Geochemistry and tectonic significance of proto‐ophiolitic metamafic units from the Serbo‐Macedonian and western Rhodope massifs (Bulgaria‐Greece)

Abstract

Dispersed Triassic (?) metamafic rocks occurring in the Serbo‐Macedonian and western Rhodope massifs of southern Bulgaria and northern Greece are important crustal components of early Mesozoic oceanic crust formation in the Tethyan realm. The Volvi and Therma metamafic bodies of the Serbo‐Macedonian Massif and metamafic rocks at Rila Mountain of the western Rhodope Massif consist mainly of gabbros and basalts that show a strong overprint of Alpine amphibolite‐facies metamorphism and deformation. Only clinopyroxenes in the Volvi body represent preserved primary phases. High‐Ti and low‐Ti groups have been identified geochemically within the metamafic rocks. The incompatible trace‐element and REE‐enriched high‐Ti group displays an E‐MORB signature consistent with a rift‐spreading centre tectonic setting; in contrast, the low‐Ti group exhibits geochemical features largely comparable to the high‐Ti group as well as HFSE and REE depleted compositions and an arc‐related signature. Comparison with Triassic rift‐related volcanic suites in adjacent tectonic zones show that these metamafic rocks are fully comparable in terms of their trace elements, REE ratios, and normalized patterns, suggesting that collectively they represent the remnants of a regionwide Triassic rifting event. Enriched mantle components, together with an arc component likely influenced by the late Palaeozoic‐early Mesozoic Palaeotethyan subduction, were involved in the petrogenesis of the metamafic rocks. Based on regional geology and geochronology, we interpret the metamafic rock suites as the products of intra‐continental rifting within the Serbo‐Macedonian/Rhodope continental margin. Thus, these proto‐ophiolitic mafic rock assemblages represent precursors of the Neotethyan early crust formation along the Eurasian plate boundary following the closure of Palaeotethys.