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The origin and age of the metamorphic sole from the Rogozna Mts., Western Vardar Belt: New support for the one-ocean model for the Balkan ophiolites

This study reports new geochronological and petrochemical data from the metamorphic sole beneath the Rogozna Mts., Western Vardar ophiolite belt. The Rogozna metamorphic sole is located at the base of an Ibar serpentinite nappe and consists of (i) high-grade andalusite–garnet–sillimanite gneisses and cordierite-bearing hornfels (mostly listwanitized), (ii) medium-grade pyroxene amphibolites and hornfels, amphibolites, amphibolite schists and metagabbros and (iii) low-grade micaschists and talc-chlorite schists. Selected samples of the Rogozna amphibolites and talc-chlorite schists were subjected to the electron microprobe, SEM-EDS, 40Ar/39Ar analysis and whole-rock geochemistry. The Rogozna amphibolites are medium- to fine-grained rocks with nematoblastic texture and pronounced foliation. They consist of green amphibole (~70 vol.%) with variable silica contents (6.4 to 7.8 Si a.p.f.u.), as well as Mg# (molMg/[Mg+Fetot] ; 0.53 to 0.77) and variably albitized plagioclase (~30 vol.% ; Ab24–Ab98). Amphibolites are overprinted by a retrograde assemblage containing actinolite, epidote, clinochlore, sericite, chlorite and magnetite. The amphibolites formed due to metamorphism of two basaltic suites: subalkaline/tholeiitic and alkaline. Subalkaline/tholeiitic amphibolites possess low Zr, Nb, Y, Th, Hf, TiO2 and P2O5 values and a LREE-depleted patterns typical for the N-MORB to BAB (back-arc basalt) origin. Alkaline amphibolites show elevated concentrations of Zr, Nb, Y, Th, Hf, TiO2 and P2O5 with a LREE-enriched patterns typically displayed by ocean island basalt (OIB). Amphibolites crystallized during intra-oceanic thrusting at temperatures between 685 ºC–765 ºC and at a depth of 12–17 km. 40Ar/39Ar cooling ages of amphibole range from 165–170 Ma and slightly postdate the sole formation.

Metamorphic sole; Western Vardar belt; Inta-oceanic closure; Middle Jurassic; Ar/Ar dating

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