Petrografia e suscetibilidade magnética dos granitoides arqueanos da Vila São Francisco

Abstract

In the São Francisco Village, east of Xinguara city, Rio Maria Domain, hololeucocratics granitoids and metabasics rocks arise. Based on field features and petrographics data was possible individualize the granitoids in: a) TTGs - are average equigranular tonalites trondjhemites with typical compositional banding, being constituted by plagioclase and quartz, having the biotite as principal fase iron magnesian, besides zircon, titanite, opaques, allanite, epidote, apatite and white micas as accessory minerals. Those rocks were related in this work to the TTG granitoids from Rio Maria; b) Deformed granites - are average equigranular leucomonozogranites and leucosienogranites (mafics minerals < 10%) with incipient deformation, mineralogically composed by quartz, plagioclase and alkali-feldspar, biotite, opaques,titanite, apatite, allanite, epidote and zircon. Those granitoids keep strong similarity with the Xinguara leucogranites; c) Isotropic granites - Occur in the form of two differing plutons, their rocks present monzogranitic and siengranitic composition with equigranular texture and mineralogy constituted by microcline, quartz and plagioclase as essential minerals , biotite ± amphibole, as varietals titanite, allanite and zircon as primers accessories. The characteristics of these rocks allow associate them to the Jamón Suite, specifically to the Manda Saia Granite. The magnetic susceptibility measure of the 31 samples of granitoid vary from 0,0304 to 10,076 (x10 -3SI) with an average value of 2,857 (x10- 3SI). Those values are considered low to the granitoids and are justified by the hololeucocratic character of these rocks, being poor in opaques minerals and consequently in magnetite, the principal responsible mineral through the rocks magnetization. There is similarities in terms of SM between the groups of granitoids studied. The TTGs and the Isotropic Granite exhibit bigger spread of SM values, although the SM values of the sample of deformed granites are comparatively more homogeneous. The great volume of rocks of Rio Maria Granodiorite registered in this region in previous geological maps, are not cartographed in this works, whereas, was identified the existence of TTGs rocks and the increase of the occurrence area of the Xinguara Granite in relation to the referred maps. In this way, this work contributed to compose the geological frame of Rio Maria Domain, characterized in geological terms, petrographics and magnetic behaviour of the rising granitoids of São Francisco Village.