Thuringian-Franconian-Vogtland Slate Mountains

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Geological overview map of the Thuringian-Franconian-Vogtland Slate Mountains. Meaning of the numbers in the legend: 1-3 = undeformed post-Variscan overburden, 4-10 = Variscan deformed rocks, 11 = igneous intrusive rocks, 12-14 = structural geological elements. 1 = Triassic, 2 = Upper Permian (Zechstein), 3 = Upper Carboniferous and Lower Permian (Rotliegend), 4 = Lower Carboniferous, 5 = Devonian sedimentary rocks, 6 = Devonian Diabase and Spilite, 7 = Silurian, 8 = Ordovician, 9 = Cambrian, 10 = Precambrian, 11 = Variscan granitoid rock, 12 = main faults, 13 = edge of the Münchberg gneiss mass (probably part of a thrust cover), 14 = border of the "Bavarian facies" of the Paleozoic succession (possibly part of a thrust cover). Abbreviations: BG = Bergener Granit, SH = Schleuse-Horst, VK = Vesser complex. According to Henningsen & Katzung (2006), Linnemann (2003) and GÜK 200 (sheets CC5526 Erfurt, CC5534 Zwickau, CC 6326 Bamberg, CC6334 Bayreuth).

Under the term Thuringian-Franconian-Vogtland Slate Mountains (also Thuringian-Franconian-West Saxon Slate Mountains or, since it is completely crossed by the Saale , Saalisches Schiefergebirge ), the central German mountain ranges Thuringian Slate Mountains and Franconian Forest as well as the vast majority of the Vogtland are due to their common geological features summarized. The Thuringian-Franconian-Vogtland Slate Mountains are rump mountains of the Central European Variscides and are attributed to the Saxothuringian . The in-Thüringisch Fränkisch-Vogtländische Schiefergebirge digested varizisch folded rocks form a discontinuous sequence of Neoproterozoic to the lower carbon . Typical rocks are quartzite , greywacke and clay slate , all of which were created from marine deposits .

Spatial and geological delimitation

Regional geology

Thuringian-Franconian-Vogtland slate mountains + Münchberg mass
Structure of the Variscides in Central Europe.jpg
Classification of the variscids in Central Europe. The Thuringian-Franconian-Vogtland Slate Mountains together with the Münchberger Masse form the westernmost part of the above-ground Saxothuringian (see red marking).

The Thuringian-Franconian-Vogtland Slate Mountains are among the Central European Variscides. In the structure of the European Variscides according to Kossmat , the Thuringian-Franconian-Vogtland Slate Mountains are part of the Saxothuringian. This is the only sub-region of the Saxothuringian in which almost exclusively rocks come to light,

  • which were included in only one, namely the Variscan orogeny,
  • and which were in the uppermost areas of the earth's crust during this mountain formation, so that pressure and temperature conditions were not sufficient to cause rock metamorphoses (this is also referred to as flat-crustal deformation ).

Internal structure

The Thuringian-Franconian-Vogtland Slate Mountains are internally divided into north-east-south-west ( Variscan ) trending saddles (also known as anticlinories ) and hollows (also known as synclinories ). The names of these structures are, from northwest to southeast, Schwarzburger Sattel , Teuschnitz-Ziegenrücker Mulde , and Bergaer Sattel . The latter is cut off to the southeast by the Vogtland disturbance from the Vogtland main hollow (actually more of a semi-hollow). The Mehltheurer Mulde immediately southeast of the Vogtland Fault is a partial trough in the northwest of the Vogtland main trough and continues to the south-west in the form of the very narrow Blintendorfer Mulde . The southeastern part of the Vogtland main hollow, also known as the Vogtland saddle , merges into the crystalline part of the Erz and Fichtel Mountains to the southeast.

The Teuschnitz-Ziegenrücker Mulde is divided into a northeastern ( Ziegenrücker Mulde ) and a southwestern part ( Teuschnitzer Teilmulde ) by a north-west-southeast ( Hercynian ) trending nest structure , the Franconian Forest Cross Zone . The western part of the transverse zone is named after the place Gräfenthal Gräfenthaler Horst , the eastern part after Bad Lobenstein Lobensteiner Horst .

stratigraphy

Precambrian

The oldest rocks in the Thuringian-Franconian-Vogtland slate mountains can be found in the Schwarzburger Sattel. These Neoproterozoic rocks belong to the Katzhütte group and were already folded and partly metamorphosed in the Cadomian orogeny well before the Variscan orogeny . It is predominantly greywacken and clay slate, silica and black slate, as well as phyllites and quartzites.

Phanerozoic

The Phanerozoic rocks of the Thuringian-Franconian-Vogtland Slate Mountains form two, mostly only slightly different sequences, which are called "Thuringian facies" and "Bavarian facies". The Thuringian facies are represented in almost the entire Thuringian-Franconian-Vogtland slate mountains, while the Bavarian facies are limited to a border around the Münchberg gneiss mass. The differences between the two “facies” are that at a certain time of deposition, different deposition conditions prevailed in the two deposition areas (primarily with regard to the depth of the sea and the relative distance from the origin of the sediments). Since rocks from the Bavarian and Thuringian facies occur in the south of the Thuringian-Franconian-Vogtland slate mountains directly and seamlessly next to each other, there is partly the view that the formations of the Bavarian facies together with the Münchberg gneiss mass as a tectonic cover during the main phase of the Variscan mountain formation from larger Distance to their current position. Another hypothesis explains the facies differences by the fact that locally narrow uplifts and subsidence of the earth's crust ensured that the conditions in the deposit area of ​​the Bavarian facies were different from those in the rest of today's Thuringian-Franconian-Vogtland slate mountains.

Cambrian

Silurian alum and silica slate with sulfate dripstones in the Saalfeld fairy grottoes
Devonian clay slate with layers of lime nodules (lime knot slate), planks near Saalfeld
The “stone rose” near Saalburg-Ebersdorf: Devonian pillow lava transformed by recent weathering
Devonian diabase in the Dörtendorf quarry northwest of Greiz . This is a locally limited occurrence in Upper Ordovician quartzites of the Graefental group in the northern part of the southeast flank of the Bergaer saddle.
The Peterstein, a rock made of Devonian diabastuff in the gorge of the White Elster near Cossengrün ( Steinicht ), between Greiz and Plauen.
Quarry in a coal-lime olistholith in the Wildflysch of the "Bavarian Facies", Döbra-Poppengrün near Hof
Asked steep unterkarbonische greywacke and shale in opencast mine Kamsdorf . The opencast mine is already in the transition area to the Thuringian Basin. Therefore, the carbon here is discordantly overlaid by Zechstein carbonates .

The Cambrian seems to be represented by a layer gap in the predominant part of the distribution area of ​​the Thuringian facies . The so-called Vesser complex is generally regarded as Cambrian . This is counted on the northwest flank of the Schwarzburger saddle, but is isolated in the middle of the Rotliegend rocks of the Thuringian Forest. In addition, the Vesser complex is located on the south-eastern edge of the Central German Crystalline Sill (Southern Phyllite Zone) and differs from the slate mountains further east in that it consistently contains medium-grade metamorphic rocks. Originally sandy-clay sediments were converted into quartzite or phyllite and carbonate sediments into marble. A large part of the Vesser complex, however, consists of rocks of volcanic origin (metarhyolites, andesites, dacites and basites as well as corresponding tuffs) which are partly strongly enriched with the iron ore mineral magnetite .

In the Bavarian facies, deposits of Cambrian age are reliably documented on the basis of fossils . There occur shale-quartzite alternation as well as volcanic breccias and tuffs .

Ordovician

Ordovician rocks of the Thuringian facies emerge in all three saddle structures of the Thuringian-Franconian-Vogtland slate mountains. Although these deposits are isolated from one another, the rock formations from the Schwarzburger Sattel to the Vogtland-Sattel can be correlated with one another relatively easily. Typical are quartzites ( Frauenbach quartzite , Phycodes layers ) and clay slate (" leather slate ", " stylus slate "). The Schmiedefeld formation is switched between leather slate and stylus slate . a. through mostly from Chamosite - oolitics distinguishes existing iron ore horizon.

In the Bavarian facies, clay slate dominates (“ Leimitz slate ”, “ edge slate series ”), associated with rocks that go back to a diabase - keratophyr magmatism. The leather slate is represented here by the Döbra sandstone deposited in shallow water .

Silurian

Silurian rocks of the Thuringian facies are exposed in the seamless Ordovician-Lower Carboniferous sequence on the southeast flank of the Schwarzburger Saddle. Further to the east, the Silurian appears in the form of small "island deposits". Typical rocks are graptolite-containing silica and alum slate and limestone ("ocher limestone").

In the Bavarian facies, instead of ocher limestone, "Orthoceren limestone" occurs.

Devon

Devonian deposits occur in the distribution area of ​​the Thuringian facies primarily at the transitions between the saddles and the hollows. Typical rocks are calcareous knot slate (including a plank formation ) and clay slate (including the " tentaculite slate "). In the east of the Thuringian-Franconian-Vogtland Slate Mountains there are also volcanic rocks such as diabase (including pillow lavas) and tuffite, which are summarized under the mining term " scarf stone ". These scarf stone series contain u. a. Iron ores of the Lahn-Dill type .

In the Bavarian facies, silica slate dominates.

Lower carbon

The slate mountains under the carbonic deposits in the Thuringian-Franconian-Vogtland slate mountains are the youngest rocks to be captured by the Variscan mountain formation. In the distribution area of ​​the Thuringian facies, they occur predominantly in the trough structures. While fine-grained, dark clay slate (roof and soot slate) still predominate in the lower Carboniferous, in fact only flysch sediments occur in the lower Carboniferous . In the Thuringian facies these are available as typical gray-wacke-slate-change sequences. Conglomerate wildflysch also occurs only in the highest Upper Carboniferous .

The Bavarian facies in the Lower Carboniferous shows the starkest contrast to the Thuringian facies. The flysch deposits there are clearly coarser in section. Wildflysch often occurs there in the form of breccias and conglomerates with sometimes meter-sized blocks ( olistholiths ) of various Devonian and Carboniferous rocks. Large blocks of coal-limestone indicate that the region of origin of the wildfly was at least partially a shelf region covered by a shallow sea .

Upper Carboniferous and Permian

The deposition of marine sediments ends with the Upper Carboniferous and therefore there is generally no longer any distinction made between Thuringian and Bavarian facies (in some cases this distinction is no longer made with the onset of flysch sedimentation and the "Bavarian" wildflysch is simply the proximal equivalent of the Thuringian flysch Facies whose delivery area happens to consist of pre-flysch rocks of the Bavarian facies). In addition, the upper carbon is represented by granitoid rock. In contrast to other Variscan Rump Mountains, the occurrence of such granitoids in the Thuringian-Franconian-Vogtland Slate Mountains is relatively low. The only thing worth mentioning in this context is the Bergen granite , which geologically is already attributed to the Ore Mountains. Due to the enormous heat that emanated from the granite at the time, the Ordovician slates in its surroundings have been changed by contact metamorphosis, so that they are more resistant to erosion today than the granite itself on the one hand and the non-metamorphic slates on the other side of the contact zone. The village of Bergen , which gives the granite its name, is therefore surrounded by an approximately ring-shaped ridge.

A relatively large occurrence of terrestrial deposits from the Upper Carboniferous and Permian (Rotliegend) lies east of Sonneberg in the Stockheim Basin . There, a sequence of volcanic rocks (including deposits of pyroclastic flows ) over a series of coal-bearing layers, red conglomerates and freshwater limestone to dune sandstones is deposited discordantly on sub-carbonic rocks . Other larger Rotliegend occurrences can be found in Schleuse-Horst (named after the small river Schleuse ), where they mainly cover Cambodian-Ordovician rocks of the Schwarzburger Saddle.

Deposits of the Younger Permian (Zechstein), which are represented by limestones (including reef limestone ), occur primarily in the northern border of the Thuringian-Franconian-Vogtland slate mountains at the transition to the Thuringian Basin. The outcrops of this northern border show the Zechstein discordance , which is often found on the edges of the Variscan mountain ranges , i.e. deposits of the Zechstein (often limestone) are stored horizontally on folded and therefore mostly not horizontal sub-carbonic or older rocks. Sometimes small remains of Rotliegend are still trapped between the deposits of the Zechstein and the older Paleozoic (e.g. on Bohlen near Saalfeld). The relatively powerful Rotliegend series of the Stockheim Basin is also overlaid by Zechstein sediments.

Geological history

At the end of the Precambrian , the crustal clod, on which the Thuringian-Franconian-Vogtland slate mountains are located today, was included in the Cadomian mountain formation, whereby the Neoproterozoic rocks and the like. a. of the Schwarzburger Saddle experienced a first folding. This folded Precambrian formed and still forms the basement for the Paleozoic rocks.

In the Cambrian, after extensive erosion of the Cadomian Mountains, the crust began to expand in the area of ​​today's Thuringian-Franconian-Vogtland Slate Mountains. This created rift breaks , which were the preliminary stages of the later Rheic Ocean . The formation of these rifts was accompanied by volcanism, which u. a. the creation of the Vesser complex. Although oceanic crust was already formed at their deepest points, these rift breaks were probably still relatively narrow in the Cambrian and therefore there were only a few regions that served as deposition areas. This is possibly one reason why there are hardly any Cambrian rocks in the Thuringian-Franconian-Vogtland slate mountains. Another possible reason for the low occurrence of Cambrian rocks is an interim uplift phase at the turn of the Cambrian to the Ordovician, during which Cambrian deposits were removed again.

The Cambrian rift valley expanded in the further course of the Paleozoic Era to form a sea basin, the Rheic Ocean. The Paleozoic sea cover of the region of today's Thuringian-Franconian-Vogtland Slate Mountains lasted a total of 180 million years. The crust, which is now strongly compressed, then formed an extensive, tectonically calm shelf area on the northern edge of the great southern continent of Gondwana . There, in the Ordovician, Silurian and Devonian regions, the fine-grained deep sea sediments were deposited, which are available today as pebble, alum, black, calcareous or “ordinary” slate. Limestone formed in shallower water . Numerous fossils are evidence of life in these seas . Ground-dwelling invertebrates such as trilobites , brachiopods , tentaculites and sea ​​lilies are typical , but also pelagic organisms such as graptolites or cephalopods ( orthocerates in the Silurian, goniatites in the Devonian). Organisms also lived directly in the sediment, as evidenced by trace fossils such as phycodes (in the Ordovician phycode quartzite) or thalassinoides (in the Silurian ocher limestone).

With increasing approach to the then southern edge of Europe ( Avalonia ), the Variscan mountain formation began in the Upper Devonian. It is controversial whether the crust on which the Thuringian-Franconian-Vogtland slate mountains, the Fichtel and Ore Mountains and the Sudetes are stored, was an independent small continent called Saxothuringia , or whether it was an integral part of the northern edge of Gondwana until the collision with Avalonia stayed. With the beginning of the Variscan mountain formation there was a volcanic episode, in the course of which u. a. Lava (rhyolite, diabase) and tuff rocks were formed.

The final collision with Avalonia began in the Lower Carboniferous. The Saxothuringian sea basin was pushed closer and closer together and the sediments and rocks that had already been deposited, including the Cadomian basement, were folded and literally stacked on top of one another. During this period the Münchberger gneiss mass and possibly most rocks of the "Bavarian facies" probably were as ceiling thrusts transported to its present position. The tectonic processes led to numerous earthquakes, as a result of which sediments and already solidified rock repeatedly slipped into the remaining basin areas. The result is the flysch series in the Teuschnitz-Ziegenrücker and the Mehltheurer Mulde, which are available as an alternating sequence of greywacken and slate. Immediately on the continental slopes, the coarsest landslides were deposited, which form the wildflysch of the "Bavarian facies". The flysch, however, was not excluded from mountain formation, but was sooner or later also included in folding and thrust processes, depending on the distance to the mountain formation front.

The Variscan orogeny came to an end in the Upper Carboniferous. Gondwana was now united with Europe and there were no more sea basins in today's Germany. The newly formed mountains partially collapsed under their own weight and magmas penetrated into the fault zones, leaving behind granitoid rock bodies. In addition, the mountains were exposed to weathering and erosion and were gradually eroded again. The corresponding erosion debris (Rotliegend Molasse) of the then Thuringian-Franconian-Saxon part of the Variscan Mountains has been preserved to this day in the Thuringian Forest, in the Erzgebirgsvorlandenke and in the Stockheimer Basin on the southern edge of the Franconian Forest.

In the Upper Permian there was a sea invasion in Central Europe. The so-called Zechstein Sea also flooded the edge areas of the now largely eroded mountains, leaving behind mostly limestone. In particularly shallow waters, slowly growing, muddy small reefs form, which are mainly built up by bryozoa .

At the beginning of the Mesozoic , in the Triassic, the Zechstein Sea had withdrawn again. Hardly anything of the Variscan Mountains was left on the surface of the earth. Already in the Permian, but increasingly in the Triassic, Gondwana began to break away from Europe again, with the Saxothuringian now remaining on the southern edge of Europe. As at the beginning of the Paleozoic Era, the drifting apart of the continents was accompanied by a subsidence of the crust. Therefore, the entire region of today's Thuringian-Franconian-Vogtland Slate Mountains in the Triassic and in the early and middle Jura was part of an extensive deposit area in what is now Central Europe, which was periodically flooded by the sea and took up huge series of sand, clay and limestone.

From the Upper Jurassic, however, the region fell dry and belonged to the northern edge of a land mass known as the Rhenish-Bohemian Island . The dry-falling resulted in the post-variscan deposits gradually being eroded again.

In the Cretaceous and in the early Cenozoic era , the great southern continent of Gondwana had already disintegrated and one of the larger fragments, Africa, was moving towards the southern edge of Europe together with a few smaller northern upstream continental fragments: the alpine mountain formation reached its main phase. The formation of the Alps has such an effect that the crust in what is now Central Germany was raised (Saxon tectonics), which also affected the area of ​​today's Thuringian-Franconian-Vogtland Slate Mountains. The increased erosion caused by the elevation now led to the fact that Variscan rocks were increasingly exposed and the current state gradually emerged.

geomorphology

The sub-landscapes of the Thuringian-Franconian-Vogtland Slate Mountains that are best known by name are Thuringian Slate Mountains , Franconian Forest and Vogtland Slate Mountains . However, this division into cultural regions does not particularly suit the geological or geomorphological conditions. The East Thuringian Slate Mountains are geologically similar to the Franconian Forest and geomorphologically to the Vogtland, but in neither of the two aspects is noteworthy to the higher Thuringian Slate Mountains. In the 19th century the latter was still assigned to the Thuringian Forest and the state border was viewed as the border with the Franconian Forest.

The Handbook of the Natural Region Divisions of Germany again denoted from the 1950s to the main unit Thuringian Slate Mountains only its higher southwest part, extended by the Franconian Forest. This refined follow-up work The natural space units on sheet 141 Coburg, aptly referred to as Thuringian-Franconian Slate Mountains , was published decades later . The East Thuringian Slate Mountains are assigned to the Vogtland as its north-western part. This division into montane and submontane shares corresponds more closely to the geomorphological conditions. The north of the Mont part has been designated as a Schwarza-Sormitz area for several years by both the Federal Agency for Nature Conservation (BfN) and the Thuringian State Institute for Environment and Geology (TLUG), with slightly different demarcations .

Natural allocation

Geological overview map
Natural space map

The geological units can be assigned to the natural areas as follows:

Deviations of the natural area boundaries from the geological ones

The usual natural boundaries differ somewhat from the geological boundaries:

Geotopes and geotourism (selection)

  • The “Schwarze Crux” mine in Vesser near Suhl: volcanic iron ores from the Cambrian Vesser complex.
  • Saalfeld fairy grottoes : Former mine in Silurian alum and pebble slate. A special feature are the Diadochit stalactites, which form bizarre shapes.
  • Slate quarry on Winterberg near Ludwigsstadt : Geotope with tentaculite slate and Nereite quartzite from the lower Devonian.
  • Bohlen near Saalfeld: Geotope and type locality of the Upper Devonian Bohlen formation.
  • Stone rose : Devonian lava pillows which, when weathered, have the appearance of a blossoming rose bud.
  • Lehesten slate park : Former open-cast roof slate mining in sub-carbon roof and soot slates in the Franconian Forest transverse zone.

See also

Individual evidence

  1. ^ A b Henningsen, Katzung: Introduction to the geology of Germany. 2006.
  2. ↑ a b c Linnemann: The structural units of the Saxothuringic. 2003.
  3. ↑ GeoViewer of the Federal Institute for Geosciences and Raw Materials ( information )
  4. ^ Dietrich Franke: Regional Geology East. Geological online reference work for East Germany with around 2500-page encyclopedia (PDF; 19 MB) and separately downloadable maps and tables
  5. ↑ Lentz: The northern Vogtland around Greiz. 2006
  6. ↑ Peter Bankwitz: On the geology of the Cambrian iron ore deposit Schwarze Crux, north of Vesser / Thuringian Forest (SE flank of the Central European Crystalline Zone). Journal of Geological Sciences. Vol. 31, No. 3, 2003, pp. 205-224 ( ResearchGate )
  7. ↑ Kunert: The Franconian Forest Cross Zone. 1999.
  8. ↑ a b Linnemann: Sedimentation and geotectonic framework. 2003.
  9. ^ Dill: Sediment petrography of the Stockheim Rotliegend basin. 1988
  10. ^ Kroner, Hahn: Sedimentation, deformation and metamorphosis in the Saxothuringian. 2003.
  11. ^ Ziegler: Geological Atlas of Western and Central Europe. 1990

literature

  • Dierk Henningsen, Gerhard Katzung: Introduction to the geology of Germany . 7th edition. Spektrum Akademischer Verlag, Munich 2006, ISBN 3-8274-1586-1 .
  • Uwe Kroner, Torsten Hahn: Sedimentation, Deformation and Metamorphosis in the Saxothuringian Age during the Variscan Orogeny: The Complex Development of North Gondwana during Continental Subduction and Leaning Collision . In: Geologica Saxonica. 48/49, 2003, pp. 133-146.
  • Volker Kunert: The Franconian Forest Cross Zone: Development of a thermal anomaly in the Saxothuringian. Dissertation. Giessen 1999, DNB 958422281 . (online) .
  • Sebastian Lentz: The northern Vogtland around Greiz: a regional inventory in the area of ​​Greiz, Weida, Berga, Triebes, Hohenleuben, Elsterberg, Mylau and Netzschkau . Böhlau-Verlag, Cologne, 2006, ISBN 3-412-09003-4 .
  • Ulf Linnemann: The structural units of the Saxothuringic . In: Geologica Saxonica. 48/49, 2003, pp. 19-28.
  • Ulf Linnemann: Sedimentation and geotectonic framework of the basin development in the Saxothuringian (Neoproterozoic - Lower Carboniferous) . In: Geologica Saxonica. 48/49, 2003, pp. 71-110.
  • Peter Ziegler: Geological Atlas of Western and Central Europe , Den Haag 1990, ISBN 90-6644-125-9 .

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