Pseudosection modeling and U-Pb geochronology on Piranga schists: role of Brasiliano Orogeny in the Southeastern Quadrilátero Ferrífero, Minas Gerais, Brazil

Yanne Da Silva Queiroz,Renato De Moraes,Hanna Jordt-Evangelista,Bernhard Schulz,Julia Schmiedel,Edgar Medeiros-Júnior,Cristiano Lana,Victor Matheus Tavares Fernandes,Maximiliano Martins,Marco Paulo De Castro,Gláucia Queiroga

doi:10.1590/2317-4889201920180136

Abstract

ABSTRACT In the Southeastern Quadrilatero Ferrifero, a package of metapelitic rocks previously attributed to the Archean Rio das Velhas Supergroup crops out in Piranga locality. This study presents the mineral chemistry and U-Pb-Hf zircon geochronology on foliated staurolite-garnet mica schists. Garnet and staurolite index minerals are syn- to post-kinematic towards the main schistosity. Garnet porphyroblasts display well-developed compositional zoning of Mg-Fe-Mn-Ca, with increase of almandine and pyrope and decrease of spessartine towards the rim, implying in prograde metamorphic pattern. Estimates of P-T values for the metamorphic peak resulted in temperatures between 630 to 650oC and pressure around 7 kbar. Pseudosections show well-defined stability fields in amphibolite facies, with a metamorphic path displaying progressive increase in P-T conditions. Maximum depositional age of 1,875 ± 51 Ma is established for the Piranga mica schists pointing to a depositional history that is younger than those previously described. Metamorphic Cambrian ages characterize the strong influence of deformational processes related to the final stages of Brasiliano Orogeny in the Southeastern Quadrilatero Ferrifero.

Highlights

Geochronological and petrological studies are essential in ancient and polydeformed cratonic areas, such as Quadrilátero Ferrífero – QF (Alkmim & Marshak 1998)
QF is a significant iron ore province in the world and is located in the Southern edge of São Francisco Craton (SFC), in Minas Gerais State (Fig. 1), Brazil, fringed to the East by the Neoproterozoic Araçuaí Orogen and to the South by Supplementary data Supplementary data associated with this article can be found in the online version: Supplementary Table A1, Supplementary Table A2, Supplementary Table A3, Supplementary Table A4, Supplementary Table A5 and Supplementary Table A6
We present an integrated study of metamorphism and geochronology on three samples of staurolite-garnet mica schists from Southeastern QF, providing new insights on the stratigraphic setting and role of the Brasiliano Orogeny in the QF scenario

Summary

Introduction

Geochronological and petrological studies are essential in ancient and polydeformed cratonic areas, such as Quadrilátero Ferrífero – QF (Alkmim & Marshak 1998). 630–490 Ma) (PedrosaSoares et al 2007, Alkmim & Teixeira 2017, Aguilar et al 2017, Cutts et al 2018). Metamorphic grade is higher in the QF Eastern portion and closer to igneous intrusions and uplift zones of the crystalline basement (Dorr II 1964, Herz 1978, Jordt-Evangelista et al 1992, Marshak et al 1992), mostly related to the Rhyacian-Orosirian Orogeny (Fig. 1). Aguilar et al (2017) and Cutts et al (2018) obtained Paleoproterozoic ages for monazite, titanite, and zircon grains for basement and supracrustal rocks, suggesting a Rhyacian-Orosirian overprint (Fig. 1). Chemale Jr. et al (1994) and Alkmim & Marshak (1998) have pointed a Neoproterozoic influence based on structural studies. Th-U-Pb in situ monazite dating from pelitic schists in upper units of QF (Schmiedel 2015, Fig. 1) reported ages

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Discussion

Conclusion