The Araxá Group in the South-Southwest Region of the Goiás State

Abstract

In the S – SW region of Goiás State, Brazil, the Araxá Group is constituted of a metasedimentary sequence containing schistoseand gneissic (garnet-biotite-quartz schists, feldspatic garnet-biotite-quartz schists, garnet-biotite-quartz paragneisses,with muscovite and locally amphibole, epidote, kyanite and staurolite. This sequence presents intercalations of metaultramaficrocks (serpentinite, actinolite schist, talc schist, chlorite schist), metamafic ones (amphibolite, amphibole schistcontaining or not garnet, garnet amphibolite) and associated granitic bodies. Chemically, the Araxá Group metasedimentspresent peraluminous composition, showing enrichment in LILE, when compared with HFSE and REE, and displayingnegative anomalies of Nb, Ta, Sr, P and Ti. Their chemical composition is that of greywake and the chemical characteristicsof the sediments are generated in magmatic arcs. Isotopic data for Sm/Nd – model ages (TDM) between 1,04 – 1,51 and1,76 – 2,26 Ga – and U/Pb (predominance of zircon with ages < 900 Ma) suggest that these metasediments have Neoproterozoicrocks as the source rocks. Chemical and isotopic characteristics of the studied metasediments suggest that theirsource are rocks originated in magmatic arcs and that they were deposited in a fore arc basin developed in the margins ofNeoproterozoic island arcs.

Keywords

• Brasília Belt
• Araxá Group
• Geochemistry
• Geochronology Sm/Nd and U/Pb.