Ductile deformations along the south-western contact of the Rila-Rhodope batholith, West Rhodopes, Bulgaria

Abstract

We have determined the deformation features along the southern and south-western contacts of the Rila-Rhodope batholith, as well as in the host metamorphic rocks, in order to clarify the deformation conditions and emplacement mechanism of this large granitic pluton. The studied area is located in the southwest Bulgaria, northeast of the town of Gotse Delchev. The field and microstructural observations along cross-sections of the contact suggest syntectonic emplacement of the Rila-Rhodope batholith relative to the last amphibolite facies metamorphism. The features of the granites and their host rocks that support this conclusion are: (1) conformity of the magmatic foliation and lineation to the solid-state foliation and mineral stretching lineation in the granites, as well as in the host metamorphic rocks; (2) identical synkinematic shear determined in both the granites and their host rocks indicating top-to-the SW direction of the tectonic transport; (3) presence of non-deformed veins of granitoid material indicating the existence of granitic melts after the imposing of the ductile deformation; (4) solid-state deformation at amphibolite facies conditions. The intrusion of the granites could be related to the period of extension of the Rhodope Massif resulting in exhumation of the deeper parts of the crust and the development of the Rhodope metamorphic core complexes during Paleogene times. Another ductile shear zone existing between the two distinguished metamorphic units is also reported. It predates the one along the contact of the batholith and is characterized by higher degree of shearing deformation.