The Quarenta Ilhas Formation consists of basic to intermediate subvolcanic rocks, with tholeitic affinity and ages around 1.78Ga. The magmatic mineralogy is composed by olivine, pseudomorfosed by ferrous-saponite, plagioclase varying from labradorita to oligoclase (An65Ab35 a An20Ab80), Fe-Ti oxides (Ilm87-95 and Usp22-37), diopside to augite (Wo44-35En44-21Fs38-16), with ferro-hornblende (as coronitic texture), alkali-feldspar and quartz in the most differentiated rocks. Petrographic and geochemical data point to an evolution through fractional crystallization from diabase/gabbro to quartz diorite, with fractionation of olivine+ilmenita, magnetite+plagioclase+augite, and crystallization of ferro-hornblende, alkali-feldspar and quartz in the later stages. The affinity with tholeiitic subalkaline magma is indicated by features of major elements, normative minerals (olivine+hypersthene and quartz+hypersthene) and high Y/Nb and La/Yb ratios. High Cs, Rb, Ba and K, and low Nb, Ta and Zr, suggest a lithospheric mantle source, enriched in LILE and depleted by subduction. The REE pattern is LREE enriched faced to HREE, that suggest a source of garnet lherzolitic composition. The emplacement of the Quarenta Ilhas subvolcanic bodies follow the orogenetic activity of the Transamazonian Cycle (~2.0Ga), the post-collisional Uatumã magmatismo (~1.88Ga) and the anorogenic magmatism of the Madeira Suite (~1.83Ga), in a fully intracratonic setting