THE SUNSAS OROGEN IN WESTERN AMAZON CRATON, SOUTH AMERICA AND CORRELATION WITH THE GRENVILLE OROGEN OF LAURENTIA, BASED ON U-PB ISOTOPIC STUDY OF DETRITAL AND IGNEOUS ZIRCONS

A SHRIMP U-Pb study of zircon and titanite from eight rocks indicates that the Sunsás Orogen was built in a broad time range (1450-1100 Ma) corresponding to a full orogenic cycle. The Sunsás Orogen contains three main orogenies: Santa Helena (mostly juvenile), Candeias (continental arc), and Nova Brasilândia (collisional), comparable in age to those present in the Grenvillian Orogen of North America. Eighty-nine detrital zircon grains from five samples were collected from late-Sunsás and post-Sunsás rocks and have age profiles with distinctive modes at 1560 Ma, 1450 Ma, 1320 Ma, and 1190 Ma. Ages about 1560 Ma are interpreted as derived from Serra da Providência granitoids, located to the east and northeast of the Sunsás Orogen inside the older Juruena Province (1.81-1.51 Ga), and may be comparable to circa 1540 Ma rocks present in the eastern Grenville Orogen in the Wakeham Group. Ages about 1450 Ma are typical of Santa Helena (SW Mato Grosso) and San Ignácio (Bolivia) Belts, and represent the first orogeny of the Sunsás Cycle, correlated to the Pinwarian of the Grenville Orogen and the Eastern Granite Rhyolite Province of Laurentia. The cluster of 1320 Ma ages represents the imprint of the second, Candeias Orogeny, comparable in age to the 1350-1310 Ma gneisses of the Mount Holly Complex of Vermont. The Candeias Granite has an age about 1337 ± 8 Ma and Candeias metamorphism is detected in metamorphic zircon rims (1324 and 1339 Ma) from both Serra Providência (GR333, 1510 Ma) and Jamari Complex (JL78, 1752 Ma). The third orogeny corresponds to zircon ages of 1190-1128 Ma (Nova Brasilândia Orogeny), which are equivalent in age to the Elzevirian Orogeny of the Grenvillian Orogen. The four youngest detrital zircons (1099-1060 Ma) are not related to any known orogeny in Southwest Amazon Craton. Possible correlatives include post-orogenic tin granites such as Santa Clara and Rio Pardo suites. Rocks comparable in age to the Ottawan Orogeny of Laurentia were not detected. Zircon populations from the post-Sunsás Palmeiral and Pacaás-Novos Formations suggest that they are Sunsás-derived foreland basins and are broadly correlative to the Dardanelos, Apiacás, Aguapeí II and Prainha Formations of the Amazon Craton. These units are comparable to the post-Grenvillian Middle Run basin in the eastern Midwest, USA and the Torridon basin, Scotland.