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23-710: In central Europe the Saxothuringian Zone is situated between the Rhenohercynian Zone to the northwest and the Moldanubian Zone to the southeast. The Hercynian metamorphism of the former zone is generally lower grade; that of the latter zone higher grade than that of the Saxothuringian Zone. West of the Vosges the zone is displaced to the north by a major strike-slip fault , the Bray Fault . The Saxothuringian Zone

46-513: A fold belt of west and central Europe, formed during the Hercynian orogeny (about 350 to 280 million years ago ). The zone consists of folded and thrust Devonian and early Carboniferous sedimentary rocks that were deposited in a back-arc basin along the southern margin of the then existing paleocontinent Laurussia . The Rhenohercynian Zone, named for the Rhine River and

69-508: A deep foreland basin . This filled with the products of erosion in the Hercynian mountains and the contemporaneously uplifted London-Brabant Massif to the north. During the Westphalian, the basin was completely filled and rose above sea level. The Rhenohercynian basin was filled with Devonian and Carboniferous sediments. Sedimentation was often disrupted by tectonic phases , but nevertheless

92-671: A high grade (up to eclogite facies ). These allochthonous nappes can probably be correlated with the Teplá terrane in the Moldanubian Zone further south. The Saxothuringian Zone is often also supposed to include the Mid-German Crystalline High , which then forms the northern part of the zone and lies directly next to the Rhenohercynian Northern Phyllite Zone . The Mid-German Crystalline High crops out in

115-621: Is in some places transected by Permo - Triassic grabens and intramontane basins filled with Rotliegend sediments and older deposits. The Eger Graben in the northwest of the Czech Republic and the Saar-Nahe Basin in western Germany are examples of such structures. The Saxothuringian Zone consists of early Paleozoic marine sediments that were deposited in the Saxothuringian Basin . They were slightly metamorphosed during

138-737: The Belgian coal measures . Early Devonian The Early Devonian is the first of three epochs comprising the Devonian period, corresponding to the Lower Devonian series . It lasted from 419.2 ± 3.2  to 393.3 ± 1.2 and began with the Lochkovian Stage 419.2 ± 3.2  to 410.8 ± 1.2 , which was followed by the Pragian from 410.8 ± 3.2  to 407.6 ± 1.2 and then by

161-793: The Cadomian orogeny (in the Ediacaran, 650-550 million years ago) and intruded by felsic plutons during the Cambrian and Ordovician (540-420 million years ago). In some places klippes of allochthonous crystalline rocks are found on top of these two units. These klippes are the Münchberg complex , Wildenfels complex and Frankenberg complex . They consisted originally of a sequence of deep-marine ( flysch ) sediments of Ordovician to Devonian age (480-360 million years old) and early Paleozoic mid-oceanic ridge basalts . The latter have been metamorphosed at

184-606: The East-Silesian basin of southern Poland . The sedimentary rocks that were laid down in the basin are often weakly metamorphic ( greenschist facies ). Most geologists consider the South-Portuguese zone to be a continuation of the zone to the west. Whether the Rhenohercynian Basin was a continuous feature or rather a string of temporaneously interconnected smaller basins is not well understood, because in many places

207-611: The Emsian , which lasted until the Middle Devonian began, 393.3 ± 1.2 million years ago . During this time, the first ammonoids appeared, descending from bactritoid nautiloids . Ammonoids during this time period were simple and differed little from their nautiloid counterparts. These ammonoids belong to the order Agoniatitida , which in later epochs evolved to new ammonoid orders, for example Goniatitida and Clymeniida . This class of cephalopod molluscs would dominate

230-635: The Hercynian Forest of Antiquity, forms a narrow zone through western and central Europe, from Cornwall and Ireland in the west to the Harz mountains of central Germany in the east, including the Rhenish Massif ( Ardennes , Taunus , Eifel and Hunsrück ). The total length of this ancient basin (the Rhenohercynian Basin ) could have been more than 2500 km. In the east the basin merges with

253-740: The folded sequences of Cornwall, the Ardennes , the Eifel and the Harz. From the Frasnian age (380 million years ago) the mafic volcanism ended, and the basin came locally under compressional stress , which led to folding and thrusting in the sedimentary rocks. Somewhere near the end of the Devonian, a subduction zone developed under the Mid-German/Normannian highs and Rhenohercynian crust began to subduct. This

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276-760: The Devonian and Carboniferous rock strata are covered with younger deposits. Parts of the basin have their own names, like the Cornwall basin in Cornwall, the Munster basin in Ireland or the Rhenisch basin in Belgium and Germany. The Rhenohercynian Zone is a part of the northern foreland of the Hercynian orogeny. It has a lower grade of metamorphism than the Saxothuringian Zone to

299-688: The Hercynian orogeny. The sedimentary sequence is assumed to be continuous from the Ediacaran to the Visean (330 million years ago). These metasediments form a wide zone north of the city of Dresden in Saxony . Tectonostratigraphically, gneisses (high-grade metamorphic rocks) and granites are found under these metasediments. They crop out as the competent massifs of the Ore Mountains and Saxonian Granulite Massif . They were deformed and recrystallized during

322-747: The Ligerian cordillera. In the Siegenian/Pragian and Emsian the Rhenohercynic basin was a back-arc basin behind this cordillera. Tectonic subsidence in a system of horsts and grabens together with basaltic volcanism resulted in the creation of new oceanic lithosphere . In the Middle Devonian a second basin, the Saxothuringian / Armorican basin , developed south of the Rhenohercynian basin. To

345-774: The Odenwald, the Spessart and the northern Vosges. It consists of Proterozoic orthogneisses and early Paleozoic volcanic ( amphibolites with MORB- protoliths and tuffs ) and sedimentary ( pelites , calcareous schists and marbles ) rocks that were metamorphosed at high grade during the Hercynian orogeny (up to amphibolite facies ). These rocks were intruded by two generations of plutons: Silurian to Early Devonian (440-400 million years old) granitoids and middle Carboniferous (Hercynian, 340-325 million years old) granites. Rhenohercynian Zone The Rhenohercynian Zone or Rheno-Hercynian zone in structural geology describes

368-588: The continental margin. It separated the London-Brabant Massif to the north from the Normannian and Mid-German Highs to the south. In the Middle Devonian (from 390 million years ago) a subduction zone existed south of Laurussia, where oceanic lithosphere of the Rheic Ocean subducted beneath the Mid-German/Normannian highs. Volcanism above the subduction zone created a cordillera -type mountain chain,

391-620: The continents of Laurussia (north) and Gondwana (south) from the Silurian onwards. The southern margin of Laurussia was formed during the Caledonian orogeny of the Silurian period, about 420 million years ago . In the Gedinnian/Lochkovian (Early Devonian) the southern part of the Caledonian mountain belt became a region of north–south extension . An elongated basin was formed parallel to

414-466: The destruction of the last oceanic crust of the basin. Its sedimentary fill was, however, not (totally) subducted but instead thrust northward. During the later part of the Carboniferous period ( Westphalian and Stephanian ) the Rhenohercynian zone formed the foreland of a relatively fast-developing Hercynian mountainbelt to the south. Isostatic subsidence of the foreland resulted in the development of

437-470: The south, meaning its rocks have generally been at smaller depths and under lower temperatures. The Subvariscan Zone north of the Rhenohercynian Zone was untouched by Hercynian metamorphism. During the Hercynian orogeny, the Rhenohercynian zone was folded and thrust internally. It was thrust over the foreland to the north (the London-Brabant Massif and other Avalonian terranes ). From the south it

460-411: The total thickness of the sediments can in some places be more than several kilometers. When a foreland basin was formed in the Rhenohercynian zone, this was filled with upper Carboniferous ( Pennsylvanian ) flysch and molasse sediments. The Namurian is characterized by flysch, in the Westphalian this gradually grades into molasse and other continental deposits, among which the thick coal layers of

483-592: The west some crustal convergence took place, and the Normannian High was partly thrust over the sedimentary basin fill of the Rhenohercynian basin. The Rhenohercynian basin disappeared when the continent Gondwana collided with Laurussia in the course of the Carboniferous period (the Hercynian orogeny ). The sedimentary rocks in the basin were thrust in a series of piggyback basins over the northern foreland (the London-Brabant Massif). These rocks now form

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506-582: Was overthrust by the Mid-German Crystalline High , part of the Saxothuringian Zone. The metamorphic grade or degree of metamorphism increases towards the south or southeast. The southern edge of the Rhenish Massif lies in the Northern Phyllite Zone , which has a higher grade than other parts of the zone. The Rhenohercynian basin was situated north of the Rheic Ocean , the ocean that spread between

529-638: Was the short Bretonnic phase of the Hercynian orogeny. It was followed, from the Tournaisian (early Carboniferous, 355 million years ago) till the end of the Visean by a new period of extension. During the Sudetic (main) phase of the Hercynian orogeny (330-320 million years ago, Late-Visean and Namurian / Serpukhovian ) compressional tectonics had the upper hand again. In the Namurian age full-scale continental collision between Laurussia and Gondwana resulted in

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