Abstract
The study reports petrography and mineral chemistry data about an ultramafic vein that cuts the Rabrovo serpentinite (near Valandovo, Southern Macedonia). The serpentinite occurs as a block within a shearing zone of the East Vardar Zone tectonic mélange. The vein corresponds to medium-grained olivine websterite that sometimes displays cumulate-like textures. It is composed of low-Al orthopyroxene (Mg#[mol MgO*100/(MgO + FeOt)]~85, Al2O3<2 wt.%), clinopyroxene (Mg# = 82–86), olivine (Mg#~84) and spinel (Cr#[mol Cr2O3/(Cr2O3 + Al2O3)]~0.4, which, according to geothermometric calculations, equilibrated at 750–850 oC. Its pyroxene-rich modal composition suggests that this rock cannot represent a normal lithospheric mantle. Instead, it is supposed that it was formed via magmatic precipitations in the mantle lithosphere. In addition, the Rabrovo olivine websterite shows similar mineral chemical compositions to many other orthopyroxene-rich lithologies worldwide, which origin is commonly associated with subduction settings. Therefore, its presence is considered as additional evidence that the East Vardar ophiolites represent typical supra-subduction ophiolites.
Highlights
IntroductionThe East Vardar Zone has the most pronounced supra-subduction signature of all the Balkan ophiolite belts
The Balkan Peninsula is known from the existence of several ophiolite belts which are part of a much broader ophiolite domain that can be traced from the Western Mediterranean to the Himalaya
Based on the composition of mantle xenoliths entrained in Palaeogene mafic alkaline rocks of East Serbia, some authors [10, 11] argued that the mantle underneath the present day East Serbia possesses supra-subduction signatures
Summary
The East Vardar Zone has the most pronounced supra-subduction signature of all the Balkan ophiolite belts This setting was first, at least indirectly, suggested by [3] Maksimović and Majer (1981) and [8] on the basis of the higher depletion extent found in the East Vardar peridotites with respect to the Dinaride and West Vardar peridotites. Based on the composition of mantle xenoliths entrained in Palaeogene mafic alkaline rocks of East Serbia, some authors [10, 11] argued that the mantle underneath the present day East Serbia possesses supra-subduction signatures These authors further postulated that this subcontinental mantle slice may, represent suboceanic mantle portions that were accreted during the closure of the East Vardar Zone (see [12]). One of the strongest independent evidence for this hypothesis was derived from the presence and characteristics of a sub-group of olivine websterite xenoliths. [13] studied these orthopyroxene-rich xenoliths in detail and concluded that they represented lithospheric precipitates of boninite-like magmas similar to those commonly found in sub-arc settings
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