Superposition of structures in the interference zone between the southern Brasília belt and the central Ribeira belt in the region SW of Itajubá (MG), SE Brazil

Abstract

ABSTRACT:The study area is localized in the Socorro nappe, part of the southern Brasília belt, with a minor part in the Embu terrane, part of the central Ribeira belt. Three phases of deformation were detected, Dn-1, Dn and Dn+1. Sn-1 seems to be generally transposed into Sn, but in the northwestern part it is well preserved, dipping about 60º to W and SW, with a stretching and/or mineral lineation plunging down dip. The main foliation in most of the area is Sn, dipping about 70º to SSE. Dn folds are tight to isoclinal, with axes that plunge about 40º to SW. Quartz-feldspathic segregation veins are folded by Dn. The structures related to Dn-1 and Dn are cut and modified by four important shear zones ascribed to deformation phase Dn+1. Two samples of a granite that is elongated along the Caxambu shear zone, and also cut by it, were dated. One yielded a crystallization age of 575 ± 5 Ma, and the other one, from the shear zone, an age of 567 ± 8 Ma, interpreted either as representing the age of movement along the Caxambu shear zone, or as metamorphic growth.KEYWORDS: structural geology; geochronology; Socorro-Guaxupé nappe; Embu terrane. RESUMO:

Automated petrography analysis by QEMSCAN® of a garnet-staurolite schist of the San Lorenzo Formation, Sierra Nevada de Santa Marta massif

“…This relationship between deformation and development of progressive schistosity surfaces has been reported in different studies (e.g., Bell and Rubenach, 1983;Ríos et al, 2003;Chattopadhyay and Ghosh, 2007;Vinagre et al, 2016;Castellanos et al, 2001Castellanos et al, , 2004Castellanos et al, , 2016aCastellanos et al, , 2016bGarcía et al, 2017). Our observations suggest that during a first step of deformation (D 1 ), the original structure of the protholith was affected as revealed by a first metamorphic foliation (S 1 ).…”

Metamorphic modeling and petrochronology of metapelitic rocks from the Luminárias Nappe, southern Brasília belt (SE Brazil)

“…An alternative interpretation is that the area faced two metamorphic events, an older one at ca. 632-615 Ma, related to the collision of the southern Brasília belt, and a younger one at about 600 Ma related to collision of the Ribeira belt, as proposed in literature (Trouw et al 2013b, Coelho et al 2017, Reno et al 2012, Peternel et al 2005, Vinagre et al 2016.…”