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Cornubian batholith
The Cornubian batholith is the group of associated granite intrusions which underlie the south-western peninsula of Great Britain. The main exposed masses of the batholith are seen at Dartmoor, Bodmin Moor, St Austell, Carnmenellis, Land's End and the Isles of Scilly. It formed during the early Permian period, from about 300 to 275 Ma, at a late stage in the Variscan orogeny. The granites are classified as ''S-type'', interpreted to be derived from the partial melting of a sedimentary protolith. The intrusions are associated with significant mineralization, particularly tin, for which the area has been famous since about 2000 BC. It takes its name from ''Cornubia'', the Medieval Latin name for Cornwall.
==Extent and geometry==
From gravity and magnetic geophysical data, the batholith is interpreted to extend from about 8°W, more than 100 km southwest of the Isles of Scilly, to the eastern edge of Dartmoor. The negative gravity anomaly, caused by the relatively low density of the granites compared to average continental crust, is linear and trends WSW-ENE, parallel with that associated with the Haig Fras granite.
The shape of the batholith and the relationship between the individual plutons and the main mass of the granite remained entirely speculative until gravity data began to be used to constrain the thickness and shape of the batholith by modelling. The initial work by Martin Bott suggested that the batholith had an overall trapezoidal shape with a base to the batholith at about 10–12 km. However, current understanding of granite pluton shape suggest that most are either laccolithic or lopolithic. Comparisons with other examples would suggest that the thicknesses of the individual plutons would be in the range 3–5 km, based on their outcrop widths.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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