Fission track data from the Mesohellenic Trough and the Pelagonian zone in NW Greece: Cenozoic tectonics and exhumation of source areas.

Abstract

The Mesohellenic Trough (MHT) trends parallel to the structural fabric of the Hellenides and covers the suture between the Apulian microplate and the Pelagonian block. It comprises an up to ∼4 km thick middle Eocene to upper Miocene sedimentary sequence. We have studied the thermal history of the Pelagonian basement and the provenance of the detrital material in the clastic sediments of the MHT by fission track dating. Apatite and zircon fission track (AFT, ZFT) analysis is applied to samples from the Pelagonian microcontinent along the eastern border of the MHT, and AFT analysis to the sedimentary rocks in the southern MHT. Eocene AFT age populations in the sedimentary strata indicate a proximal position of the Pelagonian microcontinent, which shows the same or even younger AFT ages, as the source area of the detrital material in the MHT. Late Cretaceous to Palaeocene age populations point to a more distant or structurally higher (now eroded) source area. The Eocene orogenic event caused only weak thermal overprinting in rocks of the Pelagonian microcontinent.In its eastern part, the AFT ages show only partial resetting, if any, whereas in its western part the ages were clearly reset during the Eocene event. AFT age-elevation relations, correlation of zircon and apatite FT ages from the same samples, and thermal modelling based on AFT ages and track length distributions were all used to reconstruct the low-temperature cooling history of the Pelagonian basement adjacent to the MHT. The results document fast cooling and exhumation in the Eocene that were possibly related to thrusting and associated erosion, followed by slow cooling and exhumation during Oligocene and Miocene time. This scenario is confirmed by the AFT data from the detrital material in the MHT sedimentary strata. The slow cooling period coincides with a stagnation period or crustal extension and possible reheating, which is probably also responsible for the partial rejuvenation of the ages of the detrital apatites in the oldest (Eocene) formation in the sediment sequence of the MHT.