Relationships between sanukitoids and crust-derived melts and their implications for the diversity of Neoarchaean granitoids: A case study from Surmansuo and nearby areas, Eastern Finland

Abstract

Relationships between sanukitoids and crust-derived melts and their implications for the diversity of Neoarchaean granitoids: a case study from Surmansuo and nearby areas, Eastern Finland We present new isotopic data (U-Pb and Sm-Nd) from the Neoarchean granitoids of the Lentua complex, which is a part of the Western Karelia subprovince of the Fennoscandian Shield. Compositionally, the samples are granitoids belonging to the sanukitoid suite and K-rich granitoids. Certain samples interpreted as partial melts of pre-existing crust in this study display more mafic compositions than previously described from the surrounding areas. This indicates, at least locally, a source poorer in SiO2 than the TTG (Tonalite-Trondhjemite-Granodiorite) suite granitoids, which are the likely sources for the majority of the anatectic granitoids within the Lentua complex. Based on new geochronological data (LA-MC-ICPMS U-Pb on zircon), the sanukitoids and anatectic granitoids are at least partly coeval (2.69 Ga) in the area, but interaction between the two felsic magmas was limited. The dated sanukitoid sample is distinctly younger (2687±8 Ma) than the average age of the sanukitoids of the Western Karelia subprovince (2718±3 Ma) indicating, together with one previously published sanukitoid age, the existence of a younger sanukitoid phase. This study gives new important constraints to understanding the formation of the Western Karelia subprovince by expanding the observed compositional heterogeneity and the temporal overlap of the different Neoarchean granitoid suites.