Abstract: Late Cretaceous to Tertiary Thermal Evolution of the Southern Carpathians: Evidence from Apatite Fission Track Data

BOJAR, ANA-VOICA, FRANZ NEUBAUER, and HARRY FRITZ

This study focuses on the Upper Cretaceous and Cenozoic thermal evolution of the Southern Carpathian arc that is situated westwards to the Getic Depression. In the klippen region the Southern Carpathians include from footwall to hangingwall the Danubian, the Severin flysch and the Getic nappes that were assembled during Cretaceous nappe stacking.

In order to constrain the post-stacking uplift history of this area, an extensive fission-track survey (ages and confined length measurements) has been carried out on apatite (external detector method). As apatite chemistry represents the second factor controlling the annealing behavior of tracks, microprobe measurements have been done on apatites collected from all units. From footwall to hangingwall, apatite fission-track data gave the following results: A) Danubian basement and cover sequences: 36+/-4, 34+/-4, 34+/-4, 27+/-3 Ma, with mean confined track lengths around 12 micrometers and standard deviations ~ 2 micrometers. Microprobe analyses of apatites from the Danubian basement indicate F concentrations of 3-3.5 wt%; B) Severin nappe (Liassic to Aptian): 45+/-5, 46+/-7, 45+/-5 Ma, with mean track lengths around 12.5 micrometers and standard deviation ~ 2.5 micrometers. The chemical composition show a larger variation with 2.6-4 wt% F and 0-0.4 wt% Cl; C) Getic nappe: 68+/-5, 67+/-7, 57+/-4 Ma, with mean lengths around 13.5 micrometers, standard deviation ~ 1.5 micrometers. Another group of ages within the Getic nappe include 52+/-5, 47+/-5, 42+/-6 41+/-3 Ma, with mean confined track lengths around 11 micrometers, and larger standard deviation ~ 2 micrometers. Microprobe analysis indicate 2.5-3 wt% F and 0.05-0.3 wt% Cl.

Thus for modeling the time-temperature path for Danubian granites the annealing model for fluorapatite (Crowley et al., 1991) was chosen. For the Getic realm samples, the Durango model (Laslett et al., 1987) appears to be more appropriate. The pattern of FT data suggests slow cooling after the Senonian nappe stacking. The final cooling to temperatures under 60 degrees took place in the Lower Miocene, during an accelerated phase of uplift The total amount of post-Senonian erosion is estimated to be in order of 4-5 km, assuming a geothermal gradient of ~ 20/km.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria