Growing the Paleo- to Mesoproterozoic margin of the SW Amazonia and the transition from an accretionary to a collisional system

Abstract

Despite a general consensus of a petrogenetic link in Paleo- to Mesoproterozoic times between the Rio Apa Terrane (RAT) and the Ventuari-Tapajos ´ and Rio Negro-Juruena provinces of the SW Amazonian Craton, their connection with the adjoining Paragua ´ Terrane is still tentative. Here, we test the connection between SW Amazonia, Rio Apa and Paragua ´ terranes by comparing an extensive dataset of new and published zircon U–Pb–Hf isotopic data. A locally weighted scatterplot smoothing (LOWESS) curve based on a near continuous zircon εHfT time series (~1400 data) indicates that the Western domain of the RAT, the San Diablo domain (southern Paragu´ a Terrane), and the Ventuari-Tapajos ´ Province are characterized by a crustal reworking array associated with the recycling of the Amazonian Archean crust. Change-point statistical analysis indicates the time of a switch from this reworking array to an episode of juvenile input into the magmatic sources at 1809–1805 Ma (95 % confidence), giving rise to the juvenile Eastern domain of the RAT, the Paragua ´ Terrane and the Rio NegroJuruena Province. This secular zircon εHfT evolution is interpreted to represent a switch from advancing (crustal reworking) to retreating (juvenile input and crustal growth) episodes in the Paleo- to Mesoproterozoic accretionary orogen of SW Amazonia. Similar temporal isotopic patterns are recorded in modern accretionary orogens such as the Andes. This data supports a petrogenetic link between the RAT, the Paragua ´ Terrane, and the SW Amazonian Craton. We postulate that the Mesoproterozoic Alto Guapor´e orogeny (ca. 1470–1430 Ma, accretionary phase) eventually juxtaposed the high-pressure/medium-temperature (amphibolite facies) RAT and the high-temperature (granulite facies) Paragua ´ Terrane along the SW margin of Amazonia, establishing a paired metamorphic belt during Rodinia assembly. The newly formed RAT-Paragua-Amazonia ´ connection lasted until at least ca. 1110 Ma based on the expression of the Rincon del Tigre-Huanchaca large igneous province that crosscut the Amazonia-Paragu´ a and RAT. The timing of fragmentation and drift of the RAT and the Paragua ´ Terrane from the SW Amazonia is still unknown.