Mineralogy, petrology, and origin of the Pedra Branca Suite: a tonalitic-trondhjemitic association with high Zr, Ti and Y, Carajás Province, Amazonian Craton

Arthur Santos Da Silva,Gilmara Regina Lima Feio,Allan Cardek Brunelli Gomes,José De Arimatéia Costa De Almeida,João Paulo Silva Alves,Roberto Dall’Agnol

doi:10.1590/2317-4889202020190093

Abstract

Abstract The Pedra Branca suite (2.75 Ga) is located in the Canaa dos Carajas domain in the southeastern Amazonia Craton. It diverges from typical TTG in mineralogical and geochemical terms, by the presence of hornblende and clinopyroxene and because it has a high content of HFSE (Zr, Y, Ti, and Nb). It belongs to the low-K subalkaline series, which varies from metaluminous to peraluminous, and are mostly calc and ferroan granitoids. Amphibole is calcic and classified as ferroan-edenite, and hastingsite. Plagioclase is mainly oligoclase. The Fe/(Fe + Mg) ratios found in the amphiboles indicate that these granitoids were formed under high to moderate fO2 conditions. Geobarometric calculations suggest pressures between 9.3 and 71 Kbar for the origin and 4.8-53.4 Kbar for the emplacement. Geothermometric calculations suggest initial crystallization temperatures between 945 and 862°C, and the water content in the magma is estimated to be higher than 4 wt%. The magma source was defined as tholeiitic continental gabbro melted in an extensional setting (Carajas Rift) with geochemical features similar to diabase from Nova Canada (PA). The Pedra Branca magma was originated by partial melting (~28%), leaving a residue with plagioclase (An40), hornblende, clinopyroxene, and may or may not have magnetite.

Highlights

Archean cratons are commonly composed of greenstone belts and granitoids, among which tonalite-trondhjemite-granodiorite associations stand out (TTG; Windley 1996)
Another characteristic comparing to other TTG rocks from Rio Maria Domains in the Carajás Province (CP) is the presence of amphibole and relicts of clinopyroxene (Sardinha et al 2004, Gomes and Dall’agnol 2007, Feio et al 2013, Sousa 2015)
Previous geological mapping performed in the Canaã dos Carajás region (Feio et al 2013, Gomes 2003, Gomes and Dall’Agnol 2007, Sardinha et al 2004) were able to recognize and individualize several geologic units previously encompassed in the Xingu Complex, among which the Pedra Branca suite

Summary

INTRODUCTION

Archean cratons are commonly composed of greenstone belts and granitoids, among which tonalite-trondhjemite-granodiorite associations stand out (TTG; Windley 1996). The Pedra Branca Suite (PBS; Gomes and Dall’agnol 2007, Feio et al 2013) outcrops in Canaã dos Carajás region, southeastern Pará State, Brazil This tonalite-trondhjemite suite shows both similarities and differences with typical Archean TTG. It is similar to TTG suites in classificatory terms such as low Sr, K content and low K/Na ratios, diverge from TTG since it has distinct geochemical features such as high HFSE content (Ti, Zr, Y, and Nb), low transitional elements (Cr and Ni) Another characteristic comparing to other TTG rocks from Rio Maria Domains in the CP is the presence of amphibole and relicts of clinopyroxene (Sardinha et al 2004, Gomes and Dall’agnol 2007, Feio et al 2013, Sousa 2015). The latter is intruded by the Neoarchean (~2.75–2.73 Ga) Estrela, Igarapé Gelado, and Serra do Rabo granites

RESULTS

DISCUSSION

CONCLUSIONS