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

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▸ 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.

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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)

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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

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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 Paci c 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 Paci c 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. These crystalline nap- Siberia pes were thrust onto the Baltic shield over hundreds of kilometres, as can be seen China from the example of the Jotun Nappe. E Prototethys Baltica The thin obducted nappes of Aurdal and NAm K Synfjell are mainly composed of Early A

Palaeozoic sediments. At the extreme Rhea east, the Oslo Graben is visible, which is a G o n d w a n a SAm Africa rift within the Baltic shield that is largely filled with Permian igneous rocks. In the west, towards the North Sea, there are Late Cambrian (500 Ma) ophiolitic rocks overlying the Jotun Nappe, relics of the Iapetus Ocean. Prototethys Panthalassa Fragments of this ocean were not sub- ducted during the collision between Siberia Baltica and North America, but instead NAm incorporated into the developing moun- tain chain. Iapetus A certain similarity can be seen Baltica when comparing the cross-section G o n d w a n a through Scotland with that through Mountain chain Scandinavia. The cross-section shown Rift Shape of present-day continents in Fig. 1.3 has been adapted from

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NW Scotland SE

1 Mo GO 1 BM

0 0

–1 –1

–2 –2

[km] [km]

5km Palaeozoic magmatic rocks Sediments

Loch Ailsh intrusion Durness Formation (Ordovician dolomites)

Dykes An t-Sron Formation (Cambrian dolomites)

Palaeozoic magmatic rocks Pipe Rock (Cambrian quartzite)

Lewisian (gneisses, metasediments) Lower Quartzite (Cambrian quartzite)

Torridonian (Precambrian clastics)

Mo Moine rust Crystalline basement (Laurentia) GO Glen Oykel rust Lewisian (gneisses, schists) BM Ben More rust

WNW Scandinavia ESE

l nel Oslo Graben Jotun Valdres Sy Aurdal 0 Jotun 0

Jotun Western Gneiss Complex Shield Baltic

Moho

–50 –50 [km] [km]

50km

Oslo Graben Baltica Permian magmatic rocks: Late Precambrian - Late Palaeozoic granite /volcanite Ophiolites and sediments sediments Late-/post-orogenic sediments Crystalline basement of Baltica

Devonian conglomerate Lithospheric mantle

Elliott & Johnson (1980). In this case, is exposed in the Outer Hebrides in the the Precambrian crystalline basement northwest of Scotland. The ‘Lewisian’ has also been included in the structure has a greater affinity to the crystalline of the nappe. This ‘Lewisian’ basement basement of the North American

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­craton in the foreland of the Ocean. Towards the northeast, the ◂ Figure 1.3 Geological cross-sections through the Appalachians in Canada and Greenland Rheic Ocean met up with the Proto- Caledonian orogen in than to the Baltic Shield. From a geo- Tethys Ocean, which separated the Scandinavia and Scotland. logical perspective, the Outer Hebrides continental masses of Siberia and In both cases, the crystalline must thus be regarded as part of North China. The Old Red Sandstone is the basement is affected by America. product of erosion of the Caledonian thrusting and is involved in The highest unit, the Moine Nappe mountain chain and the Appalachians, the nappe structure. Complex, has been almost completely and represents delta deposits at the Transport, however, occurred eroded in this cross-section. However, margin of the continent (i.e., close to in opposite directions in the degree of metamorphism in the the Caledonian mountain chain). Sandy Scandinavia and Scotland. rocks below permits the clear conclu- clastic sediments were also deposited at Source: Based on Elliott & sion that there was once a thick nappe the northern margin of Gondwana (in Johnson (1980). pile overlying the currently visible rock today’s Atlas). Pure limestones and formations (Strachan et al. 2002), shales were deposited in the Rheic and because the Moine Nappe Complex Proto-Tethys oceans in the Devonian, exhibits a higher degree of metamor- which are now exposed in the Eastern Caledonides: phism than the rocks below it. Alps. A microcontinent can be seen bivergent orogen, The chronology of the formation of in the centre of the Rheic Ocean. basement involved these nappes can be narrowed down Sedimentation is patchy here, indicat- in thrusting based on the example of the Loch Ailsh ing shallow water depth. These sedi- intrusion: the Glen Oykel Thrust is ments have been preserved, for example, cross-cut by the intrusion (so, is older), in the North Alpine foreland, in the while the Ben More Thrust displaces Vosges, the Black Forest and in the and transports the intrusion (so, is Bohemian Massif. This microcontinen- younger) and the Moine Thrust caps tal zone is also called Moldanubicum. the intrusion and is therefore also The closure of the Rheic Ocean and younger. The Loch Ailsh intrusion is collision of the continents North dated at 434 million years ago (Silurian). America–Baltica and South America– It can be regarded as synorogenic, as it Africa led to the Variscan orogen is located chronologically between the (Fig. 1.1). The collision stages mainly formation of the Glen Oykel and the occurred around the Devonian– Ben More or Moine thrusts. Carboniferous transition, 345 million In great contrast to Scandinavia, years ago, and then in the Early the nappes in Scotland (and in the Carboniferous, 320 to 300 million Appalachians) were transported in a years ago. In Europe, the Rhenish northwesterly direction. Overall, the Schiefergebirge, the Ardennes, the Caledonian mountain chain therefore Cantabrian Mountains on the Iberian exhibits a bivergent nappe structure, a Peninsula, as well as the mountain- structure that is typical for mountain ous areas in Brittany and in the chains that emerge from a continent– Massif Central originated. On the continent collision. North American side, the Southern The Rheic Ocean remained intact Appalachians were uplifted. Therefore, after the collision between Baltica and the Appalachians have a more complex North America (Rhea in Fig. 1.2). The history of formation and are the prod- continent Gondwana, which included uct of more than one collision. the land masses of South America and Plate convergence between Siberia Africa, lay to the south of the Rheic and Baltica led to the uplift of the Ural

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Mountains (Fig. 1.2). The Proto-Tethys subcontinent from Africa and another was reduced to an almost closed sea rift opened up between Africa and the basin, the Palaeo-Tethys. For example, as Variscan mountain chain. This rift for- is shown In Fig. 1.2, Baltica migrated mation and the associated ingress of the from the Southern Hemisphere, north- Tethys Ocean towards the west are cru- wards across the Equator and into the cial to the understanding of the geology Northern Hemisphere during the period of the Alps and are therefore discussed from the Late Cambrian to the Early in more detail below. Carboniferous. The southern tip of the welded continent underwent a glaciation in the Early Carboniferous. 1.2 Break-up of Pangaea and opening The internal structure of the Variscan of the Alpine Tethys mountain chain in Europe is illustrated in Fig. 1.4 in a cross-section through The plate tectonic processes during Variscides: Germany (redrawn from Matte 1991). A the break-up of the megacontinent, bivergent orogen, bivergent nappe pile was formed during Pangaea, had a variety of effects on the basement involved in thrusting the collision, which also includes the Alps when they were formed later on. crystalline basement, similar to the case The small ocean basins and microconti- for the Caledonian mountain chain. nents that originated during this ­process The nappes at the continental margin of resulted in a complicated juxtaposi- Gondwana were transported to the tion of different sedimentary environ- southeast and on the margin of Baltica to ments: deep-sea basins, shelf seas and the northwest. The thick Palaeozoic sedi- ­submarine rises. The very different ments of the Rhenish Slate Mountains sedimentary facies representing these were pushed over each other like tiles and environments are now visible in the folded. The basal detachment of the nap- Alps juxtaposed vertically and laterally, pes took place in a thick slate horizon. in apparent complete disorder. The At the core of the orogen there is a verti- ­palaeogeographical shapes of the sedi- cally oriented fault that can be followed mentary basins affected the architecture from Portugal to Bohemia, which prob- ably represents a component of strike- slip motion. Even though the exposure of NW Sub-Variscides Rheno-Hercynic the core of the orogen is only patchy and Rheinisches Schiefergebirge is often covered by younger sediments, remnants of the Rheic Ocean can be 0 found in a variety of locations in the form Figure 1.4 Geological ▸ of ophiolites. cross-section through the In the early Jurassic, 200 million Variscan orogen in central –50 Europe. The crystalline years ago, the welded continental mass [km] basement is affected by that became Pangaea had migrated 100km thrusting and involved in the ­further to the north and experienced nappe structure. But the a degree of anti-clockwise rotation Palaeozoic sediments transport directions on (Fig. 1.2). The ocean between Africa Carboniferous either side of the orogen are and Asia became the Tethys. However, Devonian opposite. Source: Matte movements had now started that slowly Palaeozoic (1991). Reproduced with led to the break-up of Pangaea. For permission of Elsevier. example, one rift separates the Indian

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of the Alps when these basins were precursor to the Atlantic and extended as closed during the formation of the Alps. far as Mexico. In the Early Cretaceous, The break-up of Pangaea is illustrated 120 million years ago, North America in three snapshots in time in Fig. 1.5. and Africa drifted further apart and the A level of uncertainty is associated with Central Atlantic was born. In the north, all of these plate reconstructions, which Iberia separated from North America. is why these palaeogeographic maps also The movement of Iberia was due to a vary greatly from one author to the next. spreading ridge in the west (mid-oceanic Figure 1.5 was simplified and redrawn ridge of the Atlantic as it was opening from illustrations by Blakey (2008). In up) and a transform fault to the north the Early Triassic (Keuper), 230 million and to the south of Iberia. In the north, years ago, Pangaea broke up along a rift further spreading systems extended that opened up between Gondwana and either side of Greenland. These were the Laurasia. The rift originated in the forerunners for the opening up of the Tethys, and extended along an arm of the North Atlantic. Tethys between the continental masses of Figure 1.6 shows a simplified plate Arabia and Greece–Italy. The Palaeo- reconstruction for the Jurassic– Tethys was then closed by subduction, Cretaceous transition (about 145 mil- such that the Turkish landmass was lion years ago), adapted from Wortmann welded to Laurasia (Baltica) in the et al. (2001). Opinions diverge on the Middle Jurassic (Dogger), 170 million exact geometries of the individual years ago. The eastern part of the rift basins, but the solution given in Fig. 1.6 shifted to the north and now separated is a combination of their essential char- the landmass Greece–Italy from Laurasia. acteristics. This shows a continental This small ocean basin is referred to as fragment extending from Iberia in a the Ligurian or Piemont Ocean in Alpine northeasterly direction and composed geology. The rift expanded to the west of Corsica–Sardinia–Briançon, which and separated Africa–South America became separated from Iberia. The from North America. This rift was the Corsica–Sardinia–Briançon continental

SE Saxothuringian Barrandian Moldanubian Taunus Spessart Central Bohemian Gießen nappe shear zone Molasse Basin 0

–50 [km]

Crystalline basement

Post-Variscan sediments Baltica

Palaeozoic sediments with Africa / Gondwana ophiolites Seismic Moho Petrologic Moho

Lithospheric mantle

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Figure 1.5 The break-up Early Cretaceous (120 Ma) Briançon microcontinent corresponds of Pangaea shown in three to the Valais Basin, and that in the time slices. Positions of southeast corresponds to the Penninic plates are based on Blakey Grl Baltica (2008) and Scotese & Sager Ocean. A transform fault separated Iberia from Europe and acted as a local (1988). Grl, Greenland; It, Tu North America Italy; Gr, Greece; Tu, Turkey; Tethys plate boundary during the drift of SAm, South America; Wr, Iberia It Gr Iberia away from North America. Wrangellia; Mex, Mexico. Another transform fault connects the Atlantic Arabia Piemont with the Penninic Ocean. The Africa opening up of the Atlantic occurred Paci c SAm simultaneously with an oblique open­ ing up of the Ligurian–Piemont and Penninic oceans. The Dauphinois– Middle Jurassic/Dogger (170 Ma) Helvetic realms on the southeastern margins of Europe and the Southalpine Grl Baltica Dolomites to the north of the Adriatic Paci c and in the Eastern Alps between the L a u r a s i a Tu Vardar and Penninic Ocean are of North America ­particular relevance to today’s Alps. It Tethys Gr Figure 1.7 illustrates the broad palaeo- Africa geographical situation at the Barremian–

Wr Mex Aptian transition, 125 million years SAm Arabia ago. The reconstruction is based on G o n d w a n a Wortmann et al. (2001). The Ligurian– Piemont Ocean is characterized by mul- tiple transform faults that indicate Late Triassic/Keuper (230 Ma) progressive oblique opening up of this

Paci c ocean. A transform fault separates the Grl Baltica Adriatic from the microcontinents L a u r a s i a Bakony, Austroalpine and Tiza. The Palaeo-Tethys P a n g a e Valais Basin opened up further due to the Tu thinning of the continental margin of North It Tethys America a Gr Baltica, or Europe, and evolved oceanic crust only in certain locations, in ‘pull- Arabia South Africa apart basins’. In contrast, the Piemont America G o n d w a n a Ocean had a mid-oceanic ridge that led to the formation of oceanic crust. Initial Rift Spreading zone The Adriatic continental margin and Transform fault the Austroalpine microcontinent were stretched in an east–west direction by the opening up of the Piemont and the fragment corresponds to the so-called Penninic oceans. The normal faults in Briançon microcontinent, a submarine the future Austroalpine and Southalpine rise that can be traced from the Western realms are evidence of this. Alps through to the Swiss Alps. The The Alps originated as a result of sea basin to the northwest of the ­convergent plate movements between

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Figure 1.6 Plate 30°N reconstruction for the Berriasian (ca. 145 million years ago), simplified after Europe ic et v el Wortmann et al. (2001). The H - is Ligurian (Li)–Piemont (Pi) no hi e I beria p VS n Ocean stretches between the 25°N au i D p l a microcontinents of Iberia and o Vo r ardin. t Vardar n Pe s Tiza Adria. It is disrupted by a u Cors.-S Pi Brianço A Alboran transform fault and continues as the Penninic (Pe) Ocean Bakony Dolomites between the Briançon and 20°N Southalpine Drau Austroalpine continental Li Adria fragments. Narrow basins, the Vocontian (Vo) and Valais (VS) straddle the southern Africa margin of the European continent. Cors-Sard, Land Passive margin Spreading ridge Active margin Corsica–Sardinia continental Epicontinental sea Ocean Transform fault Modern coast line fragment. Source: Wortmann et al. (2001). Reproduced with permission of John Wiley & Sons.

Figure 1.7 Plate 30°N reconstruction for the

Europe Barremian (ca. 125 million ic et v years ago), simplified after el n H a - e s c e Wortmann et al. (2001). The i n o O in i h p p l Ligurian–Piemont Ocean is au c a D VS i o I beria n r n i t now wider and aligned with 25°N Vo n s ardin. n u Brianço e A Tiza Vardar the Penninic Ocean. Cors.-S P Similarly, the Southalpine

Bakony and Austroalpine domains Alboran are now aligned. Cors-Sard, n ea c Dolomites Corsica–Sardinia continental 20°N O SouthalpineAdria Drau t fragment; Vo, Vocontian n o m basin; VS, Valais basin. ie P Source: Wortmann et al. Africa - rian Ligu (2001). Reproduced with permission of John Wiley & Sons. Land Shelf sea Spreading ridge Active margin Epicontinental sea Ocean Transform fault Modern coast line

Baltica/Europe and Africa–Arabia. The Piemont–Penninic ocean was closed During this process, the sea basins that by subduction proceeding in a westerly lay between, the Piemont Ocean and the direction in the Cretaceous, the Valais Valais Basin, were closed up by subduc- Basin by a collision in the Cenozoic tion. This occurred in two separate stages. between the Briançon microcontinent

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and the Adriatic continental margin, four millimetres and more each year. ­proceeding in a more north–south direc- Movement in the west is slightly slower, tion and, later on, between the Briançon that is, Africa is rotating anti-clockwise microcontinent and the European very slightly. Arabia is moving much ­continental margin. The complex palaeo- faster, at 25 millimetres per year, in a geography illustrated in Fig. 1.7 leads northern direction. The jump in speed is us to surmise that the subduction and taking place in a strike-slip fault that the collision process led to an even more originates in the spreading ridge in the complex geometry in the mountain chain Red Sea and extends northwards through that was being uplifted. the Gulf of Aqaba, via the Dead Sea and the Sea of Galilee. The Turkish block is moving in a westerly direction by 1.3 The Alpine system in Europe 25 millimetres per year. The plate bound- ary in the north of this block is to be The Alpine mountain ranges originated found in the North Anatolian fault line, a in the Cretaceous and in the Cenozoic. seismically active dextral strike-slip fault. These ranges include, for example, the This drift to the west changes its direc- ‘young’ European mountain ranges (Betic tion to south-southwest in the Aegean. Cordillera, Pyrenees, Alps, Apennines, Its speed increases, as the Aegean is Carpathians, Dinarides). Of note is that expanding in the same direction. The these mountain ranges are winding and plate movements are revealed to be quite arc-shaped. Figure 1.8 summarizes the complicated, even just between Africa, continuing present-day motions (based Arabia and the Turkish block. Further on Kahle et al. 1995), which provide an north, this becomes even more compli- insight into the plate tectonic processes cated to understand. during the formation of these mountain In the East Carpathians, there is ranges. Africa is moving­ to the north by currently an active subduction zone that

Europe

arpathi C ans

s Eastern Alp lps A rn e t

s

e W Dinaride

Figure 1.8 The tectonic s Apennine Balkans plates in the present-day Miocen

Alpine system. Open arrows e Hellenides Pontides with velocities (mm/a) Betic Cordillera 25mm/a show the direction of plate Rif motions, simple arrows Tell-Atlas

indicate directions of 6mm/a 35mm/a 25mm/a thrusting within the Alpine 4mm/a orogens. Double arrows denote areas of extension and opening of ocean rust fault/Subduction Arabia basins. Source: Kahle et al. Normal fault/Extension Africa (1995). Reproduced with Strike-slip fault

permission of Elsevier. 1000km

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Vienna Munich

Trieste Venice Milan

Nice

is plunging towards the west. The Ligurian Basin opened up under similar ▴ Figure 1.9 Digital elevation model of the Alps Eurasian plate is sinking and simulta- circumstances. At that point, the and neighbouring areas. neously exhibiting slab retreat or roll Corsica–Sardinia microcontinent sepa- Within the Alps, major back, that is, the plate boundary is mov- rated from Europe and, during the sub- valleys running parallel and ing towards the east in this subduction sequent rotation away from Europe, across the orogen are clearly zone. As a result of this, the Pannonian new oceanic crust developed in the discernable. Large lowland Basin on the plate above is being Ligurian Sea. Therefore, movements areas lacking relief stretch stretched in an east-west direction. The of the smallest blocks between the across the foreland of the Tiza block at the base of the Pannonian two colliding continental plates also Alps. They correspond to the Basin is being squeezed out laterally occurred in this case. Rhine Graben in the north, towards the east by the pincer move- Even today, active horizontal motion the Bresse–Rhone Graben ment between Europe and Africa (or can be measured in the Alps (Tesauro in the west, the Po Basin in the south and the Pannonian Apulia). However, at the same time, the et al. 2005). The southern margin of the Basin in the east. Source: US Apennines and the Dinarides are also body of the Alps is moving slowly Geological Survey. moving towards each other. Stretching towards the north-northwest, at about and new formation of oceanic crust has 1.2 millimetres per year, and the north- been detected in the Tyrrhenian Sea in ern margin is moving at only about the hinterland of the active Apennines 0.7 millimetres per year, but in the same (Facenna et al. 2002). This process direction. This indicates that the Alps started about five million years ago. A are contracting by about 0.5 millimetres little earlier, in the Miocene, the per year in a NNW–SSE direction.

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The complicated present-day pattern Some authors therefore only subdivide of movement gives an impression of the Alps into the Western Alps and the how the movements that occurred dur- Eastern Alps. While the three-part ing the formation of the Alps must be division is preferred here, this is simply envisaged. The sizes of the ocean basins due to the internal structures, which are and continents or microcontinents that hereby easier to classify in a compre- were involved were modest in compari- hensible manner. son with the dimensions in the classic Across this mountain chain, the subduction orogens of the Andes or Alps are subdivided into tectonic units the North American Cordillera, or in that belong to specific palaeogeograph- the collision mountain chains of the ical domains. The palaeogeographical Himalayas or Appalachians. However, ­affiliation is defined by the Mesozoic the convergent movements were quali- sedimentary environment in these units. tatively comparable and made the Alps Based on this structure, we can distin- into a mountain chain with such a guish a belt of sedimentary rocks that highly heterogeneous structure. belong to the European continental margin and are exposed in the extreme external regions of the Alps, that is, 1.4 Structure of the Alps extreme west and north. These rock for- mations are referred to as ‘Dauphinois’ The mountainous body of the Alps and ‘Helvetic’. A second belt of sedi- extends in a wide arc from Nice to mentary rocks, summarized using the Vienna. The Po Basin lies within the term ‘Penninic’, is located in a more arc. It is morphologically distinct due to central position, that is, it lies further its low altitude and minimal relief, as to the east or south. The associated is made clear in the digital elevation Mesozoic sediments were deposited in model in Fig. 1.9. Long, narrow basins marine basins between the European with no relief are visible outside the and Adriatic continental margins. A Alpine arc: the Rhone–Bresse Graben third belt of sedimentary rocks is to be in the extreme southwest, the Rhine found mainly in the most internal loca- Graben in the north. In the far east of tion, towards the Po Basin. These units the region, the Alps disappear under the are referred to as ‘Austroalpine’ and Vienna Basin. ‘Southalpine’ and are allocated to the Along this mountain chain, the Alps Adriatic continental margin. In general, Western Alps are subdivided into the Western Alps, the Penninic units lie on top of the Central Alps Central Alps and Eastern Alps. The Helvetic and the Austroalpine unit Eastern Alps Eastern Alps run more or less east–west on top of the Penninic. All these units and their western boundary is located are actual nappe complexes that were on an approximate line through transported hundreds of kilometres St Margrethen–Chur–Sondrio. In the from their substratum in the form Central Alps, the course of the moun- of relatively thin sheets of rock. tain chain changes from east–west to Figure 1.10 shows the distribution almost north–south. The Western Alps of these nappe complexes throughout run from north to south, but form a the Alps. tight arc round the western end of the The Austroalpine nappe complex Po Basin. The boundary between the makes up almost the entire Eastern Central and Western Alps is diffuse. Alps. It is only at the outer margins in

0002087327.INDD 14 3/11/2014 10:56:30 AM 15 Structure of the Alps 1.4

the north and east that Penninic and formation in the Alps, this banana- ▸ Figure 1.10 Simplified tectonic map of the Alps and Helvetic nappes can still be recognized shaped mountain range was com- their foreland. The Jura in the footwall of the Austroalpine nap- pressed, folded and pushed to the Mountains, and pes. In the centre of the Eastern Alps, in northwest. Dauphinois–Helvetic nappe the Tauern Window, the Austroalpine Younger, Cenozoic basins demarcate system are part of the nappe complex is eroded, such that a the edge of the Alps. In the north of the European continental margin, spectacular view of the Penninic and Alps, the Molasse Basin extends from the Austroalpine and Helvetic nappes lying below is revealed. Vienna, via Munich into the Swiss Southalpine nappe systems A smaller, but otherwise equivalent, Central Plateau and peters out in a represent the Adriatic margin. window is found slightly to the west, in westerly direction. The Molasse Basin The Penninic nappe system the Lower Engadin. Further to the is a foreland basin that developed in the in between is derived from west, the Austroalpine nappe complex Oligocene–Miocene after Alpine nappe the Valais basin, the Briançon microcontinent and the is almost fully eroded in the Central formation and was then filled with clas- Penninic Ocean. Two tectonic Alps. However, small erosional rem- tic deposits from the uplifting Alps. In windows (inliers) in the nants, called klippen or outliers, remain the course of the most recent nappe Engadin and Tauern prove as evidence for the original distribution. movements, the Molasse Basin was that the Penninic and The largest of these klippen is to be mainly compressed at its southern mar- Helvetic nappes have a found in the region of the Dent gin and even pushed to the northwest subsurface continuation Blanche. in the region of the Jura Mountains. towards the east. On the The Southalpine nappe complex and The rift system with the Rhine other hand, klippen (outliers) the adjacent Dolomites to the east are Graben and the Rhone–Bresse Graben of Austroalpine units at the separated from the Austroalpine nappe is visible outside the Jura. The two rift transition between the complex by a major fault, the peri-­ basins are connected to each other by Central and Western Alps indicate the former extension Adriatic fault system. This continues a transform fault system. Basement of the Austroalpine nappes eastwards into the Karawanks, where it uplifts exposing crystalline rocks flank towards the west. A, B and C separates the Dinarides from the Eastern the rift basins on both sides: the Black indicate the locations of the Alps. The Southalpine nappe complex, Forest and Vosges, and the Massif cross-sections shown in the Dolomites and the Dinarides, Central and Massif de la Serre. Fig. 1.11. were tectonically independent of the Finally, the Po Basin is visible in the Austroalpine nappe complex. Only south of the Alps, a foreland basin the affinity of the Mesozoic sediments to shared by the Alps and the Apennines. the Adriatic continental margin consti- Clastic sediments up to ten kilometres tutes a common element. thick were deposited in this basin in the The distribution of the Penninic Cenozoic. The basin fill was partially European margin nappe complex also reveals a large klip- affected by the Alpine nappe move- Piemont Ocean pen in the region of the Central Alps, ments, resulting in fold and thrust Adriatic margin on the northern margin of the Alps. structures. This is to be found in the French–Swiss Figure 1.11 shows three schematic, Prealpine and in the Chablais region in simplified cross-sections through the France. Further smaller klippen are to Alps. These show commonalities and dif- be found in central Switzerland. These ferences between the West, Central and klippen also provide evidence that the Eastern Alps. All three cross-sections­ are Penninic nappes once covered large based on insights gained from reflection parts of the Alps. seismic investigations conducted within The Jura Mountains are visible in the framework of three large national and Fig. 1.10 at the outermost margin of international research programmes. The the Central Alps. At the end of nappe cross-section through the Western Alps is

0002087327.INDD 15 3/11/2014 10:56:31 AM 16 1 The Alps in their plate tectonic framework

Strasbourg 5° 10°

Vosges 48° European Foreland Black Forest Molasse Basin

Rhine Graben

Basel Konstanz

47° Bresse Graben Jura Mountains

Helvetic nappe system

Penninic En nappe Geneva system In Si 46° Southalpine nappe system Massif central Lyon

Valence Basin B Milan

A

45° Valence Penninic Torino nappe Dauphinois system nappe system

Genova

Avignon 44°

Valensole Basin

Nice Provence Platform

Marseille Esterel

5° 10°

based on the Franco-Italian project the Swiss National Research Project, ECORS-CROP (Nicolas et al. 1990, NFP 20 (Pfiffner et al. 1997) and, finally, Roure et al. 1996, Schmid & Kissling the cross-section of the Eastern Alps is 2000), that through the Central Alps on based on the ­Germano-Austro-Italian

0002087327.INDD 16 3/11/2014 10:56:32 AM 17 17 Structure of the Alps 1.4

15° Bohemian Massif

Vienna Munich 48°

Salzburg

Austroalpine nappe system Rechnitz

Graz 47° Br Ka Vienna Basin

Klagenfurt Pu La Ba Gi Dolomites Ga

46° Zagreb

Trieste Pannonian Basin C Venice Adriatic Foreland

Dinarides Po Basin 45° 15°

Tectonic Map of the Alps rust fault (saw teeth on upper block)

Normal fault (ticks on upper block) Si Simplon fault Rimini Br Brenner, Ka Katschberg fault Strike-slip fault Peri-Adriatic fault system: In Insubric, Gi Giudicarie, Pu Pustertal, Apennines Ga Gailtal, La Lavanttal, Ba Balaton fault En Engadin Fault

Cenozoic 1:3250000 intrusives 100km

project TRANSALP (TRANSALP mology, as well as local earthquake working group 2002, Lüschen et al. 2004). tomography studies by Waldhauser et al. The structure of the lower crust has been (2002), Diel et al. (2009) and Wagner determined from controlled-source seis- et al. (2012).

0002087327.INDD 17 3/11/2014 10:56:33 AM 18 1 The Alps in their plate tectonic framework

Western Alps WNW ESE (Geneva)(Aosta) (Ivrea) Jura Mountains Chaînes subalpines Po Basin

0 0

–20 –20

Moho –40 –40

–60 –60

[km] [km]

100km

Central Alps NNW Insubric SSE Fault Aarau Luzern (Varese) Molasse Basin Ivrea

0 Aar 0

-20 Moho -20

-40 -40

-60 -60

[km] [km]

Eastern Alps NW SE (Munich) (Treviso) Molasse Basin Northern Calcareous Alps Dolomites

0 0 Tauern

–20 –20

Moho –40 –40

–60 –60

[km] [km]

0002087327.INDD 18 3/11/2014 10:56:34 AM 19 Structure of the Alps 1.4

European continental margin Adriatic continental margin Jura Mts & Helvetic nappe system Penninic nappe system Austroalpine & Southalpine nappe systems Cenozoic Mesozoic oceanic crust

Mesozoic of Helvetic - Mesozoic sediments Dauphinois nappe system Cenozoic Allochthonous Mesozoic Crystalline basement/ of Jura Mountains European upper crust Mesozoic of Austroalpine Autochthonous Mesozoic of European Foreland Mesozoic of Southalpine

Permo-Carboniferous Adriatic upper crust

European upper crust Adriatic lower crust Strike-slip along Insubric Fault: European lower crust Lithospheric mantle motion away from observer Lithospheric mantle motion towards observer

The cross-section through the between crust and mantle is unique and ▴ Figure 1.11 Three schematic cross-sections Western Alps shows how the crust is due to an inherited geometry from through the Western, Central of the European continental margin the time of the formation of the and Eastern Alps based on plunges below the Alps in an east- Piemont Ocean. Remnants of this geological and geophysical southeast direction, beneath both the ocean can be found in the thin band of data. The upper crust in mantle and the crust of the Adriatic ophiolites interlayered with detached these cross-sections is continental margin. The steep contact pieces of upper crustal crystalline base- shortened considerably by contains a strike-slip component (the ment nappes. thrusting and folding, eastern portion moved towards the The European crust also plunges whereas the lower crust and north). Thrust faults in the European below the Alps in a south-southeast lithospheric mantle show a crust indicate substantial compression direction in the cross-section of the much simpler structure. in an east–west direction, which at least Central Alps. The upper crust has been Locations of the cross-sections are shown doubled the thickness of the crust. peeled off the lower crust and piled up in Fig 1.10. Larger basement uplifts in the Chaînes into a nappe pile composed of crystal- subalpines and the Penninic nappe line basement nappes. The lower crust complex lead to the conclusion that iso- runs underneath the compressed mar- lated crystalline basement blocks were gin of the Adriatic plate. Similar to the overthrust in a westerly direction on to cross-section of the Western Alps, the the foreland over a distance of more Adriatic mantle and the lower crust are than 100 kilometres. The Mesozoic in a shallow position. They were pushed sediments of the Jura Mountains were northward along a south-dipping thrust also affected by this and were actually fault cutting across the entire litho- thrust on to the Cenozoic sediments of sphere, a style that is referred to as the Bresse Graben. On the Adriatic thick-skinned tectonics. A steep fault, side, the crustal blocks were thrust on the Insubric fault, separates the rocks of top of each other in an easterly direc- the Adriatic and European plates. The tion. These structures are covered by the fault exhibits two movement compo- Po Basin fill and are known only from nents. The packages of upper crust from seismic investigations. Lower crust the European margin that had been reached the surface of Earth in the Ivrea peeled off moved southwards and up Zone, and mantle rocks almost did. along a steeply dipping thrust fault and, This elevated location of the boundary in some instances simultaneously, the

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Adriatic block moved horizontally Window on a cushion of Penninic nap- westwards in a dextral fashion. Klippen pes. The Northern Calcareous Alps of Helvetic and Penninic nappes made were telescoped together into a nappe of sedimentary rocks lie to the north of complex as early as the Cretaceous, the Aar massif. These were sheared off when some of the thrusting occurred in their crystalline substratum and pushed a westerly direction. over 100 kilometres in a northerly direction. During this process, they also ended up on top of the internal, south- References ern portions of the Cenozoic fill of the Molasse Basin. Blakey, R., 2008, Regional Paleogeographic In the cross-section through the Views of Earth History, Northern Eastern Alps, although the European Arizona University, http://jan.ucc.nau. crust also sinks below the Adriatic con- edu/~rcb7/RCB.html tinental margin in a southerly direction, Diel, T., Husen, S., Kissling, E. & the extent of shortening appears slightly Deichmann, N., 2009, High-resolution lower. Similarly, the Adriatic litho- 3-D P-wave model of the Alpine crust. Geophysical Journal International, 179, sphere plunges toward the European 1133–1147. plate in a northerly direction. In both cases, the lower crust is thickened con- Elliott, D. & Johnson, M. R. W., 1980, Structural evolution in the northern siderably at their interface. A promi- part of the Moine thrust belt, NW nent basement uplift of crystalline rocks Scotland. Edinburgh Geological Society is present and emerges in the Tauern Transactions, Earth Sciences, 71, 69–96. Window. A steep fault on the south Facenna, C., Speranza, F., D’Ajello side of the Tauern Window, the Caracciolo, F., Mattei, M. & Oggiano, G., Pustertal fault, separates the Eastern 2002, Extensional tectonics on Sardinia Alps from the Dolomites. In the (Italy): insights into the arc-back-arc tran- Dolomites, multiple thrust faults are sitional regime. Tectonophysics, 356/4, visible. They have a south-directed 213–232. transport and extend deep down into Kahle, H.-G., Müller, M. V., Geiger, A., the crystalline rocks of the crust. The Danuser, G., Mueller, St., Veis, G., Billiris, continuation of these thrust faults H. & Paradissis, D., 1995, The strain field deeper down and their merger with the in northwestern Greece and the Ionian Islands: results inferred from GPS meas- large thrust fault at the base of the urements. Tectonophysics, 249, 41–52. Tauern massif is speculation. The struc- ture of the lower crust, at least, is fairly Lüschen, E., Lammerer, B., Gebrande, H., Millahn, K., Nicolich, R. & TRANSALP certain based on the teleseismic investi- Working Group, 2004, Orogenic struc- gations. There are Mesozoic sediments ture of the Eastern Alps, Europe, from overlying the Tauern crystalline base- TRANSALP deep seismic reflection pro- ment that are comparable to those in filing. Tectonophysics, 388, 85–102. the Helvetic nappe complex in the Matte, Ph., 1991, Accretionary history and Central Alps. In turn, Penninic nappes crustal evolution of the Variscan belt in overlie these sediments and are them- Western Europe. Tectonophysics, 196, selves overlain by Austroalpine nappes. 309–337. A larger complex of Austroalpine nap- Nicolas, A., Polino, R., Hirn, A., Nicolich, pes, called the Northern Calcareous R. & Ecors-Crop working group, 1990, Alps, lies to the north of the Tauern Ecors-Crop traverse and deep structure of

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the western Alps: a synthesis. In: Roure, Tesauro, M., Hollenstein, C., Egli, R., F., Heitzmann, P. & Polino, R. (eds), Deep Geiger, A. & Kahle, H. G., 2005, Structure of the Alps, Mémoires de la Continuous GPS and broad-scale defor- Société Géologique de France, Paris, 156, mation across the Rhine Graben and 15–28. the Alps. International Journal of Earth Sciences, 94, 525–537. Pfiffner, O. A., Lehner, P., Heitzmann, P., Mueller, S. & Steck, A. (eds), 1997, Deep TRANSALP working group, 2002, First Structure of the Swiss Alps: Results of deep seismic reflection images of the NRP 20, Birkhäuser, 380 pp. Eastern Alps reveal giant crustal wedges. Geophysical Research Letters, 29/10, Roure, F., Bergerat, F., Damotte, B., 10.1029/2002GL014911, 92-1-92-4. Mugnier, J.-L. & Polino, R. (1996), The Ecors-Crop Alpine seismic traverse, Wagner, M., Kissling, E. & Husen, S., 2012, Mémoires de la Société Géologique de Combining controlled-source seismology France, 170, 113 pp. and local earthquake tomography to derive a 3-D crustal model of the western Schmid, S. M. & Kissling, E., 2000, The arc Alpine region. Geophysical Journal Inter­ of the Western Alps in the light of geo- national, 191, 789–802. physical data on deep crustal structure. Tectonics, 19/1, 62–85. Waldhauser, F., Lippitsch, R., Kissling, E. & Ansorge, J., 2002, High-resolution teleseis- Scotese, C. R. & Sager, W. W., 1988, mic tomography of upper-mantle structure Mesozoic and Cenozoic plate reconstruc- using an a priori three-dimensional crustal tions. Tectonophysics, 155, 27–48. model. Geophysical Journal International, Strachan, R. A., Smith, M., Harris, A. L., & 150, 403–414. Fettes, D. J., 2002, The Northern Wortmann, U. G., Weissert, H., Funk, Hp. & Highland and Grampian terranes. In: Hauck, J., 2001, Alpine plate kinematics Trewin, N. H. (eds), The Geology of revisited: The Adria Problem. Tectonics Scotland, Geological Society of London, 20/1, 134–147. 81–147.

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