Rhyacian evolution of the eastern São Luís Craton: petrography, geochemistry and geochronology of the Rosário Suite

Bruna Karine Correa Nogueira,Rafael Estumano Leal,Paulo Sergio De Sousa Gorayeb,Marco Antonio Galarza,Elton Luiz Dantas

doi:10.1590/2317-4889201720160114

Bruna Karine Correa Nogueira, Rafael Estumano Leal + Show 3 more

Open Access

https://doi.org/10.1590/2317-4889201720160114

Copy DOI

Abstract

ABSTRACT: The São Luís Cráton comprises an area between northeast Pará state and northwest Maranhão that exposes Paleoproterozoic granitic suites and meta-volcanosedimentary sequences. In the east of this geotectonic unit, about 70 km south of São Luís, there is a portion of the São Luís Craton, represented by the intrusive Rosario Suite (RS). This work is focused on rocks of this suite, including petrographic, lithochemical and geochronological studies to understand the crustal evolution of these granitoid rocks. The rock spectrum varies from tonalitic to granodioritic, quartz dioritic and granitic compositions, and there are partial structural and mineralogical changes related to deformation along transcurrent shear zones. The geochemical studies show granitic metaluminous compositions of the calc-alkaline series with I-type affinity typical of magmatic arc. Rare earth elements show marked fractionation and slight Eu positive or negative anomalies (Eu/Eu* = 0.82 to 1.1). Zircon U-Pb data provided consistent ages of 2165 ± 7 Ma, 2170 ± 7 Ma, 2170 ± 7 Ma, 2161 ± 4 Ma and 2175 ± 8 Ma, dating emplacement of these granitoids as Paleoproterozoic (Rhyacian). Sm-Nd isotopic data provided model ages (TDM) of 2.21 to 2.31 Ga with positive values of εNd +1.9 to +3.2 (t = 2.17 Ga), indicating predominantly Rhyacian crustal sources for the parental magmas, similar to those ones found in other areas of the São Luís Craton. The data, integrated with published geological and geochronological information, indicate the occurrence of an important continental crust formation event in this area. The Paleoproterozoic evolution between 2.17 and 2.15 Ga is related to the Transamazonian orogeny. The granitoids of the Rosario Suite represent the main phase of continental arc magmatism that has continuity in other parts of the São Luís Craton and can be correlated with Rhyacian accretionary magmatism in the northwestern portion of the Amazonian Craton that amalgamated Archean terrains during the Transamazonian orogeny.

Highlights

On the African side, several studies based on structural, geochemical, geophysical and geochronological data demonstrate the existence of Archean and dominantly juvenile Paleoproterozoic crust (Abouchami et al 1990, Boher et al 1992, Gasquet et al 2003)
We identified five main lithological types: meta-melatonalite, meta-tonalite, meta-granodiorite, meta-monzogranite, and andesite dykes
The geochemical characteristics combined with the field, petrographic, geochronological and isotopic data indicate that studied rocks are co-genetic and that compositional variations are associated with magmatic fractionation process

Summary

INTRODUCTION

In models of global supercontinent reconstruction, the São Luís Craton and the northeastern portion of the Amazonian Craton (to the east of the Guayana Shield) have been considered remnants of the West African Craton preserved in the northern South American Platform after the breakup of the Pangea Supercontinent (Hurley et al 1967, Torquato & Cordani 1981, Lesquer et al 1984, Brito Neves et al 2000, Klein and Moura 2008). The study area is located approximately 70 km south of São Luís, in Maranhão State, northeastern of Brazil, where the easternmost fragment of the craton is exposed as a set of granitic rocks named by Rodrigues et al (1994) and Gorayeb et al (1999) as the Rosário Suite (Fig. 1). The São Luís Craton consists generally of three main Paleoproterozoic rock associations: a meta-volcanosedimentary succession, volcanic sequences and granitoids (Fig. 1). We identified five main lithological types: meta-melatonalite, meta-tonalite, meta-granodiorite, meta-monzogranite, and andesite dykes They are generally exposed in hill tops, gravel-extraction quarries and outcrop slabs on the banks and beds of rivers, such as the Rio Munim, in the town of Presidente Juscelino (Fig. 2) (in Appendix A are the coordinates of the points in the map). The meta-tonalites contain many leucotonalite veins, pegmatites and aplites, which are genetically related to granodiorite nearby and the youngest magmatic phases of the suite, probably the most evolved felsic phases of magmatic differentiation of the suite (Gorayeb et al 1999)

ANALYTICAL PROCEDURES

Findings

CONCLUSIONS