Abstract
The study of Paleoproterozoic rocks is crucial for understanding Earth's tectonic evolution during the time when most of the modern crust and ore deposits were formed. The rocks of the Brazilian Amazonian Craton record some of the most-complete and best-preserved Paleoproterozoic magmatic and volcanic episodes on Earth. Following previous investigations, we present new lithofaciological and stratigraphic records of the felsic rocks of the Tapajós Mineral Province (TMP) (~2–1.88 Ga) and the São Felix do Xingú region (SFX) (~1.88 Ga) which, combined with new petrological and geochronological data, help providing a more complete understanding of the tectonic, magmatic and volcanological evolution of the Amazonian Craton. This magmatism/volcanism is thought to be formed in a late-/post-orogenic to extentional regime confirmed by the new geochemical data presented here. The transition from late-convergent to extensional tectonic setting could register the beginning of the taphrogenesis that marked the Amazonian Craton throughout the Mesoproterozoic. The volcanological approach of this contribution can serve as a strategy for the modelling of the evolution of Precambrian volcano-sedimentary basins around the world. The large amount of rocks analyzed are divided into primary and secondary volcaniclastic products depending on if they resulted from a direct volcanic activity (pyroclastic) or processes that reworked pyroclastic fragments. Furthermore, the deposits are subdivided into massive and stratified, depending on their primary mechanisms of transport and emplacement. By confirming the results from previous studies, our study permits to depict a more precise paleo-environmental picture of the processes that occurred in the Amazonian Craton during the Late-Paleoproterozoic. In particular, the presence of large regional-scale fissural systems and caldera collapses produced large silicic explosive volcanic eruptions, also accompanied by the emission of large volume effusive products. Although studies on the Amazonian Craton are still scarce and controversial, the present study provides new evidence that this volcanism may have formed one of the largest Silicic Large Igneous Provinces (SLIP) on earth. Our data also confirm that at least two major Paleoproterozoic periods of formation of volcanic rocks exist in the Amazonian craton. This point is of great relevance for any future interpretation of the geological evolution of this craton.
Highlights
Lines 785-789: Rev: "Here we image that an ideal late-convergent to extensional geotectonic environment was likely similar to that proposed in our discussion paragraph, where a post-orogenic to extensional regime for the period ~ 1.88 Ga was characterized by the emission of large volcanic felsic products." This sentence sounds very confusing and should be rephrased
This study is the result of the lithofaciological analysis carried out during the
The two models are very similar only differing for the size of the hypothesized magma chambers and the shape of the fissural vents
Summary
This Eon represents the time just before the proliferation of 59 oxygen accumulation and complex life on Earth. This period was likely the most 60 tectonically active in Earth’s history. 65 The Amazonian Craton (AC) is one of the largest preserved Precambrian terrains in the 55 world (4.6x106 km2) (Almeida et al, 1981). It occupies approximately half of the Brazilian territory and it is the location of important mineral resources such as gold, iron, copper, and tin, among others The 71 geological investigation of the AC has recently seen a renewed interest of the national
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