Caledonian Folding

all the tectonic processes—folding, mountain building, and granitization—of the end of the early Paleozoic and beginning of the middle Paleozoic. These processes marked the end of the development of the geosynclinal systems that had existed since the end of the Proterozoic and beginning of the Paleozoic. The term was introduced by the French geologist M. Bertrand in 1887.

Regions of Caledonian folding in Europe include the Caledo-nides of Ireland, Scotland, Wales, northern England, the northwestern part of the Scandinavian Peninsula, and the islands of Spitsbergen and in Asia, the Caledonides of central Kazakhstan (the western part), Zapadnyi Saian, Gornyi Altai, Mongolian Altai, and southeastern China. Also included among the Caledonides are the folded structures of Tasmania and the Great Dividing Range of eastern Australia, northern and eastern Greenland, Newfoundland, and the northern Appalachians. In addition sections of Caledonian folding have been identified in the Urals, in the northeastern part of the Verkhoiano-Chukotka folded region, in eastern Alaska, in the central and northern Andes, and in certain other younger folded structures.

The earliest phases of Caledonian folding date back to the middle and end of the Cambrian (Salair, or Sardinian); the primary phases encompass the end of the Ordovician, the beginning of the Silurian (Taconian), the end of the Silurian, and the beginning of the Devonian (late Caledonian); and the concluding phases cover the middle of the Devonian (Acadia, or Svalbard). Formations from the period of geosynclinal subsidence are clay slate, graywacke, or sometimes flysch and carbonate, spilite-keratophyre, or diabase. There are intrusions of ultrabasic rocks in the interior zones of many Caledonian geosynclines. In the Silurian, and especially in the early and middle Devonian, thick reddish continental beds of Molasse formation (the ancient red sandstone of the British Isles) developed extensively in intermon-tane troughs. Incomplete development and the absence of fore-deeps are considered to be characteristic of Caledonides. The Caledonides of Scotland, Scandinavia, eastern Greenland, and Newfoundland, where large tectonic sheets (overthrust blocks) are known, are the most complex in structure.

The young platforms that formed at the site of the Caledonides were distinguished by great mobility. After the cessation of vertical movements and leveling of the relief these platforms were tectonically activated in the late Paleozoic in connection with the Hercynian tectogenesis in adjacent geosynclines. New activity, leading to the restoration of mountain relief in most of the areas of Caledonian folding, occurred in Neocene and Anthropogenic times. Caledonian mountain building caused tectonic activity in certain areas of the Baikal folding, for example, on the southern margin of the Siberian platform.