Geology and LA-ICP-MS U–Pb geochronology of the Nova Brasilândia belt, SW Amazonian Craton: New ages, re-evaluation of existing geochronological data, and implications for the evolution of the Sunsás orogen

Abstract New geological and LA-ICP-MS U–Pb geochronological data, combined with literature data, are used to characterize more precisely the timing of tectonic events in the Nova Brasilândia belt in the southwestern Amazonian Craton, Rondonia, Brazil. The U–Pb ages of zircon crystals were obtained in the rocks of the Rio Branco domain in the southern part of the belt. They reveal a period of sedimentation between 1241 ± 7.5 and 1137 ± 9 Ma and high-grade metamorphism between 1137 ± 9 and 1127.6 ± 2.3 Ma. Mafic-felsic magmatism of the Rio Branco Suite was dated between 1119.7 ± 2.7 and 1106.2 ± 2.8 Ma. U–Pb ages from specific groups of recrystallized zircon (cores and rims) extracted from high-grade calc-silicate gneiss (1019 ± 15 Ma), metagabbro (1016.7 ± 3.9 Ma), and anatectic granite (1011.3 ± 9.6 Ma) may represent episodes of metamorphic recrystallization and the youngest migmatization. The LA-ICP-MS U–Pb zircon ages establish the timing of two orogenic phases: an accretionary phase between approximately 1137 and 1106 Ma and overprinted metamorphism during the final collisional phase between approximately 1096 and 1011 Ma. The Nova Brasilândia orogeny recorded on the southwest margin of the Amazonian Craton can be described as an accretionary-collisional type that developed between approximately 1137 and 1010 Ma.