Late Miocene Increasing Exhumation Rates in the Eastern Part of the Alps – Implications from Low Temperature Thermochronology

Home , Gurktal Alps

doi: 10.1111/ter.12221 Late Miocene increasing exhumation rates in the eastern part of the Alps – implications from low temperature thermochronology

Andreas W€olfler,1 Walter Kurz,2 Harald Fritz,2 Christoph Glotzbach1 and Martin Danisık3 1Institut fur€ Geologie, Leibniz Universitat€ Hannover, Callinstraße 30, Hannover D-30167, Germany; 2Institut fur€ Erdwissenschaften, Karl-Franzens Universitat€ Graz, Graz A-8010, Austria; 3John de Laeter Centre for Isotope Research, Department of Applied Geology, The Institute for Geoscience Research (TIGeR), Curtin University, GPO Box U1987, Perth, WA 6845, Australia

ABSTRACT A new set of apatite fission-track and apatite (U–Th)/He data operated simultaneously during lateral extrusion of the East- reveals a hitherto undated late Miocene exhumation pulse in ern Alps. As the higher late Miocene/Pliocene exhumation the eastern part of the Eastern Alps. While distinct parts of rates are restricted to a single tectonic block, namely the Nie- the study area, including the Seckauer Tauern, have been at dere Tauern, we infer a tectonic trigger that is probably near surface conditions (<100 °C) since the Eocene, the neigh- related to a change in the external stress field that affected bouring Niedere Tauern experienced enhanced cooling and the Alps during this time. exhumation in the middle Miocene and again at the late Mio- cene/Pliocene boundary. Middle Miocene exhumation is inter- Terra Nova, 00: 1–9, 2016 preted as a result of tectonic escape and convergence that

thermochronological point of view, and perturbation of isotherms, which Introduction this part of the Alps is less well may result in false conclusions about The existing low-temperature ther- investigated than other areas such as exhumation rates in the upper crust mochronological datasets from the the Tauern Window or the Western (Stuwe€ et al., 1994; Braun, 2002). To European Alps have been success- Alps (e.g. Foeken et al., 2007; Luth estimate the influence of topography fully used to derive an orogen-wide and Willingshofer, 2008; Vernon on perturbation of isotherms and erosional history, which indicates an et al., 2008). In particular, AHe data, thermochronological data, we correct increase in erosion rates during the which have the lowest closure tem- the derived exhumation rates follow- late Miocene and Pliocene (Vernon perature (~60 °C) among all ther- ing the recently proposed approach of et al., 2008; Herman et al., 2013). mochronometers, are rare, and thus Glotzbach et al. (2015). In addition, Although the findings from ther- the late stages of final exhumation we use conventional thermal-history mochronological data agree with from shallow crustal depths with modelling to constrain the near sur- those from studies based on indepen- temperatures <100 °C are not well face cooling history of the study area. dent approaches such as sediment- constrained. Accordingly, this region budget analysis or cosmogenic may bear an undiscovered thermal Geological setting nuclides (Kuhlemann et al., 2002; signal that can provide valuable Wittmann et al., 2007; Wagner et al., information about the late Neogene The European Alps (Figs 1a,b) are 2010; Legrain et al., 2014a,b), the exhumation history of the Eastern the result of the convergence between discussion about possible drivers (cli- Alps. the European and Adriatic plates. In mate change vs. tectonics) of the Low-temperature thermochronol- the course of their collision during late-stage uplift is ongoing (Ceder- ogy has been proven to be a powerful the Palaeogene, the Penninic domain bom et al., 2004, 2011; Willett, 2010; tool to infer the exhumation history was overridden by the Austroalpine Herman et al., 2013; Baran et al., of rocks in qualitative as well as quan- nappes, formerly part of the Adriatic 2014). titative ways (Reiners and Ehlers, plate (Schmid et al., 2004). Subse- To contribute to this debate, we 2005). However, thermochronology quent crustal-scale folding, orogen- provide new apatite fission-track has distinct limitations for estimating parallel extension and lateral extru- (AFT) and apatite (U–Th)/He (AHe) exhumation rates. In particular, the sion led to the formation of the data to infer exhumation rates from palaeo-geothermal gradient is usually Tauern Window (Fig. 1b; Ratschba- the eastern part of the Eastern poorly constrained so that the depth cher et al., 1991; Frisch et al., 1998; Alps (Figs 1 and 2). From the of the closure temperature can be Rosenberg et al., 2007). Although specified only vaguely. Therefore, we the timing of rapid cooling and collected samples from different ele- footwall exhumation in the Tauern € Correspondence: Andreas Wolfler, Institut vations to calculate exhumation rates Window is well constrained for the for Geology, Leibniz University of from the slope of the age–elevation early and middle Miocene (Fugen-€ Hannover, Callinstraße 30, Hannover relationship (AER). However, such schuh et al., 1997; Luth and Willing- D-30167, Germany. Tel.: +0049 511 762 interpretations are often hampered by shofer, 2008; Scharf et al., 2013; 3871; fax: +0049 511 762 2172; e-mail: inhomogeneities in the thermal field Favaro et al., 2015), the relative woelfl[email protected]

17° 16° 15° (a)

17° 5° 7° 9° 11° 13° 15° Neogene and Quarternyry sediments Donau WienWien München 48° 48° Nappes derived from the Tethys Wien Zürich Adria derived units Maribor 48° 46° 46° Penninic nappes Milano Europe derived units 17° 11° 13° 15° 44°

(b) SEMP

Tauern Window Graz 47° 47° BF KF DAV Pannonian MV Fig. 2 basin PF MariborDrava

46° 17° 16° Adamello 15° 46° 14° 10° 11° 12° 13° Neogene sedimentary and magmatic rocks Upper Austroalpine nappe system: Penninic nappe system: European derived units

Upper Cretaceous to Paleogen sediments Drauzug-Gurktal and Ötztal- Piemontais Helvetic and of the Gosau Group Bundschuh nappe system Ultrahelvetic nappes Units derived from the Meliata-Vardar domain Koralpe-Wölz nappe system Brianconnais undeformed European continent Adriatic plate Silvretta-Seckau nappe system Valais

Dinarides Subpenninic nappes

Southalpine unit Lower Austroalpine subunit

Fig. 1 (a) Simplified tectonic map of the Alps. (b) Tectonic map of the Eastern Alps following the nomenclature of Schmid et al. (2004) (modified after Froitzheim et al., 2008). BF, Brenner normal fault; KF, Katschberg normal fault; DAV, Defer- eggen–Antholz–Vals fault; SEMP, Salzach–Ennstal–Mariazell–Puchberg fault; PF, Pustertal fault as part of the Periadriatic fault system; MV, Moll€ valley fault. contributions of orogen-parallel are sparse; the existing data indicate kilometers during the whole Ceno- extension by normal faulting, strike- segmentation of the Austroalpine zoic. The Niedere and Seckauer slip faulting and compression are still upper crust into tectonic blocks with Tauern are bordered by the Salzach- a matter of discussion (Lammerer, different cooling histories (Frisch tal–Mariazell–Puchberg fault 1988; Fugenschuh€ et al., 1997, 2012; et al., 1998; Fig. 2). The Niedere (SEMP), the Paltental-Liesingtal Kuhlemann et al., 2001; Linzer et al., Tauern revealed middle Miocene fault (PLF), the Pols-Lavanttal€ fault 2002; Rosenberg and Garcia, 2011). AFT ages (Hejl, 1997; Reinecker, (PoLF),€ the Mur-Murz€ fault (MMZ) Our study area is situated within 2000) documenting cooling that is and the Niedere Tauern South fault the Austroalpine nappe complex to contemporaneous with the cooling of system (NTSFS; Fig. 2). the east of the Tauern Window Penninic units of the eastern Tauern The Niedere Tauern and the (Fig. 1b), in the so-called Niedere Window (Reinecker, 2000; Wolfler€ Northern Calcareous Alps are char- and Seckauer Tauern (Fig. 2). It et al., 2011). The Austroalpine units acterised by high relief with steep comprises polymetamorphic rocks to the south and east of the Niedere slopes and an average elevation of that experienced the most recent Tauern show Cretaceous zircon fis- 1.67 km; on the other hand, the metamorphism during the late Creta- sion track ages (Kurz et al., 2011), Seckauer Tauern and the Sau and ceous (Schmid et al., 2004) and sub- Eocene to Oligocene AFT ages (Hejl, Koralpe are characterised by lower sequent cooling, as indicated by 1997; Reinecker, 2000; Wolfler€ et al., relief and a distinctly smoother muscovite K–Ar ages of 95–70 Ma 2010) and Oligocene to early Mio- topography with an average eleva- (Frank et al., 1987). Low-tempera- cene AHe ages (Legrain et al., tion between 1.44 and 1.12 km ture thermochronological data from 2014a), showing that this region (Figs 1 and 2; Frisch et al., 2000a). the eastern part of the Eastern Alps resided at a depth of only a few In the late Oligocene and early

PLF Northern Calcaraous Alps

SEMP Niedere Tauern Seckauer Tauern Ju9: 48.5±7.4 16.0±1.6 19.4±1.5 43.7±2.5 38.6±1.4 14.4±1.1 15.4±1.3 Ju10: 46.3±4.0 17.8±2.6 Ju7: 44.4±6.4 So9: 16.9±2.6 19.6±1.6 PöLF Ju8: 42.4±4.2 6.6±0.5 22.9±4.0 23.8±3.5 23.8±3.5 So7: 15.9±2.3 B Ju11: 40.9±5.9 6.3±0.3 So11: 15.9±2.5 38.9±5.2 15.3±2.0 A So13: 15.0±2.6 So8: 15.2±2.1 47.1±4.3 So14: 14.3±2.5 FoB 6.1±0.3 15.6±1.8 So15: 13.9±2.4 8.6±2.3 So6: 14.1±2.1 NTSFSTB So5: 14.1±1.0 Koralpe 5.7±0.9

Tauern Window MMZ

30.9±4.0 GöF Saualpe 32.3±3.3 32.9±2.7 17.3±1.2 Gurktal Alps 23.0±4.2 35.1±3.1 29.0±2.4 KF Ju11: 40.9±2.3 AFT this study 43.9±9.5 AHe this study

12.9±1.4 43.7±2.5 AFT Hejl (1997)

22.9±4.0 AFT Reinecker (2000)

MV 8.6±2.3 AFT Bertrand (2013) 03.5 7 14 21 28

N Kilometers

Fig. 2 Digital elevation model of the study area with new and previously published AFT and AHe data. The Niedere and Seck- auer Tauern are bordered by the sinistral Salzachtal–Ennstal–Mariazell–Puchberg fault (SEMP) and the Paltental-Liesingtal fault (PLF) to the north and the sinistral Mur-Murz€ fault (MMZ) and the Niedere Tauern South fault system (NTSFS) to the south. The dextral Pols-Lavanttal€ fault (PoLF)€ separates the Niedere and the Seckauer Tauern. These fault zones were active during Middle Miocene lateral extrusion (Ratschbacher et al., 1991). We note that the complex geometry and the possible tem- poral and structural interplay between the NTSF and the MMZ are still not fully understood and require further investigations (e.g. Reinecker, 2000; Wolfler€ et al., 2011). Go,€ Gortschitz€ fault; MMZ, Mur-Murz€ fault; MV, Moll€ valley fault; TB, Tamsweg basin; FoB, Fohnsdorf basin. AFT and AHe data from the eastern Tauern Window range from 25 to 3 Ma and from 15 to 8 Ma respectively (Foeken et al., 2007; Staufenberg, 1987; Wolfler€ et al., 2008, 2012; Bertrand, 2013).

Miocene, the study area was charac- enhanced block movement in the et al., 1998). The modern topogra- terised by lowlands and hilly areas course of lateral extrusion led to the phy of the eastern Tauern Window with a northward-directed drainage formation of intramontane basins and adjacent eastern Austroalpine system (Frisch et al., 1998). At the (Fig. 2) and differential exhumation units formed in the late Miocene, early/middle Miocene boundary, and uplift of crustal blocks (Frisch contemporaneous with a switch from

© 2016 John Wiley & Sons Ltd 3 Early to Late Miocene exhumation rates in the Eastern Alps • A. W€olfler et al. Terra Nova, Vol 0, No. 0, 1–9 ...... aN–S- to an E–W-directed parameters can be varied to test, for are given in the supporting informa- drainage system (Frisch et al., 1998; instance, possible variations in the tion. Foeken et al., 2007; Robl et al., palaeo-topography by applying a ‘to- 2008, 2015). pographic ampliﬁcation factor’. This Results and discussion factor linearly scales the present topography: a factor of 0.5 reduces Samples and methods Data and modelling results relief by 50% and a factor of 1.5 For AFT and AHe analysis, we col- increases relief by 50% (Glotzbach The samples from the Seckauer and lected six orthogneisses and eight et al., 2015). Niedere Tauern display Eocene and micaschists, which were treated using For thermal-history modelling, we middle to late Miocene AFT and standard magnetic and heavy liquid used the HeFTy software (Ketcham, AHe ages respectively (Fig. 2). The separation techniques. Details of 2005) with the annealing algorithm apparent exhumation rate deduced AFT and AHe analytical methods of Ketcham et al. (1999). More from the AER is 0.14 mm/yr for the are given in the supporting informa- details on the modelling approaches Seckauer Tauern (Fig. 3a), indicating tion. The slopes of the AER were corrected for the effect of isotherm 3000 perturbation caused by topography. (a) Seckauer T auern The age perturbations at sample 2500 localities were estimated by taking into account the dominant wave- AFT: 0.14 mm year–1 2000 lengths and amplitudes of the topog- R 2 = 0.98 raphy using a Fast Fourier 1500 Transform (FFT) algorithm (Glotz- Elevation (m) bach et al., 2015). The age perturba- 1000 tion was calculated assuming a steady-state topography, but also for 500 Cret. Palaeogene possible palaeo-topographies with Maas. Palaeocene Eocene Olig. higher or lower relief. In general, a higher relief results in a lower AER- 70 60 50 40 30 derived exhumation rate and vice Age (Ma) versa. The steps involved in the (b) Niedere Tauern: Profile A 3000 quantiﬁcation of the age peraturba- tion are (Glotzbach et al., 2015): AFT: AHe: 2500 0.54 mm year–1 1.0 mm year–1 1 Decomposing topography (digital R 2 = 0.89 R 2 = 0.98 2000 elevation model (DEM) with 1 km

resolution) using a FFT algorithm 1500

along N–S, E–W, NW–SE and Elevation (m) – NE SW proﬁles. 1000 2 For each combination of wavelength, amplitude, exhumation rate Early M. Middle M. Late Miocene Pli. P. and geothermal gradient, the age 20 15 10 5 0 perturbation was previously esti- Age (Ma) mated with PECUBE (Braun et al., 2012). (c) Niedere Tauern: Profile B 3000 3 The age perturbation along each AFT: 2500 decomposed proﬁle and Fourier 0.52 mm year–1 series is calculated based on the R 2 = 0.97 2000 PECUBE-derived age perturbation dataset. 1500

4 Combining the age perturbations Elevation (m) of all Fourier series along all pro- 1000 files yields an age perturbation map the same size as the input Early M. Middle M. Late Miocene Pli. P. DEM. 20 15 10 5 0 Age (Ma) The resulting age perturbation map can be used to estimate the site- Fig. 3 Age–elevation relationships of the data, and apparent exhumation rates specific potential perturbation of derived from them. Exhumation rates (in mm/yr) are calculated as error-weighted thermochronological ages caused by linear best fit (solid red lines) with 95% confidence level (dashed lines). Black topography and to correct ages, squares are AFT data; white circles are AHe data. Cret., Cretaceous; Maas., Maas- age–elevation profiles and the result- trichtian; Olig., Oligocene; Early M, Middle M., Early and Middle Miocene; ing exhumation rates. Input model Pli., Pliocene; P., Pleistocene.

4 © 2016 John Wiley & Sons Ltd Terra Nova, Vol 0, No. 0, 1–9 A. W€olfler et al. • Early to Late Miocene exhumation rates in the Eastern Alps ...... that the samples cooled slowly with contradiction probably arises from slowly through the APAZ and little exhumation and the ages have limitations caused by the unknown HePRZ and were at near surface probably not been affected by the geothermal gradient and/or the conditions by Eocene to Oligocene development of topography. Slow chemical composition. Although times (Table 2). cooling rates can also be inferred Dpar values are between 1.57 and The middle Miocene AFT ages of from the relatively small track length 1.58 lm, typical of a fluorine-apatite the Niedere Tauern yield apparent distribution and thermal-history composition, little is known about exhumation rates of 0.54 and modelling (Fig. 4c, Table 1). It the role of ions such as OH, Mn, Sr 0.52 mm a1 (Fig. 3b,c). In contrast, should be noted that sample Ju11 or the REE content (Barbarand the AHe data yield an apparent yields AFT and AHe ages that over- et al., 2003; Spiegel et al., 2007). In exhumation rate of 1 mm a1, thus lap within their error range, which summary, we suggest that the Seck- indicating increasing exhumation usually implies fast exhumation. This auer Tauern had already cooled rates from the middle to the late Miocene. Regardless of the topographical amplification factor, the (a) AFT (b) AHe corrected exhumation rates of the AFT data are slightly higher than ~0.5 mm a1 (Fig. 4a) and thus equal to those calculated from the AER. The AHe data from the same profile show a relationship between topographical amplification and exhumation rate (Fig. 4b), indicating that the exhumation rate calculated from the AER is an overestimate. Assuming a topographical steady state (amplification factor = 1), the corrected exhumation is ~0.8 mm a1 (star in Fig. 4b). We suggest that the lower temperature Modelled AFT age (Ma) Modelled AHe age (Ma) Exhumation rate (km/Ma) Exhumation rate (km/Ma) isotherms were warped sufficiently to affect the AHe ages but not the AFT data, which may be attributed to the topography. Stuwe€ et al. (1994) suggested a significant influ- Topographic amplification factor Topographic amplification factor ence on the 110 °C isotherm of a wavelength of ~20 km, a relief of (c) Seckauer tauern (d) Niedere tauern ~3 km and denudation rates of ~ 1 0 1kmMa . However, these condi- sample Ju9 sample So6 tions are clearly not met in the Nie-

50 HePRZ HePRZ dere Tauern, which are characterised

APAZ APAZ by a topographical wavelength of 100 ~3–6 km and a relief that hardly 150 exceeds 2 km. Independent of the chosen palaeo-topography (ampli- 200 ﬁcation factor), corrected exhuma- 50 40 30 20 10 0 25 20 15 10 5 0 tion rates from the AHe system Time (Ma) Time (Ma) exceed those from the AFT system (Fig. 4a,b). This observation implies Fig. 4 Topographical correction of (a) AFT and (b) AHe data from Profile A that there might have been an epi- ° 1 (Figs 2 and 3b) assuming an initial crustal geothermal gradient of 20 Ckm (for sode of faster cooling at the late details see Glotzbach et al., 2015). We have modelled, for a large variety of param- Miocene/Pliocene boundary, which eter combinations (exhumation rates and topographical amplification factors), ther- can also be seen with conventional mochronological ages and resulting apparent exhumation rates from the AER. The modelled and observed AER have been compared to find the best fitting parameter thermal-history modelling (Fig. 4d). combination, which is marked as a thick red line. The thin red lines are the 95% confidence intervals. The thin black lines are modelled AFT and AHe ages assum- Implications for the study area ing continuous exhumation. The small stars are the modelled parameter combinations (exhumation rate and topographical amplification factor). (c,d) Thermal- During the early and middle Mio- history inverse models for (c) the Seckauer and (d) the Niedere Tauern using the cene, the Eastern Alps were affected HeFTy programme (Ketcham, 2005). Input parameters: central AFT age with 1r by large-scale extension that resulted error, corrected AHe ages, track length distributions and Dpar values as kinematic in block segmentation and extrusion parameter. Light grey paths: acceptable fit; dark grey paths: good fit; black line: towards the Pannonian basin in best fit. the east (Frisch et al., 2000b). This

m) process was accompanied by fast : l

D cooling and exhumation of footwall q units exposed in the Tauern Win- dow (Frisch et al., 2000b). However,

(L) Dpar ( our results document that exhuma- N tion can also be observed in distinct parts of the hangingwall. m) l While the Niedere Tauern experienced exhumation at a rate of

and longitude coordinates 1 degrees of freedom (where ~0.5 mm a , the Seckauer Tauern n m) SD (

l and other areas such as the Gurktal Alps and the Koralpe (Fig. 2) did ) for 2 not experience substantial exhuma- v tion and surface uplift (Frisch et al.,

(Ma) MTL ( 2001). We attribute this to the r

1 inﬂuence of the north-directed com-

pression caused by the Adriatic plate; thus, tectonic escape occurred in a compressional regime (Robl and Stuwe,€ 2005). The observed ): number of counted spontaneous (induced) tracks; i cooling and exhumation of the Nie- N ( (L): number of horizontal confined tracks; Dpar: average dere Tauern was accommodated by s N ) (%) Age (Ma) N

2 faulting along the NTSF (Reinecker, v (

P 2000), the SEMP (Keil and Neu- bauer, 2009, 2011) and the PoLF€ to

d the east (Fig. 2). N The AHe data from the Niedere Tauern reveal a hitherto undated

D exhumation pulse, which is probably q ): probability of obtaining chi-squared value ( 2

v responsible for the formation of the ( i P modern topography. Indeed, if we N consider an exhumation rate of ~0.8 mm a1, the palaeo-topography i

q of the Niedere Tauern was of the same magnitude as it is today s

N (Fig. 4b). Late Miocene surface uplift is evi- ): spontaneous (induced) track densities; I

q dent in other parts of the Eastern ( s q S Alps, such as the Northern Calcare- q ous Alps (Frisch et al., 2001), the N eastern Tauern Window (Baran et al., 2014), the eastern margin of the eastern Alps and parts of the Pannonian basin (Fig. 1; Bada et al., 2001; Wagner et al., 2010; : number of tracks counted on dosimeter;

d Legrain et al., 2014a,b) and the N northern Molasse Basin (Genser ); 2 et al., 2007). In addition, enhanced

: number of dated crystals; fault activities since the later Mio-

N cene, as documented for the eastern Periadriatic fault system (Polinski track cm

5 and Eisbacher, 1992; Nemes et al., 10 1997), the Moll€ valley fault (MV; 9 Fig. 2) (Wolﬂer€ et al., 2012), the PoLF€ (Wolﬂer€ et al., 2010; Reis- chenbacher and Sachsenhofer, 2013) the MMZ and the SEMP (Rei- necker and Lenhardt, 1999; Decker

Apatite fission track data. et al., 2005; Hausmann et al., 2010; Plan et al., 2010), show that the eastern part of the Eastern Alps is is number of crystals minus 1); MTL: mean track length; SD: standard deviation of track length distribution; dosimeter track density ( n etch pit diameter ofare fission given tracks; in ages the were WGS calculated 84 using datum. the zeta calibration method (Hurford and Green, 1983); glass dosimeter CN 5; latitude Table 1 Sample code Lithology Elevation (m) Latitude Longitude Ju7Ju8Ju9Ju10Ju11 GraniteSo5 GraniteSo6 1680 Micaschist GraniteSo7 1362 2301 GraniteSo8 1912So9 Micaschist 1287 47.330418So11 Micaschist 1540 47.325427 14.518054 47.342347So13 Micaschist 1228 14.514228 14.541166 22So14 Granite 2283 47.335502 21 7.8729So15 Granite 22 47.324057 14.520842 Micaschist 47.195901 1920 8.2975 137 8.4125 14.515253 22 Micaschist 2350 47.188714 14.069738 2450 129 128 4.367 22 8.4125 Micaschist 2091 47.222788 14.070178 20 4.824 4.272 8.4125 128 76 Micaschist 1650 14.064759 20 5.9819 129 19.379 75 1369 47.209907 65 4.469 20 4.8652 86 47.244726 19.386 4424 47.234757 14.070576 19.371 5.061 5.6881 68 69 10.016 47.233173 14.149451 4424 87 14.049588 4424 20tectonically 19.363 77 79 144 47.219989 14.148289 20 74 8.532 90 20 6.1354 19.355 4424 19.394 47.213407 14.150686 20 4.6975 8.856 121 4.7480 87 4424 86 4424 14.157098 20 3.5627 19.402 123 44.4 66 69 10.014 86 92 20 3.4858 19.410 4424 42.4 48.5 54 142 7.331 6.950 2.3950 4424 84 53 quite 19.418 5.872 103 46.3 6.4 101 91 51 4424 6.051 19.433 40.9 14.1 4.2 19.425 7.4 89 88 4.274active. 4424 4424 19.441 92 14.8 4.0 79 87 12.85 91 19.457 4424 15.9 5.9 2.1 19.449 4424 90 12.55 15.2 2.0 4424 93 0.73 12.99 15.9 2.3 89 16.9 1.09 12.62 15.0 2.1 80 0.67 13.76 14.3 2.5 2.6 50 1.11 13.9 1.57 2.6 74 1.59 0.77 13.66 2.5 23 2.4 1.59 65 1.59 0.78 13.72 1.58 1.60 13.75 55 0.91 1.61 1.56 1.01 67 1.56 1.60 50 1.57 1.58 1.58 1.64

What caused the late Miocene exhumation in the Eastern Alps? STDEV (Ma)

et al. In addition to a climatic driver (Cederbom et al., 2004; Herman et al., 2013), lithospheric processes

Average age (Ma) (Lippitsch et al., 2003; Genser et al.,

r 2007) and a change in the regional 1 stress ﬁeld (Horvath and Cloetingh, 1996) have been discussed as the main driver for an orogen-wide late Miocene/Pliocene acceleration of ero- Corr. Age (Ma) sion rates. From our data, given the

relatively small study area, we cannot rule out either a climatic-driven impact on the late Neogene erosional

Ft % history of the Alps or a change in the lithosperic structure. Since the Eastern Alps were affected by enhanced late Miocene fault activity, and higher exhumation rates are observed only in the Niedere Tauern, we favour a tectonic-induced trigger. This may be a consequence of the change in relative plate motion of the African plate with respect to Europe from NNW to NW (Caputo et al., 2010). However, we argue that tectonic forces caused by the rotation of the Adriatic plate probably acted simultaneously with lithospheric-scale

TAU (%) Th/U eU Unc. age (Ma) processes such as mantle delamina- tion (Kissling et al., 2006) or slab unloading (Baran et al., 2014). The overall observed surface uplift in the Eastern Alps (Genser et al., 2007) is probably not detectable by low-tem- He (mol) %

4 perature thermochronology, so that the revealed higher exhumation rates in the Niedere Tauern are solely due to tectonic forces. He; TAU: total analytical uncertainty; Unc. age: uncorrected age; Ft: alpha recoil correction factor after Farley Sm (ng) %

4 Acknowledgements 147 The thoughtful and constructive com- Sm; ments by three anonymous reviewers 147 greatly improved the manuscript. We also U; thank our editor Jean Braun for consider- 238 ate handling of the manuscript and help- U (ng) % ful comments. Th; 238 232 References Bada, G., Horvath, F., Cloetingh, S., Coblentz, D.C. and Toth, T., 2001.

Th (ng) % Role of topography-induced Th)/He data. – 232 gravitational stresses in basin inversion: the case study of the Pannonian basin. Tectonics, 20, 343–363. Baran, R., Friedrich, A.M. and 232 0.021 0.1492 4.23 0.065 4.1 0.2372 0.318 0.076 4.13 4.3 0.056 0.893 4.3 0.053 4.12 0.088 0.115 4.13 0.649 4.3 0.019 0.183 1.5 0.665 4.12 0.9 4.3 0.162 3.575 4.2 E-143 0.267 4.3 0.219 3.750 0.212 1.3 E-14 0.178 0.7 0.091 4.1 1.3 4.4 4.3 0.140 1.445 4.1 E-12 0.072 4.1 0.7 4.3 0.131 0.132 1.3 0.090 1.0 9.875 0.103 4.1 0.090 E-13 4.4 4.3 132.13 2.975 4.1 0.465 1.3 E-13 0.061 0.9 4.3 0.118 1.3 4.9 65.26 0.064 4.3 1.2 4.950 0.155 0.072 E-13 4.2 3.9 4.3 2.770 1.3 E-13 44.72 4.3 0.9 0.076 0.116 1.3 4.2 0.8 5.2 0.077 1.078 0.305 E-12 0.2 83.16 4.4 1.623 1.3 0.83 E-12 55.89 4.8 1.0 0.2 5 0.325 1.3 0.78 3.4 1.1 5.0 1.225 0.105 E-12 56.29 5 3.3 0.2 7.700 1.3 E-13 5.9 43.59 0.85 5.6 2.221 1.3 5 3.4 5.0 0.2 5.0 2.420 23.44 0.80 3.4 0.2 0.4 31.7 21.71 5 0.86 6.1 2.277 37.3 0.3 5 0.2 2.032 16.44 0.80 0.2 6.1 5.7 43.5 0.4 24.81 5 0.82 5.8 26.4 1.1 5 6.3 0.81 0.4 1.2 0.9 7.1 5 0.83 0.4 6.1 5 1.5 0.3 6.1 39.4 0.81 0.5 0.9 45.2 5 0.75 0.4 5 0.3 2.4 6.6 53.9 2.7 35.2 38.2 0.5 3.3 2.1 1.6 38.8 5.2

Apatite (U Schlunegger, F., 2014. The late Miocene to Holocene erosion pattern of the Alpine foreland basin reﬂects Eurasian slab unloading beneath the (1996). Elevation, coordinates and lithology can be found in Table 1. Single crystals marked in grey were not used for the age calculation. The erroneous old ages are probably due to micro-inclusions. Table 2 Sample code Crystal # SO5 1SO7SO8 1 0.039 1 4.1SO9 0.304 0.144 1 0.108 4.1JU9 4.3 0.142 0.020 4.1 1 0.098JU11 1.141 4.3 1.8 0.125 4.1 1 4.3 0.124 1.325 E-14 0.525 0.406 1.4 0.9 4.1 0.439 4.3 4.3 3.125 E-13 0.9 0.055 0.204 1.3 4.1 1.715 0.267 E-12 3.4 4.3 1.3 0.193 24.98 1.0 0.069 4.4 2.8 9.050 2.120 E-13 4.3 1.3 35.17 1.0 0.284 0.094 4.4 5.3 7.725 50.31 E-13 0.1 1.3 0.7 0.71 4.8 0.186 5 3.4 3.273 E-12 61.55 0.2 1.4 0.82 5.4 6.4 2.239 3.4 5 0.2 18.95 0.75 0.3 29.9 5 6.5 2.258 0.2 20.22 0.82 6.5 36.0 0.4 5 1.0 0.4 0.81 6.6 5 1.2 0.85 37.1 0.4 5 2.2 42.5 2.6

western Alps rather than global climate Frank, W., Kralik, S., Scharbert, S. and Hejl, E., 1997. „Cold spots” during the change. Lithosphere, 6(2), 124–131. Thoni,€ M., 1987. Geochronological Cenozoic evolution of the Eastern Alps: Barbarand, J., Carter, A., Wood, I. and data from the Eastern Alps. In: thermochronological interpretation of Hurford, T., 2003. Compositional and Geodynamics of the Eastern Alps (H.W. apatite fission track data. structural control of fission-track Flugel€ and P. Faupl, eds), pp. 272–281. Tectonophysics, 272, 159–173. annealing in apatite. Chem. Geol., 198, Deuticke, Vienna. Herman, F., Seward, D., Valla, P.G., 107–137. Frisch, W., Kuhleman, J., Dunkl, I. and Carter, A., Kohn, B., Willett, S.D. and Bertrand, A., 2013. Exhuming the core of Brugl,€ A., 1998. Palinspastic Ehlers, T.A., 2013. Worldwide collisional orogens, the Tauern Window reconstruction and topographic acceleration of mountain erosion under (Eastern-Alps). A geochronological, evolution of the Eastern Alps during a cooling climate. Nature, 504, 423–426. modeling and structural study. Unpubl. late Tertiary tectonic extrusion. Horvath, F. and Cloetingh, S., 1996. Doctoral dissertation, Freie Universitat€ Tectonophysics, 297,1–15. Stress-induced late-stage subsidence Berlin, 175 pp. Frisch, W., Szekely, B., Kuhlemann, J. anomalies in the Pannonian basin. Braun, J., 2002. Quantifying the effect of and Dunkl, I., 2000a. Tectonophysics, 266, 287–300. recent relief changes on age–elevation Geomorphological evolution of the Hurford, J. and Green, P.F., 1983. The relationships. Earth Planet. Sci. Lett., Eastern Alps in response to Miocene zeta age calibration of fission-track 200, 331–343. tectonics. Z. Geomorphol., 44, 103–138. dating. Chem. Geol., 41, 285–312. Braun, J., van der Beek, P., Valla, P., Frisch, W., Dunkl, I. and Kuhlemann, J., Keil, M. and Neubauer, F., 2009. Robert, X., Herman, F., Glotzbach, C., 2000b. Post-collisional orogen-parallel Initiation and development of a fault- Pedersen, V., Perry, C., Simon-Labric, large-scale extension in the eastern controlled, orogen-parallel T. and Prigent, C., 2012. Quantifying Alps. Tectonophysics, 327, 239–265. overdeepened valley: the Upper Enns rates of landscape evolution and Frisch, W., Kuhlemann, J., Dunkl, I. and Valley, Austria. Austrian J. Earth Sci., tectonic processes by thermochronology Szekely, B., 2001. The Dachstein 102,89–390. and numerical modeling of crustal heat paleosurface and the Augenstein Keil, M. and Neubauer, F., 2011. The transport using PECUBE. Formation in the Northern Calcareous Miocene Enns Valley Basin (Austria) Tectonophysics, 524–525,1–28. Alps – a mosaic stone in the and the North Enns Valley Fault. Caputo, R., Poli, M.E. and Zanferrari, geomorphological evolution of the Austrian J. Earth Sci., 104(1), 49–65. A., 2010. Neogene-Quaternary tectonic Eastern Alps. Int. J. Earth Sci., 90, Ketcham, R.A., 2005. Forward and stratigraphy of the eastern Southern 500–518. inverse modeling of low-temperature Alps, NE Italy. J. Struct. Geol., 32, Froitzheim, N., Plasienka, D. and thermochronometry data. In: Low- 1009–1027. Schuster, R., 2008. Alpine tectonics of Temperature Thermochronology: Cederbom, C.E., Sinclair, D.H., the Alps and Western Carpathians. In: Techniques, Interpretations, and Schlunegger, F. and Rahn, M.K., 2004. The geology of Central Europe (T. Applications (P. Reiners and T.A. Climate-induced rebound and McCann, ed.), Geol. Soc. London Spec. Ehlers, eds). Min. Soc. Am. Rev. Min. exhumation of the European Alps. Publ., 2, 1142–1232. Geochem., 58, 275–314. Geology, 32, 709–712. Fugenschuh,€ B., Seward, D. and Ketcham, R.A., Donelick, R.A. and Cederbom, C.E., van der Beek, P., Mancktelow, N., 1997. Exhumation in Carlson, W.D., 1999. Variability of Schlunegger, F., Sinclair, H.D. and a convergent orogen: the western apatite fission-track annealing kinetics Oncken, O., 2011. Rapid extensive Tauern Window. Terra Nova, 9, 213– III: extrapolation to geological time erosion of the North Alpine foreland 217. scales. Am. Mineral., 84, 1235–1255. basin at 5-4 Ma. Basin Res., 23, 528– Fugenschuh,€ B., Mancktelow, N.S. and Kissling, E., Schmid, S.M., Lippitsch, R., 550. Schmid, S.M., 2012. Comment on Ansorge, J. and Fugenschuh,€ B., 2006. Decker, K., Peresson, H. and Hinsch, R., Rosenberg and Garcia: estimationg Lithosphere structure and tectonic 2005. Active tectonics and Quaternary displacement along the Brenner Fault evolution of the Alpine arc: new basin formation along the Vienna Basin and orogen-parallel extension in the evidence from highresolution teleseismic Transform fault. Quatern. Sci. Rev., 24, Eastern Alps. International Journal of tomography. In: European lithosphere 307–322. Earth Sciences (Geologische dynamics (R.A. Stephenson and D.G. Farley, K.A., Wolf, R.A. and Silver, Rundschau) (2011), 100, 1129-1145. Int. Gee, eds). Mem. Geol. Soc. London, 32, L.T., 1996. The effects of long alpha- J. Earth Sci., 101, 1451–1455. Int. J. 129–145. stopping distances on (U-Th)/He ages. Earth Sci., 101, 1451–1455. Kuhlemann, J., Frisch, W., Dunkl, I. and Geochim. Cosmochim. Acta, 60, 4223– Genser, J., Cloetingh, S. and Neubauer, Szekely, B., 2001. Quantifying tectonic 4229. F., 2007. Late orogenic rebound and versus erosive denudation by the Favaro, S., Schuster, R., Handy, M.R., oblique Alpine convergence: new sediment budget: the Miocene core Scharf, A. and Pestal, G., 2015. constraints from subsidence analysis of complex of the Alps. Tectonophysics, Transition from orogen-perpendicular the Austrian Molasse Basin. Global 330,1–23. to orogen-parallel exhumation and Planet. Change, 58, 214–223. Kuhlemann, J., Frisch, W., Szekely, B., cooling during crustal indentation – Glotzbach, C., Braun, J. and van der Dunkl, I. and Kazmer, M., 2002. Post- Key constraints from 147Sm/144Nd and Beek, P., 2015. A Fourier approach for collisional sediment budget history of 87Rb/87Sr geochronology (Tauern estimating and correcting the the Alps: tectonic versus climatic Window, Alps). Tectonophysics, 665,1– topographic perturbation of low- control. Int. J. Earth Sci., 91, 818–837. 16. temperature thermochronological data. Kurz, W., Wolfler,€ A., Rabitsch, R. and Foeken, J.P.T., Persano, C., Stuart, F.M. Tectonophysics, 649, 115–129. Genser, J., 2011. Polyphase movement and ter Voorde, M., 2007. Role of Hausmann, H., Hoyer, S., Schurr, B., on the Lavanttal Fault Zone (Eastern topography in isotherm perturbation: Bruckl,€ E., Housman, G. and Stuart, Alps): reconciling the evidence from apatite (U-Th)/He and fission track G., 2010. New Seismic data improve different geochronological indicators. results from the Malta tunnel, Tauern earthquake location in the Vienna Swiss J. Geosci., 104(2), 323–343. Window, Austria. Tectonics, 26, Basin area, Austria. Austrian J. Earth Lammerer, B., 1988. Thrust-regime and TC3006. doi:10.1029/2006TC002049. Sci., 103(2), 2–14. transpression-regime tectonics in the

Tauern Window (Eastern Alps). Geol. post-collisional evolution of the Eastern the European Alps confirmed by isoage Rundsch., 77,43–56. Alps: the example of the Lavanttal analysis of a fission-track database. Legrain, N., Stuwe,€ K. and Wolfler,€ A., Basin. Int. J. Earth Sci., 102, 517–543. Earth Planet. Sci. Lett., 270, 316–329. 2014a. Incised relict landscapes in the Robl, J. and Stuwe,€ K., 2005. Continental Wagner, T., Fabel, D., Fiebig, M., eastern Alps. Geomorphology, 221, 124– collision within finite indenter strength: Hauselmann,€ P., Sahy, D., Xu, S. and 138. 2. European eastern Alps. Tectonics, 24, Stuwe,€ K., 2010. Young uplift in the Legrain, N., Dixon, J., Stuwe,€ K., TC4014. doi:10.1029/2004TC001741. non-glaciated parts of the eastern Alps. Blanckenburg, F. and Kubik, P., Robl, J., Hergarten, S. and Stuwe,€ K., Earth Planet. Sci. Lett., 295, 159–169. 2014b. Post-Miocene landscape 2008. Morphological analysis of the Willett, S.D., 2010. Late Neogene erosion rejuventation at the eastern end of the drainage system in the Eastern Alps. of the Alps: a climate driver? Annu. Alps. Lithosphere, 7(3), 3–13. Tectonophysics, 460, 263–277. Rev. Earth Planet. Sci., 38, 411–437. doi:10.1130/L391.1. Robl, J., Prasicek, G., Hergarten, S. and Wittmann, H., von Blankenburg, F., Linzer, H.-G., Decker, K., Peresson, H., Stuwe,€ K., 2015. Alpine topography in Kruesmann, T., Norton, K.P. and Dell0Mour, R. and Frisch, W., 2002. the light of tectonic uplift and Kubik, P.W., 2007. Relation between Balancing orogenic float of the Eastern glaciations. Global Planet. Change, 127, rock uplift and denudation from Alps. Tectonophysics, 354, 211–237. 34–49. cosmogenic nuclides in river sediment Lippitsch, R., Kissling, E. and Ansorge, Rosenberg, C.L. and Garcia, S., 2011. in the central Alps of Switzerland. J. J., 2003. Upper mantle structure Estimating displacement along the Geophys. Res., 112, F04010. beneath the Alpine orogeny from high- Brenner Fault and orogen-parallel Wolfler,€ A., Dekant, C., Danisık, M., resolution teleseismic tomography. J. extension in the Eastern Alps. Int. J. Kurz, W., Dunkl, I., Putis, M. and Geophys. Res., 108(8), 5–15. Earth Sci., 100, 1129–1145. Frisch, W., 2008. Late stage differential doi:10.1029/2002JB002016. Rosenberg, C.L., Brun, J.P., Cagnard, F. exhumation of crustal blocks in the Luth, S.W. and Willingshofer, E., 2008. and Gapais, D., 2007. Oblique central Eastern Alps: evidence from Mapping the post-collisional cooling indentation in the Eastern Alps: fission track and (U-Th)/He history of the eastern Alps. Swiss J. insights from laboratory experiments. thermochronology. Terra Nova, 20, Geosci., 101(1), 207–223. Tectonics, 26, TC2003. doi:10.1029/ 378–384. doi:10.1111/j.1365- Nemes, F., Neubauer, F., Cloetingh, S. 2006TC001960. 3121.2008.00831.x. and Genser, J., 1997. The Klagenfurt Scharf, A., Handy, M.R., Favaro, S., Wolfler,€ A., Kurz, W., Danisık, M. and Basin in the Eastern Alps: an intra- Schmid, S.M. and Bertrand, A., 2013. Rabitsch, R., 2010. Dating of fault orogenic decoupled flexural basin? Modes of orogenparallel stretching and zone activity by apatite fission track Tectonophysics, 282, 189–203. extensional exhumation in response to and apatite (U-Th)/He Plan, L., Grasemann, B., Spotl,€ C., microplate indentation and roll-back thermochronometry: a case study from Decker, R., Boch, R. and Kramers, J., subduction (Tauern Window, eastern the Lavanttal fault system (Eastern 2010. Neotectonic extrusion of the early Alps). Int. J. Earth Sci., 102, 1627– Alps). Terra Nova, 22, 274–282. Alps. Constraints from U/Th dating of 1654. Wolfler,€ A., Kurz, W., Fritz, H. and tectonically damaged speleothems. Schmid, S.M., Fugenschuh,€ B., Kissling, Stuwe,€ K., 2011. Lateral extrusion in Geology, 38, 483–486. B. and Schuster, R., 2004. Tectonic the Eastern Alps revisited: refining the Polinski, R.K. and Eisbacher, G.H., 1992. map of overall architecture of the model by thermochronological, Deformation partitioning during Alpine orogen. Eclogae Geol. Helv., 97, sedimentary and seismic data. polyphase oblique convergence in the 93–117. Tectonics, 30, TC4006. doi:10.1029/ Karawanken Mountains, Southeastern Spiegel, C., Kohn, B., Raza, A., Rainer, 2010TC002782. Alps. J. Struct. Geol., 14, 1203–1213. T. and Gleadow, A., 2007. The effect Wolfler,€ A., Stuwe,€ K., Danisık, M. and Ratschbacher, L., Frisch, W., Linzer, of long-term low-temperature exposure Evans, N., 2012. Low temperature H.G. and Merle, O., 1991. Lateral on apatite fission track stability: a thermochronology in the Eastern Alps: extrusion in the Eastern Alps, part 2: natural annealing experiment in the implications for structural and structural analysis. Tectonics, 10, 257– deep ocean. Geochim. Cosmochim. Acta, topographic evolution. Tectonophysics, 271. 71, 4512–4537. 541-543,1–18. doi:10.1016/ Reinecker, J., 2000. Stress and Staufenberg, H., 1987. Apatite fission- j.tecto.2012.03016. deformation. Miocene to present-day track evidence for postmetamorphic tectonics in the Eastern Alps. Tubinger€ uplift and cooling history of the eastern Received 11 November 2015; revised ver- Geowiss. Arb., 55, 78. Tauern Window and the surrounding sion accepted 30 May 2016 Reinecker, J. and Lenhardt, W.A., 1999. Austroalpine (Central Eastern Alps, Present-day stress field and deformation Austria). Jb. Geol. Bundesanst., 13, in eastern Austria. Int. J. Earth Sci., 571–586. Supporting Information € 88, 532–550. Stuwe, K., White, L.B. and Brown, R., Additional Supporting Information Reiners, P.W and Ehlers, T.A., 2005. 1994. The influence of eroding may be found in the online version Low-Temperature Thermochronology: topography on steady-state isotherms. of this article: Techniques, Interpretations, and Application to fission track analysis. Applications. Min. Soc. Am. Rev. Min. Earth Planet. Sci. Lett., 124,63–74. Data S1. Data repository. Geochem., 58, 620. Vernon, A.J., van der Beek, P.A., Reischenbacher, D. and Sachsenhofer, Sinclair, H.D. and Rahn, M.K., 2008. R.F., 2013. Basin formation during the Increase in late Neogene denudation of