1 The Alps in their Plate tectonic Framework 1.1 Older Mountain Chains in Europe 1.2 Break-up of Pangaea and opening of the Alpine Tethys 1.3 The Alpine System in Europe 1.4 Structure of the Alps COPYRIGHTED MATERIAL 0002087327.INDD 1 3/11/2014 10:56:20 AM 2 1 The Alps in their Plate Tectonic Framework ▸ Figure 1.1 Tectonic Rocks can be found in the Alps that and is compressed. During this process, map of Europe showing range in age from one billion years to the uppermost portions of the crust are mountain ranges coloured according to their age of present times. The rocks themselves – pushed upwards and gradually build a formation and associated sedimentary, igneous, metamorphic and mountain chain. This process is called terranes and continents. unconsolidated rock – cover the entire orogenesis or mountain-building. conceivable spectrum. Many of these A number of such collisions between rocks and their formation can be under- continents, or orogenies, have occurred stood only within the context of the during the geological evolution of geological structure of Europe and the Europe. Accordingly, we distinguish associated plate tectonic processes. In between Caledonian, Variscan and the following therefore, the plate tec- Alpine orogens. The continental plates tonic framework for Europe, the older involved in these collisions were North mountain chains and the younger America, Siberia, Baltica/Europe and Alpine mountain ranges in Europe will Africa and are also called terranes. The be considered briefly. tectonic map in Fig. 1.1 takes this divi- sion into consideration. Europe has also been subdivided into Eo-, Palaeo-, 1.1 Older Mountain Chains in Europe Meso- and Neo-Europe, based on the relative ages of these orogenies. It must From a geological perspective, the be noted that the terranes mentioned European continent has a highly cheq- above contain rock units that are relics uered history. Although the Alps are an of even older, fully eroded mountain integral component of this continent chains. and are, essentially, a spectacular moun- Eo-Europe is a large geological tain chain, their origin lies in the recent structure, a welded block that experi- geological history of the continent. enced no further orogenies after the In order to understand the geological Precambrian. Two geological provinces structure of Europe, the individual are distinguished within Eo-Europe: regions need to be classified according the Baltic Shield and the Russian to the age of their consolidation. In this Platform. case, the term consolidation is taken to The Baltic (or Fennoscandian) mean the welding of continents, follow- Shield is a convex bulge or shield cover- ing on from the motion of plates. ing a large area, which is composed of a Almost all of the mountain chains in highly metamorphic crystalline base- Europe originated as a result of plate ment (Baltica in Fig. 1.1). Multiple, Baltic Shield movements, where an ancient ocean very ancient and fully eroded mountain was swallowed up in a subduction zone chains can be distinguished within and the continental blocks subsequently these series of rock formations. The collided with each other. The density of oldest rocks in the Baltic Shield are continental crust is relatively low and, three to three and a half billion years therefore, buoyancy acts against it sink- old and were encountered in a deep drill ing to greater depths once it has entered core obtained in the region of Kola, to a subduction zone. As a result, conti- the south of the White Sea, as well as in nental crust remains close to the surface Lapland. Geology of the Alps: Revised and updated translation of Geologie der Alpen, Second Edition. O. Adrian Pfiffner. © 2014 John Wiley & Sons, Ltd. Published 2014 by John Wiley & Sons, Ltd. 0002087327.INDD 2 3/11/2014 10:56:21 AM 1.1 Older Mountain Chains in Europe 3 Baltic Urals Shield Caledonides Russian Platform C ar pa th ia n Alps s Pyr Caucasus enees Dinarides Apennines s Balkan Pontides Alborz Hellenides Betic Cordillera Rif Tell-Atlas Zagros Middle Atlas Sahara-Atlas High Atlas 1000km Mountain ranges Terranes Alpine North America Africa Phanerozoic sediments Variscan Siberia Arabia Traces of cross-sections Caledonian Baltica/Europe The Russian Platform is the sedi- depressions or basins with thick sedi- mentary cover over the Baltic Shield mentary successions as well as zones and is composed of Neoproterozoic with a thin sedimentary cover. The sedi- non-metamorphosed sediments, over- ments of the Russian Platform reflect Russian Platform lain by Cambrian rocks as well as a the later phases of mountain-building series of rock formations that extend that took place at its margins. Examples into the Cenozoic. In the southeast, the are the famous Old Red Sandstone, platform plunges beneath the foreland continental fluviatile sediments of the of the Caucasus, to the north of the Middle to Late Devonian that are the Caspian Sea, and in the east and west, erosional product from the (Caledonian) beneath the forelands of the Ural and mountains in Norway and Scotland, the Carpathian Mountains. The internal Permo-Triassic continental lagoon sedi- structure of the plate contains local ments in the foreland of the (Variscan) 0002087327.INDD 3 3/11/2014 10:56:22 AM 4 1 The Alps in their Plate Tectonic Framework Urals and the Cenozoic continental more detail later on. The linear moun- formations in the foreland of the tain chains of the Pyrenees and the Caucasus and Carpathians. Sediments High and Middle Atlas share the com- of the Russian Platform are usually mon trait that an orogeny is mainly marine deposits in the centre (with the characterized by strike-slip motion exception of the Early Carboniferous along linear faults. In addition to the coal swamps in the area of Moscow), strike-slip motion, a compressive com- but the sea retreated towards the south ponent caused a shortening of the mar- after the Early Cretaceous and the gins of the fault lines, which was Russian Platform became subaerial. responsible for the actual ‘up-folding’ of Palaeo-Europe refers to the these mountain chains. Caledonian orogen that extends across A simplified illustration of Europe’s Scandinavia to Ireland. Other parts plate tectonic evolution and the origins are found in Greenland and the of the Caledonian and Variscan orogens Appalachians. This broad geographical is provided in Fig. 1.2. This figure distribution is sufficient to indicate that shows how several continents were later plate movements fragmented this welded into a megacontinent, Pangaea, Early Palaeozoic mountain chain. Plate over the course of 300 million years. movements responsible for this were, In the Late Cambrian (500 million for example, the opening up of the years ago), the southern continent, North Sea from the Permian onwards Gondwana, unified the extant land and the opening up of the North masses of South America, Africa and Atlantic starting in the Jurassic. parts of Asia. The continents of Baltica Meso-Europe includes the Variscan (approximately Sweden, Finland and orogen that originated in the Late Russia today), Siberia and North Palaeozoic. With the exception of the America were surrounded by oceanic Urals, the Variscan mountain chain basins, in which thick sedimentary can be followed as a continuous range, deposits accumulated. At the northern which in Germany and France is gener- continental margin of Baltica, 1400 ally completely eroded and covered metres of grey and reddish arkoses, con- with younger sediments, as illustrated glomerates, limestones and shales were by the island-like distribution of rem- deposited in the shallow part of the nants of these mountains shown in Iapetus Ocean during the Proterozoic Fig. 1.1. (about 600 million years ago). The Finally, Neo-Europe comprises a arkoses also contain tillites, that is, fos- series of mountain chains that origi- silized diamictites (glacial deposits that nated in the Jurassic (Turkey), in the indicate very ancient glaciations). The Cretaceous (parts of the Alps and Cambrian starts with a basal conglom- Pyrenees), but mainly in the Cenozoic. erate that contains alum slate, that is, These mountain chains are often wind- a dark pelite rich in iron sulphide. ing and arc-shaped. In addition to the The marine sedimentation continued Alps, good examples are the Carpathians in the Ordovician–Silurian, with clay, and the Betic Cordillera–Rif–Tell– limestone and turbidite deposits. Atlas system. This arc shape is essen- Greenstones with gabbro and perido- tially due to the geometry of the plate tite, typical rock associations in a newly boundaries of the different associated developing oceanic crust, originated in microplates, a point that is discussed in the Iapetus Ocean itself. Finally, 6000 0002087327.INDD 4 3/11/2014 10:56:22 AM 1.1 Older Mountain Chains in Europe 5 Figure 1.2 Plate tectonic metres of Torridonian arkoses, con- Early Jurassic (200 Ma) evolution of Europe shown glomerates, sandstones, greywackes and Europe in four time slices. Positions pelites were deposited at the North of plates are based on Blakey American continental margin in the NAm Tethys (2008) and Scotese & Sager Proterozoic. This was followed by (1988). A, Appalachians; quartzites in the Cambrian and then Africa K, Caledonides; E, Ellesmere thick dolostones, which continued to be SAm orogen; V, Variscan orogen; deposited into the Ordovician. U, Urals; NAm, North The Iapetus Ocean was gradually Pacic America; SAm, South closed through subduction and a large America. mountain range was formed due to the collision of Baltica with North America: Late Carboniferous (300 Ma) the Appalachians in North America Siberia and the Caledonian orogen in Europe U (Scandinavia and the Bristish Isles). NAm N China Pacic Baltica Figure 1.3 shows two cross-sections V through the Caledonian mountain chain. A Palaeo-Tethys The cross-section through the Caledonian mountain chain in Scandinavia shows SAm how the Baltic Shield was overthrust in Africa an easterly direction by large thrust sheets Ice cap containing the Precambrian crystalline basement of the past continental margin of Baltica and its Proterozoic–Palaeozoic Early Devonian (400 Ma) sedimentary cover.