The Jurassic South Albanian ophiolites: MOR- vs. SSZ-type ophiolites

Abstract

Within the western belt of the southern Albanian ophiolites, the Voskopoja ophiolite consists of three subunits: Voskopoja, Morava and Rehove. These are predominantly lherzolites with minor harzburgites and dunites in the mantle section. Above come ultramafic and mafic cumulates including wehrlites, troctolites and olivine gabbros. Gabbronorites are restricted to the Morava subunit. Isotropic clinopyroxene gabbros, extrusives and sediments are present only in Rehove and Voskopoja. The volcanic section is dominated by basaltic breccias, including megablocks with sheeted dykes, pillow lavas and isolated dykes. The basaltic breccias grade upwards into sandstones, in turn, interlayered with argillites and cherts of Jurassic age. The basalts are predominantly clinopyroxene–plagioclase basalts, either aphyric or plagioclase phyric. Geochemically, they are divided into four groups: (1) an intermediate Ti and Zr group with low Ni (hereafter called low-Ni group), (2) an intermediate Ti–Zr group with high Ni (hereafter called high-Ni group), (3) a high-Ti–Zr group and (4) a low-Ti–Zr group. The high-Ni content in group 2 is interpreted as originating from olivine and spinel xenocrysts. Apart from the high-Ni content, groups 1 and 2 are comparable with the volcanics of the “low- to high-Ti intermediate ophiolites.” By contrast, group 3 is more comparable to the high-Ti ophiolitic extrusives in the western ophiolite belt of northern Albania. Group 4 consists SSZ-type basalts and is widespread in the volcanics of the eastern ophiolite belt. Comparison of the ultramafic–mafic cumulates and the basaltic volcanics with those in the northern part of the western belt in Albania and the Pindos ophiolite indicates that there is a systematic variation in petrography and geochemistry from north to south in the western belt, with an increasingly distinct SSZ signature towards the south. Ultramafic and mafic cumulates, as well as basalts from the Shebenik massif in the eastern belt, are similar to those of Voskopoja, implying a genetic relationship.