Martin Danišík

Burial and exhumation of Corsica (France) in the light of fission track data

[1]xa0The Mesozoic and Cenozoic exhumation and cooling history of Corsica is reconstructed by fission track (FT) data on basement and sedimentary rocks. Apatite ages are 105–16 Ma; zircon ages are 160–145 Ma. The Jurassic and Cretaceous ages show that parts of the Variscan basement escaped Alpine influence. The basement was thermally affected by rifting prior to Jurassic opening of the Ligurian-Piedmont Ocean; then it cooled to near-surface temperatures. In Paleocene-Eocene times, subduction buried parts of the basement and overlying flysch to greater depth. In the Oligocene, both collapse of the nappe stack and rifting prior to opening of the Ligurian-Provencal Basin affected the apatite FT system of the basement in different, partly overlapping areas causing a complex age pattern. The study shows that thorough analysis of FT data and thermal modeling allow to assign age populations to distinct cooling processes even when several thermotectonic events contributed to generate an intricate age pattern.

Tectonic control on the late stage exhumation of the Aar Massif (Switzerland): Constraints from apatite fission track and (U‐Th)/He data

[1]xa0We examine the hypothesis that Pliocene exhumation of the external massifs in the central Alps is controlled by climatic change. New thermochronological data from the western Gastern-Aar massif are used to investigate the timing, extent, and reasons for Neogene exhumation. Our data reveal that exhumation was constant with 0.5 km/Ma over the last 10 Ma in the north. In the southern part, exhumation was of the same order until ∼3.5 Ma but then increased gradually toward the south to values of up to 1.2 km/Ma, resulting in overall northward tilting of the western Aar massif. We explain this accelerated exhumation in the south after ∼3.5 Ma mainly by tectonic denudation in the footwall of the Rhone-Simplon fault and discuss changes in deep crustal configuration, which may have triggered south directed normal faulting. We propose that the Rhone river was structurally trapped by the Rhone-Simplon normal fault zone, which additionally enhanced erosion in the southern section of the Aar massif. Climatic forcing may have an impact in the very late stage of exhumation due to Alpine glaciation in the late Pliocene.

Neogene exhumation history of the Mont Blanc massif, Western Alps

[1]xa0The contribution of climate and tectonics to the Neogene exhumation history of the European Alps is studied in the Mont Blanc (MB) massif using low-temperature thermochronology. Apatite fission track and (U-Th-[Sm])/He data suggest that the MB massif was exhumed episodically: Rapid exhumation (2.5 ± 0.5 km/Ma) before 6 Ma is followed by an episode of slow exhumation and a period of accelerated exhumation (>1 km/Ma) after ∼3 Ma. Comparing the exhumation rates of the MB massif with reported exhumation rates of all other external crystalline massifs (ECM) shows that the MB massif is the only ECM that experienced rapid exhumation before 6 Ma, which is possibly related to NW and minor SE directed thrusting of the MB massif. The data demonstrate that the Messinian base level drop (∼5.5 Ma) and the increase in atmospheric moisture caused by an intensification of the Atlantic Golf Stream (4.6 Ma) did not affect the exhumation of the external Alps. All ECM, except the Gotthard massif, show an increase in exhumation rates at ∼3 Ma. We interpret this as the result of normal faulting along orogen-parallel faults and beginning Alpine glaciation. The relative impact of these processes on the exhumation of the ECM can vary spatially and temporally, mainly depending on differences in geology and geomorphology. In the case of the MB massif we propose that the acceleration in exhumation rates at ∼3 Ma is caused by rapid valley incision related to glaciation, and that the recent relief of the MB massif is thus a young feature.