Detailed studies of four granite plutons, two in southern Finland and two in southwestern New Mexico, indicate considerable petrologic variation for and bring new insights into the petrogenesis of the mid-Proterozoic A-type granites. The rapakivi plutons of Bodom and Obbnäs are the westernmost intrusions of the classic rapakivi area of southeastern Finland and show, despite their close proximity and temporal association, geochemical (including isotopic) differences indicative of different sources. The Bodom pluton comprises a series of porphyritic granites (hornblende-, hornblende-biotite, and biotite-granite) and an even-grained biotite-hornblende granite; the Obbnäs pluton is composed of porphyritic hornblende-biotite granite intermingled with minor even-grained granodiorite. The granites of both plutons are aluminous A-type, but the Obbnäs granite exhibits higher average TiO2, CaO, MgO, P2O5, Ba, and Sr and lower FeO*/ (FeO*+MgO), K2O, Rb, and Nb than the Bodom granites. Mineral chemistry implies that the plutons were crystallized at ~ 900 to 800 ºC and ~ 2.7 to 5.0 kbar under low fO2. The two plutons have slightly different initial Nd isotope compositions (and possibly also different initial Sr isotopes) indicating a slightly older overall source for the Obbnäs pluton. Two sets of diabase dikes (Kopparnäs and Vihti) are associated with the plutons; the dikes at Kopparnäs may be part of a different (high-Nb, high-Ti) magma type tha
