Geochemistry of metaeclogites from the Central and Eastern Rhodope Mts. (Bulgaria)

Metaeclogites from the Chepelare and Ardino areas (Central Rhodope Mts.) and from the Bela-Reka area (Eastern Rbodope Mts.) have been the subject of this study. The Central Rbodope metaeclogites occur as separate lenses in the migmatized gneisses of the Chernatitsa Subgroup and also show various degrees of amphibolitization and migmatization. The Eastern Rhodope metaeclogites are found in two morphological types. Some are tabular bodies (up to several km long) associated with ultrabasic plates, highly diaphthorized. Together with garnet-mica schists they form a well-defined unit belonging to the Bela-Reka Group. Others are lenses in the migmatized rocks of the Krumovitsa Group and are also affected by rnigmatization.
   Regardless of the complex metamorphic transformations, the protoliths of all metaeclogites studied show basaltoid character of pronounced tholeiitic trend of differentiation. Their geochemical characteristics indicate a close relationship to the ocean type of crust (MORB), and their spatial association with ultrabasic plates and isolated ultrabasic lenses suggests that they may be interpreted as parts of metaophiolite associations.
   The rocks show a moderate extent of fractionation and cumulation of the original melt. A relatively low degree of partial melting of the mantle during the generation of protolithic magma is indicated by the relative enrichment in incompatible immobile elements such as Ti and Cr, by the high Ce/Yb ratio and by the marked alkaline affinity of the metaeclogites studied.
   Enrichment in light rare-earth elements (LREE) is a typical feature of the metaeclogites referring them to the E- and T-types of MORB. This is even better shown by the MORB-normalized patterns of the highly incompatible elements which indicate an apparent tendency in the protoliths of approaching WPB. The primary geochemical characteristics of the eclogite have not been changed essentially by the metamorphic transformations excepting the migmatization processes which have led to an increase in K and LREE.
   Although the geochemistry of metaeclogites from the tabular bodies and from the lenses show no significant differences they cannot be regarded as contemporaneous. This conclusion is based on the different types of metamorphic rocks embedding them as well as on the differences in the metamorphic transformations which affected them. Both, however, are of allochthonous nature and represent fragments of an ancient ocean crust which a variety of tectonic events has brought up into their present-day continental position.