Western European rift system

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The Western European Rift System is a belt-like network of rift fractures and associated volcanic centers that generally crosses the European continent in a north-northeast-south-southwest direction. The first forerunners go back to the Permian , but the peak of development did not occur until the Mesozoic and especially the Cenozoic .

Geographical description

The Western European Rift System, engl. Western European Rift System or Western European Rift Belt , stretches from the North Sea in the north to the Atlantic coast of Africa in the south and has a maximum length of more than 3000 kilometers. Being in the Cenozoic to Training Direction central part that European Cenozoic rift system (Engl. European Cenozoic Rift System or abbreviated ECRIS ) extending from the Lower Rhine Basin in the north to the south end of the Spanish Valencia trough extends to the south, measures 1,100 km.

The rift valley system begins in the north with the north-south running Viking Trench , which separates the Shetland Islands from Norway . To the south it is joined in the central area of ​​the North Sea by the NNW-SSE-oriented central ditch , which changes direction to NS in its southern section and ends about 50 kilometers before reaching the North Frisian Islands . This North Sea trench system has a total length of 1000 kilometers with a variable width of 25 to 100 kilometers. The expansion of the crust is still noticeable over a much wider range of 200 to 300 kilometers.

Satellite image and geological map of the Oslo Trench

The SSW traversing Oslo trench was formed, offset to the east of the main strand of the North Sea trench system, which merges into the Skagerrak trench to the south ; the latter ends with reaching the OSO-crossing carefree Tornquist zone . Separated by this significant fault zone , the Horn Graben follows further south , which is off the west coast of Denmark . The Horn Graben has a kinked course with a central section trending SSE. In the south it reaches the East Frisian Islands and then merges into the Emsgraben .

The main strand of the rift system then continues on the Dutch mainland with the south-east running Roer Graben , engl. Roer Valley Graben , (or Ruhr-Graben or Rur-Graben) again. After crossing the Rhenish Slate Mountains , the Roer Graben meets the SSW-oriented Rhine Graben , which in turn continues via the Wetterau and the Leinegraben further to NNE into the North German Plain . The Leinetalgraben finds a possible continuation to NNE in the Braunschweig-Gifhorn fracture zone . The fork of the Rhine Graben with the Roer Graben forms a triple point which is marked by the largest volcano in Europe, the Vogelsberg . To the east, separated from the actual rift system, the ONO-trending Egergraben has formed.

The Rhine Graben ends in northern Switzerland with a somewhat diffuse, right-shifting fault zone north of the Jura ( Burgundian transfer zone ). It is continued in the Bresse Graben , offset to the west, and in the Roanne Graben / Forez Graben and Limagne Graben / Cher Graben of the northern Massif Central, which run parallel to the Bresse Graben . The almost NS-oriented Bresse Graben goes south into the Saône Graben and then into the Rhône Graben . The latter reaches the northern Mediterranean via the Valence , Manosque and Alès gorges and flows into the Golfe du Lion . Further to the southwest, break -in basins cut through the eastern edge of the Pyrenees, such as the Cerdagne , the Empordá basin and the La Selva basin . The north-east Iberian volcanic province around Olot is related to these basins. In northeastern Catalonia, the Valles Trench follows , which leads to the approximately 400-kilometer-long Valencia trough along the east coast of Catalonia . A little further to the east, the oceanic Provençal basin and the rift systems of Corsica and Sardinia formed in the western Mediterranean in a straight extension of the Rhône valley .

There is much to suggest that the Valencia Trough is not the southern endpoint of the Western European Rift System. Rather, the expansion process continued from the Pliocene with the injection of alkaline magmas along the east coast of Spain further to the southwest. This volcanic expansion zone manifests itself in the southeast Iberian volcanic province around Murcia and Cabo de Gata ; it then crosses the Alboran Sea (with the volcanic Isla de Alborán ), runs through the Ras Tarf and Gourougou volcanic area near Melilla, the eastern Rif in Morocco and, with the basalt province of the Middle Atlas, frames the western edge of the Middle and High Atlas . Via the South Atlas Fault and accompanied by the volcanic rocks of Jebel Siroua and Foum-el-Kous , it reaches the Atlantic at Agadir and then follows the stretched continental margin of the northwest coast of Africa over the Canary Islands to Cape Verde .

Development over time

The Herchenhainer Höhe on the Vogelsberg

The Caledonian orogeny had passed into a post-orogenic collapse stage in the Devonian Mountains, combined with significant north-east-facing, left-shifting crustal movements between Greenland and Europe and the resulting crock basins filled with thousands of meters of Old Red sediments . In the following period from the Carboniferous to the Cretaceous , the continental crust of northwestern Europe was exposed to multiple distensive tensions after the end of the Variscan orogeny due to the Pangean decay process , which led to the formation of rift systems in the North Sea and the North Sea area.

The oldest example is the Oslo Trench in southeast Norway , the development of which began in the Pennsylvania ( Kasimovian ) 305 million years ago BP and lasted until the Triassic ( Anisian ) 240 million years ago. This generally NNE trending rift system has a total length of 400 kilometers and extends from Lake Mjøsa to the Carefree Tornquist Zone, with the marine section being formed by the Skagerrak Trench.

At about the same time, the rift activity of the so-called Arctic-North Atlantic Megarift began in the Greenland and Norway Seas , which was ultimately to lead to the final separation of Greenland and Northern Europe in the Paleocene / Eocene . During the Permian and Triassic, the megarift worked its way south into the north and eventually the central Atlantic.

From the Zechstein ( Capitanium ) onwards, the first opening movements took place at the Viking Trench, which enabled the Zechstein Sea, advancing from the Arctic shelf area via the megarift, to access the southern North Sea. At the Permian / Triassic border, the development of the central and southern North Sea rift system, which lasted around 175 million years and basically represents a failed branch of the Arctic-North Atlantic mega-rift, finally began. Rift activity in the North Sea Trench was fully developed from Dogger to the early Lower Cretaceous (175 to 140 million years BP), but it only peaked at the Jura / Cretaceous border. The last movements in the North Sea trench system then occurred at the end of the Paleocene .

The central part of the Western European Rift System was not activated until the Cenozoic. The earliest rift fracture segments were the Saône, Limagne and Bresse rifts, the oldest sediments of which date back to the Middle Eocene ( Lutetian ). Rift activity in the Rheingraben did not begin until a little later in the Upper Eocene ( Bartonian ), at the same time the northern part of the Leinegraben collapsed. The beginnings of the Eger moat also go back to the bartonium. In the beginning of the Oligocene ( Rupelian ), the rift worked its way from the Rhine Rift to the northwest, broke through the Rhenish Slate Mountains and opened the Roer Rift to the southern Netherlands, which was reached during the Chattian . To the north-northeast, the connection from the Rheingraben to the Leinetalgraben was established at the same time. The Roer and Leinegraben thus made it possible for the first time to establish a close sea connection from the foreland basin of the Alps to the northwestern European basin . During the chat, the rift then propagated from the Saône trench southwards to the Golfe du Lion and on to the Valencia trough. It is possible that in the Oligocene there was a temporary sea connection from the Alpine foothills to the Paris Basin via the trenches in the Massif Central .

The sea connections to the alpine foreland broke off again in the early Miocene , as the Massif Central and the Rhenish Slate Mountains were thermally elevated at this time. In the period from Aquitanium to Serravallium , the sea in the Rheingraben reached the Mainz Basin one last time , afterwards (in the Tortonium ) the sea definitely retreated to the south, as the southern Rhine Rift, together with the Vosges and the Black Forest, was raised from the Serravallium.

Already during the Chattium the rifts had started to shift from the Rhône valley into the Provençal basin and into the southeast part of the Valencia trough. The spread in the two areas lasted about 8 million years into the early Burdigalium (20 million years BP). It caused the Corso-Sardinian crust block from the Middle Aquitanium to detach from southern France and northeast Iberia in a slight counter-clockwise rotation. At the same time, the Balearic Islands / Betids had moved away from the Kabyle block, forming the Algerian basin, and caused crust shortening in the southeast area of ​​the Valencia trough. This resulted in a temporary decline in rift activity in the rest of the Valencia trough. After the end of the upheavals in the external zone of the Betides and on the Balearic Islands in the Langhium , expansion tectonics started again on the northwestern edge of the Valencia trough, which continues unabated to this day.

Magmatism

Rift zones are mostly associated with magmatic activity . They are the surface expression of an under strain that are available lithosphere . This stretching causes an increase in the underlying asthenosphere proportional to the stretching factor β, with a simultaneous drop in pressure. The pressure drop can often be sufficient to reach the liquidus limit and cause an adiabatic melting of the mantle rocks ( decompression melt ). Accordingly, numerous magma foci can also be localized along the Western European Rift System.

The Oslograben is a prime example of magmatism associated with rift zones. Basaltic volcanism began in the Oslo Graben and also in the Horn Graben to the south on the Carbon-Permian border 300 million years ago BP. The volcanic activity began in the Oslo Trench with a basaltic shield volcanism that was no more than 1,500 meters thick, which was followed by up to 3,000 meters of extracted Latin rhombic porphyry lavas (295-275 million years BP) during the main rift activity . The volcanic style then changed in the period 275-240 million years BP to central volcanoes and collapse calderas with mixed chemical compositions. At the same time, composite batholites ( Larvikite and Syenite ) with intermediate and granitic chemistry intruded . After 240 million years of BP, only gait intrusions took place that lasted into the Triassic.

Due to the low level of exposure, the Oslo trench is clearly dominated by the magmatites, which occupy 5100 km² (compared to 1400 km² for the volcanic rocks). Geochemically, two different magma sources can be identified, which suggest a heterogeneous upper mantle below the rift. A very slightly depleted HIMU sheath component (with ε Nd +1 and ε Sr −10 to −15), responsible for the basal nephelinites and some alkali basalts around Skien as well as a somewhat more clearly depleted sheath component (with ε Nd +4 and ε Sr - 10) responsible for all other volcanic rocks. The anatectic , granitic and syenitic intrusives were in turn heavily contaminated in the upper crust.

The initial development in the area of ​​the North Sea Trench took place without significant igneous activities, only during the Middle Triassic there was a volcanic episode in the south central trench west of the Ryngkøbing-Fyn high . Only in the Callovian 160 million years ago BP is a huge volcanic center in the field of the triple-established Viking Graben / Central Graben / Moray Firth Witch Ground Graben ( Forties province ), after starting the Aalenian (a wide east-west oriented bulge Central Nordseedom ) had developed in the central area of ​​the North Sea. In the southern Viking trench, on the western edge of the central trench and in the Egersund basin , relatively minor flank volcanism was also recorded at the same time. In the Forties Province, porphyritic alkali basalts and ankaramites , which are no more than 1500 meters thick, and Hawaiites and Mugearites to a lesser extent , cover an area of ​​around 10,000 km². The magmas in the other named occurrences are undersaturated, ultrapotassic and nephelinitic. In the late Kimmeridgian , the spread in the North Sea Trench reached its maximum, but was only accompanied by minor volcanism on the western flank of the central trench.

The associated with the European Cenozoic rift system magmatism, known as European Cenozoic volcanic province (Engl. European Cenozoic Volcanic Province or ECVP ) is spread over a 1200 km wide area. The volcanic centers located directly in trenches are in the minority, some extraction areas are even up to 200 kilometers from the nearest rift.

Basalt tuff chimney from Jusi near Urach

The first magmatic pulses made themselves felt before the rift breaks began. In the area of ​​the Egergraben and on the Rhine south of Koblenz they even go back as far as the Upper Cretaceous ( Campanium ) (77 million years ago BP), in the Massif Central with duct intrusions (nephelinites and olivine melilites ) into the Middle Paleocene ( Zealand ) 62 million years ago BP . In the Eifel , activities began 45 million years ago in the Middle Eocene (Lutetian) roughly at the same time as the first rift breaks in the Massif Central and lasted until the end of the Oligocene 24 million years ago. After a longer period of dormancy, volcanism was then revived in the late Middle Pleistocene 200,000 years ago BP. The volcanic activities in the Siebengebirge and in the Westerwald began with the Upper Oligocene ( Chattian ) (28 and 25 million years BP). The volcanism in the Siebengebirge lasted until the end of the Miocene ( Messinian ) 6 million years ago BP, in the Westerwald it ended 15 million years ago BP in the Middle Miocene (Langhian). In the Lower Miocene (Burdigalium), the Vogelsberg volcano (active in the period 19-15 million years BP) and the Kaiserstuhl volcano (active from 18-13 million years BP), the volcanic rocks of the Rhön (20-14 million years BP), the Hessian Depression (Period 20 - 10 million years BP) and the Grabfeld ( Heldburger Gangschar ). The volcanic area of ​​the Hegau and Urach developed from the Middle Miocene (Langhian) and was eruptive until the end of the Tortonian (period 15 - 7 million years BP). The volcanic activity in the Massif Central and in the Eifel persisted into the Holocene (last eruptions took place in the Northeast Iberian volcanic province 11,500 years ago and in the Eifel 11,000 years ago, in the Massif Central even 3450 years ago), in the Egergraben they are a little earlier came to a standstill in the Middle Pleistocene 260,000 years ago.

Starting from the Aubrac , the volcanic rocks of the Massif Central continue south. The Grands Causses , the surroundings of Saint-Affrique and the Larzac are penetrated by predominantly Miocene volcanic vents. The Pliocene Escandorgue volcanism follows to the south. The line ends at Saint-Thibéry and Cap d'Agde on the Mediterranean with 1.0 to 0.6 million year old Pleistocene volcanic structures. There is also volcanic activity in the Golfe du Lion. It then follows in northeastern Catalonia the northeast Iberian volcanic province (10.0 - 0.1 million years BP), which leads to the volcanism of the Valencia trough. In the Valencia trough, a 24-18.6 million year old initial phase (Chattium to early Burdigalium) and a 10.0 to 0.3 million year old late phase (Tortonium to Middle Pleistocene) can be distinguished, separated by a pause. The first phase is of a calcareous nature and is related to the Betiden thrust of the Balearic Islands . The late phase is composed of only slightly differentiated alkali basalts.

The Southeast Iberian volcanic province was active in the period 15-2.6 million years BP (Langhium - end of Piacenzian). An age of 10.7 - 7.5 million years BP (Tortonium) was determined for the Alborán Island and the surrounding crustal areas. The northern Moroccan stratovolcano Gourougou falls in the period 9.0 - 2.6 million years BP (Tortonium - end of Piacenzian). In the basalt province of the Middle Atlas, the ages range from 16.25 to 0.6 million years BP (Langhium - Middle Pleistocene). The volcanic rocks along the South Atlas Fault are Late Miocene, ie 10 to 6 million years old BP (Tortonian to Messinian).

The Teide in Tenerife

In the Canary Islands, the stage of shield volcanism on Fuerteventura began 20.6 million years ago BP (Burdigalium), but the activities of the submarine substructure ( seamount stage ) can be traced back at least to the Oligocene, if not the Eocene, 48 million years ago. Volcanism first migrated north-northeast to Lanzarote , which was reached BP 15.5 million years ago, then to the west. For example, El Hierro did not build BP (Old Pleistocene) on a shield volcano until 1.12 million years ago.

The Cape Verde Islands are diachronous, similar to the Canaries. The shield volcanic stage goes back to Sal around 18 million years BP (Burdigalium), whereas it only began on Fogo since the Young Pleistocene. The substructure in Sal is older than 24 million years BP (Chattium).

Both the Canary Islands and Cape Verde have remained active to this day.

Geochemical composition of the igneous rocks

The volcanics of the European Cenozoic Volcanic Province generally emerged from primitive, mafic, alkaline magmas, with basalts , basanites , nephelinites and leucitites predominating among the rocks . The magmas encountered can generally be classified into three types:

The two differentiation series come from a single starting magma, which in turn is a mixture of a depleted DM component and a more enriched HIMU shell component. The nephelinites are a mixed series of the HIMU component and an EM component (enriched mantle component), with the potassium-stressed rocks moving towards the EM component and the sodium-stressed rocks lingering near the HIMU component.

All types of magma can be found in the Massif Central. The North Hessian Depression contains mainly sodium-stressed rocks of the two differentiation series, nephelinites and melilite nephelinites are rare here. The Quaternary Westeifel volcanic field is predominantly potash, even if sodium-emphasized alkali basalts, basanites and melilite nephelinites can be found. The East Eifel also contains many potassium-accentuated volcanics. The Lower Silesian volcanic rocks, the eastern foothills of the Eger rift system, are strongly sodium-stressed and consist mainly of nephelinites, basanites, alkali basalts and rare melilithites . The volcanic rocks of the Kaiserstuhl, Hegau and Urach are also predominantly sodium-stressed (nephelinites and melilithites) with occasional magmas of a potassium differentiation series. Of course, the very rare carbonatites of the Kaiserstuhl are noteworthy here .

In the Nordostiberischen volcanic province, four rock groups can be distinguished: Alkaliolivinbasalte , Leucitbasanite, Nephelinbasanite and trachytes. The Southeast Iberian volcanic province is characterized by a very diverse range of volcanic rocks, including calcareous (basaltic andesites, andesites and dacites ) and shoshonite rocks ( banakites and latites), ultrapotassic lamproites and alkaline basalts.

The volcanic rocks of the Alborán Island and the Alborán Sea are low Potassian island tholeiites, including basalts, basaltic andesites, andesites, and rare dacites. In the volcanic center of Ras Tarf in northern Morocco, calcareous andesites were extracted, whereas on Gourougou there are clearly high Potassian to Shoshonite basalts, basaltic andesites and andesites.

The volcanic rocks found in the basalt province of the Middle Atlas are alkali basalts, basanites, nephelinites and crust-contaminated sub-alkaline basalts. The magmas emerged with partial melting from spinel and garnet- bearing , pargasitic peridotites . The volcanic rocks accompanying the South Atlas Fault are basalts and phonolites at Jebel Siroua and Ankaramites at Foum-el-Kous.

The active stratovolcano of Fogo

Primitive alkali basalts and basanites, differentiated trachytes and phonolites as well as very differentiated olivintholeiites were predominantly mined in the Canary Islands . The lavas of Cape Verde can be divided into two groups: into a strongly alkaline group with picrites, foidites and phonolites and a moderately alkaline group with picrobasalts, basanites, tephrites, tephrophonolites, phonotephrites, phonolites and trachytes. The relatively frequent occurrence of carbonatites is remarkable.

Spreading

Using gravity measurements , Ramberg calculated a crustal expansion of 6 to 10 kilometers in the Oslo Trench. In the area of ​​the Viking Trench, an expansion of the upper crust of 20 kilometers was determined by means of reflection seismics from the Jura, from the Zechstein base a value of up to 30 kilometers is assumed. The central ditch spread from the Zechstein by 25 kilometers. For the Horn trench and the Danish part of the central trench, a total of a maximum of 15 kilometers is estimated.

On the basis of fault offsets, the very small value of 0.6 kilometers for the upper crustal area of ​​the Roer Trench results. For the entire crust, however, an expansion of 1 to 2 kilometers should be more realistic. In the Rheingraben the upper crust elongation is 5 to 7 kilometers. The Valencia trough has a fairly high spread value of 35 kilometers.

causes

To explain the origin of the Western European Rift System, two different causes are considered. As mentioned above, the southern advance of the Arctic-North Atlantic megarift is held responsible for the North Sea part. The central part may have been triggered by the continental collision of the Alps and Pyrenees with Europe. The compressive stresses (σ 1 ) generally exerted by the two orrogens in the north direction forced the European lithosphere to stretch east-west, which in the brittle upper crustal area led to rift fractures when the tensile strength was exceeded (for example, the evasive movement of the European lithosphere pushed the Paris Basin to the north-west ). The tensile stresses used the existing discontinuity and fracture surfaces of the previous Variscan orogeny, which mapped the course of the rift fractures. The central part is therefore a passive rift system.

There is no geophysical question about the fact that the moor depth is reduced under many rift segments . To what extent hot, surging deep-seated Manteldiapire (Engl. Mantle plumes ) to this reduction contributed and thus play a role in the genesis of the rift is still controversial. Rather, it is assumed that the associated magmas originate in the lower lithosphere and upper asthenosphere. Ripping open the upper crust is ultimately responsible for their ascent.

The subsidence of the individual rift segments was dominated by repeated changes in the orientation of the tension field . This resulted in an interplay between the compressions in the foreland of the two orogenes and the tensile stresses in the more distant, regional environment, the whole thing superimposed by thermally induced bulges in the rift area.

From the late Oligocene and early Miocene onwards, the rift system was driven south along the Spanish east coast with the simultaneous opening of the Algero-Provençal basin, breaking through the alpine folds of the western Mediterranean (Pyrenees, Betides, Rif, Atlas). At the same time, however, starting from the Pelagic Shelf, a rift arm penetrated through the Strait of Messina into the internal area of ​​the Apennines to the north.

Ultimately, the Western European rift system must be viewed in a much broader geodynamic framework. The development of the mega rift system Gulf of Suez / Red Sea / East African Rift , the rift systems in Libya and the lateral displacement of the Dead Sea also ran parallel to his training .

The temporal overlap of these mega rift systems with the late stage of the alpine development cannot be explained solely by a plate collision between Africa / Arabia and Europe. Rather, it points to the gradual establishment of a completely new type of stretching field, which will possibly lead to the breaking of the current continent configuration.

Individual evidence

  1. ↑ El Azzouzi, M. et al .: Petrology and K-Ar chronology of the Neogene-Quaternary Middle Atlas basaltic province, Morocco . In: Bulletin de la Société Géologique de France . tape 181 , 2010, p. 243-257 .
  2. ↑ Neumann, R. E.- include: The Oslo Rift: a review . In: Tectonophysics . tape 208 , 1992, pp. 1-18 .
  3. ^ Ziegler, PA: North Sea rift system . In: Tectonophysics . tape 208 , 1992, pp. 55-75 .
  4. ↑ Malkovsky, M .: The Mesozoic and Tertiary basins of the Bohemian Massif and their evolution . In: Tectonophysics . tape 137 , 1987, pp. 31-42 .
  5. ^ Zagwijn, WH: The Netherlands during the Tertiary and the Quaternary: a case history of Coastal Lowland evolution . In: Geol. Mijnbouw . tape 68 , 1989, pp. 107-120 .
  6. ^ Banda, E. & Santanach, P .: The Valencia trough (western Mediterranean) . In: Tectonophysics . tape 208 , 1992, pp. 183-202 .
  7. ↑ Rehault, JP et al .: The Western Mediterranean Basin . In: DJ Stanley & FJ Wezel (Eds.): Geological Evolution of the Mediterranean Basin . Springer, New York 1985, pp. 101-129 .
  8. ^ Latin, D. & Waters, FD: Basaltic magmatism in the North Sea and its relationship to lithospheric extension . In: Tectonophysics . tape 208 , 1992, pp. 77-90 .
  9. ↑ Meyer, R. & Foulger, GR: The European Cenozoic Volcanic Province is not Caused by mantle plumes . In: www.MantlePlumes.org . 2007.
  10. ↑ Ryan, WBF et al: Petrology and geochemistry of the Valencia Trough volcanic rocks . In: Init. Rep. DSDP . tape 13 , 1972, p. 767-773 .
  11. ↑ Martí, J. et al .: Cenozoic magmatism of the Valencia Trough (western Mediterranean): relationship between structural evolution and volcanism . In: Tectonophysics . tape 203 , 1992, pp. 145-165 .
  12. ^ Wilson, M. & Downes, H .: Mafic alkaline magmatism associated with the European Cenozoic rift system . In: Tectonophysics . tape 208 , 1992, pp. 173-182 .
  13. ↑ Wedepohl, KH: Origin of the Tertiary basaltic volcanism in the northern Hessian Depression . In: Contrib. Mineral. Petrol. tape 89 , 1985, pp. 122-143 .
  14. ^ Mertes, H. & Schminke, H.-U .: Mafic potassic lavas of the Quaternary West Eifel volcanic field. I. Major and trace elements . In: Contrib. Mineral. Petrol. tape 89 , 1985, pp. 330-345 .
  15. ↑ Wörner, G. u. a .: Sr, Nd, and Pb isotope geochemistry of Tertiary and Quaternary alkaline volcanics from West Germany . In: Earth Planet. Sci. Lett. tape 79 , 1986, pp. 107-119 .
  16. ↑ Blusztajn, J. & Hart, SR: Sr, Nd and Pb isotopic character of Tertiary basalts from southwest Poland . In: Geochim. Cosmochim. Acta . tape 53 , 1989, pp. 2689-2696 .
  17. ↑ Schleicher, H. et al.: Isotope studies on alkaline volcanics and carbonatites from the Kaiserstuhl, Federal Republic of Germany . In: Lithos . tape 26 , 1990, pp. 21-35 .
  18. ↑ Gill, RCO et al .: Depleted arc volcanism in the Alboran Sea and shoshonitic volcanism in Morocco: geochemical and isotopic constraints on Neogene tectonic processes . In: Lithos . tape 78 , 2004, p. 363-388 .
  19. ↑ Kogarko, L .: Characteristics of alkali magma differentiation at the Cape Verde Islands . In: Geochemistry International . tape 46 (11) , 2008, pp. 1071-1080 .
  20. ↑ Ramberg, IB: Gravimetry interpretation of the Oslo Graben and associated igneous rocks . In: Nor. Geol. Unders. tape 325 , 1976, pp. 1-194 .
  21. ^ Ziegler, PA & Van Hoorn, B .: Evolution of the North Sea Rift . In: Am. Asoc. Pet. Geol. Mem. Band 46 , 1989, pp. 471-500 .
  22. ↑ Remmelts, G. & Duin, EJ Th .: Results of a regional deep seismic survey in The Netherlands . In: Coll. Colloq. Semin. tape 48 . Edition Technip, Paris 1990, p. 335-343 .
  23. ↑ Doebl, F. & Teichmüller, R .: To geology and geothermal today in the central Upper Rhine Graben . In: Fortschr. Geol. Rheinl. Westf. Band 27 , 1979, pp. 1-17 .