Metasomatic gabbroids – markers in the tectono-metamorphic evolution of the Eastern Rhodopes

Abstract

Metasomatic gabbroids – markers in the tectonometamorphic evolution of the Eastern Rhodopes. Pegmatite-aplitic veins cut the serpentinites of Precambrian ophiolite association in Byala Rcka anticline. As a result, bimetasomalic reactions took place and dyke-like bodies of metasomatic rocks, similar to gabbros appear. The bodies are concordant with the schistosity of the serpentinites. The rocks have coarse-grained, spotted or slightly schistose structure. Their mineral composition is dominated by zoisite, epidote, and plagioclase ranging between albite-oligoclase and anorthite. Thc other common minerals are diopside, quartz, talc, chlorite, amphibole (actinolite and hastingsite), grossular, K-feldspar, titanite, dolomite. The texture is commonly pseudomorphos, corrosional, simplectitic, diablastic. The varying chemical composition of the metasomatites distincts them from the petrochemical group of the basic magmatic rocks. On the other hand, they differ in structure, texture, character of the deformation, and chemical and mineral composition from the earlier metamorphosed basic magmatic rocks which are components of the ophiolitic association. The metasomatic gabbroids are synmetamorphic, postdeformation reaction products related to the differentiates of later deep level migmatization of the Prarhodopian Supergroup. They were formed during the second metamorphic event of the second metamorphic cycle. Probably, the metasomatic gabbroids were synchronous to the gneiss-granites from the Orlov vruh peak. Temporally they follow the stage of syndeformation metamorphic recrystallisation and mark the beginning of the ultrabasic rock assimilation. The metasomatic gabbro ids are important markers in the evolution of the metamorphic basement of the Rhodope massif.