Cretaceous to Cenozoic thermal evolution of the southwestern South Carpathians: evidence from fission-track thermochronology

The southwestern South Carpathian orogen is composed of various nappe compl exes which were assembled during the Cretaceous-Cenozoic orogeny. These are from footwall to hangingwall: (1) the Danubian nappe complex including a C adomian/Variscan basement; (2) the Arjana and Severin units with Jurassic t o Early Cretaceous rift and oceanic sequences; and (3) the Getic nappe comp lex with Variscan continental basement. Fission track (FT) thermochronology on apatite, zircon and sphene from samples collected from various units of the South Carpathians, in conjunction with field constraints and previous geochronology is used to characterise the Alpine tectonic events and to res tore the pattern and amount of exhumation since the Cretaceous. Zircon from the flysch unit and the Danubian Liassic cover sequence yields FT ages aro und 200 Ma suggesting cooling of the rift flanks prior to the opening of th e Severin rift. Zircon and sphene from the Getic and Danubian basement unit s yield FT ages averaging 110 Ma and indicating cooling under 240 degrees C of the basement contemporaneous with, or postdating thrusting. Apatite FT ages display a decreasing age trend from the hangingwall (65 Ma) to the foo twall units (30 Ma). The age data and corresponding horizontal confined tra ck length distributions suggest that exhumation of the nappe pile occurred in two stages: the first is related to the Late Cretaceous nappe stacking a nd the second one to the final thrusting of the South Carpathians onto the top of the Moesian platform. Apatite FT ages along major brittle wrench fau lts indicate reheating above ca. 120 degrees C during fluid flow associated with fault (re)activation during Oligocene and Neogene times. Thus, shear zone rocks experienced a higher temperature overprint during Cenozoic time than rocks of the unaffected nappe pile. Temperatures of hydrothermal flow along these zones decreased below 100 degrees C progressively starting with the Late Oligocene-Early Miocene when the area began to override the Moesi an platform. (C) 1998 Elsevier Science B.V. All rights reserved.