Geochemistry of volcanic and subvolcanic rocks and biostratigraphy on radiolarian cherts from the Almopias ophiolites and Paikon Unit (Western Vardar, Greece)

Abstract

The Almopias and Paikon “sub-zones” in northern Greece represent the easternmost part of the Vardar Domain. Volcanic sequences in the Paikon sub- zone largely consist of calc-alkaline volcanic rocks with very minor normal-type (N-) mid-ocean ridge basalts (MORB) and boninites. These data confirm that the Paikon volcanics have originated in a volcanic arc setting developed during the Middle to Late Jurassic times on the westernmost continental margin of the European plate. The Almopias “sub-zone” consists of several ophiolite-bearing tectonic units showing a complex combination of different metamorphic, litho-stratigraphical, and age characteristics. The Liki, Nea Zoi, and Vrissi units (central Almopias) are ophiolitic melanges, the Mavrolakkos and Krania units (eastern Almopias) consist of volcanic sequences, and the Ano Garefi unit (eastern Almopias) includes serpentinized peridotites and overlying basaltic lavas. The Liki unit underwent metamorphism and deformation under amphibolite-facies condition and includes rocks showing N-MORB and low-K island arc tholeiitic affinities. The Nea Zoi unit incorporates N-MORBs of unknown age and Late Triassic calc-alkaline rocks. The Vrissi unit includes an incomplete volcanic sequence consisting of MORB-type volcanics linked with and crosscut by Middle-Late Jurassic arc-type volcanic rocks and dykes. The Mavrolakkos unit consists of sheeted dykes, lavas, and individual dykes with N-MORB affinity, which are crosscut by dykes showing volcanic arc affinity. The Krania unit consists of Middle-Late Jurassic N-MORB series tectonically associated with calc-alkaline volcanics and dykes. Basalts of the Ano Garefi unit have alkaline affinity, whereas dikes cutting the peridotites show enriched-type MORB chemistry. Our data show the occurrence in the Almopias units of Middle-Late Jurassic N-MORB lavas associated with overlying coeval volcanic arc-type lavas and/or intruded by volcanic arc-type dykes. A major point arising from this paper is that some of the Almopias ophiolitic units do not correlate with the other ophiolitic units in the Dinaride-Hellenide belt and some could correlate with the northernmost extension of the Vardar zone in the South Apuseni - Transyl- vanian ophiolitic belt in Romania.