Role of topography in isotherm perturbation: Apatite (U‐Th)/He and fission track results from the Malta tunnel, Tauern Window, Austria

Abstract

[1] Apatite (U-Th)/He and fission track age determinations of samples from a 20-km-long, nearhorizontal tunnel in the Hochalm-Ankogel Dome (eastern Tauern Window, Austria) are presented in order to determine the role of (paleo)-topography in perturbing isotherms in the shallow crust. Apatite fission track ages show no systematic correlation with distance along the tunnel or elevation. Two age components in the fission track data indicate cooling through $120°C at approximately 20 Ma and $80°C at approximately 6 Ma. Surface and tunnel (UTh)/He ages (17-9 Ma and 13-5 Ma, respectively) are consistently younger than the equivalent fission track ages. (U-Th)/He ages vary systematically along the tunnel with older ages at the northern and southern tunnel portals and younger ages in the central section. Geological factors (faulting, lithology) appear to have had little effect on this age distribution. The (U-Th)/He age pattern is inconsistent with rock cooling underneath the present-day Hochalm-Ankogel Dome topography. The age minimum is interpreted to coincide with a paleotopographic maximum in the Hochalm-Ankogel Dome and suggests that the 40-60°C isotherms were warped sufficiently to affect apatite (U-Th)/He ages. The tunnel apatite (U-Th)/He ages match synthetic He ages derived from a twodimensional numerical model of landscape evolution. Integrating the thermal model results with the data allows the relief development to be constrained and we calculate that the present-day Hochalm-Ankogel Dome topography was formed at 7 to 10 Ma.

Thermochronological constraints on the long-term erosional history of the Karkonosze Mts., Central Europe

“…Apatite and zircon fission track data can provide temporal constraints in rapidly eroded orogens as well as in intraplate settings with lower erosion rates. Recently, fission track method has been complemented by the revived (U-Th-[Sm])/He dating method, further enhancing the potential of thermochronology in geomorphological studies (e.g., Belton et al, 2004;Foeken et al, 2007;Gunnell et al, 2009).…”

Tracing metamorphism, exhumation and topographic evolution in orogenic belts by multiple thermochronology: a case study from the Nízke Tatry Mts., Western Carpathians

“…Despite demonstrated feasibility by several studies (e.g. House et al 1998House et al , 2001Foeken et al 2007), in our case this approach failed for two reasons: Firstly, the key requirement of this approach is that AHe ages are cooling ages, which allow straightforward calculation of erosion. Here, however, as proven by modelling results, AHe ages are not cooling ages related to a distinct cooling event, but are apparent ages resulting from a complex thermal history with a phase of reheating.…”

Orogen-parallel extension and topographic gradients east of the Tauern window: a possible indication of intra-orogenic raft tectonics?

“…2 ± 1.9 Ma), could be explained by a horizontal thermal gradient and/or the activation of adjacent normal faults and thrust faults. The AHe-ages are generally younger than the AFT ages; ages younger than 15 Ma indicate a slower cooling rate, which followed rapid cooling at ~ 20 Ma (Foeken et al, 2007). Vertical age-profiles suggest time-integrated denudation rates of 160 -240 m/Ma (Staufenberg, 1987); 2 to 3 km seems to be a plausible amount of erosion.…”

“…Published thermochronological data form the basis of this study (Stauffenberg, 1987;Hejl, 1997Hejl, , 1998Reinecker, 2000;Frisch et al, 2001;Foeken, 2007;Wölfler et al, 2008Wölfler et al, , 2011Wölfler et al, , 2012. In recent decades, a variety of thermochronological methods with increasing complexity was used to infer exhumation rates in the context of topographic gradients.…”

“…We plotted all published AFT, AHe and ZHe data from the Penninic basement of the Tauern window (Staufenberg 1987;Foeken et al 2007;Wölfler et al 2011Wölfler et al , 2012. The data refers to the Sonnblick Dome (SD) south of the Möll Valley fault and the Hochalm Dome (HD) north thereof (Fig.…”