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By P. A. Floyd, C. S. Exley, M. T. Styles (auth.)

This quantity illustrates many of the major facets of magmatic task from Devonian (408 million years in the past) to early Permian (270 million years in the past) instances in SW England. this era covers the innovative improvement of the Variscan mountain-building episode, from preliminary basin formation to ultimate deformation and the next improvement of a fold mountain belt - the Variscan Orogen. either extrusive (volcanic) and intrusive (plutonic) rocks are present in the orogen, and chart many of the levels of its magmatic improvement. The websites defined during this quantity are key localities chosen for conservation simply because they're consultant of the magmatic heritage of the orogen from initiation to stabilization. a number of the earliest volcanic task within the Devonian is represented through submarine basaltic and rhyolitic lavas constructed in subsiding basins, attributable to the attenuation of the present continental crust. sometimes, vast rifting and attendant magmatism produced slim zones of precise oceanic crust, while somewhere else basaltic volcanism is expounded to fractures within the continental crust on the margins of the basins. After the filling of the sedimentary basins, and their deformation brought on by crustal shortening (late Carboniferous Period), additional job is manifested via the emplacement of the Cornubian granites and later minor basaltic volcanism within the early Permian. bills of the constituent components of this historical past have enriched geological literature from the 19th century onwards, and feature contributed to the development and realizing of magmatic and tectonic processes.

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Igneous Rocks of South-West England

This quantity illustrates the various major elements of magmatic task from Devonian (408 million years in the past) to early Permian (270 million years in the past) occasions in SW England. this era covers the innovative improvement of the Variscan mountain-building episode, from preliminary basin formation to ultimate deformation and the next improvement of a fold mountain belt - the Variscan Orogen.

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1), from east to west: the Dartmoor, Bodmin Moor, St Austell, Carnmenellis, Tregonning-Godolphin, Land's End and Isles of Scilly bodies (approximate exposed areas are, respectively, 650 km 2, 220 km 2, 85 km 2, 135 km 2, 13 km 2, 190 km 2 and 30 km 2). 1)' Each of the major outcrops is itself made up of more than one intruSion, and recent work (Hill and Manning, 1987) suggests that some may contain many more intrusions than hitherto suspected. 1). 1), Pb and Sr isotopes (Hampton and Taylor, 1983), and general chemistry and mineralogy which show such features as high K20INa20 and low FeZ03iFeO ratios, high normative corundum, and rare or absent hornblende, sphene and magnetite.

1)' Each of the major outcrops is itself made up of more than one intruSion, and recent work (Hill and Manning, 1987) suggests that some may contain many more intrusions than hitherto suspected. 1). 1), Pb and Sr isotopes (Hampton and Taylor, 1983), and general chemistry and mineralogy which show such features as high K20INa20 and low FeZ03iFeO ratios, high normative corundum, and rare or absent hornblende, sphene and magnetite. These are all characteristics of the 'Stype' granites sensu Chappell and White (1974).

1976; Kirby, 1979b) and this is good evidence to suggest that they are part of an ophiolite complex. The Traboe Complex has more primitive chemical compositions but, as they are plutonic rocks that have formed by crystal fractionation, they cannot be directly compared with the Landewednack type which are dominantly metabasaltic lavas. A consensus of opinion has yet to emerge, but the most recent and most detailed study by Sandeman (1988) favoured the composite intrusive model. Hornblende Schists The Hornblende Schists were divided by Flett and Hill ( 1912), into two types, the Landewednack type and the Traboe type.

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