The Giessen nappe (german: Gießener Decke) is a

tectonic Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents ...

nappe In geology, a nappe or thrust sheet is a large sheetlike body of rock that has been moved more than or above a thrust fault from its original position. Nappes form in compressional tectonic settings like continental collision zones or on the o ...

in the southeastern part of the Rhenish Massif in western

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...

. The nappe is an "alien" (

allochthon upright=1.6, Schematic overview of a thrust system. The hanging wall block is (when it has reasonable proportions) called a nappe. If an erosional hole is created in the nappe that is called a window (geology)">window. A klippe is a solitary out ...

ous) unit in the Rhenohercynian zone of the

Hercynian orogeny The Variscan or Hercynian orogeny was a geologic mountain-building event caused by Late Paleozoic continental collision between Euramerica (Laurussia) and Gondwana to form the supercontinent of Pangaea. Nomenclature The name ''Variscan'', comes f ...

, it was

thrust Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that sys ...

over the usual slightly

metamorphosed Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...

Devonian and Carboniferous

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

s in this zone. The Giessen nappe is often correlated with the Harz nappe in the

Harz The Harz () is a highland area in northern Germany. It has the highest elevations for that region, and its rugged terrain extends across parts of Lower Saxony, Saxony-Anhalt, and Thuringia. The name ''Harz'' derives from the Middle High German ...

and similar units in the

Bohemian Massif The Bohemian Massif ( cs, Česká vysočina or ''Český masiv'', german: Böhmische Masse or ''Böhmisches Massiv'') is a geomorphological province in Central Europe. It is a large massif stretching over most of the Czech Republic, eastern Ger ...

in the

Czech Republic The Czech Republic, or simply Czechia, is a landlocked country in Central Europe. Historically known as Bohemia, it is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the southeast. The ...

. These units form the rare erosional leftovers of small

microcontinent Continental crustal fragments, partly synonymous with microcontinents, are pieces of continents that have broken off from main continental masses to form distinct islands that are often several hundred kilometers from their place of origin. Caus ...

s that were during the Hercynian orogeny squeezed between the

paleocontinent A paleocontinent or palaeocontinent is a distinct area of continental crust that existed as a major landmass in the geological past. There have been many different landmasses throughout Earth's time. They range in sizes, some are just a collection ...

s Gondwana to the south and

Laurussia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pan ...

to the north.

Outcrop area

Giessen nappe outcrops cover about 300 km² from the western edge of the

Vogelsberg The is a large volcanic mountain range in the German Central Uplands in the state of Hesse, separated from the Rhön Mountains by the Fulda river valley. Emerging approximately 19 million years ago, the Vogelsberg is Central Europe's largest ...

over Braunfels,

Wetzlar Wetzlar () is a city in the state of Hesse, Germany. It is the twelfth largest city in Hesse with currently 55,371 inhabitants at the beginning of 2019 (including second homes). As an important cultural, industrial and commercial center, the un ...

and

Gießen Giessen, spelled Gießen in German (), is a town in the German state (''Bundesland'') of Hesse, capital of both the district of Giessen and the administrative region of Giessen. The population is approximately 90,000, with roughly 37,000 univers ...

, almost to

Marburg Marburg ( or ) is a university town in the German federal state (''Bundesland'') of Hesse, capital of the Marburg-Biedenkopf district (''Landkreis''). The town area spreads along the valley of the river Lahn and has a population of approxima ...

. The river

Lahn The Lahn is a , right (or eastern) tributary of the Rhine in Germany. Its course passes through the federal states of North Rhine-Westphalia (23.0 km), Hesse (165.6 km), and Rhineland-Palatinate (57.0 km). It has its source in t ...

flows along the northern part of the nappe until it crosses the nappe between Gießen and Wetzlar to continue flowing westwards to the

Rhine ), Surselva, Graubünden, Switzerland , source1_coordinates= , source1_elevation = , source2 = Rein Posteriur/Hinterrhein , source2_location = Paradies Glacier, Graubünden, Switzerland , source2_coordinates= , so ...

Lithology and stratigraphy

The Giessen nappe consists of a thin sequence of slightly metamorphosed Lower and Middle Devonian slates and

radiolarite Radiolarite is a siliceous, comparatively hard, fine-grained, chert-like, and homogeneous sedimentary rock that is composed predominantly of the microscopic remains of radiolarians. This term is also used for indurated radiolarian oozes and ...

s covered with Upper Devonian to Lower Carboniferous

greywacke Greywacke or graywacke (German ''grauwacke'', signifying a grey, earthy rock) is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lit ...

s. At some spots along the base of the Giessen nappe alien tectonic slices of

metabasalt Amphibolite () is a metamorphic rock that contains amphibole, especially hornblende and actinolite, as well as plagioclase feldspar, but with little or no quartz. It is typically dark-colored and dense, with a weakly foliated or schistose (flak ...

occur. Chemical analysis of these rocks shows they were originally mid ocean ridge basalts.Grösser & Dörr (1986) Especially the Upper Devonian to Lower Carboniferous greywackes are clearly different from the rocks of this age of the Rhenohercynian basin, that now form the

footwall In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

of the Giessen nappe. This difference in lithology led German geologist

Franz Kossmat Franz Kossmat ( 22 August 1871 in Vienna – 1 December 1938 in Leipzig) was an Austrian-German geologist, for twenty years the director of the Geological Survey of Saxony under both the kingdom and the subsequent German Republic. Kossmat wa ...

in 1927 to the conclusion that the Giessen nappe is an allochthonous unit. The base thrust of the Giessen nappe consists of

cataclasite Cataclasite is a cohesive granular fault rock. Comminution, also known as cataclasis, is an important process in forming cataclasites. They fall into the category of cataclastic rocks which are formed through faulting or fracturing in the upper ...

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of ...

s and

mylonite Mylonite is a fine-grained, compact metamorphic rock produced by dynamic recrystallization of the constituent minerals resulting in a reduction of the grain size of the rock. Mylonites can have many different mineralogical compositions; it is a ...

s and forms a semi-horizontal thrust plane. Locally the thrust plane can be deformed by late stage folding and thrusting. Erosion has separated some small pieces of the nappe from the central mass, forming small

klippe 350px, Schematic overview of a thrust system. The shaded material is called a window_(geology).html"_;"title="nappe._The_erosional_hole_is_called_a__window_(geology)">window_or_fenster._The_klippe_is_the_isolated_block_of_the_nappe_overlying_aut ...

s in the vicinity of Braunfels and Wetzlar. Internally, the rocks of the nappe are isoclinally folded and cut by shear zones.

Notes

Literature

*; 1988: ''Die geologische Entwicklung der östlichen Lahnmulde (Exkursion C. am 7. April 1988)'', Jahresberichte und Mitteilungen des oberrheinischen geologischen Vereins, Neue Folge 70, pp. 43-74. *; 1990: ''Stratigraphie, Stoffbestand und Fazies der Gießener Grauwacke (östliches Rheinisches Schiefergebirge)'', Geologische Abhandlungen Hessen 91, p. 94. *; 1986: ''MOR-Basalte im östlichen Rheinischen Schiefergebirge'', Neues Jahrbuch für Geologie und Paläontologie 12, pp. 705–722. *; 2004
''Palaeogeography and tectonic structure of allochthonous units in the German part of the Rheno-Hercynian Belt (Central European Variscides)''
International Journal of Earth Sciences 93, pp. 414–431. *; 2006
''Tectonostratigraphic development of the Devonian and Carboniferous in the Brunovistulian terrane, Czech Republic''
in: (eds.): ''Carboniferous Conference Cologne. From Platform to Basin'', Kölner Forum für Geologie und Paläontologie 15, . *; 1927: ''Gliederung des varistischen Gebirgsbaus'', Abhandlungen der Sächsischen Geologischen Landes-Anstalt 1, p. 39. *; 1992: ''Geologie von Mitteleuropa'', Schweizerbarth’sche Verlagsbuchhandlung, Stuttgart (5th ed.), . {{coord, 50, 34, 50, N, 8, 35, 14, E, region:DE-HE_type:landmark_source:kolossus-dewiki, display=title Geology of Germany Hercynian orogeny Rhenish Massif Geology of Europe