| Detrital zircon fission-track analysis, a common tool for provenance and exhumation studies, has been tested on modern river sediments from over 16 rivers draining the European Alps toward their fore- and hinterland. The outcome of this study shows that detrital zircon fission-track results are reproducible, and that all major grain-age components in a drainage area can be detected, even in larger scale drainages like the Rhone river system. Erosional yield seems more important than the areal distribution of cooling ages, indicating that areas that erode faster have an higher input, with respect to zircon yield, given similar lithologies. One result of this study is that the distribution of fission-track grain-ages changes downstream in a river system with increasing drainage area. Nevertheless, the signal of fast orogenic exhumation can be detected in the river deltas, even if the deltas are up to 1000 km away from the orogenic sediment sources.; Furthermore, analysis of over 30 stratigraphic samples from the alpine fore- and hinterland allowed the reconstruction of the long-term exhumation of the Alps. Exhumation is defined as all processes like normal faulting, ductile thinning and erosion, which contribute to the unroofing of deeply seated rocks and their rise to the Earth's surface. With respect to the zircon fission-track system, the Alps are in an exhumational steady-state since the Oligocene. The exhumational signal is evident in a relatively symmetric fashion in the fore- and hinterland. The long-term average exhumation rate of the areas with the fastest exhumation is about 0.7 km/m.y.; Additionally, the closure temperature for fission-tracks in natural zircon was determined with samples from the Gold Butte block, SE Nevada, at 194 ± 18°C for a ∼17°C/km geothermal gradient and a 0.46°C/m.y. cooling rate. This estimate is in good agreement with previously published field-based estimates, which indicates that the closure temperature of fission-tracks in zircon is about 240°C in orogenic settings like the European Alps with a more common cooling rate of 15°C/m.y. |
