Lateral extrusion in the eastern Alps, PArt 2: Structural analysis

Abstract

The late Oligocene‐Miocene tectonic style of the Alps is variable along strike of the orogen. In the Western and Central Alps, foreland imbrication, backthrusting, and backfolding dominate. In the Eastern Alps, strike‐slip and normal faults prevail. These differences are due to lateral extrusion in the Eastern Alps. Lateral extrusion encompasses tectonic escape (plane strain horizontal motion of tectonic wedges driven by forces applied to their boundaries) and extensional collapse (gravitational spreading away from a topographic high in an orogenic belt). The following factors contributed to the establishment of lateral extrusion in the Eastern Alps: (1) a rigid foreland, (2) a thick crust created by indentation and earlier collision, (3) a decrease in strength in the crust due to thermal relaxation, (4) a crustal thickness gradient from the Eastern Alps to the Carpathians, and, possibly, (5) a disturbance of the lithospheric root. Northward indentation by the Southern Alps causes thickening in and in front of the indenter and tectonic escape. Gravitational spreading attenuates crustal thickness differences. Indentation structures occur in the western Eastern Alps and comprise folds, thrusts, and strike‐slip faults. These structures pass laterally into spreading structures, which encompass transtensional and normal faults in the eastern Eastern Alps. The overall structural pattern is dominated by escape structures, namely, sets of strike‐slip faults that bound serially extruding wedges. Structural complexity arises from (1) interference of major fault sets, (2) accommodation of displacement differences between the Eastern Alps and their fore‐ and hinterland, (3) displacement transfer from the Eastern Alps toward the Carpathians which act as a lateral unconstrained margin, and (4) crustal decoupling, which partitions extrusion into brittle upper plate and ductile lower plate deformation. The kinematics of lateral extrusion is approximated by an extrusion‐spreading model proposed for nappe tectonics.

Cenozoic granitoids in the Dinarides of southern Serbia: age of intrusion, isotope geochemistry, exhumation history and significance for the geodynamic evolution of the Balkan Peninsula

“…of the Alps and the magmatic belt paralleling the Mid-Hungarian fault zone (localities 1, 2 and 3 in Fig. 9), we emphasize that the subduction polarity in the Alps, including that within the Western Carpathians north of the Mid-Hungarian fault zone, merely representing the eastern prolongation of the Alps before Miocene lateral extrusion (Ratschbacher et al 1991), is opposite to that of the Dinarides during the time span considered . Hence, in spite of the temporal coincidence, there cannot be a direct link between the Alpine-Mid-Hungarian magmatic belt and the Dinaridic-Hellenidic magmatic belt of which our area of investigation is a part.…”

K/Ar geochronology of igneous amphibole phenocrysts in Miocene to Pliocene volcaniclastics, Styrian Basin, Austria

“…This event gen er ated sinistral fault sys tems to the north and dextral fault sys tems to the south (Periadriatic lin ea ment and as so ci ated strike-slip zones) of the Alps. Lat eral mo tion of the crust includes tec tonic es cape of wedges and extensional col lapse from the mor pho log i cal high of the Tauern win dow area to wards the ba sin (Ratschbacher et al, 1991). Re lated to this event, the Al pine-Carpathian realm and Pannonian Ba sin were formed by col li sion-re lated Mio cene ex ten sion.…”

Hydrogeological properties of fault zones in a karstified carbonate aquifer (Northern Calcareous Alps, Austria)

“…Five stages of deformation (D1-D5) are identified in the Hochschwab massif (see unpublished report by Decker in Table 1), the most important being (1) NW-directed dextral transpressional stacking of nappes during the Late-Early Cretaceous to late Eocene, (2) N-directed thrusting (EoceneOligocene) and (3) eastward lateral extrusion of crustal wedges along (E)NE-striking sinistral strike-slip faults such as the SEMP (Salzach-Ennstal-Mariazell-Puchberg fault zone) during the Miocene (Decker et al 1994;Linzer et al 1995) The investigated fault zones are all part of the SEMP, which is 400 km long and crosses all Austroalpine tectonostratigraphic units (Decker et al 1994;Linzer et al 1995Linzer et al , 2002Peresson and Decker 1997;Ratschbacher et al 1991), forming the lateral ramp of the eastward extrusion of the Eastern Alps in the course of the post-collisional exhumation of the Tauern window (Linzer et al 2002) (Fig. 1a).…”