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-Tapajós and Rio Negro-Juruena provinces of the SW Amazonian Craton, their connection with the adjoining Paraguá Terrane is still tentative. Here, we test the connection between SW Amazonia, Rio Apa and Paraguá 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 Paraguá Terrane), and the Ventuari-Tapajós 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 Paraguá Terrane and the Rio Negro-Juruena 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 Paraguá Terrane, and the SW Amazonian Craton. We postulate that the Mesoproterozoic Alto Guaporé orogeny (ca. 1470–1430 Ma, accretionary phase) eventually juxtaposed the high-pressure/medium-temperature (amphibolite facies) RAT and the high-temperature (granulite facies) Paraguá Terrane along the SW margin of Amazonia, establishing a paired metamorphic belt during Rodinia assembly. The newly formed RAT-Paraguá-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-Paraguá and RAT. The timing of fragmentation and drift of the RAT and the Paraguá Terrane from the SW Amazonia is still unknown.