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

• Autores: A. Kounov, D. Seward, D. Bernoulli, Jean-Pierre Burg, A. Ivanov
• Localización: Geotemas (Madrid), ISSN 1576-5172, Nº. 4, 2002 (Ejemplar dedicado a: INTERNATIONAL WORKSHOP ON FISSION TRACK ANALISIS: THEORY AND APPLICATIONS), págs. 107-110
• Idioma: inglés
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• Resumen

  • In the Kraishte area NE-SW directed extension was associated with the formation of the shallow-dipping detachment fault zones which produced the denudation and exhumation of the amphibolite-facies basement rocks (Osogovo - Lisets complex) andformation of sedimentary basins in the hanging wall. Volcanic activity was contemporaneous with sedimentation; apatite and zircon fission track ages on interbedded tephra range from 45 to 40 Ma. Later, (32 - 30 Ma), subvolcanic trachytic to dacitic and rhyolitic bodies were intruded into the sediment. Tectonically the Osogovo-Lisets complex forms the footwall of Tertiary detachments and the Morava nappe and Struma unit rest in the hanging wall (Fig. 1). This assertion is confirmed by the zircon FT ages obtained in the both units. The ZFT ages from the hanging wall range between 298 and 69 Ma, while the oldest ZFT age in the footwall of the Osogovo detachment is 47 Ma. The hanging wall had thus cooled to 250°C by 70Ma at the latest. In general, Osogovo - Lisets complex yields apatite ages ranging between 46 and 27 Ma and long mean track lengths ranging between 14.65— 14.13 pm. The close similarity of the zircon and apatite ages, as well as the long lengths, is indicative ofrapid cooling ofthe footwall ofthe Osogovo detachment, typical of metamorphic core complexes. On the other hand, the apatite ages from the hanging wall are between 66 and 29 Ma, with mean track lengths ranging between 14.68 - 12.15pm. We suggest that some samples within the basins have been partially or fully reset due to burial. Later exhumation beginning at 39(?) Ma was driven probably by a new set of normal faults, cutting the old detachment which was by that time inactive.