Topographic Evolution of the Eastern Alps: the Influence of Strike-Slip Faulting Activity
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Topographic evolution of the Eastern Alps: The influence of strike-slip faulting activity Thorsten Bartosch1, Kurt Stüwe1, and Jörg Robl2 1INSTITUTE OF EARTH SCIENCES, UNIVERSITY OF GRAZ, 8010 GRAZ, HEINRICHSTRASSE 26, AUSTRIA 2INSTITUTE OF GEOGRAPHY AND GEOLOGY, UNIVERSITY OF SALZBURG, 5020 SALZBURG, HELLBRUNNERSTRASSE 34, AUSTRIA ABSTRACT We present the results of a numerical model that was used to investigate aspects of the landscape evolution of the Eastern European Alps in the Miocene. The model allows the consideration of strike-slip faulting, an inherent feature of the Miocene tectonics in the Eastern Alps, within a viscous medium. Mechanical deformation of this medium is coupled with a landscape evolution model to describe surface processes. For the input variables, the activity history of strike-slip faulting in the Eastern Alps was compiled from literature sources. The results pres- ent a major improvement in the predicted topographic development over earlier models in terms of the location and build-up of valleys and mountain ranges that form in response to the strike-slip faulting activity. Intramontane basin formation is predicted and the metamorphic dome of the Tauern Window evolves dynamically in the simulations, related to well-known east-west–striking strike-slip faults in the region. It is interesting that the metamorphic dome formation is predicted by the model without explicit consideration of the low-angle detachments bounding the dome in the west and east, suggesting that metamorphic domes can form in transpressional or strike-slip environments. The model underpredicts the mean elevation of the Eastern Alps by several hundreds of meters, which is interpreted in terms of an independent non-convergence-related event of the past 5 m.y. that has been inferred previously from other field data. Time-series analysis of elevations reveals a clear correlation between maximum height and the amount of strike-slip activity and a nonequilibrium state between uplift and erosion. We interpret this in terms of future topographical growth of the Eastern Alps. LITHOSPHERE; v. 9; no. 3; p. 384–398; GSA Data Repository Item 2017083 | Published online 24 January 2017 doi:10.1130/L594.1 INTRODUCTION Royden et al., 1983). The Miocene lateral extru- the lateral extrusion is computed by plan-view sion of the Eastern Alps involved both compres- geometrical back rectification. This information The development of the Alpine orogeny is sional lateral escape tectonics and gravitational is then migrated into a finite element model and an ongoing multistage tectonic process between collapse of unstable crustal blocks (Ratschbacher validated with current fault locations. The results the stable European plate and the northeastward et al., 1991a, 1991b), and is thought to have been of this model are interpreted in terms of their moving and rotating Adriatic plate (Froitzheim intimately related to the early topographic evo- predictions for the evolution of topography in et al., 2008; Handy et al., 2010). The topographic lution of the Eastern Alps (Frisch et al., 1998; the Eastern Alps. evolution of this orogeny started after the final Frost et al., 2009; Linzer et al., 2002; Robl et subduction of the Penninic Ocean in the Eocene al., 2008b; Sachsenhofer et al., 2003; Wölfler et GEOLOGICAL SETTING and is ongoing (Hergarten et al., 2010). In the al., 2011). However, details of the topographic Miocene, the eastern part of this orogeny was evolution since the Miocene and the interaction According to Nocquet and Calais (2003), associated with large horizontal kinematics nor- of topography development with the strike-slip the tectonic processes in the Alps during the mal to the convergence direction, mostly accom- faulting are not very well known. past 30 m.y. have been dominated by a stable modated by orogen-scale strike-slip faults. This In this paper we expand on an early simpli- European plate, while the Adriatic plate is mov- so called lateral extrusion of the Eastern Alps fied modeling study (Robl et al., 2008b) by using ing ~5 mm/yr in a north to northwest direction, (Ratschbacher et al., 1991a, 1991b) was predom- a refined numerical modeling approach to pre- performing a counterclockwise rotation-like inantly facilitated by the rollback of a subduction dict aspects of the geomorphic evolution of the movement. However, the kinematic condition zone east of the Alps, which also opened the Eastern Alps since the late Oligocene. In particu- for the Adriatic plate motion is not uniformly Pannonian Basin (Horvath and Cloetingh, 1996; lar we consider the influence of temporal varia- described in the literature. Decker et al. (1994) tions of strike-slip faulting activity on the devel- and Ratschbacher et al. (1991b) assumed a linear opment of topography. In order to obtain the northward movement of a rectangular indenter, Thorsten Bartosch http://orcid.org /0000 -0003 input variables for the model, a time history of while palinspastic reconstructions (Frisch et al., -1432 -7330 relevant Miocene strike-slip activity is compiled 2000, 1998) imply more complex kinematics, *Bartosch: [email protected]; Stüwe: [email protected]; Robl: joerg.robl@ from literature sources and a geometrical recon- including translation and clockwise rotation to sbg.ac.at struction of fault geometry prior to the onset of the east of Bolzano (Fig. 1). Linzer et al. (2002) 384 © 2017 Geological Society of Americawww.gsapubs.org | For permission | toVolume copy, contact9 | Number [email protected] 3 | LITHOSPHERE Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/9/3/384/999065/384.pdf by guest on 24 September 2021 Strike-slip faulting influence on the topographic evolution of the Eastern Alps | RESEARCH 10° 11° 12° 13° 14° 15° 16° 17° A European Foreland Vienna 48° 48° Salzburg SEMP2 MM2 IN SEMP1 Innsbruck MM1 Graz 47° DAV PL 47° Austroalpine MV Klagenfurt PA Bolzano Pannonian Basin 46° 46° Southalpine 50 km B Basin abbr. − FO FohnsdorfGÖGöriach GR Gröbming HF Hieflau Vienna KL KlagenfurtOBObdach PS Parschlug TM Tamsweg VB 48° VB Vienna WA Wagrain ssee−Lammertal 48° Salzburg Traunsee WB Wolfsberg König SEMP2 Northern Calcareous Alps GÖ MM2 IN GR HF WA PS SEMP1 FO Innsbruck MM1 Ahorn Katschberg Styrian block Brenner det. Gleinalm det. Tauern Window TM Graz OB 47° Jaufen 47° PL K Passeier DAV MV oralm Pusterta ZW WB KL PA Mauls l Engadine e Bolzano Peio Tonale Giudicari 46° 46° Major fault abbr. DAV Defreggen−Antholz−Vals IN Inntal MM1 Upper Mur valley MV Möll valley MM2 Mürz valley PA Periadriatic line SEMP1Salzach valley PL Pöls−Lavanttal SEMP2Ennstal−Mariazell 10° 11° 12° 13° 14° 15° 16° 17° Figure 1. The simulation area of the Eastern Alps. The southwest vertex of both maps constitutes the Euler pole of the Adriatic plate. (A) Topographic map of the Eastern Alps showing the seven major fault zones considered in this study (yellow lines) and the assumed boundaries of rheology contrast (green lines). (B) Map of the same region showing the location of the Tauern Window (TW), the Northern Calcareous Alps (NCA), the most important intramontane basins, and most regional names used in the text. LITHOSPHERE | Volume 9 | Number 3 | www.gsapubs.org 385 Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/9/3/384/999065/384.pdf by guest on 24 September 2021 BARTOSCH ET AL. estimated a linear north-northeast translational Tauern Window between 17 and 5 m.y. Their data Eastern Alps from the somewhat stronger South- displacement of the Adriatic plate with almost are consistent with increased sedimentation in alpine unit over a length of ~700 km (Robl and no rotation. For the present-day, Nocquet and the Molasse basins starting ca. 18 m.y., as docu- Stüwe, 2005b). In the target region, it consists Calais (2003) estimated an exclusively coun- mented by Kuhlemann et al. (2002). of several faults (locally named the Tonale, Giu- terclockwise rotation of the Adriatic plate at a Evidence has emerged that a renewed surface dicarie, Mauls, and Pustertal). Based on fault rate of φ˙ = 0.52°/m.y. with the Euler pole being uplift event, uplifting the Eastern Alps by at least gouge and pseudotachylite dating, Müller et al. located close to Milan, Italy. 500 m, commenced ca. 7–4 m.y. (Legrain et al., (2001) revealed variable activity for individual The geomorphological evolution of the Alps 2014; Wagner et al., 2010, 2011). This event is parts of the fault. Two time frames, from 32 to 29 that accompanies this kinematic frame is the sub- now well documented at the eastern edge of the m.y. for the North Giudicarie (thrusting), Tonale, ject of much debate, but the generally accepted Alps where glacial carving during the past 2 m.y. and Pustertal, and 22 to 16 m.y. for the Tonale, onset of topography development is the begin- was absent, but it appears to have also affected Pustertal, Jaufen, and Passeier faults are most ning of subsidence in the Alpine foreland basins both the northern and southern Molasse (Genser striking (Table 1). Zwingmann and Mancktelow (Linzer et al., 2002). This started ~30 m.y. ago et al., 2007) and may therefore be much wider (2004) dated illites in mylonites in the Mauls and was largely synchronous with the final sub- spread than is currently documented. The event fault as 16 m.y. and also considered the nature of duction of the Penninic Ocean, the head-on col- appears to be of large wavelength and unrelated individual fault segments of the PA to be nonco- lision of the Adriatic and European continental to fault activity. While it has been argued that the eval. Additional minor times of activity that are plates, and the formation of a new plate boundary young uplift of the Alps may correlate with ero- shown in Figure 2 are listed in Table 1 for the PA between the two, the Periadriatic line (Fig.