Unusual PGE Distribution in the Mafic-Ultramafic Rocks of the Early Paleoproterozoic(2.5-2.35 Ga)Drusite(Coronite)Complex of the Belomorian Region,Northern Karelia,Russia

摘要

The PGE pattern and PGM was studied in the rocks of numerous small mafic-ultramafic intrusions of the Early Paleoproterozoic(2.46-2.35 Ga)drusite complex of the Belomorian mobile belt,eastern Baltic Shield,Russia.The chondrite-normalized PGE pattern in the studied rocks(gabbronorites,pyroxenites,and plagioclase lherzolites)is similar to that of the primitive mantle,regardless of the composition of these rocks.It was shown for the first time that different rock types of the drusite complex contain minerals of all six PGE,which makes these rocks principally different from the coeval large layered mafic-ultramafic intrusions with Pd-Pt mineralization at the adjacent Kola and Karelian cratons.This is presumably related to the generation conditions of the parental magmas of the siliceous high-magnesian series(SHMS)and to the practically complete absence of differentiation during the emplacement of the intrusions.Owing to this,the drusite intrusions retained the primary PGE distribution,which is presumably typical of the parental melts of SHMS and was only partially modified by allochemical metamorphism.