Neoproterozoic: the late Precambrian terranes that formed Eastern Avalonia
Published:January 01, 2006
The late Proterozoic rocks of England and Wales comprise part of eastern Avalonia. Characterization of the basement rocks in southern Britain allows the recognition of five distinct terranes in this part of eastern Avalonia known as the Monian Composite Terrane, the Cymru Terrane, the Wrekin Terrane, the Charnwood Terrane and the Fenland Terrane (Gibbons & Horák 1996; Pharaoh & Carney 2000; Fig. 2.1). During the Neoproterozoic, eastern Avalonia was situated on the NE margin of Gondwana on the southern margin of the Ran Sea (Nance & Murphy 1996; Hartz & Torvik 2002; Fig. 2.2a–d). The Ran Sea itself was formed as a result of rifting of the older Rodinian continental landmass (Fig. 2.2). Avalonian tectonics during this late Proterozoic period were driven by subduction on the NE margin of Gondwana, resulting in associated magmatism and arc basin development. With progressive obliquity of subduction, arc magmatism was replaced by a regime dominated by large-scale transform faulting that progressively dissected and dispersed the arc. The switch from arc mag- matism to intra-continental wrench-related volcanism and magmatism was diachronous, and is first seen in western Avalonia (Murphy et al. 2000). Neoproterozoic sediments of the Avalon Terrane are almost exclusively siliciclastic or volcaniclastic and were deposited within numerous geographically restricted strike-slip basins (Pharaoh et al. 1987a; Nance et al. 1991; McΙlroy et al. 1998; Hartz & Torvik 2002; Fig. 2.3).
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The Geology of England and Wales
This second edition of The Geology of England and Wales is considerably expanded from its predecessor, reflecting the increase in our knowledge of the region, and particularly of the offshore areas. Forty specialists have contributed to 18 chapters, which cover a time range from 700 million years ago to 200 million years into the future. A new format places all the chapters in approximately temporal order. Both offshore and economic geology now form an integral part of appropriate chapters.
Most of England and Wales is formed from part of a single terrane, Avalonia, and its pre-Cambrian (Neoproterozoic) history is preserved in patches. However the time intervals from the Cambrian to the present day are well represented in our sequences and the Cambrian, Ordovician, Silurian and Devonian systems were all defined here. William Smith's map of England and Wales was the world's first geological map of a country and the British Geological Survey's copy is reproduced in the introductory chapter. This chapter, by the editors, consists of a broad overview aimed particularly at the non-specialist while guiding the reader towards the appropriate succeeding chapters. The volume concludes with a look at the future, from the short-term effects of climate change and sea-level rise to the position of our region in a possible plate tectonic configuration 200 million years hence.
While the authors have taken a ‘dynamic’ view of the evolution of the area over geological time, they have also ensured that the geological evidence on which the interpretations are based is reviewed thoroughly. Hence the volume provides a valuable resource for both Earth scientists and the broader community.