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論文

Low-temperature constraints on the Alpine thermal evolution of the central parts of the Sredna Gora Zone, Bulgaria

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

Geologica Carpathica, 73(1), p.3 - 23, 2022/02

 被引用回数:1 パーセンタイル:18.92(Geosciences, Multidisciplinary)

The central parts of the Sredna Gora Zone in Bulgaria have experienced a complex Alpine tectonic evolution. The main tectonic and thermal events since the end of the Triassic are the Late Jurassic-Early Cretaceous (Early Alpine) and Late Cretaceous-Paleogene (Late Alpine) compression/transpression separated by Late Cretaceous island-arc magmatism and intra/back-arc extension and basin formation. During the Cenozoic, the area was mainly under post-orogenic extension. Here, we present the first apatite and zircon fission-track results and new muscovite and biotite $$^{40}$$Ar/$$^{39}$$Ar age analysis on late Carboniferous-Permian granitoids together with Late Cretaceous volcanic and subvolcanic rocks and Late Maastrichtian-Danian conglomerates from the Panagyurishte basin, which allowed us to reveal the Alpine thermal and tectonic evolution of the Central Sredna Gora Zone. Our new results disclosed the existence of several thermal and cooling episodes related to different tectonic and magmatic events in the studied area. The 40Ar/39Ar dating of samples from the metamorphic basement constrain the thermal peak of an Early Alpine thermal event at about 139-137 Ma at temperatures between $$sim$$ 300 and 400$$^{circ}$$C. Through the apatite FT dating and thermal modelling, the time of a Late Alpine (post-Danian) event was constrained at 65-55 Ma, during which the tectonically buried sediments of the Panagyurishte basin attained temperature of $$<$$ 120$$^{circ}$$C. The Cenozoic cooling and exhumation of the Central Sredna Gora Zone metamorphic basement was related to post-orogenic extension and denudation which took place probably at two stages during middle Eocene to Oligocene.

口頭

Low-temperature thermochonological constraints on the Alpine evolution of the central parts of Sredna Gora Zone, Bulgaria

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

no journal, , 

We present the first apatite and zircon fission-track results coupled with new muscovite and biotite $$^{40}$$Ar/$$^{39}$$Ar analysis on samples from the pre-Mesozoic granitic basement and the Upper Cretaceous to Danian volcano-sedimentary cover, which allowed us to reveal the Alpine thermal and tectonic evolution of the central parts of Sredna Gora Zone. Our new results disclosed the existence of several heating and cooling episodes related to different tectonic and magmatic events in the studied area.

口頭

Thermochronological evolution of the Plovdiv pluton, Bulgaria

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

no journal, , 

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 $$^{40}$$Ar/$$^{39}$$Ar multiple single grain fusion dating, and apatite and zircon fission-track (FT) analyses. $$^{40}$$Ar/$$^{39}$$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 80.43$$pm$$0.43 Ma. Eighteen zircon and 28 apatite grains yield zircon FT age of 55.6$$pm$$2.8 Ma and apatite FT age of 36.1$$pm$$3.1 Ma. The obtained $$^{40}$$Ar/$$^{39}$$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 250$$^{circ}$$C 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.

口頭

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

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

no journal, , 

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 $$^{40}$$Ar/$$^{39}$$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 $$^{40}$$Ar/$$^{39}$$Ar weighted mean ages of 92.12 $$pm$$ 0.60 Ma (amphibole) and 89.17 $$pm$$ 0.34 Ma (biotite) are interpreted as representing the time of cooling below ca 300$$^{circ}$$C after the emplacement of the sampled magmatic bodies. Four rock samples yield apatite FT ages between 48.6 $$pm$$ 4.1 Ma and 37.7 $$pm$$ 3.7 Ma. Modelling of the apatite fission track data using HeFTy software revealed two stages of rapid cooling below ca 120$$^{circ}$$C - 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.

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