The Oripää granite revisited: Elemental geochemistry, Nd isotopes, and implication to terrane boundary

Abstract

The Paleoproterozoic Oripää granite in the Loimaa area in southwestern Finland (Fig. 1a; Nironen, 1999) is a small, heterogeneous leucogranite pluton that was emplaced within the synorogenic (1.89–1.87 Ga) plutonic and supracrustal rocks of the Arc complex of southern Finland at ~1.85 Ga (Kurhila et al., 2005, 2011). The Oripää granite has been considered to belong to the “microcline granites” (leucogranites) of the Late Svecofennian granite–migmatite zone (LSGM zone; Ehlers et al., 1993). In terms of its relatively radiogenic Nd isotope character (positive initial ε Nd value) and relatively old age (Rämö & Nironen, 2001; Kurhila et al., 2005) it is, however, rather different from the main leucogranite bodies of the LSGM farther south. We have analyzed new samples from the Oripää granite and its country rocks (tonalite, quartz diorite, amphibolite) for Nd isotopes and elemental geochemistry in order to further characterize the Oripää granite and the bedrock around it. Our results show that the Oripää granite is consanguineous with its immediate country rocks and that the terrane boundary marking transition from the Arc complex of western Finland to the Arc complex of southern Finland is located just north of the Oripää granite at this longitude.