Contrasting Fe-enrichment trends and redox paths in calc-alkaline granitoids from Cima d'Asta, southern Alps, Italy: the control of PH2O

The Cima d'Asta granitoid complex forms a high-K metaluminous calc-alkaline suite. The main pluton (MP) consists of biotite monzogranites with subordinate biotite ± hornblende tonalites and granodiorites. Fine-grained basic-intermediate rock types are present as small satellite bodies (Cima di Mezzogiorno: CM, Ponte Gardellin: PG and Arinas-Redasega: AR) around the main pluton as well as mafic microgranular enclaves (MME). The satellite bodies originated under different PH2O conditions. CM-PG and AR-MP rocks show distinct Fe/(Fe+Mg) evolution trends both in whole rock and biotite compositions. In addition, the two rock groups follow distinct redox paths. These contrasting characteristics could be related to: 1) distinct magma sources or to 2) different PH2O conditions. Mineral chemistry, trace and REE patterns as well as isotopic features strongly support an origin from a common source and favour the second hypothesis.