Leucocratic inclusions in the endocontact of Early Proterozoic orthoamphibolites, which occurs in Archean granite gneisses of the Impilakhtinskaya dome structure, were studied. The inclusions have predominantly smoothed contours. The inclusions are represented by plagioclase glomerocrysts enclosed in an amphibolite. Two versions of the origin of plagioclase glomerocrysts are considered: 1 - derivatives of basaltoid melt that formed a dike-like body; 2 - xenoliths of Archean rocks in which orthoamphibolites occur. Glomerocrysts are characterized by uniform inclined spectra of rare earth element (REE) contents with enrichment in light and depletion in heavy REE relative to the chondrite standard; a positive europium anomaly is clearly expressed. Orthoamphibolites corresponding to the initial basaltoid melt from which glomerocrysts could crystallize, negative complementary europium anomalies were not established; such a fact is diacult to explain within the framework of the first version. The presence of individual angular inclusions, enrichment in calcium and aluminum of the melanocratic matrix, and heterogeneous REE spectra for this matrix allow us to assume the process of contamination of the basaltoid melt by trapped detrital material within the framework of the second version. Archean rocks of the TTG series and anorthosites are considered as a source of detrital material (xenoliths). Archean anorthosites and TTG complexes, occurring as individual massifs or in associations, are key components in reconstructing the composition and evolution of the Earth’s early crust. From this perspective, studying these glomerocrysts allows us to expand our understanding of the early Precambrian magmatism of the Baltic Shield. We have established that the composition of plagioclases (An32-75) of glomerocrysts poorly corresponds to the composition of plagioclases of the TTG series rocks (An10-50), but agrees with the compositions of plagioclase of Archean anorthosites (An40-90). The REE spectra of the studied xenoliths demonstrate unconditional similarity with the REE spectra of Archean anorthosites and obvious diberences with the TTG series rocks. Thus, the first evidence of the existence of anorthosites in the core of the Impilakhta dome (and in the Northern Ladoga region as a whole) has been obtained, which is an additional contribution to the general models of the development of the Archean lithosphere.