Geometria, cinemática e modelamento tectônico das rochas do Grupo Vila Nova, região de Pedra Branca do Amapari – AP.

Abstract

The studied area is located at Pedra Branca do Amaparí region, center south Amapá state, at about 190 km from Macapá. The rocks exposed in this region comprise Palaeoproterozoic granites (Lafon et al., 2008) and greenstone belts related to Vila Nova Group. The Vila Nova Group represents a Palaeoproterozoic greenstone belt metamorphosed and deformed under greenschist to amphibolite facies conditions. This Group belongs to the Maroni-Itacaiúnas Province setting, in the eastern boundary of the Guianas Shield. The data obtained in this research point to the presence of ductile and brittle fabrics elements such as spaced and continous foliations, flexural, tight, open parasitic and isoclinal folds, structural and mineral lineation, kink bands and oblique to normal faults. Foliations are the main structures and display anastomotic patterns with a N-S and NE-SW preferred orientation. They have shallow to steep dips mainly to NW and SE. Flexural folds occur in the banded iron formations and amphibolitic rocks in centimeter to meter scale, with shallow to moderate plunging axes (12º to 50º) to NW, NE and SW. Stretching lineation is defined by elongation of quartz grains and shows shallow to steep plunges generally to NW. Boudins are also defined by quartz grains and normally occur between banded iron formation foliation planes, where they configure sigmoidal features. The data obtained suggest that the rocks composing the Vila Nova Group were deformed in consequence of diapirism of adjacent granite plutons, associated with partitioned transpression in the post-diapirical state when occurred compartimentation between simple shear and pure shear components. Transpression shows a sinistral component of simple shear and a E-W shortening pure shear component.