Thermochronological evolution of the Plovdiv pluton, Bulgaria

ブルガリアPlovdiv深成岩体の熱年代学的発達

Balkanska, E.*; Kounov, A.*; Georgiev, S.*; Anti, M.*; 田上 高広*; 末岡 茂   ; Wijbrans, J.*

Balkanska, E.*; Kounov, A.*; Georgiev, S.*; Anti, M.*; Tagami, Takahiro*; Sueoka, Shigeru; Wijbrans, J.*

The Plovdiv pluton is intruding the Maritsa strike-slip fault zone, situated in the southern part of the Sredna Gora Zone, in the area of the town of Plovdiv. Here, we present the first thermochronological results from this pluton in order to reveal the thermal and tectonic evolution since its emplacement in the Late Cretaceous. A monzonite rock sample was collected from the Sahat Tepe Hill in Plovdiv for Ar/Ar multiple single grain fusion dating, and apatite and zircon fission-track (FT) analyses. Ar/Ar data obtained from twelve amphibole grains are ranging between 83.3 and 78.5 Ma. The total fusion experiments of 8 grains give a weighted mean age of 80.430.43 Ma. Eighteen zircon and 28 apatite grains yield zircon FT age of 55.62.8 Ma and apatite FT age of 36.13.1 Ma. The obtained Ar/Ar age is identical with the zircon U-Pb age from the Plovdiv pluton and is related to cooling of the magmatic body to temperatures immediately after its emplacement. As suggested by the zircon FT age the Plovdiv pluton cooled bellow 250C in the early Eocene. This cooling could be related to thermal relaxation following the early Eocene magmatic pulse in the Rhodope Zone. Another possibility is to be associated with post-orogenic cooling following the middle to late Paleocene Late Alpine compressional event in the central parts of Sredna Gora Zone. The Eocene cooling and exhumation of the Plovdiv pluton between 44 and 42 Ma, suggested by the apatite thermal modelling, could be related to the period of denudation and extension, associated with the formation of the Thrace basin. Such scenario is in accordance with the thermochronological data from the neighboring areas.