Caracterização geológica, petrográfica e geoquímica do Trondhjemito Mogno e Tonalito Mariazinha, Terreno Granito-Greenstone mesoarqueano de Rio Maria, SE do Pará

Abstract

The Mogno Trondhjemite is one of the largest TTG units of the Rio Maria Granite-Greenstone Terrane (RMGGT). It was considered as representative of a second generation of Archean TTG in that terrane. However, field, petrographical, geochemical, and geochronological studies demonstrate the existence of two distinct TTG units in its main area of occurrence. For the dominant TTG unit, showing NW-SE to EW foliation and distributed in the eastern and western domains of the mapped area, the term Mogno Trondhjemite was maintained. The new TTG unit, which occurs in the center-western domain and displays a NE-SW to NS dominant trend, is named as Mariazinha Tonalite. Hence, the original area of occurrence of the Mogno Trondhjemite was significantly reduced. Moreover, Pb-Pb zircon ages indicate that the Mogno Trondhjemite and the Mariazinha Tonalite are neither coeval, nor related to the second generation of TTGs of the RMGGT. The two TTG studied units are composed of epidote-biotite tonalites and trondhjemites of the high Al2O3 type, with geochemical characteristics similar to those of the typical Archean TTG granitoids. Compared with the Archean TTG units of the Xinguara region, the Mogno Trondhjemite geochemical characteristics are transitional between those of the Caracol Tonalitic Complex and the Água Fria Trondhjemite, while those of the Mariazinha Tonalite approaches those of the Caracol Tonalitic Complex. The studies undertaken in the Mogno Trondhjemite and associated Archean granitoids demonstrated that the TTG series of the RMGGT are more diversified and complex than previously admitted. The domain of the second Archean generation of TTG of the RMGGT was drastically reduced and a new Archean TTG association, the Mariazinha Tonalite, was identified and characterized.