Inherited tectonic structures controlling the deformation style: an example from the Helvetic nappes of the Eastern Alps

Zerlauth, Michael; Ortner, Hugo; Pomella, Hannah; Pfiffner, Othmar-Adrian; Fügenschuh, Bernhard

doi:10.1007/s00015-014-0167-7

Cited by 18 publications

(12 citation statements)

References 16 publications

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“…4) shortening for the eastern block. In the Vorarlberg area in Austria, a continuation of this west-east shortening gradient is observed from 30 % just east of the Rhine Valley to 16 % in the Iller Valley (Zerlauth et al 2014). In our model, there is an additional shortening gradient inside the western block ( Fig.…”

Section: Shortening Estimatementioning

confidence: 89%

The Alpstein in three dimensions: fold-and-thrust belt visualization in the Helvetic zone, eastern Switzerland

2014

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To investigate the geometrical relationships between folding and thrust faulting, we built a 3D geological model of the Helvetic fold-and-thrust belt in eastern Switzerland from several existing and two newly drawn cross-sections in the Säntis area. We partly redrew existing cross-sections and validated them by checking for line length balance; to fill areas with no data we drew additional cross-sections. The model was built based on surface interpolation of the formation interfaces and thrusts between the cross-sections, which allowed generating eight main surfaces. In addition, we used cave data to validate the final model in depth. The main structural elements in the Säntis area, the Säntis Thrust and the Sax-Schwende Fault, are also implemented in the model. The result is a 3D structural model of the area, which provides an intuitive way for examining a portion of a complex structural nappe. The 3D model highlights the shapes of the main anticlinesyncline pairs and how these fold trains vary laterally in amplitude and wavelength. It shows how lateral variations in fold style correlate with regional shortening gradients as determined from line-length balancing. The model also clearly shows the lateral extension, the trend, and the variation in displacement along the principal faults. The reconstruction of horizons in 3D allows the investigation of cross-sections in any given direction. The 3D model is useful for developing and understanding how the internal nappe structures, namely folds and thrust faults, change along strike due to palaeogeographic and stratigraphic variations. Lateral stratigraphy variations correlate with different deformation responses of the nappe. Changes can occur either abruptly across transverse faults or in a more gradual manner. Keywords Central Alps Á Helvetic nappes Á Säntis Thrust Á 3D modelling Á Line balancing Á Depth validation with cave data Editorial handling: A. G. Milnes.

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Section: Shortening Estimatementioning

confidence: 89%

The Alpstein in three dimensions: fold-and-thrust belt visualization in the Helvetic zone, eastern Switzerland

2014

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“…In the regional cross section from the tilted Molasse to the Prätigau Flysch of eastern Switzerland, the base of the Helvetic thrust sheets is seen to descend gradually to the south (Figure b). The southern end of the cross section shows the eastern end of the Aar massif with the NHF in the parautochthonos Molasse [compare Pomella et al ., ; Zerlauth et al ., ].…”

Section: Datamentioning

confidence: 99%

“…FAT = Frontal Alpine thrust, PA = Periadriatic line. (b) Regional cross section from the Foreland Molasse to the internal part of the Alpine orogenic wedge [ Pomella et al ., ; Zerlauth et al ., ]. For location, see B of inset.…”

Section: Introductionmentioning

confidence: 99%

Geometry, amount, and sequence of thrusting in the Subalpine Molasse of western Austria and southern Germany, European Alps

et al. 2015

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In this paper we review the structure of the most external thrust belt of the Alps between the Rhein valley and Salzburg based on a new tectonic map and the (re)interpretation of seismic sections. Specifically we address the correlation between deformation in the Subalpine Molasse and the Alpine thrust belt in general and focus on the control of sedimentary facies on the structural style. A dramatic change in architecture from a ramp-flat structure to buckle folding is related to a change from coarse-grained fans to fine-grained deposits within the Subalpine Molasse. Additionally the interaction of escape tectonics with postcollisional shortening controls the decrease of late Early Miocene and younger shortening within the Subalpine Molasse from 50 km near the Rhine valley to almost zero near Salzburg. Transfer of shortening into the hinterland, which is the zone of lateral escape, ended foreland propagation of the Alpine thrusts and initiated a general break-back sequence of thrusting. Throughout this time the thrusts remained active. In such a scenario, tectonic units on top of the Subalpine Molasse are expected to undergo clockwise rotation around vertical axes. As thrusting in the Subalpine Molasse is closely related to contemporaneous transport and shortening within the tectonically higher Helvetic thrust sheets, amounts of Miocene differential shortening and related clockwise vertical axis rotation are minimum amounts. True clockwise vertical axis rotation is probably larger than the 12°deduced from the Subalpine Molasse thrust belt.

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“…Only a few studies describe thrust‐dominated transpression as a result of oblique convergence (e.g. Pfiffner, ; Linzer et al ., ; Norris & Cooper, ; Zerlauth et al ., ). Syn‐tectonic deposits in a zone of thrust‐dominated transpression have only been studied at the northern margin of the Venetian basin of the European Southern Alps (Massari et al ., ,b, ; Mellere et al ., ).…”

Section: Discussionmentioning

confidence: 97%

“…However, the observations and experiments presented here can be applied to any setting with high‐angle faults dissecting growing folds. Most thrust belts have such high‐angle faults, for example the Southern Pyrenees (e.g., Puigdefabegras et al ., ) the Helvetic (e.g., Zerlauth et al ., ) and Subalpine Molasse (e.g., Ortner et al ., ) thrust belts of the Alps and the Swiss Jura (e.g., Affolter & Gratier, ). The reason that growth strata geometries as reported have not been recognized before is probably the outstanding outcrop in the study area.…”

Section: Discussionmentioning

confidence: 99%

Geometry of growth strata in a transpressive fold belt in field and analogue model: Gosau Group at Muttekopf, Northern Calcareous Alps, Austria

et al. 2015

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The thrust sheets of the Northern Calcareous Alps were emplaced during Late Cretaceous thrustdominated transpression expressed by thrust sheets segmented by closely spaced tear faults. Thrust sheet-top sediments were deposited during thrusting and associated fold growth and were controlled by active folding and tearing. We observe two types of angular unconformities: (1) Angular unconformities above folds between tear faults conform with the model of progressive unconformities. Across these unconformities dip decreases upsection.(2) Here, we define progressive unconformities that are related to tear faults and are controlled by both folding and tearing. Across these unconformities both strike and dip change. In growth strata overlying folds dissected by high-angle faults, such unconformities are expected to be common. We used analogue modelling to define the geometry of the tear faults and related unconformities. Within the syn-tectonic sediments, a steep, upward flattening thrust within a broader, roughly tulip-shaped drag zone develops. The thrust roots in the tear fault in pre-tectonic deposits and is curved upward toward the downthrown block. Vertical offset on the thrust is related to differential vertical uplift caused by, for example, growth of folds with different wavelength and amplitude on either side of the tear fault. Formation of progressive unconformities is governed by the relationship between the rates of deposition and vertical growth of a structure. Fault-related progressive unconformities are additionally controlled by the growth of the vertical step across the tear fault. When the rates of vertical growth of two neighbouring folds separated by a tear fault are similar, the rate of growth across the tear fault is small; if the first differ, the latter is high. Episodic tear fault activity may create several angular unconformities attached to a tear fault or allow the generation of angular unconformities near tear faults in sedimentary systems that have a rate of deposition too high to generate classical progressive unconformities between the tear faults.

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Inherited tectonic structures controlling the deformation style: an example from the Helvetic nappes of the Eastern Alps

Cited by 18 publications

References 16 publications

The Alpstein in three dimensions: fold-and-thrust belt visualization in the Helvetic zone, eastern Switzerland

The Alpstein in three dimensions: fold-and-thrust belt visualization in the Helvetic zone, eastern Switzerland

Geometry, amount, and sequence of thrusting in the Subalpine Molasse of western Austria and southern Germany, European Alps

Geometry of growth strata in a transpressive fold belt in field and analogue model: Gosau Group at Muttekopf, Northern Calcareous Alps, Austria

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