Timing of Cenozoic extension in the Kraishte region (SW Bulgaria): evidence from fission track analysis

摘要: The Kraishte zone (SW Bulgaria) is situated between the Serbo-Macedonian high-grade metamorphic unit, the Rhodope" massiP'and the European active margin (Srednogorie volcanic arc). The Alpine history of the Kraishte area includes Cretaceous (post-Valanginian) nappe stacking followed by Eocene to Oligocene (Miocene?) extension, which was responsible for the exhumation of metamorphic units that presumably are part of the Serbo-Macedonian" massir'. The Morava nappe consists of slightly metamorphosed Devonian limestone, lower Palaeozoic schists and pre-Silurian continental basement rocks. It overrides the Strouma unit which includes Variscan basement rocks and Mesozoic sediments. Tithonian to Valanginian flysch deposition preceded nappe emplacement, which predated the Eocene clastic sedimentation that unconformably covered the nappe structures.The NE-SW directed extension was associated with retrogressive metamorphism of greenschist-facies and the formation of the shallowdipping detachment fault zones which produced the denudation and exhumation of the amphibolite-facies basement rocks (Osogovo-Lisets complex) and formation of sedimentary basins in the hanging wall. In the basins, sedimentation was initially continental with alluvial deposits (Eocene) evolving in the Oligocene to deep water with the deposition of turbidites (Moskovsky & Shopov, 1965). Volcanic activity was contemporaneous with sedimentation; apatite and zircon fission track ages on interbed-