PETROGRAPHIC-GEOCHEMICAL CHARACTERS AND K-Ar AGES OF LATE CRETACEOUS VOLCANIC ROCKS IN THE BOR ZONE - PART OF THE TIMOK MAGMATIC COMPLEX (EASTERN SERBIA)

摘要

This paper describes the petrographic-geochemical characters and provides the K-Ar dating of the volcanic rocks cropping out in the Brestovacka Banja area (SW of Bor) and in the Bor mine area, both belonging to the Timok Magmatic Complex (TMC, Eastern Serbia). The studied volcanics comprise: a/ coherent volcanic rocks with lava flow and feeder dyke facies; b/ autoclastic deposits with autobreccia and hyaloclastite facies and c/ pyroclastic rocks with pyroclastic flow and pyroclastic fall deposit. The subalkaline affinity with a calc-alkaline tendency (SiO_2 from 51.47% up to 60.48% and medium-K character) is confirmed in all the analyzed samples, which can be referred to the basalt and/or andesite clans. New radiometric data suggest the K/Ar isochron age of about 89.7 and 76.7 Ma for the Bor mine area and for the Brestovacka Banja area, respectively, pointing to a Turonian to Maastrichtian age for the volcanism of the TMC. Further investigations should provide more precise data about the age of the hydrothermal fluids and of the mineralization. The presence of different volcanic facies at the relatively small area indicates a polyphase character of the volcanic activity under on continental and marine conditions. The elucidated calc-alkaline character, the lithologic characteristics typical for stratovolcanic complexes as well as the major oxide composition and the trace element content and ratio as shown in the discrimination diagrams, indicates subductive affinity of magmas.