Geological structure of Great Britain

A useful approach to considering Britain's geological structure is to examine the various terranes from which it is composed. These are essentially continental fragments whose boundaries are generally defined by faults. Individual terranes typically contain suites of structures, the histories and form of which differ from those of neighbouring terranes. Terranes of Scotland The Hebridean terrane is defined to the east by the Moine Thrust, beyond which lies the Northern Highlands terrane. This area in turn abuts against the Central Highlands (or Grampian) terrane along the Great Glen Fault. Similarly the Highland Boundary Fault separates the Central Highlands terrane from the Midland Valley terrane, which is itself separated from the Central Southern Uplands terrane by the Southern Uplands Fault. Each of these terranes form a part of the former continent of Laurentia whose southeastern margin is defined by the Iapetus Suture Zone, which runs parallel to the English-Scottish border, though some miles to its south. Terranes of England and Wales The Central Southern Uplands terrane extends across the northernmost part of England. Its southern margin is the Iapetus Suture, south of which lies the Leinster–Lakesman terrane which includes the Lake District and North Pennines. The majority of the rest of England and Wales north of the Variscan Front are considered to constitute the Avalon composite terrane. Central to this composite terrane is the triangular-shaped Midlands Microcraton; within it, the north–south aligned Malvern line (or 'Malvern lineament') divides the Wrekin terrane in the west from the Charnwood terrane in the east. The Isle of Anglesey and parts of the Lleyn peninsula are deemed to be composed of numerous micro-terranes, known collectively as the Rosslare–Monian terrane. Pennine Block & Basin Province Northern England is characterised by a series of fault-bound blocks separated by sedimentary basins whose origin can be traced back to the Carboniferous period. The North Pennines are formed on the Alston Block which is defined to the west by the Pennine Fault and to the north by the Stublick and Ninety Fathom Faults. It is separated from the Askrigg Block to the south by the Stainmore Trough. This latter block, coincident with the Yorkshire Dales, is defined to the west by the Dent Fault and to the south by the Craven Fault System. The Northumberland and Gainsborough Troughs lie to the north and south of these two blocks. ==Structural legacy of mountain-building episodes==