Actas de congresos
Ar-Ar step heating ages for milonitic low angle shear zones rocks in the Rio Apa Terrane, south of the Amazonian Craton
Fecha
2014Registro en:
South American Symposium on Isotope Geology, 9, 2014, São Paulo
Autor
Ruiz, Amarildo Salina
Sousa, Maria Zelia Aguiar de
Lima, Gabrielle Aparecida de
Filho, Manoel Souza Dagrella
Institución
Resumen
This work presents geological, structural and geochronological (Ar-Ar step heating inmuscovite)
results obtained for the milonitic rocks in low angle shear zones in order to discuss its deformational and tectonic significance for the crustal evolution of the Rio Apa Terrane, southernmost part of the Amazonian Craton. The Rio Apa Terrane consists of a continental cratonic fragment, which has been divided by Cordani et aI. (2010) into two tectonic blocks (eastern and western blocks) with distinct crustal evolution and separated by a suture zone. Thrust zones occur both the western and the eastern blocks and display cinematic indicators which indicate a low angle ductile deformation, with top tectonic transpor! (vergence) moving to NWW. The Rio Apa Complex consists of grey-green colored leucocratic syeno to monzogranitic gneisses with biotite and garnet as the mafic minerais.
The shear zone rocks display foliated arrangement with dominant milonitic and protomilonitc textures, characterizedby muscovite-garnet milonite gneiss, oriented N10-20El10-30'SW. 4°ArP9Ar step heating dating on muscovite from milonite showmetamorphism ages of 1302 ± 4 Ma and 1295 ± 6 Ma suggesting that the low angle shear zones are contemporaneous to the regional thermal event previously registered by the K-Ar and 4°Arf39Ar radiometric ages by Cordani et aI. (2010) both in the western as western block of the Rio Apa Terrane.