Paleoproterozoic (~2.0 Ga) volcano‐plutonism in the southeastern region of the Amazon Craton: Petrological aspects and geotectonic implications

Abstract

Detailed studies on the volcano‐plutonic associations of the Amazon Craton (AC) have been conducted since the 1980s. Since then, several issues concerning the definition of the lithostratigraphic units and their role in the AC evolution have been improved. Recently, a volcano‐plutonic association of around 2.0 Ga was described in the south‐central part of the AC, named as Jarinã Formation (volcanic rocks) and Vila Rica Intrusive Suite (granitoids). The present work deals with the unexpected occurrence of this volcano‐plutonic association in the southeastern region of the Amazon Craton. In the study area (Santaninha region), the rocks of the Jarinã Formation comprise two volcanic successions with distinct petrographic and compositional features. The amount and shape of the phenocrysts and crystal fragments allow the individualization of effusive and pyroclastic rocks. The geochemical character indicates that the volcanic rocks belong to two distinct successions as follows: intermediate to acid magnesian I‐type and acid ferroan A‐type. The I‐type succession shows high MgO, TiO2, P2O5, and Sr content and low K2O, Zr, Nb, Ta, Y, and heavy rare earth element and consists of undeformed andesitic to dacitic ignimbrites and subordinate effusive rhyodacites. The A‐type succession present high K2O, FeOt, Zr, Nb, Ta, Y, and heavy rare earth element content and low TiO2, P2O5, and Sr and comprises undeformed rhyolitic ignimbrites and subordinate effusive rhyolites. The granitoids of the Vila Rica Intrusive Suite crosscut the volcanic rocks of the Jarinã Formation and include two phaneritic facies as follows: coarse‐ to medium‐grained granite and medium‐grained granite. The MgO, TiO2, P2O5, Sr, K2O, Zr, Nb, Ta, Y, and rare earth element content demonstrate that the medium‐grained granite facies present geochemical characteristic of I‐type granites. Laser‐ablation inductively coupled plasma mass spectrometry U–Pb zircon data indicate crystallization ages of 2,009 ± 9 Ma for the I‐type dacitic ignimbrite, 1,994 ± 16 Ma for the A‐type rhyolitic ignimbrite, and 1,995 ± 14 Ma for the I‐type medium‐grained granite. These ages agree with the previous data of the Jarinã Formation in the south‐central region of the Amazon Craton and of the Vilca Rica Intrusive Suite in the southeastern of the Amazon Craton. The understanding of the geological context of these units carry on meaningful implications to the contextualization of the ~2.0 Ga volcano‐plutonic event in the AC and, consequently, to the compartimentalization of its geotectonic provinces.