Petrografia e geoquímica do Granito Manda Saia, Província Carajás.

Abstract

The Manda Saia granite is located to southeast of the of Xinguara town and it is represented by two semicircular plutons separated by the Mesoarquean basement of the Rio Maria Domain. The bodies crosscut in the northern portion the Mesoarquean TTG granitoids and the Rio Maria Granodiorite, and in the south, eastern and western portions they are intrusive in the metabasalts of the sequence greenstone belt of the Babaçu Group. The Manda Saia pluton is formed by rocks of isotropic aspect, grayish pink in color and monotonous textural variation. They are hololeucocratic rocks of medium-to-coarse heterogranular texture, occasionally porphyritic, which are classified as monzo- and syenogranites. Biotite is the main ferromagnesian mineral and amphibole is rare and interstitial. Secondary minerals are clay minerals, sericite, muscovite, fluorite and chlorite. Manda Saia pluton is formed by peraluminous rocks that present a restricted and high SiO2 contents (74.80 and 77.70wt.%), and high Fe/(Fe+Mg) ratios. Their REE pattern is marked by enrichment in light and heavy REE and moderate negative Eu anomaly. The pluton can be classified as ferrous type-A granite and akin to the reduced types and those most evolved from the oxidized granites of the Carajás Province. The occurrence of interstitial amphibole identified in the Manda Saia granite also is observed in the plutons of the Velho Guilherme Suite. On the other hand, the frequent occurrence of magnetite combined with the compositional aspects of its rocks, also shows that the Manda Saia granite is akin to the leucogranitic facies of the oxidized granites from Jamon Suite. The emplacement of the Granite Manda Saia is linked to extensional tectonics and the transport of magma that resulted in the emplacement of the plutons in shallow crustal levels (~ 1.0 ± 0.5 kbar) through a dyke feeding system.