GEOCHEMICAL CHARACTERISTICS OF THE MAIN ROCKS TYPES OF THE KORSUN'-NOVOMYRHOROD ANORTHOSITE-RAPAKIVI GRANITE PLUTON

Abstract

The geochemical features of most distributed rocks from the Korsun'-Novomyrhorod Pluton are considered. The obtained data give reason to assume that the association of basic and intermediate rocks of the pluton was formed because of the differentiation of the primary melt, similar in composition to high alumina tholeiites. It can be inferred that anorthosites were the earliest rocks that appeared in the early stages of plagioclase crystallization. The chondrite-normalized patterns of REE from anorthosites are characterized by the classical distribution of REE for such rocks, with significant positive Eu-anomalies at low REE concentrations. Further evolution of the residual melts enriched by mafic components could lead to the formation of gabbro-anorthosites. Less distributed gabbronorites and norites were formed because of crystallization of residual melts after segregation of anorthositic and gabbro-anorthositic cumulates. Considering the high iron content in all types of rocks, the basic rocks crystallized from residual melts that were genetically related to anorthosites. But ore-bearing norites (Nosachiv-type), in contrast to most distributed basic rocks, had been formed in the early stages because of simultaneous accumulation of feldspar and ilmenite, followed by gravitational precipitation at lower levels of magmatic chambers. The genesis of monzonite-syenite rocks is more enigmatic. Their geochemical features very resemble those in gabbroic rocks, which gives reason to consider them as a result of residual melts crystallization after escaping from anorthositic and gabbronoritic bodies. Subsequent migration and protracted differentiation of such K-enriched melts could cause the appearance of the high-Fe syenites of the Velyka Vyska-type, enriched in REE, Y, Zr, partially Nb, and depleted in Sr and Ba. Although the geochemical characteristics of rapakivi show significant similarities to monzonitic rocks, their genesis remains problematic. It's worth noting that our findings are more consistent with continental crust melting caused by ascending intrusions of basic composition.