Mafic magmatism associated with the Goiá magmatic arc in the Anicuns region, Goiás central Brazil: Sm - Nd isotopes and new ID-TIMS and SHIMP U-Pb data

Rocks exposed in the Anicuns region, in the eastern part of the Goiás magmatic arc, are represented dominantly by amphibolites (metavolcanic and metaplutonic) and metapelitic rocks. New U-Pb results demonstrate that this association is Neoproterozoic and that mafic rocks crystallized during two main periods: ca. 890-815 and 630-600 Ma. Metagabbro and metadiorite samples JHL-14, JHL-15, JHL-23, AMB-01, and JHL-26B have U-Pb zircon ages of 886±5, 862±5, 815±10, 856±15, and 839±9 Ma, respectively, and compose the older group. The Late Neoproterozoic intrusive Anicuns-Santa Bárbara gabbro-diorite and Americano do Brasil suites are coeval. Four samples from the first (SB-01, JHL-04, JHL-22C, and JHL-19) yield U-Pb ages of 598±8, 612±6, 623±13, and 622±6 Ma, respectively, whereas zircon grains from one norite sample of the Americano do Brasil complex yield a concordia age of 626±8 Ma. All mafic rocks investigated present T_DM model ages of ca. 1.0 Ga, comparable to the model ages of metaigneous rocks of the Goiás magmatic arc. The ε_Nd(T) values are strongly positive, indicating the depleted nature of the mantle source (MORB-like), similar to volcanic and plutonic rocks of the arc-type volcano-sedimentary sequences exposed to the west. The lithological associations that constitute the supracrustal sequences in the Anicuns area, however, are more compatible with an origin in an oceanic or forearc setting than in an intraoceanic arc setting (rocks of andesitic/dacitic/rhyolitic composition are absent. ¹⁴⁷Sm/¹⁴⁴Nd ratios for most of the mafic rocks investigated, however, are smaller than 0.19 and indicate a relative enrichment in LREE, which is not characteristic of N-MORB mafic magmas.