Thermochronological constraints on the thermal evolution of magmatic rocks associated with Chelopech Au-Cu deposit, Bulgaria

熱年代学によって制約されたブルガリア・チェロペック金・銅鉱床に関連した火成岩の熱的進化

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

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

The Chelopech high-sulphidation epithermal Au-Cu deposit in Bulgaria is part of the Panagyurishte Ore District situated within the Late Cretaceous Apuseni-Banat-Timok-Sredna Gora metallogenic belt. The time of the magmatic and ore-forming events in the Chelopech area were previously well constrained by zircon U-Pb geochronology at 92.5-91 Ma. Here we provide the results of the first apatite fission-track (FT) together with biotite and amphibole Ar/Ar multiple single grain fusion analysis on the Late Cretaceous magmatic rocks associated with the Chelopech Au-Cu deposit. These rocks were sampled in aim to reveal the post-magmatic/metallogenic evolution of the area, which includes a Late Cretaceous-Paleocene (Late Alpine) compression followed by an Eocene-Miocene extension. The obtained results reveal at least three major cooling episodes since the Late Cretaceous. The Ar/Ar weighted mean ages of 92.12 0.60 Ma (amphibole) and 89.17 0.34 Ma (biotite) are interpreted as representing the time of cooling below ca 300C after the emplacement of the sampled magmatic bodies. Four rock samples yield apatite FT ages between 48.6 4.1 Ma and 37.7 3.7 Ma. Modelling of the apatite fission track data using HeFTy software revealed two stages of rapid cooling below ca 120C - the first one between 52 and 45 Ma probably related to the syn- to post-Late Alpine thrusting denudation and the second one between 38 and 35 Ma triggered by the post-orogenic middle to late Eocene extension and exhumation.