Petrogenesis of estrela granitoid and implications for the evolution of the rio doce magmatic arc: Araçuaí-Ribeira orogenic system, SE Brazil

Abstract

The Rio Doce arc, developed between ca. 630 and 580 Ma, is composed of a series of plutonic bodies, which constitute its root (G1 supersuite). These represent a swarm of pre-collisional, calc-alkaline, magnesian, predominantly granodioritic to tonalitic plutons that experienced a prolonged period of anatexis and metamorphism during the transition to the syn-collisional stage (ca. 585 Ma) of the Araçuaí Orogen. The Estrela granitoid (ca. 606 ± 13 Ma) and its associated leucogranite (613 ± 10 Ma), detailed in this work through field, petrographic, lithogeochemical, isotopic, and geochronological data, represents a new contribution for the understanding of the G1 supersuite. The studied rocks exhibit granodioritic to tonalitic (Estrela granitoid) and syenogranitic (leucogranite) composition, emphasizing the character of an expanded calc-alkaline series. The Estrela granitoid exhibits negative εNd(t) (− 7.0 to − 9.2) and εHf(t) (− 4.7 to − 8.7) values, and intermediate ratios of 86Sr/87Sr (0.709473–0.710611), which together with the Mesoproterozoic to Paleoproterozoic TDM Nd model ages (1442–2206 Ma) point to a crustal source with possible contributions from mantle derived magmas. In addition, high values of Ba–Sr are identified in the Estrela granitoid, related to a mantle source previously enriched and/or to the participation of sediments in the source. Therefore, the interaction of a magma derived from the juvenile mantle wedge with basement rocks and possibly sediments carried by subduction is here proposed as the main source for the development of the pluton. This granitoid, as well as the other lithotypes present in the study area, present characteristics compatible with the formation in a subduction environment, being crystallized in intermediate to deep depths of the crust (22–25 km) at about 770 °C and in higher conditions of oxygen fugacity.