Geology and geochemistry of deformed granites from the Querari Complex, Rio Negro Province, NW-Amazonian Craton, Brazil

Paulo Gomes,Marcia Carneiro,Marcelo Almeida,Rielva Nascimento,Renata Veras

doi:10.29396/jgsb.2021.v4.n1.3

Abstract

The Querari Complex corresponds to the basement rocks from Uaupes Domain and represents one of the least studied units in the northwest of the Rio Negro Province, Amazonian Craton. In this paper, we present new field geology, petrographic, and geochemical data of deformed granites from the Querari Complex. Based on our results, we suggest the differentiation of the Querari Complex into two magmatic facies. The Pana-Pana Facies comprise mainly porphyritic syeno to monzogranites with biotite as the main mafic mineral, and titanite, epidote, and allanite as accessory phases. The rocks of the Pana-Pana Facies have calc-alkaline and metaluminous affinities. The Matapi Facies have a syenogranite composition, coarse to porphyritic texture with magmatic muscovite and biotite, normative corundum higher than 1% (1.85-2.06), and mostly a peraluminous character. Both facies are generally enriched in silica and have a small spectrum of variation. (67.5 to 70.1 wt.% Pana-Pana Facies - 71.1 to 73 wt.% Matapi Facies), but they differ by the high Al2O3, Fe2O3, MgO, CaO, Sr, and Ba contents in the Matapi Facies. Geological and geochemical compositions suggest that the magmatic precursors of these rocks of Matapi Facies may be derived from partial melting of metasedimentary sources, whereas the Pana-Pana Facies are probably derived from a meta-ignea source of intermediate composition, such as tonalitic gneisses. The rocks of the Querari Complex would have been generated in the collisional tectonic settings during the Paleoproterozoic (between 1778 and 1740 Ma). During this 1.78-1.74 Ga tectono-magmatic event (D1), the magmatic fabric (S0) and the parallel S1 foliation have been developed, with NE-SE orientation. A subsequent tectonic event (D2) was responsible for the folding S1 foliation, creating the S2 axial planar foliation with an approximate orientation E-W. This D2 event is thought to represent a Calymmian (1.52 - 1.48 Ga) tectono-metamorphic event, associated with widespread I- and S-type granite emplacement in the Rio Negro Province. The deformation textures, as well as the mineral paragenesis for the Pana-Pana and Matapi facies, reveal temperature conditions at upper amphibolite facies, up to 700oC. Finally, the D3 tectono-metamorphic event comprises the reactivation of many NE-SW ductile shear zones with sinistral kinematic, creating a mylonitic foliation (S3) in the rocks of the Querari Complex. This D3 tectono-metamorphic event is probably linked to the intracratonic K´Mudku tectono-metamorphic event (between 1317 and 1198 Ma) of the Amazonian Greenvillian-Sunsas continental collision.

Highlights

Granitic rocks are one of the main components for geotectonic reconstruction studies, owing to their inherent feature of registering tectono-metamorphic events in a determined area, recorded by their structural and geochemical characteristics (e.g., Pitcher 1997, Janoušek et al 2020)
We suggest that, in the Querari Complex, three events have been recognized, and they must go through the following considerations: (i) the S0 foliation parallel to the S1 foliation with NE-SW direction; (ii): the S2 foliation is oriented to ENW-WSW with a similar dip to the S2 foliation of the Cauaburi Complex, and both of them have been created on upper amphibolite facies and; (iii) the last event reworks the older NE-SW structures, to what happens at the Cauaburi Complex, but under high-temperature conditions
The PanãPanã and Matapi facies are characterized by high contents of large-ion lithophile elements (LILE) and low High Field Strength Element (HFSE)/LILE ratios

Summary

Introduction

Granitic rocks are one of the main components for geotectonic reconstruction studies, owing to their inherent feature of registering tectono-metamorphic events in a determined area, recorded by their structural and geochemical characteristics (e.g., Pitcher 1997, Janoušek et al 2020). The Rio Negro Province has been initially subdivided into two tectono-stratigraphic domains: Imeri (east) and Alto Rio Negro (west) (Fig. 1b; Almeida 2006). Gomes et al - JGSB 2021, 4 (1), 43 - 60 field, geochemical, and geochronological data from basement rocks and intrusive granitoids, Almeida et al (2013) reviewed the previous domains and subdivided the Alto Rio Negro Domain into two new domains: the Içana and Uaupés domains (Fig. 1b). The Içana Domain comprises several migmatites, orthogneisses and metagranitoids with crystallization ages at ca. The Uaupés Domain comprises mainly orthogneisses and calc-alkaline metagranitoids with monzogranitic to dioritic composition with 1740 ± 2 Ma (Single-zircon Pb-evaporation), all included in the Querari Complex (Almeida et al 2013)

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Conclusion