying out research on the PreCambrian rocks and using Anglesey’s plate tectonic setting as an ancient parallel for modern day Japan.

This led to an international conference/workshop with 41 papers presented.

Geotectonic evolution of UK with special reference to England and Anglesey island

Maruyama, S.(1), Windley, B.F.(2) and Wood, M.(3)

(1) Tokyo Institute of Technology (2) University of Leicester (3) GeoMon Anglesey Geopark

Abstract

The British Isles has served as one of the world standard areas for the orogeny interpreted by plate tectonics back to 1970s’. The simplified model is the two times of collision orogeny first by Laurencia against Baltica or intra-oceanic arc in Early Paleozoic and collision again with Africa in Late Paleozoic. Before the final collision against continent or arc, oceanic plate subduction must have occurred to proceed the Pacific-type orogeny or Cordilleran-type (Dewey and Bird, 1971).

     Pacific- and collision-type orogeny have been improved in concept, as four components in spatial arrangement, the former composed of (1) orogenic core but a thin slab of regional metamorphic belt with high-P/T thermal gradients cut on both by a paired faults on the top by normal and bottom reverse faults, (2) a huge batholith belt 200-300km wide on the continent side with (3) a fore-arc basin in between, and (4) structural bottom by accretional complex at ocean side (Maruyama, 1997). The similar components and spatial arrangement occur, except (2) of a huge batholith belt in the case of collision-type. Therefore, the Pacific-type plays a critical role to grow continental crust, whereas collision-type never, instead extensive deformation of pre-existing continental crust occurs.

     Recently, new observations of common occurrence of arc subduction without accretion and ubiquitous tectonic erosion of hanging wall of overriding plate instead of formation of accretionary complex, are being settled. These lead a new concept of 2nd Continents which are stable in mantle transition zone (410-660km depth, and stable on the bottom, Kawai et al., 2009), and plays a critical role to warm up the hydrous upper mantle by self-heating because of enriched U, K and Th (Senshu et al., 2009).

     Based on this new framework of orogeny mentioned above, and the data set we have obtained, we speculate the geotectonic development of British Isles, specifically focused to England and Anglesey Island. Two times of collision orogeny and 3-4 times of Pacific-type orogeny occurred in UK, and the latter has grown major part of England, and huge amounts of TTG crusts and arkosic sediments must have subducted underneath UK in the Paleozoic. Those joined to parts of 2nd Continents in the mantle and caused the selective opening of mid-Atlantic Ocean at 190Ma, relatively earlier than North and South Atlantic.

. Ocean plate stratigraphy and its imbrication in an accretionary orogen: The Mona Complex, Anglesey-Lleyn, Wales, 2010 Maruyama, Kawai & Windley. (download PDF) Geological Society London Special Publications 338(1):55-75 DOI:10.1144/SP338.4)

Mineral isograds and metamorphic zones of the Anglesey blueschist belt, UK: implications for the metamorphic development of a Neoproterozoic subduction–accretion complex, KAWAI, WINDLEY et al. 2006 https://doi.org/10.1111/j.1525-1314.2006.00656.x

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