Acta Geologica 43. (2000)
1. szám - S. Karamata - V. Knežvic - V. Cvetkovic: Petrology of the Triassic basaltoid rocks of Vareš (Central Bosnia)
$02203" 302293 Acta Geologica Hungarica, Vol 43/1, pp. 1-14 (2000) Petrology of the Triassic basaltoid rocks of Vares (Central Bosnia) Stevan Karamata Vera Knezevié, Vladica Cvetkovié Serbian Academy of Sciences and Arts, Belgrade Faculty of Mining and Geology, Belgrade The study represents lithological and geochemical characteristics of the Triassic basaltic rocks of the Vares area (Central Bosnia). This effusive complex belongs to the NNW-SSE elongated Borovica-Vares-Cevljanovidi-Kalinovik zone which is a part of a large belt of Triassic rift-related igneous provinces in Montenegro, Albania, Greece and Turkey. The Vares volcanics represent the earliest products of the volcanic activity related to the Triassic rifting. In this volcanic complex two units have been recognized: the lower one is composed of green pillow lavas and subordinate coherent lava flows and dykes; the upper unit consists of in situ and resedimented hyaloclastic deposits interlayered with coherent and pillowed lava flows, rare dykes and sills. Within both units of the Vares series thin chert intercalations occur. The volcanic activity was characterised by peaceful effusions of basaltic lava either coherent or fragmented by supercooling and quenching. The Vares basaltic rocks bear evidences of low-Ti tholeiites which differentiation was dominated by fractionation of olivine, clinopyroxene and plagioclase. The parental magma surely originated within the intracontinental rifting geotectonic setting. However, the questions as whether the rift was a mantle plume phenomenon and what is the role of the subduction processes in the rift initiation and in providing the mantle source likely request additional investigation. Keywords: basalt, rifting, Triassic, hyaloclastic deposits, lava flows, within-plate basalts, volcanic arc basalts, Dinarides, VareS, Bosnia Introduction The basaltoid rocks of the Vares area, in the earlier literature often refered to as "melaphyres from Vares" (Karamata 1952), are products of the Triassic rift magmatism of the Borovica-Vares-Cevljanoviéi-Kalinovik zone (BVCKZ) (Karamata 1988). This volcanic zone extends from Borovica, Vares and Zvijezda at the northwest and north, then goes further to the south to Cevljanoviéi, eastern vicinity of Sarajevo and finally to Igman, Bjelasnica and Kalinovik (Fig. 1). During the second half of this century appeared papers about the Vares volcanics (e.g. Karamata 1952, 1960, 1988; Pamié 1963) along with some regional investigation (e.g. Karamata 1978; Pa mié 1982). The BVCKZ developed after rifting of the northern margin of the Gondwanaland, i.e. during extensional subsidence in the Paleozoic complex now divided into the Central Bosnian Mts. and Bosnian-Durmitor terranes (?) at the southwest and the Drina-Ivanjica terrane at the northeast (Karamata et al. 1994). Addresses: S. Karamata: Knez Mihajlova 35, YU-11000 Belgrade, Yugoslavia V. Knezevií, V. Cvetkovk: Dusina 7, YU-11000 Belgrade, Yugoslavia E-mail: cvladica@eunet.yu Received: 13 July, 1999 0236-5278/2000/$ 5.00 © 2000 Akadémiai Kiadó, Budapest