The Rio Dourado Intrusive Suite - 1.88 Ga A-type Granite - Southeastern Amazonian Craton - Mato Grosso - Brazil

The Rio Dourado Intrusive Suite (RDIS) is composed of granitic rocks which are exposed in the southeastern AmazonCraton, Central Amazon Province. These granites intruded into the Paleoproterozoic granites of the Vila Rica IntrusiveSuite. The predominantly pyroclastic felsic volcanic rocks of the Iriri Group are coeval and spatially associated with theintrusive granites. Petrographic studies allow us to divide the Rio Dourado granites into: biotite granites, amphibole-bearingbiotite granites and granophyric granites. Modal compositions range from monzo to syenogranites. The oxidized A-typegranite is characterized by FeO/FeO+MgO ranging from 0.8 - 0.95, high contents of FeOT and low contents of CaO, as wellas peraluminous composition. In the tectonic discrimination diagrams, samples of these granites plot in the post-collisionalfield. REE patterns show enrichment in the LREE relative to HREE and negative Eu anomalies. Negative anomalies ofTa and Nb, as well as depletion in the HREE, features which are typical of A-type granites of post-collisional settings, are observed in multi-element diagrams,. Ce, Yb, Nb and Ga contents are transitional between those of A2 and A1-type granites. U-Pbzircon dating by TIMS yielded an age of 1876 ± 39, whereas negative values of εNd (-3 to -10) and model ages (TDM) between 2.6 and2.8 Ga indicate it was formed by re-melting of older (possibly Archean) crust.