Geochemical and thermodynamic modeling of the petrogenesis of A1-type granites and associated intermediate rocks: A case study from the central Fennoscandian Shield

The origin of ferroan A-type granites in anorogenic tectonic settings remains a long-standing petrological puzzle. proposed models range from extreme fractional crystallization mantle-derived magmas to partial melting crustal rocks, or involve combination both. In this study, we apply whole-rock chemical and Sm-Nd isotopic compositions thermodynamically constrained modeling (Magma Chamber Simulator, MCS) decipher the genesis suite A1-type peralkaline peraluminous associated intermediate rocks (monzodiorite-monzonite, syenite) southwestern margin Archean Karelia craton, central Finland, Fennoscandian Shield. These plutonic were emplaced at ca. 2.05 Ga during an early stage break-up craton along its western show trace element affinities ocean island basalt-type magmas. positive ?Nd(2050 Ma) values (+1.3 +2.6), which are only slightly lower than estimated contemporaneous depleted mantle value (+3.4), but much higher average TTGs (–10) surrounding bedrock, indicating that these essentially derived source. granite samples overlap (–0.9 +0.6 –3.2 +0.9, respectively) somewhat those suggesting mafic parental must have assimilated some amount older continental crust their fractionation, is consistent with crust-like signatures members. MCS indicates can explain major characteristics rocks. generation requires further coupled assimilation crust. processes took place middle upper (?2–4 kbar, ?7–15 km) involved large amounts clinopyroxene, plagioclase olivine. Our results highlight importance FC-AFC petrogenesis support general perception become more by They suggest variable fractionation paths upon onset may broad variety felsic igneous often observed closely time space within same complex.