Engadin window

The Lower Engadine Engadine window or window is the geological term for an in southwest-northeast extending, elongated- oval tectonic window in the Lower Engadine between Zernez (Graubünden) and Landeck (Tyrol ) in the Austrian and Swiss Alps. The dimensions of the window are 17 times 55 km, it is about equally in Switzerland and Austria.

Geological significance

The Lower Engadine window plays just like the Rechnitz window, Tauern window and the about 20 km north-west lying Gargellenfenster for the exploration of the architectural style of the Alps a major role. Here the deeper subsoil comes to light, which is almost anywhere else in Austria covered by the ceiling of the Austroalpine tectonic. Tectonic uplift and subsequent erosion originally auflagernden ceiling are gone, so that today the middle of the framing of gneisses and amphibolites of the Austroalpine crystalline ceiling window-like lower Penninic ceilings are open-minded. These blankets are from the Penninic Outside the European continental shelf, most likely the nordpenninischen Valais Ocean ( Valais trough ). They were run over during the orogeny of the alpidischen originating from the south Adriatic plate, the rocks build today Austroalpine.

Geological construction

The northeast-southwest - trending Lower Engadine window displays within its Austroalpine framing an onion- like structure following tectono - metamorphic zones (of tectonically higher after tectonically deeper):

• Fimber zone (including Arosa zone)
• Tasna zone
• Shed zone of Champatsch
• Pfundser zone

Pfundser zone

The deepest parts of the window are Bündnerschiefer the Pfundser zone, which are rich in ophiolites at higher altitudes. Your sequence can be three parts, in the basal horror Bünderschiefer, in the Saderer yoke series and in the Colorful Bündnerschiefer. The ages can be the lack of shale fossils date bad for the deposition of the Grey Bündnerschiefer but is expected from the Lias period to Campanian. For the trapped ophiolites of the period is recognized Callovian to Cenomanian in general. The Saderer yoke series comes from the Maastrichtian, dated on the basis of Orbitoiden. The Colorful Bündnerschiefer rich then to the Eocene. The Bündnerschiefer form a northeast-southwest - trending anticlinal bulge with fairly steep dip on the flanks. In the middle of their axial culmination they reached epizonale grade metamorphism ( high-pressure low-temperature metamorphism, HP / LT - lower greenschist facies with formation of actinolite, and pumpellyite Karpholith ). The amphibolite of the ophiolite show next crossite and lawsonite even blauschieferfazielle overprint on the basis of glaucophane. The metamorphosis reached prints between 1.1 and 1.3 GPa in the lower section of the Pfundser zone ( Mundin unit), corresponding to a depth of about 30 to 35 kilometers, at a temperature of 350 to 375 ° C. In higher areas ( Arina unit), the metamorphic conditions weakened to 0.6 GPa and 300 ° C. It is not known whether, in the Grisons shales known in the Tauern Window Central gneisses with auflagerndem Hochstegenkalk are still available. Note: Recently, the classical tripartite division of Bündnerschiefer is questioned (see Bertle 2004). It is replaced by the following sequence ( from the hanging wall to the footwall ):

• Malmurainza lineup. Former Colorful Bündnerschiefer; more than 100 meters thick turbidites from the Upper Cretaceous.
• Fuorcia - d'Alp lineup. From the Albian, 10 meters in thickness. Results from a Oceanic Anoxic Event.
• Gault formation. Flyschoide, sandy- clayey sequence from the Aptian / Albian, about 40 meters thick.
• Tristel lineup. Turbiditische Tristelschichten from the Barremian / Aptian, approximately 30 meters.
• Shale from the Neocomian. Perform tuffites at the base, about 20 meters thick.
• Ophiolites. Tholeiitic pillow lava, basalt, basalt transitions, breccias of pillow lava, hyaloclastite and isolated radiolarites. The thickness can not be specified exactly, but it is more than 100 meters. The ophiolites are considered to be oceanic crust of the Valais trough due to geochemical criteria.

Due to the Isoklinalfaltenbaus found on Piz Mundin with from overturned storage and reduplications the previously recognized with 1500 to 2000 meters widths are estimated only at approximately 500 meters.

Shed zone of Champatsch

The Bündnerschiefer the Pfundser zone be run over by the shed zone of Champatsch (also zone of Roz- Champatsch - Pezid ), a tectonically very complex sequence. It begins with an exploration Ling zone from the nordpenninischen area. Squamous are here Altkristallin, quartzites and carbonates from the Triassic ( crystalline limestone, clayey- marly shale and dolomite), marbles from Jurassic and Cretaceous, ophiolites ( with Tristelschichten and Gault ) and Cretaceous flysch mixed together. The mining zone Ling shows affinities to the Wildflysch Feuerstätter ceiling.

At the same level the unterostalpine Stammerspitze unit is eingeschuppt. As Härtling it forms the distinctive summit of Stammerspitze and Burgschrofens. Your sequence starts with triasssischem main dolomite and Kössener layers, followed by the Jurassic Lias colorful and Liasbrekzien, then stain marl, quartzite, radiolarites and finally Aptychenschichten. Due facies relationship it is interpreted as an extension arm of the Err - Bernina ceiling.

About the prospecting Ling zone, the actual zone of Roz- Champatsch - Pezid connects to, which is also very disturbed. It forms a slaty - sandy- calcareous sequence from 200 to 1000 meters in thickness. The zone contains Grey Bündnerschiefer with inliegenden Colorful Grisons shales and argillaceous equivalents of Tristelschichten and Gault and is interpreted as a low metamorphic flysch.

The scales zone of Champatsch is run over by the Tasna zone.

Tasna zone

The mittelpenninische Tasna zone begins with the ophiolitreichen Ramoscher zone in the southwest, which merges into the Prutzer zone to the northeast. The Ramoscher zone leads phyllonitisiertes Altkristallin, which may be originated from Paleozoic, followed by rudimentary Permomesozoikum consisting of Ladiser quartzite ( Lower Triassic), dolomite lenses and Colorful Keuper with plaster. You probably comes from a intrapenninischen threshold region. However, the associated Ophiolitmassen with Magnesitgängen, nickel ore and copper enrichments are problematic in such an interpretation, unless the Ramoscher zone represents the immediate transition region of continental facies ( Briançonnais ) dar. for oceanic facies of the Valais trough The Ophiolitmassen consist mainly of serpentinitisiertem peridotite with associated Ophicalciten and Serpentinitbrekzien. Lenticular Metagabbros can be found in and near the peridotite.

The zone contains Prutzer secured Paleozoic, composed of quartz phyllite and dolomite iron with tetrahedrite, chalcopyrite and arsenopyrite. Here are quite powerful Ladiser quartzite, fossiliferous Triassic rocks as well as Grey and Colorful Bündnerschiefer.

About the Ramoscher zone pushes the very different structures Tasna ceiling. It leads at their base the Tasna granite, a green ( by chloritization ), epimetamorphen granite gneiss, which occurs also in the Falknisdecke and in the Sulzfluh. About this crystalline base unit of continental origin follows usually a scantily trained Permotrias with Kristallinbrekzien and rhyolites, transgredierendem main dolomite, quartzite Keuper with plaster and colored shales, fossil -rich Steinberger Lias and Falknisbrekzien, then pelagic limestones from the Middle Jurassic and finally Malmkalke. Furthermore Cretaceous Neokomschiefer, Tristelschichten follow with Orbitoliniden, powerful sandstones of the Gault ( at Piz Tasna ), glauconite - quartzites, only a few meters thick expectant quartz sandstones, gray marl and Couches Rouges with Globotruncanids from the Upper Cretaceous. The conclusion of the Tasna ceiling forms Paleogene flysch. The Tasna ceiling was metamorphosed under the conditions of the lower greenschist facies.

Fimber zone

The Fimber zone (including Arosa zone) results in association with various Flyschen ( Idalpsandstein from the Dogger, possible flysch from the Malm, the Neocomian and the Aptian, and Höllentalflysch from the Cenomanian / Turonian ) Tasna mining charges. It will also provide a highly deformed tectonic mixing zone, which consists of Triassic dolomites, quartzites, radiolarites, black shales from the Hauterivian / Aptian and in particular ophiolites ( which is missing in the subjacent Tasna ceiling). The Ophiolitfolge Idalp is composed of serpentinites, gabbros, diabases and basalts of südpenninischen Ocean. It has a double metamorphosis: an oceanic high-temperature metamorphism and a subsequent high-pressure metamorphism. The high-pressure metamorphism took place at pressures between 0.7 and 0.9 GPa and temperatures around 250 ° C instead of ( transition from greenschist to Blauschieferfazies ).

The intensive Tektonisierung the Fimber zone is based on the vorgosauisch made ​​( before the Coniacian ) traverse is the Silvretta.

Eastern Alps framework

The Penninic nappe stack in the Lower Engadine window is passed over from the south of the Silvretta blanket that forms the western and northern part of the frame. Along their base they occasionally shows Pseudotachylith course - witness the vacated at the overthrust processes frictional heat. Under the actual Silvretta blanket is still a holey carpet of Central Eastern Alps track floes, the subsilvrettiden Triassic floes remained. This represents the southwestern part of the framing and may be viewed as the northernmost arm of the hochgeschürften Scarl blanket from the Engadine Dolomites. The eastern window frame is made from the huge Ötztal- ceiling, slid along the Schlinig subduction in a WSW direction across the Silvretta blanket and the Dolomites. Because of these conditions already described Bruno Sander the Lower Engadine window as scissor window. In the northeast are found as framing then permomesozoische sediments, which were based on the eingeschuppt Thial - Puschlin - interference between the Silvretta blanket and the following north Phyllitgneiszone.

Engadine lineament

On its southeast side of the window is cut from a supraregional disorder of the Engadine disorder ( also Engadine Engadine lineament or line). This is a sinistral lateral displacement, but at the same time raised the northwest side of the window, so that on the southeast side of the fantastic about the Graubunden slate rock sequences partially mutilated (such as the Tasna zone) are present or absent ( it lacks the Cham -splasher Schuppenzone ).

Tectonic development

The tectonic evolution of the Lower Engadine window is explained in the context of north-south directed thrusting of the Austroalpine on the tripartite Pennine sedimentation. Took place towards the end of the Lower Cretaceous in the Upper Barremian / Aptian million years ago, around 125 to 120 are Austroalpine the transition from a passive to an active continental margin and put it first Subduktionsvorgänge at his or her foot. This led to the gradual emergence of a Akkretionskeiles below the slowly passing to the north in motion crystalline ceiling system (Silvretta Blanket, Ötztal- ceiling). In this accretionary wedge piled now inside the window is open-minded tektonometamorphen zones. The paleogeographic arrangement of these zones is reflecting in its current spatial arrangement in the ceiling stack resist: the südpenninische Fimber zone ( with the Arosa zone) as the southernmost unit is located immediately below the Austroalpine, including following the further north emerging field of Tasna zone ( the northernmost foothills of mittelpenninischen Briançonnais ) and at the bottom the most in the north situated nordpenninischen zones - Schuppenzone of Champatsch and Pfundser zone of the Valais trough.

For the northern movement of the on -propelled Austroalpine can be first movement phases in the Albian, Cenomanian and Turonian differ in where the turonische phase of the already mentioned vorgosauischen phase corresponds. During the Gosau ( in Campanian ) of südpenninische sedimentation ( Fimber zone) is swallowed, during which learns of the Eastern Alps region has a first metamorphosis ( Eo- alpine metamorphism in front of about 110 and 90 million years, with Abkühlaltern to 65 million years ago). Between the Upper Campanian and Paleocene it should already come to an initial increase in the isostatic approach to forming Akkretionskeiles, indicated by exposure of marine Gosausedimentation in Carinthia. During the Paleocene and Eocene of the nappe stack then moved up in the nordpenninischen and even in the Helvetic sedimentation and ended the Akkretionsvorgang. The enormous ballast led to the rise in temperature and resulted in the Penninic the window inside during the Upper Eocene, the Oligocene and Lower Miocene, a metamorphosis of the lower greenschist facies ( actual alpine metamorphism in the period from 38 bis 16 million years BP, with thermal maximum 30 million years). Most of course was the lowermost zone Pfundser affected ( Mundin unit).

On the Alpine metamorphism was followed by the general uplift and further cooling of the orogen, documented by radiometric age determinations on micas and fission track ages of zircon and apatite.

The narrowing of the Eastern Alps was, however, does not end there, but subduction and accretion shifted on the northern edge of the Alps. In this context, then it came in the time frame: 10 bis 5 million years BP (Upper Miocene ) and the convexity of the Lower Engadine window. The actual erosive origin of the window began at the latest Messinian ( Sarmatian ) to around 7 million years, as from that date for the first time units from the lowest Silvretta blanket were cut from the Inn and can be detected as Pseudotachylitgerölle in the Chiemgau molasses. From the Pliocene the area around the Lower Engadine Window is subject to isostatic adjustment movements.

Regardless of the northwest -southeast direction to running in a north-south a higher floor was laid in a transverse, ostgerichtete subduction of the Silvretta blanket and the Scarl blanket under the Ötztal ceiling ( Schlinig subduction ). However, this movement also had an effect on units in the eastern part of the window inside and therefore had to have taken place after the bulge in the Upper Miocene ( There but are also much older middle Cretaceous and Paleogene movements on this fault plane is known, furthermore it should have been effective as a Detachment of the extensional be ).

The linksverschiebende Engadine lineament was first visible in Rupelium 30 million years ago, as evidenced by the offset of the Kontaktaureole to the Bergeller Pluton.