U–Pb detrital zircon ages from the Aguapeí Group (Brazil): Implications for the geological evolution of the SW border of the Amazonian Craton

Abstract

New U–Pb detrital zircon data of metasedimentary rocks of the Aguapeí Group, SW Amazonian Craton, are presented in this work. Three samples were analyzed by ICPMS laser ablation in order to estimate the age of the source areas of the sediments and the maximum depositional age of the basin. The samples show an Archean age of 2515Ma not yet reported in the region. Paleoproterozoic ages of 2015Ma, 1897Ma and 1812Ma were not reported in this area either, but are observed 1000–1200km to NE, in the Rio Negro-Juruena province. The group of ages ranging from 1655Ma to 1608Ma may represent zircons from the Lomas Maneches orogen, described in Bolivia. The group of zircons with ages of 1544Ma may be related to the Cachoeirinha (in Mato Grosso) or Serra da Providencia (in Rondonia) magmatic suite. The group of ages of ca 1485Ma, 1417Ma and 1411Ma may represent zircons from the adjacent Santa Helena orogen, in Mato Grosso state. Data presented in this work suggest that the maximum depositional age for the Aguapeí sediments is 1.26Ga, the youngest age among the detrital zircons analyzed. The U–Pb ages in zircon define important time constraint for the Aguapei Group sedimentary rocks deposition. In addition, the results here reported define new challenges in order to identify rocks not yet found in the region that may result in a more complete framework for SW Amazonian Craton crustal evolution.