Cretaceous magmatic evolution of the Srednogorie Zone (Bulgaria) and the continuous evolution into the Rhodopen Massif (Bulgaria, Greece)

The Apuseni–Banat–Timok–Srednogorie (ABTS) belt of extensive calc-alkaline magmatism and Cu–Au mineralization is related to the subduction of the Tethys ocean beneath the European continental margin during the late Cretaceous time. Major economic porphyry-style and high-sulphidation ore deposits are restricted to certain segments along the belt and are aligned on the Panagyurishte corridor (Central Srednogorie) in Bulgaria and the Timok region in Serbia. The resent study reviews the geology, geochemistry and geochronology of igneous events in the Srednogorie/Timok Zone, some features of the related Cu-Au mineralization and the continuos magmatic evolution to the South (Rhodope Masif). The Srednogorie Zone (central and eastern part) revealed U–Pb zircon dates from subvolcanic intrusions and major plutons, supplemented by published Ar-Ar and Re-Os age data for the hydrothermal ore deposits, a general younging of magmatism from 92.1 ± 0.25 Ma in the north (Elatsite deposit) to 78.53 ± 0.15 Ma in the south (Capitan Dimitrievo pluton). The Timok region shows the starting point of the magmatism at 90-86.6 Ma and to end with the intrusion of plutons about 82-78 Ma (see Moll et al., 2010, this volume). Economic Cu–Au mineralizations in both sections are related to subvolcanic/ volcanic suites and are dated in the range of 92 to 86 Ma in Bulgaria and mainly about 86-84 Ma in the Timok zone. The age progression correlates in two profiles (Central-Eastern Srednogorie) with an isotopegeochemical trend (Sr-Nd, Hf-zircon data) of decreasing crustal input into mantle-derived magmas. The age and geochemical trends are explained as a consequence of slab retreat during oblique subduction.
   The Cretaceous magmatism continues into the Rhodope Massif. The western Rila batholith gives a zircon age of 69.26 ± 0.26 Ma and a granite at the western border of the Rila batholiths an age of 61± 1.5 Ma (LA-ICPMS) which are interpreted as the time of emplacement; NW of Dospat an U/Pb zircon age of 77 ± 1.3 Ma and further to south at Elatia-Barutin the zircon dating show magmatic age of 55.93 ± 0.28 Ma. The ε-Hf characteristics change from the border Srednogorie Zone/Rhodope Massif of +10 (T-80 Ma) to +2-6 in the central part of the RM and to +1-3 (T-56Ma) at Elatia-Barutin. The crustal input of the Cretaceous/Tertiary magmatism increases to south which is documented by Sr-Nd isotope tracing data and the model of the slap retreatment (Srednogorie Zone) has to be change for the geodynamic interpretation.