Chemical composition of Late Svecofennian granite in the Bothnian Basin, central Sweden

Late Svecofennian granite is frequent in the Bothnian Basin, especially in zones of rapidly changing metamorphic grade but also in areas, where the metamorphic grade is elevated. The granite is essentially undeformed, but weakly foliated or lineated rocks are common; more rarely are rocks strongly foliated. X-ray fluorescence was used for major-element and ICP-MS for trace-element analyses. The chemical composition is almost invariably peraluminous, calc-alkaline and strict granitic. The mean of the molecular ratio Al2O3/(CaO+Na2O+K2O) is 1.3 with an almost normal distribution. It straddles the boundary between S- and I-type granites (where the value 1.1 is used as the boundary). The source is made up of mixtures in any proportions of igneous and sedimentary rocks, and this boundary is not a strict boundary between source rocks. Trace-element variation is immense. Rare earth element patterns are somewhat different for I- and S-type granites, but otherwise no systematic difference depending on the I/S character has been found. The metasedimentary rocks in the source were probably enriched in Sr and show evidence of oxidation. Breakdown of biotite and, probably to some extent, muscovite delivered the necessary volatiles for melting. Volatiles were important for the evolution of the granite giving non-CHARAC effects among others tetrad effects to the low-temperature granite. Degrees of melting were moderate and probably variable but cannot be quantified. Zr-saturation temperatures vary (820 +/- 148 degrees C (2 sigma)), but are higher for I-type than for S-type granites. The lowest temperatures occur in low-grade areas probably representing high intrusion levels.